Development and Investigation of Bio-based Environmentally ...

154
Development and Investigation of Bio-based Environmentally Friendly Fire Retardant PLA Composites Von der Fakultät für Maschinenbau der Technischen Universität Chemnitz Genehmigte Dissertation zur Erlangung des akademischen Grades Doktor-Ingenieur (Dr.-Ing.) Vorgelegt Von Dipl.-Ing. Pengcheng Zhao aus Liaoning, VR China Tag der Einreichung: 11.01.2019 Tag der Verteidigung:18.04.2019 1. Gutachter: Prof. Dr.-Ing. Michael Gehde 2. Gutachter: Prof. Dr.-Ing. Udo Wagenknecht

Transcript of Development and Investigation of Bio-based Environmentally ...

Page 1: Development and Investigation of Bio-based Environmentally ...

Development and Investigation of Bio-based Environmentally

Friendly Fire Retardant PLA Composites

Von der Fakultät für Maschinenbau der

Technischen Universität Chemnitz

Genehmigte

Dissertation

zur Erlangung des akademischen Grades

Doktor-Ingenieur

(Dr.-Ing.)

Vorgelegt

Von Dipl.-Ing. Pengcheng Zhao

aus Liaoning, VR China

Tag der Einreichung: 11.01.2019

Tag der Verteidigung:18.04.2019

1. Gutachter: Prof. Dr.-Ing. Michael Gehde

2. Gutachter: Prof. Dr.-Ing. Udo Wagenknecht

Page 2: Development and Investigation of Bio-based Environmentally ...

Bibliografische Beschreibung

Pengcheng Zhao

Thema

Development and investigation of bio-based environmentally friendly fire retardant PLA

composites

Dissertation an der Fakultät für Maschinenbau der Technischen Universität Chemnitz,

Professur Kunststoffe, Chemnitz, 2018

152 Seiten, 55 Abbildungen, 37 Tabellen, 221 Literaturzitate

Referat

In der vorliegenden Dissertationsarbeit wird auf die Thematik der Entwicklung von

Polymerwerkstoffen, basierend auf vollständig natürlichen Resourcen, eingegangen.

Die vorliegende Lösung beruht auf der Compoundierung von Polylactid mit

unterschiedlich modifizierten Vanillin. Ziel war es, flammschutzwirkende Komponenten

einzubringen und die Abhängigkeiten zwischen Zusammensetzung und Eigenschaften

aufzuklären. Dem liegt die Absicht zugrunde, optimale Werkstoffe zur Verfügung zu

stellen, die sich durch deutlich verbesserte flammhemmende und mechanische bzw.

thermo-mechanische Eigenschaften auszeichnen.

Die erzeugten modifizierten Vanillin-Derivate sowie deren Composite wurden

hinsichtlich der physikalischen und chemischen Struktur mittels REM, EDX, FTIR, NMR,

DSC, TGA, SEC und Zugversuch charakterisiert. Zur Bestimmung der flammwidrigen

Eigenschaften wurden UL-94 V, LOI und CCT durchgeführt. Es hat sich gezeigt, dass

System aus PLA und einem Vanillin-Phosphorsäure-Ester in Bezug auf werkstofflichen

Eigenschaften insgesamt die optimale Leistung aufwies. Die Materialen ergaben eine

verbesserte Zähigkeit und erheblich erhöht flammwidrige Eigenschaften. In einem

weiteren Schritt wurden MMT und APP, zwei kommerzielle Flammschutzmittel, mit dem

PLA/VP System kombiniert. Die daraus abgeleiteten Resultate bewiesen eine

synergistische Wirkung zwischen VP und MMT bzw. APP und führten zu besseren

Brandklassen bei LOI und UL-94 Brandtests.

Schlagworte

Polylactide, bio-basierend, umweltfreundlich, Vanillin, Flammschutzmittel, Polymer

Composite, Flammteste

Page 3: Development and Investigation of Bio-based Environmentally ...
Page 4: Development and Investigation of Bio-based Environmentally ...

Bibliografische Beschreibung

Pengcheng Zhao

Theme

Development and investigation of bio-based environmentally friendly fire retardant PLA

composites

Dissertation at the Faculty of Mechanical Engineering, Chemnitz University of

Technology, Professorship of Plastic Materials, Chemnitz, 2018

152 Pages, 55 Figures, 37 Tables, 221 Literatures

Abstract

The present work demonstrates the development of fully bio-based polymeric

composites. It was realized by the compounding of poly(lactic acid) and differently

modified vanillin. The aim of this work was to introduce flame retardant components into

PLA and to study the flame retardant mechanism. The intention of this approach is the

preparation of optimized PLA composites with significantly improved flame retardant,

mechanical as well as thermo-mechanical properties.

The modified vanillin and the PLA composites based on those vanillin derivatives were

characterized by means of SEM, EDX, FTIR, NMR, DSC, TGA, SEC and tensile test for

their physical and chemical structures. UL-94 V, LOI and CCT were carried out to

determine the corresponding flame retardant properties. The results showed that, the

PLA/VP system represented the best overall performance. The PLA/VP composite

exhibited increased toughness and significantly improved flame retardancy. In addition,

two commercialized flame retardants, MMT and APP, were introduced into the PLA/VP

system, respectively. It was suggested that there were synergic effects between VP and

MMT as well as APP. The combined used flame retardants resulted in an improved

classification in UL-94 and LOI tests

Keywords

Poly(lactic acid), bio-based, environmentally friendly, vanillin, flame retardant, polymer

composite, fire test

Page 5: Development and Investigation of Bio-based Environmentally ...
Page 6: Development and Investigation of Bio-based Environmentally ...

vi

Contents

1 Introduction .................................................................................................. 1

1.1 Fundamental of Biopolymer ................................................................ 1

1.2 Brief Overview of Polymer Combustion .............................................. 2

2 Synopsis of the Work ................................................................................... 4

3 Literature Review ......................................................................................... 6

3.1 Green Polymeric Material ................................................................... 6

3.2 Material Fundamentals ....................................................................... 7

3.2.1 Poly (Lactic acid) ....................................................................... 7

3.2.2 Vanillin ..................................................................................... 13

3.3 Combustion of Polymer .................................................................... 15

3.4 Flame Retardancy of Polymers ........................................................ 16

3.4.1 Basic Explanation of Polymer Flame Retardancy ................... 16

3.4.2 Classification of Flame Retardant ........................................... 18

3.4.3 Strategies of Developing Flame Retardant PLA ...................... 19

4 Experimental: Materials, Processing and Characterization Methods ......... 24

4.1 Material Description .......................................................................... 24

4.2 Synthesis section .............................................................................. 24

4.2.1 Synthesis of bis(5-formyl-2-methoxyphenyl) phenylphosphonate

24

4.2.2 Synthesis of bis(5-((E)-(allylimino)methyl)-2-methoxyphenyl)

phenylphosphonate............................................................................ 25

Page 7: Development and Investigation of Bio-based Environmentally ...

vii

4.2.3 Synthesis of bis(2-methoxy-5-((E)-((3-(triethoxysilyl)propyl)imino)

methyl)phenyl) phenylphosphonate .................................................... 26

4.3 Preparation of flame retardant PLA Composites ............................... 27

4.3.1 Melt Compounding .................................................................. 27

4.3.2 Extrusion.................................................................................. 28

4.3.3 Melt Spinning ........................................................................... 29

4.3.4 Injection Molding ...................................................................... 29

4.3.5 Compression Molding .............................................................. 30

4.4 Characterization Techniques ............................................................. 31

4.4.1 Structure Characterization ....................................................... 31

4.4.2 Gel Permeation Chromatography ............................................ 31

4.4.3 Morphological Characterization ............................................... 31

4.4.4 Rheological Characterization ................................................... 31

4.4.5 Thermal Properties Tests ......................................................... 32

4.4.6 Mechanical Properties Tests .................................................... 32

4.4.7 Flammability and Combustibility .............................................. 33

4.4.8 Mechanism Studies ................................................................. 36

5 Results and Discussion .............................................................................. 38

5.1 VP based PLA Composites ............................................................... 38

5.1.1 Structural Characterization ...................................................... 39

5.1.2 Morphology of VP and PLA/VP Composites ............................ 42

5.1.3 Thermal Decomposition Behavior ............................................ 43

Page 8: Development and Investigation of Bio-based Environmentally ...

viii

5.1.4 Thermal Crystallization Behavior ............................................. 49

5.1.5 Flammability ............................................................................ 52

5.1.6 Combustion Behavior .............................................................. 53

5.1.7 Rheological properties ............................................................ 57

5.1.8 Mechanical Properties ............................................................. 60

5.1.9 Conclusion .............................................................................. 66

5.2 VPA and VPS based PLA Composites ............................................. 67

5.2.1 Characterization of VPA and VPS ........................................... 68

5.2.2 Thermal Decomposition Behavior ........................................... 71

5.2.3 Flammability ............................................................................ 75

5.2.4 Combustion Behavior .............................................................. 76

5.2.5 Mechanical Properties ............................................................. 78

5.2.6 Conclusion .............................................................................. 79

5.3 PLA/VP Composite with Conventional Flame Retardants ................ 80

5.3.1 PLA/VP Composite with Montmorillonite ................................. 81

5.3.2 PLA/VP Composite with APP .................................................. 93

5.3.3 Conclusion ............................................................................ 106

6 Summary ................................................................................................. 107

6.1 Synthesis and characterization of VP ............................................. 108

6.2 Performance of PLA/VP composites .............................................. 108

6.3 Further modification of VP and VP used in combination with

commercialized flame retardant .............................................................. 109

Page 9: Development and Investigation of Bio-based Environmentally ...

ix

7 Outlook ...................................................................................................... 111

References ..................................................................................................... 112

List of Figures ................................................................................................. 133

List of Tables ................................................................................................... 137

Publications .................................................................................................... 139

Page 10: Development and Investigation of Bio-based Environmentally ...

x

Abbreviations

PLA Poly (lactic acid)

FR Flame retardant/ flame retardancy

MMT Montmorillonite

APP Ammonium polyphosphate

VP Bis(5-formyl-2-methoxyphenyl) phenylphosphonate

VPA Bis(5-((E)-(allylimino) methyl)-2-methoxyphenyl)

phenylphosphonate

VPS Bis(2-methoxy-5-((E)- ((3-(triethoxysilyl)propyl)

imino)methyl) phenyl) phenylphosphonate

PHA Polyhydroxyalkanoates

PCL Poly (ε-caprolactone)

PBS Polybutylene succinate

LA Lactic acid

PLLA Poly (L-lactic acid)

PDLA Poly (D-lactic acid)

ROP Ring opening polymerization

GA Glycolic acid

PHB Poly(β-hydroxybutyrate)

PBAT Poly(butylene adipate-co-terephthalate)

PEG Poly(ethylene glycol)

WPC Wood plastic composites

Page 11: Development and Investigation of Bio-based Environmentally ...

xi

LDH Layered double hydroxide

EG Expandable graphite

CNTs Carbon nanotubes

UV Ultraviolet

IFRs Intumescent flame retardants

POSS Polyhedral oligomeric silsesquioxane

mPLA Modified PLA

pHRR Peak of heat release

LOI Limiting oxygen index

DAB Diaminobenzidine

PMMA Poly (methyl methacrylate)

ATH Aluminum trihydrate

AHP Aluminum hypophosphite

HPAPC Hexa(phosphaphenanthrene

aminophenoxyl)-cyclotriphosphazene

HBPE Hyperbranched poly(phosphamide ester)

UL-94 The Standard for Safety of Flammability of Plastic

Materials for Parts in Devices and Appliances testing

PER Pentaerythritol

MEL Melamine

TPM Tris(2-hydroxyethyl) isocyanurate polyphosphate

VA Vanillin

Page 12: Development and Investigation of Bio-based Environmentally ...

xii

APTES 3-Aminopropyltriethoxysilane

TEA Trimethylamine

PPDC Phenylphosphonic dichloride

NMR Nuclear magnetic resonance

FTIR Fourier transform infrared spectroscopy

SEM Scanning electron microscopy

TGA Thermogravimetric analysis

DSC Differential scanning calorimetry

CCT Cone calorimetry Test

HRR Heat release rate

TTI Time to ignition

THR Total heat release

ML Mass loss

TSP Total smoke production

SPR Smoke production rate

CO Carbon oxide

CO2 Carbon dioxide

TG-FTIR Thermogravimetry- Fourier transform infrared

spectroscopy

DTG Differential thermal gravity

MFI Melt flow index

av. EHC Average effective heat of combustion

Page 13: Development and Investigation of Bio-based Environmentally ...

xiii

Symbols

Mw Molecular weight

Wt.-% Weight percent

Φ Diameter

Tx% the temperature at x% weight loss

Tmax the temperature at maximal weight loss rate

Ea Apparent activation energy

T Temperature

β Heating rate

R Ideal gas constant

E Activation energy

α Degree of conversion

r2 Goodness of fit

Tg Glass transition temperature

Tcc Cold crystallization temperature

Tm Melting Temperature

∆Hcc Cold crystallization enthalpy

∆Hm Melting enthalpy

Χc Weight fractional crystallinity

G’ Storage Modulus

G’’ Loss Modulus

Page 14: Development and Investigation of Bio-based Environmentally ...

xiv

Acknowledgment

The accomplishment of this thesis is the commencement of my research life

accompanied and supported by many kind-hearted people. I could not have

completed this thesis without the assistance from them. I extend my profound

gratitude to all of them.

First of all, I want to give the special thanks to Prof. Udo Wagenknecht, Prof.

De-Yi Wang and Dr. Ines Kühnert for providing me the opportunity at

Leibniz-Institute for Polymer Research Dresden and giving me necessary

support. I would like to express my sincere gratitude and indebtedness to my

supervisor Dr. Andreas Leuteritz for accepting me in his research group and also

for his support, encouragement, insightful comments and guidance throughout

this work.

I thankfully acknowledge Prof. Michael Gehde for giving the opportunity to join

his outstanding department in the faculty of mechanical engineering faculty of

Technical University Chemnitz.

My sincere thanks go to the colleague of IPF for their support and assistance in

the work. I also would like to thank Mrs. Sabine Krause, Dr. Hartmut Komber, Dr.

Mikhail Malanin, Mr. Holger Scheibner, Dr. Regine Boldt, Mrs. Maria Auf der

Landwehr and Mrs. Petra Treppe for their help in analysis work. I am truly

grateful to Mrs. Anna Ivanov, Mr. Christian Lehmann, Mr. Andreas Scholze and

Mr. Bernd Kretzschmar for the preparation of specimens.

Furthermore, I gratefully thank Mrs. Anne Hofmann for her assistance in the

administrative issues and Mrs. Anna Ivanov for the friendly office time. I would

like to express my sincere gratitude to Dr. Zhiqi Liu, Dr. Baobao Chang, Mr.

Yilong Li, Mr. Xueyi Wang, Dr. Jaime Alejandro Puentes-Parodi and Mr. Sajid

Naseem for those help and fruitful discussions.

For the financial support, I am truly thankful to the China Scholarship Council

Page 15: Development and Investigation of Bio-based Environmentally ...

xv

(Ph.D. Program Nr. 201308080080) and IPF scholarship.

Last but not the least, my sincere thanks would go to my family. In particular,

huge indebtedness to my parents for their unconditional support, and special

thanks to my beloved wife Yan Yan for her love and understanding. Their love,

encouragement and great confidence in me, help me go through the most

difficult time.

Page 16: Development and Investigation of Bio-based Environmentally ...

Introduction 1

1 Introduction

1.1 Fundamental of Biopolymer

The development of polymeric materials has a history of more than 150 years

since the first man-made polymer, which is based on nitrocellulose and known

as celluloid, was obtained in the 1860s by Parkes and Hyatt.[1] In the following

decades, numerous kinds of synthetic polymeric materials were invented and

began to replace conventional materials in various fields.

Figure 1-1: Plastic production since 1950[2]

Today, plastic materials are ubiquitous and one of the most versatile materials.

The applications of plastic are technically endless so that the consumption of

plastic is extremely huge. Usually, synthetic plastics or petrochemical plastics

consist of macromolecule with long carbon chain and are thus durable and high

resistant to moisture and chemical solvents, which are actually one of the best

properties of plastics. However, for short-term applications, this advantage is,

unfortunately, the biggest problem: the duration of degradation does not match

their expected useful life. Only a tiny part of the used products is recycled and

Page 17: Development and Investigation of Bio-based Environmentally ...

Introduction 2

reprocessed. The accumulation of plastic waste has become a serious

environmental and social issue.[3] According to statistic, the total amount of

plastic products manufactured since 1950 is more than 8000 million tons, and

60 % of those are discarded. Assuming the current developing rate and

regulations against plastic consumption is not changed, the number of total

amount of plastic waste will be increased to 25000 million tons by the year 2050,

and more than 12000 million tons will be discarded in the natural environment.[2]

On the other hand, the great demand for plastic products and the

overconsumption has caused more and more serious concerns regarding the

fossil resource depletion. Thus, biopolymer has attracted rapidly growing

attentions both in academy and industry. The application of biopolymers offers a

promising solution for the sustainable development of society.[4]

1.2 Brief Overview of Polymer Combustion

Most of the polymeric materials, both natural and synthetic, are highly

inflammable. The widespread use of polymeric materials leads to a dramatic

increase in fire risk in our day-to-day life. For example, 2 million accidental fires

are reported in Europe every year, which cause more than 4000 deaths and

70000 injuries as well as 120 billion € of economic losses. Thus, there are great

sociological and economic pressures on the whole society to produce plastic

products with certain flame retardancy.

Figure 1-2 presents the schematic diagram for the development of heat flux in a

burning room as a function of time. Additionally, the influence of proper flame

retardant (FR) is also illustrated.[5] The fire scenario can be basically divided

into three stages: ignition, development and fully developed fire. The ignition will

occur when the combustible materials exposed to open fire or high temperature

under the existence of oxygen. If the materials are not flame retardant, the

evolved heat will cause rapid development of the temperature in the room, and

Page 18: Development and Investigation of Bio-based Environmentally ...

Introduction 3

reach the so-called “flash over”. Then, the fire will be fully developed and the

temperature in the room might reach over 1000 °C. The fire may spread to the

whole building and cause structural damage. In comparison, for flame retardant

materials, the ignition and flash over could be significantly delayed and the

average escape time will be longer.

Figure 1-2: Schematic illustration of the heat flux vs time in a fire[5]

Page 19: Development and Investigation of Bio-based Environmentally ...

Synopsis of the Work 4

2 Synopsis of the Work

The ultimate goal of this thesis is to develop new environmentally friendly flame

retardant composites and study the impact of flame retardant on the properties

of PLA as well as the mechanism behind. In this work PLA was used as the

polymeric matrix and vanillin was selected as the raw material to synthesize

flame retardant. In particular, three different vanillin derivatives with functional

groups were synthesized and used to improve the flame retardancy of PLA.

Furthermore, two commercialized flame retardants, MMT (montmorillonite) and

APP (ammonium polyphosphate), were introduced into the flame retardant PLA

composites respectively to study the synergic effect between the vanillin

derivative and MMT/APP. Meanwhile, the thermal properties, micromorphologies,

combustion behavior and mechanical properties of these PLA composites were

investigated in details.

Chapter 3 is a brief review of the state of the art. The importance of developing

green polymer is first presented, followed by an overview of the PLA composites

reinforced by different biomass. The second part of the review is the basis of

polymer combustion and flame retardant fundamental as well as the state of art

of flame retardant PLA.

In Chapter 4, the raw materials and processing methods are described in detail.

The synthesis pathway and characterization techniques used in this thesis were

introduced.

In Chapter 5, all experimental results are illustrated and discussed, including the

synthesis and structure characterization of the vanillin based flame retardants:

bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP), bis(5-((E)-(allylimino)

methyl)-2-methoxyphenyl) phenylphosphonate (VPA) and bis(2-methoxy-5-((E)-

((3-(triethoxysilyl)propyl)imino)methyl) phenyl) phenylphosphonate (VPS). All the

Page 20: Development and Investigation of Bio-based Environmentally ...

Synopsis of the Work 5

flame retardants are used in PLA matrix to enhance the flame retardancy. In

addition, VP is used in combination with MMT and APP. The properties of all the

PLA composites are characterized and the relation of composition and

properties relation is studied.

The final Chapter 6 provides an overall conclusion and a brief outlook for

possible further work.

Page 21: Development and Investigation of Bio-based Environmentally ...

Literature Review 6

3 Literature Review

3.1 Green Polymeric Material

The history of use of polymeric materials can be traced to centuries ago when

mankind started to use natural polymer like cellulose and gum.[1] Since last

century the primary raw materials of polymeric materials have converted to fossil

resources when people learned the way to produce synthetic polymers and

attracted by the multifarious and excellent properties of synthetic plastics.

However, the massive manufacture and overconsumption of plastic production

are causing serious environmental issues and petroleum resource depletion is a

further challenge. With awareness of the need for sustainable development,

recent years have seen more and more researches focus on biopolymers.[6, 7]

Figure 3-1: Type of polymeric materials and examples[3]

Biopolymer denotes polymeric materials either bio-based or biodegradable. That

Page 22: Development and Investigation of Bio-based Environmentally ...

Literature Review 7

means, biopolymers should be able to be produced from renewable feedstocks

such as agro-resources or undergo complete decomposition into carbon dioxide

and water under various natural conditions. They are environmentally friendly

either at “the cradle”, at “the grave” or both.[3] Figure 3-1 illustrates the

classification of polymeric materials. The common biopolymer family includes

starch, chitosan, cellulose, polyhydroxyalkanoates (PHA), poly (lactic acid)

(PLA), poly (ε-caprolactone) (PCL), polybutylene succinate (PBS), etc.[8] Among

them, PLA is one of those polymers, which can also fulfill both criteria and is

considered as a promising replacement of conventional petroleum-based

plastics.[9, 10]

Besides biopolymer, biocomposites have attracted increasing attention.[11]

Many efforts have been done to develop biocomposites with improvement in

desired properties. For examples, many natural fibers and particles are used in

polymeric materials as a reinforcement, such as jute, flax, hemp, ramie, sisal,

kenaf, rice and wood powder.[12, 13] While some biomass can be used as a

modifier or functional additives in plastic, such as alginate, catechin, cellulose,

chitosan, cyclodextrin, lignin, phytic acid and starch.[6]

3.2 Material Fundamentals

3.2.1 Poly (Lactic acid)

3.2.1.1 Synthesis and Manufacture

PLA is a linear aliphatic polyester. Lactic acid (LA), also known as milk acid, is

the basic building block for PLA.[14] LA can be produced from biomass like corn,

sugarcane, sugar beet and cassava by fermentation. There are four unique

groups including hydroxyl and carboxyl groups in the structure of LA, therefore

LA can exist in different optically active enantiomers, LLA and DLA.[15] PLA can

be produced in homopolymers of poly(L-lactic acid) (PLLA) and poly(D-lactic

Page 23: Development and Investigation of Bio-based Environmentally ...

Literature Review 8

acid) (PDLA) or copolymer of poly(D,L-lactic acid) (PDLLA), depending on the

use of different enantiomers.[16] The synthesis procedure is illustrated in Figure

3-2. The ratio of D- and L-enantiomers can dramatically influence the properties

of PLA, such as glass transition temperature, crystallinity and melting point. The

most common synthetic techniques to produce PLA are polycondensation

(including solution polycondensation and melt polycondensation) and ring

opening polymerization (ROP).[14]

Figure 3-2: Synthesis of PLA[17]

Since the structure of LA contains both hydroxyl and carboxyl, the

polymerization can occur by self-condensation. The reaction can take place

whether under the presence of a solvent or by heating the monomer over critical

temperature. Some researchers have obtained PLA with a molecular weight (Mw)

between 20000 and 30000 by using polycondensation, some even produced

PLA with Mw as high as 600000. However, it is very difficult to use these methods

in industrial scale, while the equilibrium reactions are strongly affected by

various parameters. For example, the water generated by the reaction could

lead to degradation of long PLA molecular chains. Impurities caused by solvent

and side reactions are also unavoidable disadvantages. Besides, the solution

Page 24: Development and Investigation of Bio-based Environmentally ...

Literature Review 9

polycondensation technique consumes a large number of organic solvents,

which is also considered as potential pollutants to the environment.[18]

In contrast to polycondensation, ROP is considered to be an important and

effective technique to PLA with high molecular weight. By controlling reaction

conditions and application of catalysts, it is possible to control the ratio and

sequence of D- and LLA and also the molecular weight of the final product. The

ROP technique also has some drawbacks: it requires strict purity of the lactide

monomer; the use of metal-based catalyst limits the application in special fields

like medicine and food packaging. Hence, many researchers are making effort to

develop a new approach to solve these problems.[19] The advantages and

disadvantages of different PLA synthesis techniques are summarized in Table

3-1.

Table 3-1: Comparison of different PLA synthesis techniques[18]

Synthesis techniques Advantages Disadvantages

Solution

polycondensation

Easy to control, economical Low molecular weight,

impurities, pollution

Melt polycondensation Low molecular weight,

high temperature

Ring-opening

polymerization

High molecular weight High requirement on raw

material, high cost

New approaches High molecular weight,

efficient, no pollution, etc.

Under development

3.2.1.2 Modification and Application

PLA possess some promising features such as excellent mechanical and optical

Page 25: Development and Investigation of Bio-based Environmentally ...

Literature Review 10

properties. PLA is widely used in medical components, packaging materials,

automotive and electrical components as well as house holdings.[20, 21]

However, its broadened application field has been limited by the shortcomings,

such as brittleness and inflammability.[22] Many efforts have been done in order

to reinforce the mechanical properties of PLA without destroying the

biodegradability. In order to achieve these, numerous methods of modification

have been developed, involving copolymerization, physical blending and

composition. For example, the introduction of functional monomers into the

backbone of PLA or incorporation of functional additives like a nucleating agent,

plasticizer and flame retardant.

Chemical Modification

Some inherent properties such as brittleness, low thermal stability and

flammability pose considerable scientific challenges and restrict the application

field of PLA. The incorporation of strange monomers into the backbone of PLA is

one of the most common chemical modification strategies to overcome the

limitations. Extensive research has been done to synthesize PLA copolymers via

different techniques, such as polycondensation, cationic, anionic and

coordination insertion ring opening polymerization. Monomers with specific

properties are employed to enhance the versatility of PLA. For instance,

copolymer of LA and GA (glycolic acid) is widely used in bio-medicine as the

competitive suture; PLA-co-PCL copolymer shows adjustable plasticity

depending on the LA/CL ratio. Beside of copolymerization with monomers, other

techniques like block copolymer, branched copolymer and dendritic copolymer

of PLA were also successfully synthesized in the last decades.[14]

Blending

Physical blending with other polymers is another feasibility to render PLA

different properties.[23-25] Furthermore, it can also reduce the cost of the final

Page 26: Development and Investigation of Bio-based Environmentally ...

Literature Review 11

product, since the price of PLA is relatively higher than most petroleum plastics.

Considering the sustainability, PLA is usually blended with renewable and/or

biodegradable components, including PCL, poly(β-hydroxybutyrate) (PHB),

poly(butylene adipate-co-terephthalate) (PBAT), poly(ethylene glycol) (PEG),

chitosan and starch. [8, 26-30]

Composition

The daily increasing demand for polymeric materials inspirits the development of

high performance polymer, especially in the form of polymeric composites.

Despite PLA processes excellent mechanical properties, thermal plasticity and

biocompatibility, some improvements such as toughness are still necessary for

end-use applications.[17, 31, 32]

Using filler to reinforce polymeric material is very common in the production and

processing stages.[33-35] In the beginning, the reinforcement of PLA was mainly

focused on fibers, especially natural fibers due to the lower cost and weight

specific properties.[12, 36, 37] Natural fibers can be obtained from either plants

or animals. Wood plastic composites (WPC) are typical natural fiber based

polymer composites and attract growing interests.[38] Nonwood fibers can be

produced from different parts of plants, such as leaf, bast, seed, straw or fruit.

The primary advantage of leaf fiber is, they usually have excellent impact

properties. Examples of leaf fibers include sisal, henequen, palm, banana leaf

and pineapple leaf.[39-41] The main disadvantage of this kind of fibers is their

hydrophilic nature which causes poor interaction to hydrophobic polymeric

materials. The most common solution is to use a surface modifier like silane

coupling agent to enhance the interfacial adhesion.[42] Compared to leaf fibers,

bast fibers such as ramie, flax, kenaf, hemp, jute and abaca show better

adhesion to polymeric materials, therefore are used to enhance the mechanical

properties.[42-47] Leaf and bast fibers usually have long dimension thereby

Page 27: Development and Investigation of Bio-based Environmentally ...

Literature Review 12

polymeric composites based on such types of fibers possess good reinforced

performance and used to prepare structural applications. Fibers derived from

fruit and seed such as cotton, coconut and coir are usually used in the

non-structural application.[48, 49] Other examples for natural resources of fibers

include bamboo, red algae, silk and so on. Table 3-2 provides the comparison of

some fiber reinforced PLA composites.

Table 3-2: Comparison of different fibers reinforced PLA composites

Types Fiber Description Reference

Wood Wood flour Storage and flexural moduli increase with

filler volume fraction

[50, 51]

Leaf Sisal Surface treatment is necessary to improve

the interfacial adhesion

[41, 52]

Bast Ramie Act as reinforcing filler [42, 47]

Flax Increase stiffness and flexural strength [53, 54]

Kenaf Improve tensile and storage moduli [43-45]

Seed/

Fruit

Coconut Enhanced tensile strength and modulus [48]

Cotton Improve tensile and impact strength [49]

Straw Rice straw Enhance tensile strength and crystallinity [55]

Grass Bamboo Improve flexural and thermal properties [56]

Artificial Cellulose Improve storage modulus, poor adhesion

between untreated cellulose and matrix

[13, 57]

With the development of nanotechnology, nanoparticles such as montmorillonite

Page 28: Development and Investigation of Bio-based Environmentally ...

Literature Review 13

(MMT),[58-60] layered double hydroxide (LDH),[61] expandable graphite (EG),

cellulose whisker[62, 63] and carbon nanotubes (CNTs) have gained

tremendous attention. The nanocomposites show excellent properties because

the nanoparticles have a small size, huge specific surface area and many

modification feasibilities. For instance, the incorporation of MMT into PLA leads

to enhanced mechanical properties, degree of crystallinity and thermal

stability.[64-66] Depending on the different modifier, LDH can provide UV

absorption, corrosion resistance, degradability enhancement and flame

retardancy.[67-73] Extensive researches focused on PLA/CNTs composites

have been carried out. The results show that, like many other PLA based

composites, PLA/CNTs composites possess different improved performances in

mechanical properties, thermal properties, etc. In addition, one of the unique

advantages is, the introduction of CNTs into PLA can provide electrical

conductivity to the matrix.[74-76]

3.2.2 Vanillin

Vanillin (4-hydroxy-3methoxybenzaldehyde), is a major component of the extract

of vanilla beans and responsible for its flavoring properties. Therefore, vanillin is

one of the most commonly used industrial flavoring agent in foods, beverages,

perfumes, cosmetics and pharmaceuticals.[77-79] In a scientific aspect, vanillin

has been found to possess some important pharmacological properties such as

antibacterial and anti-inflammatory activities.[80-85]

The natural vanilla extract is a mixture of vanillin and hundred different

compounds. Besides, growing and harvesting of vanilla plants are high-cost

processes. Thus, vanillin obtained from natural extract contributes less than 1%

of the total vanillin production. Around 85% of the worldwide synthesized vanillin

is produced from petroleum-based intermediates.[86] However, only the vanillin

produced from natural materials can be recognized as “natural vanilla aroma”.

Page 29: Development and Investigation of Bio-based Environmentally ...

Literature Review 14

The global annual demand of vanillin as a flavoring agent is estimated to be

around 20000 tons. The increasing market has inspirited the development of the

techniques to produce artificial vanillin.[87-89] Recently, with the development of

technology, the problems of low yield and purity have been solved, promoting

the lignin-to-vanillin process again one of the most promising sustainable

methods.[90, 91] The proposed mechanism is described in Figure 3-3.

Figure 3-3: Proposed mechanism of the lignin-to-vanillin process[86]

Lignin is the second abundant renewable resource with around 50 million tons of

annual production, suggesting vanillin produced from lignin a feasible

sustainable technique. In fact, vanillin is currently the only aromatic compound

produced from lignin at industrial scale. For these reasons, extensive researches

have been tried to use vanillin as a renewable resource in material development.

Since vanillin has both aldehyde and hydroxyl groups in its structure, most of the

works are focused on the possibility to use vanillin as a building block for

different resins.[92-100] Others have tried to use vanillin directly in polymeric

matrix as functional additives due to its antioxidant or antimicrobial

properties.[101-105]

Page 30: Development and Investigation of Bio-based Environmentally ...

Literature Review 15

3.3 Combustion of Polymer

With numerous outstanding advantages that polymeric materials provided, there

is still an inescapable and vital drawback for nearly all polymers related to their

high flammability. The combustion of the polymer is a very complicated process

involving several stages: ignition, fire development and extinction. When

polymer exposes to sufficient heat, pyrolysis and degradation will occur. The

typical thermal decomposition process consists of several steps which could be

illustrated as following:[106]

Chain initiation RH −−−−> R· + H·

Chain propagation R· + O2 −−−−> ROO·

RH + ROO· −−−−> ROOH + HO·

Chain branching ROOH −−−−> RO· + HO·

2ROOH −−−−> ROO· +RO· +H2O

Chain termination 2R· −−−−> R-R

R· +HO· −−−−> ROH

2RO· −−−−> ROOR

2ROO· −−−−> ROOR + O2

As the result of the chain reaction, the polymer turns into combustible products

and volatile. These products will be ignited by the surrounding heat and release

more heat as feedback. Then a self-sustainable combustion is established,

promoting the thermal degradation of the polymer and increasing the release of

combustible products. The fire will spread to the whole surface of the polymer

and consume all the material with high velocity. The combustion behavior of

polymer is illustrated in Figure 3-4.

Page 31: Development and Investigation of Bio-based Environmentally ...

Literature Review 16

Figure 3-4: Mode of action of polymer in fire[107]

3.4 Flame Retardancy of Polymers

The three basic elements of fire are heat, fuel and oxygen. In order to stop a fire,

it is necessary to remove at least one of the three conditions from the fire. Since

the middle of last century, some basic idea of flame retardant has been proposed,

such as using additives to interrupt the thermal degradation of the polymer in

order to decrease the release of combustible products or applying an external

fire resistant coating to isolate polymer from oxygen. Today the modes of action

of flame retardants during the combustion of fire are considered mainly as gas

phase and condensed phase as well as the synergism.

3.4.1 Basic Explanation of Polymer Flame Retardancy

3.4.1.1 Gas Phase

In gas phase mechanism, there is interaction between flame retardant and

polymer, which interferes the chemical reaction in polymer combustion. There

are plenty of chemical reactions in polymer combustion. However, the most

important reactions that release free radicals, which propagate the chain

reaction, are followed:[107]

Page 32: Development and Investigation of Bio-based Environmentally ...

Literature Review 17

H• + O2 = OH• + O•

O• + H2 = OH• + H•

The main exothermal reaction which releases the most energy sustaining the

combustion is:

OH• + CO = CO2 + H•

Flame retardant (FR) acts in the gas phase can serve as radical scavenger

which interrupts the propagation reaction. The exothermal processes are thus

stopped, the system cools down, and the supply of combustible gases is

reduced and eventually completely suppressed. For instance, halogens exhibit

high efficiency as flame inhibitors. However, the application of

halogen-containing FRs is restricted in many areas due to health and

environment issues, and phosphorus-containing FRs, are getting more popular

as the replacement. The PO• radicals generated by FRs have been proved to

involve the destruction of hydrogen atoms, showing high efficient quenching

effect. Moreover, some FRs can release nonflammable gases such as water,

and dilute the concentration of combustible gas or lower the environmental

temperature.

3.4.1.2 Condensed Phase

The condensed phase mechanism postulates an interaction between flame

retardant and the polymer. The interaction between flame retardant and polymer

takes place usually at a lower temperature and leads to char formation, which is

probably the most important explanation for condensed phase mechanism. It

serves as the barrier between oxygen, heat and the polymer surface. Therefore,

the carbonaceous layer with good thermal stability and low thermal conductivity

has a good effect on preventing the conversion of polymer to combustible gas. It

is reported that a continuous and compact protective char layer contribute better

Page 33: Development and Investigation of Bio-based Environmentally ...

Literature Review 18

lowering the heat release. The carbonaceous layer can serve as a barrier which

can reduce both the heat and mass transfer. In particular, the intumescent flame

retardants (IFRs) are typical examples. IFRs can generate nonflammable gases

and expand the carbonized or vitreous layer. It is also been proved that the

combination of metal oxides with some conventional IFRs, the quality of the char

can be further improved.

3.4.2 Classification of Flame Retardant

The flame retardant industry has rapid development in the last decades, many

species of FR have been explored. The FRs can be classified into different

categories as following:[108, 109]

Halogenated FRs

Halogenated FRs are primarily based on chlorine and bromine and exhibit high

flame retardant efficiency. However, more and more halogenated FRs are

restricted due to environmental issues.[110]

Inorganic FRs

Inorganic FRs represent the largest fraction of the global flame retardant market.

This category includes metal hydroxides, silicon dioxide, antimony compounds,

boron compounds and other metal compounds.[73, 111-114] Some compounds

of this group, e.g. antimony oxides, must be combined with bromine or chlorine

to be effective. Others like metal hydroxides and silicon dioxide can be used

independently. However, a significant high loading is necessary to achieve a

satisfying flame retardant effect.

Nitrogen-containing FRs

A typical example of this category is melamine. It can transform into a

cross-linked structure during the combustion and release inert gas which can

Page 34: Development and Investigation of Bio-based Environmentally ...

Literature Review 19

dilute the combustible products.[115-119]

Phosphorus-containing FRs

These compounds can work both in the gas phase and condensed phase. On

one hand, PO• radicals are able to cut off the propagation reaction of the

polymer. On the other hand, phosphorus promotes the formation of char,

inhibiting the mass transfer and the pyrolysis process.[120-124]

Nanofillers

The development of nanocomposites technology has encouraged numerous

interest in the research of flame retardant polymeric materials because the

incorporation of nanofillers improves dramatically flame retardancy and various

other properties of polymer matrix at loadings as low as 3%-5%. In the last years,

various nanofillers with flame retardant effect based on different compounds

have been developed, such as montmorillonite (MMT), layered double hydroxide

(LDH), graphene, metal oxides, polyhedral oligomeric silsesquioxane (POSS),

sepiolite, halloysite etc.[113, 125-129]

3.4.3 Strategies of Developing Flame Retardant PLA

Originally, PLA was only used in short-term application such as packaging

materials, which have no requirement on flame retardancy. In recent years, with

the increasing concern of environmental issue and depletion of fossil resources,

PLA is considered as a promising solution and its application has rapidly spread

to other field like automotive and electrical components as well as house

holdings, for which the flammability a potential risk. Thus, improved fire

resistance of PLA based materials is an urgent task for our day-to-day safety.

The strategies are summarized as follows:

Page 35: Development and Investigation of Bio-based Environmentally ...

Literature Review 20

3.4.3.1 Chemical Copolymerization

The primary properties of polymeric materials are normally determined by the

chemical structure. In order to overcome the inherent limitation, it is a common

strategy to prepare a copolymer.[50, 130] Wang et al. prepared a

phosphorus-containing PLA by chain extending reaction.[131] The modified PLA

(mPLA) showed excellent flame retardancy and was used as FR for virgin PLA.

With 5 wt.-% loading, the compound could pass V-0 rating in the UL-94 test.

When the loading increased to 10 wt.-%, the peak of heat release (PHRR) value

decreased by around 20 % and the material exhibited a LOI (limiting oxygen

index) value as high as 35 %. Xiong et al. synthesized a copolymer of LA and

diaminobenzidine (DAB) via melt polycondensation.[132] Different reaction

conditions such as temperature, time, catalyst and the molar ratio of raw

materials were studied. The product, P(LA-co-DAB) showed better thermal

stability and higher char yield, suggesting a better flame retardant performance.

3.4.3.2 Blending Approach

The blending of other polymers can impart desired properties such as thermal

stability, ductility, flame retardancy, etc. to the matrix polymer. Kimura et al.

blended PLA with polybutylene succinate (PBS) for use in computer housings.

The blends showed improved fire performance. With the combined application of

FR, the materials exhibited V-2 rating in the UL-94 test, compared no rating of

virgin PLA.[133] To improve the fire performance, Bocz et al. blended PLA with

thermoplastic starch;[53] Teoh et al. prepared blends with PLA and poly (methyl

methacrylate) (PMMA).[134] The PHRR of materials was reduced due to the

charring effect of the strange polymer. Besides conventional plastics, polymeric

flame retardants have been developed and used in PLA.

Poly(bis(phenoxy)-phosphazene), a conventional FR with the trade name

SPB-100 was blended with PLA. High LOI value and V-0 rating were achieved,

Page 36: Development and Investigation of Bio-based Environmentally ...

Literature Review 21

as PHRR in cone calorimeter test decreased by more than 50 %. The main

mechanism of enhanced flame retardancy by blending was mainly related to the

improved charring effect, leading to easier formation of protective layer.[135]

3.4.3.3 Inorganic Flame Retardant Additives

The non-halogenated inorganic FRs include mainly metal oxide, hydroxide and

salt.[136-139] Aluminum trihydrate (ATH) is a widely used FR due to the low cost

and smoke production.[140] Nishida et al. prepared PLA/ATH composites by

solution compounding.[141] In this particular case, ATH was used as FR as well

as a catalyst to accelerate the depolymerization of PLA. The composites were

considered as recyclable feedstock. However, high loading of ATH (50-65 wt.-%)

was necessary to achieve a satisfactory flame retardant effect, which led to a

negative effect on the mechanical properties. Cheng et al. introduced MMT into

PLA/ATH composites to lower the ATH loading without losing satisfactory flame

retardancy.[142] With a total filler loading of 40 wt.-%, the PLA composites could

obtain V-0 rating in the UL-94 test.

Aluminum hypophosphite (AHP) is another well-known FR for polymeric

materials.[143, 144] Tang et al. studied the influence of AHP on the flame

retardancy of PLA. The PLA/AHP composite with 20 wt.-% loading passed V-0 in

UL-94 test and exhibited a LOI value as high as 28.5 %.[145] Zhou et al.

combined used AHP with other conventional FR in PLA. The composites

showed improved anti-dripping properties and more compact char layer after the

cone calorimeter test, suggesting a synergic effect.[146]

3.4.3.4 Organic Flame Retardant Additives

In recent years, many organic FR containing phosphorus, nitrogen and/or silicon

were synthesized and exhibited high flame retardant efficiency in PLA.[147-158]

Hexa(phosphaphenanthrene aminophenoxyl)-cyclotriphosphazene (HPAPC)

was synthesized by Jiang et al. and blended with PLA. At a loading of 10 wt.-%,

Page 37: Development and Investigation of Bio-based Environmentally ...

Literature Review 22

the composite passed V-0 rating in UL-94 and the LOI value was improved to

35.6 %.[159] Li et al. synthesized a hyperbranched poly(phosphamide ester)

oligomer (HBPE) and melt blended with PLA. HBPE was proved to be a highly

effective FR for PLA. With only 2 wt.-% of HBPE, the PLA composite exhibited a

LOI value as high as 33 % and passed V-0 rating in UL-94.[160] Similarly, Liao et

al. reported an efficient polymeric FR (PNFR) containing phosphorus, ester

groups and phenyl rings for PLA.[161] LOI value was improved to 31.5 % and

UL-94 V-0 was achieved with 3 wt.-% PNFR.

3.4.3.5 Intumescent Flame Retardant System

An intumescent flame retardant (IFR) system usually consists of an acid source

which yields acid species upon heat, a carbonization agent which decomposes

at the right temperature and a blowing agent which can expand the char

layer.[106] Char formers are mainly hydroxyl-rich compounds such as starch and

polyols. Examples for the acid source are ammonium salts and phosphates.

Blowing agents are compounds which can release gases upon heat like urea

and melamine. IFR is a widely used FR for various polymeric materials, such as

polyester, polyamide and polyolefin. A classic example for IFR is the combination

of ammonium polyphosphate (APP) and pentaerythritol (PER), in which acts as

a charring agent and acid source at the same time and PER as the carbonization

agent.[162, 163] Recently, many other compounds which can be used as IFR

have been synthesized and reported.[164-171] To prepare composites with

higher bio-based content, starch[172-174], lignin[175-179], β-cyclodextrin[180]

were used as charring agent. Song et al. prepared PLA/PEG/APP (polyethylene

glycol 6000) composites with considerable flame retardancy and toughness at

the same time.[181] Fontaine et al. reported highly fire resistant PLA composites

based on APP and melamine (MEL) incorporated with MMT.[182, 183] With 30

wt.-% of APP/MEL (5:1), PHRR was reduced by 87 %. Zhao et al. synthesized

another macromolecular charring agent tris(2-hydroxyethyl) isocyanurate

Page 38: Development and Investigation of Bio-based Environmentally ...

Literature Review 23

polyphosphate (TPM) and applied in PLA.[184] The composite with 25 wt.-%

APP/TPM (2:1) acquired an LOI value of 36.5 % and achieved V-0 in the UL-94

test without dripping behavior observed. PHRR was reduced by 68 %.

3.4.3.6 Use of Nanoparticles

Nanocomposite technology is a relatively new research interest. In recent years,

great efforts have been done to develop nanoparticles with different functions,

including a flame retardant effect. To date, many FR nanoparticles have been

used in PLA matrix, such as MMT,[142, 183, 185-188] LDH,[187, 189-191]

CNTs,[46, 47, 192, 193] EG,[135, 187, 194, 195] POSS[196-199] and many

other clay mineral.[200-205] Chow et al. and Liu et al. investigated the influence

of organo-modified MMT on the fire resistance of PLA.[185, 206] Improved

anti-dripping behavior and reduced PHRR were observed. The mechanism was

proposed to be the enhancement on the melt stability and the physical barrier

effect. Some researchers tried to combine other FR with MMT.[186-188] The

addition of MMT was proved to be able to promote the formation of char. CNTs

have been found to have a similar effect as MMT. Bourbigot et al. introduced

MWCNT into PLA by reactive extrusion. The composite showed an anti-dripping

effect and a lower burning rate in the LOI test.[192]

3.4.3.7 Combination of Flame Retardants

Sometimes it is necessary to improve more than one properties of the matrix,

thus more than one fillers or additives are needed.[207] For instance, natural

fibers which are common reinforcement for PLA, are usually combined used with

conventional FR like APP to achieve improvement in mechanical and fire

performance simultaneously.[42-45, 208, 209] Similarly, the organic-inorganic

hybrid can enable a better dispersion of inorganic fillers in the polymeric matrix

with desired properties.[178, 210]

Page 39: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 24

4 Experimental: Materials, Processing and Characterization Methods

4.1 Material Description

Various chemicals were used in synthesis and processing as follows: Poly (lactic

acid), Ingeo Biopolymer 6202D was purchased from NatureWorks LLC. Vanillin

(VA) and 3-Aminopropyltriethoxysilane (APTES) were purchased from TCI

Deutschland GmbH. Phenylphosphonic dichloride (PPDC, 90%), trimethylamine

(TEA), allylamine, sodium sulfate anhydrous, magnesium sulfate anhydrous,

tetrahydrofuran, ethanol and ethyl acetate were purchased from Sigma-Aldrich

Corporation. Modified montmorillonite with the trade name Cloisite® 30B was

supplied by BYK-Gardner GmbH. Ammonium polyphosphate (APP, degree of

polymerization ≥ 1000, density = 1.9 g/cm3, solubility ≤ 0.50 g/100ml (25 °C

in water)) was kindly provided by Budenheim company. All the materials were

used without further purification.

4.2 Synthesis section

4.2.1 Synthesis of bis(5-formyl-2-methoxyphenyl) phenylphosphonate

The synthesis path of bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP) is

shown in Figure 4-1. In detail, 0.2 mol Vanillin (VA) and 0.2 mol triethylamine

(TEA) were dissolved in 200 ml tetrahydrofuran in a three-neck flask with

magnetic stirring. Then, 0.1mol of PPDC, which dissolved in 100 ml of

dichloromethane, was added into the flask dropwise in 2 hours. The temperature

was kept at 0-5 °C with an ice bath during the addition. Then, after removing the

ice bath, the mixture was stirred for another 5 hours at room temperature,

orange solution and white precipitates were produced. The white precipitates,

trimethylamine hydrochloride salts, were filtered off. The resulting liquid was

condensed using rotary evaporation and again dissolved in ethyl acetate. Then

Page 40: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 25

the solution was washed with water for 4-5 times and subsequently dried with

sodium sulfate anhydrous for 2 hours. After filtration and removing the ethyl

acetate by rotary evaporation, the resulting syrup-like product was dried in a

vacuum oven for 24 h at room temperature. Finally, yellow powder,

bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP), was successfully

fabricated.

Figure 4-1: Synthesis path of VP

4.2.2 Synthesis of bis(5-((E)-(allylimino)methyl)-2-methoxyphenyl)

phenylphosphonate

Bis(5-((E)-(allylimino)methyl)-2-methoxyphenyl) phenylphosphonate (VPA) was

synthesized from VP and allylamine. In a 500 ml round-bottom flask, 4.26 g VP

(0.01 mol) and 2 g magnesium sulfate anhydrous were added in 200ml ethanol

with stirring and maintained at 78 °C under cooling reflux. Then, 1.14 g (0.02 mol)

allylamine, which was dissolved in 100 ml ethanol, was slowly added in the

above solution with vigorous stirring. After 8 hours, the solution was cooled to

room temperature and dried with magnesium sulfate anhydrous for 2 hours.

After removing the precipitate and the solvent, a dark red solid, VPA, was

acquired. The reaction route is shown in Figure 4-2.

Page 41: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 26

Figure 4-2: Synthesis Path of VPA

4.2.3 Synthesis of bis(2-methoxy-5-((E)-((3-(triethoxysilyl)propyl)imino)

methyl)phenyl) phenylphosphonate

The synthesis of bis(2-methoxy-5-((E)-((3- (triethoxysilyl)propyl)imino)methyl)

phenyl) phenylphosphonate (VPS) was similar to that of VPA. In a 500 ml

round-bottom flask equipped with a magnetic stirrer, a heating bath and cooling

reflux, 4.26 g VP (0.01 mol) and 2 g magnesium sulfate anhydrous were added

in 200ml ethanol. Then, 4.42 g (0.02 mol) APTES was dissolved in 50 ml ethanol

and slowly added into the solution. The temperature of the system was

maintained at 78 °C for 8 hours and cooled to room temperature. Then, the

solution was dried, filtered and condensed via rotary evaporation. The mixture

was moved into a vacuum oven to remove the rest solvent. The final product,

VPS, was obtained as a dark red viscous liquid. The synthesis path is shown in

Figure 4-3.

Figure 4-3: Synthesis Path of VPS

Page 42: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 27

4.3 Preparation of flame retardant PLA Composites

4.3.1 Melt Compounding

The flame retardant PLA composites were prepared with Plasticorder mixer

(chamber size: 50 or 30 cm3, Plastograph, Brabender, Germany) with a rotation

velocity of 60 rpm at 160°C using 6 min compounding cycle. The PLA granulates

and additives were dried in a vacuum oven at 40 °C overnight before processing.

According to the recipe, granulates and additives were mixed in sequence.

Information like torque, the temperature of the chamber and molten polymers

were monitored by computer. When the torque reached a plateau of minimum, it

indicated that the additives were homogeneously dispersed in polymer matrix.

Then the mixture can be collected from the chamber and granulated via an

electrical cutter. The recipes of flame retardant PLA composites processed by

plasticorder are shown in Table 4-1.

Figure 4-4: Mixing chamber of plasticorder (left) and extruder (right)

Page 43: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 28

Table 4-1: Recipe of Vanillin and Vanillin derivative based flame retardant PLA

Sample PLA

(wt.-%)

VA (wt.-%) VP (wt.-%) VPA

(wt.-%)

VPS

(wt.-%)

PLA 100 0 0 0 0

PLA10VA 90 10 0 0 0

PLA1VP 99 0 1 0 0

PLA2VP 98 0 2 0 0

PLA5VP 95 0 5 0 0

PLA10VP 90 0 10 0 0

PLA5VPA 95 0 0 5 0

PLA10VPA 90 0 0 10 0

PLA5VPS 95 0 0 0 5

PLA10VPS 90 0 0 0 10

4.3.2 Extrusion

Extrusion is one of the most common processing plastic methods to produce a

homogenous mixture of polymer and additives. The individual extruder

employed to obtain flame retardant PLA composites was a twin-screw extruder

(Paralleler Doppelschnecken-Extruder Process 11, Thermo Fisher Scientific)

with a screw diameter of 11 mm. Molten polymers were extruded through a 3

mm die with the temperature of 195 °C (Zone 1), and the temperature of the melt

with the value between 195 and 200 °C was determined via an external

thermometer. The extrudate was directly cooled by a water bath and

subsequently granulated via an electrical cutter. Default extrusion parameters

are described in Table 4-2.

Page 44: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 29

Table 4-2: Default extrusion parameters

Temperature (°C) Screw speed

(rpm) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7

195 195 190 185 180 180 180 250

4.3.3 Melt Spinning

Melt spinning is one of the most economical and one of the simplest processing

technique of fiber manufacture. This method can be considered as a specialized

extrusion to create multiple continuous polymer filaments. Generally, polymer

granules are first heated above their melting point and then extruded through the

spinneret, where the melt is filtered to remove any un-melted, which could lead

to the weak point of the fiber. Afterwards, the fibers undergo hot drawing by roll

machine with specific winding speed to achieve fiber orientation. The winding

speed is a critical element to influence the tenacity and stiffness of the fibers.

Default processing parameters are described in Table 4-3

Table 4-3: Default spinning parameters

Temperature Nozzle Propulsion speed Winding speed

190 °C Φ=0.3 mm 10 mm/min 1000 and 2000 m/min

4.3.4 Injection Molding

Injection Molding is the most widely shaping process to convert pellets into

articles, especially into complex forms or those require high dimensional

precision for plastic materials. Samples for tensile and impact tests, LOI and

UL94 measurements were prepared using an injection machine (BOY 22 A HV,

BOY Machines, Inc., Germany) with a screw diameter of 18 mm and clamping

force of 220 kN. Default injection parameters are described in Table 4-4

Page 45: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 30

Table 4-4: Default injection molding parameters

Temperature (°C) Injection flow

(mm/s) Zone 1 (Nozzle) Zone 2 Zone 3 Zone 4

185 185 170 160 30

4.3.5 Compression Molding

Compression molding is commonly used for forming articles that do not have

complicated features, for example, it is very efficient to prepare different sheets

via hot compression molding machine because of the ease and low expense to

produce compression mold. In this particular work, this method was used to

prepare sample plates for cone calorimetry tests. Moderate amount of granules

were placed in the compression mold, which located between two metal sheets.

The sheets and mold were pre-heated at 195 °C for 3 minutes on the heating

plate of the compression machine. Then the bubbles were removed by manually

casting and releasing pressure vigorously. Subsequently, the pressure was

maintained at 50 kN for firstly 1.5 minutes at 195 °C, and then the mold and

material were cooled down with built-in circulating water cooling system under

the same pressure for 4 minutes. Finally, the resultant sample sheets were

removed from the mold.

Figure 4-5: Injection molding machine (left) and hot compression machine (right)

Page 46: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 31

4.4 Characterization Techniques

4.4.1 Structure Characterization

1H, 13C and 31P Nuclear Magnetic Resonance (NMR) measurements were

performed with a Bruker Avance III 500 spectrometer (Rheinstetten, Germany)

operating at 500 MHz. CDCl3 was used as the solvent and the solvent signal

was used for internal calibration (CDCl3: δ(1H)=7.26 ppm).

The Fourier transform infrared spectroscopy (FTIR) of the Vanillin and its

derivatives were obtained using the FTIR-spectrometer Vertex 80v (Bruker,

USA). The samples were directly measured using attenuated total reflection

(ATR)-objective (20x, Gecrystal) in FTIR-Microscope. The used spectroscopic

range was 4000-600 cm-1. The resolution was 4 cm-1.

4.4.2 Gel Permeation Chromatography

The molecular weights of PLA and processed PLA were determined by means of

size exclusion chromatography (SEC) equipped with HPLC pump (Serie 1200,

Agilent Technologies). Samples were dissolved with Chloroform and pre-filtered

to remove the unsolvable fillers. The flow rate was controlled at 1mL/min.

4.4.3 Morphological Characterization

Scanning electron microscopy (SEM) with energy dispersive X-ray analysis

(EDX) was observed via a microscope (Carl Zeiss SMT, Germany) to study the

morphological features of Vanillin and its derivatives and their dispersion in PLA

matrix.

4.4.4 Rheological Characterization

Rheological behavior of the composites was evaluated utilizing an ARES

rheometer (Rheometrics Scientific, USA) with the sample dimension

Page 47: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 32

diameter=20mm and thickness=2mm. Dynamic frequency sweep tests were

carried out at 170 °C with 10% strain in the frequency range of 0.1-100 rad/s.

4.4.5 Thermal Properties Tests

The thermogravimetric analysis (TGA) was carried out using a

thermogravimetric analyzer, TGA Q5000 (TA Instruments, USA) in the range

between room temperature and 800 °C at different heating rates under nitrogen

atmosphere as follows: 10 K/min as default single heating rate, Multiple heating

rates 10, 20, 30, 40 K/min measurements were done in order to study thermal

decomposition kinetics of PLA and PLA composites.

The differential scanning calorimetry (DSC) was performed using a differential

scanning calorimeter, DSC Q2000 (TA Instruments, USA) to study the thermal

behavior of PLA composites. The samples were firstly heated from room

temperature to 200 °C and keep the temperature for 3 minutes under a nitrogen

atmosphere to get rid of the thermal history. Then the samples were cooled

down to 25 °C. Finally, the samples were subjected to a second heating to

200 °C. The changing rate of temperature was kept at 10 K/min during all the

scanning.

Melt flow index (MFI) of composites was determined utilizing a Göttfert MI-4

according to DIN-ISO-1133-2005 at 170 °C with a weight of 2.16kg.

4.4.6 Mechanical Properties Tests

Tensile tests have been done with a Zwick 1456 (model 1456, Z010, Ulm

Germany) with cross head speed 1 mm/min according to DIN EN ISO

527-2/1BA/1 for tensile bars and with cross head speed 100 mm/min according

to ASTM D 2256 for filaments. For each composition at least 5 specimens were

tested to establish reproducibility. Prior to tests, all the specimens were stored in

a desiccator for at least 48 hours and then carried out at 23 °C and 50 %

Page 48: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 33

humidity.

Impact tests were performed on a pendulum impact tester (PSW 4J, Zwick,

Germany) to determine the Charpy impact strength according to ISO 179/1eU

with the specimen dimension of 80 x 10 x 4 mm3, and for each composition, at

least 10 specimens were tested to establish reproducibility. Prior to tests, all the

specimens were stored in a desiccator for at least 48 hours and then carried out

at 23 °C and 50 % humidity.

4.4.7 Flammability and Combustibility

The limited oxygen index (LOI) test was first proposed by Fenimore and Martin

in 1966 to evaluate the ease of ignition of materials by given their LOI value.

Figure 4-6 illustrates the schematic set up of the LOI measurement. The test

sample was vertically placed at the center of a glass chimney, with the inside

filled with a mixture of oxygen and nitrogen. The sample was inflamed with a

burner from the top. The LOI value is defined as the minimum oxygen

concentration [O2] in the mixture that either sustains the burning of the specimen

for 3 minutes or the flame reaches the mark 5 cm from the top of the specimen.

The LOI value can be expressed as follow:

𝐿𝑂𝐼 =[𝑂2]

[𝑂2] + [𝑁2]× 100%

In this work, the LOI tests were carried out using an Oxygen Index instrument

(FTT, UK ) with the specimen dimensions of 127 x 6.5 x 3 mm3, and the LOI

values were determined according to the international standard (ISO 4589).

Page 49: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 34

Figure 4-6: Schematic set up of LOI (left) and UL-94 V (right) instruments[211]

The set of UL-94 tests has been approved by “Underwriters Laboratories Inc.” to

determine the safety of flammability of plastic materials parts in devices and

appliances. It contains a series of flammability tests (94 HB, 94 V, 94 VTM, 94 5V,

94 HBF, 94 HF and radiant panel). The most commonly used test method is

UL-94 V for investigating the ignitability and flame spread when materials

exposed to a small fire. In the test 5 specimens are tested. The sample is

vertically fixed on sample clamp as shown in Figure 4-6. A burner flame with a 20

mm height and a power of 50 W is applied to the bottom of the specimen for 10

seconds. The after-flame time t1 (the time required for the flame to extinguish) is

recorded. After extinction, the burner flame is applied for another 10 seconds,

the after-flame time t2, after glowing time t3 (the time required for the fire glow to

disappear) and whether the dripping causes the cotton beneath the specimen to

ignite, are recorded. For each material, 5 specimens must be tested. Then

according to the standard shown in Table 4-5, the UL-94 classification of

materials can be determined as V-0, V-1 or V-2.

Page 50: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 35

Table 4-5: Classification of materials for the UL-94 V tests

Criteria Condition V-0 V-1 V-2

After flame time (t1 or t2) for each individual

specimen

≤ 10 s ≤ 30 s ≤ 30 s

Total after flame time (t1 + t2) for all 5 specimens of

any set

≤ 50 s ≤ 250 s ≤ 250 s

After flame and after glowing time (t2 + t3) for each

individual specimen after second flame application

≤ 30 s ≤ 60 s ≤ 60 s

Flaming dripping allowed No No Yes

Cotton ignited by dripping from any individual

specimen

No No Yes

Flame or glowing to the clamp No No No

In this work, the UL-94 V tests were performed according to ASTM D 3801,

using a horizontal vertical flame chamber, HVUL2 (ATLAS MTS, USA) with the

specimen dimension of 130 x 13 x 3.2 mm3.

Cone calorimetry Test (CCT) is one of the most effective bench scale polymer

fire behavior test methods.[212] It is based upon the principle of oxygen

consumed during the combustion process of the polymer. It is approved that the

heat released by a burning specimen is proportional to the total oxygen

consumption. The cone calorimeter is able to measure the gas flow, oxygen, CO,

and CO2 concentration and smoke density in the combustion products. Figure

4-7 illustrates the schematic set up of a cone calorimeter. During the test, a

sample sheet with a surface of 100 x 100 mm2 is wrapped with aluminum foil

covering the sides and bottom and located horizontally in the load cell. An

Page 51: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 36

external incident radiant flux can be applied from above by means of a

temperature controlled conical heater. The inflammable volatile products, which

are released by the degradation of the specimen, will be ignited by the electric

spark. The quantity of heat released per unit of time and surface area, heat

release rate (HRR), can be calculated on the basis of oxygen consumption of

13.1 MJ for 1kg of oxygen and expressed in kW/m2. The evolution of HRR over

time, particularly the peak of HRR (pHRR), is usually taken into account in order

to evaluate fire hazard. In addition, many further valuable parameters of the

combustion can also be recorded, such as the time to ignition (TTI), total heat

release (THR), mass loss (ML) of the sample, CO and CO2 production, total

smoke production (TSP), smoke production rate (SPR) and smoke toxicity index,

etc.[213, 214]

Figure 4-7: Schematic set up of a cone calorimeter[211]

4.4.8 Mechanism Studies

Thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) was

carried out using a thermogravimetric analyzer, TGA Q5000 (TA Instruments,

USA) coupled with Fourier transform infrared spectrometer, Nicolet iS50

Page 52: Development and Investigation of Bio-based Environmentally ...

Experimental: Materials, Processing and Characterization Methods 37

(Thermo Electron, USA) in the range between room temperature and 800 °C at a

heating rate of 10 K/min under nitrogen atmosphere. The FTIR spectra of

evolved gaseous products were recorded in the range of 4000-600 cm-1 with a

resolution of 4 cm-1 and averaging 8 scans.

Scanning electron microscopy (SEM) with energy dispersive X-ray analysis was

observed via a microscope (Carl Zeiss SMT, Germany) to study the

morphological features of char after cone calorimetry tests.

Page 53: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 38

5 Results and Discussion

5.1 VP based PLA Composites

Vanillin (VA) is one of the most promising bio-based and bio-degradable raw

material for polymer synthesis. It also shows the potential to be used as a

functional additive. In this subchapter, the impact of vanillin on the properties of

PLA will be discussed. In addition, a novel vanillin derivate,

bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP), was synthesized

according to the procedure described in Figure 4-1 and characterized by FTIR

and NMR. VA and VP were mixed with PLA via plasticorder according to the

recipe shown in Table 5-1 and then injection molded to prepare different samples

with a suitable dimension for different measurements. The morphology of the

sample was first investigated using SEM with EDX. Then, the thermal

degradation behaviors were studied via TGA and DSC. Afterwards, the influence

of VA and VP on the mechanical properties of PLA were determined. Finally, the

flame retardant properties of PLA composites and the mechanism were

investigated via LOI, UL-94 V, CCT and TG-FTIR.

Table 5-1: Recipe of pure PLA and its composites

Sample PLA (wt.-%) VA (wt.-%) VP (wt.-%)

PLA 100 0 0

PLA1VP 99 0 1

PLA2VP 98 0 2

PLA5VP 95 0 5

PLA10VP 90 0 10

PLA10VA 90 10 0

Page 54: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 39

5.1.1 Structural Characterization

5.1.1.1 FTIR Spectroscopy

In order to identify the desired structure as described in the experimental part,

VP and VA were characterized by FTIR, the FTIR spectra of VA and VP are

shown in Figure 5-1, and the assignment of the main vibrational modes for VA

and VP are listed in Table 5-2.

Table 5-2: Assignment of the main vibrational modes for VA and VP

Vibration VA VP

υ (C=O) 1660 1685

υ (O-H) 3138

δ (O-H) 1198

υ (C-OH) 1150

δ (CH3) 1427,1452 1421,1463

υ (C-C arom.) 1508,1584 1501,1590

υ (P=O) 1267

υ (P-O-C) 1146, 1214

υ (P-ph) 905, 1111

In the spectrum of VA, the strong intensity broad band centered at 3138 cm -1

could be assigned to OH stretching vibrations. The broad range of 2700-3500

cm -1, which disappears in the spectrum of VP, is due to the intermolecular

hydrogen bonding.[215] Weak bands observed at 3026 and 2947 cm-1 could be

attributed to CH3 asymmetric stretching vibrations. The weak band at 2864 cm-1

and very strong band observed at 1660 could be assigned to CH stretching

vibrations and C=O stretching vibrations of the aldehyde group respectively. The

strong bands at 1584 and 1508 cm-1 are attributed to CC stretching vibrations of

the benzene ring. The bands centered at 1452 and 1427 cm-1 could be due to

Page 55: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 40

the asymmetric deformation vibrations of CH3 group. The bands observed at

1398, 812 and 731 cm-1 could be assigned to CH, O=C-H and C-C-CHO

deformations related to the aldehyde group, respectively. While the medium and

strong bands at 1198 and 1120 cm-1 are due to the CCH deformation of the

benzene ring. The bands observed at 1298 and 1150 could be attributed to

C-O-H deformation and C-O stretching vibrations related to the hydroxyl group.

And the band appears at 1024 cm-1 is due to the O-CH3 stretching vibrations. In

comparison of the spectrum of VA, a few new characteristic bands have been

obtained: the very strong band appears at 1267 cm -1 could be assigned to the

P=O stretching vibrations,[216] and the bands observed at 1111 and 905 cm-1

could be attributed to P-C stretching vibrations related to the benzene ring. The

FTIR spectra confirmed the desired structure as described in the experimental

part.

Figure 5-1: FTIR Spectra of VA (black) and VP (red)

5.1.1.2 NMR Spectroscopy

In order to further validate the successful synthesis of VP, 1H-, 13C- and 31P-

NMR were carried out and shown in Figure 5-2. In the case of 1H NMR, the

structure of VP was confirmed by the appearance of chemical shifts at 7.53, 7.63

Page 56: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 41

Figure 5-2: 1H (top), 13C and 31P (bottom) NMR spectra of VP

and 8.05 ppm corresponding to label 5, 4 and 3 attributed to protons of the

benzene ring from phenylphosphonic dichloride (PPDC); the chemical shifts at

7.40, 7.44 and 7.45 ppm (labeled 8, 7 and 6 in Figure 5-2-a) are assigned to the

protons of the benzene ring of vanillin. The chemical shifts at 3.80 and 9.91 ppm

correspond to the protons from the methoxy and aldehyde groups of vanillin. In

the 13C NMR spectra of VP, chemical shifts at 123.71, 128.42, 132.27 and

133.38 ppm are attributed to the carbons from PPDC; the chemical shifts at

Page 57: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 42

55.95, 110.96, 122.14, 124.90, 134.26, 144.60, 151.60 and 190.80 ppm are

assigned to the carbons from vanillin. The result of 31P NMR is also shown in

Figure 5-2(bottom). The chemical shift at 12.7 ppm is assigned to the phosphor

from PPDC, and the single signal indicates the high purity of the product. In

summary, all these NMR results mentioned above correspond well with the

desired structure from the experimental part, and further confirm the formation

and the high purity of VP.

5.1.2 Morphology of VP and PLA/VP Composites

The morphology of VA and VP, as well as flame retardant PLA composites based

on them, were observed via Scanning electron microscopy (SEM) coupled with

energy dispersive X-ray analysis (EDX). As shown in Figure 5-3, VA has a

rod-like shape with a smooth surface (left). However, the surface of VP is relative

rougher and some small particles clung to each other (right). The morphological

surface of VP is obviously different from that of VA, indicating the occurrence of

modification. And the EDX spectrum of VP with the presence of phosphorus

(blue) has further confirmed the chemical modification.

Figure 5-3: The morphology of VA and VP by SEM (left) and EDX (right)

The cross-section scans of PLA composites were also observed and the pictures

are demonstrated in Figure 5-4. Both samples showed dense plane with an

extremely smooth surface, indicating that both VA and VP are well miscible with

Page 58: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 43

the matrix. The bright areas and dots seemed to be VA and VP dispersed in the

matrix. VA presented two types of dispersion in the matrix, micro-particles in

nanometer level and circles in roughly 50 μm. By contrast, VP showed uniform

nano-dots, revealing a highly improved dispersion. The reason for the

agglomeration of VA could be associated with its inter molecule hydrogen

bonding. However, the hydroxyl group in VP was removed by modification.

Hence, VP didn’t present inter molecule hydrogen bonding. The difference could

be also observed by FTIR (Figure 5-1).

Figure 5-4: SEM pictures of PLA/VA (left) and PLA/VP (right) composites

5.1.3 Thermal Decomposition Behavior

Thermogravimetric analysis (TGA) was employed to evaluate the thermal

decomposition behavior of VA and VP, as well as their effect on the thermal

stability of PLA and its composites.

Table 5-3: Data obtained from TGA plots of VA and VP

Sample T5% (°C) T50% (°C) Tmax (°C) Residue (wt-%)

VA 124 165 175 0

VP 286 348 343 24.5

Tx% was the temperature at x% weight loss of the samples. Tmax was the temperature at

the maximum rate of weight loss. Residue was the yield at 600 °C.

Page 59: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 44

Firstly, the thermal decomposition of VA and VP under a nitrogen atmosphere

was evaluated via normal TGA with the heating rate of 10 K/min. The resulting

curves are shown in Figure 5-5. The temperature at which the weight loss of

sample was 5% can be considered as the initial decomposition temperature. The

relative thermal stabilities of samples were evaluated by comparing the

temperature at 50% weight loss, the temperature at maximum weight loss rate

as well as char residue at 600 °C. These detail data are summarized in Table

5-3.

Figure 5-5: TG (left) and DTG (right) plots of VA and VP

Like many other food additives, vanillin is relatively more sensitive to heat than

normal additives for thermoplastics. The TGA results showed that pure vanillin

started to lose weight at around 80 °C corresponding to a slight peak on the DTG

(differential thermal gravity) curve, and subsequently showed a T50% of 165 °C,

indicating that vanillin has a volatile nature. And this poor thermal stability leads

to the decomposition and evaporation of vanillin during the processing of its

polymer composites. In comparison with pure vanillin, the thermal stability of the

modified one, VP, was significantly improved, T5%, T50% and Tmax were shifted

from 124, 165 and 175 °C to 286, 348 and 343 °C, respectively. It showed an

improvement of more than 160 °C. Furthermore, the residue of VP at 600 °C in a

nitrogen atmosphere was around 30%. These properties make VP a

considerable additive for plastic.

Page 60: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 45

The next step consisted in the evaluation of the effect of VP on the thermal

oxidative decomposition of PLA. The relative thermal stabilities of the samples

were compared by the value of T5%, T20%, Tmax as well as char residue at 600 °C.

TG and DTG curves of the samples are presented in Figure 5-6 and the data are

summarized in Table 5-4. As shown in Figure 5-6, there was only one

degradation step for the pure PLA ranging from 300 to 400 °C. As for the PLA/VA

composite, the degradation obviously consisted of two steps. The first step was

from around 150 to 300 °C and the weight loss in this stage was about 10%,

which corresponded to the loading of vanillin in the composite. It can be also

observed from the DTG plots of PLA/VA that the rate of weight loss in the

temperature range 160 to 300 °C was almost constant, indicating the weight loss

was only corresponding to the evaporation of vanillin. Comparing with the TG

plots from Figure 5-5, the beginning temperature was higher than the initiation of

the weight loss of VA. This should be due to that the PLA matrix was not melted

until 160 °C, and vanillin was completely released only when the sample was

heated above its boiling temperature (285 °C). Consequently, the thermal

stability of PLA was decreased after the introduction of VA.

Figure 5-6: TG (left) and DTG (right) plots of PLA and its composites

In the case of PLA/VP composites, based on the results in Table 5-4, the residue

at 600 °C remained at the same level, the differences were negligible. Besides,

the value of T20% of PLA1VP, PLA2VP, PLA5VP and PLA10VP were shifted from

Page 61: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 46

344 °C of PLA to 350, 352, 357 and 357 °C, respectively, while Tmax shifted from

363 °C of PLA to 366, 369, 373 and 380 °C, respectively, indicating the thermal

stability of material was improved, even when the loading of VP was only 1%

and the improvement was stronger as the loading of VP rose. However, another

interesting result found in TG was that the value of T5% of the samples reached

the maximum when the loading of VP was 2%. It can be supposed that on one

hand, the introduction of VP could improve the thermal stability of PLA; on the

other hand, VP decomposed at a lower temperature than PLA. The

decomposition seemed to be not noticeable when the loading of VP lower than

2%. However, when the samples were further heated, VP could react with PLA

and enhance its thermal stability. Hence, T20% and Tmax shifted to a higher

temperature as the loading of VP increased.

Table 5-4: Data obtained from TGA plots of PLA and its composites

Sample T5% (°C) T20% (°C) Tmax (°C) Residue (wt-%)

PLA 326 344 363 0

PLA1VP 331 350 366 0.8

PLA2VP 333 352 369 0.2

PLA5VP 325 357 373 0.3

PLA10VP 324 357 380 0.7

PLA10VA 225 334 362 0.6

Tx% was the temperature at x% weight loss of the samples. Tmax was the temperature at

maximum rate of weight loss.

Furthermore, the thermal decomposition kinetics of PLA/VP composite was

studied by means of Flynn-Wall-Ozawa method. In this work, multiple heating

rate TGA, by which the heating rate was set as 10, 20, 30, and 40 K/min, were

performed to determine the necessary parameters. The fitted curves of lnβ

against 1/T at different conversion for PLA and PLA10VP (10 wt.-% VP) are

Page 62: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 47

shown in Figure 5-7, and the resulting parameters, apparent activation energy

(Ea) as well as the coefficients of determination (r2) obtained from the fitted

curves of lnβ against 1/T are listed in Table 5-5. Generally, the basic

decomposition kinetic during the TGA measurement can be described via the

following equation:

𝑑𝛼

𝑑𝑇=

𝐴

𝛽𝑒(−

𝐸

𝑅𝑇)𝑓(𝛼)

Where α is the degree of conversion, T is the temperature in kelvins, β is the

heating rate, A is the pre-exponential factor, R is the ideal gas constant and E is

the activation energy. Using the Doyle’s approximation, the following expression

can be obtained:

lg 𝛽 = lg𝐴𝐸

𝑅𝑔(𝛼)− 2.315 − 0.4567

𝐸

𝑅𝑇

It can be seen that the fitted curves, lnβ plotted against 1/T, give straight lines

with slope m= -0.4567Ea/R during a series of measurements with different β at a

certain degree of conversion. Through this relationship, a series of Ea values can

be calculated corresponding to every α value.

Figure 5-7: Fitted curves of lnβ against 1/T at different α of PLA (left) and PLA10VP (right)

As shown in Figure 5-7, the fitted curves of lnβ against 1/T at different α of PLA

were almost parallel at different values of α, while the slope of fitted curves of

Page 63: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 48

PLA10VP slightly increased with risen α value. Based on the calculated Ea

values from Table 5-5, both PLA and PLA10VP showed a similar decreasing

trend. The addition of VP raised the Ea value of PLA until the degree of

conversion reached 0.8. However, the enhancement decreased with rising α.

For example, when α was 0.1, Ea of PLA was 9 kJ/mol lower than that of

PLA10VP, while then difference reduced to only 0.6 kJ/mol when α was 0.7.

Furthermore, the difference shifted continually in a minor way, and when α

reached 0.9, Ea of PLA was already 3.1 kJ/mol higher than that of PLA10VP. It

can be concluded that the addition of VP had two opposite effect on the thermal

decomposition of PLA, which reach the equilibrium when α was between 0.7 and

0.8. On one hand, the thermal stability could be improved due to the antioxidant

effect of vanillin segment; further, thermal decomposition of VP could release

phosphonic acid, which could accelerate the decomposition of PLA. Therefore,

when more phosphonic acid was produced at high temperature, the reduction

effect on the thermal stability was stronger, and the composite decomposed

faster.

Table 5-5: Calculated values of Ea and r2 of PLA and PLA10VP at different α

PLA PLA10VP

Conversion (α) Ea (kJ/mol) r2 Ea (kJ/mol) r2

0.1 100.9 0.98994 108.9 0.98428

0.2 98.9 0.99052 109.1 0.99378

0.3 97.1 0.99224 104.6 0.9930

0.4 96.6 0.99475 103.9 0.99043

0.5 95.6 0.99268 100.1 0.99034

0.6 94.8 0.99492 96.7 0.98562

0.7 94.0 0.98914 94.6 0.98731

0.8 93.4 0.99201 93.0 0.98848

0.9 95.5 0.99233 92.4 0.98652

Page 64: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 49

5.1.4 Thermal Crystallization Behavior

Different crystallization characteristics could affect various bulk properties of

polymer composites. Understanding the crystallization behavior of materials has

both analytical and practical importance. Differential scanning calorimetry (DSC)

was used to estimate the thermal characteristic of PLA and PLA/VP composites.

The samples were measured under a N2 atmosphere with 10 K/min

heating/cooling rate. In Figure 5-8, the comparison of the DSC thermographs of

the second heating between PLA and PLA/VP composites with various VP

loadings is presented. Additionally, Table 5-6 summarizes the data obtained from

this heating run and also the calculated degree of crystallinity of all the samples.

The thermal history of samples was removed by keeping the temperature at

200 °C for 3 minutes. Then the samples were cooled down to room temperature,

following immediately by the second heating, so that all the samples had the

same thermal history.

Figure 5-8: DSC plots of PLA and PLA/VP composites

The DSC curves of PLA and PLA/VP composites revealed similar thermal

crystallization behavior. The sample underwent following thermal events

successively with increasing temperature: the glass transition (characterized by

Page 65: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 50

the glass transition temperature Tg), the exothermic cold crystallization

(characterized by the cold crystallization temperature Tcc and the cold

crystallization enthalpy ∆Hcc) and two steps endothermic melting process

(characterized by melting temperature Tm1 and Tm2 as well as the melting

enthalpy ∆Hm).

Table 5-6: Data obtained from DSC of PLA and PLA/VP composites

Sample Tg

(°C)

Tcc

(°C)

Tm1

(°C)

Tm2

(°C)

∆Hcc

(J/g)

∆Hm

(J/g)

Χc (%)

PLA 60.6 113.7 160.1 166.0 33.00 33.08 35.5

PLA1VP 59.5 115.3 159.6 165.4 34.02 34.07 37.0

PLA2VP 59.2 112.9 158.6 165.4 32.89 34.56 37.9

PLA5VP 56.8 111.7 156.3 163.9 32.63 33.56 37.9

PLA10VP 53.6 115.4 154.9 162.5 31.66 31.75 37.9

Based on the thermographs and the data from Table 5-6, it can be concluded

that the addition of VP altered the Tg of samples continuously to the minor

direction. As the loading of VP was 10 wt.-%, Tg of the sample was shifted from

60.6 °C of PLA to 53.6 °C. That was considered to be attributed to the

plasticization effect of VP. The small molecular VP enhanced the chain segment

mobility of PLA. Furthermore, at around 113 °C, PLA represented a sharp

exothermic peak, corresponding to the cold crystallization process during the

heating. Comparing with that, after the introduction of VP, the peaks of Tcc of the

samples showed a decreasing trend as the loading increased, suggesting the

incorporation of VP enhanced cold crystallization ability of matrix polymer.

Besides, the crystallization enthalpies of the samples decreased with rising

loading of VP, suggesting that VP had a nucleating effect and can accelerate the

crystallization speed of PLA. However, by more specific analysis, it was

Page 66: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 51

observed the Tcc value decreased to lowest 111.7 °C with 5 wt.-% loading. When

the loading continued rose to 10 wt.-%, although the cold crystallization enthalpy

was lower, the Tcc shifted to higher 115.4 °C. Proposed reason for that was that,

higher loading of filler resulted in more agglomeration and hindered the cold

crystallization.[65]

Parallel to the shift of Tg, the Tm values of the samples were also altered to the

lower direction due to the plasticization effect of VP, and the shift rose with

increasing VP loading. All the samples showed double endothermic melting

peaks model, which has been reported for several semicrystalline polymers.

This bimodal peaks phenomenon was considered to be associated with the

different crystalline structures in the polymer. During the slow DSC scans, the

less perfect and unstable structure had enough time to melt and recrystallize into

the crystal with higher structural perfection, which melted at higher temperature.

According to the theoretical melting enthalpy of perfectly crystalline PLA, the

weight fractional crystallinity of the samples can be calculated based on the

following equation:

𝑥𝑐 =∆𝐻𝑚

(1−∅)∆𝐻𝑚∗ × 100%

Where Φ is the weight fraction of the filler in the composites, ΔHm is the melting

enthalpy calculated from the DSC curves and ΔHm* equals 93.1 J/g as

reference.[65, 217]

As shown in Table 5-6, the crystallinity of PLA represented an increasing trend

after the introduction of VP. However, it reached the highest value when the

loading of VP was 2 wt.-% and kept at the same value even when the loading

increased to 10 wt.-%. It could be explained by the good dispersion of VP in the

polymer matrix. In other words, when the filler dispersed well enough in the

polymer matrix, the particles amount in the matrix were very huge, which was

Page 67: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 52

able to support the nucleation and promote the growth of crystals of the polymer

matrix.

Interestingly, the content of VP also affected the magnitude of the double melting

peaks of the samples. Firstly, with 1 wt.-% of VP, the first melting peak was

higher than that of PLA. It could be ascribed to the acceleration effect to the

crystallization of PLA. However, the low loading was only enough to accelerate

to form less perfect crystallization. When the loading of VP continued to increase,

the fraction of the first melting peak gradually decreased, suggesting that VP

contributed to form crystallization with higher perfection.

5.1.5 Flammability

In this work, LOI and UL-94 were applied to evaluate the flammability of PLA

composites. LOI is a quantitative method which shows the minimum oxygen

concentration of an oxygen/nitrogen mixture to maintain the combustion of the

sample, while the UL-94 measurements provide a qualitative classification

presenting extinguishment or upward spreading behavior of flame after the

ignition from bottom of samples, and the samples are classified by no rating, V-2,

V-1 and V-0, where the V-0 demonstrates the best flame retardant rating. The

results of LOI and UL-94 tests of PLA and PLA composites are summarized in

Table 5-7. Results showed that the LOI value of pure PLA was 21.4%, revealing

that PLA was an easily flammable material. It was also observed that during the

UL-94 tests, the samples were burned to the sample holder with intensive

burning dripping behavior and high velocity, and the cotton was ignited by the

droplets. With 10 wt.-% of VA, some of the samples can self-extinguish in about

10 seconds. However, the cotton under the samples was still ignited by the

flaming dripping, and LOI value decreased from 21.4% of PLA to 19.5%. Reason

for this result is that vanillin is flammable and volatile at high temperature, it can

be ignited more easily than PLA. By contrast, after the introduction of VP, the

Page 68: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 53

samples showed a positive effect both in LOI and UL-94 tests. When the loading

of VP were 5 wt.-% and 10 wt.-%, the LOI values of the composites were

improved to 25.8% and 26.3%. Furthermore, both of the composites passed V-0

level in UL-94 tests, and the cotton was not ignited. It seemed that the

introduction of VA and VP has changed the melt flow behavior of PLA. The ease

of flow could take heat away in large scale. This could be the reason for the

better results of UL-94. Nevertheless, all the results suggested that VP can

provide good flame retardancy to PLA.

Table 5-7: LOI, UL94 and MFI results of PLA and PLA composites

Sample LOI (%) UL-94 Rating * MFI (g/10min) Ignition of cotton

PLA 21.4 No rating 6.0 Yes

PLA5VP 25.8 V-0 15.9 No

PLA10VP 26.3 V-0 59.5 No

PLA10VA 19.5 No rating 28.4 Yes

* Sample thickness of UL-94 tests was 3.2mm

5.1.6 Combustion Behavior

Cone calorimeter test (CCT) is one of the most efficient methods to investigate

the flame retardant properties of polymeric materials. The consumption of

oxygen is recorded to calculate the heat release of the measured samples.

Curves obtained from the CCT are presented in Figure 5-9 and Figure 5-10, the

corresponding characteristic parameters are collected in Table 5-8, including

time to ignition (TTI), peak of heat release rate (pHRR), total heat release (THR),

total smoke production (TSP), average effective heat of combustion (av. EHC)

and residual mass.

Page 69: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 54

Table 5-8: Data obtained from CCT of PLA and PLA composites

Sample TTI

(s)

pHRR

(kW/m2)

THR

(MJ/m2)

TSP

(m2)

Residue

(%)

PLA 68±3 407±16 66.0±0.9 0.32±0.17 0.5±0.2

PLA10VA 64±5 396±2 64.9±0.7 0.57±0.19 0.9±0.3

PLA5VP 76±4 370±14 62.8±1.1 1.53±0.09 6.0±0.1

PLA10VP 79±2 292±28 62.6±1.7 3.33±0.18 7.7±0.5

Based on the results obtained from CCT, it can be seen that TTI of PLA was 68 s.

When pure PLA was ignited, it exhibited fiercely combustion and consumed all

the material, showing a total heat of 66.0 MJ/m2, with a pHRR value of 407

kW/m2. After the introduction of pure vanillin, the pHRR and THR value

decreased slightly to 396 kW/m2 and 64.9 J/m2, respectively. However, the TTI

was 64 s, which is 4 s earlier than pure PLA. It could be explained by the volatile

nature of Vanillin. When the material was melted by heat radiation, vanillin was

evaporated and then decomposed earlier than PLA into gaseous flammable

products. Hence, the specimen was ignited faster than pure PLA. In comparison,

VP and PLA demonstrated better cooperation towards flame retardancy. The

pHRR and THR value of PLA5VP were reduced to 370 kW/m2 and 62.8 J/m2,

respectively. When the loading of VP increased to 10 wt.-%, the pHRR and THR

value of sample decreased further to 292 kW/m2 and 62.6 J/m2, respectively. In

addition, TTI values of PLA/VP composites were delayed to 76 and 79 s

respectively.

Page 70: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 55

Figure 5-9: HRR plots of PLA and PLA composites

As shown in Figure 5-9, the HRR curves of pure PLA, PLA5VP and PLA10VA

exhibit a similar pattern. After the ignition, the heat release increased fast and

continuously to the peak, suggesting that the flame spread rapidly into the

surface of the entire specimen. The broad peak indicated that the combustion

consumed all the material without any inhibition, corresponding to the slow

decreasing of HRR after the peaks. Interestingly, the HRR of PLA10VP grew

rapidly to the peak after the ignition and decreased immediately from 292 kW/m2

to around 200 kW/m2. The reason for that was supposed to be the

decomposition of VP, which simultaneously provide combustible gas products

and phosphor-containing segments. The combustible products were ignited and

contributed to the strong release of heat. And immediately the combustion was

suppressed by the phosphor-containing segments due to the radical capture

effect. As a consequence, the HRR of PLA10VP exhibited a sharp peak direct

after the ignition due to the evolved phosphor containing radical scavenger.

When all these products were consumed, the combustion behavior of the rest

specimen was similar like pure PLA, showing broad peak until all the material

was burned off. Hence, it can be concluded that the incorporation of VP can

Page 71: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 56

significantly reduce and delay the heat release in PLA composites.

As mentioned before, although the introduction of both VA and VP can reduce

the THR of specimens in comparison with pure PLA, the reduction was not that

distinct. However, in Figure 5-10-(a) more obvious difference of the development

of THR could be found: the curve of PLA10VP was almost linear and its slope

was much lower than that of other curves, indicating that the combustion of

PLA10VP was much slower. Consequently, its THR at the same time after the

beginning of measurement was also much lower than that of other samples. This

result also matched with the curves of mass loss of the samples based on Figure

5-10-(b). The mass loss rate of PLA10VP kept almost constant and was much

slower than that of other samples.

Considering the few residues remained after the CCT (Table 5-8), it was unlikely

that those residues could act as a barrier or protective layer to reduce the heat

release. So the action in gaseous phase should mainly contribute to the flame

retardant property of the PLA composites. The release of gaseous products and

smoke were very important parameters to estimate the combustion behavior of

materials, especially for the action in gaseous phase. The total smoke

production (TSP) and the ratio of CO/CO2 are presented in Figure 5-10-(c) and

(d). It can be seen from Figure 5-10-(d), the first peak of pure PLA was around

0.03, while that of PLA5VP and PLA10VP was around 0.08 and 0.13 respectively.

It was considered to be associated with the radical scavenger effect of

phosphor-containing products evolved by VP, which lead to incomplete

combustion of the samples. The double peaks at the beginning of the curve of

PLA10VA could be explained by the earlier ignition of the volatile vanillin and its

acceleration effect to the ignition of PLA. The peaks at the end of the curves

could arise from the thermal degradation of the samples without the presence of

fire.

Page 72: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 57

Figure 5-10: THR (a), Mass loss (b), TSP (c) and CO/CO2 ratio (d) plots of PLA and PLA

composites

5.1.7 Rheological properties

The rheological performance of PLA and PLA composites are presented in

Figure 5-11. The complex viscosity of neat PLA presented low dependency in

the lower frequency range. A Newtonian plateau was obtained in the range

0.1-10 rad/s, while a slight shear thinning behavior was observed at the higher

shear rate. The complex viscosity gradually decreased with rising VP loading,

indicating that VP possessed notable plasticization effect for PLA. For PLA10VP,

the complex viscosity was reduced by more than an order of magnitude. In

addition, the Newtonian plateau was extended to high frequency range, almost

no shear thinning behavior was observed. For all the samples, G’’ was overall

higher than G’, indicating that the samples were more viscous than elastic.

Comparing with neat PLA, both G’ and G’’ of composites were declined with

Page 73: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 58

increasing VP loading. In case of PLA10VP, G’’ decreased by two over the entire

frequency range, while such notable difference in G’ only observed at the higher

shear rate. In summary, the lubricant effect of VP led to the decrement of

strength provided by the entanglements of PLA chain, thereby reducing the melt

viscosity and enhancing the processability of PLA. Since the dripping behavior

could be considered as a low shear rate phenomenon, the results of rheological

measurements further supported the results obtain in LOI and UL-94 tests.

Figure 5-11: Rheological properties of PLA and PLA composites: (a) Complex viscosity; (b)

Storage modulus; (c) Loss modulus

5.1.7.1 Analysis of evolved gaseous products

To further understand the decomposition and flame retardant mechanism,

TGA-FTIR was employed to study the evolved gaseous products. The 3-D

images and FTIR spectra of involved products for PLA and PLA10VP are shown

in Figure 5-12. The thermal degradation process of PLA has been intensively

studied by many researchers.[153, 154, 218] According to the results, the main

gas products from degradation products of PLA were water (3577 cm-1),

Hydrocarbons (2900-3000 cm-1), CO2 (2350 cm-1), CO (2114 and 2182 cm-1),

carbonyl compounds (1762 cm-1) and aliphatic ethers (1100-1250 cm-1). An

obvious decreasing at 1238 cm-1 (related to C-O stretching) for PLA10VP was

observed.

Page 74: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 59

Figure 5-12: 3D-images of evolved gaseous products for (a) PLA (b) PLA10VP; (c) Total

absorbance vs time for PLA and PLA10VP; (d) Absorbance at 1238 cm-1 vs time for PLA

and PLA10VP (c) At Tmax for PLA and PLA10VP; (d) Zoom in on selected area. (Tmax

appeared at 47 min)

In addition, the total absorbance of PLA was also stronger than that of PLA10VP,

indicating that the incorporation of VP led to an overall reduction of evolved

gaseous products. Furthermore, as can be seen in Figure 5-12-(e), two bands at

1266 and 1284 cm-1 appeared, which could be assigned to P-C and P=O,

Page 75: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 60

respectively. This could be the reason for the reduction of C-O containing

products evolved. The phosphorus-containing compounds were considered to

be able to strongly interact during the radical reactions especially at high

temperature, and thus reduce the flammability as it is demonstrated and

discussed in cone calorimeter results.[153]

5.1.8 Mechanical Properties

5.1.8.1 Effect of different fillers

The first selective criterion for a specific material in the application is the

mechanical performance. When developing a new functional additive for

polymeric materials (in this work, flame retardant), it is therefore also necessary

to evaluate the impact of incorporating this additive to other properties of the

final composites. The stress-strain curves of PLA and PLA Composites are

shown in Figure 5-13, and the results of Young’s modulus, tensile strength,

elongation at break and impact strength are summarized in Table 5-9.

Figure 5-13: Tensile test plots of PLA and PLA composites

It is widely known that PLA is a stiff thermoplastic polymer. Based on the results,

pure PLA exhibited a high rigidity (3700 MPa), a high tensile strength (57 MPa)

Page 76: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 61

and a low elongation at break (3 %). Despite the introduction of VA improved

slightly the elongation at break to 4 %, some mechanical properties were notably

deteriorated: the Young’s modulus decreased to 2900 MPa while the tensile

strength declined to 42 MPa. In case of PLA/VP composites, comparing the

significant improvement of elongation at break of PLA/VP composites (11 % for

PLA5VP), the decreasing of tensile strength and Young’s modulus was

negligible. In contrast, the introduction of some molecular additives led to an

increase in the impact resistance of PLA. The impact strength of PLA10VA,

PLA5VP and PLA10VP was improved from 16 kJ/m2 of PLA to 17, 18 and 18

kJ/m2, respectively. This result can be explained by the lubricant effect of the

additive, which enhanced the chain mobility of PLA.

Table 5-9: Data obtained from tensile test of PLA and PLA composites

Sample Young’s

modulus

(MPa)

Tensile

strength

(MPa)

Elongation

at break

(%)

Impact

resistance

(kJ/m2)

PLA 3700±100 57±1 3±1 16±2

PLA5VP 3500±100 54±1 11±3 18±3

PLA10VP 3500±200 52±1 9±3 19±2

PLA10VA 2900±100 42±1 4±2 17±3

As the SEM results of the samples showed (Figure 5-4), due to the

intermolecular hydrogen bonding the phase size of VA was much bigger than

that of VP. So the plasticization effect of VP to PLA was better than that of VA.

Besides, the agglomeration caused stress concentration in composites. It can be

seen from the specimens after tensile tests that the microcracks of PLA/VA

specimens were more random and developed from the edge to the middle of

specimens, and most of the cracks crossed less than 1/4 of the specimen’s width

Page 77: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 62

(shown in Figure 5-14). By contrast, the microcracks of PLA/VP specimens were

finer and most of them crossed the specimen’s width. The cracks developed

from the breakage to both ends of the specimens. This phenomenon indicated

that the stress transfer across specimens was much better in PLA/VP

composites due to the homogeneous structure. This was in good agreement

with the better dispersion of VP observed in SEM. Consequently, VP had a

plasticization effect, which caused decreasing of stiffness and improvement of

elongation at break. Besides, the agglomeration of filler could also cause

deterioration of various mechanical properties. Hence, as the loading of VP rose,

there was more chance that agglomeration formed, so the elongation at break of

samples decreased. Nevertheless, VP could significantly improve the elongation

of PLA with similar tensile strength.

Figure 5-14: Pictures of tensile bar after tests of PLA10VA (left) and PLA10VP (right)

5.1.8.2 Effect of different processing methods

PLA can be processed using almost all the nowadays processing methods, and

its properties can be altered depending on different processing conditions. In this

work, PLA and PLA composites were mainly mixed via plasticorder and extruder,

and then further converted into desired specimens for tests. To investigate the

Page 78: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 63

influence of different processing techniques on the mechanical properties of PLA

and PLA/VP composite, the materials were prepared via different processing

methods. Figure 5-15 shows the stress-strain curves of original PLA (PLA O) and

processed PLA via plasticorder (PLA B) and extruder (PLA E), as well as those

of PLA10VP composite. It is well known that PLA undergoes shear forces and

thermal degradation which lead to change of molecular weight. So the alteration

of molecular weight of PLA was monitored via size exclusion chromatography

(SEC). The detail results are summarized in Table 5-10.

Based on the results, it can be seen that, after processing, the samples showed

decrease in molecular weight, from 125000 to 101000 for PLA B and to 109000

for PLA E, respectively. The reduction of molecular weight can be attributed to

thermal and mechanical unzipping and chain scission reactions caused by heat

and shear force, which are also responsible for an increase in chain segment

mobility.[10, 219] Thus PLA E showed an improvement in elongation at break.

Figure 5-15: Tensile test plots of PLA and PLA/VP composites processed via different

methods

On the other hand, a slight increase in tensile strength, from 55 to 57 MPa for

PLA B and to 61 MPa for PLA E, can be observed. By contrast, it is interesting to

Page 79: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 64

find that, the Young’s modulus PLA B (3700 MPa) was higher than PLA E (3300

MPa). The different processing techniques are the most responsible for the

change of properties. Generally, at the same temperature and rotational speed,

the shear rate of the extruder is higher than that of plasticorder. On the other

hand, it takes more time for a plasticorder to achieve a similar dispersion of filler

as an extruder does. Consequently, the materials processed with plasticorder

undergo more thermal degradation, whereas those processed with extruder

suffer more mechanical load. In addition, the different cooling rate of the molten

polymer after compounding is a potential factor to affect the crystallinity of

samples. Compared to the water bath cooling system of extrusion, after mixing

with plasticorder, samples were air cooled to room temperature. Despite the

materials underwent other thermal history, the differences of both experimental

sets in terms of mechanical behavior as well as crystallization and degradation

were not very large.

Table 5-10: Parameters of PLA and PLA/VP composites processed via different methods

Sample Young’s

modulus

(MPa)

Tensile

strength

(MPa)

Elongation

at break

(%)

Impact

resistance

(kJ/m2)

Molecular

weight

(g/mol)

PLA O* 3600±200 55±1 11±1 16±1 125000

PLA B* 3700±100 57±1 3±1 16±2 101000

PLA E* 3300±400 61±1 9±2 16±1 109000

PLA10VP B 3500±200 52±1 9±3 19±2 90400

PLA10VP E 3400±100 61±2 13±3 17±3 107000

* O (Original) means as received, B (Brabender) means processed by Brabender

plasticorder, E (Extruder) means processed by mini extruder

An additional study highlighting the processability of PLA/VP system was

performed. One of the most challenging processes for multicomponent materials

Page 80: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 65

is melt fiber spinning, as small changes in material properties like defects,

agglomerates and inadequate phase changes usually lead to problems in

spinnability.

Filaments of PLA and PLA/VP composites were prepared by means of melt

spinning with a take-up speed with 1000 and 2000 m/min, corresponding to titer

of 8 and 4 tex, respectively. Mechanical properties of fibers in bundles (10

monofilaments) were obtained and showed in Table 5-11. As listed, typical

mechanical properties for non-drawn PLA fibers were observed, tensile strength

between 20 and 25 cN/tex and elongation at break in the range of 50-100%. The

properties showed a take-up speed dependence due to the increased molecular

orientation with higher speed.

Table 5-11: Mechanical parameters of fibers for PLA and PLA/VP composites

Sample Titer

[tex]

Young’s

modulus

[cN/tex]

Tensile

strength

[cN/tex]

Elongation

at yield [%]

Elongation

at break [%]

PLA_1000 8.5 323.8±11.4 18.6±1.7 88.1±5.4 104.6±1.6

PLA_2000 4 454.5±7.0 22.9±0.7 46.8±2.5 57.8±2.2

5VP_1000 8 294.2±6.7 10.5±0.9 118.5±1.2 136.7±2.6

5VP_2000 4 446.5±32.7 17.7±1.6 52.5±6.7 64.2±1.6

10VP_1000 8 276.0±30.5 10.5±1.0 128.6±2.5 140.7±6.3

10VP_2000 3.8 312.9±12.4 12.5±5.0 61.9±2.2 70.3±1.9

20VP_1000 8 258.0±10.3 12.0±3.7 110.7±4.7 126.3±2.8

20VP_2000 3.5 321.7±19.5 12.5±1.2 51.8±8.1 64.8±1.1

* Sample name e.g. 5VP_1000 means fibers with 5 wt.-% VP and wound at 1000 m/min

Page 81: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 66

Compared to neat PLA, all tested PLA/VP compositions generally showed a

distinct decrease of nearly 50% in maximum tensile strength, however with a

noticeable increase in strain behavior, significantly for lower take-up speeds. VP

seems to have a slight plasticizing effect, independently of the added VP content,

and particularly for fibers wound at low speed: neat PLA shows elongation at

break of about 105 % and PLA/VP values ranging from 125-140 %. For higher

speeds, here shown for 2000 m/min, the strain properties of the fibers seem to

be nearly independent of the added amount of VP compared to neat PLA

(elongation at break for all specimens about 60-70 %).

5.1.9 Conclusion

In this part, a novel bio-based flame retardant, VP was successfully synthesized.

VP exhibited remarkable flame retardant efficiency. At very low loadings (5 and

10 wt.-%), PLA/VP composites achieved V-0 rating in UL-94 tests and improved

notably the LOI value from 21.4 for PLA to 25.8 % for PLA5VP and 26.3 % for

PLA10VP. In addition, in the cone calorimeter tests, an obvious reduction of

PHRR value was observed for PLA10VP. The most important is, the introduction

of VP didn’t cause any deterioration of the mechanical properties like many

flame retardants, in contrast, the elongation at break of PLA was significantly

improved from 3 % to 9 % (PLA10VP), i.e. the relative increase was as high as

200 %. This results may indicate VP as a promising flame retardant also for

other polymer systems and offer new possibilities for bio-based multifunctional

polymeric composites. However, the dripping behavior of PLA composites by

burning is still unsolved. To enhance the anti-dripping property, further

modification of VP would be done in the next step. Further it could be shown that

the system PLA/VP had a very good processability even with highly demanding

processes like melt fiber spinning.

Page 82: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 67

5.2 VPA and VPS based PLA Composites

In this subchapter, two derivatives of vanillin were synthesized based on VP

according to the procedure described in Figure 4-2 and Figure 4-3 and

characterized by FTIR and NMR. Crosslinkable groups were introduced into the

structure of VP, aiming to form protective layers during the combustion and

prevent the dripping behavior of PLA. It was expected that the double bond in

bis(5-((E)-(allylimino)methyl)-2-methoxyphenyl) phenylphosphonate (VPA) could

contribute or/and improve the char yield during the combustion, and the siloxane

structure in bis(2-methoxy-5-((E)-((3- (triethoxysilyl)propyl)imino)methyl)phenyl)

phenylphosphonate (VPS) was expected to be able to form a condensed layer

consisting of SiO2 and/or carbon which can isolate the material from heat and

oxygen. Structure of VPA and VPS were characterized by 1H NMR and FTIR.

Since the main target of this subchapter is to enhance the prevention of dripping

behavior of PLA, the study of properties of composites will be focused on the

flame retardancy. LOI, UL-94 and CCT were employed to evaluate the flame

retardant properties of composites. Thermal degradation behavior and

mechanical properties were investigated via TGA and tensile test. PLA

composites were prepared via plasticorder according to the recipe shown in

Table 5-12 and then injection molded to prepare different samples with a suitable

dimension for different measurements.

Table 5-12: Recipe of VPA and VPS based PLA composites

Sample PLA (wt.-%) VPA (wt.-%) VPS (wt.-%)

PLA5VPA 95 5 0

PLA10VPA 90 10 0

PLA5VPS 95 0 5

PLA10VPS 90 0 10

Page 83: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 68

5.2.1 Characterization of VPA and VPS

5.2.1.1 FTIR Spectroscopy

VPA and VPS were characterized by FTIR in order to identify their chemical

structure, the FTIR spectra of VPA and VPS are shown in Figure 5-1, and the

assignment of the main vibrational modes for VA and VP are listed in Table 5-2.

In the spectrum of VPA (Figure 5-16), series of new bands appeared: the broad

band centered at 3187 cm-1 could be attributed to NH stretching vibrations and

its hydrogen bonding. The bands at 3061 and 3003 cm-1 could be assigned to

alkene CH stretching vibrations, and those at 2934 and 2835 cm-1 could be

corresponding to aliphatic CH stretching. The band at 1707 cm-1 could be related

to C=C stretching from the allylamine structure. The C=O stretching vibrations

for VP at 1660 cm-1 was replaced by the C=N stretching for VPA at 1641 cm-1. In

addition, the bands in the 1470-1420 cm-1 region could be attributed to alkene

CH bending vibrations.

Table 5-13: Assignment of the main vibrational modes for VPA and VPS

Vibration VP VPA VPS

υ (C=O) 1685

δ (C-CHO) 729

υ (C=N) 1641 1644

υ (N-H) 3187

υ (C=C) 1707

υ (Si-O-C) 1101,1072

υ (C-H) 3100-2800 3100-2800

δ (C-H) 1470-1420 1470-1420

υ (P=O) 1267 1226 1274

υ (P-O-C) 1196, 1146 1198,1158 1193,1160

υ (P-ph) 1111, 905 1124,919 1115,915

Page 84: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 69

Figure 5-16: FTIR spectrum of VP (black) and VPA (red)

Figure 5-17: FTIR spectrum of VP (black) and VPS (red)

Compared to the spectrum VPA, several different new bands appeared in that of

VPS (Figure 5-17) due to the successful boning between APTES and VP. The

bands in the 3000-2800 cm-1 region should be attributed to aliphatic CH

stretching. The C=O stretching vibrations for VP at 1660 cm-1 was also absent

and replaced by C=N stretching at 1644 cm-1. The bands in the 1470-1420 cm-1

region could be assigned to CH bending vibrations. In addition, the strong bands

Page 85: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 70

at 1101 and 1072 cm-1 should be corresponding to SiO asymmetric deformation

vibrations. The FTIR spectra confirmed the desired structure as described in the

experimental part.

5.2.1.2 NMR Spectroscopy

The chemical structures of VPA and VPS were further confirmed via 1H NMR. As

shown in Figure 5-18, the chemical shifts at 8.06, 7.59, 7.50, 7.46, 7.32 and 7.12

ppm (labeled 6, 7, 8, 9, 10 and 11) are assigned to the protons of the benzene

ring. The peak at 8.21 ppm (labeled 5) is attributed to the proton of the

carbon-nitrogen double bond. The chemical shifts at 6.05, 5.18 and 4.24 ppm

(labeled 1, 2 and 3) correspond to the aliphatic and alkene protons, which are

related to allylamine. The peak at 3.78 ppm (labeled 4) is assigned to the

protons from the methoxy group of vanillin.

Figure 5-18: 1H NMR spectrum of VPA

Based on the spectrum of VPS (Figure 5-19), several new peaks can be found

comparing to that of VP. The location of peaks corresponding to protons from

benzene rings has slightly changed, which are 7.91, 7.57, 7.48, 7.42, 7.30 and

Page 86: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 71

7.09 ppm (labeled 8, 9, 10, 11, 12 and 13). The peak at 8.17 ppm (labeled 7) is

assigned to the protons from carbon-nitrogen double bond. The peak at 3.74

ppm (labeled 2) corresponds to the protons from the methoxy group. The peaks

at 3.83 and 1.24 ppm (labeled 1 and 5) are attributed to the protons from

siloxane group, and the peaks at 3.59, 1.81 and 0.67 ppm (labeled 3, 4 and 6)

are assigned to aliphatic protons, which are related to APTES.

Figure 5-19: 1H NMR spectrum of VPS

In summary, all these NMR results mentioned above correspond well with the

desired structure from the experimental part, and further confirm the formation

and the high purity of VPA and VPS.

5.2.2 Thermal Decomposition Behavior

The thermal degradation behavior of VPA and VPS as well as their PLA

composites were characterized via TGA at a heating rate of 10 K/min and a

nitrogen atmosphere. The TG and DTG plots are presented in Figure 5-20 and

the detail parameters are summarized in Table 5-14. TGA results of VP is shown

as a reference.

Compared to VP, the decomposition of VPA and VPS started at a lower

Page 87: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 72

temperature. Both of them started to decompose before 100 °C, the T5% value of

VPA and VPS were 163 and 174 °C, indicating lower thermal stabilities at low

temperature than VP. The weight loss in this range (50 °C to 300 °C) could be

related to the decomposition of the carbon-nitrogen double bond. However, the

T50% value of VPA and VPS were significantly improved to 417 and 480 °C,

respectively. In addition, the maximal rate of weight loss decreased from 1.87 of

VP to 0.33 and 0.29 %/°C of VPA and VPS, respectively.

Table 5-14: Data obtained from TGA plots of VPA and VPS

Sample T5% (°C) T50% (°C) Tmax (%/°C) Residue (wt-%)

VP 286 348 1.87 24.5

VPA 163 417 0.33 32.3

VPS 174 480 0.29 43.5

Tx% was the temperature at x% weight loss of the samples. Tmax was the maximum rate

of weight loss. Residue was the yield at 600 °C.

Figure 5-20: TG (left) and DTG (right) plots of VP, VPA and VPS

The decomposition process is changed from one step to multiple steps. The rate

of weight loss from 300 °C to 500 °C decreases significantly. This suggests the

further modification of VP leads to the formation of a protection layer. In the case

of VPA, based on the chemical structure, the char layer generated by the first

Page 88: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 73

decomposition step consists mainly of carbon. In the range from 300 °C to

500 °C, the weight of the sample was reduced from 85% to 38%, and the char

residue at 600 °C was 32.3 wt.-%. In case of VPS, it can be seen that the first

decomposition step was similar to that of VPA. However, the rate of weight loss

in further steps was lower than that of VPA. In the range from 300 °C to 500 °C,

the weight of the sample was reduced from 87% to 49%. The reason could be

that a ceramic layer consisting of Si-O-Si structure was formed and could

provide better protection than char layer of VPA. Furthermore, due to the

presence of the ceramic layer, VPS showed a char residue of 43.5 wt.-% at

600 °C.

Figure 5-21: TG (left) and DTG (right) plots of VPA and VPS based PLA composites

TG and DTG plots of VPA and VPS based PLA composites are shown in Figure

5-21. The detail data are summarized in Table 5-15. It can be observed that the

thermal degradation process of PLA composites occurred mainly in the

temperature range from 300 °C to 400 °C. With increasing concentration of VPA

and VPS, this process shifted to a higher temperature.

In the case of PLA/VPA composites, the T5% value of PLA5VPA and PLA10VPA

was 318 and 308 °C, the T20% value was 341 and 336 °C, respectively.

Furthermore, the Tmax value of amounted to 363 and 361 °C. It can be concluded

that the thermal stability of PLA/VPA composites was lower than pure PLA.

Page 89: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 74

Based on the TGA results of PLA/VP composites, the main reason was amine

generated from decomposition of carbon-nitrogen double bond. It accelerated

the decomposition of PLA and overpowered the stabilization effect of vanillin

segment. However, it contributed to the char yield. The residue at 600 °C of

PLA5VPA and PLA10VPA varied to 2.5 and 4.6 wt.-%. It was in good agreement

with the residue of pure VPA and its concentration in composites, indicating that

VPA didn’t induce the char formation of PLA.

Table 5-15: Data obtained from TGA plots of VPA and VPS based PLA composites

Sample T5% (°C) T20% (°C) Tmax (°C) Residue (wt-%)

PLA 326 344 363 0

PLA5VPA 318 341 363 2.5

PLA10VPA 308 336 361 4.6

PLA5VPS 329 349 370 2.8

PLA10VPS 322 348 372 4.8

Tx% was the temperature at x% weight loss of the samples. Tmax was the temperature at

the maximum rate of weight loss. Residue was the yield at 600 °C.

In the case of PLA/VPS composites, the T5% value of PLA5VPS and PLA10VPS

was 329 and 322 °C, and the T20% value was 349 and 348 °C, respectively. This

suggested that VPS decomposed earlier than PLA. The first decomposition step

of VPS caused quick weight loss, so at a lower temperature, the higher the

concentration of VPS, the faster the samples loss its weight. As discussed in the

previous subchapter, the vanillin segment can reduce the thermal degradation

rate of PLA. Therefore, at a higher temperature, when the vanillin segments

were released, they depressed the thermal degradation of PLA. With rising VPS

concentration, increased the Tmax value of the composites. In addition, a ceramic

condensed layer of SiO2 could also protect the composite from heat and lower

the thermal degradation. Consequently, PLA5VPS and PLA10VPS showed a

Page 90: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 75

Tmax value of 370 and 372 °C, respectively.

5.2.3 Flammability

The flammability of PLA/VPA and PLA/VPS composites was evaluated by LOI

and UL94 measurements. The results are listed in Table 5-16. It can be

observed that all the composites based on VPA and VPS passed V-0

classification in the UL-94 test. The LOI value of PLA5VPA, PLA10VPA,

PLA5VSP and PLA10VPS amounted to 29.8%, 30.5%, 24.5% and 25.0%,

respectively. Compared to PLA/VP composites, at the same concentration, the

LOI values of PLA/VPA composites increased significantly; by contrast, these of

PLA/VPS composites decreased slightly. This can be explained by the change of

melt flow rate at a high temperature of the composites. It is well known that, for

polymeric materials in a fire, dripping and flowing of the molten polymer can

enormously take the heat and degraded products away, so that the difficulty of

ignition or maintenance of burning of the material is elevated. In the case of the

LOI test, a higher concentration of oxygen is necessary to ignite the sample.

Table 5-16: LOI, UL94 and MFI results of PLA composites based on vanillin derivatives

Sample LOI (%) UL-94 Rating * MFI (g/10min) Ignition of cotton

PLA 21.4 No rating 6.0 Yes

PLA5VP 25.8 V-0 15.9 No

PLA10VP 26.3 V-0 59.5 No

PLA5VPA 29.8 V-0 61.0 No

PLA10VPA 30.5 V-0 109.2 No

PLA5VPS 24.5 V-0 7.2 No

PLA10VPS 25.0 V-0 9.6 No

* Sample thickness of UL-94 tests was 3.2mm

It can be concluded that the LOI and UL94 results of PLA/VPA and PLA/VPS

composites were affected by two factors. The first one is the MFI of materials.

Page 91: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 76

Material with higher MFI drips faster and takes more heat away. So higher MFI

altered the flame retardancy in a positive direction. The second one is the ratio of

effective component in flame retardant. As discussed in the previous subchapter,

the phosphor-containing segment is most responsible to the enhanced flame

retardancy of PLA composites. However, compared to VP, the ratio of the

phosphor-containing segment in VPA and VPS decreased. So the modification

of VP altered the flame retardancy to the negative direction. In the case of

PLA/VPA composites, the extremely high MFI overpower the negative effect. So

the LOI values of these samples were significantly improved. In contrary, for

PLA/VPS composites, the LOI values decreased due to the negative effect.

5.2.4 Combustion Behavior

The curves obtained via cone calorimeter test are shown in Figure 5-22 (HRR)

and Figure 5-23 (THR and CO/CO2 ratio), the detail parameters are listed in

Table 5-17.

Table 5-17: Data obtained from CCT of PLA and PLA composites

Sample TTI

(s)

pHRR

(kW/m2)

THR

(MJ/m2)

Residue

(%)

PLA 68±3 407±16 66.0±0.9 0.5±0.2

PLA5VPA 70±5 406±17 62.1±1.3 0.8±0.1

PLA10VPA 68±6 478±74 62.4±0.8 2.6±0.5

PLA5VPS 62±3 397±27 63.0±0.2 7.7±1.0

PLA10VPS 68±9 417±18 64.0±0.5 5.6±0.8

The main purpose of further modification of VP was to introduce a protective

layer by condensation of Si-derivatives and thus improve the char yield of the

PLA composites, expecting it can form a ceramic layer and protect the

Page 92: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 77

underlying material. Based on Table 5-17, the char residue of PLA5VPA,

PLA10VPA, PLA5VPS and PLA10 VPS was 0.8%, 2.6%, 7.7% and 5.6%,

respectively. The char yield of PLA composites was higher than that of neat PLA.

However, the heat release could not- be reduced. This result implied the char

layer was not sufficient and stable to protect the underlying material from heat.

Figure 5-22: HRR plots of PLA/VPA and PLA/VPS composites

Interestingly, it is observed that the pHRR values of PLA/VPA and PLA/VPS

composites increased with rising VPA or VPS concentration. In detail, the pHRR

of PLA5VPA, PLA10VPA, PLA5VPS and PLA10VPS were 406, 478, 397 and

417 kW/m2, respectively. The pHHR values of samples with 10 wt.-% of vanillin

derivative were even higher than that of pure PLA. Based on the THR curves, it

was detected, at the same time, the heat release of PLA composites was higher

than that of pure PLA, while the total heat release was lower. It could be also

observed from Figure 5-23, there was no notable difference of the first peaks of

CO/CO2 ratio between PLA and PLA composites. The reason for these results

could be inferred as follow. On one hand, the high release of CO was due to

incomplete combustion of the polymer. In this work, it was mainly caused by the

radical capture effect of the phosphor-containing segment. In comparison with

Page 93: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 78

VP, the ratio of phosphor in VPA and VPS was lower. Hence, VPA and VPS were

less efficient to suppress the combustion of PLA. On the other hand, the

carbon-nitrogen double bond in the structure of VPA and VPS were relatively

less stable to heat. Combustible products could be released by its

decomposition process, which could accelerate the ignition or/and the

combustion of the composites. Consequently, the pHRR of PLA became higher

when the loading of VPA or VPS increased.

Figure 5-23: THR (left) and CO/CO2 ratio (right) plots of PLA/VPA and PLA/VPS composites

5.2.5 Mechanical Properties

The stress-strain curves of PLA/VPA and PLA/VPS Composites, as well as pure

PLA, are shown in Figure 5-24, and the parameters of mechanical properties are

summarized in Table 5-18. PLA is a highly rigid thermoplastic with a tensile

strength of 57 MPa, a Young’s modulus of 3700 MPa and an elongation at break

of 3.0 %. After the introduction of VPA and VPS, all the samples showed lower

elongation at break than pure PLA and broke without any yield behavior. The

composites could sustain hardly any deformation at all. The tensile strength

decreased with rising filler loading, while the Young’s modulus shows totally

opposite trend. The tensile strength of PLA10VPA and PLA10VPS was 40 and

51 MPa, while the Young’s modulus was 3500 and 3400 MPa, respectively. The

reason for that could be, some of the crosslinkable groups reacted with other

Page 94: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 79

molecular and limited the molecular mobility of PLA.

Table 5-18: Data obtained from tensile test of PLA and PLA composites

Sample Young’s

modulus

(MPa)

Tensile

strength

(MPa)

Elongation

at break

(%)

Impact

resistance

(kJ/m2)

PLA 3700±100 57±1 3.0±0.6 16±2

PLA5VPA 3400±100 45±1 1.4±0.1 14±1

PLA10VPA 3500±100 40±4 1.5±0.1 12±1

PLA5VPS 3300±300 57±3 2.0±0.2 18±2

PLA10VPS 3400±200 51±2 1.7±0.1 15±3

Figure 5-24: Tensile test plots of PLA and PLA composites

5.2.6 Conclusion

In this part, two further modification of VP were realized. The products, VPA and

VPS, were characterized via 1H NMR, FTIR and TGA, and mixed with PLA via

plasticorder. The composites showed good performance in small-scale

flammability test (LOI and UL94). In addition, the char yield of the composites in

Page 95: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 80

the cone calorimeter test was significantly improved, e.g. PLA5VPS showed a

residue of 7.7% compared to 0.5% of neat PLA. However, the pHRR value of

composites increased with rising filler loadings. When PLA containing 10 wt.-%

of VPA or VPS, the pHRR value of material was higher than that of pure PLA.

The reason for that could be, the decomposition of VPA and VPS released

combustible products and accelerated the combustion process. Moreover,

despite the Young’s moduli and tensile strength remained at an acceptable level,

the composites could hardly sustain deformation. It strongly limited the

application of these materials. Hence, other methods to enhance the

anti-dripping properties of PLA need to be found. Addition of inorganic filler into

PLA would be a promising way. It will be discussed in the next subchapter.

5.3 PLA/VP Composite with Conventional Flame Retardants

In the previous subchapter, PLA/VP composites showed promising performance

both on flame retardancy and mechanical properties. Furthermore, two modified

VP, VPA and VPS, were proved to be able to enhance the char yield of PLA

during the combustion. The results showed that the char layers generated by the

VPA and VPS were improved but insufficient to hinder the combustion of PLA.

Hence, using conventional flame retardant, which could catalyze char forming, is

a reasonable choice.

VA and VP were mixed with PLA via plasticorder according to the recipe shown

in Table 5-1 and then injection molded to prepare different samples with a

suitable dimension for different measurements. The morphology of the sample

was first investigated using SEM with EDX. Then, the thermal degradation

behaviors were studied via TGA and DSC. Afterwards, the influence of VA and

VP on the mechanical properties of PLA were determined. Finally, the flame

retardant properties of PLA composites and the mechanism were investigated

via LOI, UL-94 V, CCT and TG-FTIR.

Page 96: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 81

5.3.1 PLA/VP Composite with Montmorillonite

Montmorillonite (MMT), also known as clay, is a mineral silicate with two

dimensional layered structure, which is used in various application areas,

including as flame retardant for plastics. In addition, polymer nanocomposites

based on MMT have shown remarkable improvement compared to pure

polymers, such as rigidity, crystallinity and so on. Furthermore, as a member of

the smectite family, MMT is literally powdered rock. It has no environmental

pollution or/and impact to nature and doesn’t destroy the biodegradability of the

biodegradable polymer when MMT is incorporated in polymers. On the other

hand, owing to the inorganic structure of pristine MMT, its compatibility with the

polymer is relatively low. Hence, the MMT used in this work, with the trade name

“Cloisite 30B”, is organically modified with methyl, tallow, bis-2-hydroxyethyl,

quaternary ammonium chloride, to enhance the compatibility with PLA. The

composites were prepared via a mini extruder according to the recipe in Table

5-19. The morphology of composites was observed using SEM. The thermal

degradation behaviors were studied via TGA and DSC. The flame retardant

properties and the mechanism were investigated via LOI, UL-94 and CCT. And

the mechanical properties were determined by tensile test.

Table 5-19: Recipe of PLA/VP/MMT composites

Sample PLA (wt.-%) mPLA* (wt.-%) MMT (wt.-%)

PLA5MMT 95 0 5

PLA10MMT 90 0 10

mPLA5MMT 0 95 5

mPLA10MMT 0 90 10

*mPLA was PLA/VP composite which contained 10 wt.-% VP

5.3.1.1 Morphology

The cross section of the tensile bars of PLA10MMT and mPLA10MMT were

Page 97: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 82

observed using SEM, and the obtained micrographs are shown in Figure 5-25. It

was found that PLA/MMT has a relatively smooth surface with MMT

agglomerations randomly embedded inside. By contrast, the dispersion of MMT

in mPLA was better and the particle size was smaller. It is interesting to find that,

the amount of MMT in mPLA/MMT composite of this individual cross section

seems to be higher than that in PLA/MMT composite. Considering the smaller

particle size and the more homogenous dispersion, it could be concluded that,

the miscibility of MMT in mPLA was better than that in pure PLA.

Figure 5-25: SEM pictures of PLA/MMT and mPLA/MMT composites

5.3.1.2 Thermal Decomposition Properties

TG and DTG plots of PLA/MMT and mPLA/MMT composites are shown in

Figure 5-26 and the resulting data are summarized in Table 5-20. The T5% values

of PLA/MMT and mPLA/MMT composites decreased with increasing MMT

concentration. The decrements of mPLA/MMT composites were 39 °C and

45 °C compared to those of PLA/MMT composites when the concentration of

MMT at 5 wt.-% and 10 wt.-%. And T5% values of all composites were lower

compared to that of pure PLA. This could be explained by that, the organic

modifier of MMT is less thermally stable than PLA, and the presence of VP

further accelerated the decomposition progress.

Page 98: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 83

Table 5-20: Data obtained from TGA plots of PLA and PLA composites

Sample T5% (°C) T20% (°C) Tmax (°C) Residue (wt-%)

PLA 326 344 363 0

PLA5MMT 324 346 366 2.9

PLA10MMT 318 347 366 5.9

mPLA5MMT 285 351 371 5.9

mPLA10MMT 273 351 370 7.9

Tx% was the temperature at x% weight loss of the samples. Tmax was the temperature at

the maximum rate of weight loss. Residue was the yield at 600 °C.

Figure 5-26: TG (left) and DTG (right) plots of PLA and PLA composites

It is known well that, the incorporation of clay into the polymer can enhance

overall thermal properties due to the superior heat insulation and mass transport

barrier effect. [107, 220] On the other hand, based on the result, the

concentration difference of MMT didn’t show notable influence on the T20% and

Tmax values of the composites. The T20% values of mPLA5MMT and

mPLA10MMT both amounted to 351 °C and Tmax values were 371 °C and

370 °C, respectively. The T20% values of PLA5MMT and PLA10MMT were

346 °C and 347 °C and Tmax values both amounted to 366 °C. The results

indicated that low concentration of MMT was already sufficient to act as an

insulator, and a small amount of VP could further suppress the thermal

Page 99: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 84

decomposition of PLA, which came to a good agreement with the conclusion of

the previous results (Chapter 5.1.3). In addition, VP seemed to be able to

enhance the char yield of the PLA composites.

5.3.1.3 Thermal Crystallization Behavior

Figure 5-27 shows the DSC plots of PLA/MMT and mPLA/MMT composites, and

the corresponding data are represented in Table 5-21. The corporation of MMT

into MMT led to a slight decrement of Tg. It could be explained by the fact that

MMT could cause degradation of PLA, and PLA with lower molecular weight

showed correspondingly lower Tg. Different from Tg, the influence of MMT on Tcc

was more complicated. It has been clarified by various researches that MMT

could promote the nucleation of the polymer at low loading. However, when the

loading of filler increases, agglomeration will form, which could limit the mobility

of the molecular chain. For the PLA/MMT composites, the cold crystallization

peak became from sharp to broader with increasing MMT loading. The melting

enthalpy of the second melting phase also declined with rising loading. In the

case of PLA10MMT, there was only one melting peak left, which corresponded

to the less perfect crystalline structure. In, summary, despite the fact that higher

MMT loading increased the crystallinity of PLA, the aggregates still prevent PLA

from forming perfect crystallization.

Table 5-21: Data obtained from DSC plots of PLA and PLA composites

Sample Tg

(°C)

Tcc

(°C)

Tm1

(°C)

Tm2

(°C)

∆Hcc

(J/g)

∆Hm

(J/g)

Χc (%)

PLA 60.6 113.7 160.1 166.0 33.00 33.08 35.5

PLA5MMT 60.0 112.3 159.8 165.2 32.61 32.83 37.1

PLA10MMT 59.6 121.4 161.2 -- 32.91 33.71 40.2

mPLA5MMT 54.4 110.3 153.6 162.2 31.70 32.49 40.8

mPLA10MMT 53.9 106.9 153.0 162.2 28.24 31.18 41.3

Page 100: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 85

In comparison, for mPLA/MMT composites, the increasing of MMT loading didn’t

have a notable effect on Tg and Tm of the matrix polymer. However, it did promote

the cold crystallization behavior, as evidenced by the decrement in Tcc and ∆Hcc

values. As discussed in the previous chapter, VP could function as a plasticizer

and nucleating agent for PLA, the lubrication and nucleating effect may

overpower the negative influence caused by the aggregates of MMT.

Furthermore, the appearance of VP could improve the dispersion of MMT in PLA

and reduce the forming of aggregates. Hence, for the samples mPLA5MMT and

mPLA10MMT, the bimodal melting peaks appeared at the same temperature

with a similar sweep, while Tg and Tm decreased with rising MMT loading.

Figure 5-27: DSC plots of PLA and PLA composites

5.3.1.4 Flammability

The results of LOI, UL94 and MFI tests of PLA/VP/MMT composites are listed in

Table 5-22. The LOI value of PLA5MMT and PLA10MMT was 20.9% and 23.6%,

while that of mPLA5MMT and mPLA10MMT amounted to 26.7% and 26.1%.

Page 101: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 86

Table 5-22: Results of LOI, UL94 and MFI tests of PLA and PLA composites

Sample LOI (%) UL-94 Rating * MFI (g/10min) Ignition of

cotton

PLA 21.4 No rating 6.0 Yes

PLA5MMT 20.9 No rating 2.9 Yes

PLA10MMT 23.6 No rating 1.9 Yes

mPLA5MMT 26.7 V-0 21.7 No

mPLA10MMT 26.1 V-0 15.8 No

MMT is widely used as a flame retardant for polymeric materials, especially as

anti-dripping and char agent. Based on the MFI results, it could be found that the

incorporation of MMT could reduce the melting flow rate of PLA. Despite MMT

could introduce protection char layer into PLA, it also prevented the taking away

of heat by melting flow of polymer. Hence, at low loading (5 wt.-%), the sample

showed lower LOI value than pure PLA, while at higher loading (10 wt.-%), more

protection char layer was formed, and the LOI value increased. However,

regardless of the anti-dripping effect, both PLA5MMT and PLA10MMT presented

no rating in the UL-94 test and were burned out faster to the clamp compared to

PLA. Large pieces of burning materials were observed, and the cotton beneath

sample was ignited.

In the case of mPLA/MMT composites, the melting flowability of materials, which

was most responsible for the enhanced flame retardancy, was significantly

improved by the introduction of VP. The MFI of samples changed from 6.0

g/10min of PLA to 21.7 g/10min of mPLA5MMT and 15.8 g/10min of

mPLA10MMT, respectively. Higher MMT loading contributed to higher restriction

of dripping. Thus, the LOI value decreased with rising MMT content. However,

both mPLA5MMT and mPLA10MMT passed V-0 in UL-94 test, indicating

Page 102: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 87

dramatic improvement on flame retardancy comparing to PLA/MMT composites.

5.3.1.5 Combustion Behavior

The combustion behavior of mPLA/MMT composites was evaluated utilizing a

cone calorimeter test and compared with that of PLA/MMT composites. The

important parameters obtained are listed in Table 5-23. The HRR plots of the

composites are represented in Figure 5-28, and curves of other major

parameters are shown in Figure 5-29. Comparing to PLA, the TTI of PLA5MMT

and PLA10MMT was earlier, from 68 s of PLA to 66 s and 63 s, respectively. TTI

of mPLA/MMT was also slightly lowered with rising MMT loading. The decreased

melting flowability caused by MMT should be responsible for that. Without the

protection of thermal stable structure, such as a stable char layer, the lower the

flowability, the faster the polymer was ignited.

Table 5-23: Data obtained from CCT of PLA/VP/MMT composites

Sample TTI

(s)

pHRR

(kW/m2)

THR

(MJ/m2)

TSP

(m2)

Residue

(%)

PLA 68±3 407±16 66.0±0.9 0.32±0.17 0.5±0.2

PLA5MMT 66±5 312±1 64.2±0.9 0.42±0.02 4.7±0.7

PLA10MMT 63±2 276±1 64.1±1.2 0.52±0.01 8.5±1.1

mPLA5MMT 67±3 383±11 64.4±1.6 2.57±0.02 3.7±0.9

mPLA10MMT 66±6 383±9 64.0±0.4 2.67±0.05 6.5±0.5

Based on Figure 5-28, it can be seen that the pHRR value of PLA5MMT,

PLA10MMT, mPLA5MMT and mPLA10MMT was reduced from 407 kW/m2 of

PLA to 312, 276, 383 and 383 kW/m2, respectively. The HHR curves of

PLA/MMT composites showed after the first peak broad plateau, suggesting

protection char layer was formed and the heat released rate was

correspondingly suppressed. In comparison, the HRR curves of mPLA/MMT

Page 103: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 88

composites processed similar shape as PLA. This could be explained by the fact

that the presence of VP has significantly improved the melting flowability of PLA,

which elevate the difficulty to form char layer during the combustion of samples.

The curves of THR and mass loss of PLA composites are shown in Figure 5-29

(a) and (b). It could be found that the THR of PLA composites was only slightly

decreased compared to PLA. However, the shape of curves of PLA/MMT

composites indicated that in the interval between 150 s and 300 s, the heat

release was significantly declined, and the reduction increased with higher MMT

loading. Parallel to THR, the curves of mass loss of PLA/MMT composites

showed a similar pattern. For mPLA/MMT composites, comparing to PLA, the

differences in THR and mass loss were negligible. Interestingly, at same MMT

loading, the char residue was reduced after the introduction of VP into PLA/MMT

composites. This was also due to the enhanced melting flow rate. Char layers

were destroyed by the flowing of the molten polymer before stable protection

layer was formed.

Figure 5-28: HRR plots of PLA/VP/MMT composites

Figure 5-29 (c) and (d) show the curves of TSP and CO/CO2 ratio of PLA

composites, which give the information of the gaseous products evolved during

Page 104: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 89

the combustion of samples. The TSP was increased with rising MMT loading,

which was due to the organic modifier in MMT. And the incorporation of VP was

responsible for the further dramatic improvement. The mechanism was already

discussed in the previous chapter. Another interesting difference between

PLA/MMT and mPLA/MMT composites was found in the curves of the CO/CO2

ratio. The first sharp peak corresponded to the ignition of samples. After that, for

PLA/MMT composites, the ratios were kept at a low level until the end of the

tests; in contrary, for mPLA/MMT composites, a second mountain like peak

appeared. This should be due to the release of the phosphor-containing

component evolved by the decomposition of VP and led to incomplete

combustion of PLA.

Figure 5-29: THR (a), Mass loss (b), TSP (c) and CO/CO2 ratio (d) plots of PLA composites

Page 105: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 90

5.3.1.6 Possible Flame Retardant Mechanism

The digital photos and SEM pictures of the residue of samples after cone

calorimeter tests are shown in Figure 5-30 and Figure 5-31 respectively. A

notable amount of char can be observed. The quality of the char layer was

improved with increasing MMT loading both in PLA/MMT and mPLA/MMT

composites. PLA/MMT composites left thicker char with separated domains,

whereas the residue of mPLA/MMT composites was much less but cohesive.

Figure 5-30: Residue of samples after cone calorimeter test of PLA/MMT composites (top)

and mPLA/MMT composites (bottom) with 5 wt.-% (left) and 10 wt.-%(right) MMT

As observed in the SEM pictures, the residue of mPLA/MMT composites showed

foam-like microstructure with many pores, while that of PLA/MMT composites

was more compact. It was reported that the flame retardant mechanism of MMT

in PLA was mainly as a physical barrier. By increasing the melt stability of PLA,

the presence of MMT promoted the formation of char. However, the introduction

of VP improved the melt flow rate of the composites, allowing the gaseous

product evolved by combustion to escape easier from the melt, as evidenced by

Page 106: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 91

the pores observed in SEM. Hence, the barrier effect of char was reduced.

Figure 5-31: SEM pictures of char layer after cone calorimeter test of PLA10MMT (top) and

mPLA10MMT (bottom) for surface (left) and inner (right) residue

5.3.1.7 Mechanical Properties

Figure 5-32 shows the stress vs strain curves of PLA and PLA composites, and

the primary parameters are listed in Table 5-24. The tensile strength of

PLA5MMT, PLA10MMT, mPLA5MMT and mPLA10MMT were 55, 57, 40 and 39

MPa, respectively. Their Young’s modulus was 4400, 4600, 3600 and 3800 MPa,

respectively.

Various researches have focused on the mechanical properties of clay

reinforced PLA composites. As reported, the incorporation of clay leads to

obvious improvement of Young’s modulus because the rigidity of inorganic fillers

is normally much higher than that of polymeric materials. Furthermore, due to

the high specific surface area of the nano-size particles and also the existence of

organic modifier, the adhesion between clay and matrix can be kept at a

relatively good level. Thus, for PLA/MMT composites, the tensile strength didn’t

Page 107: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 92

decrease a lot. In the case of mPLA/MMT composites, antagonistic effects are

present. Tensile strength and Young’s modulus of mPLA were lowered due to the

plasticization effect of VP. However, the addition of MMT elevated again the

Young’s moduli of the mPLA/MMT composites.

Table 5-24: Data obtained from tensile tests of PLA/VP/MMT composites

Sample Young’s

modulus

(MPa)

Tensile

strength

(MPa)

Elongation

at break

(%)

Impact

resistance

(kJ/m2)

PLA 3300±100 61±1 6.0±2.1 16±1

PLA5MMT 4400±100 55±1 1.7±0.4. 16±1

PLA10MMT 4600±100 57±1 1.5±0.1. 14±2

mPLA5MMT 3600±100 40±1 4.9±0.4 19±4

mPLA10MMT 3800±100 39±1 4.3±0.6 13±2

Figure 5-32: Tensile test plots of PLA/VP/MMT composites

On the other hand, an unavoidable fact is the incorporation of inorganic fillers

apparently led to the deterioration of poor ductility of PLA. The elongation at

Page 108: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 93

break declined from 6.0 % of PLA to 1.7% and 1.5% of PLA5MMT and

PLA10MMT, respectively. Interestingly, the elongation at break of mPLA5MMT

and mPLA10MMT was reduced to only 4.9% and 4.3%. A possible explanation

was that there was some interaction between MMT and PLA, which made the

material so rigid that the lubricant effect of VP could not enhance the chain

mobility of PLA that obvious anymore. Nevertheless, the improvement in

elongation at break was still notable when comparing to PLA/MMT composites.

5.3.2 PLA/VP Composite with APP

Ammonium polyphosphate (APP), with the chemical formula [NH4PO3]n(OH)2, is

an inorganic ammonia salt of polyphosphoric acid. Nowadays, APP is mostly

commercially produced and used as a flame retardant for polymeric materials,

where it performs as part of intumescent flame retardant (IFR). In addition, APP

consists of the elements of N, P, O and H, it can be also used as fertilizer. Hence,

the incorporation of APP into PLA will not destroy the biodegradability of material.

The composites were prepared by means of extrusion according to the recipe in

Table 5-25.

Table 5-25: Recipe of PLA/VP/APP composites

Sample PLA (wt.-%) mPLA

(wt.-%)

APP (wt.-%)

PLA5APP 95 0 5

PLA10APP 90 0 10

PLA20APP 80 0 20

mPLA5APP 0 95 5

mPLA10APP 0 90 10

mPLA20APP 0 80 20

*mPLA was PLA/VP composite which contained 10 wt.-% VP

Page 109: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 94

The morphology of composites was characterized using SEM. The thermal

degradation behaviors were determined using TGA and DSC. The flame

retardant properties and the mechanism were investigated via LOI, UL-94 and

CCT. And the mechanical properties were evaluated by the tensile test.

5.3.2.1 Morphology

The cross section of the tensile bars of PLA20APP and mPLA20APP were

observed utilizing SEM, and the obtained micrographs are shown in Figure 5-33.

It was found that for both samples, APP has well dispersed in PLA matrix, taking

into account the size of APP of D50 = 5 µm. By contrast, in the same size of

section, there were more APP particles in mPLA20APP, despite the particle size

of APP in both PLA composites were similar, possibly indicating that the

dispersion of APP in mPLA20APP was better. Furthermore, the cross section of

APP particle in PLA20APP and mPLA20APP showed an interesting difference.

The cross section of APP in mPLA20APP was smoother. It could be contributed

to that during the thermal processing APP has reacted with VP.

Figure 5-33: SEM pictures PLA/APP and mPLA/APP composites

5.3.2.2 Thermal Decomposition Properties

TG and DTG curves of PLA and PLA composites are represented in Figure 5-34

and the corresponding parameters are summarized in Table 5-26. Different

decomposition phases are characterized by T5%, T20% and Tmax.

Page 110: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 95

Table 5-26: Data obtained from TGA plots of PLA/VP/APP composites

Sample T5% (°C) T20% (°C) Tmax (°C) Residue (wt-%)

PLA 326 344 363 0

PLA5APP 332 350 367 3.7

PLA10APP 334 350 368 4.7

PLA20APP 332 348 366 6.4

mPLA5APP 288 330 368 5.1

mPLA10APP 288 329 364 6.9

mPLA20APP 292 330 364 7.8

Tx% was the temperature at x% weight loss of the samples. Tmax was the temperature at

the maximum rate of weight loss. Residue was the yield at 600 °C.

As shown in Table 5-26, the addition of APP slightly improved the thermal

stability of PLA, as reported in many results, this was contributed to its inorganic

nature and higher thermal stability than PLA.[221] However, the decomposition

of APP could lead to release of phosphoric acid and catalyze the thermal

degradation of PLA. There was a critical loading of APP, above which the

catalytic effect would overpower the improvement. For PLA/APP composites in

this study, the critical loading was possibly the critical concentration. T5%, T20%

and Tmax values decreased slightly when the concentration rose to 20%. In

contrast, the char residue at 600 °C increased continuously with rising APP

loading.

For mPLA/APP composites, the thermal decomposition process consisted of

four stages. Comparing the results of the previous study (subchapter-5.1.3), it

can be suggested that the first stage in the range between 200 and 300 °C could

be related to the reaction between VP and APP, and the second stage between

300 and 350 °C could be due to the decomposition of VP structure. The third

stage, which showed the maximal decomposition rate, should be corresponding

Page 111: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 96

to the decomposition of the PLA matrix under the catalytic effect of APP. This

stage was also the most responsible to the char formation. In the fourth stage

between 400 and 500 °C, unstable char was decomposed. The loading of APP

didn’t have a notable influence to the first three stages. However, the fourth

stage showed a strong dependency on APP concentration. Furthermore, at

same APP loading, the char yields of mPLA/APP composites were higher than

that of PLA/APP composites, indicating a synergic effect between APP and VP.

Figure 5-34: TG (left) and DTG (right) plots of PLA/VP/APP composites

5.3.2.3 Thermal Crystallization Behavior

The DSC curves of PLA/APP and mPLA/APP are illustrated in Figure 5-35 and

Figure 5-36, the corresponding parameters are listed in Table 5-27. For

PLA/APP composites, there was no remarkable change in Tg value observed

after the incorporation of APP into PLA. For PLA5APP and PLA10APP, the cold

crystallization capability seemed to be lower than that of PLA. The Tcc valued

shifted to a higher temperature and the peaks became broader. In addition, there

was only one melting peak corresponding to less perfect crystallization structure.

Comparing PLA20APP with PLA10APP, the Tcc valued shifted to lower direction

with sharper cold crystallization peak, and the second melting peak for a

structure with higher perfection appeared again. Furthermore, the crystallinity of

samples increased to the maximum with 20% APP loading. All the results

Page 112: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 97

suggested that the crystallization capability of PLA was enhanced with

increasing APP loading.

Table 5-27: Data obtained from DSC plots of PLA and PLA composites

Sample Tg

(°C)

Tcc

(°C)

Tm1

(°C)

Tm2

(°C)

∆Hcc

(J/g)

∆Hm

(J/g)

Χc (%)

PLA 60.6 113.7 160.1 166.0 33.00 33.08 35.5

PLA5APP 60.2 123.9 161.6 -- 34.15 34.18 38.6

PLA10APP 60.2 125.0 161.9 -- 33.00 33.37 39.8

PLA20APP 59.8 114.7 160.1 165.8 30.98 32.38 43.5

mPLA5APP 55.9 111.3 155.8 163.6 30.93 31.94 40.4

mPLA10APP 55.8 113.0 156.4 163.8 29.24 31.42 42.2

mPLA20APP 57.4 115.4 158.0 164.8 27.03 28.12 43.1

Figure 5-35: DSC plots of PLA/APP composites

Comparing with PLA, the Tg of mPLA5APP was about 5 °C lower due to the

plasticization effect of VP. When the APP loading increased, the Tg value was

altered to the higher direction, indicating that the chain mobility of PLA was

Page 113: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 98

limited by the APP particles. In parallel with the change in Tg, Tcc and Tm also

increased gradually with rising APP loading, and the melting peak corresponding

to higher perfection structure shifted down at the same time. All the results

suggested a reduced crystallization capability. A possible explanation could be

that with increasing APP loading, more and more VP reacted with APP and lose

its lubricant effect. These deductions were in good agreement with the TGA

results.

Figure 5-36: DSC plots of mPLA/APP composites

5.3.2.4 Flammability

The LOI, UL-94 and MFI results of PLA, PLA/APP and mPLA/APP composites

are listed Table 5-28. It was observed that the addition of VP into PLA could

remarkably improve the flame retardancy of PLA. The LOI values of PLA5APP,

PLA10APP and PLA20APP amounted to 29.6%, 30.4% and 31.3%. And with the

existence of VP, LOI values of mPLA5APP, mPLA10APP and mPLA20APP were

further improved to 32.1%, 34.6% and 40.7%. By careful analysis, the LOI

values of mPLA/APP showed greater loading dependency of APP. This

suggested a synergized action between VP and APP. The MFI of both

composites systems declined when the loading of APP increased from 5 % to

Page 114: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 99

Table 5-28: Results of LOI and UL-94 tests of PLA/VP/APP composites

Sample LOI (%) UL-94 Rating * MFI (g/10min) Ignition of cotton

PLA 21.4 No rating 6.0 Yes

PLA5APP 29.6 V-0 5.5 No

PLA10APP 30.4 V-0 5.2 No

PLA20APP 31.1 V-0 6.5 No

mPLA5APP 32.1 V-0 32.8 No

mPLA10APP 34.6 V-0 24.4 No

mPLA20APP 40.7 V-0 128.7 No

Figure 5-37: Pictures of samples after LOI test: (a) PLA5APP, (b) PLA10APP (c) PLA20APP

(d) mPLA5APP (e) mPLA10APP (f) mPLA20APP

10 %. It can be explained by the inorganic nature of APP. However, when the

loading further increased to 20%, the MFI values were again elevated.

Especially for the mPLA20APP, showed a huge increase from 24.4 g/10min of

mPLA10APP to 128.7 g/10min. Based on the results of TGA, this change could

be induced by thermal degradation of PLA. Another change observed in LOI

Page 115: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 100

tests was the enhanced anti-dripping properties. As shown in Figure 5-37, the

PLA/APP composites still exhibited strong dripping behavior, even when the

loading of APP was at 20%. For mPLA/APP composites, the dripping behavior of

PLA was well hindered at 10% of APP loading, and there was almost no dripping

observed for the sample mPLA20APP, indicating that the combination of VP and

APP could contribute to char formation. In summary, the addition of VP in could

lead to further improved flame retardancy of PLA/APP composites.

5.3.2.5 Combustion Behavior

In order to understand the combustion behavior of PLA/APP and mPLA/APP

composites, cone calorimeter tests were carried out. The primary parameters

obtained in the tests are listed in Table 5-29. The HRR curves are represented in

Figure 5-38, and the THR, mass loss, TSP as well as CO/CO2 ratio are

illustrated in Figure 5-39. The TTI was slightly delayed after introducing of APP

due to its higher thermal stability than PLA. However, incorporation of VP into

PLA/APP composites led to earlier TTI. It could be due to the earlier start of

decomposition in combination with the rather high MFI value.

Table 5-29: Data obtained from CCT plots of PLA/VP/APP composites

Sample TTI

(s)

pHRR

(kW/m2)

THR

(MJ/m2)

TSP

(m2)

Residue

(%)

PLA 68±3 407±16 66.0±0.9 0.32±0.17 0.5±0.2

PLA10APP 71±5 357±13 58.4±1.0 1.92±0.02 9.8±1.2

PLA20APP 70±9 341±3 52.9±2.5 1.37±0.21 19.3±0.9

mPLA10APP 65±3 318±26 55.6±0.4 2.01±0.14 12.0±1.1

mPLA20APP 66±2 297±8 50.1±0.5 1.95±0.05 20.9±0.5

Page 116: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 101

Figure 5-38: HRR plots of PLA/VP/APP composites

The pHRR of PLA10APP, PLA20APP, mPLA10APP and mPLA20APP were 357,

341, 318 and 297 kW/m2, respectively. Obviously, the incorporation of VP into

PLA/APP composites could further suppress the heat release of PLA during the

combustion. The curve shape of PLA/APP composites was similar to that of PLA

but with lowered pHRR. In comparison, for mPLA20APP, the HRR rose quickly

to pHRR and then went down rapidly. As reported in many investigations, during

combustion of polymeric materials containing APP, APP will decompose into

phosphoric acid and ammonia.[42, 162, 195] The phosphoric acid can react with

active groups to form unstable phosphate ester, which could turn into char upon

dehydration. A compact and expanded carbon foam can protect the polymeric

materials from fire by isolating the materials from heat and matter transfer. The

valley in the HRR curve of mPLA20APP suggested the formation of the

protective layer. As the sample further exposed to heat, the HRR increased

again. It was due to the fact that the established char layer was not stable

enough and was burned through as the test continued. Nevertheless, the heat

release rate was well suppressed by incorporating APP and VP together into

PLA.

Page 117: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 102

THR is another parameter to evaluate the fire safety of the polymeric material. At

the end of the tests, the THR of PLA amounted to 66.0 MJ/m2. As the THR of

PLA10APP, PLA20APP, mPLA10APP and mPLA20APP declined to 58.4, 52.9,

55.6 and 50.1 MJ/m2 respectively. This indicated that the introduction of APP has

increased the incombustible component and also protected parts of the samples

from fire. Since the released heat was generated by the combustion of samples,

the study of mass loss of sample could also help to understand the combustion

process. It was observed, samples with 20 wt.-% APP loading presented as high

as 80%-100% more residue than those with 10 wt.-%. Whereas at the same

APP loading, the char yields of mPLA/APP composites were only increased by

1%-2% when compared to those of PLA/APP composites. The results revealed

that higher char quality of mPLA/APP composites was mainly responsible for the

lower THR values.

Figure 5-39: THR (a), Mass loss (b), TSP (c) and CO/CO2 ratio (d) plots of PLA/VP/MMT

composites

Page 118: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 103

The information of gaseous products evolved during the combustion are

illustrated in Figure 5-39-(c) and –(d). It was observed that for PLA/APP

composites, low APP loading led to an increase in TSP due to the phosphorus

acid evolved by decomposition of APP. By contrast, at high APP loading,

charring occurred during the combustion, which exhibited smoke suppression

effect. As found in previous work, the incorporation of VP into PLA led to

significant improvement in TSP due to the incomplete combustion. In case of

mPLA/APP composites, incomplete combustion still existed, that was evidenced

by the continuous high level of CO/CO2 ratio shown in Figure 5-39-(d). However,

PLA10APP, mPLA10APP and mPLA20APP showed the same TSP values at the

end of combustion, suggesting the char layer with better smoke suppression

effect were formed in mPLA/APP composites.

5.3.2.6 Possible Flame Retardant Mechanism

The digital photos and SEM pictures of the residue of samples after cone

calorimeter tests are shown in Figure 5-40 and Figure 5-41 respectively. All the

samples showed expanded char layers which could act as a barrier to hinder the

transmission of fuel and oxygen. The amount and quality of residue increased

with rising APP loading. In fact, mPLA/APP composites showed more cohesive

char structure. For example, no obvious open hole was observed from the digital

photo of mPLA20APP. The microstructures of the outer and inner surface for

char residue were obtained to further understand the relationship between char

and flame retardancy of PLA composites. As observed, the inner structures of

both composites were similar. The outer surface of PLA20APP, however,

showed more pores than mPLA20APP. In addition, the amount of char residue of

mPLA/APP composites was higher than that of PLA/APP composites (Table

5-29), suggesting that there was synergic effect between VP and APP, which

contribute to the formation of char.

Page 119: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 104

Figure 5-40: Residue of samples after cone calorimeter test of PLA/APP composites (top)

and mPLA/APP composites (bottom) with 10 wt.-% (left) and 20 wt.-%(right) APP

Figure 5-41: SEM pictures of residue after cone calorimeter test of PLA20APP (top) and

mPLA20APP (bottom) for surface (left) and inner (right)

Page 120: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 105

5.3.2.7 Mechanical Properties

Figure 5-42 shows the stress vs strain curves of PLA and PLA composites, and

the primary parameters are listed in Table 5-30. Different from PLA/MMT

composites, the Young’s moduli of PLA/APP and mPLA/APP composites

decreased with rising APP loading. The higher the APP loading, the more

phosphorus acid would be generated during the thermal processing, the faster

the PLA would degrade.

On the other hand, it has been reported that APP demonstrated plasticization in

some polymeric matrix. This could be the explanation that the elongation at

break of PLA/APP composites was improved with rising APP loading, while the

tensile strength showed a declining trend. In addition, APP and VP seemed to

have synergic action on the plasticization effect. The sample mPLA20APP

exhibited an elongation at break as high as 29%, while its tensile strength was

kept at the same level as PLA20APP. This was a dramatic improvement for the

rigid PLA material.

Table 5-30: Data obtained from tensile tests plots of PLA/VP/APP composites

Sample Young’s

modulus

(MPa)

Tensile

strength (MPa)

Elongation

at break (%)

Impact

resistance

(kJ/m2)

PLA 3300±100 61±1 6±2 16±1

PLA5APP 3400±100 45±1 4±1 31±5

PLA10APP 3400±100 43±1 5±1 32±4

PLA20APP 3300±400 41±1 11±2 30±3

mPLA5APP 3500±100 42±1 6±1 21±4

mPLA10APP 3500±200 39±1 7±1 18±2

mPLA20APP 3300±100 37±2 29±3 20±3

Page 121: Development and Investigation of Bio-based Environmentally ...

Results and Discussion 106

Figure 5-42: Tensile test plots of PLA/VP/APP composites

5.3.3 Conclusion

In this subchapter, VP was introduced into two flame retardant PLA composites

systems: PLA/MMT and PLA/APP. For PLA/MMT composites, the introducing of

VP didn’t show improvement in the cone calorimeter test, but it did enhance the

flame retardancy in small scale tests like LOI and UL94. A remarkable

improvement was observed in ductility and processability of the composites. In

case of PLA/APP composites, introducing of VP led to significant improvement

of flame retardancy evidenced by increasing LOI values as well as better quality

of char residue acting as heat and matter barrier, which was the primary reason

for the decreased pHRR and THR values. Moreover, VP synergized with APP as

an excellent plasticizer for PLA.

Page 122: Development and Investigation of Bio-based Environmentally ...

Summary 107

6 Summary

The ultimate goal of this work was to develop environmentally friendly bio-based

functional polymer composites that would possess good flame retardancy and

fulfill the desired mechanical properties for conventional applications. PLA has

attracted more and more attention in the last decades due to its excellent

mechanical properties and is considered as a promising candidate to replace

petroleum-based plastics. But PLA does exhibit some disadvantage such as

high flammability and brittleness. In order to overcome those shortcomings, the

research has been done focused as follows:

The first motivation was to synthesize novel functional additives to improve the

flame retardancy and ductility of PLA. To execute that plan, phosphor-containing

compound was a suitable candidate, since many phosphor containing

compounds were highly efficient flame retardant or flame retardant intermediates.

Besides, some phosphor containing compounds had a lubricative effect when

used in a proper polymeric matrix. Vanillin, another bio-based resource, was

used as raw material of the functional additive. As consequence, VP was

successfully synthesized based on vanillin and phenylphosphonic dichloride.

The chemical structure of VP was confirmed by NMR and FTIR.

Next target was to use the synthesized VP as a flame retardant and plasticized

in PLA. Different processing methods, including melt blending, extrusion, hot

compression, injection molding and melt spinning were employed to process

PLA/VP composites. The thermal behavior, mechanical properties as well as

flame retardancy of composites were studied by various characterization

techniques.

The last goal was to prevent the dripping behavior of PLA during the combustion.

Two pathway, further chemical modification of VP and introduction of filler, were

suggested. By means of chemical modification, crosslinkable groups were

Page 123: Development and Investigation of Bio-based Environmentally ...

Summary 108

introduced into the structure of VP. VPA and VPS, were successfully synthesized.

By physical melt compounding, MMT and APP, two commercialized flame

retardant were incorporated into PLA/VP composites. The thermal behavior,

mechanical properties as well as flame retardancy of composites were evaluated

by various characterization techniques as well.

6.1 Synthesis and characterization of VP

Bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP) was synthesized based

on vanillin and phenylphosphonic dichloride. In the FTIR spectrum of VP, the

appearance of peaks assigned to P=O and P-O-C evidenced that vanillin was

successfully chemical linked to phenylphosphonic dichloride. Besides, the

results of 1H-, 13C- and 31P-NMR proved the high purity of the product. It was

observed via SEM that after the modification the surface of VP show higher

toughness and signal of the element phosphor was found by EDX. The melting

point of VP was determined by DSC. In comparison with vanillin, the thermal

stability of VP was significantly improved, allowing a processing temperature of

at least 280 °C.

6.2 Performance of PLA/VP composites

PLA composites with different loading of VP were prepared by means of melt

compounding and extrusion and then processed into tests specimen with

different dimensions utilizing hot compression, injection molding and melt

spinning. PLA and PLA composites based on vanillin were also prepared as

references.

The micromorphology, thermal behavior, flame retardancy, combustion behavior

and mechanical properties of selected samples were extensively investigated. In

comparison to vanillin, VP showed better miscibility in PLA. It was observed via

SEM that VP dispersed in PLA as nano-size particles. The thermal stability of

PLA was enhanced by the incorporation of VP, even at the loading 1wt.-%. And

Page 124: Development and Investigation of Bio-based Environmentally ...

Summary 109

the improvement increased with rising VP loading. Using multiple heating rate

TGA, it was found that the introduction of VP led to an elevation of activation

energy of the thermal decomposition of PLA. The Tg and Tm values of PLA

composites declined with increasing VP loading, indicating that VP could

improve the mobility of the molecular chains of PLA, showing a potential of VP

as a plasticizer for PLA. In the small-scale flame retardancy tests, PLA/VP

composites also exhibited excellent performance. The samples with 5 wt.-% VP

could pass V-0 level in UL-94 test and with 10 wt.-% VP showed an LOI value of

26.3%. In the cone calorimeter test, the sample PLA10VP reduced the pHRR

value by more than 25% compared to PLA. Finally, in the tensile test, PLA/VP

composites demonstrated good tensile strength and Young’s modulus as well as

significantly improved elongation at break.

6.3 Further modification of VP and VP used in combination with

commercialized flame retardant

In the following work, two different flame retardants, VPA and VPS, were

successfully synthesized based on VP. Despite the thermal stabilities of VPA and

VPS were unexpectedly not good as VP, PLA composites based on VPA and

VPS exhibited good flame retardancy in small-scale tests. Both PLA5VPA and

PLA5VPS passed V-0 level in UL-94 tests. And PLA with 10 wt.-% VPA showed

an LOI value as high as 30.5%. In cone calorimeter tests, both PLA/VPA and

PLA/VPS composites showed enhanced char yield after the measurements,

indicating that the carbon-carbon double bond of VPA and silanol group of VPS

did contribute to the formation of char. However, both PLA/VPA and PLA/VPS

composites exhibited no suppression effect of heat release and high brittleness

in mechanical test. The applications would be limited as small articles such as

pendant and decorations.

As the applications VPS and VPS couldn’t decrease the dripping behavior of

PLA during combustion, two commercialized flame retardants, MMT and APP,

Page 125: Development and Investigation of Bio-based Environmentally ...

Summary 110

were employed. Compared with PLA/MMT composites, with the introduction of

VP, the sample showed better flame retardancy small-scale tests. In particular,

the addition of 10 wt.-% VP allowing the samples passed V-0 level of UL-94 test,

while PLA5MMT and PLA10MMT showed “no rating”. And the LOI values of

samples with VP were higher than that of PLA/MMT composites. Furthermore,

addition of VP could slightly improve the ductility of PLA/MMT composites.

In case of PLA/APP composites, the incorporation of VP led to overall

improvement. For example, the sample mPLA20APP show an LOI value as high

as 40.7%, and remarkable intumescent behavior was observed both in LOI and

cone calorimeter tests. Both the pHRR and THR values were reduced by about

25% compared to PLA. Most surprisingly, notable synergic effect between VP

and APP was observed in tensile tests. The elongation at break of mPLA20APP

was improved to 28.2% compared 6.0% of PLA.

The results of this part of work implied various flame retardant mechanism of VP

or VP segment when they combined used with different components. In the

PLA/VP system, one of the main flame retardant effects of VP was to improve

the melt flowability of PLA to remove the heat and material from the burning area.

However, the introduction of MMT has limited this effect. Additionally, the

increased melt flowability elevated the difficulty of the formation of continuous

char layer, which was the main flame retardant mechanism of MMT.

Consequently, VP and MMT showed antagonistic effect on the flame retardancy

of PLA.

Comparing to that, distinct synergic effect was observed between VP and APP.

The appearance of VP resulted in significant increase of char yield in the fire

tests (LOI and CCT) for PLA/APP composites. Together they acted as an

intumescent flame retardant system and provided excellent flame retardancy. In

particular, mPLA/20APP presented the best flame retardant performance (LOI,

UL-94 and CCT) among all the specimens.

Page 126: Development and Investigation of Bio-based Environmentally ...

Outlook 111

7 Outlook

The work presented a novel pathway to prepare environmentally friendly flame

retardant PLA composites. Despite several achievements have been done in this

work, it also offers different possibilities for continuing researches.

The modification of vanillin allowed its application as a flame retardant for PLA

whose processing temperature was above 170 °C. This method could be used in

another polymeric matrix.

The modification of vanillin was towards the improvement of flame retardancy. It

could be otherwise modified focus on different functions.

Textile fabricated from PLA should be prepared and its properties should be

determined and studied.

The additives and fillers used in this work were considered and selected to keep

the biodegradability of PLA. The biodegradability of the PLA composited need to

be studied.

The presence and/or generation of water during thermal processing play a

determined role in the degradation of PLA.

Page 127: Development and Investigation of Bio-based Environmentally ...

References 112

References

1. Feldman D (2008) Polymer History. Designed Monomers and Polymers

11(1):1-15.

2. Geyer R, Jambeck JR, & Law KL (2017) Production, use, and fate of all

plastics ever made. Science Advances 3(7).

3. Lackner M (2000) Bioplastics. Kirk-Othmer Encyclopedia of Chemical

Technology, (John Wiley & Sons, Inc.).

4. Crank M, Patel M, Marscheider-Weidemann F, Schleich J, Hüsing B, &

Angerer G (2005) Techno-economic Feasibility of Large-scale Production

of Bio-based Polymers in Europe (PRO-BIP).

5. Irvine DJ, McCluskey JA, & Robinson IM (2000) Fire hazards and some

common polymers. Polymer Degradation and Stability 67(3):383-396.

6. Mülhaupt R (2013) Green Polymer Chemistry and Bio-based Plastics:

Dreams and Reality. Macromolecular Chemistry and Physics

214(2):159-174.

7. Babu RP, O'Connor K, & Seeram R (2013) Current progress on bio-based

polymers and their future trends. Progress in Biomaterials 2(1):8.

8. Yu L, Dean K, & Li L (2006) Polymer blends and composites from

renewable resources. Progress in polymer science 31(6):576-602.

9. Dorgan JR, Lehermeier HJ, Palade L-I, & Cicero J (2001) Polylactides:

properties and prospects of an environmentally benign plastic from

renewable resources. Macromolecular Symposia 175(1):55-66.

10. Garlotta D (2001) A Literature Review of Poly(Lactic Acid). Journal of

Polymers and the Environment 9(2):63-84.

11. Iwata T (2015) Biodegradable and Bio-Based Polymers: Future Prospects

of Eco-Friendly Plastics. Angewandte Chemie International Edition

54(11):3210-3215.

12. Faruk O, Bledzki AK, Fink H-P, & Sain M (2012) Biocomposites reinforced

with natural fibers: 2000–2010. Progress in polymer science

37(11):1552-1596.

13. Frone A, Berlioz S, Chailan JF, Panaitescu D, & Donescu D (2011)

Cellulose fiber ‐ reinforced polylactic acid. Polymer Composites

32(6):976-985.

14. Ren J (2010) Biodegradable Poly (Lactic Acid): Synthesis, Modification,

Processing (Springer).

Page 128: Development and Investigation of Bio-based Environmentally ...

References 113

15. Fukushima K & Kimura Y (2006) Stereocomplexed polylactides (Neo‐

PLA) as high‐ performance bio‐ based polymers: their formation,

properties, and application. Polymer International 55(6):626-642.

16. Jing Y, Quan C, Liu B, Jiang Q, & Zhang C (2016) A Mini Review on the

Functional Biomaterials Based on Poly(lactic acid) Stereocomplex.

Polymer Reviews 56(2):262-286.

17. Vink ET, Rabago KR, Glassner DA, & Gruber PR (2003) Applications of

life cycle assessment to NatureWorks™ polylactide (PLA) production.

Polymer Degradation and stability 80(3):403-419.

18. Xiao L, Wang B, Yang G, & Gauthier M (2012) Poly (lactic acid)-based

biomaterials: synthesis, modification and applications. Biomedical

science, engineering and technology, (InTech).

19. Castro-Aguirre E, Iñiguez-Franco F, Samsudin H, Fang X, & Auras R

(2016) Poly(lactic acid)—Mass production, processing, industrial

applications, and end of life. Advanced Drug Delivery Reviews

107(Supplement C):333-366.

20. Chen Y, Geever LM, Killion JA, Lyons JG, Higginbotham CL, & Devine

DM (2016) Review of Multifarious Applications of Poly (Lactic Acid).

Polymer-Plastics Technology and Engineering 55(10):1057-1075.

21. Farah S, Anderson DG, & Langer R (2016) Physical and mechanical

properties of PLA, and their functions in widespread applications — A

comprehensive review. Advanced Drug Delivery Reviews 107:367-392.

22. Bourbigot S & Fontaine G (2010) Flame retardancy of polylactide: an

overview. Polymer Chemistry 1(9):1413-1422.

23. Lai S-M & Lan Y-C (2013) Shape memory properties of melt-blended

polylactic acid (PLA)/thermoplastic polyurethane (TPU) bio-based blends.

Journal of Polymer Research 20(5):140.

24. Labrecque LV, Kumar RA, Davé V, Gross RA, & McCarthy SP (1997)

Citrate esters as plasticizers for poly(lactic acid). Journal of Applied

Polymer Science 66(8):1507-1513.

25. Modi S, Koelling K, & Vodovotz Y (2013) Assessing the mechanical,

phase inversion, and rheological properties of

poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) blended

with poly-(l-lactic acid) (PLA). European Polymer Journal

49(11):3681-3690.

26. Ali F, Chang Y-W, Kang SC, & Yoon JY (2009) Thermal, mechanical and

rheological properties of poly (lactic acid)/epoxidized soybean oil blends.

Polymer Bulletin 62(1):91-98.

Page 129: Development and Investigation of Bio-based Environmentally ...

References 114

27. Bo L, Long J, Hongzhi L, Lili S, & Jinwen Z (2010) Different Effects of

Water and Glycerol on Morphology and Properties of Poly(lactic acid)/Soy

Protein Concentrate Blends. Macromolecular Materials and Engineering

295(2):123-129.

28. D'Amico DA, Iglesias Montes ML, Manfredi LB, & Cyras VP (2016) Fully

bio-based and biodegradable polylactic acid/poly(3-hydroxybutirate)

blends: Use of a common plasticizer as performance improvement

strategy. Polymer Testing 49(Supplement C):22-28.

29. Arrieta MP, Castro-López MdM, Rayón E, Barral-Losada LF,

López-Vilariño JM, López J, & González-Rodríguez MV (2014)

Plasticized Poly(lactic acid)–Poly(hydroxybutyrate) (PLA–PHB) Blends

Incorporated with Catechin Intended for Active Food-Packaging

Applications. Journal of Agricultural and Food Chemistry

62(41):10170-10180.

30. Jacobsen S & Fritz HG (1996) Filling of poly(lactic acid) with native starch.

Polymer Engineering & Science 36(22):2799-2804.

31. Jamshidian M, Tehrany EA, Imran M, Jacquot M, & Desobry S (2010)

Poly‐Lactic Acid: production, applications, nanocomposites, and release

studies. Comprehensive Reviews in Food Science and Food Safety

9(5):552-571.

32. Murariu M & Dubois P (2016) PLA composites: From production to

properties. Advanced Drug Delivery Reviews 107:17-46.

33. Raquez J-M, Habibi Y, Murariu M, & Dubois P (2013) Polylactide

(PLA)-based nanocomposites. Progress in Polymer Science

38(10):1504-1542.

34. Murariu M, Dechief A-L, Ramy-Ratiarison R, Paint Y, Raquez J-M, &

Dubois P (2015) Recent advances in production of poly(lactic acid) (PLA)

nanocomposites: a versatile method to tune crystallization properties of

PLA. Nanocomposites 1(2):71-82.

35. Yingwei D, Salvatore I, Di ME, & Luigi N (2005) Poly(lactic

acid)/organoclay nanocomposites: Thermal, rheological properties and

foam processing. Journal of Polymer Science Part B: Polymer Physics

43(6):689-698.

36. Graupner N, Herrmann AS, & Müssig J (2009) Natural and man-made

cellulose fibre-reinforced poly (lactic acid)(PLA) composites: An overview

about mechanical characteristics and application areas. Composites Part

A: Applied Science and Manufacturing 40(6):810-821.

37. Mukherjee T & Kao N (2011) PLA based biopolymer reinforced with

natural fibre: a review. Journal of Polymers and the Environment

Page 130: Development and Investigation of Bio-based Environmentally ...

References 115

19(3):714.

38. Liu X, Khor S, Petinakis E, Yu L, Simon G, Dean K, & Bateman S (2010)

Effects of hydrophilic fillers on the thermal degradation of poly(lactic acid).

Thermochimica Acta 509(1):147-151.

39. Chapple S & Anandjiwala R (2010) Flammability of Natural

Fiber-reinforced Composites and Strategies for Fire Retardancy: A

Review. Journal of Thermoplastic Composite Materials 23(6):871-893.

40. Kozłowski R & Władyka‐Przybylak M (2008) Flammability and fire

resistance of composites reinforced by natural fibers. Polymers for

Advanced Technologies 19(6):446-453.

41. Orue A, Jauregi A, Peña-Rodriguez C, Labidi J, Eceiza A, & Arbelaiz A

(2015) The effect of surface modifications on sisal fiber properties and

sisal/poly (lactic acid) interface adhesion. Composites Part B: Engineering

73:132-138.

42. Shumao L, Jie R, Hua Y, Tao Y, & Weizhong Y (2010) Influence of

ammonium polyphosphate on the flame retardancy and mechanical

properties of ramie fiber‐reinforced poly (lactic acid) biocomposites.

Polymer International 59(2):242-248.

43. Shukor F, Hassan A, Saiful Islam M, Mokhtar M, & Hasan M (2014) Effect

of ammonium polyphosphate on flame retardancy, thermal stability and

mechanical properties of alkali treated kenaf fiber filled PLA

biocomposites. Materials & Design (1980-2015) 54(Supplement

C):425-429.

44. Cho D, Woo Y, & Lee K (2014) Flame retardant kenaf/PLA biocomposites:

Effect of ammonium polyphosphate. The 19th International Conference

on Composite Materials.

45. Netnapa E, Mariatti M, Hamid ZAA, Todo M, & Banhan L (2016) Dielectric

Breakdown Strength and Flammability Properties of Flame Retardant

Filler/PLLA-PLA Microsphere/Kenaf Fiber Composites. Procedia

Chemistry 19(Supplement C):290-296.

46. Hapuarachchi TD & Peijs T (2010) Multiwalled carbon nanotubes and

sepiolite nanoclays as flame retardants for polylactide and its natural fibre

reinforced composites. Composites Part A: Applied Science and

Manufacturing 41(8):954-963.

47. Yu T, Jiang N, & Li Y (2014) Functionalized multi-walled carbon nanotube

for improving the flame retardancy of ramie/poly(lactic acid) composite.

Composites Science and Technology 104(Supplement C):26-33.

48. Jang JY, Jeong TK, Oh HJ, Youn JR, & Song YS (2012) Thermal stability

and flammability of coconut fiber reinforced poly(lactic acid) composites.

Page 131: Development and Investigation of Bio-based Environmentally ...

References 116

Composites Part B: Engineering 43(5):2434-2438.

49. Graupner N (2008) Application of lignin as natural adhesion promoter in

cotton fibre-reinforced poly(lactic acid) (PLA) composites. Journal of

Materials Science 43(15):5222-5229.

50. He S, Guo Y, Stone T, Davis N, Kim D, Kim T, & Rafailovich M (2017)

Biodegradable, flame retardant wood-plastic combination via in situ

ring-opening polymerization of lactide monomers. Journal of Wood

Science 63(2):154-160.

51. Shah BL, Selke SE, Walters MB, & Heiden PA (2008) Effects of wood

flour and chitosan on mechanical, chemical, and thermal properties of

polylactide. Polymer Composites 29(6):655-663.

52. Orue A, Jauregi A, Unsuain U, Labidi J, Eceiza A, & Arbelaiz A (2016) The

effect of alkaline and silane treatments on mechanical properties and

breakage of sisal fibers and poly(lactic acid)/sisal fiber composites.

Composites Part A: Applied Science and Manufacturing 84:186-195.

53. Bocz K, Szolnoki B, Marosi A, Tábi T, Wladyka-Przybylak M, & Marosi G

(2014) Flax fibre reinforced PLA/TPS biocomposites flame retarded with

multifunctional additive system. Polymer Degradation and Stability

106(Supplement C):63-73.

54. Dorez G, Taguet A, Ferry L, & Cuesta J-ML (2014) Phosphorous

compounds as flame retardants for polybutylene succinate/flax

biocomposite: additive versus reactive route. Polymer Degradation and

Stability 102:152-159.

55. Qin L, Qiu J, Liu M, Ding S, Shao L, Lü S, Zhang G, Zhao Y, & Fu X (2011)

Mechanical and thermal properties of poly(lactic acid) composites with

rice straw fiber modified by poly(butyl acrylate). Chemical Engineering

Journal 166(2):772-778.

56. Lee S-H & Wang S (2006) Biodegradable polymers/bamboo fiber

biocomposite with bio-based coupling agent. Composites Part A: Applied

Science and Manufacturing 37(1):80-91.

57. Iwatake A, Nogi M, & Yano H (2008) Cellulose nanofiber-reinforced

polylactic acid. Composites Science and Technology 68(9):2103-2106.

58. Krikorian V & Pochan DJ (2003) Poly (l-Lactic Acid)/Layered Silicate

Nanocomposite:  Fabrication, Characterization, and Properties.

Chemistry of Materials 15(22):4317-4324.

59. Krishnamachari P, Zhang J, Lou J, Yan J, & Uitenham L (2009)

Biodegradable Poly(Lactic Acid)/Clay Nanocomposites by Melt

Intercalation: A Study of Morphological, Thermal, and Mechanical

Properties. International Journal of Polymer Analysis and Characterization

Page 132: Development and Investigation of Bio-based Environmentally ...

References 117

Characterization 14(4):336-350.

60. Wang D-Y, Gohs U, Kang N-J, Leuteritz A, Boldt R, Wagenknecht U, &

Heinrich G (2012) Method for Simultaneously Improving the Thermal

Stability and Mechanical Properties of Poly(lactic acid): Effect of

High-Energy Electrons on the Morphological, Mechanical, and Thermal

Properties of PLA/MMT Nanocomposites. Langmuir 28(34):12601-12608.

61. Leng J, Kang N, Wang D-Y, Wurm A, Schick C, & Schönhals A (2017)

Crystallization behavior of nanocomposites based on poly(l-lactide) and

MgAl layered double hydroxides – Unbiased determination of the rigid

amorphous phases due to the crystals and the nanofiller. Polymer

108(Supplement C):257-264.

62. Oksman K, Mathew AP, Bondeson D, & Kvien I (2006) Manufacturing

process of cellulose whiskers/polylactic acid nanocomposites.

Composites science and technology 66(15):2776-2784.

63. Petersson L, Kvien I, & Oksman K (2007) Structure and thermal

properties of poly (lactic acid)/cellulose whiskers nanocomposite

materials. Composites Science and Technology 67(11):2535-2544.

64. Wei P, Bocchini S, & Camino G (2013) Nanocomposites combustion

peculiarities. A case history: Polylactide-clays. European Polymer Journal

49(4):932-939.

65. Wen X, Lin Y, Han C, Zhang K, Ran X, Li Y, & Dong L (2009)

Thermomechanical and optical properties of biodegradable

poly(L-lactide)/silica nanocomposites by melt compounding. Journal of

Applied Polymer Science 114(6):3379-3388.

66. Krikorian V & Pochan DJ (2005) Crystallization Behavior of Poly(l-lactic

acid) Nanocomposites:  Nucleation and Growth Probed by Infrared

Spectroscopy. Macromolecules 38(15):6520-6527.

67. Das A, George JJ, Kutlu B, Leuteritz A, Wang D-Y, Rooj S, Jurk R,

Rajeshbabu R, Stöckelhuber KW, Galiatsatos V, & Heinrich G (2012) A

Novel Thermotropic Elastomer based on Highly-filled LDH-SSB

Composites. Macromolecular Rapid Communications 33(4):337-342.

68. Kang N-J, Wang D-Y, Kutlu B, Zhao P-C, Leuteritz A, Wagenknecht U, &

Heinrich G (2013) A New Approach to Reducing the Flammability of

Layered Double Hydroxide (LDH)-Based Polymer Composites:

Preparation and Characterization of Dye Structure-Intercalated LDH and

Its Effect on the Flammability of Polypropylene-Grafted Maleic

Anhydride/d-LDH Composites. ACS Applied Materials & Interfaces

5(18):8991-8997.

69. Leuteritz A, Kutlu B, Meinl J, Wang D, Das A, Wagenknecht U, & Heinrich

Page 133: Development and Investigation of Bio-based Environmentally ...

References 118

G (2012) Layered Double Hydroxides (LDH): A Multifunctional Versatile

System for Nanocomposites. Molecular Crystals and Liquid Crystals

556(1):107-113.

70. Naseem S, Lonkar SP, Leuteritz A, & Labuschagné FJWJ (2018) Different

transition metal combinations of LDH systems and their organic

modifications as UV protecting materials for polypropylene (PP). RSC

Advances 8(52):29789-29796.

71. Wang D-Y, Das A, Leuteritz A, Mahaling RN, Jehnichen D, Wagenknecht

U, & Heinrich G (2012) Structural characteristics and flammability of fire

retarding EPDM/layered double hydroxide (LDH) nanocomposites. RSC

Advances 2(9):3927-3933.

72. Wang X, Sporer Y, Leuteritz A, Kuehnert I, Wagenknecht U, Heinrich G, &

Wang D-Y (2015) Comparative study of the synergistic effect of binary

and ternary LDH with intumescent flame retardant on the properties of

polypropylene composites. RSC Advances 5(96):78979-78985.

73. Wang Z, Han E, & Ke W (2005) Influence of nano-LDHs on char formation

and fire-resistant properties of flame-retardant coating. Progress in

Organic Coatings 53(1):29-37.

74. Akbari A, Majumder M, & Tehrani A (2015) Polylactic Acid (PLA) Carbon

Nanotube Nanocomposites. Handbook of Polymer Nanocomposites.

Processing, Performance and Application: Volume B: Carbon Nanotube

Based Polymer Composites, eds Kar KK, Pandey JK, & Rana S (Springer

Berlin Heidelberg, Berlin, Heidelberg), pp 283-297.

75. Bourbigot S, Fontaine G, Gallos A, Gérard C, & Bellayer S (2009)

Functionalized-Carbon Multiwall Nanotube as Flame Retardant for

Polylactic Acid. Fire and Polymers V, ACS Symposium Series,

(American Chemical Society), Vol 1013, pp 25-34.

76. Gonçalves C, Gonçalves I, Magalhães F, & Pinto A (2017) Poly(lactic acid)

Composites Containing Carbon-Based Nanomaterials: A Review.

Polymers 9(7):269.

77. Fache M, Boutevin B, & Caillol S (2015) Vanillin, a key-intermediate of

biobased polymers. European Polymer Journal 68:488-502.

78. Fache M, Viola A, Auvergne R, Boutevin B, & Caillol S (2015) Biobased

epoxy thermosets from vanillin-derived oligomers. European Polymer

Journal 68(Supplement C):526-535.

79. Jagadish RS, Raj B, & Asha MR (2009) Blending of low-density

polyethylene with vanillin for improved barrier and aroma-releasing

properties in food packaging. Journal of Applied Polymer Science

113(6):3732-3741.

Page 134: Development and Investigation of Bio-based Environmentally ...

References 119

80. Abraham D, Mehanna A, Wireko F, Whitney J, Thomas R, & Orringer E

(1991) Vanillin, a potential agent for the treatment of sickle cell anemia.

Blood 77(6):1334-1341.

81. Buslovich A, Horev B, Rodov V, Gedanken A, & Poverenov E (2017)

One-step surface grafting of organic nanoparticles: in situ deposition of

antimicrobial agents vanillin and chitosan on polyethylene packaging films.

Journal of Materials Chemistry B 5(14):2655-2661.

82. Celebioglu A, Kayaci-Senirmak F, Ipek S, Durgun E, & Uyar T (2016)

Polymer-free nanofibers from vanillin/cyclodextrin inclusion complexes:

high thermal stability, enhanced solubility and antioxidant property. Food

& Function 7(7):3141-3153.

83. Xavier JR, Babusha ST, George J, & Ramana KV (2015) Material

Properties and Antimicrobial Activity of Polyhydroxybutyrate (PHB) Films

Incorporated with Vanillin. Applied Biochemistry and Biotechnology

176(5):1498-1510.

84. Peng H, Xiong H, Li J, Xie M, Liu Y, Bai C, & Chen L (2010) Vanillin

cross-linked chitosan microspheres for controlled release of resveratrol.

Food Chemistry 121(1):23-28.

85. Sabaa MW, Mohamed RR, & Oraby EH (2009) Vanillin–Schiff’s bases as

organic thermal stabilizers and co-stabilizers for rigid poly(vinyl chloride).

European Polymer Journal 45(11):3072-3080.

86. Fache M, Boutevin B, & Caillol S (2015) Vanillin production from lignin

and its use as a renewable chemical. ACS Sustainable Chemistry &

Engineering 4(1):35-46.

87. Ma X-k & Daugulis AJ (2014) Transformation of ferulic acid to vanillin

using a fed-batch solid–liquid two-phase partitioning bioreactor.

Biotechnology Progress 30(1):207-214.

88. Thakur VK, Thakur MK, Raghavan P, & Kessler MR (2014) Progress in

Green Polymer Composites from Lignin for Multifunctional Applications: A

Review. ACS Sustainable Chemistry & Engineering 2(5):1072-1092.

89. Laurichesse S & Avérous L (2014) Chemical modification of lignins:

Towards biobased polymers. Progress in Polymer Science

39(7):1266-1290.

90. Araújo JDP, Grande CA, & Rodrigues AE (2010) Vanillin production from

lignin oxidation in a batch reactor. Chemical Engineering Research and

Design 88(8):1024-1032.

91. Clark JH (2007) Green chemistry for the second generation

biorefinery—sustainable chemical manufacturing based on biomass.

Journal of Chemical Technology & Biotechnology 82(7):603-609.

Page 135: Development and Investigation of Bio-based Environmentally ...

References 120

92. Fache M, Auvergne R, Boutevin B, & Caillol S (2015) New vanillin-derived

diepoxy monomers for the synthesis of biobased thermosets. European

Polymer Journal 67(Supplement C):527-538.

93. Fache M, Darroman E, Besse V, Auvergne R, Caillol S, & Boutevin B

(2014) Vanillin, a promising biobased building-block for monomer

synthesis. Green Chemistry 16(4):1987-1998.

94. Firdaus M & Meier MAR (2013) Renewable co-polymers derived from

vanillin and fatty acid derivatives. European Polymer Journal

49(1):156-166.

95. Harvey BG, Guenthner AJ, Meylemans HA, Haines SRL, Lamison KR,

Groshens TJ, Cambrea LR, Davis MC, & Lai WW (2015) Renewable

thermosetting resins and thermoplastics from vanillin. Green Chemistry

17(2):1249-1258.

96. Sini NK, Bijwe J, & Varma IK (2014) Renewable benzoxazine monomer

from Vanillin: Synthesis, characterization, and studies on curing behavior.

Journal of Polymer Science Part A: Polymer Chemistry 52(1):7-11.

97. Stanzione III JF, Sadler JM, La Scala JJ, Reno KH, & Wool RP (2012)

Vanillin-based resin for use in composite applications. Green Chemistry

14(8):2346-2352.

98. Van A, Chiou K, & Ishida H (2014) Use of renewable resource vanillin for

the preparation of benzoxazine resin and reactive monomeric surfactant

containing oxazine ring. Polymer 55(6):1443-1451.

99. Wang S, Ma S, Xu C, Liu Y, Dai J, Wang Z, Liu X, Chen J, Shen X, Wei J,

& Zhu J (2017) Vanillin-Derived High-Performance Flame Retardant

Epoxy Resins: Facile Synthesis and Properties. Macromolecules

50(5):1892-1901.

100. Zhang C, Madbouly SA, & Kessler MR (2015) Renewable Polymers

Prepared from Vanillin and Its Derivatives. Macromolecular Chemistry

and Physics 216(17):1816-1822.

101. Dalmolin LF, Khalil NM, & Mainardes RM (2016) Delivery of vanillin by

poly (lactic-acid) nanoparticles: development, characterization and in vitro

evaluation of antioxidant activity. Materials Science and Engineering: C

62:1-8.

102. Kayaci F & Uyar T (2012) Encapsulation of vanillin/cyclodextrin inclusion

complex in electrospun polyvinyl alcohol (PVA) nanowebs: Prolonged

shelf-life and high temperature stability of vanillin. Food Chemistry

133(3):641-649.

103. Kumar R, Sharma P, & Mishra PS (2012) A review on the vanillin

derivatives showing various biological activities. International Journal of

Page 136: Development and Investigation of Bio-based Environmentally ...

References 121

PharmTech Research 4(1):266-279.

104. Kwon J, Kim J, Park S, Khang G, Kang PM, & Lee D (2013)

Inflammation-Responsive Antioxidant Nanoparticles Based on a

Polymeric Prodrug of Vanillin. Biomacromolecules 14(5):1618-1626.

105. Sangsuwan J, Rattanapanone N, & Rachtanapun P (2008) Effects of

vanillin and plasticizer on properties of chitosan-methyl cellulose based

film. Journal of Applied Polymer Science 109(6):3540-3545.

106. Wilkie CA, Morgan AB, & Nelson GL (2009) Fire and Polymers V

(American Chemical Society) p 456.

107. Horrocks AR, Price D, & Price D (2001) Fire retardant materials

(woodhead Publishing).

108. Morgan AB & Wilkie CA (2007) Flame retardant polymer nanocomposites

(John Wiley & Sons).

109. Wang X & Wang DY (2017) 4 - Fire-retardant polylactic acid-based

materials: Preparation, properties, and mechanism. Novel Fire Retardant

Polymers and Composite Materials, (Woodhead Publishing), pp 93-116.

110. Hartzell GE, Grand AF, & Switzer WG (1990) Toxicity of Smoke

Containing Hydrogen Chloride. Fire and Polymers, ACS Symposium

Series, (American Chemical Society), Vol 425, pp 12-20.

111. Gao Y, Wang Q, Wang J, Huang L, Yan X, Zhang X, He Q, Xing Z, & Guo

Z (2014) Synthesis of Highly Efficient Flame Retardant High-Density

Polyethylene Nanocomposites with Inorgano-Layered Double Hydroxides

As Nanofiller Using Solvent Mixing Method. ACS Applied Materials &

Interfaces 6(7):5094-5104.

112. Chen Y, Zhan J, Zhang P, Nie S, Lu H, Song L, & Hu Y (2010) Preparation

of Intumescent Flame Retardant Poly(butylene succinate) Using Fumed

Silica as Synergistic Agent. Industrial & Engineering Chemistry Research

49(17):8200-8208.

113. Durin‐France A, Ferry L, Lopez Cuesta JM, & Crespy A (2000)

Magnesium hydroxide/zinc borate/talc compositions as flame‐retardants

in EVA copolymer. Polymer International 49(10):1101-1105.

114. Pan Y-T, Trempont C, & Wang D-Y (2016) Hierarchical nanoporous silica

doped with tin as novel multifunctional hybrid material to flexible poly(vinyl

chloride) with greatly improved flame retardancy and mechanical

properties. Chemical Engineering Journal 295(Supplement C):451-460.

115. Gu L, Chen G, & Yao Y (2014) Two novel phosphorus–

nitrogen-containing halogen-free flame retardants of high performance for

epoxy resin. Polymer Degradation and Stability 108(Supplement

Page 137: Development and Investigation of Bio-based Environmentally ...

References 122

C):68-75.

116. Zhuang R-C, Yang J, Wang D-Y, & Huang Y-X (2015) Simultaneously

enhancing the flame retardancy and toughness of epoxy by lamellar

dodecyl-ammonium dihydrogen phosphate. RSC Advances

5(121):100049-100053.

117. Fu X, Liu Y, Wang Q, Zhang Z, Wang Z, & Zhang J (2011) Novel synthesis

method for melamine polyphosphate and its flame retardancy on glass

fiber reinforced polyamide 66. Polymer-Plastics Technology and

Engineering 50(15):1527-1532.

118. Chen Y & Wang Q (2007) Reaction of melamine phosphate with

pentaerythritol and its products for flame retardation of polypropylene.

Polymers for Advanced Technologies 18(8):587-600.

119. Feng C, Zhang Y, Liu S, Chi Z, & Xu J (2012) Synthesis of novel triazine

charring agent and its effect in intumescent flame ‐ retardant

polypropylene. Journal of applied polymer science 123(6):3208-3216.

120. Liu Y, Wang D-Y, Wang J-S, Song Y-P, & Wang Y-Z (2008) A novel

intumescent flame-retardant LDPE system and its thermo-oxidative

degradation and flame-retardant mechanisms. Polymers for Advanced

Technologies 19(11):1566-1575.

121. Zhao B, Hu Z, Chen L, Liu Y, Liu Y, & Wang Y-Z (2011) A

phosphorus-containing inorganic compound as an effective flame

retardant for glass-fiber-reinforced polyamide 6. Journal of Applied

Polymer Science 119(4):2379-2385.

122. Zhao C-S, Huang F-L, Xiong W-C, & Wang Y-Z (2008) A novel

halogen-free flame retardant for glass-fiber-reinforced poly (ethylene

terephthalate). Polymer Degradation and Stability 93(6):1188-1193.

123. Qian Y, Wei P, Jiang P, Zhao X, & Yu H (2011) Synthesis of a novel hybrid

synergistic flame retardant and its application in PP/IFR. Polymer

Degradation and Stability 96(6):1134-1140.

124. Xiao D, Li Z, De Juan S, Gohs U, Wagenknecht U, Voit B, & Wang D-Y

(2016) Preparation, fire behavior and thermal stability of a novel flame

retardant polypropylene system. Journal of Thermal Analysis and

Calorimetry 125(1):321-329.

125. Tang Y, Hu Y, Li B, Liu L, Wang Z, Chen Z, & Fan W (2004)

Polypropylene/montmorillonite nanocomposites and intumescent,

flame-retardant montmorillonite synergism in polypropylene

nanocomposites. Journal of Polymer Science Part A: Polymer Chemistry

42(23):6163-6173.

126. Tang Y, Hu Y, Wang S, Gui Z, Chen Z, & Fan W (2003) Intumescent flame

Page 138: Development and Investigation of Bio-based Environmentally ...

References 123

retardant–montmorillonite synergism in polypropylene‐layered silicate

nanocomposites. Polymer international 52(8):1396-1400.

127. Laachachi A, Ball V, Apaydin K, Toniazzo V, & Ruch D (2011) Diffusion of

Polyphosphates into (Poly(allylamine)-montmorillonite) Multilayer Films:

Flame Retardant-Intumescent Films with Improved Oxygen Barrier.

Langmuir 27(22):13879-13887.

128. Laufer G, Kirkland C, Cain AA, & Grunlan JC (2012) Clay–Chitosan

Nanobrick Walls: Completely Renewable Gas Barrier and

Flame-Retardant Nanocoatings. ACS Applied Materials & Interfaces

4(3):1643-1649.

129. Ma HY, Tong LF, Xu ZB, & Fang ZP (2008) Functionalizing carbon

nanotubes by grafting on intumescent flame retardant: nanocomposite

synthesis, morphology, rheology, and flammability. Advanced functional

materials 18(3):414-421.

130. Yuan X-Y, Wang D-Y, Chen L, Wang X-L, & Wang Y-Z (2011) Inherent

flame retardation of bio-based poly(lactic acid) by incorporating

phosphorus linked pendent group into the backbone. Polymer

Degradation and Stability 96(9):1669-1675.

131. Wang D-Y, Song Y-P, Lin L, Wang X-L, & Wang Y-Z (2011) A novel

phosphorus-containing poly (lactic acid) toward its flame retardation.

Polymer 52(2):233-238.

132. Xiong J-F, Luo S-H, Wang Q-F, Wang Z-Y, & Qi J (2013) Synthesis and

characterization of a novel flame retardant, poly(lactic acid-co-3,3′

-diaminobenzidine). Designed Monomers and Polymers 16(4):389-397.

133. Horikoshi VKKVY (2005) Bio-based polymers. Fujitsu Sci. Tech. J

41(2):173-180.

134. Teoh E, Mariatti M, & Chow W (2016) Thermal and flame resistant

properties of poly (lactic acid)/poly (methyl methacrylate) blends

containing halogen-free flame retardant. Procedia Chemistry 19:795-802.

135. Mu X, Yuan B, Hu W, Qiu S, Song L, & Hu Y (2015) Flame retardant and

anti-dripping properties of polylactic

acid/poly(bis(phenoxy)phosphazene)/expandable graphite composite and

its flame retardant mechanism. RSC Advances 5(93):76068-76078.

136. Murariu M, Bonnaud L, Yoann P, Fontaine G, Bourbigot S, & Dubois P

(2010) New trends in polylactide (PLA)-based materials:“Green” PLA–

Calcium sulfate (nano) composites tailored with flame retardant

properties. Polymer Degradation and Stability 95(3):374-381.

137. Wen X, Gong J, Yu H, Liu Z, Wan D, Liu J, Jiang Z, & Tang T (2012)

Catalyzing carbonization of poly(l-lactide) by nanosized carbon black

Page 139: Development and Investigation of Bio-based Environmentally ...

References 124

combined with Ni2O3 for improving flame retardancy. Journal of Materials

Chemistry 22(37):19974-19980.

138. Liu X-Q, Wang D-Y, Wang X-L, Chen L, & Wang Y-Z (2011) Synthesis of

organo-modified α-zirconium phosphate and its effect on the flame

retardancy of IFR poly(lactic acid) systems. Polymer Degradation and

Stability 96(5):771-777.

139. Liu X-Q, Wang D-Y, Wang X-L, Chen L, & Wang Y-Z (2013) Synthesis of

functionalized α-zirconium phosphate modified with intumescent flame

retardant and its application in poly(lactic acid). Polymer Degradation and

Stability 98(9):1731-1737.

140. Kalali EN, De Juan S, Wang X, Nie S, Wang R, & Wang D-Y (2015)

Comparative study on synergistic effect of LDH and zirconium phosphate

with aluminum trihydroxide on flame retardancy of EVA composites.

Journal of Thermal Analysis and Calorimetry 121(2):619-626.

141. Nishida H, Fan Y, Mori T, Oyagi N, Shirai Y, & Endo T (2005) Feedstock

Recycling of Flame-Resisting Poly(lactic acid)/Aluminum Hydroxide

Composite to l,l-lactide. Industrial & Engineering Chemistry Research

44(5):1433-1437.

142. Cheng K-C, Yu C-B, Guo W, Wang S-F, Chuang T-H, & Lin Y-H (2012)

Thermal properties and flammability of polylactide nanocomposites with

aluminum trihydrate and organoclay. Carbohydrate Polymers

87(2):1119-1123.

143. Wu N & Li X (2014) Flame retardancy and synergistic flame retardant

mechanisms of acrylonitrile-butadiene-styrene composites based on

aluminum hypophosphite. Polymer Degradation and Stability

105(Supplement C):265-276.

144. Cheng K-C, Chang S-C, Lin Y-H, & Wang C-C (2015) Mechanical and

flame retardant properties of polylactide composites with hyperbranched

polymers. Composites Science and Technology 118(Supplement

C):186-192.

145. Tang G, Wang X, Xing W, Zhang P, Wang B, Hong N, Yang W, Hu Y, &

Song L (2012) Thermal Degradation and Flame Retardance of Biobased

Polylactide Composites Based on Aluminum Hypophosphite. Industrial &

Engineering Chemistry Research 51(37):12009-12016.

146. Zhou X, Li J, & Wu Y (2015) Synergistic effect of aluminum

hypophosphite and intumescent flame retardants in polylactide. Polymers

for Advanced Technologies 26(3):255-265.

147. Ke C-H, Li J, Fang K-Y, Zhu Q-L, Zhu J, Yan Q, & Wang Y-Z (2010)

Synergistic effect between a novel hyperbranched charring agent and

Page 140: Development and Investigation of Bio-based Environmentally ...

References 125

ammonium polyphosphate on the flame retardant and anti-dripping

properties of polylactide. Polymer Degradation and Stability

95(5):763-770.

148. Gu L, Qiu J, & Sakai E (2017) Effect of DOPO-containing flame retardants

on poly(lactic acid): Non-flammability, mechanical properties and thermal

behaviors. Chemical Research in Chinese Universities 33(1):143-149.

149. Tao K, Li J, Xu L, Zhao X, Xue L, Fan X, & Yan Q (2011) A novel

phosphazene cyclomatrix network polymer: design, synthesis and

application in flame retardant polylactide. Polymer degradation and

stability 96(7):1248-1254.

150. Liao F, Zhou L, Ju Y, Yang Y, & Wang X (2014) Synthesis of A Novel

Phosphorus–Nitrogen-Silicon Polymeric Flame Retardant and Its

Application in Poly(lactic acid). Industrial & Engineering Chemistry

Research 53(24):10015-10023.

151. Wei L-L, Wang D-Y, Chen H-B, Chen L, Wang X-L, & Wang Y-Z (2011)

Effect of a phosphorus-containing flame retardant on the thermal

properties and ease of ignition of poly (lactic acid). Polymer degradation

and stability 96(9):1557-1561.

152. Zhao X, de Juan S, Guerrero FR, Li Z, Llorca J, & Wang D-Y (2016) Effect

of N,N′-diallyl-phenylphosphoricdiamide on ease of ignition, thermal

decomposition behavior and mechanical properties of poly (lactic acid).

Polymer Degradation and Stability 127(Supplement C):2-10.

153. Zhao X, Guerrero FR, Llorca J, & Wang D-Y (2016) New Superefficiently

Flame-Retardant Bioplastic Poly(lactic acid): Flammability, Thermal

Decomposition Behavior, and Tensile Properties. ACS Sustainable

Chemistry & Engineering 4(1):202-209.

154. Chen X, Zhuo J, & Jiao C (2012) Thermal degradation characteristics of

flame retardant polylactide using TG-IR. Polymer Degradation and

Stability 97(11):2143-2147.

155. Jing J, Zhang Y, & Fang Z (2017) Diphenolic acid based biphosphate on

the properties of polylactic acid: Synthesis, fire behavior and flame

retardant mechanism. Polymer 108:29-37.

156. Jing J, Zhang Y, Tang X, & Fang Z (2016) Synthesis of a highly efficient

phosphorus-containing flame retardant utilizing plant-derived diphenolic

acids and its application in polylactic acid. RSC Advances

6(54):49019-49027.

157. Lin H-J, Liu S-R, Han L-J, Wang X-M, Bian Y-J, & Dong L-S (2013) Effect

of a phosphorus-containing oligomer on flame-retardant, rheological and

mechanical properties of poly (lactic acid). Polymer Degradation and

Page 141: Development and Investigation of Bio-based Environmentally ...

References 126

Stability 98(7):1389-1396.

158. Mauldin TC, Zammarano M, Gilman JW, Shields JR, & Boday DJ (2014)

Synthesis and characterization of isosorbide-based polyphosphonates as

biobased flame-retardants. Polymer Chemistry 5(17):5139-5146.

159. Jiang P, Gu X, Zhang S, Wu S, Zhao Q, & Hu Z (2015) Synthesis,

Characterization, and Utilization of a Novel

Phosphorus/Nitrogen-Containing Flame Retardant. Industrial &

Engineering Chemistry Research 54(11):2974-2982.

160. Li Z, Wei P, Yang Y, Yan Y, & Shi D (2014) Synthesis of a hyperbranched

poly(phosphamide ester) oligomer and its high-effective flame retardancy

and accelerated nucleation effect in polylactide composites. Polymer

Degradation and Stability 110:104-112.

161. Liao F, Ju Y, Dai X, Cao Y, Li J, & Wang X (2015) A novel efficient

polymeric flame retardant for poly (lactic acid) (PLA): Synthesis and its

effects on flame retardancy and crystallization of PLA. Polymer

Degradation and Stability 120(Supplement C):251-261.

162. Bourbigot S, Bras ML, & Delobel R (1993) Carbonization mechanisms

resulting from intumescence association with the ammonium

polyphosphate-pentaerythritol fire retardant system. Carbon

31(8):1219-1230.

163. Lim K-S, Bee S-T, Sin LT, Tee T-T, Ratnam CT, Hui D, & Rahmat AR

(2016) A review of application of ammonium polyphosphate as

intumescent flame retardant in thermoplastic composites. Composites

Part B: Engineering 84:155-174.

164. Chen Y, Wang W, Liu Z, Yao Y, & Qian L (2017) Synthesis of a novel

flame retardant containing phosphazene and triazine groups and its

enhanced charring effect in poly(lactic acid) resin. Journal of Applied

Polymer Science 134(13):n/a-n/a.

165. Chen Y, Wang W, Qiu Y, Li L, Qian L, & Xin F (2017) Terminal group

effects of phosphazene-triazine bi-group flame retardant additives in

flame retardant polylactic acid composites. Polymer Degradation and

Stability 140(Supplement C):166-175.

166. Feng C, Liang M, Jiang J, Huang J, & Liu H (2016) Flame retardant

properties and mechanism of an efficient intumescent flame retardant

PLA composites. Polymers for Advanced Technologies 27(5):693-700.

167. Shabanian M, Kang N-J, Wang D-Y, Wagenknecht U, & Heinrich G (2013)

Synthesis of aromatic–aliphatic polyamide acting as adjuvant in polylactic

acid (PLA)/ammonium polyphosphate (APP) system. Polymer

Degradation and Stability 98(5):1036-1042.

Page 142: Development and Investigation of Bio-based Environmentally ...

References 127

168. Xuan S, Wang X, Song L, Xing W, Lu H, & Hu Y (2011) Study on

flame-retardancy and thermal degradation behaviors of intumescent

flame-retardant polylactide systems. Polymer International

60(10):1541-1547.

169. Zhan J, Song L, Nie S, & Hu Y (2009) Combustion properties and thermal

degradation behavior of polylactide with an effective intumescent flame

retardant. Polymer Degradation and Stability 94(3):291-296.

170. Reti C, Casetta M, Duquesne S, Delobel R, Soulestin J, & Bourbigot S

(2009) Intumescent Biobased-Polylactide Films to Flame Retard

Nonwovens. Journal of Engineered Fabrics & Fibers (JEFF) 4(2).

171. Zhan J, Wang L, Hong N, Hu W, Wang J, Song L, & Hu Y (2014)

Flame-retardant and Anti-dripping Properties of Intumescent

Flame-retardant Polylactide with Different Synergists. Polymer-Plastics

Technology and Engineering 53(4):387-394.

172. Reti C, Casetta M, Duquesne S, Bourbigot S, & Delobel R (2008)

Flammability properties of intumescent PLA including starch and lignin.

Polymers for advanced Technologies 19(6):628-635.

173. Wang J, Ren Q, Zheng W, & Zhai W (2014) Improved Flame-Retardant

Properties of Poly(lactic acid) Foams Using Starch as a Natural Charring

Agent. Industrial & Engineering Chemistry Research 53(4):1422-1430.

174. Wang X, Hu Y, Song L, Xuan S, Xing W, Bai Z, & Lu H (2011) Flame

Retardancy and Thermal Degradation of Intumescent Flame Retardant

Poly(lactic acid)/Starch Biocomposites. Industrial & Engineering

Chemistry Research 50(2):713-720.

175. Cayla A, Rault F, Giraud S, Salaün F, Fierro V, & Celzard A (2016) PLA

with Intumescent System Containing Lignin and Ammonium

Polyphosphate for Flame Retardant Textile. Polymers 8(9):331.

176. Costes L, Laoutid F, Brohez S, Delvosalle C, & Dubois P (2017) Phytic

acid–lignin combination: A simple and efficient route for enhancing

thermal and flame retardant properties of polylactide. European Polymer

Journal 94(Supplement C):270-285.

177. Zhang R, Xiao X, Tai Q, Huang H, & Hu Y (2012) Modification of lignin

and its application as char agent in intumescent flame‐retardant poly

(lactic acid). Polymer Engineering & Science 52(12):2620-2626.

178. Zhang R, Xiao X, Tai Q, Huang H, Yang J, & Hu Y (2012) Preparation of

lignin–silica hybrids and its application in intumescent flame-retardant

poly(lactic acid) system. High Performance Polymers 24(8):738-746.

179. Costes L, Laoutid F, Dumazert L, Lopez-cuesta J-M, Brohez S, Delvosalle

C, & Dubois P (2015) Metallic phytates as efficient bio-based

Page 143: Development and Investigation of Bio-based Environmentally ...

References 128

phosphorous flame retardant additives for poly(lactic acid). Polymer

Degradation and Stability 119(Supplement C):217-227.

180. Feng JX, Su SP, & Zhu J (2011) An intumescent flame retardant system

using β‐cyclodextrin as a carbon source in polylactic acid (PLA).

Polymers for Advanced Technologies 22(7):1115-1122.

181. Song YP, Wang DY, Wang XL, Lin L, & Wang YZ (2011) A method for

simultaneously improving the flame retardancy and toughness of PLA.

Polymers for Advanced Technologies 22(12):2295-2301.

182. Fontaine G & Bourbigot S (2009) Intumescent polylactide: A

nonflammable material. Journal of Applied Polymer Science

113(6):3860-3865.

183. Fontaine G, Gallos A, & Bourbigot S (2014) Role of montmorillonite for

enhancing fire retardancy of intumescent PLA. Fire Safety Science

11:808-820.

184. Zhao X, Gao S, & Liu G (2016) A THEIC-based polyphosphate melamine

intumescent flame retardant and its flame retardancy properties for

polylactide. Journal of Analytical and Applied Pyrolysis 122:24-34.

185. Chow WS & Teoh EL (2015) Flexible and flame resistant poly (lactic

acid)/organomontmorillonite nanocomposites. Journal of Applied Polymer

Science 132(2).

186. Li S, Yuan H, Yu T, Yuan W, & Ren J (2009) Flame‐retardancy and

anti‐ dripping effects of intumescent flame retardant incorporating

montmorillonite on poly (lactic acid). Polymers for Advanced Technologies

20(12):1114-1120.

187. Fukushima K, Murariu M, Camino G, & Dubois P (2010) Effect of

expanded graphite/layered-silicate clay on thermal, mechanical and fire

retardant properties of poly(lactic acid). Polymer Degradation and Stability

95(6):1063-1076.

188. Ye L, Ren J, Cai S-y, Wang Z-g, & Li J-b (2016) Poly (lactic acid)

nanocomposites with improved flame retardancy and impact strength by

combining of phosphinates and organoclay. Chinese Journal of Polymer

Science 34(6):785-796.

189. Ding P, Kang B, Zhang J, Yang J, Song N, Tang S, & Shi L (2015)

Phosphorus-containing flame retardant modified layered double

hydroxides and their applications on polylactide film with good

transparency. Journal of Colloid and Interface Science 440(Supplement

C):46-52.

190. Leng J, Purohit PJ, Kang N, Wang D-Y, Falkenhagen J, Emmerling F,

Thünemann AF, & Schönhals A (2015) Structure–property relationships of

Page 144: Development and Investigation of Bio-based Environmentally ...

References 129

nanocomposites based on polylactide and MgAl layered double

hydroxides. European Polymer Journal 68(Supplement C):338-354.

191. Wang D-Y, Leuteritz A, Wang Y-Z, Wagenknecht U, & Heinrich G (2010)

Preparation and burning behaviors of flame retarding biodegradable poly

(lactic acid) nanocomposite based on zinc aluminum layered double

hydroxide. Polymer Degradation and Stability 95(12):2474-2480.

192. Bourbigot S, Fontaine G, Gallos A, & Bellayer S (2011) Reactive extrusion

of PLA and of PLA/carbon nanotubes nanocomposite: processing,

characterization and flame retardancy. Polymers for Advanced

Technologies 22(1):30-37.

193. Hu Y, Xu P, Gui H, Wang X, & Ding Y (2015) Effect of imidazolium

phosphate and multiwalled carbon nanotubes on thermal stability and

flame retardancy of polylactide. Composites Part A: Applied Science and

Manufacturing 77:147-153.

194. Wei P, Bocchini S, & Camino G (2013) Flame retardant and thermal

behavior of polylactide/expandable graphite composites. Polimery

58(5):361-364.

195. Zhu H, Zhu Q, Li J, Tao K, Xue L, & Yan Q (2011) Synergistic effect

between expandable graphite and ammonium polyphosphate on flame

retarded polylactide. Polymer Degradation and Stability 96(2):183-189.

196. Song L, Xuan S, Wang X, & Hu Y (2012) Flame retardancy and thermal

degradation behaviors of phosphate in combination with POSS in

polylactide composites. Thermochimica Acta 527(Supplement C):1-7.

197. Wang X, Xuan S, Song L, Yang H, Lu H, & Hu Y (2012) Synergistic Effect

of POSS on Mechanical Properties, Flammability, and Thermal

Degradation of Intumescent Flame Retardant Polylactide Composites.

Journal of Macromolecular Science, Part B 51(2):255-268.

198. Fox DM, Novy M, Brown K, Zammarano M, Harris RH, Murariu M,

McCarthy ED, Seppala JE, & Gilman JW (2014) Flame retarded

poly(lactic acid) using POSS-modified cellulose. 2. Effects of intumescing

flame retardant formulations on polymer degradation and composite

physical properties. Polymer Degradation and Stability 106(Supplement

C):54-62.

199. Fox DM, Lee J, Citro CJ, & Novy M (2013) Flame retarded poly(lactic acid)

using POSS-modified cellulose. 1. Thermal and combustion properties of

intumescing composites. Polymer Degradation and Stability

98(2):590-596.

200. Li Z, Fernández Expósito D, Jiménez González A, & Wang D-Y (2017)

Natural halloysite nanotube based functionalized nanohybrid assembled

Page 145: Development and Investigation of Bio-based Environmentally ...

References 130

via phosphorus-containing slow release method: A highly efficient way to

impart flame retardancy to polylactide. European Polymer Journal

93(Supplement C):458-470.

201. González A, Dasari A, Herrero B, Plancher E, Santarén J, Esteban A, &

Lim S-H (2012) Fire retardancy behavior of PLA based nanocomposites.

Polymer Degradation and Stability 97(3):248-256.

202. Stoclet G, Sclavons M, Lecouvet B, Devaux J, Van Velthem P, Boborodea

A, Bourbigot S, & Sallem-Idrissi N (2014) Elaboration of poly(lactic

acid)/halloysite nanocomposites by means of water assisted extrusion:

structure, mechanical properties and fire performance. RSC Advances

4(101):57553-57563.

203. Kambel RD, Aliyu BA, Barminas JT, & Akinterinwa A (2017) Synthesis and

Application of Polylactic Acid/Kaolin Nanocomposite as a Flame

Retardant in Flexible Polyurethane Foam. International Journal of

Materials and Chemistry 7(1):14-19.

204. Isitman NA, Dogan M, Bayramli E, & Kaynak C (2012) The role of

nanoparticle geometry in flame retardancy of polylactide nanocomposites

containing aluminium phosphinate. Polymer Degradation and Stability

97(8):1285-1296.

205. Qian Y, Wei P, Jiang P, Li Z, Yan Y, & Ji K (2013) Aluminated mesoporous

silica as novel high-effective flame retardant in polylactide. Composites

Science and Technology 82(Supplement C):1-7.

206. Jiajia L, Keqing Z, Panyue W, Bibo W, Yuan H, & Zhou G (2015) The

influence of multiple modified MMT on the thermal and fire behavior of

poly (lactic acid) nanocomposites. Polymers for Advanced Technologies

26(6):626-634.

207. Avinc O, Day R, Carr C, & Wilding M (2012) Effect of combined flame

retardant, liquid repellent and softener finishes on poly(lactic acid) (PLA)

fabric performance. Textile Research Journal 82(10):975-984.

208. Wang Y-Y & Shih Y-F (2016) Flame-retardant recycled bamboo chopstick

fiber-reinforced poly(lactic acid) green composites via multifunctional

additive system. Journal of the Taiwan Institute of Chemical Engineers

65(Supplement C):452-458.

209. Guo Y, He S, Zuo X, Xue Y, Chen Z, Chang C-C, Weil E, & Rafailovich M

(2017) Incorporation of cellulose with adsorbed phosphates into poly

(lactic acid) for enhanced mechanical and flame retardant properties.

Polymer Degradation and Stability 144(Supplement C):24-32.

210. Cao Y, Ju Y, Liao F, Jin X, Dai X, Li J, & Wang X (2016) Improving the

flame retardancy and mechanical properties of poly(lactic acid) with a

Page 146: Development and Investigation of Bio-based Environmentally ...

References 131

novel nanorod-shaped hybrid flame retardant. RSC Advances

6(18):14852-14858.

211. Laoutid F, Bonnaud L, Alexandre M, Lopez-Cuesta JM, & Dubois P (2009)

New prospects in flame retardant polymer materials: From fundamentals

to nanocomposites. Materials Science and Engineering: R: Reports

63(3):100-125.

212. Babrauskas V (1984) Development of the cone calorimeter—A

bench-scale heat release rate apparatus based on oxygen consumption.

Fire and Materials 8(2):81-95.

213. Hirschler MM (2015) Flame retardants and heat release: review of data

on individual polymers. Fire and Materials 39(3):232-258.

214. Nazaré S, Kandola BK, & Horrocks AR (2008) Smoke, CO, and CO2

Measurements and Evaluation using Different Fire Testing Techniques for

Flame Retardant Unsaturated Polyester Resin Formulations. Journal of

Fire Sciences 26(3):215-242.

215. Gunasekaran S & Ponnusamy S (2005) Vibrational spectra and normal

coordinate analysis on an organic non-linear optical

crystal-3-methoxy-4-hydroxy benzaldehyde.

216. Liu Y, Pan Y-T, Wang X, Acuña P, Zhu P, Wagenknecht U, Heinrich G,

Zhang X-Q, Wang R, & Wang D-Y (2016) Effect of phosphorus-containing

inorganic–organic hybrid coating on the flammability of cotton fabrics:

Synthesis, characterization and flammability. Chemical Engineering

Journal 294(Supplement C):167-175.

217. Anderson KS & Hillmyer MA (2006) Melt preparation and nucleation

efficiency of polylactide stereocomplex crystallites. Polymer

47(6):2030-2035.

218. Zou H, Yi C, Wang L, Liu H, & Xu W (2009) Thermal degradation of poly

(lactic acid) measured by thermogravimetry coupled to Fourier transform

infrared spectroscopy. Journal of thermal analysis and calorimetry

97(3):929.

219. Fan Y, Nishida H, Shirai Y, Tokiwa Y, & Endo T (2004) Thermal

degradation behaviour of poly(lactic acid) stereocomplex. Polymer

Degradation and Stability 86(2):197-208.

220. Pluta M, Galeski A, Alexandre M, Paul MA, & Dubois P (2002)

Polylactide/montmorillonite nanocomposites and microcomposites

prepared by melt blending: Structure and some physical properties.

Journal of Applied Polymer Science 86(6):1497-1506.

221. Ding Y, McKinnon MB, Stoliarov SI, Fontaine G, & Bourbigot S (2016)

Determination of kinetics and thermodynamics of thermal decomposition

Page 147: Development and Investigation of Bio-based Environmentally ...

References 132

for polymers containing reactive flame retardants: Application to

poly(lactic acid) blended with melamine and ammonium polyphosphate.

Polymer Degradation and Stability 129:347-362.

Page 148: Development and Investigation of Bio-based Environmentally ...

List of Figures 133

List of Figures

Figure 1-1: Plastic production since 1950 .......................................................... 1

Figure 1-2: Schematic illustration of the heat flux vs time in a fire ...................... 3

Figure 3-1: Type of polymeric materials and examples ...................................... 6

Figure 3-2: Synthesis of PLA.............................................................................. 8

Figure 3-3: Proposed mechanism of the lignin-to-vanillin process ................... 14

Figure 3-4: Mode of action of polymer in fire .................................................... 16

Figure 4-1: Synthesis path of VP ...................................................................... 25

Figure 4-2: Synthesis Path of VPA ................................................................... 26

Figure 4-3: Synthesis Path of VPS ................................................................... 26

Figure 4-4: Mixing chamber of plasticorder (left) and extruder (right) ............... 27

Figure 4-5: Injection molding machine (left) and hot compression machine (right)

......................................................................................................................... 30

Figure 4-6: Schematic set up of LOI (left) and UL-94 V (right) instruments ...... 34

Figure 4-7: Schematic set up of a cone calorimeter ......................................... 36

Figure 5-1: FTIR Spectra of VA (black) and VP (red) ....................................... 40

Figure 5-2: 1H (top), 13C and 31P (bottom) NMR spectra of VP......................... 41

Figure 5-3: The morphology of VA and VP by SEM (left) and EDX (right) ........ 42

Figure 5-4: SEM pictures of PLA/VA (left) and PLA/VP (right) composites ....... 43

Figure 5-5: TG (left) and DTG (right) plots of VA and VP ................................. 44

Figure 5-6: TG (left) and DTG (right) plots of PLA and its composites ............. 45

Figure 5-7: Fitted curves of lnβ against 1/T at different α of PLA (left) and

Page 149: Development and Investigation of Bio-based Environmentally ...

List of Figures 134

PLA10VP (right) ................................................................................................ 47

Figure 5-8: DSC plots of PLA and PLA/VP composites .................................... 49

Figure 5-9: HRR plots of PLA and PLA composites .......................................... 55

Figure 5-10: THR (a), Mass loss (b), TSP (c) and CO/CO2 ratio (d) plots of PLA

and PLA composites ......................................................................................... 57

Figure 5-11: Rheological properties of PLA and PLA composites: (a) Complex

viscosity; (b) Storage modulus; (c) Loss modulus ............................................ 58

Figure 5-12: 3D-images of evolved gaseous products for (a) PLA (b) PLA10VP;

(c) Total absorbance vs time for PLA and PLA10VP; (d) Absorbance at 1238

cm-1 vs time for PLA and PLA10VP (c) At Tmax for PLA and PLA10VP; (d) Zoom

in on selected area. (Tmax appeared at 47 min) ................................................ 59

Figure 5-13: Tensile test plots of PLA and PLA composites .............................. 60

Figure 5-14: Pictures of tensile bar after tests of PLA10VA (left) and PLA10VP

(right) ................................................................................................................ 62

Figure 5-15: Tensile test plots of PLA and PLA/VP composites processed via

different methods .............................................................................................. 63

Figure 5-16: FTIR spectrum of VP (black) and VPA (red) ................................. 69

Figure 5-17: FTIR spectrum of VP (black) and VPS (red) ................................. 69

Figure 5-18: 1H NMR spectrum of VPA ............................................................. 70

Figure 5-19: 1H NMR spectrum of VPS ............................................................ 71

Figure 5-20: TG (left) and DTG (right) plots of VP, VPA and VPS ..................... 72

Figure 5-21: TG (left) and DTG (right) plots of VPA and VPS based PLA

composites ....................................................................................................... 73

Figure 5-22: HRR plots of PLA/VPA and PLA/VPS composites ........................ 77

Page 150: Development and Investigation of Bio-based Environmentally ...

List of Figures 135

Figure 5-23: THR (left) and CO/CO2 ratio (right) plots of PLA/VPA and PLA/VPS

composites ....................................................................................................... 78

Figure 5-24: Tensile test plots of PLA and PLA composites ............................. 79

Figure 5-25: SEM pictures of PLA/MMT and mPLA/MMT composites ............. 82

Figure 5-26: TG (left) and DTG (right) plots of PLA and PLA composites ........ 83

Figure 5-27: DSC plots of PLA and PLA composites ........................................ 85

Figure 5-28: HRR plots of PLA/VP/MMT composites ....................................... 88

Figure 5-29: THR (a), Mass loss (b), TSP (c) and CO/CO2 ratio (d) plots of PLA

composites ....................................................................................................... 89

Figure 5-30: Residue of samples after cone calorimeter test of PLA/MMT

composites (top) and mPLA/MMT composites (bottom) with 5 wt.-% (left) and 10

wt.-%(right) MMT .............................................................................................. 90

Figure 5-31: SEM pictures of char layer after cone calorimeter test of

PLA10MMT (top) and mPLA10MMT (bottom) for surface (left) and inner (right)

residue ............................................................................................................. 91

Figure 5-32: Tensile test plots of PLA/VP/MMT composites ............................. 92

Figure 5-33: SEM pictures PLA/APP and mPLA/APP composites ................... 94

Figure 5-34: TG (left) and DTG (right) plots of PLA/VP/APP composites ......... 96

Figure 5-35: DSC plots of PLA/APP composites .............................................. 97

Figure 5-36: DSC plots of mPLA/APP composites ........................................... 98

Figure 5-37: Pictures of samples after LOI test: (a) PLA5APP, (b) PLA10APP (c)

PLA20APP (d) mPLA5APP (e) mPLA10APP (f) mPLA20APP ......................... 99

Figure 5-38: HRR plots of PLA/VP/APP composites ...................................... 101

Figure 5-39: THR (a), Mass loss (b), TSP (c) and CO/CO2 ratio (d) plots of

Page 151: Development and Investigation of Bio-based Environmentally ...

List of Figures 136

PLA/VP/MMT composites ............................................................................... 102

Figure 5-40: Residue of samples after cone calorimeter test of PLA/APP

composites (top) and mPLA/APP composites (bottom) with 10 wt.-% (left) and

20 wt.-%(right) APP ........................................................................................ 104

Figure 5-41: SEM pictures of residue after cone calorimeter test of PLA20APP

(top) and mPLA20APP (bottom) for surface (left) and inner (right) ................. 104

Figure 5-42: Tensile test plots of PLA/VP/APP composites ............................ 106

Page 152: Development and Investigation of Bio-based Environmentally ...

List of Tables 137

List of Tables

Table 3-1: Comparison of different PLA synthesis techniques ............................ 9

Table 3-2: Comparison of different fibers reinforced PLA composites .............. 12

Table 4-1: Recipe of Vanillin and Vanillin derivative based flame retardant PLA

......................................................................................................................... 28

Table 4-2: Default extrusion parameters .......................................................... 29

Table 4-3: Default spinning parameters ............................................................ 29

Table 4-4: Default injection molding parameters .............................................. 30

Table 4-5: Classification of materials for the UL-94 V tests .............................. 35

Table 5-1: Recipe of pure PLA and its composites ........................................... 38

Table 5-2: Assignment of the main vibrational modes for VA and VP ............... 39

Table 5-3: Data obtained from TGA plots of VA and VP ................................... 43

Table 5-4: Data obtained from TGA plots of PLA and its composites ............... 46

Table 5-5: Calculated values of Ea and r2 of PLA and PLA10VP at different α . 48

Table 5-6: Data obtained from DSC of PLA and PLA/VP composites .............. 50

Table 5-7: LOI, UL94 and MFI results of PLA and PLA composites ................. 53

Table 5-8: Data obtained from CCT of PLA and PLA composites ..................... 54

Table 5-9: Data obtained from tensile test of PLA and PLA composites ........... 61

Table 5-10: Parameters of PLA and PLA/VP composites processed via different

methods ........................................................................................................... 64

Table 5-11: Mechanical parameters of fibers for PLA and PLA/VP composites 65

Table 5-12: Recipe of VPA and VPS based PLA composites ........................... 67

Page 153: Development and Investigation of Bio-based Environmentally ...

List of Tables 138

Table 5-13: Assignment of the main vibrational modes for VPA and VPS ......... 68

Table 5-14: Data obtained from TGA plots of VPA and VPS ............................. 72

Table 5-15: Data obtained from TGA plots of VPA and VPS based PLA

composites ....................................................................................................... 74

Table 5-16: LOI, UL94 and MFI results of PLA composites based on vanillin

derivatives ........................................................................................................ 75

Table 5-17: Data obtained from CCT of PLA and PLA composites ................... 76

Table 5-18: Data obtained from tensile test of PLA and PLA composites ......... 79

Table 5-19: Recipe of PLA/VP/MMT composites .............................................. 81

Table 5-20: Data obtained from TGA plots of PLA and PLA composites ........... 83

Table 5-21: Data obtained from DSC plots of PLA and PLA composites .......... 84

Table 5-22: Results of LOI, UL94 and MFI tests of PLA and PLA composites .. 86

Table 5-23: Data obtained from CCT of PLA/VP/MMT composites................... 87

Table 5-24: Data obtained from tensile tests of PLA/VP/MMT composites ....... 92

Table 5-25: Recipe of PLA/VP/APP composites ............................................... 93

Table 5-26: Data obtained from TGA plots of PLA/VP/APP composites ........... 95

Table 5-27: Data obtained from DSC plots of PLA and PLA composites .......... 97

Table 5-28: Results of LOI and UL-94 tests of PLA/VP/APP composites ......... 99

Table 5-29: Data obtained from CCT plots of PLA/VP/APP composites ......... 100

Table 5-30: Data obtained from tensile tests plots of PLA/VP/APP composites

....................................................................................................................... 105

Page 154: Development and Investigation of Bio-based Environmentally ...

Publications 139

Publications

Journals

Pengcheng Zhao, Zhiqi Liu, Xueyi Wang, Ye-Tang Pan, Ines Kühnert,

Michael Gehde, De-Yi Wang and Andreas Leuteritz. Renewable Vanillin

Based Flame Retardant for Poly(lactic acid): a Way to Enhance Flame

Retardancy and Toughness Simultaneously. RSC Advances, 2018,

Submitted

Pengcheng Zhao, Zhiqi Liu, Michael Gehde, Ines Kuehnert and Andreas

Leuteritz. Effect of phosphorus-containing modified magnesium hydroxide

on the mechanical properties and flammability of PLA/MH composites. AIP

Conference Proceedings, 2017

Pengcheng Zhao, Andreas Leuteritz, Claudia Hinüber, Harald Brünig, Ines

Kühnert. Flame resistant and halogen-free fibers based on

phosphate-modified vanillin and poly (lactic acid), In preparation

Conferences

Poster

Pengcheng Zhao, Zhiqi Liu, Michael Gehde, Ines Kuehnert and Andreas

Leuteritz. Effect of phosphorus-containing modified magnesium hydroxide

on the mechanical properties and flammability of PLA/MH composites.

Europe Africa Conference 2017, Dresden.

Oral presentation

Pengcheng Zhao, Michael Gehde, De-Yi Wang, Ines Kuehnert and Andreas

Leuteritz. Design of vanillin based flame retardants for PLA composites.

Technomer 2017, Chemnitz.