Composites and Foams based on Polylactic Acid (PLA)

142 Pages·2016·5 MB·English

Composites and Foams based on Polylactic Acid
(PLA)

Thèse
Hedieh Teymoorzadeh
Doctorat en génie chimique
Philosophiae doctor (Ph.D.)
Québec, Canada

© Hedieh Teymoorzadeh, 2016

Résumé
Cette étude est destinée à la production et à la caractérisation des composites d'acide

polylactique (PLA) et des fibres naturelles (lin, poudre de bois). Le moussage du PLA et
ses composites ont également été étudiés afin d'évaluer les effets des conditions de
moulage par injection et du renfort sur les propriétés finales de ces matériaux. Dans la
première partie, les composites constitués de PLA et des fibres de lin ont été produits par
extrusion suivit par un moulage en injection. L'effet de la variation du taux de charge (15,
25 et 40% en poids) sur les caractéristiques morphologique, mécanique, thermique et
rhéologique des composites a été évalué. Dans la deuxième étape, la poudre de bois (WF)
a été choisie pour renforcer le PLA. La préparation des composites de PLA et WF a été
effectuée comme dans la première partie et une série complète de caractérisations
morphologique, mécanique, thermique et l'analyse mécanique dynamique ont été
effectués afin d'obtenir une évaluation complète de l'effet du taux de charge (15, 25 et
40% en poids) sur les propriétés du PLA. Finalement, la troisième partie de cette étude
porte sur les composites de PLA et de renfort naturel afin de produire des composites
moussés. Ces mousses ont été réalisées à l'aide d'un agent moussant exothermique
(azodicarbonamide) via le moulage par injection, suite à un mélange du PLA et de fibres
naturelles. Dans ce cas, la charge d'injection (quantité de matière injectée dans le moule:
31, 33, 36, 38 et 43% de la capacité de la presse à injection) et la concentration en poudre
de bois (15, 25 et 40% en poids) ont été variées. La caractérisation des propriétés
mécanique et thermique a été effectuée et les résultats ont démontré que les renforts
naturels étudiés (lin et poudre de bois) permettaient d'améliorer les propriétés mécaniques
des composites, notamment le module de flexion et la résistance au choc du polymère
(PLA). En outre, la formation de la mousse était également efficace pour le PLA vierge et
ses composites car les masses volumiques ont été significativement réduites.
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Abstract
This study reports on the production and characterization of natural fiber reinforced

polylactic acid (PLA) composites. Foaming PLA and its composites was also undertaken
to investigate the effect of injection molding conditions (shot size) and natural fiber (flax
and wood flour) content on the final properties of the final products.
In the first part, PLA was mixed with flax fiber via extrusion and further processed by
injection molding to manufacture the final parts. The effect of flax fiber content (15, 25,
and 40% wt.) on the morphological, mechanical, thermal, and rheological properties of
the composites was evaluated.
In the second step, wood flour (WF) was selected to reinforce PLA. Compounding of
PLA and WF was carried out in a twin-screw extruder followed by injection molding to
obtain the test specimens. A complete series of morphological, mechanical, thermal, and
dynamic mechanical analysis was performed to get a complete evaluation of WF addition
(15, 25, and 40% wt.) on the properties.
Finally, the last step studied PLA composites with natural fibers for the purpose of
foaming. Foaming was carried out using an exothermic foaming agent
(azodicarbonamide) via injection molding. Injection foaming proceeded after mixing
PLA and natural fibers by extrusion. In this case, the shot size (amount of material
injected into the mold: 31, 33, 36, 38, and 43% of the machine capacity) and
reinforcement content (15, 25, and 40% wt.) were varied. The characterization included
mechanical and thermal properties. The results showed that both flax and wood flour led
to increased mechanical properties including flexural modulus and impact strength.
Moreover, foaming was also effective for neat PLA and PLA composites, i.e. the overall
density of the parts was significantly reduced.
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Table of Contents

Résumé
Abstract
.......................................................................................................................................................... iii
Table of Contents
........................................................................................................................................................... v
List of tables
...................................................................................................................................... vii
List of figures
................................................................................................................................................. xi
Abbreviations
............................................................................................................................................ xiii
Acknowledgement
.............................................................................................................................................. xv
Foreword
................................................................................................................................... xix
Chapter 1. Introduction on biopolymers
..................................................................................................................................................... xxi
1.1 Plastics
.............................................................................................. 1
1.2 Renewable-resource-based plastics
...................................................................................................................................................... 1
1.2.1 Polysaccharides
................................................................................................ 3
1.2.1.1 Polysaccharides from vegetal sources
................................................................................................................................. 4
1.2.1.2 Polysaccharides from marine sources
.......................................................................... 4
1.2.2 Proteins
........................................................................... 5
1.2.2.1 Proteins from animal sources
................................................................................................................................................. 6
1.2.2.2 Proteins from vegetal sources
.......................................................................................... 6
1.2.3 Fatty-acid based polymers
.......................................................................................... 7
1.2.4 Biotechnologically-derived polymers
............................................................................................................. 7
1.2.5 Bacterial polymers
........................................................................................ 9
1.2.5.1 Polyhydroxyalkanoates (PHA)
......................................................................................................................... 10
1.2.5.2 Polylactic acid (PLA)
.................................................................................... 11
Chapter 2. Polylactic acid (PLA)
...................................................................................................... 12
2.1 Synthesis of lactic acid
......................................................................................................... 14
2.2 Synthesis of lactide monomers
.................................................................................................................... 14
2.3 Polymerization of lactide monomers
..................................................................................................... 15
2.3.1 Polycondensation
.......................................................................................... 16
2.3.2 Ring-opening
........................................................................................................................... 17
................................................................................................................................... 20
vii
Chapter 3. PLA modification
3.1 Totally biodegradable PLA composites
................................................................................................................ 22
3.2 PLA composite foams
..................................................................................... 22
3.3 Thesis Objectives
...................................................................................................................... 26
Chapter 4. Biocomposites of Flax Fiber and Polylactic Acid: Processing and Properties
............................................................................................................................... 32
Résumé
34
Abstract
......................................................................................................................................................... 34
4.1 Introduction
........................................................................................................................................................ 35
4.2 Materials and methods
......................................................................................................................................... 36
4.2.1 Composite preparation
..................................................................................................................... 39
4.2.2 Mechanical characterization
................................................................................................................. 39
4.2.3 Thermal properties
....................................................................................................... 39
4.2.4 Scanning electron microscopy (SEM)
......................................................................................................................... 40
4.2.5 Density
.................................................................................... 40
4.2.6 Rheology
............................................................................................................................................... 41
4.3 Results and discussion
........................................................................................................................................... 41
4.3.1 Scanning electron microscopy (SEM)
..................................................................................................................... 41
4.3.2 Density
.................................................................................... 41
4.3.3 Mechanical properties
............................................................................................................................................... 43
4.3.4 Thermal Properties
.................................................................................................................. 43
4.3.5 Rheology
........................................................................................................................ 44
4.4 Conclusion
........................................................................................................................................... 45
Acknowledgement
........................................................................................................................................... 51
Chapter 5. Biocomposites of Wood Flour and Polylactic Acid: Processing and Properties
.................................................................................................................................... 52
Résumé
......................................................................................................................................................................... 53
Abstract
......................................................................................................................................................... 53
5.1 Introduction
........................................................................................................................................................ 54
5.2 Materials and methods
......................................................................................................................................... 55
5.2.1 Sample preparation
..................................................................................................................... 56
5.2.2 Mechanical characterization
........................................................................................................................ 57
....................................................................................................... 58
viii
5.2.3 Thermal properties

5.2.4 Dynamic mechanical analysis (DMA)
......................................................................................................................... 58
5.2.5 Scanning electron microscopy (SEM)
.................................................................................... 60
5.2.6 Density
.................................................................................... 60
5.3 Results and discussion
............................................................................................................................................... 62
5.3.1 Scanning electron microscopy (SEM)
..................................................................................................................... 62
5.3.2 Density
.................................................................................... 62
5.3.3 Mechanical properties
............................................................................................................................................... 63
5.3.4 Dynamic mechanical properties
.................................................................................................................. 63
5.3.5 Thermal properties
................................................................................................ 66
5.4 Conclusion
......................................................................................................................... 67
Acknowledgment
........................................................................................................................................... 68
Chapter 6. Morphological, Mechanical, and Thermal Properties of Injection Molded PLA
...................................................................................................................................... 68
Foams/Composites based on Wood Flour
Résumé
........................................................................................ 69
Abstract
......................................................................................................................................................... 69
6.1 Introduction
........................................................................................................................................................ 70
6.2 Materials and methods
......................................................................................................................................... 71
6.2.1 Sample Preparation
..................................................................................................................... 73
6.2.2 Scanning Electron Microscopy (SEM)
........................................................................................................................ 73
6.2.3 Foam Cell Characterization
................................................................................... 76
6.2.4 Mechanical Characterization
........................................................................................................ 76
6.2.5 Thermal Properties
...................................................................................................... 76
6.2.6 Density
........................................................................................................................ 77
6.3 Results and Discussion
............................................................................................................................................... 77
6.3.1 Density
.................................................................................................................... 77
6.3.2 Foam cell morphology
............................................................................................................................................... 77
6.3.3 Cell Diameter
................................................................................................................. 79
6.3.4 Cell-Population Density
.................................................................................................................................. 82
6.3.5 Skin thickness
............................................................................................................... 84
.................................................................................................................................. 85
ix
6.3.6 Mechanical Properties
6.3.6.1 Shot size
.................................................................................................................. 86
6.3.6.2 Wood Flour Reinforcement
............................................................................................................................... 86
6.3.7 Thermal Properties
........................................................................................... 88
6.3.7.1 Shot size
........................................................................................................................ 91
6.3.7.2 Wood Flour
............................................................................................................................... 91
6.4 Conclusion
......................................................................................................................... 92
Acknowledgements
........................................................................................................................................... 93
Chapter 7. Conclusions and recommendations
.................................................................................................................................. 94
7.1 Conclusion
............................................................................... 95
7.2 Recommendations
........................................................................................................................................... 95
References
............................................................................................................................. 97
Appendix (A): Injection molding condition
................................................................................................................................................... 99
A.1 PLA/wood flour and flax fiber composites
.................................................................................. 109
A.2 Neat foamed PLA
........................................................................... 109
A.3 Foamed PLA/wood flour composites
.......................................................................................................................... 110
Appendix (B): Comparison of mechanical properties between commercialized
..................................................................................... 111
composites and PLA based composites reinforced with wood flour and flax fiber
B.1 Introduction
........ 112
B.2 Discussion
...................................................................................................................................... 112
B.3 Reference
........................................................................................................................................ 112
Appendix (C): DSC thermographs of the samples
.......................................................................................................................................... 116
..................................................................... 118

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