JEC COMPOSITES MAGAZINE - Issue #52 - October 2009 - 39

Biocomposites tensile stiffness of the matrix was hardly affected by seawater at temperatures up to 40°C but the composite lost stiffness and strength. Fibre/matrix interface weakening was the main damage mechanism induced by wet ageing, but both matrix and fibre cracks also appeared over longer periods. More information: www.jeccomposites.com Contact: antoine.le-duigou@univ-ubs.fr Acknowledgments Antoine Le Duigou and his supervisors wish to thank the Brittany region for its financial support under the NAVECOMAT Project on developing biocomposites for marine composites. Plasmor, Finot, French marine research institute Ifremer, the University of South Brittany, and Catherine Chabaud are all involved in this project. Fig.3: Force vs. crosshead displacement – typical curve References [1] Baley C., Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase. Composite Part A: Applied Science and Manufacturing, 2002. 33(7): p. 939-948. [2] Bodros E., Pillin I., Montrelay N., and Baley C., Could biopolymers reinforced by randomly scattered flax fibre be used in structural applications? Composites Science and Technology, 2007. 67(3-4): p. 462-470. [3] Le Duigou A., Pillin I., Bourmaud A., Davies P and Baley C., Effect of recycling ., on mechanical behaviour of biocompostable flax/poly(l-lactide) composites. Comp. Part A, 2008. 39(9): p. 1471-1478. [4] Le Duigou A., Davies P and Baley C, Interfacial properties of flax/poly(L-lactide) ., biocomposite. Proceeding of the 16th Journée Nationale des Composites-Toulouse, 2009. [5] Le Duigou A., Davies P and Baley C., Study of interfacial bonding of flax/Poly(L., Lactide). in 17th International Conference on Composite Materials. 2009. Edinburgh [6] Herrera-Franco P and Drzal L., Comparison of methods for the measurement of . fibre/matrix adhesion in composites. Composites, 1992. 23(1). [7] Baley C., Grohens Y., Busnel F and Davies P Application of interlaminar test to ., ., marine composites. Relation between glass fibre/polymer interfaces and interlaminar properties of marine composites. Applied Composite Materials, 2004. 11: p. 77-98. [8] Zinck P Wagner H.D., Salmon L., and Gerard J.F Are microcomposites realistic ., ., models of the fibre/matrix interface? I. Micromechanical modelling. Polymer, 2001. 42(12): p. 5401-5413. [9] Baley C., Davies P Grohens Y., and Dolto G., Application of Interlaminar Tests to ., Marine Composites. A Literature Review. Applied composite materials, 2004. 11(2): p. 99-126. [10] Zhandarov S. and Pisanova E., The local bond strength and its determination by fragmentation and pull-out tests. Composites Science and Technology, 1997. 57(8): p. 957-964. [11] Nairn J., On the use of shear-lag methods for analysis of stress transfer in unidirectional composites. Mechanics of Materials, 1997. 26(2): p. 63-80. [12] Parlevliet P Bersee H., and Beukers A., Residual stresses in thermoplastic ., composites – A study of the literature– Part I: Formation of residual stresses. Composite Part A: Applied Science and Manufacturing, 2006. 37(11): p. 1847-1857. [13] Bourmaud A., Riviere J., Le Duigou A., Raj G., and Baley C., Investigations of the use of a mussel-inspired compatibilizer to improve the matrix-fiber adhesion of a biocomposite. Polymer Testing, 2009(1-5). [14] Le Duigou A., Davies P., and Baley C., Seawater ageing of Flax/PLLA biocomposites. Polymer Degradation and Stability, 2009. 94(1151-62). energy release [11] were used to evaluate interfacial bonding. PLLA being a thermoplastic polymer, different cooling rates were applied together with annealing for 72 hours at 50°C to understand the effects of thermal stress and polymer morphology on interfacial properties. Table 1: Summary of micromechanical results Material τapp (MPa) τult (MPa) 65.0 ± 23 80.5 ± 25.5 95.7 ± 19 40.6 ± 13.1 70.9 ± 14.7 Gic (J/m ) ² Flax/PLLA (air cooling) 15.3 ± 3.3 Flax/PLLA (cooling 10°C/min) Flax/PLLA (cooling 1°C/min) Flax/PLLA (annealing) Glass/polyester 18.2 ± 1.8 22.2 ± 3.4 9.9 ± 1.5 14.2 ± 0.4 28.5 ± 17 32.6 ± 14 41.4 ± 16.8 12.9 ± 1.6 41.1 ± 6.5 The interfacial properties of flax/PLLA bonding are in the same range as those measured for glass/polyester (Table 1). The results show that interfacial properties (τapp, τult, Gic) are altered by cooling. Slow cooling kinetics improves interfacial shear strength (IFFS) due to a higher crystallinity rate and the formation of a transcrystalline area around the fibre. This increases thermal residual stress [12], inducing low-intensity interactions (Van Der Waals, etc.) between the droplet and the fibre. A faster cooling rate reduces IFSS due to lower crystallinity and the absence of a transcrystalline region. The interfacial properties of flax/PLLA bonding can reach interesting values when monitored by cooling kinetics. However, only lowenergy interactions can be created. For this reason, complementary work was carried out to study the use of a low-environmentalimpact biocompatibilizer to create a chemical bond between natural fibres and PLLA [13]. The first results highlighted the positive effect of dopamine treatment on the mechanical properties of hemp/PLLA biocomposites. The issue of flax/PLLA biocomposite durability in a seawater environment was also raised [14]. The purpose was to overcome the paradox between biocompostable and durable material. Samples of pure PLLA, injection-moulded and film-stacked flax composites using the same PLLA matrix were examined at different temperatures (20, 40 and 60°C) for three months. The No52 October 2009 / jec composites magazine
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JEC COMPOSITES MAGAZINE - Issue #52 - October 2009

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