| Résumé | This paper aims at developing natural fiber biocomposites based on biopolymers reinforced with wood fibers obtained from a thermo-mechanical refining process. Polylactide (PLA) and polylactide/thermoplastic starch blends (PLA/TPS) were used as matrices. Two grades of PLA, an amorphous and a semi-crystalline one, were considered with the purpose to investigate the effect of wood fibers on the crystallinity, and therefore, on mechanical properties of composites. Two grades of thermoplastic starch (TPS), different in plasticizer content and nature, were used. TPS content in the PLA/TPS blends was 50%. Moreover, two wood fiber types were selected, a hardwood (HW) and a softwood (SW), to state the effect of the fiber type on the biocomposite properties. Finally, the impact of different additives on biocomposite properties was studied with the purpose to enhance the biopolymer/wood fiber affinity with the best impact on the final mechanical performance. The biocomposites containing 30% by weight of wood fibers were obtained by co-rotating twinscrew extrusion. The properties are described in terms of morphology, thermal, rheological, and mechanical properties. With respect to wood type, there was almost no differentiation between reinforce ability of SW and HW for the studied formulations. Similar observations were done regarding the two grades of PLA on the mechanical properties (i.e. tensile strength and elastic modulus) of biocomposites. Concerning the thermal properties, semi-crystalline PLA biocomposites shown an increase in crystallization kinetics and a decrease of the fully crystallinity due to the wood fibers presence. A twofold increase in elastic modulus and an increment in tensile strength of 11% were observed for uncompatibilized PLA/wood fiber composites. Despite good tensile results and an inherent affinity between PLA and wood fibers, further improvement was reached by increasing the adhesion in adding coupling agents and by preserving the PLA molecular weight using a branching agent. The best mechanical results were achieved for composites containing the branching agent, most probably due to the branching of the PLA chains. PLA/wood fiber biocomposites present higher mechanical properties than polypropylene counterpart and are very promising candidates for many applications, especially in construction interior applications |
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