The effect of size and delignification on the mechanical properties of polylactic acid (PLA) biocomposites reinforced with wood fibres via extrusion

Abstract

Natural fibres are promising candidates for polymer reinforcement due to their specific properties and renewability. To investigate the influence of wood fibre (WF) alkaline treatment on the mechanical properties of wood-plastic composites (WPCs), alkalised and raw WF-reinforced polylactic acid composites (40/60 wt%) were compounded using two different lengths of WF (100 and 400 μm) in the presence of maleic anhydride as the coupling agent. The structural analysis confirmed the removal of lignin and hemicellulose components from the fibres. The reinforcement increased the tensile and flexural moduli up to 140% and 137%, respectively, in the presence of a coupling agent. For raw fibre-reinforced composites, the tensile and flexural strengths increased by 12% and 12%, respectively. In contrast, alkalised fibres showed inferior performance, suggesting that the removal of hemicellulose and lignin added to the shear forces during extrusion led to their mechanical loss. Although all composites showed a decreased impact strength, the short fibre composites increased their properties by adding maleic anhydride. It can be clearly shown that short fibre-reinforced PLA performed mechanically better than the long counterparts and that the alkaline treatment did not produce better outcomes than the pristine raw fibres.