Polylactide (PLA)-based composite materials reinforced with ball-milled celluloses were manufactured by extrusion blending followed by injection molding. Their surface morphology from impact fracture were imaged with scanning electron microscopy (SEM) and investigated by calculating their fractal dimensions. Then, linear regression was used to explore the relationship between fractal dimension and impact strength of the resultant cellulose/PLA composite materials. The results show that filling the ball-milled celluloses into PLA can improve the impact toughness of PLA by a minimum of 38%. It was demonstrated that the fracture pattern of the cellulose/PLA composite materials is different from that of pristine PLA. For the resultant composite materials, the fractal dimension of the impact fractured surfaces increased with increasing filling content and decreasing particle size of the ball-milled cellulose particles. There were highly positive correlations between fractal dimension of the fractured surfaces and impact strength of the cellulose/PLA composites. However, the linearity between fractal dimension and impact strength were different for the different methods, due to their different R-squared values. The approach presented in this work will help to understand the structure–property relationships of composite materials from a new perspective.

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Polylactide (PLA)-based wood-plastic composites (WPCs) were successfully manufactured by extrusion blending followed by injection molding. The effects of polyhydroxyanoates (PHAs) on the mechanical and thermal properties and the morphologies of the PLA-based WPCs were investigated with mechanical testing, thermal analysis, and scanning electronic microscopy (SEM). The inclusion of PHAs in the PLA-based WPCs produced an increase in the impact resistance and a decrease in the tensile strength. The brittle-ductile transition of the impact strength for the PLA-based WPCs toughened with PHAs was confirmed when the wood flour content was between 15 and 35 wt %. SEM images showed that the fracture surfaces of the PLA-based WPCs toughened with PHAs were rougher than that of their nontoughened counterparts. The ternary PLA-based WPCs exhibited ductile fracture during mechanical testing. Differential scanning calorimetry (DSC) showed that addition of PHAs into the composites caused deviations of the cold crystallization temperature and melting temperature of PLA. Thermogravimetric analysis indicated that the PHAs reduced the thermal stability of the PLA-based WPCs. PHAs can be a green toughening agent for PLA-based WPCs. The specific properties evidenced by the biocomposites may hint at their potential application, for example, in the automotive industry and civil engineering.

Wood plastic composites (WPCs) composed of polylactide (PLA), pine wood flour (WF), and SBS were successfully manufactured through extrusion blending followed by injection molding. The impact strength and elongation at the break of the PLA-based WPCs toughened with SBS were higher than their non-toughened counterparts, in contrast to the decrease in the tensile strength.There was a percolation process in brittle-ductile transition of the impact strength for the SBS-toughened WPCs when the WF content was between 15 and 35 wt%. TGA indicated that SBS had no significant effect on the thermal stability of the resulting hybrid composites.

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