Effects of wood flour and chitosan on mechanical, chemical, and thermal properties of polylactide

Composites of polylactide (PLA, 100-60 wt%) and wood flour (0-40 wt%) were prepared to assess the effects of wood filler content on the mechanical, chemical, thermal, and morphological properties of the composites. The polysaccharide chitosan (0-10 wt%) was added as a potential coupling agent for the PLA-wood flour composites. Addition of wood flour significantly increased the flexural modulus and the storage modulus of PLA-wood flour composite, but neither the wood flour nor chitosan had an effect on the glass transition temperature (T,). Fourier transform infrared spectra did not show any evidence of covalent bonding, but chitosan at the interface between wood and PLA is thought to have formed hydrogen bonds to PLA-carbonyl groups. SEM images of fracture surfaces showed that fiber breakage was far more common than fiber pullout in the composites. No evidence of discrete chitosan domains was seen in SEM micrographs. When added at up to 10 wt% (based on wood flour mass), chitosan showed no significant effect on the mechanical, chemical, or thermal properties of the composites, with property changes depending on wood flour content only.