Effects of different preparation methods (solvent casting and melt blending) on properties of chitosan-filled polylactic acid biocomposite films

Biocomposite films based on chitosan (CS) and polylactic acid (PLA) were prepared using two different methods; (1) solvent casting and (2) melt blending followed by hot-press methods. Polyethylene glycol (PEG) and polyvinyl alcohol (PVOH) were respectively incorporated as compatibilizer and processing aid. Thermal stability of solvent casted and hot-press composites were comparable and slightly lower than PLA, whereas the presence of PEG and PVOH lowered the thermal stability of the composites in N2 and in air. The secant modulus and ultimate stress of the hot-press films were clearly higher (about 80%-90%) whereas elongation was much lower than those of the solvent-casted films. XRD results revealed that the solvent-casted films exhibited semi-crystalline characteristics whereas the amorphous property was mostly observed for the hot-press films. The sharper XRD peaks of the casted and hot-press samples clearly observed with chitosan loading. Coarse surface after fracture was observed for the casted composite films whereas relatively smooth surface with a number of dispersed chitosan droplets was seen for the hot-press films. The presence of PEG and PVOH improved the dispersion of chitosan and slightly increased the water adsorption of the composites. The higher water adsorption capacity was observed for the casted composite films. The obtained results indicated that solvent casting and melt blending methods significantly affected the final properties of the material products, especially tensile and crystallinity characteristics of the chitosan-filled PLA biocomposite films.