A response surface study on microstructure and mechanical properties of poly(lactic acid)/thermoplastic starch/nanoclay nanocomposites

Poly(lactic acid) was modified with thermoplastic starch and nanoclay in order to reduce its brittleness and enhance its mechanical properties, respectively. First, two mixing protocols were used to compound poly(lactic acid), 36 wt% sorbitol-plasticized starch, and nanoclay as screening runs. Afterwards, nine experimentally designed – using response surface method – samples were produced via the best protocol with different thermoplastic starch and nanoclay contents. Blend morphology and mechanical properties of poly(lactic acid), poly(lactic acid)/thermoplastic starch samples, and poly(lactic acid)/ thermoplastic starch/nanoclay nanocomposites were investigated via X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy, as well as tensile and impact testings. Incorporation of sorbitol as plasticizer resulted in well-dispersed thermoplastic starch in poly(lactic acid) matrix even in the absence of any compatabilizer, as witnessed by field emission scanning electron microscopy, and consequently increased the melt strength of the nanocomposites. X-ray diffraction patterns and transmission electron microscopy micrographs showed intercalated microstructure for the prepared nanocomposites. In the end, response surface methodology was applied to study the mechanical behavior of the nanocomposites in terms of thermoplastic starch and nanoclay contents.