Enhancing the flexibility and thermal properties of polylactic acid/thermoplastic starch blends through selective plasticization

Abstract

This study investigates the impact of polyethylene glycol (PEG) and dioctyl terephthalate (DOTP) as plasticizers on the mechanical, microstructural, thermal, and crystalline properties of polylactic acid/thermoplastic starch (PLA/TPS) blends. While plasticization reduced tensile and Izod impact strengths by 60 %, it significantly improved ductility and impact strength by 268 % when using DOTP and lower molecular weight PEG (LWPEG), due to their lubrication capabilities and decreased frictional forces between polymer chains. This facilitated easier disentanglement before the chains ruptured under the load. Morphological analysis revealed a well-dispersed droplet-matrix structure with smaller droplet sizes (22.41 ± 4.9 μm for DOTP and 20.98 ± 4.7 μm for LWPEG) compared to pure PLA/TPS (49.97 ± 14.3 μm). Differential scanning calorimetry (DSC) showed reduced glass transition, crystalline, and melting temperatures, with plasticizers migrating to the TPS phase, enhancing crystallinity. DOTP, in particular, promoted β-type crystal formation, improving Young's modulus, ductility, and impact strength. Overall, DOTP demonstrated superior plasticization effects, yielding the best droplet-matrix morphology and highest crystallinity, making it the most effective plasticizer for enhancing PLA/TPS properties.