Improving the performance of polylactic acid/polypropylene/cotton stalk fiber composites with epoxidized soybean oil as a high efficiency plasticizer.

Polylactic acid (PLA) can serve as a biodegradable alternative to traditional petroleum-based plastics, but its poor impact resistance and high production costs limit its applications. In this study, different contents of epoxidized epoxy soybean oil (ESO) were added as plasticizer to melt blend with polylactic acid (PLA), polypropylene (PP) and cotton stalk fiber (CSF), examining its impact on the mechanical properties, thermal stability, microstructure, and crystallization behavior of the blends. The results indicated that ESO reacted with PLA and CSF to form branched polymers and microgels. With increasing ESO content, the blends exhibited increased initial thermal decomposition temperature, impact strength, and elongation at break, while stiffness, maximum decomposition rate, and crystallinity decreased. When the mass ratio of CSF to ESO was 2:1, the notch impact strength and elongation at break of PLA/PP/CSF/ESO blends were 1.63 times and 1.98 times higher than those of PLA/PP/CSF blends, respectively. Moreover, a reduction in surface grooves of CSF and formation of a gel layer were observed. Importantly, this study opens an effective new pathway for the utilization of waste natural fibers and the widespread application of biodegradable composite materials, contributing to environmental protection, resource conservation, and cost reduction.