Properties and application of PLA/mung bean starch composites: Effect of the soft segment molecular weight of PCL-based polyurethane prepolymer

The escalating crisis of global plastic pollution has intensified the demand for eco-friendly and biodegradable materials. Polylactic acid (PLA) stands as a prominent candidate in this regard, valued for its biodegradability and biocompatibility. However, incorporating fillers to reduce cost and modify properties often introduces challenges in interfacial compatibility. In this study, a polycaprolactone-based polyurethane prepolymer (PCLPU) was synthesized as a compatibilizer to improve the poor interfacial adhesion between PLA and mung bean starch (MBS). PLA/MBS/PCLPU composites were prepared by melt extrusion, and the influence of the soft segment molecular weight of PCLPU on the structure and properties of the composites was systematically investigated. Results indicate that PCLPU enhances the toughness of the composites through a combination of chemical bonding and physical cross-linking. Although PCLPUs with different soft segment molecular weights all contributed to toughening, a lower molecular weight promoted more complete chemical cross-linking, resulting in more pronounced improvements in mechanical performance. In particular, the composite compatibilized with the lowest-molecular-weight prepolymer (PLAPSPU-500) exhibited the most significant enhancement, with a 27.14% increase in tensile strength, 162.67% in elongation at break, 175.00% in impact strength, and 31.62% in flexural strength, compared to PLA/MBS composites without compatibilizer. This work provides a viable strategy for developing high-performance PLA-based biodegradable composites, thereby facilitating the broader adoption of sustainable materials.