Dynamic transesterification network toughening polylactic acid based on epoxidized soybean oil

To improve the toughness of PLA without loss of biodegradability. In this study, a reversible ester exchange network (VEC) based on bio-based materials—epoxidized soybean oil (ESO) and anhydrous citric acid (CA)—was generated in situ during the extrusion molding process of poly(lactic acid) (PLA) via a simple and efficient preparation method. Focusing on the toughening performance of VEC on PLA, it was found that the R-value of VEC (the equivalent ratio of CA carboxyl groups to ESO epoxy groups), catalytic system, polymerization time, and VEC content were the key parameters influencing the mechanical enhancement. The results demonstrated that VEC acted not only as a nucleating agent to promote PLA crystallization but also as a plasticizer facilitating molecular chain mobility. Rheological analysis showed that VEC enhanced the melt strength of PLA and intensified shear thinning behavior, thereby enriching the structural complexity and broadening the processing versatility of PLA-based products. More importantly, PLA and VEC chemically interacted to improve phase compatibility. Notably, the addition of only 5 wt% VEC resulted in the formation of a complete internal toughening network, yielding elongation at break and impact strength values that were 49.1 times and 2.27 times greater, respectively, than those of neat PLA. PLA/VEC waste products can be effectively recycled via re-extrusion. During the recycling and remodeling process, a relatively complete dynamic VEC network is re-established within the composite, with the elongation at break reaching 38.4 times that of neat PLA, indicating significant application potential. PLA/VEC can undergo complete degradation under alkaline conditions within 30 days.