Research on Toughening Polylactic Acid by an Epoxy Soybean Oil Curing Network Based on Dynamic Cross-Linking

In this study, our primary focus was the efficient synthesis of epoxidized soybean oil and anhydrous citric acid within a polylactic acid (PLA) matrix through a ring-opening reaction catalyzed by zinc acetate. Our objective was to establish a dynamic and reversible ester exchange network. Subsequently, we introduced the cured epoxidized soybean oil network into the PLA matrix through dynamic cross-linking, aiming to enhance the compatibility of epoxidized soybean oil within the PLA matrix. This process resulted in the preparation of a series of PLA composites characterized by improved toughness. We conducted a comprehensive analysis of the influence of various carboxyl/epoxy equivalent ratios (R values) on the mechanical properties, thermal characteristics, and chemical structures of the PLA composites. Our findings demonstrated that, during the dynamic cross-linking process, both epoxidized soybean oil and citric acid underwent ring-opening reactions and chain reactions with the PLA matrix, culminating in the formation of a well-defined network cross-linking structure. These chain reactions within the system significantly enhanced the internal compatibility of the blends. Our experimental results conclusively indicated that optimal toughness was achieved when the R value was set to 0.1, with the addition of 5 parts per hundred resin (phr). This configuration resulted in an elongation at break of 315% and an impact strength of 28.5 kJ/m(2).