Research on Toughening Polylactic Acid by an Epoxy Soybean Oil Curing Network Based on Dynamic Cross-Linking
Feng Zhao, Ruilong Xu, Xu Zhang, Jiawang Zheng, Wei Liu, Shuai Zhao, Lin Li
Abstract
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 .