Fully Biodegradable Long-Chain Branched Polylactic Acid with High Crystallization Performance and Heat Resistance

A biobased modifier, epoxidized cardanol, was used as a multifunctional coagent to develop long-chain branched polylactic acid (LCB-PLA) together with peroxide by a one-step reaction. The molecular structure of LCB-PLA was evaluated from weight-average molecular weight, intrinsic viscosity, and shear rheology. The results showed that the branching degree of LCB-PLA was enhanced with the increased addition amount of epoxidized cardanol due to the unique structure consisting of an epoxy group and a long carbon chain with multiple unsaturated bonds. The generated LCB-PLA exhibited improved crystallization performance and significant heat resistance. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) analyses showed that the long-chain branched structure could play the role of a nucleation site, resulting in the improved crystallization performance of PLA. Especially, for 0.3 wt % peroxide-modified PLA with 0.8 wt % epoxidized cardanol (PLA/0.3T/0.8E), the crystallinity of LCB-PLA reached approximately 44%, increasing the Vicat softening temperature (VST) and heat deflection temperature (HDT) to 156.2 and 82.5 degrees C, respectively, after a simple annealing treatment. Moreover, the annealed LCB-PLA exhibited better hydrolysis resistance than linear PLA in the early degradation stage, while it degraded rapidly in the later stage. In short, this work provided a green route to obtain LCB-PLA, which exhibited excellent crystallization properties and heat resistance.

Automated summary

In this study, a biobased modifier called epoxidized cardanol was used to develop long-chain branched polylactic acid (LCB-PLA) with peroxide. The LCB-PLA exhibited improved crystallization performance and heat resistance, making it a green and promising material.