Study on the Synergistic Effect of Hydrazine Nucleating Agents and Stereocomplex Crystals on Improving the Crystallization Behavior and Heat Resistance of Polylactic Acid

The poor heat resistance of polylactic acid (PLA) limits its use in heat-resistant packaging and tableware. To circumvent this issue, stereocomplex crystals (SCs) of PLA have shown great potential owing to their high melting point of above 220 degrees C. However, the slow rate of formation and limited proportion of SCs in PLA materials severely limits the improvement in heat resistance. In industry, where a fast production is often required to reduce costs, it is difficult to prepare PLA materials with a high proportion of SCs. In this study, the effects of the introduction of decanedioic acid, 1,10-bis(2-benzoylhydrazide) (TMC) and the poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) content on the proportion and crystallization rate of SCs were explored. Among the prepared TMC/PDLA/PLLA composites, the sample with a TMC/PDLA/PLLA composition of 0.5%/30%/70% exhibited the highest SCs crystallinity (38%) and the highest Vicat softening temperature (96 degrees C). Moreover, the semi-crystallization time was reduced from 8.3 for PLLA to 2.3 min, resulting in a 64.3% reduction in complete crystallization time. The heat resistance and deformation resistance of the mixed samples in water were also improved, which allowed the samples to be continuously heated for 1 h in water at 97 degrees C while maintaining good deformation resistance.