Lightweight, Strong and High Heat-Resistant Poly(lactide acid) Foams via Microcellular Injection Molding with Self-Assembly Nucleating Agent

Abstract

Poly(lactide acid) (PLA) foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams, such as polystyrene (PS) foams. Nevertheless, PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength. In this study, a high-performance PLA foam with well-defined cell morphology, exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding (MIM) process. Differential scanning calorimetry (DSC) results revealed that the added hydrazine-based nucleating agent (HNA) significantly increased the crystallization temperature and accelerated the crystallization process of PLA. Remarkably, the addition of a 1.5 wt% of HNA led to a significant reduction in PLA’s cell size, from 43.5 µm to 2.87 µm, and a remarkable increase in cell density, from 1.08×10⁷ cells/cm³ to 2.15×10¹⁰ cells/cm³. This enhancement resulted in a final crystallinity of approximately 55.7% for the PLA blend foam, a marked improvement compared to the pure PLA foam. Furthermore, at 1.5 wt% HNA concentration, the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improvements of 136% and 463%, respectively. Additionally, the Vicat softening temperature of PLA blend foam increased significantly to 134.8 °C, whereas the pure PLA foam exhibited only about 59.7 °C. These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance, which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications.