Poly (lactic acid) (PLA) has high potential to replace conventional petroleum-based plastics in a wide range of applications. However, the high brittles, thermal degradation, low melt strength and low viscosities of PLA pose challenges for its processing and performance satisfied for industrial use. Previously, we have shown that natural rubber (NR) incorporated into PLA improved the melt strength and viscosity and thus the processability of biopolyesters. Chain extension is a practical and cost-effective method of improving PLA processability by enhancing the molecular weight and re-bonding degraded chains. We hypothesized that addition of epoxy-based chain extenders will work synergistically with natural rubber to improve the elongational viscosity and strain hardening of PLA. The thermal transition, thermal degradation, mechanical and moisture barrier properties were studied to provide a comprehensive view of the chain-extended and NR-modified PLA. The results shows that chain extender with higher functionality (Joncryl 4368) had a more significant effect on chain extending, branching and restoring of PLA. Although the chain extender or the NR alone reduced both the dynamic and steady shear viscosities and minimally affected the elongational viscosity of PLA, they together resulted in shear-thickening and strain-hardening of PLA, suggesting a synergistic effect of the chain extender and NR on improving PLA rheological performance. The improved elongational viscosity of PLA was comparable to film grade low density polyethylene (LDPE). Additionally, NR addition significantly reduced the water vapor permeability of PLA. The PLA with improved melt viscosity and moisture barrier are promising for film and flexible packaging applications.

聚乳酸 (PLA) 具有在广泛应用中替代传统石油基塑料的巨大潜力。然而，聚乳酸的高脆性、热降解、低熔体强度和低粘度对其满足工业用途的加工和性能提出了挑战。以前，我们已经表明，将天然橡胶 (NR) 掺入 PLA 可以提高熔体强度和粘度，从而提高生物聚酯的加工性能。扩链是一种实用且经济的方法，可通过提高分子量和重新键合降解的链来提高 PLA 的加工性能。我们假设添加环氧基扩链剂将与天然橡胶协同作用，以提高 PLA 的拉伸粘度和应变硬化。热转变、热降解、研究了机械和防潮性能，以全面了解链延长和 NR 改性的 PLA。结果表明，具有更高官能度的扩链剂（Joncryl 4368）对PLA的扩链、支化和恢复有更显着的影响。尽管扩链剂或 NR 单独降低了动态和稳态剪切粘度并且对 PLA 的拉伸粘度影响最小，但它们一起导致了 PLA 的剪切增稠和应变硬化，表明扩链剂和 NR 对 PLA 具有协同作用提高 PLA 的流变性能。PLA 的改进拉伸粘度与薄膜级低密度聚乙烯 (LDPE) 相当。此外，添加 NR 显着降低了 PLA 的水蒸气渗透性。