Pasteurization-Triggered Heat-Resistant Enhancement of Packaging Films Derived from a Star-Shape Toughened Polylactide Stereocomplex.

A process for enhancing polylactide films' heat resistance, shape stability, and toughness has been developed. A star-shaped poly-(ε-caprolactone--d-lactide) (starPCL--PDLA) copolymer was synthesized by using a four-armed PCL macroinitiator. The material was blended with linear poly-(l-lactide) (-PLLA) to form a specific amount of stereocomplex, which endows the material with improved heat resistance. The effect of blend composition on their thermal and heat-resistant properties, toughness, and dynamic mechanical properties was investigated. The melt viscosity was optimized for a blown-film process by the star-shaped polymer's unique rheology. A pouch form package was fabricated with the blends, whose thermal-resistant performance was assessed by in-package thermal pasteurization. The pouches exhibited no visual deformation at the pasteurization temperatures, especially those containing 20 wt % starPCL--PDLA, while -PLLA could not withstand similar treatment conditions. This specific blend also showed an increased toughness of 4.5 times compared to that of -PLLA due to the appropriate content of the flexible PCL star blocks. The properties of the blends were studied by differential scanning calorimetry and wide angle X-ray scattering to understand the role of the star copolymer. Since the extruded pouch initially contains a low amount of crystallinity, the pasteurization triggered the formation of stereocrystals and homocrystals, leading to property enhancement. The judicious design of a star copolymer able to induce stereocomplexation results in high-performance PLA-based degradable packaging.