Foam Injection Molded Stereocomplex PLA : Processing, Thermal Behavior and Foam Structure

Abstract

In this study, the processing of stereocomplex poly(lactic acid) (sc‐PLA) via continuous compounding followed by thermoplastic foam injection molding (FIM) is investigated. Various nucleating agents are compounded with a mixture of poly(L‐lactide) (PLLA) and poly(D‐lactide) (PDLA). The crystalline material structures are greatly influenced by the cooling conditions of the extruded strand. In particular, a controlled two‐stage cooling strategy, consisting of initial air cooling followed by water‐bath cooling, effectively suppresses cold crystallization and promotes a predominantly stereocomplex crystallization behavior of the granulates. PLLA and PDLA are compounded with the aluminum complex NA‐21 and talc as nucleating agents and processed into foamed specimens using FIM with nitrogen as a physical blowing agent. X‐ray diffraction confirms a primarily stereocomplex crystalline structure in the foamed specimens, and scanning electron microscopy reveals a closed‐cell foam morphology within the PLA matrix. The present study thus demonstrates the feasibility of stereocomplex crystallite formation in thermoplastic foam injection molding, establishing a processing route for sc‐dominated PLA foam parts that combines the density reduction of foaming with the elevated melting range of the stereocomplex crystalline structure.