Solid and microcellular polylactide nucleated with PLA stereocomplex and cellulose nanocrystals

Abstract

Blending polylactide (PLA) with poly(d-lactide) (PDLA) and cellulose nanocrystals (CNC)-based stereocomplex (SC) nanohybrids presents practical approach to produce fully biobased blends and nanocomposites with enhanced properties. This paper investigated the nucleation effect of PLA/PDLA and PLA/PDLA-g-MAH/CNC nanohybrids at low loading levels on the non-isothermal crystallization, morphology, as well as thermal and thermo-mechanical properties of PLA-based samples. Neat PLA, blends and nanocomposites were produced by conventional and microcellular injection molding. Nitrogen (N2) in a supercritical state was used as the physical blowing agent for preparation of microcellular samples. CNC-based SC showed superior nucleating efficiency compared to SC nucleating agents. However, low mold temperature resulted in relatively low degree of crystallinity (~ 15%). In addition, decrease in cell size and increase in cell density of microcellular samples have been observed after introduction of both nucleating agents. Slight increase in mechanical properties of nucleated samples compared to neat PLA has been ascribed to the higher degree of crystallinity. Despite these, decrease in all mechanical properties of microcellular samples has been noticed when compared to solid counterparts. Furthermore, dynamic mechanical analysis (DMA) reveals subsequent foaming and dramatic decrease in dimensional stability of microcellular samples above glass transition temperature (Tg). The storage modulus in a glassy region has been improved in both solid blends and nanocomposites. In addition, shift of Tg due to restricted chain mobility of PLA due to retarded relaxation of amorphous regions due to SC interactions has been observed.