Influence of Interfacial Enantiomeric Grafting on Melt Rheology and Crystallization of Polylactide/Cellulose Nanocrystals Composites

Incorporating the surface-grafted cellulose nanocrystals (CNCs) with enantiomeric polylactide (PLLA or PDLA) is an effective and sustainable way to modify PLLA, but their difference in promoting matrix crystallization is still unrevealed. In this paper, the CNCs with identical content and length of PLLA and PDLA (CNC-g-L and CNC-g-D) were prepared and blended with PLLA. The rheological properties of PLLA/CNC-g-D are greatly improved, indicating that the stereocomplexation can significantly improve the interfacial strength as compared with the conventional van der Waals force in PLLA/CNC-g-L. Surprisingly, the matrix crystallizes at a higher rate in PLLA/CNC-g-L than PLLA/CNC-g-D. PLLA/CNC-g-L15 reaches its half crystallinity in 8.26 min while a longer period of 13.41 min is required for PLLA/CNC-g-D15. POM observation reveals that the superior crystallization behavior in PLLA/CNC-g-L is originated from its higher nucleation efficiency and faster growth rate. The formation of low content of sc-PLA at the interface can restrict the diffusion of PLLA but contribute less to generate crystalline nuclei, which synergistically leads to the retarded crystallization kinetics in PLLA/CNC-g-D. Revealing the mechanism of different interfacial enantiomeric grafting on the melt rheology and crystallization of PLLA is of great significance for the development of high-performance polylactide materials.