Exclusive formation of poly(lactide) stereocomplexes with enhanced melt stability via regenerated cellulose assisted Pickering emulsion approach

Abstract

Stereocomplexation of enantiomeric poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) endows the Polylactide (PLA) with outstanding heat resistance and durability. However, PLA with exclusive stereo-complexation (sc-PLA) is difficult to achieve. Both stereo-complexation PLA and homo-crystallization PLA (hc-PLA) often formed together when PLLA and PDLA blended. In this research, a new strategy was proposed to prepare the PLA with exclusive stereo-complexation (without homo-crystallization) by Pickering emulsion approach, where regenerated cellulose (RC) was used to stabilize the PLLA/PDLA blends and form RC/sc-PLA microsphere. The DSC result shows that the PLA composites prepared in this method presents single melt peak around 220 °C, which is the characteristics of sc-PLA. Most important, this 0.5%RC/sc-PLA possesses excellent melt stability. It does not divide into stereo-complexation and homo-crystallization during the 3 heating cycles. The results indicate that Pickering emulsion approach firstly provide the limited space to limit the diffusion of macromolecular chains and fully combine PLLA and PDLA chains and form complete RC/sc-PLA microspheres. Then the microspheres were hot pressed into films and homogeneous distribution of RC as heterogeneous nucleation agent provides nucleation sites. The intermolecular hydrogen bonding between RC and PLA improves crystallization property and stabilizes the stereo-complexation. This study provides a strategy to prepare the PLA materials with exclusive stereo-complexed crystal and excellent melt stability, which determines the heat resistance and repeated processing.