Ternary Synergistic Toughening of Polylactic Acid Foams by Elastomer, Rolling and Supercritical Fluid Foaming for Enhanced Anisotropy

Abstract

Poly(lactic acid) (PLA) is a widely used biodegradable polymer, but its brittleness severely limits its further applications. In this study, anisotropic poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) foams were prepared by combining melt blending and rolling process as well as supercutical fluid (SCF) foaming. Adding a second phase elastomer of TPU and SCF foaming could significantly improve the toughness of PLA. However, rolling process endowed PLA with anisotropy. The results indicated that the crystallinity and elongation at break of rolled PLA/TPU blend showed a stepwise increase with the rolling temperature and rolling rate increased. Particularly, when the rolling temperature is 75°C and the rolling rate is 50%, the crystallinity of rolled PLA/TPU blends is 210.2% higher than that of pure PLA and the elongation at break increased from 4.0% to 59.0%, respectively. Additionally, SCF foaming further improved the elongation at break of rolled PLA/TPU blend reached 76.8%, increased by1820.0%. What’s more, anisotropic highly oriented and elongated cell structures of PLA/TPU foam were obtained due to the orientation of molecular chain by rolling process before with anisotropic properties, which lays a solid foundation for the large-scale application of PLA/TPU composites.

Keywords: Poly(lactic acid), toughening, rolling process, supercritical fluid foaming, oriented and elongated cell structures