A facile strategy for preparation of strong tough poly(lactic acid) foam with a unique microfibrillated bimodal micro/nano cellular structure

Abstract

This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO₂ foaming. PIF processing widened the foaming window of PLA to 40-120 °C, while supercritical CO₂ foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (T_s). Both micron and nano cells showed decreasing cells size and increasing cell density as T_s elevated. The orientation factor as well as internal stress of PLA foams decreased with increased T_s. Compared with P-PLA samples, PLA foam prepared at T_s of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of CO bond from 1763 to 1766 cm^-1). Furthermore, PLA foam prepared at T_s of 40 °C presented excellent impact strength (32.3 kJ/m²), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO₂ foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications.

Keywords: Internal stress; Poly (lactic acid); Pressure-induced-flow processing; Supercritical CO(2) foaming; Toughness.