A Study of the Crystallization, Melting, and Foaming Behaviors of Polylactic Acid in Compressed CO2

TLDR

The study examined how compressed CO₂ influences the crystallization and melting of linear polylactic acid. Compressed CO₂ markedly accelerated PLA crystallization, achieving 16.5 % crystallinity in one minute at 100 °C and 6.89 MPa, while foaming during gas release shortened the time to crystallization equilibrium and produced a single DSC melting peak with only modest dependence on treatment conditions.

Abstract

The crystallization and melting behaviors of linear polylactic acid (PLA) treated by compressed CO2 was investigated. The isothermal crystallization test indicated that while PLA exhibited very low crystallization kinetics under atmospheric pressure, CO2 exposure significantly increased PLA’s crystallization rate; a high crystallinity of 16.5% was achieved after CO2 treatment for only 1 min at 100 °C and 6.89 MPa. One melting peak could be found in the DSC curve, and this exhibited a slight dependency on treatment times, temperatures, and pressures. PLA samples tended to foam during the gas release process, and a foaming window as a function of time and temperature was established. Based on the foaming window, crystallinity, and cell morphology, it was found that foaming clearly reduced the needed time for PLA’s crystallization equilibrium.