Sorption and Diffusion Behavior of Carbon Dioxide into Poly(l-lactic acid) Films at Elevated Pressures

Equilibrium sorption amount, desorption diffusion coefficients and sorption diffusion coefficients of CO2 in poly(l-lactic acid) (PLLA) films at elevated pressures were determined by the gravimetric method, in which the Fick's diffusion model was applied to analyze both the desorption and sorption processes. The equilibrium sorption amount of CO2 in PLLA increased with lowering temperature and elevating pressure at the temperature range from 40 to 60 °C and pressure from 104 to 2×104 kPa. Desorption diffusion coefficients were greatly influenced by the equilibrium sorption amount, and they were in the same order of magnitude as the sorption diffusion coefficients. The scan electron microscope (SEM) photos demonstrated that there was no foaming phenomenon of the PLLA film during desorption and sorption processes. The XRD spectra implied that the crystalline degree of PLLA film decreased after CO2 processing. It was concluded that PLLA polymer could be well swollen and plasticized by supercritical CO2.