Equilibrium sorption amount

desorption diffusion coefficients and sorption diffusion coefficients of CO

2

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 CO

2

in PLLA increased with lowering temperature and elevating pressure at the temperature range from 40 to 60 ℃ and pressure from 10

4

to 2×10

4

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 CO

2

processing. It was concluded that PLLA polymer could be well swollen and plasticized by supercritical CO

2

.