Sorption and diffusion of supercritical carbon dioxide in poiy(vinyl fluoride)

Abstract

Sorption and diffusion of supercritical carbon dioxide (SCCO2) in poly (vinyl fluoride) (PVF) at 40CC and 20 MPa are shown in this study. The saturated sorption in the PVF specimen with 3.8 t m thickness has been observed at 40¢XC and 20MPa for 3 h. A gravimetric method was used to measure the mass gain of CO2 in the PVF specimen under ambient conditions. The sorption amount (Ms) of CO2 in the PVF specimen was 5.66 wt%. Ficks diffusion model has been applied to calculate the desorption diffusivity (Ddof CO2 in the PVF specimen. The diffusivily of CO2 in PVF specimen was 7.7x1013m2/s for short time period and l.1x1013 m2/s for long time period. The interaction between CO2 and the PVF specimen has also been investigated by the FTIR spectrum. According to the spectra of the different time periods at the bending mode (£h2) of CO2 near 660 cm -1 the desorption of CO2 in the PVF specimen completely finished about I h venting from high-pressure cell. The wide split of IR bands at the antisymmetric stretching mode (£h3) of CO2 near 2340 cm -1in the PVF specimen indicated that there were bonding forces between CO2 and C-F group of PVF specimen. The peak at 2340 cm -1 vanished after 2 to 4 h venting from high-pressure cell. Comparing with the untreated PVF specimen, the stretching mode of C-F group near 828 cm-1 of the treated PVF specimen has a shift of 1.5 cm-1. It showed that there was weak dipole-dipole interaction between C-F group and CO2. Furthermore, the glass transition temperature (Tg) was measured by LT-DSC. The Tg of the treated PVF specimen has a shift of about 5.3C to a lower temperature, and this result indicated that plasticization phenomenon has occurred in the treated PVF specimen. Copyright ? 2007 Materials Research Society.