Tetsuo Kasai

Diffusion and sorption for carbon dioxide in kapton at extremely low pressure

Pressure-dependent solubility and diffusion coefficients for carbon dioxide in glassy polymers have been well described using the “dual sorption and transport model.” However, the plastisization effect by high-pressure carbon dioxide seems to promote the pressure dependence of the sorption and transport coefficients. To avoid the relaxation process by the plastization which is superimposed on the diffusion process, the diffusion and sorption of carbon dioxide were measured at extremely low pressure (below 1 cmHg). Linear isotherms observed for CO2 sorption into Kapton were interpreted in terms of the dual model equation at extremely low pressure. From the permeation curve of the Kapton/CO2 system, the diffusion and permeation coefficients were obtained according to the usual manner, and both coefficients were independent of pressure. Sorption and transport parameters were obtained from sorption isotherms and average values of the permeation coefficients. The parameters thus obtained were substituted in an approximated dual sorption and transport equations at extremely low pressure and the pressure independence of the diffusion and permeation coefficients were sufficiently reproduced. It is a good technique to experiment at such extremely low pressure when the validity of the dual model is evaluated.