Permeation, solution, and diffusion of water in some high polymers

Abstract

The equilibrium sorption isotherms of water in polyethylene terephthalate, ethyl cellulose, and rubber hydrochloride have been measured at 25°C. by means of the quartz helix technique. The permeability constants and the diffusion constants have been measured on the same polymers and on polyethylene and polypropylene by the time‐lag technique of Barrer but with a modified apparatus. The solubility coefficients from the sorption measurements (values for polyethylene and polypropylene have been previously reported) are compared with those obtained as the quotient of the permeability and diffusion constants. In the case of polyethylene, polypropylene, and polyethylene terephthalate, excellent agreement between the two sets of values were obtained, but with rubber hydrochloride and ethyl cellulose the sorption values are much higher. These differences are interpreted in terms of clustering of water vapor in the film at higher relative humidities. The modified time‐lag technique showed concentration‐independent diffusion constant for all five polymers.