Kinetics of water vapor diffusion in resins

The water vapor sorption and desorption kinetics were monitored in methyl methacrylate–acrylonitrile–butadiene–styrene copolymer (MABS), bromobutyl, ethylene–propylene–butadiene monomer (EPDM) rubber, and butyl rubber at various temperatures by gravimetric method. Modified thermogravimetric analysis system was built and used. The geometry of the samples was approximating that of the infinite two-sided plane sheet of certain thickness. The coefficients of water vapor diffusion in polymers were deduced by comparing the experimentally monitored kinetics and kinetics computed using diffusion coefficients as adjustable parameters. The activation energies of water vapor diffusion in these polymers were deduced in the temperature range from 30 to 75 °C. The activation energy of diffusion was 45.9 kJ mol −1 in bromobutyl rubber, 46.4 kJ mol −1 in butyl rubber, 60.3 kJ mol −1 in EPDM rubber, and 43.5 kJ mol −1 in MABS. Compensation effect was observed for water vapor diffusion in this series of polymers. Compensation effect parameters were determined to be, a = −23.9/ln(cm 2 s −1 ) and b = 0.49/(mol kJ −1 ) × ln(cm 2 s −1 ), in fair agreement with published data for water diffusion in polymers.