The Sorption and Diffusion of Water in Polyurethane Elastomers
The sorption and permeation of water has been measured at several temperatures for three polyurethane elastomers, namely, Adiprene CM with a polyether soft segment and Elastothane ZR625 and Genthane S both with polyester soft segments. The equilibrium sorption behaviour of all three materials is similar and the heat of dilution is zero, or close to zero, over most of the concentration range. The results indicate a comparatively strong interaction between the water and the polymer but the isotherms themselves do not exhibit significant Langmuir-type curvature at lower relative pressures. A Zimm-Lundberg analysis of the isotherms reveals that clustering of the sorbed water tends to dominate over most of the relative-pressure range. This is consistent with the observation that the diffusion coefficient, D, decreases with concentration for all three elastomers. The concentration dependence of D, bearing in mind the moderate water solubilities of these materials, is rather weak and the activation energy for diffusion is virtually constant. The results suggest that competing processes are operative which tend to oppose the effect of clustering on D.
KeywordsSorption Isotherm Silicone Rubber Soft Segment Cluster Function Sorbed Water
Unable to display preview. Download preview PDF.
- 2.D. Machin and C. E. Rogers,“The Concentration Dependence of Diffusion Coefficients in Polymer-Penetrant Systems”, C.R.C. Critical Reviews in Macromolecular Science, C.R.C. Publ. Cleveland, 1972.Google Scholar
- 3.J. A. Barrie, Diffusion in Polymers (J. Crank and G. Park eds.), Academic, New York, 1967.Google Scholar
- 7.Ludbrook, B., Thesis, University of London, (1972).Google Scholar
- 14.A. C. Newns and G. S. Park, J. Polymer Sci., C22, 927 (1969).Google Scholar
- 15.J. B. Alexopoulos, J. A. Barrie, J. C. Tye and M. Fredrickson, Polymer, London, 9, 57 (1968).Google Scholar