Water absorption isotherms for cured bisphenol A type epoxy resins: Effects of isotherm temperature and resin hardener

Water‐sorption isotherms have been determined for some bisphenol‐A‐type epoxy resins cured with either 4,4′‐diamino diphenyl methane (DDM), phthalic anhydride, or polyamide, Versamid 115. The absorption isotherms for the diamine‐cured resin are reversible and that at 0.2°C is linear for the whole accessible range of relative pressures (0 ⩽ h ⩽ 1). With increase in temperature deviations from Henry's law occur at successively lower relative pressures. It is shown that these deviations from Henry's law are related to a concentration dependence of the isosteric heat of absorption. Sorption by both the polyamide and phthalic‐anhydride‐cured resins is not reversible; there are weight increases following an absorption–desorption cycle.