Modeling liquid absorption of highly cross-linked epoxy resins in aqueous electrolyte solutions

The solvent absorption of an epoxy o-cresol novolac resin composite has been measured in different aqueous electrolyte solutions (NaCl, CaCl₂ and MgCl₂) at different salt concentrations from 0.1 to 0.3 mg/l. Next to the total solvent uptake, which was measured by a gravimetric measurement, the absorption of ions was determined by ion chromatography and by atomic absorption spectroscopy. The measured solvent absorption in equilibrium was calculated by combining the ePC-SAFT equation of state with a network term, which takes into account elastic forces in the polymer network counteracting a further solvent absorption. In order to model the solvent absorption kinetics, the equation of state was combined with a Maxwell-Stefan diffusion approach and the viscoelastic Kelvin-Voigt model for chain relaxation. The model parameters were only fitted to the absorption in pure water, what was only possible because the epoxy resin absorbed a neglectable amount of ions. The fully predictively calculated values for the absorption in electrolyte solutions are in qualitative agreement to the measured data.