Quantifying the influence of cross-linking percentage on polymer-solvent interactions using the Flory-Huggins model in PVA pervaporation membranes

Poly(vinyl alcohol) (PVA) membranes are popular in pervaporation, where interaction between polymers and solvents and the level of cross-linking have a significant effect on swelling, sorption, and transport behavior. The swelling behavior of chemically cross-linked polyvinyl alcohol membranes in various solvents in the presence of two cross-linking agents, including glutaraldehyde and maleic acid, was methodically studied. The equilibrium swelling was used to estimate the Flory-Huggins interaction parameter (χ), which is a measure of the thermodynamic affinity between the polymer network and the penetrant molecules. This parameter is particularly important in pervaporation simulations, where the parameter χ is an expression of the thermodynamic affinity of the solvent and polymer in the membrane phase, which is directly related to the behavior of solvent sorption and can be applied to explain permeation fluxes in solution diffusion-like transport models. The degree of equilibrium swelling was clearly correlated with the percent and the type of cross-linking agent, which allowed correlating χ with the degree of cross-linking density. The results indicate that the swelling ratio and the corresponding values of χ are affected by the type of crosslinker, the degree of cross-linking, and the character of the solvent-polymer system, so different behaviors are found in the acidic and alcoholic solvents. The correlations developed in this work provide reliable information on Flory-Huggin’s interaction parameter for use in pervaporation sorption and contribute to the rational design and optimization of cross-linked PVA membranes for separation applications.