In this study, we demonstrate that organic solvent-water mixture treatments can reduce the equilibrium moisture adsorption of protein-based elastomers, without the necessity of modifying the protein before the synthesis. We hypothesize that by altering protein conformation to expose hydrophobic groups and increase the β-sheet content, we can mitigate the moisture-induced softening of protein copolymers. The protein copolymers were synthesized by copolymerizing whey protein with hydroxyethyl acrylate. Whey protein was chosen because its primary component, β-lactoglobulin, has a well-characterized structure, and they were attached to the polyacrylate because hydrophilic monomers can be directly blended with protein without the addition of surfactants, which allows us to focus on the chemical treatments’ effects on the copolymer. Our results show that submerging the whey protein copolymers in dilute acetonitrile or methanol solutions prior to drying significantly improves moisture resistance of the copolymers. Furthermore, analysis of the proteins’ secondary structure conformation change reveal a strong correlation between higher β-sheet content and reduced moisture uptake at high relative humidity (100%), though this correlation is insignificant at moderate relative humidity (~50%).
Overall, this work contributes to the development of sustainable plastic alternatives by demonstrating the possibility of reducing moisture adsorption of protein copolymer using a simple, scalable method.