2025 AIChE Annual Meeting

Post Polymerization Treatments for Tuning Equilibrium Moisture Adsorption of Whey Protein Copolymer

Proteins, as natural polyamides, can be synthesized into biodegradable protein copolymers as a sustainable alternative of fossil fuel derived plastics. Proteins have been shown to enhance mechanical properties when incorporated into elastomers due to their inherent stiffness when dry. However, protein copolymers’ material properties suffer from moisture sensitivity because they tend to change as a function of relative humidity, limiting the copolymers’ practical applications. This is due to the plasticizing effect of water, which soften the protein domains by disrupting intermolecular interactions. We aim to address this issue by increasing protein hydrophobicity. This work builds upon previous efforts to increase hydrophobicity by modifying protein functional groups, mutating the protein, and blending with hydrophobic plasticizers, where we will treat protein copolymers with organic solvent-water mixtures that vary by organic solvent, solvent concentration, pH value, and temperature.

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.