Protein-Based Elastomers as Replacements for Polyurethanes

Proteins are biopolymers widely studied for materials applications due to their abundance as waste feedstock and their structural role in producing high performance materials in biological systems. While greater utilization of proteins in materials can provide a sustainable alternative to petroleum-derived polymers, proteins are generally brittle and have high softening temperatures in the absence of plasticizer, making them unsuitable for many applications. Inspired by the chemical and structural similarity between the hard blocks of polyurethanes and the b-strands of proteins, we hypothesized that natural protein materials could be utilized in polyurethane like hard-soft copolymers in order to overcome these limitations and produce sustainable commodity materials.<br/><br/>Simple bioconjugation strategies allow the preparation of polyfunctional proteins that can be co-polymerized with a wide variety of different monomers to produce thermoset plastics. These materials have variable modulus, toughness, and extensibility depending upon the protein content, degree of protein functionalization, and monomer choice. While hydrophilic monomers were first used to enable facile copolymerization with the protein, this leads to strong humidity-sensitivity. To reduce this effect, we developed formulations based on oleophilic monomers using surfactants to compatibilize the protein and monomer before polymerization. This leads to a two-fold reduction in water uptake while preserving the favorable mechanical performance of the materials. Tuning the surface charge of the protein biomass via chemical reaction was further explored in order to control the humidity sensitivity, leading to further stabilization of mechanical properties across a broad range of environmental conditions. Recently, we have also demonstrated that thermal treatment to induce changes in protein conformation can lead to substantial strengthening of the materials, and that this approach generalizes across a wide range of different protein feedstocks and purities. Overall, this work demonstrates the ability to produce biomass-based materials that can mimic the mechanical response of polyurethanes while simultaneously managing moisture uptake, demonstrating promising steps towards a new sustainable material platform.