(43f) Protein Nanofibrils As Reinforcing Components in Copolymers and Composites

Proteins are promising renewable feedstock for materials manufacture due to their renewability and large volumes produced in agricultural waste streams. Beyond their availability, proteins possess a unique ability to self-assemble into hierarchical nanostructures, making them particularly attractive for material applications. Among these, protein nanofibrils have garnered significant interest due to their highly crystalline cross-β structures, which enable them to be some of the strongest proteinaceous materials. These fibrillar structures can be induced in a wide range of proteins through controlled denaturation and hydrolysis processes. In this work, we explore the integration of protein nanofibrils into copolymers and composite materials.

Whey protein is selected as the model agricultural protein, and nanofibrils are synthesized through acid hydrolysis. This process exposes hydrophobic patches while inducing repulsive forces between positively charged proteins, driving their assembly into β-sheet crystalline fibrils. We demonstrate that these protein nanofibrils exhibit stability in a variety of neat organic solvents, and their robustness allows for further functionalization. To fabricate elastomers, the nanofibrils are modified with polymerizable methacrylamide groups and subsequently copolymerized with a rubbery polymer. This results in a nanofibril-reinforced copolymer with enhanced mechanical strength and toughness compared to materials synthesized using the globular protein.

Additionally, protein nanofibrils are incorporated into composites through melt blending with polymers. However, their hydrophilic surface presents compatibility challenges with hydrophobic polymer matrices, leading to difficulties in achieving homogeneous dispersions. To address this, protein nanofibrils are conjugated to polymers to improve interfacial interactions. Structure–property relationships of these materials are further investigated using Fourier-transform infrared spectroscopy, wide-angle X-ray scattering, and atomic force microscopy. Overall, this work provides a strategy to leverage the self-assembly of protein nanofibrils for engineering partially renewable copolymers and composites with improved mechanical properties.