(302c) Proteins As Biodegradable Reinforcing Fillers in Plastics

Proteins are promising renewable feedstock for materials manufacture due to their large volumes produced in agricultural waste streams. They have underexplored potential as fillers in composites. As fillers represent a major component in many conventional plastics, developing alternative fillers from biomass sources presents an opportunity to replace a significant volume fraction of plastics with renewable and potentially biodegradable components. Besides renewability and biodegradability, proteins offer an ability to form hierarchical nanostructures. Under relatively mild conditions, they have been shown to form highly crystalline nanofibrils.

Here, we investigate the use of protein nanofibrils as reinforcing fillers in blends with polyethylene. We hypothesize that these bio-fillers impart mechanical strength to composites through extensive hydrogen bonding. Whey protein is selected for this study, and nanofibrils are prepared by partially hydrolyzing the protein in acidic solutions. As a result of the exposure of hydrophobic patches and repulsive forces between positively charged proteins, the proteins assemble into β-sheet crystalline fibrils. To improve compatibility of the protein nanofibrils and hydrophobic polymers, which is necessary for achieving good dispersion and adhesion, we modify the nanofibrils by esterification. Esterification is performed with alcohols of different alkyl lengths, which resulted in proteins with enhanced intermolecular β-sheets and hydrophobicity. Protein nanofibrils are then melt blended with the polymer matrix, and are characterized with tensile testing. Structure-property relationships are further studied using Fourier-transform infrared spectroscopy and atomic force microscopy. Overall, this work provides a strategy to leverage the assembly of protein nanofibrils to engineer partially renewable polymer composites.