Bioadhesive Design Toward Renewable Composites: Adhesive Distribution and Molecular Adhesion

Improvements in renewable compositions of adhesives are key for advancing the existing wood industry and developing biocomposites. Building upon prior studies on fundamental interactions between model compounds of fiber and bioadhesives, more complex bioadhesives are investigated. Cold denaturation of soy protein isolate (SPI) in dilute sodium hydroxide provide sufficient physical strength for wood composites. Due to swelling, 5% epoxy resin is added to the SPI adhesive resulting in improved physical strength and water resistance. The SPI and epoxy are evenly distributed on the fiber surface, while additional SPI fills the gaps between fibers based on fluorescence microscopy and X‐ray photoelectron spectroscopy. Molecular dynamics (MD) simulations show that the physical strength of the composites increases with the content of SPI, with the number of hydrogen bonds (H‐bonds) as primary driver; in MD simulations, the composite strength is highest at 3% epoxy, though higher epoxy doses results in more H‐bonds. In ReaxFF MD simulations, other contributions (e.g., van der Waals energy) show no correlation. The developed bioadhesive and the interaction mechanism demonstrate here emphasize the weak physical interactions in these materials, though covalent bonds and other larger scale phenomena are important as well for macro performances of the bioadhesives.