An innovative biomass-based wood adhesive generated from peony seed meal: Its preparation and properties

Plant protein-based adhesives, particularly those derived from soybean meal (SM), have been available for various product applications. However, the high cost of SM has limited large-scale manufacturing, despite sufficient production capacity. Peony seed meal (PSM) is abundant in proteins, polysaccharides, and polyphenols, the protein in PSM contains highly hydrophobic amino acids, resulting in low water solubility and water holding capacity. It is worth investigating whether the unique composition of hydrophobic amino acids in PSM protein can enhance the water resistance of PSM-based adhesives. Additionally, the lower price of PSM, which is approximately two-thirds of the cost of SM, makes it a more valuable raw material for adhesives. Herein, we report a simple and practical approach for preparing PSM-based wood adhesives by utilizing the highly active cross-linking agent of polyamidoamine-epichlorohydrin (PAE). The results showed PSM-based adhesives possessed excellent adhesion, especially the adhesive of "PSM-36%", with the wet bond strength and the aged bond strength reaching 1.60 and 0.83 MPa, respectively, meeting the standards outlined for indoor-use plywood (>= 0.98 MPa). Mechanistic studies indicated that the adhesion mechanism of such PSM-based adhesives might involve high solid content, low viscosity, high thermal stability, and the formulation of covalent bonds and hydrogen bond networks. A simple and effective approach was used to enhance the performance of PSM-based adhesive by incorporating PAE into a cross-linked network. This was achieved by establishing robust connections between PSM and PAE through several interactions, such as hydrogen bonding, ring-opening reactions between PAE's azacyclic structure and PSM protein side chains, as well as interactions between PSM polysaccharides and polyphenols. image