Properties of wheat gluten based wood adhesives enhanced by transglutaminase and epichlorohydrin

Bio-based eco-friendly products are well-received globally due to increasingly scarce petroleum resources and growing public concern about human health risks and environmental concerns. In this study, wheat gluten (WG) as the raw material modified with transglutaminase (TGase) and epichlorohydrin (ECH) was used to develop an eco-friendly bio-based adhesive. Effects of TGase and ECH on the properties of the adhesive were emphatically discussed. The dry and wet shear strengths of the combined modified adhesive achieved at 3.21 MPa and 0.81 MPa, which was higher than the Chinese National Standard II plywood requirements (0.7 MPa). Meanwhile, the solid content and the protein surface hydrophobicity H0 were increased to 28.27 % and 636.54, respectively. These improvements were mainly because, during the modification, the structure of WG became more stretched after ethanol treatment. Then the TGase promoted the cross-linking of the protein molecules and enhanced the cohesion strength of the adhesive system. Finally the ECH further cross-linked and aggregated with exposed active groups to varying degrees, and formed a compact three-dimensional cross-linked network structure, which allowed the WG-based adhesive to form a smoother and more uniform microscopic surface and better water resistance. The obtained adhesives might be utilized to substitute petroleum-derived adhesives in the plywood sector, providing ideas and references for future eco-friendly adhesive research and increasing the high value usage of wheat starch processing by-products.