A bio-based adhesive based on soy protein-gelatin with high cold compression strength, toughness, and water resistance

In order to reduce the harm of formaldehyde-based adhesives and solve the problem of petroleum resource shortage, green and formaldehyde free bio-based adhesives have great market development potential. Soy protein adhesive is expected to solve these problems, but it has disadvantages such as low cold compression strength and high bonding brittleness, making it difficult to carry out large-scale industrial applications. This study introduced gelatin and triglycerides (TGA) into soy protein (SM) adhesive to construct a double bond composite system. TGA undergoes cross-linking reaction with soy protein to form a cross-linked structure as the skeleton structure, which endows the adhesive with strength and water resistance; and gelatin (Gel) forms hydrogen bonds with soy protein as sacrificial bonds, improving the toughness and cold compression performance of the adhesive. Compared with pure SM adhesive, the dry/wet shear strength of modified SM/2-Gel/TGA adhesive increased by 27.8 % and 400 %, respectively, reaching 2.3 MPa and 1.4 MPa. The moisture absorption rate of the modified adhesive decreased by 16.5 %, the residual rate increased by 10.0 %, and the fracture strain increased by 52.2 % to 14 %. In addition, in the adhesive treated with cold pressing, the lap strength increased by 25.1 % to 4.23 MPa, indicating that the cold pressing strength, bonding toughness, and water resistance of the modified adhesive were effectively improved. This study provides a new way for preparing green, formaldehyde free high-performance bio-based adhesives.