High water retention bio-mass adhesives inspired by hydrogels for engineering applications

Soybean meal (SM)-based adhesive, which is sustainable and releases no aldehyde, can play an important role in the development of green adhesives. However, natural SM-based adhesives lack water retention ability, which makes it tedious to apply in engineered materials. This work designed a polymer entanglement system by free radical polymerization of acrylamide (AAm). As a small molecule filler, succinic acid (SA) entered the polyacrylamide (PAAm) cross-linking network. The hydrophilic amide groups of PAAm can adsorb water molecules through hydrogen bonding interactions, while the introduction of SA achieved hydrogen bonding interlocking between carboxyl and amide groups on water molecules, firmly locking water molecules in the three-dimensional network of PAAm. This not only improved the cohesion of the adhesive, but also achieved excellent water retention performance.The prepressing strength of the plywood with the prepared adhesive was 1.05 MPa, which grew by 104 times in contrast to unmodified one (0.01 MPa) after the veneer was once opened and evaporated in the air for 1 h. In addition, the water content of the modified adhesive was found to be multiplied by 69.5 % after 3 days, in contrast to the unmodified adhesive. The dry and wet shear strengths of the modified adhesive were 2.47 and 1.21 MPa, which were 61.8 % and 317.2 % higher than the SM adhesive. A SM-based adhesive system that enhanced water retention while increasing strength was created, achieving excellent water retention, high bonding strength, and excellent long-term prepressing performance. As a green adhesive, this is a good reference for the further development of soy protein adhesives in engineering applications. • Preparation of water-retaining adhesives inspired by hydrogels. • The prepressing strength of adhesive increased by 104 times compared with initial one. • Dense hydrogen bonding enhances water retention and strength of the adhesive. • Water-retaining structure is formed by building polymers and small molecule fillers.