Ammonium salt-induced soybean flour-based adhesive with stable low viscosity, long open time, excellent water retention and bonding property

Soybean flour-based adhesives are sustainable and eco-friendly, but their widespread applications are limited by high viscosity, short open time, and low water retention. In this study, ammonium chloride (AC) and bis (2-hydroxyethyl) dimethyl ammonium chloride (BIS), soybean flour (SF), and self-synthesized co-crosslinker comprising polyamidoamine-epichlorohydrin (PAE) and melamine-urea-glyoxal (MUG) resins were used to prepare a novel, effective, and room-temperature stable SF-based adhesive. The BIS and AC effectively generated hydrogen bonding with polar groups in SF, thus disrupting the intermolecular hydrogen bonding of soybean proteins, promoting protein dissolution, and inhibiting the reconstruction among dissolved soybean protein chains. This process reduced the viscosity of the obtained adhesive and kept it relatively stable. In addition, the BIS and AC combined with water molecules through strong hydrogen bonds to improve water retention by 23.8 % and prolonged the open time of obtained adhesive by 95.7 % compared with commercial SF-based adhesive. The dry and soaked wet strengths of adhesive after 12 h storage at room temperature were 1.98 MPa and 0.77 MPa, respectively, which were 182.8 % and 10 % higher than the required value of Chinese Standard GB/T 9846–2015 for Class II plywood, indicating long pot life and excellent bonding property. This novel ammonium salt-induced strategy is an effective approach for preparing SF-based adhesive with significant potential for commercial applications, advancing the use of soybean meal in bio-adhesives. • A novel soybean flour-based adhesive by ammonium salt-induced strategy was prepared. • Ammonium salt endowed obtained adhesive with low viscosity and long open time. • The water retention of soybean flour-based adhesive was improved by 23.8 %. • Optimal adhesive showed excellent bonding strength and water resistance. • This strategy promotes the industrial utilization of soybean meal in bio-adhesives.