Properties of soybean-flour-based adhesives enhanced by attapulgite and glycerol polyglycidyl ether

- Attapulgite was used as an enhancer to modify soybean-flour-based adhesives.
- Attapulgite formed a physical crosslinking structure in the adhesives system.
- The soybean-flour-based adhesives show superior water resistance after modified.
- The modified adhesives are formaldehyde-free, easy to use and readily available.
- The modified method can promote the industrialization of soy protein adhesives.

Soybean-flour (SF)-based adhesives were prepared using renewable glycerol polyglycidyl ether (GPE) as a cross-linking agent and low-cost attapulgite (ATP) as an enhancer to provide an excellent soy protein adhesive for the plywood industry. The shear strength, solid content, rheology, crystallinity, infrared spectra and morphological properties of the ATP modified SF (AMSF) adhesives were investigated in detail. The results indicated that the shear strength and water resistance of the AMSF adhesives improved significantly. The viscosity and solid content of the MSF adhesive increased when ATP was introduced, and these parameters could meet the requirement set by the China National Standard and ANSI/HPVA HP-1-2000, meanwhile. The crystallinity, infrared spectra, and morphology of AMSF indicated that no chemical reaction occurred between ATP and the modified soybean-flour (MSF) adhesive. The ATP acted as a bridge joint due to its rod-like structure that was inserted in the MSF adhesive and used as a physical bond to increase the shear strength of the AMSF adhesive. After ATP was introduced, the fracture surface of the cured AMSF adhesive became smoother and more compact. The AMSF adhesive is potentially independent of petrochemicals, formaldehyde-free, easy to use and readily available, which will promote the industrialisation of soy protein adhesives.