Research Progress on Formaldehyde‐Free Wood Adhesive Derived from Soy Flour

Soy‐based adhesives have been regarded as the most suitable candidates for wood industry. For a widespread use of soy‐based adhesives, new technologies need to be developed to improve the water resistance. An overview on the methods to improve water resistance of soy‐based adhesives is presented. Denaturants were once considered necessary to modify soy protein. However, water‐resistant soy adhesives could be prepared by simply removing water‐soluble carbohydrates and low molecular peptides from soy flour. In addition, proper grafting and cross‐linking agents help to prepare water‐resistant soy‐based adhesives, which are used widely to bond interior wood composites. In particular, a new type of polyamidoamine (PADA) resin and an itaconic acid‐based polyamidoamine‐epichlorohydrin (IA‐PAE) resin were synthesized to perform as cross‐linking agents for soy‐based adhesives. This review concludes that soy‐based adhesives have great potential for use in numerous applications. However, future work is still needed to make soy‐based adhesives more competitive with synthetic adhesives.