Modification of Soy-based Adhesives to Enhance the Bonding Performance

Soy protein (SP) which exists in soy flour, soybean meal, soy protein concentrate, and soy protein isolate is one of the vegetable proteins. It represents a very practical and inexpensive material for bio-based adhesives. The positive public perception of SP makes it very competitive as a wood adhesive. While SP is weak in adhesion strength and water resistance compared to the traditional formaldehyde-based resins, the performance of the SP adhesive bonded composites would be significantly improved if a strong chemical bonding between the SP adhesive with the cellulosic materials can be achieved. In order to enhance the bonding performance, this chapter presents the current modification methods of soy- based adhesives, which describes: (1) Chemical modifications including alkali denaturation, surfactant denaturation, organic solvent denaturation, enzymatic treatment, epoxy groups crosslinking, formaldehyde compounds crosslinking, acylation and silanation; (2) Physical modification including compression, high temperature treatment, ultrasound treatment and blending with hydrophobic additives; (3) Nanoparticle modification using cellulosic nanofibers, inorganic nanoparticles and nano-clays. In addition, it also illustrates the use of the soy adhesive as a substitute for other adhesives in this chapter.