Adhesion Properties of Soy Protein Subunits and Protein Adhesive Modification

Environmental concerns and the need for sustainable development have stimulated investigations of plant protein-based adhesives. Soy protein, which has been used for wood adhesives for centuries, is a promising biodegradable adhesive with great potential as an alternative to current synthetic petroleum-based adhesives. This chapter contains a review of soy protein subunit characterization and their adhesion properties when used as wood adhesives. Glycinin was found to be the main contributor to adhesion strength of soy protein. The basic and β subunits with larger portions of hydrophobic amino acid were shown to have greater adhesion properties than their respective subunits, acidic and a’ a. Soy latex adhesives with high protein content (33%-38%), good flowability, long storage life and good adhesion performance can be produced by in situ sodium bisulfite modification in soy flour-water extract. Protein modification uses physical and chemical methods to improve adhesion 60 properties by altering protein molecular structure and conformation. This chapter also describes current technologies for soy protein adhesion improvement, including cross-linking, protein blends (synthetic adhesives, lignin, wet-strength resin), enzymatic treatment, and nano technology.