Comparing Soy Flour Wood Adhesives to Purified Soy Protein Adhesives

Abstract

While economics dictate that soy-based wood adhesives be made with soy flour, much of the recent literature on soy-based wood adhesives has involved using soy protein isolate. The obvious assumption is that the additional carbohydrates in the flour but not in the isolate only serve as inert diluents. Our studies have shown that the isolate can provide 10 times the wet bond shear strength than the soy flour at near neutral pH. Various models to explain the difference in wood adhesive performance between soy flour and purified soy products were examined. Prior studies eliminated some hypotheses by showing that using different soy flours or adding chaotropic agents (urea, guanidine hydrochloride, or dicyandiamide) or surfactants (sodium dodecyl sulfate or cetyltrimethylammoniumbromide) did not improve wet bond strength. In this study, adding a variety of carbohydrates to commercial soy protein isolate caused some drop in wet bond strength, but the carbohydrate plus commercial isolate is still much better than soy flour or a commercial soy concentrate. This cast doubts on the carbohydrate interference model, and left still unexplained why the commercial isolate is so much better than other soy products.

Citation

Frihart, Charles R.; Lorenz, Linda F. 2013. Comparing Soy Flour Wood Adhesives to Purified Soy Protein Adhesives. In: International Conference on Wood Adhesives, 2013; pp. 592-600.