Effects of phosphorus-containing additives on soy and cottonseed protein as wood adhesives

Authors: Cheng, Huai; Ford, Catrina; Dowd, Michael; He, Zhongqi

Submitted to: International Journal of Adhesion and Adhesives
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2017
Publication Date: 7/15/2017
Citation: Cheng, H.N., Ford, C., Dowd, M.K., He, Z. 2017. Effects of phosphorus-containing additives on soy and cottonseed protein as wood adhesives. International Journal of Adhesion and Adhesives. 77:51-57.

Interpretive Summary: There has been recent interest in using plant-based proteins as sustainable and eco-friendly replacements for formaldehyde-containing resins in wood adhesives. This is driven in part by the desire to decrease dependence on petroleum resources and in part to decrease exposure to formaldehyde, which is a known carcinogen. However, soy protein is more costly than formaldehyde-based resins, and its adhesive properties are generally inferior. We have shown earlier that cottonseed protein isolate performs better than soy protein isolate in both dry adhesive strength and hot water resistance. In this work, we aim to improve the adhesive performance of cottonseed protein even further in order to offset the protein’s cost/benefit disadvantage. We have shown that several commonly available and cheap phosphorus-containing compounds can serve as promoters for cottonseed protein. When added in optimal amounts, some of these promoters can improve the adhesive performance of cottonseed protein adhesives by 40%. This work will make cottonseed protein more attractive for use in wood adhesive formulations.

Technical Abstract: Soy and cottonseed proteins appear promising as sustainable and environment-friendly wood adhesives. Because of their higher cost relative to formaldehyde-based adhesives, improvement in the adhesive performance of proteins is needed. In this work, we evaluated the adhesive properties of soy and cottonseed protein formulations that included phosphorus-containing acids and esters. For cottonseed protein isolate, most of these additives improved dry adhesive strength, with methylphosphonic acid, phosphorous acid, and phosphoric acid increasing the dry strength by 47, 44, and 42%, respectively, at their optimal concentrations. For soy protein isolate, these additives did not show significant benefits. The phosphorus-containing additives also improved the hot water resistance of the cottonseed protein formulations but showed either no effect or a negative effect for the of soy protein formulations. Thus, the combination of cottonseed protein with phosphorus additives appears to be attractive as wood adhesives.