Soy and cottonseed protein blends as wood adhesives

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

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2015
Publication Date: 2/5/2016
Citation: Cheng, H.N., Ford, C., Dowd, M.K., He, Z. 2016. Soy and cottonseed protein blends as wood adhesives. Industrial Crops and Products. 85:324-330.

Interpretive Summary: Wood adhesives are used for the production of wood composites. Because of environmental regulations regarding emission of organic compounds including formaldehyde, wood adhesives based on soy proteins have gained attention in the past 15 years. Some of the issues that need to be addressed include lower cost, increased adhesive strength, and improved water resistance. Earlier, we showed that cottonseed protein exhibits superior adhesive strength and water resistance relative to soy protein. In this work we studied two types of blends: 1) blends of soy protein and cottonseed protein, and 2) blends of protein with several polysaccharides. In the first case, we showed that cottonseed/soy proteins can be blended together in different ratios to give a range of adhesive properties and hot water resistance. In the second case, when cottonseed or soy protein is blended with different polysaccharide components, the dry adhesive properties of the blends are similar to those of the base protein even with fairly dilute levels of protein. In view of both dry and wet adhesive strengths, cottonseed protein is superior to soy protein in these protein/polysaccharide blends. For product development where cost/performance is important, the blending of cottonseed protein with a cheap polysaccharide such as starch or cellulose may be of particular interest.

Technical Abstract: As an environmentally friendlier alternative to adhesives from petroleum feedstock, soy proteins are currently being formulated as wood adhesives. Cottonseed proteins have also been found to provide good adhesive properties. In at least some cases, cottonseed proteins appear to form greater shear strength and improved hot water resistance compared with soy proteins. In the present study, blends of soy and cottonseed proteins were prepared, and their adhesive properties were found to decrease steadily with increased levels of soy protein in the formulations. In addition, cottonseed- and soy-based adhesives were also formulated with xylan, starch, or celluloses to determine the influence of polysaccharide fillers on protein-based adhesive properties. In some cases, adhesive shear strength was retained even when the cottonseed or soy protein was mixed with up to 75% polysaccharide. For cottonseed protein/polysaccharide formulations, hot water adhesive resistance was retained when the blend contains about 50% polysaccharides. Soy protein formulations and its polysaccharide blends generally exhibited somewhat lower hot water resistance. In view of the ability of cottonseed protein/polysaccharide blends to retain shear strength and hot water resistance properties, these blends may provide an opportunity to decrease the amount of protein used in adhesive formulations, thereby decreasing cost.