Soon, plywood might go vegetarian.
The ubiquitous building material owes its strength to multiple wood sheets with their grains at right angles and tenacious glue between the layers. Now, researchers are proposing that plywood be manufactured using glue made with soy flour rather than with powdered cattle-blood protein, as is done conventionally. The vegetable-containing adhesive might reduce the wood’s cost and alleviate health concerns among mill workers.
A leading incentive for finding such an alternative is workers’ fears of breathing in cattle-blood dust and disease agents it might carry, says Mila P. Hojilla-Evangelista of the U.S. Department of Agriculture’s Agricultural Research Service (ARS) in Peoria, Ill. Furthermore, there are few suppliers of the blood protein, which helps make the glue sticky and durable.
In work funded by the United Soybean Board, Hojilla-Evangelista and her colleagues developed and tested several glue formulations that use different amounts of soy ingredients from a variety of suppliers. Three glues that contain soy flour—a combination of soy protein and starch—have properties comparable to those made with the blood protein, says Hojilla-Evangelista. In tests, the soy-containing glues were at least as strong as the conventional glue and had comparable water resistance, she says.
The new glues also had foaming behavior comparable to that of blood-protein glue. Foaming is an essential trait for glue used in one of the major methods for making plywood. During this manufacturing process, known as foam extrusion, machines squirt the glue in evenly spaced lines onto each successive ply, says Rick Haig of ARS.
Good foaming ensures that the glue will coat the entire sheet when another layer of wood is pressed on. Foam extrusion uses less glue than other techniques, such as brushing, rolling, or spraying, he says.
Pacific Adhesives Co. of Portland, Ore., which makes foam-extrusion equipment, is now testing the ARS formulations. In these experiments, the soy-containing glues foam just as well or better than blood-containing glue, says company president Tom Demaree. The company is still examining the soy glues’ adhesive properties, he says, and is planning full-scale mill trials.
Paper and wood materials giant Georgia-Pacific is also testing several formulations of the new glue, says company researcher Mel Foucht in Decatur, Ga. “I think that it has a lot of potential,” he comments. For one thing, he says, the soy-containing glue has a longer shelf life than conventional glue. He speculates that the soy glue might not be limited to foam-extrusion processes.
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Ultimately, cost may determine the new glues’ fate. The soy glues are slightly less expensive than those that contain animal protein, Hojilla-Evangelista says. Although modest, such savings could add up for mills that use tons of glue annually to make industrial quantities of plywood.