Nature’s Glue

Nontoxic, soy-based adhesives and wood-plastic composites are some of the new products emerging from Kaichang Li’s OSU laboratory in the Department of Wood Science and Engineering. Soy may help prevent cancer not only on your kitchen table but also in your kitchen table.

Nontoxic, soy-based adhesives and wood-plastic composites are some of the new products emerging from Kaichang Li’s OSU laboratory in the Department of Wood Science and Engineering.

By Lee Anna Sherman

Soy may help prevent cancer not only on your kitchen table but also in your kitchen table.

Across campus from OSU’s Linus Pauling Institute, where nutrition scientists have been studying soybeans’ place in a healthful diet (see “The Zinc Link,” page 22), another OSU scientist has found a way to use those same protein-rich beans in everyday wood products — paneling, cabinets, desks and, yes, the table where you eat your meals. These soy-based wood composites are free of the cancer-causing chemical formaldehyde, which for decades has been a mainstay of adhesives used in plywood, particleboard and furniture.

The wood adhesive breakthrough of Kaichang Li, an associate professor in OSU’s College of Forestry, is just one of many bio-based products and processes under investigation in labs across the university. While Oregon Governor Ted Kulongoski, the Oregon Innovation Council and others work to secure Oregon’s prominence in the new “carbohydrate economy”— drafting bills to boost bio-fuels development and considering a new bio-products research initiative — OSU scientists are at work on the technical challenges. Among them: wood-plastic composites made from recycled carpets, botanical sources of natural rubber, wastewater-generated electricity, cellulose as a source of ethanol and edible coatings for fresh foods (see Growing Technology sidebar.)

Although Li made his bio-based discovery just a few years ago, his interest in nontoxic composites dates back to his post-doctoral studies at the University of Georgia, where he was researching ways of making wood pulp with fungi. His Scandinavian colleagues told Li about seeing the “reddish skin” of woodworkers using formaldehyde-based glues in their native Sweden. “They all said those glues are nasty materials to work with,” says Li.

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But it wasn’t until a weekend at the Oregon Coast several years later that true inspiration hit. Equipped with a plastic bucket and rubber boots, Li was scouring the craggy outcroppings for mussels in anticipation of a savory seafood dinner. Suddenly, he was struck by the tenacity with which the blue-shelled mollusks clung to the rocks, even as waves pummeled mercilessly and tides tugged relentlessly. Taking some of these tough little shellfish back to his lab, he began investigating their natural superglue. Prior studies of the proteins forming the mussels’ stringy, clingy tentacles showed a unique combination of amino acids, clearly an evolutionary adaptation to the mussels’ ecological niche. Such a powerful, waterproof bond was just what the woodproducts industry needed to replace the formaldehyde-based formulas, Li concluded.

The trouble was, mussel protein is rare. It wouldn’t be practical or, more to the point, cost-effective, to use it directly. Still, the idea had formed and, just like those stubborn mussels, Li wasn’t about to let go. The scientific question he began to investigate with funding from the U.S. Department of Agriculture was, Can you convert an abundant protein — such as soy — into a strong and water-resistant adhesive like the mussel protein? The commercial question was, Can you make the new adhesive at a price competitive with the traditional resin, which costs only about 30 cents a pound?

Li was pretty sure the answer to both questions was yes. “Protein is protein,” he points out, “and all proteins consist of different combinations of amino acids.”

In comparing mussel and soy proteins, Li discovered that the amino acid compositions of the two proteins are quite distinct. Mussels contain high levels of certain amino acids that are lacking in soy. At the same time, mussels lack certain amino acids that are abundant in soy. So, using mussels as a model, Li and his research group experimented with chemically modifying the soy protein. They blocked some of the soy amino acids, those that the mussels lack. Simultaneously, they transferred mussel amino acids into the soy. “We turned soy proteins into mussel adhesive proteins,” Li says.

Manufacturing the mussel-mimicking adhesive via the chemical-modification route, however, would be too costly. So, to make the new adhesives competitive with traditional adhesive technologies, Li developed a “curing agent” that could readily modify soy under heat during the production of wood-composite panels.

Finally, with funding support from Columbia Forest Products and Hercules Inc., Li’s group honed the process for commercial use, running scaled-up experiments and mill trials.

“For 50 years,” Li says, “the wood products industry has been arguing about what levels of formaldehyde emissions are safe for humans. But now some companies are taking a different approach — instead of explaining how much formaldehyde is wafting out of their wood products, they’re saying, ‘Our products are essentially formaldehyde-free.’”

Li’s bio-based breakthrough — which he calls a “whole new concept” in wood composites — is revolutionizing the nation’s $4.4 billion wood adhesives industry. The Portland-based behemoth Columbia Forest Products — North America’s largest manufacturer of hardwood plywood and hardwood veneer — is carving out a significant niche in the fast-growing “green” housing and construction fields. It took less than three years after OSU patented three adhesive formulas and licensed them to Delaware-based chemical giant Hercules Inc., for Columbia to convert its seven hardwood plywood plants to the nontoxic soy-based adhesives. The company, which produces more than half of U.S. interior wood composites, estimates that it replaced 47 million pounds of formaldehyde-based resins with soy-based adhesives in 2006.

This year, Columbia is beginning production of formaldehyde-free particleboard. Plywood and particleboard have distinct adhesive requirement, Li notes. Plywood uses the glue to bind thin layers of wood. Particleboard, on the other hand, is formed from sawdust-like bits of wood bonded together. One particleboard plant can consume as much adhesive as five plywood plants, according to Li.

“Particleboard creates a dramatic new demand for soy-based adhesives,” he notes.

For Oregon, whose forest industry employs more than 85,000 workers statewide, novel wood products like Li’s adhesive help fuel demand and bolster communities, particularly in rural counties hit hard by recent downturns in logging and manufacturing. Wood-plastic composites offer another potential boost. Li’s research team is developing a nontoxic alternative for outdoor construction: decks, cabins and children’s play structures. The new material, besides being strong and lightweight, would be free of such hazardous chemicals as arsenic and chromate, found in some treated wood.

The research focuses on the adhesion between the water-absorbing wood and the water-resisting plastic. Better adhesion translates to stronger materials. A novel wood-plastic composite using recycled carpets and wood is the team’s latest breakthrough.

Wood can also be a competitive source of liquid fuel in Oregon. A recent analysis by OSU economists found that ethanol made from wood cellulose yields the highest “net energy” return (84 percent), compared with canola (69 percent) and corn (20 percent) after subtracting production and transportation costs.

Just as fuels made from these sources can reduce U.S. dependence on foreign petroleum, soy-based adhesives can lessen the nation’s need for foreign sources of natural gas, from which formaldehyde is derived. “I get lots of phone calls about this new adhesive,” says Li. “One person said, ‘This is one of the greatest inventions I’ve seen in the past 50 years in terms of affecting peoples’ lives.’”