Nature provides inspiration for important new adhesive

Researchers from the College of Forestry at Oregon State University have developed a new group of adhesives that may revolutionize a large portion of the wood products industry, and have important environmental and economic benefits.

The discovery has already resulted in three pending patents and should lead to a wide range of new products. But it was originally based on the aroused curiosity of Kaichang Li, an OSU assistant professor, who was harvesting mussels one day from their rocky home at the ocean's edge.

Li observed mussels being pounded by ocean waves, and wondered how they could cling so tenaciously to rocks by their thread-like tentacles.

"I was amazed at the ability of these small mollusks to attach themselves so strongly to rocks," said Li, who is an expert in wood chemistry and adhesives in the OSU Department of Wood Science and Engineering. "Thinking about it, I didn't know of any other type of adhesive that could work this well in water and withstand so much force."

Li decided to look much more closely at the chemistry of the mussels' byssus, which are small threads that attach them to rocks and other surfaces. The byssus thread is a protein with a very unusual composition - an abundant level of a phenolic hydroxyl group and an amino group - that results in the ability of mussels to stick tightly to surfaces despite being inundated in water.

"Clearly the mussels have evolved with the ability to make this protein so they can cling to rocks despite wave forces," Li said. "It's quite remarkable, just an incredibly unique natural feature."

The mussel protein is a superior adhesive, but not readily available. In trying to identify a protein that could be adapted for this purpose, Li had another inspiration at lunch - while eating tofu.

"Soy beans, from which tofu are made, are a crop that's abundantly produced in the U.S. and has a very high content of protein," Li said. Soy protein is inexpensive and renewable, but it lacks the unique amino acid with phenolic hydroxyl groups that provide adhesive properties. Li's research group was able to add these amino acids to soy protein, and make it work like a mussel-protein adhesive. Then they began to develop other strong and water-resistant wood adhesives from renewable natural materials using mussel protein as a model. The research work has resulted in 11 papers in journals such as Macromolecular Rapid Communications and the Journal of Adhesion Science and Technology.

The new wood adhesives are made from natural resources such as soy flour and lignin. They may replace the formaldehyde-based wood adhesives currently used to make some wood composite products such as plywood, oriented strand board, particle board, and laminated veneer lumber products - all major components of home construction and many other uses.

One of these patented adhesives is currently cost-competitive with a commonly used urea-formaldehyde resin, researchers say, but does not use formaldehyde or other toxic chemicals. Formaldehyde fumes are associated with some health problems, including eye and throat irritation. The chemical has been shown to be a human carcinogen, and in some circumstances it may be a concern in some residential building products.

The other key advantage of the new adhesives is their superior strength and water resistance.

"The plywood we make with this adhesive can be boiled for several hours and the adhesive holds as strong as ever," Li said. "Regular plywood bonded with urea-formaldehyde resins could never do that."

The first commercial application of the adhesive will be to make decorative hardwood plywood for high-quality interior uses. But the adhesive can also be used in making softwood plywood, particleboard, medium density fiberboard, oriented strand board, and the laminated veneer lumber that is finding increasing use to replace conventional joists and beams in construction.

Techniques have also been explored to create the new adhesives from tree bark or wood decayed by brown rot fungus. Regardless of the material used to produce the adhesives, they are renewable and may reduce the need for the currently used urea-formaldehyde wood adhesives that have health concerns, and are based on increasingly expensive petroleum.

"This technology looks extremely promising in a variety of markets," said Brian Wall of the OSU Office of Technology Transfer, which has already reached the first licensing agreement with a company on a product that will be in commercial application soon. "We are actively talking to and looking for additional licensees."

A few years ago, the forest products industry in the U.S. and Canada was spending more than $2 billion a year on wood adhesives, and the wood composites industry is one of the largest manufacturing sectors in the United States.

"Based on the successful commercial application of our adhesives, the wood adhesive industry and wood products industry are going to see some major changes in the next few years," Li said. "It appears our adhesives will have a huge impact in the creation of improved wood products that work better and are safe in the environment."

The new adhesive should improve both work and living environments, and enhance the global competitiveness of U.S. companies, researchers say. They can also provide another market for the nation's soybean farmers - the new adhesives use a tremendous amount of soy flour.

Source : Oregon State University