With public awareness of the need for efficient use of timber and protection of forestlands has come a shift in the source of raw materials from old-growth forests to intensively managed, short-rotation, forest plantations.

Unfortunately, the demand for wood products cannot be met even with the fastest growing trees. Although these tree "crops" are adequate for such products as paper, the wood from these trees does not have the properties necessary for structural products. As the world population continues to grow, we must discover ways to produce the materials we need from renewable resources.

The College of Natural Resources at Virginia Tech has been working on a process to enhance the strength and stiffness of low-density wood species using steam, heat, and mechanical compression. The processes has been termed "Viscoelastic Thermal Compression," or VTC (which some people interpret as meanting "Virginia Tech compressed" wood).

"Viscoelastic" describes the natural characteristic of the polymers that comprise the cell wall in all wood plants. Wood is made of three primary polymers -- cellulose, hemicellulose, and lignin. These polymers have both viscous (ability to flow) and elastic (ability to springback) behavior. Heat and moisture can be used to manipulate the viscoelastic behavior.

Wood is also a porous material, being comprised of long slender cells. About one-half the volume of wood is void space, but this varies widely by species and rate of tree growth. The strength and stiffness of wood is directly proportional to density. The VTC process increases the density of wood by softening the cell wall prior to compression in a mechanical device.

"We have increased density by as much as 130 percent, with comparable increases in strength and stiffness," reports Fred Kamke, professor of wood science. "We have also stumbled upon a phenomenon that increases strength and stiffness beyond what is expected from density increases alone. Although we don’t completely understand what is happening, we believe the high temperature during the process chemically modifies the cell wall, resulting in the creation of additional covalent bonding at the molecular level."

Implementing the VTC process to turn low-density wood into high performance products will require more complex processing techniques and increased manufacturing cost, he explains. But there is a significant return on investment. "The extra effort can be considered a trade-off for a 50 to 75 year deduction in harvest rotation time. This means, at the current level of timber demand in the United States, the land area required for timber harvesting could be reduced to less than 25 percent of what is needed today."

Virginia Tech first discovered this viscoelastic behavior by accident in 1985. Since that time, the university's researchers have received funding from the USDA to build a laboratory-scale device to produce and evaluate VTC wood, to optimize the process, and to determine the influence of the VTC process on other wood properties.

In addition to his composites research, Kamke directs the one-year old Wood-Based Composites Center (http:// /www.wbc.vt.edu), a group composed of faculty members from Virginia Tech's wood science department and several other colleges and universities with support from industry. The cooperative effort addresses the educational and research needs of the wood-based composites industry.

Virginia Tech has been a leader in education and research for the broader forest products industry for more than 30 years. Recognizing that composites are the future of the wood products industry, the center is a long-term commitment by the university and involves a concentration of resources and faculty in this critical field. The center’s lab is housed at the Brooks Forest Products Center and specializes in adhesives, manufacturing of composites, materials science, performance of composites, and resources and marketing.

Current industry members include Borden Chemical, Georgia Pacific Resins, Huntsman Polyurethanes, National Starch and Chemical, Neste Resins, Champion International, Dow Chemical Company, J. M. Huber Corp., Louisiana-Pacific, and Weyerhaeuser.