In the future, manufacturers of forest products will be reconstituting smaller and smaller pieces of wood. Modern technology already combines small pieces, particles, or strands of wood and other polymers to produce bigger boards. Modern skis are made from foam core wrapped in wood, not cut from trees with a 20-inch diameter.
Wolfgang Glasser, professor emeritus of wood science and forest products, who founded the Biobased Materials Center at Virginia Tech, holds up a small block of flooring made in Japan. The product has a millimeter-thick surface layer of acetylated wood on a mundane base of plywood. The inner layers, where a beautiful surface does not matter, consist of a fiber core.
“It will never change color or develop a stain. It never needs to be resealed. It won't shrink. Essentially, it will never break down,” says Glasser. "In finding a way to make floors from their scarce lumber supply, the Japanese have concocted a floor with better properties."
Fred Kamke, composites researcher with Virginia Tech's Brooks Forest Products Center, says the fastest growing segment of the wood-based composites industry is structural lumber substitutes. Oriented strand board (OSB) - a structural panel made from wood strands bonded with a water durable adhesive - is now used for floor and roof sheathing. Hardboard and medium density fiberboard are used in furniture, cabinets, and exterior siding.
"The properties and attributes of composites are engineered to match the needs of the consumer, and in most cases the composite out-performs the solid wood from which it was born," says Kamke.
I-beams made with plywood, OSB, or metal tubing as the "web" material are becoming popular as floor joists in residential construction. A new product, called parallel strand lumber (PSL), is made from eight-foot long strips of wood, combined with adhesive, and extruded through a microwave curing process to produce an 18-inch by 48-inch billet in virtually any length desired. PSL is essentially a reconstituted rectangular tree, says Kamke. "PSL can be used just like solid wood, only it's stronger and much more versatile."
Economics and supply and demand drive it all. The top layer of the Japanese floor block costs $1.50 per pound. The fiber core layers beneath cost from five to 50 cents a pound. For the furniture industry the ramifications of composites are immense, says Kamke.
Some of the savings may disappear, however, until research can provide inexpensive non-toxic processing and adhesives for composite manufacture. If the government increases regulation of potentially toxic materials, as it did with the use of formaldehyde in home construction materials, more expensive processes and adhesives will have to be used. Research is underway to find ways to use wood's own glues and to harness nature's self-assembly techniques to bind material molecules together.
That's right - "biobased materials" are not only made of particles of wood bonded together; now, scientists are gluing together molecules from wood residues.
Glasser manipulates the molecules that make up the chemistry of wood (and peanut hulls, coconut husk, straw, and other such agricultural residue). He combines these cellulose, hemicellulose, and lignin molecules with other materials for applications Nature may never have intended, but would approve.
Scientists such as Glasser are inventing materials that will be stronger, tougher, more adaptable, more conductive, lighter, quieter, more flexible, more sensitive, thinner, faster, more elastic, more versatile - and biodegradable. "Nature knows how to get rid of it's polymers," he says.
For example, he has a grant from IBM to create printed circuit boards made with lignin and without lead so that the material will safely degrade when equipment is discarded.
Glasser has also received funding to study the surface modification of cellulose fibers and films. "We want the material to self-assemble into molecular composites, just as many of nature's materials do. One aim is to develop cotton-like fibers with sort of a Teflon-coating so that you end up with a light-weight, water-repellent fiber."
Natural resource products you know include bandages and baby diapers. New research results from Virginia Tech include:
– a process to combine pieces of wood with recycled plastics to form structural composites, and reduce the amount of material that ends up in a landfill;
– a non-toxic cellulose processing technique that could be used to make artificial skin, better bandages, and improved membranes for kidney dialysis machines;
– biomass-derived sorbents to purify water contaminated with pesticides;
– adhesives, coatings, and foam products from lignin-based polymers; and
– films and thermoplastics from xylan-derivatives of agricultural residue.
— Written by Lynn Davis, College of Natural Resources
