Online Edition | Washington State University | Pullman, Washington | Friday, October 5, 2001

Research News
Navy salutes plastic wood
By Tina Hilding, College of Engineering and Architecture

When it comes to building docks, piers and houses, it’s hard to improve on wood as a building material. But the U.S. Navy is betting more than $10 million that WSU’s Wood Materials and Engineering Laboratory can go one better.

Wood has always been a popular building material. It’s light and can be cut to size easier than steel or concrete. Fastening also is easy. But, as anyone who has had a leaky pipe, a leaky roof or a dock at the lake knows, wood rots and falls apart if it sits in water for a long time.

In recent years, the WMEL has been the leader in a quiet revolution to improve wood’s performance through the use of wood/plastic composites. The composites, made from a combination of the plastic found in milk jugs and wood fiber, were developed in the past decade and have become popular in the commercial market for such light-load applications as doors, windows, siding, flooring and decking.

In October, the U.S. Navy will begin installing support timbers that are wood/plastic composites on piers in Rhode Island and California, replacing the creosote-treated timbers that have created significant environmental concern. Designed at the WMEL as part of a $6.1-million contract, the composites look like wood, but they won’t degrade after being soaked for years in water, and they are resistant to the fungi that love to eat wood. Unlike the earlier versions of wood/plastic composites, the ones being used for the Navy piers can support heavy loads.

SEALING IN MOISTURE
Mike Wolcott, associate professor in the WMEL, has been the principal investigator on the Navy pier project. This year, he and a team of researchers received a two-year contract valued at about $4 million to study the condition of land-based wood structures owned by the Navy in coastal areas.

In the 1970s, a new era of energy-efficient materials and methods created significant changes in the residential construction industry. Homes were built with plastic coverings and insulation that helped to seal in heat and save on cooling costs. Those same seals, however, also lock in moisture. A generation later, researchers are trying to identify problematic areas of durability in the wood structures and possible material-based solutions to the problems.

"We are helping the Navy assess how big a problem they have with durability," Wolcott said.

The contract, provided by the Office of Naval Research, calls for assessing the feasibility of using the thermoplastic/wood composites to increase the structures’ durability. Besides WSU, other entities involved in the project include the University of Maine, Pennsylvania State University, U.S. Forest Service, Naval Research Laboratory, Naval Facilities Engineering Service Center, Honeywell Corp. and Strandex Corp.

HEATING UP PERFORMANCE
Throughout its history, WSU’s wood laboratory has led the way in developing new and improved products from forest resources, Wolcott said. In earlier years, the need to make better use of resources drove scientists and engineers to develop a wood product that combined the waste from wood processing with synthetic resins. The resulting plywood and particleboard contained between 3 and 15 percent plastic.

In recent years and with improvements in technology, he said, the emphasis has changed to improving the performance of the products.

Researchers found that the thermosetting resins used in traditional particleboard undergo chemical changes when they are heated. Once cured, the resins become solid, but they can’t be reprocessed.

Newly developed thermoplastics have changed that. The composites, which are solid at room temperature, become fluid when heated. However, the transformation does not change its chemical composition. This discovery allows researchers (and ultimately manufacturers) to extrude the material, forming it into complex, efficient and stronger product shapes.

By having the plastic be a more significant part of the composite, the performance of the material can be improved. In particular, the plastic acts as a barrier to moisture and fungus, providing resistance to decay. In short, the product is water resistant.

MELTDOWN
While increasing moisture resistance is one aspect of improved performance, the researchers also seek to improve the development of the wood/plastic composite forms. Imperfection in forms can result in poor performance in construction.

To that end, Wolcott is focusing on rheology, or the study of melt flow, to improve product forms. (Melt flow refers to the way the material flows when it is heated.)

Engineers do not clearly understand how highly filled plastics flow when they’re heated to form shapes. For instance, he says, the addition of very low levels of additives significantly alters the flow of the materials in ways very different from just plastics. Better understanding of melt flow will enable the engineers to make more precise dies.

BEYOND SALAD DRESSING
The researchers also are looking at additives that will help the wood and plastic better meld. Like oil-and-vinegar salad dressings, wood and plastic don’t naturally mix. When developing wood/plastic composites, the researchers agitate the two to mix them. However, the mechanical forces can break down, fracture or damage the wood, resulting in a lower performance product. The lab continues to work on developing and improving additives to improve the interaction between the two materials.

ORGANIC PLASTIC
Ultimately, Wolcott says, wood-synthetics composites are mere precursors to future advances in biomaterials. Wolcott and environmental engineer Frank Loge have become interested in a bacterium that produces a biodegradable polyester type of thermoplastic when it consumes sugar. While humans produce fat to store the extra sugar they eat, the bacteria produce plastic.

Wood contains polymers that degrade to sugars during processing. They are not very useful to the products’ end performance. Wolcott and Loge’s idea is to have the bacteria consume the sugars and use the plastic it produces to make wood/plastic composites. Relying on biomass to produce a material that acts like a synthetic would use renewable rather than nonrenewable resources, like oil, to make synthetics.

Wolcott envisions that the WMEL will again be on the cutting edge of developing these materials into useful products. The best part, he says, is that the work makes a difference in people’s lives.

"It doesn’t sit in a library someplace," Wolcott said.