Using Waste Products

Picture: Timber

Wood-plastic composites, often used for such things as outdoor decking, are one of the fastest growing components of the wood composites industry. "Composite products made from wood and plastic are highly desirable for their low maintenance and ability to resist rot," said Kaichang Li, an associate professor in the Oregon State University. "But their use has been limited because of high cost and low strength, a result of inadequate adhesion between the wood fibres and plastic."

Fundamentally, Li said, this is because wood and plastic are like oil and water, and do not mix well. Wood is hydrophilic – it absorbs water – and plastic is hydrophobic, repelling it. A "compatibilizer," typically a polymer that bridges the interface between the wood and plastic in these products, improves stress transfer and increases their strength and stiffness.

The new wood-plastic composites use superior “compatibilizers” developed in Li's laboratory, and an innovative technology for mixing wood and thermoplastics such as nylons, in which the melting temperature of the plastic is higher than the wood degradation temperature.

With this approach, the new wood-plastic composites can use very inexpensive plastics such as those found in old carpet fibres – about 4.4 billion pounds of which are now wasted every year, going into landfills where they are extremely slow to biodegrade and pose a significant waste disposal problem.

They could also open the door for improved utilization of low-grade woody biomass from needed thinning of Oregon forests, which is increasingly being done to improve forest health and prevent catastrophic wildfire.

The technology may prompt a major expansion of the wood-plastic composite industry into new types of products and uses, experts say. In particular, such products may help further replace wood treated with chemical preservatives, some of which have already been banned due to health and environmental concerns.; Source: Oregon State University