Woodfibre Plastic Composites: No Deck Is An Island

Meeting rooms at the 7th annual International Conference on Woodfiber-Plastic Composites were overflowing, a testament to the interest in the fastest growing segment of the plastics industry. Sales of WPC and other natural fibre-based products have been growing at a rate of 25% annually since 1998, creating a rapidly expanding R&D sub-industry and numerous collaborations between processors, suppliers, universities and other research groups.

“We are witnessing the beginning of a new industry,” said professor John Balatinecz, University of Toronto, Faculty of Forestry.

Demand for WPC deck boards and railing has played a critical role in the development of this new industry. Plastic decking and railing systems of all types, both WPC-based and non-WPC based, captured more than 11% of the residential deck-building market across North America, according to a recent report issued by the Environment & Plastics Industry Council. EPIC estimates sales of plastic decking products will grow to about US$845 million by 2005 from US$395 million in 2001.

Yet, the success of plastic decking had some conference speakers concerned that the fledgling plastic wood- and natural-fibre composite industry could be putting all its eggs in one basket.

“While there is still a lot of potential for growth in decking, the market may be becoming saturated with capacity and competition,” said professor Don Bender, Washington State University. He said new research and development is ready to push WPC products into largely untapped, non-traditional areas such as structural, industrial, marine and low-rise construction markets.

STRUCTURAL AND MARINE APPLICATIONS SHOW PROMISE

Traditional plastic lumber has lower stiffness and flexural modulus compared with natural wood, which has generally limited the applications of these materials in structural applications. New grades of compounded WPC lumber, as well as innovative designs and tooling, are getting around these limitations.

The U.S. Navy has recently granted Bender and his colleague, WSU professor Mike Wolcott, funds to demonstrate the commercial feasibility of manufacturing code-conforming products for marine structural applications, such as load-bearing marine decking and fendering or chocking, the wall portion of a pier against which boats dock.

Bender says that unlike residential decking, the initial cost of marine decking and timber is a less important factor in determining what type of decking system is eventually installed at a marina or port. Long-term reduction of maintenance and replacement costs of dock and pier decking structures in the harsh marine environment is more important for operators of these facilities. The market for replacement of degraded marine timber is estimated to be 7,000 to 8,000 tons/yr, worth about US$250 million.

In order to demonstrate the suitability of WPC materials in these applications, Bender’s group designed, tested and manufactured deck boards installed at a U.S. Navy facility in Rhode Island. The boards were extruded into hollow, 4 in. x 6 in. sections on a Milacron 86-mm in-line conical twin-screw extruder at Washington State’s engineering lab. The PVC boards were filled with 50% pine wood flour. The sections were designed to withstand a 600 lb/ft2 distributed load, much higher than 40 lb/ft2 generally taken as the standard for non-load-bearing residential deck surfaces. The deck section was also designed to hold a 16,000 lb. midspan single-point load from forklift travel.

In another project, the WSU facility designed and made pier chockings installed at a Naval facility in California. The 4 in. x 12 in. chocks were co-extrusions consisting of an inner foam web and an outer high-density flange. The two-layer structure facilitates dissipation of energy during docking maneuvers. The foam webbing is made of HDPE and approximately 45% maple wood flour; while the flange is a blend of HDPE and approximately 30% maple wood flour. In both projects, the research group used a Simplex Solutions Inc. enhanced modeling program to optimize mechanical properties such as strength, stiffness, water resistance, decay resistance and processing characteristics.

TOTAL IMMERSION

The University of Maine’s Advanced Engineered Wood Composites (AEWC) Center is investigating potential structural applications for WPC materials, according to Doug Gardner, professor of wood science at the university. Gardner said the Center is developing composite formulations consisting of polypropylene, wood fibre, glass-fibre and carbon.

“We prefer using polypropylene as a base resin in wood- and natural-fibre composite blends because we feel it has better mechanical and processing properties,” Gardner reported. He says HDPE has become the standard base resin for wood-plastic composites simply because it was the most widely available recycled resin when the industry started producing plastic lumber.

The facility has also been working on developing a variety of non-structural marine applications. In one demonstration project, it produced about 1000 sq. ft. of WPC marine decking installed at a U.S. Coast Guard pier as a replacement for pressure-treated wood. The 5/4 in. by 6 in. planks are made of 60% wood, polypropylene and an additives package consisting of lubricants, coupling agents and colorants. The planks are extruded on a Davis-Standard parallel twin-screw Woodtruder. The Woodtruder has a L/D of 28:1 and a mounted single-screw, side-injection extruder. Gardner said the WPC planks have a flexural modulus of 685,000 psi, which makes them stiffer than WPC lumber commonly used in residential decking, but not as stiff as natural wood.

Gardner reports that his R&D facility, which has a mandate to develop proprietary and licensable technology, is also working on commercializing marine retaining walls made from WPC materials. The aim is to develop a product that will offer cost and performance advantages over concrete, steel and solid plastic retaining walls currently in use.

“Compared to a straight plastic wall, a retaining wall made from woodfibre plastic composite materials is cheaper, plus the wood adds stiffness,” says Gardner. The applications are especially challenging because part or most of the wall will be continuously immersed in water. “We have to carefully evaluate how much wood we can put into this, because we have to have good encapsulation.”

NEW MARKETS, NEW THREATS

In the view of John Balatinecz, professor emeritus, University of Toronto, Faculty of Forestry, processors and designers must look beyond the decking and railing market for growth in wood- and natural-fibre plastic composite applications. Balatinecz, filling in for James Morton of Principia Partners (Exton, PA), presented an overview of current and emerging applications for natural- and wood-fibre composites.

Balatinecz observed that WPCs, materials originally developed as an outlet for plastic scrap, have emerged today as highly engineered materials with demonstrated superior performance. He said one of the reasons decking has predominated over other commercialized WPC products is that it is relatively cheap to get into. The most important emerging markets for WPC materials over the next five to 10 years will be windows/doors, roofing, fencing and furniture. According to a report released by Freedonia Group Inc. (Cleveland, OH), U.S. demand for fencing products is growing at an annual rate of nearly 5% and is expected to reach $3.3 billion in 2007. Presently, vinyl fencing is the dominant plastic product, but the report concedes that wood-plastic lumber, especially in styles that imitate wood, will most likely take up an increasing fraction of sales as new products are introduced. Balatinecz said furniture, in particular, is a market with huge, untapped potential for new applications of WPC materials

“There are many furniture components, such as seat back and arm rails, that are tremendously wasteful to produce from wood. Processors need to talk with furniture manufacturers to see if it would be feasible to make these parts from wood-plastic.”

Demand for
decking has made North American producers leaders in WPC technology, but Europe is leading in producing natural-fibre plastic composites for applications such as automotive parts. Europe also has a better supply of recycled plastic materials.

Balatinecz reminded the audience, with attendees from around the world, that the wood- and natural-fibre plastic composite industry was still in its infancy, with many challenges ahead. Manufacturers and processors can expect to deal with price pressures, renewed competition from alternative materials and product lines, and the need to continuously improve the performance and quality of products made from WPCs.

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Standards crucial for structural WPC

Standards can sometimes be used to exclude new products from the marketplace, Don Bender, professor, Wood Materials & Engineering Lab, Washington State University, told the audience at the 7th International Conference on Woodfiber-Plastic Composites. This can happen when testing and other standards for new products have yet to be developed, making buyers more inclined to use old products for which standards exist.

Bender said three ASTM testing standards for structural wood- and natural-fiber plastic composites are currently in draft form and being balloted for final approval in ASTM committees. One standard relates to test methods for evaluating mechanical and physical properties of WPC products; a second standard establishes design values for WPC products; a final standard establishes performance ratings for WPC deck boards and guard rail systems. In the U.S., the standards apply to civilian, non-military applications only. Final standards are expected to be approved within the next 12 months.

On the Canadian side, the Canadian Construction Materials Centre, a branch of the National Research Council in Ottawa, is working with manufacturers to develop tests to assess whether plastic-based products comply with building code requirements.