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February 2004

Plastic Lumber Gains Acceptance for Structural Applications

Recycled plastics have been a valuable resource for makers of a wide variety of building products for years. Among those products, plastic lumber has been gaining market acceptance among builders and homeowners alike. Compared to similar, time-honored wood products, plastic lumber is maintenance free, will not rot or mildew and is holding up exactly as promised over time. These qualities, along with engineering advances in reinforcing fibers, have resulted in plastic lumber products well suited for more structural applications.

Alan Robbins is president of the Plastic Lumber Trade Association and president of the Plastic Lumber Company of Akron, Ohio. According to Mr. Robbins, “Structural applications for plastic lumber products are a very new area, and the market needs for building materials with qualities of plastic lumber are enormous,” he said. Plastic lumber does not deteriorate and will not leach anything into surrounding water, soil or other aspects of the environment. In addition, insects are not attracted to it. From the standpoint of fabrication, plastic lumber offers builders most of the characteristics of traditional wood building materials, eliminating the need for special tools or training.

A deck supported by recycled HDPE plastic.Plastic lumber is typically made from recycled high-density polyethylene (HDPE) plastics. Postconsumer items such as discarded milk and bulk water jugs are the feedstock for many plastic lumber products. Without reinforcement though, polyethylene based plastic lumber is more flexible than wood products of the same dimensions.

Mark Siemon, president of Phoenix Recycled Plastics, Inc. of Norristown, Pennsylvania, manufacturers of plastic lumber said, “A significant portion of our business involves outdoor decking projects. In the beginning, our plastic lumber products were used primarily on the surface of the deck, with traditional treated lumber framing underneath. We first became involved with structural applications when our customers began asking for an all-plastic deck.”

To achieve the required integrity for structural applications, recycled HDPE is blended with glass fibers for additional strength and rigidity. Bedford Technology, LLC in Worthington, Minnesota has been producing plastic lumber for 12 years, and structural plastic lumber for the past 4 years. Bedford president Brian Larsen notes, “The blend includes a percentage of glass strands, a portion of which is derived from recycled post-industrial glass. This results in a structural plastic lumber product with improved strength and flexure – up to four times as stiff a normal plastic lumber and with much less creep than HDPE,” he said. “Creep” is the tendency of plastic lumber to expand or contract, effectively changing length with prolonged exposure to heat or extreme cold.

Bedford Technology offers a full line of structural plastic lumber products in the full range of dimensional lumber sizes from 2 x 2s to as large as 10 x 10 beams up to 20 feet in length. All products are offered in a wide range of maintenance free colors.

Significant milestone
A deterrent for choosing structural plastic lumber over traditional wood building products has been the lack of an acceptable testing standard for manufacturers. In response, the American Society of Testing and Materials, or ASTM, have been busy developing standards for testing structural plastic lumber.

Once in place, the standards will establish a benchmark for engineers to gauge material performance and greatly simplify the process of specifying materials for the job. According to Brian Larsen, who sits on the committee developing the new standards, “The process with ASTM is moving along nicely. We expect the standards to be finished and in place in 6 months to a year.”

Bright future
Applications for structural plastic lumber include such items as railroad ties, retaining wall and landscaping “timbers,” and marine pilings, as well as plastic lumber in all of the popular sizes for building projects. Nearly all sizes of dimensional lumber (traditional wood building products) – such as 2 x 4s, 2 x 6s and larger – are now available in structural plastic. The availability of these sizes opens huge new markets for outdoor furniture, benches and municipal accessories such as bike stands, trash can enclosures and park fixtures now made from recycled plastics.

“There is tremendous interest right now in structural plastic lumber,” said Brian Larsen. “We feel the industry is poised to go straight up. With near zero maintenance and a long service life, municipalities and marine applications hold great promise for new projects involving plastic. And more and more homeowners are interested in eliminating CCA treated lumber from their yards as well,” he added.

Structural Plastic LumberTreated wood ban helps
Some of the recent interest in plastic lumber has been due to in part to the Federal government’s general ban on the sale of CCA (chromated copper arsenate) pressure treated lumber. Increased government concern over the potential health risks associated with arsenic in this type of traditional “treated lumber” lead to the ban on sales to consumers, for non-industrial uses, effective December 31, 2003.

Under the ban, retailers with inventories of CCA treated lumber are allowed to sell those stocks. Once depleted, sales of treated lumber will be restricted to that treated with copper azole and alkaline copper quaternary (ACQ) only. The only exception to the ban on CCA treated lumber is industrial applications such as marine waterfronts, where the acceptable treatments don’t provide adequate long-term performance.

Compared to CCA, copper azole is a more environmentally friendly compound, but wood treated with copper azole doesn’t hold up as well. ACQ treated lumber is in widespread use throughout Europe and Asia. When treated to standards, the new-generation preservatives provide roughly equal performance. Both copper azole and alkaline copper quaternary rely on copper as the primary active ingredient with an organic fungicide (azole or quaternary) to protect against copper-resistant fungi.

The new generation preservatives are expected to boost prices for treated lumber by as much as 30%. This increase will bring treated lumber prices a bit closer to plastic lumber of the same size. Historically, plastic lumber products have been priced two to three times higher than similar wood materials.

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