More than just decking

Innovation is the key to growing the wood-plastic composite (WPCs) market. Yet, while all attendees at the 8th International Conference of Woodfiber-Plastic Composites in Madison, WI, doubtless agreed with this assessment offered by Lou Rossi, senior partner at Principia Partners (Exton, PA), it was less obvious how to achieve this goal.

Rossi reported that WPC penetration in the multi-billion dollar decking/railing market is expected to grow from 15% in 2004 to 25% in 2009, an increase of only about 2% per year. He said the WPC segment of the decking industry is maturing and the industry faces challenges achieving higher growth.

“Advances in innovation can’t simply be more tweaks to basic decking products,” Rossi said. “For example, in the manufacture of WPC planks, the industry has gone from a 5×4-inch plank to a hollow, or tongue-and-groove, [then] back to a 5×4-inch plank.”

Other examples of tweaking include switching from reclaim to virgin plastics, and from one type of wood to another, Rossi said. Also, WPC decking producers have only marginally expanded their colour palettes, from one to two colours up to five colours for some product lines.

“Sooner or later you run out of tweaks,” Rossi explained.

Rossi pinpointed aesthetics and colour as two areas where WPC decking and railing manufacturers could innovate to differentiate themselves from competitors.

In Principa’s 2003 survey of composite decking needs, homeowners rated aesthetics and colour choices, along with design flexibility, as the most important factors influencing their satisfaction with composite decking systems.

Taking the innovation credo to heart, Keller Products Inc. (Manchester, NH), a manufacturer of furniture products, has launched a project to explore and develop new markets for extruded parts made of WPCs.

The company began the project by evaluating many types of WPC materials, in attempt to find a material with similar properties to wood, said John Keller, the firm’s chief operating officer.

“Traditional wood-plastic composites are made from 60% wood flour in a polyethylene (PE) or polypropylene (PP) matrix, and are chemically resistant at the surface,” Keller explained. “They won’t accept paint or stain.”

So far, Keller Products’ top candidate feels like real wood, is sandable, paintable and accepts most stains. The U.S.-made material is 30 to 40% wood flour, with an acrylonitrile-butadiene-styrene copolymer (ABS) base, Keller said. ABS provides benefits such as good impact resistance, which is important in applications like trimboards.

Keller Products is using a new, 1.5-inch, single-screw Davis-Standard extrusion line at its Extrusion Technology Center to evaluate the material for applications in the furniture industry. Keller believes there is a large growth potential for WPCs in the ready-to-assemble furniture market, including shelving, desks and bookcases. He also sees potential for WPCs in marine applications, such as boat cabin trim, which is traditionally made of wood.

Keller is optimistic that the paintability of the new product will distinguish the company in the marketplace. “In a trimboard, for instance, you can apply an antique brown finish to the WPC, and match the base wood of a room or hallway,” he said.

THE NEXT WAVE

In fact, WPCs have already sailed into the view of the U.S. Navy, which is investing in research to commercialize WPCs in marine applications.

Wood replacement was costing the Navy US$250 million a year, and the Navy set out to explore WPCs as a possible to reducing its pier maintenance costs.

In 2001, the Navy presented Washington State University (WSU) with a US$4 million, two-year contract to study wood timber in coastal areas. After preliminary studies proved that WPCs could significantly reduce costs, the Navy awarded WSU another US$1.6 million in 2002.

In one of the first applications of WPCs in shipyards, WSU designed and manufactured pier chocking for a naval facility in Port Hueneme, CA. The 4×12-inch chocks were co-extrusions consisting of an inner foam web and an outer high-density flange. The foam webbing is made of about 45% maple wood flour and 55% high-density polyethylene (HDPE).

According to John Hermanson, an engineer with the U.S. Forest Products Laboratory (Madison, WI), the inner foam layer helps with energy dissipation during docking maneuvers. Like foam webbing, the outer or flange layer, of the chocks consists of a blend of HDPE and about 30% maple wood flour. Hermanson said the boards are easily machined and have performed well since being installed in 2003.

In another project, the WSU group designed, tested and manufactured deck boards that were installed at a Naval facility in Rhode Island.

The boards were extruded into hollow 4×6-inch sections using an 86mm in-line conical, twin-screw extruder. The polyvinyl chloride (PVC) deck boards were filled with 50% pine wood flour.

Hermanson said one of the unique things about the boards was the high loading rate they were designed to withstand. Each section was designed to withstand up to 600ft/lb distributed load, much higher than the 40ft/lb commonly used for non-load bearing residential deck surfaces. The deck section was also designed to hold a 16,000lb midspan single-point load from forklift travel.

“The boards were designed using a computational process to balance shape and thickness with structural needs,” Hermanson said. “Also, the boards are unique [because] no nails were used and [because they] are held in place by v-shaped grooves and rails below the surface.”

Another non-traditional area of growth for WPCs is in recreational bridges. A 2004 WSU survey discovered there were 7,468 trail bridges in the U.S. with 194 projects to upgrade or build new bridges. Many of the bridges are short span, where the main performance requirements are durability and strength. WSU found that bridge manufacturers rated the durability as one of the most appealing aspects of WPCs.

FOAMING, OTHER ADDITIVES IMPROVE WPC PERFORMANCE

Despite the durability of WPCs, processors still have the challenge of making plastic look and feel like real wood.

To resolve this problem, processors of WPCs have begun exploring structural foam molding as a method for replacing products that have been traditionally made of wood because products made of structural foam have physical properties much like real wood.

“Foam will be the next wave of wood replacement after decking,” said Don Murray, industrial sales manager of American Wood Fibers (Columbia, MD), a seller of wood flour and plastic master batches.

During the past three years, more foam WPCs have appeared, Murray noted. The new composites are based on ABS, acrylic-styrene-acrylonitrile (ASA), styrene acrylonitrile monolayer, two-layer and three-layer profiles. Profiles with larger dimensions and complex shapes are also being made. Density reductions, in comparison to non-foamed material, range from 5 to 50% and while reductions in wood-filler levels range from 3 to 60%.

“Most wood-foam profiles are co-extruded with unfoamed cap layers over foam cores,” said Murray. “The cap layers may be a few thousandths of an inch thick to provide colour, decoration or UV stability.”

U.S. Forest Products Laboratory’s Hermanson said he is seeing an increase in the demand for foam WPCs.

“Foaming provides a lower density board that improves energy absorption. The lower density is more of a match to real wood. That means a foamed WPC board performs more like real wood, which makes installers happy,” he said.

DuPont has recently introduced a new coupling agent, Fusabond, which could significantly improve strength and reduce water absorption in wood-polyethylene (PE) composites, the company said. Injection molded samples of high-density polyethylene (HDPE) with 25% wood flour, coupled with small amounts of Fusabond W PC-576D, produced improvements in tensile and flex strength compared with WPCs contain
ing no coupling agent.

Earlier trials with a typical WPC formulation consisting of HDPE with 55% wood filler, showed that adding 0.5% Fusabond W PC-576D could provide a three-fold reduction in water absorption after 30 days, a two-fold increase in strength, as well as higher stiffness, compared with no coupling agent.

“A reduction in water absorption in WPC products is important because it helps improve resistance to rot,” said Megan O’Brien, marketing programs manager for DuPont Industrial Polymers (Wilmington, DE). “This helps in the longevity of the product and improves warranty performance.”

The enhanced performance of Fusabond W PC-576D is a result of a new coupling technology that involves an ethylene copolymer with an anhydride functionality incorporated in its polymer backbone.

“This (new polymer structure) allows us to build in much higher levels of anhydride than our earlier grades,” O’Brien said. “This creates more sites for chemical links between cellulose fibers and the polymer matrix.”

At the WPC conference, engineers from the Norwegian University of Science and Technology described a one-step process for producing silane cross-linked PE/wood composites. Researchers, Magnus Bengtsson and Kristiina Oksman, said the method is better suited to industrial processes than either post treatment of WPCs with silane solution, or a two-step process. Silane cross-linking produces a WPC with better properties, including improved stiffness.

A study conducted by researchers at Epoch Composite Products Inc. (Lamar, MO), found variations in the weathering characteristics of the WPC depended on the types of additives and colourants used in the formulation. The study used up to 50% wood flour filler in virgin and reprocessed HDPE resin, with different colour pigment packages added at a concentration of 5%.

The study found that the addition of an UV anti-oxidant package, improved surface stability and integrity, but did not prevent colour shift. The study also found that mixed-metal oxide pigments were not effective in WPC, and that reprocessed material adversely affected weathering characteristics. Surface degradation was observed in 100% of WPCs with reprocessed HDPE.

STRIVING FOR INNOVATION

However, research into WPCs will eventually pay off because of the massive potential market for the material. The potential market for WPC technology is US$26 billion,” Principia’s Rossi told attendees. “At US$5 billion in current sales, WPC is less than 20% of the way there.”

Untapped markets for WPC include building products, industrial, infrastructure, transportation and consumer goods.

With innovation on the minds of all the WPC Conference attendees, Dr. Hans Korte of Innovationsberstung Holz & Fasern (Wismar, Germany), described a study that found differences in the properties of WPCs made on different production equipment

Equipment variations included two different hot-cool-mixing devices, two different twin-screw extruders, a single-screw extruder and a hot press. WPCs produced on different equipment were found to have different properties — in some cases significant — such as modulus of elasticity, density and water absorption, even when the wood to polymer ratio was the same. Korte could not fully explain the results.

Researchers in the civil and environmental engineering department at the University of Maine gave details of the structural design of an innovative hollow extruded WPC sheet piling used in a waterfront retaining structure.

Waterfront retaining walls are usually made of either wood, metal, concrete, or vinyl. The objective of the research was to develop a WPC structure that would be more durable and cost-effective than those materials. The researchers are currently developing prototype designs of the sheet piling based on a material composed of 40% PP, 50% wood flour and 10% additives.

Finite Element Analysis was used to confirm a preliminary design of a 13-foot high wall with an optimized, hollow “Z” section geometry. The first extrusion runs were conducted in July at the University of Maine’s research facility, with full-scale structural testing scheduled for the fall. Critical issues to be answered are durability and creep after marine exposure.

CUSTOMER NEEDS DRIVE INNOVATION

However, all this research would not be conducted unless the customers could truly benefit from the technlogy.

“More than 50% of innovation comes from the voice of the customer,” Principa’s Rossi says. Other key factors in innovation include competitive pressures, internal development and new technologies.

DuPont’s O’Brien says innovations in foaming technology are helping manufacturers build lightweight parts, drive down costs and fine-tune products for specific applications.

“They’re still trying to optimize the process,” she reports. “The key is getting a uniform cell size within the wood-plastic composite material during processing.”

O’Brien said she also sees potential for WPC market expansion in the area of architectural trim, primarily indoor and outdoor decorative moldings.