Knocking On Wood

CPI Plastics Group Ltd. hasn’t always been into “wood”. Better known as a manufacturer of custom extrusion profiles, the Mississauga, Ont.-based company entered the wood replacement market five years ago when president and owner Peter Clark secured a long-term licensing agreement from Britain-based Extrudawood International to manufacture and sell a line of thermoplastic products based upon the Extrudawood technology. Total sales of the wood-replacement Extrudawood product line is expected to bring in millions of dollars of revenue for the company this year.

As it turns out, profiles manufactured from Extrudawood, while they have the color, graininess and texture of wood, contain no wood. They are made almost entirely of polystyrene. The key to achieving a natural wood appearance is an additives package and proprietary processing technology, says Stephen Clark, president of Eon Outdoor Systems Inc., the division under which the decking and outdoor furniture product utilizing the Extrudawood profile is designed and distributed.

Walt Disney World Co. has recently placed a $150,000 order for Extrudawood which will be used to make outdoor furniture at its Orlando, FL theme park. The order came to fruition when Disney World specified that several contractors who normally produce products for Disney made from wood utilize maintenance-free Extrudawood. In addition, sales of the Eon deckboard product, which has been in the market only two years, has jumped to $10 million this year, up from $1.8 million in 1999.

“Today the average consumer is much more aware of the costs and time of maintenance,” says Stephen Clark. “The difference with this product in comparison to ordinary plastic lumber is that it combines a high-quality wood-like appearance and feel with durability.”

The company anticipates continued high growth of its decking system. Currently, the total North American decking product market is estimated to be $2 to $3 billion per year, only a fraction of which is plastic or wood-fibre/plastic composite. Eon sells the deckboard system through large retail outlets such as Home Depot and Loews; however the majority of sales thus far have been through independent lumber chains, which sell directly to construction contractors, according to Clark. To encourage contractors to promote and use Eon decking, the company has started a contractor incentive program which allows contractors to keep a certain percentage of sales.

Clark touts the environmental benefits of his company’s plastic decking system, as well as its resistance to water, rot, cracking, insects, splinters and warping. Clark also reports that the deck boards are uniquely designed to eliminate the need for surface nails and screws during installation. Instead, a T-Clip fastener, which fits into a groove on the side of each board, holds the boards securely in place. The T-Clips also allow decking boards to expand and contract while maintaining uniform spacing. The thermal expansion properties of plastic can be up to two times that of wood and is one the critical differences between plastic and wood decking, Clark notes.

Eon is currently offering its decking in cedar and redwood shades and has plans to launch either pine or mahogany in the near future. Clark says the cost of Eon decking is about double that of pressure-treated lumber, 20 percent more than cedar and on par with redwood. At present more than 90 percent of its sales are in the U.S.

CPI Plastics has over 40 extrusion lines dedicated to running Extrudawood product lines, which include Eon decking and outdoor furniture, as well as slats for vertical blinds, spa cladding and other products. The company has uniformly purchased Davis-Standard equipment for its reliability, competitive cost and flexibility, says Clark.

MARRIAGE OF WOOD AND PLASTIC

OPENING NEW MARKETS

Plastic lumber, made mainly from recycled polyolefins, has been used as a wood replacement for a number of years, primarily in non-load bearing applications with low appearance requirements. It is precisely these limitations of plastic lumber that have sparked a surge of interest in wood-fibre/plastic composites, which are informally defined as plastic containing 30 to 70 percent wood or natural-fibre filler. Depending on the type of plastic and extrusion process, the wood fibre can enhance aesthetics, improve structural properties and reduce weight, while costing significantly less than glass-fibre reinforcement.

“There’s a tremendous amount of new interest in wood/plastic composites from small and large companies in the building materials market,” says Keith Kay, sales project engineer, Krupp Werner & Pfleiderer.

Kay says that such interest is mostly a result of demand in the retail market for materials and products that are less maintenance intensive and more durable than wood, while still providing the look, function and feel of wood. The process is also environmentally-friendly, using a waste by-product, saw dust, and saving trees. On the downside, wood/plastic composite is currently two to three times more costly than ordinary lumber. Kay expects the price for wood/plastic composite to fall as the technology gets refined and more processors get into the market, thereby increasing supply. He also sees the market for wood/plastic extending beyond decking, presently its main market, into areas such as fencing, siding, shingles, furniture, playground equipment and, an especially promising business, railroad ties.

“This is a market that’s really in its infancy,” says Kay. “It will improve with age.”

An example of the exciting potential of wood/plastic composites to deliver new products to the market is Synthetic Hardwood, a product currently in the final stages of commercial development by Synthetic Hardwood Technologies, Inc. in Guelph, Ont. According to SHW Technologies president Frank Maine, the patented Synthetic Hardwood product grew from efforts to identify higher-end, larger volume markets for oriented polymer technology. Oriented polymers are thermoplastic polymers that have been processed in such as way as to straighten the polymer chain backbone, resulting in an increase in strength, stiffness and impact strength in comparison to non-oriented polymers.

Maine had been using the technology to make clear drumsticks from polypropylene. While the plastic drumsticks performed as well or better than wood drumsticks, market acceptance was limited by lack of a wood appearance. Having monitored the wood/plastic composite area for years, Maine experimented with the addition of wood-fibre to oriented polypropylene and obtained a material with a natural wood-like grain. Having demonstrated the technology could be used to make a drumstick with a wood-like appearance, Maine decided to target the billion dollar hardwood flooring market.

Maine says the wood-fibre/oriented-polymer composite has roughly three times the strength of wood, and approximately the same stiffness. As well, Synthetic Hardwood is completely water resistant, making it ideal for high-humidity and/or coastal locations, as well as other applications, such as below-grade basements.

Synthetic Hardwood profiles are made in a two-stage batch extrusion process in which polymer and wood fibre are first compounded, then run through the orientation process, yielding the oriented profile. Work is under way to convert the process to run continuously. SHW has started initial production runs in its 20,000 sq. ft. plant and will eventually be putting in 16 lines capable of producing 3 million sq. ft. of synthetic flooring a year.

“We have a whole bunch of orders we can’t fill yet,” says Maine, who reports the company is building all its own machines. “We’re pioneering brand new technology.”

Maine expects to be cost competitive with hardwood flooring which sells in the range of $5.50 to $8.50/sq. ft., and is targeting Synthetic Hardwood to sell at $4.00 to $6.00/sq. ft.

EQUIPMENT AND PROCESSING MEET COMPOSITES’ DEMANDS

Processing wood-fibre/plastic composites has special concerns, the foremost of these being moisture removal fro
m the wood before it is mixed with plastic. Machinery suppliers have built extrusion equipment with a variety of features designed to accomplish this.

Milacron bills its CM92 conical twin screw extruder as one of the highest output extruders for wood/plastic composites, capable of 1000 to 1800 lb./hr. of processing output. The extruder comes with a vertical integrated feed system (V) and a material enhancement delivery system (MEDS). According to Chris Weinrich, engineering and product manager, ExtrusionTek Milacron, the combined V-MEDS configuration provides effective feeding of the low bulk density woodflour material through an auger-type mechanism that compresses the material into the screws. It also drives out moisture by raising the temperature of the material prior to entering the extruder with a co-rotating pre-heater system.

“One of the biggest adjustments (in processing wood/plastic composites) is how to convey the woodflour itself,” says Weinrich. “Typically processors are not used to dealing with fluffy, low bulk-density materials with inherent high moisture.”

Weinrich says another challenge when processing wood/plastic composites is ensuring the wood doesn’t burn. The CM92’s counter-rotating conical twin-screw design helps prevent burning by providing effective mixing and pumping at a low rpm, which reduces shear, and therefore heat.

Krupp Werner & Pfleiderer’s ZSK 58 is designed to process wood/plastic composites in stages. In the first barrel section, a co-rotating intermeshing twin-screw reduces the moisture content of wood flour from four to 12 percent to less than one percent, according to Krupp Werner & Pfleiderer’s Keith Kay. Next, plastic and additives are mixed into the barrel through a side-feeder and the final sections of the screws mixes and encapsulates the wood inside the plastic. Finally, the wood/plastic composite is dropped through a vent into a single-screw pump, which is used to create pressure for the extruded profile.

“Twin screws are good at mixing, but not pumping,” says Kay, explaining the rationale of design. Kay says they have achieved rates up to 1500 lb./hr. and are looking at building systems capable of delivering up to 3500 lb./hr. “Rate is king when it comes to wood/plastic composites. If you have anything less a 1000 lb./hr. on an extruder it is almost uneconomical to go into production.”

According to business area manager for Davis-Standard, Dave Murdoch, the company’s Woodtruder is designed in a versatile tandem extrusion arrangement, featuring a primary parallel twin-screw extruder and a mounted single-screw, side-injection extruder. Moisture is removed in the first section of the primary extruder. Plastic is melted and injected from the side-injection extruder into the primary extruder at a point mid-way along its length, encapsulating the wood.

“It’s a highly versatile set-up,” Murdoch notes. “Because the plastic and wood are fed separately, its easy to change materials, wood-plastic ratios and other set-up parameters.”

One way of optimizing the wood-like texture of a wood/plastic profile is through embossing, brushing or scouring. Custom Downstream Systems supplies brush and scouring tables and embossing stands specially designed for wood/plastic composite profiles. CDS also sells a variety of downstream equipment for pipe and profile extrusion, including haul-off pullers, spray cooling tanks and other equipment to maximize efficiency.

EXTRUSION – PROFILE

Synthetic Hardwood, from SHW Technologies, is a made from mixture of polypropylene and wood fibre that has been put through an orientation process which stretches and aligns the molecular chains. The resulting wood/plastic composite has roughly three times the strength of wood and about the same stiffness.