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Auto Engineers Take a Close Look at Wood Composites
Doug Smock, Contributing Editor -- Design News, September 8, 2008
Anyone remember "woodies" (early station wagons in which the rear bodywork was crafted from wood)? They pretty much died out by the 1960s after a few unfortunate efforts to match the look with plastics.
Well, they could make a comeback. Soaring hydrocarbon costs coupled with growing interest in green design are fueling renewed interest in wood and wood-like plants as engineering materials. Several European OEMs use molded wood composites for interior cosmetic components. Two North American toy makers are now using wood composites.
Use of wood thermoplastic composites is already well established for decking and fencing materials. New developments allow the materials to be reliably injection molded, according to suppliers. Wood can be used in loadings above 60 percent with plastics such as polyethylene, polypropylene, ABS, polystyrene and thermoplastic olefin elastomers (TPOs). The "wood" can be wood waste, rice hulls, palm fiber waste or flax. The wood waste can be pine, maple or oak.
A new Toyota concept car introduced this year, the 1/X, includes parts made from a bioplastic derived from kenaf and ramie plants. "The result is a roof that improves heat insulation, emits less carbon dioxide, increases the amount of light entering the cabin and reduces noise," says Toyota's announcement on the car. Ramie is a fibrous plant native to eastern Asia. Kenaf has been used as reinforcement in plastics for more than a dozen years.
From an engineering perspective, wood-plastic composites are said to produce an end-product with structural rigidity, a natural finish, a pleasing aroma and marketable performance capabilities. Good candidates are parts with thick walls and parts that could benefit from rigidity and dimensional stability. Wood-plastic composites, however, are less shatter-resistant than many injection-molded plastics and cannot tolerate excessive impact. Higher loadings of plastic can improve impact performance.
Cost savings
Wood-plastic composites often cost and weigh less than unfilled or glass-filled plastics. They often compete head-to-head with calcium carbonate-filled or talc-filled polypropylene, in which case the primary benefit is cosmetic.
Most engineers wouldn't consider wood a viable injection-molding material. Wood may begin to degrade at temperatures above 392F. As a result, it isn't used with higher temperature polymers. Typical temperatures for molding wood/PP composites are 340F to 370F for the rear zone and 380F to 410F for the front zone. Wood also affects melt flows, but in a positive way. Wood/PP actually flows well at relatively low temperatures and pressures. Molders run wood-plastic composites at lower temperatures, saving energy and reducing cycle times.
Some care is required in design.
"For any material you have design criteria you are going to want to adhere to," says Ed Trueman, CEO of JER Envirotech, a custom compounder in Vancouver, BC that has developed a moldable wood-plastic composite. "Certainly you want to avoid abrupt radius; you want to have soft corners. Our product is somewhat shear-sensitive as you might imagine because the wood component is somewhat sensitive to shear conditions and elevated process temperatures." Gating that reduces shear is a good idea.
Two American toy companies are making major moves with wood-plastic composites produced by JER Envirotech.
The new Sprig Adventure Series, which features interchangeable figurine characters with LED-based headlamps, are injection molded with a product called Sprigwood, jointly developed by JER and Sprig Toys, a manufacturer based in Fort Collins, CO. "In addition to their excellent performance and eco-friendly inputs, JER's thermoplastic biocomposite compounds provide our products with an organic feel, color and wood smell," says Craig Story, CEO of Sprig Toys. The company plans to expand its line of toys with the new composite in 2009.
Rolco Inc. of Kasota, MN recently launched a new line of board game pieces composed of thermoplastic biocomposite compound, including a pawn that was designed specifically for JER's material.
"The board game industry is feeling pressure from consumers and retailers to be more green," says Vern Olson, Rolco's founder and director of research and development. "We had been testing wood-plastic composites for a number of years with limited success. Then, in 2006 we began exploring the use of JER's proprietary formulations and we were able to achieve excellent results." Rolco conducted in-depth R&D, particularly in the areas of coloring and multi-shot injection molding. Rolco is a specialty injection molder operating 32 injection molding lines, including nine multi-shot machines. Rolco is one of the few remaining U.S. injection molders producing board game components, including pawns, houses, hotels, spinners and poker chips. It markets these items to board game designers, manufacturers and wholesalers worldwide through traditional channels as well as on its website.
Luxury trim
Auto producers like GM offer wood interior trim for luxury models. Efforts to introduce wood-plastic composites are in the early stages in the U.S. "Static, nonsafety applications have been our traction initially into the automotive market," says Trueman. European automotive OEMs make greater use of wood-plastic composites. A Belgian company called Beologic supplies compounds filled with 25-85 percent of conditioned wood fibers in a matrix of PVC, PP or PE. These compounds are now being sold by Arkema, which estimated the wood-plastic composite market in Europe is growing up to 20 percent annually. Bo Systems GmbH was founded in 2003 in Sontra, Germany to produce wood composite parts for interior automotive applications.
Wood composites used for extruded decking and fences haven't performed particularly well. Problems such as shrinking and fading can be accommodated with processing and additives. Likewise, the material has been slow to catch on with injection molders because of problems such as inconsistent quality, inconsistent supply and processing issues.
JER Envirotech feels it has the problems solved with a
material originally developed with the National Resources Council of Canada in
a patent
awarded in 2006. The specific purpose of the research was to develop a material
with better mechanical properties and improved service temperature, fire
resistance and biological resistance. The new composite is comprised of a
polyolefin, cellulosic filler, a carboxylic acid and a basic reactive filler.
That's part of the magic of how this material is now entering the realm of
injection molding.
JER uses specially designed equipment and process capability to reduce the moisture
content of the wood. "Wood in its green state is north of 25-percent moisture
content," says Trueman. Moisture and polymer create a huge compromise on
physical and mechanical properties. If you cannot extract the moisture
efficiently you have no balance of properties. Therein is the secret: the
ability to reduce the moisture to less than 0.5 percent internally."
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Auto Engineers Take a Close Look at Wood Composites
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Wood decking has primarily had problems with moisture penetration through the wood fibers at the end of each plank. The exposure of car interiors to moisture in this manner is highly unlikely. Wood composites are not really knew when one considers that the first plastic, celluloid was invented in 1868 by mixing pyroxylin, made from cotton (one of nature's polymerics), and nitric acid, with camphor. Celluloid was still being used in car interiors into the 1950's.
Bruce Stenman - 2008-29-9 11:00:22 EDT -
Design Tips for Engineers: Adhesives for Stronger Aluminum Extrusion Joints link does not connect. Please post website or fix the link.
Richard Chwa - 2008-29-9 06:39:06 EDT
