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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