Woodfibre Plastic Composites: Large, as in Life
One reason that wood-fibre plastic composite products such as decking cost as much as two times more than natural wood products is the high capital costs for equipment to wash and/or sort recycled pla...
One reason that wood-fibre plastic composite products such as decking cost as much as two times more than natural wood products is the high capital costs for equipment to wash and/or sort recycled plastic materials. Many processors buy pre-washed recycled materials from outside sources, essentially absorbing this cost.
What if the washing step could be eliminated? This is essentially what Superior Polymer Systems, Inc. (Tilsonburg, ON) has done in the design of its high flow mold process. The process allows manufacturers to use heavily contaminated recycled plastic directly, eliminating the costly wash and densification steps. The SPS system can be used to manufacture large-sized timber, such a marine chocking pilings and railroad ties, at throughput rates as high as 10,000 kg/hr. Recycled plastic can be used in combination with glass fibre, wood flour, rubber and nylon to achieve filler rates as high as 50%.
Bill Krygsman, SPS Inc. president, describes the high flow process as a closed-mold system that is a blend of injection and extrusion processes. A single- or twin-screw extrusion system produces a continuous melt, which enters the mold under controlled pressure. The mold maintains cavity pressure during cooling, which in turn controls material density, foaming and shrinkage to produce a part with uniform consistency and properties. A filling station in combination with a diverter valve system allows a processor to fill and switch molds without interrupting production, facilitating the continuous production of a variety of different sized parts.
“You can run as many as 40 molds at one time on this system,” says Krygsman, who reports that several large U.S. manufacturers of plastic and wood-plastic lumber have certified railway ties made on the SPS system at a testing center in Colorado. The railway ties contain glass fibre and other additives, but no wood.
UP NEXT: NYLON/WOOD COMPOSITES
SPS has recently developed a modified version of the high flow process that will accept post-consumer nylon carpet as a feedstock. Krygsman says the development is significant and opens up the possibility of making new composite materials.
Krygsman says one of the more exciting potential applications is nylon/wood/plastic composite timber for use in structural applications, such as the support joists of residential decking systems.
“A 3 in. by 10 in. plank impregnated with nylon would have the structural strength to meet ASTM test methods for decking materials.”