Nylon 6, taken from scrap carpet, can be successfully blended into wood-plastic composites, according to research from the Atlanta-based Georgia Institute of Technology. Nylon 6/6 does not work as well, because the wood fibers degrade.
Nylon is well-established for use with fiber-reinforced composites, but not for deck board or other products that use natural fibers. The reason? Wood and other natural fibers degrade and burn at temperatures above 392°F, which is well below the melting points of nylon 6 (437°F) and nylon 6/6 (509°F).
Conventional wisdom was that high melting point means nylon is not suitable for use in wood-plastic composites, said John Muzzy, a professor and chairman of polymer engineering at the Georgia Institute of Technology.
``We sort of broke the rule of thumb that you can't work with materials that have to be processed over 200°C,'' Muzzy said during Antec 2007. Muzzy presented research done by graduate student Xiaolin Xu.
Polyethylene is the most common reason for extruding with wood-flour. But in Georgia, the carpet capital of America, there is a lot of interest in finding uses for post-consumer carpet.
Carpet manufacturers, through the Carpert America Recovery Effort, want to divert 40 percent of old carpet from going to landfills by 2012. Today, only 4 percent of waste carpeting gets recycled or reused.
Muzzy said currently the biggest use of recycled carpet is shredding it and making underlay pads for new carpet. Another option: grinding the carpet up, shredding it and separating the materials for use as a plywood substitute or additive for some automotive parts.
For the study, the Georgia Institute of Technology used an NFM/Welding Engineers nonintermeshing, counter-rotating twin-screw compounding extruder in its laboratory. Researchers extruded out a hot log of the nylon/wood material, then compression molded the mixture into test plaques. Additional plaques were grouped for injection molding on a Sumitomo injection press with 75 tons of clamping force.
Muzzy said the study shows Nylon 6 does work. But there's a catch: at high extrusion temperatures, fiber dispersion is good and the wood fibers visibly degrade. With lower extrusion temperatures, there is less wood degradation, but the dispersion of the fibers is poor.
With a higher melting temperature, nylon 6/6 did not fare as well. ``It's really kind of debatable as far as the nylon 6/6,'' Muzzy said. ``That's pushing it too far.''