A recycling first: carpets!
According to various industry estimates, anywhere from 2.1 billion to 3.4 billion lb of carpet is thrown away every year in the U.S. Of the fiber in this waste, 75% is relatively high-value nylon 6 and 66; 16% is PP; and the remaining 9% is PET polyester and small amounts of acrylic and wool, according to the Polymer Processing Institute at Stevens Institute of Technology in Hoboken, N.J. This waste is collected in bulk from carpet installers and municipal pickups.
The move to recycle carpet is being orchestrated by the carpet industry, which is concerned that it won't be long before legislators and the public wake up to the massive amount of carpet being thrown away. Groups of distributors, big mills like Shaw Industries Inc. in Dalton, Ga., and the resin companies that supply them are all active. Monsanto Chemical Group's Fiber Div. Technical Center in Pensacola, Fla., supports emerging recycling ventures. DuPont Co. in Wilmington, Del., is working with Houston-based Browning-Ferris Industries to collect carpet for its pilot plant in Glasgow, Del., where developmental grinding and chemical recycling of used nylon carpet will be conducted for such products as geotextile reinforcing systems. And BASF Corp. Fibers Div. in Enka, N.C., is working with Shred-Tech, a shredding machine builder in Cambridge, Ont., to develop carpet recycling technology.
The predominant material, nylon, has a huge potential market in automotive applications if it can be rendered pure enough. Cars use 200 million lb/yr of nylon, according to Sandy Labana, Ford Motor Co.'s manager of polymer science and point man for plastic recycling. Many applications for nylon underhood parts are black, so mixed-color contamination isn't a problem. "If the nylon |from carpets~ is the same as molding-grade nylon," Ford's Labana says, "We could use it all."
SEPARATION IN ITS INFANCY
Unlike the ever-changing multi-resin systems used in packaging and cars, carpet resins are consistent and simple. Face or tufting fiber in a carpet is almost always of a single resin, which makes it easier to recover. But different fibers from different carpets don't necessarily mix well, so one carpet recycler takes nylon 6 and throws out the rest, while another takes only nylon 66, and so on. Since face fiber is only about 55% of the carpet's weight, the amount thrown away is considerable: web fiber (10%) and mineral-filled latex (35%) by weight. Flame retardants and metal dyes are also contaminants. So to get 25 million lb of usable resin, a recycler may take in 50 million lb of carpet and landfill half.
Separation technologies for carpet components are in their infancy. Shred-Tech's system for BASF starts with a high-torque, low-speed grinder to chop the carpet, followed by a high-speed, low-torque grinder to free crumbs of latex backing, which are removed by a mechanical shaker.
Sterling Blower in Forest, Va., offers a dry-grinding and air-classification system; three such systems are in commercial operation processing clean carpet waste with no latex backing. "Carpet recycling is Sterling's project of the year," says marketing v.p. Harold Goldman. Sterling also has an R&D grant to build a wet system to clean and separate PP fiber from the calcium carbonate/latex backing. Georgia Institute of Technology in Atlanta devised a chemical process for dissolving the latex, but it was considered too expensive.
What is said to be the only approach that restores nylon to its original quality is DuPont's chemical recycling of nylon 66 back to adipic acid and hexamethylene. DuPont shears nylon face fiber off the carpet back.
THE NYLON'S NOT FOR BURNING
A recent "peer review" meeting with the U.S. Department of Energy, conducted by the Polymer Processing Institute at Stevens, discussed projects needed to conserve "embodied energy" in plastics. Embodied energy is calculated by adding the energy consumed in manufacturing a plastic to the combustion energy content of the original feedstock used to make the polymer. In terms of energy efficiency (not necessarily profitability), nylon is far more efficient to recycle than to burn. The idea is that if it takes more than twice as much energy to make a plastic than you get back by burning, you're better off recycling the plastic, from an energy point of view. Whereas, if a plastic has less than a 2:1 ratio of embodied energy to heat of combustion, it's considered practical to use as fuel. HDPE, for example, takes 36,500 Btu/lb of energy to make and gives 20,000 Btu/lb back when burned. That's a 36/20 ratio of embodied energy, or less than 2:1, which means that from an energy standpoint, HDPE is nearly as efficient to burn as to recycle. The energy ratio for nylon, however, clearly favors recycling over burning. Nylon takes up to 90,400 Btu to make, but gives off only 13,200 Btu when burned--for a whopping 7:1 ratio.
GETTING VALUE FROM WASTE
Most of the emerging carpet recyclers expect to charge a tipping fee for accepting waste carpet to help defray their recycling and waste-disposal costs. But tipping fees can vary greatly. In Minnesota, for instance, they're $95/ton, but only $15/ton in Georgia, where most carpet recyclers are located. (Carpet weighs about 4 lb/sq yd.)
Carpet recyclers take a variety of approaches to getting value out of old carpet. For years, most of them have needle-punched used fiber into felt-like carpet underpads, which sell for $3-4/yd. Leggett & Platt in Nashville, Tenn.; Permafirm Pad Co. in Los Angeles; and three recyclers in Dalton, Ga. (P & G Industries, Crown America and Columbia Recycling) all make felt carpet padding out of virgin carpet scrap.
Columbia, probably the biggest, says it reuses 2 million lb/week of virgin carpet waste, or about 100 million lb/yr. An unusual and profitable variation is at LaGrange Molded Products in LaGrange, Ga., a maker of PP, nylon and polyester automotive carpet. LaGrange doesn't reuse its waste fiber, but recovers the vinyl carpet backing. This alone paid for the equipment (designed by Sterling Blower) in six months, a technical source at LaGrange says. JPS Automotive Products (formerly part of J.P. Stevens) in Greenville, S.C., has ground and extruded waste carpet into pellets to add to new carpet backing for years.
Only a few firms recycle carpet fiber into commercial pellets or molded products. A Minneapolis firm appears to be ahead of the pack with two developmental pellet compounds from recycled carpet. United Recycling Inc. (a unit of Environmental Technologies, also in Minneapolis) was set up three years ago, initially funded by Twin Cities-area carpet dealers. URI has a grinding and extrusion pilot plant and expects to have a 25-million-lb/yr commercial plant operating by May. Its process uses PP and nylon carpet, so long as it's not backed with foam rubber.
URI took two years in developing a pair of proprietary nylon/PP blends for injection molding. "Injection molders in the area were leery about putting our resin into their machines, but they made pens and frisbees for samples with no trouble," says URI founder Charlie Pyle. He says carpet dyes can be masked: "We made off-white frisbees." URI's primary market, however, is internal. It has extruded prototype carpet tack strip from recycle, which cuts easily and performs as well as traditional wood strip. This application is potentially a 3-4 million lb/yr regional market, Pyle says.
Also targeting wood replacement is another small venture-capital carpet recycler. Seawolf Industries Inc. in New Smyrna Beach, Fla., has developed a patented process for converting carpet of mixed resin types, including latex backing, into a layered, board-like composite called "C-Board." Seawolf plans to shred carpet to 1-in. or longer fibers. Some of the dirt shakes loose in grinding, and unwashed fibers are mixed with a thermosetting matrix resin, which the company won't identify. (Seawolf, it may be noted, has considerable experience in FRP made from glass-reinforced unsaturated polyester.) This fiber-filled matrix is then laminated between glass-fiber mat and a layer of denser fiber fill.
FIRST COMMERCIAL RECYCLED CARPET COMPOUNDS COMPOSITION URI 20-001 URI 10-001 Nylon 6, min. % 60 75 PP, max. % 15 10 Other Polymers, max. % 10 10 Inorganic Fill., max. % 15 15 Moisture, max. % 2 2 PROPERTIES Specific Gravity 1.1 0.92 Tensile Str., psi 5500 3300 Elongation, % 10 10 Flex. Modulus, psi 115,000 110,000 MFI, g/10 min 6.0(1) 8.6(2) Extrusion/Injection Molding Temp., F 500-550 450-550 1 Condition R 2 Condition L Source: United Recycling Inc.
Boards will be formed in "a low-cost, low-pressure press to produce items like trailer flooring, roofing panels and siding," the company says, but doesn't have a prototype press built yet. The market it has identified is plywood-replacement flooring for ocean shipping containers and truck backs because C-Board doesn't absorb water or spilled chemicals and is lighter, stronger, and easier to clean than wood.
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|Title Annotation:||Technology News|
|Author:||Schut, Jan H.|
|Date:||Apr 1, 1993|
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