Nylon from Carpets

The last example of chemical recycling of a specific plastic is the recycling of nylon from carpets. The RECAM (recycling of carpet materials) project is one... 

Polymer Engineering and Science 41, No.9, Sept.2001, p.1457-70 REVIEW RECYCLING OF NYLON FROM CARPET WASTE... 

In an industrial application dissolution/reprecipitation technology is used to separate and recover nylon from carpet waste [636]. Carpets are generally composed of three primary polymer components, namely polypropylene (backing), SBR latex (binding) and nylon (face fibres), and calcium carbonate filler. The process involves selective dissolution of nylon (typically constituting more than 50wt% of carpet polymer mass) with an 88 wt % liquid formic acid solution and recovery of nylon powder with scCC>2 antisolvent precipitation at high pressure. Papaspyrides and Kartalis [637] used dimethylsulfoxide as a solvent for PA6 and formic acid for PA6.6, and methylethylketone as the nonsolvent for both polymers. 

Patent Number EP 1104753 A1 20010606 PROCESS FOR RECOVERING MONOMERIC UNITS OF A NYLON FROM WHOLE CARPET... 

Disclosed is a process for recovering monomeric units of a nylon from whole carpet composed of fibres of the nylon and a backing composed of non-nylon components, the fibres being bound to the backing and the carpet containing between 15 and 35 wt.% of the nylon. It involves the steps of a) mechanically separating the whole carpet into a carpet mixture, which contains between 35 and 55 wt.% of nylon, and a depleted carpet mixture, and exposing the carpet mixture to conditions under which depolymerisation of the nylon is effected. 

This fall, the closed-loop Evergreen Nylon Recycling plant will start up in the US, a joint venture of DSM Chemicals North America and AlliedSignal. The facility will recover 45,000 m.t./year of caprolactam by depolymerising the fibres from 100,000 m.t./year of discarded nylon-6 carpets. Meanwhile in Germany, Lurgi is building the Polyamid 2000 AG facility. It will process 120,000 m.t./year of carpet waste and recover 10,000 m.t./ year of caprolactam from nylon-6 carpets and 13,000 m.t./ year of nylon-6-6 from nylon-6-6 carpets. 

Increasing the contact pressure exerted by the drag sled on a treated nylon plush carpet had relatively little effect on the transfer of chlorpyrifos residues to the cloth sampling medium (36 13 p.g at 2100 Pa, to 56 28 p.g at 4500 Pa, and to 43 10p.g at 15 600 Pa). Increasing the traverse speed of the drag sled reduced the amount of chlorpyrifos transferred from 56 28 Rg at 7 cm/s to 31 21p.g at 20 cm/s. The amount of transfer increased relatively uniformly with traverse distances up to 10 m. Static (3 s) transfer of chlorpyrifos to the sled averaged 0.6 p,g, or about half of that transferred to the PUF roller. The mean amounts transferred to the drag sled cloth increased from 4.2 p.g over the first 17 cm traversed, to 8.6 p,g over 92 cm, 124 p,g over 3 m, and 302 p.g over 10 m. 

Waste carpet typically contains large quantities of Nylon 6, which can be converted back into caprolactam. Recycling processes are described in U.S. 7,115,671, U.S. 6,111,099 (both to DSM B.V.), and U.S. 5,359,062 (to BASF). Determine the economics of recovering caprolactam from carpet waste if the waste is available at a cost of -30/metric ton (i.e., you are paid 30/ton to accept it). How does this compare to burning the waste carpet in an incinerator with a steam turbine cogeneration plant ... 

Lem, K.W. Letton, A. Izod, T.P.J. Lupton, F.S. Bedwell, W.B. Composition Containing Caprolactam-Free Residue from Depolymerization of Nylon 6 Carpet and Use Thereof in Paving Asphalt, Plastic Lumber and Crack Sealants. US Patent 6,214,908, April, 10, 2001, USP 6,414,066, July 2, 2002. 

Pickets of the same size were also made from a polypropylene-Nylon blend (carpet scrap)—and subjected to water submerging for a short- and long-term test. Despite a generally recognized hygroscopicity of Nylon, the pickets absorb only a little water (Table 12.10)... 

FIGURE 12.53 U.S. production of synthetic fiber staple and tow showing the relative quantities of acrylic fiber produced compared to nylon, polyester, and polyolefin. Acrylic production peaked in the late 1970s. One of the major factors was the decline of the acrylic carpet market, now dominated by nylon. (From Manufactured Fiber Producer Handbook, 1996 Fiber Organon, February 1997, Fiber Economics Bureau, pub.)... 

Companies can resolve their sourcing problems by developing their own infrastructure for collection. These collection schemes typically involve customers who supply dean and relatively homogeneous material which can be made into useful products [23, 24]. One example is the DuPont Partnership for Carpet Reclamation, which recovers nylon carpets from carpet companies for mechanical and chemical recycling. This scheme generates material approved for under-the-bonnet automotive applications. 

Many carpet manufacturers, fiber and chemical suppliers, recycling companies, and academic institutions are actively pursuing various methods to recycle fibrous waste. The approaches include chemical processes to depolymerize nylon and other polymers, recovery of plastic resins from carpet fibers, direct extrusion of mixed carpet waste, composites as wood substitutes, fibers for concrete and soil reinforcement, waste-to-energy conversion, and carpet as feedstock for cement kilns. 

Applications of Dopolymerized Nylon 6 Chemical recycling of nylon 6 carpet face fibers has been developed into a closed-loop recycling process for waste nylon carpet [25, 30-32]. The recovered nylon 6 face fibers are sent to a depolymerization reactor and teeated with superheated steam in the presence of a catalyst to produce a distillate containing caprolactam. The crude caprolactam is distilled and repolymerized to form nylon 6. The caprolactam obtained is comparable to virgin caprolactam in purity. The repolymerized nylon 6 is converted into yam and tufted into carpet. The carpets obtained from this process are very similar in physical properties to those obtained from virgin caprolactam. 

In 1994, Monsanto patented a process to recycle aU the components of postconsumer nylon 6,6 carpet, without separation, into a filled thermoplastic product suitable for injection molding [62, 63]. It used a twin-screw extruder to accomplish high-intensity mixing of the thermoplastic from carpet samples. The recycled material contained 35-67 wt% nylon, 8-21 wt% polypropylene, 5-29 wt % SBR, and 10-40 wt % inorganic filler. In one study, no compatibilizer was used [62]. The carpet samples were fed directly into a twin-screw extruder operating at about 250-260°C and at a shear rate of 200-400 s The tensile... 

Other studies on the use of polypropylene fibers from carpet waste in concrete [81], used tire cords in concrete [82, 83], and using recycled nylon fibers to reduce plastic shrinkage cracking in concrete [84] have also been reported and reviewed [85]. Gordon et al. [86] used the waste nylon fibers and ground carpet to stabilize asphalt concrete. Increase of asphalt content in asphalt concrete is favorable because it leads to more durable roads. But it is limited by the resultant flushing and bleeding of pavements and possible permanent deformation of the pavement. Addition of 0.3 wt% waste fibers increased the allowed asphalt content by 0.3-0.4 wt%. 

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