Fiber Recycling in the United States

Transcription

1 Fiber Recycling in the United States Youjiang Wang School of Materials Science & Engineering, Georgia Institute of Technology Atlanta, Georgia USA Abstract Due to the growth in world population and overall improvement of living standard, global fiber consumption has been steadily increasing in the past few decades, which leads to a higher amount of post industrial and post consumer fiber waste. This paper discusses some recent activities on fiber and textile recycling in the United States. Introduction World fiber production has been steadily increasing in the past few decades, now exceeding 68 million tons per year. In general, applications of fibers belong to the following three broad categories: apparel, home furnishing, and industrial. In the United States of America alone, about 13.1 million tons of textile waste was generated, accounting for 5.3 wt % of the total municipal solid waste (MSW), and 15% of textile waste was recovered in 2010 [1]. The outlets of the recovered textile waste include reuse and recycling. Additional amount of waste is collected for energy recovery. Overall, 54% of the municipal solid waste was landfilled, 12% incinerated in waste-toenergy facilities, and 34% recovered for recycling or composting. Over the last few decades, the generation, recycling, composting, and disposal of MSW in the US have changed substantially. While solid waste generation has increased from 1.7 to 2.0 kg per person per day between 1980 and 2010, the recycling rate has also increased from less than 10% of MSW generated in 1980 to about 34% in 2010 (Figure 1) [1]. Similarly, as the textile waste in MSW increased over the last decade, the amount of recycling also increased accordingly, keeping the recycling rate nearly unchanged at approximately 15% (Table 1) [2]. Recovery from the waste stream includes reuse of a product in its original form, a common practice for clothes, and recycling to convert the waste into a product. Typically recycling technologies are divided into primary, secondary, tertiary, and quaternary approaches. Primary approaches involve recycling industrial scrap; secondary recycling involves mechanical processing of a post consumer product. Tertiary recycling involves processes such as pyrolysis and 1

2 hydrolysis, which convert the plastic wastes into basic chemicals, monomers or fuels. Quaternary recycling refers to burning the fibrous solid waste and utilizing the heat generated. All these four approaches exist for fiber recycling [3,4,5]. There have been significant activities and new innovations in fiber recycling recently in the US and around the globe that can lead to significant increase in fiber recycling rate in the future. Some of the activities are discussed in this paper. Fig. 1. US MSW recycling rates, 1960 to 2010 Table 1. Textile waste generation, recovery and recycling rate, 2001 to 2010 Year Total (MT) Recovered (MT) Percent recycling Carpet Waste Recycling Carpet recycling in the US is led by Carpet America Recovery Effort (CARE) and its members [6]. The amount of carpet waste generated is about 3 million tons per year in the U.S. [6,7], and about 4-6 million tons per year worldwide. Figure 2 shows the trends in carpet recycling and diversion (including recycling, reuse, waste to energy, etc.) from 2002 to 2010, during which a drastic increase in recycling can be seen, especially between 2002 and 2008 [8]. 2

3 Figure 3 shows that 58% of the recycled post-consumer carpet is manufactured into engineered resins. 31% of the recycled post-consumer carpet is manufactured back in carpet, either as carpet fiber (18%) or carpet backing (13%). Fig. 2. Post-consumer carpet recycling and diversion in the US, Fig. 3. End Products Manufactured from Used Carpet [8] The majority of polyamides used commercially are nylon 6,6 and nylon 6. Among the many companies contributing to carpet recycling, Shaw Industries and Universal Fibers produce nylon carpet fibers from carpet waste. Shaw operates the Evergreen Nylon Recycling facility which produces caprolactam from nylon 6 carpet waste by depolymerization. The waste carpets are collected, sorted and then subjected to a mechanical shredding process before depolymerization. Nylon 6 is made by polymerizing a single monomer, the caprolactam, and the process may be reversed. The recovered nylon 6 face fibers are sent to a depolymerization reactor to produce a 3

4 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 yarn and tufted into carpet. The carpets obtained from this process are very similar in physical properties to those obtained from virgin caprolactam. The polymer can be recycled again without degradation to properties. In 2010 Shaw recycled more than 40,000 tons of postconsumer nylon 6 carpet in a Cradle to Cradle process. The post consumer carpet contains nylon 6 fibers, backing (mostly polypropylene), adhesives and other components. The co-product that is separated from the process is then used in a wasteto-energy process, while calcium carbonate filler reclaimed is recycled into Shaw s EcoWorx polyolefin thermoplastic carpet tile backing [9]. Depolymerization of nylon 6,6 is more complicated than that of nylon 6 because nylon 6,6 is made of two monomers, the adipic acid and hexamethylene diamine (HMDA). Depolymerization of nylon 6,6 to recover adipic acid and HMDA has been demonstrated [10,11,12] but has not been implemented in commercial operations. Therefore processing nylon 66 polymer from post consumer carpet back to carpet fibers is very challenging. Universal Fibers developed technologies to clean and reprocess reclaimed nylon carpet into pellets in a melt extrusion process. The recycled pellets are combined with virgin nylon 66 polymer to make carpet fibers in a broad range of colors [8,9]. 2. Textile Fibers from Recycled Polymer Depolymerization of polyethylene terephthalate (PET) converts the waste chemically into either the base monomers, namely, ethylene glycol (EG) and terephthalic acid (PTA) by hydrolysis, or dimethyl terephthalate (DMT) by methanolysis, or into oligomers by glycolysis or solvolysis [13], or specialty chemicals [14]. The Eco Circle program operated by the Teijin Limited [15] converts used textiles into DMT which is then repolymerized into PET to make textile products. This program has participants all over the world, including many in the US, such as Patagonia. Patagonia has recycled over 27 tons of used clothing since the program bebuted in 2005, and it expects to make all its clothing recyclable [9]. Unifi started a program to make its Repreve PET fibers with post-industrial textile waste content in 2000 [9]. Currently, however, most of the recycled PET textile products use PET bottles as raw material. Besides Unifi, other companies making recycled PET fibers in the US include Foss Manufacturing LLC (eco-fi ), Poole Co. (EcoSure ), Mohawk Industries, and Shaw Industries [9]. Cotton textile waste traditionally is recovered for composting, for use as wipes, and for processing into insulation materials, mats, and other products. Circle LLC 4

5 developed technologies to recover cotton fibers from post industrial cotton waste without significantly damaging the cotton fibers [9]. The recycled cotton fibers find applications ranging from nonwovens to high quality long staple apparel yarns. 3. Recycling of Blended Textiles Obtaining high quality products from waste containing a blend of different materials is difficult, expensive, or even not feasible. Some of the processes discussed earlier require different levels of component separation, and some others require a single type of known material as the feedstock. Some composite products and processes may use blended fibers as reinforcement or matrix [16,17,18]. In a recent study, a process was developed for removing the spandex component in a nylon 6/spandex blended fabric by selective degradation so that the nylon component can be recovered for recycling [19]. In this process, the fabric first undergoes a heat treatment step, followed by a washing process. Using only ethanol for washing, the spandex component can be removed while the nylon component retains its original fabric form, allowing the nylon to be further recycled into resin by melt processing or depolymerization. 4. Summary A large amount of fibrous waste is disposed of in landfills each year. This not only poses economical and environmental concerns to the society but also represents a waste of resources. Significant effort on fiber recycling has been made in recent years in the US and around the globe that will not only bring significant increase in fiber recycling rate in the future but also more high-end products to the market. References 1 U.S. Environmental Protection Agency: Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2010, (2013). 2 U.S. EPA: (2013). 3 Scheirs, J.: Polymer Recycling, Science, Technology and Applications. John Wiley & Sons, New York (1998). 4 Wang, Y. (ed.): Recycling in Textiles, Woodhead Publishing, Cambridge (2006). 5

6 5 Wang, Y.: Fiber and Textile Waste Utilization, Waste & Biomass Valorization, Vol. 1, No. 1 (2010) (2013). 7 Peoples, R.: Carpet Stewardship in the United States A Commitment to Sustainability, in Y. Wang (ed.) Recycling in Textiles, pp , Woodhead Publishing, Cambridge (2006). 8 Carpet America Recovery Effort (CARE): 2010 Annual Report, (2013). 9 Rodie, J.B.: From Waste to Worth, Textile World (Nov./Dec. 2010) Miller, B.: Nylon Hydrolysis, U.S. Patent 2,840,606 (1958). 11 Polk, M. B., LeBoeuf, L. L., Shah, M., Won, C.-Y., Hu, X., Ding, Y., Polym.- Plast. Technol. Eng., 38 (3), 459, Bodrero, S., Canivenc, E., Cansell, F.: Chemical Recycling of Polyamide 6.6 and Polyamide 6 through a Two Step Ami-/Ammonolysis Process, 4th Annual Conference on Recycling of Fibrous Textile and Carpet Waste, Dalton, Georgia, May 17-18, Nadkarni, V.: Recycling of Polyesters, in Fakirov, S. (ed.) Handbook of thermoplastic polyesters - homopolymers, copolymers, blends, and composites, Part V, Wiley-VCH, Weinheim (2002). 14 Shukla, S.R., Harad, A.M., Jawale, L.S.: Recycling of waste PET into useful textile auxiliaries, Waste Management, 28(1), (2008). 15 Teijin Limited: Closed-loop Recycling System ECO CIRCLE, (2013). 16 Wang, Y.: Utilization of Recycled Carpet Waste Fibers for Reinforcement of Concrete and Soil, in Y. Wang (ed.): Recycling in Textiles, pp , Woodhead Publishing, Cambridge (2006). 17 Miraftab, M., and Lickfold, A.:Utilisation of Carpet Waste in Reinforcement of Substandard Soils, J. Industrial Textiles, 38(2), (2008). 18 Muzzy, J.: Composite Products from Post-Consumer Carpet, in Y. Wang (ed.): Recycling in Textiles, pp , Woodhead Publishing, Cambridge (2006). 19 Yin, Y., Yao, D., Wang, C. and Wang, Y.: Removal of Spandex from Nylon/Spandex Blended Fabrics by Selective Polymer Degradation, Textile Research Journal, in press (2013). 6