Fiber Recycling Technologies

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. 

Because of the higher value of nylon resin in comparison with other polymers used in carpet, nylon carpet has been looked at as a resource for making virgin nylon via depolymerization. The majority of polyamides used commercially are nylon 6,6 or nylon 6, and the largest supply of waste for recycling of nylons is obtained from used carpets. The waste carpets are collected, sorted, and then subjected to a mechanical shredding process before depolymerization. 

Acid hydrolysis of nylon 6 wastes [21, 22] in the presence of superheated steam has been used to produce aminocaproic acid, which under acid conditions is converted to e-caprolactam, and several patents have been obtained by BASF [23, 24]. Acids used for the depolymerization of nylon 6 include inorganic or organic acids such as nitric acid, formic acid, benzoic acid, and hydrochloric acid [23, 25]. Orthophosphoric acid [24] and boric acid are typically used as catalysts at temperatures of 250-350°C. In a typical process, superheated steam is passed through the molten nylon 6 waste at 250-300°C in the presence of phosphoric acid. The resulting solution underwent a multistage chemical purification before concentration to 70% liquor, which was fractionally distilled in the presence of base to recover pure e-caprolactam. Boric acid (1%) may be used to depolymerize nylon 6 at 400°C under ambient pressure. A recovery of 93-95% e-caprolactam was obtained by passing superheated steam through molten nylon 6 at 250-350°C [23]. 

Sodium hydroxide has been used successfully as a catalyst for the base-catalyzed depolymerization of nylon 6. At 250°C, a pressure of 400 Pa, and a sodium hydroxide content of 1%, the yield of e-caprolactam was 90.5% [26]. 

Catalytic Pyrolysis Catalytic pyrolysis has been studied as a hybrid process for recovering caprolactam from nylon 6 followed by high-temperature pyrolysis of the polypropylene into a synthetic natural gas. Czemik et al. [27] investigated the catalysis of the thermal degradation of nylon 6 with an a-alumina supported KOH catalyst in a fluidized-bed reactor. In the temperature range of 330-360°C the yield of caprolactam exceeded 85%. 

---

Dreamworks, LifeCycle, MoistureShield, A.E.R.T. Epoch/Evergrain Environmental Recycling Technologies Weyerhaeuser Epoch Composite reported(50% wood fiber) 50% wood fibers ESR-I625 (6/1/2005)... 

ChoiceDek Channeled Advanced Environmental Recycling Technologies, Inc. HDPE, wood fiber 100... 

M. K. Mishra, ed., Polymer-Plastics Technology and Engineering, Special Issue, Polymer and Fiber Recycling 38(3) (1999). 

Residential decking is a large component of plastic lumber sales. Major manufacturers using recycled plastics include Trex and Advanced Environmental Recycling Technologies (AERT) with plastic/wood fiber composites, and U.S. Plastic Lumber Corp. with both structurally foamed HDPE and plastic/wood composites. ... 

See also Biosynthetics Ghemical Engineering Engineering Environmental Chemistry Fiber Technologies Forestry Nanotechnology Recycling Technology Silviculture. 

See also Chemical Engineering Engineering Fiber Technologies Polymer Science Recycling Technology Structural Composites. 

Yamasaki Y. Overview of Recycling Technology in Textile Industry in Japan and the World. Japan Japan Chemical Fibers Association 2004. 

Mckean WT, Jacobs RS. 1997. Wheat Straw as a Paper Fiber Source. Prepared for Recycling Technology Assistance Partnership (ReTAP) by The Clean Washington Center and Domtar Inc. http //www.cwc.org/ paperZpa971rpt.pdf (accessed 1 August 2010). 

---