High-quality separation and recovery of nylon and dyes from waste carpet via non-destructive dissolution and controlled precipitation for sustainable recycling

Abstract

Pure recycled nylon fibers were developed for the first time from carpets without environmentally irresponsible dye destruction and costly polymer degradation. The lack of economically viable separation technology has resulted in more than 97 % of carpets ending up in landfills, posing severe environmental and health concerns. A sustainable and cost-effective separation and purification technology is the key to successful carpet recycling on a large scale. Impurities removal via depolymerization, although technically feasible, faces intolerable economic challenges, limiting its large-scale application. Cost-effective spinning of dye-containing nylon into fibers did not work since acid dyes considerably lowered the crystallinity and mechanical properties of re-spun fibers. Here, we present a closed-loop recycling approach involving controlled dissolution and precipitation (ReNylon via D&P), allowing for the complete separation of nylon and dyes without damaging their chemical structures. The non-destructive dissolution in butanediol completely removed the colored nylon fibers from both the face and back of carpets. The temperature-induced precipitation resulted in colorless amorphous nylon separated from acid dye solution. Recycled colorless fibers from purified nylon demonstrated the same quality as fibers before the recycling. Acid dyes from carpet were redyed onto nylon in an energy-conservative butanediol-based solution and showed identical dyeability and colorfastness to virgin dyes. The overall costs based on preliminary estimation to produce nylon fibers via our recycling is less than 23 % of that via the petroleum-based method, indicating a high economic viability of the recycling. This clean recycling process minimized waste generation by recovering more than 99 % of biodegradable and low-toxic butanediol. The recycling technology could also apply to other textile blends for closed-loop circulation.