Profitable and environmentally responsible recycling of fibers and reactive dyes from afterlife cotton textiles via controlled dye hydrolysis, fiber swelling and dissolution

Abstract

We have developed sustainable cotton recycling to provide high-quality cellulose fibers as well as dyes. Because of the lack of simple, non-destructive, and environmentally responsible discoloration technologies, recycled cellulosic products have lower and inconsistent quality and thus limited values. For example, recycling cotton via the spinning of colored cotton into colored cellulose fibers faces challenges since dyes seriously disrupt the spinnability of cellulose dopes. Here, we demonstrate a clean technology to completely recycle all reactive dyed cotton and dyes via controlled dye hydrolysis, fiber swelling, and dissolution. Controlled dye hydrolysis cleaved the covalent bonds between reactive dyes and cellulose. Fiber swelling in N-Methylmorpholine N-oxide (NMMO)/water almost eliminated the physical interactions between dyes and cellulose. As a result, dyes, with different functional groups and chromogenic structures, were separated from cotton. The discolored cotton in NMMO demonstrated desirable spinnability without adding any new cellulose pulp. The high molecular weight makes 100% recycled lyocell fibers tougher than wood-derived lyocell. Separated reactive dyes, with unchanged chromogenic structures, demonstrate desirable dyeability as acid dyes. Recycling cotton is cost-effective to obtain cellulose pulp, the starting materials to produce lyocell, compared to the classic Kraft wood process. The NMMO was recyclable and provided consistent results of cotton discoloration for at least 5 use cycles.