Abstract

Most textile waste is either incinerated or landfilled today, yet, the material could instead be recycled through chemical recycling to new high-quality textiles. A first important step is separation since chemical recycling of textiles requires pure streams. The focus of this paper is on the separation of cotton and PET (poly(ethylene terephthalate), polyester) from mixed textiles, so called polycotton. Polycotton is one of the most common materials in service textiles used in sheets and towels at hospitals and hotels. A straightforward process using 5–15 wt% NaOH in water and temperature in the range between 70 and 90 °C for the hydrolysis of PET was evaluated on the lab-scale. In the process, the PET was degraded to terephthalic acid (TPA) and ethylene glycol (EG). Three product streams were generated from the process. First is the cotton; second, the TPA; and, third, the filtrate containing EG and the process chemicals. The end products and the extent of PET degradation were characterized using light microscopy, UV-spectroscopy, and ATR FT-IR spectroscopy, as well as solution and solid-state NMR spectroscopy. Furthermore, the cotton cellulose degradation was evaluated by analyzing the intrinsic viscosity of the cotton cellulose. The findings show that with the addition of a phase transfer catalyst (benzyltributylammonium chloride (BTBAC)), PET hydrolysis in 10% NaOH solution at 90 °C can be completed within 40 min. Analysis of the degraded PET with NMR spectroscopy showed that no contaminants remained in the recovered TPA, and that the filtrate mainly contained EG and BTBAC (when added). The yield of the cotton cellulose was high, up to 97%, depending on how long the samples were treated. The findings also showed that the separation can be performed without the phase transfer catalyst; however, this requires longer treatment times, which results in more cellulose degradation.

Highlights

  • Today, there are well-established systems for the material recycling of glass, metals, and paper

  • The yield of terephthalic acid (TPA) was calculated as the percentage of the theoretical yield of TPA that can be obtained from Poly(ethylene terephthalate) (PET) assuming that the PET is formed by the esterification of equimolar amounts of TPA and ethylene glycol (EG)

  • The process started with the degradation of PET into disodium terephthalate and ethylene glycol (EG)

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Summary

Introduction

There are well-established systems for the material recycling of glass, metals, and paper. Since there are systems for the collection of textiles (Elander and Ljungkvist 2016), a major barrier to accomplish textile recycling is the large mix of materials, coatings, dyes, and non-textile objects (Wang 2006). This diversity is especially challenging in the chemical recycling of textiles. Due to greater awareness of the high environmental cost of textiles, the interest in textile recycling has increased very much in recent years This creates a high demand for the development of recycling technology. Chemical recycling requires pure fractions, and the development of separation processes is a central issue for the progress of textile recycling

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