Development of an efficient route for combined recycling of PET and cotton from mixed fabrics

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.

Cellulose Fibers for High-Performance Textiles Functionalized with Incorporated Gold and Silver Nanoparticles

“…Polyester can only be dissolved at high temperatures in hazardous solvents such as dimethyl sulfoxide or hexafluoro isopropanol, which also affect the molecular integrity of cellulose (Serad 1993;Farah et al 2014). Therefore, most approaches have rather focused on the degradation of polyester employing various types of hydrolysis reactions (Barot & Sinha 2015;Oakley, Gorman & Mason 1992;Palme et al 2017;Shen et al 2013). These procedures leave the macromolecular properties of cellulose largely unaffected, while the cotton residue can be recovered for subsequent recycling processes (Palme et al 2017).…”

“…Therefore, most approaches have rather focused on the degradation of polyester employing various types of hydrolysis reactions (Barot & Sinha 2015;Oakley, Gorman & Mason 1992;Palme et al 2017;Shen et al 2013). These procedures leave the macromolecular properties of cellulose largely unaffected, while the cotton residue can be recovered for subsequent recycling processes (Palme et al 2017). Nonetheless, the depolymerized building blocks of polyester need to undergo repolymerization or chain extension reactions to create a closed loop economy (Awaja & Pavel 2005;.…”

Recycling

“…Even with only 12% of recycled content, recycled denim fabric has a much lower environmental impact than a similar virgin fabric, for instance, a reduction in water consumption by 9.8%, energy consumption by 4.2%, and CO 2 . Recycled shoes made from PET bottles, CDs, care tires, and other synthetic materials have also been on the market for more than a decade (Sarioğlu and Kaynak 2017;Kaynak and Sarioglu 2018;Palme et al 2017) (https://www. brooksrunning.com/en_us/06-17-2009.html).…”

Tearing of post-consumer cotton T-shirts and jeans of varying degree of wear

“…There are many promising research initiatives that discover the possibility to utilize discarded cotton and polycotton waste as raw materials for dissolving pulp for further regeneration into viscose or Lyocell fibres. [2][3][4] However, there is a much simpler and energy-efficient route with potential to preserve more of the added value in compliance with the European Parliament and Commission 5 waste management directive. The tearing process starts by sorting on main fibre type and colour.…”