The team led by Shi Sheng, director of the Textile Department at the College of Light and Textile Engineering, Taiyuan University of Technology, has cracked the technology for large-scale, high-efficiency separation of waste polyester-cotton blended fabrics under atmospheric pressure. The achievement won the global championship in the 2022 UNIDO Carbon Neutrality Technology Solutions solicitation and the second prize of the 2023 China National Textile and Apparel Council Technology Invention Award.

Key points

  • China generates more than 20 million tons of waste textiles each year, of which waste polyester-cotton fabrics account for about 15 million tons, roughly 65% of the total
  • The National Development and Reform Commission and two other departments have proposed a recycling rate of 25% for waste textiles by 2025 and 30% by 2030
  • Shi Sheng's team holds 22 national invention patents, has built a pilot production line with Anhui Tianzhu Textile, and Taiyuan Yuqiang Materials has built a pilot line with an annual output of 3 tons of fiber-plastic composite profiles

Why polyester-cotton blends must be cracked

China is the world's largest textile producer, accounting for more than 50% of global textile fiber processing. Its annual fiber consumption totals about 30 million tons, with per capita fiber consumption exceeding 20 kilograms. If waste textiles continue to be incinerated or landfilled, one ton of landfill requires 3 to 5 square meters of land, and one ton of incineration generates 3.2 tons of carbon emissions. In contrast, utilizing 1 kilogram of waste textiles can reduce carbon dioxide emissions by 3.6 kilograms and save 6,000 liters of water.

Waste textiles fall into two categories: waste filaments and scraps generated during spinning, weaving, dyeing and cutting, which have clear compositions and have basically formed a recycling industry chain; the difficult part is old clothing and home textiles discarded during use. Shi Sheng pointed out that old clothing materials are mixed, and a single garment often blends multiple fibers, making separation the key to recycling. Among these, polyester-cotton blended fabrics generate about 15 million tons annually, about 65% of total waste textiles. Because of their complex structure, difficulty in separation and degradation, the industry calls them "black material," and at present they are almost entirely incinerated or landfilled. Shi Sheng's team therefore made polyester-cotton blends its main focus.

How to achieve large-scale separation under atmospheric pressure

The early approach was to prepare an acidic aqueous solution of oxalic acid and water, and at 130 degrees Celsius convert cotton fibers into powdered cotton-based cellulose while polyester remained unaffected, thereby achieving separation. But one part oxalic acid requires a thousandfold water ratio, resulting in enormous water use during batch processing and wastewater treatment problems. The team then introduced a reactor with a rotating system, using rotation to wet the fabric with the solution and greatly reducing water use; it also customized a small blended-fabric separation prototype capable of processing about 4 kilograms of fabric per batch, and replaced the acidic aqueous solution with a deep eutectic solvent, causing cotton fibers to swell and be rapidly cut and separated at significantly lower reaction temperatures, ultimately achieving large-scale, high-efficiency separation under atmospheric pressure.

The separated products have clear destinations: polyester fibers can be re-spun into yarn; cotton-based cellulose can be used in papermaking and coating additives, and after carbonization can also be made into high-value carbon materials such as cotton-based carbon microspheres.

Diversified utilization pathways and industrialization progress

Shi Sheng proposed an integrated "beauty, textile, separation, material" four-in-one plan, with the principle of using artistic transformation when possible instead of physical and chemical means, and using physical opening into regenerated fibers when possible instead of degradation separation and chemical regeneration. His team participated in formulating three national standards, including the Technical Specification for Waste Textile Recycling and the Technical Specification for Waste Textile Regeneration and Utilization. On the application side, the team cooperated with Anhui Tianzhu Textile Technology Group to establish the Anhui Provincial Engineering Research Center for Waste Cotton Textile Regeneration Technology and Comprehensive Utilization and a pilot production line, and jointly carried out the "High-Value Utilization of Waste Hotel Linens" project, in which discarded hotel bedding and towels are sorted, cleaned and disinfected, then opened, carded and drawn into regenerated yarn for products such as intangible cultural heritage Miao embroidery bags, shopping bags, sofa fabrics and carpets, while also formulating two related group standards. Shanxi Yuqiang Materials Co., Ltd. worked with the team to develop new fiber-plastic composite profiles based on waste textiles and has built a pilot production line for 3 tons of panels per year, with products used for park fences, walkways, garbage storage areas and sanitation tool benches.

At the policy level, in March 2022 the National Development and Reform Commission, the Ministry of Commerce and the Ministry of Industry and Information Technology jointly issued the Implementation Opinions on Accelerating the Recycling of Waste Textiles, proposing a recycling rate of 25% by 2025 and a relatively complete recycling system with a 30% recycling rate by 2030. Shi Sheng said achieving this goal will mean the rise of a new green industry with resource, environmental, economic and employment value.

Significance for the industry

The recycling of waste textiles is still constrained by an incomplete recycling system, weak key technologies and low comprehensive utilization efficiency, with the identification, sorting, separation and regeneration of mixed fibers being the core bottleneck. This breakthrough in polyester-cotton blend separation technology and the implementation of supporting pilot lines provide a verifiable process path for large-scale, high-value treatment of polyester-cotton waste fabrics, which make up the majority.

Source: New Observation: Exploring the Path of Industrialized Recycling of Waste Textiles · Originally published 2024-01-02