Blended Textile Separation (Hydrothermal Treatment)

Introduction

Population growth and rapid changes in fashion trends are causing major textile waste concerns. Recent studies show that fashion alone generates at least 39 million tonnes of waste every year, with only 15% being recycled post-consumption. Fashion recycling is essential for the achievement of a circular economy by preserving and conserving natural resources, and as such we need effective methods that will encourage more recycling by consumers and not only manufacturers. Anifa Mvuemba’s recent virtual fashion show is proof that technology and fashion is the alliance young creators and designers can use to achieve long lasting, meticulous aesthetics while reducing environmental impacts caused by fashion production processes. Science is also an ally that has reared its head a lot more in recent years to assist in making fashion more environmentally responsible. It is essential to highlight methods that aid innovation and sustainability for the health of our planet such as the hydrothermal treatment used for recycling waste blended textiles.

Hydrothermal Treatment

The recycling technology we have today only makes it possible to mechanically recycle single fibre fabrics such as denim and wool. However, waste textiles are made of blends of different types of fibres in order to improve fit, durability and longevity. It is therefore important to highlight chemical processes capable of breaking down blended fabrics like hydrothermal treatment. Hydrothermal treatment is the treatment of biomass, a plant or animal material used for energy production, or in various industrial processes as raw substances for a range of products. The biomass is treated in water at high temperatures and pressure. Depending on the temperature, pressure or treatment time different reactions take place so as to deliver different products. The chemical hydrothermal treatment selectively decomposes cotton into cellulose powders, the main component of cotton fibres. The cellulose powder is then viable for re-spinning into new cotton fibres, while the polyester is re-used to create material for new products and continuing the circular cycle of material re-usability.The hydrothermal treatment is an effective method for breaking down chemical bonds from waste materials, yet we should still look into the methods involved in the treatment to factor out the negative aspects of this process. 

Hydrothermal Method

In recent years a number of methods have been developed for the solubilisation of cellulose to separate it from Polyethylene-Terephthalate (PET), a synthetic substance widely used to make polyester fibres. The hydrothermal treatment requires a step by step process in which the material can be broken down into its original chemical components and cotton fibres. The first step will require all the hard objects such as buttons and zippers to be removed from the garment. The next step requires the cutting down of the garment into appropriate sized pieces, followed by pouring water and the chemical solution into a reactor. Cotton fibres have limited solvents and are insoluble in most common organic liquids, with the most common solution choice being methyl-morpholine oxide (NMMO). NMMO is one of the cellulose solvents, which is used industrially for the spinning of cellulosic fibre. In this process the solution dissolves up to 30% of cellulose and is almost totally recyclable. The process is then completed in a half to two hours time frame, resulting in the decomposition of cotton fibres while the polyester fibres remain intact. Finally the cellulose based powders and polyester fibres are recovered through filtration. The completion of this process releases cellulose powders and polyester fibres in their most natural compositions.

Useful clothes at a landfill.

Benefits of using the Hydrothermal Treatment

The science and technology behind the hydrothermal treatment is fast and simple. The equipment required for this process is basic and can be scaled up to fit in more garments. The green chemical used is biodegradable and does not use any organic solvents, meaning that it will not cause secondary pollution. The separation process is efficient with a 98% recovery rate of all polyester fibres, permitting fibre to fibre recycling. This treatment has presented the opportunity to reduce demand for raw materials to turn into fibre, while reducing textile waste in landfills. The hydrothermal treatment is a solution to the recycling of blended textiles and encourages a circular method of manufacturing and recycling. This process is by far the most efficient system we have for recycling blended textiles so far while maintaining low environmental impacts. We should, however, remind ourselves that this does not mean we can continue to consume fashion with no care. We still have a responsibility to conserve the raw materials we have left and learn a lot more about ethical consumption and production in fashion. Our manufactures have the responsibility to share information about recycling methods, tools and benefits. It is evident that the fashion industry can rely on technology and science to achieve a circular economy while reducing their waste and spread of fossil fuels into the environment.   

Sources

  • Wang Shuhua, Yu Xiaoying, Chen Xiaogang, Hou Wensheng & Niu Mei (2020) Recycling of Cotton Fibers Separated from the Waste Blend Fabric, Journal of Natural Fibers, 17:4, 520-531, DOI: 10.1080/15440478.2018.1503130
  • Zou, Y., N. Reddy, and Y. Yang. 2011. Reusing polyester/cotton blend fabrics for composites. Composites: Part B: Engineering 42:763–70. doi:10.1016/j.compositesb.2011.01.022. 

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