At the spring meeting of the American Chemical Society in San Francisco 2017, doctoral candidate Simone Haslinger, Dr Michael Hummel and Prof Herbert Sixta presented a simple method to separate cotton from polyester in textile waste. Here they describe the underlying problem and explain how their solution can overcome one of the main challenges in textile recycling.
The textile waste kaleidoscope
There are currently 7.6 billion humans on this planet – and none is like the other. We all differ in our personalities, talents, looks, and tastes. And just as the fingerprints of two people don’t look the same, there are probably no two wardrobes in the world that contain exactly the same set of clothes. Clothes are a beautiful way to express our individuality and celebrate diversity. However, this diversity can become a challenge when trying to recycle old clothes, garments, and fabrics. They represent a wild mix of different materials with different colors, buttons, zippers, prints, embroideries, and many more. Thus, pre-sorting is required to categorize and group the textile waste according to certain criteria. At present, this is still mostly done manually and is very time-consuming. But the level of automation is increasing steadily, making textile waste sorting more and more efficient.
Cotton and polyester – intimate constituents of many textiles
A major share of textiles and fabrics on the market are not made from one material, but are blends of several fibers to achieve certain properties and functionalities. Even after successful pre-sorting, the separated garments often contain several materials. By far the most prominent mixture on the market is cotton and polyester. When isolated, both offer great potential to be reused and serve as raw material for the production of virgin cotton and polyester fibers, respectively. However, when mixed together neither of the material can be processed. Thus, another separation according to the chemical nature of the material is needed to turn the textile waste into a suitable feedstock.
A way out of the dilemma
We have been working for a number of years now on a technology to produce man-made cellulosic fibers from any cellulose containing feedstock (i.e. cotton, paper, card, bamboo…) – we call this technology the Ioncell process. Integrating the separation of cotton and polyester into this process would allow to remove one additional process step and provide important energy and cost savings. Simone has started to use cotton-polyester mixtures as raw material and has developed specific process conditions to dissolve only the cotton fraction while the polyester parts remained solid. Polyester can be simply filtered off to be melted and processed again. The remaining cotton solution can be spun directly via the Ioncell process into new, high-quality cellulosic textile fibers. The established process did not compromise the integrity of either constituent and so a complete recycling of the mixed textile waste is possible. This was a major step for us towards feasible textile recycling.
See the full interview that Simone and Michael gave at the press conference of the ACS spring meeting in San Francisco 2017 here.