Researchers have developed a quantification tool that measures how much elastane is actually present in a garment. They have conducted experiments to show that the tool can be used to separate elastane from mixed textiles. Segregation/removal of elastane from blended textiles has so far been a big hindrance in textile recycling.
- The team of researchers has developed methods that not only detect elastane better and in a more environment-friendly way than before, but can also separate it in a gentle way in order to recover other fibres undamaged at the same time. The key here is to find the right solvents.
- The researchers are from TU Wien, also known as the Vienna University of Technology.
- The findings— 'New separation process for elastane from polyester/elastane and polyamide/elastane textile waste'—have been published in the journal Resources, Conservation and Recycling. The authors are Emanuel Boschmeier, Vasiliki-Maria Archodoulaki, Andreas Schwaighofer, Bernhard Lendl, Wolfgang Ipsmiller and Andreas Bartl.
The context: Starting in 2025, used textiles are to be collected and recycled throughout the EU. Improved recycling processes are urgently needed to deal with the huge amount of discarded textiles that will then have to be produced again in an efficient and environmentally friendly way.
- A primary reason for the lack of fibre-to-fibre recycling is that textiles often consist of two or more fibre materials, making the entire product unsuitable for immediate recycling. Because of that, a variety of different sorting technologies such as near-infrared monitoring systems are necessary to sort textile waste according to their composition.
- Without a provision of pre-sorted waste streams, textile recycling can hardly be accurate since current technologies require mono-materials instead of multi-material textiles. In many cases it is imperative to separate one type of fibre to make another type of fibre recyclable. Textiles containing elastane fibres are particularly affected by this aspect.
The problem at hand: Elastane (EL), also known as spandex or its well-known brand name Lycra, is defined as containing at least 85 wt.-% of a segmented polyurethane which can be stretched to multiple times its original length (100–600%). When the applied force is removed, it immediately reverts to its original shape.
- This elastic fibre is usually used in lower concentrations in textiles and enhances the stretchability and body-shaping behaviour. Cotton or wool fabrics often contain elastane in the low single digits’ region (1–5 wt.-%), while some fabrics containing either polyester or polyamide can have contents up to 20 wt.-%. For instance, sports products or medical textiles such as bandages contain high elastane amounts because they generate pressure comfort on the skin.
- Although the production volume of this fibre type is only ~1% (1.2 million metric tonnes) of the total fibre production, elastane is frequently used in blended textiles.
- When it comes to textile recycling, all the advantages of elastane in the wear phase make room for profound challenges in textile recycling processes. Since elastane fibres are based on segmented polyurethanes, they can cause a variety of problems if textile waste is processed without prior removal of EL.
- These include filter clogging in melt-extrusion processes, creation of undesirable strings in cutting machines, or small crumbs on recycled fabrics. Thus, appropriate processes for separating EL from blended textile fabrics would be highly desirable and could make a considerable number of textiles that are currently only feasible for thermal recovery suitable for recycling.
Finding a way out: The first step for the researchers was to find a reliable and fast method to accurately detect elastane content in textiles. They discovered that no such method existed until now. The usual test methods use a solvent that is classified as harmful to health and are also extremely time-consuming.
- The researchers developed the "Elastane Quantification Tool” which measures how much elastane is actually present in a garment. It is based on mid-infrared spectroscopy.
- The next step was to find a method to separate elastane from other fibres. The researchers experimented with different solvents and carried out theoretical studies. They finally came across a harmless solvent that selectively removes the elastane, leaving the reusable fibres intact.
- A patent application has been filed for the method. Now, materials such as polyester or polyamide can be almost completely recovered, and even the solvent itself can be recovered and reused.
- Even when wool is combined with polyester and elastane, the individual components can be used: the wool is broken down with enzymes under mild, harmless conditions. This method produces an amino acid cocktail that can be used in the cosmetics industry or in fertiliser production. In the next step, elastane is separated and recyclable polyester remains to be reused.
What they said:
Many of the materials we use to manufacture clothing are easily recyclable as pure materials - such as cotton, polyester or polyamide. But elastane, even if it is only mixed in small quantities, makes recycling using conventional methods impossible.
— Emanuel Boschmeier (Lead Author)
PhD student, Institute of Chemical, Environmental and Bioscience Engineering
TU Wien
