A doctoral thesis at the University of Boras has found that mechanical processes reduce the recyclability of textiles and experiments show how the right kind of pre-treatment can provide longer fibres and improve spinnability. However, recycling can never be the only solution and advocates the use-repair-restyle to make way for a more sustainable textile-fashion industry.
THE THESIS: Katarina Lindström, a textile engineer worked on the doctoral thesis—Mechanical Textile Recycling: Identifying Factors Impacting Fibre Quality—in Textile Technology at the Swedish School of Textiles along with Master's students from Saxion University of Applied Science in the Netherlands, contributed unique knowledge about mechanical recycling: which processes and materials give the best results.
EXPERIMENTING: Many textiles today are made of mixed materials, which are more difficult yet not impossible to recycle.
- Unlike chemical recycling, mechanical processes do not consume as much water or chemicals. Broadly speaking, the textile is cut and torn into smaller pieces in different stages. Sometimes water or lubricant is added to make it easier to separate the fibres from each other. This process is tough on the fibres, which are, of course, designed to hold the textile together.
- If the fibres are too finely broken up during the process, it is not possible to spin them into new yarns. In this case, the material is downgraded to fill material or nonwoven fabric. But there is a lot that can be done to get longer, open fibres that could be used for yarns and textiles.
- Some of the experiments tested friction between fibres and some see how open a material is. In this context, “open” means that the fibres have been freed from the textiles.
- In the comparison of two lab-scale recycling machines, woven and knitted constructions and yarns with different twists were examined. The aim was to see how the construction itself affects recyclability. The results showed that a looser textile with a lower twist yielded longer fibres. And the less mechanical processing, the better the quality of the fibres. To achieve this, lubricants were added.
- Lubricants reduce friction, and this proved to be particularly successful with polyester. With lubricants, less heat was required in the process, which is otherwise a challenge as it can lead to the polyester melting.
- The tests conducted also displayed how the length of the fibre is affected by the direction in which the textile is fed into the machine.
- The experiments also imitated how the use of a garment affects recyclability, i.e. how clothes are broken down by use and how it affects the length of the fibre, and investigated how the right kind of pre-treatment can provide longer fibres and improve spinnability.
WHAT THEY SAID:
So far, very little about the subject has been described in the research. The industry does have knowledge on the topic, but these are trade secrets that it likes to keep to itself. If we are to achieve the goals of a more sustainable textile industry, we must become more open with this knowledge.
— Katarina Lindström
Textile Engineer, Swedish School of Textiles
University of Borås
