On average, every European buys 26 kilograms of clothing per year. According to a Greenpeace survey, around half of the clothes in our wardrobes are discarded after three years at the latest. The amount of waste this generates is enormous. The particular problem: in the past, textiles were not considered in the context of material cycles. Only one per cent of discarded textiles end up being reused and made into new items of clothing, the rest are disposed of in landfill sites or incinerated – but the EU wants this to change.
On the way to a circular economy
The mechanical recycling of textiles and textile blends is a crucial step in the circular economy. In view of the growing amount of textile waste and the associated environmental challenges, it is essential to develop effective recycling methods.
In the ‘TexKreis’ research project, the IKK – Institute of Plastics and Circular Economy at Leibniz Universität Hannover is focussing in particular on the mechanical recycling of textiles. In cooperation with the project partners Vaude, Gerry Weber and Forbo Movement Systems, the IKK is analysing various textile products – from sports equipment and women’s fashion to textile-reinforced conveyor belts. This primarily involves post-industrial waste made from polyester, polyester-elastane blends and TPU-polyester blends, on the basis of which recycling concepts are to be developed. The textile materials are seen as plastics and less as fibres – with the aim of being able to transfer them into alternative applications. The project is supported by the expertise of Barlog Plastics, EREMA and Gross+Froelich, so that the findings and specific recyclate developments can then be put into practice.The knowledge and technology transfer will be carried out by TecPart – Verband Technische Kunststoff-Produkte and the AFBW – Alliance for fiber-based materials Baden-Württemberg.
Challenges of mechanical textile recycling
The mechanical recycling of textiles faces various challenges, which can be reduced to four main points.
1. Diversity of materials: Many textiles consist of complex mixtures that are difficult to recycle. The development of effective separation and processing methods is therefore crucial. In addition, the compositions are often unknown, so that comprehensive characterisations are necessary and the materials often have to be considered individually.
2. Quality: Mechanical recycling can lead to a loss of quality. This can limit the use of recycled materials in high-quality applications.
3. Recycling of mixed fabrics: When recycling blended fabrics consisting of different fibres (for example, polyester and elastane), the challenge lies in separating the different materials. As purely mechanical processes such as tearing machines are often not sufficient to separate the fibres effectively, thermomechanical processes come into play. Under certain circumstances, these can facilitate the separation of the fibres through heat treatment. Overall, however, the recycling of mixed fabrics is particularly difficult and has so far been difficult to implement as fibre-to-fibre recycling.
4. Technological challenges: In the past, technological limitations in particular set limits to recycling. The development of efficient technologies for mechanical and thermomechanical recycling is necessary in order to increase recycling rates and improve the quality of recycled materials.
How does the mechanical recycling of textiles work?
Mechanical recycling essentially consists of four steps: preparation, pre-treatment, recycling process and further processing. These merge seamlessly into one another and require meticulous execution in order to obtain a high-quality polymer at the end. In addition, there are a number of process-related challenges when processing textiles.
During preparation, the textile waste is collected and pre-sorted. The materials can be categorised according to composition or quality, for example. This phase is particularly important – because the material that is used at the beginning (input) has a significant influence on the quality of the end product (output).
During pre-treatment, the collected and pre-sorted materials are shredded for better handling. Typically, shredders or granulators are used to break the material down into small pieces. If necessary, other types of material can then be separated and buttons or zips can be removed from unwanted foreign materials.
A special feature of shredding is that the textile fibres fan out in the process. The material becomes fluffy and difficult to flow and dose and would not be able to be processed in the extruder in this way. One way to counteract this challenge is to recompress the textile fibres into pellets. The material is then heated and melted in an extruder. It is possible to add additives to the polymer melt in order to adapt the properties to the subsequent application or to purify the melt using filtration, for example. The melt is then pressed through a die and cooled. The resulting recyclate can now be further processed into injection moulded components.
The mechanical recycling of textiles and textile blends offers promising approaches for reducing waste and conserving resources. In this way, it is possible to save raw materials and reduce the environmental impact of textile production.
How can textile waste be reduced and the environment protected?
There are various approaches to reducing the gigantic amounts of waste. The simplest and most effective way is to avoid waste – starting with production, but of course also by reducing consumption. If clothing is discarded, it should be reused for as long as possible, for example as second-hand goods. Once the end of the utilisation phase has been reached, processes such as mechanical or chemical recycling should be used before the material is finally recycled and disposed of (see Figure 3).
The development of efficient recycling technologies and the promotion of a circular economy are crucial to making the textile industry more sustainable and minimising its environmental impact. Through targeted measures and investment in research and development, the mechanical recycling of textiles can become an important part of a sustainable future. Further studies should show the extent to which the previously unutilised potential can be exploited.
It is also important not only to look at textiles from the end of the utilisation chain, but also to think about the recycling cycle right from the design stage. Which materials are used? Can mono-materials be used? Can blends and mixed fabrics, which are much more difficult to recycle, be reduced or, in the best case, avoided?
Many of these questions are currently being actively addressed in order to develop solutions, and some promising approaches already exist. Ultimately, however, it is up to us how and whether we actually realise these possibilities.
