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Key Takeaways
- Mechanical recycling reaches a physical limit with cotton because of the fibre's inherent characteristics.
- Chemical recycling can recover cellulose and convert it into a high-quality raw material. However, it has yet to achieve commercial-scale success.
- The main challenge lies not with the technology itself, but elsewhere in the value chain.
- A specific grade of pure cotton from the textile rental and laundry sector could provide a reliable starting point for feedstock supply.
- Even if the technical challenges are overcome, two factors will ultimately determine commercial success: supportive regulatory frameworks and stable markets for recycled materials.
Cotton is indispensable to the textile and apparel industry as well as the textile services sector. The natural fibre gives workwear and hospitality and healthcare textiles a pleasant handle and excellent moisture absorbency. Its high resistance to alkalis also contributes to the outstanding wash durability required for B2B textiles. However, cotton is less advantageous when it comes to recyclability. Its characteristic fibre length limits mechanical recycling: the shredding process shortens the fibres, restricting their use in low-pilling, high-strength yarns. As a result, recycled cotton is typically reused only in very small proportions as a blend with virgin fibres.
The greatest hopes for high-value recycling of cotton textiles therefore rest on chemical recycling. The aim is to recover the cellulose contained in cotton and process it into a suitable recycled dissolving pulp. This pulp can then be used as a raw material for regenerated cellulose fibres such as viscose, modal and lyocell. To achieve this, post-consumer textiles must first be sorted, mechanically shredded and chemically processed. Interfering components such as polyester, elastane, dyes, finishes and other contaminants must be removed as completely as possible. The resulting pulp must meet stringent purity requirements and have an appropriate degree of polymerisation to ensure it can be processed in existing fibre production systems.
In principle, there are two approaches to recovering cellulose from cotton textiles. The first is to recover the cellulose as dissolving pulp for the production of new regenerated cellulose fibres. The second is to depolymerise the cellulose into smaller molecules or sugar building blocks. Depolymerisation does not produce pulp suitable for spinning directly into fibres. Instead, it yields chemical intermediates that can be used in applications such as the chemicals or plastics industries. Processes based on ionic liquids likewise require cellulose of suitable quality as a feedstock. In both cases, chemically recycled cellulose can only be produced if the post-consumer textiles have first undergone appropriate pre-treatment and purification.
Dr Marina Crnoja-Cosic, an expert in regenerated cellulose fibres and founder and Managing Director of MCC Innovare, has more than 25 years of experience in the man-made cellulose fibre industry. She is well acquainted with the strengths and limitations of the various recycling technologies and explains:
“Chemical recycling of cotton offers tremendous potential for a circular textile economy. However, its long-term success depends not only on the performance of the technologies themselves, but above all on the availability of high-quality, well-sorted post-consumer textiles. This, in turn, requires efficient sorting and pre-treatment processes.”
The purity of the textile feedstock remains a major challenge, as most textiles are made from two or more different fibre components. However, pure cotton textiles withdrawn from textile rental services could provide an important starting point for raw material supply. They meet the required feedstock specifications, as they are clean, available in large volumes and have a consistent material composition.
However, the chemical recovery of cellulose faces significantly greater obstacles. “At present, there is a lack of suitable regulatory frameworks to encourage investment and support the use of recycled raw materials throughout the entire value chain. Above all, however, there must be stable markets for the recycled products obtained,” summarises Dr Marina Crnoja-Cosic. And it is precisely these that are currently not in sight.
Factors Influencing the Chemical Recycling of Cotton
| Parameter | Viscose Process | Lyocell Process (NMMO) | Ionic Liquid-Based Processes |
|---|---|---|---|
| Requirements for recycled cotton textiles | Requires the extensive removal of foreign fibres and contaminants; the quality of the dissolving pulp has a major influence on the process. | High requirements regarding the purity and homogeneity of the dissolving pulp; foreign fibres and finishing chemicals can impair process stability. | Likewise requires high-quality cellulose; contaminants and a low degree of polymerisation negatively affect solubility, spinnability and fibre properties. |
| Influence of feedstock quality | High – the degree of polymerisation and purity determine the quality of the resulting fibres. | High – clean, preferably single-fibre cellulose is essential for producing high-quality fibres. | High – despite the performance of the solvents, the quality of the input pulp remains a key success factor. |
| Cellulose solvent performance | High | High | Very high |
| Resource consumption | Medium to high (particularly due to chemical use and pulp preparation). | Medium (closed-loop solvent system with a high recovery rate). | Currently medium to high, depending on the recovery of the ionic liquid and process design at industrial scale. |
| Technology readiness / industrial scale-up | Industrially established and widely deployed on a commercial scale worldwide. | Industrially established with continued market growth. | Still largely at the pilot or demonstration stage; commercial-scale implementation is under development. |
| Costs | Medium to high | High | Currently high to very high |
References:
Fink, H.-P., Weigel, P., Purz, H.-J., & Ganster, J. (2001). Structure Formation of Regenerated Cellulose Materials from NMMO-Solutions. Progress in Polymer Science, 26(9), 1473–1524
Hummel, M., Michud, A., Tanttu, M., Asaadi, S., Ma, Y., Hauru, L. K. J., Parviainen, A., King, A. W. T., Kilpeläinen, I., & Sixta, H. (2016). Ionic liquids for the production of man-made cellulosic fibers – opportunities and challenges. In: Advances in Polymer Science, Vol. 271, Springer, S. 133–168.
Sayyed, A. J., Deshmukh, N. A., & Pinjari, D. V. (2019). A critical review of manufacturing processes used in regenerated cellulosic fibres: viscose, cellulose acetate, cuprammonium, LiCl/DMAc, ionic liquids, and NMMO-based lyocell. Cellulose, 26, 2913–2940
