Every year, millions of tonnes of cotton are produced worldwide, while vast quantities of textiles are discarded or incinerated. Although cotton consists of almost pure cellulose, only a small proportion of the material is recycled into new textiles.
In her mid-term study, Elise Meurs, an industrially associated PhD candidate in the EXACT Research School, investigates how cellulose pulp derived from recycled cotton behaves during the initial stages of the viscose process, the industrial method used to produce regenerated cellulose fibres. The aim is to enable the large-scale use of textile waste and thereby reduce the need for virgin raw materials from forests or cotton cultivation.
Textile Waste as a New Resource
Viscose is typically produced from so-called dissolving pulp derived from wood or cotton linters, a by-product of the cotton industry. Cotton-based textile waste, however, has emerged as a highly promising raw material because it already contains large amounts of pure cellulose.
"The challenge is that recycled cotton does not always behave in the same way as conventional raw materials during the manufacturing process. For industry to use the material efficiently, we need a better understanding of what happens to the fibres during processing," says Elise Meurs.
Fibres Swell Rapidly
In the first stage of the viscose process, the cellulose is treated with a concentrated sodium hydroxide solution. The fibres then swell, becoming more accessible to the chemical reactions required later in the process to produce new textile fibres.
The study shows that most of the swelling occurs within the first few minutes. Cotton-based pulps, whether derived from recycled textiles or cotton linters, swell more than conventional wood-based pulp. This helps to make the fibres receptive to further processing, but the high swelling also makes it more difficult to remove excess liquid and obtain a target dryness after the first activation treatment.
The researchers believe that the structure of the fibres could contribute to an explanation of these observed differences. Recycled cotton fibres have thinner cell walls and larger central cavities, which could enable them to absorb greater amounts of liquid.
Cleaner Materials with Less Waste
Another important finding concerns the purification of the raw material. During the first phase of the viscose process, unwanted substances are dissolved and removed from the pulp. Wood-based pulp contains more impurities from the outset than cotton-based materials and therefore loses more material during processing.
This suggests that recycled cotton could not only help reduce textile waste but also contribute to more efficient use of resources during production.
A Step Towards Circular Clothing
"Our research shows that recycled cotton textiles have significant potential as a raw material for viscose production. The material results in high swelling of the fibers, low yield losses and high purity in the early stages of the process towards viscose, indicating promising performance. At the same time, more knowledge is needed about its behaviour in the later stages of production, when the cellulose is dissolved and spun into new fibres," says Elise Meurs.
If these challenges can be addressed, the textile industry could move closer to a truly circular model, where old cotton garments are transformed into raw materials for new textiles time and time again.
