Researchers have discovered a technique to recycle clothing made of cotton, becoming the first to produce a viscose filament yarn made of recycled cotton.

The fibre, produced by researchers at Germany's Fraunhofer Institute for Applied Polymer Research, can be used for the mass manufacture of textiles.

"Cotton clothing is usually incinerated or it ends up in the landfill," says researcher André Lehmann. "Now it can be recycled several times to contribute to greater sustainability in fashion. This will also broaden the base of raw source materials for pulp production in the textile industry.

"The starter material for viscose rayon fibres has been wood-based cellulose. By optimising the separating processes and intensifying the filtration of foreign fibres in the spinning process, we will eventually be able to establish recycled natural cotton fibre as a serious alternative source of cellulose and base raw material."

Working on behalf of Swedish company Re:newcell, the research team succeeded in converting the pulp from recycled cotton into viscose rayon fibres made of pure cellulose.

The textile industry usually uses pulp as the starter material for producing regenerated cellulosic fibres such as viscose rayon, modal and lyocell. This pulp does not melt, so it has to be dissolved into a solution and passed through a spinneret to be spun into cellulosic fibres. The feedstock for this pulp is usually wood.

"However, Re:newcell sent us cellulose sheets made of recycled cotton and asked us to find out if they could be converted into viscose rayon fibres," adds Lehmann. "We were able to extract the foreign fibres from the pulp by setting the right parameters for both the dissolving and spinning processes, for example, with effective filtration stages."

This yielded a filament yarn – that is, a continuous strand of fibre several kilometers long consisting of 100% cellulose, the quality of which is comparable to that of wood-based regenerated cellulosic fibre. Compatible with the standard industrial process for making viscose rayon, the new fibres spun from this cotton pulp are suitable for mass manufacturing.

"We were able to meet Re:newcell's high purity standards for the new fibre," says Lehmann, who calls this filament yarn a cotton-based regenerated cellulosic fibre. It holds up well in comparison to commercially available viscose rayon fibres and exhibits the same properties.