Researchers at Lund University (Sweden; www.lth.se) have succeeded in converting worn-out cotton sheets into new viscose fibers using a process that — for the first time — enables all of the viscose to be recycled. Current recycling methods often require a high percentage of virgin fiber to make products from recycled textiles. As a result, old textiles are instead typically incinerated.
“Cellulose chains, the main component in plant fibers, are complex and long,” explains Edvin Bågenholm-Ruuth, doctoral student in chemical engineering at Lund University. “Cotton textiles are also intensively treated with dyes, protective agents and other chemicals. And then there is all the ingrained grime in the form of skin flakes and fats,” he says.
Bågenholm-Ruuth and his colleagues have developed a process, described in a recent issue of Cellulose, to loosen up and convert the complex cotton fibers into viscose fibers. The process uses hydrated zinc chloride (ZnCl2.4H2O) as a solvent and swelling agent to convert waste cotton textiles into a dissolving pulp. The pulp can then be used to make viscose dope, a spinning solution that can be spun into stable viscose fibers.
The process has the advantage of using ZnCl2.4H2O, a soluble, inexpensive salt, and requires a smaller percentage of carbon disulfide compared to standard viscose-spinning processes. The result is good-quality viscose fiber, even though the process needs to be further optimized, Bågenholm-Ruuth says. Also, an additional step may be required for recycling old clothing that has been dyed.
Startup company ShareTex AB (Bjärred, Sweden; www.sharetex.com) is working to further develop the technology. The process could be demonstrated at commercial scale within five to seven years.