University researchers in the US have been able to separate blended cotton and polyester fabric using enzymes.
- The findings will hopefully lead to a more efficient way to recycle the fabric’s component materials, thereby reducing textile waste.
- The researchers have also found that the process needs more steps if the blended fabric is dyed or treated with chemicals that increase wrinkle resistance.
- The findings are significant since enzymes are nature’s own tools for speeding chemical reactions.
The Breakthrough Research: The research project was led by Sonja Salmon, associate professor of textile engineering, chemistry and science at NC State University.
- The study, Enzymatic textile fiber separation for sustainable waste processing, has been published in Resources, Environment and Sustainability.
- The lead author was Jeannie Egan, a graduate student at NC State. The co-authors included Siyan Wang, Jialong Shen, Oliver Baars and Geoffrey Moxley.
- Funding was provided by the Environmental Research and Education Foundation, Kaneka Corporation and the Department of Textile Engineering, Chemistry and Science at NC State.
The Backdrop: According to the US Environmental Protection Agency (EPA), consumers throw away 11 million tonnes of textile waste into US landfills each year. Researchers wanted to develop a method of separating the cotton from the polyester so each component material could be recycled.
The Project: The researchers used a “cocktail” of enzymes in a mildly acidic solution to chop up cellulose in cotton. [Cellulose is the material that gives structure to plants’ cell walls.]
- The idea is to chop up the cellulose so it will “fall out” out of the blended woven structure, leaving some tiny cotton fibre fragments remaining, along with glucose. [Glucose is the biodegradable byproduct of degraded cellulose.]
- Then, their process involves washing away the glucose and filtering out the cotton fibre fragments, leaving clean polyester.
- This is a mild process — the treatment is slightly acidic, like using vinegar. The researchers also ran it at 50 degrees Celsius, which is like the temperature of a hot washing machine.
- The team compared degradation of 100% cotton fabric to degradation of cotton and polyester blends, and also tested fabric that was dyed with red and blue reactive dyes and treated with durable press chemicals.
- In order to break down the dyed materials, they had to increase the amount of time and enzymes used. For fabrics treated with durable press chemicals, they had to use a chemical pre-treatment before adding the enzymes.
- The chosen dye has a big impact on the potential degradation of the fabric.
- The researchers also found that the biggest obstacle so far was the wrinkle-resistant finish. The chemistry behind that creates a significant block for the enzyme to access the cellulose.
- Without pre-treating it, they achieved less than 10% degradation. But after, with two enzyme doses, they were able to fully degrade the wrinkle-resistant finish.
- The polyester could now be recycled, while the slurry of cotton fragments could be valuable as an additive for paper or useful addition to composite materials.
What They Said:
We can separate all of the cotton out of a cotton-polyester blend, meaning now we have clean polyester that can be recycled. In a landfill, the polyester is not going to degrade, and the cotton might take several months or more to break down. Using our method, we can separate the cotton from polyester in less than 48 hours. It’s quite promising that we can separate the polyester to a clean level. We still have some more work to do to characterize the polyester’s properties, but we think they will be very good because the conditions are so mild. We’re just adding enzymes that ignore the polyester.
— Sonja Salmon (corresponding author)
Associate Professor, Textile Engineering, Chemistry and Science
NC State University