Emerging Recycling Research: Separating Natural Fibers from Synthetic

Written by Tirsa Parrish

 

Many in fashion are working to make the industry more environmentally friendly by using sustainable products and processes. Textile waste is a huge issue. According to the United States Environmental Protection Agency (EPA), 11 Million tons of textile waste ends up in US landfills each year. This does not account for all the textile waste that is shipped overseas.

Breakthrough Recycling Research

Researchers at North Carolina State University have found a groundbreaking way to separate out cotton from polyester fibers in poly-cotton blends. This could soon lead to wide-spread recycling of garments made from these blended fabrics. 

 

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. 

 

Blue cotton fabric on a table with a jug and flask of blue liquid. Small squares of the fabric are on a metal tray and filtered pressed fibers create a blue disk as part of the garment recycling process.

A cotton knit fabric dyed blue and washed 10 times to simulate a worn garment is enzymatically degraded to a slurry of fine fibers and “blue glucose” syrup that are separated by filtration. Both of these separated fractions have potential recycled value. Image via texfash.com

Breaking Down The Process

The goal of this work was to develop a laboratory process to break-down and separate cut fabric into purified cotton and polyester to promote textile recycling. Separating the fibers means each component can then be recycled. 

Key terms: 

  • Enzymes jump-start biochemical reactions 

  • Cellulose is the material that gives structure to plants’ (like cotton) cell walls

  • Glucose is the biodegradable byproduct of degraded cellulose

A “cocktail” of enzymes in a mildly acidic solution (approximately equivalent to the acidity of vinegar) was used to break down the cellulose in the cotton. Since polyester is a synthetic fiber, it contains no cellulose and is not affected by this process.

 

The idea is to chop up the cellulose so it will “fall out” out of the blended woven structure, leaving some tiny cotton fiber fragments remaining, along with glucose. Then, their process involves washing away the glucose and filtering out the cotton fiber fragments, leaving clean polyester.

 

There are several ways to speed up chemical reactions. Enzymes do some of the work, but heating and vigorously stirring the enzymatic solution makes the process happen even faster. 100% cotton fabric was broken down into a slurry of < 2mm (less than ⅛ inch) cotton solids and water soluble degradation products at 122 F (the temperature of very hot tap water). 

 

Fabrics with dyes or coatings, such as needed for wrinkle resistance, slows down the process. The additives wrap around the fibers creating a barrier making it more difficult for the enzymes to reach the cotton and begin breaking it down. A pre-treating process and a secondary enzyme dose was required to penetrate that barrier and fully break down the cotton.

 

olycotton fibers and cleaned cotton fibers under a microscope. Bottom: polycotton blend after different enzymatic treatments.

Top: Optical microscopy with red plate and crossed polars, where fiber diameters are about 20 microns; Bottom: macroscopic appearance of large solids after treatment and drying. Image via sciencedirect.com

Separating Fibers Increases Circularity

Once the cotton was washed away from the woven polyester, both could now be recycled. Polyester can be recycled into new clothes or a variety of other applications while the slurry of cotton fragments could be valuable as an additive for paper or a useful addition to composite materials. The glucose-rich process syrups could be used to produce fuels and chemicals by fermentation.

 

Sonja Salmon believes this innovative process can reduce textile waste in a sustainable way. “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.”