Scientists develop a new way to convert cotton recycling into materials such as spandex, nylon and more
Latest: An estimated 25 million tons of cotton textiles are discarded worldwide each year. If you add up the different types, a total of 100 million tons of textiles are discarded. In Sweden, most of the material goes directly to the incinerator, which becomes district heating. Elsewhere, the situation is even worse, as old clothes often end up in landfills.
“Considering that cotton is a renewable resource, this is not particularly energy efficient,” says Edvin, a researcher in chemical engineering at Lund University
“Some fabrics still have fibers so strong that they can be reused,” Ruuth said. “It’s done today, and more may be done in the future. But a lot of discarded fabrics have fibers that are too short to be reused, and all Sooner or later the cotton fibers become too short for a process called fiber regeneration.”
Where Edvin Ruuth works, the Department of Chemical Engineering in Lund, has accumulated a great deal of knowledge about the use of microorganisms and enzymes, etc.
Knowledge of the conversion of “harder” carbohydrates into simpler molecules. This means that everything from biowaste and black liquor to straw and wood chips can be turned into bioethanol, biogas and chemicals.
Now, researchers have also succeeded in breaking down the plant fiber in cotton — cellulose — into smaller components. This time, however, no microorganisms or enzymes were involved; instead, the process involved soaking the fabric in sulfuric acid. The result is a clear, dark, amber sugar solution.
“The secret lies in finding the right combination of temperature and sulfuric acid concentration,” Ruuth noted. It is reported that he worked with doctoral student Miguel Sanchis-Sebastiá and professor Ola
Wallberg fine-tuned the “recipe” together.
Glucose is a very flexible molecule and has many potential uses, Ruuth said. “Our plan is to produce chemicals that in turn can be made into various types of textiles, including spandex and nylon. Another use could be the production of ethanol.”
From an ordinary sheet, they extracted 5 liters of sugar liquid, which contained the equivalent of 33 sugar cubes per liter. You can’t turn this liquid into a soft drink, however, because it also contains corrosive sulfuric acid.
One of the challenges is to overcome the complex structure of cotton cellulose.
“Cotton is unique in that its cellulose has a high degree of crystallinity. This makes it difficult for chemicals to break down and re-use its components. In addition, there are a lot of surface treatments, dyes and other contaminants that have to be removed. And in Structurally, a terry towel is very different from an old pair of jeans,” says Ruuth, “so finding the right acid concentration, the right number of treatment stages and the right temperature is a very delicate process.”
Ruuth said the concept of hydrolyzing pure cotton itself is not new, it was discovered in the 19th century. The difficulty is how to make this process efficient, economically feasible and attractive.
“Many people who try end up not using a lot of cotton, and others do better, but with unsustainable cost and environmental impact,” Ruuth said.
When he started making dextrose from fabric a year ago, the rate of return was a paltry three to four percent. Now he and his colleagues have reached 90%.
Once the recipe is complete, its use will be relatively simple and inexpensive.
To make this process a reality, however, logistics must play a role. There is currently no established method for managing and sorting the various textiles that are not sent to general clothing donation points.
Fortunately, a recycling centre unlike anywhere else in the world is currently being built in Malmö, where sensors are used to automatically sort laundry. Some clothing will be donated, rags can be used in industry, textiles with thick enough fibers can be made into new fabrics, and the rest will be used for district heating.