PET and Polyester: PET is one of the most widely used plastics in the world. PET, the most familiar type of plastic beverage bottle, is produced in 70 million tons per year and is growing every year. One-third of the world's PET product is used to produce polyester and other synthetic textiles.
Polyester is the second most used textile in the world and poses a threat to the environment, especially since much of it is never recycled. This fabric, made from a mixture of plastic and cotton, is difficult to separate and therefore difficult to recycle. Now, a group of young chemists at the University of Copenhagen have invented a green and surprisingly simple solution using a household raw material.
Shriaya Sharma and Yang Yang demonstrate the methodology
From clothes to sofas to curtains, polyester fibers dominate our daily lives, with a staggering 60 million tons of this popular fabric produced each year. However, polyester production has an impact on the climate and the environment, as only 15 percent of polyester is recycled, while the rest ends up in landfills or incinerated, resulting in more carbon emissions. Recycling polyester fibers is a major challenge, especially in the process of separating plastic fibers from cotton fibers, of which blended fabrics are made, without losing either of them in the process. Conventional recycling methods typically prioritize the protection of the plastic component, resulting in the loss of cotton fibers. In addition, these methods are costly, complex and generate metal wastes due to the use of metal catalysts, which can be cytotoxic and contaminate the process.
Yang Yang, Li Jiwu and Shriaya Sharma in the lab
In a remarkable breakthrough, a group of young chemists have come up with a surprisingly simple solution to a pressing problem that could revolutionize sustainability in the textile industry.
"The textile industry is in dire need of a better solution for processing blended fabrics such as polyester/cotton. Currently, there are very few practical ways to recover both cotton and plastic, which is usually an either/or situation. However, with our newly discovered technology, we can depolymerize polyester into monomers while recycling hundreds of grams of cotton, using a very simple and environmentally friendly method. This unmarked catalytic approach could be a game changer," Yang Yang, a postdoctoral fellow in Jiwoong Lee's group at the University of Copenhagen's Department of Chemistry, explains that he is the lead author of the scientific research article.
Cut polyester clothing into small pieces and place in a container with hartshorn salt and mild solvent
Hartshorn salt and 24-hour "baking."
This new method requires no special equipment, just heat, non-toxic solvents and common household ingredients.
"For example, we can take a polyester dress, cut it into small pieces and put it in a container. Then, add a little mild solvent and then add hartshorn salt, which many people know as a leavening agent in baked goods. Then we heat it up to 160 degrees Celsius and let it sit for 24 hours. The result is a liquid in which plastic and cotton fibers settle into different layers." Shraya Sharma, a PhD student in Jiwoong Lee's group in the Department of Chemistry and co-author of the study, explains.
In this process, hartshorn salt, also known as ammonium bicarbonate, is broken down into ammonium, carbon dioxide, and water. The combination of ammonia and carbon dioxide acts as a catalyst, triggering a selective depolymerization reaction that breaks down the polyester while retaining the cotton fibers. Although ammonia is toxic when used alone, when combined with carbon dioxide it is both environmentally friendly and safe. Due to the mild nature of the chemicals involved, the cotton fibers remain intact and in excellent condition.
Previously, the same research team demonstrated that carbon dioxide can be used as a catalyst to break down nylon without leaving any traces.
This discovery inspired them to explore the uses of hartshorn salt. Nonetheless, the researchers were pleasantly surprised when their simple recipe was successful.
Carlo Di Bernardo, Ph.D. student and study co-author, said, "At first, we were happy to see that it worked so well on PET bottles alone. Then we were ecstatic when we realized it worked on polyester fabrics as well. It's indescribable. It performed so simply, almost too well to be true."
Processed intact cotton fibers
While the method has only been tested at the lab level so far, the researchers noted its scalability and are currently in contact with companies to test the method on an industrial scale.
Yang Yang concluded, "We want to commercialize this technology with great potential. Hiding this knowledge behind the walls of a university would be a huge waste."
Depolymerized plastics on polyester fibers
