Salt and “baking” – a simple combination solves serious environmental problems



Depolymerized plastic from polyester fabric

Chemists at the University of Copenhagen have developed an environmentally friendly way to recycle polyester using Harthorn salt, creating a breakthrough in textile recycling. The top is a plastic depolymerized from polyester fabric.Credit: Bettina Illemann Larsen/University of Copenhagen

Polyester is the second most used fiber in the world, but it poses an environmental threat, especially because so little of it is recycled. The fabric is a mixture of plastic and cotton, making it difficult for the industry to separate and recycle. But a group of young chemists at the University of Copenhagen have invented an environmentally friendly and surprisingly simple solution using a single ingredient found at home.

From clothing to sofas to curtains, polyester is at the heart of our daily lives, and a staggering 60 million tonnes of this popular fabric are produced each year. However, polyester production has a negative impact on the climate and environment as only 15% of it is recycled and the rest ends up in landfill or incineration, contributing to more carbon emissions.

Recycling polyester poses major challenges, especially in separating the plastic and cotton fibers that make up blended fabrics without losing them in the process. Traditional recycling methods often prioritize preserving plastic components, resulting in the loss of cotton fibers. Additionally, these methods are expensive and complex, and the use of metal catalysts generates metal waste, which can be cytotoxic and contaminate the process.

Yang Yang, Jieun Lee, Shriya Sharma

Yang Yang, Jieun Lee, and Shriaya Sharma in the laboratory;Credit: Bettina Illemann Larsen/University of Copenhagen

In a remarkable advance, a group of young chemists has uncovered a surprisingly simple solution to this pressing problem, which could revolutionize sustainability in the textile industry.

“The textile industry urgently needs better solutions for processing blended fabrics such as polyester/cotton.Currently, there are few practical ways in which both cotton and plastic can be recycled, and there are usually only two However, using our newly discovered technology, we can simultaneously depolymerize polyester into monomers using an incredibly easy and environmentally friendly approach, and at scale of hundreds of grams. “This traceless catalytic methodology could be a game-changer,” explains Yang Yang, a postdoctoral researcher in the Jieun Lee Group at the Department of Chemistry at the University of Copenhagen. He is the lead author of a scientific research paper.

24 hours in the “oven” with Hartshorn salt

This new method requires no special equipment. All you need is heat, a non-toxic solvent, and common household materials.

“For example, we cut a polyester dress into pieces and put them in a container. Then we add a small amount of a mild solvent, followed by Harthorn salt, which many people know as a leavening agent in baked goods. Then , heat the whole thing to 160 degrees Celsius Then leave it for 24 hours. The result is a liquid in which the plastic and cotton fibers are deposited in separate layers. “This is a simple and cost-effective process,” explains study co-author Shriaya Sharma, a doctoral student in the Jieun Lee group in the Department of Chemistry.

Intact cotton fiber after processing

The cotton fiber remains intact after processing.Credit: Bettina Illemann Larsen/University of Copenhagen

In the process, Harthorn salt, also known as ammonium bicarbonate, is broken down into ammonia, CO2, and water. The combination of ammonia and CO2 acts as a catalyst, causing a selective depolymerization reaction that breaks down the polyester while preserving the cotton fiber. Ammonia alone is toxic, but when combined with CO2, it is environmentally friendly and safe to use. Due to the mild nature of the chemicals involved, the cotton fibers remain intact and in excellent condition.

Previously, the same research group demonstrated that CO2 can act as a catalyst to decompose materials such as nylon without leaving traces, among other things. This discovery inspired them to explore the use of Hartshorn salt. Nevertheless, the researchers were pleasantly surprised that their simple recipe yielded successful results.

“At first, we were excited to see that it worked so well with just a plastic bottle. Then when we discovered that it also worked on polyester fabrics, we were just overjoyed. “It was indescribable. It’s almost impossible that it was this easy to play,” says doctoral student and study co-author Carlo Di Bernardo.

Cut polyester dress into small pieces

Cut the polyester dress into small pieces and place them in a container containing Harthorn salt and a mild solvent.Credit: Bettina Illemann Larsen/University of Copenhagen

The method has so far only been tested at the laboratory level, but the researchers note its scalability and are currently in contact with companies to test the method on an industrial scale.

“We want to commercialize this technology, which has such great potential. It would be a huge waste to hide this knowledge within the walls of universities,” said Yang. he concludes.

Shriya Sharma and Yang Yang

Shriya Sharma and Yang Yang demonstrating the method.Credit: Bettina Illemann Larsen/University of Copenhagen

pets and polyester

PET is the most widely used type of plastic in the world. The production volume of PET, the most commonly used plastic for beverage bottles, has reached 70 million tons per year and is increasing year by year. One-third of the world’s PET production is used to make polyester and other synthetic fibers.

We also tackle waste

The new recycling method, based on Harthorn salt (ammonium bicarbonate), can be used not only for PET plastic alone, but also for mixed materials of PET and cotton.

“Even if you throw away your dirty plastic waste in a container, you will still get high-quality cotton and plastic monomers from it. A plastic bottle with some juice residue in it will do too. Just fill it and start the reaction. It still works,” says Shriaya Sharma.

Reference: “Catalytic Fabric Recycling: Glycolysis of Blended PET Using Carbon Dioxide and Ammonia” (Yang Yang, Shriaya Sharma, Carlo Di Bernardo, Elisa Rossi, Rodrigo Lima, Fadhil S. Kamounah, Margarita Poderyte, Kasper Enemark -Rasmussen, Gianluca Ciancaleoni, Author) Ji-Woon Lee, July 17, 2023, ACS Sustainable Chemistry and Engineering.
DOI: 10.1021/acssuschemeng.3c03114

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