A Simple Kitchen Ingredient Revolutionizes Polyester Recycling and Addresses Environmental Concerns

Researchers at the University of Copenhagen have developed an eco-friendly technique for recycling polyester, using ammonium bicarbonate, also known as hartshorn salt. This innovation provides a significant advancement in the area of textile recycling. The photograph credits go to Bettina Illemann Larsen of the University of Copenhagen, capturing depolymerized plastic derived from polyester fabric.

As the second most commonly used textile globally, polyester poses considerable environmental challenges, primarily due to its low recycling rate. Comprising both plastic and cotton, the fabric has long been a challenge for the industry to efficiently separate and recycle. Nonetheless, a team of emerging chemists from the University of Copenhagen has devised an eco-friendly, yet remarkably simple, solution that utilizes a common household substance.

Polyester pervades our daily existence, from apparel to furniture to drapery, with an astonishing 60 million tons produced each year. Unfortunately, its production wreaks havoc on both the environment and climate, as merely 15% gets recycled while the remaining either becomes landfill waste or gets incinerated, contributing to increased carbon emissions.

The primary difficulty in polyester recycling lies in disentangling the composite plastic and cotton fibers without sacrificing either material. Traditional recycling techniques tend to focus on retaining the plastic content at the expense of losing the cotton fibers. Moreover, these conventional approaches are not only expensive and intricate but also produce metal waste due to the use of metal-based catalysts, which have the potential to be cytotoxic and compromise the recycling process.

In a significant development, these young chemists have introduced a remarkably straightforward solution to this urgent issue, with the potential to transform the textile industry’s sustainability practices radically.

“The dire need for an improved methodology to manage composite fabrics like polyester-cotton blends cannot be overstated. Currently, there are minimal viable approaches that allow for the recycling of both cotton and plastic. However, our newly developed technique enables the depolymerization of polyester into its constituent monomers while simultaneously extracting cotton in substantial quantities, all through an eco-friendly and uncomplicated process. This catalytic approach devoid of traces could serve as a game-changer,” elucidates postdoctoral researcher Yang Yang, the lead author of the scientific paper, who is affiliated with the Department of Chemistry at the University of Copenhagen under the Jiwoong Lee research group.

The Role of Ammonium Bicarbonate and Heat Treatment

The innovative procedure necessitates no specialized apparatus. It involves heating, a harmless solvent, and a readily available household item.

“We could, for instance, take a polyester outfit, shred it into fragments, and place it in a receptacle. Following that, we introduce a mild solvent and hartshorn salt, commonly employed as a rising agent in baking. The mixture is then heated to 160 degrees Celsius and left for 24 hours. The ensuing liquid separates the plastic and cotton fibers into discrete strata, providing a cost-efficient and straightforward process,” states Shriaya Sharma, a Ph.D. candidate affiliated with the Jiwoong Lee research group at the Department of Chemistry, and a co-author of the study.

The process decomposes the ammonium bicarbonate into ammonia, carbon dioxide, and water. This amalgamation of ammonia and carbon dioxide serves as a catalyst, instigating a selective depolymerization that breaks down the polyester while leaving the cotton fibers intact. Although ammonia in isolation can be harmful, its combination with carbon dioxide makes it eco-friendly and safe. Due to the mild nature of the involved chemicals, the cotton fibers are preserved in excellent condition.

The research group had previously established that carbon dioxide could act as a catalyst for decomposing other materials like nylon, which led them to investigate the use of hartshorn salt. They were pleasantly surprised by the effective results yielded by their uncomplicated formula.

“We were initially delighted to observe its effective performance on PET bottles alone. Upon realizing that it also worked efficiently on polyester textiles, our excitement was immeasurable. The process’s simplicity was almost too good to be true,” comments Carlo Di Bernardo, a Ph.D. student and another co-author of the study.

Although only verified in the laboratory setting, the researchers are actively discussing with various corporations to evaluate the technique’s industrial-scale feasibility.

“Commercializing this technology, which holds considerable promise, is our ultimate aim. Retaining such valuable knowledge within academia would be a missed opportunity,” concludes Yang Yang.

Relevance to PET and Waste Recycling

Polyethylene terephthalate (PET) is the most extensively used plastic globally, with an annual production volume of 70 million tons, showing a year-over-year increase. About one-third of this production is utilized for creating polyester and other synthetic textiles.

The newly discovered recycling approach, based on ammonium bicarbonate, is effective not only for pure PET plastic but also for blends of PET and cotton.

“Even if the plastic waste is contaminated, for example, a bottle with juice residues, the method still functions effectively. Quality cotton and plastic monomers can still be extracted,” asserts Shriaya Sharma.

Citation

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

Frequently Asked Questions (FAQs) about Eco-friendly Polyester Recycling

More about Eco-friendly Polyester Recycling

• Original Scientific Research Article in ACS Sustainable Chemistry & Engineering
• University of Copenhagen Department of Chemistry
• Overview of Polyester and Environmental Impact
• Current Challenges in Textile Recycling
• Introduction to Hartshorn Salt
• Global Polyester Production Statistics
• Effects of Plastic Waste on the Environment