Water and UV radiation effectively and quickly break down the cross-linked polymers in diaper liners without the use of any chemicals. This process allows recycled plastic molecules to be repurposed for a variety of uses. Superabsorbent materials such as sodium polyacrylate are key ingredients in a variety of hygiene and medical products such as diapers, bandages and dressings. Typically, these cross-linked polymers, known for their high absorbency, are insoluble in water. Traditionally, strong acids have been necessary to recycle them.

After the super absorber absorbs enough water, it turns into a liquid when exposed to UV light. They can then be reused. Source: KenPekarsky, KIT

At high temperatures, absorbent materials do not melt, they simply degrade. However, after about 16 hours at 80 degrees Celsius, the acid "severs" the chains that stabilize the polymer, allowing for recycling. The process is complex and expensive, so superabsorbents are rarely reused. Every year, approximately 2 million tons of super absorbers are thrown into the trash or incinerated.

Researchers from the Institute of Biological and Chemical Systems, the Institute of Biointerfaces and the Institute of Chemical Technology and Polymer Chemistry of the Technical University of Technology have now discovered that cross-linked sodium polyacrylate polymers degrade under UV light after absorbing moisture.

"The chains connecting the polymers break when exposed to light. The chains connecting the polymers are broken by light," explains Pavel Levkin, professor at the Institute of Biological and Chemical Systems. "Then, they become very loose and swim in the water, turning into liquid fibers." In the study, researchers cut linings from traditional diapers, soaked them with water and then placed them under a 1,000W light. "This method using ultraviolet light is about 200 times faster than using acid," Levkin said. "

The team then used known processes to convert the liquid into new binders and dyes. "It is very important to observe that this substance is soluble and processable. Most likely, it can also be transformed into many other products," the scientist explains.

In the tests, the researchers used clean diapers. But superabsorbents can also be isolated from used diapers. "So there's no reason why something close to practical use can't be done," Levkin said. By using solar energy, this recycling method can optimize the ecological environment without increasing costs. We have identified a promising super absorber recycling strategy. This will significantly reduce environmental pollution and contribute to a more sustainable use of polymers."

Reference: "From diapers to thickeners and pressure-sensitive adhesives": Li Shuai, Johannes M. Scheiger, Wang Zhenwu, Birgit Huber, Maxi Hoffmann, Manfred Wilhelm and Pavel A. Levkin published in "ACS Applied Materials and Interfaces" on September 7, 2023.

DOI:10.1021/acsami.3c06999

Compiled from: ScitechDaily