Disposable diapers are a huge source of waste globally, largely because they are difficult to recycle. However, a new process can recycle the "superabsorbent" polymer used in diaper liners - even if they are filled with excrement. Most disposable diaper liners are made from a polymer called sodium polyacrylate, which changes from a dry state to a hydrogel when it absorbs liquid.
The past method of recycling this material was to soak it in strong acid and then heat it to 80ºC (176ºF) for about 16 hours. This process breaks down the cross-linked polymer chains that make up the gel, allowing it to be recycled. Unfortunately, this technique is rarely used because it requires a lot of time and materials.
Looking for a more effective alternative, scientists at the Karlsruhe Institute of Technology in Germany soaked sodium polyacrylate diaper linings with water and then exposed them to ultraviolet light from a 1,000-watt light bulb at room temperature. After just five minutes, the polymer gel dissolves into a liquid and flows into a collection tank. The scientists then used existing processes to convert the liquefied sodium polyacrylate into adhesives and dye thickeners.
Professor Pavel Levkin from the University of Karlsruhe explained: "The chains connecting the polymers are broken by light. They then become very loose and swim in the water, turning into liquid fibers... This method using ultraviolet light is about 200 times faster than the method using acid."
Although clean diaper liners were used in the experiment, the scientists believe the method would work just as well with used liners. "We have found a promising strategy for recycling superabsorbents," Levkin said. "This will significantly reduce environmental pollution and contribute to a more sustainable use of polymers." "
A paper on the research was recently published in the journal Applied Materials and Surfaces.