Researchers have found a way to give plastic waste a second life. Materials chemists at the University of Vienna have found a way to convert several types of plastic waste into water-attracting polymer networks. These can absorb water even in dry climates and release it again when it warms moderately, for example from sunlight.
The new initiative offers a way to give plastic waste a second life as an adsorbent for atmospheric water production.
Discarded plastic packaging materials can be converted into useful products
This method can transform discarded plastic packaging materials, old CDs, and even LEGO bricks into materials that absorb significant amounts of moisture from the air.
Certain plastics are made of aromatic polymers whose molecular structures contain rings of six carbon molecules. These rings act as convenient sites to connect the polymer chains together, forming a porous network with tiny interior spaces. A subsequent treatment with sulfuric acid adds sulfonic acid groups, which attract water even from relatively dry air, according to a press release.
The researchers managed to create such water-loving molecular sponges using various polystyrene packaging materials, old polycarbonate CDs and LEGO bricks made from acrylonitrile butadiene styrene as starting materials. They have also successfully treated a select mix of plastic waste, proving the versatility of these raw materials, the press release said.
The results, published in Chem Circularity, show a route from various aromatic plastic wastes to functional materials for storing atmospheric moisture. The ability to process a mixture provides opportunities to reduce sorting requirements within compatible waste streams. In addition to instrument integration and long-term durability, transfer beyond the laboratory also requires the assessment of variable raw materials, solvent and reagent recovery, production costs and environmental impacts. Answering these questions will determine the extent to which this second life for plastic waste can contribute to the circular economy and water supply.
General purpose polystyrene sponge
The team found that the general-purpose polystyrene sponge used to make disposable cutlery and CD cases can absorb nearly 60% of its own weight in water from moist air and as much as 20% in dry, desert-like conditions. The water can then be released back into collection using mild heat sources such as sunlight, with most adsorption/desorption occurring within an hour. The sponges withstand the cycle process well and can therefore be used again and again to obtain water.
The team highlighted that recent efforts provide an opportunity to convert several aromatic plastic wastes into effective materials for producing water from air, including mixed plastic feedstocks. Further work is underway to assess the long-term performance and overall resource requirements of the sponges.
“We demonstrate this approach using aromatic plastic waste from packaging, CDs and LEGO bricks. Through hyper-crosslinking and sulfonation, these substrates are converted into polymer networks for water binding, giving existing polymeric materials a second life without first breaking them down into monomers,” the researchers said in the study.
