Producing Adsorbents from Plastic Waste for Atmospheric Water Harvesting

Chemists from the University of Vienna have found a way to give plastic waste a second life. Using this method, several different types of plastic can be converted into polymer networks that draw water from the air. These materials can absorb water even in dry climates and can be released again using mild heat sources such as sunlight.The new study offers a second life for plastic waste as an adsorbent used to collect water from the air.

Waste plastic packaging materials can be transformed into useful products.

Using this method, waste plastic packaging materials, old CDs, and even LEGO pieces can be transformed into materials that capture significant amounts of moisture from the air. Some plastics consist of aromatic polymers containing rings of six carbon atoms in their molecular structure. These rings provide suitable points for linking polymer chains together to form a porous network with small internal voids. According to the press release, a subsequent sulfuric acid process adds sulfonic acid groups that draw out water even from relatively dry air. Researchers successfully produced these hydrophilic molecular sponges using various polystyrene packaging materials, old CDs made of polycarbonate, and LEGO pieces made of acrylonitrile-butadiene-styrene as starting materials. According to the same statement, they also successfully processed a mixture of selected waste plastics; this result demonstrates the versatility of the method among these starting materials. The findings published in Chem Circularity reveal a way of converting various aromatic plastic wastes into functional materials for capturing atmospheric moisture. The ability to process a mixture offers opportunities to reduce the separation requirement in compatible waste streams. For the method to be taken out of the laboratory, it is necessary to evaluate variable starting materials, solvent and reagent recovery, production costs, and environmental impacts; in addition, the integration with devices and long-term durability must be investigated. Addressing these issues will determine to what extent this second life given to plastic waste can contribute to circular material management and water supply.

Sponge made from general-purpose polystyrene

The team found that the sponge, made from general-purpose polystyrene used to make disposable forks and CD cases, can adsorb water equal to nearly 60% of its own weight in humid conditions and about 20% in dry, desert-like conditions. Water can be released and recaptured using mild heat sources such as sunlight; most of the adsorption/desorption cycle occurs within an hour. The sponges withstand this cycle well, meaning they can be used repeatedly to produce water. The team emphasized that the latest study reveals a way to convert various aromatic waste plastics, including mixed plastic feedstocks, into effective materials for water production from air. Studies are ongoing to evaluate the long-term performance and total resource requirements of the sponges.”We demonstrate this approach using aromatic waste plastics derived from packaging, compact discs, and LEGO pieces. Hypercrosslinking and sulfonation transform these starting materials into polymer networks that capture water, thereby granting a second life to existing polymer materials without first breaking them down into monomers,” the researchers said in the study.