A plant-inspired waterproof coating could soon become a safer and more sustainable alternative to forever chemicals like the PTFE used in waterproof clothing.
Per- and polyfluorinated alkyl substances, known as PFAS or forever chemicals, have proven both a blessing and a curse for modern society. Their manifold useful properties, which include having high heat resistance, while being both water- and greaseproof, inert and durable, have made them a staple of many consumer products, from cookware and clothing to medical tools and electrical insulation. More recently, concerns around their long-term persistence in the environment, and the resulting impacts on human health, have meant regulation has tightened substantially and scientists are now working to develop greener and cleaner alternatives.
But, as is often the case, nature may have already found the solution. 鈥淧lants transport water across very long distances using this structure called suberin,鈥� says , a chemical engineer at Washington University in St Louis, Missouri. Composed of a mixture of greasy long-chain fatty acids, suberin combines with the plant polymer lignin to form a super-waterproof surface that lines the tiny vessels and tubes of the plant鈥檚 internal plumbing system.
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Drawing inspiration from these natural pipes, Yuan鈥檚 team recreated this waterproof coating from a combination of paper industry waste and animal fat. They spray-coated the suberin-like slurry onto glass, metal and cotton surfaces where the individual particles quickly self-assembled to form a continuous waterproof layer.
Unlike PFAS coatings, whose many carbon-fluorine bonds directly repel water molecules, the new coating operates by a completely different mechanism, says , an organic chemist at Wageningen University & Research in the Netherlands. The precisely nanostructured surface creates lots of tiny pockets of air, which effectively minimise direct contact between the coated material and water droplets on the surface 鈥� similar to the seen on the leaves of many plants.
The new structure proved resistant to both contamination by limescale and mechanical wear, and showed a similar level of water resistance to state-of-the-art forever chemical coatings like PTFE. 鈥淚t uses an interesting approach. Textiles will be one of the first sectors affected by PFAS restrictions, so it could be a good alternative,鈥� says , a materials scientist at the University of Milano-Bicocca in Italy.
The team is already exploring applications in food packaging, such as the internal linings of drinks cans, but the coating鈥檚 lower heat tolerance compared with PTFE means bakeware is currently off the table.
The versatile properties of such a material mean there is no shortage of potential uses. The real step forward though, is the completely bio-based nature of the coating, says Zuilhof. Suberin鈥檚 chemical structure is easily degraded under composting conditions and the team showed their nature-inspired material likewise broke down completely, without releasing harmful residues into the environment. 鈥淭hey鈥檝e basically turned a waste product into something valuable, and that鈥檚 quite cool,鈥� says Zuilhof. 鈥淚 think this will be a source of inspiration to find other bio-based materials from different waste streams.鈥�
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