Waste from plants could take the place of “forever chemicals” in waterproof coatings, according to engineers at Washington University in St. Louis. They have developed a plant-based material that makes water bead up and run off and, they say, breaks down in the environment.The coating is called SLIP, short for superhydrophobic lignin-integrated particles. It’s made from lignin, a plant waste material, and fatty acids. It aims to replace PFAS, the polyfluoroalkyl substances used in food packaging, fire protection, and waterproofing.Why forever chemicals are hard to replacePFAS earned the nickname “forever chemicals” because of the impact they have on the environment and human bodies. They also cost society billions of dollars in health and environmental damage. Yet the chemicals themselves are relatively cheap and plentiful, which is a big reason manufacturers rely on them. So the WashU team looked for an alternative that is also cheap and abundant.Lignin fits that description. “We actually use this waste material to turn it into a valuable product,” said Joshua Yuan, a professor and chair of energy, environmental and chemical engineering at WashU McKelvey Engineering.Copying a trick from plant plumbingThe researchers took cues from xylem, the vascular tissue that carries water through plants. Xylem contains a waterproof molecule called suberin. The team built suberin’s structure into lignin particles by linking lignin to fatty acids, then added a polylactic acid binder. The result was a highly water-repellent material that is also mechanically robust and stable under ultraviolet light, the study found.When the coating breaks downIn tests, water bounced off the new material. “The water will just run off,” said Puneet Dhatt, a first author. The team also tested the coating with wood-degrading fungus and found that it broke down into harmless organic matter within the expected time.Lignin and fatty acids “evolved to degrade in the environment for a long time,” Dhatt said. Yuan added that SLIP “is not going to stay in the environment forever.”A $1.1 billion estimateThe WashU team worked with researchers at Texas A&M University to estimate the savings. Looking at the global health and environmental harm from forever chemicals, the Texas group estimated that replacing them with SLIP in waterproofing could avoid as much as $1.1 billion in societal damage each year.SLIP doesn’t do everything PFAS does, the researchers said, but it covers a large share of the waterproof coatings used in modern manufacturing. It could be used in packaging and as a coating for construction materials. The next step is to make it oil- and fireproof to broaden its uses. The team is also working to scale up production and fit it into biorefinery and paper and pulping operations.“This study represents the perfect example where we learn from nature and design a sustainable material critical to our society,” Yuan said, with a life cycle similar to natural polymers.The study was published in the journal Matter.