New coating makes natural fabrics waterproof
For everyone who has ever been stuck in the rain, it’s obvious that water-resistant fabrics are very convenient. However, conventional water-repellent coatings have been shown to persist in the environment and accumulate in our bodies, so for safety reasons, they are likely to be phased out.
Most fabrics that claim to be water-repellent are actually water-resistant. If you’re standing in the rain, eventually, the water will seep through. With water-repellency, on the other hand, drops just bounce back.
Currently used coatings to make waterproof generally consist of long polymers with perfluorinated side-chains. Short-chain polymers are not nearly as persistent in the environment, but are not as water repelling as their longer counterparts. In addition, most coatings are liquid-based. To make the fabric water-repellent, it is immersed in the liquid and dried out, but the fabric breathes not as much as before, as the pores get clogged. In another manufacturing process, the pores can be reopened, but this costs time and undoes some of the water protection.
The coating developed by the MIT engineers contains shorter-chain polymers that confers some hydrophobic properties, which are enhanced with some extra chemical processing. The coating process is also different than common coatings. The process is called initiated chemical vapour (iCVD). This process does not involve any liquids and can be done at low temperature. It produces a thin, uniform coating that follows the contours of the fibres and leaves the pores open. A kind of sandblasting of the surface can enhance the water-repellency even more.
The process works on many kinds of fabrics, including natural ones like cotton and linen, and even on nonfabric materials like paper. The waterproof coating has been tested with standard rain tests, but also works with other liquids like coffee, ketchup and soy sauce.
Images: Varanasi and Gleason research groups