Coating offers safer way to make fabrics water repellent
发布时间：2024年6月4日 05:47
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(Credit: MIT)
Researchers at Massachusetts Institute of Technology have developed a more effective water-repellent coating for fabrics that is also less harmful than existing coatings.
Researchers at Massachusetts Institute of Technology have developed a more effective water-repellent coating for fabrics that is also less harmful than existing coatings.
Current hydrophobic coatings contain long polymers with perfluorinated side-chains, which can accumulate in the environment and in human body tissue. In the United States, the Environmental Protection Agency is revising regulations on their use, which has driven the development of new, more planet-friendly coatings.
Because they are liquid-based, existing coatings also require the fabric to be immersed in the substance and then dried, which can clog the pores on its surface and make the fabric less breathable.
This means that air has to be blown through the fabric to reopen pores, which adds a second manufacturing step, increases the cost, and reduces the effectiveness of the waterproof coating.
A research group at MIT built on previous research showing that polymers with fewer than eight perfluorinated carbon groups do not collect and accumulate in the environment as much as those with eight or more.
The MIT researchers, including professors Kripa Varanasi and Karen Gleason, and former postdoc Dan Soto, used shorter polymers which had been enhanced with some extra chemical processing to make them better at repelling water. They then used a new coating technique, developed by Gleason, called initiated chemical vapour deposition (iCVD).
This produced a very thin coating that following the contours of the fibre, and did not block pores, eliminating the need for a second manufacturing stage.
“The biggest challenge was finding the sweet spot where performance, durability, and iCVD compatibility could work together and deliver the best performance,” said Soto. “Many fabrics can benefit from this technology. There’s a lot of potential here.”
The coated materials have been subjected to repeated washings with no degradation of the coatings, and also have passed severe abrasion tests, with no damage to the coatings after 10,000 repetitions. Eventually, under severe abrasion, “the fibre will be damaged, but the coating won’t,” said Varanasi.
He said the coating was a step closer to truly water-repellent materials, rather than just water-resistant ones. “Most fabrics that say ‘water-repellent’ are actually water-resistant,” he said. “If you’re standing out in the rain, eventually water will get through.” Ultimately, “the goal is to be repellent – to have the drops just bounce back”.
Because they are liquid-based, existing coatings also require the fabric to be immersed in the substance and then dried, which can clog the pores on its surface and make the fabric less breathable.
This means that air has to be blown through the fabric to reopen pores, which adds a second manufacturing step, increases the cost, and reduces the effectiveness of the waterproof coating.
A research group at MIT built on previous research showing that polymers with fewer than eight perfluorinated carbon groups do not collect and accumulate in the environment as much as those with eight or more.
The MIT researchers, including professors Kripa Varanasi and Karen Gleason, and former postdoc Dan Soto, used shorter polymers which had been enhanced with some extra chemical processing to make them better at repelling water. They then used a new coating technique, developed by Gleason, called initiated chemical vapour deposition (iCVD).
This produced a very thin coating that following the contours of the fibre, and did not block pores, eliminating the need for a second manufacturing stage.
“The biggest challenge was finding the sweet spot where performance, durability, and iCVD compatibility could work together and deliver the best performance,” said Soto. “Many fabrics can benefit from this technology. There’s a lot of potential here.”
The coated materials have been subjected to repeated washings with no degradation of the coatings, and also have passed severe abrasion tests, with no damage to the coatings after 10,000 repetitions. Eventually, under severe abrasion, “the fibre will be damaged, but the coating won’t,” said Varanasi.
He said the coating was a step closer to truly water-repellent materials, rather than just water-resistant ones. “Most fabrics that say ‘water-repellent’ are actually water-resistant,” he said. “If you’re standing out in the rain, eventually water will get through.” Ultimately, “the goal is to be repellent – to have the drops just bounce back”.
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