We all know that natural fabrics like wool, cotton, linen, and silk are not exactly waterproof. But now, a team of researchers at MIT say they have come up with a coating that not only adds water-repellency to natural fabrics (and synthetic ones) but is also more effective than current DWRs.
Traditional DWR treatments use long polymers with perfluorinated side-chains. Due to environmental concerns, most outdoor brands have switched to DWRs made from shorter-chain polymers as supposedly they do not persist and bioaccumulate nearly as much as the longer-chain versions (the industry acknowledges this is not an end-all solution as it’s still a PFC). The problem is that these shorter-chains do not have as much of a water-repelling (or hydrophobic) effect.
Another problem with existing DWRs is that they are liquid-based, so the fabric has to be immersed in the liquid and then dried out. This tends to clog all the pores in the fabric, so the fabrics no longer can breathe as they otherwise would. That requires a second manufacturing step in which air is blown through the fabric to reopen those pores.
To create the new coating, the MIT team took a shorter-chain polymer enhanced with some extra chemical processing; and a different coating process, called initiated chemical vapor deposition (iCVD). The iCVD coating process, which does not involve any liquids and can be done at low temperature, produces a very thin, uniform coating that follows the contours of the fibers and does not lead to any clogging of the pores, thus eliminating the need for the second processing stage to reopen the pores.
The process works on many different kinds of fabrics, including cotton, nylon, and linen, and even on non-fabric materials such as paper. And it turns out, this new coating outperforms conventional long-chain DWRs — water simply bounces off the surface of the material.
The questions remaina, however, if this new improved short-chain DWR is still harmful to the environment, even if it performs better.