|MadSci Network: Chemistry|
Scothguard is the 3M trade name for a fluropolymer that is hydrophobic as you say, but is also chemical resistant. To be a water or chemical repellant in textiles something must prevent the interaction of the water with the fibers in the fabric. Fluropolymers do this by coating the fibers with a polymer barrier in the same way that Teflon coats a frying pan. Even though water repellantcy is the selling point, the fluropolymers are barriers to all except specific chemicals. The way I view it, the fluropolymer acts like a plastic sheet on top of the fabric. Any liquid coming in contact is repelled, in that it can't pass through the barrier. Good question.
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