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Hydrophobic coating 3

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sdk_imported

sdk_imported

Mechanical
May 16, 2002
49
I'm looking for a hydrophobic coating that I can apply to polyester acoustic mesh. The ideal solution would be either a spray or dipping process. Any suggestions?
 
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I'm not much of a fan of the "new" Scotchguard and similar products, since they banned the perfluoro-whatever that the old stuff had in it. But, then, I live in a wet climate...

Silicone oil or grease, applied directly, might work as well as, or better than, some of the other materials. Check the Dow website, they may even be willing to send you a sample jar.
 
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You can make your own super hydrophobic spray for fabrics. I made some and it was really effective. It actually bonds chemically to the fabric.

You will need:

1 spray bottle like you use to spray plants
2 100 ml solvent (I used hexane or heptane)
3 5ml of octadecyl trichlorosilane (or other long hydrocarbon chain organosilane)

Mix 2 and 3 in container 1. Spray onto fabric. Allow to dry.

We were able to achieve outstanding hydrophobicity e.g. on a polyester jacket. You could make a pool of water inches deep and it would just sit there for hours not wetting the jacket at all.

The easier path is, as suggested, to buy some shoe water repellent from The Show Locker or similar.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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Thanks for the helpful feedback. Biocompatibility is an issue here that I probably should have mentioned earlier. The "make your own" suggestion might be a good choice because we can control the process tightly and know what is in the product. I'll investage ...
 
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The best biocompatible surfaces are made of polyethylene oxide (also known as polyethylene glycol or PEG) because it's protein rejecting. That's what you coat things that go inside the body with to prevent issues. I would therefore make a similar coating to the one I just mentioned. For that you need:

PEG trimethoxy silane available as Dynasilan 4144 from Evomik Degussa. That is just being made obsolete and replaced with an almost identical product which is not yet listed in their literature.

For product info download this, then call them and ask what the replacement is called. I am sure you can get a sample. Momentive have a similar product too.


Like all organosilanes you need to hydrolyse off the methyl groups at which point it will polymerise to give a nice biocompatible coating on your fabric.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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Ah, Chris! You are a prince among men. Now you just need to market the above in handy packages (along with any pertient safety information - the MSDS for the first one reads like rocket fuel) and sell it on ebay, to make your well-deserved fortune...If it works as advertised, I (and many other parents of kids learning to ski in the rainy NW) will shower you with cash.
 
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Hi btrueblood,

Thanks mate. I've made some nice materials in my time and still doing it too. The millions are slow in arriving but there is hope yet! With a growing family it would come in handy.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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Want to know an easy way to make a Lotus-Effect self-cleaning surface?

I used a can of spray paint and some hydrophobic silica, e.g. from Cabot or Degussa. You spray the paint onto the surface you want to coat, then while the paint is still wet, you dip it into the silica. The silica sticks in as the paint dries and you get an extremely good Lotus-Effect surface. You can shoot a hard jet of water at it and it still won't wet at all. Or you can play with a drop of water on it. The water will roll around with virtually no resistance so it's really hard to keep it on the surface.

I need to add that the PEG surface I mentioned will be biocompatible but definitely not hydrophobic. PEG is water-soluble and the reasons it's so biocompatible is that it forms a surface of solubilized PEG brushes composed mainly of water.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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Chris,

I can see the consumer issues with your hydrophobic spray...one idiot with a lit cigarette...but it still sounds like something I'd like to try unless you recommend not doing it. I've got a lot of lightweight raingear/snowgear/footwear I've thrown away when the "DWR" craps out, and having a real hydrophobic finish that could be reapplied would be worth the effort. I've tried just about every name-brand spray/wash, and they all generally crap out within a few hours of wear, or less.

Any suggestions for a source for the organosilanes, stateside? The MSDS lists water as a reactant, presumably you spray onto a fully dry surface and avoid getting anything wet until the chemical has dried/cured?
 
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Hi btrueblood,

I applied the coating I mentioned to a red Tenson brand jacket that we bought cheap used from a charity store. We also applied it to an umbrella. The water repellence on the umbrella was incredibly. The crops bounced off so well that you spray people for yards around.

The secret is that the trichlorisilanes are very reactive so they bond chemically to the fabric (that's not marketing speak, I am 1. a PhD chemist and 2. not trying to sell you anything).

The easiest source for the silanes for testing is that's where I got mine. Commercially, good sources are Momentive, Evonik, Dow Corning and Wacker (contact me if you want contact names to friends who work there and are technical experts).

The hydrocarbon silane is what I used.

Trichlorododecylsilane


I searched and see this fluoro version which will cost more but give an even more hydrophobic and oleophobic coating.

Trichloro(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)silane


Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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