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Soften silicone but not damage plastic?

Soften silicone but not damage plastic?

Soften silicone but not damage plastic?

I'm trying to figure out how to remove silicone (vinyl polysiloxane derivative) from a plastic tube which has channels that mix the two parts when they're shot through. The problem is that it dries before it can be cleaned. Is there some kind of solvent that could be used that will soften the silicone but not damage the plastic?

RE: Soften silicone but not damage plastic?

Acetone will swell and degrade silicone but not if the static mixing tube is set solid. Plastic static mixers are meant to be disposable. If you do want to reuse them, you must blow out most of the silicone before it sets with compressed air to open a channel for flow of cleaning solvent.
By the way, silicone does not "dry", it cures or cross-links. For historical reasons, the cross-linking reaction of alkyd resins (oil paints) is called "drying". But otherwise, "drying" refers to the evaporation of solvents.

RE: Soften silicone but not damage plastic?

What solvent then can keep the silicone "wet" (not drying, not curing) in the time AFTER the process cycle finishes, and before the residue can be blown out?

RE: Soften silicone but not damage plastic?

In addition to the advice here, I'd recommend a conversation with the raw material vendor's technical authority for their advice.

Good luck,

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Soften silicone but not damage plastic?

WD40 works to remove old silicone from tiles etc. Not sure that it actually dissolves the silicone, but I have had some luck with it softening the old caulk.

RE: Soften silicone but not damage plastic?

After the silicone is mixed and sets, the silicone is crosslinked and is impossible to remove with a solvent.

Replace the tubes.

RE: Soften silicone but not damage plastic?

...but crosslinked or not, silicone or any other rubber can be softened (swollen) by a solvent to the point where it becomes so weak that it can be mechanically removed. There are commercial preparations for softening room temperature vulcanizing silicone after it has cured, but I don't recall seeing active ingredients on the list.

Regrettably, merely swelling the material isn't going to be enough for you to get it out of the tiny channels of a static mixer ejector tip.

Most solvents have little to no effect on polyethylene, which is often what is used to make the disposable static mixer tips you're talking about. So a thorough flush immediately after use with acetone would probably do the job- although the tips aren't expensive and are intended to be disposable. Chances are, you'll use more acetone than the tip is worth.

RE: Soften silicone but not damage plastic?

Bimr - impossible? A dangerous word to use, especially in engineering!

At a previous employer we used to use a lot of silicone adhesives on high value components and put a bit of effort in to salvaging them. This product range from Eastman-Dynaloy is worth a look http://www.dynaloy.com/products/silicone-solvents-... although it may well be aggressive to your mixer nozzle. You could also look at Dow's DS-2025 product which is similarly aggressive: http://www.dowcorning.com/applications/search/defa... .

RE: Soften silicone but not damage plastic?

Right you are Scotty. Looked at the product sheets which are not too informative.

RE: Soften silicone but not damage plastic?

Agreed that the datasheets aren't brilliant. We had mixed results on different silicones - neutral cure types behaved differently to acetic cure types IIRC. If this is a recurring task then it is worth a trial on the specific material involved.

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