How can you dissolve rubber?

Question

How can you eliminate rubber attached to metal without torching it?

Answer 1

Chuck's right, but then you could just use gasoline.  Kinda slow but it will soften the rubber enough to scrape it off.

Answer 2

I know of three things to rid something of cured natural rubber.  These "things" aren't readily available, so I'm posting this answer for chemists who have run into some "rubber-problems"; also included  are solvents anyone can buy and are identified as such.



(1) I've had a couple round bottom flasks over the years with rubber septa stuck in them; and I find that that best way to get it out (without breaking the glass of course) is to reflux the septum with xylenes (bp~140C) for around 15 hours.  Of course depending on the size of the rubber (and flask) the time and amount of solvent may vary.  In the end the rubber expands 5-7x its original size, becoming very gelatinous (with the consistency of a giant Chinese noodle). The solvent will not literally "dissolve" the rubber, however you can easily cut through the mass using a spoonula or some other blunt instrument (it cuts like butter), then pull out the larger pieces with forceps.  The last time I wasted my time doing this (summer of '96) there was a residue on the inside of the flask after I reclaimed the xylenes in vacuo; this was removed with simple agitation using a cleaning brush, soap (Alconox) and water.  There may be other solvent systems one could use, but chloroform is too expensive; methylene chloride (bp 39C) "God's solvent" may work, I've never tried it.  THF (tetrahydrofuran) certainly causes rubber and Teflon to swell, so again, maybe. Toluene (bp 111) would probably be as effective as xylenes.  Butanone (MEK) and acetone are readily available at a hardware store (in paint solvent/stripping section) but these solvents are exceedingly flammable and shouldn't be boiled/played with where fumes can accumulate.  Out of the solvents mentioned above only chloroform and methylene chloride (dichloromethane) are non-flammable.  You should not inhale chloroform, but methylene chloride is non-toxic.  Careful though, as it will also attack plastics. Carburetor cleaner (50% xylenes 50% diacetone alcohol) you can buy easily.  Not to mention it will clean almost anything; the two solvents have covered all the bases of polarity.

(2) Observed annoyingly, 99% bromine.  You may have noticed after using, perhaps a Pasteur pipette and rubber bulb, while adding bromine to a reaction flask that the bulb has hardened; especially if the bromine was left in the pipette for longer than ~30 minutes.  This is, of course, because bromine is adding to the double bonds of the rubber.  This method is more expensive and more dangerous to hardening (rather than softening) rubber which is easily "crumbled" or scraped off. The object which you would like to be "rubber-free" must be resistant to bromine, but the method is quick and works well.  This usually is an unfortunate event in the lab where the rubber becomes "bromine-hard" and pipette bulb is wasted.  

(3) Of course I've made many rookie mistakes in my career, one was generating ozone and using rubber tubing as a route of delivery.  The rubber collapsed and shattered instantly.  This is of course what is happening to rubber exposed to the natural environment---ozone in the atmosphere cleaves double bonds (ozonolysis) and your rubber is rendered broken!  This is a long process but you can attribute old-rubber cracking to ozone. This is a very stupid way to get rid of rubber, but I felt like mentioning it anyhow, because it is effective (and interesting).  I hope this information can help someone, if not at least increase your chemical-knowledge.