Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: paul.fr on 07/05/2007 18:51:29

Title: Why does superglue make a cotton-bud smoke or catch fire?
Post by: paul.fr on 07/05/2007 18:51:29
when you put superglue on to cotton buds, the bud either smokes/smoulders or can set alight! I am guessing that something is happening chemically, but what?

this can be dangerous to do, please do not try it unless all safety precautions are undertaken. ie awareness of flames and possible toxins given off by the fumes.

If Dave is passing, perhaps he could tell us if the fumes given off are toxic.
Title: Re: Why does superglue make a cotton-bud smoke or catch fire?
Post by: rosy on 08/05/2007 00:06:21
Having had a quick look at the structure of cyanoacrylate on wikipedia (http://en.wikipedia.org/wiki/Cyanoacrylate) I'd make a guess as to what's going on:

Normally, superglue in the tube is made up of lots of little units (monomers), which, when the glue cures, link up to become long chains of those units (polymers).

In order to start the reaction off some water is normally needed.. damp things stick better/quicker than dry ones and the glue goes hard faster on a humid day.

In cotton wool, which is made of cellulose, a polymer of sugar molecules, there are lots and lots of hydroxy (-OH or alcohol groups), which can start the reaction in the same way as the water does, only because there are lots of them they can start many more reactions at once.

Since the reaction gives out heat, the cotton bud therefore gets hot (and as it becomes hotter so the reaction goes faster etc), and it may get hot enough to catch fire.

I wouldn't like to guess what the fumes might be, as I don't know which out of the cyanoacrylate or the cotton bud would break down first, and to what extent any nasties would be burnt before evaporating.

It's certainly not something I'd want to do indoors!
Title: Re: Why does superglue make a cotton-bud smoke or catch fire?
Post by: paul.fr on 08/05/2007 09:26:52
I wouldn't like to guess what the fumes might be, as I don't know which of the cyanoacrylate and the cotton bud would break down first, and to what extent any nasties would be burnt before evaporating, but it's certainly not something I'd want to do indoors.

Many thanks for your reply, Rosy. So we agree that it's best to do this outside?
Title: Re: Why does superglue make a cotton-bud smoke or catch fire?
Post by: _Stefan_ on 08/05/2007 12:26:11
The gas might be C02 and some other carbon/hydrogen molecules, maybe H2O as well.
Title: Re: Why does superglue make a cotton-bud smoke or catch fire?
Post by: rosy on 08/05/2007 12:29:14
It might, if the combustion goes all the way it mainly will be, but I'd definitely expect to see some other muck in there too... if you see smoke you aren't seeing complete combustion as smoke is unburnt carbon and ither particles. I wouldn't recommend assuming it's innocuous.