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Cotton is mostly cellulose, a plant saccharide. Superglue refers to a class of cyanoacrylates. What is it about the two that causes ignition?

I'd imagine that the cellulose in cotton is in its linear form and not in its ring form since the ring-linear form interconversion only occurs in solution. Is it that the cellulose attacks the cyanoacrylate?

The three hydroxyl groups, one primary and two secondary, in each repeating cellobiose unit of cellulose are chemically reactive

So, do the hydroxyl groups attack the carbonyl group in superglue?

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    $\begingroup$ This might be pure ignorance on my part, but what exactly do you mean by "linear form" and "in solution"? I've never heard of (water-)soluble cellulose, and "linear form in solution" reminds me rather of the mono-sugars, but not the polymer. $\endgroup$
    – Gerhard
    Commented Jan 17, 2015 at 20:34
  • $\begingroup$ I found your post after my son came to me with 2 burnt Q-tips. He used the Q-tips to apply super glue to something, they started to smoke and the ends were black. It would appear that cotton can catch on fire when super glue is applied. He did not put anything else on the Q-tips. $\endgroup$
    – Kathy Mondazzi
    Commented Jan 1, 2017 at 5:33
  • $\begingroup$ I don't have an answer, but I just recently had an incident with super glue. I was opening a container and a large amount squirted out all over my hands. I reached for the first available thing which was Kleenex and it started to smoke and I could feel it getting warm. I dropped the super glue container to the ground and it ran to the sink. It did not spread any further. Now I know what was happening, I had some inkling based on my ChE degree but I have not practiced in nearly 25 years so I am a bit rusty. $\endgroup$
    – Dan
    Commented Feb 2, 2017 at 22:05

2 Answers 2

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Though the monomers in cyanoacrylate glues contain an ester, their polymerization doesn't rely on that ester group directly. The Wikipedia article for cyanoacrylates shows the polymerization more clearly than I can easily explain in words. The many hydroxyl groups in cellulose do start polymerization effectively, and the large surface area of cotton wool provides a large number of sites for the glue to cure.

When I read your question I was curious; I had never heard of this before. I searched the internet and was only able to find one or two examples of people actually trying this successfully, and both of them looked dubious. I've spilled superglue on cotton shirts and pants any number of times and while it cures almost instantly, it has never caught my shirt on fire.

I decided to try it myself, and I soaked a cotton ball in superglue to see what would happen. The glue cured extremely rapidly, producing very irritating (colorless) fumes, and the mass of glue and cotton got warm, but it was nowhere near hot enough to ignite - my tap runs hotter than the glue got. There may be a particular type of glue that cures significantly more exothermically, but I'm inclined to think that this is an internet hoax, and Popular Science agrees.

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    $\begingroup$ Maybe you used enough superglue that the thermal mass of the glue itself kept the temperature down? $\endgroup$
    – hBy2Py
    Commented Jan 6, 2016 at 17:33
  • $\begingroup$ @Brian It's possible, but the videos that say that superglue will ignite cotton also use lots of it. To be clear, I'm 100% open to being wrong if given good evidence, but neither Popular Science nor I can make it happen, and there are an awful lot of internet hoax videos of this sort. $\endgroup$
    – Jason Patterson
    Commented Jan 6, 2016 at 21:55
  • $\begingroup$ Aha, perhaps not, then. Maybe the 'igniters' presoaked the cotton with rubbing alcohol or something... <shakes head> $\endgroup$
    – hBy2Py
    Commented Jan 7, 2016 at 0:34
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    $\begingroup$ But the important point is that the reaction is fairly exothermic because of the presence of many OH groups on the surface and the surface area is high. This means that, given the right conditions, it is possible to cause ignition. $\endgroup$
    – matt_black
    Commented Feb 25, 2016 at 11:41
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    $\begingroup$ The hydroxyl groups don't, it's the adsorbed water on the cellulose. And if it produced fumes, that means it whas just about to catch fire. How on earth did you "measure" those 315K? At that temperature, neither superglue nor cotton produce fumes! $\endgroup$
    – Karl
    Commented Apr 26, 2019 at 20:51
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Cyanoacrylates include methyl 2-cyanoacrylatecommonly sold under the trade names "Super Glue".In general, cyanoacrylate (consists of monomers of cyanoacrylate molecules) is an acrylic resin that rapidly polymerises in the presence of water (specifically hydroxide ions), forming long, strong chains, joining the bonded surfaces together. Because the presence of moisture causes the glue to set, exposure to normal levels of humidity in the air causes a thin skin to start to form within seconds, which very greatly slows the reaction. Because of this cyanoacrylate is applied thinly, to ensure that the reaction proceeds rapidly and a strong bond is formed within a reasonable time.

enter image description here

So to sum up, 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.

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  • $\begingroup$ Not exactly. Alcohol is not sufficiently basic (much less than water) to be a really good nucleophile. But cotton is polar, and thus is loaded with water. $\endgroup$
    – Karl
    Commented Apr 26, 2019 at 20:43

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