What on earth just happened to my airlock?

[Mihkelj]

I don't normally make wine, but I had some rhubarb and kind of winged it. Fermented it in a plastic bucket at first, then transferred to a small glass carboy. I never use carboys for beer, so I bought a rubber (I presume) stopper for it and added an airlock. Today I went to check on it and found the airlock drooping to one side, almost parallel to the ground. Tried to twist it upright and the airlock broke off. It seems that the part of the airlock that was touching the stopper had kind of melted. The bottom part of the airlock was still inside the stopper.
Here are some pictures:
The stopper

the airlock

So is it safe to assume the material of the stopper didn't get along with the plastic of the airlock or am I actually making some kind of solvent instead of wine?

 

[Electrake]

S locks are super cheap, I break at least one a week. I personally love them because it's easier to see positive pressure early in fermentation, but i break them every other time i want to clean them!!

 

[Mihkelj]

I've never broken one before and usually use them with buckets and a rubber grommet. But the part that was in contact with the stopper had literally shrunk and gone soft.

 

[Electrake]

rhubarb rocket fuel then?

 

[flars]

What did you fill the air lock with? Strong cleaning solutions can do strange things to plastics.

 

[Mihkelj]

Standard Starsan solution. Had to have a taste for my peace of mind. It's strong, but still wine and not acetone or vinegar.

 

[Rob2010SS]

Interesting... Looks like it was heated almost...

 

[IslandLizard]

Interesting... Looks like it was heated almost...

Yeah, that is looking very strange! Was that a properly diluted Starsan solution or the concentrate? Or perhaps something else? The way it shrunk, then drooped and broke off.

Was there any heating wire nearby that kinda strangled it?

 

[Mihkelj]

It was properly diluted starsan. In theory, none of the Starsan in the airlock would have touched the "molten" part, the part that failed was the approx 1cm in direct contact with the rubber stopper.

 

[Lefou]

I've never experienced any of my plastic three piece airlocks falling apart like this. Plastics are technically oil-based polymers and some are susceptible to dissolving in certain aromatic compounds.
I usually keep a few airlocks around because they aren't very durable.
As a kid, I tried cleaning a small plastic magnifying lens with a gasoline-dampened paper towel. It fogged the plastic and then turned it into a sticky mess. Pretty interesting lesson.

Something similar happens with silver when it comes in contact with acid-based paper and rubber bands. Sulfides form and cause discoloration. Simple chemistry can clear that up, but looks like your plastic airlocks definitely won't stand up to the rubber stoppers.