A couple of years ago I bought a 1 gallon container of windshield washer fluid and stuck it in the back of the garage somewhere. Last night I went to dig it up and found it on the top shelf of a rack. Weird thing was that the plastic container had been collapsed inwards - I would estimate the volume of the container was reduced by about 50% (based on refilling it and measuring afterwards) with what appeared to be about the same amount of air remaining as was in it originally. I didn’t remember having ever used it before and couldn’t imagine in any event why someone would want to compress the container, but whatever, it is what it is. But when I took off the cap I found that the bottle was still sealed, with that silver plastic thingy they glue across the top firmly in place. I had to gouge it out with my key, and when I did, I could hear and feel the vacuum being released and the container relaxing and expanding a bit.
So ISTM that somehow or other the liquid had been escaping from the container and the resulting vacuum had forced the container to compress inwards. But how in the world might this be possible?
A large difference in atmospheric pressure could cause some of what you describe. Atmospheric pressure would have to be a lot higher now than when you bought it to explain a 50% reduction in volume.
And my estimate of 50% compression is not a wild guess. After I emptied the contents I refilled it with water and poured it into a 1/2 gallon milk container, and it was just a tiny bit over the top. Since as noted the 1 gallon container had relaxed and expanded a bit after I broke the seal, I think it’s safe to assume the compressed size was about 50% of the original gallon.
What I’m wondering about is whether changes in temprature might be somehow involved. That garage gets pretty hot in the summer and gets close to freezing in winter. But in any event, how the liquid could vanish with the airtight seal unbroken needs to be explained.
Obvious explanation is the container leaks whatever the contents is when it’s hot and the pressure is high and then contracts when it’s cold and the pressure drops. The details of how might be known by a materials expert, but it’s that or quantum tunneling.
Your container of washer fluid was originally half methanol (and possibly some other volatile liquid like ethanol). During storage, warmth in your garage has caused the methanol to evaporate and because the container is fairly weak, it was not able to draw air back in to replace the loss.
I suspect that it is no longer any good as antifreeze. What you have is basically coloured water.
A few years ago, I was checking out the emergency supplies at an office and found several of the individual 8-ounce water boxes had shriveled. They were a couple years out of date, but I wouldn’t have expected water to escape from foil/paper/plastic laminated Tetra Paks.
They’d been stored inside a locked cabinet in an office, pretty much a textbook “cool, dark and dry” location. Curious about the shrinkage, I poked a straw into one and it hissed a bit and started to return to its original shape.
When the pressure inside the container is higher than ambient (for example, when the contents are warm), the lid may be lifted slightly and this may allow the pressure to be released.
When the pressure inside the container is lower than ambient, the tendency will be for external atmospheric pressure to push the lid down more tightly - so there is an asymmetry in the process.
That alone wouldn’t provide a consistent loss of volume over time, except maybe the material of the container has a tendency to retain the crumpling that it acquires when it cools - so over time, there could be a continual loss of content.
The culprit in OP and all the other cases is the seal. Read here how the sealing is done Induction sealing - Wikipedia
In the OP the isopropyl alcohol reacts with the seal “wax” making it weak. In the water bottle case it could be summer heat or sunlight. Once compromised the seal acts like a one way valve (check valve) letting contents out when hot but not back in when cold. This is the same way a diaphragm check valve works https://macsaputra.files.wordpress.com/2010/01/dual-plate-check-valve.png
