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Why does a plastic water bottle suck inward on itself, with it being full of water and unopened for years? Answered

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PET plastic isn't necessarily gas proof long term but it would take some external lack pressure to suck air out - I go with pressure or temperature changes over time.

It's partially because of the difference in temperature between when the bottle was sealed and the current temperature, say the bottle is sealed at 25°C, and we look at it later at 15°C, as the bottle is a closed system (nothing can get in or out) so the number of particles of water and air in the bottle stays the same.
When bottle was sealed the particles were vibrating more (because they had more thermal energy), so not as many could fit in than if they were vibrating less (so at a cooler temp). So once the bottle is put somewhere colder, the particles in the bottle slow down, so they don't put as much pressure on the bottle, however the air outside still does. This outside pressure causes the bottle to collapse inwards until the space per particle is equal inside and outside the bottle.
For a really strong bottle that can't collapse the water inside it would be forced to vapourise to increase pressure.

Small amounts of air/water can get out through tiny holes in the plastic, but this doesn't have much effect.

TLDR;
- pressure is how often and with how much force the particles hit something
-thermal energy(temperature) is how much particles move
-pressure decreases when temperature decreases
-pressure increases when volume decreases

Temperature decreases so volume needs to decrease too to counteract it. Because pressure must stay constant.

Pressure X volume = (mass of particles/molecular mass) ×8.31× temperature
Molecular mass is how many proton and neutrons there is.

Because it lost air after a time that it's not opened. ( An unopened bottled water has air inside after it was produced)

Bettix's link shows graphically what is going on.

The important section is labeled: Moisture Vapor Migration

So I looked at several plastic water bottles to see what they are made of. Use the plastic recycling codes as a guide:

https://en.wikipedia.org/wiki/Recycling_codes

What I found was there was a mix of (1) PET and (1) PETE

From https://en.wikipedia.org/wiki/Polyethylene_terephthalate in the Physical Properties it says

It makes a good gas and fair moisture barrier

Fair, not Good.

So amazing as it seems, the water is very slowly migrating through the plastic (in microscopic amounts) and when it gets to the outside it evaporates. Air from outside does not go in the opposite direction to replace the water. As the bottle is still sealed, the reduction of water in the bottle causes it to collapse so that the pressure inside the bottle matches the external pressure.

This is exactly what I've been trying to find in my research. It's the only thing that really makes sense out of the possible explanations. I watched a video of someone scared that the plastic was leaching so much into the water, that it made the plastic flimsy. 🤔

I have cases of water stacked on top of each other which increases the pressure on the bottom ones substantially. I've seen water in the cases outside of the bottles too that had not been evaporated.

Thank you for your logical explanation!

I just got a new home this pass September and I'm freaking out about maybe a strange pressure?
I noticed it with Milk at first and thought it was strange so we stopped with the plastic milk thinking it was something with the company but now all my water is doing it.

Something is going on.

I'm starting to wonder what is making my water bottles sink into themselves.

I have gotten several different kinds
of bottles and put them all on my counters after getting back home from the store, within minutes all of them a total of 56 bottles from great value to Dasani as I got 4 kinds today including a gal of water that is a Wal-Mart company water, all have now sunk inward.

WTH would make everyone of them do that within minutes?

I went back and got some more and put them all over our home and in every room it did the same thing within minutes.

I know this home was built back in 1800. But I haven't seen any report on this land having pressure problems, I know its a big home a total of 15 rooms but that shouldn't matter...

http://www.bettix.co.uk/plastics-fluorination/why-fluorination-the-problem -Here's the only solution to stop the paneling of bottles, get your bottle fluorinated.

I am wanting to know the answer to the same question. I believe this experience of collapsed unopened water bottles is a little more detailed than we are told. Does the plastic degrade? Lots of people probably have cases of water that have had this experience after storing for a few years.

Is it dangerous to consume?

Has it been moved to a lower altitude?

Because leaving water in a plastic bottle for years just SUCKS! Don't do it.

Lots of reasons, I think most likely is nacho's suggestion that the bottle is permeable and lets some gas out.

Gasses dissolve in the liquid, thus acting as a liquid and not exerting their pressure on the bottle walls.

The plastic in the bottle could be actively 'eating' the gasses - I have no grounds to support this theory, but given that some plastics off-gas, it makes sense they might react with and store some gasses.

. Could be that some germs have used up all the Oxygen, Nitrogen, &c.
. Maybe plastic bottle are ever so slightly gas permeable and the gas gets pumped out with temperature fluctuations and/or variations in pressure.
. Magic!