# What happened to this 10 year old unopened plastic bottle?

A colleague of mine found this unopened Aquarius bottle (non-carbonated drink) that was 10 years past its expiration date.

The bottle was collapsed inward which would suggest that the pressure in the bottle was lower then outside the bottle.

Can someone explain what happened here? Also, what happened to the air inside the bottle?

• Not that I doubt you, but as a clarification: Are you sure some idiot didn't squeeze it like that and leave it lying around 10 years ago ;-) Jan 12 '18 at 14:54
• As someone who has never had any of it: Is this drink carbonated? Jan 12 '18 at 14:55
• Nope, that didn't happen. We opened the bottle and it was still very firmly shut close. This is not a carbonated drink. Jan 12 '18 at 14:55
• The bottle was stored in a closet for 10 years, it was never taken out Jan 12 '18 at 15:08
• Okay, and the temperatures normally lie in what range? 25-27 degrees Celsius (normal room temp.) or something else? Jan 12 '18 at 15:09

Since the drink is not carbonated, no liquid has been escaping the bottle, and the components don't seem to be able to participate in any kind of chemical reactions involving gaseous products, I assume the gas that's been leaked is air.

I also cannot imagine any kind of chemical reaction involving consumption of this amount of air leading to such a severe bottle deformation. My theory is that air simply escaped over time through the bottleneck. There are 2 parts made of 2 materials with different thermal expansion coefficients:

• the bottle itself (polyethylene #1 (PET), or polyethylene terephthalate (PETE));
• the screw cap (polypropylene (PP)).

Due to the construction of the joint, both parts basically act as a pressure equalization valve. I suspect that the coefficients of thermal expansion are chosen in such a way that when heated, excess gas would slowly escape in order to minimize the risk of explosion when the storing conditions for the finished product is not met. So, when the bottle is heated, the air is slowly leaking out. Once the temperature drops, the "valve" closes and the process stops. Over the course of 10 years, there surely were many temperature fluctuations making air leave the bottle little-by-little.

• If nothing can fix oxygen or perhaps CO2 from some fermentation, it must be something like that. Jan 12 '18 at 16:50
• What do you think of forming CO2 which might selectively permeates out? Jan 12 '18 at 16:53
• I guess if fermentation took place, it would be noticeable, but it looks like OP has no complaints regarding the color or smell. And there is no membrane that can selectively pass $\ce{CO2}$ through; the lid-bottle joint is hardly that selective:) Jan 12 '18 at 16:59
• I agree. But for selectivity I mean the bottle . I thought for some reason it could be more permeable to CO2 than nitrogen and oxygen. Jan 12 '18 at 17:07
• Oh. But how? PET is not quite porous, and if it were, then smaller diatomic gases (oxygen and nitrogen) should've escaped first, I think. Jan 12 '18 at 17:15