Do Ice Blocks Have A Shelf Life?

[numan]

My ice bricks (specifically bricks, NOT packs) don't seem to last as long as they used to and I have to swap them after about 6/7 hours instead of around 12 as I did when they were new. Does anyone know if they have a shelf life, as I've trawled the web for half an hour to no avail and am getting a bit frustrated now! Cheers!

[bhg481]

I don't see why they should have a shelf life unless the chemical inside them decomposes with time. They rely on a feature of all materials called "Latent Heat of Fusion" whereby a lot of heat is absorbed without change in temperature as a substance changes from solid to liquid. We've had some for decades now that we still use but only whilst we're defrosting the freezer, so not for long periods as we used to do when camping.

[numan]

That was actually my question: does the chemical inside them decompose with time. I use mine constantly, as I have to keep samples in an upstairs room without a fridge, so I think my situation is quite unusual. Hence, not being able to find an answer.
Thanks anyway

[ummmm]

I would guess that they do have a shelf life. Most things do. Luckily they are very cheap now.

[theprof]

To be honest numan, this is a difficult question to answer. I'll try to explain. Most modern ice packs contain an organic glycol mixed with water and a carboxymethylcellulose salt. The water contents is about 60%, the carboxymethylcellulose no more than about 5% with the glycol making up the rest. Now I know that carboxymethylcellulose sounds like a horribly complex chemical, but we've all seen it in the form of wallpaper paste. In this case, it's included to stop the liquid in the ice packs from sloshing around excessively. Packs with these substances are pretty stable but the glycol can be affected by light over time.

The other type of ice pack can contain ammonium nitrate, calcium ammonium nitrate and urea or sometimes each of these compounds alone. The ammonium salts are hazardous and are rarely used in some countries but urea is pretty harmless. These compounds have varying solubility in water, but the reaction between all three of them and water is endothermic which is ideal for the purpose used. Again, the shelf life of these compounds in solution is not ideal for the purpose, but they are cheap chemicals and the packs cost very little to manufacture.

These differences do make it difficult to assess whether your ice packs are behaving as they should. Old ice packs do lose their ability to maintain low temperatures over time but because the chemicals they contain vary so much, no one can tell you how long you can expect them to last.

If you gave me an ice pack to assess via qualitative and quantitative analysis in my uni labs, I could tell you exactly why, but short of that we can only guess from the properties of the compounds they contain.

[numan]

Thank you theprof. Your penultimate paragraph told me all I need to know. It wasn't really that I didn't want to go and get new ones, more that I was curious, once I got the idea into my head that they weren't working as well as they used to. I will go and get new ones and make a note of how long it takes till I think the same thing is happening. I'm a bit of a geek when it comes to wanting to know how anything and everything works!
Thanks again

[Gromit]

What are Ice Blocks. What are they for/use ?

[bhg481]

Gromit - used for keeping things cool.

https://www.amazon.co.uk/s?k=ice+block&;ref=nb_sb_noss_1

[Gromit]

Cheers bhg481.