sploople Posted January 9, 2010 Share Posted January 9, 2010 Newb here... didn't know where else to post this.... I realize there are rigid solids that will hold a vacuum for a very long time, but is there any flexible plastic or fabric that will hold a medium vacuum for a very long time? Another way of asking this... is there a plastic -- or even a coating that can be applied to a plastic-- which will not allow any molecules found in the atmosphere through? An actual zero-permeable material? How long will the bags used in vacuum food storage hold their vacuum? Link to comment Share on other sites More sharing options...
swansont Posted January 9, 2010 Share Posted January 9, 2010 Flexible material tends to collapse under a pressure differential, so it does not "hold" a vacuum. Hydrogen and Helium diffuse through a lot of materials, so there is probably no zero-permeable material. Link to comment Share on other sites More sharing options...
insane_alien Posted January 9, 2010 Share Posted January 9, 2010 swansont is right, there is no material fabric or otherwise that is completely non permeable. your best best would probably be a mylar film, perhaps with a kevlar layer if it has to take extreme pressures. Link to comment Share on other sites More sharing options...
michel123456 Posted January 9, 2010 Share Posted January 9, 2010 I suppose the original question is about air vacuum only. Not physical vacuum. Merged post follows: Consecutive posts merged How long will the bags used in vacuum food storage hold their vacuum? Vacuum storage food bags are usually made of multi-layered membranes, like (from outside to inside, paper, aluminium foil, pvc membrane. need check). Impermeability is achieved through the layered addition of the different materials. But it is only air vacuum under controlled hygienic atmosphere. If it were true vacuum,he recipient would crush down as mentionned by Swanson. They hold only because there is something inside, like coffee bags. I suppose they have to stand quite longer than the expiration date of the product. Link to comment Share on other sites More sharing options...
insane_alien Posted January 9, 2010 Share Posted January 9, 2010 yes, you need a frame to support the membrane but the pointis that it can hold against a ~1atm pressure difference. Link to comment Share on other sites More sharing options...
sploople Posted March 4, 2010 Author Share Posted March 4, 2010 swansont is right, there is no material fabric or otherwise that is completely non permeable. your best best would probably be a mylar film, perhaps with a kevlar layer if it has to take extreme pressures. Insane Alien... thanks for the tips! Let me put some bounds on the requirements of this material. Say we can produce a high to ultra high vacuum with this material while it is placed over an internal skeleton... Is there a material that would hold for a decade before it leaked in enough atmospheric gases to be lowered to a medium vacuum? We have been tinkering with a small experiment in my mom's kitchen, and are now curious as to how long a vacuum bubble would last!! THANKS FOR THE HELP! Link to comment Share on other sites More sharing options...
Radical Edward Posted March 4, 2010 Share Posted March 4, 2010 Insane Alien... thanks for the tips! Let me put some bounds on the requirements of this material. Say we can produce a high to ultra high vacuum with this material while it is placed over an internal skeleton... Is there a material that would hold for a decade before it leaked in enough atmospheric gases to be lowered to a medium vacuum? We have been tinkering with a small experiment in my mom's kitchen, and are now curious as to how long a vacuum bubble would last!! THANKS FOR THE HELP! you'd need something like thick metal and weld it shut. Link to comment Share on other sites More sharing options...
sploople Posted March 4, 2010 Author Share Posted March 4, 2010 Thanks for the quick response. Is this to say that even a layered membrane, such as the suggested mylar and kevlar, or something similar to that of vacuum pack bags, wouldn't hold for 10 years? Would they even hold for 1 year? Link to comment Share on other sites More sharing options...
insane_alien Posted March 4, 2010 Share Posted March 4, 2010 doubtful. when you get to vacuums you notice just how leaky everything is. Link to comment Share on other sites More sharing options...
Mr Skeptic Posted March 4, 2010 Share Posted March 4, 2010 You could construct your flexible vacuum balloon thingie by having a skeleton held (mostly) rigid by compressed air; overall you'd have to have at least as much air inside the skeleton as you could remove from inside to get a vacuum, to prevent atmospheric pressure from collapsing it. I don't know of anything completely impermeable though. Link to comment Share on other sites More sharing options...
swansont Posted March 4, 2010 Share Posted March 4, 2010 If you know the leak rate, you can estimate how long a particular level of vacuum will last. I know of devices where the system was pumped out and welded shut. But they don't have to hold a great vacuum. Link to comment Share on other sites More sharing options...
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