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I want to know if there are some fairly common thermoplastics that allow water to pass through (by diffusion) at a relatively high rate (on the order of days). For example, PET water bottles leak water by diffusion but it's extremely slow - it will take 100 years to let the water through.

Another way of asking my question is "what are some thermoplastics with very high diffusion coefficient for water?". I thought PMMA (Acrylic) was one but in my experiment it was too slow.

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    $\begingroup$ We can probably be more helpful if we know the application. Can you give more detail about what you're trying to do? What was your experiment, in brief, and how slow was the diffusion? $\endgroup$ – Air May 8 '15 at 18:31
  • $\begingroup$ PTFE plastic objects can be fabricated by pressing and "sort of sintering" from powder and you can probably make a material that is as permeable as you wish. $\endgroup$ – Russell McMahon May 9 '15 at 13:53
  • $\begingroup$ I don't want to go through pores, I want to go through the solid material itself. $\endgroup$ – Nic May 12 '15 at 21:10
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Polyamide / Nylon

In our subsea work we generally avoid this in applications in contact with water/seawater as it is hygroscopic.

I cannot give you exact values as there are many polyamide grades and some are less hygroscopic than others, so you'll need to research further.

It would definitely be worth considering as a potential candidate for your experiment.

EDIT: I have made an assumption in this answer so it's best if I state it here.

Hygroscopic materials absorb water. I have assumed that they will also let water pass through them if a pressure difference exists across the material.

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I recall (I think) there is a company called Poron that makes porous plastics with various pore sizes. You can "dial in" the diffusion rate you want by selecting the right thickness of material and pore size.

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  • $\begingroup$ @Nic: In lieu of your comment above about not wanting a porous material, you might be surprised to know that there are no 'solid" materials anywhere in the universe, all "solids" are just illusions, see the writings of Buckminster Fuller ! $\endgroup$ – William Hird May 13 '15 at 17:11

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