Re: Diffusion of vapor through polymers  

Posted by on October 09, 2004 at 14:33:12:

In Reply to: Diffusion of vapor through polymers posted by Michael on January 30, 2004 at 11:39:01:

The permeability of 100% Water in a high Molecular Weight grade / isotactic Polypropylene equals 5 E-10 gram / m x s at 25 degrees Celsius and 1 bar.

The Water permeability in PP Polypropylene as a function of the temperature can be roughly estimated by use of the Arrhenius Equation. From experimental data at lower tempeatures than 25 degrees Celsius we acquired the Arrhenius Activation Energy for permeability: 48 kJ/mole The extrapolated permeability is the following (mind that this is a very rough estimation, and will not be very significant anymore at 95 degrees Celsius (*less than the significance that is shown below):

Permeability 40 C: 3 E-9 gram / m x s
Permeability 95 C: 5 E-7 gram / m x s

Based on a coating thickness of 2.5 mm and one year the total permeation (total mass transfer, or flux) will be:

Flux 40 C: 4 E+1 gram / m2 x year
Flux 95 C: 6 E+3 gram / m2 x year

What you see from these figures is that these thermoplastic and partly crystalline polymers, like Polypropylene, show an enormous increase in permeability with temperature. Do not hestitate to contact for more information.

Kind regards,

: Hello,
: Nice's exactly what I need...
: I'm doing research in application in which a polymer mebrane (eg PP, 2,5mm) seals a hot water tank (--> direct contact of hot water and PP). The temperature in the tank varies between 40°C and 95°C over one year.

: I would like to calculate the diffusion of water out of the tank.
: How do you think I could do it?
: Any hint is welcome as I don't know much about diffusion. I read your theory part, but couldn't associate it with my application.

: In building engineering, the number of diffusion resistance µ is known. Like I found in "Verfahren zur ein- und zweidimensionalen Berechnung des gekoppelten Feuchtetransports in Bauteilen mit einfachen Kennwerten" Dissertation at the university of Stuttgart/Germany by Künzel 1994, it is dependant of the solubility and the temperature and the relative humidity. But I don't know the exact relationship.

: I'm looking forward to reading any comment
: Michael


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