Permeability of Polypropylene with Ethanol?

[JMOwen]

I'm trying to find out the transfer rate of methanol through a ~1mm sheet of Polypropylene. Can any one help?

I've done a fairly extensive search on the web and have good data for HDPE which is a reasonable match I beleive but its PP data that I specifically require.

Thanks for your help

 

[patprimmer]

Have you asked the major PP suppliers.

I am sure it will vary considerably from grade to grade, with co-polymers being more permeable.

Permeability for a polymer type is generally inversely proportional to degree of crystallinity, so it does vary with grade and even colour in the same grade.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Demon3]

In addition to what Pat said I'd like to add that as methanol is polar and PP not, the solubility of methanol in PP will be very low and that will give a low permeabilty. I would guess that diffusion through a 1mm sheet of PP will be extremely slow indeed.

 

[thermcool]

i have done some study on the determination of the permeability for the ultra high density (UHMW) polyethylene wicks with water and ethanol and for copper wick using water.

In the permeability test, wettability of the sample with the fluid is very critical and effects the outcomes of the test. Polypropylene is naturally hydrophobic polymer so it will not give any good results with water. As for the methanol, the sample will give wettability but to what degree is dependent on the sample type. Normally i have seen the alcohols give very good wettability with the hydrophobic as well as hydrophilic polymers.

For your experiment you can make the fluid pass through the membrane under different pressure, if the permeability shows drastic change with the pressure then your sample is giving poor wettability with the fluid where as if the permeability value is more or less constant with applied pressure (i.e. for high as well as low pressure) then you are getting more or less closer to true values.

To check the wetting of the sample you can also do a simple test, in which you take a dry sample of polypropylene and weight it. Take the dimensions of the sample. you have the volume and mass of the sample, from this you can calculate the density of the porous matrix. Now you can look for the polypropylene density which is around 0.95 g/cm3.
Using this information, you can calulate the porosity of the sample i.e. porosity = 1-(density of porous matrix/poroisity of the polypropylene).

Now, you soak this sample completely with the working fluid (which is methanol in your case) and weight the fluid saturated sample. (be careful to allow enough time to seak the sample, while dipping into the fluid place it from one side only so that the air inside the porous matrix is expelled out of the other side). From the weight of the sample before and after soaking with liquid fluid, you can calculate the porosity value again. if you pososity reading from the original dry test experiment matches (80-90%) to the soaking test then you can consider a good wettability between the porous medium and the given working fluid. if not you have to choose the fluid accordingly.

For an idea!! Normally, for the polyethylene wick with pore size around 10 micrometer, porosity of 38% the darcy or specific permeability with good wetting working fluid will be of the order of 10 raise to the power -13 (minus 13).

Hope it helps.