Estimate relationship between 3 values?

Question

I have to to estimate the relationship between OTR (cc/m^2/day) & WVTR (g/m^2/day)
WVTR is for water vapor transmission rate
OTR is for oxygen transmission rate
In the two tests, effective surface area of film tested was 10 cm^2
Here is the result I have to find the relation (it's have to include thickness of the plastic film)

plastic 1082 have a thickness of 0.0044 in
WVTR : 4.8
OTR : 120

Plastic 1083 have a thickness of 0.0045 in
WVTR : 0.88
OTR : 2.6

With that, I will find the WVTR value for a plastic of 0.00289 inche and OTR known value

Please show me how to find the relation between thickness, WVTR and OTR

Thanks a lot!

Answer 1

About the only help I can offer is that in general, diffusion rates are inversely proportional to membrane thickness. In your data which pertains to two different film materials of nearly identical thicknesses, there does not seem to be a constant ratio of OTR to WVTR. I'd guess that may reflect differences in pore size. I'd expect the ratio to be fairly constant with identical materials of different thicknesses. You say you want to project a WVTR with a film of a different thickness whose OTR is already known. If it's one of the materials you already tested, I'd say assume the same OTR/WVTR ratio, and it would be interesting to verify that the inverse thickness assumption is approximately right, which you can do with the known OTR and thickness values. However, if it's a material you haven't tested, I'd say you don't have enough information yet.