Water Vapor Transmission Rate (WVTR)
Water Vapor Transmission Rate (WVTR)
(OP)
Hello All.
A supplier of polymer bag is rating their product for WVTR at 0.048 GMS/100SQ INCHES/24 HOURS.
A) What is GMS ?
B) Will this be able to replace the Masson Jar we are using now?
Note:
We keep dry pellets in Masson Jar so the %RH is kept constant. We do this so can measure the relative viscosity at a later date. This method is bulky and we are looking for other containers.
A supplier of polymer bag is rating their product for WVTR at 0.048 GMS/100SQ INCHES/24 HOURS.
A) What is GMS ?
B) Will this be able to replace the Masson Jar we are using now?
Note:
We keep dry pellets in Masson Jar so the %RH is kept constant. We do this so can measure the relative viscosity at a later date. This method is bulky and we are looking for other containers.





RE: Water Vapor Transmission Rate (WVTR)
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Water Vapor Transmission Rate (WVTR)
RE: Water Vapor Transmission Rate (WVTR)
So if I knew what was GMS I could calculate how much moisture can cross this type of plastic (our lab is at 50%RH - 23C)and how long I can keep the product dry (below 100ppm.
If the period is shorter than 24 hrs I would forget about these bags.
We keep 250ml of product.
Thanks
RE: Water Vapor Transmission Rate (WVTR)
Assuming that GMS means grams, as Cory suggested, I calculate about a 2 ppm per day increase in water content, assuming your pellets have a specific gravity of around 1. I'd also say the numbers could be in error by as much as an order of magnitude, due to the probable large difference between your vapor concentration and the water vapor environment they did their permeation test in. So, a 50 ppm change could take roughly 25 days, or as little as 2.5 days. If those look like workable numbers, get some samples of the bag material, and run some tests.
You could improve on the numbers by putting the bag containing pellets into a second, outer bag, which also contains a (regenerable, indicating) dessicant.
RE: Water Vapor Transmission Rate (WVTR)
A bag inside a bag will help a lot, especially if the outside bag also contains a desiccant. Your dry granules might be a convenient desiccant. ie put your 250 grams in a bag. expel all air or purge with dry gas, seal the bag. Put the sealed bag in another bag with some dry granules in it. Expel all air and seal it. You then have your original barrier plus a second barrier at a much lower concentration gradient for the water vapour.
24 hours sounds fairly doable to me. You might find a better bag, with thicker wall or better resin. The world is full of plastic bags in very many configurations.
Another choice might be a paint pail. That is how we store retained hygroscopic samples. We also have a small vacuum oven in case we do need to dry granules.
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.
RE: Water Vapor Transmission Rate (WVTR)
You are correct. I made a WAG of 100 sq. inches.
RE: Water Vapor Transmission Rate (WVTR)
0.048 g/100 sq in/24 hrs x (80/100) x (50/100) = 0.0192 g/24 hrs
0.0192/250 g = 76.8 ppm
So, if started with 50 ppm water, end up with about 126 ppm water (assuming no absorptivity decrease). Need either less permeable or thicker material for the bags.
See how the Water Vapor Transmission Rate (WVTR) is measured per ASTM F1249 at
http:
Also, '4-mil polyethylene will only pass about 0.05 grams/sq. ft./24 hrs at 75° F and 100% RH.'
http://www.drierite.com/catalog3/page17b.cfm
CoryPad: As 0.048 is close to the 0.05 grams in the Drierite catalog example, perhaps this metrification applies for the sq. in. units: 100 sq. in. = 1 sq. ft.???
RE: Water Vapor Transmission Rate (WVTR)
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.