water vapor permeation rate for polycarbonate/ABS

[mattdent]

I am after the WVPR for a given thickness of 1mm for both polycarbonate and abs, both injection moulded grades, and for an enclosure do you use the overall area and the thinnest area in any calculations?

 

[btrueblood]

You can search on

http://www.matweb.com

for that specific parameter, and it will list data available for a very wide variety of PC and ABS grades.

You will typically find manufacturer's quoted values for film and extrusion (sheet) grades. If you are lucky, you may find some quoted values for injection molding grades also. What you find may or may not be the best possible permeability available amongst the bewildering variety of plastic formulations out there. You will find the values vary dramatically, even for a "specific" plastic. Chris and/or Pat will be along soon, and if you are lucky, will tell you what additives increase and/or decrease the permeability for those two plastics. There are, or may be, coatings you could use to help reduce permeation rates.

You will probably want to contact a supplier shortly after that effort, and speak to them directly about what your requirements are (temperature will be the biggie). They can then make some suggestions, and if you are lucky, may give you ballpark figures to work with.

For calculations, use the overall internal area, and then pick an "average" thickness. The numbers you calculate are gonna be ballpark, no matter what, there is just too much variability in the data to have much confidence. In the end, you will want to peform a test on your actual hardware before believing anything...and once the mold is done, changing grades of plastic to test something different is...well, not necessarily easy, but surely do-able. Changing grades of ABS will probably be simpler than changing from ABS to PC.

Good luck!

 

[Demon3]

I am pretty sure that WVTR will vary greatly depending upon the way the ABS is made. There are two way. Solution ABS and emulsion ABS. The former is used by Dow and the latter by BASF for example. The latter, emulsion process leaves loads of surfactant in the plastic and that draws water in quite extensively.

So, don't just take a generic value, make sure it is for the manufacturer you intend to use.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry