×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

water vapor permeation rate for polycarbonate/ABS

water vapor permeation rate for polycarbonate/ABS

water vapor permeation rate for polycarbonate/ABS

(OP)
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?

RE: water vapor permeation rate for polycarbonate/ABS

You can search on 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!

RE: water vapor permeation rate for polycarbonate/ABS

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

www.phantomplastics.com
Consultant to the plastics industry

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources