×
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

Dimensional changes due to water absorption

Dimensional changes due to water absorption

Dimensional changes due to water absorption

(OP)
I found this old thread that relates to my problem but unfortunately it never got answered.
thread334-73835: Water absorption – Calculating the change on a dimension
I'm fairly sure that the % volumetric change of a component isn't the same as the % water absorption but I assume there must be some relationship even if it's material specific. I would be interested to know what it is, if it exists.
Secondly can anyone tell me what effect pressure has on the water absorption of polymers, and what happens when the pressure is removed?
I'm working on ROVs that are deployed to 3000m and have several components made from a Nylon 66 (probably not a good choice of material) based bearing material and I'd like to be able to quantify the affect of the sea water pressure on the dimensions.
Thanks,
Pete

RE: Dimensional changes due to water absorption

Lots of graphs for you: Here

And you are correct - PA6.6 would not be my first choice material either.

No idea of pressure implications though, sorry.

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

RE: Dimensional changes due to water absorption

(OP)
Thanks Pud, that will at least get me started.

Pete

RE: Dimensional changes due to water absorption

If you have access to Moldflow, take a look at the PVT curves for your material. I make 3000 meters to be 4371 psi for seawater with a apecific gravity of 1.025. That should be in the range of PVT data in the program. ALso, I think the bulk modulus can be used to determine volume change from a hydrostatic pressure. The bulk modulus K = E/[3*(1-2n)] = V*dp/dV, where E is Youngs modulus, V is volume, and n is Poisson's ratio.

RE: Dimensional changes due to water absorption

(OP)
Thanks for the reply Rick, a valid point about the compressibility of the plastic. But the point I'm having problems with is what effect does pressure have on the water absorption.

RE: Dimensional changes due to water absorption

There seems to be a fair amount of technical publications on the internet about pressure vs. water absorption of plastics and rubber.

RE: Dimensional changes due to water absorption

My best guess is that pressure will have very little effect on moisture adsorption amount but higher pressure may may it adsorb faster.

Chris DeArmitt - PhD FRSC

Plastics & Materials Consulting
www.phantomplastics.com

Plastic Training Seminars
www.plastictraining.com

RE: Dimensional changes due to water absorption

(OP)
Chicopee, I'd be interested in what you found I failed to turn up anything

RE: Dimensional changes due to water absorption

Hi PeterSI,

You might also look at a free trial of brand new CheFEM prologue simulation software. This program quickly tells you the dimensional change of engineering polymers (including Nylon 6,6) and composites when exposed to a wide range of chemicals (including Water on 3000 meter depth), and a lot more...

Check the program at: CheFEM prologue simulation.

Hope this helps.

Kind regards,
CheFEM development team

RE: Dimensional changes due to water absorption

Chris, would not increasing the pressure reduce free volume, therby inhibiting moisure from migrating deeper into the plastic? Just a thought.

RE: Dimensional changes due to water absorption

Rick, that might be a very transient effect. Once the water is absorbed there is no pressure difference between the water inside the bulk polymer and the water outside, so the polymer is not compacted. The pressure effect on absorption would be due to the higher concentration of water under pressure (higher density). This effect would be small.

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