Nylon Water Absorbtion 1

[jbyszewski]

Is there an industry standard for testing Nylon in new products? I am particularly concerned with the effect of water absorbtion in a tightly fitting assembly. Is there any standard or controlled method of exposing nylon parts to a specific amount of moisture?

 

[patprimmer]

Not that I am aware of, and I have been involved in technical support and marketing of nylon for about 30 years.

Even if there was a Standard test, that does not mean it would represent your conditions of use.

The main problem with conditioning nylon, is that it absorbs a lot of water very quickly onto the surface, but takes a very long time to evenly diffuse through the moulding.

This can be accelerated with temperature and concentration gradient (ie in hot or boiling water) but this can lead to other inconsistencies, like anealing and overconditioning of the surface.

Nylons tend to aneal in air at about 180 deg C but they aneal in water at about 60 deg C (both depending on the type of nylon).

To accelerate conditioning, you can treat in water at ambient, 55 deg C or at 100 deg C, then dry the surface in an oven, until it is a bit to dry, then leave at 22 Deg C and 55% RH until it is all at equilibrium, or leave at the average ambient conditions of use, if they are known and consistent.

Time frames are very dependant on section thickness, and uniformity.

Many laboratories only test nylon dry because of the problems with obtaining CONSISTENT results for conditioned parts.

I have a lot more detailed info, but before I write an epic, I would need to know exactly what you are doing and why you are doing it.

To simply reach reasonable toughness, many people simply treat in hot water for a short time, or ambient water for a few weeks. Most of the toughness is aquired when the skin is conditioned. It normally does not need to be uniform through the moulding, unless the absolute maximum performance is required.

To control dimensions accurately, it is much more difficult, and uneven distribution of moisture causes internal stresses that can distort dimensions

Regards
pat