Nylon as a moisture barrier 3

[btrueblood]

I have some extruded Nylon 6 tubing that became surplus from our shop. I'd like to use it for making some waterproof containers (that I could dye to an appropriate color for its use), sealing the ends with an O-ring plug. Somehow I got the idea that the hygroscopic (moisture absorbing) property of nylon would mean that it might transmit moisture vapor to the inside, where it could condense and pool over time. Searching Matweb did not help, most of the moisture tranmission data there applied to films, not thick sections.

So, two questions

1. Is nylon a reasonably decent (i.e. as good as polyethylene) barrier for moisture ingress?

2. Would soaking the nylon, after dyeing, in a silicone oil improve moisture vapor barrier properties, or would doing so tend to degrade the material?

 

[Demon3]

1. Nylon is not a good barrier to water for the reasons you suspected.

2. Soaking in silicone oil should not harm the nylon but should not help the barrier because it won't go into the nylon (silicone oil is apolar and nylon very polar so it won't dissolve)

However, I very much doubt that the water will get through and pool up.



Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[CoryPad]

Chris (and others),

Could you please share technical aspects of this product:

http://www51.honeywell.com/sm/capran/prod-info-n2/capran.html

for the end use proposed by btrueblood? It is a similar polymer, different product form, has acceptable(?)
moisture barrier properties.

 

[Demon3]

I would expect biaxially oriented film to have better barrier properties than the surplus extruded grade which will presumably be injection molded. Plus, some of those films have barrier layers applied.

You could of course injection mold the container and apply a barrier film by in-mold decoration.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Nylon layers are used in film for oxygen barrier.

If moisture barrier is required, PE or PvDF is used as an extra layer.

I have seen condensation from vapour transmission inside sealed nylon mouldings in some circumstances. Although nylon has a strong affinity for nylon, the diffusion rate is very slow and of course dependant on concentration gradient and is accelerated by temperature and RH on each surface.

For condensation to form on a thick moulding it will take considerable time with a low RH inside and a high RH on the outside at a higher temp, then a temperature drop so the RH inside goes over 100%.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[btrueblood]

Thanks all. Will probably end up using the stuff anyway (can't beat the price), but not trust it for true moisture proofing (end use might be outdoors, where the temperature/RH cycling mentioned by Pat becomes a concern). There is a possibility to add a blown film liner or heat shrink to the outside, just to provide a second barrier.

Thanks again due to Pat, who mentioned dyeing of nylon awhile back. Took some tube scraps home last night, picking up some cheap all-purpose dark-green cloth dye from the drugstore on the way. Boiling the parts with a little vinegar added to the mix to lower the pH gave lovely results.

Should add, this test was performed outdoors, on my campstove, using my camping stainless steel coffeepot. I.e. my wife's new stove, nice counters, and good cookware were in no way harmed, nor even threatened, by this little experiment.