How do extrusion processing conditions impact the elongation properties of Nylon 12? 1

[Mistahcox]

Our company has had on-again off-again issues hitting elongation specs for a few customers (specifically one more than others). In some cases, our product underperformed and in some they have overperformed.

One instance we had a tech from a company come to us and show us how they perform their pull tests on the Nylon 12 tubing being ran for said company. During and even after a few hours of the run, our elongation %'s were around 30% below their low limit. When we shipped the product to them however, they had no issues and reported %'s +60 or higher than we or the visiting tech could get - they were in a bind an agreed to try the parts.

*I know pull speed / rate of travel has a large effect on elongation testing but are there factors / settings in the process that can change how the material stretches after the being extruded?

*Can nylon 12, specifically Vestamid ML21, be processed so that when it is still warm (during production), its at its maximum elongation and once reaching ambient temp and humidity becomes brittle and doesn't stretch as far?

*Can it be ran so that the opposite effect occurs? Once settling to temp & moisture equilibrium, elongation increases?

Like i mentioned earlier, we've had instances that went both ways were elongation seemed to decrease after the run as well as seeming to increase after the run. The company dose attempt to use the product in either situation and has seen mixed results. So before we do a deep dive and start a project I thought I'd ask some experts who may have ran into this before.

 

[3DDave]

Nylon properties are affected by moisture; you didn't mention controlling for that.

https://www.amcopolymers.com/resources/blog/nylon-and-moisture-absorption

 

[Compositepro]

Yes, nylon absorbs moisture from the air and must be completely dried prior to extrusion. Then it will take time to reabsorb moisture afterward. The flexibility and elongation are strongly affected. The wall thickness and ambient humidity control the rate of change and ultimate moisture content. Equilibrium can take days or weeks.

 

[Mistahcox]

3DDave - correct, we don't have controls humidity / moisture. The tubes must travel through a water bath before the cutting step so roughly 3' stays submerged for maybe 2 seconds at a time.

Compositepro - we've had failures where elongation decreased over time / they stretched farther at our facility than when used & tested by the customer. It is a company in Ireland so there is a lengthy trip across the Atlantic.

We dry our Nylons for at least 4 hours at 140°F so there should be little to no moisture when being extruded.

I understand the effects of moisture absorption so maybe a different (maybe not better, but at least different) question would be, does how the material is processed effect moisture absorption?

 

[Pud]

You might find this paper of use. Haven't read conclusions but problem sounds familiar.

https://www.sciencedirect.com/science/article/pii/S2590048X20300911

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[Mistahcox]

Pud, thank you very much for this article. VERY useful stuff.

We've discussed the draw down and water bath distance / air gap as factors but didn't have the machine availability to run multiple tests at multiple settings for comparison. This gives a us great starting point.

 

[Felix Wang]

Thanks a lot for information above! We also have a difficult to let the elongation down for ML21 tube from the extrustion process. The burst is better with lower elongation tube. Could you give me idea for it? Thank you!