Nylon-12 Processing

[gregory620]

My application uses nylon-12 tubing. During the processing, I take the tubing and neck one side of it down to a smaller OD. using a hot die assembly. Recently we switched colors of the tubing from a blue to a gray color. My understanding is that this implies that the pellets used for the nylon extrusion change but material properties should be the same. However when I try my hot die process, I find that the gray tubing is harder to pull through the die and it's more brittle and tends to break more often as I pull it through. OD and ID dimensions of the gray and blue tubes were the same. Any ideas as to what has changed?

 

[patprimmer]

Any number of things.

It might be a different MFI or molecular weight. This effects the viscosity of the melt.

There might be an increase in powder fillers like calcium carbonate.

Pigments act as nucleating agents. Higher levels of crystallinity effect melting point and properties when approaching melting point.

It might not really still be nylon 12 as another nylon might have been available in the colour so was used as a replacement.

If one was very old stock there might be enough moisture present to create a problem.

The colour might be added as a master batch and there might be different amounts of or a different type of carrier resin in the master batch.





Regards

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[Demon3]

Pat's run-down is spot on and comprehensive. Therefore I'll just add that my best guess is Pat's option 3. I.e. the new pigment nucleated crystallization and makes it brittle. Speculation only mind you. You could run a DSC to get the crystallinity and crystallization onset temperature and see.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[unclesyd]

Take Demo3's about the DSC but If you have some of your good stuff run it at the same time.