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dgowans (Mechanical)
12 Dec 07 9:25
What are the major differences between these two grades of nylon?

I've found that nylon 12 is more resistant to chemicals, and I've also seen that nylon 12 may retain more of it's mechanical properties after UV exposure.  Are there other significant differences?

I've received a request from our purchasing department to switch a nylon 12 cable tie to nylon 6/6 in order to reduce cost.  We're using the cable ties to mount a piece of our equipment to a pipe in an outdoor environment.  I'm not too concerned about chemical resistance but UV stability and performance over a wide temperature range are critical.  We would at the very least switch to a UV stabilized nylon 6/6.

All thoughts and comments are welcomed.
CoryPad (Materials)
12 Dec 07 9:40
The major differences are that polyamide 6,6 has higher strength, stiffness and temperature resistance than polyamide 12, but it has higher water absorption and less chemical resistance.  These properties are the result of the polymer chain structure: PA 6,6 has more amide linkages per chain, so it has more interchain bonding.  The amide linkages are also the sites for chemical degradation, so having a more olefin-like structure gives PA 12 its higher chemical resistance.

If you don't need the chemical resistance, then a UV-stabilized PA 6,6 could be considered.

Regards,

Cory

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Helpful Member!  Pud (Mechanical)
12 Dec 07 9:45

Nylon 12 is around 4 times the cost of 6.6.....
patprimmer (Publican)
12 Dec 07 9:45
Nylon type 12 is a lot more expensive than type 6.6.

Appart from qualities already mentioned, type 12 is tougher and more ductile and shrinks somewhat less when moulding.

Regards

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Pud (Mechanical)
12 Dec 07 9:47


Forgot - nylon 6.6 does not like Zinc salts - if you are tieing onto a galvanized pipe, be very, very afraid!!

Pud (Mechanical)
12 Dec 07 9:48


Up early Pat!!
Demon3 (Materials)
12 Dec 07 10:01
One more comment. If you are getting your cable ties from an experienced supplier then no problem but as molded nylon 6,6 will be brittle and not work well as a cable tie. Once exposed to water in the atmosphere they are fine (the water plasticises the nylon). I even heard that one company  puts a drop of water in each bag before shipping to help ensure the ties get their plasticiser.

As Cory explained nylon 12 is like a cross between PE and nylon 6,6 if that helps you imagine it's properties. You can compare at www.matweb.com

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

patprimmer (Publican)
12 Dec 07 10:17
I certainly know more than one moulder who packs nylon mouldings in a plastic bag with 1 or 2% of water by weight of nylon in the bag.

Cable ties tend to be thin and are conditioned by atmospheric moisture in a fairly short time frame. Depending on conditions, it is a mater of weeks normally.

Pud is correct about susceptibility to zinc salts.

The correct UV stabilisers give quite a long life outdoors.

Yes, I am up quite late.

Regards

eng-tips, by professional engineers for professional engineers
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Pud (Mechanical)
12 Dec 07 10:18


If you are not running continuously over say 80 deg C, you may as well use nylon 6. Even cheaper.
dgowans (Mechanical)
12 Dec 07 11:15
All,

Thanks very much for the information.  The susceptibility to zinc salts is enough to convince me to steer clear of nylon 6/6.
Pud (Mechanical)
12 Dec 07 13:31
You're welcome - glad to be of assistance.
Pud (Mechanical)
13 Dec 07 10:08
dgowans,

I have a hunch that you can get cable ties in PBT - this should be cheaper than PA12 and no zinc problem as PA. Good outdoors too "as is" - excellent with uv stabilizers.


Cheers


Harry

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