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Creepy nylon

big spool of nylon rope sitting on top of a large stump in a garden

I posted yesterday about the possibility of using nylon rope instead of 14 gauge electric fence wire on our next gate.

Turns out that was a creepy suggestion that should be avoided for this particular application.

The main reason I was considering nylon was because we have a massive spool of it. (Thanks Mom)

A timely comment from Roland was what set me straight. The nylon rope would more than likely stretch over time due to the constant stress of the turnbuckle. The material science term for this influence is known as creep. A word that creeped its way into the music industry not once but three times in recent history thanks to bands like Radiohead, TLC, and Stone Temple Pilots.

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Are you sure that is nylon. It looks like polypropylene. Nylon can stretch as much as 30 percent and return to normal. It is a giant rubber band and that's why it is used as anchor line on boats. It's strength is in it's stretch. Dacron(polyester I think) on the other hand stretches very little. Take a piece of that and see if it floats. Nylon does not float.

Comment by Oldfool Mon Apr 2 17:33:13 2012
Oldfool --- Good point on the differences! Sounds like Mark might get away with using this rope to brace his gates after all.
Comment by anna Mon Apr 2 19:03:10 2012

From a photo I cannot identify a type of plastic, but take a look at the spool. If it is the original spool, there might be an identification label on it. :-)

Ordinary rope made from plastic is usually braided. This will elongate quite a lot when new because the braid stretches during the first uses. (This is a completely seperate matter from the creep of the fibers themselves, btw.)

The rope with the least elongation made e.g. for use on sailing vessels usually has a kernmantle contruction, where a core of unidirectional fibers is held together by a braid. Since the core is already straight, you won't get the stretching that you get from a full braided rope.

But the thermoset plastics itself will still creep a lot (compared to metals and thermosets). This is a very slow process though. It is usually measured on a logarithmic scale as elongation over 10ⁿ hours under a constant force, where n is an integer roughly in the range 1-7.

Comment by Roland_Smith Tue Apr 3 15:59:15 2012
Roland --- Excellent point, as usual, about the weave of the rope! Sounds like this rope is no good as a tensioner even if it isn't nylon. (Which it looks like it's not since Mark did a float test.)
Comment by anna Tue Apr 3 16:57:29 2012

Both polyamide ("PA", nylon) and polyethylene terephthalate ("PET" dacron) have a density higher than water, so they should both sink (unless there is air trapped in the braid!)

The most used polymers like polyethylene ("PE") and polypropylene ("PP") have a density lower than that of water, though.

There are multiple lists of polymer densities on the interwebs, like this one.

Comment by Roland_Smith Tue Apr 3 17:25:35 2012

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