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MrBillM
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Polyester
http://www.mapability.com/ei8ic/contest/rope.php
The following article was written by Dr.Barry L. Ornitz WA4VZQ, a PhD chemical engineer
who has worked for several manufactur-ers of plastics and chemicals, has quite a bit of
experience with the physical and chemical properties of plastics, and is familiar with
the chemical and ultraviolet resistance of polymers.
Polypropylene rope is most commonly used here in the States as "ski rope." It is inexpen-
sive, light weight, strong and it floats. But the polymer structure of polypropylene
(and most other polyolefins like polyethylene, etc.) is not resistant to ultraviolet.
When exposed to sunlight, it quickly degrades from the ultraviolet radiation. The result
is considerable weakening of the rope along with surface oxidation. The loss of tensile
strength is naturally a bad thing for a guying application. The surface oxidation is of
not much concern here, but when used as an insulator (such as on the ends of a wire dipole),
the oxidized surface becomes wettable allowing surface contamination to adhere. This can
increase the RF losses of the rope slightly. If you observe polypropylene rope after a
season or two outdoors, you can visibly see the surface degradation and you can often
seen numerous broken strands.
To slow the degradation of polypropylene rope, or any plastic for that matter, anti-
oxidants and ultraviolet inhibitors may be added. These increase the life of the rope
somewhat, but they do not offer ever-lasting protection. Certain colors offer better
ultraviolet protection too. I am sure that most people are familiar with the fact that
organic dyes and pigments fade. Red is probably the worst offender, followed by yellow.
Bright white and black generally hold up the best. In polypropylene rope, the black will
generally do better than the white. Since the polypropylene is naturally translucent, it
takes little white pigment (usually titanium dioxide) to make it white. Black is cheaply
obtained by adding carbon black to the polymer melt. The white pigment tends to reflect
the ultraviolet while the carbon black tends to absorb it and convert it to heat. With
its low pigment loading, black polypropylene is probably better than the white.
A much better choice is nylon rope. It is strong, readily available, and has a fairly
high ultraviolet resistance. It does stretch considerably, and this is an important
consideration in antenna work. Chemically, the nylons are in a family known as polyamides.
Their chemical resistance is normally good except in areas where acid conditions exist.
These tend to occur in industrial areas with high smog or where acid rain is prevalent.
Again bright white or solid black is to be preferred in outdoor use.
Probably the best rope materials for outdoor use are the polyesters. Typically these are
polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), although I suppose
polyethylene naphthalate (PEN) ropes exist today. The most common material is PET [more
properly called poly(ethylene terephthalate)], known under such trade names as Dacron
(DuPont), Fortrel (Wellman), Kodel (Eastman), A.C.E. (Honeywell). etc. [For some reason,
rope vendors at many USA hamfests tend to charge a premium for Dacron, probably because
of the name recognition.]
Polyester ropes have very low stretch making them excellent for guying applications.
They are excellent in both chemical and ultraviolet resistance. The polyester materials
have an interesting property that makes them especially ultraviolet resistant. These
materials fluoresce upon exposure to ultraviolet light; they absorb ultraviolet radiation
and re-emit it as light at a longer wavelength. Generally the emission is in the near-
infrared region but some materials fluoresce in the visible spectrum too. This is an
effective way of getting rid of the energy absorbed from the ultraviolet and it provides
much of the ultraviolet resistance seen in these materials. Their chemical resistance is
even better than the nylons. Black or white colors are still to be preferred, although I
have seen surplus military rope in the traditional olive-drab color that should perform
well. Since the polyesters are generally clear, they take more white pigment to color
them than to the polypropylene materials. Thus the white rope is almost as good as black
for long-term use.
There are other specialty ropes available such as those made from polyaramides (Kevlar
and Nomex by DuPont) and polyimides. The Kevlar ropes are extremely strong, but they
require special stranding and covering to avoid abrasion problems; their abrasion
resistance is quite poor. There are also composite ropes made with a core of one
material which is clad with a woven covering. These tend to be rather specialized
and are probably not worth much discussion. However there are polyester covered
polypropylene ropes on the market today. These rely on the good strength of the
inexpensive polypropylene core, while the jacket provides considerable protection
of the core from sunlight. Wire ropes are also commonly available, and entire books
have been written on their design and application. It is usually best to consult the
manufacturers directly about applications of these specialty ropes.
I hope this gives a better explanation of why you might not want to use polypropylene
in many applications. However, I do like to use polypropylene ropes for Field Day antennas.
These are used only a few days each year, and the bright colors can provide contrast to
prevent people from walking into them! They are inexpensive enough to discard too.
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Alm
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Why in the world the OP have come up with the idea of using a rope on chairs, I don't know.
The chairs are typically a loose weave of flat straps or a piece of cloth. Get a piece of Sunbrella fabric and have a local mujer with a sewing
machine to put it on, she'll be happy to make a few bucks. Sunbrella is very UV-resistant. It's used on boat canopies, biminis etc.
Or again, buy a length of 2" synthetic strap, preferably Polyester if you find it cheap. This will be more work for you.
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surabi
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Quote: Originally posted by Alm  | Why in the world the OP have come up with the idea of using a rope on chairs, I don't know.
The chairs are typically a loose weave of flat straps or a piece of cloth. Get a piece of Sunbrella fabric and have a local mujer with a sewing
machine to put it on, she'll be happy to make a few bucks. Sunbrella is very UV-resistant. It's used on boat canopies, biminis etc.
Or again, buy a length of 2" synthetic strap, preferably Polyester if you find it cheap. This will be more work for you. |
As the OP, I can tell you that the kind of chairs I am talking about are often done with some kind of rope, or alternatively, strapping. I happen to
be a professional upholsterer, and work almost exclusively with Sunbrella, so I know all about it. There is no way, with the way these chair frames
are made, that a piece of fabric can be attached, believe me. So no "mujer with a sewing machine" who wants to make a few bucks.
And these chairs are not done with a loose weave, but a tight one.
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freediverbrian
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First thing there is not a rope on a boat it is called a line. If you want is long lasting line get a" yacht braid" line polyester cover over a
polyester core. It is used for halards and running rigging on sail boats. It will last for years, look at West Marine stores not at home depot. Cotton
will rot , poylpropiline turns to dust.
[Edited on 4-25-2017 by freediverbrian]
[Edited on 4-25-2017 by freediverbrian]
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MrBillM
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Boat Rope Dope
Good One !
I've used that many times over the years.
Of course, splitting hairs, IF there isn't a Bell, there isn't a rope.
BTW, it's Halyard.
Derived from: Haul Yard.
Which on a flagpole (ashore) WOULD be a rope.
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freediverbrian
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I was corrected by Willard guy about the rope on the ships bell and now it is gone ?? I loved the correction and he was right, 😀 as for my
spelen I don't give a *****
[Edited on 4-26-2017 by freediverbrian]
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