Thanks for the information, Owen.

"Owen Duffy" wrote in message
...

Polyethylene and polypropylene ropes are rapidly destroyed in sunlight.

Barry,

There is a type of rope known here as Silver Rope. I understand that
it is manufactured from UV stabilised polyethylene and claims
resistance to sunlight. It is also claimed to be resistance to most
acids and alkalis.

It is a very low cost rope, white in colour, and is widely used in
marine applications.

I have halyards and tails of this stuff that have been in the weather
for 10 years with no significant degradation (superficially or
observed when the strands are opened up).

Silver Rope is about half the price of Dacron rope (though only about
80% of the strength of Dacron). It takes knots well (as well as the
better synthetic fibre ropes, it has a slightly greasy feel), good
abrasion resistance and it is easy to splice.

Owen

Ultraviolet stabilizers can only do so much for polyolefin plastics. But
these plastics do resist acids and other chemicals very well. I suspect
this rope material contains a significant amount of titanium dioxide
pigment. Unlike carbon black which absorbs the ultraviolet, the titania
reflects it. What normally happens with polyolefins containing significant
amounts of titanium dioxide is that the surface degrades quickly leaving a
layer of the exposed pigment to reflect most of the ultraviolet, thereby
protecting the polymer underneath. In some cases, the oxidized surface
will hold moisture and conductive salts slightly reducing its insulating
and dielectric properties.

One reason polyester ropes stretch so very little has to do with how the
fibers in the rope are made. After the fiber filaments are extruded, they
are immediately stretched. This axially orients the polymer chain and
gives it a much higher strength. The same thing is done when making soft
drink bottles out of polyester. They start with what is known as a parison
(or preform) which is injection molded. This preform has the screw top
molded in. The bottom of the parison is heated in an infrared oven above
the polyester's glass transition temperature (around 90 to 95 C for
polyethylene terephthalate). It is then placed in a mold and inflated to
create the bottle shape, This inflation does bi-axial stretching of the
polymer backbone giving the bottle its great strength.

If you want to perform a simple experiment, take a PET bottle and hold its
neck or cap area with a pair of long pliers. Carefully pour boiling water
(100 C) into the bottle. This is above the plastic's glass transition
temperature. The bottle will shrink, much like heat-shrink tubing, but it
will not completely return to its original size. If you do this
experiment, be VERY careful as boiling water will spill out the top of the
bottle as the bottle shrinks.

I used to work in the research laboratories of Eastman Chemical Company.
Eastman made PET, PEN, PETG (glycol-modified PET, used in
microwave/conventional oven dinners), as well as polyethylene and
polypropylene. Some of their liquid crystal polymers would make excellent,
very high-strength rope, but the cost would be rather prohibitive for most
hams. I still have a large bag of fiberglass filled PET tensile test bars
from my days there. These make wonderful antenna and open-wire line
insulators.

73, Barry WA4VZQ