Originally posted by LuvNik
Polypropylene breaks down in the sun very quickly. Is it the cheap yellow stuff?
Beware generalizations!
In beachcombing flotsam-jetsam marine cordage, a favorite
pastime, I'm impressed at the variety of the stuff--in
nature of material, & in the physical structure. In the
case of PP ropes, that material comes in a variety of
fiber shapes (round, ovalish, flattened, & filmlike).
PP is frequently used in combination with polyester;
some arborist ropes I believe have PP core fibers.
Marine cordage includes ropes with PP core fibers (of
yarns in laid rope), and ropes with PP mixed equally
with PS at the surface (e.g., strands comprising two
yarns each of PP & PS, alternately orders; braided
ropes with PS strands running one way, PS the other
--in a tight 8-strand rope, this gives a cross-section
rather square new, rectangular upon compression to a
drum, etc.--, and even PS/PP fibers adjacent in strands
of a more *hollow* 8-strand).
There is also a general material known as "co-polymer",
in which--usually--polys -propylene & -ethylene are
at the "molecular" level; there's at least one brand
that combines PP with polyester ("karat"). This is
advertised to significantly increase the strength
and abrasion resistance, and the material I've seen
is all in a flattish fiber, yielding a softish fuzz
upon abrasion. ("danline", "polysteel", "ultra blue")
Below is what the Cordage Institute's "Fiber Rope
Technical Information & Application Manual" has to
say about PP:
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Polyporopylene [PP] rope stabilization.
Ropes made of PP are suitable for many general-purpose
uses as long as the characteristics of the fiber are
recognized and appropriate precautions taken.
A major factor is that unstabilized PP is very liable
to destruction by light-heat-oxygen. This sensitivity
is due largely to the fact that each alternate carbon
atom in the polymer chain is "tertiary". This means
a carbon atom joined to three others, instead of only
two as in unbranched polyethylene. It has been found
that a hydrogen atom attached to such a tertiary carbon
is easily "pried off" by heat and light. Oxygen, so
often right at hand, replaces the hydrogen. Right here
is the beginning of the end of filament integrity.
Stablizer systems have been developed to protect
against UV; but the need is note everywhere reocognized
and ropes are offered [that] are not satisfactory.
Protection against UV sunlight cna be achieved either
by the use of chemical stabilization, most commonly
referred to as "hindered amine light stabilizer"
(HALS), or by pigmentation during the extrusion process.
Black is preferred, as it functions as the best absorber
or "quencher" of the energy from sunlight wave lengths.
Stabilizers do add to the cost, but merely spending
money does not ensure stability. The rope user must
[ensure] that the ropemaker is (1) aware of the problem,
(2) technically competent, and (3) conscientious.
Outdoor exposure is the matter of central interest.
Accelerated aging is ovens and in various fading and
weathering units correlate very poorly with outdoor
exposure and cannot be relied upon in judging rope
quality. This appears to be due to the fact that the
light intensities at different wave lengths--most
particularly in ultraviolet--do not correspond to
natural sunlight. Much effort has been devoted to
developing light sources and light filters, but
outdoor exposure remains the only completely reliable
method of testing.
The destructive effect of outdoor exposure varies
widely with latitude and with season, so location of
use should be taken into consideration.
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