On Fri, 29 May 2020 09:14:08 -0700 (PDT), wrote:

Why would you have the least curiosity about the failure of a
polyethylene container after nearly 20 years of often exposure
to UV?

Perhaps because this is a technical newsgroup, and not a political
forum? I'm told that most important discoveries start with someone
doing something ordinary, noticing that the results were not what was
expected, and often saying "That's odd".

It isn't as if this sort of failure is unusual.

Oddly, I haven't seen it before with HDPE. Usually, the plastic
becomes less flexible and eventually breaks. However, this bottle
crumbled when I touched it, with very little force applied.

Take a like bottle and leave in out on a table in direct sunlight
for one summer and it will do the same thing.

Incidentally, when I used to design marine radios, we would put
samples of the plastic parts on the roof for extended periods and
watch them deteriorate. I was there for 9 years and saw quite a few
failures. Later, I analyzed the type of failure from cross section
cuts, some polish, and a microscope. UV embitterment doesn't go very
deep and really only affects the surface. I haven't looked at the
pieces yet, but at first glance, the damage is all the way through the
plastic. To be fair, most of the plastic I dealt with was ABC or some
kind of styrene derivative, which acts differently from HDPE. Also,
plastics that were either silk screened black or included a graphite
filler to provide UV protection, lasted much longer. So, if you want
your HDPE water bottle to last, buy one that's black.

Drivel: I had an experiment to test the effects of sunlight on a
Teflon tape and a PVC tape covering for antenna and coaxial cable
connectors on my roof for about 20 years. It worked fairly well, but
the experiment was cut short when a tree fell on my experiment:
http://www.learnbydestroying.com/jeffl/pics/Storm-Damage-2011-12-03/



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558