Polyethylene

... Regarding the PE question, do you want the official party line or
not?   Officially, we consider polyethylene, polypropylene, cellulose
triacetate and polyester to be the inherently (hmm probably bad
spelling...) good plastics.  Now for the "but" statement.

A number of the producers (manufacturers) of all of the plastics vary. I
have seen some polyethylene plastics that have yellowed severely,
although the degradation products are supposed to be safe.  I have also
seen some polyethylene that was producing an oily liquid that
permanently damaged some slides.  It was not in every slide slot on the
page, but was on many pages.  I have also seen slip agent coming out of
polyethylene pages (although more often from polypropylene pages.)  This
slip agent is most often the amide derivative of erucic acid (to quite
the company's notes).  It comes out as a waxy layer.  Obviously you
don't want it on your slides even though it is quite inert.  Cellulose
triacetate is not good around things that are degrading and producing
acid by-products.  I also know that at least some of the triacetate
sleeves available, are about 15% plasticizer.  Although I have never seen
a problem with plasticizers in triacetate, it is certainly possible.
Even polyester has potential problems, although again, I have never ever
heard of any problems with it (apart from being sharp and smooth and
staticy and....)

The bottom line is that we do feel that all of the above mentioned
plastics are safe (at least for photographic use), but that you do have
to be careful about batches and producers.  Unfortunately when we buy
from a supplier we have no idea who their supplier is and often
suppliers are switched.

-doug

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                  Conservation DistList Instance 5:19
                 Distributed: Sunday, September 8, 1991
                        Message Id: cdl-5-19-009
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