Zip lock bags yellowing

Emanuele Marconi <emanuele.marconi<-at->usd<.>edu> writes

>Have you ever had similar experiences with (old or new) polyethylene
>bags yellowing?  I am wondering if this can be caused by a
>plasticizer or any other additive used in the production.

I haven't experienced Ziploc bags yellowing before, but I have
experienced polyethylene bags/sheeting/tubs yellowing and
embrittling before.  After about 20 years it seems to have degraded
to the point that it will tear easily along folds, or even crack in
uncreased areas, and I've experienced the handles breaking off of
polyethylene tubs when trying to lift them when they get older. That
was a bit of a humorous story: they were tubs of wet archaeological
material that had been in cool wet storage for about 20 years.
They'd grown a nice thick layer of slime mould on top, and as a
co-worker went to lift the tub, the handles broke, causing the tub
to plummet to the counter, and a tidal wave of slime mould to land
on my head.  Fortunately the artefact (and my head) were unharmed.
Hope that helps,

Valerie Tomlinson
Conservator
Auckland War Memorial Museum
The Domain
Private Bag 92018
Victoria Street West,
Auckland 1142
New Zealand
+64 9 306 7070ext 7304


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                  Conservation DistList Instance 30:3
                   Distributed: Friday, June 3, 2016
                        Message Id: cdl-30-3-003
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