Zip lock bags yellowing

            ....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...

Yellowing of polyethylene bags is the main symptom of oxidation,
particularly if exposed to ultraviolet radiation.  Oxidation causes
the formation of carbonyl groups and other Chromophore  (colour
inducing) chemical groups to form.  As oxidation progresses, the
material disintegrates and smells 'sweaty'.  New polyethylene
contains anti-oxidant additives but these are exhausted on contact
with air over time.  Polyethylene does not contain plasticizers, but
is highly effective at absorbing oily materials and therefore may
feel sticky.

Yvonne Shashoua
Senior Research Scientist
National Museum of Denmark


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                  Conservation DistList Instance 30:3
                   Distributed: Friday, June 3, 2016
                        Message Id: cdl-30-3-002
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