Storing objects in sealed plastic bags

Eliza McKenna <eliza.mckenna<-at->awm<.>gov<.>au> writes

>I am seeking some advice on storing collection in polyethylene bags.
>We have recently had a clothes moth infestation and had to freeze
>our entire textiles store. ...
>...
>...  For items that are less vulnerable to off-gassing, such
>as textiles, we are interested to see if we can keep these stored in
>plastic for as long as possible, even permanently. ...

In my experience, low density polyethylene bags manufactured from
virgin, rather than recycled polymer, oxidize to the stage of
physical disintegration after about 10 years at ambient and in the
dark.  If they are exposed to UV light, perhaps by being stored by a
window, the degradation rate is doubled.  Recycled material
disintegrates after around 5 years because it contains lower
concentrations of antioxidants than virgin materials.

Polyester bags, such as those prepared from Melinex or Mylar film,
degrade by reacting with water (hydrolysis) rather than oxygen and
therefore are more stable than polyethylene in air.  However, they
are also more expensive and require higher temperatures to heat seal
them.

Yvonne Shashoua
Senior Researcher
Environmental Archaeology and Materials Science
National Museum of Denmark


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                  Conservation DistList Instance 29:45
                 Distributed: Saturday, April 16, 2016
                       Message Id: cdl-29-45-003
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