Preserving plastic

Danelle Orange <daorange [at] dwu__edu> writes

>I have several donations of plastic signs and bags from the 1970s
>...
>... What would be the best way to preserve these?

Plastic bags from the 1970s are most likely made from low density
polyethylene (LDPE).  They deteriorate by oxidation and are very
sensitive to light, especially ultraviolet radiation. The label
'recyclable' may refer to the fact that starch has been mixed with
the polyethylene to accelerate its breakdown in landfill sites. The
plastic signs, if rigid, are most likely to be made either from
polystyrene or from acrylic, polymethyl methacrylate (commercially
known as Plexiglas or Perspex). Both polystyrene and polymethyl
methacrylate degrade by oxidation.

In general, long term storage of plastics requires low, preferably
no light and low temperatures. For every ca. 10C the plastics are
cooled, the rate of oxidation will be halved. If the bags and signs
are stored in a domestic freezer, careful handling and packaging is
required to prevent physical damage to the cold, brittle materials
on removal from the freezer.

Yvonne Shashoua
Senior Researcher
Department of Conservation
National Museum of Denmark


                                  ***
                  Conservation DistList Instance 22:41
                Distributed: Wednesday, January 21, 2009
                       Message Id: cdl-22-41-002
                                  ***