Polyethylene deterioration

The following is posted on behalf of Ginette Clement

    My name is Ginette Clement.  As part of my last year of the
    Techniques de Museologie program from College Montmorency, I am
    doing an internship at Parks Canada at the Quebec Service
    Centre, in Quebec city under the supervision of Kateri Morin,
    conservator.

    We are presently replacing some storage bags made of
    polyethylene sheet (done 20 years ago) that now show signs of
    deterioration.  Our aim, in writing to you, is to generate an
    awareness of problems with the use of polyethylene and to find
    solutions for long term storage without worries. Your
    observations of this type of storage material, possible
    explanation of the deterioration process or any advice has to
    which brand of polyethylene sheet we should use from now on is
    welcome.

    Here are some notes we have made on altered packs from our
    collections.

    Type of degradation: The plastic sheet is heavily yellowed, very
    brittle and many bags are disintegrating on contact.  The
    degradation can take many forms: on the top surface generally,
    very localized with precise round shapes, on the edge, or on the
    back of the pack.  It appears that the first signs of
    degradation were noticed more than 7 years ago.  You can access
    pictures showing different type of deterioration at :
    <URL:http://cf.photos.yahoo.com/ginetclement> in the
    "polyethylene" file.

    Typical packaging: These bags contain archaeological leather and
    wood.  All of these have been treated with polyethylene glycol
    (PEG) and in some cases other products have been used such as
    t-butonal and Cetavlon (an antiseptic). Nevertheless bags with
    other objects treated and packed the same ways do not show these
    deteriorations. Information gathered from the conservation
    reports led us believe that in many instances the bags were made
    in 1983 and all were done in the same lab.  We also find in some
    packages (approximately 2 cm thick)  white coroplast and layers
    of microfoam that do not show any signs of degradation.  A table
    that summarises our investigations has been compiled and can be
    shared on request.

     Conclusion: This investigation showed no general trend in the
     type of objects, or in the storage condition.  This would
     suggest that this degradation is associated with the quality of
     polyethylene sheet used.  We would appreciate any of your
     storage stories or observations that might help us.

    We can be reached at

        Kateri Morin
        Parks Canada
        3, Passage du Chien -d'Or
        C.P. 6060, Haute-Ville
        Quebec, Quebec G1R 4V7
        kateri.morin [at] pch__gc__ca

Kateri Morin


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                  Conservation DistList Instance 16:67
                 Distributed: Wednesday, April 30, 2003
                       Message Id: cdl-16-67-003
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