Plastics and condensation

In response to the posting of Jenny Barnett in Conservation DistList
Instance: 14:26 Wednesday, November 8, 2000, I did some research
recently based the bread bag theory mentioned. I was interested in
the relationship of the tideline formation at the wet/dry interface,
and the cellulosic discolouration noted our humid climatic
conditions, for which there was inadequate biological evidence.

The analytical investigation comprised a simulated environmental
procedure followed by FTIR, crystallinity index measurement and
reagent staining.  While evidence of a direct relationship was not
conclusive, an interesting finding was that the inclusion of
polyester strips between the paper samples revealed severe oxidative
degradation in  the area of the adjacent fibres.

The mechanism of evaporation, resultant upon either fluctuations in
environmental conditions or in an unstable equilibrium moisture
content of materials enclosed in a microclimate, results not only in
mechanical stress, but in the formation of peroxides at the point of
evaporation.  Plastic enclosures create points or areas of moisture
accumulation at which this reaction takes place, unless the
environmental conditions are constant.

Another important consideration for enclosures is that the moisture
exchange is a response of the equilibrium moisture content of the
material to a change in temperature within the airspace. The
inclusion of additional absorbent wrapping materials acts not only
as a buffer, in taking up excess humidity, but reduces the available
airspace.   The autocatalytic degradation  is probably best
controlled by close-fitting enclosures of paper or board that do not
create points of moisture accumulation, and in their design, allow
for the dissipation of degradation products in the interchange
between enclosure and surrounding atmosphere.

For more on this, see:

    McCrady, E.  (1984).  Accelerated aging and the effects of
    enclosure. Abbey Newsletter, 8 (2), 28-29.
    <URL:http://palimpsest.stanford.edu/
        byorg/abbey/an/an08/an08-2/an08-208.html>

        **** Moderator's comments: the above URL has been wrapped
        for email. There should be no newline.

    Hofenk de Graaff, J.  (1994).  Research into the cause of
    browning of paper mounted in mats. In Verschoor, H. & Mosk, J.
    (Eds.), Contributions of the Central Research Laboratory to the
    field of conservation and restoration. Amsterdam: Central
    Research Laboratory for Objects of Art and Science., 21-42.

    Eusman, E.  (1995).  Tideline formation in paper objects:
    cellulose degradation at the wet-dry boundary. Conservation
    Research, 1995, 11-27.

Dr D P Peters
Campbell Collections of the University of Natal
220 Marriott Road
Durban  4001
South Africa
+27 31 209 5066
Fax: +27 31 209 1622


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                  Conservation DistList Instance 14:29
                 Distributed: Monday, November 20, 2000
                       Message Id: cdl-14-29-001
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