Offgassing from plywood shelving

Karen Potje <kpotje [at] cca__qc__ca> writes

>In reply to Claudius Schettini's problem of a science library with
>new veneered plywood shelving, Sean Harrison suggests that a clear
>latex sealant will trap gases inside.  Although there are references
>in the conservation literature to the use of clear acrylic varnish
>as a vapour barrier, I think recent literature indicates that no
>transparent coating is going to provide a really good vapour
>barrier.  The clear acrylic varnish might slow down emissions but
>won't stop them.
>...
>I'm not sure how worrisome this should be to Claudius Schettini.  No
>one knows what levels of acids in the environment will have a
>harmful effect on paper

Some investigations of the effect of acetic acid on paper have been
done at CCI by A.-L. Dupont and J. Tetreault. The result of this
research has been submitted to Studies in Conservation in January
1999. This is an extract of the summary submitted papers entitled
"Cellulose degradation in an acetic acid environment":

   "... Concern about the harmful effects of these acidic compounds
    on cellulosic materials led to the present study. The aim was to
    assess the effect of acetic acid vapour on pure cellulose paper
    using cold extraction pH and viscometric determination of degree
    of polymerization (DP) of cellulose dissolved in cadoxen. A
    system of acetic acid-water-salt was used to generate acetic
    acid in vapour phase in hermetically closed desiccators; Whatman
    No. 1 paper samples were then exposed to this environment. The
    degree of degradation immediately after exposure varied from
    none to a significant change. An 80-day exposure to 3 mg/m3
    acetic acid produced no detectable depolymerization of the
    cellulose and a small decrease in pH; 40- and 80-day exposures
    to 20 mg/m3 acetic acid led to 3.3% and 11% depolymerization,
    respectively; and 40-day exposure to 200 mg/m3 led to 37%
    depolymerization. Samples exposed to 20 or 200 mg/m3 acetic acid
    showed a substantial decrease in DP and pH as compared with
    controls after artificial aging at 80 deg. C and 65% RH for 30
    or 60 days; there was no such decrease in samples exposed to 3
    mg/m3 acetic acid. This suggests that the effect of acetic acid
    on paper likely occurs over the long term. A positive
    correlation was found between decreased pH and DP. Concerns
    about acid-emitting materials being in contact with or in the
    vicinity of paper-based materials in museums and archives are
    discussed based on these results, and preventive measures are
    recommended".

CCI recently released a Technical Bulletin on "Coatings for Display
and Storage in Museums." Many questions have been raised in the past
related to the offgassing and the barrier film properties of the
paints applied on wooden substrates. The bulletin tries to cover the
overall problematic of coatings in museums and archives for wood,
metal and cementitious substrates. Copies can be purchased by
contacting CCI.

    Publication Section: 613-998-3721 ext. 250
    <cci-icc_publications [at] pch__gc__ca>

Online ordering can also be done by visiting "The Bookstore" in CCI
web site at: <URL:http://www.cci-icc.gc.ca/>

Jean Tetreault
Conservation Scientist
Canadian Conservation Institute

                                  ***
                  Conservation DistList Instance 13:9
                  Distributed: Thursday, July 22, 1999
                        Message Id: cdl-13-9-001
                                  ***