Odor in enclosures

Elizabeth Morse <elizabeth_morse<-a t->harvard< . >edu> writes

>Not too long ago, we ordered some enclosures made using binder's
>board, acrylic-coated book cloth, alkaline/buffered lining paper,
>and PVA.  We noticed that the enclosures had a particularly strong
>vinegar odor when they arrived.

This problem of acetic acid release ("vinegar odor") from PVAcetate
adhesives continues to be a problem for conservators.  Vinyl
adhesives used in box production and those sold as conservation grade
materials still contain acetate, despite the fact that we have known
for many years that this is unstable and potentially damaging for
certain materials. The reason for the fact that these adhesives are
still sold and used for boxes and enclosures seems to be simply
cost, since reversibility is perhaps irrelevant for box making. They
were originally found useful for binding purposes because of their
physical flexibility when dry and, more recently, their ready
reversibility--they are non-crystalline and frequently plasticised,
extended in quantity and modified for tack and reversibility using a
variety of additives.

Instead of using polyvinyl acetate (PVAc strictly speaking) I have
recently been using polyvinyl alcohol (genuine PVA) for boxes and
envelopes.  It is sold as a powder; I place a required amount in
water and then, in a microwave oven, 'cook' it for a few minutes until
all the powder has dissolved and I have an even, completely clear
solution, the thickness depending on the percentage solution and my
needs.

It is fairly high tack, smooth and clean to use (it can be
rubbed off the paper I use for archival sleeves).  It does not seem
to be reversible in cold water (it is in hot water) but then I do
not want my enclosures reversed!  It is of more concern to me that,
when managing the archival repackaging of large collections of
papers and books that I am not placing proportionately large
quantities of acetic-acid-evolving materials into my otherwise
controlled storage environment.

Pure PVAlcohol can be bought in a
bewildering variety of molecular weights from most good chemical
suppliers such as SIGMA/ALDRICH and BDH/MERCK.  PVAlcohol is
derived, through hydrolysis, from PVAcetate and therefore its
production presumably involves a further stage of refinement, but
nevertheless it is not much more expensive than the commonly
available PVAcetates.

It is possible to modify standard, commercial PVAcetate to help
ameliorate the acetic acid problem.  Calcium hydroxide powder can be
added to neutralise the free acidity and help buffer against future
acid release, calcium carbonate if relatively high alkalinity is a
problem.  Unfortunately I have been unable to find out precisely the
quantities of acetic acid used in the production of standard
PVAcetate and so have not been able to calculate a suitable
weight-for-weight formula for this neutralisation.  This treatment
does not seem to adversely effect the adhesive's reversibility.  It
is encouraging to note that the W J Barrow Research Laboratory
endorsed this approach back in 1965 and the work
(Permanence/Durability of the Book - IV, Polyvinyl Acetate (PVA)
Adhesives for use in Library Bookbinding) still seems to be fairly
definitive, although perhaps someone has found a more up-to-date
publication?

One interesting and perhaps slightly reassuring observation made by
the Barrow lab should be quoted here, even if it turns out to be
misleading if anyone has better information:

   "Effects of Acidic Decomposition Products on Paper.  An acidic
    gas, probably acetic acid, was consistently liberated by all
    samples of PVA[cetate] adhesive during heat-aging.  The question
    arose whether this gas would be absorbed by paper to which the
    adhesive might be applied...and lead to its deterioration.

    To answer this question, a near-neutral paper (pH 6.9) was
    dipped in solutions of Samples 9 and 10 and they showed a pH 6.1
    and 6.0 respectively (Table 20).  One gram of each was placed in
    a screw-top test tube and heat-aged for 3 days after which they
    dropped to pH 4.7 and pH 5.7.  Upon exposure to air for 14 days
    they reverted to pH 6.1 and 6.2.

    These tests indicate that the acidic gases produced by the PVA
    adhesives are very volatile and are unlikely to remain in paper
    for long periods of time.  Under normal circumstances it may be
    doubted whether, because of its high volatility and freedom to
    escape, the gas materially changes the pH of a book...in any
    event the buffered adhesives release fewer decomposition
    products..."

Good, healthy fresh air seems to be the answer!

Chris Woods
Senior Archive Conservator
Dorset Record Office

                                  ***
                  Conservation DistList Instance 10:68
                Distributed: Wednesday, January 29, 1997
                       Message Id: cdl-10-68-004
                                  ***