PVA emulsion

Andrew Hart <ashart [at] email__unc__edu> writes

>I'm very interested in ideas or experience anyone can share about
>unexpected change in PVA from a single supplier, brown film, unusual
>odor, or mold.

Jade 403 and the other PVAs are emulsions, meaning that they are
waterborne dispersions of the PVA polymer stabilized by surfactants.
You have a fantastic bacterial medium there, so when used in
commercial products (like Jade) they are normally augmented with
some sort of biocide (Dowicil 75, Kathon LX, Skane M-8, Biocheck
410, Proxel, Vanicide, zinc oxide, etc and in older formulations
dioxin, formaldehyde, and phenyl mercury compounds).  Most of these
will be consumed through their biological activity over time.  For
proof of this, just open a decade old tube of acrylic emulsion paint
and take a whiff.   You'll easily detect that sour smell.
Incidentally, most of the emulsion products (acrylic, PVA, etc) that
are supplied by industrial giants like Rohm and Haas do not have the
biocide added at that point.  They are often quite alkaline due to
the addition of ammonia that is necessary for the emulsion, and the
high pH is relied upon to stave off infection for the short time
before they are blended into commercial products with additional
biocides.  Hence, their shelf lives can be quite short if they have
been opened previously.

In your case, Jade 403 likely has a biocide in it--Down et al.
(Studies, 1996) have identified formaldehyde in the product, which
could have been added by itself or been generated through the normal
activity of formaldehyde producing biocides like Dowicil.  What
might be occurring is that the product you are obtaining is the last
of a large batch being used up by your supplier, or even their
supplier.  I imagine they are not buying the PVA by the gallon, but
rather by the drum, tanker car, etc.  These last remnants may have
already consumed most of the initial biocide.  The other possibility
is that the batch was simply poorly produced without enough biocide,
or in such a manner that an unusually strong bacterial content was
introduced.

The brown color and the separation are both commonly encountered in
infected emulsions.  I have also observed in acrylic emulsions a
light grey color. One would be ill advised to use the tainted
product.  The bacterial growth will likely fade away as the water is
removed from the system upon drying, but the discoloration and the
fact that the emulsion has been compromised will no doubt lead to
poor performance.

Dr. Gregory Dale Smith
Andrew W. Mellon Assistant Professor of Conservation Science
Buffalo State College
Art Conservation Department
1300 Elmwood Ave., RH#230
Buffalo NY 14222
716-878-4646 office
716-878-5025 department
Fax: 716-878-5039


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                  Conservation DistList Instance 19:2
                 Distributed: Wednesday, June 22, 2005
                        Message Id: cdl-19-2-003
                                  ***