PVA emulsion

Nine people (mostly conservators and preservation librarians as well
as one vendor rep) have replied to me with helpful observations
about PVA. I think there is enough overlap in experience that a
summary will be of interest to others.

To begin with, a combination of brown film, odor, and/or mold has
occurred occasionally over the last few years in both Jade 403 and
Jade 711 from at least two different sources, both known as reliable
conservation suppliers. The problem is usually isolated to a single
shipment and is resolved when the supplier replaces the bad batch
with a fresh supply. While not exactly the same characteristics, in
fairness, I should note that Jade is not the only brand mentioned in
replies to my query. One person reported staff complaints about a
container of Wisdom PVA with lumps and an unusually strong vinegar
smell. A couple others did not mention a specific variety of PVA.

A likely cause, at least some of the common problems, seems to be
related to regulations that went into effect about four or five
years ago prohibiting use of formaldehyde as a preservative in PVA,
which one respondent noted is manufactured primarily as a food
packaging adhesive. The same reply offered the caveat that vendors
selling a product under the Jade 403 name do not necessarily buy
their supply from the same source. That said, the Jade products many
libraries and conservation labs have used for years probably have a
shorter shelf life and greater vulnerability to mold than they did
in the past.

One person recalled, about eight years ago, sending a sample of PVA
with very similar problems to the manufacturer for analysis. The
manufacturer determined that the cause was related to a change or
contamination in the resin purchased to produce the glue.
Interestingly, the manufacturer did not believe that particular
irregularity would affect the adhesive properties of their product.
All the same, they replaced the PVA and the library had no further
problems.

Exposure to extremes of heat and cold in shipping are known to spoil
PVA. Contamination is also possible if brushes are dipped directly
into the supply container rather than decanting into smaller
containers. Similarly, pouring unused glue back into a larger
container can contaminate the supply. The problem we have had, with
the characteristic "brown swirls," as one person aptly described it,
has occurred in a several libraries, like UNC's, that use a lot of
PVA and have good practices for storing adhesives and cleaning
brushes and containers. In such cases, the problem is most likely
beginning with the supplier, who may or may not be going through
their own supply fast enough to avoid shelf life problems. For that
matter, we have no way of knowing how long or consistent the time
delay is between manufacture and shipment to the vendors we order
from. It is also possible for problems to be introduced during the
stages of repackaging and shipping that occur along the way.

The upshot seems to be that there are precedents for getting an
unusable batch of PVA, even from reputable sources, and the best
course of action is to seek replacement from the supplier and/or
order from another source. This summary is based on informal
observations others have shared with me. Perhaps someone else can
explain what's happening in more scientific terms (although,
hopefully, in a way that someone without much knowledge of chemistry
can understand!).

Thanks to all who replied. Please post clarifications to the list or
let me know offline if I misunderstood any of the information sent
to me.

                                ---

After sending the above summary, I received an informative email
from Jeff Wisdom of Wisdom Adhesives. I expect his explanation will
be of interest to many on the list so, with Jeff's permission, I'll
just quote from his email:

   "In one of your emails you had mentioned a Wisdom product that
    was seen to be lumpy.  In this case I would say that the product
    was more than likely frozen.  When a PVA product freezes it
    becomes like cottage cheese and will not return to its original
    state. [text and header from a forwarded email exchange deleted]

   "Although, I cannot speak of the Jade 403 PVA specifically, I can
    comment about the changes in the adhesive industry that have
    occurred over the past 5-7 years.

   "Due to environmental pressures from the EPA and other regulatory
    agencies over the past several years, base polymer manufacturers
    have been required to change their processes.  The focus of the
    regulatory agencies is for manufacturers to reduce the amount of
    VOC's (Volatile Organic Compounds)in their adhesive
    formulations.  These changes are good for the environment but
    also cause problems for the adhesive manufacturer.  In the past
    one VOC, namely Formaldehyde served as an excellent preservative
    in adhesives.  This chemical has now been virtually eliminated
    in all adhesive processes thus shortening shelf life.

   "In the past adhesives could remain fresh and stable for up to a
    year.  We now recommend that all adhesives used by our customers
    are manufactured, sold, and consumed by our customers within a
    60-90 day period.  Although other preservatives are added to the
    manufacture of adhesives, they do not command the shelf lives of
    the past.

   "All of the symptoms described by Andrew Hart are sure signs of
    an adhesive that has passed it's shelf life.  Brown swirl, sour
    odor followed by mold is a common sign of preservative failure
    caused by reformulation due to environmental regulations.

   "To avoid these problems, only order adhesive that can be
    consumed within 60-90 days and make sure that the manufacture
    date of your adhesive is also within that 60-90 day period."

Jeff welcomed further inquiries about his company's products and
about more general issues related to PVA. His email address is
jeffwisdom<-a t->wisdomadhesives< . >com

Andrew Hart
Preservation Librarian
CB#3910, Davis Library
University of North Carolina at Chapel Hill
Chapel Hill, NC 27514-8890
919-962-8047
Fax: 919-962-4450


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                  Conservation DistList Instance 19:2
                 Distributed: Wednesday, June 22, 2005
                        Message Id: cdl-19-2-002
                                  ***