Polyvinyl acetate resin

I recently learned from Dow, the parent company of Union Carbide,
that Union Carbide is no longer manufacturing PVAc resins (AYAA,
AYAC, AYAF and AYAT). This was confirmed by representatives at both
Talas and Conservation Support Systems who said Union Carbide
stopped supplying the resins about three years ago.

According to the representatives I spoke with at Dow and
Conservation Support Systems the division of Union Carbide that
manufactured the PVAc resins was spun-off to a company called
Ashland Chemicals.  Conservation Support Systems informed me that
Ashland is continuing to make the AYAF but has abandoned the
manufacture of the other grades.  Conservation Support Systems is
currently selling the Ashland Chemicals AYAF and Mowilith 20 (a PVAc
resin made in Germany).  I am currently trying to reach someone at
Ashland to confirm that they are manufacturing the AYAF, and to
obtain technical data and an MSDS for it.

Talas is still selling a series of products they are calling AYAA,
AYAC, AYAF and AYAT but these are not made by Union Carbide.  When
Union Carbide stopped supplying the resins, Talas found a new
supplier/manufacturer and asked for grades that would be equivalents
of the Union Carbide AYA_ series and this is what they are selling.
They were not willing to divulge the name of the manufacturer but
they do provide technical data for these new resins on their
website:

    <URL:http://talasonline.com/photos/chemicals/ayaa.pdf>

When I compared this data to what is published for the Union Carbide
products, I noted several discrepancies.  It appears that the resins
Talas is selling may not be direct equivalents, even though they are
using the same AYA_ designations.  The reported molecular weights
and glass transition temperatures of these new Talas AYA_ resins are
significantly different from those reported by Union Carbide (1989
company lit) and Horie for the originals:

Molecular Weight of Talas Polyvinyl Acetate Resins

    AYAC = 10,000-15,000
    AYAA = 90 x 103  +/- 10 x 103
    AYAF = 290 x 103 +/-20 x 103
    AYAT = 130 x 103 +/-20 x 103

Glass Transition Temperature 0C of Talas Polyvinyl Acetate Resins

    AYAC = 33
    AYAA = 42
    AYAF = 44
    AYAT = 43

Molecular Weight of Union Carbide Polyvinyl Acetate Resins (Union
Carbide Product literature, 1989)

    AYAC = 12,800
    AYAA  = 83,000
    AYAF = 113,000
    AYAT = 167,000

Glass Transition Temperature 0C of Union Carbide Polyvinyl Acetate
Resins (CV Horie)

    AYAC = 16
    AYAA = 21
    AYAF = 24
    AYAT = 26

A further problem is that the MSDS currently posted on the Talas
website is for the old Union Carbide materials.  I spoke with the
representative from Talas who was very concerned about these issues.
He stated that they will talk to their manufacturer to discuss these
differences and see if they can get a better match for the Union
Carbide grades.  He also has directed his staff to edit their
catalog and website to make it clearer that the resins they are
selling are not the AYA_ resins from Union Carbide.  He also said he
would get an MSDS for the new material.  I explained to him that
without knowing the manufacturer and seeing an MSDS most
conservators would not be comfortable using the new product.

In addition to trying to find out more about the Ashland Chemical
AYAF and the new PVAc supplied by Talas, I am also gathering
information about the Mowilith resins (20, 30, 40 and 50) as well as
McGean B-15 and B-25 (formally Vinac B-15 and B-25) to evaluate them
as possible replacements.  I wanted to make sure the conservation
community was aware that the Union Carbide resins used in this field
since the 1940s may no longer be available (except perhaps for one
grade) and to present what I have learned thus far about possible
replacements.  Any opinions and suggestions about replacements are
welcome.

Samantha Alderson
Conservator
Division of Anthropology
American Museum of Natural History
Central Park West at 79th Street
New York, NY 10024
212-769-5446


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                  Conservation DistList Instance 22:35
                 Distributed: Monday, December 8, 2008
                       Message Id: cdl-22-35-002
                                  ***