Cellulose acetate butyrate

Kate Winston Moomaw <kwm208 [at] nyu__edu> writes

>I am researching options for repairing a sculpture made from
>cellulose acetate butyrate sheet (aka CAB, brandnames: Uvex and
>Gemex).  I am looking for potential adhesives and fill materials
>that are transparent and otherwise compatible.  If anyone has any
>experience with this material and has suggestions of what to try or
>what to definitely avoid, I would be grateful.

I've used B-73 polyvinylbutyral in ethanol in a cast film to fill in
losses in metal objects.  It can be cast on silicone release film,
then trimmed to size.  It remains flexible and can be attached to
the area by wetting the edges of the fill with ethanol.  It can also
be cast in place if you have access to both sides of the gap, and
the object material is not sensitive to solvents.  The drawback in
your case is that the B-73 film is slightly yellowish.  It's also
difficult to cast it without getting bubble inclusions, but I
usually paint the fills so that's not a problem.  Another difficulty
in your case would be joining the fill without marring the edges of
the object.

Sharon Blank, in "An introduction to plastics and rubbers in
collections", Studies in Conservation, V. 35 1990-53-63, states that
cellulose acetate-butyrate, first produced in 1932, while having
more water resistance than cellulose acetate, is more sensitive to
organic solvents.  She suggests that PVAc and solvents work well to
repair cellulose acetate/cellulose acetate-butyrate. You might try
casting a PVAc such as AYAF or AYAT and see how that works.  Those
resins do tend to cold-flow when used as joint adhesives under some
conditions.  Paraloid B-72 might work as it has a Tg of 65 deg. C as
opposed to 18-29 deg. C for the PVAc's (See Horie, "Materials for
Conservation", 1987).

Paul S. Storch
Senior Objects Conservator
Daniels Objects Conservation Laboratory (DOCL)
B-109.1, Minnesota History Center
345 Kellogg Blvd. West
St. Paul, MN  55102-1906
651-297-5774
Fax: 651-297-2967


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                  Conservation DistList Instance 19:26
                Distributed: Saturday, November 19, 2005
                       Message Id: cdl-19-26-008
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