Acrylonitrile Butadiene Styrene (ABS)

I am looking for advice on how to treat and prevent further damage
to a large hollow form made of vacuum formed Acrylonitrile Butadiene
Styrene (ABS) plastic.   The form is about 50 inches in diameter at
the widest point and is irregular in shape.  It appears to having
been fabricated by adhering together 8 petal shapes that have
vacuumed-form horizontal striations which allow them to bend easily.
The tips of petal shapes meet  at the top and bottom of the form
(like the sections of a beachball--or of an orange) and are adhered
together along all the joints, which are then painted over to
conceal them.

When I first looked at this object 4 years ago there were a few
narrow intermittent openings along some joints  Now, on one of the
joints what used to be an intermittent opening (Like a broken line
about 3 inches long) there is  continuous 3 inch long opening. The
opening is slight--at its widest point you can just barely slip the
tip of a sheet of 10mm photocopy paper into it.  The release of
stress at this opening has allowed the hollow plastic form to sprint
up a tiny bit higher  on one side of the joint  than that on the
other side.  I can use gentle pressure to push the edges very close
together but I'm not sure I could close it completely and I don't
know how I would apply equal pressure long enough for an adhesive
added there to dry.

Should we treat this object?  If I could find an objects specialist
who could work on this object I would be happy to hire them to do
the work. Is there anyone with experience treating plastics who
lives within a reasonable drive of Montreal?

Or, can anyone advise me and my staff (we are paper, book and photo
conservators) on how to carry out treatment ourselves?  (We are
accustomed to treating architectural models and toys--most wood and
paper but sometimes with plastic bits too) but have never treated
this kind of free-form blob-shaped hollow object.)

According to my research, ABS plastic is pretty chemically stable:
it doesn't tend to yellow or get more brittle or gooey as it ages
but has poor solvent resistance.  It has good dimensional stability
and moderate strength, but has a tendency to stress crack.  What
kind of adhesive would hold the sides of the opened-up area together
without adding any bulk between the two sides, and without causing
yellowing or dissolution of the ABS plastic?  The original adhesive,
by the way, is visible in some areas and does appear to have
yellowed.

What kind of clamping or wrapping technique could we use to hold the
two sides of the opening in place while the adhesive sets?

Can we ensure that closing up this opening won't cause other stress
cracks to open up on other joints?

Whether we treat this object or not, is there anything we can do to
keep this deterioration from going further?  We are keeping the
object in a custom-made box that cushions it lightly and it's in a
climate-controlled vault, but the object has been requested for
loan. If we do loan it I would like to have it treated first. We
will pack it in its padded box within a padded crate to minimise
vibration that could make the damage get worse.

I'd appreciate hearing some good ideas,

Karen Potje
Chef, Service de la conservation/restauration
Centre Canadien d'Architecture


                                  ***
                  Conservation DistList Instance 21:50
                 Distributed: Wednesday, March 26, 2008
                       Message Id: cdl-21-50-016
                                  ***