Deterioration of polyurethane sculptural relief panels

After the first which Terry connors sent to me (and Cc:'d to the
DistList) concerning the Jim Dine panels, Terry sent this message,
in response to Scott Williams' comment.  I send it to the DistList
with her permission:

    My only comment about Scott's comments concerns the development
    of stresses in plastic over time. When I did my own study of
    wood-polyurethane composites, one of the tests I did was to
    study what happened when deformations were applied for a
    prolonged period of time. The stresses in the polyurethane
    decreased with time (relaxation phenomenon), a common
    occurrence. Based on this type of result I would think that the
    "stress release" Scott describes cannot be referring to a stress
    of long duration (though he probably knows a lot more about this
    than I do), but if present it must result from some short-term
    change--like moisture change and consequent dimensional change
    in the underlying panel.

    Scott made me wonder--Is it possible that the panel was not cast
    upon the wood mounting? Polyurethane adheres very, very well to
    wood (in fact, there are commercial adhesives made out of the
    stuff for that very reason). I had assumed in my earlier answer
    that they were adhered in some way, and I had not considered the
    possibility that they were mounted using some sort of floating
    support system; if this were the case then a wood problem would
    appear to be very unlikely. (What I'm thinking of is sort of
    what kitchen cabinet manufacturers use when they make a common
    cabinet front with molding around a raised panel--the panel
    isn't glued into the frame, allowing it to shrink and swell
    slightly without breaking or buckling).  (Karen's comment:  I
    will examine the panels thoroughly to try to determine how the
    wood and plastic layers are attached together.)

    We'll all have to give this one some long thought I think.

    Terry


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                  Conservation DistList Instance 15:49
                Distributed: Saturday, January 12, 2002
                       Message Id: cdl-15-49-004
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