Hot melt adhesives

Hot-melt adhesives (glue sticks) are available in a wide variety of
compositions, usually based on EVA (ethylene vinyl acetate
copolymer) mixed with a hydrocarbon resin, and often Kraton (a
synthetic rubber), although formulations based on polypropylene,
nylon, and other polymers (even epoxy) are available.  Although many
of the ingredients may be considered "archival" per se, the sheer
variety of compositions and proprietary nature of these materials
make recommendations difficult.  We opted for a 3M
polypropylene/resin box-sealing formula because it seemed a good bet
and was soluble in solvents after cooling, but accelerated aging and
an Oddy test would be more reassuring (until they change the
formula).

If I were shopping for this kind of stuff, I'd first prioritize a
list of desired properties:  Does it need to be clear or can it be
amber colored? Do I need a low temp melt or not?  A high temperature
melt may be OK for box board, but inappropriate for, say, Ethafoam.
What about cooling time? Flexible or rigid?  Soluble?  Vanilla
flavored?, etc.  Then I'd contact the reps and ask for the
impossible ("you want low off-gassing too?!?").  I'd probably end up
with a couple of products that rate a C+ but were used on space
shuttle circuit boards.  After testing, I'd use the stuff with
slight nagging disquiet, and double up on the archival tissue for
good measure.

John Burke
Chief Conservator
Oakland Museum of California

                                  ***
                  Conservation DistList Instance 11:6
                  Distributed: Wednesday, July 2, 1997
                        Message Id: cdl-11-6-001
                                  ***