Discoloured fluted polypropylene

Johanna Alcock mentioned discolouration problems with polypropylene
exposed to the cut surface of polyethylene foam.  Most closed cell
polyethylene foam is made by direct gassing with nitrogen but some
is made by chemical blowing agents. These are frequently based on
azodicarbonamide which in theory degrades at extrusion temperatures
to give gaseous CO2, H2O and NH3. It might be worthwhile asking the
foam supplier which method they used on this material to give a
pointer to the research.

Colin Williamson

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                  Conservation DistList Instance 9:77
                   Distributed: Monday, May 20, 1996
                        Message Id: cdl-9-77-002
                                  ***