A mechanistic study into the flame retardant and smoke supressant properties of molybdenum trioxide in brominated polyester thermosets
The use of molybdenum trioxide as a smoke suppressant and
flame retardant in bromine-containing polyester thermosets has been
studied. Oxygen index studies showed that Mo03 has a synergistic
flame retardant effect when incorporated into the brominated
polyester resins. During flaming combustion, polymers containing
Mo03 produced less smoke and more char.
Thermogravimetric studies indicated that the inclusion of Mo0 in the polymer affected its degradation profile. The Mo0 3 3 was found
to have no effect on the first of the three observed weigfit loss
steps, which appeared to be due to the loss of phthalic anhydride
from the resin. Changes were observed in the temperatures and
weight losses of both of the subsequent degradation steps. Again
it was found to increase the char levels and lower the temperature
of char oxidation. No transfer of molybdenum to the vapour phase
was observed, no evidence being found for the formation of a
volatile molybdenum halide on oxy-halide. MoO was recovered
practically quantitatively after polymer degra~ation in air,
although in nitrogen it ended up as the carbide. Further evidence
for the condensed phase mechanism was found in nitrous oxide index
studies of the polyester where the index increased in the presence
Changes were observed in both the condensed and vapour phase
degradation products in the presence of Mo03• Elemental analysis
of the solid residues remaining after heating the polymer
formulations showed that Mo03 accelerated the loss of halogen to
the vapour phase. This effect is thought to be responsible for
the flame retardant activity of Mo03.
Inclusion of MoO into the polyesters resulted in a change
in the ratio of aroma~ic to aliphatic degradation products.
Overall the quantity of aromatics evolved was reduced. Since
these are the precursors of smoke in flaming combustion, their
attenuation could account for the smoke reduction properties of
Mo03 in the presence of bromine.