flammability of PHB (repeating unit C4H6O2), and the material
safety data sheets of Mirel also indicate that there is no test data yet
for flammability.
Combustion of solid fuels is a complex process described by
Glassman [2], analogous to the combustion of polymers. The
combustion of solids requires that the solid be chemically broken
down into smaller pieces and vaporized to serve as the initial fuel
for ignition. Once ignition begins, the heat of combustion feeds into
further melting and decomposition of the solid to produce more
small fragments which can evaporate and burn.
This study uses models to estimate the potential flammability of
PHB. If flammability of PHB is low, then PBRFs may not need to be
added, or added in reduced quantities, which would address the
environmental and health concerns regarding the polybrominated
flame retardants. Flame retardants do not prevent the eventual
combustion of polymers, but delay the ignition or the speed of
initial burning of the materials, or both, to give occupants more
time to escape. Flames are quenched or slowed by PBFRs by
creating an inert char layer, quenching gas phase chain branching
reactions, or by other means.
The potential flammability of PHB will be examined by evaluating
its propensity to ignite and to sustain combustion once
ignited. For simplicity, only pure PHB will be examined, neglecting
other ingredients. Potential flammability of the biopolymer will be
evaluated with respect to the two main components of flammability,
ease of ignition and speed of burning.