Abstract:
The utility of expandable graphite as a flame retardant for PVC, plasticized with 60 phr of a
phosphate ester, was investigated. Cone calorimeter results, at a radiant flux of 35 kW m-2,
revealed that adding only 5 wt.% expandable graphite lowered the peak heat release rate from
325 ± 11 kW m-2 to 63 ± 23 kW m-2 and the total heat release from 55 ± 11 MJ m-2 to only
10.7 ± 0.3 MJ m-2. All samples containing expandable graphite ignited and burned only very
briefly before flame out. The remarkable effectiveness of the expandable graphite is
attributed to an excellent match between the exfoliation onset temperature of the graphite and
the onset of decomposition of the PVC. This means that the exfoliation of the graphite forms
a protective barrier layer at the right place at the right time. In addition, the simultaneous
release of halogen species by the polymer matrix and the exfoliating graphite prevents the
formation of a flammable air fuel mixture.
