Flexible PVC flame retarded with expandable graphite

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.