Combustion behaviour of epoxide based nanocomposites with ammonium and phosphonium bentonites

The influence of different organobentonites on the decomposition and the combustion behavior of an epoxy resin were examined. The epoxy resin flexibilised with poly(tetrahydrofuran) (PTHF), with hydroxyl endgroups. The bentonite was modified with either an ammonium or a phosphonium salt. The thermal decomposition of the PTHF induced by the initiator, used for the cationic polymerisation, did neither take place for the nanocomposite based on the ammonium bentonite nor for that based on the phosphonium bentonite. This improved decomposition characteristic lead to a larger time to ignition for both kinds of nanocomposites compared to the not modified polymer, which is not the case for other polymer/clay nanocomposites described in the literature. The fire behavior was investigated using limiting oxygen index (LOI), a horizontal burner test and a cone calorimeter. The forced flaming conditions in the cone calorimeter were varied using different, external heat fluxes between 30 and 70 kW.m(-2). The fire behavior of the nanocomposites was improved in comparison to the polymer, and phosphonium bentonite was superior to ammonium bentonite. The main mechanism is a barrier formation resulting in a reduction of the fire growth rate, which was more pronounced in the case of high external heat fluxes.