Thermal characterization and flammability of polypropylene containing sepiolite-APP combinations

The effects of sepiolite on fire behavior of ammonium polyphosphate-based intumescent flame retardant (IFR)/polypropylene (PP) were investigated. The disaggregation of sepiolite bundles has been provided by wet-milling as the zeta potential value decreased from −9.6 to −31.3 mV. PP and additives were compounded by a twin-screw extruder and molded by injection. A total additive content of 20 wt% in PP and various proportions of sepiolite (1.0–10.0 wt%) in flame retardant (FR) formulation were studied. The flammability of the samples was measured by limit oxygen index (LOI) test and cone calorimetry. The LOI of neat PP (19%) was increased to 32.2% when sepiolite and IFR were used. The peak heat release rate of neat PP (1566.4 kW/m 2 ) was also significantly reduced (94.7 kW/m 2 ) when sepiolite was added with IFR. Thermal analyses results showed that, at higher temperature (700°C), IFR and sepiolite increased the char residue (9 wt%) compared to neat PP (0 wt%).