Effect of Flame Retardants on the Thermal, Burning, and Char Formation Behaviour of Polypropylene-Nanoclay Compounded Polymers

Abstract

The effect of different flame retardant types on the thermal stability, flammability and char formation tendency of polypropylene (PP) nano/micro composite is studied. PP, compatabiliser, nanoclay, UV-stabiliser and different flame retardants have been compounded in a twin screw extruder to produce polymers with improved thermal and flame retardant properties. Thermal analysis has been used to study the thermal properties, and limiting oxygen index (LOI) and slightly modified UL-94 test for flammability of the samples. All flame retardants acting in the condensed phase (phosphorus- and nitrogen- containing) lowered the rate of decomposition, whereas halogenated flame retardants had a little effect. The addition of nanoclay with or without flame retardants increased the thermal stability of all samples and helped in char formation. All samples with flame retardants and no clay, burnt completely, which is not unexpected, given the low levels (5%) of flame retardants used here. However, the flame spread was low. On addition of clay to the compounded polymer, a change in burning behaviour was observed, flame spread was reduced and samples self-extinguished, except for the one containing melamine phosphate. A tube furnace was used for char formation at different temperatures and the charred structures have been examined with digital images, optical and scanning electron microscopy, and FTIR. This information has been used to understand the mechanisms of thermal degradation of different flame retarded PP - nano/micro composite samples.