Performance of different intumescent ammonium polyphosphate flame retardants in PP/kenaf fibre composites

The paper compares the flammability and degradation performance of polypropylene (PP)/kenaf fibre composites under three different intumescent ammonium polyphosphate (APP) flame retardants. Intermeshing co-rotating twin screw extruder melt mixing approach was used to prepare the composites. The initial morphological analysis reveals that twin screw melt compounding has provided an effective homogeneous dispersion and distribution of particles, irrespective of their different particle sizes and surface energies. The thermogravimetry analysis (TGA) proves that the presence of intumescent coating of APP1 improves the thermal stability and decomposition temperature over the others. UL-94V tests and cone calorimeter analysis show that the amount of APP content and the high aspect ratio of the particles are the key factors in obtaining homogeneous flame retardant blend, which tends to decrease sustained combustion and reduce the peak heat release rates of the composites. Morphological analysis of char residue further proves that the cross-linking density of the char provides better insulation for underlying material even though the initial swelling increases the degradation temperature through pronounced blanketing effect. Further analysis using different APP particles recorded competitive mechanical properties.