Effect of Sepiolite on the Combustion and Thermal Decomposition of Intumescent Flame Retardant Polypropylene

We added modified sepiolite to a polypropylene (PP)/ammonium polyphosphate (APP)/di-pentaerythritol (DPER) composite to study the effect of sepiolite on the retarding behavior of the intumescent flame retardant (IFR) PP flame. The flame retarding behavior of the PP/IFR composite was tested using the limiting oxygen index (LOI) and cone calorimeter tests (CONE). The results show that sepiolite increases the LOI value of the PP/IFR and it is more effective than other nano-fillers such as layered double hydroxides (LDH) and organic montmorillonite (OMMT). The sepiolite decreases the heat release rate (HRR) and the total heat release (THR) of the PP/IFR composite. The flame-retardant mechanism of the PP/IFR/sepiolite system is also discussed in terms of catalytic charring after analysis by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). For the binary APP/DPER mixture, sepiolite reduces the mass loss rate and increases the amount of residue at high temperature under nitrogen and air atmospheres. This has been considered to be strongly associated with the interaction between sepiolite and APP. FTIR and XPS results show that the P-O-Si bond forms at high temperature for binary mixtures of APP/sepiolite. With the addition of sepiolite to the PP/IFR, the char residue burnt is dense and homogeneous, which is important for the flame retardant performance.