Influence of the Polymer/Inorganic Filler Interface on the Mechanical, Thermal, and Flame Retardant Properties of Polypropylene/Magnesium Hydroxide Composites

The relationship between the interface structure and the macroscopic properties of composites composed of isotactic polypropylene (iPP) and magnesium hydroxide (MH) was investigated with a focus on mechanical properties, thermal stability, and flame retardancy. Surface treatment of MH was carried out using dodecanoic acid (DA) and dodecylphosphate (DP), both of which interacted with MH to form submonolayer coverages. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that both organic reagents adhere to the MH surface via ionic interactions. Even low amounts of organic reagents on the MH surface were sufficient to improve the mechanical, thermal, and flame retardant properties of the composites. The incorporation of 1.8 wt% of DP in (70/30) iPP/MH-DP composite decreased the peak heat release rate (PkHRR) to 39% compared with that of neat iPP. Since the effects of DA with the same dodecyl chains were not significant, it is concluded that the phosphate groups in DP provide flame retardancy.