Ammonium polyphosphate (APP) surface was modified with (3-aminopropyl)triethoxysilane (KH550), then microencapsulated by silicone in situ polymerization of tetraethyl orthosilicate (TEOS), finally surface-modified with (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane to prepare the hydrophobic APP (M-APP). The structure and surface elemental composition of M-APP were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and the results indicated that M-APP was the target product. The wettability of the modified APP was measured by water contact angle(CA) test and the CA reached 134 degrees, which demonstrate the modified APP possessed obviously hydrophobic property. The modified APP mixed with triazine char foaming agent(CFA) with the mass ratio of 4 1 to prepare intumescent flame retardant(IFR) and afterwards IFR was incorporated into polypropylene(PP) to prepare flame retardant PP composites. The flame retardancy and thermal degradation behavior of PP composites were evaluated by limiting oxygen index(LOT), vertical burning(UL-94) and thermal gravimetric analysis (TGA) tests. The water resistant property of the flame retarded PP materials were evaluated by water resistant test, and the mechanical properties were measured by the tensile, flexural and impact strength test, the compatibility between the flame retardant and polymer was investigated by scanning electron microscopy(SEM). The results indicated that the modified APP/CFA/PP composite reached UL-94 V-0 flammability rating when the loading amount of IFR was 23%, the PP composite after water resistance test still successfully passed UL-94 V-0 rating and the mass loss was only 0.92%. Under the same experimental conditions, the APP/CFA/PP composite after water resistance test was no rating in vertical burning test and the mass loss was 2.45%. It can be deduced that hydrophobic modification of APP can greatly improve the water resistance of the flame retardant PP material. The TGA results indicated that the incorporation of IFR into PP matrix improved the thermal stability and char-forming ability of PP composite, the formed intumescent char layer during combustion protect the underlying matrix from further combustion and degradation, consequently enhanced the flame retardancy of PP materials. The results of SEM and mechanical test revealed that the modification of APP improved the compatibility between the flame retardant and PP matrix, which resulting in the increase of the mechanical properties of the flame retarded PP composites.
