Study on inorganic modified ammonium polyphosphate with precipitation method and its effect in flame retardant polypropylene

A novel inorganic modified ammonium polyphosphate (IMAPP) is prepared by the chemical deposition reaction which proceeds on the particle surface of APP. IMAPP is characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), water solubility, water contact angle (WCA) and thermogravimetric analysis (TGA). Results show that the chemical deposition reaction produces aluminum hydroxide and aluminum phosphate on the particle surface, which has improved its water resistance and reduced its thermal decomposition rate. Then IMAPP is incorporated with dipentaerythritol (DPER) in the flame retarded polypropylene (FR-PP). The flame retardancy of FR-PP is investigated by means of limiting oxygen index (LOI), UL 94 and cone calorimeter tests. Compared with PP/DPER/APP composite, the PP/DPER/IMAPP has higher LOI value and can reach the V-0 rating easily. Studies on the char-forming behaviour of PP/DPER/IMAPP demonstrate that IMAPP has contributed to the formation of compact intumescent char during combustion. The formation of ceramic, continuous and homogeneous surface shielding over the PP matrix protects the underlying matrix and enhances the thermal stability of condensed phase, thereby reducing the heat release rate (HRR), total heat release rate (THR) and mass loss (ML) of FR-PP significantly. Finally, TGA coupled with Fourier transform infrared spectrometry (TG-FTIR) is used to analyze the thermal degradation process of PP/DPER/IMAPP composite. Based on the above results, the flame retardant mechanism is discussed.