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As an important plastic in our life, polypropylene (PP) are widely used in such fields as electric casings, cars, electronics, interior decorations, insulation materials, architectural materials and so on. However, it is easy to flame, accompanying the emission of thick smoke and poisonous gases, which restricts its application range, especially for the automotive manufacture and the electronic industry. Therefore, it is important and necessary to improve the fire retardant behavior of PP so as to expand its applications.Magnesium hydroxide (about 2μm) and aluminum hydroxide (about 10μm) flame retardant powders in large sizes were modified with silane coupling agent KH-550 by mechanical ball-milling. The effects of surface modification on the particle size, morphology and dispersibility were discussed. The results showed that the mechanical ball-milling was more conducive to the size refinement and dispersibility of particles, and the optimum modification condition was achieved in acidic medium. The reaction mechanism was analyzed and discussed too. In view of ammonium polyphosphate (APP) in relatively small size (<1μm), the conventional surface modification was carried out on APP particles. The dispersability, compatibility and thermal stability of modified APP were greatly enhanced.By comparison of the modification effects of different flame retardants, APP was finally choosed to be added in PP. The flame retardant APP/PP composite was obtained. X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), thermo gravimetric-differential thermal analysis (TGA-DTA), melting flow rate (MFR) and Limiting oxygen index (LOI) were used to analysis and characterize APP/PP composites in terms of the crystal structures, section morphologies, thermal stability, crystallization behavior, melt flow rate and the flame retardant performance. The mechanical properties of composite were also tested. The results indicated that the thermal stability of APP/PP composites was increased with the addition of APP, with a result of MFR decreasing at first and then increasing. The interfacial binding force between APP and the matrix had been improved due to heterogeneous nucleation of APP, which also inhibited the drop of the mechanical properties of composites when APP loading greater than 13%. With the increase of APP loading, the LOI value and the thermal stability of the composites obviously increased. When APP loading was up to 20 wt.%, the LOI value reached 30%. The composites could be self-extinguished after ignited, due to the char formation and droplet resistance of APP. The modified APP brought good mechanical properties to the composites, with the tensile strength, impact strength and elongation all improved.In summary, APP could be used as an acid source and a gas supplier at the same time, combined with promoting char formation. Compared with three-phase intumescent flame retardant system, the exclusive use of APP as flame retardant enhanced the flame retardant efficiency, and decreased the production cost and simplified the processing condition.
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