Abstract: A halogenfree intumescent flame-retardant (IFR) was surfacemodified with the silane, titanate, and Al-Ti and Al-Si complex coupling agents. A comparative study of the effects of surface modification on the bulk density and the angle of repose of IFR was performed. The effects of surface modification on limited oxygen index, dispersion property, mechanical properties and flame retardancy of polypropylene (PP)/IFR composites were investigated. The combustion behaviors of the composites were evaluated by cone calorimeter before and after the surface modification of IFR. The results indicated that the Al-Si complex coupling agent had a high efficiency in surface modification. With the surface modification by use of the Al-Si complex coupling agent, the dispersion of IFR in PP matrix was enhanced greatly, and the flame retardancy and impact toughness of the composites were improved. Furthermore, the heat release rate, total heat release, smoke production rate, and total smoke production of the composites were reduced by 30 %.

Key words: polypropylene, intumescent flame-retardent, halogen-free, coupling agent, surface modification