Synthesis and characterization of dicyclic silicon-/phosphorus-grafted alumina and its application in improving flame retardancy of epoxy resin

A new phosphorous/silicon/aluminum hybrid flame retardant (SAlu) was prepared by a surface grafting modification of alumina with a polymer (SDPS). The polymer was prepared by a condensation reaction between 3,9-dichloro-2,4,8,10-tetrahydroxy-3,9-diphosphate heterocyclic-3,9-dioxide [5.5] undecane (SPDPC) and diphenyldisiloxol. The structure of the SAlu was further characterized by Fourier transform infrared spectroscopy, X-ray diffraction, UV–Vis absorption, and particle size analysis. Thermogravimetric analysis showed that SPDS was grafted over 40% of the alumina surface. When introduced into epoxy resin, SAlu effectively improved the thermal stability and carbonization rate of the epoxy composites at high temperature. Carbonization studies showed that SAlu promoted formation of a ceramic-carbon coking structure with a porous morphology of aggregates, which isolate combustible materials, heat, and oxygen. These features improved the flame retardant performance of the composite. The solidified materials were evenly dispersed in the network structure to improve the elastic deformation ability and glass transition temperature of the solidified resin.