| Modification of nano-silica coated with poly(methyl methacrylate)(PMMA), melamine formaldehyde resin (MFR) and butanol modified melamine formaldehyde resin (BMFR) by emulsion polymerization method and prepolymer coating method was investigated in the dissertation. Composition, structure and properties of modified silica were analyzed by means of Fourier transform infrared spectroscopy(FTIR), thermogravimetric analysis(TG), scanning electron microscopy(SEM) and particle size analyzer. Modified silica was used in intumescent flame retardant EVA composites(EVA/IFR) and its effects on tensile properties, flame retardant properties and thermal degradation behaviors were studied. Emphasis was given to effects of modified silica on charring properties of the system.The following conclusions could be drawn: (1) Modification degree could be better evaluated by combination of encapsulated mass and particle size. The modified silica with the most encapsulated mass possessed the smallest particle size, which could be interpreted as the better dispersed silica particles. (2) The results of FTIR and TG revealed successful modification of silica coated with PMMA, MFR and BMFR. As observed by SEM, conglomeration of nano-silica particles was lessened and dispersibiliby of silica in EVA was improved after modification. (3) Study on thermal degradation of composites indicated enhanced charring by modified silica, among which MFR coated silica possessed best charring effects according to lower weight loss rate and more residue left. (4) Tensile properties and flame retardant properties of the composites were affected by the dispersibility and surface structure of modified silica.
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