Study On Flame Retardancy And Mechanism Of Pmma/ommt Nanocomposites

In this thesis, PMMA/OMMT nanocomposites with different contents of OMMTwere prepared by melt intercalation method. The microstructure of montmorillonitewhich was intercalated by PMMA was analysed by X-ray diffraction（XRD）andtransmit ssion electron microscopy（TEM）, thermal gravimetric analysis(TGA) andcone calorimeter were used to analyze the thermal decomposition properties andflame retardant properties of the nanocomposites. The structure, flame retardantproperties and mechanism of their fire residue were studied in detail by digital camera,scanning electron microscope（SEM）and X-ray diffraction（XRD）.The XRD and TEM analyses showed that the modified organic montmorillon--ite(OMMT) which was treated by using cetrimonium bromide from sodium basedmontmorillonite (Na+-MMT) can be intercalated by PMMA through melt intercalationmethod and formed an intercalated structure, while PMMA was incompatible withMMT. The thermal decomposition properties of PMMA/OMMT nanocompositeswere studied using thermal gravimetric analysis (TGA). The results showed thatbecause of the shielding effect from the intercalation structure the peak decompositiontemperature of PMMA/OMMT nanocomposites increased compared with the purePMMA. Studies on the flame retardant properties of PMMA/OMMT nanocompositeswith the cone calorimeter burning experiment had shown that the heat release rate（HRR）and mass loss rate（MLR）of the composites dropped apparently, showingexcellent flame retardant properties; The microstructure and composition of the fireresidue of PMMA/OMMT nanocomposite were studied in detail. The resultsdisplayed that it is composed of a skin-cellular layer in submicro scale, and anano-scale network strcure in microscale. The well combination of the skin-cellularlayer and the network structure acts as an effective barrier to reduce flammability of the composites, and the shielding effect of the residue enhanced with its thickness.The fire residues formed during burning process contain a small amount ofcarbonaceous material which can resist to the high temperature of550℃and700℃,apart from the mainly silicate. This component will reduce the decompositionrate and hence combustible gases in the burning process decreased resulting in theheat release rate reduction. However, as the burning proceeded, the temperature ofnanocomposites raised gradually, most of the carbonaceous material weredecomposed in the presence of oxygen. So, the total heat release of thenanocomposite was not significantly reduced.