Preparation Of The Mesoporous Silica Microspheres By PICA Method And Application To The Nanocomposites Foaming Agent

The pores of the microcellular foam are small and dense,and are evenly distributed.The cells actually play a role in the toughening of rubber particles,which is higher than that of ordinary plastics.In this thesis,mesoporous silica microspheres were prepared by polymerization-induced colloid coagulation(PICA)from the different silica sols.The particle size and dispersion of mesoporous silica microspheres were controlled by adjusting the preparation parameters.In addition,the size of the silica sol particles was also adjusted by the method of adding silicon there for the mesoporous silica microspheres with different pore size were produced.The obtained monodisperse mesoporous silica microspheres having uniform particle size.Then the blowing agents azodicarbonamide(AC)and 4,4 '-oxobenzene sulfonyl hydrazide(OBSH)were introduced into the channels of the silica resulted in the novel superfine nanocomposite blowing agents.Finally,the new foaming agents were applied to the epoxy resin system.The main achievements are as follows:(1)The mesoporous silica microspheres were prepared by PICA method.The silica sol was obtained with TEOS as the silicon source under acidic conditions.The mesoporous silica microspheres with particle size distribution range of 3?5?m and well dispersion with the average pore size of 3?4nm were prepared by adjusting the parameters such as the reaction temperature,the molar ratio of urea to formaldehyde,the total amount of urea and formaldehyde as well as the concentration of surfactant,etc.When silicon powder was used as the silica source,the size and dispersion of silica sol were controlled by adjusting the times of silicon coating and dilution.The silica sol particles size was adjustable from 20nm to 45nm whereas the average pore diameter changed from 6.2nm to 17.8nm.The morphologies of microspheres could be further improved by diluting the silica sol.(2)The nanocomposites foaming agents AC/SiO2 and OBSH/SiO2 were prepared by solution impregnation method.The effects of the pore size of the silica microsphere,the concentration of impregnation solution and washing methods on the loading of foaming agents were investigated.The loading of AC was increased up to 31.7%with the pore size of silica microspheres increased.The particle size of the AC/SiO2 was decreased to a rage of 3?10?m by washing.When the mesoporous silica microspheres loaded with OBSH,the loading of OBSH showed a maximum of 28.6%with the increase of the concentration of OBSH.Washing with methanol could effectively prevent the agglomeration of composite foaming agent.The particle size of the composite blowing agent OBSH/SiO2 with monodispersion was in the range of 3-10?m.(3)AC/SiO2 and OBSH/SiO2 composite foaming agents were applied to the epoxy resin.The effects of the foaming temperature,foaming agent dosage and curing agent dosage on the foam were investigated.The composite foaming agent AC/Si02 resulted in the foam with an average cell diameter of 59.9?m and a cell density of 3.5×105 cells/cm3.A foam with an average cell diameter of 48.2?m and a cell density of 8.3×105 cells/cm was obtained by using OBSH/SiO2 foaming agent.