Study On Preparation And Properties Of Modified Fumed Silica

Surface single and composite modification of silica was studied by using fumed silica as raw material,methyl trimethoxysilane and 3-chloro-2-hydroxypropyl trimethyl ammonium chloride as modified agent in this paper.The effect of factors such as amount of modified agent,preprocessing temperature,preprocessing time,reaction temperature, reaction time,flux of nitrogen gas,amount of alkali on surface modification degree was discussed by respectively using continuous dry method and periodic dry method. Modification degree was determined by measuring surface hydroxyl number and electric charge zero of fumed silica.The experiment results showed that when silica is modified by using methyl trimethoxysilane,enhancing preprocessing temperature and extending preprocessing time are conducive to reducing surface hydroxyl number of silica,the better process conditions of silica modified by continuous dry method are that amount of methyl trimethoxysilane 30%,preprocessing temperature 350℃,preprocessing time 10min,reaction temperature 350℃,reaction time 10min,flux of nitrogen gas 1.5m~3/h;the better process conditions of silica modified by periodic dry method are that amount of methyl trimethoxysilane 15%, preprocessing temperature 120℃,preprocessing time 30min,reaction temperature 160℃, reaction time 30min;surface modification degree of periodic dry method is better than that of continuous dry method.Surface electric charge zero of silica modified by 3-chloro-2-hydroxypropyl trimethyl ammonium chloride increases with increasing amount of modified agent and reaction time,the better process conditions are that amount of modified agent 30%,reaction temperature 120℃,reaction time 30min,amount of alkali 1.5%,amount of adding water 6%.The better process conditions of composite modification are that amount of methyl trimethoxysilane 30%,amount of 3-chloro-2-hydroxypropyl trimethyl ammonium chloride 40%,reaction temperature 130℃, reaction time 30min,amount of alkali 2%,amount of adding water 6%. The results of ratio surface area and methanol value of silica showed that ratio surface area of modified silica decreases and hydrophobic property enhances.IR test proved that part of hydroxyl on silica surface is replaced by organic group of modified agent. Measurement of transmittance in ethanol and SEM showed that surface hydroxyl number of silica less,dispersion better,size of secondary aggregates smaller.The results of antibacterial measurement showed that silica with grafted quaternary ammonium group can restrain growing bacteria of starch paste and enhance storage stability of starch paste,the better adding amount is 3%.