Preparation Of Hollow Silica Nano-dispersion And Its Application In PMMA

Plexiglass(polymethyl methacrylate,PMMA)has the advantages of high transparency,high strength,easy processing,and light weight,which is widely used in military,construction,automotive and other industries.However,the thermal and sound insulation capabilities of PMMA are weak,which limits its application in related industries.In order to improve the performance of PMMA,functional auxiliaries can be added into it.Hollow silica(SiO2)has the advantages of low thermal conductivity,sound insulation,and environmental friendliness,making it a good inorganic functional agent.In addition,SiO2 has a low refractive index,and combining it with a transparent organic matrix can reduce the refractive index of the material,thereby reducing light reflection and improving transparency.However,since the refractive index of hollow SiO2 is different from that of optically grade organic materials,when the particles are large or poorly dispersed in the organic matrix,light scattering is likely to be caused,resulting in the decrease of the transparency of the organic materials,and affecting the thermal and sound insulation effects.Therefore,how to synthesize nano-hollow SiO2 with small particle size and uniform dispersion is the key scientific issue in the preparation of optical-grade organic-inorganic nanocomposites.In this thesis,the preparation of nano-hollow SiO2 took monodisperse nano-zinc oxide as a template and was synthesized by reverse phase microemulsion method.Then high-transparent hollow SiO2/PMMA nanocomposites with good heat insulation and sound insulation were prepared by in-situ bulk polymerization.The effects of preparation conditions on the morphology and dispersion of nano-hollow SiO2 were studied,and the effects of the addition of hollow SiO2 on the optical,thermal and sound insulation properties of composite materials were also discussed.The research contents and conclusions are as follows.Using nano-zinc oxide monodisperse in cyclohexane as a template,nano-hollow SiO2 was synthesized by inverse microemulsion method,the influence of preparation process conditions on the morphology and dispersion of nano-hollow SiO2 was investigated,and the suitable preparation process was determined.The suitable conditions are as follows:use ethyl orthosilicate as raw material,ammonia concentration is 25%,molar ratio of ammonia to zinc oxide is 100,mass ratio of silicon-zinc element is 30,reaction temperature is 25?,modifier is added after 11 h of reaction,the amount of modifier added is 100 wt%of product quality,the modification temperature is 25? and modification time is 1 h.The average diameter of the prepared hollow SiO2 particles is 20 nm,and the thickness of the shell layer is about 7 nm.The hollow SiO2 can be dispersed in methyl methacrylate(MMA)and methyl isobutyl ketone(MIBK),forming a highly transparent nano-hollow SiO2/MMA and hollow SiO2/MIBK liquid dispersion.Taking hollow SiO2/MMA liquid dispersion as raw material,optical grade hollow SiO2/MMA nanocomposites were prepared by in-situ bulk polymerization method.The effects of the amount of hollow SiO2 on the optical,thermal and sound insulation properties of the composite material were studied.The results show that the addition of nano-hollow SiO2 can significantly increase the visible light transmittance of the material,reduce the thermal conductivity of the material,and increase the sound absorption coefficient of the material.Compared with the material without nano-hollow SiO2,when the amount of nano-hollow SiO2 is 2 wt%,the visible light transmittance of the hollow SiO2/PMMA nanocomposite is increased by 2%at 500 nm,the sound absorption coefficient is increased from 0.069 to 0.119,with an increase of 72%,and the thermal conductivity is decreased from 0.226 W/m·K to 0.1988 W/m·K,reduced by 12%(The addition of 4.5 wt%hollow SiO2 can reduce the thermal conductivity by 24%).In addition,the addition of nano-hollow SiO2 can also significantly improve the tensile properties of the composite.Compared with the material without the addition,when the mass percentage of nano-hollow SiO2 is 1 wt%,the tensile strength,elongation at break were increased by 30%and 68%.