Preparation Of Nano-ZnO Monodispersion By High-Gravity Method And The Application In Pmma Optical Materials

Ultraviolet(UV)rays will cause photoaging of the polymer,and damage its optical and mechanical properties,which shortening the lifetime seriously.UV stabilizers can suppress these hazards effectively enhance the UV aging resistance of material.As an excellent inorganic UV stabilizer,zinc oxide(ZnO)can absorb ultraviolet rays,and has the characteristics of green,non-toxic,environmental protection,high efficiency,etc.However,for optical grade polymer materials such as polymethyl methacrylate(PMMA),the nanoparticles must have small size and disperse in the polymer matrix evenly,which ensure that there will be no light scattering due to the difference in refractive index of the two or the agglomeration of nanoparticles,so as to maintain the transparency of the material and give full play to the nano effect.Therefore,how to achieve the nano-scale dispersion of nano-ZnO with small and uniform particle size distribution in an optical-grade polymer matrix is a key scientific issue in the preparation of transparent organic-inorganic nanocomposites.In this work,the monodispersed ZnO nanoparticles in methyl methacrylate(MMA)were synthesized based on the technique of high-gravity reaction precipitation method combined with wet modification.The ZnO/PMMA nanocomposites and the ZnO/Cesium-doped tungsten bronze(CWO)/PMMA ternary nanocomposites were prepared by in-situ bulk polymerization.The effect of the preparation process conditions on the nano-ZnO morphology,particle size and dispersion were mainly researched.The effect of the preparation process conditions on the optical,mechanical and aging resistance properties of nanocomposites were also researched.The main research contents and results of the paper are as follows.Under high-gravity environment,nano-ZnO liquid monodispersion was synthesized by reactive precipitation method combined with wet modification technology.The effect of preparation process conditions on the nano-ZnO particle size distribution and dispersibility in MMA was investigated.The optimum process conditions for the preparation by the high gravity method are determined:the speed of the rotating bed is 2500 rpm,the reaction medium is pure methanol,the amount of TEOS is 15 wt%,the modifier is silicon coupling agent,the amount of modifier is 100 wt%,the modification time is 1 h and the modification temperature is 70?.The nano-ZnO with a particle size of about 6 nm and ellipsoidal shape is obtained.The particles are monodispersed in liquid phase MMA,forming a highly transparent ZnO/MMA nanodispersion.The dispersion still exhibits a high visible light transmittance even with a solid content of 20 wt%.Compared with the kettle method,the nano-ZnO prepared by the high-gravity method has a smaller particle size and better dispersion.The ZnO/PMMA binary nanocomposites were prepared by the in-situ bulk polymerization of ZnO/MMA nanodispersion.The effect of the polymerization conditions on the properties of the composites was studied.A highly transparent ZnO/PMMA binary nanocomposite with strong UV shielding ability and good aging resistance was prepared under the preparation process conditions:the initiator is BPO,the amount of initiator is 0.3 wt%of the dispersion and the pre-polymerization temperature is 80?.When the thickness of the spline is 2 mm and the amount of ZnO nanoparticles is 1 wt%,the visible light transmittance of the material at 550 nm is 92%and ultraviolet rays below 360 nm can be completely shielded.In addition,the photoaging resistance,thermal stability and mechanical properties of nanocomposites have been enhanced due to the addition of ZnO nanoparticles.The nanocomposites after UV-enhanced irradiation for 200 h are not yellowing,and the visible light transmittance at 500 nm remains at 92%.The notched impact strength,elongation at break and tensile strength of the composites are decreased by 5%,3%,and 6%respectively,far lower than that of pure PMMA.The commercially available nano-CWO dispersed in butyl acetate was transformed into MMA and mixed with the ZnO/MMA dispersion to synthesize the ZnO/CWO/PMMA ternary nanocomposites with dual functions of light aging resistance and heat insulation by in-situ polymerization.The effects of the types of commercially available CWO dispersions and the amount of nanoparticles added on the properties of the composite were investigated.When the CWO nanodispersion is butyl acetate phase and the amount of CWO and ZnO nanoparticles are 0.3 wt%and 3 wt%respectively,the nanocomposites have excellent optical,aging resistance and thermal insulation properties.The ultraviolet rays below 360 nm can be shielded completely,the blocking rate at near infrared 1000 nm is 92%and the visible light transmittance at 500 nm is 75%.More importantly,the ternary nanocomposites have excellent photoaging resistance.After UV-enhanced irradiation,the materials still remain the same visible light transmittance as before irradiation basically.The notched impact strength,elongation at break and tensile strength of the composites are decreased by 2%,5%and 3%respectively,far lower than that of pure PMMA.In addition,the heat insulation test indicates that at the same condition of near infrared light,the temperature rises 8.3? on the other side of neat PMMA,while the temperature on the other side of the ternary nanocomposite only increases by 2.2?,exhibiting excellent thermal insulation.