Study On The Preparation And Properties Of Monodispersed Zinc Oxide And Its Nanocomposites

In the natural world,ultraviolet(UV)rays have a series of hazards such as skin aging,DNA damage,and performance reduction of materials.UV stabilizers can effectively suppress these hazards,especially enhancing the anti-UV aging property and elongating the lifetime of polymer materials,thus gain increasing attentions and studies.Among numerous UV stabilizers,nano zinc oxide(ZnO)has the potential to replace organic UV stabilizers for anti-UV-aging of transparent resins due to its advantages of high transparency,good stability and environmental friendliness.At present,it is difficult to obtain highly transparent nanocomposite materials because most of the commonly applied ZnO particles are oversize and have poor dispersion in the polymer matrices.Moreover,nano ZnO has a certain photocatalytic property,which will accelerate the degradation and shorten the lifetime of polymer when directly used as a filler.These disadvantages limit the application of nano ZnO as UV stabilizer to some extent.Therefore,how to realize the nano-scale dispersion of nano ZnO in the resin matrix and inhibit its photocatalytic activity is the key to prepare high performance resin/ZnO nanocomposites.vIn this work,to synthesize light-functional resin-based nanocomposites,transparent dispersions of ZnO dispersed in different liquid phases will be firstly prepared via high-gravity method combined with surface modification techniques.Second,based on ZnO nanodispersion in cyclohexane,a reverse microemulsion method will be applied to prepare ZnO@SiO2 nanodispersion.Finally,ZnO-resin nanocomposites with high transparency,strong UV screening ability and enhanced light aging resistance will be synthesized by solution blending method to realize nanoscale dispersion and nano effect.Besides,to block near infrared(NIR)irradiation,tungsten bronze nanocrystalswill be introduced,endowing the nanocomposites with heat insulation and anti-light-aging capabilities.The main contents and results are as follows:(1)By using the zinc acetate dihydrate and potassium hydroxide as raw materials,ZnO nanoparticles with good dispersion and average size of 6 nm were prepared via stirring tank method through exploring the processing conditions.On the basis of this,the transparent ZnO monodispersion was successfully manufactured by high-gravity technology combined with surface modification method.The effects of preparation and modification conditions on the size and dispensability of ZnO nanoparticles were studied.The optimum conditions are determined:the speed of the high-gravity rotating bed is 2600 rpm,the raw materials mol ratio is 0.57:1,the concentration is 0.6 mol/L,the reaction temperature is 70℃,the feed rate is 200 mL/min,the reacting time is 4 min,and the amount of TEOS is 15 wt%.The prepared ZnO nanoparticles have a size of 3～5 nm with uniform particle size distribution and are monodispersed in liquid medium.Compared with that of the stirring tank method,ZnO nanoparticles prepared by the high-gravity technology have smaller particle size with narrower distribution,and better optical performance.(2)The dichloromethane(DCM)phase TZ(ZnO coated with a slight amount of SiO2)nanodispersion was prepared by high-gravity technology combined with surface inorganic-organic continuous layer coating method,based on which polylactic acid(PLA)/TZ and PLA/TZ/cesium tungsten bronze(CWO)were fabricated.The prepared TZ nanoparticles with size of 4 nm were monodispersed in DCM,and the nanodispersions have high transparency even with high solid content of 60 wt%.The method of preparing TZ nanodispersion also can be applied to synthesize TZ nanodparticles dispersed in different polar liquid medium by tailing the types of modifiers.The prepared PLA/TZ and PLA/TZ/CWO nanocomposites both have highvisible transmittance,good UV screening ability and certain light aging resistance.TZ nanoparticles also achieve nano-scale dispersion in PLA matrices that the PLA/TZ composite can maintain the same visible transmittance as pure PLA at solid content of 60 phr.Moreover,the PLA/TZ/CWO ternary nanocomposite has good NIR absorbing ability and the heat insulation test indicates that with the same irradiating condition,temperature rises 10.2℃ in the other side of pure PLA film coating glass,while only 2.3℃ for that of PLA/TZ/CWO nanocomposite coating glass,showing significant thermal insulation.(3)Based on the ZnO nanodispersion in cyclohexane prepared by high-gravity technology,reverse microemulsion method was proposed to prepare core-shell structured ZnO@SiO2 nanoparticles and their nanodispersion in toluene.Furthermore,ethyl cellulose(EC)/ZnO@SiO2 transparent nanocomposites were prepared on the basic of ZnO@SiO2 nanodispersion.The suitable preparation conditions of ZnO@SiO2 nanodispersion were determined,and the photocatalytic degradation of methylene blue by ZnO@SiO2 nanoparticles as well as the photo aging resistance of EC/ZnO@SiO2 composites were studied.The optimum material specifications for preparing ZnO@SiO2 toluene phase nanodispersion by reverse microemulsion method is:60 μL ammonia,6.5 mg ZnO,5 μL TMOS,20 μL additional water,60 μL C18-silane.The as prepared ZnO@SiO2 nanoparticles with average size of 12 nm have an obvious core-shell structure and excellent dispersion in toluene.Additionally,the nanoparticles have a much lower photocatalytic activity in photo-degrading methylene blue,compared with ZnO nanoparticles without or with a slight silica coating,which indicates thicker silica coating can effectively inhibit the photocatalytic properties of ZnO.The as prepared ethyl cellulose(EC)/ZnO@SiO2 nanocomposites have good UV screening ability and high visible transmittance.ZnO@SiO2 nanoparticles also achieve nano-scale dispersion in EC matrices that the nanocomposite can maintain the same visible transmittance as pure EC at solid content of 64 phr.In addition,EC/ZnO@SiO2 nanocomposite exhibites excellent light aging resistance,which can maintain its original optical properties after UV irradiation for 100 h while obvious reductions of visible transmittance occur for pure EC and EC composites filled with ZnO coated with a slight of SiO2.The results confirm again that thicker silica coating can eliminate the photocatalytic property of ZnO and make it better when applied as a UV stabilizer.(4)A simple wet chemical method was used to controllably synthesize the sodium-cesium double-doped tungsten bronze(NaCWO)dispersion.Based on NaCWO and ZnO@SiO2 nanodispersion,the EC/NaCWO/ZnO@SiO2 ternary nanocomposite with both UV and NIR screening ability was prepared through solution mixing method.The effects of preparation conditions on the morphology and microstructure of NaCWO crystals,as well as the optical properties of dispersions and ternary nanocomposites were investigated.The results show that NaCWO nanocrystals with different crystal phase and morphology can be obtained under different anionic ligand environment,including hexagonal phase with short rod-shaped particles,cubic phase with truncated tetrahedral-shaped particles and irregular morphology particles,as well as mixed crystal phase with mixed morphology of long rods-shaped and irregular particles can be obtained under different anion ligand environments,including short rods with hexagonal phase,truncated tetrahedrons with cubic phase,irregular morphologies with cubic phase,etc.Prolonging the reaction time can increase the metal doping amount of tungsten bronze,and obtain a dispersion with better optical properties.When reacting for 20 h,the prepared hexagonal phase rod-shaped tungsten bronze dispersion has better optical properties with 96.5%NIR light barrier at 1000 nm and the maximum visible light transmittance of 84%.The as prepared EC/NaCWO/ZnO@SiO2 nanocomposite has strong UV blocking ability and excellent UV-aging resistance,which can remain the optical performance after accelerated UV-aging process for 81 h.