Jet Grinding And Surface Modification Of ZnO Nanoparticles And Its Application In Rubber

As a potentially useful inorganic material, ZnO nanoparticles show both photoconductivity and photocatalytic activity. Furthermore, ZnO is a technologically important material. Thus, ZnO nanoparticles have been wildly used in many fields, such as rubber, coating, gas sensors, chemical sensors, catalysts for photo-catalytic degradation instead of titania nanoparticles, etc. However, reaggregation of nanoparticles due to their high surface energy and strong polarity has become a major issue, which makes it difficult to disperse uniformly in organic solvents and polymers and impedes the applications of ZnO nanoparticles to some extent. For this reason, various techniques have been applied to obtain uniformly dispersible nanoparticles. Surface modification is one of the most efficient methods to deal with nanoparticles in order to prevent reaggregation, which has attracted tremendous attentions.There are many methods to surface modification. The method of jet grinding and surface modification belongs to mechanochemical surface modification process, which is coupling ultrafine grinding with surface modification and is a novel one to produce ultrafine powder. As a relatively new type of surface modification, the process has many advantages compared with more traditional one, such as low cost, simple operation, narrow size distributions, high efficiency, and so on, which has wide foreground application of industrialization. So stearic acid and diethoxydimethyl silane are used to modify ZnO nanoparticles by the process of jet grinding and surface modification in fluidized-bed jet mill. The modified ZnO nanoparticles are applied in rubbers as cure activation, and the effect of modified ZnO nanoparticles on the mechanical properties and cure characteristics of rubbers is also studied. The main research work is as follow:(1) Industrial ZnO nanoparticles were modified with stearic acid and diethoxydimethyl silane using fluidized-bed jet mill by batch operation, respectively, by one of the integrated process named dry mixing and surface modification process. Firstly, the ZnO raw material was mixed with modifying agents in mixing machine, then the pre-mixture was ultrafine grinding in jet mill and the modified product was gotten. The deagglomeration and surface modification of ZnO nanoparticles were investigated. The products were characterized by TEM, SEM, XRD, TG, FT-IR, XPS and Nano-ZS90 laser granularity instrument. The experimental results show that chemical reaction occurs between stearic acid and ZnO nanoparticles, and diethoxydimethyl silane molecules effectively cap the ZnO nanoparticles, and the agglomeration of modified ZnO nanoparticles is reduced severely due to the adsorption of stearic acid and diethoxydimethyl silane on the surface of ZnO nanoparticles in comparison with initial ZnO nanoparticles, and the efficiency of grinding operation is improved greatly. In addition, the lattice structure of ZnO nanoparticles is not damaged after modification and the modified ZnO nanoparticles have better dispersibility in organic solvents due to the lipophilic groups on the surface of ZnO nanoparticles.(2) The dry ultrafine grinding of ZnO nanoparticles with liquld additives was carried out using a fluidized-bed jet mill. Liquid additives used were methanol, ethanol and ethylene glycol. All of the experiments were carried out by batch operation. The ground products were characterized by SEM, XRD, FT-IR and Nano-ZS90 laser granularity instrument. The experimental results show that alcohol and glycol additives are satisfactorily effective for the ultrafine grinding of ZnO nanoparticles. The principal effect of additives in ultrafine grinding is considered to be the increase in flowability and the control of reagglomeration of nanoparticles due to the alkoxylation of hydroxyl groups on the ZnO nanoparticles surface.(3) Industrial ZnO nanoparticles were modified with stearic acid by the other integrated process named jet grinding and surface modification process in fluidized-bed jet mill by batch operation. The deagglomeration and surface modification of ZnO nanoparticles were investigated. The products were characterized by SEM, XRD, TG, FT-IR and Nano-ZS90 laser granularity instrument. The experimental results show that stearic acid molecules chemically adsorb on the surface of ZnO nanoparticles, and the agglomeration of modified ZnO nanoparticles is reduced severely in comparison with initial ZnO nanoparticles, and the efficiency of grinding operation is improved greatly. In addition, the lattice structure of ZnO nanoparticles is not damaged after modification and the modified ZnO nanoparticles have better dispersibility in organic solvents due to the lipophilic groups on the surface of ZnO particles.(4) Two types of modified ZnO nanoparticles using the integrated process were applied in different varieties of rubbers as cure activator and the effects of them on the cure characteristics and mechanical properties of rubbers were also studied in comparison with initial ZnO nanoparticles. The experimental results show that modified ZnO nanoparticles have better effect on the mechanical properties and cure characteristics of rubbers than the unmodified ZnO nanoparticles.