Study On Surface Modification Of Nano-zno And Its Application In Polyester Coating

It is a hot reaearch point that nano-particles have been applied preliminary in the field of the functional coatings. However, the nano-particle easily aggregate due to it's high surface energy, which will lead to degrade it's performance when nano-particle is added in the coating.As the hydrophilicity of the nano-particles, it's difficult to disperse uniformly into resins, so air gaps is present at the interface of the high polymer. When the vapor in the air was entered in the polymer through the gap, the polymer may become embrittlement, which results that the coatings'performance will fall down. In order to reduce or eliminate agglomeration and increase the dispersion of the nano-particle in coatings,it's necessary to modify the surface of nano-particle.In this project, the modification of nano-ZnO and its application in polyester coating were investigated. The nano-ZnO particle was pretreated with silane coupling agent (KH550). In order to graft the stearic acid on it's surface, the coupling grafting method and CDI activating grafting method were employed respectively. The unmodified and modified nano-ZnO's surface structure were characterized by Transform Infrared Spectrophotometer(FT-IR), Scanning Electron Microscopy (SEM), spectrophotometry and activation index to evaluate the combination means between nano-ZnO particle and organic molecule and the effects of modifying the surface on the dispersion and stability of nano-ZnO in organic media. Meanwhile, In order to gain the optimum technique conditions, the influence of solvents, the amount of coupling agent, coupling time, stearic acid content, the grafting time of stearic acid and reaction temperature on the modification effectiveness had also been investigated. The results of activation index and spectrophotometry showed that the modified nanoparticles by two methods all transform from hydrophilic to lipophilic and the dispersion in organic solvents was improved and the modified particle by the CDI activating grafting is better than that of coupling grafting. The infrared spectra illustrated that both the CDI activating grafting and coupling grafting can succeed to chemically graft stearic acid onto the surface of nano-ZnO. SEM results showed that both the methods reduce improve nano-ZnO particles'agglomeration, of which the CDI activating grafting method is better. At the same time, the optimum modified technique conditions of the coupling grafting method were the coupling agent content of 2%, coupling time of 8h, the stearic acid content of 2%, stearic acid grafting time of 3h, modified temperature of 60℃.The ZnO/polyester nanocomposite coating was prepared through adding the modified nano-ZnO particles into the unsaturated polyester coating by the blending method and the properties of the nanocomposite film, such as tensile strength, break elongation, water absorption rate, hardness, adhesive force, acid resistance and base resistance, affected by the modification method of nano-ZnO and its adding amount were investigated. The properties of the unsaturated polyester coating have been improved to some extent when the modified particles were added. Furthermore, the mechanism of nano-ZnO modifying the unsaturated polyester film was discussed.