Waterborne Coatings Modified By Nano ZnO And Nano Silica Sol

With the development and progress of coatings technology,waterborne environmentally-friendly coatings are becoming more and more popular.However,waterborne coatings,such as waterborne polyurethane and waterborne polyacrylate coatings,have some disadvantages,such as their poor water resistance,low hardness,poor thermal stability,and so on.These shortcomings can be improved by hybridizing organic polymers and inorganic nanoparticles and preparing them to be two-phase,multifunctional,and structured coatings.This thesis provided an effective method for improving the performance of waterborne coatings and preparing excellent waterborne coatings.In the experimental,nano-zinc oxide particles(ZnO NPs)and nano-iron oxide particles(Fe₂O₃ NPs)were chemically combined to prepare composited nanoparticles(CPs)that absorb light in both the ultraviolet and the visible regions,which achieved full spectrum utilization.CPs were added to the waterborne polyurethane acrylate(WPUA)as the inorganic photoinitiators.The CPs had dual functions,both inorganic photoinitiators and nano particles fillers,which removed the harm to the environment and humans caused by the small organic molecules produced by the photolysis and incomplete reaction of the organic photoinitiator.Moreover,the hardness,water resistance,and thermal stability of their inorganic-organic hybrid films prepared after the addition of the nanoparticles had been improved.The modified silica sols were also added to the waterborne polyacrylate(WPA),and the influence of silica sols on the performance of waterborne polyacrylates was investigated.The addition of silica sols improved the comprehensive performance of their hybrid coatings.First,the Fe₂O₃ NPs prepared by hydrothermal method and zinc acetate were dispersed in ethanol.Then,nano-zinc oxide and nano-iron oxide composite particles(ZnO@Fe₂O₃ CPs)were prepared by the sol-gel method in an ice-water bath.The CPs were added to the waterborne polyurethane acrylate to obtain the inorganic-organic hybrid coatings(CPs/WPUA)of the ZnO@Fe₂O₃ CPs and polyurethane acrylates.CPs and inorganic-organic hybrid films were characterized by Fourier transform infrared spectroscopy,ultraviolet spectroscopy,scanning electron microscope and X-ray diffraction,etc.The results showed the CPs have strong light absorption at about 360 nm in the ultraviolet region and about 590 nm in the visible region.Compared with the direct physical blending of two kinds of nano-zinc oxide and nano-iron oxide nanoparticles(MPs),CPs had better dispersibility and photoinitiation efficiency than MPs.When the molar ratio of the CPs was 1:1 and the addition amount was 0.4 wt%,the dispersion effect of the CPs in the hybrid coating was the best,and the photoinitiation efficiency was great.The highest photoinitiated conversion rate of hybrid coatings was 37.77%.The hardness,water resistance and mechanical properties of the hybrid coatings'films had been improved compared with the films of the pure WPA.The hardness was H,and the water absorption rate was 1.09%.Diacetone acrylamide(DAAM)was used as a modifier to modify the silica sol.The modified silica sol was used as the core,and methyl methacrylate,?-methacrylic acid and butyl acrylate were used as raw materials.The modified silica sol/polyacrylate inorganic-organic hybrid coating(DAAM-SiO₂/WPA)with core-shell structure was prepared by the semi-batch emulsion polymerization.The modified silica sol and hybrid films were characterized by infrared spectroscopy,scanning electron microscopy and transmission electron microscopy,etc.The results demonstrated that when the amount of DAAM was 3wt%,the comprehensive performance of the hybrid emulsion and film was the best.The water contact angle of the hybrid film was 67°,the water absorption was 11.27%,the tensile strength was 7.22 MPa,and the elongation at break was 431.39%.Gel permeation chromatography analysis presented that DAAM self-polymerized on the surface of silica.Transmission electron microscopy depicted that the inorganic-organic hybrid emulsion was core-shell structure.Analysis of the results of differential scanning calorimetry reflected that the addition of silica sol increased the glass transition temperature of the films.Thermal stability results exhibited when the thermal weight loss of the hybrid emulsion film was 5wt%,the temperature was 319?.Compared with pure polyacrylate film,the water resistance,thermal stability and mechanical properties of the inorganic-organic hybrid film had been significantly improved.Moreover,compared with the direct physical mixing solution of polyacrylate emulsion and silica sol(SiO₂/WPA),the storage stability of modified silica sol/polyacrylate hybrid emulsion was more than 12 months at room temperature.The inorganic and the organic phase had excellent compatibility and uniform dispersion.As a crosslinking agent,adipic acid dihydrazide was added to the modified silica sol/polyacrylate composite emulsion to obtain a room temperature self-crosslinking emulsion.Fourier transform infrared spectroscopy described that DAAM and adipic acid dihydrazide had ketohydrazine cross-linking reaction to form hydrazone group(-C=N-).The analysis of differential scanning calorimetry showed that the cross-linking reaction increased the glass transition temperature of the films.The TG results presented that cross-linking reaction has little effect on the thermal stability of the films.The various tests of films performance reflected that the water resistance,hardness and tensile strength of the films after cross-linking reaction had been significantly improved.The water absorption rate of the WPA film was reduced from 29.92%to 16.43%,the hardness was increased from B to H,and the tensile strength was increased from 4.37 MPa to 12.18 MPa.And the water absorption of the DAAM-SiO₂/WPA hybrid film was decreased from 11.27%to 7.88%,the hardness was changed from HB to 2H,and the tensile strength was increased from 7.22 MPa to 13.54 MPa.However,the elongation at break of the films becomed worse,that was,the toughness becomeed bad.The elongation at break of the pure WPA film was reduced from 374.79%to170.26%,and the elongation at break of the DAAM-SiO₂/WPA hybrid film was decreased from 431.49%to 66.38%.For pure WPA,the cross-linking reaction slightly deteriorate the transparency of the films,and the transmittance was reduced from 98%to 95%.But for DAAM-SiO₂/WPA,the cross-linking reaction improved the transparency of the films,and the transmittance was enlarged from 94%to 96%.