Preparation Of Insulation Pigments And Their Applications On Solar Reflecting Heat Insula-Tion Coatings

Insulation building envelopes are widely applied for their advantages on saving building energy consumption and improving the function of the buildings. And the insulation materials are vital to improve the insulation performance of building envelope. Amoung diverse insulation materials, insulation coatings are widely used because of their good insulation performance, economic reasons, applying convenience and their advantages on insensitivity to thermal stress. In addition, the application of solar heat reflecting insulation coatings can reduce the surface temperature of building envelope, save cooling energy, ameliorate urban heat island effect and reduce the smog probability. Generally, functional pigments are vital to fulfill the high reflecting performance of solar heat reflecting insulation coatings. However, the widely use of solar heat reflecting insulation coatings has not forced substantial emergency of functional pigments and the effective functional pigments for the solar reflecting insulation coatins are still needed. Thus, the development of new functional pigments for the solar heat reflecting insulation coatings is still a promising field.In this dissertation, we studied the preparation and application of reflecting and emissive pigments for solar reflecting insulation coatings based on the research status of the solar reflecting coatings. Core-shell structured hollow titania microspheres, porous titania microspheres and titania/ethyl cellulose (EC) composite porous microspheres were prepared as reflecting pigments, in which the synergistic effect between titania and microvoids can be realized to improve the light-scattering power of reflecting pigments; zinc oxide (ZnO) nanosheets, ZnO nanosheets based spherical aggregates and ZnO nanorod/mica composite powders were prepared as emissive pigments, in which the relative high emissivity of nanosized ZnO particles and the good dispersibility of nano ZnO based aggregates were both taken in consideration. Thus, a solution for preparation of functional pigments was suggested in the dissertation. The main results are as follows:Core-shell structured hollow titania microspheres and macroporous titania microspheres were prepared and the effects of composition and process route on the final structure were studied systematically:(1) Titania gel microspheres were first prepared by sol-gel process in O/W emulsions with1:1of ethyl acetoacetate (EAA)/tetra-n-butyl titanate (TBT) molar ratio and1:2of TBT/1-octanol volume ratio.(2) The core-shell structured hollow microspheres were prepared by heating the obtained titania gel microspheres at constant heating rate.(3) The macroporous titania microspheres were prepared by using polyvinylpyrrolidone (PVP) as the pore inducer in manufacturing process of titiana microspheres; the macropores inside the porous microspheres were induced by phase separation initiated by PVP; the inner pore size increased with increasing the additive PVP from0.190g to1.903g and the corresponding inner pore sizes of the microspheres obtained with different additive PVP increased from～500nm to～1.3μm.Titania/ethyl cellulose (EC) composite porous microspheres were prepared.(1) EC composite porous microspheres were prepared in O/W emulsion by solvent diffusion with0.4/10,0.8/10and1.2/10of EC/ethyl acetate (EA) mass ratio, and the average particles sizes were2.6,15.7and23.1μm, respectively; the interconnected porosity were72%,74%and68%, respectively.(2) Titania particles were added to fabricate titania/EC composite porous microspheres, while the added titania did not affect the spherical structure of obtained powders much; the addition of titania particles greatly affected the inner structure of the obtained microspheres; the interconnected porosity of the obtained microspheres with0.1/0.8,0.2/0.8and0.4/0/8of titania/EC mass ratio were56%,54%and51%which were much less than that of the microspheres obtained without titania particles.Zinc oxide (ZnO) nanoparticles with high emissivity and its aggregates were prepared and the effect of different state of aggregation on the resulting emissivity was studied by comparing the two particles.(1) ZnO nanosheets were prepared by hydrothermal process with zinc acetate dehydrate as precursor, NaOH as the mineralizer; the size of the obtained nanosheets was approximately400nm, while the thickness was in the range of20～50nm.(2) Multifunctional additives such as lactic acid, citric acid and sodium polyacrylate were used to fabricate ZnO nanosheets based spherical aggregates.(3) The emissivities of the ZnO nanosheets and nanosheets based spherical aggregates in8-14μm wavelength region were0.90and0.88, respectively.ZnO nanorod/mica composites particles were prepared to further illustrate the effect of different state of aggregation on the resulting emissivity.(1) ZnO nanorod/mica composites particles were prepared by chemical liquid deposition; the ZnO nanorods deposited on the mica plates had the preferential orientation of the c axis with150nm of diameter and550nm of length.(2) The density of ZnO nanorods on mica surface was controlled by different density of ZnO seed crystal on mica surface which was controlled by different colloid concentration; the density of ZnO nanorods on mica surface increased with increasing colloid concentration, and the emissivity of the obtained composite particles in8～14μm wavelength region were0.800,0.841,0.858and0.863, respectively; however, the ZnO nanorods based spherical particles attained0.851of emissivity in8-14μn wavelength region.The titania/EC composite porous microspheres as reflecting pigment and the ZnO nanosheets based spherical aggregates as emissive pigment were used to prepare a solar reflecting insulation coating to confirm the synergistic effect between the two pigments to enhance the insulation performance.(1) When the amount of the additive titania/EC composite porous microspheres was5.0wt.%, the obtained coatings attained the best heating insulation performance; the temperature of the sample plate after300minutes irradiation by infrared lamp was67.7℃, while the temperature of the sample plate coated with coatings without pigments was85.6℃(2) The effect of emissive ZnO nanosheets based spherical aggregates was also confirmed by adding the spherical aggregates particles to the coatings obtained with5.0wt.%titania/EC composite porous microspheres; it was demonstrated that the additive ZnO particles further improve the insulation performance of the solar reflecting insulation coating; the temperature of the sample plate after300minutes irradiation was63.9℃.