Studies On Nano-TiO₂ Grafting Modification On Micropcms And Its Application In Heat Insulation And Energy-saving Coil Coatings

Due to a wide range of colours, easy cut to required lengths, bent, profiled or deep drawn, without damaging the organic coating, the prepainted coil has numerous applications in various industries, such as in the construction industry, the automotive and transport industries, etc. The need for intelligent solar heat management solutions like thermal insulating coatings is increased with more requirement of energy-saving, especially in coil coatings. Along with the development of polymer technology, microcapsulation of phase change materials (microPCMs) with a higher reflectivity to sunlight provides a means to solve the super-cool problem and interfacial combine with circumstance materials. There are many advantages of microencapsulated PCMs, such as increasing heat transfer area, reducing PCMs reactivity towards the outside environment and controlling the changes in the storage material volume as phase change occurs. The objective of this study is to synthesize microcapsules containing paraffin with melamine-formaldehyde (MF) shell by in situ polymerization, and graft nanosized TiO₂(rutile type) to the surface of microPCMs for a higher reflectivity to sunlight, and then energy-saving coil coatings were prepared using TiO₂-grafted microPCMs and surface modified potassium titanate whisker(PTW). The encapsulating mechanism of microPCMs was studied by focused beam reflectance measurement (FBRM) and molecular simulation.MicroPCMs with paraffin core and MF resin shell were prepared using in situ polymerization. The effect of emulsifier style, prepolymer's feed rate, core/shell ratio and molecular weight of the emulsifier styrene-maleic anhydride copolymer (SMAH) on the surface morphology, size distribution and thermal properties of microPCMs were studied with Scanning electron microscopy (SEM) method and differential scanning calorimetry (DSC). When the mass ratio of SMA1000PH emulsifier to paraffin is 1.5%, the feed rate of prepolymer is 0.35mL/min and the mass ratio of paraffin to prepolymer is 3:1, the phase change latent heat and PCM content reach to the maximum value of 126.7 J/g and 71%, respectively. Irregular spherical microPCMs with mean diameter of 8¹0μm are obtained. The dissipative particle dynamics (DPD) simulation method was used to study the aggregation behavior of SMAH at interface of n-heneicosane/water and the molecular dynamics (MD) method was used to study the arrangement of SMAH molecule on the n-heneicosane/water interface. DPD simulation results show that accumulation behavior occurrs when the SMAH is added. With the increase of molecule weight of SMAH, the density of n-heneicosane in box increases and solubilization of SMAH is strengthened in the system. According to the results of MD simulation, a microencapsulation forming model is developed. The forming process of shell consists of three steps: (1)small prepolymer particles assembles to bigger ones; (2)big prepolymer particles areabsorbed by SMAH and aggregated in the surface of n-heneicosane drops; (3) prepolymer particles condensate and form a shell. The results show that surface morphology of microPCMs is affected greatly by the molecule weight of SMA. Low molecule weight SMAH is suitable for rough surface encapsulation, while high molecule weight results in a smooth surface.Nanocomposite microspheres were successfully prepared by grafting TiO₂ particles to microPCMs via chemical reaction method. The effects of surface modification of nano TiO₂ particles, dosage and adding time of TiO₂ dispersion on the surface morphology and thermal storage properties of the mocrosphere ware investigated. The results indicate that the optimized method is immediate adding the TiO₂ dispersion when all the prepolymer was added to the reaction system, and the optimal mass ratio of TiO₂ to microPCMS is 10%.Energy-saving coil coatings were prepared using saturated polyester as film former material, TiO₂-grafted microPCMs and surface modified PTW as fuctional thermal storage material and thermal insulation material, high reflectivity black 30C940 as pigments. The thermal properties and mechanic behaviors of coil coatings were investigated. It was indicated that the usages of microPCMs, TiO₂-grafted microPCMs and surface modified PTW have a great effect on the thermal properties of coatings. When the mass ratio of black pigments to white pigments is 5:95, the mass ratio of modified PTW to coatings and TiO₂-grafted microPCMs to coatings is 1.5% and 3% respectivly, the heat reflectivity and the total solar reflectance reach to the maximum value of 93.9% and 87% respectively without reducing the mechanic behaviors of the coil coatings.