Preparation, Characterization And Application Of Phase Change Thermal Storage Mcirocapsules And Nanocapsules Containing N-dodecanol

With the rapid development of global industry, the energy sources in the world are missing day by day. Phase change materials (PCM) can be used for energy storage and utilization through the phase change latent heat during their phase change process, which is helpful to improve energy efficiency and develop new renewable energy. However, PCM have many disadvantages, such as flowing during the phase change process, bad compatibility and corrosion. Microcapsule or nanocapsule technology can be used to fabricate new phase change thermal storage composite materials, which is an effective method to solve those problems. In this work, n-dodecanol with high phase change latent heat and suitable phase change temperature was encapsulated as core by in-situ polymerization with melamine-formaldehyde (MF) resin as shell, and the microcapsules containing phase change material (microPCMs) synthesized were modified by different kinds of modifiers. The phase change thermal storage nanocapsules with n-dodecanol as core and polymethyl methacrylate (PMMA) as shell were prepared through miniemulsion polymerization. Phase change thermal storage composite gypsum board and waterborne composite coating were prepared by incorporating phase change thermal storage microcapsules and nanocapsules containing n-dodecanol into ordinary gypsum board and waterborne coating. The structure and properties of phase change thermal storage microcapsules and nanocapsules containing n-dodecanol were studied. The thermal energy absorbing and releasing performances of phase change thermal storage composite gypsum board and waterborne composite coating were studied and their applications in the fields of energy saving were explored, which provide technical basis for the practical application. The main research contents and achievements are listed as following:Firstly, n-dodecanol was used to be encapsulated by in-situ polymerization with monomers of melamine and formaldehyde, and microPCMs with high phase change latent heat, suitable phase change temperature and compact structure were prepared with MF resin as shell and n-dodecanol as core. The influence of emulsifier type, emulsifier amount, PCM polarity, emulsification stirring speed and feeding mass fraction of n-dodecanol on the thermal storage properties, encapsulation efficiency and morphology of microPCMs were studied by using DSC, TG, SEM, FTIR, and laser particle diameter analyzer and the formation mechanism of microPCMs were discussed. It's found that the dispersion and charge effect of emulsifiers have great influence on the formation of MicroPCMs and anionic styrene-maleic anhydride copolymer (SMA) emulsifier is helpful for the encapsulation of n-dodecanol with MF resin. The optimal preparation condition of MicroPCMs containing n-dodecanol is that emulsification stirring speed is 4500 r/min, mass ratio of emulsifier to n-dodecanol is 4.8%, and the feeding mass fraction of n-dodecanol is 81%. MicroPCMs with the maximum phase change latent heat of 187.5J/g, encapsulation efficiency of 93.1%, phase change temperature of 21.5℃, mean diameter of 30.6μm and polydispersity index of 1.190 are obtained.Secondly, three kinds of modifiers hydrophilic nano-SiO2, sodium chloride (NaCl) and polyvinyl alcohol (PVA) were used to modify MF resin, respectively, and modified microPCMs were prepared by in-situ polymerization with modified MF resin as shell and n-dodecanol as core. The influence of modifier type and modifier amount on the thermal storage properties, cracking ratios and morphology of modified microPCMs were studied by using DSC, SEM and FTIR. It's found that the phase change latents of modified microcapsules increase firstly and decrease subsequently with the increasing of the amount of modifier, while the cracking ratios decrease firstly and increase subsequently. PVA is the best modifier, by which microPCMs modified possess the optimal comprehensive performances. When the mass ratio of PVA to shell material is 2%, the phase change latent heat of modified microPCM increases by 16.9% and the cracking ratio deceases by 68.6%.Thirdly, n-dodecanol was used to be encapsulated by miniemulsion polymerization with main monomers of MMA, co-emulsifier of n-hexadecane (HD) and polymerisable emulsifier of DNS-86, and uniform phase change thermal storage nanocapsules with high phase change latent heat and suitable phase change temperature were prepared with PMMA as shell and n-dodecanol as core. The influence of emulsifier, co-emulsifier, initiator, co-monomer and feeding mass fraction of n-dodecanol on the structure and properties of nanocapsules were studied by using DSC, TG, TEM, FTIR, and laser particle diameter analyzer and the formation mechanism of nanocapsules were discussed. It's found that application of co-emulsifier n-hexadecane with the way of adding into water phase is helpful for the encapsulation of n-dodecanol with PMMA. The optimal preparation condition of PMMA nanocapsules containing n-dodecanol is that the mass ratio of polymerisable anion emulsifier DNS-86 to oil phase is 3%, the mass ratio of co-emulsifier n-hexadecane to oil phase is 2%, the mass ratio of oil-soluble initiator azobisisobutyronitrile (AIBN) to total monomer is 2%, and the feeding mass fraction of n-dodecanol is 48%. Under the condition, nanocapsules with the phase change latent heat of 98.8J/g, phase change temperature of 18.2℃, encapsulation efficiency of 82.2% and main diameter range of 50-100nm are obtained. Hydrophilic co-monomer acrylamine (AM) and acrylic acid (AA) is helpful for encapsulation of PCM n-dodecanol. When mass ratio of AM to total monomer is 4%, the phase change latent heat of nanocapsule and encapsulation efficiency of n-dodecanol reach to the highest value of 109.3J/g and 91.6%, respectively.Finally, composite gypsum board and waterborne acrylate composite coating with the function of phase change thermal storage were prepared by incorporating microcapsules and nanocapsules containing n-dodecanol into ordinary gypsum board and waterborne acrylate coating, respectively. The influence of phase change thermal storage microcapsules and nanocapsules on the thermal storage properties, temperature adjusting performance, and heat-insulating ability of composite gypsum board and waterborne acrylate composite coating were studied. Architecture model was made with gypsum boards to stimulate the variation of indoor temperature of the model under the light of iodine tungsten lamp and test the application effect of phase change thermal storage gypsum board and waterborne acrylate coating. With the increasing of the contents of phase change thermal storage microcapsules and nanocapsules, the phase change latent heat and thermal storage effect of phase change thermal storage gypsum board and phase change thermal storage waterborne acrylate coating increase. When the mass content of microcapsules in gypsum board is 30%, the phase change latent heat of composite gypsum board is 45.6J/g, the time of temperature increasing from 10℃to 48℃increases by 130% and the time of temperature decreasing from 48℃to 10℃increases by 120%, and the indoor temperature of model with composite gypsum board is 4℃lower than that of model with ordinary gypsum board. When the mass content of nanocapsules in waterborne acrylate coating is 50%, the phase change latent heat of waterborne acrylate composite coating is 54.3J/g, the temperature of composite acrylate coating is 2.5℃lower than that of coating without thermal storage nanocapsules, and the indoor temperature of model with waterborne acrylate composite coating-gypsum board is 2.5℃lower than that of model with ordinary gypsum board.