Preparation And Characterization Of Micro PCMs For Stearic Acids

In the previous researches of MicroPCMs, almost all of them are are using urea formaldehyde resin, melamine resin and phenolic resin as wall material, using nonpolarity paraffin as the core material. These microcapsules are containing formaldehyde and can’t tolerant with alkali. The core material is expensive and not easy to get. In this paper, two kinds of wall material MicroPCMs were prepared using phase change material of stearic acid(SA) as the core material, respectively with polystyrene(PS) and calcium carbonate(CaCO3) as wall material.The MicroPCMs were prepared using stearic acid as the core material, polystyrene(PS) as wall material by in-situ polymerization. The influence on stearic acid MicroPCMs preparation of key factors, including type and content of emulsifier and initiator, core/wall ratio, cross-linking agent content, dispersant content, reaction temperature and time, as well as stirring speed were systematically evaluated. The morphology, chemical structure, phase transition temperature and enthalpy, thermal properties of the stearic acid MicroPCMs were investigated by scanning electron microscopy(SEM), fourier transform infrared spectroscopy(FT-IR), differential scanning calorimetry(DSC) and thermal gravimetric analysis(TGA). The results show that the best conditions for preparation of MicroPCMs were: the core/wall ratio is 2:1, the dispersing agent PVP as 3.75% of the wall, the emulsifier 1631 as 2.5% of the core, the cross-linking agent PETRA as 18.75% of the wall, the initiator K2S2O8 as 5.63% of the wall, reaction for 4h at 80℃. In this case, the embedding rate is 61.82%. The microscope and SEM images show that the microcapsules are spherical with the structure of core-shell. As the agitation speed raising from 600 rpm to 1000 rpm, the particle size of the microcapsules reducing from 81.13μm to 5.83μm. The phase transition temperature of stearic acid MicroPCMs prepared is similar to stearic acid, the melting temperature interval for 53.5-63.2℃, the solidification temperature interval for 51.8-45.3℃, and the average value on heat is 116.75J/g. The TGA curves show that polystyrene wall material has a certain protective effect on the core material of stearic acid.The inorganic wall MicroPCMs were prepared using stearic acid as the core material, CaCO3 as wall material. The influence on MicroPCMs preparation of key factors, including core/wall ratio and content of emulsifier were systematically evaluated. Then, the FIRT, SEM, PSD, DSC and TAG were measured. The results show that the best conditions for preparation of MicroPCMs were: the core/wall ratio is 3:1, the emulsifier 1631 as 0.8% of the core, The agitation speed was 400 rpm, reaction for 0.5h at 70℃. In this case, the embedding rate is 76.94%. The SEM images show that the microcapsules were spherical, and the PSD measured that the particle size of microcapsule is 0.59μm. the FIRT curves show that microcapsules are core-shell structure. The phase transition temperature of stearic acid MicroPCMs prepared is more than stearic acid, the melting temperature interval for 116.5-135.8℃, the solidification temperature interval for 123.5-114.5℃, and the average value on heat is 145.30J/g. The TGA curves show that the CaCO3 wall material has good insulation properties.This paper compares two kinds of microcapsules, PS / SA MicroPCMs and CaCO3 / SA MicroPCMs, between preparation and thermal properties. Compared with PS / SA microcapsules, CaCO3 / SA microcapsules are more economical and environmentally friendly, have higher embedding rate and heat storage capacity, but poor thermal conductivity and the particle size is not easy to control.