Preparation, Performance And Application Of Alginate-paraffin Phase Change Microcapsules

Phase change materials can store heat by its characteristic of absorbing or releasing large heat in its phase transition process. So it is widely used in energy storage. As a solid-liquid phase change material in common, paraffin have moderate heat storage density and low cost, which can be largely used for energy storage. However, using paraffin alone is easy to leakage, phase separation, volume expansion, corrosion, poor thermal stability and so on. These can be effectively solved that we use microencapsulation technology in the paraffin particles by coating a stable membrane. This is of great importance for improving the effect of application and expaning application field of phase change materials.In this paper, alginate-paraffin phase change microencapsules were prepared by emulsification-gelation, which combination the internal curing and the external curing with sodium alginate as wall material and paraffin wax for core material. And used chitosan secondary coating alginate-paraffin phase change microencapsule. The effect of emulsion systems, the dosage of raw materials and reaction conditions during the preparation on alginate-paraffin phase change microencapsules were investigated by using optical microscopy to observe the morphology of microcapsules and calculating the loading efficiency of microcapsules. The surface morphology, chemical composition, thermal properties, size distribution and intensity of microcapsules were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning differential scanning calorimetry (DSC) and laser particle size analyzer and centrifugal force field, respectively. The prepared microcapsules were used in building materials. And tested the thermal constants and compressive strength of phase change energy storage composite building materials by thermal constants Tester and universal material testing machine, which studying the effect of microencapsules on the thermal performance and strength of phase change energy storage compound building materials. The main conclusions are as follows:1. The effect of emulsion type, proportion and dosage, the dosage of raw materials and reaction conditions during the preparation on alginate-paraffin phase change microencapsules were investigated. The results show that:When Tween-80 and Span-80 mixture with volume ration 6:4 as emulsifier, and the dosage of emulsifier is 12 mL (in 100 mL), mass ratio of sodium alginate and paraffin 1:1, CaCO3 0.75 g (per 3 g sodium alginate), emulsifying time 60 min, internal gelation time 30 min, external gelation time 30 min, stirring speed 600 r/min, the good spherical shape microcapsules are obtained, with an average diameter is about 71μm, the particle size distribution in 10-120μm, and the loading efficiency is 86.24%. DSC analysis reveals that the phase transition temperature of microencapsules is 52.07℃and the latent heat is 64.52 J/g.2. Using chitosan secondary coating alginate-paraffin phase change microencapsule to modify microcapsule wall, and found that:when the chitosan concentration is 0.8% and dip it in the chitosan solution 2h, the good spherical shape microcapsules are obtained, with an average diameter is about 91μm, the particle size distribution in 20-160μm and the wax content of 32.25%. DSC analysis reveals that the phase transition temperature of microencapsules is 52.69℃and the latent heat is 45.42 J/g. Compare with the microcapsules before modified, it have more smooth spherical shape, better compactness and mechanical strength is increased to 3 times the original.3. The effect of microcapsule on the thermal performance and strength of phase change energy storage composite building materials were investigated by testing its thermal constants and compressive strength. We found:with the increase of the content of microcapsule, the thermal conductivity and the thermal diffusivity of phase change energy storage composite building materials decreases, but the heat capacity increases in 45℃. This indicates that phase change energy storage composite building materials can play better the performance of the thermostat. The compressive strength of phase change energy storage composite building materials along with the increasing content of microcapsules decreased. when the content of microcapsules is 5%, the compressive strength of phase change energy storage composite building materials mixed with chitosan modified microcapsules 10% larger than materials mixed with sodium alginate-paraffin phase change microencapsules. This shows that the compactness of phase change energy storage composite building materials mixed with chitosan modified microcapsules is better, and internal structure more uniform.