Study On Preparation And Properties Of Paraffin Microencapsulated Phase Change Materials

In recent years,the energy crisis and environmental pollution have become a common problem faced by human beings.Phase change materials?PCMs?can achieve the purpose of storing and releasing thermal energy during the phase change process.The use of PCMs has become effective means to improve energy efficiency and reduce environmental problems.Solid-liquid phase change materials have a wide range of phase change temperature,high heat storage density,economy and environmental protection,and have become the current research hotspot.But solid-liquid phase change materials have the problem of easy leakage during using.A common solution is preparing microencapsulated phase change materials?MPCMs?through microencapsulation technology.In this paper,paraffin microcapsules were prepared to use organic and inorganic materials as wall materials,then composite materials were prepared by compounding microcapsules and phosphogypsum,and the properties of microcapsules and composite materials were studied.?1?Phase change microcapsules were prepared by using the complex coacervation method with gelatin and sodium alginate as the wall material and paraffin as the core material.The effects of gelatin/sodium alginate mass ratio?wall material ratio?,core/wall mass ratio?core-to-wall ratio?,volume of Ca Cl₂ solution,emulsification time,complex coacervation time and volume of HAc solution on the encapsulation rate and encapsulation efficiency of microcapsules were investigated,and the structure,morphology and thermal properties of the microcapsules were characterized and analyzed.The results showed that the optimum technological conditions were as follows,the wall material ratio was 3:0.75,the core-wall ratio was 1.5:1,the volume of Ca Cl₂ solution was 50 m L,the emulsification time was 60min,the complex coacervation time was 30 min,and the volume of HAc solution was 8 m L.Under these conditions,the encapsulation rate and encapsulation efficiency of the obtained MPCM were 82.12%and 83.61%,respectively.MPCM was approximately spherical in structure,but there were adhesion between microcapsules.The results of TGA showed that microcapsules had good thermal stability.?2?Phase change microcapsules with Zn O as wall material and paraffin as core material were prepared by in-situ precipitation method.The effects of emulsifier dosage,paraffin dosage,adsorption time,emulsification rate,titration time of 100m L zinc acetate solution?titration time?on the encapsulation rate and encapsulation efficiency of microcapsules were investigated,and the structure,morphology and thermal properties of the microcapsules were characterized and analyzed.The results showed that the optimum technological conditions were as follows,the emulsifier dosage was 1.4 g and the paraffin dosage was 10 g,the adsorption time was 180 min,the emulsification rate was 800 r/min,and the titration time was 60 min.Under these conditions,the encapsulation rate and encapsulation efficiency of the obtained MPCM were 41.20%and 40.06%,respectively.The melting temperature and latent heat of melting were 59.3°C and 63.62 J/g,respectively.The microencapsulation process of paraffin did not change the chemical structure of paraffin and Zn O.MPCM was spherical structure with rough surface,and the microencapsulation of paraffin had a protective effect on paraffin.?3?According to the results of TGA and compressive strength,the pretreatment conditions of phosphogypsum were determined as follows:constant temperature drying at 160°C for 3 h,and the dosage of retarder was 0.04%of dosage of phosphogypsum.The prepared gelatin/sodium alginate-coated paraffin phase change microcapsule was directly blended with the treated phosphogypsum to obtain the phase change composite material for energy storage using phosphogypsum as matrix.The results showed that with the increase of the mixing amount of MPCM,and the latent heat of the phase change of the composite material also increased,but the compressive strength decreased.MPCM and phosphogypsum were simply physical mixing without chemical changes,and the prepared composite material had good properties of heat storage and release.