Preparation And Application Of Polyurea PCM Microcapsules

Phase change materials can change the bulk structure through variation of the orderly structure of their own material molecules under a certain condition.At the same time,they can absorb or release considerable heat during the proceed of structure changing.The feature of transferring and storing heat can be applied in regulating temperature,storing energy,alleviating the contradiction between energy supply and demand in time and space and improving the efficiency of energy utility.Organic solid-liquid energy storage phase change materials have attracted widespread attention from researchers due to their smaller phase change volume changes and higher latent enthalpy.However,phase transitions are accompanied by leakage and low thermal conductivity,which has always limit the application of solid-liquid phase change material.The microencapsulation of phase-change materials was conducive to improve the properties of phase change materials and avoid the leakage.In this paper,aliphatic esters were developed as a new type of organic solid-liquid phase change energy storage materials,and a new phase change microcapsule of polyurea-coated esters was synthesized by interfacial polymerization.Finally,the mixed solution of microcapsules and polyurethane were compounded into fabric to acquire thermos-regulating fabric by means of coating and padding.The specific research content is as follows:1.In order to obtain organic phase change storage materials with suitable phase transition temperature,high enthalpy value and high thermal stability,this study prepared aliphatic esters with different chain lengths,which have good crystal structure.The phase change temperature range is 0?-55?,the enthalpy is above 150 J/g,and the longer the chain length,the higher the phase transition temperature is.The initiative thermal weight loss temperatures of this series of ester phase change materials are all above 190?,and the longer the molecular chain,the higher the thermal weight loss temperature is,which stands for better thermal stability.Among them,lauric dodecanoate was selected as the object of optimization process research because of its suitable phase transition temperature and high enthalpy value.The effects of reaction temperature,catalyst type,and catalyst concentration on esterification were explored deeply through orthogonal experiments,and a set of process routes in fabricating high-purity lauric dodecanoate was established.2.Microencapsulation of lauric dodecanoate by polyurea through interfacial polymerization.Based on the good compatibility between esters and isocyanate monomers,this experiment abandoned the traditional method of adding a co-solvent in the process of microencapsulation of phase change materials with a polyurea shell,and the polyurea microcapsules containing lauric dodecanoate were successfully prepared in the reaction without co-solvents.The parameters such as emulsifier type,emulsifier concentration,emulsification stirring rate,reaction temperature,and core-shell ratio were adjusted.The influence of these parameters on the experiment was analyzed and the better experimental conditions were summarized.The results of thermal performance characterization of the obtained polyurea phase change microcapsules showed that the melting phase transition temperature range of the microcapsules was 18-35?,and the phase change enthalpy varied from 100 J/g to 140 J/g depending on the core-shell ratio.The crystallization phase transition enthalpy was similar to the melting enthalpy.The initial thermal weight loss temperature of the microcapsules exceeds 200?,which shows better thermal stability than traditional solid-liquid organic materials.The thermal conductivity test at room temperature found that the thermal conductivity of the lauric dodecanoate phase change material was 0.28 W/mK,which is higher than that of ordinary organic phase change materials;the maximum thermal conductivity of the microcapsules could reach 0.21 W/mK.The Infrared thermogravimetry revealed the process of interfacial polymerization reaction synthesizing polyurea.Due to the good compatibility of the ester phase change material and isocyanate monomers,some oligomers formed in the inner of micelle remained in the core material and could not be further polymerized.After 100 thermal cycles,the microcapsules still maintain latent heat which is similar to the initial state,indicating that the wall of microcapsules has good stability and prevent the core material from leakage,and the microencapsulated phase change materials possess good durability.3.The above phase-change microcapsules and polyurethane were mixed and compounded on the fabric to prepare thermo-regulating fabric.A series of modified fabrics were prepared by coating and padding the fabrics with solution containing different content of microcapsule.The test found that the modified fabric had a melting endothermic phase transition behavior at about 33? and a crystal exothermic phase transition behavior at about 23?.With the increase of the content of microcapsules in the mixed solution,the enthalpy value range of the coated fabric is 18 J/g-25 J/g;the enthalpy value range of the padding fabric is 9 J/g-16 J/g.The test results of the temperature regulation performance showed that the fabric could delay the temperature descending rate during a certain period in a temperature changing environment.