Structural Design,Preparation And Thermal Performance Regulation Of Phase Change Microcapsules

Phase change materials(PCM)can automatically store and release energy according to the change of ambient temperature,and can maintain the ambient temperature within a certain range.According to this characteristic,PCM can be applied to many fields,such as building energy saving,solar energy storage and temperature regulating textiles.PCM can not only eliminate peak and fill valley to improve energy utilization efficiency,but also provide a suitable working microenvironment for human body and instruments.Organic PCM has attracted extensive attention due to its small volume change,high enthalpy value and variety.However,organic PCM also brings problems such as easy leakage and poor compatibility,which limit the application of PCM to a certain extent.PCM microencapsulation can effectively solve the above problems.By in situ polymerization to synthesize the high cladding rate,high core wall than the phase change microcapsules,and in order to solve the problem of phase change microcapsules supercooling degree and widen the phase transition temperature range of phase change microcapsules,and to design of core material,mixing with different phase transition temperature range of phase change microcapsules,improves the phase change microcapsules in different areas of application value.Finally,through the design of the shell wall,graphene oxide(GO)was introduced to prepare the composite shell wall phase change microcapsule,which effectively improved the temperature sensitivity of the phase change microcapsule.Specific research contents are as follows.Firstly,paraffin A with melting point of 28 ? was used as core material,melamine formaldehyde(MF)was used as wall material,and phase change microcapsules were prepared by in-situ polymerization.Through the study,it is found that the phase change microcapsule formed by the microencapsulation of paraffin A has good thermal property and sealing property,which can not only effectively prevent the leakage of paraffin A,but also show excellent temperature control performance.In the third chapter,the influence of polymerization parameters on the morphology,thermal properties and sealing properties of microcapsules was studied.The effects of polymerization parameters on the structure and application properties of microcapsules were revealed.The results show that the core-wall ratio and monomer ratio have great influence on the morphology,thermal properties and sealing performance of microcapsules.If the core wall ratio is too small or too large,the encapsulation rate of the microcapsule decreases,and the sealing performance of the microcapsule decreases with the increase of the core wall ratio.When the core wall ratio is 5.5:1,the encapsulation rate of the microcapsule reaches the highest,and the sealing performance is relatively good.Appropriate increase of formaldehyde/melamine ratio can improve the toughness of the shell wall of microcapsules,but too large ratio will lead to the reduction of the degree of cross-linking of the shell wall of microcapsules,thus reducing the sealing performance of microcapsules.When the ratio of formaldehyde/melamine is 3:1,microcapsules have the best sealing property and the highest coating rate.Under the optimized conditions,phase change microcapsules with high coating rate,good sealing and thermal properties can be prepared.In the fourth chapter,the binary core phase change microcapsules were prepared by remixing low melting point paraffin A with high melting point paraffin B(53 ?),and the influence of the ratio of binary core material on the thermal properties of the microcapsules was studied.It is found that the microencapsulation of the binary core material does not affect the phase transformation characteristics of the binary core material,and the microcapsule undercooling degree decreases with the increase of the proportion of paraffin B.When the ratio of paraffin A to paraffin B is 7:3,the microcapsule undercooling degree decreases by 70.5%.With the increase of dosage of paraffin B,binary phase transition temperature range of the core material also will increase,when the rate of paraffin wax and wax B is 3:7,dual core material microcapsule has the obvious phenomenon of double melting peaks,the widest range of phase change temperature and and at this point the dual core material of microcapsule has good heat preservation performance at low temperature stage,has the very good absorption of heat in high temperature stage.Finally,the effect of GO on the thermal conductivity of phase change microcapsules was studied.With the addition of GO,the encapsulation rate of microcapsules decreased,but the lowest encapsulation rate could be maintained at85.6%.The 30wt% microcapsule/epoxy resin composite was analyzed by thermal infrared imaging.The microcapsules showed good temperature regulation performance,and the nano-composite phase change microcapsules with GO added were more sensitive to the temperature change.Through the study in this paper,the corresponding relationship between the polymerization parameters and the particle structure and application performance of the microcapsule was clarified,and the morphology and thermal properties of the microcapsule were effectively adjusted.Reasonable design of core material can effectively reduce the degree of supercooling of microcapsules,and can also broaden the range of phase change temperature of microcapsules,enhance the application performance of microcapsules.Finally,the shell wall of the microcapsule was designed to effectively improve the sensitivity of the microcapsule to the temperature response.The results of this paper have a good reference value for the preparation of microcapsules with high coating rate,good phase transition temperature/temperature range and sensitive temperature response.