Preparation And Crystallization Behavior Of N-octadecane@amino Resin Microcapsules

Phase change materials(PCMs)are materials that can absorb or release heat in the process of phase transition,so as to achieve the function of thermal energy storage and temperature regulation.The latent heat of phase change materials can be used to store and utilize energy,which has a wide range of applications in construction,cold storage,aviation and other fields.However,there are still some problems in the use of phase change materials:inorganic phase change materials will appear supercooling phenomenon and easy to occur phase separation,organic phase change materials volume change obviously and easy to leak.These shortcomings bring limitations to the large-scale production and application of phase change materials.The phase change material was made into microcapsules so that the phase change process was always in the microcapsule,it is a simple and effective way to modify phase change materials.In this paper,n-Octadecane @ MF resin microcapsules were successfully prepared by in-situ polymerization using n-Octadecane as the core material and melamine formaldehyde(MF)resin as the wall material.The microcapsules were in regular spherical shape,with uniform particle size and good dispersion.The results of DSC test showed that the encapsulation rate of microcapsules was 61.09%,and the microcapsules still had good energy storage capacity.TG test showed that the initial weight loss temperature of n-Octadecane in microcapsules was about 10 ℃ higher than that of nOctadecane,indicating that microencapsulation had a good protective effect on nOctadecane.However,the nucleation ability of the microcapsules was poor and the particle size was small,resulting in the supercooling degree of the microcapsules did not decrease compared with n-Octadecane,but slightly increased.By using long chain fatty acids eicosanoic acid and docosanoic acid as nucleating agents to study the nucleation and crystallization process of microcapsules.It was found that the addition of eicosanoic acid and docosanoic acid had no effect on the coating process of microcapsules.However,with the increase of fatty acid content,the dispersion of microcapsules became worse.Through XRD test,it can be seen that the orientation of microcapsules with fatty acids is more regular,and the crystallinity of microcapsules with docosanoic acid is higher.The results of DSC showed that when0.1wt% eicosic acid was added,the proportion of α peak was the largest,which was63.9%.Then,with the increase of eicosic acid content,the proportion of α peak decreased gradually,indicating that the addition of eicosic acid had an adverse effect on the heterogeneous nucleation of microcapsules.TG results showed that there was no significant difference between the microcapsules without eicosic acid,indicating that the addition of eicosic acid had no obvious effect on the thermal stability of microcapsules.The proportion of α peak in microcapsules added with docosanoic acid increased with the increase of docosanoic acid content.When 1.2wt% of docosanoic acid was added,the proportion of α peak was the largest.The decomposition temperature of the wall material was about 27 ℃ higher than that of the microcapsules without eicosic acid,which indicated that the addition of docosanoic acid not only promoted the heterogeneous nucleation of microcapsules,but also improved the thermal stability of the wall materials.The crystallization behavior of microcapsules was studied,Ozawa method can be used to describe the non isothermal crystallization behavior of microcapsules with eicosic acid.Because of the complex crystallization process,the microcapsules with docetanoic acid can not be described by Ozawa method,but by Mo method.