Effects of parameters of the shell formation process on the performance of microencapsulated phase change materials based on melamine-formaldehyde

Abstract

Shell formation process is a very vital step in the fabrication of melamine-formaldehyde microencapsulated phase change materials (microPCMs). In this research, the effects of parameters in this process, including system pH value, initial temperature and dropping rate of the prepolymer, were studied systematically to prepare microPCMs with potential application in thermo-regulated textiles. The various properties of obtained microcapsules were investigated by scanning electron microscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Revised encapsulation efficiency (RE) was calculated with a new method based on the results of DSC and TGA, and was used to characterize the encapsulation efficiency of the microPCMs. The experimental results indicated moderate pH, such as 4.6, benefited the formation of regular spherical capsules with high encapsulation efficiency. The products prepared at low pH were almost irregular aggregates, while the microcapsules formed at high pH were easily damaged. It was found that the microcapsules synthesized at a lower initial temperature, such as 40℃, presented poor appearance and low encapsulation efficiency. The suitable initial temperature for shell formation was about 75℃. With the decrease of the dropping rate, the surface morphology of microPCMs showed obvious improvement, while the increment speed of RE was slow. The medium dropping speed could be selected to ensure the encapsulation efficiency as well as the productivity in this experiment. It was also found that RE could reflect the effects of these parameters more accurately in comparison with the conventional apparent encapsulation efficiency (AE).