Microencapsulated n-alkanes as energy-storage materials have promising application prospects. The microcapsules containing 100-50 wt% of n-octadecane, 0-20 wt% of paraffin and 0-30 wt% of cyclohexane were synthesized by in-situ polymerization using melamine-formaldehyde polymer as shell. Cyclohexane was removed after heat-treated the microcapsules at 100℃. The morphologies, cell parameters, phase change properties, thermal stable temperatures of these microcapsules were examined. The diameters of these microcapsules are lower than 5 μm. The effect of paraffin in the microcapsules on the cell parameters of n-octadecane is negligible. The paraffin is effectively used as a nucleating agent to decrease the degree of supercooling. The melting enthalpy is decreased from 132 J/g to 111 J/g due to the increase of the cyclohexane contents. The thermal stable temperature is enhanced 6-16℃ after heat-treated the microcapsules at 160℃ for 30 min.
Acrylonitrile-methyl methacrylate copolymer was synthesized in aqueous solution by Redox. The copolymer was mixed with 10-40 wt% of microencapsulated n-octadecane (MicroPCMs) in water. Copolymer films containing MicroPCMs were cast at room temperature in N, N-Dimethylformamide solution. The copolymer of acrylonitrile-methyl methacrylate and the copolymer films containing MicroPCMs were characterized by using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analyzer (TG), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), etc. The microcapsules in the films are evenly distributed in the copolymer matrix. The heat-absorbing temperatures and heat-evolving temperatures of the films are almost the same as that of the MicroPCMs, respectively, and fluctuate in a slight range. In addition, the enthalpy efficiency of MicroPCMs rises with the contents of MicroPCMs increasing. The crystallinity of the film increases with the contents of MicroPCMs increasing.
