5.0–50.0 vt% of cyclohexane was mixed with 95.0–50.0 vt% of n-octadecane as the oil-phase during the emulsion process in the in situ polymerization of melamine-formaldehyde. By heat-treating the microcapsules in an oven at 100°C, the cyclohexane was removed and expansion space was formed inside the microcapsules. The microcapsules were characterized by using FTIR, SEM, DSC, TGA, and gas chromatography. When the microcapsules are heattreated at temperatures higher than 180°C, Tm, △Hm, Tc, and △Hc of the microcapsules decrease. The attenuation of enthalpy of the microcapsules containing expansion space is obviously lower than that of the control sample, however. The permeability of the microcapsule shell decreases with the increase of cyclohexane content. There is a maximum between the thermal stabilities of the microcapsules and the cyclohexane contents. The microcapsules synthesized with 30.0-40.0vt% of cyclohexane have the highest thermal stabilities, with 230°C and 289°C in air and nitrogen atmosphere, respectively. The thermal stable temperatures are approximately 67°C and 102°C higher than that of the control sample, respectively. The expansion space inside the microcapsules allows the n-octadecane to expand in the temperature rising process and exert lower pressure to the shell, therefore keeping the shell intact and increasing the thermal stabilities of the microcapsules.

Microencapsulated phase change materials (MicroPCMs) used as thermal insulating coating and fabrics are usually required to have a prominent thermal stability and a lower permeability.MicroPCMs with a prominent thermal stability and a lower permeability were fabricated by feeding an appropriate content of cyclohexane into n-octadecane followed by heat-treatment at a suitable condition. Microcapsules containing 18-19% reserved expandable space are synthesized at 30-40wt.% cyclohexane in the oil phase, which have a highest thermal resistant temperature -270 ◦C, and a lower permeability, less than 1.2%. The weight loss of microcapsules is mainly attributed to the leakage of n-octadecane from some broken capsules, so improving their uniformity can efficiently enhance their thermal stability and lower the permeability.

A series of microcapsulescontaining n-octadecane with a urea-melamine-formaldehyde copolymer shell were synthesized by insitu polymerization. The surface morphology, diameter, melting and crystallization properties, and thermal stability of the microcapsules were investigated by using FTIR, SEM, DSC, TGA and DTA. The diameters of the microcapsules are in the range of 0.2-5.6µm. The noctadecane contents in the micro-capsules are in the range of 65-78wt%. The mole ratio of urea-melamine has been found to have no effect on the melting temperature of the microcapsules. Two crystallization peaks on the DSC cooling curve have been observed. The thermal damage mechanisms are the lique-fied n-octadecane leaking from the microcapsule and breakage of the shell due to the mismatch of thermal expansion of the core and shell materials at high temperatures. The thermal stability of materials can be enhanced up to 10℃ by the copo-lymerization of urea, melamine and formaldehyde in a mole ratio 0.2:0.8:3. The thermal stability of 160℃ heat-treated microcapsules containing 8.8% cyclohexane can be further enhanced up to approxi-mately 37℃.

以正二十烷、 聚乙烯和乙丙橡胶等为原料经熔融挤出，制成正二十烷含量 10%~65%的共混切粒。以正十八烷微胶囊和聚乙烯为原料经熔融挤出， 制成微胶囊含量 10%~60%的共混切粒。采用差示扫描量热仪和熔融指数仪测试了多种组成切粒的相变性能和流动性能。切粒的热焓随相变材料含量的增高而增大，含65正二十烷的切粒的热焓为160 J/g左右，含有6 0 wt微胶囊的切粒的热焓为70 J /g左右。切粒的熔融指数随相变材料或相变材料微胶囊添加量的增高呈现指数增大或反S曲线的形式。