Expansion space and thermal stability of microencapsulated n-octadecane

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 degrees 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 heat-treated at temperatures higher than 180 degrees C, Tm, Delta Hm, Tc, and Delta 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 30.0-40.0 vt% of cyclohexane have the highest thermal stabilities, with 230 degrees C and 289 degrees C in air and nitrogen atmosphere, respectively. The thermal stable temperatures are approximately 67 degrees C and 102 degrees 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. (c) 2005 Wiley Periodicals, Inc.