Improvements in the thermal conductivity and mechanical properties of phase-change microcapsules with oxygen-plasma-modified multiwalled carbon nanotubes

The thermal properties and mechanical properties are the key factors of phase-change microcapsules (microPCMs) in energy-storage applications. In this study, microPCMs based on an n-octadecane (C18) core and a melamine-urea-formaldehyde (MUF) shell supplemented with O-2-plasma-modified multiwalled carbon nanotubes (CNTs) were synthesized through in situ polymerization. Meanwhile, two different addition methods, the addition of modified CNTs into the emulsion system or into the polymer system, were compared and examined. Scanning electron microscopy micrographs showed that the microPCMs were spherical and had a broadened size distribution. Fourier transform infrared testing demonstrated that the modified CNTs did not affect C18 coated by MUF resin. The results indicate that the thermal conductivity and mechanical properties of the microPCMs were remarkably improved by the addition of a moderate amount of modified CNTs, but the heat enthalpy and encapsulated efficiency decreased slightly. Moreover, the thermal conductivity and mechanical properties of microPCMs modified with CNTs directly added to the polymer system were superior to those with CNTs added to emulsion system. In particular, when 0.2g of modified CNTs were added to the polymer system, the thermal conductivity of the microPCMs was improved by 225%, and the breakage rates of the microPCMs at 4000rpm for 5, 10, and 20min decreased by 74, 72, and 60%, respectively, compared with that of the microPCMs without modified CNTs. (c) 2017 Wiley Periodicals, Inc.