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

Abstract

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 O2‐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 0.2 g 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 4000 rpm for 5, 10, and 20 min decreased by 74, 72, and 60%, respectively, compared with that of the microPCMs without modified CNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45269.

Design of a novel multilayer low‐temperature protection composite based on phase change microcapsules

“…To prevent the leakage and control the volume change of C18 during phase transition process, phase‐change microcapsules (microPCMs) have been developed and used. MicroPCMs have a stable core–shell structure and the PCMs as core surrounded by organic/inorganic shell . MicroPCMs embedded in textiles or flexible polymer matrices have the function of thermal energy storage (TES).…”

Photo‐thermal conversion and heat storage characteristics of multi‐walled carbon nanotubes dispersed magnetic phase change microcapsules slurry

“…As illustrated in Figure 8A, octadecane, PCMs and MPCMs, accompanied by almost identical phase change properties, showed a single endothermic peak during melting process, suggesting that the encapsulated phase change material did not react with the shell material and the surfactant 34 . However, according to Figure 8B, two exothermic peaks were observed for all the PCMs during solidifying process, which was attributed to the heterogeneous and homogeneous crystallization of octadecane inside microcapsules 39 . Moreover, the supercooling phenomenon of octadecane can also be found from melting and crystallizing processes.…”

“…This was because octadecane was encapsulated into MPCMs by the shell serving as a physical protective barrier, which slowed the escape of volatile products during the heating process, 47 thus boosting the thermal stability of MPCMs. In addition, the second degradation stage began at about 360°C, and the weight loss was mainly attributed to the pyrolysis of MF resin and the thermal decomposition of octadecane inside some MPCMs with thicker MF resin shell because they cannot escape until the shell started to decompose 39,48 …”

“…The phase change properties of PCMs and MPCMs as well as the heat capacity of slurry were assessed by a differential scanning calorimetry (DSC; DSC25, TA, USA), where the temperature range was from −180 to 725°C, the temperature accuracy was ±0.1°C, the temperature precision was ±0.01°C and the enthalpy precision was ±0.1%. The encapsulation efficiency of microcapsules was evaluated by Equation ) 39 : where E is the encapsulation efficiency (%), ΔH m,microcapsules and ΔH c,microcapsules the melting and crystallizing enthalpy of microcapsules (g J −1 ), respectively, ΔH m,octadecane and ΔH c,octadecane the melting and crystallizing enthalpy of octadecane (g J −1 ), respectively.…”

Improvements in thermal conductivity and mechanical properties of HDPE/nano‐SiC composites by the synergetic effect of extensional deformation and ISBS

“…Due to their high thermal conductivity and low coefficient of thermal expansion, thermal conducting fillers can be used as heat‐conducting bridges in HDPE . However, in general, the addition of high content of thermal conducting fillers often decreases the mechanical properties of the composites . If nanoparticles are uniformly dispersed in the matrix, the composites' mechanical properties and thermal conductivity can be improved simultaneously …”