Preparation and characterization of multifunctional phase change material microcapsules with modified carbon nanotubes for improving the thermal comfort level of buildings

•DOPO-modified multi-walled carbon nanotube (d-CNT) was successfully synthesized.•The d-CNT was embedded into the phase change material microcapsule (d-c-MPCM).•The d-c-MPCM shows excellent thermal stability and heat transfer performance.•The d-c-MPCM was doped into the rigid polyurethane foam (RPUF/d-c-MPCM).•The RPUF/d-c-MPCM exhibits good flame retardancy and temperature regulation ability. Excellent temperature regulation and flame retardancy are the keys to the wide application of phase change material microcapsules (MPCMs) in building fields. In this study, the flame retardant carbon nanotube (d-CNT) modified by 9,10-dihydro-9-oxa-10 phosphaphenanthrene-10-oxide (DOPO) was successfully embedded into the MPCM (d-c-MPCM) by in-situ polymerization. The scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) experimental results showed that DOPO was grafted onto the carbon nanotube (CNT) surface and the d-CNT was successfully added to the microcapsule with a particle size of 150 nm. The d-c-MPCM displayed better thermal stability than other MPCMs due to the presence of CNT and DOPO, which was demonstrated by thermogravimetric analysis (TGA) and micro-combustion calorimeter (MCC) tests. The differential scanning calorimetry (DSC) results of MPCMs showed that the phase transition temperature and latent heat of d-c-MPCM are 31.14 ℃ and 103.21 J/g, respectively. The flame retardancy and temperature control ability of microcapsules were detected by adding d-c-MPCM to the rigid polyurethane foam (RPUF/d-c-MPCM). In the cone calorimeter test, RPUF/d-c-MPCM significantly reduced the heat release and increased the residual mass of foam during combustion. These improvements in thermal stability and flame retardancy resulted from the synergistic effect of CNT and DOPO on the formation of char layer. Finally, the small room model and infrared thermal imager results proved that RPUF/d-c-MPCM made indoor temperature fluctuation more gentle, and the maximum indoor temperature is only 26.6 ℃. These unique properties will significantly facilitate the practical application of the MPCMs in building insulation materials.