Emulsion stability and cross-linking of PMMA microcapsules containing phase change materials

The microencapsulation of paraffin as a phase change material (PCM) using poly methyl methacrylate (PMM) as a shell was investigated by means of suspension polymerization. The increase in the emulsion stability by using mixed surfactants was studied. It was observed that a mixed surfactants system induces long-term emulsion stability and monodisperse droplets size distribution. Also, the use of mixed surfactants reduces significantly the buckles in microcapsules significantly. The effect of using pentaerythritol tetraacrylate (PETRA) as a cross-linker agent on the diverse properties of PCM microcapsules such as morphology, energy storage density, shell permeability and thermal stability has been investigated. Adding PETRA to the system improves the surface morphology and produces microcapsules with a much higher PCM content. For example, the core/shell mass ratio of 2:1 produces microcapsules with regular spheres having smooth surfaces. TGA results show two steps thermal degradation of microcapsules. The mass loss was similar to the non-encapsulated PCM until all the PCM was dissipated (step 1). Following that the microcapsules experienced lower rate of mass loss of the shell, which depends on its thickness (step 2).