Changes in microcapsules under heating: the effect of particle size on thermal stability and breakability

In this work, the effect of particle size on the thermal stability and bursting phenomenon of the microcapsules with a melamine resin shell was studied. The heat-induced change process and mechanism of the prepared microcapsules were derived. Firstly, the microcapsules with different particle sizes were prepared and characterized via encapsulation efficiency measurements, optical microscopy, and scanning electron microscopy. The thermogravimetric analysis curves of the samples were calculated, analyzed, and compared with the samples’ particle size and distribution, and the changes and differences in the microcapsules under heating environment were macroscopically studied. Furthermore, thermo-microscopic image analysis of the samples was conducted using a laboratory-combined instrument system, and their dynamic morphology in a temperature-increasing environment was microscopically investigated. On the basis of these data, it was found that the thermal bursting phenomenon occurred when the microcapsule particle size was larger than the “critical dimension.” And as the particle sizes decreased, their heat rupture resistance was improved, and the trend of change was described by an exponential function (y = 133.64 + 94.76 × 0.85x). When the microcapsule size was smaller than the critical dimension, the thermal bursting phenomenon disappeared and the thermal stability was depended on the degradation temperature of the MMF shell.