Preparation and properties of ammonium polyphosphate microcapsules for coal spontaneous combustion prevention

Ammonium polyphosphate (APP) is a type of fire-fighting material that has excellent performance; however, it also has the disadvantage of facile deliquescence. Microcapsule technology is therefore employed in this study to use melamine resin as encasing material in the preparation of melamine–formaldehyde resin-microencapsulated APP. The performance of prepared microcapsules is characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric experiments. The experimental results show that the same APP characteristic peaks (e.g., N-H stretching vibration peaks) and characteristic absorption peaks of melamine-formaldehyde (MF) resin (e.g., vibration peak of MF ring) are exhibited by the microcapsules. Furthermore, the coated microcapsule surface is rough because of the adsorption of solid particles, indicating that the wall material successfully covers the core material. Thermogravimetric analysis shows that the microcapsules can effectively increase and decrease the maximum weight loss rate temperature and maximum weight loss rate, respectively. When the microcapsule content constitutes 15% of the total sample mass, the maximum weight loss rate and coal temperature decrease and increase by 0.58%/min and 13°C, respectively. This significantly inhibits the composite coal-oxygen process, indicating the improved fire-fighting performance afforded by microcapsules. The Research provides a new direction for the development of fire-fighting materials.