Flame retardancy and degradation process of precipitation construction of double-shell flame-retardant microcapsules

In order to address the issues of poor smoke suppression, substrate compatibility, and strong hygroscopicity associated with ammonium polyphosphate, this study employed an in-situ precipitation method to construct a double-shell ammonium polyphosphate microcapsule, with ethyl cellulose and nano-silica serving as shell materials. The microcapsule exhibited improved flame retardancy and fire safety compared to ammonium polyphosphate alone, as evidenced by significant reductions in both maximum heat release rate and total heat release, as determined by thermal-gravimetric analysis (TGA), microcalorimetry (MCC), and vertical burning tests (VBT). Furthermore, the real-time Fourier transform infrared (RT-FTIR), scanning electron microscopy (SEM), and Raman spectrum analyses revealed that the modified kraft paper produced a cross-linked network structure formed by the silica-based substrate and cellulose during combustion, which facilitated the formation of a carbon layer and provided sustained flame retardancy. Physical and hygroscopicity tests demonstrated that the microcapsule exhibited superior compatibility with substrates. Overall, these findings demonstrate that microencapsulation of ammonium polyphosphate effectively addresses the challenges of compatibility and hygroscopicity, while enhancing its flame-retardant efficacy, thus significantly advancing its application in flame retardant materials.