Fabrication of diatomite-based microencapsulated flame retardant and its improved fire safety of unsaturated polyester resin

To achive excellent fire resistance, new microcapsule flame retardants (DMCAD and DMPPD) were prepared using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide combined with melamine cyanurate or melamine polyphosphate as the shell material and diatomite as the core material. The successful assembly of DMCAD and DMPPD was detailed characterized by Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Meanwhile, the flame retardancy and thermal stability of the unsaturated polyester resin (UPR)/DMCAD and UPR/DMPPD composites were also studied. The addition of DMCAD and DMPPD effectively improves the flame retardance properties of UPR, and the effect of DMPPD was better. The limiting oxygen index (LOI) of UPR/DMPPD-3 increased by 11.6% when compared with that of UPR, and the sample achieved V-0 rating. Moreover, the peak heat release rate (pHRR) and the total heat release (THR) rate of UPR/DMPPD-3 were reduced by 67% and 26%, respectively. Under nitrogen condition and air condition, UPR/DMPPD showed better thermal stability and char-forming ability from the thermogravimetric (TG) results. Residual char of the UPR composites was systematically analyzed with SEM and XPS. Finally, the flame retardant mechanism of DMPPD was proposed.