Highly flame-retardant materials of different divalent metal ions alginate/silver phosphate: Synthesis, characterizations, and synergistic phosphorus-polymetallic effects

Three kinds of divalent metal ions (Ca2+, Cu2+, Zn2+) alginate/silver phosphate (MAlg/Ag3PO4) hybrid materials were prepared via an in-situ method, and the composites were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Fourier transform infrared spectrum (FTIR). To investigate their flame-retardant properties and phosphorus-polymetallic flame-retardant effects, the combustion behavior and flammability of the composites were assessed by using the thermogravimetric analysis (TGA), limiting oxygen index (LOI) and micro-calorimeter tests (MCC). The results show that the three composites were thermally stable, among which the LOI of CaAlg/Ag3PO4, CuAlg/Ag3PO4 and ZnAlg/Ag3PO4 were 62.6 %, 46.5 % and 79.8 %, respectively, which were much higher than the prescribed flame retardants which was 27 %. According to the TGA, the thermal stability was ZnAlg/Ag3PO4 > CaAlg/Ag3PO4 > CuAlg/Ag3PO4. The heat release capacity (HRC) of the above three materials was 49 J/(g·K), 69 J/(g·K), 41 J/(g·K), respectively, and the fire safety performance was also in the same order as the thermal stability. By using the thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS), the flame retarding mechanism of MAlg/Ag3PO4 and the synergistic effect of Ag3PO4 and divalent metal ions were proposed based on the experimental data.