Comparative study on flame retardancy of phosphates modified waterborne styrene-acrylate emulsion-based coatings: Experiment and DFT calculation

Novel intumescence flame retardant coating (IFRC) is facilely prepared for flame-retarding plywood using waterborne styrene-acrylate emulsion (SAE) based coatings as the binder, and zinc phosphate (ZnP) and aluminum triphosphate (ATP) are employed to improve its fire resistance with an emphasis of elaborating the discrepancy between ZnP and ATP. The results determine that an appropriate dosage (2 wt%) of ATP or ZnP is crucial to enhance its flame retardancy, evidenced by the highest flame retardancy index of 1.84 and 1.52, the lowest fire growth index of 0.22 and 0.27 kW·m−2·s−1, respectively, due to the heat sink effect from their dehydrations. Furthermore, the reasons for that ATP holds a superior fire resistance to ZnP in the SAE-based IFRCs are explored, according to density functional theory calculation and condensed phase analysis. It verifies that the higher total potential of ATP and sharply increased integral density of state (DOS) of Al(PO3)3 (derives from dehydration of AlH2P3O10·2H2O) favor an improved fire resistance, compared with that of dehydration from Zn3(PO4)2·4H2O to Zn3(PO4)2. It proposes a novel approach for quantitatively investigating the flame-retarding mechanisms of organic-inorganic hybrid coatings.