Synergistic effects of sodium polyacrylate-loaded ammonium polyphosphate in combination with ScYSZ to enhance the flame retardancy and thermal insulation properties of epoxy-polyamide coatings

In this study, a “three-source” intumescent flame-retardant SAPP, obtained by the modification of ammonium polyphosphate (APP) with low-crosslinked sodium polyacrylate (SAP), was employed to enhance the fire resistance properties of epoxy-polyamide (EP) coatings. Scandia and yttria-co-stabilized zirconia (ScYSZ) compound, was incorporated into SAPP/EP to enhance the flame retardancy and thermal insulation properties. It was found that, the incorporation of 19.4 wt% SAPP and 3.2 wt% ScYSZ into the EP coating (S-SAPP/EP2), achieved a limiting oxygen index (LOI) of 31.3 % and corresponded to a UL-94 V-0 rating. Additionally, use of the cone calorimeter test (CCT) combined with the thermogravimetry test (TG) revealed that the binary intumescent flame-retardant (IFR)–metal oxide system could endow the EP coatings with superior synergistic effects to enhance their flame retardancy, smoke suppression, charring, and thermal insulation properties. Compared with pure EP, the total heat release (THR) and the total smoke production (TSP) of S-SAPP/EP2 were reduced by 61.3 % and 67.8 %, respectively, which are also superior reductions to those achieved for SAPP/EP. Moreover, further analysis of the char residues of S-SAPP/EP2 showed that the binary IFR–metal oxide system endowed the EP coatings with a superior synergistic effect for the generation of crosslinking and P–O–C aromatic structures during combustion, which effectively contributed to the formation of a high-quality char layer and the highest thermal insulation properties reported for EP coatings.