Influence of modified ammonium polyphosphate on the fire behavior and mechanical properties of polyformaldehyde

Abstract In this work, three kinds of APP, coated with melamine (MF‐APP), silane (GW‐APP), epoxy (MC‐APP) were employed to compound with novolac resin (Novolac) and melamine (ME), aimed to study the effect of the modified APP on the flame‐retardant performance, mechanical properties, and thermal stability of polyformaldehyde (POM). The results showed that composites with modified APP exhibited better flame retardant and mechanical performance than that with unmodified APP. In contrast, GW‐APP had the best synergistic effect with Novolac and ME, and POM/GW‐APP composites reached UL‐94 V‐0 rating and its limit oxygen index (LOI) value was up to 34.0%. The morphology of the carbon layer showed that the silane coating material can promote the charring process in condensed phase better than epoxy and melamine coating materials in flame retardant POM system, leading to the formation of integrated char layers with more quantity and higher quality, which effectively delayed the mass and heat transfer during combustion.