Fire‐retardant synergy of tris(1‐methoxy‐2,2,6,6‐tetramethyl‐4‐piperidinyl)phosphite and aluminum hypophosphite/melamine hydrobromide in polypropylene

Abstract

AbstractFire‐retardant synergy of tris(1‐methoxy‐2,2,6,6‐tetramethyl‐4‐piperidinyl) phosphite (NORPM) and aluminum hypophosphite (ALHP)/melamine hydrobromide (MHB) in polypropylene (PP) was researched by limiting oxygen index (LOI) measurement, vertical burning test, and cone calorimetric test (CCT). The results reveal that NORPM, together with ALHP/MHB, has an exceptional fire‐retardant synergy in PP. For the FR‐PP containing 1.0 wt% of ALHP and 1.5 wt% of MHB, combining NORPM in 0.20 wt% concentration can make its LOI value increases from 19.0% to 26.1%, the fire‐retardant efficiency (EFF) increases from 0.48 to 3.07, synergistic efficiency (SE) is as high as 2.18, the vertical combustion rating can be improved from none to UL 94 V‐2, fire performance index (FPI) increases from 58.7 to 84.9, and various heat release parameter values are reduced markedly. NORPM induces the synergy with ALHP/MHB primarily by the mechanisms as follows: active free radicals formed through the decomposition of NORPM, such as CH3, CH3O, nitro radicals and amino radicals, together with PH3 and HBr, trap active radicals (HO·) for combustion. Consequently, the reaction chain of combustion is terminated, which makes gaseous phase fire retardancy more efficient.