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The fire-retardant synergy of tris(1-methoxy-2,2,6,6-tetramethyl-4-piperidinyl)-phosphite (NORPM) and melamine hydrobromide (MHB)/aluminum diethylphosphinate (ADEP) in polypropylene (PP) was characterized by UL-94 tests, limiting oxygen index (LOI) determination and cone calorimetry tests (CCT). NORPM exhibits an exceptional synergy in PP. The LOI and fire-retardant effectivity (EFF) of S-3 (the loadings of MHB and ADEP 1.00 and 1.50 wt%, respectively, no NORPM) were 19.0% and 0.48%, respectively, however, the LOI and EFF of S-15 (the loadings of NORPM, MHB and ADEP 0.2, 1.00 and 1.50 wt%, respectively) significantly increased to 25.5% and 2.85%, respectively, synergistic effectivity (SE) of NORPM is 2.03, and the fire-retardant rating was improved from none to UL 94 V-2 and the total heat release (THR) and peak heat release rate (PHRR) dropped obviously by adding the 0.2 wt% NORPM. The analysis by thermogravimetry-mass spectrum analysis (TG-MS) of the PP samples and the residues in the CCT revealed that NORPM, MHB and ADEP induced the synergy primarily by the following modes: CH3O·, aminyl radicals, CH3·and nitro radicals formed through the cracking of NORPM, along with the free radicals such as PO·, PO2· and HPO· pyrolyzed from ADEP and HBr from MHB, which quenched the active radicals, such as HO·, H·, ROO·, R· and broke down the radical source. The chain oxidation reaction of combustion was accordingly interrupted, which brought about the more exceptional fire-retardant effect than that of MHB/ADEP. [ABSTRACT FROM AUTHOR]

Bis(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)sebacate (NORSM) was found to perform an exceptional synergistic effect with tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBPC)/Sb2O3 in HIPS. The LOI of fire retardant HIPS (FR-HIPS) with 16 wt% of TTBPC/Sb2O3 increased from 23.8% to 25.2%, the flame retardant rating of FR-HIPS was improved from UL 94 V-2 to UL 94 V-0, and various heat release parameters such as peak heat release rate, total heat release, and mean effective heat of combustion were greatly lowered by combining NORSM of 0.50 wt%. The Py-GC/MS results revealed that NORSM induced the role of synergistic effect; the main mechanisms were as follows: the active radicals such as methoxy radicals and aminyl radicals produced by the pyrolysis of NORSM promote the release of bromine radicals from TTBPC and the formation of HBr and CO2, which improves the flame retardancy of TTBPC/Sb2O3; the above active radicals, together with HBr, quench active free radicals, such as the hydroxyl radical (OH), and decompose the free radical source, which interrupts the chain reaction during combustion and results in a more efficient flame retardant effect in gaseous phase. [ABSTRACT FROM AUTHOR]