Function of the aryl group in bis DOPO phosphonate on reducing fire hazards of polyamide 6 composites

Abstract

AbstractThe increased integration interaction of bis 9,10‐dihydro‐9‐oxa‐ 10‐phospaphenanthrene‐10‐oxide (DOPO) phosphonate (abbreviated as FR) including ethyl‐(FR1), phenethyl‐(FR2), naphthalene‐(FR3) with the aryl group and hexa‐phenoxy‐cyclotriphosphazene (HPCP) on flame‐retardant polyamide 6 (PA6) were investigated. The role of the aryl group in FR on flame‐retarding PA6 was analyzed. Results showed that PA6 composites with greatly reduced fire hazards possessed a high‐limiting oxygen index value of 34% and achieved a UL‐94 V‐0 rating and sharply decreased peak heat release rate by simultaneously adding FR and HPCP. Flame inhibition effect acted as the main mechanism for FR and HPCP in flame‐retarding PA6. Gas phase action increased with the number of aryl groups. HPCP played a catalytic effect in the condensed phase. Particularly, the result of residue analysis after cone test implied that char surface with network structure was formed, and the structure became compact and continuous with the increase in the number of aryl groups. Furthermore, the aryl group played an important role in aiding the PA6 composites in the construction of a network protective char layer on the surface during combustion.