Unveiling the combustion inhibiting mechanisms of various metal ions in multivalent phosphorus intumescent flame retardant system for thermoplastic polyurethane

In this study, renewable bio-based metal ion-doped (Co 2 + , Mn 2+ , Ni 2+ and Cu 2+ ) phytic acid melamine salts (PAMEL-M) are synthesized via one-pot method, and cooperates with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and expanding graphite (EG) to construct an intumescent flame retardant (IFR) system for TPU. The flame retardant TPU composites with additives of 10 wt% DOPO, 7 wt% EG and 3 wt% PAMEL-Co (TPAMEL-Co3 b ) demonstrates superior synergistic enhancement, passing the UL-94 V-0 rating and the limiting oxygen index (LOI) reach 31.2 %. The peak heat release rate (pHRR), total heat release rate (THR), and peak smoke production rate (pSPR) values of TPAMEL-Co3 b are significantly reduced by 86.2 %, 50.4 %, and 70.4 %, respectively, compared to those of pure TPU. In addition, the fire retardant mechanism of different metal ions in multivalent phosphorus system of TPU composites is thoroughly discussed. This work provides a reference for the construction of a more efficient intumescent flame retardant（IFR） system and the study of smoke suppression and catalytic charring of metal ions.