A novel biobased intumescent flame retardant through combining simultaneously char-promoter and radical-scavenger for the application in epoxy resin

A biobased intumescent flame retardant (PAD) with different oxidation state of phosphorus was synthesized successfully via combining phytic acid (PA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The chemical structure and performance of PAD were characterized by FTIR, H-1 NMR, P-31 NMR, and TGA, respectively. After introducing 5wt% PAD into epoxy resin, the EP samples exhibited expansive behavior during combustion and left char residue with 14.4% mass and 2.4 cm height. Meanwhile, the combination of 5wt% mixture of PAD and a borate (DOT) demonstrated good synergistic effect and further improved the flame retardancy of EP sample, as reflected by increased LOI value of 29%, V-0 rating in UL-94 test and char residue of 15.4%. Compared with neat EP sample, the PHRR and FIGRA reduced by 42.8% and 42%, respectively. Moreover, the initial decomposition temperature (T-5wt%) also increased to 350 degrees C. Finally, SEM/EDS, Raman, TG-IR, and Py-GC/MS were employed to evaluate the flame-retardant mechanism. This novel intumescent flame retardant PAD functioned in both condensed and gas phases, and the synergistic effect of PAD and DOT brings out excellent flame retardancy for epoxy. (C) 2022 Elsevier Ltd. All rights reserved.