Novel exploration of the flame retardant potential of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-functionalized metallophthalocyanines in epoxy composites

A series of novel 1-oxo-4-hydroxymethyl-2,6,7-trioxy-1-phosphabicyclo[2,2,2]octane (PEPA)-functionalized metallophthalocyanines (PEPA-MPcs, M = Al, Co, Ni, Zn, and Ce) have been successfully synthesized and characterized. The obtained PEPA-MPcs were added to epoxy resin (EP) to prepare a variety of flame retardant composites (EPP-MPcs) and their thermal behavior and flame retardancy were investigated using thermogravimetric analysis (TGA), the limiting oxygen index (LOI), and cone calorimetry. The flame-retardant mechanism was systematically analyzed in the gas and condensed phases, respectively. The highest LOI value of EP containing 2 wt.% PEPA-MPcs was increased by 19% to 27.6% when compared to pure EP. The peak of heat release rate (pHRR) and the total heat release (THR) values observed for EPP-AlPc were reduced by 64.3% and 48.6%, respectively. The main flame retardant mechanism of the PEPA-MPcs is the synergistic effect of the P and N atoms, including the dilution of highly non-flammable gases in the gas phase and the formation of an intumescent char layer from the condensed phase. Furthermore, the char residues of the EPP-MPcs were significantly increased via the catalysis and surface enrichment of the metal atoms, which reduced the fire hazards of the EP composites. In addition, the EPP-MPcs exhibit excellent mechanical properties and uniform dispersions. This work provides a new approach to the preparation of metal containing/non–halogen/phosphorus-containing flame retardants.