A macromolecular intumescent flame retardant with thermal cross-linking groups for poly(ethylene terephthalate) with enhanced fire safety

To improve the flame retardancy of poly(ethylene terephthalate) (PET) without loss of its mechanical properties, a macromolecular intumescent flame retardant (SPPO) with thermal-responsive groups was developed in an effective way. As 8 wt% of SPPO was melt-blended into PET, the prepared PET/SPPO composite achieved a V-0 rating during UL-94 tests without melt-dripping, and exhibited substantial reduction in the total heat release (THR), peak heat release rate (PHRR), total smoke production (TSP) and average carbon monoxide yield (av-COY) by 44.8%, 39.0%, 63.3% and 45.8%, respectively, in comparison with pure PET. The improved flame retardancy of this composite was considered to be ascribed to the formation of intumescent residues of SPPO. The generated physical barrier effectively inhibited the melt-dripping and increased the melt viscosity by triggering the cross-linking reactions of the CN groups in SPPO during burning. The tensile strength was also well-retained for PET composites when different contents of SPPO were added into PET, demonstrating the good compatibility between SPPO and PET matrix, which can meet the requirements of industrial application.