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 V0 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 (avCOY) 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 increased the melt viscosity by triggering the cross-linking reactions of the C equivalent to N groups in SPPO, effectively inhibiting the melt-dripping of PET 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.