High-fire-safety thermoplastic polyester constructed by novel sulfonate with benzimidazole structure

The flammability of thermoplastic polyesters and the subsequent heavy smoke and severe melt drips formed after ignition are the main obstacles hindering their widespread application. In this study, a novel ionic monomer containing sulfonate and benzimidazole was synthesized and incorporated into the main chain of poly(ethylene terephthalate) (PET, used as a model thermoplastic polyester) by melt copolymerization. The synergetic effect of ionic aggregation and carbonization endowed the obtained copolyester with high melt viscosity and excellent char-forming ability at high temperatures. The copolyester having a monomer content of 8 mol.% easily achieved the Underwriters Laboratories Inc 94 (UL-94) V-0 flammability rating without dripping and the limiting oxygen index value reached 33.0 vol.%. In addition, the total smoke production, peak heat release rate, and maximum CO production decreased by 45.2%, 60.5%, and 75.0%, respectively, compared with those of PET. In addition, the copolyester was spinnable, and showed greater adsorption efficiency (99.6%) for a cationic dye from solution compared to PET (6.5%), demonstrating the excellent affinity of the copolyester for the cationic dye. The obtained inherently fire-safe PET copolyester has great potential for applications in flame retardant textiles, artwork base materials, and decorative materials for transportation applications.