The synergetic effect of bis(2‐hydroxyethyl) terephthalate from glycolysis of poly(ethylene terephthalate) on the intumescent flame retardancy of waterborne polyurethane

Abstract In light of the escalating accumulation of polymer waste in daily life, chemical recycling of polymers and value‐added utilization of products have gained considerable attention in recent years. Researchers have widely explored the potential of bis(2‐hydroxyethyl) terephthalate (BHET) derived from the glycolysis recycling of poly(ethylene terephthalate) (PET) waste in the synthesis of polymers or concrete. In this study, we synthesized BHET through glycolysis recycling of PET, and combined it with microencapsulated ammonium polyphosphate (SiO 2 @APP) and carboxymethyl chitosan to design a series of intumescent flame‐retardant waterborne polyurethane (IFRWPU). The synergistic effect of BHET and SiO 2 @APP was demonstrated, and the resulting IFRWPU with 12.5 wt% IFR and 3 wt% BHET achieved a limit oxygen index of 25.8% and a 73% reduction in the peak heat release rate in flame retardancy tests. Furthermore, the interaction of BHET and flame retardant was discussed using the analysis of char residue and pyrolytic gas. Overall, this work provides a novel strategy to construct superior flame‐retarded waterborne polyurethane with admirable bonding performance. Highlights The application of glycolysis product of PET in the flame‐retardant modification of WPU. The synergistic enhancement of flame retardancy between BHET and IFR was confirmed. The intumescent flame‐retardant was composed of SiO 2 @APP and CMCS.