Bis(2-hydroxyethyl) terephthalate (BHET), the alcoholysis monomer of waste polyethylene terephthalate, can form a cross-linked network structure with the polyurethane main chain because of the unique structure of active hydroxyl groups. In this work, organic small molecular BHET was applied as a new chain extender in polyurethane synthesis. A green and facile method was proposed to fabricate waterborne polyurethane (WPU) by recycling waste polyester. It was found that WPU was successfully prepared by using BHET as chain extender. Compared with polyurethane prepared by small molecular chain extender 1,4-butanediol (BDO), mechanical strength and thermal stability of polyurethane were remarkably enhanced by the incorporation of BHET. Meanwhile, the water absorption rate of the polyurethane is reduced. The tensile strength of WPU/BDO materials with 3.77 wt% BDO was 5.3 MPa, while WPU/BHET materials with 3.77 wt% BHET was 9.4 MPa. Furthermore, the elongation at break of WPU/BHET materials reached the maximum with 5.66 wt% BHET. Moreover, WPU/BHET materials prepared by using BHET as a chain extender have better thermal stability in high temperature environments. BHET with distinctive structure and the uniform dispersion will have more potentials for the preparation of high-performance polyurethane composites, especially for green recycling of polyester materials.bis(2-hydroxyethyl) terephthalate (BHET), chain extender, cross-linked network, mechanical strength, waterborne polyurethane (WPU)

Incorporation of functional nanofillers can unlock the potential of polymers as advanced materials. Herein, singlelayered and three-dimensional reduced graphene oxide (rGO)/ Ti 3 C 2 T x (B-rGO@Ti 3 C 2 T x ) nanohybrids were constructed using bis(2-hydroxyethyl) terephthalate (BHET) as a coupling agent between rGO and Ti 3 C 2 T x through covalent and hydrogen bonds. It is found that BHET can not only resist the weak oxidization of Ti 3 C 2 T x to some degree but also prevent the self-stacking of Ti 3 C 2 T x and rGO sheets. Then, B-rGO@Ti 3 C 2 T x was used as a functional nanofiller and three-dimensional chain extender for preparing the waterborne polyurethane (WPU) nanocomposite through in situ polymerization. Compared with WPU nanocomposites with an equivalent amount of Ti 3 C 2 T x /rGO@Ti 3 C 2 T x , although containing an equivalent amount of BHET, WPU/B-rGO@Ti 3 C 2 T x nanocomposites show significantly improved performance. For example, 5.66 wt % of B-rGO@Ti 3 C 2 T x endows WPU with a high tensile strength of 36.0 MPa (improved by 380%), thermal conductivity of 0.697 W•m −1 •K −1 , electrical conductivity of 1.69 × 10 −2 S/m (enhanced by 39 times), good strainsensing behavior, electromagnetic interference (EMI)-shielding performance of 49.5 dB in the X-band, and excellent thermal stability. Therefore, the construction of rGO@Ti 3 C 2 T x nanohybrids with the aid of chain extenders may unlock new possibilities of polyurethane as smart materials.

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 (SiO2@APP) and carboxymethyl chitosan to design a series of intumescent flame‐retardant waterborne polyurethane (IFRWPU). The synergistic effect of BHET and SiO2@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 SiO2@APP and CMCS.