Highly effective flame‐retarded polyester diol with synergistic effects for waterborne polyurethane application

ABSTRACT In this article, a novel bi‐reactive flame retardant (FRD) was successfully synthesized for waterborne polyurethane (WPU). The chemical structures of FRD were characterized by Fourier‐transform infrared spectra and 1 H and 31 P nuclear magnetic resonance. Then, the FRD was incorporated into polyurethane backbone to prepare a series of flame‐retarded WPU (FRWPU). The flammability characteristics of FRWPU were measured by limited oxygen index (LOI), UL‐94, and cone calorimeter (CCT) tests. The FRPWU‐7 had a high LOI value of 30.5% with UL94 V‐0 rating. Moreover, the CCT values indicated that FRD induced the gaseous phase quenching effect of phosphorus‐containing free radicals derived from the decomposed phosphaphenanthrene group on the gas‐phase flame retardancy. Scanning electron micrographs and Raman spectra exhibited that FRD promoted the charring formation of phosphorus‐rich char layer with graphitized surface and honeycomb‐like intumescent structure in WPU matrix during burning. This study provides a new way to design a novel reactive P–P flame retardant consisted of the phosphaphenanthrene group and intumescent flame retardant for WPU application. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137 , 48444.