Efficient Hyperbranched Flame Retardant Derived from Quercetin for Use in Epoxy Resin with Well-Balanced Comprehensive Performance

Abstract

Traditional flame retardants, often derived from petrochemical sources, pose significant environmental and health concerns due to their potential toxicity and persistence in the environment. In this study, a biobased hyperbranched polymer flame retardant named QB was synthesized using quercetin and phenylphosphoryl dichloride by a one-step method. The QB copolymer was characterized via Fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography, revealing its high thermal stability and polymeric nature, with a weight-average molecular weight of 78 299 g/mol. QB was subsequently incorporated into bisphenol A-type epoxy resins using 4–4 diamino diphenylmethane as a curing agent to prepare the flame-retardant epoxy composite. With additions of only 1 wt % QB, EQB-1 achieved a UL 94 V-0 rating in the vertical burning test and an impressive limiting oxygen index (LOI) value of 28.2%. Moreover, the addition of the 3 wt % QB in EP resulted in a maximum reduction of 32.9% in the peak of heat release rate and a 37.4% reduction in the smoke produce rate, indicating its outstanding flame-retardant and smoke suppression properties, which are attributed to a mainly condensed-phase flame-retardant mechanism. Furthermore, the impact and flexural strength of the composite were maintained and a slight improvement was observed. The findings of this research are expected to contribute to the development of environmentally friendly flame-retardant epoxy systems that meet industry standards while promoting the use of renewable materials. This work supports sustainability by replacing petrochemical flame retardants with renewable quercetin-based materials, reducing toxicity and environmental impact.