Preparation and properties of eugenol based flame-retarding epoxy resin

In this work, eugenol, a phenolic monomer derived from lignin, was reacted with phenylphosphinyl dichloride to produce the intermediate compound bis(4-allyl-2-methoxyphenyl) phenylphosphinate (BEP), which was then epoxydized to yield the bio-based epoxy monomer bis(2-methoxy-4-(oxirane-2-methyl) phenyl) phenylphosphinate (BEEP). Subsequently, it was reacted with commercial bisphenol A-type epoxy resin (DER) in varying proportions and cured using 4,4′-diaminodiphenyl disulfide (APDS) to obtain the flame-retarding epoxy resin. The flame-retardant performance of the bio-based epoxy resin was analyzed, and it was observed that a significant enhancement in flame resistance was achieved when the mixture ratio of DER to BEEP stands at 7:3, the limiting oxygen index (LOI) reaching 27.4% and UL-94 reaching V-0 grade. The improvement of flame retardancy primarily arises from the introduction of phosphorus, which produces free radicals capable of inhibiting the combustion chain reaction and can improve the surface structure of the epoxy resin. Furthermore, the epoxy resin possesses recyclability, maintaining a bending strength of 73% after being reprocessed. This study may provide an insight for the study of bio-based flame-retarding epoxy resin.