Biobased Reactive Flame Retardant With the Phenylethylamine Structure for Enhancing Flame Retardancy and Mechanical Properties of Epoxy Resins

A bio-based reactive flame retardant (PVD) was synthesized using vanillin, phenethylamine, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). This study aimed to enhance epoxy resin's fire resistance and evaluate the strength of EP/PVD composites for eco-friendly specialized applications. The chemical structure of PVD was confirmed using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The effect of PVD on the curing kinetics of EP was studied using non-isothermal differential scanning calorimetry (DSC). During combustion, PVD releases ∙PO 2 and ∙PO radicals, which capture the active ∙H and ∙OH radicals generated during the combustion of EP. This results in a significant quenching effect, thereby achieving flame retardancy. EP with 7.5 wt% PVD and 0.49 wt% phosphorus (EP/PVD-7.5) exhibited a V-0 rating in UL-94 vertical burning tests and a limiting oxygen index (LOI) of 32.4%. Additionally, compared to pure EP, EP/PVD-7.5 showed a 41.7% reduction in the peak heat-release rate during cone calorimetry tests. The dual-phase flame-retardant effect of PVD was confirmed by the analysis of the residual char and its pyrolysis behavior. Furthermore, EP/PVD exhibits superior mechanical properties and transparency compared to pure EP, indicating that PVD holds promise as a flame retardant for EP.