Evaluation of O-vanillin derived schiff-base intumescent flame retardants in epoxy resin applications: Flame retardancy, smoke emission, and mechanical property

A Schiff base flame retardant, identified as 6,6′-((1E,1′E)-((methylenebis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol) (OV-DDM), was synthesized in this study using O-vanillin and 4,4′-diaminodiphenylmethane. A flame retardant was formulated by combining OV-DDM and ammonium polyphosphate (APP) to modify commercially available epoxy resins. In a comparative analysis between the unmodified epoxy resin and its modified version with integrated flame retardants, significant enhancements were discerned in the flame retardant properties of the latter. The ultimate oxygen index (UL-94 V-0 grade) for the epoxy resin treated with flame retardants was 28.9%. considerable augmentation in the flame retardant index (FRI) was recorded. Four distinct methods resulted in epoxy resins with superior FRIs (exceeding 10), and the highest observed value was 21.4. Adding OV-DDM/APP to epoxy resins does not affect their energy storage modulus and mechanical properties, and there is a small increase in these properties. The OV-DDM/APP compound facilitated the formation of a densely expanded carbon residue structure, thereby improving fire safety performance. The current study introduces a simple approach for incorporating Schiff base compounds into flame retardant epoxy resin, suggesting considerable potential for this resin as an effective intumescent flame retardant.