Synthesis of a syringaldehyde derivative to enhance the fire resistance and structural strength of epoxy resin

Abstract In light of growing environmental apprehensions, the threat of global warming, and the depletion of oil reserves, it is advisable to opt for bio‐epoxy resins sourced from sustainable materials. In response to these issues, syringaldehyde (SH) flame retardant epoxy resin derivatives have been formulated and synthesized. Initially, SH was reacted with 4, 4‐diaminodiphenylmethane (DDM) to yield an intermediate compound, DDM‐SH. Subsequently, the inherently flame‐retardant curing agent (DDM‐SH‐DOPO) and the bio‐based epoxy monomer (DDM‐SH‐EP) were produced by reacting with DOPO and epichlorohydrin, respectively. These resulting compounds were then integrated into bisphenol A epoxy resin, enhancing its flame retardant and mechanical characteristics. The flammability was assessed through limiting oxygen index (LOI), UL‐94, and cone calorimeter tests. The DDM‐SH‐EP‐20/5 sample exhibits notable improvements. It elevates the LOI to 25.3%, achieving a UL‐94 rating to V‐0 and effectively reducing smoke and heat release from the epoxy resin. The ternary cross‐linking network formed between DGEBA, DDM‐SH‐EP, and DDM‐SH‐DOPO primarily contributes to this mechanical enhancement, DDM‐SH‐EP‐20/5 has excellent overall performance, bending strength and bending modulus are 103% and 108% higher than DGEBA/DDM. This study offers a viable solution for producing flame‐retardant epoxy resin with superior mechanical properties.