Synthesis of a histidine-magnesium hydroxide curing agent and improving the flame retardant, smoke suppression of epoxy resin composites

Conventional curing agents typically possess a single property and the challenge of inadequate interfacial adhesion between inorganic flame-retardant additives and the epoxy resin (EP). This study presents a multifunctional flame retardant curing agent (HFP-MM) synthesized by functionalizing magnesium hydroxide (MH) with L-histidine (HIS), phosphite, and melamine (MEL). This curing agent was compounded with varying amounts (wt%) of Ammonium polyphosphate (APP) and added to EP to establish an intumescent flame retardant system. The results indicate that EP formulation containing 10 wt% HFP-MM and 10 wt% APP achieved UL-94 V-0 level and exhibited the limiting oxygen index (LOI) measurement reaching 29.6 %. Furthermore, compared to the flame retardant free of EP, the peak heat release rate, peak CO production rate and total smoke production were dropped by 88.9 %, 86.0 % and 74.8 %. Regarding flexural performance, the flexural modulus and flexural strength increased by 129.6 % and 137.4 %, respectively. The functionalized MH flame-retardant curing agent prepared in this study, when applied to EP, exhibits excellent flame-retardant and mechanical properties, proving effective in reducing the fire hazard of EP materials.