Flame Retardancy of Epoxy Resin Enhanced by Silicone‐Modified Aluminum Diethylphosphinate in Synergy With Melamine Cyanurate and a Char‐Forming Agent

ABSTRACT To enhance the flame retardancy of epoxy resin (EP), aluminum diethyl phosphinate (ADP) was surface‐modified using phenyl trimethoxysilane (PTMS). The modified ADP (PTMS@ADP) was then used as a main flame retardant, in combination with melamine polyphosphate (MPP) as a synergistic acid source and triazine carbonization agent (CFA) as a carbon source, to fabricate an intumescent flame retardant system (PTMS@ADP/MPP/CFA), hereafter referred to as IFR system. This system was incorporated into EP materials to investigate the flame retardancy of the resulting composites. The synergistic flame‐retardant effects among PTMS@ADP, MPP, and CFA were analyzed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and char residue analysis. The results show that the carbon residue rate of PTMS@ADP after modification is increased to 37.4 wt %, which is 63.3% higher than that of ADP, showing higher thermal stability at high temperature. Under a constant total loading of 15 wt %, the optimal ratio of PTMS@ADP:MPP:CFA was found to be 3:2:1, achieving the highest LOI value of 33.5%, with all samples meeting the V‐0 rating. Additionally, the char yield at 600°C increased by 89.6% compared with pure EP. Cone calorimetry tests revealed that the average heat release rate and total smoke production were reduced by 40.7% and 29.7%, respectively, indicating that the IFR system significantly improved both the flame retardancy and smoke suppression of the EP composites. The mechanical properties of the EP composite were significantly reduced when ADP was added alone. In contrast, the mechanical properties of the composite were improved upon the addition of PTMS@ADP or PTMS@ADP/MCA/CFA, although they remained lower than those of pure EP. Based on the comprehensive test results of flame retardancy and mechanical properties, the PTMS@ADP/MCA/CFA composite is suitable for applications requiring high flame retardancy with relatively lower demands on mechanical performance.