Application of Melem and Aluminum Diethylphosphinate in the Synergistic Flame Retardancy of PA6: Composites Preparation and Properties

Triazine compounds are widely used as nitrogen-based halogen-free flame retardants. The commonly applied melamine has issues like low decomposition temperatures and a single flame-retardant element. Herein, melem (MEL), the trimer melamine with higher thermal stability, was synthesized using a one-step calcination method. It was mixed with aluminum diethylphosphinate (ADP) to obtain a synergistic flame retardant. Using the melt blending process, the polyamide 6 (PA6) composites of PA6, MEL, and ADP were produced. The composites containing MEL and ADP exhibited excellent flame-retardant performance, including self-extinguishing time, droplet count, and residual carbon content. When the mass ratio of MEL to ADP was 1:3 and the total loading reached 20 wt%, the PA6 composites achieved a V-0 rating in vertical burning (UL-94) tests, with limiting oxygen indices (LOI) reaching 33.5%. MEL decomposed into inert gases to provide gas-phase flame retardancy, while ADP and MEL synergistically promoted the formation of a dense carbon layer, providing solid-phase flame retardancy. The tensile strength of PA6/20MEL-ADP-1 was reduced by 29.61% compared to PA6. Its excellent comprehensive performance enabled its application in automobiles and electronic components. This work provides a synergistic strategy for high thermal stability triazine flame retardants and high-performance fire-retardant PA6.