Synthesis of aluminum methylcyclohexylphosphinate and its use as flame retardant for epoxy resin



A novel aluminum phosphinate—aluminum methylcyclohexylphosphinate (Al(MHP))—was synthesized by reacting n-butyl methylphosphonite with cyclohexene, followed by reacting with anhydrous AlCl3. The products were characterized with gas chromatography, Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, phosphorus nuclear magnetic resonance, X-ray fluorescent spectroscopy, and thermogravimetric (TG) analyses. After blending with epoxy resin (EP), flame retardancy was estimated with the use of limited oxygen index (LOI) and UL-94 test, and thermal stability was investigated using TG analysis. The morphologies and composition of the char obtained after being heated at 300 °C for 20 min followed by 500 °C for 3 min in the muffle furnace were characterized by scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis. Results showed that Al(MHP) is an efficient flame retardant for EP, and Al(MHP)/EP can pass UL-94V-0 rating with an LOI of 28.8% by adding 15 wt.% of Al(MHP). TG results showed that the presence of Al(MHP) in EP increases the char yield and depresses the thermal decomposition. SEM-EDX analysis showed that the char obtained at 300 °C is coherent and consists of P-rich components; at higher temperature (500 °C), the char becomes tiny and loose and phosphorus element is released into gas. Compared with neat EP, composites have lower water absorption. Copyright © 2012 John Wiley & Sons, Ltd.