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 degrees C for 20 min followed by 500 degrees 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 degrees C is coherent and consists of P-rich components; at higher temperature (500 degrees C), the char becomes tiny and loose and phosphorus element is released into gas. Compared with neat EP, composites have lower water absorption. Copyright (c) 2012 John Wiley & Sons, Ltd.