Synthesis and characterization of a novel P/N containing flame retardant and its effect on flame-retardancy, thermal and mechanical properties of epoxy/clay nanocomposites

A P/N containing flame retardant DOPO-QN was synthesized by a reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 8-hydroxyquinoline (QN). Its chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) like 1 H, 13 C, 31 P NMR, and high-resolution mass spectrometry (HRMS) techniques. The synthesized DOPO-QN was employed as an additive type flame retardant in combination with clay nanomer 1.34TCN (NC) in diglycidyl ether of bisphenol A/4,4ʹ-diaminodiphenlsulfone (DGEBA/DDS) to synthesize epoxy thermosets. The fire behavior of synthesized epoxy thermosets was studied by UL-94, limiting oxygen index (LOI), and cone calorimeter tests. The EP/DOPO-QN (1.5%P)/NC sample passed the UL-94 test with a V-0 rating and LOI value of 26.5%. A decrease in peak heat released, carbon monoxide, and carbon dioxide emissions was observed in the cone calorimeter test. Thermogravimetric analysis (TGA) of epoxy thermosets showed an increase in thermal stability at a higher temperature range on the formation of nanocomposites. Also, a remarkable improvement in storage modulus was observed for the EP/DOPO-QN (1.5%P)/NC sample containing 2.0% NC in dynamic mechanical analysis (DMA).