Solvent‐free synthesis of phosphate‐containing imidazole fluid for flame retardant one‐component epoxy resin with long pot life, low curing temperature and fast curing rate

Abstract

The design of flame retardant one-component epoxy resin (EP) with long pot life, low curing temperature and fast curing rate has been challenging in the industry. Herein, we synthesized a phosphate-containing imidazole fluid (TA) as the thermal latent curing agent of EP. Based on simple structural design, TA endows EP with excellent curing properties, storage properties, and flame retardant properties. According to DSC results, EP/TA systems exhibit low curing temperature and fast curing rate during operation. The rotary rheometer test confirms that the viscosity curve of EP/TA system maintains longterm stability at 40 C. The X-ray photoelectron spectroscopy (XPS) data reveals that TA releases imidazole intermediates and phosphorous compounds during curing. The former provides conditions for fast curing of EP, while the latter gives EP intrinsic flame retardant properties. With the addition of 20 wt.% TA, EP/TA-4 achieves UL-94 V-0 rating and 28.5% of LOI value. The study of flame retardant mechanism shows that the flame retardancy of TA mainly comes from the protective effect of phosphorus-rich char layer, the dilution effect of non-combustible gas and quenching effect of phosphorous compound. Besides, due to no solvent involved, the synthesis strategy of TA is environmentally friendly, showing a great potential of industrial application.