Novel castor-oil-based flame-retardant and flexible epoxy resins: synthesis and properties

A novel castor-oil-based and phosphorus-containing epoxy resin (flame-retardant epoxy resin (FREP)) and a curing agent – castor oil polybasic acid (AACO) – with high flame retardancy and flexibility were successfully synthesized. The chemical structures of FREP and AACO were characterized by Fourier transform infrared spectrometry (FTIR) and hydrogen-1 ( 1 H) nuclear magnetic resonance spectroscopy. The epoxy resin components were prepared by using bisphenol A epoxy resin (diglycidyl ether of bisphenol A (DGEBA)) with different mass contents of FREP and AACO. DGEBA with 40 wt% FREP (FREP40) possessed a large limiting oxygen index of 29.3%. Cone calorimetry showed that the heat release and smoke production were reduced for both DGEBA with 20 wt% FREP (FREP20) and FREP40 in comparison with those of pure resin (FREP0), indicating that the smoke release and fire hazard of epoxy resin composites with FREP were reduced. Thermogravimetry–infrared spectroscopy suggested that the yields of toxic carbon monoxide (CO), carbon dioxide (CO 2 ) and other pyrolysis products were significantly reduced. FTIR and X-ray photoelectron spectroscopy showed that FREP40 outperformed FREP0 in carbon-forming capacity. The introduction of FREP and AACO effectively increased the elongation at break of pure epoxy resins. FREP and AACO provide a promising strategy for synthesis of epoxy resins with excellent flame retardancy, smoke suppression and flexible performance.