Flame retardant, mechanical properties and curing kinetics of DOPO-based epoxy resins

A halogen-free flame retardant epoxy resin was prepared consisting of DOPO-based glycidyl ether of cresol formaldehyde novolac and diglycidyl ether of bisphenol A cured by micronized dicyandiamide with accelerator U-52. The optimized epoxy resin formula contained 1.5 wt% of phosphorus and achieved UL-94 V-0 grade and LOI of 32%, with high tensile strength and impact strength of 48 MPa and 14.5 kJ/m2, respectively. Curing reaction kinetics for the DOPO-containing epoxy with 1.5 wt% of P was investigated by DSC through both non-isothermal and isothermal scanning. A two-parameter autocatalytic equation of the Å esták-Berggren model was constructed with experimentally determined kinetics parameters, which described the non-isothermal curing reaction rate quantitatively. For the isothermal curing kinetics, the Kamal-Sourour model was adopted to express the autocatalytic effect. The parameters of the reaction rate constant and reaction order were evaluated by curve fitting, and the calculated curve described the observed reaction rate fairly well. The determined kinetics parameters reflected the characteristics of the autocatalytic reaction for the curing of the phosphorus-containing epoxy system.