Preparation, Cure, Characterization, and Mechanical Properties of Reactive Flame-Retardant Cyanate Ester/Epoxy Resin Blends and Their Carbon Fiber Reinforced Composites

This study explores the formulation space of flame retardant thermoset polymers, specifically involving blends of epoxy and cyanate ester (EP/CE) and a reactive phosphorus-based flame retardant, poly (m-phenylene methylphosphonate) (PMP). Two CE monomers were investigated, each blended with the same epoxy monomer (DGEBA) in a 1:1 weight ratio. The impact of phosphorus concentration on the neat (neat meaning no fibers were present) resin blends was characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The flammability and mechanical characteristics were assessed using micro-combustion calorimetry (MCC) and dynamic mechanical analysis (DMA). Carbon fiber composite panels were successfully fabricated using a wet layup process and autoclave curing with a fiber volume fraction (Vf) of approximately 0.5. DMA testing of the cured composite laminates pinpointed that the average Tg of the EP/CE blend was reduced with PMP addition by up to 39 °C at a phosphorous level of 3 wt%. Cone calorimetry tests confirmed the effectiveness of the flame retardant by reducing the peak Heat Release Rate (HRR) by approximately 27%. The integration of PMP into EP/CE only marginally reduced the 3-point flexural strength (6–15%) and modulus (7–13%) relative to baseline samples.