Effective halogen-free flame retardants for carbon fibre-reinforced epoxy composites

The effectiveness of halogen-free flame retardants such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) for carbon fiber-reinforced epoxy resins which avoids many disadvantages like poor compatibility, release of toxic gases upon burning as compared to other common compounds is discussed. Using these flame retardants, the flame retardancy of neat epoxies can be improved at phosphorus contents as low as 3 wt%, thereby limiting processing difficulties and severe degradation of the resulting physical and mechanical properties. The addition of the DOPO-based compounds reduce the total heat evolved (THE) and the peak of heat release rate (pHRR) effects, indicating an improvement in terms of flame spread and fire load. DOPO components yield radical trapping in the gas phase, resulting in an incomplete oxidation in the flame zone and, decreases effective heat of combustion. Critical properties related to the fracture toughness of modified composites can be maintained effectively allowing the use of such compounds in composites for demanding applications.