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

Excerpt

The flammability and fire behaviour of fibre-reinforced epoxy composites has drawn increasing attention worldwide since the fire performance of such parts for transport applications especially is critical and is facing increasingly severe environmental legislation. Much progress has been made in improving the thermostability and flame retardancy of neat epoxy resins using a variety of compounds [1]. In particular, halogen-free compounds such as the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) successfully increase the flame retardancy of epoxy resins [2‐7] while avoiding many disadvantages such as poor compatibility, migration of the compound, and release of toxic gases upon burning as compared to other common compounds. Using such DOPO-based compounds, the flame retardancy of neat epoxies can be improved at phosphorus contents as low as 3 wt% [4, 7], thereby limiting processing difficulties and the often severe degradation of the resulting physical and mechanical properties [8]. The use of either non-reactive or reactive DOPO-based compounds with tailored chemical structures especially leads to optimised overall performance levels of neat epoxy resins at low phosphorus contents [7]. However, there still exists a lack of understanding concerning the use of such compounds for the manufacture and application of fibre-reinforced epoxy composites, especially with regard to the often negatively affected delamination resistance of such composites for demanding applications. …