Non-halogen radical generators for enhanced flame retardancy of plastics

Although radical generators as flame retardant synergists have been known and used for many years mainly in polystyrene formulations novel chemical classes have been developed more recently and introduced into the market. The new radical generators are based on nitrogen compounds optionally in combination with sulfur and silicone. Alkoxyamines are commercially the most successful structures, however, sulfenamides and oxyimides can outperform those. Potential application fields have been extended from the original polyolefins in thin sections to polystyrenes, epoxides, polyurethanes, and others. The mechanism of radical generators originates mainly from formed radicals in the burning process, which induce a fast degradation of the polymer chain. Flame retardancy is achieved by removing the substrate from the flame. Synergistic mixtures of radical generators with phosphorus compounds are of particular importance achieving flame retardancy of many substrates at low loadings. The chapter provides an overview on state-of-the-art radical generator chemistries, applications, and performance with focus on recent developments.