Research progress on flame retardant methods of polymer direct blending

Direct blending of flame retardants into polymer matrices is one of the most common and straightforward methods for preparing flame retardant materials, holding significant importance in industrial applications. This review systematically summarizes recent advances in polymer flame retardant materials prepared by direct blending, with a focus on various strategies including conventional additive-type flame retardants (inorganic and organic), organic-inorganic hybrid systems, "all-in-one" intumescent flame retardance, nanocomposite approaches, in-situ reinforcement, catalytic carbonization, and directly added bio-based flame retardants. The flame retardant mechanisms and application performances of these strategies are discussed in detail. Analysis shows that through component design and structural control (e.g., hybridization, nanonization, integration, catalytic carbonization), the limiting oxygen index (LOI) of the materials can be significantly enhanced, enabling them to pass the UL-94 V-0 rating, while effectively reducing the peak heat release rate (pHRR), total heat release (THR), and smoke production. Furthermore, the mechanical properties can be simultaneously improved. Finally, it is pointed out that the development of novel flame retardant systems characterized by high efficiency, environmental friendliness, multifunctional synergy, and good matrix compatibility is a crucial future direction for polymer flame retardant materials.