Synergistic flame retardant strategies in polymers: A review of metal-organic frameworks and inorganic particles with multi-mechanism insights

Flammability is currently one of the main safety constraints that limit the further application extension of polymeric materials. The development of effective fire-retardant solutions that are both environment-friendly and have little impact on matrix properties is of great importance for polymer safety. By blending metal-organic frameworks (MOFs) into inorganic flame retardants, the prepared composites can take advantages of both MOFs and inorganic flame retardants, i.e. tunability of structure and high specific surface area for the former and thermal stability for the latter. Therefore, blending MOFs into inorganic flame retardants is a robust approach to prepare synergistic fire-retardant solutions. Due to the complexity of combustion reactions, different kinds of flame retardants may exhibit different flame retardant mechanisms. Classifying flame retardent systems based on their mechanisms will be helpful to reveal the intrinsic relationship among structure, property, and fundamental idea. Following the above concept, preparing flame retardent system by blending different kinds of MOFs and inorganic particles will be more effective in both design strategy and flame retardant performance. In this review, different MOF-inorganic material flame retardant systems will be summarized according to their flame retardant behaviors, and current challenges and future developments in this field will also be discussed for a prospective look at the systematic design of materials.