Recent advances in fire-retardant carbon-based polymeric nanocomposites through fighting free radicals

Polymeric materials are ubiquitously utilized in modern society and continuously improve quality of life. Unfortunately, most of them suffer from intrinsic flammability, significantly limiting their practical applications. Fundamentally, free-radical reaction is a critical "trigger" for their thermal pyrolysis and following combustion process regardless of the anaerobic thermal pyrolysis in the condensed phase or aerobic combustion of polymers in the gaseous phase. The addition of free radical scavengers represents a promising and effective means to enhance the fire safety of polymeric materials. This review aims to offer a state-of-the-art overview on the creation of fire-retardant polymeric nanocomposites by adding fire retardants with an ability to trap free radicals. Their specific modes of action (condensed-phase action, gaseous-phase action, and dual-phases action) and performances in some typical polymers are reviewed and discussed in detail. Following this, some key challenges associated with these free-radical capturers are discussed, and design strategies are also proposed. This review provides some insights into the modes of action of free radical capturing agents and paves the avenue for the design of advanced fire-retardant polymeric nanocomposites for expanded real-world applications in industries.