Flame Retardancy in Polymeric Materials: A Short Overview

Metals have been replaced by polymers in many applications due to the favorable mechanical and chemical properties of polymers. But flammability and combustibility of polymeric materials are their major shortcoming that limiting their applications. Beside these concerns, toxic gases produced during combustion of polymeric materials increase the fire hazards. To overcome these problems, numerous attempts have been made to improve the flame retardancy of polymeric materials. Pyrolysis of polymer by thermal treatment leads in the formation of highly reactive •O, •H and •OH radicals. The first two species are mainly converted to the hydroxyl radical (•OH) and the •OH radical affords the required heat for fire propagation in an exothermic reaction. Thus, •OH prevention would result in avoiding fire spreading. Halogenated flame retardants produce halogen radicals or volatile phosphate retardants releasing •HPO, •PO or •PO2 radicals, which can inhibit •OH radical formation. For reducing flammability of the polymers, it is possible to either change the polymer structure or create a protecting layer on the surface of polymers and textiles using surface coating. This paper aims to give a short overview on fundamentals of polymeric materials combustion, modes of action of flame retardants in both vapor and condensed phase including: heat sink, barrier layer, intumescent effect, prevention of flame propagation, as well as, recent developments in nanostructure flame retardants. We also highlight the applications of flame retardants in polymeric materials and composites, toxicity of flame retardant and the fire retardancy tests, which have been used to describe fire behavior, nature and modes of flame retardant materials.