Contents


Preface

Polymers have entered almost every aspect of modern life, thanks to their unparalleled properties such as lightweight, chemical resistance, electrical

important [17, 18].

test, among others [66].

insulation, and easy processing, to name a few [1, 2]. However, common polymers are flammable because of their chemical structures, which consist of hydrogen and carbon atoms [3–5]. Inflammability properties in polymers are important for specific applications such as building insulation, aerospace parts, and firefighter uniforms [6]. To address polymer flammability issues, adding flame retardants into polymers is common [5, 7–13]. However, for traditional flame-retardant additives, high loading is usually needed to meet flame retardancy demands, which can lead to deteriorated mechanical properties and environmental issues [14–16]. Fire protection becomes crucial. Developing novel sustainable flame retardants is

In addition to high flame retardancy, polymers with superior resistance to heat are essential for preventing burn injury under extreme conditions [19–23]. Common thermal insulation materials work by reducing conductive heat flow and, to a lesser extent, convective heat flow [24]. Radiant barriers and reflective insulation systems work by reducing radiant heat gain [24]. Thermally insulative materials could reduce the heat release rate [6]. Developing multifunctional polymers with excellent flame retardancy and superior thermal insulation is of fundamental interest and technological importance [10]. Thermal insulation properties can be improved by manipulating porous nanostructures in polymers to reduce solid conductivity, gaseous conductivity, and radiation heat transfer [25]. Advanced multifunctional polymers with low thermal conductivity on the order of 0.01 W m-1 K-1 have been developed [9, 19, 22, 26–34]. Various polymer foams, polymeric sponges, and composite aerogels with good thermal insulation and fireproof properties have been reported [10, 19, 22, 27, 35–44]. Formed char materials can also act as thermal insulation layers [45–47]. The thermal conductivity of char layers varies along with the evolution of the intumescent structures [47, 48]. Further investigation into the relationships between flame retardancy behaviors and polymer structures is needed [49]. Boosting flame retardancy and thermal insulation performance in polymers without deteriorating their mechanical property (e.g., compressive strength) and

releasing toxic gases/products is highly desired [50–57].

Over the past decades, different flame retardants have been developed [6, 7, 20, 28, 33, 58–60]. Heat transfer influences processes in the ignition, growth, spread, decay, and extinction of fire [61, 62]. Flame retardants act either in the vapor phase or condensed phase to inhibit or to stop combustion processes through a chemical and/or physical mechanism [5, 60]. The flammability of polymer is also dependent on fire conditions — the transport of oxygen from the environment to the burning surface [26, 62, 63]. The polymer flammability behaviors have been explored by their ignitability, flame-spread rate, and heat release characterizations [64, 65]. Depending on the targeted polymer application, one or more specific flammability criteria need to be satisfied. Fame retardancy properties can be evaluated by various tests, which include limiting oxygen index, vertical burning test, cone calorimeter
