Molecules Featuring the Azaheterocycle Moiety toward the Application of Flame-Retardant Polymers

Abstract

Flame retardancy is a desirable property of polymer materials, and the molecular design of novel flame-retardant structures considers three main aspects: (i) the chemical structure should have suitable thermal degradation temperature and a high tendency to form char; (ii) the flame-retardant molecule should not compromise the mechanical properties of the polymer matrix; and (iii) the molecule should have low inherent toxicity and generate minimal or no harmful substances to humans and the environment during degradation. Azaheterocycles and their derivatives are an important class of nitrogen-containing flame retardants, which achieve good flame retardancy by diluting the concentration of oxygen and fuel gas on the polymer surface in the gaseous phase and promoting the amount of char residue in the condensed phase. At the same time, azaheterocycle-containing flame retardants possess excellent designability and appropriate thermal degradation temperature of most of their structures, producing gases with low toxicity when subjected to thermal decomposition. Moreover, azaheterocycles and their derivatives have promising potential in the synthesis of novel flame retardants and flame-retardant polymers. This review mainly summarizes the methods of improving the flame retardancy of polymeric materials using azaheterocycle-containing compounds and the applications of azaheterocycle-containing flame retardant molecules. Meanwhile, this review also identifies the main challenges for the future development of azaheterocycle-containing flame retardants.

Flame retarded polyurethane vitrimers containing isocyanurate rings: Synthesis and properties

“…16 Additionally, the noncombustible gas generated from decomposition serves to dilute oxygen and other combustible gases, thus facilitating flame retardancy. 17 It has been verified in previous studies that the isocyanurate ring structure shows excellent thermal stability and charring characteristics in combustion. In this case, isocyanurates are considered to be potential in the construction of intrinsic flame retarded polymer materials.…”

“…N‐containing components exhibit significant heat absorption during the combustion, thereby effectively cooling the polymer surface 16 . Additionally, the noncombustible gas generated from decomposition serves to dilute oxygen and other combustible gases, thus facilitating flame retardancy 17 . It has been verified in previous studies that the isocyanurate ring structure shows excellent thermal stability and charring characteristics in combustion.…”

“…Notably, CO 2 production (CO 2 P, see Figure S2c) is high (0.09-0.14 g/s) for all three samples. Inert gases released by decomposition of isocyanurate, which could take away the heat in the gas phase and dilute the oxygen concentrate, 17,23,62 thereby accelerating the extinguishment of combustion. These results are in line with previous studies in lecture, 23,24,26 in which isocyanurate-based materials showcase excellent flame retarded behavior.…”

Research Progress on the Preparation Methods for and Flame Retardant Mechanism of Black Phosphorus and Black Phosphorus Nanosheets

“…While they can inhibit combustion, they also produce toxic substances such as dioxins, bromides, and chlorides, which degrade the base material's strength, heat resistance, and other properties [79][80][81]. Common nitrogen-based flame retardants include carbamates [82,83], phosphorus-nitrogen mixed flame retardants [84], and nitrogen heterocyclic compounds [85]. However, practical application has revealed that these flame retardants can produce nitrogen oxides and other pollutants.…”

Three-Dimensional Cross-Linking Network Coating for the Flame Retardant of Bio-Based Polyamide 56 Fabric by Weak Bonds

“…Aza-heterocycles and their derivates are commonly used to modify fabric surfaces for flame retardancy through endothermic decomposition [ 21 , 22 , 23 ]. This process releases non-combustible gases, such as nitrogen oxides, NH 3 , CO 2 and H 2 O, which dilute the concentration of oxygen and fuel gas on the fabrics [ 24 ]. They also encourage condensed phase char formation with nitrogen content.…”