With the explosive development of material science and technology in the 1950 s, organic polymer materials began to widely used in various fields of production and life. Today, polymer materials as the main ingredient of plastics, rubber, textile, coating becoming indispensable element of production, we applied polymer material items such as appliances, tableware, transport brings great convenience to our lives and at the same time also brought a lot of potential safety hazard.
Due to the oxygen index of polymer materials is low, the air with 21% oxygen content is sufficient to meet the majority of polymer combustion conditions. In addition, the polymer materials of smoke and toxic gases released when burning, endanger human body health not only, and will cause the pollution of environment. In order to reduce the flammability of polymer materials, prevent fire, flame retardant arises at the historic moment. Flame retardant is can be used to prevent flammable materials, which prevent the material from being ignition and flame spread restraint additives.
There are a lot of the kinds of flame retardants, according to the composition generally can be divided into two categories, organic flame retardants and inorganic flame retardants. Organic flame retardants including phosphorus-containing flame retardants and phosphorus - nitrogen organic phosphorus flame retardants, flame retardant, silicone flame retardants, etc. We will flame retardant mechanism of the flame retardant selection is presented in several categories.
Phosphorus-containing flame retardants is an important member of organic fire retardant agent, it is the main component of halogen organic matter. Under the condition of high temperature polymer degradation maintenance free radicals are produced by combustion of organic matter factor, and at the time of phosphorus-containing flame retardant on the thermal decomposition of hydrogen halide (HX) gas can capture free radicals, thus achieve the goal of stem the spread of the flame. In addition, the hydrogen halide itself does not burn and density than air, in the form a gas barrier layer on the surface of polymer material, block polymer materials contact with oxygen.
Phosphorus - nitrogen flame retardant with phosphorus and nitrogen as the main element. This kind of flame retardant, also known as expansion type flame retardant, when heated, the reason for this is that this type of flame retardants in surface can produce a uniform layer of the carbon foam layer, have the effect of isolating heat and oxygen. Generally by the acid source expansion type flame retardant system (dehydrating agent), carbon source (into carbon agent) and air (nitrogen source, foaming source) of three parts. After heated, released by the acid source can esterification multivariate alcohol and inorganic acid can be used as dehydrating agent; Temperature rise further, inorganic acid react with polyol (carbon source) generated esters, and in the sticky molten state. Reaction process of water vapor and the non-combustible gases produced by the gas source already expansion foam in the molten state of the system, at the same time, the multivariate alcohol and ester dehydration carbonized, form inorganic substances and carbon residue, and response to a rise of temperature, gel and cure, the final formation of the porous carbon foam layer.
Inorganic flame retardants are expandable graphite, hydroxide, red phosphorus or poly phosphate, etc., usually is several different inorganic mixture. Under the high temperature, expanded graphite rapid expansion, the strength of the polymer surface carbon layer, can be separated from the fuel from the source of heat; Hydroxide heated absorb a lot of heat and release water vapor, dilute combustible gas, generated refractory metal oxide at the same time; Red phosphorus or polyphosphates combustion generated metaphosphate vitreous, form a protective film can be overridden in the burning body, form of phosphoric acid has a strong to take off the water at the same time, the polymer can be carbonized form carbon isolation layer.
All this can be found that the effect of flame retardant can be summarized as: (1) release of the burning heat, not burning gas is released (2) diluted, isolation combustible and combustion-supporting gas, (3) the production and the free radical reaction composition, organic matter (4) the formation of solid insulation.
