Chemical Industry: Detailed explanation of the mechanism of action of flame retardants

The mechanism of action of flame retardants is more complicated and involves various factors, but the role of flame retardants is nothing more than The purpose of cutting off the combustion cycle is achieved through physical and chemical means. Regarding the mechanism of action of flame retardants, there are still many aspects that are unclear, but the views that have been published so far can be summarized into the following aspects.

(1) The dehydration of flame retardant decomposition products causes organic matter to carbonize and the combustion of plastics is decomposition and combustion, while usually simple substances do not undergo evaporation combustion and decomposition combustion to generate flames. Therefore, if the thermal decomposition of plastics can be made to proceed quickly and decompose to carbon without remaining in the flammable material stage, combustion can be prevented. For example, use phosphates or heavy metalsaltcellulose impregnated with aqueous solution. After drying, it is only carbonized and charred when heated, and it is difficult to cause combustion that produces flames. This is due to phosphoric acid Salt causes a dehydration reaction in cellulose, thereby promoting the formation of solid carbon.

When organic When phosphorus compounds are exposed to flame, the following decomposition reaction occurs:

Organophosphorus compound monophosphate-metaphosphate-polymetaphosphate

The final polymetaphosphoric acid is a very strong dehydrating agent that can promote the carbonization of organic compounds, and the carbon black film produced Flame retardant effect.

(2 ) The flame retardant decomposes to form a non-volatile protective film. The flame retardant decomposes at the temperature of resin burning, and its decomposition products form a non-volatile protective film covering the surface of the resin, thereby isolating the air to achieve the purpose of flame retardancy. This is the case when using borax-boric acid mixtures and phosphorus as flame retardants.

Phosphorus halide(R4PX) is generated by thermal decompositionphosphorusand alkyl halides(RX). PhosphorusEasily oxidized to form phosphorus oxide compounds(R3PO), and then further decomposes to form polyphosphate vitreous body. This continuous vitreous body forms a protective film. Covering the polymer surface isolates oxygen and exerts its flame retardant effect.

(3 ) The decomposition product of the flame retardant cuts off the free radical chain reaction and decomposes into wicks when the plastic is burned. The wicks are further oxidized and decomposed at high temperatures to produce HO–Free radicals,HO·The chain reaction of free radicals keeps the flame burning going on. In the combustion process of polymers, flame combustion is the most important. Therefore, if the chain reaction of H0 and free radicals can be cut off, it will be effective. to prevent flames from burning.

0%~15% Clor4%~5 % of Br can achieve a flame retardant mouth; if used together with a free radical initiator.thenOnly4%~8% of C1 or 0. 5%~3% Br is enough.

Oxidationantimony(Sb2O3) is very ineffective when used alone as a flame retardant, but when used in combination with halides It has excellent effect, the main reason is that halogenation is generated at high temperatureantimony span>.

SbCl3(boiling point 223℃ ) and SbB r3Boiling point288 ℃They are all volatile substances with higher boiling points, so they can stay in the combustion zone for a longer time. HalogenatedAntimonyCan promote polymers in liquid and solid phases. Dehydrohalogenation of flame retardant systems and carbonization of polymer surfaces. At the same time, it can captureHO·Free radical. Therefore, oxidationantimonyCombined use with halogen-containing flame retardants is the most widely used flame retardant formula.

(1) Heat of combustion Dispersion and dilution of flammable substances

HydrogenAluminaIt is one of the flame retardants with this function. It is not very flame retardant, so it is added in an amount of up to 40 to 60 parts, which doubles as a filler. When plastics burn,hydrogenAluminum oxide decomposes and absorbs large amounts of heat.

Because the combustion heat is absorbed by the polymer, the temperature of the polymer is reduced, thereby slowing down the decomposition, evaporation and combustion. Aluminum hydroxide is non-flammable, when used in an amount of 40 to 60 partsfillWhen charged into the polymer, it is equivalent to diluting the flammable polymer” “. Thus improvingdifficultyInflammable.

On the other hand, while the thermal decomposition of the polymer produces flammable gas, if the polymer-retards The fuel system can decompose to produce H2O, HCl, NBr, CO2, NH3, Non-flammable gases such as N2 can dilute flammable gases to a certain extent and achieve flame retardant effects. The role of flame retardants is actually a combination of the above factors A complex process.

The added amount is as high as40 to 60 servings, which doubles as a filler. When plastics burn,hydrogenAluminum oxide decomposes and absorbs large amounts of heat.

Because the combustion heat is absorbed by the polymer, the temperature of the polymer is reduced, thereby slowing down the decomposition, evaporation and combustion. Aluminum hydroxide is non-flammable, when used in an amount of 40 to 60 partsfillWhen charged into the polymer, it is equivalent to diluting the flammable polymer” “. Thus improvingdifficultyInflammable.

On the other hand, while the thermal decomposition of the polymer produces flammable gas, if the polymer-retards The fuel system can decompose to produce H2O, HCl, NBr, CO2, NH3, Non-flammable gases such as N2 can dilute flammable gases to a certain extent and achieve flame retardant effects. The role of flame retardants is actually a combination of the above factors A complex process.