Organic And Inorganic Flame Retardants, What Is The Difference in Flame Retardant Mechanism?

Organic and inorganic flame retardants, what is the difference in flame retardant mechanism?

Organic Flame Retardant

Phosphorus and phosphorus compounds have been used as flame retardants for a long time, and its flame retardant mechanism has been studied earlier. From the flame retardant effect of phosphorus compounds in different reaction zones, it can be divided into flame retardant mechanism in the condensed phase and flame retardant mechanism in the vapor phase, and organic phosphorus flame retardant plays a flame retardant role in the condensed phase. The flame retardant mechanism is as follows:

During combustion, phosphorus compounds decompose to generate non-combustible liquid film of phosphoric acid, whose boiling point can reach 300℃. At the same time, phosphoric acid and further dehydration to generate metaphosphoric acid, metaphosphoric acid further polymerization to generate poly metaphosphoric acid. In this process, not only by the phosphoric acid generated by the covering layer to play a covering effect, and due to the generation of poly(metaphosphoric acid) is a strong acid, is a very strong dehydrating agent, so that the polymer dehydration and carbonization, changing the pattern of the polymer combustion process and the formation of a carbon film on the surface of the carbon film in order to isolate the air, so as to play a stronger flame retardant effect.

The flame retardant effect of phosphorus flame retardants is mainly reflected in the early stage of the decomposition of polymers in the early stage of the fire, because it can promote the dehydration of polymers to reduce the amount of flammable gases generated by the thermal decomposition of polymers, and the carbon film generated can also be used to isolate the outside world from air and heat. In general, phosphorus flame retardants work best on oxygenated polymers and are mainly used in hydroxylated cellulose, polyurethane, polyester and other polymers. For hydrocarbon polymers that do not contain oxygen, phosphorus flame retardants are less effective.

Phosphorus-containing flame retardants are also free radical trapping agents, and using mass spectrometry, it has been found that any phosphorus-containing compound has PO- formation when the polymer burns. It can combine with the hydrogen atoms in the flame region and play a role in suppressing the flame. In addition, the water produced by the phosphorus flame retardant in the flame retardant process can reduce the temperature of the condensed phase on the one hand, and on the other hand, it can dilute the concentration of combustible materials in the gas phase, thus better playing a flame retardant role.

Inorganic flame retardants

Inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, expanded graphite, borates, aluminum oxalate and zinc sulfide-based flame retardants. Aluminum hydroxide and magnesium hydroxide are the main varieties of inorganic flame retardants, which are non-toxic and low smoke. As a result of thermal decomposition to absorb a large number of combustion zone heat, so that the temperature of the combustion zone is reduced to the critical temperature of combustion below the combustion of self-extinguishing, the decomposition of most of the metal oxides generated by the melting point of the high, thermally stable, covered in the combustion of the solid phase of the surface to block heat conduction and heat radiation, thus playing a role in flame retardant. At the same time, the decomposition produces a large amount of water vapor, which can dilute the combustible gases and also play a flame retardant role.

Hydrated alumina has good thermal stability, can be transformed into AlO(OH) when heated at 300℃ for 2h, will not produce harmful gases after contacting with flame, and can neutralize the acidic gases released when polymer pyrolysis, less smoke, cheap, etc., so it has become an important variety of inorganic flame retardants. Hydrated aluminum oxide is heated to release chemically bonded water, absorbing the heat of combustion and reducing the combustion temperature. In playing the role of flame retardant, mainly two crystalline water plays a role, in addition, the water loss product is activated alumina, which can promote some polymers in the combustion of thick ring charring, so it has a cohesive phase flame retardant effect. From this mechanism, it can be seen that the use of hydrated alumina as a flame retardant, the amount added should be larger.

Magnesium flame retardant for the main varieties of magnesium hydroxide, is in recent years at home and abroad is developing a flame retardant, it is at 340 ℃ to start the heat-absorbing decomposition reaction to generate magnesium oxide, at 423 ℃ under the weight loss of the maximum, 490 ℃ under the termination of decomposition reaction. From the calorimetric method, it is known that its reaction absorbs a large amount of heat energy (44.8KJ/mol), and the generated water also absorbs a large amount of heat energy to reduce the temperature and achieve flame retardancy. Magnesium hydroxide's thermal stability and smoke suppression ability are better than hydrated alumina, but due to the large surface polarity of magnesium hydroxide, poor compatibility with organic matter, so it needs to be surface treated before it can be used as an effective flame retardant. In addition, its thermal decomposition temperature is on the high side, which is suitable for the flame retardancy of polymers with high decomposition temperature such as thermosetting materials.

At high temperature, the embedded layer in expandable graphite is easy to decompose by heat, and the gas generated makes the layer spacing of graphite expand rapidly to dozens to hundreds of times of the original. When expandable graphite is mixed with polymer, under the action of flame, a tough carbon layer can be generated on the surface of polymer, thus playing a flame retardant role.

Borate flame retardants are borax, boric acid and zinc borate. Currently the main use is zinc borate. Zinc borate at 300 ℃ began to release crystalline water, in the role of halogen compounds, the generation of boron halide, zinc halide, inhibition and capture of free hydroxyl, preventing the combustion chain reaction; at the same time the formation of solid-phase covering layer, isolate the surrounding oxygen, prevent the flame from continuing to burn and have smoke suppression effect. Zinc borate can be used alone or in combination with other flame retardants. At present, the main products are fine-grained zinc borate, heat-resistant zinc borate, anhydrous zinc borate and high water zinc borate.

Aluminum oxalate is a crystalline substance derived from aluminum hydroxide with low alkali content. When the polymer containing aluminum oxalate is burned, H2O, CO and CO2 are released without generating corrosive gases, and aluminum oxalate also reduces the smoke density and the speed of smoke generation. Due to the low alkali content of aluminum oxalate, it does not affect the electrical properties of the material when used in the flame-retardant wire and cable coverings.

As an efficient inorganic flame retardant, red phosphorus flame retardant has been widely used in the market in recent years. It plays the role of heat adsorbent by forming phosphoric acid derivatives in polymers, hindering the further occurrence of combustion; intercepts free radicals and improves thermal stability; and reacts with oxygen to form phosphorus oxygens, which continue to react with polymers to produce a crosslinked structure, obtaining a phosphorus-oxygen crosslinked carbonized layer.

In the application of these flame retardants, YINSU Flame Retardant Company specializes in the research and development of various material-specific flame retardants, including microencapsuled red phosphorus, nano flame retardants, antimony trioxide replacement and other forms. These products not only provide highly efficient flame retardant properties, but also have excellent physical and chemical stability, as well as outstanding performance in cost control, providing safe and reliable flame retardant solutions for the plastic modification industry.