Six flame retardant effects of magnesium hydroxide
The flame retardant effect of magnesium hydroxide flame retardant is to stop or inhibit the rate of physical or chemical changes in the combustion process of polymeric materials, specifically, these effects are reflected in the following six aspects.
1)Heat absorption effect
Its role is to slow down the rate of heating of polymer materials. For example, borax has 10 molecules of crystalline water, due to the release of crystalline water to absorb 141.8kJ/mol heat, due to its heat absorption and the temperature rise of the material is inhibited, thus producing a flame retardant effect. The flame retardant effect of alumina hydrate is also due to the heat absorption effect caused by the dehydration of its heat. In addition, some thermoplastic polymers often produce molten droplets that leave the combustion zone and carry away the heat of reaction, so they can also exert some flame retardant effect.
2)Covering effect
The effect is to form a stable cover layer at higher temperatures, or decomposition to generate foam-like material, covering the surface of the polymer material, so that the polymer material generated by thermal decomposition of combustible gases is difficult to escape, and the material plays a role in heat insulation and air insulation, thereby inhibiting material cracking, to achieve the effect of flame retardant. Such as phosphate ester compounds and fireproof foam coatings, etc. can play a role according to this mechanism.
3)Dilution effect
With this function of magnesium hydroxide flame retardant in the thermal decomposition can produce a large number of non-combustible gas, so that the polymer material decomposition of combustible gas and oxygen in the air is diluted and does not reach the concentration range of combustible, thus preventing the polymer material ignition combustion. CO₂, NH₃, HCI and H₂O can be used as dilution gases. Ammonium phosphate, ammonium chloride, ammonium carbonate, etc. can produce this non-flammable gas when heated.
4)Transfer effect
The effect is to change the mode of thermal decomposition of polymer materials, thus inhibiting the production of flammable gases. For example, the use of acid or alkali cellulose dehydration reaction and decomposition into charcoal and water, because no combustible gas, can not be ignited. Ammonium chloride, ammonium phosphate, phosphate ester, etc. can be decomposed to produce such substances, catalyzing the material thick ring carbonization, to achieve the purpose of flame retardant.
5)Inhibition effect (capture free radicals)
High polymer combustion is essentially thermal decomposition products of the free radical chain reaction, some substances can capture the burning reaction of the active intermediates HO *, H *, O *, HOO *, magnesium hydroxide can effectively inhibit the free radical chain reaction, so that the burning rate is reduced until the flame is extinguished. Commonly used bromine, chlorine and other organohalogen compounds have this inhibitory effect.
6)Enhance the effect (synergistic effect)
Some additives used alone do not have flame retardant effect or flame retardant effect is not large, but when used with other flame retardants can significantly improve its flame retardant effect, this effect is called enhanced or synergistic effect. The use of antimony trioxide with magnesium hydroxide is the most typical example. The result is that not only can the flame retardant efficiency be improved, but also the amount of flame retardant can be reduced.
