The application of modified plastics in household appliances, electronic appliances, automobiles and other fields often needs flame retardant, and flame retardant modification can be achieved by adding flame retardant. Bromine flame retardant and halogen-free flame retardant.
Flame retardant
Flame retardant, also known as flame retardant, fire retardant or fireproof agent, is a functional additive that endows flammable polymers with flame retardancy. Most of them are compounds of elements of group ⅶ a (phosphorus), group ⅶ a (bromine, chlorine) and group ⅲ a (antimony, aluminum) in the periodic table of elements.
Flame retardant principle of modified plastics
First, the endothermic effect
The heat released by any combustion in a short time is limited. If a part of the heat released by the fire source can be absorbed in a short time, the flame temperature will decrease, and the heat radiated to the combustion surface and acting on cracking the vaporized combustible molecules into free radicals will decrease, and the combustion reaction will be restrained to a certain extent. At high temperature, the flame retardant has a strong endothermic reaction, which absorbs part of the heat released from combustion, reduces the surface temperature of combustible materials, effectively inhibits the formation of combustible gases and prevents the spread of combustion.
Second, the role of coverage
After adding flame retardant into combustible materials, the flame retardant can form a glassy or stable foam covering layer at high temperature, which can isolate oxygen, and has the functions of heat insulation, oxygen isolation and preventing combustible gas from escaping outwards, thus achieving the purpose of flame retardant. For example, organic phosphorus-blocking flame retardants can produce crosslinked solid substances or carbonized layers with more stable structure when heated. On the one hand, the formation of carbonized layer can prevent the polymer from further pyrolysis, on the other hand, it can prevent the thermal decomposition products from entering the gas phase to participate in the combustion process.
Third, inhibit chain reaction
According to the chain reaction theory of combustion, free radicals are needed to maintain combustion. The flame retardant can act on the gas phase combustion zone to capture the free radicals in the combustion reaction, thus preventing the flame propagation, reducing the flame density in the combustion zone, and finally reducing the combustion reaction speed until termination.
Fourth, the asphyxiation effect of non-combustible gas
When the flame retardant is heated, it decomposes incombustible gases, and dilutes the concentration of combustible gases decomposed from combustibles below the lower combustion limit. At the same time, it can dilute the oxygen concentration in the combustion zone, prevent the combustion from continuing, and achieve the flame retardant effect.
Flame retardant grade of plastics
Flammability UL94 is the most widely used flammability standard for plastic materials. It is used to evaluate the ability of materials to extinguish after being ignited. According to the burning speed, burning time, anti-dropping ability and whether the drops are burning or not, there are many evaluation methods.
The flame retardant grade of plastics: increasing gradually from HB, V-2, V-1, V-0, 5VB to 5VA. Hb: the lowest flame retardant grade in ul94 standard.
With the development of flame retardant, there is the compounding technology of flame retardant. Flame retardant compounding technology refers to compounding among phosphorus-based, halogen-based, nitrogen-based and inorganic-based flame retardants, or inside certain types of flame retardants. In the practical application of flame retardant, a single flame retardant often has some defects, which makes it difficult to meet people's higher and higher requirements. Therefore, through flame retardant compounding technology, we can integrate the advantages of two or more flame retardants, learn from each other's strengths, and maximize the synergistic effect of flame retardants, so as to reduce the dosage and enhance the flame retardant effect.
