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The application of modified plastics in home appliances, electronic appliances, automobiles and other fields often requires flame retardancy, and flame retardant modification can be achieved by adding flame retardants. There are brominated flame retardant and halogen-free flame retardant.
Flame retardant
Flame retardant, also known as flame retardant, fire retardant or fire retardant, is a functional additive that imparts flame retardancy to flammable polymers. Most of them are compounds of VA (phosphorus), VIIA (bromine, chlorine) and IIIA (antimony, aluminum) elements in the periodic table.
Flame retardant principle of modified plastics
1. Endothermic effect
The heat released by any combustion in a relatively short period of time is limited. If it can absorb part of the heat released by the fire source in a relatively short period of time, the flame temperature will be lowered, radiating to the combustion surface and acting on the vaporized The heat of pyrolysis of combustible molecules into free radicals will be reduced, and the combustion reaction will be inhibited to a certain extent.
Under high temperature conditions, the flame retardant undergoes a strong endothermic reaction, absorbing part of the heat released by combustion, reducing the surface temperature of combustibles, effectively inhibiting the generation of combustible gases, and preventing the spread of combustion.
2. Covering effect
After adding the flame retardant to the combustible material, the flame retardant can form a glassy or stable foam covering layer at high temperature to isolate oxygen, have the function of heat insulation, oxygen insulation, and prevent combustible gas from escaping, so as to achieve flame retardancy purpose.
For example, when the organic phosphorus-inhibiting flame retardant is heated, it can produce a cross-linked solid substance or a carbonized layer with a more stable structure. The formation of the carbonized layer can prevent further pyrolysis of the polymer on the one hand, and prevent the thermal decomposition products inside it from entering the gas phase to participate in the combustion process on the other hand.
Three, inhibit the chain reaction
According to the combustion chain reaction theory, free radicals are needed to maintain combustion. Flame retardants can act on the gas phase combustion zone to capture free radicals in the combustion reaction, thereby preventing the spread of flames, reducing the flame density in the combustion zone, and ultimately reducing the combustion reaction speed until it stops.
Four, non-combustible gas asphyxiating effect
The flame retardant decomposes incombustible gas when heated, and dilutes the concentration of combustible gas from combustibles to below the lower limit of combustion. At the same time, it also dilutes the oxygen concentration in the combustion zone, prevents the combustion from continuing, and achieves the effect of flame retardancy.
Plastic flame retardant grade
Flammability UL94 rating-is the most widely used plastic material flammability performance standard. It is used to evaluate the ability of a material to extinguish after being ignited. According to the burning speed, burning time, anti-drip ability and whether the drops are burning, there are many ways to judge.
Plastic flame retardant grade: from HB, V-2, V-1, V-0, 5VB to 5VA step by step. HB: The lowest flame retardant grade in the UL94 standard.
Along with flame retardants, there is also flame retardant compounding technology. Flame retardant compounding technology refers to the compounding between phosphorus, halogen, nitrogen and inorganic flame retardants, or within a certain type of flame retardant. In the actual application of flame retardants, a single flame retardant often has certain defects and it is difficult to meet people's higher and higher requirements. Therefore, through the flame retardant compounding technology, two or more flame retardants can be combined The strengths of the flame retardant, and complement each other, maximize the synergistic effect of the flame retardant, so as to reduce the dosage and enhance the flame retardant effect.