What are the principles of flame retardant effect of plastic profiles?
Most of them are flammable. With the wide application of plastics in construction, furniture, transportation, aviation, aerospace, electrical appliances and other fields, improving the flame retardancy of plastic profiles has become an urgent task. Many occasions require materials to be flame retardant. The more common occasions are electronic appliances. The automotive industry also has flame retardant requirements, but they are generally low. Flame retardancy can be achieved by adding flame retardants.
Flame retardants: Molybdenum compounds, tin compounds, and iron compounds with smoke suppression functions also belong to the category of flame retardants. They are mainly suitable for plastics with flame retardant requirements, which can delay or prevent the combustion of plastics, especially polymer plastics. The ignition time is extended, the ignition is self-extinguishing, and the ignition is difficult.
Principle of flame retardancy
1) 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 be reduced, the heat radiated to the combustion surface and acting on the gasified combustible molecules to decompose into free radicals will be reduced, and the combustion reaction will be inhibited to a certain extent.
2) Covering effect: After adding flame retardants to combustible materials, the flame retardants can form a glassy or stable foam covering layer at high temperature, which can isolate oxygen, have the functions of heat insulation, oxygen isolation, and preventing the escape of combustible gases, and are plastic profiles, thereby achieving the purpose of flame retardancy.
For example, organic phosphorus flame retardants can produce cross-linked solid substances or carbonized layers with more stable structures when heated. The formation of the carbonized layer can prevent the further pyrolysis of the polymer on the one hand, and on the other hand, it can prevent the thermal decomposition products from entering the gas phase to participate in the combustion process.
3) Inhibition of chain reaction: According to the chain reaction theory of combustion, what is needed to maintain combustion is free radicals. Flame retardants can be used in 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 rate until it ends.
4) Asphyxiation of non-combustible gases: When heated, flame retardants will decompose non-combustible gases and dilute the concentration of combustible gases decomposed from combustibles to below the lower limit of combustion. At the same time, the oxygen concentration in the combustion zone can be diluted to prevent the combustion from continuing, achieving a flame retardant effect.
Flame retardant grade of plastic profiles: UL94 grade for flammability - This is the most widely used flammability performance standard for plastic materials. It is used to evaluate the ability of a material to extinguish after being ignited. There are multiple evaluation methods based on the burning speed, burning time, anti-drip ability, and whether the droplets burn. Flame retardant grades of plastics: from HB, V-2, V-1, V-0, 5VB to 5VA. HB: The lowest flame retardant grade in the UL94 standard.