The application of modified plastics in fields such as household appliances, electronic appliances, and automobiles often requires flame retardancy, and flame retardancy modification can be achieved by adding flame retardants. There are bromine flame retardants and halogen-free flame retardants.
Flame retardant
Flame retardants, also known as flame retardants, are functional additives that impart flame retardancy to flammable polymers. They are mostly compounds of the fifth A (phosphorus), seventh A (bromine, chlorine), and third A (antimony, aluminum) group elements in the periodic table.
Flame retardant principle of modified plastics
1、 Endothermic effect
The heat released by any combustion in a short period of time is limited. If a portion of the heat released by the ignition source can be absorbed in a short period of time, the flame temperature will decrease, and the heat radiating to the combustion surface and acting on the decomposition of vaporized combustible molecules into free radicals will be reduced, resulting in a certain degree of suppression of the combustion reaction.
Under high temperature conditions, flame retardants undergo a strong endothermic reaction, absorbing some of the heat released by combustion, reducing the surface temperature of combustible materials, effectively suppressing the generation of combustible gases, and preventing the spread of combustion.
2、 Covering effect
When flame retardant is added to combustible materials, the flame retardant can form a glassy or stable foam covering layer under high temperature, isolate oxygen, and have the functions of heat insulation, oxygen isolation, and preventing combustible gas from escaping outward, so as to achieve flame retardancy.
Organic phosphorus retardants can produce cross-linked solid substances or carbonized layers with more stable structures when heated. The formation of a carbonization layer can prevent further pyrolysis of the polymer on the one hand, and on the other hand, it can prevent the thermal decomposition products inside from entering the gas phase and participating in the combustion process.
3、 Inhibitory chain reaction
According to the chain reaction theory of combustion, what is required to maintain combustion is free radicals. Flame retardants can act on the gas-phase combustion zone, capturing free radicals in the combustion reaction, thereby preventing flame propagation, reducing the flame density in the combustion zone, and ultimately causing the combustion reaction speed to decrease until it is terminated.
4、 Non combustible gas suffocation effect
When flame retardants are heated, they decompose into non combustible gases, diluting the concentration of the combustible gases produced by the decomposition of combustibles below the lower limit of combustion. At the same time, it also has a diluting effect on the oxygen concentration in the combustion zone, preventing the continued combustion and achieving flame retardancy.
Plastic flame retardant grade
Flammability UL94 level - is the most widely used flammability standard for plastic materials. It is used to evaluate the ability of materials to extinguish after being ignited. There are various evaluation methods based on combustion speed, combustion time, anti dripping ability, and whether the droplets are burning.
Plastic flame retardant grade: gradually increasing from HB, V-2, V-1, V-0, 5VB to 5VA. HB: The lowest flame retardant grade in UL94 standard.
Along with flame retardants, flame retardant compounding technology has also been developed. Flame retardant compounding technology refers to the compounding between phosphorus based, halogen based, nitrogen based, and inorganic based flame retardants, or within a certain type of flame retardant. Due to the practical application of flame retardants, a single flame retardant often has certain defects that are difficult to meet people's increasingly high requirements. Therefore, through flame retardant compounding technology, the strengths of two or more flame retardants can be integrated, and the synergistic effect of flame retardants can be maximized to reduce dosage and enhance flame retardant effect.
