Flame Retardant Principles of Low Smoke Halogen Free Cables

Flame Retardant Principles of Low Smoke Halogen Free Cables

Halogen-free flame retardant burning smoke is small, does not produce toxic, corrosive gases. Halogen-free flame retardant additives are mainly based on phosphorus compounds and metal hydroxides. These two types of compounds, which do not volatilize and do not produce corrosive gases when burning, are known as harmless flame retardants. The following is an introduction to the flame retardant principle of halogen-free flame retardants:

1. Heat absorption

Any combustion in a relatively short period of time the heat released is limited, if you can absorb a portion of the heat released by the fire source in a relatively short period of time, then the flame temperature will be reduced, the radiation to the combustion surface and the role of the combustible molecules that have been vaporized to crack into the free radicals of the heat will be reduced, the combustion reaction will be inhibited to a certain extent. Under high temperature conditions, the flame retardant undergoes a strong heat-absorbing reaction, absorbs part of the heat released by combustion, reduces the temperature of the surface of the combustible material, effectively inhibits the generation of combustible gases, and prevents the spread of combustion.The flame retardant mechanism of Al(OH)3 flame retardant is to improve the flame retardant performance by increasing the heat capacity of the polymer, so that it absorbs more heat before reaching the thermal decomposition temperature. This kind of flame retardant gives full play to its property of absorbing large amount of heat when combining with water vapor to improve its own flame retardant ability.

2. Covering effect

After adding flame retardants in combustible materials, the flame retardants can form glassy or stable foam cover layer at high temperature to isolate oxygen, which has the effect of heat insulation, oxygen insulation and preventing combustible gases from escaping outward, so as to achieve the purpose of flame retardancy. Such as organophosphorus flame retardants can produce a more stable structure when heated cross-linked solid material or carbonized layer. The formation of carbonized layer on the one hand can prevent further pyrolysis of polymers, on the other hand, can prevent its internal thermal decomposition of products into the gas phase to participate in the combustion process.

3. Inhibition of chain reaction

According to the chain reaction theory of combustion, free radicals are required to maintain combustion. Flame retardants can act in the gas-phase combustion zone to capture the free radicals in the combustion reaction, thus preventing the propagation of the flame, so that the flame density in the combustion zone decreases, and ultimately, the combustion reaction rate decreases until termination. Such as halogen-containing flame retardants, its evaporation temperature and polymer decomposition temperature is the same or similar, when the polymer thermal decomposition, the flame retardant is also volatilized at the same time. At this time, halogen-containing flame retardants and thermal decomposition products at the same time in the gas-phase combustion zone, halogen will be able to capture the free radicals in the combustion reaction, thus preventing the spread of the flame, so that the flame density of the combustion zone to reduce the final combustion reaction rate down to the termination.

4. Suffocating effect of non-flammable gas

When the flame retardant is heated, it decomposes the non-flammable gas, and dilutes the concentration of combustible gases from the decomposition of combustible materials to below the lower limit of combustion. At the same time, it also has the effect of diluting the oxygen concentration in the combustion area, preventing the combustion from continuing and achieving the effect of flame retardant.