What is the flame retardant mechanism of expansion flame retardants?
Sucrose reacts with concentrated sulfuric acid to form a porous carbon layer.
Concentrated sulfuric acid has dehydrating properties and produces C.
Then C and concentrated sulfuric acid undergo oxidation-reduction, producing carbon dioxide and carbon dioxide gas.
The reaction continues and eventually produces a porous carbon layer. At this point, the flame retardant mechanism of flame retardants (IFR) is gradually emerging. Yes, flame retardants mainly exert their flame retardant effect by coalescing.
Generally speaking, IFR includes carbon sources (usually polyhydroxy compounds such as pentaerythritol), acid sources (such as ammonium polyphosphate), and foaming agents (such as melamine), which typically form a carbon layer through the following reaction process.
Specific steps:
1.At lower temperatures (around 150 ℃, depending on the properties of the acid source and other components), the acid source produces acids that can esterify polyols and act as dehydrating agents.
2. At a temperature slightly higher than the temperature at which the acid is released, the acid undergoes esterification with the polyol (carbon source), and the amine in the system acts as a catalyst to accelerate the esterification reaction.
The system melts before or during the esterification reaction.
The water vapor generated during the reaction process and the non combustible gas generated by the gas source cause the already melted system to expand and foam. At the same time, polyols and esters undergo dehydration and carbonization, forming inorganic substances and carbon residues, which further expand and foam the system.
When the reaction is nearly completed, the system gelatinizes and solidifies, and finally forms a porous foam carbon layer.
What is the function of the carbonized layer formed?
Make it difficult for heat to penetrate into the condensed phase.
It can prevent oxygen from diffusing from the surrounding medium into the degraded polymer material.
It can prevent the gas or liquid products generated by degradation from escaping from the surface of the material.
supplement
In fact, during the flame retardant process of expanding flame retardants, we also need to reduce the flammability of materials under the carbon layer through some means, such as:
1. Improve carbonization rate and reduce the amount of combustible products in the combustion inhibition zone.
2. Increase the thermal resistance of the carbon layer and the surface temperature of the material, reduce convective heat, increase radiation loss, and heat consumption of the heating material.
3. Increase the thickness of the carbon layer and reduce its thermal conductivity.
4. Reduce the permeability of the carbon layer and increase the viscosity of high polymer degradation liquid products, thereby reducing their mobility.
The expansion flame retardant system generally consists of three parts: acid source, carbon source, and gas source
Acids are usually inorganic acids or compounds that can form inorganic acids when heated to a certain temperature, such as phosphoric acid, phosphorus oxychloride, ammonium polyphosphate, etc; Carbon, also known as carbon, is the basis for the formation of foam carbonization layer, mainly including some multi hydroxyl compounds with high carbon content, such as pentaerythritol, starch, etc; Gas source, also known as foaming source, commonly used foaming sources include melamine, melamine, etc. The flame retardant mechanism of expanding flame retardants is as follows: acid decomposition produces a dehydrating agent, which can form esters with the carbon forming agent. After dehydration and cross-linking of the esters, carbon is formed. At the same time, the foaming agent releases a large amount of gas to help expand the carbon layer. The thick carbon layer increases the temperature gradient between the polymer surface and the carbon surface, making the temperature of the polymer surface much lower than the flame temperature, reducing the possibility of further degradation and release of flammable gases, while isolating the entry of external oxygen, thus flame retardant the polymer for a considerable period of time.
