Magnesium carbonate is a white powdery, weakly alkaline inorganic compound containing magnesium. Magnesium carbonate has stable chemical properties, is non-toxic, odorless, and non-flammable. It is a cheap, non-toxic, and environmentally friendly mineral filler, and is widely used in the preparation of flame retardants and smoke suppressants.
Flame retardant mechanism of magnesium carbonate
The flame retardant mechanism of magnesium carbonate mainly includes the following aspects:
1. Physical dilution effect: As a filler, magnesium carbonate can dilute the content of combustible components in combustible materials, reduce their calorific value, and make the material more difficult to burn. For example, adding 20% magnesium carbonate to polystyrene can increase its limiting oxygen index (LOI) from 18% to 28%.
2. Endothermic effect: Magnesium carbonate decomposes into magnesium oxide and carbon dioxide when heated. This decomposition process absorbs a lot of heat, reduces the surface temperature of the material, and delays the occurrence of combustion. Studies have shown that the decomposition endothermic effect of magnesium carbonate can reduce the peak heat release rate (PHRR) of the material by more than 30%.
3. Release of non-combustible gas: The carbon dioxide produced by the decomposition of magnesium carbonate is a non-combustible gas that can dilute the oxygen concentration in the combustion zone and inhibit the combustion reaction.
4. Inhibit free radicals: Magnesium carbonate can adsorb free radicals produced during the combustion process and terminate the combustion chain reaction. Free radicals are the main carriers of the combustion reaction, and the free radical inhibition effect of magnesium carbonate can effectively block the combustion reaction.
Smoke elimination mechanism of magnesium carbonate
The smoke elimination effect of magnesium carbonate is mainly reflected in the following aspects:
1. Adsorption of carbon black: Magnesium carbonate has a large surface area and can adsorb carbon black particles produced during the combustion process to reduce the generation of smoke. Studies have shown that magnesium carbonate can adsorb more than 70% of carbon black particles.
2. Promote carbon black coagulation: Magnesium carbonate can promote the coagulation of carbon black particles to form larger particles that are easier to capture. Larger carbon black particles are more easily captured by the filter device, thereby reducing smoke emissions.
3. Neutralize acidic substances: Some acidic substances, such as HCl, SO2, etc., are produced during the combustion process. Magnesium carbonate can neutralize these acidic substances and reduce the irritation of smoke. Acidic substances can irritate the eyes and respiratory tract, and the neutralization effect of magnesium carbonate can improve the environmental friendliness of smoke.
Preparation method of magnesium carbonate modified flame retardant smoke suppressant
The following are some common preparation methods of magnesium carbonate modified flame retardant smoke suppressant:
• Mixing method: Add magnesium carbonate and other raw materials to the mixer and mix them evenly. This method is simple and easy, but the dispersion effect is not good, and magnesium carbonate is prone to agglomeration.
• Open refining method: Add magnesium carbonate and other raw materials to the open refining mill for open refining and mixing. This method can obtain better dispersion effect, but the production efficiency is low.
• Dispersion method: Pre-disperse magnesium carbonate in a solvent, then add it to the flame retardant smoke suppressant material and mix it. This method can obtain a uniform and fine dispersion, but it requires the use of solvents, which will increase production costs.
Application of magnesium carbonate modified flame retardant smoke suppressant
Magnesium carbonate modified flame retardant smoke suppressant is widely used in plastics, rubber, textiles, building materials and other fields. For example, adding magnesium carbonate modified flame retardant and smoke suppressant to polypropylene can make it reach UL 94 V-0 flame retardant standard, and the smoke density can be reduced by more than 50%; adding magnesium carbonate modified flame retardant and smoke suppressant to rubber products can make it reach GB/T 15975 flame retardant A2 standard; adding magnesium carbonate modified flame retardant and smoke suppressant to textiles can make it reach GB 18401 flame retardant B1 standard.
The characteristics of anhydrous magnesium carbonate flame retardant are that in addition to having a larger heat absorption per unit mass, it releases carbon dioxide gas with fire extinguishing effect. Using anhydrous magnesium carbonate as a flame retardant is like the polymer matrix material carrying a carbon dioxide fire extinguisher. The released carbon dioxide forms a “carbon dioxide gas film” around the burning substrate, isolating the combustion-supporting air. From this characteristic, anhydrous magnesium carbonate flame retardant is suitable for occasions with higher requirements for electrical insulation performance, such as wires and cables.
Summary
Magnesium carbonate is an excellent and low-cost flame retardant and smoke suppressant additive, which has broad application prospects in the field of flame retardant and smoke suppressant. With the continuous deepening of research, magnesium carbonate modified flame retardant smoke suppressant