The Application of Flame Retardants in the Glue of Automatic Fire Suppression Material

 

In modern industry and daily life, fire safety is always a crucial issue. With the continuous development of materials science, flame-retardant materials have emerged as effective means to prevent and control fires. Among them, the application of flame retardants in the glue of Automatic Fire Suppression Material (AFSM, hereinafter referred to as AFSM glue) has significantly enhanced the fire resistance of the material, which is of great practical significance and broad application prospects. AFSM glue, as a special-purpose glue, needs to have the function of automatic fire suppression when a fire occurs, in order to prevent the spread of the fire and buy time for personnel evacuation and fire rescue. The addition of flame retardants can change the combustion characteristics of the glue, making it less likely to burn or reducing the burning speed in a high-temperature environment, thus achieving the effect of automatic fire suppression.

Overview of Flame Retardants

(A) Definition and Function of Flame Retardants

Flame retardants are substances that can prevent combustion, reduce the burning speed, or increase the ignition point. Their action principles mainly include the following aspects: First, the endothermic effect. When the flame retardant decomposes upon heating, it absorbs a large amount of heat, reducing the surface temperature of the material so that the material is difficult to reach the ignition point. Second, the covering effect. During the combustion process, the non-combustible substances decomposed by the flame retardant cover the surface of the material, forming an isolation film to prevent oxygen from contacting the material, thereby suppressing combustion. Third, the inhibition of the chain reaction. The flame retardant captures the free radicals during the combustion process, interrupting the chain reaction of combustion to achieve the purpose of flame retardancy. Fourth, the dilution and asphyxiation effect of non-combustible gases. The flame retardant decomposes upon heating to produce non-combustible gases, such as carbon dioxide, nitrogen, etc. These gases dilute the oxygen concentration in the combustion area, making it impossible for the combustion to continue.

(B) Classification of Flame Retardants

Flame retardants can be classified in various ways. According to their composition, they can be divided into inorganic, organic, and organic-inorganic composite flame retardants. Inorganic flame retardants mainly include aluminum hydroxide, magnesium hydroxide, zinc borate, antimony trioxide, etc. They have the advantages of good thermal stability, non-volatility, and no generation of toxic gases, but their flame retardant efficiency is relatively low, and a large amount needs to be added, which may affect the physical properties of the material. There are many types of organic flame retardants, and common ones include halogen-based, phosphorus-based, nitrogen-based, etc. Halogen-based flame retardants have high flame retardant efficiency, but they will produce a large amount of toxic and harmful gases during combustion, causing harm to the environment and human health. Phosphorus-based flame retardants play a flame retardant role in both the condensed phase and the gas phase through the action of the phosphorus-oxygen bond, and they have good flame retardant effects and the characteristics of low smoke and low toxicity. Nitrogen-based flame retardants are generally used in combination with other flame retardants and play a flame retardant role by expanding into char, with the advantages of environmental protection and low smoke. Organic-inorganic composite flame retardants combine the advantages of organic and inorganic flame retardants, which can improve the flame retardant performance and the comprehensive properties of the material at the same time. According to the flame retardant elements, they can be divided into halogen-based, phosphorus-based, nitrogen-based, silicon-based, aluminum-magnesium-based, etc. flame retardants. According to whether they contain halogen elements, they can also be divided into halogen-based flame retardants and halogen-free flame retardants. In view of the environmental hazards of halogen-based flame retardants, halogen-free flame retardants have received more and more attention and application in recent years.

Introduction to the Glue of Automatic Fire Suppression Material

(A) Characteristics and Application Scenarios of AFSM Glue

In addition to the bonding performance of ordinary glue, AFSM glue also has unique automatic fire suppression characteristics. It is usually applied in fields with high requirements for fire safety, such as aerospace, electronics and electrical appliances, construction, transportation, etc. In the aerospace field, it is used for the bonding of aircraft internal structural components to ensure that the fire can be effectively prevented from spreading in case of a fire and to protect the lives of passengers and crew members. In the electronics and electrical appliances field, it is used for the bonding of circuit boards, electrical appliance casings, etc., reducing the risk of fire caused by electrical failures. In the construction field, it is used for the sealing and bonding of fireproof doors and windows, curtain walls, partition walls, etc., improving the fire resistance of buildings. In the transportation field, it is used for the bonding of interior decoration materials and structural components of vehicles such as cars, trains, and ships, enhancing their fire safety.

(B) Working Principle of AFSM Glue

The automatic fire suppression principle of AFSM glue is mainly based on its physical and chemical changes in a high-temperature fire environment. When encountering a fire source, the flame retardants in the glue begin to play a role. Through the above-mentioned multiple methods such as endothermic, covering, inhibiting chain reactions, and dilution and asphyxiation, they prevent the glue itself and the materials bonded with it from burning. At the same time, the glue may also contain some special components, such as materials that expand when heated. These materials will expand rapidly at high temperatures to form a thick heat insulation layer, further preventing heat transfer and oxygen supply, thus achieving the effect of automatic fire suppression.

Application Principle of Flame Retardants in AFSM Glue

(A) Interaction Mechanism between Flame Retardants and Glue

1. Physical Mixing: Additive flame retardants are uniformly dispersed in the glue through mechanical blending. When a fire occurs, the flame retardants and the glue are heated at the same time, and each plays its flame retardant role. For example, when the inorganic flame retardant aluminum hydroxide in the glue decomposes upon heating, it absorbs a large amount of heat, reducing the temperature of the glue system. At the same time, the water vapor generated by the decomposition also plays a role in diluting oxygen and combustible gases.
2. Chemical Reaction: Reactive flame retardants are combined with the polymer chains of the glue through chemical reactions and become a part of the polymer structure. This bonding method enables the flame retardants to play a more effective role and has less impact on the physical properties of the glue. For example, a phosphorus-based flame retardant containing active groups can react with the epoxy groups in the epoxy resin glue, introducing the phosphorus element into the polymer chain and improving the flame retardant performance of the glue. During the combustion process, substances such as phosphoric acid decomposed by the phosphorus-based flame retardant can promote the dehydration and carbonization of the epoxy resin, forming a dense carbon layer to prevent the transfer of oxygen and heat.

(B) Action Modes of Different Types of Flame Retardants in AFSM Glue

3. Halogen-based Flame Retardants: Halogen-based flame retardants in AFSM glue mainly play a role through the gas-phase flame retardant mechanism. When the halogen-based flame retardants in the glue decompose upon heating, they will produce hydrogen halide gases, such as hydrogen chloride (HCl), hydrogen bromide (HBr), etc. These hydrogen halide gases are heavier than air and will cover the combustion surface, diluting the oxygen concentration. At the same time, they capture the free radicals during the combustion process, interrupting the chain reaction of combustion, thus achieving the purpose of flame retardancy. However, due to the generation of toxic and harmful gases during the combustion of halogen-based flame retardants, which cause harm to the environment and human health, their application in AFSM glue is gradually being restricted.
4. Phosphorus-based Flame Retardants: Phosphorus-based flame retardants in AFSM glue can play a flame retardant role in both the condensed phase and the gas phase. In the condensed phase, phosphorus-based flame retardants decompose upon heating to produce substances such as phosphoric acid and metaphosphoric acid. These acids can promote the dehydration and carbonization of the polymer materials of the glue, forming a dense carbon layer to isolate oxygen and heat and prevent the continuation of combustion. In the gas phase, the phosphorus-containing free radicals decomposed by the phosphorus-based flame retardants can capture the hydrogen free radicals and hydroxyl free radicals during the combustion process, inhibiting the chain reaction of combustion. For example, red phosphorus, a common phosphorus-based flame retardant, in AFSM glue, red phosphorus is oxidized to produce phosphoric acid at high temperatures, and phosphoric acid is further dehydrated to produce metaphosphoric acid. Metaphosphoric acid has a strong dehydrating ability, which can quickly carbonize the polymer materials of the glue and form a strong carbon layer. At the same time, the phosphorus free radicals decomposed by red phosphorus can combine with the hydrogen free radicals and hydroxyl free radicals generated during combustion, reducing the concentration of free radicals and thus inhibiting the combustion reaction.
5. Nitrogen-based Flame Retardants: Nitrogen-based flame retardants in AFSM glue mainly play a flame retardant role by expanding into char. Nitrogen-based flame retardants usually consist of a carbon source, an acid source, and a foaming agent. When the nitrogen-based flame retardants in the glue are heated, the acid source decomposes to produce an acid, and the acid reacts with the carbon source through an esterification reaction to form a viscous carbonized substance. At the same time, the foaming agent decomposes upon heating to produce a large amount of gas, causing the carbonized substance to expand and form a thick porous foam carbon layer. This foam carbon layer has good thermal insulation and oxygen isolation properties, which can effectively prevent heat transfer and oxygen supply, thus achieving the flame retardant effect. For example, melamine-formaldehyde resin, a common nitrogen-based flame retardant, in AFSM glue, when the melamine-formaldehyde resin decomposes upon heating, melamine decomposes to produce ammonia gas and cyanuric acid, and cyanuric acid reacts with formaldehyde to form a carbonized substance. At the same time, ammonia gas, as a foaming agent, causes the carbonized substance to expand and form a foam carbon layer.

Influence of Flame Retardants on the Performance of AFSM Glue

(A) Improvement of the Flame Retardant Performance of the Glue

By adding appropriate flame retardants, the flame retardant performance of AFSM glue is significantly improved. Various flame retardant test standards can be used to evaluate the flame retardant performance of the glue, such as the Oxygen Index (OI) test, the UL94 Vertical Burning test, etc. In the oxygen index test, the addition of flame retardants increases the oxygen index of the glue, indicating that the glue requires a higher oxygen concentration to maintain combustion, and the flame retardant performance is enhanced. For example, for AFSM glue added with phosphorus-based flame retardants, its oxygen index can be increased from about 20% to more than 30%, reaching the flame-retardant grade. In the UL94 Vertical Burning test, the glue added with flame retardants may be upgraded from the original non-flame-retardant grade to V-0, V-1, or V-2 grades. Among them, the V-0 grade is the highest flame retardant grade, indicating that the glue can quickly self-extinguish during the combustion process, and the dripping substances will not ignite the absorbent cotton.

(B) Influence on Other Properties of the Glue

6. Bonding Performance: The addition of some flame retardants may have a certain impact on the bonding performance of AFSM glue. For example, some inorganic flame retardants, due to their larger particle size, may not be uniformly dispersed in the glue, which may reduce the interfacial bonding force between the glue and the bonded material, resulting in a decrease in the bonding strength. And if the compatibility between the organic flame retardant and the polymer of the glue is not good, it will also affect the bonding performance. However, by reasonably selecting the type and dosage of the flame retardant, as well as adding appropriate additives, the negative impact on the bonding performance can be reduced to a certain extent. For example, select inorganic flame retardants with a smaller particle size and perform surface treatment to improve their dispersion in the glue; add compatibilizers to improve the compatibility between the organic flame retardant and the glue polymer, so as to maintain a good bonding performance of the glue.
7. Physical and Mechanical Properties: The addition of flame retardants may also affect the physical and mechanical properties of AFSM glue, such as hardness, flexibility, tensile strength, etc. Generally speaking, as the dosage of the flame retardant increases, the hardness of the glue will increase, and the flexibility will decrease. This is because the properties and structures of the flame retardants are different from those of the glue polymers, which change the intermolecular forces and the aggregation state structure of the glue. For example, for AFSM glue added with a large amount of aluminum hydroxide, its hardness increases significantly, the flexibility becomes poor, and the tensile strength may also decrease. Therefore, when selecting the flame retardant and determining its dosage, it is necessary to comprehensively consider the flame retardant performance and physical and mechanical properties of the glue to meet the actual application requirements.
8. Aging Resistance Performance: Flame retardants also have a certain impact on the aging resistance performance of AFSM glue. Some flame retardants may decompose or migrate during long-term use, resulting in a decrease in the flame retardant performance of the glue, and may also affect other properties of the glue. For example, halogen-based flame retardants are prone to decompose under the conditions of light and high temperature, releasing hydrogen halide gas, which not only corrodes the equipment but also reduces the flame retardant performance and aging resistance performance of the glue. And some organic phosphorus-based flame retardants may migrate in the glue. Over time, the concentration of the flame retardant on the surface of the glue decreases, affecting the flame retardant effect. In order to improve the aging resistance performance of AFSM glue, flame retardants with good thermal stability and low migration tendency can be selected, and additives such as antioxidants and light stabilizers can be added to delay the aging process of the glue.

Application Case Analysis

(A) Application in an Electronic Equipment Manufacturing Enterprise

An electronic equipment manufacturing enterprise used AFSM glue added with phosphorus-based flame retardants to bond electronic components when producing mobile phone motherboards. In practical applications, this glue not only has good bonding performance, which can ensure the stable fixation of electronic components inside the mobile phone, but also shows excellent automatic fire suppression performance in case of unexpected fires. Once, in a laboratory-simulated fire scene, a combustion test was carried out on the mobile phone motherboard bonded with this glue. When the fire source contacted the motherboard, the phosphorus-based flame retardants in the glue quickly played a role, and the fire on the motherboard was suppressed in a short time and quickly extinguished. After inspection, it was found that the glue formed a dense carbon layer, effectively protecting the electronic components from damage by the fire. In contrast, the motherboard bonded without flame-retardant glue burned rapidly in the fire, and the electronic components were severely damaged. Through this application, the enterprise not only improved the safety of its products but also reduced the product losses and potential safety risks caused by fires.

(B) Application in a Construction Project

In the construction of a high-rise commercial building, AFSM glue added with nitrogen-based flame retardants was used to seal and bond fireproof doors and windows. When the building was accepted, strict fireproof tests were carried out in accordance with relevant standards. In the fire simulation test, when the fire spread to the position of the fireproof doors and windows, the nitrogen-based flame retardants in the AFSM glue expanded upon heating, forming a thick foam carbon layer, which effectively prevented the transmission of flames and heat, enabling the fireproof doors and windows to maintain integrity within the specified time and preventing the spread of the fire to other areas. At the same time, due to the good bonding performance of this glue, it ensured the sealing and stability of the fireproof doors and windows during long-term use. This application fully demonstrated the important role of AFSM glue in the field of building fire prevention, providing reliable technical support for ensuring the fire safety of buildings.

Conclusion and Prospect

(A) Research Summary

The application of flame retardants in the glue of Automatic Fire Suppression Material is an important means to improve the fire resistance of materials. Through the interaction between different types of flame retardants and the glue, AFSM glue can achieve the function of automatic fire suppression when a fire occurs, providing effective protection for people’s lives and property. At the same time, we also realize that the addition of flame retardants will have a certain impact on other properties of the glue. In practical applications, various factors need to be comprehensively considered, and appropriate flame retardants and formulations need to be selected to achieve the best performance balance.

(B) Future Research Directions and Development Trends

9. Development of New High-efficiency Flame Retardants: With the increasing environmental protection requirements, future research will pay more attention to the development of halogen-free, low-toxic, and high-efficiency new flame retardants. For example, study multi-element synergistic flame retardants. Through the synergistic effect between different flame retardant elements, the flame retardant efficiency can be improved, the dosage of flame retardants can be reduced, and the impact on the environment can be minimized. At the same time, explore flame retardants with special structures and properties, such as nano flame retardants, hyperbranched flame retardants, etc., to further improve the flame retardant performance and comprehensive properties of the glue.
10. Optimization of the Composite Process of Flame Retardants and Glue: Study how to better disperse the flame retardants uniformly in the glue, improve the compatibility between the flame retardants and the glue polymers, and reduce the negative impact on the performance of the glue. Adopt advanced preparation technologies, such as in-situ polymerization, emulsion polymerization, microencapsulation, etc., to achieve the effective composite of flame retardants and glue and improve the product quality and performance stability.
11. Expansion of the Application Fields of AFSM Glue: With the increasing attention paid to fire safety by people, the application fields of AFSM glue will continue to expand. In the future, in addition to the existing fields such as aerospace, electronics and electrical appliances, construction, transportation, etc., it will also be more widely applied in emerging fields such as new energy, smart home, medical equipment, etc. At the same time, according to the special needs of different application fields, develop customized AFSM glue products to meet the diverse market demands.
12. Strengthening the Research on the Flame Retardant Mechanism: Conduct in-depth research on the flame retardant mechanism of flame retardants in AFSM glue, reveal the interaction laws between flame retardants and glue, and provide a more solid theoretical

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