A brief discussion on textile flame retardant technology
With the improvement of people’s living standards and the enhancement of people-oriented security awareness, the fireproof performance of fabrics has attracted more and more attention. Most of the fabric materials we currently use are flammable or combustible materials. Fabrics are often the first ignition items in fires, and fires cause countless casualties and economic losses every year. Therefore, how to reduce the danger of burning fabrics and the release of toxic gases when burning, and how to reduce the loss of people’s lives and property, has attracted the attention of all mankind.
1. The burning process of fiber
Fiber combustion is when the fiber material comes into contact with a high-temperature heat source and absorbs heat to undergo a pyrolysis reaction. The reaction generates a large amount of flammable gaseous decomposition products. These decomposition products burn in the presence of oxygen, and the heat generated by combustion is absorbed by the fiber. Finally, it promotes the pyrolysis and combustion of the fiber, thus forming a cyclic combustion reaction (Figure 1).
2. Fire prevention mechanism
In view of the burning process of fabric fibers, the fire protection principles of fabrics can be simply summarized into the following aspects.
1. Vapor phase fire prevention
Due to the effect of the fire retardant, some non-combustible gases are generated through thermal decomposition during the combustion process. These non-combustible gases dilute the combustible gas produced by the decomposition of the polymer on the one hand, and isolate the oxygen and the combustion material on the other hand. touch.
2. Solid phase fire protection
After the fire retardant is thermally decomposed, it quickly generates acid or alkali, which dehydrates and carbonizes the polymer to form a non-volatile carbon layer; or the fire retardant and the polymer form cross-links during combustion to change the normal decomposition and combustion mechanisms. , avoiding further oxidation and combustion.
3. Chemical reaction fire prevention
By adding appropriate chemical components and elements, it can be heated to decompose into free radicals, interrupt the strong chain reaction that occurs during the combustion process, or change the decomposition rate of polymerization to reduce the energy of the combustion system.
3. Fire prevention methods
1. Fireproof fiber
The manufacturing methods of fire-retardant fibers can usually be summarized into the following three categories.
(1) Copolymerization method
In the synthesis process of fiber-forming polymers, compounds containing fire-retardant elements such as phosphorus, halogen, and sulfur are introduced into the macromolecular chain as comonomers (reactive fire-retardant agents), and then this strong fire-retardant substances added to the fiber.
(2) Blending method
Both the copolymerization method and the copolymerization method belong to the original fiber modification. It is a method of adding fire retardant agent to the spinning melt or spinning fire retardant fiber.
(3) Graft modification
Using radiant heat, high-energy electron beams or chemical initiators to graft copolymerize fibers (or fabrics) and vinyl-type fire-retardant monomers is an effective and durable fire-retardant modification method. The fire resistance of grafted fire-resistant modified fibers is related to the type of fire-resistant elements in the graft monomer and the grafting position. The order of influence of the grafting position on the fire-retardant effect is: core grafting > uniform grafting > surface grafting.
No matter which method is used, the fiber should be given good fireproofing effect, fabric finishing properties and wearability. It can be seen that fireproof fiber is mainly for chemical fiber, that is, it has fireproof properties during the manufacturing process of chemical fiber (especially synthetic fiber). The key to fireproof technology is the type and performance of the fireproof agent.
2. Fire prevention finishing
Fire-proof finishing mainly involves surface treatment of fabrics during the finishing process, so that the fabric has fire-proof properties. The fabric fireproof finishing process is simple, requires less investment, and has quick results, making it suitable for the development of new products. The main forms of fireproof finishing for fabrics include the following.
(1) Spray method
Thick curtains, large carpets and other products that cannot be finished with general equipment can be treated with spray fireproof finishing in the next step.
(2) Dip and drying method
The process flow is: dipping→drying→post-processing.
It involves soaking the fabric in a fireproof liquid for a certain period of time, then taking it out and drying it. Sometimes the fireproof finishing can be done in the same bath as the coloring process.
（３）Padding and baking method
This method is one of the most commonly used fire-proof finishing methods. The process flow is: padding → pre-baking → baking → post-treatment.
The padding liquid is a fire retardant solution, which is suitable for fire retardant finishing of cellulose fiber fabrics.
(4) Organic solvent method
Use organic matter to dissolve the fire retardant, and then perform post-fire retardant finishing. It can shorten the finishing time. During the operation, attention must be paid to the toxicity and flammability of the solvent.
(5) PU coating method
It mixes fire retardant into resin for finishing. According to different mechanical equipment, it can be divided into scraper PU coating method, cast PU coating method and calendered PU coating method. Different products adopt different finishing methods.
Calendering PU coating method: The polymer is made into a film on a calender, and then laminated to the fabric. Generally, a mixture of PVC resin, polyvinylidene chloride resin and copolymers of such resins and fire retardants are used. Mainly Applied to the fire prevention finishing of engineering tents.
Scraper PU coating method: Coat the slurry mixed with fire retardant directly on the fabric with a scraper. Most fire retardants are made first.Apply after lotion or lotion.
Casting PU coating method: The polymer casting film is attached to the fabric under pressure. Suitable for large curtains and civil engineering supplies with high fire retardant content.
4. Fire retardant
Most of the fire retardants currently used are organic compounds of phosphorus or halogen, or organic compounds plus inorganic compounds. Some of them use polymers, such as cyclic aromatic phosphates, hydroxyethyl tetrabromobisphenol A (polyester); chlorinated Polypropylene, hexabromocyclodecane, oxalate (pentabromobenzene) ester, tribromophenyl phosphate-chlorinated paraffin, dimer of hexachlorocyclopentadiene, etc. (polypropylene); contains synergist Halide system, organic phosphorus (nylon); vinyl chloride, vinylidene chloride, vinyl bromide, antimony pentoxide, etc. (polyacrylonitrile fiber) and phenoxyphosphazene, thiophosphate (viscose), etc. .
For different fire protection mechanisms, different fire retardants are produced. The following is a brief introduction to halogen-containing fire retardants and organophosphorus fire retardants.
1. Halogen-containing fire retardant
(1) Inorganic fire retardant
The main function of inorganic fire retardants is to absorb heat, and their main advantage is their low price. The development trend of inorganic fire retardants is to provide better quality products, on the one hand, towards fine and ultra-fine particles, and on the other hand, towards improved size distribution.
(2) Organic fire retardant
The fire prevention effect of halogen-containing organic fire retardants is to produce hydrogen halide heavier than air at a certain high temperature, which is deposited on the outer layer of the burning material, diluting the surrounding air, isolating fresh air, and suffocating the burning material. At the same time, hydrogen halide can also capture hydroxyl radicals, thereby reducing flames.
Usually only compounds containing bromine or fluorine are used. Since the bond energy of C-Cl is much larger than that of C-Br, it is less likely to generate free radicals. Therefore, the fire retardant effect of chlorine-based fire retardants is worse than that of bromine-based fire retardants. many. At present, chlorine-based fire retardants are mostly used in conjunction with inorganic fire retardants, which can achieve better results.
When halogen-containing fire retardants catch fire, they will generate halogen acid, which may cause corrosion of circuit switches and other metal objects that cannot be caused by fire alone. The harm to the human respiratory tract and other organs is even more serious, and it is on the way to elimination.
2. Organophosphorus fire retardant
The mechanism of organophosphorus fire retardant is the same as that of inorganic phosphorus, but it is relatively prominent because it has a relatively small impact on the structural and physical properties of fabric materials. The usual shortcomings of organophosphorus fire retardants, such as strong fluidity, large amount of smoke, easy hydrolysis and poor thermal stability, have also been gradually overcome. Organophosphorus fire retardants mainly include halogenated phosphorus systems and non-halogenated phosphorus systems.
(1) Non-halogen phosphate
Due to the environmental impact caused by halogen-containing phosphate compounds, research programs have gradually shifted to non-halogen phosphates. The original fire protection field of halogen-containing organic compounds is being occupied by halogen-free organophosphorus compounds.
Another important feature of halogen-free organophosphorus fire retardants is the synergistic application of phosphorus and nitrogen and a good foaming carbon system. Taken together, organic halogen-containing fire retardants are gradually at a disadvantage, while non-halogen-containing organic phosphates used in fabric fire protection have relatively excellent performance and are in a dominant position.
(2) Halogen-containing phosphate
Because it contains both halogen and phosphorus, the fire retardant agent works in the same gas phase and condensed state, and the fire retardant effect is particularly ideal. Halogen-containing phosphate esters have the advantages of low volatility, colorless, bromine-free, and hydrolysis resistance. , but its heat resistance is poor, and its thermal stability needs to be improved.
5. Progress Trends in Fire Protection of Fabric Products
1. Develop new environmentally friendly fire retardants
Fire retardant science is an emerging subject. However, with the continuous advancement of industrial technology, the needs and requirements for the fire retardant industry at home and abroad have become higher and higher. In the future, the progress of fire retardants will generally have the following trends. .
Develop fire retardants that are efficient, non-toxic and have little impact on material properties. This leads to the development of reactive fire retardant agents and the development of additive fire retardant agents with good compatibility.
Develop fire retardants with synergistic effects, such as molecular or intermolecular combinations of phosphorus, nitrogen, and bromine.
2. Strengthen research on multi-functionality of fire-proof fabrics
At present, most fire-retardant fibers or fabrics only have fire-retardant functions and cannot meet the extraordinary requirements of some departments, such as fire-repellent and water-repellent, fire-repellent and oil-repellent, fire-retardant and anti-static. There is a great demand for fire-resistant protective clothing in metallurgy, forestry, chemical industry, petroleum and fire protection departments. In addition to fire protection, they also need to be water-resistant, oil-repellent and anti-static
Electricity and other functions. Therefore, it is imperative to develop fireproof multi-functional products.
3. Strengthen the development and research of fire-resistant fibers
Fire-retardant fibers are widely used in clothing fabrics, interior decoration fabrics, transportation, protective and industrial fabrics. For fire-resistant fibers, not only its fire-resistant properties should be considered, but also its spinnability and thermal and moisture comfort properties should be taken into consideration. From the perspective of environmental protection, human safety and fire prevention efficiency, the development of environmentally friendly fire-proof fibers that are halogen-free, efficient, low-smoke and low-toxic is the future development trend.
The use of fabrics is one of the important factors that pose a fire threat, and adopting fireproofing methods to treat fabrics is an important measure to reduce the risk of fire. Combined with the fire protection requirements of fabrics, we develop and produce environmentally friendly fire-proof fabrics with low toxicity, low smoke and excellent performance.This can effectively prevent the fire threat of fabrics and provide safety guarantee for the safety of people’s lives and property.
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