Application and current situation of textile flame retardant finishing technology
According to statistics, more than 20% of fire accidents in the world are caused or expanded by the burning of fabrics. Especially in residential fires, a greater proportion of fire accidents are caused by the ignition or spread of fabrics. Therefore, the fire protection function of fabrics is extremely important to eliminate fire hazards, delay the spread of fire, and thereby reduce the loss of people’s lives and property. Fire protection research on fabrics first started in industrially developed countries. Many industrially developed countries have formulated corresponding fire protection standards and testing methods for fabric products; some countries also enforce the fire protection performance standards of fabric products in conjunction with relevant laws. With the progress of urban modernization, tourism and transportation industries, industrial departments and research departments in various countries are competing to conduct research on fire-proof finishing technology for fabrics to meet the ever-expanding demand for fire-proof fabrics, and have formed a fierce competition in the international market. competition, thereby promoting the progress of fireproof finishing technology.
1 Combustion and fire prevention mechanism. The so-called “fire prevention” does not mean that fabrics after fire prevention will not burn when exposed to fire sources, but that the fabric can completely reduce its flammability and slow down the spread of fire. It is very fast and does not cause large-area burning. After leaving the flame, it can quickly self-extinguish and no longer burn or smolder. Fire retardants and combustion are closely related. The new view is that combustion should have four elements – fuel, heat source, oxygen, and chain reaction. Generally, fabric combustion can be divided into three stages, namely thermal decomposition, thermal ignition, and thermal ignition. Corresponding fire retardant agents are used to resist the four factors in different combustion stages, resulting in various fire prevention mechanisms and interruptions. Fire protection mechanism. According to the existing research results, the fire prevention mechanism can be roughly divided into the following types.
(1) Endothermic reaction: that is, heat removal. Fire retardants with high heat capacity undergo endothermic decomposition reactions such as phase change, dehydration or dehydrohalogenation at high temperatures, reducing the temperature of the fiber surface and flame zone, slowing down the rate of thermal cracking reactions, and inhibiting the generation of flammable gases.
(2) Formation of free radicals: The fire retardant absorbs heat and turns into a gas. The gas captures a large number of high-energy hydroxyl radicals and hydrogen radicals in the flame zone, reducing their concentration, thereby inhibiting or interrupting the combustion chain reaction. It plays a fire protection role in the gas phase.
(3) Melting theory: Under the action of heat and energy, the fire retardant agent transforms into a molten state, forming an impermeable covering layer on the surface of the fabric, becoming a barrier between the condensed phase and the flame, blocking heat conduction and heat transfer. Radiation reduces the heat fed back to the fiber material, thereby inhibiting thermal cracking and combustion reactions.
(4) Particle surface effect: If a certain amount of inert particles are mixed in the combustible gas, it can not only absorb the combustion heat and reduce the flame temperature, but also absorb a large amount of high energy in the gas phase combustion reaction on the surface of the particles. Hydrogen radicals are converted into low-energy hydroperoxy radicals, thereby inhibiting gas-phase combustion.
(5) Generation of non-flammable gases: The fire retardant agent decomposes endothermically to release non-flammable gases such as nitrogen, carbon dioxide, sulfur dioxide and ammonia, diluting the concentration of flammable gases at the cracking point of the fiber material below the combustion limit; or causing the center of the flame to There is insufficient oxygen in some areas, preventing combustion from continuing. In addition, this non-flammable gas also has a heat dissipation and cooling effect.
(6) Condensed phase fire protection: Through the action of the fire retardant, the thermal cracking reaction process of the fiber macromolecular chain is changed in the condensed phase reaction zone, prompting dehydration, condensation, cyclization, cross-linking and other reactions to occur until carbonization. In order to increase the carbonization residue and reduce the generation of flammable gas, the fire retardant agent can play a fire prevention role in the condensed phase.
Due to the different molecular structures of fibers and types of fire retardant agents, the fire protection effect is very complex and is not limited to the above aspects. In order to obtain the best fire protection effect, the above-mentioned mechanisms should be fully possible to work together, such as utilizing synergistic effects.
2 Classification of commonly used fire retardants: There are many types of fire retardants, and there are many ways to classify them. According to the classification of fire retardant elements, it is divided into halogen-containing fire retardants, phosphorus-containing fire retardants, nitrogen-containing fire retardants, etc.; according to the use method of fire retardants and the existence form in the polymer, it is divided into additive type and reactive type; according to fire retardant fabrics The degree of durability is divided into three types: non-durable fire retardant finishing agents, semi-durable fire retardant finishing agents, and durable fire retardant finishing agents; according to the type of compound, it can be divided into inorganic fire retardant agents and organic fire retardant agents. The following mainly introduces fire retardant agents classified according to the latter two methods.
1.1 Classification according to the durability of fabrics
(1) Non-durable fireproof finishing agent: also known as temporary fireproof finishing agent, most of which are water-soluble (or emulsion) inorganic salts. During treatment, the fire retardant is first dissolved in water, and the fabric can be used after dipping and drying; there are also two-bath padding, and the second bath uses ammonia or soda ash to deposit oxides on the fabric. This method is simple in process and cheap in price, but the feel of the fabric is poor and the fireproofing effect is greatly reduced after cleaning. Mostly used in disposable protective clothing.
(2) Semi-durable fireproof finishing agent: Fireproof fabrics treated with this process can withstand 1 to 10 times of gentle air cleaning, but are not resistant to high-temperature soaping. This method includes urea phosphoric acid method (usually called Banflam method), urea phosphate method, and ammonium phosphate-hydroxymethyl ammonium cyanide-methyl vinegar mixed solution method.
(3) Durable fireproof finishing agent: Chemical methods are used to carry out polymerization or condensation reaction on the internal surface of the fiber to form a water-insoluble polymer, which generally requires more than 30 times of washing resistance. The main methods include Ciba (CP) method and Proban method. The CP method is produced by the Swiss Ciba Company and is organized intoThe process is simple to implement and has significant fire protection effect; the disadvantage is that the strength loss of the fabric is greater, which has a greater impact on the performance of the clothing. The Proban method is manufactured by Oubrey-Wilson Co., Ltd. in the UK. The fabrics finished by this method have good fire retardant effects. In particular, the handle and strong retention of the treated fabrics are unmatched by any other finishing method. However, this method is dangerous. Large, environmental pollution is serious, so its promotion is limited.
2.2 Classification by type of fire retardant compounds
(1) Inorganic fire retardants: The main function of inorganic fire retardants is to absorb heat. The main varieties are aluminum hydroxide, magnesium hydroxide, red phosphorus, antimony oxide, molybdenum oxide, ammonium molybdate, zinc borate, zinc oxide, oxide Zirconium, zirconium hydroxide, etc. Among them, aluminum hydroxide, magnesium hydroxide, red phosphorus, and antimony oxide are widely used. In particular, aluminum hydroxide and magnesium hydroxide can not only play a fireproof role, but also can play a filling role. They have the characteristics of good thermal stability, high efficiency, smoke suppression, drip resistance, safe filling, basically no pollution to the environment and low price, and are widely used in halogen-free fireproof materials. However, inorganic fire retardant agents have poor washing resistance. This is because inorganic fire retardant agents have strong polarity and hydrophilicity, and have poor compatibility with non-polar fabrics. At the same time, in order to meet the specified fire protection requirements, a larger amount of inorganic fire retardant agent is added, which has a greater impact on the mechanical properties and finishing properties of the material. Therefore, the research on ultrafine and nanometerization of traditional inorganic fire retardants has received unprecedented attention in recent years. In addition, in order to reduce the dosage of fire retardants for the same fire retardant effect, compounding fire retardants and studying the synergistic effects of fire retardants have also been the research direction of fire retardants in recent years.
(2) Organic fire retardants: Organic fire retardants are divided into two series: phosphorus series and halogen series. The former is greatly restricted in use. Halogen fire retardants mainly include chlorine and bromine. However, the effect of chlorine-based fire retardants is much worse than that of bromine-based fire retardants. This is because it is difficult to generate free chlorine radicals. In addition, since bromide is relatively less corrosive and toxic after thermal decomposition, the same fire protection effect as chloride can be achieved by using a smaller amount. Therefore, the use of brominated fire retardants is much more common. However, judging from the overall usage, halogen-based fire retardants are gradually being replaced by other inorganic fire retardants due to their shortcomings such as containing halogen acid in their decomposition products, causing large smoke, and being harmful to the human body.
3 Fireproof finishing technology and application of fabrics
3.1 Fabric products fire-proof finishing production process The fire-proof performance of fabric products can be obtained through three methods. One is to perform fire-proof post-treatment on fabrics to achieve fire-proof purposes, but its fire-proof properties will gradually weaken or disappear with the increase of time and the number of cleanings. For natural fibers such as cotton, linen, wool, etc., only post-finishing methods can be adopted, that is, through adsorption deposition, chemical bonding, non-polar van der Waals force bonding and adhesion. Another approach is to directly produce fire-resistant fibers, which would make fabrics permanently fire-resistant. Polyester, vinylon and other synthetic fibers mostly adopt this method. The third method is to effectively combine these two methods to produce fire-resistant fabrics based on actual needs in production. In addition to considering its fire resistance, fire-retardant fabrics must also consider the toxicity and meltability of fire-retardant products to minimize damage to the human body and the environment.
(1) Fireproof fiber production process
The manufacturing of fire-resistant fibers mainly includes PU coating method, blending method, copolymerization method, graft modification method, and skin-core lamination spinning method. The PU coating method is a method in which fire-retardant agents are used to physically adsorb or chemically combine fibers during the manufacturing or production process, so that the fire-retardant agents adhere to the fibers to achieve fire prevention purposes. However, physical adsorption can easily cause problems such as moisture absorption and toxicity, while chemical adsorption can cause defects such as a decrease in fabric strength and a hardened feel. Moreover, the treatment scope of this fire prevention method is limited, and it depends on the skills of the post-finishing factory. The treatment effect is unstable and the durability is poor. This method is generally used for fireproof finishing of natural fiber fabrics and synthetic fiber blended chemical fiber fabrics. It can also be used for the treatment of pure polyester, polyacrylonitrile and other fabrics, but its application is not universal. The blending method is a method of producing fire-retardant fibers by adding fire-retardant agents during the manufacturing process of spinning chips or by adding fire-retardant agents to the spinning melt. Taking the manufacture of fire-retardant polypropylene fiber as an example, there are two methods of adding fire-retardant agents: ① Full granulation method: blend polypropylene, fire-retardant agents, and stabilizers, and then extrusion and granulation. By spinning this material, polypropylene fiber with fire-retardant properties can be produced. ② Masterbatch method: The fire retardant, carrier, stabilizer, etc. are blended and granulated. This material pellet is the masterbatch. During spinning, the masterbatch is added to the polypropylene slices in a certain proportion and mixed evenly, and then spun to produce fire-resistant polypropylene fibers. This method is more commonly adopted, lowers the spinning temperature, improves the spinnability of polypropylene, and has little impact on the strength, elongation and other qualities of the yarn. The copolymerization method is a method in which a fire retardant is added as one of the monomers during the polymerization process of the polymer and copolymerized to produce spinning chips containing fire retardant chemical units in the molecular chain. Polymers modified in this way have durable fire resistance. This method is mainly used for addition polymerization (polyacrylonitrile) and condensation polymerization (polyester, polyamide). The graft modification method uses radiant heat, high-energy electron beams or chemical initiators to graft and copolymerize fibers and fire-resistant monomers to obtain effective and durable fire-resistant modification methods. The fire resistance of grafted fire-resistant modified fibers is related to the fire-resistant elements in the graft monomer and the parts of the graft copolymer. Fire retardant modification method for sheath-core bonded spinningThis method is less commonly used, mainly because it requires complex spinning equipment. In recent years, the lamination spinning method has been used to prepare fire-resistant polyester, which mostly adopts a sheath-core structure, that is, copolymerized or additive fire-resistant polyester is used as the core and general polyester is used as the skin layer. This can not only prevent the halogen fire retardant from prematurely decomposing the hydrogen halide and leaving the flame and affecting the fire retardant effect, but also prevent the shortcomings of some phosphorus-containing fire retardants that are not resistant to high temperatures, and also allow the fiber to maintain its original appearance, whiteness and colorability. .
(2)Production process of fire-retardant fabrics
The finishing processes for fireproof finishing of fabrics mainly include the following.
a. Padding and baking method
This method is one of the most commonly used post-fire 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.
b. The process flow of the impregnation and drying method is: impregnation-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 carried out at the same time as the coloring process.
c. Coating method
It mixes fire retardant into resin for finishing. According to different mechanical equipment, it can be divided into doctor blade coating method, casting coating method and calendar coating method. Different products adopt different finishing methods.
Squeegee coating method: Apply the slurry mixed with fire retardant directly on the fabric with a scraper. Most fire retardants are first made into solutions or emulsions and then applied. Casting 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. Calendering coating method: The polymer is made into a film on a calender, and then laminated to the fabric. Generally, PVC resin, polyvinylidene chloride resin, and copolymers of such resins are mixed with fire retardants. This method is mainly adopted for the fire prevention finishing of engineering tents.
d. Spray method
Thick curtains, large carpets and other products that cannot be finished with general equipment can be treated with manual spray fireproofing in the next step. For fabrics with bulky surface patterns, tufting, and pile raising, if the padding method is used, the surface pile pattern will be damaged, so the continuous spray method is generally used.
e. Organic solvent method
Dissolve the fire retardant with organic matter, 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.
3.2 Application of fireproof finishing technology for fabrics
3.2.1 Fireproof finishing of cotton fabrics
Among various fabric materials, cotton is one of the most dangerous to burn. Its oxygen content index is only 18. It not only burns quickly, but also has great combustion-supporting properties. In addition, cotton fabric is a widely used fabric, so the research on fireproof finishing of cotton fabric was carried out relatively early and is currently progressing relatively maturely. The fire resistance of traditional cotton fabrics is mainly achieved by padding the fire retardant into the fabric, so that the fire retardant evenly penetrates into the fiber and reacts chemically with the fiber to firmly adhere to the fiber. After the fire retardant agent of the fire retardant fabric encounters high temperature or high heat, it can quickly produce gas that blocks the reaction of the OH group during the combustion process, so as to reduce the heat energy released, so that the combustion cannot continue to progress, so that the fabric has a positive effect on fire prevention. The process is simple, the cost is low, and good and durable fire protection effects can be obtained. In recent years, with the continuous progress and progress of fire-proof finishing technology, and in order to meet the market’s increasingly higher requirements for fire-proof cotton fabrics, various new fire-proof finishing technologies have gradually been explored for the fire-proof finishing of cotton fabrics. , such as: nano fire protection technology, catalytic fire protection technology, green fire protection technology, microcapsule fire protection technology, compound fire protection technology, etc.
3.2.2 Fireproof finishing of wool fabric
Wool is a natural protein fiber with complex physical and chemical structures. It has a soft feel, firm texture, good elasticity and warmth retention, and is natural and soft. It is widely used in construction, clothing, home textiles and other fields. This puts forward higher requirements for post-processing. Wool has a limiting oxygen index of about 25, a flash point of 570-600°C, and a high combustion temperature of 680°C. It is a natural flame-retardant fiber. It will not melt or drip when burned, and the foamed ash produced has good insulation. The moisture regain of wool is as high as 15%, the relative humidity is 60%, the nitrogen content is 15% to 16%, the sulfur content is 3% to 4%, and it also contains 6% to 7% hydrogen. The high nitrogen content determines that it has better fire-proof properties. If it is subjected to fire-proof finishing, higher-performance products can be developed. The fireproof finishing of wool fiber initially used inorganic boric acid, phosphoric acid and their salts. This finishing method is non-durable finishing, not resistant to water washing, and is only used for theater curtains, etc.; later, modified tetrahydroxymethylphosphorus chloride (THPC) and its derivatives and sulfamate were used to treat wool After fireproofing, it can reach a semi-permanent level; then it has progressed to using fluorine complexes and carboxylic acid complexes of titanium and zirconium to treat wool, which can reach a permanent level. In recent years, in order to meet higher requirements, high-temperature resistant fabrics made of wool and other flame-resistant fiber blended chemical fiber fabrics have been developed.
3.2.3 Fireproof finishing of polyester fabrics Polyester is a synthetic fiber with rapid development, high output and wide application range among various synthetic fibers. Its fiber fabrics are widely used in clothing, curtains, curtains, bedding, etc. Interior decoration and various extraordinary materials. The limiting oxygen index of polyester is around 21. With the widespread use of polyester fiber fabrics, its potential fire hazard is also increasing.Outstanding benefits.
my country began to conduct research on fire-resistant polyester in the early 1980s, which can be roughly divided into three stages: the first stage uses bromine-containing comonomers and polyester monomers for ternary copolymerization; the second stage is in the mid-1980s , Liaoyang Petrochemical Research Institute uses decabromodiphenyl ether-based fire retardant provided by the American Great Lakes Company to produce blended fire-retardant chips. However, both methods failed to continue industrial production due to various reasons; the third stage started in the late 1980s, when domestic textile colleges and universities began to get involved in the research of fire-resistant polyester, which played a great role in promoting the progress of this work. This research field has made great progress from products to theory. According to the production process and the introduction method of fire retardant agent, the fire retardant modification methods of polyester can be summarized into the following five types: (1) Adding reactive fire retardant agent during the transesterification or polycondensation stage for co-condensation polymerization; (2) Before melt spinning Add additive fire retardant to the melt; (3) Laminate spinning with general polyester and polyester containing fire retardant components; (4) Reactive fire retardant agent is grafted and copolymerized on polyester or fabric; (5) Polyester fabrics are subjected to fire-retardant post-treatment. The organic fire retardants used in the production of fire-resistant polyester fabrics are mostly halogen-based and phosphorus-based fire retardants. Currently, halogen-based fire retardants are used in the majority. With the in-depth research on fire and fire-proof materials and the enhancement of environmental awareness, especially since the 1990s, phosphorus-based fire retardants with low smoke and low toxicity have received widespread attention. Although phosphorus-based fire retardants do not produce toxic substances during use, various intermediates and production processes of fire retardants have certain toxicity. People will gradually pay attention to the research and application of silicon-based fire retardants and other inorganic fire retardants. . Inorganic fire retardants have the advantages of being smokeless, non-toxic, non-corrosive, safe and cheap. Inorganic substances such as boric acid, mica, ceramics and carbon black can also be used for fire-retardant modification of polyester.
3.2.4 Fireproof finishing of polyester-cotton blended chemical fiber fabrics
Polyester-cotton fabric is one of the most widely used fabrics today. It is mostly used for protective clothing and interior decoration, and requires high fire resistance. The flammability of polyester-cotton blended chemical fiber fabrics is not equal to the sum of the flammability of each fiber component of polyester and cotton. During the burning process of polyester-cotton fabric, the molten polyester component covers the surface of the pyrolyzed cotton fiber (carbon-like). The carbon structure of pyrolysis cotton blocks the thermal shrinkage of polyester fibers, so it will not automatically drip away from the burning heat source. In fact, the fibrous carbon-like coke not only supports the molten polyester, but also wicks the molten polyester body into the burning heat source, increasing the supply of fuel in the fire zone. This phenomenon is called ” “scaffolding” effect. It is this “scaffolding” effect that makes polyester-cotton blended chemical fiber fabrics much more flammable than people expected. Although a lot of research has been done at home and abroad on the flammability and fireproof finishing of polyester-cotton blended chemical fiber fabrics, so far no ideal durable fireproof finishing agent for polyester-cotton fabrics has been developed.
From the induction effect produced after cleaning the cotton fabric and the decomposition of the cotton component; the second is that the two components each adopt two different components of fire retardants. The two fire retardants do not interfere with each other and have a synergistic effect. At least these two fire retardants will not cause thermal migration.
At present, the post-finishing method of padding and baking is mainly used to obtain fire-proof properties of polyester-cotton fabrics.
3.2.5 Fireproof finishing of other synthetic fibers
Domestic research on fire-resistant nylon began in the 1970s, and development and progress have been relatively slow. This is mainly because the amide in the nylon macromolecules is more active and easily reacts chemically with the fire retardant in the molten state. Moreover, the hydrogen halide produced by many additives at high temperatures can degrade nylon macromolecules and reduce the melt viscosity, making many fire retardant agents used to make fire retardant fibers unusable. At present, the best fire retardant used in the production of fire retardant nylon in China is the NF-8702 nylon fire retardant produced by Shanxi Chemical Fiber. The production of fire-resistant nylon is mainly based on blending, and the fire-retardant agents used are mainly halide systems and organic phosphorus systems containing synergists. The production method of fire-resistant polyacrylonitrile is mainly copolymerization. The copolymerized fire-retardant monomer is mostly vinyl chloride or vinylidene chloride, and its content is generally in the range of 32% to 36%. If it exceeds 40%, the thermal stability of the polymer will decrease and the spinning performance will deteriorate. There are two polymerization methods: solution polymerization and aqueous phase polymerization. Aqueous phase polymerization is often adopted because it is suitable for large-scale production. There are many units in my country that develop fire-retardant polyacrylonitrile fibers. The limiting oxygen index of the fire-retardant polyacrylonitrile fibers they produce is above 27, but none of them has reached mass production.
4 Progress Trends in Fireproof Finishing Technology for Fabrics
Our country has successfully developed a variety of fireproof materials, creating a new approach to the fireproof technology of our country’s fabrics. However, in terms of variety, quantity and fire protection performance, there is still a big gap with developed countries. With the development of the economy and the improvement of the national legal system, the promotion and application of fire-resistant fabrics will surely attract the attention of the whole society. Fire-retardant fabrics have broad market demand in our country and have huge development potential. The progress of fire protection technology in the future will generally have the following trends.
(1) Strengthen the research on fire prevention theory. The research on fire prevention theory is the foundation of the entire fire prevention technology. The research on combustion and fire prevention theory provides a strong theoretical basis for finding new fire retardant agents, determining fire prevention methods, and improving fire prevention levels. It is very important. practical significance.
(2) Develop new low-toxic, smokeless, and pollution-free fire retardant agents to move toward halogen-free and ultra-fine fire retardants.development to reduce the harm of fire accidents to human life and the natural environment.
(3) Develop synergistic fire retardant agents, such as phosphorus, nitrogen, bromine, etc. that are combined in molecules or between molecules to improve the fire retardant effect and reduce interference with the original production process and product quality.
(4) Strengthen functional research on fire-retardant fabrics. In addition to fire-retardant functions, fire-retardant fabrics can also be given different functions according to the different needs of users, such as water-repellent, oil-repellent, bacteriostatic, and anti-static and many other functions.
(5) Attention should be paid to the environmental problems caused by fire retardant agents. The disposal of fabrics treated with fire retardant treatment must consider not causing negative impacts on the environment, such as recycling, utilization of combustion heat energy, and waste disposal.
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