Category analysis of high temperature resistant flame retardant fibers
In recent years, with the development of the economy and the improvement of the national legal system, the promotion and application of fire-retardant fabrics will surely attract the attention of the whole society. There is a lot of development and research on fire-proof fabrics abroad. Some industrially developed countries formulated fire-proof regulations for fabrics as early as the mid-1970s. In recent years, the requirements have become higher and higher, and the regulations have become more and more detailed. The Fire Protection Law of the People’s Republic of China, which came into effect on September 1, 1998, has promoted the development of fire-proof fabric technology in our country.
In recent years, my country’s research and development on fire-resistant fabrics has gradually increased and considerable progress has been made. With the acceleration of urban modernization, the progress of tourism and transportation industries, and the increase in demand for export fabrics, there is a huge potential market for fire-resistant fabrics. According to the survey, the consumption of fire protection products is mainly distributed in the steel casting industry, fire protection service industry and chemical manufacturing industry; government units mainly include: hospitals, military, and forest fire fighting service teams. In addition to clothing, flame-retardant textiles for cars, trains, and airplanes also have endless potential. In addition, if you add seat covers for movies, theaters, and auditoriums, the value will be even more considerable. As a result, the requirements for the high temperature resistance of fire-retardant fibers are getting higher and higher.
1. Thermosetting three-dimensional cross-linked fiber
The characteristic of this fiber is that at least one monomer in the fiber monomer has 3 or more functional groups, so that the fiber molecular chain can eventually form a three-dimensional cross-linked structure, and the cross-linked structure has an important effect on the fiber’s properties. High temperature resistance and fire resistance have a direct impact. Phenolic fiber and melamine formal fiber are both thermosetting three-dimensional cross-linked fibers.
(1) Melamine formal fiber (MF)
Melamine-formaldehyde fiber, commonly known as melamine fiber, is made by condensing melamine and formaldehyde in a specific solvent into a prepolymer of a certain relative molecular weight, which is solidified into fiber through centrifugal spinning at high temperature. The LOI is as high as 37 or above. When exposed to fire, it does not shrink or dissolve. It can still basically maintain its original shape up to 400°C. When carbonized at higher temperatures, there is basically no toxic gas generated, the amount of smoke is also very small, and the fiber whiteness is high. Stable color, good colorability, acid and alkali resistance and most chemical reagents. Phenolic resin fiber (Kynol)
(2) Phenolic resin fiber is a fiber with a three-dimensional cross-linked structure, which breaks the traditional concept that thermosetting resin cannot form fibers. It is based on thermoplastic pure linear polyphenolic (Novolac type) with a relative molecular mass of 300-2000. The raw material is produced by melt spinning and then cross-linking in the presence of acid and formaldehyde. Because the phenolic resin fiber is highly cross-linked and has stable chemical properties, the LOI can reach about 34. The phenolic resin fiber does not melt or burn at high temperatures. It does not shrink even if it is carbonized into a glass-like structure. The carbonization process does not contain alkenyl gases and toxic gases. produce. In practical applications, phenolic resin fibers have many defects. For example, the fibers are brittle and have low wear resistance, with a strength of only 0.882-1.323cN/dtex. The fibers have poor colorability and are prone to discoloration under sunlight.
2. Graphitized carbon fiber
Carbon fiber refers to fibers in which the carbon element accounts for more than 90% of the total mass in the chemical composition of the fiber. According to raw materials, carbon fiber can be divided into: polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and cellulose-based carbon fiber. Using special PAN fibers as raw filaments, they are pre-oxidized in an air oxidation furnace at 200-300°C to form a pre-oxidized filament with a trapezoidal structure of a conjugate system. Subsequently, they are carbonized in an inert gas at 1200-1600°C. From minutes to 10 minutes, carbon fiber can be obtained. The carbon fiber is graphitized in an inert gas at 2000-3000°C for several seconds to 10 seconds to obtain graphitized carbon fiber. At a high temperature of 2000°C, the fiber forms a graphite-like hexagonal crystal structure, and the more complete the crystal structure, the better the fiber performance.
3. Linear aromatic high temperature resistant and fire retardant fiber
The molecular main chain or side chain of this type of fiber contains rigid benzene rings. The high temperature and fire resistance of the fiber and the density of the benzene rings are closely related to the position and linking method of the benzene rings in the molecule.
(1) Aromatic fibers containing heteroatoms
Introducing one or several specific heteroatoms into the aromatic fiber molecular chain can further improve the fiber’s chemical resistance or heat and fire resistance. Polyphenyl sulfate fiber (PPS) belongs to this type.
Polyphenylene sulfate fiber was developed and produced by Philips Petroleum Company in 1973. When PPS resin is heated in the air to close to the melting point, the polymer will undergo chain stretching and cross-linking, and the relative molecular mass will be further improved. . PPS resin can be made into short fiber products by melt spinning method. The LOI can reach about 35, and it can withstand most chemical reagents. Its strength and stability in strong acids, strong alkali and organic solvents are second only to polytetrazoethylene fiber. It has rare thermal stability. At 200°C, after 54 days, there is basically no loss in breaking strength. At 260°C, after 48 hours, the fiber strength maintains 60% of its original strength.
(2) Poly-m-phenylene isophthalate fiber (MPIA) Poly-diamine isophthalate fiber is a meta-aramid fiber produced by DuPont Company, and its trade name is Nomex. MPIA is based on m-phenylenediamine.
(MPD) and chlorine isophthalate (ICI) are monomers and are produced by dry spinning after interfacial polycondensation or low-temperature solution polycondensation. The glass transition temperature of Nomex is about 270℃, the thermal decomposition temperature is as high as 430℃, the working time is up to 20000h at 200℃, and the strength remains 90% of the original, 260℃After working continuously in hot air for 1000 hours, the strength remains about 70% of the original, the MPIA fiber does not melt, and the LOI is about 32. Nomex is resistant to most acids, but its strength will decrease due to long-term exposure to strong acids or alkalis. Moreover, Nomex can slowly embrittle under high-temperature water vapor and release a small amount of flammable carbon monoxide gas when dispersed.
(3) Polyphenylene terephthalate fiber (PPTA)
PPTA’s trade name is Kevlar, which is called Nomex in my country. It is a high-strength, high-modulus, high-performance special synthetic fiber. It is also an excellent high-temperature fire-resistant fiber with a limiting oxygen index (LOI) of up to Around 30, the glass transition temperature is around 345°C, it does not melt at high temperatures, and its decomposition temperature is as high as 560°C. Kevlar can be used alone and is more commonly used in the field of laminate materials. Although Kevlar has extremely superior performance, its output is small and expensive. It is mainly used in the aerospace and defense industries, and a small amount is used for protection such as body armor.
(4) Aromatic heterocyclic fibers introduce heterocyclic groups into the molecular structure of aromatic fibers to limit the degree of freedom of molecular conformation and increase the covalent bonding energy on the main chain. It is possible to significantly improve Modulus, strength and heat resistance of fibers.
①PBI PBI fiber has high insulation and good heat resistance, with a dispersion temperature of 660°C, good thermal stability and low thermal shrinkage. FBI is high temperature, smokeless and low-toxic, with an LOI as high as 48. However, PBI has poor durability. Under the influence of sunlight, its strength and relative molecular weight drop significantly, and its stability to chemical reagents is poor. In addition, the amine monomers used to synthesize resins are carcinogenic, which limits the promotion of FBI.
②PBO
PBO is different from PBI in that it is not only a high-temperature resistant and fire-resistant fiber, but also a high-strength, high-modulus, high-performance fiber with even better mechanical properties than Kevlar. PBO is obtained by liquid crystal spinning using 2,4-diaminoresorcin hydrochloride and terephthalic acid as monomers. PBI has an LOI of 68 and a thermal dispersion temperature of 65°C.
4.Visil
Visil fiber is a new high-temperature resistant and fire-resistant viscose fiber. It is a blended fiber composed of cellulose and silicate. It has a short-term heat resistance temperature of 1300°C, a long-term use temperature of 320°C, and an LOI of about 31.
5. Polytetrafluoroethylene fiber (polytetrafluoroethylene)
Polytetrafluoroethylene fiber is the earliest developed variety among high temperature resistant and fireproof fibers. It cannot be dissolved by any solvent, and its melting point is close to its decomposition point, so it cannot be made into fibers by traditional solution or melt spinning methods. The resin obtained by emulsion polymerization can be spun by carrier, film split spinning or paste extrusion. Made by pressing. The long-term use temperature of PTFE is 120-250°C, and the strong failure temperature is 310°C. When heated to above 390°C, depolymerization begins, and the LOI is as high as 95. It is an organic fiber that is flame retardant in a high oxygen environment.
6. Other types of high-temperature-resistant fire-retardant fibers. In recent years, several new high-temperature-resistant fire-retardant resin raw materials and fiber varieties have been developed in the world. In addition to excellent high-temperature resistance and fire-retardant properties, these new varieties are closer to each other in terms of mechanical properties. Or reach the level of high-performance fibers (such as PK and PEEK), and compared with traditional high-performance fibers, the production process is simpler and the cost of the finished fiber is lower.
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