Super fiber for body armor: PBO fiber

PBO fiber PBO is the abbreviation of poly-p-phenylenebenzobisthiazole fiber (Poly-p-phenylenebenzobisthiazole). It is a reinforcing material for composite materials developed in the United States in the 1980s to develop the aerospace industry. It contains heterocyclic aromatic fibers. A promising member of the polyamide family, it is known as the 21st century super fiber.
1 Development History

PBO was invented by U.S. Air Force aerodynamics development researchers. First, the basic patent for polybenzoxazole was owned by the Stanford University Research Institute (SRI). Later, the U.S. Dow Chemical Company obtained the authorization and developed it. PBO has been industrially developed and the original monomer synthesis method has been improved. The new process has almost no isomeric by-products, improving the yield of synthetic monomers and laying the foundation for industrialization. In 1990, Toyobo Corporation of Japan purchased PBO patented technology from Dow Chemical Company of the United States. In 1991, PBO fiber was developed by Daoyi Badish Chemical Fiber Co., Ltd. on the equipment of Japan’s Toyobo Company, which greatly increased the strength and modulus of PBO fiber, reaching twice that of PPTA fiber. In 1994, Japan’s Toyobo Co., Ltd. received permission from Doichi Badish Chemical Fiber Co., Ltd. and invested a huge sum of 3 billion yen to build a 400-ton/year PBO monomer and 180-ton/year spinning production line, and began to invest part of it in the spring of 1995. Mechanized production, the production capacity reached 200 tons/year in 1998, and the trade name is Zylon. According to Toyobo’s development plan for Zylon, the production capacity will reach 380 tons/year in 2000, 500 tons/year in 2003, and 1,000 tons/year in 2008. Japan’s Toyobo is still the only company in the world that can commercially produce PBO fiber.

2. The development prospects of PBO fiber

In recent years, high-performance fiber composite reinforced materials have been widely used in construction fields such as high-rise buildings, large bridges, and ocean engineering in developed countries and regions such as Europe, the United States, and Japan. Impregnating fiber cloth with epoxy resin and pasting it on the concrete surface can greatly improve the original strength. The load-bearing capacity and earthquake resistance of the structure. In addition, in terms of bridge construction, steel wire ropes cannot be used for long bridges due to their own weight. Instead, it is hoped to use cables with light weight and high strength. Cables made of PBO fiber with high specific strength and good dimensional stability are good. choose.
PBO fiber is gradually replacing traditional material asbestos in the field of heat-resistant materials, and is currently exploring the use of PBO fiber to replace aromatic polyamide and other flame-retardant fibers in applications below 350°C. Applications above 350°C can replace inorganic fibers such as stainless steel fibers or ceramic fibers. Since inorganic fibers are hard, the products are prone to scars, which affects their performance. PBO fibers are entirely possible to overcome the shortcomings of inorganic fibers. In the past, organic fibers had insufficient heat resistance (mostly below 400°C), which limited the application and development of organic fibers. The decomposition temperature of PBO fiber reaches 650°C, which is the highest heat-resistant temperature among all organic fibers. Therefore, it is completely possible to use PBO fiber to replace the application fields above 350°C where it was difficult to use organic fiber in the past, and the application of PBO fiber heat-resistant materials can be broadened and developed.
Foreign research shows that PBO fiber still has many uses in other fields such as electrical insulation materials, satellite detection, lightweight materials, automobile industry and deep-sea oil field development. As a high-speed train car body, PBO fiber can not only reduce the weight of the car body, but also increase the strength of the car body; using the chemical corrosion resistance of PBO fiber, it can be made into various corrosion-resistant protective clothing; in aerospace, in order to reduce the limited burden, PBO fiber is suitable It is suitable for making buttons, straps, etc. used in space; in space environments ranging from -10°C to surface temperatures of 460°C, it can also be used as a material for heat-resistant detection balloons; in sports and competitive rowing sails It is mainly made of sheet-like thin plate materials made of high-strength and high-modulus fibers. In order to make the canvas deform to a minimum when it is blown by the wind, it is necessary to seek high-modulus PBO fibers to make rowing sails; in view of the PBO fiber With excellent mechanical properties, it is also a good material for manufacturing golf clubs, tennis rackets, ski poles, snowboards, surfboards, archery bow strings, and bicycle racing.
The R&D and industrialization development of key PBO fiber technologies can help my country’s PBO fiber get rid of the long-term dilemma of being subject to foreign technology monopoly and control, and embark on a path of localized and large-scale development of PBO fiber with independent innovation, bright prospects, and broad applications. It will contribute to the development, application and sustainable development of high-performance PBO materials in my country’s aerospace, national defense and civil industries.

3. Fiber properties

According to Toyobo reports, its high-end PBO fiber products have a strength of 5.8GPa (reported in Germany is 5.2GPa) and a modulus of 180GPa, which is the highest among existing chemical fibers; the heat-resistant temperature reaches 600°C, and the limiting oxygen index is 68, which is the highest in flames. It does not burn or shrink, and its heat resistance and flame retardancy are higher than any other organic fiber. Mainly used in heat-resistant industrial textiles and fiber reinforced materials.

Performance comparison of PBO and other high-performance fibers:

It can be seen from the table that the strength, modulus, heat resistance and flame resistance of PBO fiber. In particular, the strength of PBO fiber not only exceeds steel fiber, but also surpasses carbon fiber. In addition, PBO fiber has excellent impact resistance, friction resistance and dimensional stability, and is light and soft, making it an extremely ideal textile raw material.

As a super-performance fiber in the 21st century, PBO has very excellent physical, mechanical and chemical properties. Its strength and modulus are twice that of Kevlar fiber and it has the heat-resistant and flame-retardant properties of meta-aramid fiber. The physical and chemical properties completely surpass Kevlar fiber, which has led the field of high-performance fibers so far. A PBO filament with a diameter of 1 mm can lift a weight of 450 kilograms, and its strength is more than 10 times that of steel wire fibers.

4.PBO fiber surface modification

The TIFSS between the PBO fiber and the resin matrix increases, but too much coupling agent will cause the cross-linked layer of the coupling agent to be too thick, which will in turn reduce the TIFSS. The etching effect of plasma on the fiber surface first acts on the coupling agent, causing the coupling agent to form a graft cross-linked layer. This coupling agent layer can play a certain protective role on the fiber, so the σ of the PBO fiber decreases. not much.

The analysis shows that the process conditions for coupling agent and plasma modification are: the content of A-187 coupling agent is 2%, the argon low-temperature plasma treatment time is 2 minutes, the pressure is 5Opa, and the power is 30W. Among the selected coupling agents, the A-187 coupling agent has a good effect on improving the IFSS between PBO fiber development and epoxy resin. The optimal coupling agent content is 2%.

(1)When the A-187 content is 2% and the argon low-temperature plasma treatment conditions are 2min, 30W, 50Pa, the modification The ΓIFSS arsine of the final PBO fiber is as high as 10. 44MPa, which is 52% higher than the ΓIFSS modified only with coupling agent A-187, and 78% higher than the ΓIFSS of the original filament. The wettability of PBO fibers has also been greatly improved.

(2) For PBO fibers modified by argon low-temperature plasma combined with coupling agent, the decrease in ΓIFSS is not obvious over time; the increase in contact angle is not obvious, and its changes tend to be stable and slightly decrease. trend. The attenuation effect of PBO fibers modified by argon low-temperature plasma combined with coupling agent is not obvious.

5 Preparation

PBO is produced by solution condensation polymerization of 4,6-diaminophen hydrochloride (diaminoresorcin hydrochloride) and terephthalic acid using polyphosphoric acid (PPA) as the solvent. It can also be produced by dehydration of P2O5. Polycondensation, PPA is both a solvent and a polycondensation catalyst.

For the synthesis of monomer diaminoresorcin, Dow Chemical Company of the United States successfully developed the synthesis using trichlorobenzene as the starting material. In this way, no isomers are generated during the synthesis process, and the yield is very high, which is very important for the industrial production of PBO. played a big role.
The polymer spinning liquid is spun, washed and dried by dry-wet spinning method. The spinning liquid is dissolved to liquid crystallinity, and a straight chain structure can be formed when spinning using the liquid crystal spinning method. The as-spun yarn (AS yarn – standard type) has a strength of more than 3.53N/tex and an elasticity of more than 10.84N/tex. modulus. In order to increase the modulus, heat treatment can be carried out at a temperature of about 600°C to obtain a high modulus wire (HM wire – high modulus type) with a modulus of 176.4N/tex while maintaining the same strength.

6Applications

The main characteristics of PBO fiber are good heat resistance, high strength and modulus, so it is widely used.

(1)The application of filament can be used as reinforcing materials for rubber products such as tires, tapes (conveyor belts), and hoses; various Reinforcing materials for plastics and concrete; reinforcing components for ballistic missiles and composite materials; tension members for fiber optic cables and protective films for optical cables; reinforcing fibers for various soft wires such as heating wires and earphone wires; ropes and cables, etc. High tensile strength materials; heat-resistant filter materials for high-temperature filtration; protective equipment for missiles and bullets, bulletproof vests, bulletproof helmets and high-performance navigation suits; sports equipment such as tennis, speedboats and rowing boats; advanced loudspeaker vibration plates, new communications Materials; aerospace materials, etc.

(2)The application of chopped fibers and pulp can be used as reinforcing fibers for friction materials and sealing gaskets; various Resin, plastic reinforcement materials, etc.

(3)The application of yarn can be used for fire-fighting clothing; furnace work clothes, welding work clothes, etc. for heat-resistant on-site processing of molten metal. Work clothes; anti-cut protective clothing, safety gloves and safety shoes; racing suits, rider uniforms; various sportswear and active sports equipment; Carrace pilot suits; anti-cut equipment, etc.

(4) The application of short fibers is mainly used in heat-resistant cushion felts for aluminum extrusion processing; heat-resistant filter materials for high-temperature filtration; thermal protection belts, etc.