Research Status and Application Of Surface Metallized Fiber Materials

 

Abstract:

With the rapid development of technology in the fields of aviation, aerospace, military industry, electronics, etc., more functional characteristics are required for low-density and high-strength fiber materials, such as electromagnetic shielding and high conductivity. Fiber surface metallization is expected to improve its conductivity and shielding performance, and has become one of the current research hotspots. This paper introduces the commonly used surface metallization processes of fiber materials, focusing on the current status of metallization research and application progress of carbon fibers (such as carbon fibers and carbon nanotube fibers) and organic fibers (such as aramid and polyimide fibers), and looks forward to the future development trend and application prospects of metallized fiber materials.

 

Introduction

With the rapid development of technology in the aviation, aerospace, military industry, electronics and other industries, more stringent requirements are put forward for the performance of various materials. Fiber materials such as carbon fibers, aramid fibers, polyimide fibers, etc. have excellent properties of low density, high specific strength and high specific modulus, and are currently widely used lightweight structural reinforcement materials. However, compared with traditional metal wire materials, non-metallic fiber materials have some weaknesses: although carbon fiber has certain conductivity and electromagnetic shielding characteristics, it is difficult to meet the application requirements of high-performance devices; aramid and polyimide fibers are not conductive and cannot be directly used in special functional application fields such as electromagnetic shielding, wires, and space antennas. Therefore, how to achieve the integration of fiber material structure and function is one of the current research hotspots.

 

Metallization on the fiber surface is the most direct and effective way to solve the above problems. While maintaining the original excellent properties of the fiber, it gives it excellent electrical conductivity, thermal conductivity, electromagnetic shielding and other special functions. The prepared new functional materials have broad application prospects in the fields of functional devices such as space antennas, lightweight flexible wires, large-capacity capacitors, and electromagnetic shielding sheaths. This paper reviews the common methods of fiber surface metallization, and focuses on the current status of metallization research and application progress of carbon fibers (such as carbon fibers and carbon nanotube fibers) and organic fibers (such as aramid and polyimide fibers).

 

1 Common Fiber Surface Metallization Process Methods

 

Currently, common fiber material metallization process methods include electroplating, chemical plating, magnetron sputtering, chemical vapor deposition, etc.

 

1.1 Electroplating

Electroplating is to pass direct current into an electrolyte solution containing pre-plated metal salts, with the surface pre-treated fiber as the cathode. Through the electrochemical action of the plating solution and the electrode interface, the cations of the pre-plated metal in the plating solution are reduced and deposited on the substrate surface to form the target plating layer. In order to improve the wettability of the fiber in the plating solution and the bonding strength between the fiber and the plating layer, the fiber surface needs to be pretreated. Electroplating has the advantages of low temperature operation, fast plating speed, low cost, and continuous production. However, the electroplating method is limited by the uneven distribution of electric field lines, and it is difficult to plate on complex surfaces.

 

1.2 Chemical Plating

Chemical plating is a process in which metal ions are reduced to metal plating layers on plated parts with catalytic surfaces (the catalyst is generally palladium, silver and other precious metal ions) through a controllable redox reaction under the action of a reducing agent without current passing. It is also called self-catalytic plating or electroless plating. Usually, chemical plating also requires surface pretreatment of the fiber to increase the content of carboxyl and carbonyl groups on the fiber surface to improve the fiber wettability and the bonding force between the fiber and the metal ions. The most prominent advantage of chemical plating is that it can be carried out in complex components. Compared with electroplating, chemical plating has the characteristics of uniform coating thickness, fewer pinholes, no need for DC power supply equipment, deposition on non-conductors and certain special properties.

 

1.3 Magnetron Sputtering

Magnetron sputtering is to ionize argon gas at high pressure, and argon ions bombard the target material to sputter out the surface atoms and deposit them on the fiber surface. The samples prepared by magnetron sputtering have strong film-base bonding, excellent film performance, high purity, controllable film thickness and no pollution, but there are also problems such as low target material utilization, and the need to further improve the adhesion of the film base and the uniformity of film formation.

 

1.4 Chemical Vapor Deposition

Chemical vapor deposition is a process of forming a solid film on the surface of a substrate by chemical reaction using gaseous substances. The device is simple and flexible. High melting point compounds can be deposited from volatile metal organic precursors under low temperature and reduced pressure conditions.

 

Atomic layer deposition technology is a special chemical vapor deposition technology. Compared with the traditional chemical vapor deposition process, it uses different gas precursor pulses to alternately pass into the reaction chamber to periodically and intermittently deposit materials on the substrate surface.

 

It realizes automatic control of the growth process through a special self-limiting and self-saturating surface chemical reaction. It has excellent three-dimensional fit and large-area uniformity. It is particularly suitable for the gap-filling growth of complex surface morphology and high-depth and wide structures. It plays an important role in the microelectronics industry, energy catalysis, optics, nanotechnology and biomedicine.

 

In addition, the metallization methods of organic fiber materials include supercritical carbon dioxide method, in-situ one-step surface self-metallization method, surface modified ion exchange self-metallization method, direct ion exchange self-metallization method, etc., but the application range is relatively small.

 

2 Research Status Of Carbon Fiber Surface Metallization

 

2.1 Surface Metallized Carbon Fiber

Carbon fiber has many advantages such as low density, high specific strength, high specific modulus, small thermal expansion coefficient, no creep, good fatigue resistance and corrosion resistance, etc. It has been widely used in aerospace, cultural and sports equipment, automobiles, energy, machinery and other fields. The conductivity of carbon fiber is between non-metal and metal, and its electromagnetic wave shielding performance is still difficult to meet the special application requirements of large-capacity capacitors, electromagnetic shielding films, etc., which require high material conductivity and electromagnetic shielding performance. By coating metal on the surface of carbon fiber, the electromagnetic shielding ability can be improved while maintaining its performance advantages.

 

Kim et al. prepared Ni-Co/carbon fiber reinforced composite materials by electroplating, which had a shielding effectiveness of 75-80 dB in the range of 1-1.5 GHz at a current of 25-30 A/m2. Junior et al. found that the nickel content in the electroplated nickel-plated activated carbon fiber felt determines the reflectivity efficiency, and it can reflect about 93.7% of electromagnetic radiation at 8.2 GHz.

 

Aiming et al. prepared a new type of metal/ceramic composite nano-coating (Ni-P/SiC) on the surface of carbon fiber by plasma electrolytic spraying and chemical plating. The coated carbon fiber not only has good high-temperature oxidation resistance, but also has high electromagnetic absorption performance in the range of 2-18 GHz, and can absorb 99% of electromagnetic waves.

 

To further improve the conductivity of carbon fiber, Kang et al. found that carbon fiber with 200-300 nm copper coating electroplated on the surface can reduce weight by about 75% compared with copper wire of the same diameter, with conductivity of 5.9×10-6 Ω·cm and temperature coefficient of resistance of 1.14×10-3 K-1, and electrical performance is comparable to that of bulk copper (conductivity of 1.7×10-6Ω·cm and temperature coefficient of resistance of 4.04×10-3 K-1). To overcome the weight deficiency of metal wire, Yi et al. deposited copper with a thickness of 100-200 nm on a carbon fiber core with a diameter of 7 mm to obtain copper-plated carbon fiber.

 

The study of its conductivity found that metallized carbon fiber can increase the conductivity to 1000 times that of copper without significantly affecting the density of the wire. At present, material lightweighting is a key issue facing automobiles, ships, aircraft, satellites and rockets, and the use of metallized carbon fiber has significant advantages.

 

2.2 Surface Metallized Carbon Nanotube Fibers

Carbon nanotubes (CNTs) have a series of advantages such as heat resistance, corrosion resistance, good conductivity, and high strength. They can be used in flexible/stretchable conductors, artificial muscles, actuators, supercapacitors, solar cells, strain sensing fabrics, antennas, etc. The conductivity of carbon nanotube fibers is still far behind that of metals such as copper and silver. Plating conductive metals such as gold, silver, and copper on their surfaces can form lightweight and highly conductive fibers.

 

It is expected to become a lightweight conductive material or lightweight electromagnetic shielding material that surpasses copper and aluminum. Subramaniam et al. used a combination of organic solution electroplating and aqueous solution electroplating to obtain a carbon nanotube-copper composite film with a room temperature conductivity of up to 47 MS/m, which is very close to the conductivity of pure copper.

 

Leggiero et al. used Joule heating to drive chemical vapor deposition to deposit copper, platinum, nickel, palladium, ruthenium, rhodium and iridium on the surface of carbon nanotubes, and obtained a conductivity of up to 29.8 MS/m at room temperature, which is close to conventional metals such as copper (58 MS/m) and aluminum (38 MS/m).

 

Randeniya et al. found that during the deposition process, as time goes by, the amount of metal loaded on the carbon nanotube fiber gradually increases, the total fiber diameter increases, and the conductivity of the fiber also increases; but when the coating reaches a certain thickness, due to the microstructural defects of the coating, the conductivity of the carbon nanotube/metal composite fiber will reach an extreme value and no longer increase with the increase of thickness, as shown in Figure 1

 

 

 

Metallization of carbon nanotube surface is an important method to improve its electromagnetic shielding performance. Kim et al. electrolessly plated nickel on the surface of multi-walled carbon nanotubes to improve their electrical properties, thereby improving the electromagnetic interference shielding efficiency of Ni-MWCNTs reinforced epoxy nanocomposites. The higher the Ni content, the stronger the electromagnetic shielding.

 

Park et al. manufactured electromagnetic interference shielding through a complex network structure made of nickel, palladium and carbon nanotubes. Ni-Pd nanoparticles of different thicknesses can be evenly distributed on the surface of carbon nanotubes, showing good uniform conductivity, flexibility and transparency; 100 nm thick has the best shielding performance, can block 99.27% ​​of electromagnetic interference, and has been successfully applied to commercial mobile phone displays.

 

The methods for synthesizing large-scale carbon nanotube bundle structures (such as wires, strips and sheets) are constantly developing, enabling them to be used in many spacecraft structures, reducing weight while enhancing flexibility and durability. Post-processing techniques such as metallization can greatly improve the conductivity of carbon nanotube fibers, expanding their applications in the fields of conductivity and electromagnetic shielding.

 

3 Research Status Of Surface Metallization of Organic Fibers

 

3.1 Surface Metallized Aramid

Aramid is a high-performance organic fiber material with soft texture, low density and excellent mechanical properties. Metallization treatment of its surface gives it excellent conductivity, and conductive fibers with characteristics of light weight, softness and folding resistance can be obtained. It is an ideal electromagnetic shielding material or conductive material that can replace metal wires. It has been successfully used in military, aerospace and other fields.

 

DuPont of the United States has developed a conductive aramid product Aracon using magnetron sputtering technology. Its density is between aluminum and copper (Table 1), and it has the functions of eliminating static electricity, shielding radiation, and transmitting electrical signals. Aramid has the characteristics of high surface chemical inertness, good hydrophobicity, and high crystallinity. It is difficult to directly coat metal on its surface by chemical plating, and the interface bonding between the fiber and the coating is poor.

 

Therefore, it is still a challenge to develop an effective surface modification pretreatment method to improve the interface bonding between aramid and the coating. Fatema et al. formed metal iodide on the fiber surface. After reduction, the metal iodide on the surface was converted into metal particles, which were used as catalysts for subsequent chemical nickel plating.

 

Wang et al. immersed meta-aramid in an alkaline dopamine solution and deposited a PDA layer with catechol and indole groups on the fiber surface. Hong et al. immersed aramid in a DMSO aqueous solution containing silver nitrate, and made the silver nitrate penetrate into the fiber surface through swelling. The fiber was treated with a sodium borohydride aqueous solution to reduce the silver nitrate to metallic silver on the fiber surface, and the subsequent chemical nickel plating was successfully carried out.

 

DAN et al. used cross-linked chitosan with NH2 and OH functions as a chelating agent to adsorb palladium ions and form a catalytic film on the fiber surface, which successfully triggered silver deposition in the subsequent chemical silver plating stage. Through the above methods, each researcher obtained aramid with high durability and high conductivity.

 

Nadir et al. deposited copper on aramid nanofibers using chemical deposition technology and obtained a low resistance of about 1.5Ω/cm2. The copper-plated aramid nanofibers prepared have good conductivity and can be used in wear-resistant electronics, flexible displays and energy storage.

 

Zhou et al. combined oxygen plasma treatment with chemical silver plating to prepare a flexible and highly conductive meta-aramid paper (MAFP). The resistance of MAFP is as low as 1.64×10－ 4 Ω/cm2, with good temperature stability, mechanical stability and chemical stability, and the shielding effectiveness is as high as 95.47 dB, which has great prospects in the development of new all-weather flexible electronic devices.

 

Surface metallized aramid is expected to become an ideal flexible conductive material, especially in the application of various flexible electromagnetic interference shielding devices under extreme service conditions.

 

3.2 Surface Metallized Polyimide Fiber

Polyimide fiber is a new high-performance fiber with a series of excellent properties such as high strength and high modulus, flame retardancy, corrosion resistance, and high and low temperature resistance (-260～300℃).

 

Some polyimide fibers also have the characteristics of UV resistance. They are one of the organic polymer materials with the best comprehensive performance at present and are widely used in aviation, aerospace, electronics, military and other fields.

 

However, polyimide fibers themselves do not have conductivity, which limits their application in electromagnetic shielding and flexible electronic devices. Li Shuang et al. obtained conductive polyimide fibers with a resistivity of 6.67×10－ 5 Ω·cm by chemical copper plating.

 

Dong Nanxi et al. used surface modified ion exchange technology and chemical plating to obtain polyimide fibers with Ni plating on the surface. The fiber strength is about 1.2 GPa, the elongation at break is about 1.8%, and the surface resistivity reaches 1.76×10－ 4 Ω·cm, which has good interface bonding performance and wear resistance. Lin et al. prepared conductive silver/polyimide fabric by plasma pretreatment and jet-assisted chemical plating technology, with a resistivity of 1.08×10－ 4 Ω/cm2. The prepared composite material has good thermal stability and conductivity, and maintains the inherent tensile strength and flexibility of the original polyimide fiber.

 

Ding et al. prepared polyimide fabric with high conductivity and electromagnetic shielding performance by chemical nickel-tungsten-phosphorus plating process, with a resistivity of only 8.61× 10－ 5 Ω/cm2, and an electromagnetic shielding effectiveness of up to 103 dB; the material still has good antistatic properties after multiple ultrasonic cleaning and bending tests, and is expected to be used in the field of textile protection.

 

Surface metallized polyimide fiber is expected to be used for a long time in harsh electromagnetic environments, while meeting the requirements of high temperature, high pressure or foldability.

 

4 Conclusion

This paper reviews the research progress of surface metallized carbon fiber, carbon nanotube fiber, aramid fiber, and polyimide fiber.

Carbon fibers after surface metallization have excellent mechanical properties and conductivity close to that of metals. As lightweight conductive structural materials, they have broad application prospects.

 

Organic fibers have good comprehensive properties. Metallization gives organic fibers good electromagnetic properties. They are light and soft, and are expected to play an important role in textile protection, space antennas, flexible electronic devices and other fields.

 

Compared with existing mature materials, surface metallized fiber materials still have many problems. At present, there are more studies on surface metallized carbon fibers and aramid fibers, and fewer studies on surface metallized carbon nanotube fibers and metallized polyimide fibers. There are fewer practical applications, and there are problems such as unstable product quality and high production costs.

 

At present, there are few surface metallized fiber materials that are truly mass-produced and widely used in China, and there is still a lot of room for optimization and improvement of their fiber preparation process and performance. How to produce a large number of continuous metallized fiber materials that are light and soft, with excellent and stable electromagnetic properties is worth further exploration