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Carbon fiber , also called graphite fiber, is a synthetic fiber composed of very fine filaments, 5 to 10 microns in diameter, of a polymer whose main element is carbon. A carbon fiber is obtained by weaving and processing thousands of these thin filaments. These filaments have a high tensile strength, so they are extremely strong for their thickness. One form of carbon fiber, the carbon nanotube, is considered the strongest material that can be made. In general, carbon fibers have properties similar to steel, although they are much lighter, with a density similar to wood or plastic.
There are multiple applications for carbon fibers: in construction, in aerospace technology, in high-performance vehicles, in various engineering applications, in sports equipment, in musical instruments.
Carbon fibers have various energy-related applications, such as making wind turbine blades; They are also used in natural gas storage systems and electric accumulators for vehicles. In the aviation industry, this material is used in both commercial and military aircraft, as well as in unmanned aerial vehicles. They are also used in the manufacture of platforms and pipes for deep-water oil prospecting and exploitation.
The filaments that make up carbon fiber are made up of organic polymers: long chains of carbon compounds that are produced by the repeated union of the same molecule, called a monomer . Most carbon fibers, around 90%, are made from polyacrylonitrile (PAN). This polymer is generated from acrylonitrile or propylenenitrile (C 3 H 3 N), in the reaction shown in the following figure.
The specific conditions of the manufacturing processes of the material give it the particular qualities of carbon fibers. Some of these conditions are the raw materials used, the temperatures of the processes (some stages are carried out in ovens at high temperatures) or the atmosphere in which they are produced (part of the processes take place in the absence of oxygen). Manufacturing processes are proprietary to their manufacturers, so various aspects of the process are trade secrets. The highest grade carbon fiber, with the most efficient modulus of elasticity, is used in the most demanding applications, such as the aerospace industry.
Carbon fiber manufacturing processes
The manufacture of carbon fibers combines chemical and mechanical processes. The precursor raw material for carbon fibers is produced into thin filaments that are then heated to high temperatures in an anaerobic (oxygen-free) atmosphere. The high temperatures cause the expulsion of the material of all the atoms that are not carbon. In this way, the carbonization process produces a fiber composed mainly of carbon atoms in long chains, the product of the intertwining of the original filaments. These fibers can then be woven or blended with other materials to produce another type of fiber or molded into various shapes and sizes. Let us see below the sequence of processes involved in the manufacture of carbon fibers.
yarn . The polyacrylonitrile is mixed with other components and spun into fibers that unfold after washing.
stabilization . The fibers undergo chemical processes that stabilize the compounds.
carbonization . Stabilized fibers are heated to very high temperatures, between 1,000 and 2,500 degrees Celsius for long periods of time, in an anaerobic atmosphere. This is how the crystallization of carbon is generated in a high cohesion union.
Surface treatment . The surface of the fibers is oxidized to improve inter-fiber bonding in subsequent braiding.
shaped . The fibers are treated and wound on bobbins that are loaded into machines that twist them into fibers of different thicknesses and mechanical properties. These fibers can be used to weave fabrics or combined with other materials such as thermoplastic polymers in processes that use heat, pressure or vacuum, in order to form parts with specific formats and properties.
Carbon nanotubes are made using different processes than standard carbon fibers, using laser beams in special ovens in the carbonization process. Nanotubes can reach resistances twenty times greater than those of their precursors.
After completing the series of processes, carbon fibers will be obtained and each of them will be composed of thousands of carbon filaments; the number of filaments of each fiber can vary between 1,000 and 24,000, this being a manufacturing characteristic that is specified in each case.
The structure of the carbon fiber thus produced will be similar to that of graphite, which unfolds into overlapping sheets of carbon atoms with a crystalline structure whose pattern is hexagonal. Unlike graphite, carbon fiber is an amorphous material, not a crystalline one; the carbon atoms are arranged in sheets that intersect, which gives this fiber its exceptional mechanical resistance.
Carbon fiber manufacturing processes carry a number of risks and challenges. Manufacturing costs are unaffordable for some applications; For example, although it is a developing technology, the prohibitive costs of the automotive industry currently limit the use of carbon fibers to high-performance and luxury vehicles.
The surface treatment process must be carefully regulated to avoid the generation of defects that result in defective fibers. Strict process control is required to ensure product quality. In turn, these processes are associated with health and safety problems, and can cause respiratory and epidermal conditions. Carbon fibers are electrical conductors, so they can generate arcs and short circuits in electrical equipment, with the consequent risk.
A developing technology
As carbon fiber technology continues to evolve, the possibilities for its use and application will diversify and increase. Several studies related to the production of carbon fibers are being developed at the Massachusetts Institute of Technology (MIT) that already show promise in the creation of new manufacturing and design technologies to meet the demand of the industry.
MIT associate professor of mechanical engineering John Hart, a nanotube pioneer, has been working with his students to transform manufacturing technology, including finding new materials to be used in 3-printers. D commercials. Hart asked his students to think outside the box to envision 3-D printers that would work with new materials. The results were prototypes that printed molten glass, ice cream, and carbon fiber composites. Student teams also created machines capable of handling large- area parallel extrusion of polymers , as well as doing on-site optical scanning of the printing process.
John Hart worked with Mircea Dinca, an associate professor of chemistry at MIT, on a joint project with Automobili Lamborghini. It investigated the possibilities of developing new composite materials and carbon fiber that could one day allow the entire car body to be used as a battery system, as well as produce stronger and lighter structures, thinner paints, stronger catalytic converters. efficient and achieve better heat transfer in the automotive system.
With the prospect of such amazing advances it is no wonder that the carbon fiber market is projected to grow from $4.7 billion in 2019 to $13.3 billion in 2029.
Sources
- McConnell, Vicky. The Making of Carbon Fiber . Composite World , 2008.
- Sherman, Don. Beyond Carbon Fiber: The Next Breakthrough Material Is 20 Times Stronger. Car and Driver, accessed September 2021.
- Randall, Danielle. MIT researchers collaborate with Lamborghini to develop an electric car of the future . MITMECHE/In The News: Department of Chemistry, 2017. Carbon Fiber Market by Raw Material (PAN, Pitch, Rayon), Fiber Type (Virgin, Recycled), Product Type, Modulus, Application (Composite, Non-composite), End- use Industry (A&D, Automotive, Wind Energy), and Region—Global Forecast to 2029. MarketsandMarkets™, 2019.
- EurekAlert! MIT course challenges students to reinvent 3-D printing .
