Carbon fibers are polymers of carbon/graphite arranged in large sheets of hexagonal rings and confer several advantages such as high stiffness, high tensile strength, high chemical resistivity, high temperature tolerance, yet low weight and low thermal expansion.
Since the discovery of carbon fibers by Roger Bacon in 1958, they are common in the industrial arena, and have been used in a plethora of applications including, airplane, vehicle, nanotechnology, and space industries. Over the years, Bacon and others plowed the ground for further rapid research in the area of carbon fiber based material technologies. However carbon fibers have been around for a bit longer than this.
In 1897 Thomas Edison invented the first light bulb. Science historians speculate that Edison might have created the first carbon fibers too during the process. Edison used a filament to make his bulb glow. The filament was a thin strip of cotton fibers and bamboo silvers, which was heated through the electricity until it started to glow. But upon heating, the filament also became carbonized, becoming a true carbon copy of the cellulose structure- exact in shape but all carbon. Tungsten wire soon displaced these carbon filaments but they were still used by the US Navy until the 1960s because of their higher resistance to vibrations, which were inevitable in the oceanic environment.
By the end of World War II, Union Carbide was researching an alternative for tungsten wire in vacuum tubes, by carbonzing rayon, another cellulose based structure. The end of war resulted in the termination of this project, however the interest of the commercial sector in carbon fiber had been piqued. In 1957, Barnebey-Cheney Company started to manufacture carbon fiber mats from rayon and cotton. Subsequently, Union Carbide made a carbonized rayon cloth in the next year and offered it to US Airforce as an alternative to fiberglass based aircraft heat shields. While these discoveries and developments were impactful to a certain degree, they had poor mechanical characteristics which rendered them unsuitable for large scale use and manufacturing. The age of full blown carbon fiber discoveries and applications was still ahead.
The modern age of carbon fibers commenced with the development of large scale university-like laboratories in the late 1950s, which gave young researchers a relatively higher degree of autonomy to work on the areas of their interests. One such lab was instituted by Union Carbide called the Parma Technical Center. A newly graduated PhD in physics, Roger Bacon, joined the Parma in 1956. Originally working on the determination of the triple point of graphite, Bacon encountered an interesting by-product of the heated graphite, which he described in the following words: “I would examine these deposits, and when I broke one open to look at the structure, I found all these whiskers. They were embedded like straws in brick. They were up to an inch long, and they had amazing properties. They were only a tenth of the diameter of a human hair, but you could bend them and kink them and they weren’t brittle. They were long filaments of perfect graphite.” This demonstration of the viability of carbon fibers was made in 1958. In 1960, Bacon finally published a paper in the Journal of Applied Physics, making it a milestone in the research of carbon fibers and carbon nanotubes. Subsequently, in 1991, Sumio Ijimia published a paper which reported a method for the development of carbon nanotubes and scrolls. However, carbon fibers were still a laboratory phenomenon, with little feasibility of large scale application, because of the humongous cost of manufacturing- around 10$ million per pound- which they afforded. The research in the next decades would be dedicated to efficient and affordable methods of production.
Parallel to Bacon, Curry Ford and Charles Mitchell patented a method for the production of carbon fibers and cloths through heating rayon to high temperatures- upto 3000 C. This paved the way for carbon fibers to enter into the advanced composites industry, which was priorly dominated by fiberglass and boron fibers. We have seen that manufacturing carbon fiber is no easy task, we have different methods to prepare composites for the manufacturing of different products. The light nature of carbon fibers determined the swift and rapid replacement of fiberglass and boron fibers in packaging materials. In 1964, the first truly high modulus commercial carbon fibers were developed by Bacon and Wesley Schalamon from rayon using a new method called, “hot stretching”. The key was to stretch the carbon while it was being heated instead of after heating, which resulted in a ten-fold increase in the Young Modulus of the material. During this whole period the US Air Force actively supported rayon based research by Union Carbide, which supplied it with carbon based rocket nozzles, missile nose tips, and other aircraft structures. In 1969, Rolls Royce first used carbon fibre fans in the engine of the Tristar passenger jet.
During the same era, researchers in the other parts of the world, such as Japan and Britain, were busy developing carbon fibers using polyacrylonitrile (PAN), instead of rayon, which was overlooked by researchers in the US after their unsuccessful attempts with it to achieve high modulus. In 1961, Akio Shindo of the Government Industrial Research Institute in Osaka, Japan, was successful in producing carbon fibers of about three-fold modulus of that of rayon based carbon fibers. Shindo’s process was rapidly adopted by other Japanese researchers paving the way for a pilot-scale production in 1964. On the other hand at the same time, in Britain, William Watt of the Royal Aircraft Establishment successfully demonstrated the production of fibers having even higher modulus than the PAN based fibers. His model was rapidly put into commercial production. In 1970, Japan’s Toray Industries and US’s Union Carbide signed an agreement for a joint technological venture in carbon fibers, which led to PAN based fibers eventually superseding rayon based fibers, and they dominate the world market to-date.
The precursor for the next generation of carbon fibers was a new material called Pitch, which is a tar-like mixture of hundreds of branched compounds with varying molecular weights. Pitch is relatively inexpensive to be used as a raw material for the manufacturing of carbon fibers. The discovery of making carbon fibers from pitch was made by Leonard Singer- once again- at Parma. The properties of the pitch based fibers were remarkable, not only did they possess ultra high elastic modulus, but they also showed thermal conductivity, making them an ideal candidate for application which required heat removal and stiffness, such as electronic circuits and aircraft brakes. In 1981, McLaren MP4/1 first used carbon fiber monocoque. By 1986, the first bicycle carbon fiber frame was produced by Kestrel. In 1992, McLaren F1 became the first road car to have a carbon fiber monocoque chassis. In 1996, first carbon fiber helicopter blades were used in Eurocopter EC135. In 2008, first complete carbon fiber car wheels were offered for sale to the public by Carbon Revolution. By 2009, Boeing was consistently using carbon fiber to make its planes’ wings and other structures. In 2016, Ford offered carbon fiber wheels as standard equipment with its Mustang Shelby GT350 for the first time.
Today all commercial carbon fibers are made of either rayon, PAN, or pitch. Rayon based carbon fibers are mostly used in military contexts. Since the 1970s, PAN based carbon fibers have widely supplanted the rayon based carbon fibers because of their higher modulus and tensile strength, making them useful for a wide range of applications such as aircraft structures, space structures, lithium batteries, sporting goods, and structural reinforcements in the construction industry. Pitch based carbon fibers are unique because of their ultra high modulus and tensile strength making them useful in the critical military and space applications. During the last decades the cost of manufacturing carbon fibers has reduced drastically, and researchers are working to make it even lower, therefore, full blown extended application of carbon fibers in different industries is not that far.
Story by Neoma Winston
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