Sunday, May 18, 2008

[ Technical Textiles -- Carbon fibrer ]

Picture - Carbon Fiber Fabric.
Carbon fiber is a polymer which is a form of graphite. Graphite is a form of pure carbon. In graphite the carbon atoms are arranged into big sheets of hexagonal aromatic rings. The sheets look like chicken wire.

Carbon fiber is a form of graphite in which these sheets are long and thin. You might think of them as ribbons of graphite. Bunches of these ribbons like to pack together to form fibers, hence the name carbon fiber.

These fibers aren't used by themselves. Instead, they're used to reinforce materials like epoxy resin and other thermosetting materials. We call these reinforced materials composites because they have more than one component.

Carbon fiber reinforced composites are very strong for their weight. They're often stronger than steel, but a whole lot lighter. Because of this, they can be used to replace metals in many uses, from parts for airplanes and the space shuttle to tennis rackets and golf clubs.

Carbon fiber is made from another polymer, called polyacrylonitrile by a complicated heating process.


Department of Polymer Science

University of Southern Mississippi.

History of Carbon Fiber

In in 1958, Dr. Roger Bacon created the first high-performance carbon fibers at the Parma Technical Center, located outside of Cleveland,Ohio,The first fibers were manufactured by heating strands of rayon until they carbonized. This process proved to be inefficient, as the resulting fibers contained only about 20% carbon and had low strength and stiffness properties. In the early 1960s, a process was developed using polyacrylonitrile as a raw material. This produced a carbon fiber that contained about 55% carbon and had much better properties. The polyacrylonitrile conversion process quickly became the primary method for producing carbon fibers.

On the 14th January 1969, Carr Reinforcements wove the first ever carbon fiber fabric in the world.

During the 1970s, experimental work to find alternative raw materials led to the introduction of carbon fibers made from a petroleum pitch derived from oil processing. These fibers contained about 85% carbon and had excellent flexural strength.

(Common applications,are in Carbon fiber reinforced polymer or CFRP)
Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as Carbon fiber or graphite reinforced polymers. Another utilization of Carbon Fiber is its added aesthetic value to various consumer products.
Carbon Fiber as a tough and lightweight material is applied in the production of watch cases and dials. In watchmaking the material is often combined with polymer to improve its strength.
Non-polymer materials can also be used as the matrix for carbon fibers. Due to the formation of metal carbides (i.e., water-soluble AlC) and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications. The fiber also finds use in filtration of high-temperature gases, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component.
Carbon fiber is also used in compressed gas tanks, including compressed air tanks.
Each carbon filament is made out of long, thin filaments of carbon sometimes transformed to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer based on acrylonitrile used in the creation of synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing continuous filaments. A common method of manufacture involves heating the PAN to approximately 300 °C in air, which breaks many of the hydrogen bonds and oxidizes the material. The oxidized PAN is then placed into a furnace having an inert atmosphere of a gas such as argon, and heated to approximately 2000 °C, which induces graphitization of the material, changing the molecular bond structure. When heated in the correct conditions, these chains bond side-to-side (ladder polymers), forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped or round filament. The result is usually 93-95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000 °C (carbonization) exhibits the highest tensile strength (820,000 psi or 5,650 MPa or 5,650 N/mm²), while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 psi or 531 GPa or 531 kN/mm²).
There are several categories of carbon fibers: standard modulus (250 GPa), intermediate modulus (300 GPa), and high modulus (> 300 GPa).[9] The tensile strength of different yarn types varies between 2000 and 7000 MPa. A typical density of carbon fiber is 1750 kg/m3.
Precursors for carbon fibers are PAN, rayon and pitch. Carbon fiber filament yarns are used in several processing techniques: the direct uses are for prepregging, filament winding, pultrusion, weaving, braiding etc. Carbon fiber yarn is rated by the linear density (weight per unit length = 1 g/1000 m = tex) or by number of filaments per yarn count, in thousands. For example, 200 tex for 3,000 filaments of carbon fiber is 3 times as strong as 1,000 carbon fibers but is also 3 times as heavy. This thread can then be used to weave a carbon fiber filament fabric or cloth. The appearance of this fabric generally depends on the linear density of the yarn and the weave chosen. Some commonly used types of weave are twill, satin and plain.
[1]PAN aerospace/high end carbon fiber:
[2]Toray (largest worldwide manufacturer)
SOURCE[Picture and Text-History of Carbon Fiber] (Republished pending permission from Wikipedia)
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