Carbon fibers have now been available for some 35 years and in that time, many significant improvements have been made. The replacement of cellulose based precursors with PAN precursors provided carbon fibers with good strength and improved the modulus, followed later by the intermediate modulus PAN based range, whilst the pitch based fibers were available with very high moduli and were truly graphitic. In the 1980s, the US Government made it mandatory for military applications to use PAN precursor made in the USA, which heralded an increase in production of PAN precursor in the US.
As the world political situation changed, the requirement for carbon fibers in military applications has decreased, entailing major defense cuts. The emphasis has shifted to commercial applications, which have grown extensively. Therefore, it is not surprising that carbon fibers are involved in a whole gamut of applications. Developments do occur very rapidly in the composites field and some of these applications may now have been discontinued or replaced, but serve to illustrate the diverse applications of carbon fiber.
Although this represents the first stage of making carbon fiber from a PAN precursor, the production of opf does not follow exactly the same route and is tailor made for a given end use.
- Flameproof applications: The opf, with an oxidized density greater than 1.38 g/cm3, is non-flammable and finds many uses as a non-flammable material, which includes a replacement material for asbestos.
- Aviation and aerospace: There is no doubt that aircraft are an extremely safe mode of mass transport but, unfortunately, when an accident does occur, it tends to be a major disaster and possibly, the two main sources of fatality are crash impact and fire. The fire may be initiated by an electrical fault, neglected cigarettes, or the ignition of the fuel spilling from the aircraft following the crash. Danger from fire can be a result of the heat of the fire itself, from asphyxiation, or from poisoning by toxic gases released by the combustion process.
- Industrial workwear: The opf albe to maintain a barrier against 900C flame for over 5 min and provides outstanding protection against molten metal splash and welding sparks. The low thermal conductivity provides enhanced protection by reducing the rate of temperature rise through the fabric structure and absorbing and radiating heat. Unlike asbestos, opf does not fibrillate and does not cause a health and safety hazard.
The opf is also used in knitted cuffing, gloves and survival suit fabrics in the offshore industry.
- Defense and law enforcement: Firefighter’s jackets use opf and being fire and petrol resistant, opf can also be used as a protective cover for body armor. The opf can sustain protection for a few minutes and the fire test with Panox protective gear demonstrates this effectiveness.
- Transportation and furnishings: The opf based fireblocker fabrics have widespread use as aircraft seating and other forms of seating in cinemas, theatres, airports and conference centers.
- Cable insulation: The high electrical resistance and ability to withstand heat degradation makes a textile braided opf an ideal material for electrical cable insulation in civil and armed forces applications, such as in a submarine, where fire is a special hazard.
- Friction material: Chopped opf can be incorporated as an replacement into a phenolic resin to produce friction linings for automotive clutch and brake units.
- Gland packings: Some companies use opf, in the form of 10 or 20 ply spun yarns, which are impregnated with PTFE and/or graphite pastes and when braided, produce a satisfactory packing material, suitable as an asbestos replacement, able to withstand working pressure and sustained working up to 260C.
- Precursor for PAN based carbon fiber and activated carbon fibers: The opf is basically the first stage of the manufacture of PAN based carbon and activated fibers and these are discussed separately.