Production procedures using carbon fiber

Courtaulds developed many products [153] based on carbon fibers prepreg as warp sheet and tape, random fiber mats, preferred orientation mats, chopped fiber, thermoset and thermoplastic molding compounds and polytetrafluroethylene (PTFE) impregnated tow. Oxidized PAN fiber was available as continuous tow, tops, yarns, woven and knitted fabrics. 

Prepreg Courtaulds part in the prepreg business is described in section 3.6. 

Pultrusion Initially, a pultrusion line was run using a caterpillar traction unit and this was replaced by a hand-over-hand unit, which was much kinder to smaller sections. Several epoxy systems were successfully developed [154]. 

Cement Incorporating carbon fiber in a cement matrix was difficult due to the size of the cement particles, which tended to be filtered out by the fiber reinforcement, so a cement, Swiftcrete, with a very fine particle size (about 5 pm) was used. The fiber was spread as thinly as possible and sized with a water based compatible size such as sodium carboxymethylcellulose [155,156]. Composites with up to 10% F/-were obtained [157]. 

An interesting patent was filed [159], where a polymer such as PTFE could be applied by electro-deposition using a process used within the Courtaulds Group to electro-paint the inside of petrol tanks. 

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After the product has dried, it is heated or fired in a furnace or kiln. Modern ceramics generally require certain heating schedules that include the rate and duration of heating and conditions such as the presence or absence of air. This is similar to procedures used to produce carbon fibers where the heating schedule is critical to the end product s properties. 

In a similar approach, it is not the monomer, but a solution of the prefabricated polymer (polyacrylonibile in this case) in DMF that is being used. Herein the SWNTs are very finely dispersed. The product then also contains nano tubes aligned in the fiber s longitudinal direction. Another procedure resembles the method of producing carbon fibers from PAN (Section 1.2.3). Here the composite fibers are carbonized to yield a material of nanotube-reinforced carbon fibers. At a nanotube portion of as little as 3%, it already exhibits markedly improved mechanical properties. 

In 1965, Harwell, at the request of RAE, initiated the production of 35 cm long staple carbon fiber in batches of about 4.5 kg, specifically for use at RAE. Once the commercial UK companies came on stream, Harwell turned their attention to making continuous fiber, at first some 300 m long [77]. The initial production was by a semi-batch process, where the precursor was wound onto metal frames for oxidation and then off-wound and coiled into a vertical pot furnace for subsequent carbonization. A problem associated with this procedure was that the lengths of fiber had in-built kinks, which were points of incipient weakness, where the precursor had come into contact with the metal frame during oxidation. 

The blank disks for carbon brakes are produced using modified conventional textile, but are strictly proprietary procedures. Due to the fact that the opf will be converted to a PAN based carbon fiber, the product will be non-graphitic, unsized and untreated. 

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