Carbon fibre basics

basicHow is carbon fibre created?

Carbon fibre is a material consisting of tiny fibres made from carbon, the fourth-most abundant element in the universe and the chemical basis of all known life. A key feature of carbon fibre is its great strength-to-weight ratio that makes it such a prized material for manufacturing.

At Carbon Nexus, carbon fibres are made from a chemical precursor, called polyacrylonitrile (PAN). This is a very strong polymer that is converted into carbon at extremely high temperatures. Initially, this PAN precursor is spun into filament yarns, using chemical and mechanical processes. At this stage, the yarns look like super fine white hair.

The spun PAN is then stabilised through oxidation, which converts the PAN's linear chemical bonding structure to a more thermally stable ladder bonding structure. This is achieved by heating the fibres to a temperature of 300°C for up to 120 minutes in a large oven.

Once the fibres have been stabilised, they can then be carbonised. This involves heating them to 3000°C in the presence of an inert gas (e.g. nitrogen) in a furnace. Because of the extreme heat, all oxygen is removed from the ovens through the use of the gas so the fibres do not burn. Extreme heat treatment causes the fibres to expel any non-carbon atoms and form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fibre. This is what gives the fibre its great strength, despite being so light.

Following carbonisation, the resulting fibres have a surface that does not bond well with the epoxies (synthetic polymers) that are used in composite materials required for manufacturing. To create better chemical bonding properties, the surface is slightly oxidised, through the addition of oxygen atoms to the surface. This is achieved electrolytically, with the material passing through a large bath that has been electrically charged. The electrolytic process also helps to etch and roughen the surface of the fibre for better mechanical bonding.

Fibres are then washed, dried and coated to protect them from damage before they are wound onto bobbins.

The yarns of black carbon fibre are now ready to be added to various composite materials for manufacturing.