Carbon is everywhere. Can you name another atom that has so many branches of science, knowledge and uses, from carbon chemistry to carbon trading, carbon dating to carbon copies? This atom of six neutrons, six protons and six electrons can be found in the air, in the ground, in the seas and in your body. As well as your bike.
Carbon was created by the fusion of helium atoms inside stars. It’s the fourth most abundant element in the universe (after hydrogen, helium and oxygen) and your body is about 20% carbon. It has the highest melting point of all elements. It comes in three main forms: diamonds, graphite and amorphous carbon (like coal), as well as a fourth, fullerine that was discovered in the 1980s. In diamonds it forms the hardest naturally occurring substance, in graphite it is one of the softest.
Carbon fibre uses carbon but this is just one ingredient, it requires epoxy resin. Indeed the carbon fibre is just the reinforcing element, the same way steel is used to reinforce concrete. Here’s how it’s done. Apologies if you’re a chemist but I’ve summarised for the sake of brevity.
The carbon bit
The original ingredients are propylene, ammonia and oxygen which are burned with the presence of catalysts to produce acrylonitrile. A pungent liquid substance and dangerous too, being highly flammable and carcinogenic. Acrylonitrile is polymerised – ie the molecules are combined into longer chains – into polyacrylonitrile, more commonly known as PAN. Polyacrylonitrile is more stable, a rubbery and resinous vinyl polymer.
The PAN is then pyrolised, a fancy word for baked. It’s done without oxygen or flame, meaning the PAN fibres undergo a controlled decomposition in the heat, giving up non-carbon elements. The fibres come out black and richer in carbon. In addition the carbon crystallises, forming stronger bonds at the molecular level.
Typically the carbon fibres are thinner than a human hair. These fine filaments are then woven into yarn, just like tiny fibres of wool are made into a yarn of wool. The yarn in turn often used to create the weave-patterns you often see on many bike parts.
Sometimes the weave matters, sometimes it does not. Like a fine suit, the language of tailoring becomes apparent with talk of threads, twill and weave for carbon. Indeed a good quality weave ensures air isn’t trapped and the alignment can matter too. But there’s still a long way to go once the weave is ready.
Epoxy is a substance made from two chemicals. They harden when mixed together. Indeed this setting process is often crucial to the quality of the composite material and is done in very controlled conditions, for example the temperature has to be right. It is the epoxy added to the carbon fibres that creates the real composite material and the strength. A sheet of woven carbon fibres resembles woven cotton, it is lose and soft. The curing with epoxy turns this “cloth” into material than can rival steel.
Just as a steel-reinforced concrete building is a concrete building, perhaps a “carbon” frame should really be called an epoxy frame or even a plastic frame? Maybe composite is better term? Note the full term is carbon fibre-reinforced polymer or carbon fibre-reinforced plastic.
I’m not looking to rewrite the language, no it’s just that when you look at the materials involved, remember carbon is only one ingredient amongst many others. Obviously the typical bike part or frame is very far removed from a lump of coal. Indeed it requires a significant investment in chemistry, materials science and engineering.
The discovery of fullerene is leading the way to carbon nanotechnology. Some companies, for example Easton, claim to exploit this in their composite tubing for BMC and their other bike parts but this is only the beginning. Genuine exploitation of nanotechnology here could reduce the weight of carbon composite frames by substantial amounts, there is talk of increasing the strength to weight ratio by 60 times.
In recent times the cutting edge of “carbon” frame tech has gone from 1000g to about 650-700g of with Cervélo’s R5ca, the Guru Photon and the Storck Fascenario 0.6 as good examples. Each year we see a few grams saved as manufacturers find stronger fibres and master the lay-up, design, epoxies and more. But with nano technology there’s a chance we get a leap in frame performance one day.