Tennis Rackets – Hyper-Carbon

Time Line

12th Century – Tennis rackets was made from solid Hickory or ash. These made it more difficult for players to produce effective shots because they were heavy and quite awkward.

1960’s and 70s – Laciest introduced Aluminium and Prince brings Fibreglass into the production of Tennis rackets.

1980s - The manufacturers began to design lighter, graphite rackets. Graphite rackets have a rigid structure that does not bend on impact with the ball, so the strings deflect and rebound immediately. They are approximately 30% more powerful than the older wooden rackets.

1990s – Titanium is used to produce the more expensive rackets.

2002 Revolution – Wilson presents the revolutionary new material to produce Tennis rackets – HYPERCARBON

Hybercarbon is a form of carbon fibre material produced with Polyacrylonitrile.

What makes it Different from other materials?

The Transfer of Kinetic Energy

When the tennis ball is moving it contains kinetic energy. Kinetic Energy of the ball is transferred to the racket on impact as heat when the molecules of the racket vibrate. However, with Hypercarbon, little kinetic energy is transferred to heat, and most of it is re-emitted as kinetic energy. This ensures that the molecules move and vibrate less, and so give off less heat. In doing so, it does not exhaust the ball of its kinetic energy. Thus the ball is able to move off the racket with more power.

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Compared to other Materials

Hypercarbon has great strength, in and - i.e. it has a very good ability to bear high stress, meaning it takes a large force or pressure to break the material. This strength comes from the way the molecules are bonded - they are bonded in very strong covalent bonds. Strength is basically a materials resistance to failure.

Tensile Strength =

This is because when stress is applied, the strong fibres within the matrix take up the stress and if one fibre breaks the rest of the fibres ...

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Compared to other Materials

Tensile Strength =

This is because when stress is applied, the strong fibres within the matrix take up the stress and if one fibre breaks the rest of the fibres can take up the stress. This is also a reason why Hypercarbon can bear high stress.

Toughness

Hypercarbon is actually quite tough. Toughness is the opposite of brittle, resistivity to cracking easily - how hard it is to break or snap a material. Again this is to do with the bonds in carbon, which are strong covalent bonds. Brittle is basically a property of a material that says that the material is stiff but not very strong - it is easy to break or snap the material. However, Hypercarbon is tough also because cracks cannot move through the polymer matrix, as it is strong due to the fibres taking up the stress even if one of them has broken.

Hypercarbon bond

If Hypercarbon is tough, it must have high fracture energy, which is the energy required fracturing a material of a certain cross-sectional area:

Fracture Energy J, Joules Jm-2 =

Hypercarbon has high young’s modulus. Young’s modulus is the measure of the stiffness of a material, measured in Pa, Pascals or GPa, Giga Pascals. Stiffness is the ability of a material to bear high stress with little strain affecting the material. Which means that there is less extension of the tennis racket on impact of the ball. To put it in simpler terms, stiffness is how much a material stretches elastically when a force is applied.

The higher the value of Young's Modulus, the stiffer the material is.

The stiffness of the material helps the player to produce more powerful shots because the stiffer it is the more power it will have when it flicks the ball off the racket. As in a stiff material a large force is required to change the shape of an object and so a stiff material tends to want to move or change back to its original shape or position.

Hypercarbon is lightweight partly because it has low density (1.77 g/cubic cm). Another reason that could explain Hypercarbon being lightweight is that the relative atomic mass of carbon (it's mass in relation to 1/12 or the carbon-12 isotope) is only 12 compared to heavier elements that have relative atomic masses of over 100. So then, 1 Mole of Carbon will only weigh 12 grams.

Negatives

Unlike other materials such as Titanium or graphite, Hybercarbon could not be used to make the whole of the rackets because it is not hard and scratched easily. Therefore, the out side frames of the racket is made out of Titanium, then Hypercarbon is applied onto the racket layer by layer on top of standard modules graphite or high modulus graphite.

Polyacrylonitrile

Polyacrylonitrile is a form of carbon fibre. 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.

Carbon fibre 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 polymeric fibres, hence the name carbon fibre.

Polymeric fibres which are chains of polymers whose chains are stretched out straight (or close to straight) and lined up next to each other, all along the same axis.

It's important to point out that fibres are always made of polymers which are arranged into crystals. They have to be able to pack into a regular arrangement in order to line up as fibres.

Hyper carbon is made from carbon fibres of Polyacrylonitrile by a complicated heating process. when the polyacrylonitrile is heated, the heat causes the cyano repeat units to form cycles.

The heat is turned up higher, and the carbon atoms kick off their hydrogens, and the rings become aromatic. This polymer is a series of fused pyridine rings.

It is than heated again slow roasting the polymer some more at around 400-600 oC causes adjacent chains to join together like this:

This expels hydrogen gas, and gives us a ribbon-like fused ring polymer. Next the heat is turned up again, anywhere from 600 all the way up to 1300 oC. when this happens our newly formed ribbons will themselves join together to form even wider ribbons like this:

When this happens, nitrogen gas expel. The polymer achieved has nitrogen atoms along its edges, and these new wide ribbons can then merge to form even wider ribbons. As this happens, more and more nitrogen is expelled. When we're through, the ribbons are really wide, and most of the nitrogen is gone, leaving us with ribbons that are almost pure carbon in the graphite form. That's why we call these things carbon fibers. And as a result Hybercarbon is made.