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LITERATURE OF REVIEW

WHY DO SKATEBOARDERS SHOES WEAR OUT SO FAST?

Through out skateboarding history a sand paper material known as grip tape has been glued to skateboard decks. This material made for gripping onto boards also destroys sneaker soles. Grip tape causes friction between sneakers and itself, while making a grip and facilitating control of the board. Pedaling wears out sneakers like walking, but at more accelerated rates; much higher than walking. Becoming more circwnspect, there is the factor of increased movement on the board such as turning your lead foot (generally for most people the left foot, unless they skate goofy foot) back and forth in between pedaling. With the grip tape being very granular and necessary for skateboarding, it constantly and easily scrapes away at rubber soles, making sneakers wear out faster than in any other sports or hobbies. With this problem of sneakers wearing out fast and being discarded, the skateboarder with limited financial resources suffers additionally from the losses.

WHY IS GRIP TAPE NECESSARY

The grip tape is needed for a skater to maintain control over the board by the means and the uses of friction, Unforttmately grip tape helps wear at the ollie area (an area of the shoe that is just behind a person's smallest toe on the outer side of the foot) and the sole rapidly. Grip tape is necessary for street skating tricks (examples: ollies, kick flips, nose grinds and nollies) and ramp skating. If there was no grip tape vert skaters (skateboaders who skate on ramps) would lose control over their board easily, there by raising the risk of danger and serious accidents. Vert skating is already rather risky. Who needs more broken bones? Street skaters depend on their grip tape for special moves like rail sliding, when they must maintain a perfect balance and control of their board or they risk falling on their face or sliding down the rest of the rail on their groin area, OUCH!

IS KEVLAR THE ANSWER?

Kevlar, being an aramid fiber that on a weight-by-weight basis proves to be 5 times stronger than steel, makes for a possible answer. All though there are new aramid fibers that are stronger in certain criteria, Kevlar was chosen because of its vast popularity and product knowledge if the sneaker soles were to be marketed. Many snowboarding gloves are covered with Kevlar. This application relates to skateboarders since many of them snowboard in the winters and have product knowledge of the fiber. Other fibers that are also applicable for this situation are Akzo's Arenka (aramid), Celanese's Vectra (thermotropic copolyesters), Dart's Xydar (thermotropic copolyesters), and Allied-Signal's Spectra 900 (high modulus polyethylene).

HEAVY COMPETITION

A few years ago competition was so high between these companies that Allied-Signal filed a suit against DuPont in 1991, charging them with false advertising and illegally monopolizing the market. The issue was raised since the National Institute of Justice (NIJ), a branch of the Department of Justice raised their standards for bullet proof vests. The NIJ tested their current supplier's (DuPont) product which was produced from Kevlar and Allied-Signals Spectra Shield which uses Spectra 900, with a nine-millimeter gun on a 30 degree angle, there were astonishing results: Less than 50 percent of the Kevlar vests passed, while 97 percent of the Spectra Shield vests did pass.

WHAT EXACTLY IS KEVLAR?

In the early 70's DuPont introduced aramids under trade name of Kevlar and Kevlar 49, also fon-nerly known as Fiber B and PDR-49. These fibers and Kevlar 29 do not melt, for all practical purposes, other than at temperatures involving decomposition. They are nearly insoluble. Thus making conventional melt polymerization and melt spinning not feasible. Kevlar is made by the spinning of fibers from liquid crystals in a solution exhibiting a reduced viscosity, with increasing solids content as the solution becomes anisotropic. By drawing the materials at slightly elevated temperatures, the modulus (stiffness) may be increased from 59 to 124 GPA, the values for Kevlar and Kevlar 49. Kevlart melts at over 500 degrees Celsius, is exceptionally high in strength with a tenacity more than twice that of high strength nylon or polyester, and a very high modulus. The structures of these fibers are highly crystalline. Kevlar's density of 1.44 g/cm cubed is among the highest for organics, while molecular weight of its PPTA (pphenyleneterephthalamide) molecules are considered rather low. Although some details of the crystal structure of Kevlar have been uncovered by x-rays, a comprehensive model does not exist. Recent studies of crystallites in Kevlar show that the crystallites are slightly misaligned due to the fiber axis, but can be oriented by a tensile load. Since Kevlar has low compressive strength, it can knot from compressive failure due to collapsed zones. Because Kevlar has a fibrillar structure, it splits axially over distant lengths, unlike most other high strength fibers that break straight across. To fracture the material, a crack must traverse over different planes. With fibrillar fracture, it makes cutting by machine tools or projectiles difficult. Thus making it excellent material to produce bullet proof vests and helmets. Unfortunately since Kevlar is a polymer held together by an amide bond, it is degraded by UV (ultraviolet) rays.

WHY THE Z PLANE IS THE WAY TO GO?

With an X, Y plane, the strength of the Kevlug relies on the breaking resistance of the fiber. Breaking strength for Kevlar is low...

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