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February 4, 2002
Volume 80, Number 5
CENEAR 80 5 pp. 29-32
ISSN 0009-2347
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In every aspect of the games, high-tech materials are used to gain an edge


Bulleting through icy twists and turns at 90 mph, Todd Hays doesn't have time to think about polyaromatic amides. And phase diagrams can't possibly be going through Emily Cook's mind as she catapults from 70° ski jumps into split-second somersaulting twirls.

But whether or not Hays, driver of the U.S. men's bobsled team, U.S. women's freestyle ski aerialist Cook, or their fellow Olympic athletes focus midflight on the high-tech materials used in their sporting gear, most of their gear is indeed high tech from top to bottom.

ALL AROUND Olympic athletes aren't the only ones who can enjoy the performance benefits of high-tech materials in sporting equipment. Today's retail products--from skis, snowboards, snowboarding helmets, and gloves to ski bibs, pants, jackets, and other apparel--are made from materials designed for athletic performance.
In competitions where the difference between winning Olympic medals and going home empty-handed is often measured in hundredths of seconds or fractions of centimeters, manufacturers of performance equipment seek to confer every allowable advantage on athletes outfitted with their products. They do so through design innovations and by using materials that provide just the right combination of properties.

Some applications call for lightweight materials that provide structural support, vibration dampening, and stiffness. Other applications require materials that are flexible, breathable, and insulating, and that protect against impact, tearing, moisture, and wind.

Although much of the equipment used in Olympic competitions is custom made for each athlete based on his or her height, weight, sporting style, and preferences, you don't have to head out to Salt Lake City this week to see where polymer chemistry and materials science meet winter sports. Check out your local sporting goods store. There you'll find skis, snowboards, ice skates, hockey gear, sports apparel, and other cold-weather supplies that were designed with materials selected for high-level performance.

Skis are complex combinations of many materials. Manufacturers commonly use wood or synthetic cores or composites of wood and injected foams that are engineered and customized to meet the needs of various skiing styles. Ski maker K2, located on Vashon Island, Wash., for example, uses locally grown fir and spruce for its cores. Spruce is a long-fiber wood that is lightweight and flexible. Fir is more dense and known for its strength and resilience. The manufacturer blends the woods to strike a balance between low weight and responsiveness as required by the target application.

Some manufacturers mill channels (voids) into the cores to reduce weight and increase flexibility. Another strategy calls for sandwiching corrugated wood channels between laminated wood layers in order to reduce weight while maintaining strength and durability.

Woven onto the ski cores at a specified angle to the ski axis, twisted strands of fiberglass, carbon fibers, and other materials are used by some ski companies to make strong, lightweight skis with optimum torsional stiffness. The weave angle and other factors influence a ski's turning response and how well the edges grip the skiing surface in a variety of ski conditions such as light powdery snow, hard-packed snow, or ice.

Completing the ski construction, the central section is sandwiched between a highly decorated top and a precision-milled base using proprietary molding techniques and other procedures. Depending on the manufacturer and model, the principal sections of today's multilayered skis may be separated by sheets of glass, titanium, and other materials.

The large collection of materials used in skis nowadays hasn't changed dramatically in the past few years, according to Hilary W. Hartley, the North American Alpine products director for Rossignol, a major ski manufacturer in France. "The biggest differences are in the shape and length of skis," he says. Until recently, most skis were basically elongated rectangles with straight parallel edges. But now manufacturers offer "shaped" skis with hourglasslike contours.

A prime goal in designing skis with a wider shovel (front tip) and tail section and a narrow "sidecut" beneath the skier's foot is to make a product that facilitates "clean, carved" turns, Hartley explains. With conventional long, straight skis, the skis slide during part of the turn--slowing racers down.

"On straight skis, you have to use some muscle to bend the ski slightly to initiate a turn," Hartley asserts. With shaped skis, carved turns are made easily by riding on a ski's edge. The new shape, coupled with materials and construction methods, leads to a level of stability that used to be found strictly in longer skis. Short, easy-to-turn, stable skis benefit pros and beginners alike.

Manufacturers of performance equipment seek to confer every allowable advantage on athletes outfitted with their products.

THE NEW DESIGN isn't for everyone. Free-style aerialists (acrobats on skis) and ski jumpers use traditional equipment that's custom made for their sport. And contestants in downhill and super giant slalom (Super G) races, the fastest events in Olympic skiing, use relatively long skis with very little side cut. "But in slalom, which is the Alpine event with the tightest turns and slowest speeds, you'll find every Olympic athlete using shaped skis," Hartley says. American Sarah Schleper, for example, a favorite in the women's slalom and giant slalom contests, races on new-style Rossignol skis.

DuPont's Kevlar is found in skis made by many manufacturers. The polyaromatic amide material also plays a role in snowboarding gear; bobsledding; protective hockey equipment such as helmets, pads, and goalie masks; hockey sticks; ice skates; and other winter sporting equipment. (The Kevlar brand is better known for its use in bulletproof vests and sailboat sails.)

"When manufacturers need additional performance attributes from high-performance equipment, they often look to Kevlar," says Brian E. Foy, a DuPont senior marketing specialist and a manager of Kevlar sports applications.

Ski manufacturers frequently use Kevlar fibers in their products, Foy says, because of the material's vibration-dampening properties. Fiberglass and carbon fibers are used in ski construction because of their stiffness and low weight, but those materials transmit vibrations, he says.

Foy explains that skis are designed with a slight camber--a convex profile that leaves the two ends in contact with the ground while the portion below a skier's boot is slightly raised. But as a skier takes his or her skis through the motions, forces are applied to the skis causing them to flex and vibrate.

"You don't want skis to chatter--to continue vibrating after impact," Foy asserts. If vibrations can be dampened quickly, then skis remain in contact with the snow, which is essential in competitive skiing. In addition, muffling vibrations increases an athlete's endurance by lowering fatigue caused by forces associated with vibrations.

On the ice rink, top-level hockey players are notoriously tough on their sports gear. Sudden accelerations, turns on a dime, and ice-spraying stops exert tremendous forces on skating boots and blades. Coming up with a skate design that can take the punishment while providing the needed support is only part of the battle. To keep a competitive edge, hockey players insist on rugged skates that are lightweight and fit like a glove, so to speak.

To design skates with these and other qualities--like impact resistance, which is particularly important in hockey-- manufacturers turn to composites of fiberglass, carbon and graphite fibers, and Kevlar. The materials also provide great structural rigidity. "If the product doesn't retain its shape after molding, then the athlete has lost a performance edge," Foy comments. One reason for the loss is that forces that could be applied to propeling a skater forward, for example, are wasted on deforming the skate.

INSIDE THE SKATE, however, athletes can benefit from a little deformation. Specifically, manufacturers use heat-moldable foams and carbon fibers that permit players to heat their boots and step into them while they are warm to remold the skate's interior so that it fits their feet perfectly.

Sticks, too, have benefited from advanced materials. Originally all wood, hockey sticks today are made from a variety of materials. Stick shafts and blades, often made from dissimilar materials, are matched to provide optimum weight, rigidity, responsiveness, and wear resistance.

Some manufacturers make shafts from wood-carbon-glass composites. Others use fiberglass-reinforced wood or compression-molded composites of graphite and Kevlar. All-wood sticks are still available today, as are sticks made from aluminum-titanium alloys. One manufacturer, Branches Hockey of Osceola, Wis., advertises a stick that combines graphite, carbon, Kevlar, a metallic alloy, and nylon fibers.

A reason that manufacturers place so much emphasis on a hockey stick's rigidity (or flexibility) is that good players actually deform the shaft as they prepare to hit the puck. During high-speed slap shots, some athletes take a small divot out of the ice in a fast and fluid motion that bends (loads) the stick backward. The action causes the stick to whip forward as contact is made with the puck, conveying additional power to the shot. Sticks that are too stiff for a player's shooting style may shatter on impact.

Although the pool of construction materials for sporting goods is large, Foy stresses that there's more to making good equipment than simply selecting the right ingredients. The specific way in which a material is used makes all the difference in performance, he says. For example, wrapping Kevlar fiber end-to-end along the length of a ski will lead to performance characteristics that are quite different from a ski wrapped with the fiber on a 45º angle to the ski axis.

The reason for the difference, according to DuPont Fellow Vlodek Gabara, is related to the structure of the polymer from which Kevlar is made, poly(p-phenylene terephthalamide) (PPTA), and fibers formed from the polymer. "The molecular structure is rather rigid due to conjugation along the chain," Gabara says. And the molecular structure leads to a fiber structure that has many useful and direction-dependent properties.

To make polymer fibers strong, stiff, and tough, the molecular chains within the fiber need to be fully extended and perfectly aligned. PPTA chains in Kevlar line up in just that way, Gabara notes. In contrast, traditional forms of polyethylene are characterized by a lamellar structure in which molecular chains are folded. Pulling on one end of a folded chain unravels the structure, leading to a material that lacks stiffness.

"What's unique about Kevlar," Gabara points out, "is that the polymer forms liquid-crystalline solutions." Because of the chain's rigidity, the molecules pack with near perfect orientation--on a short scale--in solutions prepared within a certain range of molecular weight and polymer concentration. "That's half the job in preparing the final structure," Gabara remarks.

Orienting the neatly packed aggregates or domains on a global scale takes place during the fiber-spinning process. The process involves pumping solutions of PPTA through a spinneret--a showerhead-type device with thousands of small holes. Gabara explains that pumping the viscous solution through small holes leads to shear forces that provide the needed orientation. The pristine structure is then trapped quickly by precipitating the ordered fibers in a nonsolvent--an aqueous solution. The process forms fibers that are typically 12 µm in diameter and contain on the order of 1 billion molecules.

THE STRONGEST BONDS in the structure are covalent bonds in the polymer chains. But those aren't the only forces that come into play. Groups of chains are held together through van der Waals forces and hydrogen bonding between amide groups. The difference in strength between covalent bonds and the weaker bonds leads to anisotropy (directional dependence) in Kevlar's properties, Gabara explains. For example, stiffness along the fiber axis is on the order of 100 times greater than in the perpendicular direction. As a result, engineers need to study these differences when designing high-performance equipment.

Armchair athletes and weekend skiers probably spend little time thinking about ski wax. But for top-level skiers, the thin layer at the ski-snow interface is a major concern. Timothy C. Donnelly, a ski enthusiast and chemistry lecturer at the University of California, Davis, explains that ski waxes are typically formulated to suit a particular snow condition.

For cold hard snow, Donnelly says, skiers commonly use hard waxes to smooth the ski base, making it slick. For warm-weather skiing, athletes rely on softer waxes that help reduce drag at the ski-snow interface caused by the high water content of warm snow. Formulations include soft petrolatum wax, which is composed of low-molecular-weight hydrocarbons, relatively hard C20–C28 straight-chain paraffins, and hard C28–C50 branched alkanes.

Unfortunately, snow conditions at the top of a mountain can be different from the bottom. By customizing wax blends and adding a surfactant such as sodium dodecyl sulfate, Donnelly formulated an all-condition wax marketed under the trade name Super HotSauce. He notes that the wax has been used by medal winners in previous Olympic games. In cold snow conditions, the ski bottom remains slick and hard. But as a skier reaches warmer snow, surfactant molecules migrate from the interior of the wax layer to the exterior, where they lower surface tension and improve sliding.

NBC Sports commentator and former World Cup skier Todd Brooker notes that changing mountain conditions can mean that skiers come to a racecourse starting house with two pairs of skis--each pair waxed for certain conditions. Athletes make a decision at the last possible moment, he says. "Missing the wax could mean as much as two or three seconds in total time, which is the difference between first place and 30th."

WAXING ON Donnelly's passion for skiing grew into a new wax formulation for all snow conditions.
SPORTS APPAREL is yet another area of the winter games that has been changed by scientific advances. Manufacturers draw upon a large number of fabrics made from synthetic and natural material blends to make underwear, outerwear, footwear, hats, gloves, and other items that are comfortable, lightweight, insulating, weather-resistant, and in other ways highly functional.

As an example, GoreTex fabric, made by W. L. Gore & Associates of Newark, Del., is used to make waterproof, windproof, and breathable clothing and footwear. Gore Technical Product Specialist John J. Reaney explains that the fabric's properties are derived from expanded polytetrafluoroethylene, a low-density porous hydrophobic material.

Expanding ordinary PTFE endows the polymer with some 9 billion pores per sq inch, Reaney notes. The tiny pores are small enough to prevent liquid water from passing through the fabric but large enough to allow water vapor from perspiration to escape. He adds that the fabric is impregnated with an oleophobic material, polyalkylene oxide-polyurethane urea, to prevent penetration of oils and other contaminants that could affect the fabric's properties.

History books have little to say about ancient Greeks and the winter Olympic games. Chances are bobsledding and snowboarding weren't very popular sports in Athens around the 5th century B.C. Chemistry books don't offer much more on the subject, but they do tell us about ancient Greeks and their interest in the composition of materials. Ancient Greek chemists (philosophers) would hardly recognize the materials used in sports nowadays. But they'd be pleased to see that at least one of their four chemical elements--fire--still plays a role in the games. The Olympic torch arrives this week in Salt Lake City.

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ORDERLY Kevlar's usefulness in sports equipment is derived in part from its structure. Hydrogen bonds and van der Waals forces hold rigid polymer chains in neatly packed fibers.

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The Nerve Of Some Researchers

With the Olympic games getting under way this week, Salt Lake City is brimming with performance gear made from the latest high-tech polymers, resins, and other materials. But just a short distance from the slopes and race courses, researchers at the University of Utah are at work on another kind of high-tech material.

Bioengineering associate professor Patrick A. Tresco and coworkers have prepared a tiny version of the Olympic rings icon from living nerve cells. Measuring just a few millimeters across, the "living rings" demonstration represents an advance in tissue-engineering technology that someday may help repair spinal cord damage from sports injuries and nerve damage from other forms of trauma or disease.

Tissue engineering is a newly emerging interdisciplinary field (C&EN, Feb. 5, 2001, page 30) that promises to revolutionize modern medicine, Tresco tells C&EN. A key goal of the field is to develop replacement parts and therapies for damaged and diseased human tissues. "Our demonstration simply shows that researchers have figured out how to direct certain types of neurons to grow on two-dimensional surfaces in particular directions," Tresco remarks. The work represents one step along the way to therapeutic nerve repair.

Using photoresist techniques, Tresco and graduate student Michael E. Manwaring prepared a mold of the Olympic rings. The mold was coated with fibronectin, a protein found in human tissue, and cultured with meningeal fibroblasts. The fibroblasts grew within the mold, forming a tissue scaffold in the shape of the Olympic rings. Finally, rat nerve cells were cultured with the scaffold, resulting in ring-shaped nerve fibers. The miniature icon was then imaged after antibodies tagged with a red fluorescent dye were added to the culture.

"We are at the earliest stages of nerve repair," Tresco acknowledges. "But we're hopeful that there will be a convergence of biological discovery and engineering know-how to help rebuild the human nervous system in the future."

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Copyright © 2002 American Chemical Society

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