Astounding New Applications of Fiber- Based Products:
A Selective Review of Recent Advances
P. Radhakrishnaiah, Ph.D.
School of Polymer, Textile & Fiber Engineering
Georgia Institute of Technology
krishna.parachuru@ptfe.gatech.edu
Lecture to be presented at Techtextil North America Symposium 2008
In terms of volume, technical textiles represent a small segment of the huge textile industry; yet they are some of the most innovative and purest examples of creative design and functional product engineering. Aesthetic and decorative qualities are not requirements for a technical textile, and if one finds such a textile visually appealing, it is by pure coincidence. There is not an area of our world unaffected by the advances in technical textiles. Architecture, transportation, industry, medicine, agriculture, civil engineering, sports and apparel have all benefited from the tremendous progress and the unique collaborations that have taken place in the field. Principles of textile science and technology merge with other specialties such as engineering, chemistry, biotechnology, material/polymer science and information science to develop solutions unimaginable a century ago. Who would have thought that we would have the technology to design and some day build a forty-story tower out of carbon-fiber composite, or walk on a planet that is fifty-one million miles away, or have clothing that can automatically react and adapt to the surrounding environment? These are achievements that rely on an interface between many disciplines and require a willingness to experiment repeatedly. Greatly enhanced interdisciplinary collaborative efforts of recent years have lead to stronger, faster, lighter, safer and smarter fiber-based products.
STRONGER PRODUCTS
Incredible strength is one advantage of many of the new textile fibers, which have the capability to reinforce as well as lift hundreds of tons. Basic textile techniques have been around for centuries –weaving, braiding, knitting and embroidery – but with new fibers, coupled with new types of machinery, or even old looms that have been retooled to accommodate these fibers, the results and final products are astonishingly different.
An example of a very simple woven structure is tirecord fabric, which has been used to reinforce tires for over 115 years. Pneumatic tires were originally patented in 1845 in England by R. W. Thompson, but they were first applied to a bicycle in 1888 by John Boyd Dunlop, a Scottish veterinarian, who fitted a rubber hose to his son's tricycle and filled this tire with compressed air. Dunlop patented the pneumatic tire the same year and began limited production; within a decade it had been adopted by the automobile industry. Simultaneously, Dunlop was the first to use a canvas fabric to reinforce the rubber. Over time the canvas was replaced with nylon and rayon, and today primarily steel cord and polyester are used, except when aramids are needed in specialty vehicles and racing cars. KoSa (now Invista), a leading producer of polyester resin, fiber and polymer products, has developed a reinforcement fabric made of high-modulus, low-shrinkage polyester industrial filament yarns that is principally used in radial passenger and light truck tires. Loosely woven and heat-stabilized, it is hidden under layers of rubber, but its significant structural function contributes to successful performance, road handling and tire durability.
Large, flexible bulk containers, which on first impression seem relatively low tech and not much more than an oversized tote bag, provide more than reinforcement. These custom-designed containers, such as Super Sack® by B.A.G. Corp.®, are capable of lifting up to twelve tons of liquid or solid. Made of woven recyclable polypropylene, they have been engineered to achieve maximum container capacity while compacting to a fraction of their size when empty. An even larger container, designed to transport fresh water to the southern and eastern coasts of the Mediterranean, the Gulf States and southern California, is the Very Large Flexible Barge (VLFB), currently being designed by Buro Happold. The concept of towable bags was developed several decades ago, but the bags were used only in small sizes, as larger sizes were unreliable. The new VLFB will have the capacity to transport 250,000 cubic meters of water (over 66,000,000 gallons) – a two-day supply of water for a population of approximately one million people. Its dimensions are 1,148 feet (length) by 236 feet (width) by 46 feet (depth) and, although the material is proprietary, it will likely be made of a polyurethane-coated nylon.
FASTER PRODUCTS
Faster implies a high-performance edge in various types of sporting equipment – cars, sailboats, racing sculls and bicycles – which have all benefited from the combination of strength, rigidity and lightness attained in carbon-fiber composites. The Williams-F1, the Formula One car designed and raced in 2004, can reach sixty miles per hour within two and a half seconds, and achieve top engine speed of over two hundred miles per hour. Sailboats are attempting to reach record-breaking times of fifty knots powered only by the wind, and downhill skiers achieve speeds of more than 140 miles per hour. These exceptional performances are due to a combination of physical and mental stamina and material and technological developments. Advanced composites provide the successful link to make these events possible. Advanced composites have been available only since the 1960s, and they were primarily used in aerospace and the military until the early 1980s. All areas of the sports industry realized their enormous potential, with carbon fiber providing the highest stiffness, aramids absorbing the greatest amounts of energy, and both having the ability to replace heavier metal with lighter components. Because lightness ultimately affects speed, textile-reinforced composites are providing major new areas of opportunity for the technical textiles market.
The Williams-F1 racecar mentioned above is a blend of endurance and performance, and has achieved these goals through a combination of research in materials and electronics. Although there are many components of the Fl that are either reinforced or made exclusively out of high-performance fibers (brake discs and tires, for example), the car is made of advanced composite materials, such as carbon-fiber reinforcement within a polymer matrix, mostly taking the form of epoxy resin. Components are molded by laminating layers of the carbon/epoxy material onto a shaped mold (tool) and then the resin is cured under heat and pressure. The form of raw materials is the same as that employed in the aerospace industry, i.e., carbon fiber pre-impregnated with epoxy in a "staged" condition (partly cured, not wet, and therefore stable to handle), or what is commonly called "prepreg." Woven carbon fiber is primarily used because it can be draped and tailored into complex shapes, although unidirectional fiber is also employed. Plies of the prepreg are stacked onto the mold and sealed in a vacuum bag, which has the effect of compacting the laminate prior to curing. This assembly is then put into an autoclave, or a pressurized oven, where nitrogen is applied at around seven bar (seven atmospheres, or one hundred pounds per square inch) to properly consolidate the laminate through the bag. At the same time, the temperature in the vessel is raised to approximately 175°C (350°F) in order to cure it. After ninety minutes the part is cooled and is then ejected from the mold as a solid piece.
This same technology, at smaller and larger scales, is used to make everything from high-performance speed-skiing helmets to racing sailboats, as revealed in an interview with master boat builder Eric Goetz. Over the years it has been the elite athlete, whether a racecar driver, skier or sailor, who has played an important role in the design process. User becomes designer more and more, as racing experience is invaluable in understanding the practical and performance issues of the equipment. Beat Engel, a downhill racer, started making speed-skiing helmets for himself in the mid-1980s. Over the years he has made helmets for world champions such as Tracie Max Sachs, who clocked speeds greater than 140 miles per hour. Sachs's performance relies on the highest level of aerodynamics to permit the least resistance as she plummets down the track. Her SpeedMonster helmet completely envelops her head and neck so that legs, torso and head become like one compact bullet. The helmet is a double-shell system with a thin outer layer, used primarily to enhance performance that breaks away if she should fall, leaving behind an inner helmet for protection. Both shells are made out of woven Kevlar® compressed between two layers of woven and nonwoven glass fiber and applied with polyester resin. It is durable, fast and light.
LIGHTER PRODUCTS
The quality of lightness is always a focus of design for space and aeronautics, as we continue to be fascinated with the ongoing dream of human flight. This dream has inspired some of the most dramatic and curious inventions across all ages. Beginning with the most rudimentary handcrafted wings made from a variety of materials of their time, humans have attempted to mimic birds to achieve self-powered flight. A group of flying enthusiasts called birdmen has come closest to attaining this vision. Since the 1930s, these men have donned wing suits in order to decelerate free fall and prolong their time aloft for aerial stunts. Most of these early birdmen used a single layer of canvas, stretched from hand to foot like a bat's wing, which allowed little control and virtually no horizontal movement (glide). The breakthrough came in the early 1990s when Patrick de Gayardon invented a wing suit that was neither flat nor rigid, and had wings between his arms and body as well as his legs with an upper and lower surface that provided an inlet for air much like a modern parachute. Since then a number of suits have expanded the idea of skydiving into sky flying, such as Alban Geissler's Skyray, an attachable wing system with a rigid composite made of Kevlar and carbon fiber. Daniel Preston and Tom Parker of Atair Aerospace have developed their own wing suit, which consists of a jumpsuit and attached wings made of nonwoven polyethylene laminate and Spectra® fiber. The experience of flying in this suit is different from skydiving, as the wings fill with air as soon as the birdman spreads his limbs. The fabric has no porosity, so the wings remain rigid in flight. The shape of the wing is determined by its three-dimensional inflatable sewn structure and the position of theperson in the suit.
The birdman still relies on the parachute to land safely on the ground. Parachutes were first used to jump from an airplane in 1912. Atair Aerospace, founded in 2000 by Daniel Preston, grew out of their European counterpart, Atair Aerodynamics, established by Stane Krajnc in 1992. Atair is dedicated to creating state-of-the-art parachute designs as well as flight-navigation systems for all varieties of clients, from the military to major corporations. Their composite Parafoil improves parachutes by replacing ripstop nylon (whose construction had remained unchanged for more than the most basic building block of fifty years) with a flexible nonwoven composite material. This advanced fabric is made by sandwiching an engineered pattern of high-strength fibers, such as ultra-high molecular weight polyethylene (Spectra fiber/Dyneema®) or aramids, between layers of thin polymer foil, and then fusing them under extreme heat. The resulting Parafoils have proven to be 300% stronger, 600% less stretchable and 68% lighter than those constructed in nylon. As the canopy size grows, the strength of this composite material will increase exponentially, and the weight will decrease. This will become an enabling technology for parachutes to be used with extremely heavy cargo weights, as where nylon has proven to exhibit limitations.
Orville and Wilbur Wright may not have intentionally mimicked birds, like the birdmen, when the brothers achieved the first fully-controlled flight in an aircraft in 1902. Although this was one year before the landmark day in December when, under power, they sustained heavier-than-air flight, this earlier flight marked the invention of the airplane and officially inaugurated the aerial age. The textile that they used for covering the wings of the 1902 glider was a type of cotton muslin called "Pride of the West," typically used for ladies' slips. They purchased it off-the-shelf from Rike-Kumler Company, a department store in their hometown of Dayton, Ohio. The brothers used the muslin in its natural state and applied it on the bias. This formed a very tight surface that would distribute landing (or crashing) loads across the wing. They needed a fabric that was flexible and durable in order to achieve their groundbreaking idea for controlling the aircraft, referred to as wing warping, which entails twisting the wing tips of the craft in opposite directions.
ILC Dover's Unmanned Aerial Vehicle (UAV) is another example of innovation in wing technology. This inflatable wing, made out of a Vectran™ restraint, or outer and structural layer, and a polyurethane bladder, can be packed down to a bundle ten times smaller than its deployed wing span of seventy-five inches. It has the potential to fly into any area or situation that would endanger human life –firefighting, military, search and rescue missions – as well as when conditions need to be assessed for risk, such as avalanche/volcanic activity, iceberg patrol and forest fire survey. Although inflatable wings have been around for several decades, what has evolved during this time are smart materials like electronic textiles for adding functions to the wing. Such electronic textiles are integrated into the UAV, providing a means of controlling direction, communicated remotely. Control can be obtained simply through deformation of the wing geometry. The UAV project has benefited from using technology that ILC Dover implemented in spacesuits and the airbags for the Mars Lander, including the use of high-strength fibers. Fabrics with high strength-to-weight ratios, such as Kevlar and Vectran, have improved the packing efficiency in inflatable wing designs.
There are also more earthbound examples of lightness, which Philip Beesley and Sean Hanna discuss in their essay on textiles and architecture. Exploring areas outside of traditional textile and membrane structures, Beesley and Hanna find that advanced composites are being used more and more, and on a much larger scale, in architecture. From future projects like Michael Maltzan's house on Leona Drive to Peter Testa's forty-story tower, textile foundations are often at the core of building structures and materials.
SAFER PRODUCTS
Certainly world events have broadened the role of protective applications in recent years, and unique combinations of high-performance fibers and structures are making textiles resistant to cuts, abrasions, bullets or punctures, and providing protection against extreme cold and heat, chemical or biological hazards, radiation or high voltages. NASA and the military are playing essential roles in the research and development of textiles in this area, and they are also turning to small, cutting-edge companies such as adventure gear makers to supply their astronauts and elite soldiers.
Some of these textiles are now very familiar to us – Gore-Tex®, Mylar® and Kevlar – as they have been integrated into apparel and accessories that may be in our closets today. Cara McCarty discusses and cites examples of this phenomenon, referred to as transfer technology, and acknowledges the important role NASA has played in finding and developing materials that are tested for extreme environments like space, but eventually have great potential on Earth.
Perhaps the ultimate in protective clothing is the spacesuit, a multi-layered body armor and life-support system designed to protect against known and unknown hazards in space. Amanda Young, the official keeper of spacesuits at the Smithsonian Institution's National Air and Space Museum in Washington, D.C., discusses the evolution of the spacesuit, from the first prototypes to the most current developments. Consistent with the process used today, NASA employed the most advanced materials in their prototypes, which led to the white spacesuit that is so familiar to us now. For example, silica Beta cloth, produced by Owens Corning under contract to NASA during the Apollo program, is a nonflammable, Teflon® -coated glass fiber that was used in spacesuits and inside the command module. This was replaced in the mid-1970s with multifibrous Ortho fabric, a combination of Nomex®, Kevlar and Gore-Tex fibers, and the material of choice for spacesuits throughout the assembly of the International Space Station. Chromel-R, a metallic-fiber fabric, was developed for resistance to abrasions and cuts. The fibers were made of chromium-nickel alloy which exhibited, at the time, relatively high-tensile and tear strength. Although never used in the overall suit (except in an early prototype), it was applied to gloves and boots in the Apollo program.
The gloves that accompany the spacesuit are elaborately customized for each astronaut. Besides fitting properly, they have to be flexible and lightweight while protecting against heat and cold, and must not impede movement or dexterity. Other types of protective gloves may not be customized so much for the specific user as they are for the particular function. SuperFabric® is a new fabric that was first developed for cut and puncture resistance in the medical profession. It has since been adapted for industrial, military, recreational and household applications. For instance, Finger Armor protects two of the most vulnerable and valuable digits for professional butchers. Miniscule circular guard plates cover all sides and are bound to the nylon base fabric. The base fabric can varydepending upon the use, but it is the guard plates that provide the ultimate protection against cuts. In razor wire gloves, the guard plates are only on the palm side and spaced more widely apart than the Finger Armor. These plates also vary in terms of density, surface texture and coating, and can fulfill additional performance requirements such as enhanced grip or higher flexibility.
A counterpoint to the SuperFabric gloves is currently being used by the Army for handling razor wire – a hand-cut and sewn suede glove that is covered on the palm side with evenly spaced industrial staples. The "teeth" of the staple face inward and the interior of the glove has been lined with flannel to protect the hand from being punctured. The positioning of staples takes into account the barbs of the razor wire and performs like chain mail. Although the Army is currently testing SuperFabric to replace the staple-issued gloves, this medieval masterpiece exemplifies the ingenuity that results from necessity and an acute awareness of performance qualities in existing materials.
Motorcycle racing requires unique glove technology that, like the astronaut's glove, provides flexibility, comfort, grip and resistance to abrasion and moisture. Held GmbH, a German company that specializes in gloves, uses kangaroo hide in its Krypton glove along with palm and side-hand protection of Kevlar brand fiber ceramic and a lining of Suprotect, shock-absorbing foam. Other areas of the glove are reinforced with these materials to enhance shock resistance and provide the lightest and most protective glove possible.
SMARTER PRODUCTS
Textiles are the natural choice for seamlessly integrating computing and telecommunications technologies to create a more personal and intimate environment. Although clothing has historically been passive, garments of the twenty-first century will become more active participants in our lives, automatically responding to our surroundings or quickly reacting to information that the body is transmitting. These extraordinary examples and uses of electronic textiles are discussed by Patricia Wilson, whose interest in historical metallic embroidery has provided inspiration and guidance in her profession as a material scientist and engineer. She discusses some of the most radical and innovative work being done in this burgeoning field of electronic textiles and, from personal experience, recounts the important collaborations that have taken place between artists, designers, scientists and engineers. One of the main incubators for such interdisciplinary study and thought is the MIT Media Lab, which has produced many remarkable designers.
Three graduates recently formed SQUID Labs, a consulting and research group focused on developing breakthrough technologies in the fields of robotics, materials and manufacturing. One area they have been investigating is the incorporation of metallic fibers into ropes. These metallic fibers can be used to transmit information and act as antennas for wireless communication and, potentially more interesting, they can be used as sensors. SQUID Labs has developed an electronic rope made by braiding traditional yarns, such as nylon or polyester, with metallic yarns. There are many variables in the braiding process, including the total number and diameter of yarns, ratio of metallic yarns to polyester/nylon, and the arrangement of metallic yarns. For instance, these yarns could be entirely contained within the rope, but if testing for abrasion, then everyfew feet, a metallic yarn could migrate to the outside and then back inside the rope. This way, if conductivity is lost in a certain segment of the rope, it is assumed that abrasion has taken place on the external metallic yarn.
There are numerous applications for these intelligent ropes. Mountain climbers could rely on sensors to estimate critical strain in order to know when to retire overly stressed ropes; construction sites could reduce on-site inspection with these sensors, which would indicate when ropes have been compromised because of abrasion; and high-tension power lines, oceanic communication lines and other electric cables could be enhanced dramatically by adding a thin, intelligent rope around the outside of the cable. All of these examples employ different types of structures that have been used for centuries but have been transformed into flexible machines or computers that can transmit vital signs of their internal parts.
The variety of new and emerging applicationsfor textile products attests to the fact that textiles can be anything. They offer the versatility to be hard or soft, stiff or flexible, small or large, structured or arbitrary. They are collectors of energy, vehicles of communication and transport, barriers against physical hazards, and carriers of life-saving cures. They have been created by teams of professionals whose disciplines are diverse, yet who have joined forces with conviction and dedication to chart a course that is reinventing textiles. The future of design lies with these examples of disruptive innovation as textiles continue to push boundaries, eliminate borders between the sciences, and remain a foundation of our physical world.
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