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Fiber World

Engineered Performance

Basic commodity-type man-made fibers can be modified to produce specialty fibers.

Richard G. Mansfield, Technical Editor

W ith a lack of consensus on when to designate individual fiber types as "specialty," Textile World 's simplified definition points to one or more outstanding properties that differentiate them from commodity fibers. Generally, specialty fibers are produced in smaller amounts and usually command a premium price. Tenacity, modulus, chemical or flame resistance, or any number of differentiating performance characteristics that enable enhanced product capabilities are available in specialty fibers.

Commodity fibers are produced and used in the largest quantities and are found in the more common textile products for apparel, home furnishings, domestic and industrial uses. Examples of commodity staple fibers are cotton, polyester, polypropylene, rayon, nylon, acrylic and wool. Examples of commodity filament fibers are polyester, nylon, polypropylene, rayon, acetate and silk.

Basic commodity-type man-made fibers can be modified to produce specialty fibers by techniques such as combining different polymers to produce multicomponent fibers, or by incorporating special additives within the fibers.

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Fiber Properties

One key to developing successful niche textile products is choosing fibers with the appropriate physical properties. For many industrial textile applications, fiber strength often is a consideration (See Table 1).

If maximum tensile strength were the prime application consideration, one would expect that the fibers at the top of the chart would be in large-scale production and would be oversold. But they are, in fact, in the specialty fiber category because of their narrow balance of properties.

A major advantage of man-made fibers is the ability to balance properties such as tensile strength and elongation for specific end-uses.

The stress/strain curves shown in Figure 1 compare the tensile properties of natural fibers, such as cotton and wool, with some common man-made fibers.

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Fiber Modulus

In many industrial applications for fibers, fiber modulus as well as strength must be taken into consideration. Simply put, modulus is a measure of resistance to extension of the fiber for small extensions, or the ratio of change in stress to the change in strain after the crimp has been removed from the fiber. An easily extensible fiber has low modulus.

p36b

Figures 2 and 3 illustrate how the more conventional fibers compare in tensile and modulus properties with some of the more exotic, very high-modulus fibers such as aramids, carbon fibers and several others. Fibers with very high-modulus are used in making composite aerospace components, in which the combination of high modulus, high strength and relatively low weight enable them to replace metals in these applications.

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Specific Gravity

Selection of a fiber for its specific gravity is seldom a major reason for using a particular fiber. Exceptions to this would be using polypropylene fibers for applications in which their floatability would be an important property, such as for ropes and oil-spill cleanup products. And there are potential applications for which mixtures of fibers with different specific gravities might improve functional properties. Other important properties to consider when making and using specialty fibers include chemical and solvent resistance, selective absorption capabilities, sunlight and radiation resistance, and biocompatibility.

Maximum Value

Navigating the complexity of a fiber's physical properties and matching them to demanding end-use situations give the opportunity to illustrate the maximum value of specialty fibers. Following are some attributes by fiber type to keep in mind when engineering for performance.

Acrylic fibers exhibit low specific gravity and good acid resistance. They are available with several types of reactive groups, as well as in a fibrillating type.

Carbon fibers are suitable for  various product applications, including products that must be biocompatible. In addition, they are electrically conductive, high-temperature-resistant and have very high modulus.

Capable of withstanding temperatures of up to 2,300°F, Fiberfrax®- and Nextel®-type ceramic fibers are suitable for products that provide insulating properties.

Polyolefin fibers are thermal-bonding and include polypropylene (PP), polyethylene (PE) and PP/PE bicomponent fibers.

Kynol™ novoloid, which is similar to Bakelite®, is a carbon fiber precursor. It has moderately high modulus and good elongation. It also is non-melting and non-shrinking at high temperatures.

Hollow fibers have dialysis capabilities. Properties include high bulk and insulation.

Fibers in the fluorocarbon category include polytetrafluoroethylene (PTFE) fibers such as DuPont™ Teflon®, Gore-Tex® expanded fluorocarbon and Lenzing's PTFE products. Like carbon fibers, these fibers are biocompatible. They exhibit high chemical resistance and have low frictional properties.

DuPont Kevlar® and Teijin's Twaron® are aramid fibers known for their high modulus, high strength/ weight ratio and high-temperature resistance.

Polyetherether ketone (PEEK) melts at around 340°C. It has good strength and abrasion properties, as well as high chemical resistance.Among the polyesters, polytrimethylene terephthalate (PTT) polyester compares with nylon in elastic recovery and resilience. The fiber is dyeable and exhibits low static generation. Polyethylene naphthalate (PEN) polyester has higher strength and modulus than polyethylene terephthalate (PET) polyester.

Polyimide fibers, such as Lenzing's P84, and polyetherimide (PEI) fibers both have good heat and chemical resistance and low flammability.

Polybenzimidazole (PBI), offered by Celanese Advanced Materials, is a comfortable fiber known for its flame-resistant (FR) and high-temperature-resistant properties.

Polyvinyl chloride (PVC) has good FR and chemical-resistant properties, as well as dielectric sealability. Rhône Poulenc's Rhovyl® is one known brand of this moldable fiber.

Polyurethane spandex is widely used for its ability to confer elastic properties and aid in the molding of fabrics. Among the best-known brands of this fiber are DuPont Lycra®, Bayer Dorlastan™ and RadiciSpandex.

Polyvinyl alcohol (PVA) can be made water-soluble. It demonstrates high strength as well as abrasion resistance.

Lyocell fiber, including Tencel®, has higher wet and dry strength than conventional rayon fiber. It also can be made to fibrillate.

Polyphenylene sulfide (PPS), or sulfar fibers, including Torcon, demonstrate good high-temperature resistance and are moldable as well.

Glass fibers, manufactured by Advanced Glassfiber Yarns LLC, are cardable fibers with excellent FR properties and high-temperature resistance, as well as a soft, silky hand.

Melamine fibers, such as Basofil Fibers LLC's Basofil®, are known for their good FR properties, good hydrolysis and ultraviolet (UV) resistance.

Performance Is Key

Although many of the fibers discussed are not new in any earth-shattering manner, the totality of the available performance characteristics can provide a myriad of engineering options. As yarn- and fabric-forming methods evolve, new constructions will continue to demand performance and push the limits of available fiber technology. Given the scope of available products, the design and execution of innovative products is limited only by the imagination of the design engineer.


Honeywell's Spectra
Assists Solo Sail Around The World

Honeywell's high-performance Spectra® fiber was selected to be used in the material in the sails of the "Tommy Hilfiger Freedom America," which is competing in the Around Alone 2002-03 yacht race.

The boats launched from New York Harbor on Sept. 15, 2002, near Ground Zero, to commemorate the anniversary of the 9/11 terrorist attacks.

Spectra fiber, made from a highly engineered polyethylene, is pound-for-pound 10 times stronger than steel. It is used in a variety of applications, ranging from protective body and hard armor and reinforced cockpit doors, to cut-resistant industrial gloves, ropes and cordage, and fishing line.

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Van Liew aboard the “Tommy Hilfiger Freedom America” yacht

In sailcloth, Spectra has the strength to stand up to the fierce winds and massive ocean waves encountered in the grueling solo race, and yet it is light enough to give the American frontrunner, Brad Van Liew, the speed needed to win.

"When you're sailing a yacht with an 80-foot mast, weight can make the difference between winning and losing," said Van Liew. "Sailcloth made with Spectra fiber is ultra-lightweight to give me speed, yet strong enough to take on the harshest ocean conditions."

Around Alone is one of the most mentally and physically demanding competitive sporting events in the world. The 28,755-mile, nine-month-long sailing race circumnavigates the globe by way of five great capes.

"Spectra fiber is a natural for applications where performance and protection are crucial, from the Around Alone extreme challenge to the war against terrorism in Afghanistan," said Nance Dicciani, president and CEO, Honeywell's Specialty Materials strategic business group.

Van Liew is in first place as of TW 's press time. He has won each leg of the race to date, and has maintained a lead throughout the entire journey.

"After four grueling months at sea, the sails made with Spectra fiber continue to perform and are propelling Brad towards victory," said Tim Swinger, marketing communications manager, Honeywell's Spectra Technologies business.

February 2003



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