High-Performance Fibers Find Expanding Military, Industrial Uses

BUSINESS

High-Performance Fibers Find Expanding Military, Industrial Uses High-techfibershave competitive advantages in strength, weight, heat tolerance, and resistance to chemical breakdown Marc S. Reisch, C&EN New York

Although polymer-based, man-made fibers such as nylon and polyester have displaced successfully a large share of the textile market for natural fibers such as wool and cotton, the newest market where man-made fibers may advance t e c h n o l o g y while offering their makers great profit potential is in high-tech, highperformance fibers. In particular, new man-made fiber advances during the past 15 years have led to the discovery of fibers whose strength, weight, high heat tolerance, and resistance to chemical breakdown give them a competitive advantage over existing metals and ceramics. For instance, carbon and aramid fibers with their high strength-toweight ratio are making it possible for manufacturers to produce products that are lighter in weight and longer lasting than basic materials, such as steel and aluminum. Boron, silicon carbide, and aluminum oxide fibers may serve a similar purpose. Other fibers in woven and nonwoven uses may offer improved filtration properties because of their resistance to chemical breakdown as with polyphenylene sulfide and b i c o m p o n e n t p o l y e t h y l e n e and polypropylene fibers. A third group of fibers from silicon carbide, metal oxide, and a new polymer, PBZ, may offer outstanding heat resistance. These fibers do not make up a complete list of advanced fibers for high-tech industrial applications.

Avco uses automated chemical vapor deposition process to make boron fiber The list does include the more commercially important and developing fibers with woven, nonwoven, and composite applications. Producers are placing their bets on these fibers for future profits. However, figures supplied by the Department of Commerce show that in many cases current U.S. supply of advanced commercially available specialty industrial fibers such as aramid and carbon fibers currently outstrips demand. In particular, a 1985 study prepared by the Department of Commerce's Office of Metals, Minerals & Commodities estimated 1984 world carbon fiber demand was 3.9 million lb whereas capacity exceeded 10 million lb. It also surmised that Du Pont, the principal global supplier of aramid fiber, produced Kevlar well below its supply capability and pointed out that demand for boron fiber was not high enough to keep one producer, Composite Technology, in business. Only Avco's specialty ma-

terials division continues to supply the fiber. A feature of many of these fibers is that they are available only at high prices (such as boron at $400 per lb) and as a result tend to serve specialized markets. Raw materials tend to be expensive, manufacturing costs are high, and market development is costly. Initially they have limited applications and their markets are small, especially when compared with the $10 billion U.S. textile fibers market. But as markets develop, generated often by the high-performance requirements of military aerospace demands where costs are secondary, high-performance fibers will grow rapidly, say fiber industry executives. Although new high-tech fiber blends in composites at first will principally serve to displace metals in industrial applications, those fibers will go on to theoretical applications never possible with currently available materials, fiber producers February 2, 1987 C&EN

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Business say. The Voyager's December flight around the world without refueling could not have been achieved without advanced fiber technology. Hercules contributed carbon fiber structural composites, and other composite materials containing Du Pont aramids resulted in a light, maneuverable aircraft. Fiber producers are now staking their claim to what they hope will be large and profitable markets in the future. The carbon fibers business is among the most competitive new fibers business. Few if any carbon fiber materials manufacturers have turned a solid profit, though volume and productivity have increased over the past 15 years, and prices now run between $20 and $30 per lb. Investment in production facilities, research, and development to date, in addition to the competitive environment, account for the disparity between producer costs and profitability. "We're betting on business five to eight years a w a y , " says Glenn C. Kuebler, graphite product development manager for Hercules. The largest single U.S. producer of carbon fibers, Hercules Materials & Structures segment had $64 million in sales of carbon fibers (also called graphite fibers) and intermediate resin-treated fabrics in 1985, according to the company's annual report. Like most of the manufacturers involved in the advanced fibers business, Hercules has set its sights on future growth. Hercules chairman, president, and chief executive officer Alexander F. Giacco sees a large market for carbon fibers, most often used to reinforce resins in advanced structural composites. By the late 1990s, Giacco envisions an advanced carbon fibers market of more than $3 billion, with 50% of the market in commercial, nonmilitary applications. The military market, Giacco says, will provide the technology emphasis and production base that make advanced applications possible. Among the primary benefits of carbon fiber composites are weight savings of up to 30 to 40% in structural weight, allowing aircraft, for instance, "less takeoff gross weight, or conversely more fuel and payload for the same takeoff weight." 10

February 2, 1987 C&EN

Industrial fibers used in high-technology nonwovens, textiles, and structural composites Fiber type Alumina-boria-silica

Producer 3M

Major end uses

Nextel flexible high-heat resistant fiber for uses including ceramic reinforcement, furnace curtains, and wire and cable insulation

Aluminum oxide

Du Pont

Fiber FP metal reinforcement fiber adds strength and high-temperature stability to automotive components, and is under development for aerospace applications

Aramid

Du Pont

Kevlar and Nomex fibers for high strength, flame resistant filters, protective clothing, structural composites for aircraft and boats

Boron

Avco

Fiber used in epoxy resin and aluminum matrices for aerospace structures and sports equipment

Carbon

Hercules

Magnamite fibers for structural composites in military, aerospace, and sports equipment

Hysol-Grafil

Same purpose as above

Ashland

Carboflex fiber under development for incorporation in gears, bushings, and brake pads

BASF

Celion fiber for structural composites

Amoco

Thonel fibers for structural composites in military, aerospace, and sports equipment

Polybenzimidazole

Celanese

Used for such markets as heat protective apparel and aircraft seat fire blockers

PBZ

Dow Chemical

New family of heterocyclic rigid rod and chain extended polymers has high tensile strength and thermal stability with possible applications in structural composites

Polyethylene

Allied-Signal

Spectra fibers for high strength marine sail cloth and mooring ropes and protective clothing

Bicomponent polyethylene and polypropylene

Avtex

ES fiber for nonwoven fabrics used as diaper coverstock and for filtration

Polyimide

Dow Chemical

Polyimide 2080 under license in fiber form to Austrian producer, Lenzing. In rope form, the fiber was used to tie down insulating elements on NASA's space shuttle

Silicon carbide

Avco

Fiber used in metal matrix composites with aluminum and titanium for military aerospace and engine applications

Sulfar

Phillips

Ryton heat and chemical resistant filtration fibers

Other markets Hercules is interested in would include ships employing graphite composite structures to reduce weight for greater payload capability, reduced radar cross section, and improved ship stability. Worldwide, about 50% of carbon fiber capacity is idle, according to Clarke F. McGuire, market manager of Amoco Performance Products, successor to Union Carbide's carbon fibers and composites business. However, McGuire points out, a lot of people believe there is a large market potential for carbon fibers. "Our own fiber capacity is indicative of that/' he says. Growth areas for Amoco's carbon fibers business is most immediately in spacecraft and military aircraft, where 40% of the latest aircraft airframe weight is a carbon fiber composite. The next step is to get more large commercial airline manufacturers to substitute structural composites for metals in the large volumes already seen in military aircraft. It takes a long time for engineers to accept new material and design commercial aircraft using carbon fiber composites, McGuire says. High-performance polyacrylonitrile (PAN)-based carbon fibers of the type now produced by Hercules and Amoco must go through many steps in production. To achieve the specific modulus and denier required in production, a very pure form of PAN is required, according to Derek F. Twogood, chief executive of California-based Hysol-Grafil, a joint carbon fiber venture between the British textile and chemical conglomerate Courtaulds and U.S. adhesives manufacturer Dexter Corp. Producers must oxidize fiber tow produced from PAN at 250 °C, Twogood says, and then carbonize 98% of the fiber by raising the temperature to 800 °C. Finally the fiber molecules are graphitized by heating the fiber as high as 1400 degrees to 2500 °C. At an average of $25 per lb, carbon fibers cost 20 times as much as aluminum, Twogood says. But in their final application, the weight savings that carbon composites allow are worth the cost in military aircraft and provide long-term fuel and chemical resistance in commercial aircraft applications, he says.

"Carbon fibers sales have grown at 45% per year over the past three years," says Twogood. "It is a market for big players," he says, noting that two companies have changed hands recently. Celanese sold its carbon fibers business to BASF, and Union Carbide sold its carbon fibers business to Amoco. "You need the backing to go into it," he adds. Courtaulds itself is interested in increasing its investments and vertical integration in the carbon fibers business, Twogood notes. Already a primary producer of the PAN precursor for carbon fibers, Courtaulds recently made a bid to acquire a U.K.-based carbon fabric weaver and composite structures manufacturer, Fathergill & Harvey. Profits in carbon fibers will come in the 1990s for Courtaulds and its partner Dexter Corp., Twogood predicts. At that time it likely will "return 20% on capital invested," he says. Some of those profits, he believes, will be generated by the automotive market where carbon fibers may be a cost-effective substitute for engine, drive train, and automotive body components. Taking shape as an international competitor to Courtaulds' interests in carbon fibers and composite structures is BASF. The West German chemical concern purchased the Celanese U.S. carbon fibers and advanced composite materials business in 1985 and recently established a joint marketing venture to be called Toho Badische Structural Materials with Japanese carbon fibers manufacturer Toho Rayon. According to BASF structural materials vice president George E. Hushman, commercial airliner use of carbon fiber structures is beginning to take place. But only as confidence builds will the composites be used in wings and fuselages, and that development, he believes, "is at least two generations away." Still BASF is investing in the future with "hefty" annual investments in research and development, with a new research lab in Charlotte, N.C., and a new PAN precursor facility being readied in Williamsburg, Va., using technology licensed from Toho, Hushman says. Ashland produces carbon fiber for industrial use with a less expensive

precursor—pitch—using it for products that may not require the higher strength and modulus of products made with PAN-based fiber. Having developed the fiber technology during the past 10 years, Ashland now has an annual capacity of 250,000 to 300,000 lb of carbon fiber, according to William P. Hettinger, president of Ashland Carbon Fibers. Price of the fiber is about $9.50 per lb. Potential markets for Ashland's carbon fiber include use in brake pads as a substitute for asbestos, some structural composites for which the fiber's electrical and thermal conductivity is an advantage, hightemperature insulation, and carbon/ aramid composites for heat shields, says Hettinger. Though he notes that Ashland carbon fiber displays the strength of steel at one fifth the weight, it is "still an infant in general industrial use." Other players in pitch-based carbon fibers, made principally from Ashland's A-240 specialty pitch, are Amoco and Du Pont, which purchased Exxon's carbon fiber business. However, Du Pont does not make any commercially available carbon fibers. Looking philosophically at the array of advanced fiber material available, Du Pont's Dave S. Weir, textile fibers department R&D director, suggests a design engineer must weigh the advantage of using a particular fiber against its cost.

Use of advanced graphite composites to rise sharply

0 L-J 1984

1 I 1 I L-J L-J L-J L-J I 86 88 90 92 94 96 98

Sources: Hercules. C&EN estimates

February 2, 1987 C&EN

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Business Advanced fibers, Weir stresses, provide a most effective way of using the strength of chemical bonds within a matrix by "lining up all the forces within that matrix along a slim fiber." And, he adds, "there is no question that carbon fibers are the workhorse of advanced aerospace structural composites" where the compressive strength those fibers lend is superior to that of the aramids. But it's desirable to have a portfolio of fibers, he says, pointing out that Du Pont's aramid fibers offer unique cost/performance advantages in nonstructural composites and other systems applications. Du Pont introduced its high-heat (up to 400 °C) and chemical-resistant Nomex aramid fiber in 1961 and has found numerous applications in fire-resistant clothing and hightemperature hose and belting. According to Thomas E. Neal, industrial applications research manager, Nomex impregnated with phenolic resin has been used to form honeycomb composite structures for aircraft flooring because of its low density, light weight, and chemical and fire resistance. Industry sources say Nomex staple fiber price is about $8.00 per lb. The fiber is solvent-spun from m-phenylenediamine and isophthaloyl chloride. Introduced in 1973, Kevlar aramid fiber has higher tensile strength than Nomex and has found a number of uses, including tire cord, industrial rope, and protective clothing (for example, bulletproof vests). One of the newest high-tech uses for Kevlar that take advantage of the fiber's tensile strength is as a high-density, leadless electronic chip carrier. Made of a printed copper circuit laminated to a woven Kevlar structure, says Kevlar research manager Warren D. Hewett, it will allow designers to place more electrical connections in less space and effectively restrain copper and epoxy thermal expansion. Stronger and lighter than the specialty glass fiber it will replace, Kevlar also will be less susceptible to vibration and carrier failure. Initial application would be in military missiles and military aircraft, says Hewett. To date, Du Pont says it has invested $600 million in Kevlar 12

February 2, 1987 C&EN

PAN-based carbon fiber price has dropped 90% Price, $ per lb

0 I i i 1972 74

I

i i i i 76

78

L_l 80

I 82

L-1 84

LJ 86

Source: Hercules

R&D. Other more recent uses of Kevlar are in composite applications, including hybrid carbon and Kevlar 49, to take advantage of the compressive strength of carbon and the high tensile strength of Kevlar. According to Hewett, Kevlar 49 offers more than a 40% increase in stiffness compared with carbon fibers. Kevlar, made from p-phenylenediamine and terephthaloyl chloride reacted in hexamethyl phosphoramide solvent, ranges in price from $8.00 to $40 per lb depending on application. Celanese commercially introduced polybenzimidazole (PBI) fiber in 1983 and is trying to penetrate some of the markets in which Kevlar and Nomex aramids already are wellestablished. First used in manned spacecraft uniforms, the fiber boasts excellent resistance to chemicals and solvents, and it does not burn in air. It now also is woven into fabric form and used as an aircraft seat fire blocker and in firemen's coats. In both these end uses, PBI frequently is blended with Kevlar for the most cost-effective product, says Robert T. Moffett, PBI business director. PBI also has potential as a replacement for asbestos in high-temperature resistant gloves, industrial conveyer belts, race car driver uniforms, papers, gaskets, electric motor wiring, and composite structures, says Moffett. But it presently is priced at about $40 per lb, and "because of

the raw material and expertise required in the fiber's manufacture, it probably will remain in the upper $30 range," he says. Present capacity is 1 million lb annually, although total annual production is about 250,0001b. Celanese's high-tech fiber is prepared from tetra-aminobiphenyl and diphenyl isophthalate spun via a dry spinning process using dimethyl acetamide as the solvent. Allied-Signal's Spectra fibers compete with aramids in some markets. These high-strength, lightweight fibers are making inroads in rope and cordage uses in which, according to Ron E. Rothwell, Allied-Signal's market manager of high-performance fibers, Spectra offers better abrasion resistance and flex fatigue than the aramids. The fiber, widely used in sail cloth because of its high strength and low creep level under constant use, also has potential in boat hull reinforcement and in automotive uses in cases where it could be combined with glass or other fibers. However, because Spectra fibers have a low melt point of 150 °C, they cannot be used in highertemperature applications for which aramids or PBI can be used, he notes. Spectra 900 and 1000 are priced at between $22 and $28 per lb, respectively, and Rothwell hopes the extended-chain polyethylene-gelspun fibers will be only the first of a family of gel-spun fibers that are in R&D now and that may involve other polymers. Two new polymers, under development by Dow Chemical—PBZ and polyimide—also promise to compete with aramid fibers. Polyimide 2080, formerly produced by Upjohn whose polymers business was sold to Dow, boasts high temperature resistance (up to 400 °C) and good resistance to sulfuric acid. According to Dow senior engineer Joe A. Trombka, Polyimide 2080 has a small market. Dow only sells the solution form of Polyimide 2080 to an Austrian producer, Lenzing, which manufactures and markets fiber and fabric to compete with Du Pont's Nomex. The fiber in rope form was used to tie down insulating pieces on the space shuttle, Trombka says. No fiber pricing data is available on Polyimide 2080, which is pro-

Blankets of3M's heat-resistant Nextel fiber in engine cowls last life of aircraft duced from benzophenone tetracarboxylic acid dianhydride, toluene diisocyanate, and 4,4-diphenylmethane diisocyanate. The other Dow fiber, PBZ, is in the market development stage. Only pound quantities have been made to date, according to Dow senior associate scientist Norman L. Madison. Developed initially by SRI Research International, Dow picked up a license to develop the PBZ polymer from Commtech International Management recently. "We're gearing up now," Madison says, and unlike polyimide, Dow will "also spin fiber," in addition to creating the polymer. Madison says that PBZ, a family of heterocyclic rigid rod and chain extended polymers, could compete on the high side of the price scale with Kevlar aramid and carbon fibers in high-performance aircraft and military equipment. PBZ fibers are very stiff, strong, exhibit high tensile s t r e n g t h , and are fairly tough, he says. They appear to have the toughness of Kevlar, but show higher modulus and better thermal stability and are not so brittle as carbon fiber. A fiber commercialized in 1983 for its high-performance filtration qualities is Phillips Fibers' new polyphenylene sulfide fiber, Ryton. As a high-temperature filtration fabric (up to 190 °C in continuous use), it is easier to process into a fabric than more conventional Teflon-treated

Kevlar aramids, according to Robert L. Baker, Phillips market development director. "Coal sulfuric acid won't hydrolyze the filtration fabrics," making the fiber ideal for municipal and coal smoke stack filtration, he says. It's also possible that Ryton may displace Nomex as an electrical insulator in generators, Baker says, but at $7.85 per lb for 3-denier staple fiber, Ryton is still a little more expensive than Nomex for the same end use. Also available for filtration fabrics, but in this case for lower temperature air and liquid filtration purposes, is a bicomponent polyethylene and polypropylene fiber that Avtex has licensed recently from Chisso of Japan. Still in the market development phase, Avtex ES fiber has a wide number of potential end uses from thermal-bonded coverstock to soil erosion control fabrics and floppy discs. Fabrics made with ES fiber are strong, flame resistant, and chemical free. Currently running at $1.25 per lb, James E. Crutchfield, president of Avtex Fibers, says he hopes the fiber price can be brought closer to $1.00 per lb in the future. Well beyond the host of fibers that can improve on and replace existing materials is a new generation of especially high-performance reinforcement fibers that have allowed product breakthroughs heretofore only theoretically possible.

With its high strength-to-weight characteristics, boron fiber in epoxy, aluminum, or titanium matrices can outperform heavier homogenous metal materials. "It has all the right things going for it," says Melvin A. Mittnick, product application manager of Avco specialty materials division of Textron. In composite structures, boron, with its high specific strength and high specific stiffness, also has greater compressive strength than a carbon epoxy matrix, he says. But at $350 to $400 per lb, it is expensive. The high cost, Mittnick says, is a result of expensive raw material and a slow, although automated, production process in which boron trichloride is vaporized and chemically deposited on a resistively heated tungsten wire. The relative high cost of the fiber keeps Avco's boron sales between $10 million and $12 million annually. Production capacity is between 35,000 and 50,000 lb. But structures containing continuous filament boron allow engineers to take advantage of weight savings and performance characteristics unobtainable with heavier materials. A boron/epoxy skin on Grumman's F-14 fighter plane is 20% lighter than titanium and saves a few hundred pounds compared with titanium in the same application, Mittnick says. Boron-reinforced aluminum used in the space shuttle saved some 300 lb of weight in the spacecraft's cargo structure, compared with more conventional metal applications. However, silicon carbide eventually may be available at lower cost and may share some of the key reinforcing characteristics of boron but with the addition of high heat resistance (up to 1200 °C). Avco manufactures its continuous filament silicon carbide via chemical deposition of hydrogen and silane gases onto a carbon filament substrate, a procedure similar to that used to manufacture boron fiber. Cost of the fiber manufactured at the same level as boron would be about $100 per lb, Mittnick says, because the fiber can be manufactured five to seven times faster than boron. However, cost per pound at the present production volume of 2000 lb per year is $1000, he says. Metal matrices of silicon carbide February 2, 1987 C&EN

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Business can be manufactured and machined is still in the R&D stage, Weir notes. more easily than boron, Mittnick "We've been on it for 15 years. It's says. In addition, aluminum, titani- quite a bit ahead of its time. The um, and magnesium parts can be jury is still out on its role in the cast into shape with silicon carbide materials revolution," he says. reinforcement. Possible applications for Fiber FP One program under way now in- include composite heat exchange volves the use of silicon carbide in tubes, batteries, and helicopter engas turbine engines to produce light- gine housings. No price is available weight metal composite shafts that on the fiber. allow high operating temperatures. "There are a lot of very high-perAnother includes development of formance materials around," Weir titanium-reinforced silicon carbide stresses. However, like many other for engine fan blades that could re- advanced fiber manufacturers, Weir sult in lower engine fuel consump- asks a number of important question, Mittnick says. tions that a fiber producer must 3M's Nextel alumina-boria-silica eventually answer: Do these newer fiber also can withstand very high fibers provide a large enough voltemperatures (up to 1205 °C for ume to justify production and do N-312 and 1370 °C for N-440). Pro- they "bring value to the market duced from a combination of the place which it will pay for?" oxides of aluminum, boron, and silThe authors of a September 1986 icon in a proprietary process, Nextel technical memorandum on New was introduced commercially in the Structural Materials Technologies late 1970s. Nextel fiber can be wo- published by the Office of Technolven into fabrics that can be han- ogy Assessment recognize the same dled easily, according to Joseph T. cost concerns as Du Pont's Weir: Bailey, manager of 3M's ceramic ma- "The biggest barriers to the interials department. The fibers are being used in three major markets: electrical, in thermocoupling devices and wire insulation; industrial, in energy-saving gaskets and seals for Fuel ethanol producers, already the steel and petrochemical indus- sensing that their industry has try; and in aerospace, also as gas- bottomed out as a result of higher kets, seals, and gap fillers for which crude oil and gasoline prices, have thermal protection is necessary. received additional good news in Priced at $40 per lb for N-312 and the form of two regulatory victo$100 per lb for N-44Q, they are the ries. One regulation allows fuel ethleast expensive ceramic fibers in pro- anol to be blended with unleaded duction, notes Robert D. Carlton, gaspline that contains trace amounts 3M ceramic fibers market manager. (up to 2%) of methyl terf-butyl ether Its principal use is to replace met- (MTBE). The other grants a specific als. Used in conjunction with graph- fuel volatility exemption for ethaite fibers in aircraft composite struc- nol-blended fuels. tures, it lends higher temperature Both rulings are considered maresistance to those structures. Look- jor victories for the fuel ethanol ining into the future, Nextel has po- dustry. The MTBE ruling is particutential as a ceramic materials rein- larly important. Under previous forcement in the production of hot- interpretations of Environmental running, high-efficiency aircraft Protection Agency regulations, marengines, says Bailey. keters could not add ethanol to gasDu Pont's Weir notes that Du Pont oline containing any amount of othalso has an interest in ceramic fiber er oxygenates, such as MTBE. development with* its dry-spun polyHowever, as the use of MTBE as crystalline alumina fiber, Fiber FP. an octane enhancer becomes more Offering excellent compressive widespread, trace levels of MTBE strength, a high degree of stiffness, are cropping up in large volumes moderate tensile strength, and high- of supposedly MTBE-free gasoline. temperature stability to composites This MTBE "contamination" is unof nonferrous metals, ceramics, ep- intentional. Nevertheless, it occurs oxy, and polyimide resins, Fiber FP because of comingling in gasoline

creased use of advanced materials are cost, cost, and cost." But the authors did note that "the per-pound cost and part-for-part replacement are rarely valid bases for comparison. . . . A more fruitful approach is an analysis of the overall systems cost of a shift to advanced materials, including integrated design, fabrication, installation, and life cycle costs." Like the shift from natural to manmade fibers within the textile industry a generation ago, the shift from metal and older industrial fiber applications to fiber composite replacements do initially involve higher costs. But as fabrication technology improves, production volumes increase, and new products and processes are designed with advanced fiber applications in mind, fiber producers may eventually help foster more cost-efficient materials and as a result tap a very lucrative field for advanced composites and new heat and chemical resistant industrial fabrics. •

Fuel ethanol wins two regulatory decisions

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February 2, 1987 C&EN

distribution systems and exchange agreements among refiners. The situation is particularly severe in several southeastern states and some others, such as N e w Mexico. In Florida, for instance, officials have found trace levels of MTBE in more than 75% of gasoline samples taken from service stations. As a result, ethanol marketers have been running scared. They are well aware of the penalties for blending ethanol with oxygenatecontaining gasoline. Yet, they are finding it increasingly difficult to obtain gasoline completely free of MTBE to use as a blendstock for gasohol (90% unleaded gasoline and 10% ethanol). Now, in an interim decision, EPA has granted the ethanol industry relief from the MTBE contamination problem. Responding to a request from Herman & Associates, a Washington, D.C.-based consulting firm, EPA says it will not consider it to be a violation of the gasohol waiver (from Clean Air Act provisions) if up to 10% ethanol were added to gasoline containing up to