Introduction
High performance and specialty fibers discreetly provide the backbone for an incredible array of products that the average person never thinks about – aircraft frames, protective clothing, filter media, insulation, decorative fabric…all made from specialty fibers. The premium paid for these materials is worth it when they are providing unique levels of strength, stiffness, heat or chemical resistance, or visual effect in a product.
Their key markets are industrial, building and construction, law enforcement, military, recreational and transportation, and geotextiles. As these segments continue to grow, students in textile programs are potentially going to be providing fibers-based solutions to an expanding sector.
High-Strength, High-Modulus Fibers
Much of the recent research in high-performance fiber technology has been directed towards the development of fibers that have both high tenacity and high modulus-in simple terms, fibers that are extremely strong and extremely stiff-resisting not just bending, but stretching as well. Several of these fibers also share a high degree of thermal stability, further opening up the potential application range.
Carbon Fibers
Carbon fibers are produced from precursor materials like polyacrylonitrile, rayon, or even other organic, base fibers. The very high modulus and tensile strength largely depend upon the temperature achieved in the graphitization process. Owing to their superior nature, carbon fibers are widely used in industry for greater performance in aircraft structures and space applications, mostly used for reinforcements which are embedded inside resins including epoxide, polyester, phenolic, polyphenylene, or polyimide.
Carbon fiber production on an industrial scale occurs by one of two alternative routes.
The first starts from polyacrylonitrile; the four processes are:
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Polymerization
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Wet spinning
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Drawing
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Oxidation
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Carbonization
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Graphite annealing
The second starts from mesophase pitch and includes:
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Thermal treatment
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Melt spinning
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Oxidation
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Carbonization
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Graphitization annealing
In each case there are two surface treatments (carbonization and graphitization) with the latter at a temperature as high as 3000C; these are both determined by the need to produce a substrate with an alignment of the graphite layers along the fibre direction.
Carbon is confirmed in the finished product to be at least 90 percent by content.
Another and far less significant production line produces the carbon fibers from viscose fiber. This process has very limited commercial significance at present, but is used for making certain medical textile items.
Carbon fibers are best known for their very high tenacity, high elastic modulus, relatively high brittleness, low creep, chemical resistance, low coefficient of thermal expansion and high electrical conductivity. The high tenacity and the high elastic modulus are due to the structure of the laminated carbon and the excellent electrical conductivity is due to the free electrons moving between these laminations.
Carbon fiber staple yarns are woven into fabric or converted into noncrimp fabrics according to application, with both sorts being suitable for structural building parts and prepreg use. Textile configurations woven from carbon filament are also a common component of carbon-fibre-reinforced plastics and fiber-reinforced concrete, with the use of short fibers measuring as little as 6 mm.
Glass Fiber
Glass is inorganic, non-metallic and plant-fibre free material that, in general, as a frozen condition of super cooled liquid. The term defines glass as the product whose development is a result of avoiding crystallization by cooling a liquid from a molten condition. When glass is in the shape of fibers, it is often called fiberglass, which is manufactured by bringing thin strings of extruded (or melted) silica (or glass with similar properties) materials.
Chemically, glass is an alkali calcium silicate. The standard commercially produced type is lime-soda glass, which is produced by melting silica, calcium oxide, and sodium carbonate; where the soda ash has been replaced by potash, the product is known as potash glass.
All silicate glasses are composed of a network of SiO 2 and silicate; with the composition, fiber diameter, and addition of various other components, meaning that many different specific types (A-glass, C-glass, D-glass, E-glass, ECR-glass, R-glass, S-glass, among others) are identified by different manufacturers.
A network modifier is simply any atom that is introduced to modify the glass network to alter the properties and characteristics of the material.
Textilene grade glass fiber is based on a silica (Si0 2) core which, in its polymer form, exists as (Si0 2)n and requires high temperature processing conditions in order to produce crystallisation phenomena.
Glass fiber is obtained from the spinning of molten glass into filaments.
The process involves:
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The glass melt is maintained at a temperature of somewhere between 1250 and 1350C.
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Gravity is used to draw the molten glass through a spinneret with 1 to 2 mm diameter holes.
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There can be anywhere from 400 to 2400 individual capillaries.
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The glass is then drawn as fast as possible at the end of the spinneret.
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Cooling fins cool the filaments beneath the spinning jet.
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A water- or oil-based sizing finish is applied.
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The filaments are wound onto a cone.
Another way to produce glass fiber is to remelt a commercially available glass pellet and then draw fiber at 2000-3000m/min or more, using a spin bath and a series of spinnerets.
The wet and hot fiber can then be rapidly cooled by the appropriate means until the fiber solidifies, having been drawn out to a finer diameter. The finer fiber solidifies significantly faster than the coarse fiber and so glass fiber develops a frozen-in orientation birefringence which is very difficult to analyze directly.
If the fiber is aged or reheated, a structural transition of the fiber may occur, which is often accompanied by an increase in the density of the fiber and a contraction of the fiber.
The unusual internal structure is one factor that means glass fiber is actually stronger than solid glass of the same material.
The first fiber grade glass was soda-lime glass. Glass fiber is air-trapping because it’s made up of fixed air bubbles, so glass fiber board has high thermal insulation properties (-00.05/wm) and can be used as a thermal insulator.
The amorphous structure of glass provides stable properties along the entire length of the fiber. Moisture has a considerable effect on the tenacity (wave strength); absorbed moisture gives rise to microscopic cracks and defects, thus reducing the tenacity. Extended exposure to sunlight has no such effect.
Following cost, fiber diameter is an important variable in commercial-grade fiber; general reinforcement is 9-11 m diameter, though 13-15 m diameter fibers are used in more cost-conscious applications.
Glass fibre is widely used in chemicals and chemical engineering/ machine and pipe insulation, sound insulation, electric and electronic components, and boatbuilding. Packaged glass fibre fabrics are widely used as interior fabrics in ships, hotels, cinemas, wall fabrics, etc.
Polyphenylene Benzobisoxazole (PBO) Fibers
The PBO fibers are pretty new, and are manufactured out of a polymer called polyphenylene benzobisoxazole. Polyphenylene benzobisoxazoles, much like the arched fibers, are rigid rod polymers, and therefore are very stiff and ordered, crystalline enough to be characterized as a crystalline substance.
These are formed from benzene dihydrochloride and terephthalic acid, the same acid used in the production of polyester, and it is puffed at a high pressure through an air funnel into a bath of water to be spun.
PBO is currently manufactured by a Japanese company named Toyobo, and sold under the name Zylon.
This stiff molecular arrangement gives PBO an extremely high strength and modulus, in addition to superior thermal stability; PBO exhibits the highest tenacity and modulus of any current commercial high-performance fiber.
PBO does not melt or decompose below 1,200F.
PBO fabric has a natural gold color, is very light, and has a very soft hand with excellent flexibility.
Although it is difficult to dye, it behaves normally in most other respects.
The combination of thermal performance and low weight makes it suitable for a variety of industrial uses that include:
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Tires
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High-temperature equipment
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Sporting equipment
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Ropes
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Cables
It is also well-suited to protective clothing-especially used by firefighters, industrial workers, and race-car drivers.
Ceramic Fibers
Ceramic fibers, formed from aluminum oxide or other oxides, have an inorganic fiber tensile strength lower than most other inorganic fibers, while their strength in compression exceeds that of those other fibers.
This makes the fibers suitable reinforcement materials in aircraft, space shuttles, and submarines, since they are subjected to high forces.
Boron Fibers
Boron fibers are made by sublimating boron onto a thin tungsten wire and are used mainly to reinforce aluminum.
Cloth incorporating boron fiber was used in the drill stems NASA used to drill lunar rock samples during the moon landing missions.
Heat-Resistant Fibers
There are many fibres - both naturally occurring and artificial, organic and inorganic - which exhibit very high or even no melting points and as such have very high or no thermal stability.
For certain high tenacity and high modulus fibres that we have already mentioned, thermal stability is also a feature.
The following fibres are categorized in this way as this property determines their main area of use.
Asbestos
Textile usage of asbestos ceased totally, but the fiber’s use persists because it is the only naturally occurring mineral fiber and because it remains as insulation in many of our buildings.
Its natural fire-resistant properties once made it a desirable component, alone or in combination with other fibers, in products where that characteristic was of paramount importance:
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Insulation
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Protective clothing
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Theater fire curtains
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Ironing board covers
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Pot holders
The inhalation of asbestos fibers causes life-threatening lung disease, and the fiber itself is classed as a carcinogen.
It has therefore been withdrawn completely from fiber production, and is no longer acceptable for textile use in the US, although it may be in other countries.
Asbestos insulation installed in many commercial buildings in the 1950s and 1960s must be removed when the building is being renovated or structurally altered--a costly process.
Polybenzimidazole (PBI)
According to the Federal Trade Commission (FTC), the precursor to PBI is a manufactured fiber with a fiberforming agent that is a longchain aromatic polymer that contains repeating imidazole groups as an integral part of its polymer chain.
Commercial production of PBI was first achieved in May 1983.
Manufacturing involves:
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Synthesizing the PBI polymer
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Dissolving it in dimethyl acetamide
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Dry spinning in an oxygen free atmosphere
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Removing the solvent
PBI will not burn in air, produces very little, if any, toxic gas or smoke even at 1,040F, and is highly resistant to acids, organic solvents, and fuels.
Its low modulus and high moisture regain make it significantly more comfortable to wear than many other thermally resistant fibers.
Its largest current use by far is for both civilian and military protective clothing.
It is also a well established alternative to asbestos in:
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Protective gloves
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Gaskets
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Packing for industrial use
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Fireblocking materials
The Celanese Corporation currently manufactures PBI.
Sulfar
Other heat-resistant fibers, such as Sulfar (which has been discontinued), are defined by the Federal Trade Commission as a manufactured fiber composed of a long-chain synthetic polysulfide in which at least 85% of the sulfide linkages are directly attached to two aromatic rings.
It had appropriate tenacity, elongation, modulus, elastic recovery, and moisture regain for textile applications as well as outstanding chemical resistance.
Amoco Fabrics and Fibers Company produced Sulfar under the brand name RYTON for:
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Filtration
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Protective clothing
Sulfar has become a seldom-used heat-resistant plastic rather than a textile material.
Melamine
Melamine is one of the more recent generic fiber groups, as far as the FTC is concerned.
They define it as a manufactured fiber composed of a synthetic polymer at least 50% by weight of crosslinked melamine polymer.
The difference between it and the rest of the manufactured fibers is that it is thermosetting, unlike its fellow synthetics.
This inflexibility results in melamine fiber having:
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Very low thermal conductivity
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High heat resistance
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Low strength compared to rigid-rod polymers
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Modulus similar to cotton
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Excellent chemical stability
Its uses include:
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Protective clothing
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Airplane seats
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Soft furniture
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High-temperature filters
It is available in the name system Basofil from BASF Corporation.
Novoloid
Novoloid is a synthetic fiber, which is composed of no less than 85percent crosslinked novolac, by weight, - an amorphous phenol-formaldehyde lattice.
The polymer is made up of just carbon, oxygen, and hydrogen, and so its decomposition products at high temperatures present no danger.
Its extraordinarily low thermal conductivity further affords it a degree of insulation from heat and cold.
Gun-ei Chemical Industry, Japan, produces the novoloid fiber Kynol.
Applications include:
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Heat-resistant clothing
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Industrial felts
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Industrial fabrics
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Carbon fiber precursor
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Activated carbon for filtration
Other Specialty Fibers
Metallic Fibers
The first artificial fibers ever produced were metallic.
Gold and silver wire have been used for many centuries to adorn haute couture, silk hangings and table covers.
Looking back at historic textiles highlights the disadvantages of those pre-modern methods.
Today, metallic fibers remain decorative while also becoming more affordable.
Applications include:
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Filters
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Seals
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Abrasives
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Insulation
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Tires
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Brake linings
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Household textiles
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Military dress trimmings
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Upholstery
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Blankets
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Work clothing
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Polyester blends for hospital gowns
Chlorofibers
Chlorofibers, produced from chlorine-based polymers, were among the first synthetic fibers produced in Europe and the United States.
Saran
The Saran fibers, as defined by the FTC, are manufactured fibers made of a long-chain synthetic polymer consisting of at least 80% vinylidene chloride units by weight.
Applications include:
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Filters
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Golf course scouring pads
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Fishing netting
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Doll hair
Vinyon
Vinyon, according to the FTC, is a manufactured fiber made from a long chain of synthetic polymer with at least 85% vinyl chloride units by weight.
Applications include:
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Tea bags
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Industrial products
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Underwear
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Socks
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Bed filters
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Flame-resistant draperies
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Wall coverings
Fluoropolymer
Fluoropolymer fibers offer:
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Chemical resistance
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Flame resistance
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Wide temperature performance
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Abrasion resistance
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No moisture regain
Applications include:
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Pump packing
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Valve packing
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Gaskets
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Filtration media
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Bearings
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Office copier hardware
Teflon and Gore-Tex are examples associated with fluoropolymer technology.
Vinal
According to the FTC, vinal is a manufactured fiber made from a long-chain synthetic polymer containing 50% or more by weight of vinyl alcohol units.
Properties include:
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Melting point around 425F
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Excellent chemical resistance
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Resistance to microorganisms
Applications include:
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Industrial textiles
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Blends with cotton, rayon and silk
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Soluble support yarns
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Lace production
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Sock manufacturing
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Medical sutures
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Tissue scaffolds
The Future of High-Performance and Specialty Fibers
According to textile researcher Hearle, the three general eras of manufactured fiber are:
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First-generation fibers
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Second-generation high-performance fibers
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Third-generation smart fibers
Smart fibers are capable of sensing externally influenced parameters such as temperature or pressure and responding accordingly.
Much of this emerging research is focused on military applications, while wearable electronics are already incorporating sensors and integrated circuitry directly into fabrics.
Researchers are also studying silkworms and spiders to better understand natural fiber formation at the nanoscale.
Environmental compatibility and sustainability are expected to shape the future, with increased use of recycled materials and environmentally friendly manufacturing processes.
Conclusion
High performance and specialty fibers are chosen for high value applications requiring superior properties such as high strength, isothermal stability, corrosion resistance, or unique appearance that conventional textile fibers cannot provide.
Carbon and glass lend themselves to high-strength uses, while heat-resistant fibers such as PBI, melamine, novoloid, and others are used in protective and industrial products in all environments.
Metallic fibers, chlorofibers, fluoropolymer fibers and vinyl fill much narrower but still significant segments-decoration, filtration, high-load flame-retardant behavior and ‘soluble’ fabric formation.
The future looks to smart fibers and environmentally sustainable production techniques.
