High Technology Fibers Essay Example

fibre producers are shifting their focus to technical textiles as a means to drive creativity, innovation, and growth. This shift opens up the potential for significant growth in high tenacity and high technology man-made fibres for the technical textile industry. The expected growth is further supported by the global economic upturn in the first half of 2000. In 1998, the total world production of major textile fibres, including both natural and man-made, exceeded 55 million tonnes, with approximately 20% used in the production of technical textiles. By 2001, it is projected that nearly 25% of global fibre production will be dedicated to technical textiles. The key to this growth lies in embracing new technical textiles and technologies, replacing the traditional linear concept of material production.

CLASSIFICATION OF FIBRES

In general, there are two main groups of textile fibres: natural and man-made. Both natural and man-made fibres are used in technical textiles. However, for market structural requirements, the fibres used in technical textiles can be divided into two main categories: commodity fibres; and high-technology or speciality fibres. While commodity fibres are traditionally used in textiles like apparel, clothing, household textiles, and carpets, a majority of technical uses of textiles nowadays rely on commodity fibres. The design of items made from these fibres often requires a high level of engineering creativity. Commodity fibers can also be classified into two groups: conventional fibers such as cotton and wool.

Nearly 95% of technical textile products in Western Europe are currently made with commodity fibres, such as polyester and polypropylene. This includes 67% from conventional fibres and 28% from high-tenacity fibres. However, this chapter does not cover the specific characteristics of popular commodity

fibres due to its defined scope. High technology or speciality fibres, on the other hand, are produced using innovative materials and advanced manufacturing techniques. These fibres are known for their unique properties that enhance performance and add value to the final products. There have been several publications on this topic and related subjects in recent years.

The introduction of high-technology or speciality fibres in technical textiles has transformed the materials industry. These fibres are specifically utilized in certain types of technical textiles that necessitate distinctive properties. This includes protection against high temperatures, capacity for absorbing high impacts and dynamic energy, as well as resistance to cutting through. In simpler terms, these fibres are selected based on their suitability for specific end-uses such as protective clothing for ballistic body armour, high-risk jobs and sports (Figure 1), lightweight textile-reinforced structural components for aircraft, high-performance ropes for marine applications (Figure 2), fibre-reinforced structural panels for building construction, among others. Some examples of these well-known fibres include aramids (Kevlar, Nomex, Twaron), glass, carbon, polyethylene, polyphenylene sulfide, polyetheretherketone (PEEK), and polytetrafluoroethylene (PTFE).

High-technology fibres, which are also referred to as 'Premium Fibres', have significantly higher costs compared to commodity fibres. The price difference ranges from 10 to 500 times more expensive. Currently, premium fibres only make up around 5% of the overall market for technical textiles in Western Europe. However, their global market is growing rapidly.

FIBRE PRODUCTION: SPINNING AND DRAWING

All man-made fibers, including both commodity and high technology variants (excluding inorganic fibers), are created by spinning natural or synthetic polymers. The production process includes either melting the polymer at high temperatures or dissolving it in a solvent to achieve the desired fiber.

The three most commonly used commercial spinning techniques are melt spinning, dry spinning, and wet spinning. Gel spinning, liquid crystal spinning, and emulsion spinning are other techniques used specifically for spinning certain types of advanced fibers. Both dry and wet spinning processes are referred to as ‘Solution Spinning’. The technology of solution spinning is highly specialized for each specific fiber industry, and some of the techniques are described in patents and published literature. Solution spinning techniques are used to spin many high-technology fibers. Figure 3 illustrates the schematic diagram of the three main methods for spinning fibers.

Typically, thermoplastic polymers that do not degrade when melted are commonly extruded using the melt spinning method. This process is regarded as a secure, uncomplicated, and economical approach. The molten polymer is pushed through a spinneret nozzle, after which the extruded fiber is cooled and solidified by passing it through a chamber.

Afterwards, the melted material is extracted and wrapped around a spindle. Examples of melt-spun fibers include nylon 6, polypropylene, and polyethylene terephthalate (PET). Dry spinning, on the other hand, involves passing a polymer solution (known as the dope) through a spinneret and removing the solvent from the resulting fiber in the heated spin column before winding it onto a bobbin. Noinex, a cutting-edge fiber from the meta-aramid family, specifically poly(rn-phenyleneisothalamide), is a popular example of a dry-spun fiber. Wet spinning was the initial method used to create synthetic fibers.

The process begins with a liquid polymer solution being pumped through a spinneret into a coagulating chamber. The resulting coagulated fiber is washed to remove solvents, and often drawn and wound on a bobbin. This method is primarily used for

spinning acrylic fibers (polyacrylonitrile), although they can also be spun using the dry spinning technique. Additionally, gel spinning and liquid crystal spinning are two other processes that are gaining commercial popularity for producing high-tech fibers. Some scientists argue that gel spinning may be the only way to create ultra-high strength polyethylene fibers.

Both the development stage of the processes is similar. Depending on the polymer and spinning system, commodity fibers are commercially spun at a speed ranging from 1000 to 5000 meters per minute. However, research has been conducted on melt-spun fibers produced at a speed of 12000 meters per minute. The speed used to spin most high-technology fibers is relatively lower compared to that used for commodity fibers. The spun yarn often undergoes drawing, a process that introduces orientation and, in some cases, crystallinity into the molecular structure of the fiber. This process converts the undrawn extruded yarn into a commercially valuable material. A schematic diagram illustrating the drawing process is shown in Figure 4.

The draw ratio, which is the degree of stretch, is determined by adjusting the surface speeds of input and output rollers (v and v respectively in Figure 4). The magnitude of the draw ratio varies depending on the end use of the material. Drawing is typically done at a temperature above the glass transition point of the spun material.

USEFUL FIBRE PROPERTIES FOR TECNNICAL TEXTILES

The useful properties for technical textiles include long-term durability and dimensional stability.

The functions of technical textiles depend on various properties of the fibers.
For instance, the thermal and thermomechanical responses of fibers determine the long-term usability

of a fiber in a technical textile, especially in harsh environments like gas or liquid filtration, welders' suits, or textiles used in tires.
Having knowledge of different fiber properties allows manufacturers of technical textiles to logically estimate the suitability and durability of materials used in specific environments, reducing the risk of unwanted failure caused by stress-deformation-temperature interactions and degradative chemical reactions.
Specific fiber properties are measured for specific technical applications, and they can be grouped into different classes:
(a) mechanical properties like strength, extensibility, modulus, and elastic recovery;
(b) thermal and thermomechanical responses including melting temperature and high temperature mechanical properties;
(c) chemical characteristics such as resistance to various inorganic and organic chemicals;
(d) electrical properties like static electricity build-up, dielectric behavior, and insulating nature;
(e) abrasion and aging behaviors;
(f) surface properties such as adhesion and moisture transport behavior.

• (g) optical properties
• (h) other special properties
• High-technology fibres often possess tailor-made special properties.

For instance, fibres can be manipulated to form hollow structures, which are highly porous and strong, making them suitable for various medical applications including synthetic blood vessels and controlled drug release.

; Applications in the chemical/water industry such as purification, filtration, etc. and in civil engineering and other fields utilize tailor-made special properties found in a variety of high-tech fibers. Table I showcases the characteristics of high-tech fibers used in technical textiles, which enhance performance across a range of products.

SPECIFIC FEATURES OF CERTAIN HIGH-TECHNOLOGY FIBERS

Aromatic polyamides (Aramids) are a distinct class of aromatic polyamides with properties that differ from conventional aliphatic polyamide fibers. In 1974, the Federal Trade Commission of the USA named these fibers 'Aramid'. Dupont Company

in the USA was the first to develop aramid fiber, which entered the market in 1965.

Nomex is a meta-orientated aramid that falls under the category of commercially successful high technology fibres. There are two types of such fibres, with the first being the meta aramid group. These fibres possess high temperature resistance, moderate tenacity, and low modulus, but excel in their ability to withstand heat. Their main utility lies in their combustion resistance.

The fibres in this class have high melting/decomposition points, ranging from 600-800°C. They are extremely useful for applications that require exceptional thermal protection (such as protective apparel) and electrical insulation properties. Examples of commercially available meta-aramids include Dupont's Nomex and Teijin's Conex, which are widely used in various applications.

Figure 5 displays the chemical structures of meta-aramids and para-aramids. Meta-aramids are not as mechanically strong and rigid as para-aramids. Dupont is the leading global manufacturer of para-aramid fibers under the trade name of Keviar. Currently, various grades of Kevlar are accessible, such as Kevlar 29 and Kevlar 49.

) There are several manufacturers that produce para-aramid fibers with various properties. AKZO produces a similar material called Twaron, while Teijin in Japan has developed a copolymer-based fiber known as Technora. All of these commercially available para-aramid fibers have the para-oriented phenylene unit in their molecular structures. Figuratively, aramid fibers are typically produced using a dry-jet wet spinning process. These fibers have high tensile strengths at 300°C, similar to high tenacity commodity fibers at room temperature.

Para-aramid fibers possess tenacities that are extremely useful and remain above 300°C. In comparison, nylon 6.6 and polyester (PET) experience a significant loss of strength at approximately 220°C. Additionally, aramid fibers maintain

their tensile properties even after being subjected to heat-aging at 300°C for 1-2 weeks. Metaaramids do not have as long of a heat-aging lifetime as para-aramids. When it comes to burning, aramid fibers exhibit difficulty and do not melt like nylon6.6 or polyester fibers.

A number of applications require high flame resistance for which aramid fibers are useful. When burned, these fibers produce a thick char that acts as a thermal barrier and prevents serious burns to the skin. Aramid fibers have high volume resistivities and dielectric strengths, and they retain these properties even at elevated temperatures. Therefore, these fibers have significant potential as high temperature dielectrics, especially for use on motors and transformers. Table.

The text highlights the properties and applications of para and meta-aramid fibres. Para-aramid fibres are known for their strength, stiffness and high dynamic energy absorption capacity. These properties make para-aramid fibres suitable for ballistic performance, as well as other technical applications. Figure 7 displays a bullet-proof vest made of Keviar fabric, which utilizes multilayer para-aramid fibres. Scientists and technologists continue to discover new applications for aramid fibres, as indicated in Table III.

Aromatic polyamide-imide is a rare type of polymer suitable for fiber extrusion. One successful fiber in this category is Kermel, which is introduced in the market through a joint venture between RhonePoulencFibres and Amoco Fabrics. Kermel fiber has excellent inherent fire retardant and dimensional stability, as well as good abrasion resistance and resistance to fraying. It is lightweight and soft, with an average moisture absorption capability of 11% and good antistatic qualities. Some useful properties of Kermel fiber are its wide range of applications, including its use in personal protective

equipment such as the underwear component of racing drivers' suits and firefighter's vests. On the other hand, carbon fiber's existence was discovered in 1879 by Thomas Edison when he patented the manufacture of carbon filaments for electric lamps.

During the late 1950s, the history of carbon fibre in manufacturing high performance preforms for advanced composites to meet aerospace industry needs began. In the 1960s, William Watt and his team at the Royal Aircraft Establishment developed a successful commercial production process for carbon fibre in Farnborough, United Kingdom. This resulted in consistent expansion of both the carbon fibre market and composite products made from it due to their attractive technical properties and excellent performance. Carbon fibre is composed of at least 90% carbon obtained by controlled pyrolysis of appropriate fibres. Various precursors, such as polyacrylonitrile (PAN) and cellulosic fibres (viscose, cotton, etc.), are used to produce carbon fibres with different morphologies and specific characteristics.

Carbon fibers can be developed using different methods, such as manufacturing from fibrous precursors or through pitch extrusion. The strongest carbon fiber is produced from acrylic precursors. Overall, the conversion process of fibrous precursors into high technology carbon fibers involves three stages: I. Oxidative stabilization between 100-400°C, depending on the precursors; II. Carbonization between 700-1500°C; and III.

Graphitisation at temperatures ranging from 1500-3000°C is necessary to achieve the desired type of carbon fibre. Carbon fibre possesses exceptional strength and stiffness, making it an ideal material for aircraft structural composites. The reasons behind the popularity and dominance of carbon fibres in the aerospace industry are as follows: in terms of specific strength, carbon fibres are approximately 7 times stronger than most metals, and in terms of

tensile strength, they are around 5 times stronger. Additionally, carbon fibres have minimal expansion and contraction across a wide range of temperatures and exhibit higher resistance to fatigue compared to steel and aluminium. They also contribute to improved airworthiness and crashworthiness structures while offering significant fuel economy benefits. The use of carbon fibre composites in aircraft construction helps reduce overhaul and maintenance costs as they are less susceptible to cracks and corrosion compared to metal structures.

The applications of carbon fibres in Maui are found in composites used in various areas, including:

• aircraft and space shuttle (Figure 10)
• automotive (Figure 11)
• sports and recreational equipment (Figure 12)
• marine high performance structures (Figure 13) and general engineering
• medical implants (Figure 14)

Many carbon reinforced composite structures are made from three dimensional woven or knitted preforms. Carbon fibres produced from polyacrylonitrile and pitch precursors exhibit useful properties. Additionally, glass is a high technology fibre that is made from similar ingredients to other glass materials. Commercial glass is obtained by fusing a mixture of various metal oxides at temperatures ranging from 1300 to 1600°C.

There are multiple types of commercially available glass fibers, each with different compositions and specific technical importance. Here is an overview of some popular glass varieties:

1. 'A' glass: Contains alkali and is occasionally used for manufacturing fibers.
2. 'AR' glass: Alkali-resistant glass commonly used as fiber reinforcement in cement.
3. III. 'E' glass: Electrical glass used for electrical insulation and other applications.

‘C’ glass has a composition that offers resistance to various chemicals. IV. E’ glass has a widely accepted formulation and is commonly used in fiber and related products. The letter ‘E’ denotes electrical, as this composition exhibits high electrical resistance. V. ‘HS’ glass is a magnesium-aluminia-silica

glass that includes small quantities of several other oxides.

HS, which is short for high strength, is a type of glass known for its high strength. Another type of glass, called ‘S’ glass or VI, has a similar composition to HS glass and also has high strength when in fiber form. The use of this material in advanced composites is rapidly increasing. High technology glass fibers are typically made in the form of continuous strands. The majority, over 90%, of continuous glass fibers produced are composed of E’ glass. Figures 15 and 16 depict schematic diagrams of the production processes for continuous glass fibers, with Figure 15 illustrating the ‘two-stage’ process and Figure 16 illustrating the ‘one-stage’ process.

Glass fibres possess strength, stiffness, non-flammability, and heat resistance. They are remarkably resistant to chemicals, moisture, and attacks from micro-organisms. However, the surface damage can easily compromise the strength of glass fibre. To preserve its high performance attributes, it is typically necessary to embed or coat the fibre in a protective resin. Additionally, glass fibre is susceptible to static fatigue.

e. The strength of glass fibers decreases as the time to failure increases. Table VI below provides some important properties of glass fibers. Glass fiber is commonly used in reinforced plastics (GRP) for various applications including aircraft and aerospace, appliances and equipment, construction, consumer goods, corrosion resistant products, land transportation, and sports and leisure items. Glass fiber is an excellent alternative to asbestos because it is non-combustible, resistant to rot, highly stable, and does not pose any health risks. In automotive tire reinforcement, glass fiber is used in both radial and bias-ply constructions. When used as a breaker or

belt in bias or bias-belted tire construction, it offers a softer ride, better resistance to damage, improved stability, and lower reinforcement cost.

Glass is a beneficial addition to cement due to its low cost and easy blending. It enhances the flexural strength of composite structures, making it ideal for use in highway overlay, architectural building panels, roofing tiles, and drain pipes as a substitute for steel-mesh reinforcement. Glass fibre is also employed as a reinforcing material for high-speed roadways (Figure 17). One notable accomplishment in the use of glass fibre is its application in optical frequency communication wave guides, commonly known as 'optical fibre'. These fibres are made from highly pure silica produced via controlled process conditions.

'They are extremely delicate and need to be handled very carefully (Figure 18). Normally, fibre optic cables are reinforced (for protection purposes) with Kevlar yarn. Glass fibres suitable for optical transmission material should not have a transmission loss of more than 20 dB/km. Optical fibres used in satellite and telecommunication systems are claimed to have transmission loss less than 5 dB/km. Polyethylene, a high technology material, is now commercially available from several companies worldwide. It has exceptionally high strength and stiffness, as well as unique strength-to-weight ratios.'

The current commercial method of producing ultra-high strength and modulus uivcthvleiic fibers is dominated by the solution spinning route. This high technology polyethylene spinning method, known as "gel spinning," involves using a very high molecular weight polymer. After spinning and cooling, the filaments have a gel-like appearance, hence the name "gel spinning." The process consists of three main stages:

1. The solution of ultra-high molecular weight polyethylene is continuously extruded.
2. The solution is then spun and undergoes
   

gelation/crystallization, which can be achieved through cooling and extraction or solvent evaporation.

Figure 19 shows a line diagram of the gel spinning process. Additionally, polyethylene fiber can also be produced using the melt spinning process.

The usage of high strength and high modulus polyethylene fibre is growing rapidly, particularly in certain areas of technical textiles and also in composites. The main attributes of high technology polyethylene fibres are as follows:

• high strength and specific modulus together with high energy to break,
• low specific gravity,
• very good abrasion resistance,
• excellent chemical and electrical resistance,
• good UV resistance,

and low moisture absorption. Some useful properties of both gel-spun and melt-spun high performance polyethylene fibres are given in Table VII: An impressive combination of fibre properties contribute to the market thrust in terms of the enormous potential application areas of high performance polyethylene fibre, such as sail cloth, marine ropes and cables, protective clothing, composites e.g. sports equipment, pressure vessels, boat hulls, impact shields etc., concrete reinforcement, fish netting, and medical implants etc.

Polyvinyl alcohol (PVA) fibre has been utilized in technical textiles since the late 1980s due to its strong tenacity, excellent dimensional stability, and high resilience. However, the conventional spinning method of the fibre did not gain universal popularity across various product applications, mainly because of its strength retention issues in the presence of water, especially at high temperatures. Nonetheless, Japanese manufacturers Kurary and Unitika have developed high strength and

high modulus gel-spun PVA fibres. In addition to their remarkable strength and dimensional stability.

Gel-spun PVA fibre is known for its exceptional thermomechanical responses at temperatures as high as 170°C, making it highly thermally stable. Additionally, it exhibits great resistance to flex fatigue and creep. Even in the presence of water at high temperature, gel-spun PVA maintains its stability. This relatively new variant of PVA is currently being tested for commercial applications in various products. Among the potential uses, gel-spun PVA shows promise in belt reinforcement for tyres and mechanical rubber goods. Table VIII: 5 outlines some advantageous properties of gel-spun PVA fibre.

Spandex fibers, classified as synthetic elastomeric fibers, possess mechanical properties similar to rubber. These fibers are made from long-chain polymers containing a minimum of 85% of segmented polyurethane, with segments derived from low molecular weight polyethers or polyesters. The name "Spandex" was coined by the Federal Trade Commission of the USA.

Lycra, which was introduced by the Dupont Company in 1960, was the first spandex fiber to hit the market. Nowadays, various types of spandex fibers are available under different trade names. The manufacturing method for spandex is dependent on the chemical structure of the long chain molecule. Melt, dry, and wet spinning techniques are commonly used for commercial production. Lycra, for instance, is made using dry spinning systems.

The complete formation of the elastomeric fiber in wet spinning occurs in the coagulation bath, which is why this method of manufacturing spandex fiber is also referred to as reaction spinning. Typical spandex fibers have novel properties such as strength (tenacity), breaking extension, and power (defined as the stress in the material after being held at

an extension of 300%). Furthermore, spandex fibers have low tenacities, high extensibilities, low power requirements for large deformations, and relatively low specific gravity. While spandex fibers have similar breaking extension to natural rubber yarns, they are twice as strong. Elastic recovery, defined as the recovered extension as a percentage of the imposed extension, is excellent in spandex fibers but varies based on the amount of stretch, time held in the stretched state, and time allowed for recovery. Spandex fibers are widely used in sports and leisure garments, foundation garments, support hose, etc.

5.8 Fluorine-containing fibre - The sole significant fibre in this classification is manufactured from polytetrafluoroethylene (PTFE), which was introduced to the market by the Dupont Company as 'Teflon'. PTFE was discovered by Dupont Scientist Dr Roy Plunkett shortly before World War II. This polymer is practically insoluble in all known solvents and, consequently, cannot be spun using a solution. Additionally, the polymer's high melting point presents considerable challenges in the production of melt-spun fibre.

The fibre is created utilizing a unique method called emulsion spinning. PTFE fibres possess remarkable chemical stability, low frictional properties, exceptionally high thermal and electrical insulation capabilities, as well as an exceedingly high melting point. PTFE also exhibits exceptional heat resistance within a practical temperature range of 190°C to 260°C. Additionally, it offers strong resistance against fungus and biological agents.

PTFE is renowned for its non-sticking properties and is considered the most inert material known to humans. It finds specialized applications in high temperature and high voltage (including a wide range of frequencies) electrical insulation, corrosive chemical filtration medium, and for protecting valuable items from frictional damage. PTFE is produced and marketed

by Dupont, Hoechst (under the trade name Hostaflon), and ICI (under the trade name Fluon). Additionally, two other fibers from the class of heterocylic polymers, poly(p-phenylene benzobisthiazole) [PBZT] and poly(p-phenylene benzobisoxazole) [PBO], have emerged with notable qualities including exceptional strength, stiffness, thermal stability, chemical resistance, and environmental stability.

However, the compressive strength of these fibres is low. Some useful properties of PBZT and PBO fibres are: extremely high thermal and mechanical performance. These two fibres are particularly interesting for high performance structural applications. Currently, the fibres are known to be produced by Dow Chemical Company of the USA. 5. 10 PBI Polybenzimidazole (PBI) was first commercialised by the Hoechst Celanese company in 1983. PBI was initially developed to be used by NASA for nonflammable space research articles. PBI has since been adopted for other applications and is used either alone or in blends with other fibres.

PBI is a high regain and low modulus fibre that closely resembles cotton. It exhibits outstanding thermal stability, effective insulation, and excellent static charge dissipation. PBI fibre is non-combustible in air (with a limiting oxygen index above 41) and does not melt or drip. It provides excellent resistance to pilling, abrasion, flex, and chemicals. Table XII presents some advantageous properties of PBI fibre. Presently, PBI fibres find applications in racing drivers’ suits, thermal protective clothing for high-intensity heat (Figure 20), and hot gas filtration. They are also employed in the production of protective equipment for utility workers exposed to electrical arc flashes, inflammable chemicals, and oil.