An Over View of High Performance Fibers

Introduction:
High-performance fiber-reinforced cementitious composites (HPFRCCs) are a group of fiber-reinforced cement-based composites which possess the unique ability to flex and self-strengthen before fracturing. High-performance fibers, used in fabric applications ranging from bulletproof vests to trampolines, must have a sufficient number of chemical and physical bonds for transferring the stress along the fiber.To limit their deformation, the fibers should possess high stiffness and strength. Stiffness is brought about by the degree to which the chemical bonds are aligned along the fiber axis. In fiber-reinforced composites, the fibers are the load-bearing element in the structure, and they must adhere well to the matrix material.
 
In a sense, all fibers except the cheapest commodity fibers are high-performance fibers. High-performance fibres offer special properties due to the demands of the respective application. These demands cover properties such as high tension, high elongation and high resistance to heat and fire and other environmental attacks. They are generally niche products, but some are produced in large quantities. The natural fibres (cotton, wool, silk . . .) have a high aesthetic appeal in fashion fabrics (clothing, upholstery, carpets): Until 100 years ago, they were also the fibres used in engineering applications – what are called technical or industrial textiles.With the introduction of manufactured fibers (rayon, acetate, nylon, polyester . . .) in the first half of the twentieth century, not only were new high-performance qualities available for fashion fabrics, but they also offered superior technical properties. For example, the reinforcement in automobile tyres moved from cotton cords in 1900, to a sequence of improved rayons from 1935 to 1955, and then to nylon, polyester and steel, which dominate the market now. A similar replacement of natural and regenerated fibres by synthetic fibres occurred in most technical textiles.

The maximum strengths of commercial nylon and polyester fibres approach 10 g/den (~1 N/tex) or 1GPa*, with break extensions of more than 10%. The combination of moderately high strength and moderately high extension gives a very high energy to break, or work of rupture. Good recovery properties mean that they can stand repeated high-energy shocks.

In this respect, nylon and polyester fibers are unchallenged as high performance fibers, though their increase in stiffness with rate of loading reduces their performance in ballistic applications. It is notable that polyester has proved to be the fibre of choice for high-performance ropes with typical break loads of 1500 tonnes, used to moor oil-rigs in depths of 1000–2000m. The high-stretch characteristics of elastomeric fibres, such as Lycra, have an undeveloped potential for specialised technical applica-tions. However, because of their large-scale use in general textiles, these fibres are dealt with in another book in this series.

List of High Performance Fiber:
  1. Glass Fiber
  2. Carbon Fiber
  3. Aramid fiber
  4. PBI (polybenzimidazole) Fiber etc.
  5. PBO (polyphenylenebenzobisoxazole) and PI (polyimide) Fiber
  6. PPS (polyphenylene sulfide) Fiber
  7. Melamine Fiber
  8. Fluoropolymer (PTFE, Polytetrafluoroethylene)
  9. HDPE (high-density polyethylene)
  10. Ceramic fibers
  11. Chemically resistant fibres
  12. Thermally resistant fibres
Glass Fiber:
Glass fiber is the oldest, and most familiar, high-performance fibre. Fibres have been manufactured from glass since the 1930s. Although early versions had high-strength, they were relatively inflexible and not suitable for several textile applications. Today's glass fibres offer a much wider range of properties and can be found in many end uses, such as insulation batting, fire-resistant fabrics, and reinforcing materials for plastic composites. Items such as bathtub enclosures and boats, often referred to as `fibreglass' are, in reality, plastics (often crosslinked polyesters) with glass fibre reinforcement. And, of course, continuous filaments of optical quality glass have revolutionized the communications industry in recent years.
Glass fiber
Carbon Fiber:
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atomsCarbon fibre may also be engineered for strength. Carbon fibre variants differ in flexibility, electrical conductivity, thermal and chemical resistance. Altering the production method allows carbon fibre to be made with the stiffness and high strength needed for reinforcement of plastic composites, or the softness and flexibility necessary for conversion into textile materials. The primary factors governing the physical properties are degree of carbonization (carbon content, usually greater than 92% by weight) and orientation of the layered carbon planes. Fibres are produced commercially with a wide range of crystalline and amorphous content.
Carbon fibers
Because carbon cannot readily be shaped into fibre form, commercial carbon fibres are made by extrusion of some precursor material into filaments, followed by a carbonization process to convert the filaments into carbon.

Aramid Fiber:
Aramid fiber are among the best known of the high-performance, synthetic, organic fibres. Closely related to polyamides, aramids are derived from aromatic acids and amines. Because of the stability of the aromatic rings and the added strength of the amide linkages, owing to conjugation with the aromatic structures, aramids exhibit higher tensile strength and thermal resistance than aliphatic polyamide. The para-aramids, based on terephthalic acid and p-phenylene diamine, or p-aminobenzoic acid, exhibit higher strength and thermal resistance than those with the linkages in meta positions on the benzene rings. The greater degree of conjugation and more linear geometry of the para linkages, combined with the greater chain orientation derived from this linearity, are primarily responsible for the increased strength. The high impact resistance of the para-aramids makes them popular for `bullet-proof' body armour. For many less demanding applications, aramids may be blended with other fibres.

PBI (Polybenzimidazole):
PBI (polybenzimidazole) is another fibre that takes advantage of the high stability of conjugated aromatic structures to produce high thermal resistance. The ladder-like structure of the polymer further increases the thermal stability. PBI is noted for its high cost, due both to high raw material costs and a demanding manufacturing process. The high degree of conjugation in the polymer structure imparts an orange colour that cannot be removed by bleaching. When converted into fabric, it yields a soft hand with good moisture regain. PBI may be blended with aramid or other fibres to reduce cost and increase fabric strength.

PBO (polyphenylenebenzobisoxazole) and PI (polyimide) are two other high- temperature resistant fibres based on repeating aromatic structures. Both are recent additions to the market. PBO exhibits very good tensile strength and high modulus, which are useful in reinforcing applications. Polyimide's temperature resistance and irregular cross-section make it a good candidate for hot gas filtration applications.

PPS (polyphenylene sulfide) exhibits moderate thermal stability but excellent chemical and fire resistance. It is used in a variety of filtration and other industrial applications.

Melamine Fiber:
Melamine fiber is primarily known for its inherent thermal resistance and outstanding heat-blocking capability in direct flame applications. This high stability is due to the crosslinked nature of the polymer and the low thermal conductivity of melamine resin. In comparison with other high-performance fibers, melamine fibres offer excellent value for products designed for direct flame contact and elevated temperature exposures. Moreover, the dielectric properties, cross-section shape and distribution make it ideal for high- temperature filtration applications. It is sometimes blended with aramid or other high-performance fibres to increase final fabric strength.

Fluoropolymer (PTFE, polytetrafluoroethylene) offers extremely high chemical resistance, coupled with good thermal stability. It also has an extremely low coefficient of friction, which can be either an advantage or disadvantage, depending on the use.

HDPE (high-density polyethylene) can be extruded using special technology to produce very high molecular orientation. The resulting fibre combines high strength, high chemical resistance and good wear properties with light weight, making it highly desirable for applications ranging from cut-proof protective gear to marine ropes. Since it is lighter than water, ropes made of HDPE float. Its primary drawback is its low softening and melting temperature.

Ceramic Fiber:
Ceramic is a high performance fiber. The need for reinforcements for structural ceramic matrix composites (CMC) to be used in air at temperatures above 1000°C, as well as for the reinforcement for metals (MMCs), has encouraged great changes in small-diameter ceramic fibres since their initial development as refractory insulation. Applications envisaged are in gas turbines, both aeronautical and ground-based, heat exchangers, first containment walls for fusion reactors, as well as uses for which no matrix is necessary such as candle filters for high temperature gas filtration. Ceramic fibres can withstand such demanding conditions but also are often required to resist static or dynamic mechanical loading at high temperature, which can only be achieved by a close control of their microstructures.

Ideally, ceramic fibres should show sufficient flexibility so that preforms can be made by weaving and subsequently infiltrated by the matrix material. This can be achieved with ceramics, which have high Young’s moduli, if the fibres have sufficiently small diameters, because flexibility is related to the reciprocal of the fourth power of the diameter.

Alumina and silicon carbide bulk ceramics are widely used for their high stiffness and good high temperature mechanical properties in air; however, they are generally weak due to the presence of critically sized defects.

Chemically Resistant Fibers:
Chemically resistant organic polymeric fibres include those which are designed to resist chemical attack for acceptable periods during their service lives at both ambient and elevated temperatures. As a consequence of their generally inert structures they may also be flame resistant and so address markets where that property is also desirable.

Fluorinated fibres: PTFE, PVF, PVDF and FEP (ARH) and Chlorinated fibres: PVDC (ARH) are Chemically resistant fibers.

Thermally Resistant Fibers:

Thermally resistant organic polymeric fibres include those that resist thermal degradation and some degree of chemical attack, notably oxidation, for acceptable periods during their service lives. As a consequence of their generally inert structures, like the chemically resistant fibres in the previous chapter, they may also be flame resistant and so address markets where that property is also desirable. Their thermal resistance derives from their possessing aromatic and/or ladder-like chain structures that offer a combination of both physical and chemical resistance and the former is quantified in terms of high second order temperatures, preferably above 200 °C or so, and very high (>350 °C) or absence of melting transitions.

Thermosets (HE and HS), Melamine–formaldehyde fibres, Basofil (BASF) (HE) are Thermally resistant fibres.

Conclusion:
An ideal reinforcing fiber must have high tensile and compressive moduli, high tensile and compressive strength, high damage tolerance, low specific weight, good adhesion to the matrix materials, and good temperature resistance. Their are huge application of high performance fiber. Proposed uses for HPFRCCs include bridge decks, concrete pipes, roads, structures subjected to seismic and non-seismic loads, and other applications where a lightweight, strong and durable building material is desired.

References:

  1. High-performance fibres Edited by J W S Hearle
  2. http://en.wikipedia.org 
  3. http://stuff.mit.edu/afs/athena.mit.edu/course/3/3.064/www/slides/Advanced_Fibers_MRS.pdf
 

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