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Glass fiber

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Bundle of fiberglass

Fiberglass, (also called fibreglass and glass fibre), is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called "fiberglass" in popular usage. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of fiberglass was only made possible with the invention of finer machine tooling. In 1893, Edward Drummond Libbey exhibited a dress at the World's Columbian Exposition incorporating glass fibers with the diameter and texture of silk fibers. This was first worn by the popular stage actress of the time Georgia Cayvan.

What is commonly known as "fiberglass" today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, which has become a genericized trademark. A somewhat similar, but more expensive technology used for applications requiring very high strength and low weight is the use of carbon fiber.

Fiber formation

Glass fiber is formed when thin strands of silica-based or other formulation glass is extruded into many fibers with small diameters suitable for textile processing. The technique of heating and drawing glass into fine fibers has been known for millennia; however, the use of these fibers for textile applications is more recent. Until this time all fiberglass had been manufactured as staple. When the two companies joined to produce and promote fiberglass, they introduced continuous filament glass fibers.[1] The first commercial production of fiberglass was in 1936. In 1938 Owens-Illinois Glass Company and Corning Glass Works joined to form the Owens-Corning Fiberglas Corporation. Owens-Corning is still the major fiberglass producer in the market today.[2]

The types of fiberglass most commonly used are mainly E-glass (alumino-borosilicate glass with less than 1 wt% alkali oxides, maily used for glass-reinforced plastics), but als A-glass (alkali-lime glass with little or no boron oxide), E-CR-glass (alumino-lime silicate with less than 1 wt% alkali oxides, has high acid resistance), C-glass (alkali-lime glass with high boron oxide content, used,e.g., for glass staple fibers), D-glass (borosilicate glass with high dielectric constant), R-glass (alumino silicate glass without MgO and CaO with high mechanical requirements), and S-glass (alumino silicate glass without CaO but with high MgO content with high tensile strength).[3]

Chemistry

The basis of textile-grade glass fibers is silica, SiO2. In its pure form it exists as a polymer, (SiO2)n. It has no true melting point but softens at 2,000 °C (3,630 °F), where it starts to degrade. At 1,713 °C (3,115 °F), most of the molecules can move about freely. If the glass is then cooled quickly, they will be unable to form an ordered structure.[4] In the polymer, it forms SiO4 groups which are configured as a tetrahedron with the silicon atom at the center and four oxygen atoms at the corners. These atoms then form a network bonded at the corners by sharing the oxygen atoms.

The vitreous and crystalline states of silica (glass and quartz) have similar energy levels on a molecular basis, also implying that the glassy form is extremely stable. In order to induce crystallization, it must be heated to temperatures above 1,200 °C (2,190 °F) for long periods of time.[1]

Molecular Structure of Glass

Although pure silica is a perfectly viable glass and glass fiber, it must be worked with at very high temperatures, which is a drawback unless its specific chemical properties are needed. It is usual to introduce impurities into the glass in the form of other materials to lower its working temperature. These materials also impart various other properties to the glass which may be beneficial in different applications. The first type of glass used for fiber was soda lime glass or A glass. It was not very resistant to alkali. A new type, E-glass was formed that is alkali free (< 2%) and is an alumino-borosilicate glass.[5] This was the first glass formulation used for continuous filament formation. E-glass still makes up most of the fiberglass production in the world. Its particular components may differ slightly in percentage, but must fall within a specific range. The letter E is used because it was originally for electrical applications. S-glass is a high-strength formulation for use when tensile strength is the most important property. C-glass was developed to resist attack from chemicals, mostly acids which destroy E-glass.[5] T-glass is a North American variant of C-glass. A-glass is an industry term for cullet glass, often bottles, made into fiber. AR-glass is alkali-resistant glass. Most glass fibers have limited solubility in water but are very dependent on pH. Chloride ions will also attack and dissolve E-glass surfaces.

Since E-glass does not really melt, but soften, the softening point is defined as "the temperature at which a 0.55–0.77 mm diameter fiber 235 mm long, elongates under its own weight at 1 mm/min when suspended vertically and heated at the rate of 5°C per minute".[6] The strain point is reached when the glass has a viscosity of 1014.5 poise. The annealing point, which is the temperature where the internal stresses are reduced to an acceptable commercial limit in 15 minutes, is marked by a viscosity of 1013 poise.[6]

Properties

Glass fibers are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fiber make good thermal insulation, with a thermal conductivity of the order of 0.05 W/(m·K).[7]

The strength of glass is usually tested and reported for "virgin" or pristine fibers—those which have just been manufactured. The freshest, thinnest fibers are the strongest because the thinner fibers are more ductile. The more the surface is scratched, the less the resulting tenacity.[5] Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber.[4] Humidity is an important factor in the tensile strength. Moisture is easily adsorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more elongation before it breaks.[4] There is a correlation between bending diameter of the filament and the filament diameter.[8] The viscosity of the molten glass is very important for manufacturing success. During drawing (pulling of the glass to reduce fiber circumference), the viscosity should be relatively low. If it is too high, the fiber will break during drawing. However, if it is too low, the glass will form droplets rather than drawing out into fiber.

Glass-reinforced plastic

Main article: Glass-reinforced plastic

Glass-reinforced plastic (GRP) is a composite material or fiber-reinforced plastic made of a plastic reinforced by fine glass fibers. Like graphite-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass). Chemosetting plastics are normally used for GRP production—most often polyester (using butanone as a catalyst), but vinylester or epoxy are also used. The glass can be in the form of a chopped strand mat (CSM) or a woven fabric.[3][9]

As with many other composite materials (such as reinforced concrete), the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in compressive loading and relatively weak in tensile strength, the glass fibers are very strong in tension but have no strength against compression. By combining the two materials, GRP becomes a material that resists both compressive and tensile forces well.[10] The two materials may be used uniformly or the glass may be specifically placed in those portions of the structure that will experience tensile loads.[3][9]

Uses

Uses for regular fiberglass include mats, thermal insulation, electrical insulation, reinforcement of various materials, tent poles, sound absorption, heat- and corrosion-resistant fabrics, high-strength fabrics, pole vault poles, arrows, bows and crossbows, translucent roofing panels, automobile bodies and boat hulls. It has been used for medical purposes in casts. Fibreglass is extensively used for making FRP tanks and vessels.[3][9]

See also

Look up glass fiber in Wiktionary, the free dictionary.

Notes and references

  1. ^ a b Loewenstein, K.L. (1973). The Manufacturing Technology of Continuous Glass Fibers. New York: Elsevier Scientific. pp. 2–94. ISBN 0-444-41109-7.
  2. ^ "A Market Assessment and Impact Analysis of the Owens Corning Acquisition of Saint-Gobain's Reinforcement and Composites Business". August 2007. Retrieved 2009-07-16.
  3. ^ a b c d E. Fitzer; et al., "Fibers, 5. Synthetic Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA {{citation}}: Explicit use of et al. in: |last= (help)
  4. ^ a b c Gupta, V.B. (1997). Manufactured Fibre Technology. London: Chapman and Hall. pp. 544–546. ISBN 0-412-54030-4. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ a b c Volf, Milos B. (1990). Technical Approach to Glass. New York: Elsevier. ISBN 0-444-98805-X.
  6. ^ a b Lubin, George (Ed.) (1975). Handbook of Fiberglass and Advanced Plastic Composites. Huntingdon NY: Robert E. Krieger.
  7. ^ Frank P. Incropera (1990). Fundamentals of Heat and Mass Transfer (3rd ed.). John Wiley & Sons. pp. A11. ISBN 0-471-51729-1. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ KH Hillermeier, Melliand Textilberichte 1/1969, Dortmund-Mengede, page 26–28, "Glass fiber—its properties related to the filament fiber diameter".
  9. ^ a b c B. Ilschner; et al., "Composite Materials", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA {{citation}}: Explicit use of et al. in: |last= (help)
  10. ^ Erhard, Gunter. Designing with Plastics. Trans. Martin Thompson. Munich: Hanser Publishers, 2006.
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