Glass fiber

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For the common composite material reinforced with glass fibers, see Fiberglass. For the glass fiber used to transmit information, see Optical fiber.

Bundle of glass fibers

Glass fiber (or glass fibre) is a material consisting of numerous extremely fine fibers of glass.

Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber 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. Glass fibers can also occur naturally, as Pele's hair
.

genericized trademark
. Glass fiber, when used as a thermal insulating material, is specially manufactured with a bonding agent to trap many small air cells, resulting in the characteristically air-filled low-density "glass wool" family of products.

Glass fiber has roughly comparable mechanical properties to other fibers such as polymers and carbon fiber. Although not as rigid as carbon fiber, it is much cheaper and significantly less brittle when used in composites. Glass fiber reinforced composites are used in marine industry and piping industries because of good environmental resistance, better damage tolerance for impact loading, high specific strength and stiffness.[2]

Fiber formation

Glass fiber is formed when thin strands of

silica-based or other formulation glass are 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, and was practiced in Egypt and Venice.[3] Before the recent use of these fibers for textile applications, all glass fiber had been manufactured as staple
(that is, clusters of short lengths of fiber).

The modern method for producing glass wool is the invention of

filament glass fibers.[4] Owens-Corning is still the major glass-fiber producer in the market today.[5]

The most common type of glass fiber used in fiberglass is E-glass, which is

S-glass (alumino silicate glass without CaO but with high MgO content with high tensile strength).[6]

Pure

cullet glass, was the first type of glass used for fiberglass. E-glass ("E" because of initial electrical application), is alkali free, and was the first glass formulation used for continuous filament formation. It now makes up most of the fiberglass production in the world, and also is the single largest consumer of boron minerals globally. It is susceptible to chloride ion attack and is a poor choice for marine applications. S-glass ("S" for "Strength") is used when high tensile strength (modulus) is important, and is thus important in composites for building and aircraft construction. The same substance is known as R-glass ("R" for "reinforcement") in Europe. C-glass ("C" for "chemical resistance") and T-glass ("T" is for "thermal insulator" – a North American variant of C-glass) are resistant to chemical attack; both are often found in insulation-grades of blown fiberglass.[7]

Common Fiber Categories and Associated Characteristic[8]
Category Characteristic
A, alkali Soda lime glass/ high alkali
C, chemical High chemical resistance
D, dielectric Low dielectric constant
E, electrical Low electrical conductivity
M, modulus High tensile modulus
S, strength High tensile strength
Special Purpose
ECR Long term acid resistance and short term alkali resistance
R and Te High tensile strength and properties at high temperatures

Chemistry

The basis of

molecules can move about freely. If the glass is extruded and cooled quickly at this temperature, it will be unable to form an ordered structure.[9] 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 1200 °C for long periods of time.[4]

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 that may be beneficial in different applications. The first type of glass used for fiber was soda lime glass or A-glass ("A" for the alkali it contains). It is not very resistant to alkali. A newer, alkali-free (<2%) type, E-glass, is an alumino-borosilicate glass.[10] C-glass was developed to resist attack from chemicals, mostly acids that destroy E-glass.[10] T-glass is a North American variant of C-glass. 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.

E-glass does not actually melt, but softens instead, the softening point being "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".[11] 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.[11]

Properties

Thermal

Fabrics of woven glass fibers are useful thermal insulators 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 conductivity of the order of 0.05 W/(m·K).[12]

Selected properties

Fiber type
Tensile strength
(MPa)[13]
 Compressive strength
(MPa) 		Young's Modulus, E

(GPa)[14]

Density
(g/cm3)		 Thermal expansion
(µm/m·°C)		 Softening T
(°C)		 Price
($/kg)
E-glass 3445 1080 76.0 2.58 5 846 ~2
C-glass[14] 3300 -- 69.0 2.49 7.2 -- --
S-2 glass 4890 1600 85.5 2.46 2.9 1056 ~20

Mechanical properties

The strength of glass is usually tested and reported for "virgin" or pristine fibers—those that 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

amorphous structure, its properties are the same along the fiber and across the fiber.[9] 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.[9] Thinner filaments can bend further before they break.[15]
The viscosity of the molten glass is very important for manufacturing success. During drawing, the process where the hot glass is pulled to reduce the diameter of the fiber, the viscosity must 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 instead of being drawn out into a fiber.

Manufacturing processes

Melting

There are two main types of glass fiber manufacture and two main types of glass fiber product. First, fiber is made either from a direct melt process or a

bushing to be formed into fiber. In the direct melt process, the molten glass in the furnace goes directly to the bushing for formation.[11]

Formation

The

bushings were first used they were 100% platinum, and the glass wetted the bushing so easily that it ran under the plate after exiting the nozzle and accumulated on the underside. Also, due to its cost and the tendency to wear, the platinum was alloyed with rhodium. In the direct melt process, the bushing serves as a collector for the molten glass. It is heated slightly to keep the glass at the correct temperature for fiber formation. In the marble melt process, the bushing acts more like a furnace as it melts more of the material.[16]

Bushings are the major expense in fiber glass production. The nozzle design is also critical. The number of nozzles ranges from 200 to 4000 in multiples of 200. The important part of the nozzle in continuous filament manufacture is the thickness of its walls in the exit region. It was found that inserting a

meniscus to the nozzle as long as the viscosity is in the correct range for fiber formation. The smaller the annular ring of the nozzle and the thinner the wall at exit, the faster the drop will form and fall away, and the lower its tendency to wet the vertical part of the nozzle.[17] The surface tension of the glass is what influences the formation of the meniscus. For E-glass it should be around 400 mN/m.[10]

The attenuation (drawing) speed is important in the nozzle design. Although slowing this speed down can make coarser fiber, it is uneconomic to run at speeds for which the nozzles were not designed.[4]

Continuous filament process

In the continuous filament process, after the fiber is drawn, a size is applied. This size helps protect the fiber as it is wound onto a bobbin. The particular size applied relates to end-use. While some sizes are processing aids, others make the fiber have an affinity for a certain resin, if the fiber is to be used in a composite.[11] Size is usually added at 0.5–2.0% by weight. Winding then takes place at around 1 km/min.[9]

Staple fiber process

For staple fiber production, there are a number of ways to manufacture the fiber. The glass can be blown or blasted with heat or steam after exiting the formation machine. Usually these fibers are made into some sort of mat. The most common process used is the rotary process. Here, the glass enters a rotating spinner, and due to centrifugal force is thrown out horizontally. The air jets push it down vertically, and binder is applied. Then the mat is vacuumed to a screen and the binder is cured in the oven.[18]

Safety

Glass fiber has increased in popularity since the discovery that asbestos causes cancer and its subsequent removal from most products. However, the safety of glass fiber is also being called into question, as research shows that the composition of this material (asbestos and glass fiber are both silicate fibers) can cause similar toxicity as asbestos.[19][20][21][22]

1970s studies on rats found that fibrous glass of less than 3 μm in diameter and greater than 20 μm in length is a "potent carcinogen".[19] Likewise, the International Agency for Research on Cancer found it "may reasonably be anticipated to be a carcinogen" in 1990. The American Conference of Governmental Industrial Hygienists, on the other hand, says that there is insufficient evidence, and that glass fiber is in group A4: "Not classifiable as a human carcinogen".

The

U.S. Department of Health and Human Services
:

Synthetic vitreous fibers [fiber glass] differ from asbestos in two ways that may provide at least partial explanations for their lower toxicity. Because most synthetic vitreous fibers are not crystalline like asbestos, they do not split longitudinally to form thinner fibers. They also generally have markedly less biopersistence in biological tissues than asbestos fibers because they can undergo dissolution and transverse breakage.[24]

A 1998 study using rats found that the biopersistence of synthetic fibers after one year was 0.04–13%, but 27% for

amosite asbestos. Fibers that persisted longer were found to be more carcinogenic.[25]

Glass-reinforced plastic (fiberglass)

Main article: Fiberglass

Glass-reinforced plastic (GRP) is a

fiber-reinforced plastic made of a plastic reinforced by fine glass fibers. The glass can be in the form of a chopped strand mat (CSM) or a woven fabric.[6][26]

As with many other composite materials (such as

tensile strength, the glass fibers are very strong in tension but tend not to resist compression. By combining the two materials, GRP becomes a material that resists both compressive and tensile forces well.[27] 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.[6][26]

Uses

Uses for regular glass fiber include mats and fabrics for

FRP tanks and vessels.[6][26]

Open-weave glass fiber grids are used to reinforce asphalt pavement.[28] Non-woven glass fiber/polymer blend mats are used saturated with asphalt emulsion and overlaid with asphalt, producing a waterproof, crack-resistant membrane. Use of glass-fiber reinforced polymer rebar instead of steel rebar shows promise in areas where avoidance of steel corrosion is desired.[29]

Potential uses

Glass fiber use has recently seen use in biomedical applications in the assistance of joint replacement

lithium-ion batteries
due to its improved electronic properties.

Role of recycling in glass fiber manufacturing

Manufacturers of glass-fiber insulation can use recycled glass. Recycled glass fiber contains up to 40% recycled glass.[32][33]

See also

Notes and references

  1. ^ Slayter patent for glass wool. Application 1933, granted 1938.
  2. S2CID 136242178
    .
  3. ISBN 9780081022283
    . Retrieved 2021-07-21.
  4. ^
    ISBN 978-0-444-41109-9
    .
  5. ^ "A Market Assessment and Impact Analysis of the Owens Corning Acquisition of Saint-Gobain's Reinforcement and Composites Business". August 2007. Archived from the original on 2009-08-15. Retrieved 2009-07-16.
  6. ^ a b c d E. Fitzer; et al. (2000). "Fibers, 5. Synthetic Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA.
    ISBN 978-3527306732
    .
  7. ^ Fiberglass. Redorbit.com (2014-06-20). Retrieved on 2016-06-02.
  8. OCLC 712545628.{{cite book}}: CS1 maint: others (link
    )
  9. ^
    ISBN 978-0-412-54030-1
    .
  10. ^
    ISBN 978-0-444-98805-8
    .
  11. ^ a b c d Lubin, George, ed. (1975). Handbook of Fiberglass and Advanced Plastic Composites. Huntingdon NY: Robert E. Krieger.
  12. ^ Incropera, Frank P.; De Witt, David P. (1990). Fundamentals of Heat and Mass Transfer (3rd ed.).
    ISBN 978-0-471-51729-0
    .
  13. ISBN 978-1-4419-0735-6
    . Retrieved 29 April 2011.
  14. ^
    ISBN 978-1-139-17013-0
    , retrieved 2020-11-07
  15. ^ Hillermeier KH, Melliand Textilberichte 1/1969, Dortmund-Mengede, pp. 26–28, "Glass fiber—its properties related to the filament fiber diameter".
  16. ISBN 978-0-444-41109-9
    .
  17. ISBN 978-0-444-41109-9
    .
  18. ISBN 978-0-442-25447-6
    .
  19. ^ a b "Fiber Glass: A Carcinogen That's Everywhere". Rachel's News. Environmental Research Foundation. 1995-05-31. Retrieved 2008-10-30.
  20. ^ John Fuller (2008-03-24). "Fiberglass and Asbestos". Is insulation dangerous?. Retrieved 27 August 2010.
  21. ^ "Fiberglass". Yeshiva University. Archived from the original on 20 July 2011. Retrieved 27 August 2010.
  22. PMID 16374937
    .
  23. ^ "What does the research show about the health and safety of fiber glass?". FAQs About Fiber Glass Insulation. NAIMA. Archived from the original on 13 June 2010. Retrieved 27 August 2010.
  24. ^ Toxicological Profile for Synthetic Vitreous Fibers (U.S. Department of Health and Human Services, Public Health Services, Agency for Toxic Substances and Disease Registry), September 2004, p. 17.
  25. PMID 9707503.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link
    )
  26. ^ a b c Ilschner, B; et al. (2000). "Composite Materials". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA.
    ISBN 978-3527306732
    .
  27. ^ Erhard, Gunter. Designing with Plastics. Trans. Martin Thompson. Munich: Hanser Publishers, 2006.
  28. ^ "Reflective Cracking Treated with GlasGrid" (PDF). CTIP News. 2010. Archived from the original (PDF) on 26 February 2013. Retrieved 1 September 2013.
  29. ^ "Steel Versus GFRP Rebars?". Public Roads. September–October 2005. Retrieved 1 September 2013.
  30. ^ Electric Field-Assisted Orientation of Short Phosphate Glass Fibers on Stainless Steel for Biomedical Applications Qiang Chen, Jiajia Jing, Hongfei Qi, Ifty Ahmed, Haiou Yang, Xianhu Liu, T. L. Lu, and Aldo R. Boccaccini ACS Applied Materials & Interfaces 2018 10 (14), 11529-11538 DOI: 10.1021/acsami.8b01378
  31. ^ Nandi, S., Jaffee, A. M., Goya, K. F., & Dietz, A. G. (2019). U.S. Patent No. US10193138. Washington, DC: U.S. Patent and Trademark Office.
  32. ^ New recycling effort aims to push KC to go green with its glass, Kansas City Star, October 14, 2009
  33. ^ FAQs About Fiber Glass Insulation. North American Insulation Manufacturers Association

External links

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