Glass fiber
Glass wool, which is one product called "fiberglass" today, was invented some time between 1932 and 1933 by Games Slayter of Owens-Illinois, as a material to be used as thermal building insulation.
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.
The technique of heating and drawing glass into fine fibers has been known for millennia, and was practiced in Egypt and Venice.
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.
In its pure form it exists as a polymer, (SiO2)n. It has no true melting point but softens up to 1200 °C, where it starts to degrade.
If the glass is extruded and cooled quickly at this temperature, it will be unable to form an ordered structure.
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.
It is usual to introduce impurities into the glass in the form of other materials to lower its working temperature.
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] Fabrics of woven glass fibers are useful thermal insulators because of their high ratio of surface area to weight.
[12] (GPa)[14] The strength of glass is usually tested and reported for "virgin" or pristine fibers—those that have just been manufactured.
Moisture is easily adsorbed and can worsen microscopic cracks and surface defects, and lessen tenacity.
During drawing, the process where the hot glass is pulled to reduce the diameter of the fiber, the viscosity must be relatively low.
The important part of the nozzle in continuous filament manufacture is the thickness of its walls in the exit region.
As it falls, it leaves a thread attached by the meniscus to the nozzle as long as the viscosity is in the correct range for fiber formation.
The glass can be blown or blasted with heat or steam after exiting the formation machine.
Here, the glass enters a rotating spinner, and due to centrifugal force is thrown out horizontally.
[18] Glass fiber has increased in popularity since the discovery that asbestos causes cancer and its subsequent removal from most products.
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 North American Insulation Manufacturers Association (NAIMA) claims that glass fiber is fundamentally different from asbestos, since it is man-made instead of naturally occurring.
[23] They claim that glass fiber "dissolves in the lungs", while asbestos remains in the body for life.
Although both glass fiber and asbestos are made from silica filaments, NAIMA claims that asbestos is more dangerous because of its crystalline structure, which causes it to cleave into smaller, more dangerous pieces, citing 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.
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.
The glass can be in the form of a chopped strand mat (CSM) or a woven fabric.
[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.
[29] Glass fiber has recently seen use in biomedical applications in the assistance of joint replacement[30] where the electric field orientation of short phosphate glass fibers can improve osteogenic qualities through the proliferation of osteoblasts and with improved surface chemistry.
