Introduction
During World War I, the Germans found that they were running short of asbestos fiber. In an effort to find a substitute fiber that was noncombustible, they tried to make fibers from glass, with only limited success. After World War I, researchers continued to look for practical ways to use glass in fiber form, and the work had advanced enough by the late 1930s for the Owens-Corning Glass Company to begin mass production. Since then, glass fiber has moved from a special substitute material to an important fiber used in insulation, composites, interiors, and optical systems.
Historical Background
Drawing glass into hairlike strands dates back to ancient times. The Phoenicians probably produced the first glass fiber, and the idea was later developed further in Europe. In the 1700s, the scientist Reaumur first developed glass fiber that could be spun into yarn and woven into fabric. Glass fibre was first used commercially in the 1920s, and commercial production started in 1936. One early curiosity was the glass dress developed by Edward Drummond in 1893; glass fiber dress was first used by actress Georgia Cayyan, and it was also used in the funeral coffin of Napoleon.
ASTM Definition and Classification
According to ASTM, glass fiber is an inorganic fiber and a non-crystalline fiber. In another way of describing it, the fiber has a three-dimensional isotropic noncrystalline structure, which is quite different from the basic definition of a high-performance fiber. This unusual structure is one reason fiberglass behaves so differently from many other textile fibers.
Manufacturing of Glass Fiber
Glass fiber is made from glass that has been melted and extruded into long, fine filaments. The raw materials for glass are silica sand and limestone, with small amounts of other ingredients such as soda ash, borax, aluminum hydroxide, feldspar, and boric acid. The quantities of these materials are varied depending on the qualities desired in the fiberglass.
The selected ingredients are mixed together and melted in a high-temperature furnace, usually at about 2,400°F. Molten glass is then drawn from the furnace in the form of filaments. The diameter of the filament is controlled by the viscosity of the glass melt, the rate of extrusion, and the size of the spinneret hole. Filament fibers are collected into a bundle called a roving.
Glass fiber can be produced in both continuous filament form and in staple lengths. When staple fibers are needed, an air jet or high-pressure air and steam breaks the strands into fibers about 8 to 10 inches long and pulls them onto a revolving drum. They are then gathered into a strand and formed into a sliver, or soft, untwisted yarn. Bare glass fibers have poor abrasion resistance, so a sizing or lubricating material is applied to give them some protection. Fibers made of glass are then subject to the usual textile processes for making yarns and weaving.
Types of Glass Fiber
Several types of glass fiber are described in the literature. A-glass fiber is alkali-resistant and is said to be equal to window glass. AR-glass fiber is also alkali-resistant and is used in reinforcing cement. C-glass fiber gives better chemical resistance. E-glass fiber combines better chemical resistance with good electrical insulation and is the nearly universal formulation used in many fibers and related products, especially glass-reinforced plastics. Some notes also refer to AE-glass fiber as offering better resistance against alkalis. HS-glass is a magnesium-aluminum-silica glass with high strength, and S-glass is similar in composition to HS glass and is used in composites. In another description, S-glass is noted for better mechanical properties than the other glass fiber types.
Properties of Glass Fiber
Physical Properties
Under the microscope, glass fibers look like small glass rods, which is exactly what they are. Most are manufactured in very small diameters, around five to fifteen micrometers, to provide the flexibility needed for textile applications. The longitudinal view shows a smooth, round surface that produces a high luster. The fiber is colorless unless a ceramic pigment is added to the glass melt before it is formed. Glass fibers have a specific gravity of about 2.48 to 2.69, so they are heavy compared with many other fibers.
Mechanical Properties
Glass fibers have high breaking strength and modulus but low elongation. The high modulus and low elongation make them very brittle, and their resilience is extremely low. Glass has a tenacity of 9.6 g/d dry and 6.7 g/d wet, with only 3% to 4% elongation but excellent elasticity within that narrow range. The fibers are brittle, show poor flex abrasion resistance, and break when bent.
Chemical and Other Properties
Glass fiber is completely nonabsorbent and has no affinity for dyes. Both acids and bases can affect it, while organic solvents do not. It conducts neither heat nor electricity, which is why it is used in staple form in several insulation materials. The fiber is completely noncombustible and softens at 1,350°F or above. Glass is flameproof and melts at about 2,400°F. When held in a flame, the finish of the fabric darkens as the pigments and resins used in finishing are destroyed, but the fibers, yarns, and woven structure of the fabric remain intact.
Glass fiber is attacked by neither mildew nor insect pests. Sunlight does not damage it, and aging does not harm it. Because of its low absorbency and high melting point, glass fiber has excellent resistance to shrinkage. One of the main problems in glass fabrics is their low abrasion resistance, so they tend to break where creased and wear at points where the fabric rubs against other objects.
In practical terms, glass fiber also offers high tenacity, nonflammability, little sensitivity to moisture, good electrical insulation, better chemical resistance, relatively poor fatigue resistance, good strength in various conditions, low cost, and strong dimensional stability because changes in temperature and moisture do not affect its dimensions.
Trade names include Fiberglas®, Beta glass®, Chemglass®, J-M fiberglass®, PPG fiberglass®, and Vitron®.
Notable Commercial Forms
Beta Fiberglas®, by the Owens Corning Fiberglas Corporation, has one-sixth the denier of common glass fibers. The extremely fine filaments are resistant to breaking and abrasion. Beta Fiberglas® has about half the strength of regular glass fiber, but its tenacity of 8.2 is still greater than that of most fibers. It is used in products like window-treatment fabrics, where greater fiber flexibility is needed.
Owens Corning also produces a bicomponent fiber, Miraflex®, made from two forms of glass fused together into a single filament. As the fiber cools, the components cause the filament to twist in an irregular fashion along its length. The resulting fiber is soft, resilient, flexible, and form filling. It can be carded or needled to make a fiber batt used in home insulation and composites.
Uses and Applications
Except for special items of protective clothing in which it is one component, glass fiber has never been used for wearing apparel. Broken fiber ends scratch or irritate the skin, and the fiber also has poor abrasion resistance, is not absorbent, and lacks stretch. At one time it was used fairly extensively in draperies, curtains, lampshades, and window shades. Today, apart from some institutional curtain and drapery products, the only significant home use of glass fiber is in vertical blinds.
Glass fiber is especially suitable for flame-retardant draperies in public buildings, where the danger of fire is a concern. In these interiors, the fiber works best when bending and abrasion from drafts, opening and closing, and contact with people or pets is kept to a minimum. Its heavy weight may also require special drapery rods.
Glass fiber has long been used for technical applications. For many years it has served as a cost-effective insulating material and reinforcement, and it is considered a sophisticated material with superior heat and fire resistance properties. For low-performance plastics, glass is used as reinforcement material and roofing material in the USA. Today it is used in rubber reinforcement, filtration, composite applications, packaging, and protective clothing.
Glass fiber is widely used in the automotive industry, where it has replaced metal body parts. It is also common as a reinforcement fiber in molded plastics, or composites, in boat, car, and airplane parts. In storage tank manufacturing, glass fiber laminates are used. Glass fiber in woven structure can be used in the production of composite panels, surfboards, and similar products. Due to its excellent thermal insulation, it is used in applications where thermal insulation is required.
Glass fiber has wide technical use for noise abatement, fire protection, temperature control, and air purification. Glass is commonly used in insulation for buildings, although the glass fiber batting material used for this purpose is not classified by the glass fiber industry as a textile fiber. Ceramic fiber is used for very high-tech applications, but it is restricted to limited areas because of the high cost of the fiber.
Glass is found in geotextiles, filters, fire blankets, ironing-board covers, space suits, heat- and electrical-resistant tapes and braids, and flame-resistant mattress covers used in hotels, dormitories, and hospitals. Glass fibers are used to reinforce fabric used for printed circuits in electronics. A lightweight, durable, water-resistant material in fashion colors is used to support broken bones as they heal. Owens Corning is also researching glass yarns suitable for apparel.
Optical fibers, which are very fine fibers of pure glass, use laser beams rather than electricity to remove electrical interference. Optical fibers are found in communication and medical equipment, as well as novelty lamps. The strands of glass fiber that form the light-transmitting core of fiber-optic cable are surrounded by a sheath that keeps the light from dispersing or straying.
Soil Stabilization and Concrete Uses
The stability of soil is one of the significant areas in geotextiles. Soil stability can be lost for several reasons at ground level or on slopes, and the result can be loss of economy and life. A different technique is being used for soil preservation and stabilization, and fiber reinforcement has attracted attention because the random orientation of a flexible fibrous structure helps impart stability and strength to soil layers. This technique is already used for maintaining thin layers of soil, strengthening soil, and revamping failed slopes.
Some researchers have claimed that effective use of polyester and polypropylene fibers can reduce the development and propagation of cracks in soil and improve the strength of soil and cemented sand. However, when glass fibers are used in soil, the plastic limit and liquid limit increase while the plastic index is reduced, which indicates a reduction in compressibility of the soil.
Side by side with its application in soil separation, glass fibers are also used as reinforcing material in concrete for better properties in terms of higher mechanical properties and better stability. Although glass-reinforcing concrete materials do not offer high mechanical properties, their use as reinforcing material in concrete is very limited. Nevertheless, they offer several advantages over traditional concrete, such as a higher service life, an environmentally friendly profile, fire resistance, resistance to strains, and lighter weight. Researchers are still looking for different mechanisms to increase the mechanical strength of fiber-reinforced concrete materials.
Care and Handling
Do not machine-wash glass textiles because excessive fiber breakage can occur. Tiny glass fiber bits in the washing machine will contaminate the next load and irritate the skin of people who use those textiles. Even hand washing may produce severe skin irritation, so care labels should disclose this possibility.
Glass textiles do not require frequent washing, however, because they resist soil, and spots and stains can be wiped off with a damp cloth. No ironing is necessary, and items can be smoothed and hung to dry. Oils used in finishing may turn white fabrics gray, attract dirt and soil, and oxidize with age. Unfortunately, washing does not whiten the material, and dry cleaning is not recommended.
Use care when working with glass fiber because it has been identified as a possible carcinogen.
Manufacturers of Glass Fiber
The manufacturers of glass fibers include Central Glass Co. Ltd., Snoma Science and Technology Co. Ltd., Nippon Electric Glass Co. Ltd., and Saint-Gobain Vertex.
Conclusion
Glass fiber has moved from ancient strand drawing and early commercial use into a modern material with many technical roles. Its high tenacity, nonflammability, dimensional stability, and electrical insulation make it useful in composites, insulation, interiors, and optical systems. At the same time, poor abrasion resistance, low stretch, and the risk of skin irritation keep it out of ordinary apparel. Even so, ongoing work on glass yarns and advanced composite uses suggests that glass fiber still has room to develop further.
