Fiberglass refers to a group of products made from individual glass fibers combined into a variety of forms. Glass fibers can be divided into two major groups according to their geometry: continuous fibers used in yarns and textiles, and the discontinuous (short) fibers used as batts, blankets, or boards for insulation and filtration. Fiberglass can be formed into yarn much like wool or cotton, and woven into fabric which is sometimes used for draperies. Fiberglass textiles are commonly used as a reinforcement material for molded and laminated plastics. Fiberglass wool, a thick, fluffy material made from discontinuous fibers, is used for thermal insulation and sound absorption. It is commonly found in ship and submarine bulkheads and hulls; automobile engine compartments and body panel liners; in furnaces and air conditioning units; acoustical wall and ceiling panels; and architectural partitions. Fiberglass can be tailored for specific applications such as Type E (electrical), used as electrical insulation tape, textiles and reinforcement; Type C (chemical), which has superior acid resistance, and Type T, for thermal insulation.
Though commercial use of glass fiber is relatively recent, artisans created glass strands for decorating goblets and vases during the Renaissance. A French physicist, Rene-Antoine Ferchault de Reaumur, produced textiles decorated with fine glass strands in 1713, and British inventors duplicated the feat in 1822. A British silk weaver made a glass fabric in 1842, and another inventor, Edward Libbey, exhibited a dress woven of glass at the 1893 Columbian Exposition in Chicago.
Glass wool, a fluffy mass of discontinuous fiber in random lengths, was first produced in Europe at the turn of the century, using a process that involved drawing fibers from rods horizontally to a revolving drum. Several decades later, a spinning process was developed and patented. Glass fiber insulating material was manufactured in Germany during World War I. Research and development aimed at the industrial production of glass fibers progressed in the United States in the 1930s, under the direction of two major companies, the Owens-Illinois Glass Company and Corning Glass Works. These companies developed a fine, pliable, low-cost glass fiber by drawing molten glass through very fine orifices. In 1938, these two companies merged to form Owens-Corning Fiberglas Corp. Now simply known as Owens-Corning, it has become a $3-billion-a-year company, and is a leader in the fiberglass market.
The basic raw materials for fiberglass products are a variety of natural minerals and manufactured chemicals. The major ingredients are silica sand, limestone, and soda ash. Other ingredients may include calcined alumina, borax, feldspar, nepheline syenite, magnesite, and kaolin clay, among others. Silica sand is used as the glass former, and soda ash and limestone help primarily to lower the melting temperature. Other ingredients are used to improve certain properties, such as borax for chemical resistance. Waste glass, also called cullet, is also used as a raw material. The raw materials must be carefully weighed in exact quantities and thoroughly mixed together (called batching) before being melted into glass.
Sizing is any coating applied to textile fibers in the forming operation, and may contain one or more components (lubricants, binders, or coupling agents). Coupling agents are used on strands that will be used for reinforcing plastics, to strengthen the bond to the reinforced material.
Sometimes a finishing operation is required to remove these coatings, or to add another coating. For plastic reinforcements, sizings may be removed with heat or chemicals and a coupling agent applied. For decorative applications, fabrics must be heat treated to remove sizings and to set the weave. Dye base coatings are then applied before dying or printing.
During the production of fiberglass insulation, material is sampled at a number of locations in the process to maintain quality. These locations include: the mixed batch being fed to the electric melter; molten glass from the bushing which feeds the fiberizer; glass fiber coming out of the fiberizer machine; and final cured product emerging from the end of the production line. The bulk glass and fiber samples are analyzed for chemical composition and the presence of flaws using sophisticated chemical analyzers and microscopes. Particle size distribution of the batch material is obtained by passing the material through a number of different sized sieves. The final product is measured for thickness after packaging according to specifications. A change in thickness indicates that glass quality is below the standard.
Fiberglass insulation manufacturers also use a variety of standardized test procedures to measure, adjust, and optimize product acoustical resistance, sound absorption, and sound barrier performance. The acoustical properties can be controlled by adjusting such production variables as fiber diameter, bulk density, thickness, and binder content. A similar approach is used to control thermal properties.
The fiberglass industry faces some major challenges over the rest of the 1990s and beyond. The number of producers of fiberglass insulation has increased due to American subsidiaries of foreign companies and improvements in productivity by U.S. manufacturers. This has resulted in excess capacity, which the current and perhaps future market cannot accommodate.
In addition to excess capacity, other insulation materials will compete. Rock wool has become widely used because of recent process and product improvements. Foam insulation is another alternative to fiberglass in residential walls and commercial roofs. Another competing material is cellulose, which is used in attic insulation.
Because of the low demand for insulation due to a soft housing market, consumers are demanding lower prices. This demand is also a result of the continued trend in consolidation of retailers and contractors. In response, the fiberglass insulation industry will have to continue to cut costs in two major areas: energy and environment. More efficient furnaces will have to be used that do not rely on only one source of energy.
With landfills reaching maximum capacity, fiberglass manufacturers will have to achieve nearly zero output on solid waste without increasing costs. This will require improving manufacturing processes to reduce waste (for liquid and gas waste as well) and reusing waste wherever possible.
Such waste may require reprocessing and remelting before reusing as a raw material. Several manufacturers are already addressing these issues.
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McLellan, G.W. and E.B. Shand. Glass Engineering Handbook. McGraw-Hill, 1984.
Pfaender, H.G. Schott Guide To Glass. Van Nostrand Reinhold Company, 1983.
Tooley, F.V. "Fiberglass, Ceramics and Glasses," in Engineered Materials Handbook, Vol. 4. ASM International, 1991, pp. 402-08.
Hnat, J.G. "Recycling of Insulation Fiberglass Waste." Glass Production Technology International, Sterling Publications Ltd., pp. 81-84.
Webb, R.O. "Major Forces Impacting the Fiberglass Insulation Industry in the 1990s." Ceramic Engineering and Science Proceedings, 1991, pp. 426-31.
— Laurel M. Sheppard
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Among the objects that can be made from glass, jars and windows, made from soda lime glass, and kitchenware, made from borosilicate glass, are the older siblings of the family—the stalwarts. Fiber-optic cables, used to transmit nearly all our communications today, are the attention-grabbing youngest child. And fiberglass? It’s the middle child, of course—equally important yet often lost in the shuffle.
“Behind the scenes” is the way Pennsylvania State University’s John C. Mauro describes the roles often played by fiberglass. Mauro, a materials scientist and glass specialist who spent nearly 20 years at glassmaker Corning, notes that fiberglass quietly makes its way into carpeting, ceiling tiles, roofing shingles, and many construction materials. And when combined with plastics, the microscopic fibers make composites that are strong and stiff yet lightweight, which is why carmakers and other manufacturers use these reinforced materials to build fuel- and energy-efficient products.
“Many people may not realize that glass is made and used in fiber form because the applications are mostly hidden,” says Michelle Korwin-Edson, a senior scientist at Owens Corning, a leading fiberglass manufacturer. Fiberglass is widely used as house and building insulation, she points out, but it may go unnoticed because it’s usually covered by drywall or tucked away in an attic.
Fiberglass may not be a flashy material, but it’s ubiquitous. It’s also big business. “Today there are over 40,000 applications just for reinforcement glass fiber,” Korwin-Edson says. Worldwide, manufacturers make some 5 million metric tons of the stuff annually, mainly for insulation and composites. Market analysts estimate that the amount produced in 2017 was worth nearly $14 billion. By 2025, they predict, that figure will climb to more than $21 billion.
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Fiberglass makers have been producing the wispy material commercially since the 1930s, when it started gaining ground as a thermal insulation material for buildings. Much has changed since that time, as manufacturers have learned to tweak the glass fibers’ composition to impart properties that better suit one application or another. But many of the basics, including the key starting materials—silica sand (mainly SiO2), soda ash (or sodium carbonate, Na2CO3), and limestone (CaCO3)—remain the same.
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To form fibers in the 5-to-20-µm-diameter range, manufacturers deliver molten glass to an extrusion device that drives the hot liquid through a nozzle that has thousands of tiny holes. The setup and processing steps differ according to the type of fiber being produced. For example, making glass-wool fibers for insulation is initially similar to making cotton candy, Korwin-Edson says. Fine streams of glass emerge horizontally through holes in a rotating spinner and quickly solidify. Afterward, they are chopped by blasts of air that blow them down to a moving conveyor belt, where they are collected and formed into insulation products, including wools, mats, and boards.
Glassmakers typically use a vertical extrusion process to make so-called continuous fibers for reinforcing plastics. According to Hong Li, a senior scientist at Nippon Electric Glass, individual fibers are gathered in bundles of 200–6,000 filaments and woven into fabrics, treated with polymers (resins) to hold them together, or processed in other ways, depending on the application.
One of the first major applications for reinforcement fiber was printed circuit boards. Found in nearly every electronic device, these familiar green slabs contain E-glass fibers, which consist mainly of silica, alumina, calcium oxide (CaO), and boron oxide (B2O3), enveloped in an epoxy resin.
In addition to providing high strength and stiffness at low weight, which is typical of all glass fibers, E-glass also combines low values for dielectric constant and dielectric loss, critical properties for insulators used in high-speed electronics, Li explains. The fibers also resist thermal expansion, which keeps the size of the board constant as multiple drilling and assembly steps build complex circuitry.
Despite its name, E-glass also has applications far beyond electronics, making its way into pipes, tanks, and other industrial parts, as well as into products used in transportation and renewable energy. The long reach comes from customizing the fibers’ chemical composition.
The boron oxide component typical of E-glass, for example, provides circuit boards with some important electrical properties. But it also lowers the material’s guard against attack by acids and corrosive chemicals. So manufacturers came up with a boron-free version, dubbed E-CR, that provides acid and chemical resistance that’s used, for example, in pipes that transport and tanks that store corrosives.
Renewable energy uses tons of E-glass—literally. Each of the three 38-meter-long blades in common models of wind turbines contains nearly 3 metric tons of E-glass fibers, Li says. The fibers impart strength to the blades while keeping them light and responsive to breezes. But turbine blades need to be much stiffer than circuit boards so that they don’t flex too much and crash into the grounding pole to which they’re attached. For standard-length blades, glassmakers address that requirement chemically and physically. They remove boron from circuit-board E-glass because that element weakens silica’s glass network. And instead of forming bundles containing hundreds of 5-µm fibers, as they do for circuit-board use, they bundle several thousand fibers with diameters of 10 µm or larger.
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When it comes to increasing stiffness, bigger is better. So, too, for boosting a generator’s electrical output. That’s why engineering firms keep increasing the length of windmill blades, with today’s longest ones approaching 100 meters. Longer blades can capture more wind energy, but it’s challenging to keep them rigid.
“For today’s longer blades, traditional E-glass cannot deliver suitable stiffness,” Li says. Enter R-glass, an aluminosilicate tailor made for rigidity. A number of manufacturers make R-glass fibers and keep the proprietary formulation details to themselves. In general, though, compared with E-glass, R-glass boosts stiffness by including magnesium oxide (MgO) at concentrations above 6%, reducing CaO to less than 20%, and leaving out boron.
Decades after first commercializing high-strength glass fibers, manufacturers continue searching for chemical formulations that lead to improved ways of making them. Researchers at Sinoma Science & Technology, in Nanjing, China, and PPG Industries, in Pittsburgh, recently teamed up to study the effects of varying the concentrations of Li2O and B2O3 on magnesium aluminosilicate fibers.
They found that increasing the combined fraction of lithium and boron relative to magnesium lowered the glass’s melting temperature and suppressed crystal growth. Those findings can benefit manufacturing by reducing the energy and cost of making fiberglass. They may also improve fiber uniformity, which can minimize breakage during the fiber drawing process (J. Alloys Compd. 2017, DOI: 10.1016/j.jallcom.2017.08.294).
By far the biggest uses of fiberglass are insulation and reinforcing lightweight objects. But a small amount is used for healing. Missouri-based Mo-Sci developed a nanofibrous bioactive borate glass for animal and human use that heals chronic skin ulcers and deep wounds. The antimicrobial fibers, which gradually dissolve and are absorbed by tissue, release bioactive ions in the wound, which stimulate blood vessel growth and promote tissue healing.
In another medical development, Aldo R. Boccaccini of Friedrich Alexander University Erlangen-Nuremberg and coworkers showed that depositing bioactive phosphate glass fibers in an aligned orientation on metal body implants nudges cells to proliferate in an orderly and directional fashion, which promotes bonding between the implant and bone (ACS Appl. Mater. Interfaces 2018, DOI: 10.1021/acsami.8b01378).
Fiberglass doesn’t draw much attention, yet it’s a common material important to modern life. “People may think glass fibers are low tech,” Penn State’s Mauro says, but tuning their composition to customize properties is “cutting-edge chemistry.”
The individual fibers in fiberglass are too small to see, but don’t be fooled by their size, Korwin-Edson says. “They’re small, but they sure are mighty.”
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