Introduction
Much of the early strength of glass fiber was driven by the needs of war. During WWI, Germany needed asbestos and began experimenting with drawing glass into fine fibers as a noncombustible stand-in, with limited success. It continued research in the following decades, until by the late 1930s the process was sufficiently developed for the Owens-Corning Glass Company to begin full commercial production.
Since then, glass fiber has expanded far beyond just being asbestos’s replacement.
It is used in insulation, composites, interior products, and optical equipment.
Historical Background
Drawing hot glass into fiber has been around long before it became an industrial process. The earliest glass fibers are believed to have been made by the ancient Phoenicians, before European manufacturers perfected the process. However, the first breakthrough was achieved in the 1700s by Raumur, who successfully spun glass fiber into a form (yarn) that could be woven into fabric.
Commercial interest was low until the early part of this century, with commercial manufacturing only beginning in 1936.
However, glass was even used in fashion, when in 1893 Edward Drummond, for example, used woven glass fiber to make a famous dress, worn by actress Georgia Cayvan, and alleged to have been used to build Napoleon’s coffin, to name a few.
How ASTM Defines Glass Fiber
ASTM describes glass fibre as an inorganic, noncrystalline fibre. It is more exact to state that the glass fibre has a three-dimensional, isotropic, noncrystalline internal structure-this is very different to the structure of high-performance fibres and is, in fact, to account for many of the anomalous properties exhibited by the glass fibre with respect to typical textile fibres.
Manufacturing Process
Glass fiber starts as standard glass, melted and extruded to form long, thin filaments. Raw materials used in the production of the core are silica sand and limestone along with small amounts of soda ash, borax, aluminum hydroxide, feldspar, and boric acid. The amounts vary depending on the specific properties required in the finished fiber.
The ingredients are mixed and melted in a furnace at about 2400F. The melted glass is then drawn into fine threads. The diameter of the finished filaments depends on the viscosity of the melted glass, the rate at which it is extruded, and the size of the holes in the nozzle through which it is forced. The filaments are then bundled together in a package called a roving.
Glass fiber is produced by manufacturers either as continuous filaments or as shorter staple fibers. When producing staple fiber, jets of steam or air at high pressure crack long strands into segments about 8 to 10 inches in length, which are collected on a rotating drum and collected into a strand and then formed into a loosely twisted sliver. Glass fiber has very limited abrasion resistance, so a lubricating or a sizing finish is applied prior to subsequent processes. The fiber is then fed through usual textile processes for spinning yarns and weaving fabric.
Types of Glass Fiber
Different varieties of glass fiber are used for different applications:
A-glass has resistance to alkali and is similar in composition to normal window glass.
AR-glass is also alkali-resistant and designed to strengthen cement.
C-glass provides more chemical resistance.
E-glass is probably the most versatile. It has excellent chemical resistance and electrical properties and is used extensively in glass-reinforced plastic formations.
According to some references, AE-glass has improved alkali resistance.
HS-glass is a high-strength magnesium-alumina-silica formulation.
S-glass is similar chemically to the HS-glass and, so, is used a lot in the production of composites and is reported to have a better overall mechanical performance.
Properties of Glass Fiber
Physical Characteristics
At the microscopic level, glass fibers are simply what they seem to be - thin rods of glass. Most common types are manufactured with diameters in the range of 5-15 micrometers, quite suitable to provide the material with flexibility for textile management. Throughout the length of the fiber, there is a rounded, smooth surface providing the material with a substantial shimmer.
The material in its raw form is clear and colorless, but ceramic pigment can be incorporated in the melt to add coloration.
Glass fiber has a density of around 2.48 to 2.69.
Mechanical Behavior
The glass fiber exhibits a high tensile strength plus a high modulus, with very little extension. This combination of stiffness and low extension gives the fiber a brittle, low-resilient surface. The dry tenacity is approximately 9.6 grams per denier, falling to 6.7 gpd in the wet, and the elongation at break is limited to a relatively narrow 3 - 4%; however, the fiber has fantastic elastic recovery when under this extension limit. The fiber is generally brittle, has poor flex resistance, and is very snap-prone.
Chemical and Thermal Properties
Glass fiber does not absorb moisture (it absorbs practically none) nor does it have any natural attraction to dyes, so conventional dyeing is not straightforward. Acids and bases attack it, but it tolerates most organic solvents. Because it is an insulator to heat and electricity, staple glass fiber is used in electrical insulation.
When ignited, it does not combust but remains stable until it softens at about 1350°F and melts at or near 2400°F.
When glass fabric is set on fire, the finish and resin applied to the surface disintegrates, leaving the fiber, yarn, and woven structure unaffected.
The fiber won’t be affected by mildew or insects and is resistant to sunlight and ageing. Its low absorption of moisture and high heat accommodation result in very good shrinkage resistance. Its only practical disadvantage is poor abrasion resistance-glass fabric sections tend to split at creases and areas of continuous rubbing.
In combination, the advantages of glass fibre in practical use are its high strength at break, its total nonflammability, its only limited solubility, good dielectric properties, excellent chemical resistance, its low cost, and the very good dimensional stability because it is almost unaffected by temperature and humidity. Its disadvantages are a lower fatigue resistance and the abrasion effects discussed previously.
Some of the commercial trade names associated with glass fiber are: Fiberglas, Beta Glass, Chemglass, J-M Fiberglass, PPG Fiberglass and Vitron.
Notable Commercial Variants
This is a special type of glass fiber known as Beta Fiberglas and is formulated by Owens Corning. The fiber was spun at about one-sixth of the denier of normal glass fiber, and as such, the fineness of the filaments was thought to make them very difficult to both break and abrade. Its strength was half that of a normal glass fiber, but its strength of 8.2 was still greater than that of most other fiber types. This fiber was mainly used in window furnishings where the increased flexibility was of benefit.
Miraflex is another Owens Corning fiber. It is a bicomponent fiber which is formed by fusing two different glass compositions to each other as a single filament. As this fiber cools down, the attraction mismatch between these two components causes the fiber to extrude irregular twists along its length, which results in a soft, flexible, resilient fiber that can be used for home insulation or for composites by carding or needling the fiber into batt.
Uses and Applications
Glass fiber practically has no application in general apparel. The filament ends, when broken, can be very abrasive and harsh on skin, and its average abrasion resistance, poor absorbency, and very low stretch would not make it a good material to be used in clothing except in certain protective clothing. Previously it was widely used in curtains, draperies, lampshades and window shades, but now its only use in the home is in vertical blinds and various forms of institutional drapery.
Its nonflammability means it can be used to good effect for flame-retardant draperies in public buildings where fire safety is important, as long as the fabric is not bent excessively or subjected to too much abrasion from draughts and handling. It is likely to require heavy-duty drapery hardware due to its weight in relation to traditional fabrics.
In addition to textiles, glassfiber has a long history of use in technical and industrial fields. It has been used as an inexpensive insulation and reinforcement material for many years for its high heat and fire resistance. It is found in plastics, roofing materials, rubber reinforcement, filtration, composites, wrappings, and clothing.
Glass is widely used in the automotive industry, replacing metal where possible, for many body components and as a common reinforcement for molded composite parts such as boats, cars, and aircraft. It is also used in storage tank laminates, in composite panels, surfboards, and other molding applications, and is also popular in applications requiring good thermal insulating properties.
Glass fiber can also be used for noise reduction, protection from fire, temperature regulation, and air filters. One of the primary uses for the glass fiber is in building insulation, but the batting material used for this purpose is usually not classified as a textile fiber in the industry. Similarly, ceramic fiber can be used for extremely high-temperature applications and is also very expensive and limited in use.
Additional uses are for geotextiles, filter media, fire blankets, ironing board covers, space suits, heat- and electrically resistant tapes and braids, an electrically and heat-resistant material for shopping and commercial oven gloves, and in hotels, dormitories, and hospitals for fire-resistant mattress covers. The substrates for printed circuit boards are reinforced with glass fiber, and a water-resistant and lightweight fabric for use in medical applications is in the testing stage. Owens Corning sustains the research of fibers for clothing.
One of the most sophisticated types of use for the material is optical fiber: ultra-fine strands of completely transparent glass that carry laser light rather than current, and are unaffected by electrical interference. These are used throughout modern communications (including some of the most advanced medical equipment) as well as in novelty lighting. Within a fibre-optic cable, a core of glass that carries the light is surrounded by a specialized cladding layer that prevents the light from escaping.
Soil Stabilization and Concrete Reinforcement
Soil stability is one of the most common problems faced in geotechnics since any instability at the ground surface or in the slope may result in a large economic loss as well as safety risks. In the last few years, fiber reinforcement has been adopted to overcome this problem: a number of randomly distributed flexible fibers within the soil increases its structural stability and strength. This technique is now applied for soil layer stabilization, for the reinforcement of weak soils, and for slope remediation.
Polyester and polypropylene fibers have been thought to inhibit crack initiation and propagation in soil and to enhance the strength of cemented soil. However, glass fiber exhibits a conflicting response: the addition of glass fiber to soil increases the plastic and liquid limits and decreases the plasticity index, suggesting less compression.
As well as being used as a reinforcement material, Glass fiber can also be added to concrete as a reinforcing additive. This imparts mechanical and structural stability properties to it, albeit to a much lesser extent than other reinforcement methods. However, there are clear benefits to using it, such as increased longevity, more environmentally sustainable properties, more fire-resistant, enhanced strain resistance, and lower weight compared to traditional reinforced concrete. New work is still being undertaken in the field on ways of further increasing the strength of fiber-reinforced concrete.
Care and Handling
Glass textiles need to be washed by hand (will be damaged in the machine through excessive fibers breaking away). If washed in the machine, the glass particles can transfer to other loads and can irritate the skin of those who subsequently use the items. Hand washing can also irritate the skin, so this should be explicitly referred to on care labels for glass textiles.
Daily laundering is not inherently necessary because the fabric is not particularly susceptible to dirt, and a damp cloth can remove any stains or spots. No ironing is necessary as the fabric can be flattened by hand and hung up to dry. Eventually, the finishing oils can discolor the white fabric to a yellow or gray, attract dirt, and oxidize; washing does not reverse this process (Woolite is not recommended for cleaning).
As glass fiber has been classified as a carcinogen, it should be treated with all due care, in the controlled protective environment of a laboratory.
Leading Manufacturers
Significant manufacturers of glass fiber are Central Glass Co Ltd., Snoma Science and Technology Co Ltd., Nippon Electric Glass Co Ltd., and Saint-Gobain Vetrotex.
Conclusion
From the raft-basket making times of the ancient world, through the day-to-day insulator and DIY-reinforcement of the present, glass fiber has shown it can adapt and absorb novel processes and provide a flexible base for a great variety of industrial applications. Its low cost, high tenacity, nonflammability, stability and electrical qualities have kept it a significant composite material, an insulator and interior fitting material and optical component. However, its low abrasion resistance, zero stretch and tendency to scratch and irritate haven’t meant it has been taken up as an outer clothing textile. Further work into glass texturised yarns and novel composite applications could still find new and exciting ways of using this known material.
