Glass fibres are among the most versatile industrial materials known today. They are readily produced from raw material, which are available in virtually unlimited supply. Glass fibres are used in the manufacture of structural composites, printed circuit boards and a wide range of special-purpose products. The potential adoption of high volume glass-reinforcement for metal body parts and components, as well as by manufacturing industry in general for all sorts of industrial and domestic equipment, promises major new markets. Total world consumption of “textile” glass in technical applications was some 2.3 million tonnes per annum in 1995 and was over 2.9 million tonnes at 2000, representing over 20% of all technical fibre consumption.
Keywords: S-2 Glass, C Glass, AR Glass, D Glass, ECRGLAS, R Glass, E Glass.
In the 1700s, Reaumur recognised that glass could be finely spun into fibre that was sufficiently pliable to be woven into textiles. Napoleon’s funeral coffin was decorated with glass fibre textiles. By the 1800s, luxury brocades were manufactured by co-weaving glass with silk, and at the Columbia Exhibition of 1893, Edward Libbey of Toledo exhibited dresses, ties and lamp-shades woven from glass fibre.
Continuous glass fibres, first conceived and manufactured during 1935 in Newark, Ohio, started a revolution in reinforced composite material. During 1942 glass fibre reinforced composites was first used in structural aerospace part. In the early 1960’s high strength glass fibres, S Glass, were first used in joint work between Owens corning textile products and the United States Air Force. Later in 1968 S-2 Glass® fibre began evolving into a variety of commercial applications. High strength glass fibres combine high temperature durability, stability, transparency, and resilience at a very reasonable cost-weight-performance.
Ancient Egyptians made containers of coarse fibres drawn from heat softened glass. The French scientist, Reaumur, considered the potential of forming fine glass fibres for woven glass articles as early as the 18th century. Continuous glass fibre were first manufactured in substantial quantities by Owens corning textile products in the 1930’s for high temperature electrical applications. Revolutionary and evolutionary technology continues to improve manufacturing processes for continuous glass fibre production. Raw material such as silicates, soda, clay, limestone, boric acid, fluorspar or various metallic oxides are blended to from a glass batch which is melted in a furnace and refined during lateral flow to the fore hearth . Glass is a material which attracts people with its glossy shine. This material has many applications as mirrors, utensils, furniture, windows, and artworks. This appealing material has found its way into the textile industry as well. This hard and rigid material can also be made into fine, and glossy fibres which looks very beautiful, and feels like silk. This is known as fibre glass .
Glass is an incombustible textile fiber and has high tenacity too. It has been used for fire-retardant applications and also is commonly used in insulation of buildings. Because of its properties and low cost, glass fiber is widely used in the manufacture of reinforcement for composites. Glass filament yarns are brittle compared with the conventional textile yarns. It has been shown that the specific flexural rigidity of glass fiber is 0.89 mNmm2 tex-2 about 4.5 times more rigid than wool. As a result, glass yarns are easy to break in textile processing. Therefore, it is important to apply suitable size to the glass yarn to minimize the inter-fiber friction and to hold the individual fibers together in the strand. Glass fibers are also heat-resistant material. In earlier times such fibers were used for printed circuit boards. .
Glass fabric provides good protection against the former, because they generally have low coefficients of thermal conductivity (around 0.6W m-1K-1). Their performance against radiant heat can be greatly improved by the application of an aluminum reflective layer to one surface. It can be applied directly to the fabric, either as a very thin foil or supported on a thin polyester film. Another feature of glass fiber is that it melts at around 1000˚C, so that in the untreated form, it is unsuitable for applications at higher temperatures. Glass fibers have a very high tensile strength but are brittle because of their extreme sensitivity to cracks and surface defects .
Table No. 1: Composition ranges for Glass Fibers 
|Compo-sition range||Types Of Glass fibres|
|A GLASS||C GLASS||D GLASS||E GLASS||ECR GLASS||AR GLASS||R GLASS||S-2 GLASS|
|Na2O + K2O||14-16||7-10||0-4||0-2||0-2||11-21||0-1||0-0.2|
High strength glass fibre like S-2 Glass are composition of alumina silicates attenuated at higher temperatures into fine fibres ranging from 5 to 24 µm. several other types of silicate glass fibres are manufactured for the textile and composite industry. Various glass chemical compositions described below from ASTM C 162 were developed to provide combinations of fibre properties directed at specific end use applications.
- A GLASS – Soda lime silicate glasses used where the strength, durability, and good electrical resistivity of E Glass are not required.
- C GLASS – Calcium borosilicate glasses used for their chemical stability in corrosive acid environments.
- D GLASS – borosilicate glasses with a low dielectric constant for electrical applications.
- E GLASS – Alumina-calcium-borosilicate glasses with a maximum alkali content of 2 wt. % used as general purpose fibres where strength and high electrical resistivity are required.
- ECRGLAS – Calcium aluminosilicate glasses with a maximum alkali content of 2 wt. % used where strength, electrical resistivity and acid corrosion resistance are desired.
- AR GLASS – alkali resistance glasses composed of alkali zirconium silicates used in cement substrates and concrete.
- R GLASS – calcium aluminosilicate glasses used for reinforcement where added strength and acid corrosion resistance are required.
- S-2 GLASS – Magnesium aluminosilicate glasses used for textile substrates or reinforcement in composite structural applications which require high strength modulus and stability under extreme temperature and corrosive environments .
Glass fibre chemical composition
Chemical composition variation within a glass type is from differences in the available glass batch raw materials, or in the melting and forming processes or from different environmental constraint at the manufacturing site. These compositional fluctuations do not significantly alter the physical or chemical properties of the glass type. Very tight control is maintained within a given production facility to achieve consistency for production capability and efficiency. Table no. 1 provides the oxide components and their weight ranges for eight types of commercial glass fibres .
The drawing of glass into fine filaments is an ancient technology, older than the technology of glass blowing. Winding coarse glass fibres onto a clay mandrel was used as an early manufacturing route for a vessel. With the advent of glass blowing, similar fibre technologies were used to decorate goblets . Heating glass and making thin fibres out of it is known for ages, but still make glass fibres for textile applications is a novel concept. Thin strands of glass are extruded into numerous fibres with minute diameters suitable for textile processing. Silica, limestone, sand borax, ash, soda, and other ingredients are used in requisite proportion. They are formulated in an electric furnace from which molten glass with an approximate temperature of 2500°F flows into marble forming machines, making marbles of 15mm in diameter. Impurities are removed from these marbles, and then they are melted again in electric furnaces and extruded through spinnerets. Sometimes, glass strands are also extruded directly from molten glass without making the marbles .
Fibres passed through spinnerets can be made into two kinds of glass fibres:
- Staple Fibres: Where fibres with long qualities are made by passing the molten glass through small holes of bushing. Then a jet of compressed air is passed through the strands producing thin fibres ranging from 8-15 inches. These fibres are passed through a spray of lubricant and drying flame onto a revolving drum where they form into thin webs. Yarns are made from these webs by adopting similar methods used for cotton yarns.
- Continuous Filament Process: Where filaments of indefinite length is made. Molten glass is passed through spinnerets with hundreds of openings. These strands are carried through a winder revolving at high speed. Thus fibres are drawn out in parallel filaments of diameter of the openings. Binders are used to twist and winding to prevent breakage during yarn making .
Low-cost staple glass fibers are made and laid down in mats by processes such as steam-blowing or centrifugal spinning. They enter the protective market as thermal and sound insulation. Glass yarns for reinforcement of composites are made by melt-spinning under gravity, but drawing is not needed. The application of finish adapted to the end-use is an important feature of glass fiber production. Jones (2000) describes the composition, manufacturing and properties of glass fibers. Silica, SiO2, is the major component of glass, but varying amounts of about a dozen metal oxides are included in compositions intended for different uses. On solidification, silica forms an amorphous network with entrapped metal atoms. When expressed in GPa, glass fibers have a stiffness and strength comparable to aramid fibers, but the density is almost twice as high, so that the values in N/tex on a weight basis are much lower than for aramids. Glass softens at around 800˚C .
Glass fibre properties, such as tensile strength, young’s modulus, and chemical durability, are measured on the fibres directly. Other properties, such as dielectric constant, dissipation factor, dielectric strength, volume/surface resistivity’s and thermal expansion, are measured on glass that has been formed into a bulk sample and annealed (heat treated) to relieve forming stresses. Properties such as density and refractive index are measured on both fibres and bulk samples, in annealed or unannealed from. The properties presented in table 2 & 3 are representative of the compositional ranges in table 1 and correspond to the following overview of glass fibre properties .
Physical properties – density of glass fibre is measured and reported either as formed and reported either as formed or as bulk annealed samples. ASTM C is one of the test method used for density determinations. The fibre density is less than the bulk annealed value by approximately 0.04 g/cc at room temperature. The glass fibre densities used in composites range from approximately 2.11 g/cc for D glass to 2.72 g/cc for ECRGLAS reinforcements .
Tensile strength of glass fibres is usually reported as the pristine single-filament or the multifilament strand measured in air at room temperatures. The respective strand strengths are normally 20 to 30 % lower than the values reported in Table 2 due to surface defects introduced during the strand-forming process .
Table No.2: Physical Properties of different glass fibres
|PROPERTIES||Types Of Glass fibres|
|A GLASS||C GLASS||D GLASS||E GLASS||ECR GLASS||AR GLASS||R GLASS||S-2 GLASS|
|Softing Point °C||705||750||771||846||882||773||952||1056|
|Annealing Point °C||588||521||657||816|
|Strain Point °C||522||477||615||736||766|
The young’s modulus of elasticity of unannealed silicate glass fibres ranges from about 52 GPa to 87 GPa. As the fibre is heated, the modulus gradually increases. E Glass fibres that have been annealed to compact their atomic structure will increase in young’s modulus from 72 GPA to 84.7 GPA. For most silicate glasses, Poisson’s ratio falls between 0.15 and 0.26. The Poisson’s ratio for E Glasses is 0.22 +- 0.02 and is reported not to change with temperature when measured up to 510˚C .
High strength S-2 Glass fibres annealed properties measured at 20˚C is as follows:
Young’s modulus – 93.8 GPA
Shear modulus – 38.1 GPA
Poisson’s ratio – 0.23
Bulk density – 2.488 g /cc
Table No.3: Compare of different fibres
Chemical properties – The chemical resistance of glass fibres to the corrosive and leaching actions of acids, bases, and water is expressed as a present weight loss. The lower this value, the more resistant the glass is to the corrosive solution. The fibres are held in the solution for the time desired and then are removed, washed, dried, and weighed to determine the weight loss. The results reported are for 24-hr and 168 hr. exposures. As table 3 shows, the chemical resistance of glass fibres depends on the composition of the fibre, the corrosive solution and the exposure time .
Table No.4: Chemical Properties of different glass fibres
|PROPERTIES||Types Of Glass fibres|
|A GLASS||C GLASS||D GLASS||E GLASS||ECR GLASS||AR GLASS||R GLASS||S-2 GLASS|
|Durability (% weight loss)||CHEMICAL PROPERTIES|
|10% HCL: 24hr||1.4||4.1||21.6||42||5.4||2.5||9.5||3.8|
|10% H2SO4: 24HR||0.4||2.2||18.6||39||6.2||1.3||9.9||4.1|
|10% Na2CO3: 24hr||24||13.6||2.1||1.3||3.0||2.0|
Electrical properties – The electrical properties in table 3 were measured on annealed bulk glass samples according to the testing procedures cited. The dielectric constant or relative permittivity is the ratio of the capacitance of a system with the specimen as the dielectric to the capacitance of the system with a vacuum as the dielectric. Capacitance is the ability of the material to store an electrical charge .
Table No.5: Electrical Properties of different glass fibres
Thermal properties – The viscosity of a glass decreases as the temperature increases. Below figure shows the viscosity-temperature plots for E Glass and S-2 Glass fibres. Note that the S-2 Glass fibres temperature at viscosity is 150-260˚C higher than that of E Glass, which is why S-2 Glass fibres have higher use temperatures than E Glass .
The mean coefficient of thermal expansion over the temperature range from -30˚ to 250˚C is provided in Table 3. The expansion measurements were made on annealed bars using ASTM D 696. A lower coefficient of thermal expansion in the high strength glasses allows higher dimensional stability at temperature extremes .
Table No.6: Thermal Properties of different glass fibres
Optical properties – Refractive index is measured on either unannealed or annealed glass fibres. The standard oil immersion techniques are used with monochromatic sodium D light at 25˚C. In general the corresponding annealed glass will exhibit an index that will range from approximately 0.003 to 0.006 h .
Radiation properties – E Glass and S-2 Glass fibres have excellent resistance to all types of nuclear radiation. Glass fibres resist radiation because the glass is amorphous and the radiation does not distort the atomic ordering. Glass can also absorb a few present of foreign material and maintain the same properties to a reasonable degree. Also because the individual fibres have a small diameter the heat of atomic distortion is easily transferred to a surface for dispersion .
Glass has for many years, been one of the most underrated technical fibres. Used for many years as a cheap insulating material as well as reinforcement for relatively low performance plastic (fibre glass) and (especially in the USA) roofing materials, glass is increasingly being recognised as a sophisticated engineering material with excellent fire and heat-resistant properties. It is now widely used in a variety of higher performance composite applications, including sealing materials and rubber reinforcement, as well as filtration, protective clothing and packaging .Glass fibres are used in a number of applications which are:-
- Filtration media,
- Water proofing,
- Electrical, 
Fiber glass for insulation – For insulation, the thermal conductivity or sound transmission ability of fibrous “wool” is of the most importance. Clearly, the thermal performance will be directly related to the low thermal conductivity of the glass itself but also to the density of the material. In other words, the entrapped air provides the insulating properties but the fibers provide the supporting structure. The efficiency of air entrapment is determined by the fiber diameter and its configuration, which is a function of the fiber spinning technique . Black coated fiber glass fabric is compounded with fiber glass wool plate as the basic material and insulation boards are made which have noise reduction, fire resistance, heat insulation and convenient to use in places which have special requirements on the light sources and noise levels .
Table No.7: Typical compositions (in weight %) for glass fibers used for thermal and acoustic insulation .
|Composition||Typical mineral or slag wool||Typical fiber glass insulation||Typical high temperature grade|
Fiber glass for filtration – For filtration, the surface area of the fibers and the size of the spaces between them are the important factors. A number of spinning techniques have been developed, to produce fibers with a range of diameters from 0.05-25µm. the finest diameter fibers provide the most insulation and filtration effectiveness as a result of the pore size of the mat . The filters without binder resin retain their structural integrity without weight loss when heated up to 500°C and can therefore be used in gravimetric analysis as well as for the filtration of hot gases. Glass fiber filter without binder resin can be used for a range of applications . Fiber Glass fabric are still more suitable filter media for dust laden hot gasses, as it possess the best temperature resistant properties, dimension stability, lowest elongation and is more easily heat set. Fiber glass fabrics are widely used for filtering, molten metals, especially aluminum .
Table No.8 : Different types of filter fabric details.
|Retention rating (µm)||0.2-0.6||0.8-8.0||0.8-8.0|
|Water flow rate (mL/min/cm2)||1.6||1.3||5.8|
|Air resistance (mm of H2O @ 10.5 fpm or 5.3 cm/s)||210||48||35|
|DOP penetration @ 10.5 fpm (%)||0.10||0.08||0.03|
Reinforcements- Glass fibers are widely used in roofing application. Glass- reinforced materials includes wall panels, septic tanks and sanitary fittings. Glass fibers are used to prevent cracking of concrete, plaster and other building materials. More innovative use is now being made of glass in bridge construction . Glass fibers, the most widely used at over 90% of all reinforcements with thermoplastic or thermoset matrices, are available in many forms for producing different commercial and industrial products. Glass fiber reinforced thermoplastic materials fall into mainly two categories: aligned thermoplastic composites (ATC) and glass mat thermoplastic composites (GMT). GMT are non-woven textile technology that are being used as atypical chopped strand mat or a continuous swirl mat form, impregnated typically with polypropylene .
Medical- The glass fiber having low porosity, non-staining and hard wearing finish, GRP is ideally suited to medical applications, from instrument enclosures to X-ray beds (where X-ray transparency is important) .
Automobile- Fiber glass is often used for secondary structure on aircraft, such as fairing, radomes, and wing tips. Fiberglass is also used for helicopter rotor blades. The pilot’s cabin door of aircraft has also been made by fiber glass. The fiber glass also used in space vehicles because of high specific strength, low cost, good forming characteristics, high impact resistance and thermal stability .
Water proofing- Glass fiber scrims are used as reinforcing substrate with bitumen for water proofing. Fiberglass resin coated scrim products designed for use with tar or asphalt based water proofing compounds and for use with surfacing mastics used on insulated indoor, outdoor and underground piping, tanks and other mechanical equipment .
Electrical- The excellent insulation and durability properties make glass fabric an important constituent in the electrical industry. Woven fabrics are impregnated with varnish. These as well as open weave fabrics are used as substrate for reinforcement and backing for mica which are used in motor winding. Most of these combinations are cut into tapes before application. Glass fabric is also used in high pressure laminates because of its dimensional stability, electrical and high heat resistance properties .
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