A composite can be defined as a mixture of two or more materials, which together provide a useful combination of properties.

Examples of early composites are straw reinforced mud, reinforced concrete and plywood.

As composites are now being considered as potential replacement for metals, it is important to note that composites do not offer superior strength and modulus compared with most metals. The real advantage comes when the properties are compared on a per unit mass basis.

The largest proportion of composites are used in transportation, construction, chemical and water purification plants.

Current growth area is the automotive sector, with particular emphasis on body parts.

In the chemical industry, fiberglass tanks eliminate the need for corrosion and cathode protection, avoiding costly maintenance and repainting.

In marine applications conventional boat builders use large quantities of chopped strand mat, woven fiber mats and polyester resins.

Aerospace applications are slowly increasing as confidence builds. It is presently used in primary structures, however there are numerous applications and room for potential growth.

The main materials used for the production of glass fibers are silica sand, with various fluxes and stabilizers.

Various grades are produced to meet customer's needs.

• E - glass is the mostly commonly used in the industry
  
• S & R - glass is a premium product and is produced for the aerospace industry
  
• C - glass is used in chemical industry
  
• D - glass in electrical applications

Silica sand, borates and specialty chemicals are melted an in very high temperature furnaces, turning the mixture into molten glass. This flows by gravity through the bottom of a platinum tray via tiny orifices.

The emerging thin stream of molten glass are controlled and reduced to a precise diameter and quenched by air and water to create a filament.

The hair-like filaments are coated with chemicals that serve to protect the filaments from abrasions, avoiding static and ensuring good adhesion of fiber to the resin.

Polyester resins
The largest quantities are made from ethylene glycol with a mixture of phthalic and maleic acids and are mixed in various proportions to control reactivity.

Polyester resins can be induced to cure by means of heat, catalysts and accelerators which is normally achieved at room temperature, followed by post curing operations.

For hot press operations, catalysts are used without accelerators. Once the temperature is raised, the curing process begins and the reaction cycle is shorter.

Vinyl ester resins
Vinyl ester resins are processed in a similar manner to polyester resins, but their
chemical origin is more related to epoxy resins. They have better properties than polyester, but cost is nearly double that of polyesters.

Epoxy resin
Epoxidised materials are widely used for industrial purposes and adhesives, but a smaller group is used for the manufacture of fiber-reinforced plastics.

• Epoxy costs about four times more than polyester resins and twice of vinyl ester resins.
  
• Epoxy generally has shrinkage of about 3% on cure compared with up to 7% for polyesters.

High tensile strength
Glass is one of the strongest textile fibers, having greater specific tensile strength than steel wire of the same diameter, at a lower weight.

Dimensional stability
Low elongation under load, generally 3% or less. Glass fibers produce fabrics with excellent dimensional stability under various types of conditions.

High heat resistance
Glass fabrics have excellent heat resistance at relatively lower cost. They retain about 50% of room temperature.

Fire resistance
Composed of inorganic materials, glass fabrics are non-combustible, a natural choice when flammability is of a concern.

Good thermal conductivity
The rapid heat dissipation of glass fabrics is particularly important in electrical insulation applications.

Good chemical resistance
Like glass, fiberglass fabric is more resistant to attack and weakening by most chemicals than stainless steel, monel or titanium.

Outstanding electrical properties
Glass fabrics withstand higher temperatures and have low moisture regain. Its high dielectric strength and low dielectric constant makes it useful in the electrical industry. Does not interfere with radar or radio frequency signals.

Durability
Being inert, glass fabrics are unaffected by sunlight, fungus or bacteria.

Economical
Glass fabrics are lower in cost than many other fabrics for similar applications.