E-Glass

Over 90% of the glass fibre market is held by so-called E-glass, used mainly in a polyester matrix.

The 'E' in E-glass stands for 'electrical' and was intended to indicate that the material had low electrical conductivity. This is rarely the criterion upon which it is chosen; its popularity is mainly due to the fact that it is the cheapest glass fibre and is therefore the preferred material in general purpose products.

Both continuous and chopped E-glass is widely used. For its relatively low cost it is a remarkable material, with individual filament strengths around 3500 MPa and modulus around 80GPa. Its elongation-to-break is nearly 5%. There are basically two types, those which contain boron, and those which are boron-free. As boron is considered environmentally unfriendly, use of boron-containing E-glass can involve the addition of pollution control equipment.

The ultimate use temperature of E-glass is around 500C. The maximum service temperature for the composite will therefore be dictated by the matrix material, rather than by the reinforcement.

The corrosion resistance of E-glass with and without boron are different, with the boron-free E-glass having up to seven times the corrosion resistance of the boron-containing E-glasses (based on weight loss in sulphuric acid - Ref ASM Vol. 21 Handbook). Boron free E-glasses have approximately a 10% higher dielectric constant than boron containing E- glasses when measured at room temperature making them less suitable for electronic circuit boards and aerospace applications.