Reinforcement materials

Textile fibre is the collective term for fine fibres spun from molten glass with an approximately circular cross-section. Textile glass is manufactured from high-quality E-glass and, for specialised applications, also from R-glass and C-glass. The relatively high strength and modulus of elasticity values result from the strong bonds between silicon and oxygen within a three-dimensional network. Owing to their amorphous structure, glass fibres are isotropic, unlike carbon or aramid fibres.

After manufacture, a sizing agent is applied to the freshly formed glass fibre. This bonds the filaments together, protects the surface and acts as an adhesion promoter for the matrix.

Carbon fibres, or C-fibres, consist of over 90 per cent pure carbon and have a diameter of 5–10 micrometres.
PAN (polyacrylonitrile fibres), pitch or cellulose are generally used as raw materials.

Special properties

• High strength up to approx. 2,500°C
• Highly anisotropic
• Negative thermal expansion in the direction of the fibres
• Thermally and electrically conductive
• Good biocompatibility
• susceptible to buckling and compression
• highly corrosion-resistant
• very expensive

After manufacture, C-fibres undergo surface treatment. This involves oxidising the surface to generate as many surface oxides as possible, which can form chemical bonds with the matrix system. Immediately after pre-treatment, the surface of the fibres is coated with a fibre finish. This is a substance designed primarily to prevent water from adhering to the active surface and which contains the functional groups required for bonding to the matrix system.

Aramid fibres (Kevlar) are linear, organic polymers with high strength and stiffness. Like carbon fibre, aramid fibre exhibits a negative coefficient of thermal expansion due to its high molecular orientation (entropy effect).

Special properties

• Lightest reinforcing fibre
• highly pressure-sensitive
• Highly anisotropic
• High moisture absorption
• UV sensitivity
• poor adhesion to the matrix
• poor machinability
• very expensive

The surface of the aramid fibre is chemically inert and very smooth. Consequently, chemical or mechanical adhesion to the matrix is largely ruled out. The applied sizing serves merely a protective function here.

Basalt fibres are produced from molten basalt rock and drawn into continuous filaments. They are mineral-based and non-metallic. As a reinforcing material, they are available in various forms, including rovings, mats, non-woven fabrics and woven fabrics.

Special properties

• High resistance to temperature and chemicals
• Good mechanical strength and stiffness
• Electrically insulating
• Good resistance to moisture
• Good sound and vibration damping, depending on the fibre structure
• mineral-based raw material

Suitable basalt rovings are particularly important for pultrusion. Processability and the subsequent properties of the components depend, amongst other things, on the sizing, the resin system, the fibre content and the component geometry.

Cellulose fibre

Cellulose fibre belongs to the group of organic reinforcing fibres. It is usually made from sulphite pulp derived from beech wood or from pure cotton cellulose.

In the early days of fibre-reinforced composite technology, this fibre was used to reinforce phenolic resins. It is still found today in phenolic-impregnated paper products.

PAN fibre

Polyacrylonitrile fibre belongs to the group of synthetic organic reinforcing fibres.
PAN fibre is a high-strength fibre with a kidney-shaped cross-section. It is primarily used as a substitute material in asbestos-cement products and in brake linings.

Polyethylene fibre

Polyethylene fibre belongs to the group of synthetic organic reinforcing fibres.

PE fibre consists of highly drawn UHMW PE. Its melting point is approximately 150°C and it is prone to creep. However, it has a high impact energy absorption capacity and is primarily used as a hybrid material (in combination with other reinforcing fibres).

Ceramic fibre

Ceramic fibre belongs to the group of synthetic inorganic reinforcing fibres.
Ceramic fibre is used to reinforce metallic materials

Wood fibre

Wood fibre belongs to the group of naturally occurring organic reinforcing fibres.

Wood flour used to reinforce phenol-formaldehyde and melamine-formaldehyde moulding compounds is usually finely ground wood fibres derived from spruce or beech wood.

Polyester fibres (PET)

Polyester fibres belong to the group of organic synthetic reinforcement fibres.
They are mainly used in textiles. Their tensile strength is roughly equivalent to that of polyamide fibres, but their impact resistance exceeds that of most synthetic fibres. When processed in combination with glass fibres, this leads to improved impact resistance in composite materials.

Asbestos fibre

Asbestos fibres belong to the group of natural inorganic reinforcing fibres.

Asbestos is the oldest inorganic fibre material and was extracted from natural mineral deposits (hydrated Mg and Na silicates). For well-known reasons, it is no longer used and has been replaced.

Metal fibres

Metal fibres belong to the group of synthetic inorganic reinforcing fibres.
Metal fibres can be made from steel, brass, bronze, copper, aluminium, silver, gold and platinum.
Metal fibres are used to reinforce metallic materials.

Sisal fibre

Sisal fibre belongs to the group of natural organic reinforcing fibres.

However, despite its lower price compared to glass fibre, it failed to gain a foothold.

It was only when a substitute for asbestos was being sought in the manufacture of brake pads that sisal came back into the picture.

Polyamide fibre

Polyamide fibre belongs to the group of synthetic organic reinforcing fibres.

The most important polyamide fibres from a technical perspective are based on PA 66 and PA 6. When used in composites, they primarily improve elasticity and creep current resistance.

Boron fibre

Boron fibre belongs to the group of synthetic inorganic reinforcing fibres.

Boron fibre is produced using the resin-tow process. Tungsten serves as the substrate. A thin tungsten wire is heated electrically, causing the boron to be deposited from the gas phase.

Boron fibres are used to reinforce metallic materials.

Whiskers

Whiskers belong to the group of synthetic inorganic reinforcing materials.
Whiskers are synthetically produced single-crystal inorganic fibres. If these fibres can be oriented within a melt, the result is a composite material with exceptional strength.