Reinforcing Materials
Glassfibre
Textile fibre is the collective name for fine fibres spun from melted glass with an almost circular cross-section. This textile glass is made out of high quality E-glass and, for special applications, also out of R-glass and C-glass. The relatively high strength and modulus values are a consequence of the strong bonds between silicon and oxygen in a spatial network. Due to the amorphous structure, glass fibres are, as opposed to carbon or aramid fibers, isotropic.
After production, a coating is applied to the newly formed glass fibre. This bonds the filaments, protects the surface and constitutes an adhesion of the matrix.
Carbonfibre
Carbonfibre or C-fibre consists of more than 90% pure carbon, and has a diameter of 5-10 micrometres. As a raw material, PAN (polyacrylonitrile fibres), pitch or cellulose are generally used.
Special properties:
- high strength up to approx. 2500 °C
- strongly anisotropic
- negative thermal expansion in fibre direction
- thermally and electrically conductive
- good physical compatibility
- sensitive to creasing and pressure
- highly resistant to corrosion
- very expensive
After manufacturing C-fibres are surface-treated. The surface is oxidised to create the greatest possible number of surface oxides, which can be achieved with the matrix system chemical bonds. The surface of the fibres is, immediately after the pretreatment, coated with the fibre finish. This is a substance which initially prevents the accumulation of water to the active surface, and contains the functional groups of bonding to the matrix system.
Aramid fibres
Aramid fibres (Kevlar) are linear organic polymers with high strength and rigidity. Like the C-fibre the aramid fibre has, as a result of the high molecular orientation, a negative thermal expansion coefficient (entropy effect).
Special properties:
- lightweight fibre reinforcement
- highly sensitive to pressure
- strongly anisotropic
- high absorption of moisture
- UV-sensitivity
- poor adhesion to the matrix
- poor machining qualities by cutting
- very expensive
The surface of aramid fibres is chemically inert and very smooth. Thus a chemical or mechanical bonding to the matrix is eliminated to a large extent. The sizing applied here has merely a protective function.
Other fibres:
Reinforcing fibres in the mouldings have, above all, the task to increase the tensile strength, impact strength, and the absorption capacity for the use of the matrix materials. The achievable level greatly depends on the type, length , content and orientation of the fibre, and the interface between fibre and matrix.
Cellulose fibres
The cellulose fibre belongs to the group of the organic reinforcing fibres. It is usually made from sulphite pulp of beech wood or out of pure cotton cellulose.
In the early days of composite technology this fibre was used for reinforcing phenolic resins. Even today it is still found in phenolic laminated paper products.
PAN fibres
The polyacrylonitrile fibre belongs to the group of synthetic organic reinforcing fibres.
The PAN fibre is a high strength fibre with a kidney-shaped cross-section. It is used primarily as a replacement material for asbestos products and in brake linings.
Polyethylene fibres
The polyethylene fibre belongs to the group of synthetic organic reinforcing fibres.
The PE-fibre consists of strongly stretched UHMW PE. Its melting point is approximately 150 °C and has a tendency to creep. However, it has a high absorption capacity for impact energy, and is preferably used as the hybrid material (in combination with other reinforcing fibres).
Ceramic fibres
The ceramic fibre is classified as a synthetic inorganic reinforcing fibre. The ceramic fibre is used for the reinforcement of metallic materials.
Wood fibres
The wood fibre is classified as a natural organic reinforcing fibre.
Sawdust, which is used for the reinforcement of phenol-formaldehyde and melamine-formaldehyde moulding compounds, is usually finely dispersed wood fibres from spruce or beech wood.
Polyester fibres
Polyester fibre belongs to the group of synthetic organic reinforcing fibres.
Polyester fibre is particularly used in textiles. The tensile strength is equivalent to that of polyamide and enhances other major synthetic fibres in impact strength. In combination with glass fibres they improve the impact strength of phenol-formaldehyde moulding compositions.
Asbestos fibres
The asbestos fibre belongs to the group of inorganic natural reinforcing fibres.
Asbestos is the oldest inorganic fibre and is obtained from natural mineral deposits (hydrated Mg and Na-silicates). For well-known reasons, they are not used any more and no longer substituted.
Metallic fibres
Metal fibres belong to the group of synthetic inorganic reinforcing fibres.
Metallic fibres can be made of steel, brass, bronze, copper, aluminium, silver, gold and platinum.
Metallic fibres are used for the reinforcement of metallic materials.
Sisal fibres
Sisal fibres are classified as a natural organic reinforcing fibre.
Despite the low price as opposed to glassfibre, sisal fibres were unable to assert themselves.
They only came back into discussion when a replacement material for asbestos in brake linings was being searched for.
Polyamide fibres
Polyamide fibres belong to the group of synthetic organic reinforcing fibres.
These technically most important polyamide fibres are based on PA 66 and PA 6 They enhance composites particularly through elasticity and creep resistance.
Boron fibres
Boron fibres belong to the group of synthetic inorganic reinforcing fibre.
Boron fibres are produced by the growth process. The substrate used is tungsten. A thin tungsten wire is electrically heated and then separated from the boron in the gas phase.
Boron fibres are used for the reinforcement of metallic materials.
Whisker
Whisker is classified as a synthetic inorganic reinforcing material.
Whiskers are synthetic single-crystal inorganic fibres. If it succeeds to orientate the fibre with a melt, a composite material with an enormous strength can be obtained.
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