Fibre Agglomeration
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Fibre agglomeration
agglomerare (Latin) – to join firmly
Formation of fibre agglomerates and influence on properties
In the injection moulding process for plastic components, a wide variety of fibre orientations can occur during manufacturing, as well as fibre agglomerations, which have many different causes and represent a weak point analogous to shrink voids.
Fibre agglomeration or fibre nesting in fibre-reinforced thermoplastics is a local accumulation of fibres in the form of fibre bundles due to insufficient mixing and dispersing in the granulate or during plasticisation. It leads to a deterioration in mechanical properties, in particular a reduction in toughness and deformability or ductility.
During the manufacturing process, fibre agglomerates can form if the screw speed or back pressure is too low, if dispersing agents are missing, or if the wrong screw geometry is used.
Fibre agglomerates can also be caused, for example, by insufficient pre-drying of the fibres, so that moisture (see also: standard atmospheres) acts as a binding agent, increasing the adhesion between the fibres and making homogeneous mixing or dispersing more difficult. However, they can also be caused by overfilling the matrix or a lack of coating or inefficient coating.
| Fig. 1: | Schematic representation of a short-fibre reinforced plastic with fibre orientation and a central fibre agglomeration in a volume accumulation |
Especially in the case of flexible fibres with a rough, fragmented and partially split fibre surface, as found in natural fibres (e.g. flax, hemp) or mineral fibres, the surfaces interlock and cause fibre agglomeration through form-fitting connections.
| Fig. 2: | Transmission light microscope image of a thin section with fibre agglomerations of PA66-CF according to [1] |
See also
- Fibre-reinforced plastics fracture model
- Fibre orientation
- Fibre–matrix adhesion
- Fibre-reinforced plastics
- Glass fibre orientation
- Interlaminar shear strength
- ICIT with AE
References
| [1] | VDI 3822 Blatt 2.1.2 (2024-06): Failure Analysis – Defects of Thermoplastic Products Made of Plastics Caused by Faulty Processing |