A composite is a specific combination of two or more materials that improves the properties of the individual components. Nature itself has demonstrated the principle that high-strength fibres are the most suitable lightweight material for absorbing forces. Wood, plant leaves, muscles and bones are just a few examples of composite structures that occur naturally. Today, composites are generally understood to mean a combination of high-strength fibres and a plastic.
The fibres critically determine the mechanical characteristics of the composite, such as its strength and rigidity. The materials generally used are glass, carbon or aramid. For high-performance composites, exclusively continuous fibres (where the length of the fibre corresponds to that of the component) are used in the form of woven fabrics or non-woven fabrics. The matrix material, too, performs a crucial function. It transfers the forces between the fibres, provides support to stop them from kinking and protects them against external attack. A distinction is made between thermoset plastics and thermoplastics. Thermoplastics such as LPET, PET, PA and PPS offer clear advantages in terms of forming properties, design freedom (welding properties, insert moulding with other thermoplastics), shelf life and ease of recycling.
THE COMFIL® COMMINGLING PROCESS
COMFIL® technology makes it possible to make composite yarns by intimately blending thermoplastic fibers with reinforcing fibers. This is done through commingling the fibres at filament level with compressed air, ending up with one single end roving of intimately mixed or commingled fibers.
This composite yarn can be used as-is for thermoplastic pultrusion and filament winding. It can also be woven into a “fabric” for use in several processes including panel lamination, vacuum bag molding, compression molding and thermoforming using double diaphragms (diaphragm forming).
Unlike prepreg, it is much more flexible, and has a lower cost, because the process is a high volume industrial process. Also unlike the prepreg tapes, the fiber in this product form is not impregnated at all. The physical proximity (microns) of thermoplastic fibers to reinforcing fibers allows for quick and easy wet out during processing.
To get optimal properties in the consolidation process it is essential to have the reinforcement fibre surface fully wetted out by the matrix material. This property can be measured by detecting the air-bubble void content in a density measurement.
The picture shows a complete wetting out from a vacuum consolidated woven COMFIL®hybrid fabric
Two key advantages are the ability to achieve reinforcement contents up to 80% by weight, and the unique ability to achieve exact reinforcement % as desired, with optimal wetting of otherwise closed reinforcement fibres.
PROCESSING COMFIL® MATERIALS
The unique commingled structure of COMFIL® also makes it easy for the matrix fibres to wet out the reinforcement fibres in a variety of processes, making continuous fibre composites. These vary from low-pressure processes such as vacuum moulding, filament winding, and pultrusion, to high-pressure processes like compression moulding.
COMFIL® is easily converted into composites by heating the material above the melting point of the matrix. The matrix flows under pressure to form the composites.The following processes are commonly used to process COMFIL® materials: