Hybrid Composites with Recycled Carbon Fibres
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KeywordsCarbon Fibre Natural Fibre Hybrid Composite Semifinished Product Natural Fibre Composite
Hybrid composites made of natural fibres and recycled carbon fibres possess significantly better mechanical properties compared to conventional natural fibre composites. The potential of the new material class and its process-related challenges is part of the investigations at the Thuringian Institute of Textile and Plastics Research (TITK).
Natural fibre reinforced plastics (NFRP) have been used to manufacture components in the automotive industry for many years. The main reasons for this are the good specific material properties (high stiffness accompanied by low density), the favorable price but also the positive ecological footprint compared to other materials. Typical applications are door panels, trunk covers and instrument panels in the automobile interior. The usual grammages of such materials range from about 1600 to 2000 g/m2. With regard to the required weight optimisation in new vehicles, a reduction in the grammages of the semi-finished products is necessary. With the currently used natural fibre composites, this cannot be achieved without reducing the mechanical values (stiffness, impact strength). Hybrid composites with recycled carbon fibres (rCF), which allow a significant reduction in component weight with the same or better mechanical properties, are an alternative.
Manufacturing of Natural Fibre Semi-finished Products
▸ thermoset matrix (e.g. PUR, epoxy resin, acrylic resin, phenolic resin)
▸ thermoplastic matrix (e.g. PP).
▸ variation of matrix material (thermoplastics or thermosets)
▸ optimisation of fibre-matrix-adhesion (utilisation of coupling agents)
▸ variation of type of natural fibre (fibres with different mechanical properties)
▸ admixture of other fibre materials (e.g. glass or recycled carbon fibres).
Manufacturing of Semi-finished Products with Recycled Carbon Fibres
Composites with recycled carbon fibres possess significantly higher bending stiffness values than pure natural fibre composites.
Composite Manufacturing and mechanical Properties
The production of the natural fibre mats was carried out in the laboratory of the TITK on a carding machine. The recycled carbon fibres were integrated into natural fibre composites through homogeneous fibre mixtures as well as layer constructions. The admixture of the carbon fibres varied between 10 and 30 % by weight. The total content of reinforcing fibres in the composites was always 50 % by weight.
▸ Heating via contact plates, 210 °C, 2 min heating time
▸ Consolidation within tool at 30 °C, 1 min pressing time
▸ tensile test DIN EN ISO 527-4
▸ bending test DIN EN ISO 178
▸ determination of bending forces at constant bearing distance (30 mm) and 2 mm deflection, 10 mm/min testing speed
▸ impact test DIN EN ISO 179-1.
Composites with recycled carbon fibres possess significantly higher bending stiffness values than pure natural fibre composites. The highest mechanical properties can be achieved with layer constructions. The mechanical values are adjustable through the rCF content in the cover layers. The use of a coupling agent mostly leads to an improvement of the bending values. In the case of hybrid modifications, the bending properties could also be increased by optimising the fibre matrix adhesion.
Component Manufacturing and Testing
Summary and Prospect
Hybrid composites made of natural fibres and recycled carbon fibres possess significantly better mechanical properties compared to conventional natural fibre composites. The admixture of carbon fibres is possible by means of fibre-fibre mixtures (production of nonwovens) as well as with layer constructions (combination during nonwoven fabrication or further processing). Component manufacturing can be carried out by compression molding and if required in combination with injection molding.
Good fibre matrix adhesion and high composite densities are crucial for optimum mechanical values.
Based on the higher mechanical properties of the natural fibre / carbon fibre hybrids, it is possible to reduce the grammage of natural fibre reinforced semi-finished products and components by approx. 30 % without any loss in the mechanical properties. Good fibre matrix adhesion and high composite densities are crucial for optimum mechanical values to fully utilise the mechanical properties of the carbon fibres.
The natural fibre-carbon fibre hybrids can be used for interior components in the automotive industry. Typical applications are door panels, instrument panels and other components with higher mechanical requirements. The TITK is currently working on the optimisation and industrial implementation of the novel material together with industrial partners.
We would like to thank Josef Huber-Hesselberger for his professional and constructive support as well as Stephanie Cierpka for the practical implementation of the experiments.
- N.N.: Recycelte Carbonfaservliese. Firmenprospekt SGL Group 2016Google Scholar