Along with a number of partners, HOFZET® – the Application Center for Wood Fiber Research of the Fraun- hofer Institute for Wood Research based in Hannover – has developed new forms of bio-hybrid fibre reinforced composites (bio-HFCs) containing the highest possible bio-based content. “Bio-HFCs are already successfully employed in a range of sporting goods, such as racing cycle frames, tennis rackets and skis, where they have a number of advantageous properties,” explains Technical Textiles specialist Jana Winkelmann. “In particular, they have a low density, high vibration damping and flexible mechanical characteristics, in addition to the added benefit of containing substantial renewable raw material content. “We are developing new and practical combinations of natural and high-performance fibres, such as flax, hemp and viscose with carbon, glass or polyamide in multi-layer fabrics.
These have application-oriented properties with the potential to be scaled up for mass production, and are targeted at applications in both the automotive and construction sectors.”
ONE OF A KIND
The development work is being carried out on a special double-rapier weaving loom and Vandewiele Jacquard attachment – the only one of its kind in Europe – at the Open Hybrid Light- weight Campus (OHLF) in Wolfsburg, not far from Volkswagen AG’s parent plant.
The OHLF weaving technology is enabling the Fraunhofer experts to cost-effectively produce materials with complex, application-specific textile structures and integrated functions, in widths of up to 50cm.
At present, a key HOFZET® research focus is on composite reinforce- ments with a thermoplastic matrix – or ‘organosheets’ – which offer reversible deformation and recycling potential in comparison with thermoset composite materials. The weaving loom enables the integration of thermoplastic matrix fibres into hybrid textiles as perfect thermoplastic prepregs. These prepregs can be shaped to a required form and turned into composites using hot pressing technology. This approach enables a reduction of process steps, cycle times and production waste. Furthermore, the process allows new design freedom, which enlarges the component spectrum of fibre-reinforced composites. A robot-controlled fibre-spraying unit further expands possibilities, allowing continuous filaments and yarns to be cut to a specific length and simulta- neously wetted in an air stream with a mixture of resin and curing agent and sprayed onto a shaping tool.
In another project, flax-based multi-layer fabrics produced on the special HOFZET® weaving system are being employed to reinforce concrete.Textile-reinforced concrete has already proved to be durable, formable in diverse shapes and suitable for lightweight construction and so far has been based on carbon or glass fibres to replace the steel which is conventionally employed.
The flax-based textile is embedded in the given component in layers. Its stiffness is variable, so it can be arranged in a desired shape and could conceivably be cast to create curved contours such as domes and rounded wall elements.
“The quality of reinforced concrete made with a flax fabric is higher than that of the reinforced concrete in bridges,” says Jan Binde, a scientist at ZELUBA®, a second department of the Fraunhofer Institute for Wood Research based in Braunschweig.