by Fridolin Richter & Sebastian Kommer

Where do you see the potential of flax?

I see more potential in hemp fibres. Flax grows in a relatively limited way. The biggest growing areas are in France and Belgium, because flax needs a maritime climate to grow well. This means that the supply is relatively limited. So if there is a lot of demand for flax in the textile industry, it can quickly happen that the price of flax goes up sharply.
In comparison, hemp can be grown almost everywhere and is very cheap. Unfortunately, there is not yet the right processing technology to produce textile hemp fibres economically. However, we are working on this in some of our research projects. It would make UD Tapes and other natural fibre composites much cheaper and more sustainable.

You were active in the development of the UD Tapes made of flax and PA10.10. For which application was the tape developed? 

The UD-Tape is currently a prototype material and not yet available on the market. The polyamide 10.10 is still very new and is produced by EVONIK. It is quite expensive and is not yet produced in large quantities, so it has hardly been used so far. So it can be said that thermoplastic natural fibre laminates are in their infancy and there is not yet the one concrete application. In one of the first BMW i3, fittings made of thermoplastic natural fibre laminates were installed on a test basis, but the material properties were not sufficiently controlled during development and the part was therefore replaced by a film.

So why exactly were the UD tapes developed?

The reason for developing the unidirectional (UD) tapes was that individual sheets can be laid individually and pressed in many layers. The loads can be determined in advance by simulating the component. The fibres are laid along these load paths. The tape should only be placed where it is needed. Therefore, it makes more sense to make UD tapes and not use fabric. The approach relates to bionics or lightweight construction. We wanted to find an alternative to glass or carbon fibre composites that is 100% renewable. 

Where could natural fibre composites be used in a meaningful way in your opinion?

Areas such as e-mobility, micromobility and especially e-bikes are currently much more promising than the price-driven automotive industry. Anything that is not cheaper than the process used so far will not be used at first.
The bicycle industry has managed to make sustainability concepts palatable to people and they are very well accepted. Many people are willing to spend more money for more sustainability in this sector. The price ranges are much wider and it is more realistic to enter the market with lightweight NF components as an alternative to other fibre composites. The material is not yet 100% suitable for series production in order to offer it cheaply. Of course, this is also a question of scaling. The more that can be produced, the cheaper the material can be offered. In the beginning, it is better to have a more expensive product with less production to push the development further.

Do you work with designers at SACHSENLEINEN e.V.?

Yes, the design studio ID Berlin has developed a child seat shell for the car together with us and several other partners like Fraunhofer, EGAD and Evonik. This is a technology demonstrator with series properties that is partially made from NF UD tapes. They help us to find such applications because, as I said, at the moment it‘s still a question of application. The material is there and the properties are also very good. We are still missing the right product that all producers can get on board with and that sells well, so that we can bring it to a broad market. 

Is there also a kind of low-tech processing for natural fibre composites?

That depends on which kind of polymer is used. With thermoset resin systems, this is easily possible because you can use them together with simple and cost efficient processes like they are used for composite applications such as surfboards or bike frames. The thermoplastic PA10.10 can only be processed with complex process technology. In industry, the tape is pressed with large, two-part moulds. The moulds serve as a geometry to which the laminate can adapt after heating. You could create the mould with ureol foam and protect the surface with an aluminium adhesive tape, which provides some heat protection. Then you could try pressing it with a silicone membrane and negative pressure – in a vacuum. One problem, however, could be finding the right temperature and for the processing window. Also, heat should actually be added not only from the top, but ideally from both sides so that the tapes melt evenly and are then pressed into the desired shape.

Kay Kölzig is managing director at SACHSENLEINEN e.V.