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ThinKing May 2020: Green, robust and reasonably priced

12.05.2020

 

New plant technology for manufacturing sustainable high-performance fibres.

Is it possible to manufacture carbon fibres from renewable raw materials that have the same tensile strength values as high-performance fibres made of polyacrylonitrile (PAN)? And at a significantly lower price? Sometimes, all that is needed is to optimise one step in a process to open up a whole new range of possibilities for a material. German plant engineering company centrotherm has developed a low-pressure technology that operates in a defined process atmosphere, with low amounts of process gas and quasi-digital temperature zones. The result are low-cost carbon fibres made from alternative resources, with a significantly lower carbon footprint.

The Development Agency for Lightweighting Baden-Württemberg presents this innovation in its May 2020 edition of ThinKing. Under this label, Leichtbau BW GmbH provides a platform every month for new innovative lightweighting products or services from Baden-Württemberg.

At a glance:
- Low-cost: Price reduction of 25 percent for carbon fibres
- Green: Precursors made of renewable raw materials (cellulose)
- Robust: Same tensile strength values as with PAN precursors
- Less CO2: Carbon footprint is reduced by about 30 percent through the use of renewable raw materials and energy-efficient fibre production
- Faster: Process time is reduced by more than a third

Lightweighting is all about having the right material in the right place. Carbon fibres are a comparatively expensive material. The high cost is a result of the purchase price of the starting material, PAN, on the one hand, and the energy-intensive manufacturing process of the high-performance fibres on the other. Depending on quality, the market price for carbon fibres made of PAN is currently around 14 to 20 euros per kilogram.

Andreas Keller, Senior Manager New Technologies at centrotherm international, explains: “We took a closer look at the process step of stabilisation. There was significant potential for improvement in the previous production process for carbon fibres, which uses a circulating air furnace.” Thus, centrotherm’s low-pressure process for fibre stabilisation takes a completely new approach. The most important difference is that the process is run under low pressure and the fibre passes through defined temperature zones. The system module can be seamlessly integrated into the overall process and can replace the previous circulating air furnace.

Low pressure and accurate temperature control
The stabilisation process is a slowed exothermic reaction. It is necessary to slow the reaction as otherwise the fibres would burn due to the oxygen content of the surrounding air. The new low-pressure technology operates with negative pressure in the process chamber; therefore the oxygen concentration is lower. This eliminates the need for an expensive protective gas such as that used in a circulating air furnace. In addition, the negative pressure in the process chamber extracts water and oxygen from the precursors even at a comparatively low temperature, which has a positive effect on the fibre and also on the quality of the waste gas. Following this first heating stage, the fibre is then rapidly heated further in line with the degree of carbonisation. This is done to achieve optimised stabilisation within a process time that is just over a third shorter than usual.

To heat the fibre, the company uses the radiant heat of a heat source located directly in the process chamber. The fibre is heated to the required temperature in a virtually airless space. By this means, air currents such as those that occur in a circulating air furnace and that cause the sagging fibres to oscillate, thus reducing their quality, are avoided.

Price of high-performance fibres is reduced by roughly a quarter
It is not just the shorter process time that has a positive effect on the price of the fibres. The significantly smaller process chamber and improved insulation significantly increase the energy efficiency of the process. This has led to a reduction in operating costs by about a third. 

By replacing the comparatively expensive precursor PAN (polyacrylonitrile) with a renewable raw material such as cellulose, the price for the precursor and the operating costs for fibre production can be reduced even further.

“At this point in time, we expect the final price for carbon fibres made of cellulose to be just over ten to twelve euros per kilogram,” says Andreas Keller. Compared to high-performance fibres made of PAN, this constitutes a price reduction of about 25 percent, without having to make any concessions in terms of the tensile strength values. Tensile strength and elastic modulus remain the same. Therefore, Andreas Keller is certain that “components made of carbon will open up new market segments that were previously unattainable for financial reasons.”

Green high-performance fibres with a significantly smaller carbon footprint
In combination with this new low-pressure technology, carbon fibres made from renewable raw materials can achieve a carbon footprint that is about 30 percent lower than that of PAN-based carbon fibres. This value is based on a calculation performed by the German Institutes of Textile and Fiber Research Denkendorf (DITF) as part of a joint project with centrotherm, under the direction of Dr. rer. nat. Frank Hermanutz. For lightweighting technology, the reduced carbon footprint opens up new possibilities in various industries; for example, carbon concrete or carbon fibre-reinforced granite could be used in architecture, the automotive industry or aviation.

About centrotherm international AG
centrotherm international AG is a plant engineering company based in Blaubeuren in Baden-Württemberg, Germany. The company has been developing and implementing production concepts for the semiconductor market, microelectronics, photovoltaics and the carbon fibre industry for over 60 years. With 550 employees worldwide, this medium-sized company’s core competence is the development of thermal production solutions. For more information, please visit: www.centrotherm.de