Resin Transfer Pressing – A Novel Recycling Strategy for Carbon Fibers in the Automotive Industry

One of the greatest challenges facing society today is climate protection. To pursue this goal, legislators are setting ever stricter CO2 emission targets for the automotive industry and foster fuel saving technologies. The consistent implementation of lightweight solutions contributes in a valuable way, which makes mobility more environmentally friendly, regardless of the drive concept. According to current information, up to 10 g CO2/km can be saved per 100 kg saved vehicle weight¹.

In order to reduce the vehicle weight, high-performance fiber reinforced polymers (FRP) are increasingly being used as a material. In particular, carbon fiber reinforced polymers (CFRP) are superior to most metals and have been enjoying increasing demand for years. In addition to their high mechanical performance and low density, however, CFRP also has disadvantages, above all a high price and demanding processing. In the manufacture of CFRP components, up to 40%² of the valuable carbon fibres (CF) are also generated as production waste, for example as waste when CF fabrics have to be cut to the component geometry.

Although these dry fibers, i.e. fibers not yet wetted with resin, have the same mechanical potential as new fibers, they are difficult to monetarize due to the current market situation and must therefore generally be treated as hazardous waste at high cost.

This problem is to be solved by the research project rCF-Mobil, in which these fiber cut wastes are again used as fiber reinforcement in thermoset FRP processes in innovative and progressive process technologies. The aim is not only to achieve a significant improvement in the cost structure in the manufacture of FRP components, but also to close the material cycle. To this end, a novel and holistic approach to recycling carbon fibers in combination with a specially modified resin system (developed by Institut für Verbundwerkstoffe) will be investigated and implemented in an industry-oriented process. The project partner Wagenfelder Spinnereien GmbH develops recycled carbon fiber nonwovens (rCF nonwovens) which are to be supersaturated with resin. The resulting storable semi-finished products are used to impregnate, i.e. wet, rCF fabrics (Gustav Gerster GmbH & Co. KG) produced from fiber cut-offs in a novel resin transfer press process (RTP). The excess resin from the nonwoven is pressed into the non-crimp fabric and the entire structure is consolidated to produce the CFRP component.

The manufacturing processes to be developed are intended to be suitable for the production of CFRP components which are reinforced up to 100 % with recycled carbon fibers and are therefore particularly environmentally friendly. The basic material used is processing waste from the project partner ACE Advanced Composite Engineering GmbH. The long-term goal is the waste-free production of CFRP components through a closed recycling cycle.

¹Ernst, C. S. et al.: CO2-Emissionsreduktion bei PKW und leichten Nutzfahrzeugen nach 2020. Abschlussbericht, 2014, Aachen.

²Hohmann, A. et al.: MAI ENVIRO, Vorstudie zur Lebenszyklusanalyse mit ökobilanzieller Bewertung relevanter Fertigungsprozessketten für CFK-Strukturen. Abschlussbericht, 2015, Stuttgart.