Asahi Kasei develops closed-loop for carbon fibre recycling

The multinational Japanese chemical company, the Asahi Kasei Group, has developed new technology to recycle high-quality carbon fibre plastic compounds in collaboration with the National Institute of Technology, Kitakyushu College and Tokyo University of Science.

Carbon fibre-reinforced plastics (CFRP) are a sought-after material in many weight sensitive industries due to their unique rigidity, mechanical strength and light weight, in particular when compared to conventional glass fibre-reinforced plastics. CFRP is commonly used in the aerospace, automobile, construction and energy industries due to these properties, and the current annual growth rate is around 11 per cent.

The continuing and rising demand for CFRC will dramatically increase the amount of waste product in coming years, bringing attention to how the end-of-life of these composite products is managed. Legislation adds to the urgency around the problem: European directive 2000/53/EC requires 95 per cent of automotive vehicle components to be recovered and reused, and at least 85 per cent to be recycled.

However, CFRC is difficult and expensive to recycle: extracting carbon fibres from resin after usage is notoriously challenging. Different mechanical, thermal and chemical recycling methods have been explored, with each resulting in negative impacts on the surface chemistry and mechanical properties of fibres. The quality of the recycled fibres has, therefore, been too low quality to be used in industry.

Asahi Kasei’s new recycling method uses an ‘electrolysed sulphuric acid solution method’ to decompose the resin that the carbon fibre is embedded within to extract continuous strands of carbon fibre that are identical to the original substance. This allows for its continued use in high-performance applications and presents an inexpensive, circular solution to the end-of-life dilemma of carbon fibre plastic compounds.

The method utilises electrolyzed acid solution. As a result, oxidative active species are produced. The CFRP is then added to the acid solution and heated up to 100-150 °C. By doing this the polymer matrix is dissolved and turns into CO2 and H2O with only the carbon fibre remaining. The acid solution with the dissolved polymer matrix can be reused again, resulting in almost no waste.

Asahi Kasei is also developing a carbon fibre-reinforced thermoplastic unidirectional tape (CFRTP-UD tape) which combines the recycled carbon fibre with the company’s Leona polyamide resin. Stronger than metal, the tape is designed for use in automobile frames and bodies. Practical application is planned for around 2030.