Continuous carbon fiber recycling technology using the electrolytic sulfuric acid method

Our objective is to achieve the societal implementation of the Circular Economy Program for Automobile Carbon Fibers. This involves recycling carbon fibers sourced from carbon fiber reinforced plastics/carbon fiber reinforced thermoplastics (CFRP/CFRTP) discarded from automobiles and reintegrating them into the manufacturing processes of automobiles. Although, the existing carbon fiber recycling technology recycles the carbon fiber into a finely chopped state; it is not the original continuous carbon fiber product. A novel recycling technology is elucidated herein, referred to as the electrolytic sulfuric acid method (ESAM). The ESAM recycles carbon fibers by decomposing only the resin component of CFRP/CFRTP into CO₂ and water using oxidative active species generated by electrolytic sulfuric acid. This method can (1) be applied to all resins, (2) maintains strength of the recycled carbon fibers, and (3) regenerates continuous carbon fibers. Moreover, it is the only technology applicable to CFRP pressure tanks. The successful recycling of continuous carbon fiber from pressure tanks has been achieved, enabling the production of new tanks and unidirectional CFRTP tape. This technology recycles the original continuous carbon fiber product, thus enabling a “close” resource circulation cycle. We have not yet confirmed the number of times recycling can be performed. However, according to the method described in this paper, the recycling process can yield continuous carbon fibers without a decrease in physical properties. Therefore, theoretically, it becomes possible to recycle indefinitely and revert the fibers to their original state, provided that the strength reduction during product use is not a significant consideration.