Application of pulsed discharge to recycling laminated CFRP by the separation and recovery of carbon fiber

The recovery of carbon fiber (CF) from wasted carbon fiber reinforced plastic (CFRP) composites and the reuse of CF have been also required in the resource recycling. The previous study of recovery CF using the torrefaction reported that 15-50 % reduction in tensile strength of recovered CF compared to virgin CF. It is necessary to develop the recovery technology of CF from CFRP without reducing tensile strength of recovered CF. In this study, we evaluate the applicability of pulsed discharge with instantaneous high energy releases as a novel approach, which is already known to be effective in separating cathode particles from aluminum foil of lithium-ion batteries (LiBs) based on our previous investigation. The separation of cathode particles was caused in the interface between the foil and particles by deactivating adhesive strength of binder which connected these due to the Joule heating of the foil generated by the current of discharge. The object of this study is to applicate pulsed discharge to recover CF without attaching polymer matrix from laminated CFRP with delaminating CFRP layers by loading discharge horizontally. The tested sample sizes of laminated CFRP were 100 mm length, 30 mm width and 8 mm thickness. Two electrodes of pulsed discharge were set on the surface of sample, and the electrode gap was 50 mm. The pulsed discharge with conditions of capacitor capacity of 80 μF, charging voltage of 10 kV and charging energy in the capacitor of 4000 J was performed in the water. The CFRP layer was peeled, and fibers about 20 mm length were also recovered by the discharge. The scanning electron microscope (SEM) images for recovered fibers indicated that fibers were without the adhesion of matrix resin. It was assumed that the separation mechanism of resin from CFRP was that the insulation breakdown in resin was caused by the discharge, and the resin was removed by the plasmatization with high temperature, resulting in the recovery of CF. It is possible to consider that the volume expansion of resin induced by the plasmatization also caused the peeling of CFRP layer. The tensile strength of recovered CF was found to be 5.0 GPa by the single fiber tensile test and was 21 % less than that of the virgin one. These results indicated that pulsed discharge is effective in the recovery of CF from the laminated CFRP with the less tensile strength reduction of recovered CF.