Solubility Parameters of Carbon Fiber for CFRP Recycling

Miscibility changes of carbon fiber (CF) through carbon fiber-reinforced plastic (CFRP) recycling by thermal treatment were elucidated using solubility parameter analysis. A comparison was made among recycled CF (ReCF), acetone-washed original CF (AwCF), and ozone-treated CF (OzCF). While the Hildebrand solubility parameters (δ_t) of the three types were almost identical, only the Hansen solubility parameters (HSPs; δ_d, δ_p, and δ_h) of ReCF differed. This finding is consistent with the results obtained from X-ray photoelectron spectroscopy analysis, confirming its validity. The δ_d, δ_p, δ_h, and δ_t for CFs were as follows, respectively: 21.6, 6.4, 9.1, and 23.3 MPa^0.5 for ReCF and 20.5, 3.9, 10.6, and 23.4 MPa^0.5 for both AwCF and OzCF. The proposed method identified key solvents crucial for HSP analysis of CFs, which are benzaldehyde, ethylbenzene, methyl benzoate, and 1-methylnaphthalene. The changes in the surface properties of CF due to recycling necessitate adjustments in epoxy formulations and sizing agents to ensure effective reuse of CF.