This study assessed the changes in the fiber properties of virgin and recovered fibers from lab-scale and pilot-scale depolymerization reactors based on the thermal air oxidation-resistance characteristics. Lab-scale and pilot-scale depolymerization reactors had different depolymerization volumes. Results showed that the lab-scale and pilot-scale peak solvent temperatures were 185 °C and 151 °C, respectively. The lab-scale had highest solvent temperature rate increase because of the small depolymerization volume and the dominant role of the cavitation volume. The structural properties of the recovered and virgin fibers were intact even after the depolymerization and after the pretreatment and oxidation-resistance test. We observed 1.213%, 1.027% and 0.842% weight loss for the recovered (lab-scale), the recovered (pilot-scale) and virgin fibers because of the removal of impurities from the surface and chemisorbed gases. Further, we observed 0.8% mass loss of the recovered fibers (lab-scale) after the oxidative-onset temperature because of the “cavitation erosion effect” from the dominant of the cavitation bubbles. The “cavitation erosion effect” was subdued because of the increased depolymerization volume in the pilot-scale reactor. Therefore, negligible impact of the pilot-scale mechanochemical recycling process on the structure and surface characteristics of the fibers and the possibility of reusing the recovered fibers recycling process were characteristic. Representative functional groups were affected by the thermal oxidation process. We conducted HPLC, HT-XRD, TGA– DSC, XPS, SEM, and AFM analysis and provided an extensive discussion of the test thereof. This study highlighted how misleading and insufficient small-lab-scale results could be in developing viable CFRP depolymerization process.

    Abstract
    1 Introduction
    2 Experimental protocol
        2.1 Carbon fiber recovery process
        2.2 Fiber preparation process
        2.3 Scope and parameter determination of the thermal-resistance test
    3 Results
        3.1 Depolymerization process
        3.2 HT-XRD spectra
        3.3 TGA analysis
        3.4 FT-IR spectra
        3.5 XPS spectra
        3.6 SEM and AFM images
    4 Discussion
    5 Conclusion
    References

• Caozheng Yan(School of Economics and Management, Hubei University of Automotive Technology)
• Lewis Kamande Njaramba(Department of Environmental Engineering, College of Engineering, Kyungpook National University)
• Antony Mutua Nzioka(R&D Institute, Silla Entech Co., Ltd.)
• Benard Ouma Alunda(Department of Mining and Mineral Processing, Taita Taveta University)
• Myung‑Gyun Kim(Department of Fire and Environmental Safety, Keimyung College University)
• Ye‑Jin Sim(R&D Institute, Silla Entech Co., Ltd.)
• Young‑Ju Kim(Department of Environmental Engineering, College of Engineering, Kyungpook National University, R&D Institute, Silla Entech Co., Ltd.)