**4. Conclusions**

In this study, using a hybridization process of bamboo-derived nano/microfibers, a green and mechanically robust fibrous preform for fiber-reinforced plastics was successfully fabricated. The optimal thermocompression environment for minimizing fiber thermal degradation and obtaining a dense fibrous preform was 120 ◦C and 10-min compression conditions. As CNF was introduced into the BF/CNF preforming process, the structural stability of the fibrous preform was significantly enhanced. The hybrid phenomenon of BF/CNFs provided a nano-brush morphology that maximized the interaction with the matrix polymer on the surface of the fibrous preform and, at the same time, increased the tight bonding between the BF fibers, making the internal structure of the preform more compact. Ultimately, even when the BF/CNFs preform was used as an eco-friendly reinforcing material in biodegradable fiber reinforced plastic (PBS-BF/CNFs composites), the improved mechanical properties of the fibrous preforms could be effectively expressed. As a result, the PBS-BF/CBF15 composite material improved the tensile strength by 240% (26.4 MPa) and Young's modulus by 700% (1.6 GP) compared to the neat PBS plastics. The synthetic binder or crosslinker-free and energy-efficient micro/nano hybridized green

fibrous preforms manufacturing process has excellent potential to be widely utilized in the field of eco-friendly biodegradable fiber-reinforced composite materials in the future.

**Author Contributions:** Conceptualization, H.W.K.; methodology, J.B. and H.L.; validation, H.W.K.; data curation, J.B. and Y.Y.; writing—original draft preparation, H.W.K.; writing—review and editing, J.-K.O. and H.W.K.; funding acquisition, H.W.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was carried out with the support of 'R&D Program for Forest Science Technology (2020224D10-2122-AC02)' provided by Korea Forest Service (Korea Forestry Promotion Institute). This work was supported by Creative-Pioneering Researchers Program through Seoul National University (SNU).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare that there are no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
