## 5 Conclusions  
DBD plasma treatment, especially with Ar+O\({}_{2}\) plasma, caused considerable changes in the surface properties of HF fibers by etching and oxidizing cellulose molecules into functional groups, increasing crystallinity, and promoting surface roughness. The morphological analysis suggested that the surface modifications greatly enhanced the interfacial adhesion between epoxy resin and hemp fiber, which resulted in increases of 15.2% in tensile strength, while a better energy absorption was observed for HFRE composites than those prepared using untreated fibers. In this system, the role of ROS is significant in the oxidization of cellulose/hemicellulose and lignin components during surface modification. The application of response surface methodology (RSM) for the optimization of plasma treatment parameters revealed that the input power was most significant towards tensile strength in HFRE composites undergoing an atmospheric pressure dielectric barrier discharge and its optimal conditions were 162.63 W input power with a duration time for treatment at 10 min. The electrode configuration, gas flow dynamics, and reactor design scalability can be optimized to enable efficient surface modification in a uniform manner. These process improvements can be utilized to improve the efficiency and consistency of DBD plasma treatment for HF surface modification in industrial-scale composite manufacturing by real-time monitoring, control systems, and standardized protocols. Nonetheless, the results of this experiment will be applied to the researcher's reinforced concrete applications, which will be further studied in the future. Additionally, water absorption, compressive strength, and thermal conductivity are crucial properties for the application of composite materials in construction. These materials may need to survive environments of high humidity or pressure. Therefore, the study of these properties will be studied extensively in the future.  
**Author Contributions:** Conceptualization, C.S., K.J., P.R. and P.W.; methodology, C.S., K.J., P.R. and P.W.; validation, C.S., K.K., T.K. and P.T.; formal analysis, C.S., K.K. and P.R.; investigation, K.K., T.K. and P.T.; resource, C.S., K.J., P.W., P.R. and J.S.; writing--original, C.S., K.K. and K.J.; writing--review and editing, C.S., K.J., P.W., P.R. and J.S.; visualization, C.S., K.K. and P.W.; supervision, C.S., P.R. and P.W.; project administration, C.S. and P.W.; funding acquisition, P.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the National Science Research and Innovation Fund (NSRF) via the Program Management Unit for Human Resources & Institutional Development, Research and Innovation [grant number B16F640206]. The present study was partially supported by the Thailand Research Fund (TRF) Research Team Promotion Grant, RTA, Senior Research Scholar (N42A671052).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding authors.  
**Acknowledgments:** We wish to thank the Agriculture and Bio Plasma Technology Center (ABPlas), Science Technology Park (STeP), and Chiang Mai University for the laboratory equipment and resources support under the administration of the Materials Science Research Center, Faculty of Science, Chiang Mai University.  
**Conflicts of Interest:** The authors declare no conflicts of interest.