## 4 Discussion
### Mechanism of Crystallinity Enhancement in Cellulose Fibers by Plasma Treatment
This process can improve the surface roughness and has the effect of removing contaminants, while it does not significantly change the surface chemistry of fibers [50]. Without chemical modification, the argon plasma treatment alone can only enhance interfacial adhesion to a limited extent. The results of this study indicated that the tensile strength and energy absorption plateau stress improved to a lesser extent in the Ar plasma treatment compared to those in the co-treatment with one atmosphere argon/oxygen, as shown in Figure 7 and Table 3, suggesting the relatively poor performance of argon-based species for surface modification. Optimizing DBD Plasma Treatment Parameters and Reactor Design for Efficient Hemp Fiber Surface Modification in Composite Manufacturing  
The results of the study, and, in particular, its ANOVA analysis, have provided new insights to highlight the association between plasma parameters with the surface modification efficiency of hemp fibers. The ANOVA results (Table 4) showed that the input power had a significant effect on the tensile strength of epoxy composites reinforced with Ar+O\({}_{2}\) plasma-treated HF, as its \(p\)-value was recorded around 0.028 (\(\alpha\) = 0.05). These results indicate that the tensile strength of composites was raised to a certain degree with an increase in input power, as shown in Figure 10. Overly high powers can cause thermal damage and structural loss of the fiber as well [51]. Surprisingly, the ANOVA test results showed that the tensile strength is not commonly affected by treatment time (\(p\)-value 0.387). Contrary to the general belief that increased the exposure time results in enhanced surface modifications [52], this observation has been made with some caution. That being said, it is worth noting that although the statistical insignificance of treatment time indicates no effect on surface modification, as it falls within the range of values investigated, there was not as much change in the tensile strength for the time rangingfrom 10-50 min compared to input power. Therefore, the results of the ANOVA and RSM analysis on this study reinforce that input power was concentratedly dominantly affecting a surface modification of hemp fibers by DBD plasma treatment. The selection of a 162.63 W input power with a treatment time of ten minutes using an Ar+O\({}_{2}\) plasma is recommended under the present conditions, which may enable an improvement in the surface properties of hemp fibers, leading to an enhanced mechanical performance for hemp-fiber-reinforced composites. Designing an optimal DBD plasma reactor in order to coat natural fibers such as hemp requires considering various features and working parameters that affect the desired surface modification uniformity and efficiency. The configuration of the electrode system, flow dynamics, and scaling up of the reactor become important considerations. The electrode configuration is an important factor affecting plasma characteristics and treatment uniformity when using a DBD plasma reactor. A parallel-plate electrode configuration was employed in this study with the hemp fibers located on an aluminum tray resting over a grounded electrode as shown in Figure 1. The powered electrode was positioned at the top of the fibers, with a 1 mm discharge gap. Such an arrangement permits a uniform electric field distribution and the same plasma exposure along the fiber face [53]. This prevents localized overtreatment and provides for the uniform treatment of the fibers due to the employment of a moving tray system whereby an aluminum tray is reciprocated forward and backward at a speed of 30 cm s\({}^{-1}\). The gas flow dynamics in the DBD plasma reactor are crucial for achieving uniform treatment and avoiding localized overheating or nonuniform modification. The gas stream was oriented parallel to the surface of the fiber at both sides (Figure 1) whereby uniform exposure to the reactive species is maintained.