## 3 Results
### Structural Characterization and Chemical Composition of Hemp Fibers  
Crystallographic structure and chemical compositions of untreated hemp fiber (HF) and plasma-treated hemp fibers (HF\({}_{\text{tr}}\)) were studied by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS), respectively. The XRD patterns of HF and HF\({}_{\text{tr}}\) samples (Figure 4) showed characteristic (101) and (002) peaks of cellulose I at 20 angles of 12.2\({}^{\circ}\) and 22.8\({}^{\circ}\), respectively, that are consistent with the literature values [22]. A shoulder at around 20\({}^{\circ}\) which corresponds to the (012) plane was also detected, specifying the cellulose II crystalline phase [1; 23]. The intensity of the (002) peak, which is the sole crystalline peak for cellulose I, demonstrates considerable amorphous as well as non-crystalline fractions. Table 2 shows the crystallinity index (C.I.) of the plasma-treated HF  
Figure 3: Representative optical emission spectra of the DBD plasma.  
samples compared to untreated HF samples, showing the highest C.I. values for the N\({}_{2}\) and O\({}_{2}\) plasma-treated HF\({}_{\text{tr}}\) samples. The reason for this higher increase in crystallinity is then attributed to the selective removal of the non-crystalline and amorphous components during the plasma treatment, resulting in a relatively higher amount of crystalline cellulose.  
The results of the EDS analysis (Table 2) also showed that the O/C ratio in the N\({}_{2}\) and O\({}_{2}\) plasma-treated samples was more than the Ar plasma-treated samples. This increase in O/C ratio was attributed to the lowered carbon percent, which probably originated from the etching action involving the non-crystalline cellulose zone with ROS generated in the course of the O\({}_{2}\) plasma treatment.  
The FT-IR analysis of the HF and HF\({}_{\text{tr}}\) samples is shown in Figure 5. The stretching vibration band of the hydroxyl group (-OH) which is abundant in cellulose and hemicellulose appeared in the range 3200-3600 cm\({}^{-1}\). Finally, the bands at 2900 cm\({}^{-1}\) were associated with both the CH\({}_{2}\) stretching vibration and the CH group, an indication of the hydrocarbon structure within hemicellulose. The absorption peak at 1640 cm\({}^{-1}\) demonstrated the adsorbed water molecules in non-crystalline cellulose. The bands at 1430 cm\({}^{-1}\) and 1369 cm\({}^{-1}\) were attributed to the C-H deformation of the methoxyl group in lignin and C-H deformation (symmetric), respectively. The band at 1158 and 1060 cm\({}^{-1}\) show the  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Treatments**} & \multicolumn{2}{c}{**Compositions (\%)**} & \multirow{2}{*}{**O/C Ratio**} & \multirow{2}{*}{**C.I. (\%)**} \\ \cline{2-2} \cline{4-5}  & **C** & **O** & & \\ \hline HF & 59.50 & 40.50 & 0.68 & 45.19 \\ HF\({}_{\text{tr}}\) (Ar) & 59.03 & 40.97 & 0.69 & 45.20 \\ HF\({}_{\text{tr}}\) (Ar+N\({}_{2}\)) & 56.17 & 43.83 & 0.78 & 53.86 \\ HF\({}_{\text{tr}}\) (Ar+O\({}_{2}\)) & 55.96 & 44.04 & 0.79 & 55.63 \\ \hline \end{tabular}
\end{table}
Table 2: The elemental composition and crystallinity index (C.I.) of the HF and HF\({}_{\text{tr}}\) samples.  
Figure 4: XRD patterns of hemp fiber untreated and treated with Ar, Ar+N\({}_{2}\), and Ar+O\({}_{2}\) plasma.  
C-O stretching of ester groups and the C-OH stretching vibration in cellulose [24]. However, the result showed unique peaks for the main components of hemp fibers like cellulose, hemicellulose, and lignin. No major differences were noted in the spectra of the untreated and treated samples, but the reduction in intensity for the peaks at 3447, 2900, and 1060 cm\({}^{-1}\) related to the functional structure of hemicellulose, lignin, and amorphous cellulose was found to be more pronounced for N\({}_{2}\) and O\({}_{2}\) plasma-treated samples. This implies that plasma treatment acts selectively; therefore, it can etch and remove these non-cellulosic components at the surface of hemp fibers.