## 4 Discussion
### Mechanism of Crystallinity Enhancement in Cellulose Fibers by Plasma Treatment
For example, the ROS that are generated during Ar+O\({}_{2}\) plasma treatment have demonstrated a significantly high rate of functionalization on hemp fiber surfaces than other reactive species such as nitrogen species (RNS) or argon-based ones. The ROS,especially atomic oxygen and ozone, are known to have high oxidation potentials and reactivity towards organic compounds, and have been employed in altering the surface chemistry of hemp fibers [39]. The mechanism of ROS interaction with the fiber component, namely, cellulose, hemicellulose, and lignin, can be described as follows: Firstly, cellulose, the major component of hemp fibers, reacts with different types of ROS, mainly, atomic oxygen and hydroxyl radicals [40]. These species attack the glycosidic bonds of cellulose, resulting in the removal of non-crystalline cellulose and amorphous portions and leading to the predominant appearance of oxygen-containing groups such as \(-\)OH and C\(-\)O groups on the fiber surface [16; 41], where its glycosidic bonds were cleaved by the present fungal strains. This was because the introduction of those polar functional groups increased the surface energy and wettability, which favored their compatibility with polymer matrices [42]. An FT-IR analysis was carried out (Figure 4) The peaks attributed to cellulose were weakened after Ar+O\({}_{2}\) plasma treatment, suggesting that ROS led to the oxidation and modification of the biopolymer. Additionally, hemicellulose, which is an amorphous heteropolysaccharides,ride in hemp fibers with a lower degree of polymerization when compared to cellulose, exhibits a high vulnerability toward oxidative reactions by ROS [43]. This process leads to a higher surface roughness and, effectively, a greater specific area for covalent bonding with polymers [44]. The SEM analysis (Figure 5) showed an increase in surface roughness and the exposure of microfibrils after Ar+O\({}_{2}\) plasma treatment due to the ROS selective ablation of hemicellulose [32]. Lignin, a complex aromatic polymer found in Nutritional Trends that binds cellulose fibrils to one another, is involved as the third layer. ROS formed in the lignin atmospheric plasma treatment (Ar+O\({}_{2}\)) can interact with aromatic rings and side chains of lignin to induce oxidative degradation, leading also to the formation of some oxygen functional groups, like phenolic hydroxyl, carboxyl, and carbonyls groups [45]. For example, during the selective isolation of lignin from the fiber surface, it is removed, which exposes cellulose fibrils and increases the surface roughness that will lead to an increase in mechanical interlocking between polymer matrices [46]. In the XRD analysis, as shown in Figure 3 and Table 2, the X-ray diffractograms illustrated an increase in the crystallinity index (C.I.) of the fibers after Ar+O\({}_{2}\) plasma treatment; however, there is still a high contribution from amorphous, lignin, hemicellulose regions, which are removed during the etching process, consequently giving rise to increase portion of the residual crystalline cellulose. In contrast, RNS formed during nitrogen-containing plasma treatments, such as NH\({}_{3}\) or N\({}_{2}\) plasmas, usually provide amine (NH\({}_{2}\)) and amine functional groups (C = N) onto the fiber surface, respectively [47]. Although these groups can increase the compatibility of fibers with certain polymer matrices, inherently hindered and fully stabilized fiber surfaces have much less impact on interfacial adhesion when compared to oxygen-containing surface groups created by ROS [48]. The FT-IR analysis (Figure 4) revealed no significant changes in the Ar and Ar/N\({}_{2}\) plasma-treated fiber spectra, indicative of the involvement of RNS on surface functionalities toward N\({}_{2}\) as compared to ROS. The processes of argon-based plasma treatments used for surface cleaning and etching prevail in the physical bombardment at the fiber surface by energetic argon ions and electrons [49].