## 4 Discussion  
### Mechanism of Crystallinity Enhancement in Cellulose Fibers by Plasma Treatment  
The XRD results (Figure 4 and Table 2) show that, after plasma treatment, the crystallinity index increased remarkably for cellulose fibers. There are also other reasons which might be possible sources for this elevated crystallinity; one is the selective etching and removal of amorphous components in the bulk cellulose structure during plasma treatment [6]. Cellulose is a linearly polymerized material at the molecular level that includes crystal line regions separated by disordered amorphous domains [31]. During a plasma treatment, the high energy components such as ions, electrons, and radicals are generated selectively to attack the less stable amorphous regions [32]. The reactive species decompose the amorphous components, and, therefore, a higher relative content of crystalline cellulose was left [25]. The selective etching of the amorphous regions result in a reorganization and alignment of the remaining cellulose chains which drive to form an enhanced degree of order and crystallinity [33]. This reorganization is, in part, due, instead, to the tendency of cellulose molecules to minimize their surface energy and form stable hydrogen bonds [34]. On the basis of experimental observations and literature reports, a model for the crystallinity enhancement in cellulose during plasma treatment can be presented. This model involves several main steps. First is the formation of highly reactive species in plasma, which consists of ions, electrons, and radicals that are generated when plasma interacts with a gas [35]. These species are determined by the plasma gas composition and treatment conditions, both in type and concentration. Secondly, these reactive species can be preferentially targeted to the relatively less stable and disordered amorphous region of cellulose [36]. In this selective etching process, the amorphous components are disintegrated and removed to decrease the amorphous fraction of cellulose. Third, the excited species in plasma transfer energy to cellulose chains so that they can be rearranged locally [16]. This energy transfer will enable the re-orientation of cellulose chains and their alignment to form a better structured fitness. Fourth, the type of reactions is an equivalent depopulation and reorganization process or rearrangement.These changes are related to the disappearance/etching of amorphous regions on cellulose, which have a high surface area are present [37]. That makes the chains line up better and create stronger hydrogen bonds between them, which would yield a more crystalline form. This degree of reorganization depends on the composition of the plasma gas, where reactive gases like oxygen and nitrogen facilitate a more crystalline structure. Finally, the improved hydrogen bonding network and the induced functionalization by reactive gas plasmas (e.g., oxygen-containing groups) stabilize the newly formed crystalline organization [38]. This stabilization discourages cellulose from reverting back to their amorphous state structures. The theory agrees well with the experiments, substantiating a mechanism behind how the crystallinity of cellulose fibers is improved during plasma treatment. This work demonstrates the importance of reactive species, selective etching, energy transfer, and molecular reorganization in accessing a more crystalline cellulose, which presents a process for promoting a greater conversion to cellulose. Role of Reactive Oxygen Species (ROS) in Surface Modification of Hemp Fibers During Ar+O\({}_{2}\) Plasma Treatment  
This study provides evidence of the applicability of plasma treatment as a better choice for the surface modification of hemp fibers. The study found that Ar+O\({}_{2}\) plasma treatment produced various ROS, which are important for changing the fiber surface structure of hemp fibers.