## 2 Materials and Methods  
Existing shielding fibers are manufactured using a method of coating a polymeric resin compound mixed with a shielding material onto a nonwoven fabric; the flexibility of the shielding fibers depends on the thickness of the coating. There is also a problem with fine cracks appearing on the surface and inside the shielding sheet because of wear on the coated parts. To address this problem, in this study, polymer masterbatches of fibers (Figure 1) were developed by mixing barium sulfate and bismuth nanoparticles of size 100 nm (Sigma-Aldrich) with polyethylene terephthalate (PET). In addition, to reduce the moisture in the developed masterbatch to less than 20 ppm, a dryer zone was set, and the masterbatch was mixed with PET chips to perform vacuum drying for 36 h.  
The yarn, used for the shielding fiber fabric, was fabricated using the existing lyocell process. Normally, it is manufactured in a liquid state to which a spinning solution containing cellulose is added. However, this process has problems, such as the need for removal of the solution in the final process and adjustment of the strength of the yarn in the drawing process, which makes mass production difficult [25; 26]. Therefore, in this study, the yarn for the radiation-shielding fibers was fabricated under the conditions listed in Table 1, by using a melt spinning process in order to reduce the problems encountered in wet spinning process. A masterbatch, containing a shielding material, was mixed with PET at a temperature of 290 \({}^{\circ}\)C. In this way, a yarn, containing 5 wt% barium sulfate or bismuth oxide, was produced by the melt spinning process. The content of barium sulfate and bismuth oxide in each yarn was analyzed by energy-dispersive X-ray spectroscopy (EDS) (Hitachi, HD-2300, High-Tech Corp, Tokyo, Japan). In addition, the dispersal of the shielding material was observed with an optical microscope (field emission scanning electron microscope (FESEM), Hitachi, S-4800, High-Tech Corp, Tokyo, Japan) after thin-film sectioning with a microtome (Leica, RM2235). The process of applying the melt spinning process in a solid state consisted of four steps (Figure 2), by which two types of yarn for shielding fibers, containing barium sulfate \begin{table}
\begin{tabular}{c c} \hline \hline
**Condition** & **Adjustable Value** \\ \hline Content of fine particles in fiber (wt\%) & 5 \\ Extruder temperature range (\({}^{\circ}\)C) & 300–315 \\ Extruder pressure (Pa) & \(1.5\times 10^{-4}\) \\ Spinning pack temperature (\({}^{\circ}\)C) & 292 \\ Spinning pack pressure (Pa) & \(1.5\times 10^{-3}\) \\ Cooling time (s) & 0.43 \\ Take-off roll speed (rpm) & 3230 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Conditions for melt spinning yarn for shielding fiber. Figure 1: Polymer masterbatches for shielding fiber: (**a**) barium sulfate (50 wt%) masterbatch and (**b**) bismuth oxide (20 wt%) masterbatch. or bismuth oxide, respectively, were produced. In order to investigate the characteristics of the fabricated yarns, the fineness, tensile strength, and elongation at break were evaluated. In this process, the yarn must have sufficient strength so that there are no breakage issues, even when the material is used in weaving textile fabrics. The fabric using the shielding fiber yarn was woven at a high density using the method shown in Figure 3. Usually, the shielded fibers are laminated or the shielding materials are dispersed twice (double dispersal) to improve shielding performance. In this study, neither of these methods was applied. Therefore, the shielding performance and characteristics were compared and evaluated for only one sheet of each fabric. In addition, in the weaving process, the mineral content was adjusted to increase the weave density. The optimal condition for the textile fabrication method is the plain weave method. However, in this study, the twill weave method was applied through several experiments.