## 3 Materials and Methods
### Second Part: The Influence of Plasticization Parameters with Moisture Content  
This part of the experiment was conducted using the polycarbonate, WONDERITE(r) PC-110 produced by the CHIMEI corporation. The moisture content of the newly opened undried PC materials was found to be 1700 ppm. To reduce the moisture content of the material to 600 ppm the material was dried at 120 \({}^{\circ}\)C with a drying time of 2 h. Material with 600 ppm moisture was used to run the experimental group DOE. The moisture content of the material was measured using the moisture analyzer HC103 produced by Mettler Toledo. The detection method complied with the ASTM D570 standard test method for plastic water absorption. The injection molding machine used in this research was an oil-electric mixer, model HSP100 EH2, a direct pressure injection molding machine produced by the Japan Sodick Company. The machine parameter settings of the injection molding machine parameter settings are shown in Table 4. Table 5 shows the plasticization parameter table of the second stage experimental group. \begin{table}
\begin{tabular}{l l} \hline \hline \multicolumn{2}{c}{**HSP100 EH2–Injection Molding Machine Parameter Settings**} \\ \hline Injection speed & 20 mm/s \\ Injection pressure & 200 Mpa \\ Mold temperature & 60 \({}^{\circ}\)C \\ Packing pressure & 95 MPa \\ Packing time & 2 s \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Injection molding machine (HSP100 EH2) parameter settings. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Factor**} & \multicolumn{1}{c}{**Parameter**} & \multicolumn{1}{c}{**Unit**} & \multicolumn{1}{c}{**Level-1**} & \multicolumn{1}{c}{**Level-2**} & \multicolumn{1}{c}{**Level-3**} \\ \hline A & Barrel temperature & (\({}^{\circ}\)C) & 320 & 300 & 280 \\ B & Screw rotation & (rpm) & 50 & 100 & 150 \\ C & Back pressure & (Mpa) & 5 & 10 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Plasticization parameter table of the second stage experimental group. Figure 2: Air bubble area measurement using AutoCAD extraction tool. (**a**) Air bubble area measurement in mm\({}^{2}\), (**b**) Experiment run number versus measured air bubble area. This part of the experiment investigated the influence of the plasticization parameter back pressure, screw rotation, and barrel temperature on the appearance of moisture defects, such as silver marks, air bubbles, etc., to determine the optimized plasticization parameters to reduce the impact of moisture defects and the drying time of the hygroscopic material. Therefore, polycarbonate hygroscopic material (PC-110) with moisture content was used to perform this experimental component. Material with a moisture content of 600 ppm was molded with an injection speed of 20 mm/s, with sufficient pressure holding time to ensure that the molded product was filled without short shots. Three plasticization parameters, back pressure, barrel temperature, and screw speed, with three-levels, were used to perform the experiment to study the effect of these parameters on the appearance of moisture defects, such as silver marks, air bubbles, etc., in the transparent final product part. These plasticization parameter settings were divided into: back pressure 5 MPa, 10 MPa, and 15 MPa; barrel temperature 280 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, and 320 \({}^{\circ}\)C; screw speeds of 50 rpm, 100 rpm, and 150 rpm. The parameters were applied in all possible combinations; the plasticization combination experiment was carried out under the conditions shown in Table 5.  
Experiment runs were conducted in sequential order as specified in the experiment plan DOE (Table 6), where each row of the table represents a combination of different parameters with their levels. To ensure consistency the samples were taken after every ten repeated runs for each row combination run.