## 3 Results and Discussions
The \(x_{DSC}\) values of XLPE for 60 days at each temperature were 34.42%, 38.59%, 15.81%, and 4.05%, respectively. This result was similar to the crystallinity obtained through XRD. In addition, the lamellar thickness of the unaged XLPE was 7.29 nm. The trend of change over temperature and time is similar to the above analysis. The \(L\) values of aged XLPE for 60 days at each temperature were 7.17, 7.15, 3.91, and 3.06 nm, respectively. These analysis results indicate that the XLPE crystallinity becomes amorphous as aging progresses. \begin{table}
\begin{tabular}{c c c c c c} \hline  & **Unaged** & \begin{tabular}{c} **100 \({}^{\circ}\)C,** \\ **60 Days** \\ \end{tabular} & \begin{tabular}{c} **120 \({}^{\circ}\)C,** \\ **60 Days** \\ \end{tabular} & \
\begin{tabular}{c} **140 \({}^{\circ}\)C,** \\ **60 Days** \\ \end{tabular} &
\begin{tabular}{c} **160 \({}^{\circ}\)C,** \\ **60 Days** \\ \end{tabular} \\ \hline \(Tm\) (\({}^{\circ}\)C) & 104.71 & 104.71 & 104.12 & 72.53 & 53.79 \\ \(Tc\) (\({}^{\circ}\)C) & 94.74 & 95.12 & 95.06 & 52.72 & 42.15 \\ \(\Delta H_{m}\) (\(\text{J}\cdot\text{g}^{-1}\)) & 86.22 & 98.89 & 110.86 & 45.42 & 11.66 \\ \(X_{DSC}\) (\%) & 30.01 & 34.42 & 38.59 & 15.81 & 4.05 \\ L (nm) & 7.29 & 7.17 & 7.15 & 3.91 & 3.06 \\ \hline \end{tabular}
\end{table} 
Table 2: Results obtained from DSC measurements (second scan). Figure 9: Melting (**a**) and crystallization (**b**) temperatures of XLPE samples depending on aging time and temperature. UV-vis spectroscopy is a useful method to analyze the optical properties of materials. Among the UV-vis spectra of the XLPE sample obtained in this study, the results for the 160 \({}^{\circ}\)C deteriorated XLPE are shown in Figure 11. In unaged XLPE, the light was absorbed at 300 nm or less, and red-shifted to a longer wavelength as deterioration progressed. This phenomenon can be explained as follows. As shown in the results of the FTIR analysis, during degradation, C=O and C=C are created in the molecule, and as these bonds are continuously formed, a conjugation pi bond is produced [34]. Therefore, the highest occupied molecular orbital (HOMO) rises and the lowest unoccupied molecular orbital (LUMO) falls, thereby reducing the gap between energy levels entailing red-shift with a longer wavelength. As the deteriorated XLPE is absorbed by the short wavelength in the visible region, the complementary color, red, is observed by the eye, as shown in Figure 2. The higher the exposure temperature, the faster the formation of double bonds and of a conjugation pi bond within the molecular structure consisting of single bonds. Therefore, a rapid color change in XLPE occurred. Based on these results, the bandgap energy of XLPE was calculated through [PERSON]'s equation [35]:  
\[\left(\alpha h\upsilon\right)^{n-1}=B\left(h\upsilon-E_{bg}\right) \tag{8}\]  
where \(\alpha\), \(h\), \(\upsilon\), \(A\), and \(E_{bg}\) represent the absorption coefficient, [PERSON]'s constant, light frequency, a constant, and bandgap energy, respectively. In XLPE not exposed to heat, \(E_{bg}\) was confirmed to be 3.75 eV. The \(E_{bg}\) decreased as deterioration progressed, and this trend became more pronounced as temperature increased. Furthermore, the \(E_{bg}\) of the sample exposed at 160 \({}^{\circ}\)C for 60 days decreased to 2.05 eV. The bandgap energy reduction indicates that electrons are excited from the valence band to the conduction band by a small amount of energy, and electrons can move inside and on the surface of the insulator. This also means that the material's insulating performance is reduced. Figure 10: Crystallinity (**a**) and lamellar thickness (**b**) through DSC results of XLPE samples depending on aging time and temperature. An increase in the number of C=C bonds means shortening the PE chain length because the C=C bond is shorter than the C-C bond. Additionally, this causes the PE density to increase. However, XLPE is a crystalline polymer.