## 3 Results and Discussion
### Scanning Electron Microscopy-Fractography Study  
In order to evaluate the fracture mechanism of neat SCB-PE and all the prepared GNPs nanocomposites under tensile stress, the fracture surfaces of the samples after the tensile tests were observed using scanning electron microscopy. Figure 3 presents the fracture surface of neat SCB-PE. The sample's plane view presents plastic tearing due to the share stresses applied parallel to the fracture plane and the chain stretching of the matrix. Some superficial voids are also observed, while no intense fibril formation occurs due to the homogenous polymer chain fracture during the macromolecular chains' alignment and orientation caused by the uniaxial tensile stress [23]. Figure 3: SEM images of the fracture surface of SCB-PE after tensile test. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**A/A**} & \multicolumn{2}{c}{**Sample**} \\ \cline{3-4}  & & **SCB-PE/GNPs no BM** & **SCB-PE/GNPs w BM** \\ \hline \multirow{2}{*}{Ji} & \(E_{i}(0)\) (GPa) & 74.54 & 98.67 \\ \cline{2-4}  & \(\tau\) (nm) & 29.45 & 43.9 \\ \cline{2-4}  & \(R^{2}\) & 0.964 & 0.859 \\ \hline \multirow{3}{*}{Modified Halpin-Tsai} & \(f_{W}\) & 0.23 & 0.94 \\ \cline{2-4}  & \(\alpha\) & 9.74 & 9.88 \\ \cline{2-4}  & \(\beta\) & 0.76 & 0.47 \\ \cline{2-4}  & \(R^{2}\) & 0.928 & 0.992 \\ \hline \end{tabular}
\end{table} 
Table 3: Elastic modulus, tensile strength at yield and break, and elongation at break values of neat SCB-PE, SCB-PE/GNPs no BM and SCB-PE/GNPs w BM nanocomposites. The fracture surface of SCB-PE/0.5 GNPs no BM is presented in Figure 4a. The GNPs aggregates' presence causes unevenly cut fibrils of the matrix as seen at the fracture surface's cross-section. Some of these fibrils are curved due to the relaxation of the polymer after the failure. During the tensile stress application, the macromolecular chains' movement is restricted by the entangled GNPs in the matrix, i.e., when the GNPs form inhomogeneously distributed aggregates, their presence block the further elongation of the amorphous and crystalline regions, causing stress concentration around these areas and abrupt cut of the polymer chains leading to the formation of the uneven fibrils. On the sample's plane view, deep voids larger than 100 \(\upmu\)m in length can be seen, caused by the fibrils' stretching. On the other hand, the failure surface of SCB-PE/0.5 GNPs w BM presented in Figure 4b is characterized by smoother areas, although voids larger than 100 \(\upmu\)m but lesser in number compared to that of SCB-PE/0.5 GNPs no BM, can be observed on the plane view image. As mentioned, the elongation at break of SCB-PE/0.5 GNPs in both cases is even higher than that of neat SCB-PE. This could be attributed to the better GNPs dispersion and the stronger interfacial adhesion between the filler and the matrix. Homogeneously dispersed filler results in an evenly distributed stress transfer throughout the matrix. At the same time, good interfacial adhesion between the particle and the polymer induces a stronger bond, meaning that more stress must be applied in order for the particle to detach from the matrix and as a consequence, initiate a crack leading to the final fracture of the material [41]. During the application of the stress, a possible GNPs response is their alignment to the stress's direction, allowing the further stretching of the lamellas and amorphous areas of the matrix, leading to a smoother fracture surface like the one seen in Figure 3.  
Similar behavior of fracture with SCB-PE/0.5 GNPs no BM is presented on the SEM images of the failure surface of SCB-PE/1 GNPs no BM (Supplementary data Figure S3a). Unevently cut fibrils and large voids are formed on the surface's plane view due to the ununiformly distributed stress through the matrix caused by the GNPs aggregates and poor adhesion between the filler and the polymer. The fracture surface of SCB-PE/1 GNPs w BM is also presented in Figure S3b in the supplementary data report.