## 3 Results and Discussion  
### Performance of Crystallization  
Tables 1 and 2 show that PP has an initial crystallinity temperature (\(T_{\text{onset}}\)) of 116.21 \({}^{\circ}\)C and crystallinity temperature (\(T_{\text{c}}\)) of 111.46 \({}^{\circ}\)C, both of which shift to the high temperature zone as a result of the combination of GNs and also continuously increase as a result of the increasing content of GNs. The optimal \(T_{\text{onset}}\) of 140.67 \({}^{\circ}\)C and \(T_{\text{c}}\) of 135.01 \({}^{\circ}\)C are present when the PP/GNs conductive composites consist of 20 wt% of GNs, and are greater than those of pure PP by 24.46 \({}^{\circ}\)C and 23.55 \({}^{\circ}\)C, respectively. Similarly, \(T_{\text{onset}}\) and \(T_{\text{c}}\) of PP/CF conductive composites also shift to the high temperature zone as a result of the combination of CF, and also increase with the increasing levels of CF. When containing 20 wt% CF, PP/CF conductive composites have optimal \(T_{\text{onset}}\) (126.25 \({}^{\circ}\)C) and \(T_{\text{c}}\) (122.28 \({}^{\circ}\)C), which are greater than those of pure PP by 10.04 \({}^{\circ}\)C and 10.82 \({}^{\circ}\)C, respectively. Such results are ascribed to the combination of GNs or CF as the nucleating agent of PP, which makes the nucleation mode heterogeneous instead of homogeneous, significantly decreases the nucleation free energy, and allows the molecular chain to attach to and be arranged orderly on the nucleating agent [22,23]. GNs demonstrate a more significant influence over the \(T_{\text{onset}}\) and \(T_{\text{c}}\) of PP than CF does. Such a result is ascribed to the nanometer size effect of GNs, namely that the size of GNs is smaller than that of CF. With the same content, GNs contribute to a greater superficial area and at the same time greater nucleation sites, thereby demonstrating a greater effect on the \(T_{\text{onset}}\) and \(T_{\text{c}}\) of PP. PP has \(T_{\text{onset}}\)-\(T_{\text{c}}\) of 4.75 \({}^{\circ}\)C and \(t_{\text{1/2}}\) of 0.444 min. The combination of GNs results in a decrease in crystallization rate of PP, exemplified by an increase in \(T_{\text{onset}}\)-\(T_{\text{c}}\) of 4.79 \({}^{\circ}\)C to 6.1 \({}^{\circ}\)C and an increase in \(t_{\text{1/2}}\) of 0.477 min to 0.604 min. By contrast, 15 wt% of GNs makes for the slowest crystallization rate of PP, making \(T_{\text{onset}}\)-\(T_{\text{c}}\) 6.10 \({}^{\circ}\)C and \(t_{\text{1/2}}\) 0.604 min. Conversely, the combination of CF accelerates the crystallization rate of PP, causing \(T_{\text{onset}}\)-\(T_{\text{c}}\) to decrease to 3.70 \({}^{\circ}\)C-4.33 \({}^{\circ}\)C and \(t_{\text{1/2}}\) to decrease to 0.358 min-0.443 min. In particular, 5 wt% of CF results in the shortest crystallization rate of PP, in which \(T_{\text{onset}}\)-\(T_{\text{c}}\) is 3.70 \({}^{\circ}\)C and \(t_{\text{1/2}}\) is 0.358 min. The combination of inorganic fillers to polymers has two influences over the crystallization behavior of the polymer. Using inorganic fillers as nucleating agent allows the molecular chains of PP to nucleate and the spherocrystals to enlarge at a high temperature, and at the same time allows for more nucleation sites [24, 25, 26, 27, 28, 29]. On the other hand, the existence of  
Figure 2: **(a)** The tester, **(b)** the grips, and **(c)** the samples of tensile tests. inorganic fillers takes up a certain space, especially with nano-scale fillers, and restricts the motion and arrangement of molecular chains that influence the crystallization rate of the polymer. As a result, the crystallization rate of the polymer is inversely proportional to the inorganic fillers, but the combination of CF is proportional to the crystallization rate of PP. The degree of crystallinity (\(X_{\text{c}}\)) of PP decreases slightly when the combination of GNs is below 5 wt%, and slightly increases when the combination of GNs is above 5 wt%. Conversely, the combination of CF hardly influences the \(X_{\text{c}}\) of PP.