## 3 Results and Discussion
### Mechanical Properties Analysis  
In order to study the effect of the reinforcements on the mechanical properties of the composites, the tensile and flexural strength of different samples were tested by tensile and flexural tests. From Figure 6a, the tensile strength of CF/EP composites decreases first and then increases, and the tensile strength of F10 is the largest, which is 5.9% larger than that of EP. In the three-phase composites, the tensile strength of F5N5 is the largest, which was increased by 19.2% more than the matrix. F7N7 and F10N5 were smaller than the matrix, while it can be found that the tensile strength of the composites gradually increased with the increase of CNTs. This suggests that the addition of CNTs can improve \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \multirow{2}{*}{**E/kJ-mol\({}^{-1}\)**} & \multicolumn{6}{c}{**1 st Stage**} & \multicolumn{6}{c}{**2 nd Stage**} \\ \cline{2-11}  & **EP** & **F5N5** & **F5N10** & **F7N7** & **F10N5** & **EP** & **F5N5** & **F5N10** & **F7N7** & **F10N5** \\ \hline n = 0 & 94.8 & 88.1 & 88.6 & 97.3 & 66.7 & 1.5 & 2.3 & 1.8 & 1.9 & 1.8 \\ n = 1 & 101.0 & 91.9 & 94.5 & 103.7 & 71.1 & 8.1 & 9.4 & 8.6 & 8.8 & 8.6 \\ \hline \end{tabular}
\end{table} 
Table 4: The apparent activation energy of different samples from the way of Coats–Redfern. Figure 5: Pyrolysis kinetics fitting curve of different samples. the tensile properties of the material. From Figure 6b, the flexural strength of all materials showed a tendency to rise first and then decrease. In the two-phase system, when the CF was 0.5 wt %, the flexural strength reached 89.69 MPa, while F5N5 and F5N10 were decreased. With the increase of CF, the flexural strength was smaller. The flexural strength of F7 was reduced to 65 MPa, which was smaller than that of the matrix. The flexural strength of F7N7 was the largest and up to 104 MPa, which was improved by 50.7% more than that of EP. Flexural strength of F10N5 was also larger than F10. This indicates that a certain proportion of CNTs and CF can fully exert their mechanical synergistic effects. The reinforcement is mainly dependent on the bond strength of the interface. According to the stress transfer theory, when the composite is subjected to stress, the load is applied to the resin matrix, and then the stress will be transferred to the reinforcement by the matrix through the interface. The reinforcement played a role in the dispersion of force to a certain extent [32]. From the chemical bond theory, the functionalized CNTs can react with the modified CF to produce some kind of bonding through hydroxyl groups and other functional groups. CNTs can react with EP through their epoxy groups to form a three-dimensional network of solidified materials, resulting in an increase in the interfacial bonding strength between the substrate and the reinforcement [33]. The unique nanostructures of CNTs and the high strength of CF are the basis of mechanical enhancement. As shown in Figure 7a,b are the mechanical section of EP and CF/EP; Figure 7c,d are the mechanical section of CNTs/CF/EP at the magnification of 2.0 KX and 5.0 KX. As seen in Figure 7a, the cross-section of EP is relatively smooth, and the crack is less and extends in the same direction as the brittle fracture. It can be seen from Figure 7b that, when CF is 1.0 wt %, the carbon fibers dispersed in the resin are lessened. Some holes appear on the fracture surface, which is obviously caused by the desorption of the fiber. It can be seen in Figure 7c that CNTs are dispersed uniformly around the CF and EP except for some white areas which are not clearly scanned. The crack propagates in the direction of the force of CF, which is in line with the stress transfer theory. This demonstrates that CF can enhance the mechanical properties of EP. Since the interface between the fiber and the resin is poor under some certain conditions, the fiber is pulled out to form a hole in the EP. By zooming in (Figure 7c), the distribution of CNTs can be seen in Figure 7d.