# Physical Hybrid of Nanographene/Carbon Nanotubes as Reinforcing Agents of NR-Based Rubber Foam
## 3 Results and Discussion  
### Curing Behavior  
Controlling NR/CNT/GNS nanocomposite foams' curing process is essential to fabricate foams with specific properties and morphologies. The effect of the nanofiller's content on the curing behavior of rubber foams at 155 \({}^{\circ}\)C is displayed in Figure 1. It can be seen that increasing the CNT and GNS content accelerates the curing process by decreasing the scorch time (\(t_{s}\), the time that the curing process starts), the curing time (\(t_{90}\), when the curing process achieves 90%), the final torque or the torque of cured compounds (\(M_{H}\)), and the delta torque or the torque difference between the cured and uncured compound (\(\Delta M=M_{H}-M_{I}\)). However, it increased the curing rate (\(CRI=\frac{100}{t_{90}t_{s}}\)) [25], the initial torque, \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & & \\ \hline \multicolumn{1}{c}{**Master**} & \multicolumn{1}{c}{**ADC**} & \multicolumn{1}{c}{**Oil**} & \multicolumn{1}{c}{**Sulfur**} & \multicolumn{1}{c}{**ZnO**} & \multicolumn{1}{c}{**Stearic Acid**} & \multicolumn{1}{c}{**MBTS**} & \multicolumn{1}{c}{**CBS**} & \multicolumn{1}{c}{**CB**} & \multicolumn{1}{c}{**GNS**} & \multicolumn{1}{c}{**CNT**} & \multicolumn{1}{c}{**NR**} & \multicolumn{1}{c}{**Code**} \\ \hline
0 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 0 & 0 & 100 & S0 \\
0.771 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 0.1 & 0.1 & 100 & S0.1 \\
1.928 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 0.25 & 0.25 & 100 & S0.25 \\
3.857 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 0.5 & 0.5 & 100 & S0.5 \\
7.714 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 1 & 1 & 100 & S1 \\
11.571 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 1.5 & 1.5 & 100 & S1.5 \\
15.428 & 6 & 5 & 1.5 & 4.5 & 2 & 0.6 & 0.6 & 10 & 2 & 2 & 100 & S2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Formulation of NR/CNT/GNS nanocomposite foams. or the torque of the uncured compounds (\(M_{I}\)). \(M_{90}\) can be calculated using Equation (1) [26] as follows:  
\[M_{90}=M_{I}+0.9\ (M_{H}-M_{I}) \tag{1}\]  
The result shows that the curing rate significantly increased with increasing CNT and GNS content from 0 to 2 phr, while decreasing the scorch time and the cure time from 6.81 to 5.08 min and from 14.3 to 11.12 min, respectively. This could be related to the fact that CNT/GNS hybrid nanofiller can act as accelerators to the curing process, which is in agreement with what was observed for each nanofiller individually [27; 28]. In addition, increasing the CRI from 13.34 (in the S0 sample) to 16.55 (in the S2 sample) showed that the cure rate had tremendously increased by increasing CNT/GNS content. The higher cure rate of S2 in comparison to S0 confirmed the accelerating effect of hybrid nanofiller on cure reaction of NR foam. As demonstrated in Table 2, the initial torque (\(M_{I}\)) increased with nanofiller loading, which could be due to the increase in viscosity as a result of the presence of solid materials in the polymer matrix, which limits the chains' mobility by creating physical interactions with NR chains. Restricted viscous motions of polymer chains' segments in presence of fillers and reinforcement were reported in the literature [29]. Additionally, adding higher amounts of the physical hybrids of CNT to GNS limits the polymer chains in the sintering reaction and reduces the amount of lattice created. Such a decrease in the percentage of networks created can be seen in reducing \(M_{H}\) (Table 2) by adding higher amounts of nanohybrids.