## 3 Results and Discussion
### Curing Behaviors of NR/CR (BIIR) Blends with CV and MF  
From the curing behaviors of the virgin NR with CV/MF\({}_{3}\) and the halogenated elastomers (CR and BIIR) with ZnO/MF\({}_{3}\), it has been confirmed that MF can substantially improve the extent of curing by utilizing the in situ formed dienes because of the so-called Diels-Alder reaction. Therefore, an attempt has been made to exploit the in situ formed dienes from these elastomers to enhance the cure compatibility and other physico-mechanical properties of their blends.  
To check whether MF can act as a compatibilizing (co-curing) agent, 50/50 blends of NR with CR and BIIR have been prepared as per the formulations corresponding to the mixes 7-10. Depicted in Figure 4a,b are the representative cure curves of NR/CR-CV, NR/CR-CVMF\({}_{3}\), NR/BIIR-CV and NR/BIIR-CVMF\({}_{3}\) at 170 \({}^{\circ}\)C for 1 h. Their cure characteristics are also displayed in Table 2. Both NR/CR-CV and NR/CR-CVMF\({}_{3}\) exhibit almost the same speed of curing up to 4.4 min. Later, NR/CR-CV achieved a maximum torque of 3.91 dNm at about 25 min followed by a slight declination in the rheometric torque due to reversion. However, NR/CR-CVMF\({}_{3}\) exhibits a marching modulus curing behavior and attained a maximum torque of 6.41 dNm nearly at the end of the given curing time (at 60 min). As a result, the extent of cure in terms of \(\Delta\) torque in NR/CR-CVMF\({}_{3}\) was 80% higher compared to NR/CR-CV. Because of the marching modulus curing behavior, the \(T_{90}\) of NR/CR-CVMF\({}_{3}\) was higher than NR/CR-CV. Interestingly, no reversion was observed  
Figure 3: Curing curves of (**a**) Mixes 3 and 4 (**b**) mixes 5 and 6 at 170 \({}^{\circ}\)C for 1 h.  
in NR/CR-CVMF3 till the end of the given curing time. The shape of the cure curves NR/BIIR-CV and NR/BIIR-CVMF3 depicted in Figure 4b were similar to NR/CR-CV and NR/CR-CVMF3, respectively. However, the speed of cure in terms of \(T_{S2}\) and the extent of cure in terms of \(\Delta M\) in NR/BIIR-CV were much lower than NR/CR-CV. For instance, the \(T_{S2}\) and \(\Delta M\) values of NR/CR-CV were 3.08 min and 3.27 dnM. On the other hand, the \(T_{S2}\) value of NR/BIIR-CV was 4.97 min and its \(\Delta M\) was around 45% lower compared to NR/CR-CV. Here also, the NR/BIIR-CVMF3 exhibit a higher speed in the early stage of curing followed by a slight marching modulus curing behavior with a 182% higher extent of cure in terms of \(\Delta M\) compared to NR/BIIR-CV. As in NR/CR-CVMF3, no reversion was also observed in NR/BIIR-CVMF3 till the end of the given 60 min of curing. The possibility of Diels-Alder reaction can be considered high to explain the enhanced state of cure in NR/CR-CVMF3 and NR/BIIR-CVMF3. From the knowledge of the curing behaviors of NR/CVMF3 and CR (BIIR)/ZnOMF3 as discussed earlier, it is reasonable to believe that the Diels Alder reaction might take place in NR/CR-CVMF3 or NR/BIIR-CVMF3 in three ways. One may be the in situ formed diene from the NR phase with the maleimide moieties of MF. The second one may be the in situ formed diene from the CR (or BIIR) phase with the maleimide moieties of MF. The third possibility could be a simultaneous Diels-Alder reaction between the dienes generated in the NR phase and CR (or BIIR) phase with either end of the maleimide moieties of MF as depicted in Figure 5. In this reaction, MF acts as a coupling/compatibilizing agent between NR and CR (or BIIR), which is essential to enhance the compatibility between these rubbers in their blends.  
Figure 4: Curing curves of (**a**) mixes 7 and 8 (**b**) mixes 9 and 10 at 170 \({}^{\circ}\)C for 1 h.  
Figure 5: Plausible mechanism proposed for the compatibilisation (co-curing) effect of MF between NR and CR (BIIR) via Diels–Alder reaction.