Accelerated Sulphur Case Study

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3.1 Cure characteristics of CIIR with accelerated sulphur
The cure characteristics of CIIR with an efficient type of accelerated sulphur (EV) system at different vulcanization temperatures are depicted in Figure 2 and Table 2 respectively. The EV system used here particularly to reduce the set properties at elevated temperature as it possesses relatively less polysulfidic linkages as compared to the conventional sulphur vulcanization (CV) system. It can be seen from the figure that the vulcanization curve at 160°C has achieved the highest rheometric torque within 12 minutes of curing followed by a cure plateau region up to 35 minutes. Afterwards, the rheometric torque decreased due to reversion. The reversion is a well-known phenomenon observed
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For instance, the onset of reversion that was observed around 35 minutes at 160°C shifted to around 15 minutes at 170°C, 8 minute at 180°C and 5 minutes at 190°C respectively. Consequently, the percentage reversion was gradually increased as the vulcanization temperature increased. The percentage reversion at the 60th minutes of the vulcanization of CIIR-S at different temperatures was calculated using the equation given below [18, 19] and the values thus obtained are displayed in Table 2. (5) where MH is the maximum torque, M1h is the torque after one hour of vulcanization.
Since the extent of reversion increased as the vulcanization temperature increased, the state of curing (extent of curing) was found decreased which was reflected from the reduced values of the delta torque. For instance, the delta torque obtained at a vulcanization temperature of 160°C was 4.4 dNm which is reduced to around 40% (2.6 dNm) as the vulcanization temperature rose to 190°C.
3.2 Cure characteristics of CIIR-S in the presence of
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Represented in Figure 3(a,b) are the cure profiles of CIIR-S with different content of BMDM. For the sake of clarity, the cure curves obtained at two different vulcanization temperatures (160° and 190°C) are shown here. However, the cure curves of a representative sample CIIR-SB5 at all the vulcanization temperatures are displayed in Figure 4. The detailed cure characteristics of all the vulcanizates are also displayed in Table 2. It can be seen from the figures that the vulcanization of CIIR-S in the presence of BMDM has greatly increased the extent of curing (higher values of delta torque) without adversely affecting the rate of vulcanization. For instance, at 160°C, the ∆torque during the vulcanization of CIIR-S was raised to 42% with the incorporation of 1 phr BMDM. As the dosage of BMDM was further raised to 5 phr, the ∆ torque was dramatically increased to around 280% at the same temperature. It is worth noting that the curing curves of CIIR-SB5 depicted in Figure 4 show a gradual increase in the rheometric torque with the increase in temperature. On the contrary, the vulcanization behavior of CIIR-S (Fig-1) showed an opposite trend due to reversion. The increment in ∆torque during the vulcanization of CIIR-S with BMDM is an indirect indication of the degree of crosslinking.

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