Efficient type sulfur cure system

In fact, the physical properties obtained depend on the types of cross-hnk formed and the extent of main-chain modification by side reactions. This is usually being largely determined by the vulcanization system, although cure time and temperature also have an important effect. Generally, there are three types of typical sulfur vulcanization systems, namely, conventional vulcanization, efficient vulcanization and semi-efficient vulcanization. 

Cure System Design. There are three generally recognized classifications for sulfur vulcanization conventional, efficient (EV) cures, and semiefficient (semi-EV) cures. These differ primarily in the type of sulfur cross-links that form as shown in Figure 12, which in turn significantly influences the vulcanizate properties (33). The term efficient refers to the number of sulfur atoms per cross-link (32). 

The chemical microstructures of cis-polyisoprene (HR) vulcanised with sulfur and N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerator were studied as a function of extent of cure and accelerator to sulfur ratio in the formulations by solid-state 13C NMR spectroscopy at 75.5 MHz [29]. Conventional (TBBS/Sulfur=0.75/2.38), semi-efficient (SEV=1.50/1.50) and efficient (EV=3.00/1.08) vulcanisation formulations were prepared, which were cured to different cure states according to the magnitude of increase in rheometer torque. The order and types of the sulfurisation products formed are constant in all the formulation systems with different accelerator to sulfur ratios. However, the amount of sulfurisation has been found to vary directly with the concentration of elemental sulfur. 

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