Effect of Accelerator on Vulcanized Rubber
Rubber has become an indispensable part of the modern world.Whether it is mechanical and engine bearings necessary, or power and liquid transmission, or rotary shaft and container seals, are inseparable from this material.
Rubber is usually vulcanized with sulfur to produce tires or rubber products. The chemical reaction between sulfur and rubber is slow and inefficient. After measurement, the reaction takes about 6 hours at 140 ° C, and the excess reaction time is uneconomical at any production conditions. The rubber products produced by this reaction are susceptible to oxidative degradation and can not have the mechanical properties required for practical application. In addition, if the amount of sulfur added is insufficient, the rubber will become soft, and the addition of excess sulfur will make the rubber harder. We can overcome these restrictions by developing promoters. The accelerator can increase the rate of chemical reaction, for example, only 10 minutes at 170 ° C to produce rubber products.
The function of the accelerator is first to activate the sulfur, for example, by opening the cyclic molecular structure (S8) and forming a sulfur atom monomer. The monomer sulfur is then converted to a rubber molecule along with the added promoter residue. This unstable group reacts further with the rubber molecular chain, accelerating the remainder of the molecule, resulting in actual chemical cross-linking.
Therefore, the reaction of sulfur and accelerator is very important for the rubber industry. In this paper, a system based on high sulfur vulcanized natural rubber (NR) was investigated, and the impact of the sulfur vulcanization system on the network characteristics was investigated.
In general, sulfenamide catalysts are most commonly used in the rubber industry because of their relatively delayed reaction and the faster vulcanization efficiency in the vulcanization of rubber compounds containing carbon black. We selected two sulfenamide-based accelerators to investigate: N-Cyclohexyl-2-benzothiazolsulfenamid(CBS) and N, N-Dicyclohexyl-2 benzothiazolsulfenamid(DCBS). We compared these two promoters with reference to only sulfur-containing NR compounds and used a common truck tire compound formulation.
As shown in Fig. 1, the sulfur containing only sulfur at 180 ° C is very long. As shown in Figure 2, only a low level of sulfur is required to observe this. In addition, the vulcanization flat line was not reached after 40 minutes of reaction.
After the addition of CBS or DCBS to the NR compound, the scorch and vulcanization times of the two vulcanization systems were rapidly reduced. The CBS curve shows a shorter scorch time than DCBS. In contrast to Figure 1 and Figure 2, increasing the dose of CBS or DCBS improved the scorch delay, cure efficiency, and degree of cure.
Usually two curves will rise sharply before reaching the cure point. After reaching the maximum torque, the curve begins to drop (see Figure 1). This part of the curve shows the degradation of the polymer due to chain breakage (back to sulfur). In Fig. 2, the two curves show a good vulcanized flat line (which maintains a stable curve after reaching the maximum torque), thus providing good resistance to aging and compression characteristics.
CBS compounds have higher torque compared to DCBS, and torque values represent cross-linking densities. The cross-linking density of DCBS is low， which is due to its chemical structure and its reaction rate is longer than that of CBS.
CBS and DCBS are the only two sulfenamide-based catalysts. There are many other accelerators available for vulcanization of rubber, producing vulcanized rubber of various properties