It is Insoluble sulfur.
is amorphous form of sulfur, which is made from the heat-polymerizing of sulfur, also can be obtained by reacting sulfured hydrogen with sulfur dioxide. Insoluble sulfur is macro-molecule polymer, and there are several thousand of sulfur atoms in its molecular chains. Since it doesn’t dissolve in carbon disulfide, it is called insoluble sulfur or polymeric sulfur. Currently insoluble sulfur is mainly used in rubber industries.
Insoluble sulfur is an important rubber additive agent. It improves product quality, wear ability and resistance to both fatigue and ageing. In addition to being universally recognized as the best vulcanizing agent, it is widely used in the manufacture of tire, rubber pipe, shoes, cable and wire insulating materials, latex, all kinds of automobile rubber parts and is also a necessary component of belt tires.
Compared with sulfur (rhombic sulfur), insoluble sulfur has following merits:
1. Insoluble sulfur exists in rubber in a dispersive state. It can prevent the booming of rubber, having a better viscosity, and at the same time can ensure the outer appearance of the products with light color.
2. Insoluble sulfur can disperse uniformly in rubber, so it can prevent the conglomeration of sulfur, and reduce the tendency of being scorched during store.
3. Insoluble sulfur can prevent the blooming of rubber during its store. It make it possible to keep rubber’s characteristics uniform, overcoming the defects of bad viscosity resulted from blooming, avoiding the pollution of products as well as moulds and cut down the gelatinizing step specially appended for preventing blooming.
4. No migration in adjacent layers of rubber. The migration speed of common sulfur is very high especially in butyl rubber, and with the incorporation of insoluble sulfur, such phenomena can be avoided.
5. Shorten the vulcanization time. When reaching the temperature for vulcanization,insoluble sulfur will go through a stage of activation, that is to say, a chain de-polymerization, which can quicken the vulcanization speed, reducing the amount of sulfur used, improving the aging characteristic of products.
Therefore, due to its non-blooming characteristic, insoluble sulfur is widely used in the manufacture of radial rubber and other synthetic rubber products, also in the light-colored rubber products in which common sulfur is incorporated in high proportion.