Insoluble sulphur or polymeric sulphur is the sulphur which doesn't dissolve in carbon disulfide. It is formed either by heat polymerization of sulphur or reaction of sulphureted hydrogen with sulphur dioxide. It's a macromolecule polymer containing thousands of sulphur atoms.
Insoluble sulphur is mainly used as an additive agent in rubber industries. It has properties to improve quality, resistance to ageing and fatigue of product, wearability etc. Also it is used in the manufacturing of shoes, cable insulating materials, belt tires, rubber pipe, automobile rubber parts etc. Insoluble sulphur presented in rubber helps it in having a better viscosity. Also it ensure the light color appearance of the products. It reduces the rubber's tendency of being scorched during store. Being able to disperse in rubber, it is helpful in preventing the conglomeration of sulphur.
One of the most important feature of insoluble sulphur in rubber is, it causes no migration. Common suflur migrate too fast like in butyl rubber. Such behavior can be avoided in the incorporation with insoluble sulphur.
Insoluble sulphur minimizes the vulcanization time by chain de-polymerization. This quicken the vulcanization speed.
By owning all these properties insoluble sulphur is widely used in the manufacture of synthetic rubber products.