During recent years the scarcity and high price of fresh rubber has led to the use of enormous quantities of old rubber, reclaimed in various ways, either in combination with fresh rubber or alone. Old rubber may be simply ground to powder and employed as a filling material with fresh rubber, but the bulk of the reclaimed rubber used in manufacture goes through a series of complicated processes. The discarded rubber goods used for making reclaim, whether they be old rubber shoes or old motor tyres, usually contain a considerable quantity of cotton fibre. In order to remove this fibre the rubber is boiled with dilute sulphuric acid, and the cotton thus disintegrated can then be got rid of by grinding, combined with the use of an air blast The acid process is generally followed by an alkali process, in which the free sulphur is removed by boiling with caustic soda. The residual rubber is then heated with resin-oil, and can afterwards be manipulated more or less like ordinary unvulcanised rubber. The reclaimed rubber contains all the mineral substances originally added, so that little further mixing is required if a similar class of goods is to be remanufactured.
In addition to the methods described above, it is claimed that processes have already been perfected by which the sulphur of vulcanisation can be more or less completely removed from the old rubber. Schidrowitz states that other processes have been recently introduced by which "particles of vulcanised rubber in the shape of dust or flakes can by pressure and heat be moulded to a homogeneous mass, which, on cooling, is to all intents and purposes indistinguishable from an ordinary moulded article"