scrap rubber chunks from used tires are processed and the monomeric chemicals from which the tire rubber was synthesized are recovered . rubber chunks reduced to a finely divided size are exposed to gaseous ozone to break down the cross - linked structure of the rubber . subsequent thermal depolymerization occurs in a reactor chamber . finely divided silica is introduced within the reactor to prevent agglomeration of rubber particles and to enhance the maintenance of a uniform reactor temperature . reduced pressure within the reactor permits rapid removal of monomer vapors . once the monomer vapors are separated , silica and carbon residues are recovered separately for either recycle or disposal .