Abstract: Mechanical/chemical method and composition for de-vulcanization of rubber maintains the macromolecules, renders sulfur passive for later re-vulcanization, is cost effective, environmentally friendly and produces high quality de-vulcanized rubber to replace virgin rubber. Waste rubber is shredded, crushed and metal-removed. Modifying composition is added as the particles of shredded waste rubber are poured between two rollers that further crush the particles. The modifying composition is a mixture of (1) a proton donor that selectively breaks the sulfur bonds and renders the sulfur passive, (2) a metal oxide and (3) an organic acid that build new bonds between macromolecules for later re-vulcanization, (4) an inhibitor that prevents re-attachment of sulfur radicals with each other before the proton donor attaches itself to the sulfur and (5) a friction agent that prevents sliding of the waste rubber between the rollers. The particles are subjected to at least ten sets of rollers.