A variety of devulcanization processes have been invented to reclaim rubber from used or discarded tires and other rubber products comprising cured, or vulcanized, rubber or elastomer. The reclaimed rubber can be co-cured or co-vulcanized with virgin rubber to manufacture new tires and other rubber products at a relatively low cost if large-scale devulcanization can be carried out without degradation of the rubber. To date, however, no known devulcanization process has proven to be commercially viable and sustainable. This is attributable to the fact that every known devulcanization process is excessively expensive to construct and operate; moreover, every process is exceedingly difficult to scale up and control, and/or cumbersome to recover and purify the high-quality devulcanized rubber with minimum degradation because of one or more of the following reasons: (1) operating at an inordinately elevated pressure; (2) operating at a very high temperature; (3) being subjected to extremely large shear forces; (4) needing to use expensive vessels and mechanical devices, e.g., extruders and high-speed rollers; (5) requiring to supply a special form of energy, e.g., ultrasonic and microwave radiation; (6) being subjected to a mixture, or composition, of two or more reagents, catalysts and/or promoters, which are frequently highly toxic; (7) requiring an unusually long time even for partial devulcanization of cured rubber or elastomer; and (8) only capable of devulcanizing the surface of reclaimed rubber crumb.
The recently invented SFMC devulcanization process can carry out large-scale devulcanization without degrading the rubber at a remarkably low cost: The process can be operated under or near ambient conditions with a single, non-toxic, non-corrosive, renewable and recyclable reagent, which is green and available in many regions of the world, and without any catalysts. Naturally, a whole-scale plant of the process, comprising no more that 3 or 4 major pieces of processing equipment, is extremely easy to design, construct, start up, fine-tune, operate, control and maintain; moreover, the processing time can range from as low as several minutes to not more than 1 hour depending on the temperature under atmospheric pressure. The process yields devulcanized rubber of high quality whose properties are essentially the same as those of virgin rubber. Thus, the SFMC devulcanization process is totally green and is indeed unlike other patented or conceived rubber devulcanization processes. A simple and rational mechanism is proposed for the SFMC devulcanization process. A patent has been filed in the U.S. as well as abroad for the process.