Tire Conversion Systems
Generation 2 Scrap Tire Conversion Technologies were developed around the turn of the century. By improving the pyrolysis decomposition process, reducing its volatile content and through finer grinding of the resultant char, the Generation 2 system is capable of producing recovered Carbon Black (rCB) with better quality than that by the of Generation 1 systems. Generation 2 technologies are capable of recovering carbon black, that was originally built into tires.
Different tire parts are built using different carbon black components of different grade as shown in the ASTM Grades chart below. Since, the major concern is in-rubber performance of rCB, the surface area axis in the chart is represented by STSA (i.e. External Surface Area) and not by N2SA/BET (Total Nitrogen Surface Area), as STSA represent the carbon black surface accessible to rubber molecules.
The tire rubber fed into the conversion process contains a mix of the carbon black components originally built into the tire – this is a common issue for all generations of tire conversion technologies. In case of the Generation 2, the rCB is a mix of those components comprised of different grades and, therefore, its properties are merely averaging the respective properties of the grades built into the tire. As a result, the properties of rCB produced by a Generation 2 technology cannot ever match property values typical for higher grades.
Another issue, which is common for all generations of tire conversion technologies, is a “rCB in-rubber performance shift” phenomenon, described in various forms by a number of prominent authors (e.g. Dr. C. Gisele Jung, Ir. Jean-Paul Bouysset, Chris Norris, and others): due to a number of rCB specific (and different from vCB) qualities the rCBs with colloidal properties (e.g. surface area and structure) comparable to vCB grades ASTM N3XX, when used in-rubber, perform as grades ASTM N7XX. Therefore, one can speak of in-rubber performance shifted to the lower grades, as illustrated in the Generation 2 rCB Grades chart below.
The practical implication of the rCB in-rubber performance shift for Generation 2 tire conversion technologies is that they can only produce rCB capable of replacing vCB grades N7XX, and, at most, partially replacing vCB grades N6XX and N5XX, but have no potential to replace higher vCB grades.
The Generation 2 rCB Grades chart above illustrates a fundamental limitation of Generation 2 technologies in replacing different ASTM Grades. This diagram also illustrates the well-known fact, that a combination of surface area and structure properties, which reliably predict in-rubber performance for vCBs, cannot be used alone for predicting rCB in-rubber performance.
Currently, only a handful of companies around the world are in their initial stage of Generation 2 Technology operation. How to convert scrap tires into higher surface area and higher structure carbon black grades (e.g. used in tire tread) is a fundamental question for the rCB industry.