On the Role of Bound Rubber in Carbon-Black Reinforcement

Abstract

Abstract A simple model of filler dispersion has been used to approximate particle spacing and the portion of rubber that is restricted as a result of particulate reinforcement. For N330 black, which has an equivalent radius of 20.2 nm, the critical concentration (in SBR of Mw=344 000) for coherent carbon-gel formation upon solvent immersion is 30 phr. At this level of filler, particle-particle spacing is approximately the diameter of the average SBR random coil. In the second part of the study, compositions in which portions of free rubber had been extracted were compared to conventional mixes at the same black concentrations. Conventional and extracted vulcanizates had similar cure behavior and resistance to deformation, however, extracted samples, with excessive bound rubber had reduced strengths, consistent with the presence of inherent flaws. Apparently, the extracted samples, which are torn apart upon mastication are unable to fully reknit together even after compression molding and vulcanization.