A Study on a New Filler Dispersion Index (FDI)

The effect of mixing on filler dispersion has been shown to have remarkable affects on material properties. Many methods of measuring filler dispersion have been developed. However, none of them provides a filler dispersion index that gives the best way to control a mixing process. We developed a new method of measuring filler dispersion named FDI in order to evaluate objectively a kneading state of the compound that consists of EPDM, carbon black, and oil. A filler dispersion index (FDI) is defined as a percent ratio of complex modulus G* at 1% strain versus that at 0.01% strain. A FDI value increases along with an increase of mixing time. A FDI value of cured EPDM is proportional to that of uncured EPDM. Treating the rubber composition with an open role does not affect on a FDI value. Consequently, the FDI is found to be a better method to measure carbon dispersion comparing the optical microscope method of ASTM 2663-69. A free induction decay curve of pulsed NMR indicates a presence of hard segments with a short spin-spin relaxation time (T2). The short-T2 value measured by pulsed NMR increases along with an increase of mixing time, which is similar to the FDI.