The Dark Field Cut Surface (DFCS) Test for Estimating the Dispersion of Carbon Black in Rubber Compounds

Abstract

A test for estimating the dispersion of carbon black in rubber compounds is described. It works by examining the freshly cut surface of a specimen at low magnification in dark field illumination. Roughness of the surface related to the presence of carbon black causes increased reflection under dark field illumination. The illumination of each field of view is examined as 100 subdivisions and the relative values of these readings give a numerical estimate of the dispersion. Details of how this is done and the corrections applied to the results are described. A second paper reports some initial results obtained with the test. The test works well for certain elastomers, notably NR and SBR. The biggest advantage of the test is its ability to work rapidly and cheaply on small zones at relatively high magnification. This opens up the possibility of detailed studies of macroscopic variations in dispersion, done in reasonable times and at reasonable costs.

A study of relationships between state-of-mix, rheological properties, dynamic properties, and bound rubber content

“…The use of a dark‐field microscopy is also useful to estimate the carbon black dispersion in rubber compounds. The poorer the dispersion, the smaller the light reflectance 9, 11. However, this technique is mainly limited by its low magnification.…”