PROCESSABILITY OF EPR IN AN INTERNAL MIXER (II)

MORPHOLOGICAIL CHANGES OF CARBON BLACK AGGLOMERATES DURING MIXING

Abstract

Optical and electron microscopy is used to observe morphological changes of EPR compounds during mixing. Most of the compounds are investigated with the PI recipe, which represents the special recipe defined in the previous paper to obtain the processability index“PI value”of EPR.
A model, named“the onion model”, is proposed to explain the carbon black dispersion step: aggregates are, either individually or collectively, scraped out from the surface of agglomerates. It is shown that a mathematical expression of the model can semiquantitatively describe the changes of agglomerate diameter distribution with mixing time. The attractive force between the scraped aggregates and the agglomerate surface may mainly result from the interparticle tie molecules. Application of McKelvey′s theory for the model indicates this presumption to deduce the fundamental premise of the mathematical expression.
The whole mixing steps from pellet carbon to colloidal carbon are schematically illustrated, centering around the above model. This scheme can flexibly elucidate the delicate changes in resistivity during mixing. The colloidal carbon content is determined by the microscopic measurement of volume of agglomerates, and found to be one of the most important factors controlling the PI value. The general relation between the microscopic and the true particle diameter distribution functions is also deduced.