Influence of machine and material variables on fundamental rheological properties of rubber mixes

In rubber product manufacturing the processability of a compound is highly dependent upon the internal mixing operation. The mixer operating variables and the ingredients of the compound influence strongly the quality of the compound coming out from the mixer. In this study, which is based on a natural rubber compound, a total of eight variables, comprising five mixer variables and three material variables were changed systematically using a statistical experimental design technique; and the resulting rheological properties and carbon black dispersion levels of the mixed batches were evaluated. A prototype variable speed rotational viscometer known, as the TMS rheometer, was used in investigating the flow properties and wall slip behaviour of the rubber compounds. Rheological characterization of these compounds was based on the power-law dashpot Maxwell mechanical model. In addition, dark field reflected light microscopy (DFRLM) system was utilised in determining the carbon black dispersion level of the compounds. A second order polynomial function was used to model the relationship between the measured properties of the rubber mixes and the independent variables. A statistical computer package performed curvilinear regression analysis for such a multivariable process. A newly developed technique, known as Interactive Graphics for Process Simulation, enables the measured responses to be represented pictorially in the form of shading diagrams. By inspecting the shading diagrams, the responses can be correlated with one another, consequently establishing an optimum level of the mixer operating variables and the material variables, for meeting both the process productivity and mixed product specification objectives.