Dispersion of particulate additives in rubber using the batch operated internal mixer : a study of flow behaviour and properties of rubber mixes

As an aid to understanding the mechanics of mixing in an internal mixer laboratory scale trials have been carried out using a mixer having a transparent plastics chamber. The use of a transparent rubber and coloured 'markers' then permitted direct viewing of the characteristic flow patterns deriving from the use of three fill factors. These mixing trials have indicated the rheological properties which must be measured in order to predict the mixing behaviour of a rubber. Also considerable information is contained in the visualisations which will aid further work into control and instrumentation strategies and into fundamental design/mathematical modelling studies. A laboratory Banbury mixer and Brabender Plastograph are used to prepare the rubber compounds which are then characterised for the dispersion of compounding ingredients. For carbon black dispersion studies several techniques are employed. Capillary rheometry is used to study their stress-strain rate relationships and to obtain die swell, shear and tensile properties. Creep and elongational tests are also carried out on uncured mixes. In addition measurements on Mooney viscometer, Monsanto rheometer and analysis of bound rubber are made. These tests for filler dispersion are supported by microscopic examination of microtomed sections. Work is also geared to examine properties that are not only sensitive to changes in levels of carbon black dispersion but also that which are readily measured and can be used in industry. Measurements of mechanical phase angle and electrical resistivity are considered. Dispersion of non-black compounding ingredients is studied by X-ray microradiographic technique and the analysis of vulcanisate properties. To relate the performance of the Plastograph and Banbury mix the concept of mixing energy per unit volume of material is used.