Prediction and monitoring of filler dispersion and filler localization during the mixing process
The properties of filled rubber compounds depend in a high manner on dipersion and distribution of the filler in the rubber matrix. The characterization of macro- and microdispersion usually is performed on the final compound or even the vulcanized product. For carbon black filled rubber compounds a method on the basis of online measured electrical conductance was developed, which enables the analysis of dispersion and distribution of carbon black during the mixing process in the internal mixer. Correlations between online conductance, offline measured electrical conductivity and mechanical properties have been found. Moreover, the influence of typical ingredients of rubber formulations, such vulcanizing agents, on the dispersion kinetics of the fillers can be characterized this way and can be used to derive strategies for process optimization of the mixing step. The findings for singular rubber compounds could be transferred to binary rubber blends and dynamic vulcanizates. The method is applicable in carbon nanotubes and organoclay containing systems.
Based on the selective wetting of filler by rubber molecules a novel model (Z-model) is developed for prediction of the phase selective filler localization in binary rubber blends, for example SBR/NR, at an equilibrium state. It can be well applied for ternary rubber blends and compatibilized filled rubber compounds.
Based on the thermogravimetric analysis (TGA) and fourier transformed infrared spectroscopy (FTIR) of rubber-filler gel, a new method (wetting concept) was developed for quantitative characterization of the kinetics of filler localization in the phases of heterogeneous rubber blends. This method needs only minor efforts for sample preparation and allows for characterization of selective filler distribution depending on mixing time.
Applications:
- Selective filler localization in immiscible binary and ternary blends as well as in miscible binary blends
- Localization of compatibilizer in filled rubber compounds
- Characterization of the change of surface tension of filler in rubber compound during mixing
- Direct comparison of filler affinity to different rubber components
A comparison between the kinetics of filler localization experimentally determined by the wetting concept, and the filler localization at an equilibrium theoretically predicted by our Z-model, provides a deeper insight into the filler transfer process taking place during the mixing process.