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ABSTRACT
A new method for characterizing the carbon black dispersion in rubber compounds is introduced. This technique is based on interferometric microscopy (IFM) and utilizes the interference fringes between in-phase light beams reflected from the rubber sample and a smooth reference surface to measure the three-dimensional surface topography. The peaks and valleys present on the fresh-cut surface are representative of the carbon black agglomerates and are used to characterize the dispersion. A series of samples with different base rubbers and varying dispersion levels were created and characterized by both light microscopy and IPM. These results were used to generate a universal dispersion index based on the IFM data that correlates well with the LM dispersion index values. In addition, three-dimensional peak statistics were obtained from the IFM data and used to provide additional information about the carbon black agglomerate distribution. This data can be used for a more complete understanding of the compound behavior as a function of the carbon black dispersion and agglomerate distribution.
INTRODUCTION
Characterization of the filler dispersion within rubber compounds has been of documented interested for almost a century.1 This intense and long lasting interest in dispersion is due to the substantial changes in rubber performance and appearance that result with changes in the homogeneity of the filler dispersion.2 Additionally, economic issues are of major concern and it is important to shorten mixing cycles and improve throughput, while maintaining a good filler dispersion. These driving forces have resulted in a number of different techniques for characterization of the dispersion, including inspection of the sample by eye,3-5 light microscopy,5-11 profilometry,5,12 optical properties,13 electrical resistivity,14 reflectrometry,15 and others.16-21 Each technique has its own set of advantages and disadvantages, with the disadvantages generally being the need for a set of calibration compounds or constants for each polymer system of interest, complex sample preparation and the lack of quantitative measurements. To overcome these restrictions, the technique of interferometric microscopy22 has been applied to dispersion characterization. This technique offers the advantages of being fast, simple and quantitative with the ability to provide new information about the dispersion of the rubber system being studied.
Despite the large number of techniques developed to characterize the filler dispersion mentioned above, one of the oldest and most conceptually...