Filler migration localization

It is generally acknowledged that two distinct factors contribute to the final localization of the fillers thermodynamic effects, based on the affinity that the fillers might have with the polymers and kinetic effects that include the mode of preparation of the composites and the ability of the fillers to migrate to a different location, i.e., from one phase to the other or from one phase to the interface. These factors are critical in the prediction and control of filler localization and are described in detail below. 

Using data on the surface tension values of the rubbers and nanoclays used, the master curve of filler localization in 50/50 HNBR/NR and 50/50 HNBR/ ENR blends was calculated and is presented in Figure 6.24(a). A clay fraction of about 0.9 and 1.0 localized in the HNBR phase of HNBR/ENR and HNBR/ NR blends, respectively, was found, i.e. an almost complete localization of clay in the HNBR is predicted for both blends, when they reach a thermodynamic equilibrium state. Thus, at the beginning of the preparation of HNBR/ (NR-clay masterbatch) and HNBR/(ENR-clay masterbatch) blends, nanoclay pre-mixed in the NR and ENR phase is far away from its equilibrium state. Nanoclay is expected to migrate to the HNBR phase during the blending process. 

However, the proposed mechanism of establishing the equilibrium concentration of carbon black at the interface between polymers does not explain why carbon black does not migrate to the interface ficm one of two phases whereas such transfer occurs from another phase. Indeed, if the condition (12.1) is satisfied, the transfer of carbon black from either of two phases to the interface is thermodynamically efficient. Even with a low adhesion of a filler to the interface the local concentration of a filler at the interface would slightly exceed its concentration in phase. However, such an excess is not observed for a number of polymer pairs attributed to the first group according to the data in Table 12.2. 

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