Filler migration rubber blends

Using a dynamic mechanical thermal analysis technique the effects of fillers and rubber polarity on the distribution of filler in butadiene/nitrile rubber blends were investigated. Carbon black and silica were the fillers investigated. Filler migration between polymers was also shown. 12 refs. 

Filler Migration in Natural Rubber Blends During the Mixing Process... 

The properties of rubber-rubber blend composites depend on the size and shape and concentration of nano particles and their interactions with the individual mbber matrix. The interaction between the filler and the matrix are improved by surface modification. In the mbber industry the uniform distribution of nano particles is considered to be important as it affects the mechanical properties and performance of the composite. For mbber-mbber blend composites fillers like carbon black prefer to migrate to less polar, less viscous mbber phase whereas silica and clay particles migrate to more polar mbber phase. CNTs mainly reside in the highly polar and non-polar mbbers but not in weakly polar ones. The Tg remain unaltered for a completely incompatible blend. In the case of partially compatible blends, the Tgs of the blend components are expected to shift towards each other as compared with the pure components. Shifting of Tg of polymers to lower or higher values in a blend depends on the polarity difference and the difference in the thermal expansion coefficient of the respective polymers in the blend. 

Waxes. Paraffinic waxes function by blooming to the rubber surface to form a thin inert protective film. Since the wax is umeactive toward ozone, this film is a physical but not a chemical barrier to ozone. The number of carbon atoms per molecule of wax varies from 18 to 50. MicrocrystaUine waxes are heavier and less crystalline. They have between 37 and 70 carbon atoms per molecule. The migration rate of waxes is dependent on several factors. These include the type of rubber or blend, the amount and type of reinforcing filler, the concentration and structure of the wax, and the temperature range that the product will experience in use. 

As for natural rubber/SBR masterbatch blends, carbon black will migrate to the SBR gum phase. At equilibrium, the amount of carbon black in the natural rubber phase will depend on the particle size. For example, the amount of carbon black remaining in the natural rubber phase can drop from 41% for NSSO to only 27% when using N134. Other factors or empirical guidelines affecting the distribution of fillers include ... 

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. 

---