Nano and molecular scale of mixing

The previous sections dealt with mixing mechanisms down to the order of 0.1 pm in the rubber domains, which were also interpreted to be the ultimate size of the supermolecular flow units. 

However, the growth of bound rubber onto the surface of fillers must also be accounted for, because it is an important part of the dispersion mechanism. The mechanism of growth of the bound rubber concerns molecular interaction between rubber and filler surface this is a nano-scale phenomenon. 

In order to understand the growth of the bound rubber, we need to start from the incorporation of the filler, when the rubber-filler interaction commences. Boonstra and Medalia [11] interpreted the occurrence of the torque maximum (the second peak) as the result of filling the void of the agglomerate with rubber. This view was supported by the density measurements. The dispersion did not start, because no brown tint appeared in the rubber phase. Thus, the increase of the torque was interpreted as the result of the effective increase of the filler concentration, when the increasing amount of rubber becomes 

However, under the conditions of mixing, rubber is usually a soft solid and it does not diffuse spontaneously into the void of agglomerates. Even if rubber were assumed to be a high-viscosity fluid, it would not flow into and fill the void under the pressure generated by the rotor blade and within the incorporation time of only 1.5 - 5.0 minutes [38]. The density measurements were made with vulcanised specimens. The amount of the penetrated rubber might have increased during vulcanisation. Significant increases of the bound rubber as a result of vulcanisation were detected with the NMR by Wardell and McBrierty [39]. 

Mixing time, min Comments Torque, kgm Density, g/cm Unincorporated carbon black, % Bound rubber, % 

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