Viscosity carbon black dispersions

Rwei et al. [52] compared such a carbon black dispersed in three low viscosity media (water, squalene,... 

This research paper is devoted to the application of unit work method for the scale-up of a rabber mixing process in Banbury-type internal mixers. Mooney viscosity and carbon black dispersion factors were selected as the parameters for the determination of the state of mixing. Based on a specific compound formulation, these parameters were measured in three mixers with different chamber sizes. The method indicates the operating points of a bigger size mixer can be accurately obtained from the experimental data obtained on a small size mixer. 6 refs. 

Viscosities of concentrated suspensions of carbon black in a white mineral oil (Fisher "paraffin" oil of 125/135 Saybolt viscosity) were measured with a Brookfield viscometer as a function of OLOA-1200 content. Figure 13 shows the viscosities of dispersions with 30 w%, 35 w% and 70 w% carbon black. In all cases the viscosity fell rapidly as the 0L0A-1200 content increased from 0 to 1%, then fell more gradually and levelled off as the 0L0A-1200 content approached 2%. In many respects the reduction in viscosity with increasing OLOA-1200 content parallels the conductivity measurements both phenomena are sensing the buildup of the steric barrier, and this steric barrier weakens, softens, and lubricates the interparticle contacts. As evidenced in foregoing sections, the particles are still flocculated but can be easily stirred and separated mechanically. The onset of electrostatic repulsion at OLOA-1200 contents in excess of 2.5% did not affect viscosities. 

Figure 13. Effect of OLOA-1200 concentration (parts of OLOA-1200 per 100 parts carbon black) on the Brookfield viscosity (at 30 r.p.m.) of dispersion of carbon black in paraffin oil.

Primer Formulations. Coatings were formulated using standard techniques. Mill bases were prepared by dispersing the oligomer solution with pigments (silica, carbon black, titanium dioxide and barium sulfate in a 1 1 1 10 ratio). The viscosity of the formulation was reduced to spray viscosity by addition of solvent. 

A highly concentrated dispersion of carbon black is first prepared with a portion of the binder and solvent. The viscosity of this concentrate is a function of the particle size, structure, and surface chemistry of the black, the type of binder and its interaction with the pigment black, and the proportions of black, binder, and solvent. The final paint is made from the concentrate by adding more binder and solvent, its carbon black concentration is 3-8% referred to the solids content. Wetting agents are sometimes added to improve dispersibility and prevent flocculation. A number of concentrates for paint manufacture e.g., carbon black-nitrocellulose chips or carbon black -alkyd resin pastes, can be obtained from paint producers. 

Roll-mill for Dispersive Mixing A laboratory roll-mill with 5-in diameter rolls and 0.05 in minimum clearance between the rolls is used for dispersive mixing of carbon black agglomerates in LDPE. Calculate the roll speed needed to break up 5 of the particles per pass, assuming that the critical shear stress needed for breakup is that obtained in Problem 7.12 in the narrow clearance, and that the amount of polymer on the rolls is 50% above the minimum. Assume the same constant viscosity as in Problem 7.7. 

Carbon black loading can play an important part in obtaining quality dispersion with higher loadings producing superior dispersion, other factors being equal. However, caution should be used to ensure that the concentrate viscosity does not greatly exceed that of the compound polymer—a 3 1 concentrate-to-compound... 

The viscosity increase depends on particle size. Smaller particles increase the viscosity of the dispersion more rapidly but there is a big difference between the effect of graphite and carbon black on viscosity. It requires three times as much graphite as carbon black for a similar increase in viscosity. 

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