1985 Volume 13 Issue 1 Pages 16-24
A dispersion parameter is a quantity to estimate the quality of dispersed materials, e. g., particle size and homogeneity, in terms of the mixing condition such as the shear rate t and the mixing time t. Several types of dispersion parameters were evaluated for mixing processes, employing two types of mixers, of low density polyethylene and carbon black particles. The conventional type of parameter, E01=K01γα1t, did not correspond to the final dispersion level with sufficient precision for an optimum dispersion parameter. The observation of three definite dispersion levels depending on the mixing time led us to propose a new type of parameter, E02=K02γα1tα2. This showed better correspondence in both the laminar and the melt-fracture (turbulent) flow regions. At each of the three levels of dispersion, corresponding to three sets of α1, and α2, the parameter enabled us to estimate the final dispersion quality to within 10%.
In the laminar flow region, the ratio of α1, and α2 was 1.0: the parameter was expressed as a function of total shear strain. In the melt fracture flow region, the ratio was 2.9, which is equal to 2(1+n) where n is the power-law index for the shear stress-shear rate relation. The latter result indicates that the dispersion process depends mostly on the shear rate, but little on time, and that the energy of ficiency in the melt-fracture region is much higher than that in the laminar flow region. Application of the optimum dispersion parameter to actual mixer systems was made in two cases: one was the case of the coexistence of laminar, melt-fracture, and folding flows, and the other was that of the existence of air with agglomerated carbon black particles.