Abstract
In order to investigate the interaction among the ingredients of toothpaste, we measured the Theological properties of toothpaste using the Brookfield Synchro Lectric Viscometer.
And we found that:
(1) At low shear rate, the a relation of shear stress versus shear rate in toothpaste has been obtained in general form of the well-known Williamson's empirical equation for pseudoplasticity. η=η*+C1/C2+G Here G is the shear rate.
η* represents the limiting viscosity of toothpaste at G→∞. η does the viscosity of toothpaste at G. The C1 and C2 are the constants.
(2) First we determined C1 with modified Na-CMC in concentration percentage and kind. When C1/N is plotted as a function of concentration of Na-CMC (N), a straight line is obtained. Thus we have obtained the following empirical equation. C=aN2+bN a, b are constant. We have introduced a ratio D.P./D.S. to know the solubility of Na-CMC, and found that the constant a is proportional to D.P./D.S..
(3) We have measured C1 by varying the volume fraction of powder (φ). When log C1 is plotted as a function of the volume fraction of (φ), two straight lines of volume concentration are obtained, locating the critical point with the larger slope of the straight line beyond it than below it. When the concentration percentage of Na-CMC increases, the position of the critical point is shifted to enlarge the side of the higher concentration of φ. It is thought that the structural viscosity of toothpaste is mainly the result of the network of Na-CMC below the critical point, and is as mainly the result of interaction of the powder beyond the critical point.
