Powder-filled semisolids: Influence of powder addition to vaseline on the rheological properties.

Abstract

To evaluate the influence of solid particles on the rheological properties of semisolids, 6 inorganic powders classified as follows were added to vaseline; 1) fine and rigid powders (ZnO, TiO2), 2) porous powders (hydrated silicon dioxide (Cp), synthetic aluminum silicate (SiAl)), and 3) lubricating powders (talc, magnesium stearate (StMg)). Rheological measurements were performed by the oscillation method and continuous shear method.As determined by the oscillation method, the profiles of storage modulus (G'), loss modulus (G''), and loss tangent (tan δ) vs. powder concentration (fp) varied from powder to powder. In group 1, log G's increased monotonously on addition of ZnO, whereas they were scarcely changed at low fp but increased gradually at high fp in the case of TiO2. This difference seemed to be caused by a difference in their affinity for vaseline. In group 2, log G's changed only a little at low fp but increased rapidly at higher fp. In group 3, StMg showed the characteristic effect that it reduced G' at fp values below 0.3.Most of the powders gave maximum values of tan δ at a powder volume fraction (φp) below 0.04, and these peaks were presumed to reflect the beginning of structure formation.As determined by the continuous shear method, porous powders (group 2) increased the apparent viscosity at high shear rate (η625) but the other powders did not increase η625 so much. This suggests that the structures formed by porous powders were resistant to shear but those formed by other powders were not.