Effect of polyethylene glycols on the rheological characteristics of macloid dispersions

ABSTRACT

The effect of polyethylene glycols 400, 1500 and 4000 on the rheological characteristics of Macaloid dispersions was studied. The rheological study included investigation of the phenomena of consistency, thixotropic breakdown and structural recovery in the stationary state. The consistency of Macaloid dispersions increases in presence of PEG 400 and PEG 1500. This increase is, generally, in direct proportion to the glycol concentration. In the case of PEG 4000, the consistency of Macaloid dispersions is slightly decreased in presence of the low concentrations of the glycol and is slightly affected at the high ones. These effects were interpreted as sum of the adsorption of the glycols between the clay lamellae, the thickening effect of the glycols towards the continuous phase of the dispersions and the dehydrating effect of the glycols. The rate of increase consistency of Macaloid dispersions, on aging is generally increased in presence of low concentrations of the glycols which might indicate a slow adsorption of the glycols. This rate is, however, decreased at high glycol concentrations, which might be a result of the dehydrating effect of the glycols. The thixotropic breakdown of Macaloid dispersions, induced by increasing rate of shear, is generally increased in presence of PEG 400 and PEG 1500 and decreased by PEG 4000. On the other hand, the thixotropic breakdown by shearing is affected differently by the different concentrations of the glycols. The rate of structural recovery is affected differently by the different concentrations of polyethylene glycols. However, all systems attain complete structural recovery after a rest of an hour