Suspending Potential of Gum Systems and Their General Flow Properties

Abstract

Plotting of the logarithm of shear stress against logarithm of shear rate should be used to recognize whether the rheogram of a pseudoplastic gum system will become Newtonian or display a yield value at zero shear rate. Either Fitch or Casson plots give a reasonable measure of the yield value, although in general neither are found to hold rigidly. Rheograms may also be used to determine an index of pourability by considering the torque at some suitable higher shear rate. In this work a pourability index is defined as the logarithm of the torque at 50 seconds−1. Since Chong has shown yield value to be a measure of suspending capability, suspendability is similarly defined as the logarithm of yield value. Increasing gum concentration generally leads from Newtonian to semipseudoplastic to pseudoplastic behavior. Yield value only occurs as a limiting case following this transition. The addition of a second agent such as Cab-O-Sil can develop the yield value at levels where neither it nor the other gum displays such behavior. A plot of yield value against concentration shows clearly that there is a critical concentration required to develop this parameter. A plot of yield value against pourability index permits a relative assessment of the suspendability obtainable for a given pourability. These plots, or tables derived from them, facilitate the choice of the most suitable gum system to give a desired degree of suspending capability. Plotting of the logarithm of shear stress against logarithm of shear rate should be used to recognize whether the rheogram of a pseudoplastic gum system will become Newtonian or display a yield value at zero shear rate. Either Fitch or Casson plots give a reasonable measure of the yield value, although in general neither are found to hold rigidly. Rheograms may also be used to determine an index of pourability by considering the torque at some suitable higher shear rate. In this work a pourability index is defined as the logarithm of the torque at 50 seconds−1. Since Chong has shown yield value to be a measure of suspending capability, suspendability is similarly defined as the logarithm of yield value. Increasing gum concentration generally leads from Newtonian to semipseudoplastic to pseudoplastic behavior. Yield value only occurs as a limiting case following this transition. The addition of a second agent such as Cab-O-Sil can develop the yield value at levels where neither it nor the other gum displays such behavior. A plot of yield value against concentration shows clearly that there is a critical concentration required to develop this parameter. A plot of yield value against pourability index permits a relative assessment of the suspendability obtainable for a given pourability. These plots, or tables derived from them, facilitate the choice of the most suitable gum system to give a desired degree of suspending capability.