Volume 5, Issue 5 (May 2008)
Comparison of ASTM and CIPAC Suspension Methods
Suspension testing is a standard way of characterizing the effectiveness of dispersants in wet or dry formulations. In a suspensibility test, a measured amount of material is diluted in hard water and given a specified amount of time to settle. The settled material is recovered and used to calculate the amount of material that remained suspended, yielding a suspension percentage. Different organizations use slightly different methods to conduct this characterization, and there are few studies which allow the experimentalist to correlate results between methods. The objective of this work is to compare two standard suspension tests, ASTM and CIPAC (Collaborative International Pesticides Analytical Council) and determine their correlation, if one exists. While similar, the methods vary by a few factors including the initial volume fraction of the material and the means of recovering the settled material. Several formulations of copper (II) hydroxide, dispersed with varying amounts of acrylic polymer, were dried and sieved into granule solids and powder solids. Suspension properties were tested using both methods. Resultant suspension percentages for each formula were charted, CIPAC results versus ASTM results. The coefficient of determination (R2) for the suspension percentages of the granule and powder solids was found to be 0.976 and 0.984, respectively. The granular solids showed a one-to-one relationship (slope=1) between results generated by these methods while the powder solids did not, y=0.56+0.37. The driver for this skew may be due to different particle volume fractions between the tests, a parameter which has the potential to affect viscosity in a predictable manner and which is represented mathematically by the Krieger-Dougherty equation.