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This paper discusses a new method whereby the rate of granule breakdown, and thereby, one important aspect of Water Dispersible Granule (WDG) formulation quality can be determined objectively and quantitatively. The method uses particle size measuring apparatus to determine median particle size of a suspension of WDG's in water. Measurements are repeated at short time intervals until the median size has decreased to the size of the powder forming the granule or until the size has leveled off at some larger value.
Results can be expressed graphically, by mathematical equation, or for less critical measurement, in terms of time needed to reach original particle size. The measuring equipment must meet the following criteria: 1. It must measure a wide particle size range, from about 1 micron to about 1,000 microns. 2. It must make measurements of suspensions of relatively high concentration, approximating field concentrations. 3. It must be able to repeat measurement at intervals of a few seconds.
This paper demonstrates the method, discusses equipment used and shows results of measurements of a number of WDG's.
Water dispersible granules, laser scanning, particle size measurement instrument, dynamic particle size
Formulation Chemist, Research and Development, Powder Technology Lab, Witco Corp., Fort Worth, Texas