Evaluation of Pesticide Dispersibility in Water Dispersible Granules Using Low-Field NMR Analysis

Water-dispersible granules (WDGs) are granular formulations that rapidly disintegrate and disperse into suspensions upon contact with water. In the United States, they were once referred to as dry flowables or dry suspensions. Strictly speaking, there are differences: WDGs are produced by dry milling and granulation of pesticides (e.g. pan granulation, agglomeration, extrusion, fluidised-bed processes) followed by drying. By contrast, dry suspensions are obtained by wet-milling pesticides into suspensions and then spray-drying into solid granules.

WDGs were first developed in the 1980s as a new pesticide formulation. They quickly gained traction thanks to advantages such as safety, solvent-free composition, dust-free handling, and ease of packaging, transport, and use.

The development of pesticide formulations is closely linked to their dispersion performance. Superior pesticide varieties, suitable formulations, and effective application equipment all depend on good dispersion. Dispersion can be improved in two main ways: processing and formulation. For example, finer milling of solids improves dispersion. Early pesticide powders—made by blending active ingredients, adjuvants, and fillers—were inexpensive, easy to apply, and efficient to distribute. However, they produced dust, caused drift, and posed health and environmental hazards due to low dispersion, leading to their decline in favour of safer, better-dispersing formulations.

Low-field NMR can be applied to assess the dispersion behaviour of WDG pesticides. It enables rapid characterisation of particle dispersion, aggregation, and flocculation processes within suspensions—providing valuable reference data for R&D and quality control of pesticide formulations.

In particle dispersions, solvent relaxation rates are linearly proportional to the available particle surface area. Solvent associated with free polymers, or within loops and tails of polymers, shows little change in relaxation because mobility remains high. When polymers adsorb to particle surfaces, however, increased proportion and residence time of water molecules in near-surface regions enhance overall relaxation rates. By quantifying relaxation differences, LF-NMR provides a reliable method for evaluating particle dispersion quantitatively.