Nonionic surfactants are not generally used in water dispersible granule formulations. Common dispersants for these systems include lignin sulfonates and naphthalene sulfonates. Recent studies have shown that ethylene oxide/propylene oxide (EO/PO) block copolymers can also be used to stabilize atrazine dry flowables in both pan granulation and extrusion processes. In laboratory tests, they impart better granule hardness and provide markedly improved suspensibility compared to the anionic dispersants. Most of the formulations tested show good particle size stability over time at room and elevated temperatures. Some particle size increase was seen in some formulations at 45°C.
Blends of these dispersants can be used to provide desired performance characteristics. Combining different ratios of nonionic and anionic dispersants impart varying properties to the granules. Increasing the amount of anionic surfactant can lower the particle size and reduce settling while maintaining the hardness and suspensibility obtained from the nonionic component. The performance of the anionic/nonionic blend in the granules is favorable when compared to the classical anionic formulation.
The molecular weight of the EO/PO block can also influence particle size (measured via wet screen analysis). As the total molecular weight is raised and the EO chain length thus increased, particle size decreases and suspensibility is improved. This result indicates a better dispersive capacity for the larger molecules.
In extruded granules, EO/PO blocks offer not only improved suspensibility and hardness but also equivalent particle size to an anionic dispersant. Obvious differences exist between surfactant performance in extrusion as opposed to that in pan granulation.