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Interactions between some water-soluble polymers used as spray drift control additives in spray tank mixes and a range of anionic, sulfonated surfactants were investigated. Changes in the shear viscosity of the solutions were used as an indicator of interactions. Anionic polymers showed no viscosity increase with any of the sulfonated surfactants. Some non-ionic polymers, notably poly(ethylene oxide) (PEO), poly(vinyl alcohol) and poly(vinyl pyrrolidone) showed marked increases in viscosity in semi-dilute solutions. The extensional viscosity of very dilute (1–1000ppm) solutions of PEO, was determined by pressure and flow rate measurements in a packed bed. Extensional viscosity increased by a factor of up to 10 with added sodium dodecyl benzene sulfonate (NaDDBS). The droplet size distributions of the solutions sprayed through an agricultural spray nozzle were determined, using as examples PEO solutions of varying molecular weight, with and without NaDDBS. The droplet size distributions increased with increasing extensional viscosity. Similar experiments with anionic polymers demonstrated that the droplet size correlates with extensional viscosity, and not with shear viscosity.
Spray drift, polymers, surfactants, extensional viscosity, droplet size distribution
Associate Research Fellow, Agricultural Research Center, American Cyanamid Company, Princeton,