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The influence of absolute viscosity, surface tension, volatility, apparent viscosity-shear rate relationship, and distillation point on droplet size spectra and deposit characteristics was investigated for a wide range of petroleum and vegetable oils used in pesticide sprays, using Kromekote cards and glass plates for droplet collection. Air samplers were also used simultaneously to assess the airborne concentrations of the materials. The results indicated an increasing trend in absolute viscosities and surface tensions, and a decreasing trend in volatilities of the diluent oils, as their distillation points increased. However, the relative rate of increase in absolute viscosities was greater than that in surface tensions. As a result, the inverse relationship between viscosity and volatility was much more pronounced than the one between surface tension and volatility. The apparent viscosities of the volatile oils at high shear rates were very much lower than those of the nonvolatile oils, indicating a marked difference in the intermolecular forces of attraction. The droplet size spectra, and thus the deposit characteristics, and airborne concentrations of the diluent oils varied depending on their absolute viscosities, volatilities, and apparent viscosities at high shear rates. The droplet size spectra of the highly volatile oils consisted of very small sizes, and as the volatility decreased gradually, a progressive increase in the droplet sizes and deposits was observed. The most satisfactory combination of droplet size spectra, droplets per unit area, and spray volume deposits, and that with the least amounts of airborne concentrations, was obtained with the Dowanol TPM solvent, which was also the least volatile of the eight volatile oils studied.
absolute viscosity, surface tension, volatility, apparent viscosity, shear rate, distillation point, diluent oil, spray deposit, airborne concentrations, pesticides
Research scientist and project leader, Government of Canada, Sault Ste. Marie, Ontario