DROPLET SPREADING AND PENETRATION OF NON-AQUEOUS PESTICIDE FORMULATIONS AND SPRAY DILUENTS IN KROMEKOTE® CARDS

Abstract

ABSTRACT Spreading and penetration of droplets ranging from 40 to 450 |xm in diameter were studied in Kromekote cards (K-cards), using pesticide formulations and spray diluents of variable viscosity, surface tension, and volatility. The data were used to compute spread factors (SF, the ratio of the stain diameter, D, of a droplet on the card to the diameter, d, of the spherical droplet making the stain) for those liquids. The influence of time interval after impaction and temperature on spreading, was studied using droplets of ca. 400 |im in diameter. All liquids tested showed an increase in SF and in penetration depth, h, with increasing droplet size, but the rate of increase in h was greater than in SF. Low-viscosity liquids penetrated into the card to a much greater depth than the high-viscosity ones. Liquids that were completely non-volatile, continued to increase in stain diameter during the 36-day observation period, and showed no final stain size. Such liquids may provide erroneous SF values if this phenomenon is not taken into account. All liquids showed a slight but gradual increase in SF values with temperature, but the rate of increase was higher for non-volatile liquids than for volatile ones. The impaction energies (LE.) of droplets increased extremely rapidly when the diameter increased only gradually, and the relationship between d and LE. was non-linear. For the droplet size range studied, the impaction energy showed much less influence on the spreading and penetration of droplets than the porosity and absorbent nature of the K-cards.