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UBC Theses and Dissertations

Polymer additive to enhance the retention of crop sprays Xu, Minghuan


In pesticide and fertilizer applications, large spray droplet sizes (300-500 um) are commonly used in the field for reduced spray drift. However, retention of spray droplets after they reach the target surface can be limited by droplets splashing, rebounding, or rolling off of the surface due to their high impacting velocity and inertial energy. While polymer additives were proposed to dissipate energy during the droplet impact process, whether they can enhance the retention efficiency of crop sprays in practical field conditions is still not clear. This research work focuses on enhancing the retention efficiency with polymer additives, which is carried out in four major steps: The first step is to screen polymers suitable for spray applications. The second step is to develop an approach that provides detailed physical insight in a setup that is representative of real spray conditions to quantify retention efficiency. The third step determines the effect of extensional rheological properties on retention efficiency at various spray conditions. The work carried out in the first, second, and third steps forms a comprehensive study on the relationship between extensional rheological properties of polymer solution and retention efficiency. Then the fourth step focuses on exploring the extensional rheological properties of selected polymer additives at different solvent conditions and in agrochemical solutions. The results demonstrate that increasing the extensional relaxation time of the spray solution can increase the retention efficiency by up to 20% and in some cases achieve a total efficiency greater than 95%. It’s also suggested for a particular polymer, surface, and droplet size, the extensional relaxation time alone could be sufficient to predict retention efficiency. The results also relate the extensional relaxation time to important influencing parameters including pH, ionic strength, type of ions, etc.

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