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Research finds answers for reducing drift Chemical additives that help agri-

cultural pesticides adhere to their tar- gets during spraying can lead to forma- tion of smaller “satellite” droplets that cause those pesticides to drift into unwanted areas, Purdue University researchers have found.

Carlos Corvalan, an associate pro-

fessor of food science, said under- standing how the additives work together means they could be designed to decrease the health, envi- ronmental and property damage risks caused by drift. Corvalan, along with

Osvaldo Campanella, a Purdue profes- sor of agricultural and biological engi- neering, and Paul E. Sojka, a Purdue professor of mechanical engineering, published their results in a February issue of the journal of Chemical Engineering Science.

“When we spray liquids, we have

what we call main drops, which are drops of the desired size, and we can also have smaller satellite drops. The smaller drops move easily by wind and travel long distances,” Corvalan said. “Now that we know better how additives influ- ence the formation of satellite droplets, we can control their formation.” The research will also have applica-

tions in food processing and rocket propulsion, where drop sizes are important. When liquids are sprayed, they

start in a stream and eventually form drops. As the liquids move farther in the air, drops connected by a thin fila- ment start to pull apart. That filament eventually detaches and becomes part of the drops that were forming on either side of it. Satellite droplets form in the middle

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of filaments of pesticides containing surfactants and polymeric additives, which help the pesticides wet and adhere to plant surfaces. The surfac- tants reduce surface tension and force round drops to flatten, helping them cover more surface area on a sprayed plant’s leaves. The polymeric additives reduce viscosity — liquid resistance — making the pesticide flow easier. Polymeric additives also keep the drops from bouncing off plant surfaces. “Each additive is designed to

improve the characteristics of the main drops,” Corvalan said. “But there is a side effect.” When both additives are present in

a pesticide, the surfactant pushes more liquid toward the filament. The reduced viscosity allows liquid to flow more easily in that direction, resulting in a well-defined satellite drop forming in the filament. “When you put both additives

together, there is a synergistic effect. The force induced by the surfactant that was opposed by viscosity is no longer so strongly opposed, and this combined effect can result in the formation of satellite droplets,” Corvalan said. Drifting of agricultural pesticides

not only increases waste and cost for farmers but also can cause health, envi- ronmental and property damage, according to the U.S. Environmental Protection Agency. The results show that carefully mod-

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ulating the strength, concentration or ratio of surfactants to polymer addi- tives can mitigate or eliminate the for- mation of unwanted satellite droplets. Corvalan is now transferring the

results obtained from agricultural research into food processing and rock- et propulsion work. He said drop size uniformity is as important for fuels sprayed into rocket combustion cham- bers as for the production of food emulsions. The U.S. Department of Agriculture

National Institute of Food and Agriculture, Air Quality Program, and the Army Research Office funded the work.

20 Ohio’s Country Journal • • Mid-April 2012

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