Background: Nanoparticle formulations of pesticides have been proposed to produce a better spatial distribution of the pesticide on leaf surfaces, which provides better efficiency. Nanoparticles are well studied for drug delivery and sustained release but not in the agricultural sciences, because of the difficulty in generating stable pesticide nanoparticles with controlled particle size distribution and because the processes to generate nanoparticles are usually costly. In this paper, a model pesticide, bifenthrin, has been prepared in nanoparticle form by using the Flash NanoPrecipitation process. The process involves rapid micromixing to effect supersaturation, and polymer assembly to control particle size.
Results: A multi-inlet vortex mixer (MIVM) was developed to provide rapid micromixing, high supersaturation and rapid nucleation and growth of bifenthrin nanoparticles. Several polymeric stabilizers were tested. With an increase in pesticide loading from 50 to 91%, nanoparticle size increased from 100 to 200 nm. The stability of the nanoparticle dispersions was followed for more than 12 days. The steric stability caused by the corona structure of the hydrophilic block of the polymers prevents nanoparticles aggregation. Ostwald ripening is responsible for the slow particle size growth observed.
Conclusion: Flash NanoPrecipitation using an MIVM provides a cost-effective process to produce stable pesticide nanoparticle suspensions. Nanoparticle size depends on supersaturation, pesticide loading and type of polymer. Nanoparticle pesticides potentially provide higher efficiency, better uniformity of coverage for highly active compounds and less exposure to workers, relative to compounds solubilized in organic solvents.