Preparation And Characterization Of Two Water-insoluble Solid Nanopesticides Delivery Systems

Pesticide is an important agrochemical production which has made tremendous contributions to agricultural development and human food supply. The emerging nanopesticides have characteristics of small particle size and large specific surface area compared to conventional formulations. That can effectively improve the dispersion and stability of water-insoluble pesticides and the efficient utilization and biological activity of pesticides. It can also reduce the usage amount of pesticide and the loss of effective ingredients of pesticide, and decrease pesticide residues and environmental pollution. Most pesticides must be formulated using suitable formulations to keep bioacticity and enhance efficacy. The solid formulations are not only easy to store and transport, but also can greatly reduce even avoid the use of organic solvents and surfactants.In this paper, we used two representative water-insoluble pesticides to design and prepare two different solid nano-formulations for its physical and chemical properties and investigated the influence of process parameters on the experimental results and clarified the principles of the relevant influencing factors.1. Preparation of emamectin benzoate solid microemulsion in a self-emulsifying method. Screened from 11 kinds of surfactants with the average particle size and polydispersity index as indices, emulsifier A and emulsifier B(3/2, w/w) were selected as the compound surfactant. The solvent was low toxicity and volatile ethyl acetate and the carrier was water-soluble. After optimization, the mean particle size and polydispersity index of the aqueous dispersion were 10.3 ± 0.1 nm and 0.28 ± 0.01 respectively with an equal amount of surfactants to technical. The scanning electron micrograph observation was in agreement with the dynamic light scattering results. The crystal structure of the water-soluble carrier enhanced the formulation stability. The particle size was still less than 100 nm after storage for a month at room temperature. Bioassay against diamondback moths was measured compared to two kinds of water dispersible granules(WDGs) and the toxicity of emamectin benzoate solid microemulsion was 1.3 folds that of the other two WDGs.2. Preparation of lambda-cyhalothrin solid nanodispersion in a combination of melt-emulsification and high-speed shearing method. Screened from 9 kinds of surfactants with the average particle size and polydispersity index as indices, MRES and SDS(3/1, w/w) were selected as the compound surfactant and the content was 5% of drug amount. In the experiment, process parameters of the melting temperature, shear rate and shear time during the preparation of lambda-cyhalothrin nanosuspensions were tested and the best combination is 80 ?C melting temperature, 10000 rpm shearing speed and 10 min shearing time. In this situation, the particle size and polydispersity index of nanosuspension were 16.2 ± 0.1 nm and 0.29 ± 0.01, respectively. After solidifying by freeze-drying with the water-soluble carrier, the particle size and zeta potential were 21.7 nm and-47 mV, respectively. The pH of 7.0 indicated a neutral environment. The suspensibility of solid nanodispersion reached 99.5%, and the wetting time was half of general water dispersible granules. After 14 days storage at room temperature(25 ?C), high temperature(54 ?C) and low temperature(0 ?C) respectively, the solid nanodispersion kept well and the particle size was still below 100 nm. Bioassay results showed the toxicity of solid nanodispersion against diamondback moths were 1.4, 1.2 and 1.1 folds that of the technical, water emulsions and EC.The research results show that preparation of solid nano-formulations could simplify processing using the drug physicochemical properties, reduce costs and overcome problems such as short shelf life and transportation inconvenience of the traditional water dispersible formulations. Importantly, it may reduce the excessive use of surfactants and organic solvents, improve the dispersibility and stability of the active ingredient, improve the effective utilization and biological activity of pesticides, reduce the applications of pesticides and decrease pesticide residues and environmental pollution. The solid nano-formulations could decrease cost and increase effect and are environmently friendly as a reference for studies of other water-insoluble nanopesticides.