Preparation of Avermectin/Grafted CMC Nanoparticles and Their Sustained Release Performance

Avermectin (AVM) is a highly efficient pesticide against a variety of insects and is widely used in agriculture. However, it is susceptible to oxidation and photolysis, resulting in instability under UV irradiation and a short half-life. Herein, sodium carboxymethyl cellulose (CMC) was grafted by styrene (St), Methyl methacrylate (MMA) and butyl acrylate (BA) respectively to prepare grafted polymer nanoparticles in application for AVM sustained released. And the influence of different grafted monomer and the grafted rate on the AVM/grafted polymer nanoparticles performance was discussed. The larger the grafted rate of St was, the larger the particle size of AVM/grafted polymer nanoparticles had with a higher drug loading rate and stronger resistance to ultraviolet light. Besides, the particle size, drug loading rate and the ability of anti-ultraviolet light of grafted CMC emulsion was also influenced by the modifying agent. While the concentration of AVM was kept the same, the acrylic esters (MMA and BA) grafted emulsion have smaller particle sizes with higher drug loading rates and stronger anti-ultraviolet ability comparing to styrene (St) grafted emulsion. The effect of different amount of St and different monomer grafted on the sustained release performance of AVM/grafted polymer was also investigated. As the grafted rate of St increased, the release rate became smaller. The release speed has a sequence of CMC-g-PBA > CMC-g-PS > CMC-g-PMMA when CMC grafted with different monomer. Their sustained release curves can be described by Korsmeyer-Peppas equation. Finally, the insect toxicity test showed that insecticide toxicity against diamondback moth (Plutella xylostella L.) has no apparent difference among the AVM and AVM/grafted polymer nanoparticles indicating that AVM/grafted polymer nanoparticles can reduce the amount of organic solution used for dissolution and prolonged its service life without decreasing its insecticide toxicity.