Preparation and performance characteristics of azoxystrobin microcapsules

The novel biodegradable amphiphilic copolymer (CS-co-PLA) was synthesized by ring-opening polymerization reaction of chitosan (CS) with DL-lactide. A series of azoxystrobin-loaded microcapsules with different particle sizes were prepared by emulsion/solvent evaporation method using CS-co-PLA as wall materials, azoxystrobin as core materials and PVA as continuous phase stabilizers. The effects of mass ratio of core materials and wall materials m(azoxystrobin):m(CS-co-PLA), PVA concentration, V(oil phase):V(aqueous phase), shear rate and shear emulsification time on surface morphology, particle size and size distribution, entrapment rate and drug-loading rate of microcapsules were investigated. The sustained release performance of typical microcapsules, as well as the preparation process conditions and particle size controling methods of microcapsules were also studied. The results showed that when the conditions of PVA mass fraction (1%), m(azoxystrobin):m(CS-co-PLA)=1:4-1:1, V(oil phase):V(aqueous phase)=1:10 and shear emulsification time (5 min) were fixed,different sizes (from 280 nm to 4.5 μ m) of microcapsules could be prepared by adjusting different shear rate (3 000 r/min to 18 000 r/min). The azoxystrobin microcapsules dispersed as individual particles with a well-defined spherical shape and homogeneous distribution, and showed good sustained release performance. It could be concluded that shear rate was the main factor influencing particle size of the microcapsules.