Preparation Of Sustained Release Microcapsules By In Situ Polymerization

In situ polymerization is a new method of preparing microcapsules. The core materials were made as the disperse phase. The soluble prepolymer and acid catalyst was then added into the continuous phase. First, the prepolymer was made by the monomer. The prepolymer started to polymerize when the acid catalyst was added. And the microcapsules were produced when the material deposited on the surface of core materials. The prepolymer was soluble in the continuous phase but the polymer in the whole system was insoluble and the polymerization occurred in the core materials.Avermectins is a pesticide dominated by the stomach toxicity and contact action which with low toxicity, high efficiency, no pollution, no cross-resistance being used with other pesticides and rarely have resistance. So it is widely used in pest control. However, in the course of Avermectins is susceptible to the effects of UV and microbial decomposition, the efficacy is decreased. In order to reduce the degradation in the use, extend its efficacy, reduce the waste of resources, and reduce the drug costs, the Avermectins was encapsulated. In this paper, the formulation and process of the in situ polymerization reaction were studied, and the Avermectins microcapsules were prepared which meet the requirements.First, the HPLC detection conditions were detemined:column, Dalian, Elite Hyp--ersil (4.6mm×200mm,5um); mobile phase, methanol-water (90:10); flow rate,0.7 mL/min; detection wavelength,245nm. The method of HPLC was established to det--ermine the content of Avermectin in the microcapsules. The composition of the relea-se medium and the method of drug release test were established.In the experiment of emulsion preparation, the composition of oil phase and emulsifier was firstly selected. The mixture of mcthylbenzene and chlorobenzene with a proportion of 3:4 which dissolved Avermectins was chosen as the oil phase and the mixure of acacia and AE09 with a proportion of 1:2 was chosen as the emulsifier. The approximate range of preparation and technology of the emulsion was determined with one factor analysis. The best condition for emulsion preparation was obtained by orthogonal experiments. When the proportion of oil and water is 13 to 100,30% emulsifier was contained in oil phase, stirring shear rotate speed was 4000rpm, stirring time was 4min, a stable white emulsion which has a uniform particle size distribution was produced. In the microcapsule preparation experiment, the proportion of emulsion and prepolymer which was 1 to 3 was firstly decided. Then the parameter of the technology and the formulation in the process of acidification was tested. Through the orthogonal design the best reaction conditions of acidification was obtained:the pH was 2.5, the speed of adding acid was 3mL/min,stirring speed was 600rpm,acidified 1.5h in room temperature. The adhesion of the microcapsules was changed by adding anti-adhesives. The type and amount of suspending agent was also filtrated and the Xanthan Gum with a concention of 1.0% was used as the suspending agent of microcapsule suspension.The microcapsules with an appearance of a uniform white suspension were finally obtained. The microcapsules'diameter was 1-12μm, the span was 1.604, the content of Avermectins was 2.0±0.1%, the encapsulation rate was above 98.6%. Compared with Avermectins emulsions, the microcapsules had a significantly effect of sustained release and the release rate meet the requirements.