| Microcapsule is researching hotspot now and have broad prospects for development. Microencapsules have been made by in-situ polymerization and interfacial polymerization. And the factors that have relationship with the performance of microcapsules were investigated, and main contents is as the following aspects:1. Preparation of pirimiphos-methy microcapsules via an in-situ polymerizationMicrocapsules of pirimiphos-methy with urea-formaldehyde resin wall were prepared via an in-situ polymerization. Several reaction parameters affecting microcapsules properties. And optimal conditions of formulation and technics were as follows:The percentage of SMA was 25%, the stirrng speed was 2000rpm and last 30min, the optimum periods of acidification were 120min, the solidifying temperature under 60℃for 90min, and the optimum of the core to wall were 5:1. Under these optimum conditions, the mean particle diameter was 3.67μm and the encapsulation rate was 97.73%.The quality specifications,including suspension rate and encapsulation rate, were measured after pirimiphos-methy 20% CS was prepared by an in-situ polymerization reaction in aqueous medium. All the results were up to standard.And the best formulation was as follows:20% pirimiphos-methy,3% dispersant TERSPERSE 2700,2% wetting agent TERWET 1004,0.5% aluminum magnesium silicate,0.15% adhesive xanthan XG,0.1% silicone defoamer, water up to 100%. After hot and cold storage.the encapsulation rate was about 95%, suspension rate were above 90%.2. Preparation of pirimiphos-methy microcapsules by an interfacial polymerization reactionPirimiphos-methy microcapsules with polyurea as wall material were prepared by an interfacial polymerization reaction. The influence of polymerization monomer, the percentage of emulsifier and PVA, emulsification speed, ethylenediamine dropping, the reaction temperature, polymerization time on the quality of microcapsules were studied. And optimal conditions of formulation and technics were as follows:Polymerization monomer were toluene-2,4-diisocyanate and 1,2-ethylenediamine, the percentage of toluene-2,4-diisocyanate was 4% and 1,2-ethylenediamine was 0.4%, the dosage of mixing 0204 with 33# was 2% respectively, the stirmg speed was 1500rpm and last 30min, the polymerizing temperature under 50℃for 6h. Under these optimum conditions,the mean particle diameter of 3.88μm of pirimiphos-methy microencapsules with good shape and good controlled-release charateristics were obtained, their encapsulation rate was 98.26%.For the screening the formulation of pirimiphos-methy microcapsules, the optimal conditions were as follows:20% pirimiphos-methy,3% dispersant TERSPERSE2500,2% wetting agent TERMUL4894,0.15% aluminum magnesium silicate,0.15% adhesive xanthan XG,0.1% silicone defoamer, water up to 100%.3. Comparision of the appearance, release, biological activity of two microcapsules and characterized by IRThe SEM micrographs showed that urea-formaldehyde resin microcapsule had uniform particle size and less rough surface, and polyurea resin microcapsule particle size distribution is uneven and surface is rough. The results of IR showed that microencapsules had existed. The release results showed that between the urea-formaldehyde resin microcapsule and the polyurea resin microcapsule, the polyurea resin microcapsule had lower drug release rates.LC50 value for pirimiphos-methy CS with polyurea as wall material changed only from 26.11 mg/L to 35.12 mg/L within 32d, and pirimiphos-methy CS with urea-formaldehyde resin wall changed from 23.56 mg/L to 52.98mg/L, but LC5o value for pirimiphos-methy EC had big change. It was implied that pirimiphos-methy CS had a sustainable toxicity to Tribolium castaneum Herbst. |
