Preparation And Properties Of Phoxim Pesticide Microcapsules In Sustained Release

In recent years, the research on microcapsule has being developed rapidly in China. In-situ polymerization and interfacial polymerization are the most widely used microcapsule technologies. However, the wall material which is used in in-situ polymerization and interfacial polymerization would produce secondary pollution to the environment. To solve this problem, we have studied phoxim microcapsules with natural material as wall material and obtained the optimal conditions of formulation and technics, via three microcapsule methods which are crosslink emulsification, complex coacervation and micro-seeds. Among the three methods, the micro-seeds is firstly proposed by the author. Our study results demonstrate that the micro-seeds method is better than the other two methods. The main contents is as the following aspests:(1) Phoxim microcapsules were made by using phoxim as core effective component enclosed by chitosan as capsule wall material via crosslink emulsification. We established and optimized the technological processes of the microcapsule production:the optimal volume ratio of oil-water is 1:4, the mass ratio of core material to wall materials is 4:1,the mass ratio of emulsifier to core material is 4:1, the mass ratio of crosslinking agent to wall materials is 3:1, the revolving speed is 600 r/min. The particle size of microcapsules is uniform and mainly distributes in 20-50μm, and the microcapsules are regular spheres. The encapsulation efficiency is very low.(2) Phoxim microcapsules were made by using phoxim as core effective component enclosed by chitosan and sodium alginate as capsule wall material via complex coacervation. We established and optimized the technological processes of the microcapsule production:the mass ratio of chitosan to sodium alginate is 1:2, rotation speed of emulsification is 1300r/min, the system concentration is 0.28%, the mass ratio of core material to wall materials is 3:1, the mass of crosslinking agent is 5ml, crosslinking time is 90min. The prepared products are ununiform, and most of them are unregular lumps, and there are some microcapsules in products, The particle size of microcapsules is about 5-10μm. The encapsulation efficiency of 60% can be obtained. But the products have no slow release property.(3) The microcapsules with uniform size, obvious controlled release effect and high encapsulation efficiency was successfully obtained by the micro-seeds method witch is firstly proposed by the author. The particle size of microcapsules is uniform and mainly distributes in 80-100μm, and the microcapsules are regular spheres. The encapsulation efficiency of 80% can be obtained. The release period of 7 days can be gained.(4) The results show that the micro-seeds method is far better than crosslink emulsification and complex coacervation. The method has the advantages of simple operation, easy and high reproduction quality. The prepared microcapsules has the advantages of high encapsulation efficiency and obvious controlled release effect. More importantly than all of that, the microcapsules are intelligent, as they can decide when to start to release.