| In situ polymerization of the monomers and initiator were dispersed in thedispersed phase or continuous phase, which all the monomers and initiator weredissolved in the core internal or external. The monomer was soluble in one phase, andthe generated polymer will be deposited on the surface of the core droplets while thepolymer in the whole system is insoluble. Compared with other methods ofmicroencapsulation, in situ polymerization was relatively easy, high yield, low cost,easy to industrialize, and the wall thickness and the constant of core could be control.Avermectins was a pesticide which with low toxicity, high efficient, nopollution, no cross-resistance being used with other pesticides and rarely haveresistance. So it is widely used in pest control. But, in the course of Avermectins issusceptible to the effects of UV and microbial decomposition, the efficacy is decreased.So as to decrease waste and degradation, extend its efficacy, Avermectins should bemicroencapsulated.Above all, the HPLC conditions were determined: column, Dalian,Elite Hypersil (4.6mm×200mm,5μm); mobile phase, methanol-water(92:8);flowrate,0.8mL/min;detection wavelength,245nm.The standard curve of Avermectins is y=1.3167x-0.8319（R2=0.9992），and the method and conditions of detection wereestablished.Avermectin microcapsule was prepared by two polymerization methods of insitu polymerization. In the single factor experiment of one-step method, the influenceseffects of type and quantity of system modifiers, pH, temperature, stirring rate andvarious anti-adhesive agents and addition agents on the process of microencapsulation and the particle size of the microcapsules were investigated. According to experimentresults, prescription factors and technological factors that need to be further examinedwere established. And based on the results, orthogonal test was executed. The bestcondition was obtained: the amount of PVA is1.5%, pH was3.5, and healingtemperature is55℃. Andthe reproducibility of the optimal prescription andtechnology was verified. Urea-formaldehyde resin with a strong adhesive was a majoradhesive in domestic and international wood industry. The microcapsules may stickeach other in the formation of microencapsulation. There were few literatures explorethe problem about microencapsulated anti-adhesion, so the effects of several additiveson the state of the microcapsules were investigation and the best adhesive wasobtained.The test of two-step had three parts: preparation of prepolymer, preparationof emulsion, preparation of microcapsules. In the test of preparing prepolymer,molecule ratios of urea-formaldehyde, pH, healing time and healing temperature wereinvestigated in single factor experiment, and the approximate range was determined.Via the orthogonal test, the best prescription and process parameters were obtained:molecule ratios of urea-formaldehyde is1.8, pH is8, healing temperature is75℃andhealing time is60min. And the reproducibility of the optimal prescription andtechnology was verified. Above all, the oil phase and emulsifier was selected in theexperiment of manufacturing emulsion. The mixture of methylbenzene andchlorobenzene with a proportion of3:4which dissolved Avermectins was determinedas the oil phase and the SMA was determined as the emulsifier. Approximate rangewas determined via single factor experiment, and the best condition was obtained bythe orthogonal test: stirring rate is6000rpm, emulsifying time is3min, the amount ofemulsifier is60%and the ratio of oil and water is1:1.8. In the test of preparingmicrocapsule, the core/shell ration was1:1.5firstly determined. Approximate range wasdetermined via single factor experiment, and the best condition was obtained by theCentral Composite Design: pH is4, stirring rate is700rpm，healing temperature is30~35℃. Finally, the effects of some suspending agents on microcapsule suspensionwere investigated and the best suspending agent and its concentration were selected. |
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