| With the world population and food demand increasing, pesticides haveplayed an important role in improving people’s living standard to provide astrong guarantee of controlling insect pest of crops. However, it bringsenvironmental pollution and other issues. Microencapsulation of pesticidescan not only extend the same dose of pesticide persistence, but also improvethe utilization of pesticides and reduce the amounts of drugs, thereby reducingenvironmental pollution. It is very important to china to studysustained-release pesticide formulations on theory and application.Acetamiprid is a novel broad-spectrum activity and has certain acaricidalefficiency pesticides with good control effect on aphids in fruit and vegetablesand other certain crops, but it is used commonly with a lot of harmfularomatic solvents which got restriction in developed countries. In the presentwork, acetamiprid microcapsules, which used melamine-formaldehyde resinas shell materials, were prepared by in-situ polymerization in order to extentthe release time of acetamiprid and reduce the organic solvents to theenvironment. The main work and results are as follows:1. Melamine-formaldehyde microcapsules loaded acetamiprid were prepared by3steps. Firstly, the prepolymer solution was synthesized bycondensation polymerization using melamine and formaldehyde as rawmaterials with the pH of8.5-9.0. Secondly, a stable O/W emulsion was gottenusing sodium dodecyl sulfate as emulsifier and acetamiprid-chloroform as oil.Thirdly, acetamiprid microcapsules were prepared successfully by in-situpolymerization while2wt%hydrochloric acid solution and4wt%poly (vinylalcohol) were used as curing agent and dispersant respectively.2. Effects of the mass ratio of melamine and formaldehyde, dosage ofemulsifier, amount of acid catalyst and curing time on the size distribution,surface morphology, drug loading and encapsulation efficiency ofmicrocapsules were discussed in detail. Results showed that:(1) Themorphology and size of microcapsules became smoother and smallerrespectively with the amount of emulsifier increasing, and the microcapsuleswith9μm could be gotten when the dosage of emulsifier is1%.(2)Microcapsules adhered severely if the mass ratio of shell and core was toohigh because there was excess shell to cover acetamiprid. On the contrary, itcouldn’t cover enough if shell/core weight ratio was too low. The maximumencapsulation efficiency of the microcapsules can reached80.4%when themass ratio of shell and core was3:1.(3) The maximum drug loading ofmicrocapsules reached24.5%when the amount of hydrochloric acid was2.7wt%. The drug loading of microcapsules was significantly reduced whilehydrochloric acid was less or higher than2.7wt%.(4) The capsule wallcouldn’t crosslink more completely if the curing time was too short. As aresult, the encapsulation efficiency of the microcapsules was low.3. The drug release properties of microcapsule were investigated underdifferent conditions. The results showed that:(1) The release property gotworse with the particle size of microcapsule decreased.(2) The releaseproperty was unchanged when the curing time was more than3h.(3) The release rate sped up with the temperature of drug delivery system increased.4. The liquidity performance results showed that the target microcapsuleshad good liquidity due to the angle between microcapsules and table is about30°.5. The storage performance of microcapsules at room temperature and60℃, the encapsulation efficiency, drug loading, surface morphology andrelease performance of microcapsule were investigated respectively. Theresults showed that the storage performance of microcapsules at roomtemperature is better because the weight of microcapsules reduced about10%after more than50days in60℃, and the encapsulation efficiency, drugloading of microcapsule were decreased and the release rate was acceleratedafter6months. |
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