The Research Of Preparing Ragweed Extracting Substance Microcapsule By Complex Coacervation

Microencapsulation is a process which coats the solid, liquid and gas substance. The natural and macromolecule material are chosen as capsule wall or envelope peplos which are used for coating active substance of core material. It will become the capsule membrane particles which has the property of semipermeability and tightness. The microencapsulation can avoid the core material losing activity because of the effect of external environment. The ragweed extracting substance was selected as botanical pesticide to carry microencapsulation in this paper. The botanical pesticide was easy to losing activity due to illumination, temperature and so on. Thus, its biological activity will prolong by preparing it into microcapsule formulation. The ragweed extracting substance, chitosan, gum Arabic and sodium lignosulphonate were chosen as core material and shell material, respectively. The chitosan/gum Arabic-ragweed extracting substance microcapsule and chitosan/sodium lignosulphonate-ragweed extracting substance microcapsule were prepared by using complex coacervation method. The single factor experiment and orthogonal experiment was performed. Furthermore, the property of the microcapsule which includes morphological characteristics, particle size analysis, infrared spectroscopy characterization, thermogravimetric Analysis, controlled-release experiment and indoor toxicity measurement were also measured. The results were shown as follows.The optimum condition of the preparation of chitosan/gum Arabic-ragweed extracting substance microcapsule was obtained. The chitosan concentration was0.8%, gum Arabic concentration was2.5%, the ratio of core material and shell material was1:1.5, pH value of forming microcapsule was3.8, the time of forming microcapsule was70min. The order of effect to microcapsule was the ratio of core material and shell material> gum Arabic concentration> chitosan concentration> pH value of forming microcapsule> the time of forming microcapsule. The measurement of the property of microcapsule manifested that the appearance of microcapsule was regular and the surface was smooth. The infrared spectroscopy characterization showed that the ragweed extracting substance was coated in the microcapsule successfully. Moreover, the median diameter of microcapsule was21.48μm from the particle size distribution. And the most of the particles were distributed in the range of13.50-41.33μm. The thermostability of chitosan/gum Arabic-ragweed extracting substance microcapsule was superior to ragweed extracting substance because of the protection effect of shell material. In addition, the release rate of chitosan/gum Arabic-ragweed extracting substance microcapsule was slow. The weight loss of chitosan/gum Arabic-ragweed extracting substance microcapsule was approximately29%until the experiment finished while the weight loss of ragweed extracting substance was up to82%. Eventually, the indoor toxicity measurement demonstrated that the. chitosan/gum Arabic-ragweed extracting substance microcapsule had the effect of controlled release. Not only did it improve the mortality ratio, but it also protected the core material from volatilizing quickly.The optimum condition of the preparation of chitosan/sodium lignosulphonate-ragweed extracting substance microcapsule was obtained. The chitosan concentration was0.4%, sodium lignosulphonate concentration was2%, the ratio of core material and shell material was1:2.5, pH value of forming microcapsule was4, the time of forming microcapsule was60min. The order of effect to microcapsule was the ratio of core material and shell material>the time of forming microcapsule> sodium lignosulphonate concentration>chitosan concentration>pH value of forming microcapsule. The measurement of the property of microcapsule manifested that the appearance of microcapsule was regular. The infrared spectroscopy characterization showed that the ragweed extracting substance was coated in the microcapsule successfully. Moreover, the median diameter of microcapsule was25.77μm from the particle size distribution by applying laser particle analyzer. And the most of the particles were distributed in the range of15.43-49.84μm. The thermostability of chitosan/sodium lignosulphonate extracting substance microcapsule was superior to ragweed extracting substance because of the protection effect of shell material. In addition, the release rate of chitosan/sodium lignosulphonate-ragweed extracting substance microcapsule was slow. The weight loss of chitosan/sodium lignosulphonate-ragweed extracting substance microcapsule was approximately29%until the experiment finished while the weight loss of ragweed extracting substance was up to82%. Eventually, the indoor toxicity measurement demonstrated that the chitosan/sodium lignosulphonate-ragweed extracting substance microcapsule had the effect of controlled release. It lengthened the pesticide effect and preserved the biological activity of core material. As a consequence, the mortality ratio was improved. Not only did it improve the mortality ratio, but it also protected the core material from volatilizing quickly.It can be concluded that microencapsulation of ragweed extracting substance was superior to the ragweed extracting substance.