Preparation Of Insect Sex Pheromone Containing Microcapsules By Complex Coacervation And Their Release Behavior

To protect forest and agriculture from various pest infestations, a lot of pesticides have been used. But most of them are toxic and environment pollutants. To reduce these harmful impacts, pesticides based on insect sex pheromones have been proposed. It is known that insect mating is performed through pheromone release by female moth to attract males. Their mating process will be disrupted or ceased if one can control female pheromone release to disrupt their mating and so that to control insect reproduction.In this paper, we used one controlled release formulation named microencapsulation which was carried out by complex coacervation for loading insect sex pheromone. The obtained devices permit protection and conservation of insect sex pheromones and lead to a higher biological efficacy and improve work efficiency.In this work, poly-2-trimethylammonium ethyl methacrylate chloride (PDMC) and whey protein (WP) were chosen to coacervat, respectively, with gum acacia (GA) to form microcapsules. Dodecanol (C12H25OH), a simulacrum of insect sex pheromones, was used as the core material in the first step. Based on the primary results, insect sex pheromones species were encapsulated. With different shell/core materials ratio, this work can be presented in 3 parts: (1) Encapsulation of dodecanol by complex coacervation between PDMC and GA; (2) Encapsulation of dodecanol by complex coacervation between WP and GA; (3) Encapsulation of insect sex pheromones species by complex coacervation between WP and GA.(1) Encapsulation of dodecanol by complex coacervation between PDMC and GA. In a first step, complex coacervation of PDMC and acacia was optimized by varying experimental conditions. It was observed that a maximum complex coacervation yield of 89% was achieved with 4% of polymer concentration for the wall materials at GA/PDMC ratio of 3.22. The optimized system was used for the encapsulation of dodecanol. Increasing shell/core ratio, the loading was decreased, and the release rate was decreased thereby. Microcapsules manifested a three-step-release profile, i.e. a quick start followed by a constant plateau region and terminated by a release increase.(2) Encapsulation of dodecanol by complex coacervation between WP and GA. After the optimization of complex coacervation between WP and GA, dodecanol was encapsulated. It was shown that maximum complex coacervation yield could be achieved with 1% polymer concentration for the wall materials at WP/GA ratio of 1.5 and pH 3.5. 3% of Polyvinylpyrrolidone (PVP) relative to wall and core materials was also used. With the same polymer concentration, increasing shell/core ratio, the encapsulation rate was increased, while the loading was decreased and so was the release rate. Release rate was suppressed by addition of glutaraldehyde as the crosslink agent. Compared with PDMC/GA system, microcapsules formed by WP/GA manifested a three-step-release profile too, but with a shortened initial fast release at start, and a longer constant plateau region. As to encapsulation rate, microcapsules formed by WP/GA was much higher, it seemed that WP/GA system was much more feasible for encapsulation.(3) Encapsulation of insect sex pheromones species by complex coacervation between WP and GA. The optimized WP/GA system was used for the encapsulation of insect sex pheromone component oleyl acetate (i.e. cis-9-Octadecenyl acetate), synthesized in our lab by esterification between oleyl alcohol and acetic anhydride in the presence of p-toluenesulfonic acid as catalyst. It was found that the optimum experiment conditions for oleyl alcohol esterification were oleyl alcohol/ acetic anhydride ratio of 1/1.7 by moles, reaction temperature at 25℃for 3 hours. Similar to the encapsulation of dodecanol, the encapsulation rate was increased when increasing shell/core ratio at the same polymer concentration, while the loading and release rate were both decreased. Release rate was suppressed by addition of crosslink agent. It indicated that release of core material could be well controlled through capsule structure design. Microcapsules with hollow structure were investigated by scanning electron microscope. It was presumed that insect sex pheromone component was encapsulated in the inner of the microcapsules with shell/core structure. Compared with encapsulation of dodecanol, microcapsules with insect sex pheromone as core material manifested a less obvious three-step-release profile, and the release rate was much lowed and that release process could cover whole insect mating period to avoid repeated application.