Study On The Preparation And Properties Of Flufiprole-loaded Microcapsules

Microcapsules have great significance on decreasing application amount but increasing the work effect with the characteristics of extended-releasing and controlled-releasing effects.But so far microcapsule as a seldom-used pesticide formulation is still a bit immature.The preparation method is single and research methodology on properties and release mechanism is simple.Based on this,the paper selected flufiprole as test subject to prepare different kinds of microcapsuls by LBL technology.And in the process,we study the process routes and performance of the microcapsules.First,the best preparation conditions were determined and then the influce on releasing of microcapsuls were studied by varing coted layers,shell materials,slow-release conditions and the core materials.With simulating release kinetics equation,we studied the release mechanism of microcapsules prepared by LBL technology.The main results of this study are summarized as follows: 1.Preparation of microcapsules(1)Flufiprole were directly encapsulated with CS and ALG by LBL technology.The encapsulation rate and slow release performance of microcapsules prepared in different conditions were studied and determined the best preparation conditions: Assembly time of ervery wall was 20 min,the temperature was at room temperature,salt ion concentration of polyelectrolyte solution was 0.5 mol/L,pH was 5.1.(2)Microcapsules with different layers were prepared by CS/ALG?CS/SL?PAH/PSS respectively.The whole progress of the preparation was controlled by measuring the change of the Zeta potential and particle size and the morphology of microcapsules was characterized by microscope and SEM.The results of the experiment showed that The three types of microcapsules changed basically same.In company with the increasing of the number of coated layers the particle size increased,the zeta potential and apparent morphology changed accordingly,the zeta potential changed periodically and apparent morphology changed more rough gradually.The results of infrared spectrum indicated that there was primarily flufiprole in the prepared microcapsules and that also they were coated with polyelectrolyte as shell materials.(3)The core status here were divided into three kinds,which included the solution,oil suspending agent and solid particles.Solution contain methylene chloride and flufiprole,in oil suspending agent,corn oil as medium,3478 B as dispersant.The whole progress of the preparation was controlled by measuring the change of the Zeta potential and the morphology of microcapsules under microscope.2.Properties of microcapsules(1)Microcapsules with different assembly layers were prepared with CS and ALG as shell materials.Apparent morphology,encapsulation efficiency,drug loadings,photolysis resistance,slow-releasing performance and insecticidal activity of microcapsules were determined in the paper.The results of the experiment showed that the surface of the microcapsules was rougher than Flufiprole particles.With the increasing of coated layer numbers,encapsulation rate and the amount of drug loading both rised first then decreased.Drug loading of microcapsules coated with 4 layers reached a maximum value.Similarly,drug loading peaked of 83% when microcapsules were coated with 6 layers.In contrast,with the layer numbers increasing photodegradation rate of Flufiprole under the UV decreased obviously at beginning and then stabilized at 21.7% of 6 coated layer numbers.(2)Microcapsules with 4 layers prepared by the above mentioned three materials.Encapsulation rate,drug loadings,photolysis resistance,slow release performance,insecticidal activity of microcapsules were determined.The results of the experiment showed that the difference of encapsulation rate and drug loadings was same,from large to small is PAH /PSS,CS / SL,CS /ALG;Photolysis resistance from strong to weak was CS /ALG,PAH /PSS,CS / SL3.Release properties of microcapsules(1)Release properties of microcapsules with different assembly layersReleases of microcapsules are much the same as in those microcapslues released sharply at the beginning and then the release rate slowed down gradually.Meanwhile with the increasing assembly layer numbers the slow release performance increased and the pesticide works better,lasts Longer.(2)Release properties of microcapsules with different materialsMicrocapsules prepared by PAH /PSS have the best slow-release performance,and microcapsules prepared by CS /ALG and CS / SL were the same.(3)External environment effects on release properties of microcapsulesMicrocapsules coated 6 layers with CS and ALG as shell materials were selected as objective macrocapsuls.In this part,the influnce of release medium on release performance were studied from four different aspects: ethanol content,salt concentration,pH and temperature.The results of the experiment showed that release rate accelerated with the increasing of ethanoled when the pH of medium were neutral or alkaline,release rate increased significantly in acidic release medium.Raising the temperature of medium can significantly improve the release rate.(4)Release properties of microcapsules with different capsule core statusDifferent microcapsules release curves were simulated by kinetic equation.The results showed that: releases of three types of microcapsules are much the same as in those microcapslues released sharply at the beginning and then the release rate slowed down gradually.When the core status was solution,the release rate was the fastest.Meanwile,the core status was oil suspending agent the ralease rate was the slowest.4.Release kinetics of microcapsules(1)Release kinetics of microcapsules with different layersBringing the release dates that their cumulative release amount of microcapsules was less than 60% into model formula(Ritger Peppas),it will get the exactly similar corresponding n values showing that the release mechanism was the combination of Flake diffusion and eluviation control.(2)Releasing mechanism of microcapsules with different capsule core statusBy the aid of dynamics equation we created the release curves.The result revealed that Higuchi model model performed better with oil suspending agent and solid particles which was in agreement with the Fick's law.Core status being solution,release curves of the pesticide corresponded to zero order release kinetics equation.In the stage of slow release,release curves of microcapsules coating solution or solid particles were in line with the level 1 release kinetics equation.On the other hand,release curves of microcapsules coating oil suspending agent conformed to Higuchi model.