Spray Drying Assisted Controllable Preparation Of Colloidosomes And Study On Their Sustained Release Performance

Microcapsule is a typical material for encapsulating target substances,which has excellent properties,such as protection,stability improvement and sustained-release performance of the encapsulated core materials.At present,microcapsules have been widely used in a range of fields,such as medicine,agriculture,cosmetics and food.Colloidosomes with a uniform pore size distribution can encapsulate small molecules,and their sustainedrelease performance are stable.In addition,colloidosomes have a broad application prospect and research value.However,the preparation of colloidosomes,which are made by traditional Pickering emulsion method,needs to use a large amount of oil phase solutions,and part of the products have to be lost during the final separation of the oil phase,which declines the production efficiency.And the operation process is relatively complex and the cost is high.For this reason,this thesis proposes to use a spray drying method to prepare colloidosomes.The spray drying is a quick and one-step synthesis process and it is suitable for large-scale production.In this thesis,the latex particles used as shell materials were prepared by emulsion polymerization.The colloidosomes with controllable shell porosities were constructed by spray drying.The process conditions and the regulation rules of latex particle synthesis and the colloidosomes preparation process were investigated.The encapsulation of Congo red and the sustained-release process of colloidosomes were further studied.The main research contents and results are as follows:1.The latex particles,which are used as shell materials,were prepared by emulsion polymerization.The effects of the emulsifier quantity,initiator quantity,ratio of oil to water,and ratio of monomers on the latex particle size and size distributions were investigated.The optimal polymerization process conditions were obtained as follows:The quantity of emulsifier(sodium dodecyl sulfonate)and initiator(potassium persulfate)was 0.3 wt%and 0.4 wt%,the oil-water ratio was 1:8,and the reaction time was 10 h in a water bath at 87?.The latex particles obtained are uniformly spherical,with a narrow size distribution of 75-80 nm.Furthermore,the latex particles with different glass transition temperatures(42-87?)were prepared by adjusting the monomer ratio,and their particle size distributions were very close.2.The colloidosomes were further prepared by spray drying using the above latex particles as the shell materials.The effects of solid content of latex particles,flow rate compressed air,feed rate and inlet temperature on size distribution and sphericity of colloidosomes were investigated.The colloidosomes solid powders were produced and optimal process conditions were obtained as follows:The amount of ethanol in the solution was 20 vol%,solid content of latex particles was 4 wt%,flow rate of compressed air was 536 L/h,inlet temperature was 100?,and the feeding rate was 20.9 mL/min.The particle size distribution was 2-10 ?m,with good sphericity,and very few broken colloidosomes were observed.Further studies show that the feeding rate and inlet temperature co-affect the liquid evaporation rate during the drying process.The critical value curves and process condition range for the preparation of complete colloidosomes were obtained.With increasing the feeding rate,the average particle size of colloidosomes goes up.In addition,the BET specific surface area results of colloidosomes increase from 20.4 m2/g to 73.0 m2/g,and the BJH pore sizes increase from 5 nm to 20.7 nm with increasing the glass transition temperature of colloidosomes.3.Congo red was premixed with latex particle suspensions.The spray drying method was adopted to achieve in situ encapsulation of Congo red in the process of colloidosomes preparation.The sustained-release performance of colloidosomes was further studied.The results show that the colloidosomes encapsulating Congo red have a high spherical rate,and the encapsulation efficiency of dye molecules is about 16.5 wt%.The sustained-release rate and total release amount of dye molecules increase with the decrease of shell crosslinking degree.The release time was adjustable from 25 h to 52 h,and the highest release amount was up to 100%.The Higuchi model was further used to analyze the sustainedrelease behavior of the colloidosomes encapsulating Congo red,and the release process presents two stages.The lower cross-linking degree of the colloidosomes is,the closer the release rate constants of the two stages are.