The Preparation,Phase Transformation And Drug Loading Properties Of Microcapsules Using Kaolinite-stabilized Pickering Emulsions As Template

Microcapsule technology has been widely used in medicine,agriculture,food and chemical industry for its characteristics of immobilizing substances and isolating the external environment,etc.However,the traditional microcapsules are often using surfactant-stabilized emulsion as a template,and the wall of microcapsules is formed by a single high molecular polymer,resulting in low thermal stability and encapsulation efficiency of the microcapsules.In this thesis,solid paraffin is utilized as the core of the phase change microcapsule,and liquid paraffin dissolved with Sudan red Ⅲ is used as the core of the drug-loaded microcapsules.The microcapsules are fabricated by interfacial polymerization using kaolinite-stabilized Pickering emulsion as template.The polymerization reaction of iso-perone diisocyanate(IPDI)and water at the oil-water interface leads to produce polyurea which is compounded with kaolinite at the oil-water interface to form the microcapsule wall.The paraffin is encapsulated in the microcapsule,and then microcapsules with organic-inorganic composite materials as microcapsule walls are prepared.Optical microscope,scanning electron microscope(SEM)and Fourier infrared spectrometer(FTIR)are applied to characterize the morphology and formation mechanism of microcapsules.Differential scanning calorimeter(DSC)and thermogravimetric analyzer(TGA)are employed for thermal analysis of phase change microcapsules,and ultraviolet spectrophotometer(UV-Vis)is used to analyze the sustained-release properties of drug-loaded microcapsules.The following conclusions have been obtained:Kaolinite polyurea microcapsule exhibits good core-shell structure and dispersibility,and morphology of microcapsules is regular and spherical.The shell of the microcapsule is composed of kaolinite and polyurea.The thickness of the microcapsule wall can be controlled by regulating the amount of IPDI added,and the particle size of microcapsules can be controlled by regulating the amount of kaolinite added and adjusting the emulsification speed.The particle size distribution of microcapsules is 15 ～ 80 μm,and the average particle size is 42 μm when the amount of kaolinite in the water is 2.5 wt% and the emulsification speed is 12,000 rpm.Kaolinite can be used as an emulsifier to stabilize the high internal phase Pickering emulsion(the oil phase volume fraction is more than 74%).And using the high internal phase Pickering emulsion as a template to prepare microcapsules can effectively increase the yield of microcapsules,but the microcapsules are prone to agglomeration and adhesion.Phase change microcapsules are prepared by replacing liquid paraffin in microcapsules with solid paraffin.The microcapsule wall composed of kaolinite polyurea shows a certain plasticity,which can satisfy the volume change of the phase change material affected by temperature.The composition of the microcapsule wall do not contain any surfactants or dispersants,and the effect of the microcapsule wall on the absorption and release of heat by the phase change material during the phase transformation is small.Thus,thermal stability of microencapsulated phase change materials have been improved.The latent heat of phase transition is 175.7 J/g,the encapsulation rate is 85.3%,and the thermal decomposition temperature can be reached 218 ℃ when the microcapsule wall thickness is 0.27 ～ 0.73 μm.By mixing solid paraffin and liquid paraffin in a ratio of 9:1,mixed paraffin with low melting point of 28.6 ℃ can be prepared,and the encapsulation rate of phase change microcapsules prepared by mixed paraffin with low melting point as core material is 72%.Sudan red Ⅲ is dissolved in liquid paraffin and used as core material to prepare drugloaded microcapsules.22% of Sudan red Ⅲ in microcapsules is not released after the drugloaded microcapsules are sustained-released in anhydrous ethanol for 45 h,and the release mechanism of Sudan Red III in microcapsules obeys Fick diffusion.Increasing the thickness of the microcapsule wall and reducing the particle size of the microcapsules are conducive to slow down the release rate of Sudan Red III in the microcapsules.