溶剂挥发法制备萃取剂微胶囊

萃取剂微胶囊的制备是利用微囊化方法将萃取剂包覆起来 ,解决传统液液萃取中的两相相分散、相混合、相分离以及溶剂的损失和设备结构复杂等问题 .用简单易控制的溶剂挥发法成功制备了聚砜及聚苯乙烯材料包覆的多种萃取剂 (如磷酸三丁酯 ,2 乙基己基磷酸 ,三辛胺和Aliquat 336 )微胶囊 ,并考察了壁材和分散剂的选择对不同萃取剂进行包覆的影响 ,同时研究了搅拌速度和膜溶液组成对微胶囊的形态、萃取剂包覆量的影响 .结果表明 ,(1)用聚砜作壁材可以包覆磷酸三丁酯、2 乙基己基磷酸 ,而用聚苯乙烯可以包覆三辛胺、Aliquat336 ;(2 )对于不同的O W乳液体系 ,只有选择合适的分散剂 ,才能得到理想球形状、分散性好的微胶囊 ;(3)增大搅拌速度可以降低液滴尺度 ,从而减小微胶囊粒径 ;(4)膜溶液组成的影响则表现在两个方面 ,一是膜溶液的粘度和两相界面张力是除搅拌速度外微胶囊粒径的决定因素 ,二是膜溶液中壁材与萃取剂的比例优化时 ,才能得到萃取剂包覆量高的微胶囊 .     

用溶剂蒸发法研制维生素C微胶囊

本文用溶剂蒸发法研制了以乙基纤维素、羟两基甲基纤维素苯二甲酸酯等聚合物为包覆材料的维生素C微胶囊,探讨了微胶囊化的条件和包覆效果,并测定了微胶囊的载药量及其溶解释放性能。     

Microencapsulation of cholesteryl alkanoate by polymerization‐induced phase separation and its association with drugs

A new microencapsulation technique is presented in which cholesteryl nonanoate (CN)/poly(methyl methacrylate) (PMMA) microcapsules are produced by the induction of phase separation between CN and PMMA within the droplets during the polymerization. The concentration of CN is the most important factor determining the final morphology of the microcapsules. For example, a polynuclear type is obtained at a low concentration (<20 wt %), a mononuclear type is obtained at a medium concentration (20–30 wt %), and an irregular phase is obtained at a high concentration (>40 wt %). To evaluate the effectiveness of the technique for stabilizing an unstable drug, we selected retinol (vitamin A) as a model drug and loaded it into the CN/PMMA microcapsules. We used a process called solute codiffusion, in which a fine solvent emulsion containing the retinol was diffused uniformly into the CN/PMMA microcapsules. The loading efficiency of retinol was predicted successfully with the aid of a thermodynamic equation. In the thermal stability test of retinol, we found that an effective association with the CN phase was the most important factor determining the limit of its molecular stability. The technique reported in this article has great potential for the microencapsulation of soft materials via a simple process and for the stabilization of unstable drugs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2202–2213, 2004     

Influence of operation conditions on the microencapsulation of PCMs by means of suspension-like polymerization

Microcapsules containing PRS® paraffin wax (core) and a polystyrene shell were prepared by suspension-like polymerization. The influence of reaction temperature, stirring rate, and mass ratio of paraffin wax to styrene on the properties of phase change materials microcapsules was studied. The reaction temperature had not a significant effect on the size of the microcapsules but an increase of molecular weight and a narrow molecular weight distribution of polystyrene shell were observed when reaction temperature was increased. An exponential relationship between the stirring rate and the mean particle diameter in number has been found. It was observed that paraffin is difficultly encapsulated when the paraffin/polymer mass ratio was higher than 2.00, as a consequence of a shortage of polymer that could not completely cover the amount of paraffin added. However, when a large proportion of monomer was employed, the polymer tended to polymerize inside the droplets during the microencapsulation process forming complex inner structures. The microcapsules obtained have an interesting energy storage capacity of 153.5 J/g that makes them suitable for different applications.     

Preparation of biodegradable microcapsules through an organic solvent‐free interfacial polymerization method

We prepared microcapsules through an organic solvent‐free interfacial polymerization method, which avoids the release of volatile organic compounds arising from conventional interfacial polymerization methods for microencapsulation. These microcapsules have single and narrow particle size distribution and are spherical pellets with smooth and intact shell, and own excellent biodegradability. Additionally, these biodegradable microcapsules have a higher encapsulation efficiency compared with the microcapsules prepared through conventional interfacial polymerization method and possess sustained and controlled release of core materials.     

Novel microencapsulated liquid fire extinguishers with a nanomodified microcapsule shell

A new process has been developed for the microencapsulation of ecologically safe and highly effective fire extinguishers, including the perfluoroketone Novec 1230 (whose Russian analog is Khladon PFK-49), which has enhanced stability for use as a basic functional component in fire-extinguishing polymer materials. When Freons are microencapsulated via common methods, an intense loss of the liquid core of the microcapsule in the course of drying and storage via diffusion through the shell occurs. The stabilization effect was attained through modification of the microcapsule shell material via addition (at the stage of shell formation) of nanoparticles of the mineral layered filler montmorillonite. The processes of thermal degradation of the resulting microcapsules have been studied and a substantial improvement in stability (reduced permeability of the shell) and, hence, the possibility of their application has been shown. Laboratory fire tests of materials were performed, and the high effectiveness of fire extinguishment by microencapsulated perfluoroketone and the fire-extinguishing polymer material has been demonstrated.     

Microencapsulation of Fish Oil by Simple Coacervation of Hydroxypropyl Methylcellulose

To improve the oxidative stability and application of fish oil, it was microencapsulated by simple coacervation followed by spray drying. Simple coacervation took place by adding malt dextrin into the emulsion of fish oil and hydroxypropyl methylcellulose （HPMC） solution. Influences of several process parameters on the microencapsulation were evaluated and the oxidative stability and microstructure of microcapsules were analyzed. Results showed that the coacervation could be observed only when dextrose equivalent value （DE value） of malt dextrin, concentration of HPMC solution and fish oil percentage in microcapsules were no more than 20. 5% and 40%, respectively. Moreover, microencapsulation efficiency was higher at HPMC solution concentration of 4% and fish oil percentage of less than 30%. The oxidative stability of fish oil was improved by the microencapsulation and done best in the ease of replacing malt dextrin by 40% with acacia. Scanning electronic microscopic photographs showed that the microcapsule obtained was a round, smooth and hollow microcapsule with its wall made up of innumerable small and solid submicrocapsules with the core of fish oil.     

Microencapsulation of dichromate and paracetamol with Eudragit Retard polymers using phase separation by nonsolvent addition

A coacervation technique for microencapsulation using Eudragit Retard polymers [poly(methyl methacrylates) substituted by quaternary ammonium groups] as wall material is described, based upon phase separation using a cold chloroform-cyclohexane mixture together with polyisobutylene as a stabilizer. The effect of various parameters on the nature and properties of the microcapsules of potassium dichromate and paracetamol has been studied, in particular the alteration in wall content and structure and release rate of contents. The microcapsules are discrete, their properties are reproducible, and various degrees of sustained release are obtained.     

Effects of protective colloids on the preparation of poly(l-lactide)/poly(butylene succinate) microcapsules

Poly(l-lactide)/poly(butylene succinate) microcapsules containing an aqueous solution of sodium(+)-tartrate dihydrate were prepared by the interfacial precipitation method through solvent evaporation from (w/o)/w emulsion. The effects of poly(vinyl alcohol) used as a protective colloid in the microencapsulation were investigated regarding thermal properties, particle size distributions, surface morphologies, and release behaviors of the biodegradable microcapsules. It was concluded that encapsulation efficiency, surface morphologies, thermal properties, and releasing speed were closely related to the particle size distributions of microcapsules under different conditions of the protective colloid.     

Microencapsulated fire-extinguishing fluids and reactive fire-extinguishing composites formed on their basis

The application of microencapsulated liquid gasifiable fire-extinguishing agents as reactive filling compounds for fire-extinguishing composites is considered. A new process for microencapsulation of environmentally friendly fire-extinguishing agents possessing enhanced stability is designed. Novel composite materials are produced with these agents. The thermal-destruction processes of microcapsules containing liquid gasifiable fire-extinguishing agents of different compositions are considered. Laboratory and bench-mark firing tests of the materials are performed.     

The effect of temperature and solvent on the morphology of microcapsules doped with a europium beta-diketonate complex

Fluorescent microcapsules doped with a europium beta-diketonate complex were fabricated for the first time by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer technique. The influence of temperature and solvent treatment on the morphology of the microcapsules was investigated. Intense red light emission of the microcapsules could be clearly observed by fluorescence microscopy before and after treatment. Remarkable shrinking, decrease of the inner volume and increase of the wall thickness were observed using atomic force microscopy (AFM) and transmission electron microscopy (TEM) after thermal treatment. The shrinkage induced by annealing could be recovered by dissolving in ethanol solution, which was confirmed by AFM and TEM. Morphology variation of the luminescent microcapsules induced by annealing or solvent are both attributed to the molecular rearrangement of polyelectrolytes. While the shrinkage by annealing is an entropy driven process with formation of more coiled conformations of polyelectrolytes the morphology variation by ethanol might be due to the effective screening of electrostatic interaction within the polyelectrolyte multilayers and the changed interaction between hydrophobic fragments present in the polyelectrolytes.     

Soy glycinin microcapsules by simple coacervation method

Encapsulation of a dispersed oil phase (hexadecane) was realized by simple coacervation method using soy glycinin as the wall forming material. Suitable emulsification and coacervation conditions, that favor the formation of microcapsules wall, were identified and investigated. Mild acid (pH 2.0) and heat (55 degrees C) treatments of the reaction medium during the emulsification step enhanced significantly the deposition of coacervated glycinin around oil droplets. A pronounced correlation between glycinin concentration in the continuous phase, specific surface of the dispersed phase and the microencapsulation efficiency was also observed. Coacervation step study concerned the morphology and the stability of microcapsules. Controlled initiation of the coacervation, by slow readjustment of the pH, allowed a homogeneous precipitation of glycinin around oil droplets as well as the absence of aggregation phenomena. Since the morphology of microcapsules was considerably affected by a prolonged stirring of the reaction medium, the coacervation and reticulation time were optimized in order to preserve the homogeneity of the microcapsules size distribution and the microencapsulation efficiency.     

Synthesis of functional microcapsules containing suspensions responsive to electric fields

A sort of functional microcapsules, which contain a suspension responsive to electric fields, is prepared by in situ polymerization of urea and formaldehyde. The suspension is made up of pigment phthalocyanine green (PPG) and tetrachloroethylene. In order to solve the particles' separation from the suspension during the microencapsulation and to obtain microcapsules applying to electronic ink display, the dispersibility of the particles, the contact angles between the particles and the tetrachloroethylene, and the influences of different emulsifiers on the microencapsulation are investigated. It is found that the dispersion extent and lipophilicity of the PPG particles are improved due to their surface modification with octadecylamine. The contact angles between the modified PPG particles and the tetrachloroethylene increase, and the PPG particles modified with 2 wt% octadecylamine have the best affinity for tetrachloroethylene. The interfacial tension between C(2)Cl(4) and H(2)O with urea-formaldehyde prepolymer descends from 43 to 35 mN/m, which indicates that the polymer has certain surface activity. However, water-soluble emulsifiers have an important influence during the microencapsulation because they can absorb on the surfaces of internal phase and prevent the resin of urea-formaldehyde from depositing there. From the SEM images of shell surface and cross section, the microcapsules have relatively smooth surfaces and the average thickness is about 4.5 mum. When the microcapsules are prepared with agitation rates of 1000 and 600 rpm, the mean diameters of the obtained microcapsules are 11 and 155 mum, respectively. The particles in the capsules move toward positive electrode with a responsive time of several hundred milliseconds while providing an electric field.     

Preparation of Microcapsules by Drying-in-liquid with a [(O_Ⅰ/W_Ⅰ)/O_Ⅱ]/W_Ⅱ Multi-emulsion

IntroductionMicrocapsule is a small container with amicrometer size sealed by solid membrane,whichhas a big specific surface area and semi-permeability.Up to now,a lot of research workhas been carried out on the slow release of corematerials,immobilized enzyme or bacterium[1— 3] .Recently its application has also been studiedwidely[4— 7] .Much progress has been made for theselection of the membrane material ofmicrocapsules,but the reports onmicroencapsulized method are seldom found,especiall…     

Theoretical investigation of water exchange on the nanometer-sized polyoxocation AlO4Al12(OH)24(H2O)12(7+) (Keggin-Al13) in aqueous solution

Reaction pathways, solvent effects and reaction parameters have been investigated for the water exchange on Keggin-Al13 in the aqueous solution by performing supermolecule density functional theory calculations. The calculated results suggest a dissociative (D) mechanism for water exchange on Keggin-Al13 in the aqueous solution and indicate that both the explicit solvent effect and bulk solvent effect have obvious influence on the energy barriers.     

Influence of process parameters on the size distribution of PLA microcapsules prepared by combining membrane emulsification technique and double emulsion-solvent evaporation method

Relatively uniform-sized biodegradable poly(lactide) (PLA) microcapsules with various sizes were successfully prepared by combining a glass membrane emulsification technique and water-in-oil-in-water (w₁/o/w₂) double emulsion-solvent evaporation method. A water phase was used as the internal water phase, a mixture solvent of dichloromethane (DCM) and toluene dissolving PLA and Arlacel 83 was used as the oil phase (o). These two solutions were emulsified by a homogenizer to form a w₁/o primary emulsion. The primary emulsion was permeated through the uniform pores of a glass membrane into the external water phase by the pressure of nitrogen gas to form the uniform w₁/o/w₂ double emulsion droplets. Then, the solid polymer microcapsules were obtained by simply evaporating solvent. The influence of process parameters on the size distribution of PLA microcapsules was investigated, with an emphasis on the effect of oil-soluble emulsifier. A unique phenomenon was found that a large part of emulsifier could adsorb on the interface of internal water phase and oil phase, which suppressed its adsorption on the surface of glass membrane, and led to the successful preparation of uniform-sized double emulsion. Finally, by optimizing the process parameters, PLA microcapsules with various sizes having coefficient of variation (CV) value under 14.0% were obtained. Recombinant human insulin (rhI), as a model protein, was encapsulated into the microcapsules with difference sizes, and its encapsulation efficiency and cumulative release were investigated. The result suggested that the release behavior could be simply adjusted just by changing precisely the diameters of microcapsule, benefited from the membrane emulsification technique.     

Microfluidic fabrication of polysiloxane/dimethyl methylphosphonate flame‐retardant microcapsule and its application in silicone foams

A novel and versatile route for fabricating flame‐retardant microcapsules via microfluidics technology is reported. The flame‐retardant microcapsules were prepared with a dimethyl methylphosphonate (DMMP) core and an ultraviolet‐curable (UV‐curable) polysiloxane shell. Furthermore, a UV‐curable polysiloxane was synthesized. The synthesis mechanism of UV‐curable polysiloxane and the curing mechanism of flame‐retardant microcapsules were analyzed. To verify that DMMP was encapsulated in the microcapsules, X‐ray fluorescence was used before and after microencapsulation. The resulting microcapsules were well monodispersed and exhibited a good spherical shape with a smooth surface. In addition, the size of the microcapsules decreased dramatically with an increasing flow‐rate ratio of the middle‐/inner‐phase or outer‐phase flow rate. The thermal stability of the microcapsules was worse than shell materials but superior to DMMP. Silicone foams (SiFs) with microcapsules prepared using a dehydrogenation method achieved a relatively higher limiting oxygen‐index value than the pure SiF, which indicated that the microcapsules could enhance the flame retardation of SiFs effectively. Because of the polysiloxane shell, the microcapsules had good compatibility with SiFs, and the influence of microcapsules on the mechanical properties of SiFs was unremarkable.     

Reactivity of ethyl acetate and its derivatives toward ammonolysis: ramifications for ammonolysis‐based microencapsulation process

The reactivity of three ester organic solvents toward ammonolysis was examined in relation to the development of an ammonolysis‐based microencapsulation process. Ethyl acetate, ethyl chloroacetate, and ethyl fluoroacetate were chosen as ester organic solvents. Progesterone was considered as a model drug to be encapsulated into poly‐D , L ‐lactide‐co‐glycolide microspheres. A polymeric dispersed phase was emulsified in an aqueous phase, to which ammonia was added to initiate ammonolysis. The polarization status of a carbonyl group in the backbone of the ester was found to decide the magnitude of the ester reactivity. In fact, the simple ester ethyl acetate hardly reacted with ammonia, while ethyl chloroacetate and ethyl fluoroacetate showed greater reactivity toward ammonolysis. The rapid completion of ammonolysis led to the conversion of the water‐immiscible solvents into water‐soluble solvents, thereby providing an efficient tool for microsphere solidification. Among microencapsulation parameters, the type of dispersed solvent, the molar ratio of ammonia to a dispersed solvent, and the percentage of the progesterone payload decisively influenced the characteristics of the microspheres. Subsequently, variations in such parameters accompanied considerable influence on microsphere morphology, incorporation efficiency, thermal behavior, the degree of residual solvents, and the physical status of progesterone. Optimization of the process parameters would not only contribute to improving the ammonolysis‐based microencapsulation process, but would also permit the tailoring of microsphere properties to specific demands. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of ammonium chloride and heat treatment on residual formaldehyde contents of melamine-formaldehyde microcapsules

Microencapsulated n-octadecane with melamine–formaldehyde resin (MF) shell was synthesized by in situ polymerization. Ammonium chloride was used to reduce the residual formaldehyde content of microencapsulated phase change materials (microPCMs) caused by the inherent characteristics of MF. Moreover, microPCMs were heat-treated at 160 °C for 30 min. The surface morphology of the microPCMs fabricated at various microencapsulation periods was examined, and the shell thickness was measured. The effects of heat treatment on the surface morphology, residual formaldehyde content, phase change properties, and thermal stability of the microcapsules were systematically investigated. The globular surface of microcapsules fabricated at microencapsulation period of 120 min was smooth and compact with an average diameter about 2.2 μm, and the shell thickness was ranged from 30 to 70 nm. The thermal stability of heat-treated microcapsules enhanced significantly as microencapsulation period increased; in addition, the residual formaldehyde content of microcapsules decreased from 125 ± 1 mg/kg to 19 ± 1 mg/kg.     

Preparation and Release Behavior of Ethylcellulose Microcapsules Containing Theophylline Dispersed in Cellulose Triacetate Matrices

Using ethylcellulose and cellulose triacetate as co-wall materials, sustained release microcapsules of theophylline were prepared. The solid drug dispersed in the cellulose triacetate matrices was first prepared by solvent evaporation; then the matrices were microencapsulated by means of coacervation-phase separation of ethylcellulose from toluene solution on addition of petroleum ether. The shapes and surface characteristics of theophylline, matrices and microcapsules were examined with a scanning-electron microscope. The release of theophylline from various particles into distilled water was studied. The microcapsules had good characteristics of sustained release. The period for theophylline to dissolve from ethylcellulose microcapsules containing cellulose triacetate matrices was larger than those from only ethylcellulose microcapsules with a similar ratio of core to wall. The half-time increased with increasing content of cellulose triacetate. The release pattern which was analogous to that from only ethylcellulose microcapsules obeyed a first-order equation.