Full factorial design‐of‐experiments for preparation of crosslinked dextran microspheres

This work describes full factorial design‐of‐experiment methodology for exploration of effective parameters on physical properties of dextran microspheres prepared via an inverse emulsion (W/O) technique. Microspheres were prepared by chemical crosslinking of dextran dissolved in internal phase of the emulsion using epichlorohydrin. The input parameters were dextran concentration in the aqueous phase, crosslinking ratio, and concentrations of sodium hydroxide and span 80 as the reaction catalyst and surfactant, respectively. Chemical structure of the resulting microspheres was analyzed spectroscopically using Fourier‐transform infrared technique. Final decomposition temperature, mean particle size and its distribution and equilibrium swelling ratio were selected as output responses. Microspheres with smooth surface were obtained according to scanning electron micrographs. It was found that an increase in dextran concentration in the aqueous internal phase increases mean particle diameter of the resulting microspheres, significantly. Moreover, water uptake capacity for the microspheres was dependent on both the dextran concentration and crosslinking ratio. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

单分散多孔聚合物微球的制备及其反相色谱应用

用分散聚合的方法制得单分散微米级聚苯乙烯微球(PS),以此聚苯乙烯微球作为种子,以邻苯二甲酸二丁酯为溶胀剂,苯乙烯为单体,二乙烯基苯为交联剂,甲苯为致孔剂,采用种子溶胀聚合的方法制得粒径分布较窄的多孔高交联的聚苯乙烯-二乙烯基苯微球(PS-DVB)。研究了交联剂与致孔剂的加入量对微球形貌、粒径及孔结构参数的影响。结果表明,所得多孔微球球形圆整,库尔特测得平均粒径为5.067~5.520μm,粒径分布窄,D90/D10为1.23~1.56,孔结构可控,并以此多孔微球作为反相色谱填料基质,理论塔板数每米可达6 000~15 000,可以用作高效液相色谱(HPLC)填料。     

2‐Hydroxyethylmethacrylate carrying uniform porous particles: preparation and electron microscopy

Uniform macroporous particles carrying hydroxyl groups have been obtained in the size range 3–11.5 µm by seeded polymerization. For this purpose, uniform polystyrene particles in the size range 1.9–6.2 µm were used as seeds. The seed particles were successively swollen by dibutyl phthalate (DBP) and a monomer mixture comprising styrene, 2‐hydroxyethylmethacrylate (HEMA) and a crosslinker. Two different crosslinkers, divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA), were tested. Size distribution properties together with bulk and surface structures of the particles have been characterized by both scanning and transmission electron microscopy. While EGDMA provides uniform particles with a non‐porous surface, DVB produces uniform particles having a highly porous surface and interior. The comparison of FTIR and FTIR‐DRS spectra shows that the HEMA concentration is higher on the particle surface than within the particle interior. Seed latex size and monomer/seed latex ratios are identified as the most important variables affecting the final particles. Different seed latexes have been tried; the result is that highly macroporous particles with a sponge‐like pore structure both on the surface and in the particle interior have been obtained by use of the seed latex with the largest particles and the lowest molecular weight. An increase in the HEMA feed concentration leads to final particles with a non‐porous surface and a crater‐like porosity in the particle interior. The average pore size significantly decreases with increasing DBP/seed latex and monomer/seed latex ratios. © 2001 Society of Chemical Industry     

Novel method of preparation of a charged mosaic membrane by using dipole‐like microspheres. II. Preparation of dumbbell/egg‐like microspheres

The dumbbell‐like/egglike microspheres of poly(4‐vinylpyridine/n‐butyl acrylate)/polystyrene [P(4VP/nBA)/PS] were prepared by soap‐free seed emulsion polymerization. The effects of various polymerization parameters, such as the amount of ethyl acetate (EA) in the continuous phase, swelling time, degree of crosslinking of seed polymer, polymerization temperature, and compatibility of seed polymer and the secondary polymer, and so forth, on the formation of dumbbell‐like/egglike morphology were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that secondary particles could be eliminated either by drastically increasing the number of seed particles or by stripping EA from the seed latex by dialysis and evaporation under a vacuum. Swelling the seed particle with the secondary monomer was essential for the preparation of egglike microspheres. For the localization of PS domains on one side of the egglike particle, the most effective factors were to elevate the polymerization temperature up to 90°C and simultaneously to lower the compatibility of the polymer on the seed particle surface with the phase of PS, while using the uncrosslinked seed latex. Crosslinking the seed latex was not suitable for localizing the PS domains in the seed particle, especially when the degree of crosslinking exceeded 0.5 wt % of EGDMA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2002–2017, 2001     

相分离-溶胀法制备生物可降解PELA多孔纳米微球

采用相分离-溶剂去除法制备纳米尺度的单甲氧基聚乙二醇-聚乳酸共聚物(PELA)微球,分析了纳米微球在溶液中的形成机理;用有机溶剂对纳米微球进行溶胀制孔,制备出具有不同孔道特征的纳米微球. 结果表明,以乙醇+丙酮为油相、去离子水为水相,油相中PELA含量6.5 g/L、水相中SDS含量1%、油与水相体积比1:6、油相中乙醇含量50%(j)条件下,所制微球粒径为78.48 nm. 溶胀时间为0.5 h时,以甲苯为溶胀剂所制PELA微球具有中空单孔结构,以二氯甲烷为溶胀剂所制PELA微球具有多孔结构. 用相同方法制备了具有孔结构的聚乳酸、聚(乳酸-羟基乙酸)共聚物纳米微球,其与PELA的成孔趋势相同. 以模拟体液考察多孔PELA纳米微球的降解性能,30 d可充分降解.     

Preparation of monodisperse magnetic polystyrene microspheres and its surface chemical modification

Monodisperse magnetic polystyrene (PS) microspheres were prepared in the presence of PS seed particles and styrene‐based magnetic colloid by the method of magnetic colloid swelling polymerization. The PS seed particles were prepared in advance by soap‐free emulsion polymerization. Styrene‐based magnetic colloid was used for swelling the PS seed particles in the magnetic colloid swelling polymerization process. After polymerization, functional amino groups were introduced onto the surface of the magnetic PS microspheres by surface Friedel‐Crafts acylation reaction. The morphology, size distribution, and magnetic properties of magnetic PS microspheres were characterized with scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM), respectively. SEM showed that the magnetic PS microspheres had an average size of 1078 nm with a narrow size distribution. VSM showed that the magnetic PS microspheres were superparamagnetic, and saturation magnetization was found to be 5.714 emu/g. The concentration of functional amino groups on the surface of magnetic PS microspheres was measured by atomic absorption spectroscopy and UV−Vis spectroscopy, and the concentration of amino groups was found to be 0.168 mmol/g. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study on Preparation of Insensitive and Spherical High Bulk Density Nitroguanidine with Controllable Particle Size

In this study, the solventing‐out recrystallization method was applied to prepare insensitive and spherical high bulk density nitroguanidine (NQ). Experiments were performed at various operating conditions by using N‐methyl‐pyrrolidone (NMP) and acetone as solvent and antisolvent, respectively. The effects of different operating parameters such as NQ/NMP ratio, amount of acetone used, crystallization temperature, stirring speed and stirring time were investigated. The particle size and morphology of the prepared NQ crystals were observed by scanning electron microscopy (SEM), the bulk density was measured by the Archimedes’ method and the impact sensitivity was determined by fall hammer method. The experimental results showed that the solventing‐out recrystallization method could be used to prepare spherical high bulk density NQ with a narrow particle size distribution and the particle size could be controlled by changing the operating conditions. The bulk density of these spherical NQ particles was found to be in the range of 0.94–0.97 g cm⁻³, which is higher than that of needle‐shaped NQ particles, and they became less sensitive towards impact.     

二元溶剂体系对泡沫传输制备聚苯乙烯微球的影响

采用二氯甲烷（DCM）和丙酮（AC）组成二元溶剂体系,考察了二元溶剂体系对制备聚苯乙烯（PS）微球时泡沫的传输和微球性能的影响,并探讨了对应的作用机理。实验结果表明,随着AC质量分数的增加,体系的出泡温度升高,PS微球的平均粒径下降且粒径分布逐渐变窄,微球的结构由多孔逐渐演变为中空。这主要是由于AC对水具有一定的亲和性,会往连续相迁移,改变连续相的表面张力,并在油水界面形成一个AC/DCM的混合液膜层,该液膜层改变了溶剂挥发的过程,最终实现对微球粒径和结构的调控。     

种子溶胀法制备单分散多孔聚合物微球的溶胀动力学研究

以微米级聚苯乙烯为种球,进行了两步种子溶胀法制备多孔聚合物微球的溶胀动力学研究,用光学显微镜、马尔文粒度分析仪、扫描电镜(SEM)和比表面积孔径分布测定仪(BET)等手段,对微球的溶胀形貌和孔结构进行了表征,优选出较好的溶胀条件是:以邻苯二甲酸二丁酯为溶胀剂,用超声乳化方式制备乳液,单位质量种球所用溶胀剂量为1.5mL,在35℃下10h即可完成溶胀,得到粒径分布良好的活化微球。研究发现,超声乳化分散方式的引入,可将溶胀时间由传统的24h缩短至10h,这可能是由于超声波的空穴效应所产生的巨大磁场加速了溶胀平衡状态建立的缘故。     

Optimization of Solvent Extraction of Moringa (Moringa Oleifera) Seed Kernel Oil Using Response Surface Methodology

Extraction of seed kernel oil from moringa (Moringa oleifera) was investigated with hexane, petroleum ether and acetone as the first extraction medium at various kernel particle size, extraction temperature and residence time, which were called as independent variables. Central composite rotatable design (CCRD) of experiments was used to study the effect of solvent type, particle size, extraction temperature and residence time of solvent on the oil yield, which was called as dependent variable. The maximum oil yield of 33.1% for hexane, 31.8% for petroleum ether and 31.1% for acetone was obtained. Among the three solvents, hexane yielded the maximum oil from moringa seed kernels. Among three process parameters studied, particle size had the most significant effect on the oil yield followed by extraction temperature and time for all the solvents. Response surface methodology technique was used to optimize the independent variables for maximum oil extraction. From the optimized values of particle size (0.62 mm), extraction temperature (56.5°C) and residence time (7 h), maximum oil yield obtained was 33.5%, using hexane. Optimized values of independent variables for maximum yield were varied for other two solvents. This protocol provides improved opportunities for the medicinal use of moringa oil in addition to its popularity as a vegetable in south Asia.     

Formation of biodegradable polymeric fine particles by supercritical antisolvent precipitation process

The supercritical antisolvent (SAS) precipitation process as a “green” alternative to specialty particles recrystallization was successfully used to generate poly(L ‐lactide) acid (L‐PLA) from dichloromethane (DCM) solution using CO₂ as antisolvent. The influence of main operating parameters on the synthesis of L‐PLA particles in the SAS process was methodically examined. In particular, antisolvent addition rate (30, 40, 50, and 60 g/min), temperature (35, 40°C, 45°C, and 50°C), solute concentration (50, 75, 100, and 150 mg/10 ml), and solution addition rate (1, 2.5, 5, and 7.5 ml/min). These parameters could be tuned to give a mean particle diameter of 0.62 μm. It was found using scanning electron microscopy and laser diffraction that increasing the antisolvent addition rate and the solution addition rate, while decreasing the temperature and solute concentration, led to a decrease in the L‐PLA mean particle diameter. Furthermore, a unimodal particle size distribution was obtained at the higher solution and antisolvent addition rates. Spherical‐like primary particles have been obtained in all the experimental runs; thus, no change of particle morphology with the process parameters has been noticed. These results manifested that SAS recrystallization process is a valuable technique to generate reproducibly polymer particles with controlled size and size distribution. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Preparation of aqueous dispersible polyurethane: Effect of acetone on the particle size and storage stability of polyurethane emulsion

An aqueous dispersible polyurethane was prepared by the reaction of hydroxyl‐terminated poly(ethylene adipate), dimethylol propionic acid, 4,4′‐diphenylmethane diisocyanate, and ethylene glycol. Formation of the dispersion was achieved by phase inversion of an acetone solution of the polyurethane with water, utilizing carboxylate anion groups as the internal emulsifying sites. The amount of acetone added has a large effect on the particle diameter (0.08 to 8.61 μm) and particle size distribution of the polyurethane emulsion. The storage stability was evaluated in terms of particle size distribution breadth. The aqueous emulsion obtained with no use of acetone was sufficiently stable in storage for at least 6 months. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3455–3461, 2004     

Preparation of griseofulvin microparticles by supercritical fluid expansion depressurization process

The supercritical fluid expansion depressurization (SFED) process is a novel technique proposed recently to prepare microparticles with narrow size distribution. The process has shown a very promising potential in pharmaceutical micronization. An SFED experimental apparatus was set up and griseofulvin (GF) microparticles were prepared successfully with the solvent of the mixture of acetone and ethanol. The influences of the operation parameters, including the pressure and temperature in the mixing vessel, the solution concentration and the solution feeding rate, on the particle morphology, size and size distribution were investigated in detail. The results show that approximately spherical particles with size less than 1.5 μm can be prepared successfully by SFED process. The pressure in the mixing vessel and the solution feeding rate are two most effective parameters while the solution concentration is the next, and the temperature in the mixing vessel has little effect on the GF particles. The optimal operation condition for preparing GF micro-particles in the range of this work is: the pressure of 8 MPa and the temperature of 60 °C in the mixing vessel, the solution feeding rate of 9 ml/min and the solution concentration of 15 mg/ml.     

Pervaporation membranes from natural rubber latex grafted with poly(2‐hydroxyethyl methacrylate) (NR‐g‐PHEMA) for the separation of water–acetone mixtures

NR‐graft‐PHEMA latexes were synthesized by the use of graft emulsion polymerization. By increasing the HEMA monomer concentration, we found that the grafting percentage (GP) also increased. In addition, GP increased significantly at low initiator concentrations before it leveled off at moderate concentrations, and a slight decrease was observed at high initiator concentrations. NR‐g‐PHEMA latexes were prepared as pervaporation membranes for the separation of water–acetone mixtures. From the equilibrium swelling, the nonideal behavior of membrane swelling in water–acetone mixtures was found such that there appeared the maximum swelling degree at a certain concentration of liquid mixtures. Moreover, the water concentration at maximum swelling shifted to high water concentration with increasing amount of graft‐PHEMA. The sorption study suggested the preferential sorption of water on the membranes. Also, the sorption isotherms implied that there was a coupling between water and acetone molecules. Pervaporation separation of water–acetone mixtures was studied with NR‐g‐PHEMA membranes. As the feed water concentration increased, the partial water fluxes increased in contrast to the partial fluxes of acetone. From the permeation ratio, θ_w, the strong coupling of acetone on the water transport was observed, particularly for the membrane with high graft‐PHEMA under acetone‐rich conditions. As the feed temperature increased, the total permeation across the membranes was enhanced. The partial fluxes of water and acetone as a function of temperature followed the Arrhenius relationship by which the activation energies for permeation were estimated as 3.53 kJ/mol for water and 21.95 kJ/mol for acetone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of surfactant‐free stimuli‐sensitive microgel dispersions

A surfactant‐free method to produce responsive polymer microgels is introduced. As an example, poly(methacrylic acid) hydrogels with varying crosslinking density have been synthesized in bulk and then chopped using a high shear mechanical cutter to form microgel particles dispersed in water. The mechanical cutting technique enables the concentration and particle size distribution of the microgel suspensions to be easily controlled, therefore making the rheology of the suspensions tuneable. The particle size distribution of the dispersions, characterized using light scattering, was dependent on the speed and duration of mechanical cutting. The particle size distribution also depended on the degree of crosslinking of the hydrogel. The higher the crosslinking density, the lower the average mean diameter of the resulting microgel particles. The lower the crosslinking density of the hydrogel, the larger the difference between the maximum and minimum particle size. The time to complete swelling of the particles upon change in pH was measured to be up to 45 s, depending on the particle size. The rheology of the resulting suspensions as a function of pH was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 104: 1912–1919, 2007     

Chitosan microspheres and sponges: Preparation and characterization

In this study, chitosan microspheres and sponges were prepared and characterized for diverse biomedical applications successfully. The chitosan microspheres were obtained with a “suspension crosslinking technique” in the size range of 30–700 μm. The stirring rate of the suspension medium and the chitosan/acetic acid ratio, emulsifier, and crosslinker, that is, the glutaraldehyde concentration in the suspension medium, were evaluated as the effective parameters on the size/size distributions of the microspheres. The microsphere size/size distributions were increased with the decreasing of all effective parameters except the chitosan/acetic acid ratio. In the second part of the study, chitosan sponges were prepared with a solvent‐evaporation technique and sponges were cross‐linked either during the formation or after the formation of sponges by using a cross‐linker, that is, glutaraldehyde. When the sponges were crosslinked during the formation, fibrillar structures were obtained, while the leaflet structures were obtained in the case of crosslinking after the formation of sponges. In the last part of the study, the swelling behavior of both the chitosan microspheres and sponges were evaluated using different amounts of the crosslinker. The swelling ratio was increased in both types of structures, that is, microspheres and sponges, by decreasing the amount of the crosslinker. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1637–1643, 2000     

Dispersion polymerization of n‐butyl acrylate

The dispersion polymerization of n‐butyl acrylate (BA) was investigated using alcohol/water mixtures as the dispersion medium, 4,4′ ‐azobis‐(4‐cyanopentanoic acid) as the initiator, and polyvinylpyrrolidone (PVP) as the stabilizer. The effects of polymerization parameters, such as the alcohol/water ratio in the medium and the type and concentration of the polymeric stabilizer, on the resulting particle size and size distribution were studied. The final particle size and the stability of the dispersion system were found to be greatly influenced by the type of alcohol used in the mixture; that is, methanol or ethanol, even though the apparent solubility parameters are almost the same for the two types of mixtures. Poly(butyl acrylate) particles with controlled size and size distribution (monodisperse), and gel content were successfully prepared in a 90/10 methanol/water medium. It was found that the particle size decreased with increasing initiator concentration. This is the opposite of what was previously reported in the dispersion polymerizations of styrene and methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2692–2709, 2002     

A general compartment‐based population balance model for particle coating and layered granulation

In this work, a general multidimensional population balance (PB) model is developed to predict the coating volume distribution on polydisperse particles as a function of time during particle coating in a paddle mixer. The model adopts a compartmental approach to account for coating variation caused by particle flow heterogeneity. Simulations show that for a realistic range of seed particle size polydispersity and coating mass applied, the coating volume distribution depends on the growth rate exponent and seed particle size distribute on, with the coating volume coefficient of variance (CoV) approaching an asymptotic value as the coating‐to‐particle volume ratio increases. These effects cannot be predicted by simpler one‐dimensional models. However, the full two‐dimensional PB and simpler one‐dimensional models such as Mann's equation do predict similar sensitivity of coating volume CoV to the variation in the compartment model parameters, i.e., to changes in the particle mixing behavior in the vessel. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Semibatch anionic ring‐opening polymerization of octamethylcyclotetrasiloxane in emulsions: effect of the amount of seed polymer particles

Semibatch anionic ring‐opening polymerization of octamethylcyclotetrasiloxane with the use of seed polymer particles in emulsions was studied. The concentration of the emulsifier was set above the critical micelle concentration. We investigated the effect of the amount of seed polymer particles on the chemical kinetics and the average particle size and distribution. During monomer starving conditions the polymerization rate strongly depended on the monomer feed rate and not on the amount of seed particles. Throughout the entire monomer feed period the average particle size increased. This increase depended on the number and the size of seed particles. In emulsions with higher particle sizes higher equilibrium conversions were obtained. In our opinion, a greater extent of backbiting reactions is responsible for lower equilibrium conversions during and at the end of the process. The seeded semibatch process seems a reasonable choice for designing emulsion products with high monomer conversion and desired particle size. © 2012 Society of Chemical Industry     

Preparation and morphology study of microporous poly(HEMA–MMA) particles

Porous poly(2‐hydroxyethyl methacrylate‐methyl methacrylate) particles crosslinked with ethylene glycol dimethacrylate were synthesized by free‐radical suspension copolymerization in an aqueous phase initiated by an oil‐soluble initiator, 2,2‐azobisisobutyronitrile. 1‐octanol was used as a pore forming agent (porogen). The porous structures, the particle morphology, and the swelling capacity of the resultant polymer in water at room temperature were studied at different crosslink densities and under various porogen concentrations. The analysis via Scanning Electronic Microscopy (SEM) indicated that permanent pores remained in the dried polymeric particles prepared in the presence of the porogen at certain crosslink densities. According to the studies via the SEM pictures and the pore size distributions, higher porogen concentration promotes the formation of more pores, and higher crosslink density results in narrower pore size distribution. The swelling capacity of the particles in water at room temperature decreases with an increase in the crosslink density, and the existence of the highly porous structures enhances the swelling capacity of the porous particles of poly(2‐hydroxyethyl methacrylate‐methyl methacrylate). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 707–715, 2007