Home About us Contact
|
Home About us Contact | ||
|
|
||
Mean Particle Size (mean + particle_size)
Selected AbstractsMicroencapsulation of doxycycline into poly(lactide- co -glycolide) by spray drying technique: Effect of polymer molecular weight on process parametersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Pradip Patel Abstract Poly(lactide- co -glycolide) (PLGA) polymers with three different molecular weights were prepared, and microparticles were produced by spray drying and water-in-oil-water (w/o/w) double emulsion techniques to encapsulate 86% of doxycycline (DXY), an antibiotic drug, for the use of periodontitis. Placebo and drug-loaded microspheres and pristine DXY were analyzed by Fourier transform infrared spectroscopy, which indicated no chemical interactions between DXY and PLGA. X-ray diffraction of drug-loaded microspheres confirmed the molecular level dispersion of DXY in PLGA. Scanning electron microscopy confirmed spherical nature and smooth surfaces of the microspheres. Mean particle size as measured by laser light scattering technique ranged between 10 and 25 ,m. In vitro release of DXY performed in 7.4 pH media continued up to 72 h and depended on molecular weight of PLGA and extent of DXY loading. Antimicrobial studies performed on one formulation and placebo microspheres suggested that drug concentrations during in vitro release are above the minimum inhibitory concentration (MIC) for Staphylococcus aureus growth. Overall, the release studies depended on the molecular weight of PLGA, extent of drug loading, and the method used to prepare microspheres. Statistical analyses of release data performed using the analysis of variance (ANOVA) method agreed well with experimental observations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Long circulating nanoparticles of etoposide using PLGA-MPEG and PLGA-pluronic block copolymers: characterization, drug-release, blood-clearance, and biodistribution studiesDRUG DEVELOPMENT RESEARCH, Issue 4 2010Khushwant S. Yadav Abstract The anti-leukemic drug, etoposide (ETO), has variable oral bioavailability ranging from 24,74% with a short terminal half-life of 1.5,h i.v. necessitating continuous infusion for 24,34,h for the treatment of leukemia. In the present study, etoposide-loaded PLGA-based surface-modified nanoparticles (NPs) with long circulation were designed as an alternative to continuous i.v. administration. PLGA-mPEG and PLGA-PLURONIC copolymers were synthesised and used to prepared ETO-loaded NPs by high-pressure homogenization. The mean particle size of ETO-loaded PLGA-MPEG nanoparticles was 94.02±3.4,nm, with an Entrapment Efficiency (EE) of 71.2% and zeta potential value of ,6.9±1.3,mV. ETO-loaded PLGA-pluronic nanoparticles had a mean particle size of 148.0±2.1,nm, an EE of 73.12±2.7%, and zeta potential value of ,21.5±1.6,mV. In vitro release of the pure drug was complete within 4,h, but was sustained up to 7 days from PLGA-mPEG nanoparticles and for 5 days from PLGA-pluronic nanoparticles. Release was first order and followed non-Fickian diffusion kinetics in both instances. ETO and ETO-loaded PLGA nanoparticles labeled with 99mTc were used in blood clearance studies in rats where the two coated NPs, 99mTc- ETO-PLGA-PLU NP and 99mTc- ETO-PLGA-mPEG NP, were found to be available in higher concentrations in the circulation as compared to the pure drug. Biodistribution studies in mice showed that ETO-loaded PLGA-MPEG NP and PLGA-PLURONIC NP had reduced uptake by the RES due to their steric barrier properties and were present in the circulation for a longer time. Moreover, the NPs had greater uptake in bone and brain where concentration of the free drug, ETO, was negligible. Drug delivered from these NPs could result in a single i.v. injection that would release the drug for a number of days, which would be potentially beneficial and in better control of leukemia therapy. Drug Dev Res 71: 228,239, 2010. © 2010 Wiley-Liss, Inc. [source] Processing of urea-formaldehyde-based particleboard from hazelnut shell and improvement of its fire and water resistanceFIRE AND MATERIALS, Issue 8 2009M. Gürü Abstract The purpose of this study was to manufacture urea-formaldehyde-based particleboard from hazelnut shell and eliminate its disadvantages such as flammability, water absorption, swelling thickness by using fly ash and phenol-formaldehyde. Synthesized urea-formaldehyde and grained hazelnut shells were blended at different ratios ranging from 0.8 to 3.2 hazelnut shell/urea-formaldehyde and dried at 70°C in an oven until constant weight was reached. In addition, other parameters affecting polymer composite particleboard from hazelnut shell and urea-formaldehyde were investigated to be the amount of fly ash, amount of phenol formaldehyde and the effects of these parameters on bending stress, limit oxygen index, water absorption capacity and swelling in the thickness. The optimization results showed that the maximum bending strength was 4.1N/mm2, at urea-formaldehyde ratio of 1.0, reaction temperature of 70°C, reaction time of 25,min, hazelnut shell/urea-formaldehyde resin of 2.4 and mean particle size of 0.1,mm. Although the limited oxygen index and smoke density of composite particleboard without fly ash has 22.3 and 1.62, with fly ash of 16% (w/w) according to the filler has 38.2 and 1.47, respectively. Water absorption and increase in the swelling thickness exponentially decreased with increasing phenol formaldehyde. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis and Optical Properties of KYF4/Yb, Er Nanocrystals, and their Surface Modification with Undoped KYF4,ADVANCED FUNCTIONAL MATERIALS, Issue 19 2008Helmut Schäfer Abstract KYF4/Yb3+, Er3+ nanocrystals with a mean diameter of approximately 13,nm were synthesized at 200,°C in the high boiling organic solvent N -(2-hydroxyethyl)ethylenediamine (HEEDA). The particles crystallize in the cubic phase known from , -NaYF4 and form transparent colloidal solutions in tetraethylene glycol (TEG) or propanol. Solutions containing 1,wt % of the nanocrystals in TEG display visible upconversion emission upon continuous wave (CW) excitation at 978,nm. Growing undoped KYF4 on the surface of the KYF4/Yb3+, Er3+ nanocrystals increases the upconversion efficiency by more than a factor of 20. The XRD data of these particles, display a slight increase in the mean particle size from 13 to 15.5,nm, indicating that only a part of the subsequently added KYF4 shell material is deposited onto the particle surface. Nevertheless the performed surface modification obviously leads to core/shell structured particles. [source] SUBCRITICAL WATER EXTRACTION OF CAFFEINE FROM BLACK TEA LEAF OF IRANJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2008ANVAR SHALMASHI ABSTRACT This study examines subcritical water extraction (SCWE) of caffeine from black tea leaf. The effects of various operating conditions such as water temperature (100, 125, 150 and 175C), water flow rate (1, 2 and 4 g/min), mean particle size (0.5, 1 and 2 mm) on extraction yield and rate were determined. SCWE at 175C, water flow rate of 2 g/min and mean particle size of 0.5 mm were found to be able to recover 3.82% (w/w) of caffeine present in the black tea leaf within 3 h of extraction. In comparison to the SCWE, conventional hot water extraction showed 3.30% (w/w) extraction yield. It was found also that pressure had no effect on extraction yield and rate. PRACTICAL APPLICATIONS Recently, subcritical water has become of great interest as an alternative solvent for extraction of natural active compounds. Subcritical water, as a green solvent, can be used in many different fields of applications. In recent years, extraction of flavors, fragrances and antioxidant components from plant materials, and hydrolysis of carbohydrates, vegetable oils and fatty acids have been widely investigated by many researchers. Using subcritical water for analytical purposes, for soil remediation and applying it as a reaction media are some other interesting fields for practical applications. Subcritical water is an excellent solvent for caffeine as well as many other organic compounds but is safer than the organic solvents that are used for caffeine extraction. [source] GRINDING SPRAY-DRIED MILK POWDER NEAR the GLASS TRANSITION TEMPERATUREJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2003GREGORY R. ZIEGLER ABSTRACT The fine grinding of chocolate is typically accomplished on five-roll mills. Chocolate manufacturers consider milk powder, a component of milk chocolate, difficult to grind. Spray-dried milk powders comprise a glassy lactose matrix in which fat globules, air vacuoles and protein are entrapped. the glassy-rubbery transition in commercial milk powders usually lies between 60,70C, depending on the moisture content. A mixture of 60% wt/wt commercial whole milk powder, Tg, 60C, and 40% wt/wt cocoa butter was ground in a three-roll refiner at temperatures of 40, 50, 60, 70 and 75C. Below Tg the particles exhibited brittle fracture, while above Tg plastic deformation was evident and particles became highly asymmetric. the amount of fat liberated from the lactose matrix, so-called free fat, particle density, and mean particle size increased with grinding temperature. However, the Casson yield value and plastic viscosity of finished "white chocolate" coatings, manufactured to a constant free fat content, increased with grinding temperature, suggesting an influence of particle shape on flow behavior. [source] ,-Carotene-Loaded Nanostructured Lipid CarriersJOURNAL OF FOOD SCIENCE, Issue 2 2008A. Hentschel ABSTRACT:, Nanostructured lipid carriers (NLC) technology was used to disperse hydrophobic ,-carotene in an aqueous phase. NLC are lipid nanoparticles with a particle matrix consisting of a blend of a liquid and solid lipid. They were produced by melting the lipid blend at 80 °C and dispersing it into a hot emulsifier solution. The aim of this study was to extend the limited knowledge of melt-emulsified lipidic colloids in food systems and to evaluate the feasibility for further applications as functional ingredient in beverages. Physical stability of the NLC suspension was examined at 2 different storage temperatures by measuring the particle size with photon correlation spectroscopy (PCS) and laser diffractometry (LD). All particles containing sufficient amounts of emulsifier were smaller than 1 ,m (LD diameter 100%) at a mean particle size of around 0.3 ,m (LD) for 9 wk at 20 °C and at least 30 wk at 4 to 8 ° C. Differential scanning calorimetry (DSC) was used to study the solid state of the lipids both in the ,-carotene loaded PGMS and in the NLC particles. Propylene glycol monostearate (PGMS) when dispersed as NLC recrystallized up to 98% during storage time. Within the regarded period of 7 mo no polymorph transitions were observed. Furthermore, stability of the ,-carotene in water dependent on NLC concentration and tocopherol content was measured photospectrometrically to get an estimation of the behavior of NLC in beverages. [source] Microstructure and Relaxor Behavior of Dense Fine-Grain FeTiTaO6 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Yun Shi A new type of FeTiTaO6 ceramics with a high density was synthesized by the solid-state method. X-ray diffraction and scanning electron microscopy patterns indicate that the specimens exhibit a rutile structure and the mean particle size was about 200,300 nm. The heterovalent substitutions of Fe3+ and Ta5+ at Ti4+ site drive the incipient ferroelectric to the relaxor behavior, and a strong dispersion of the maximum dielectric permittivity appears around Tm, which shifts towards higher temperatures with the increasing frequency. The variation of Tm with frequency follows the Vogel,Fulcher relationship well, wherein Ea=0.068 eV, Tf=508 K, and f0=109 Hz. These results indicate that the nonperovskite-type FeTiTaO6 ceramic is a promising candidate for lead-free relaxor ferroelectrics in practical applications. [source] Synthesis of Zirconia Nanoparticles in a Continuous-Flow Microwave ReactorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Federica Bondioli Monodispersed zirconia colloidal spherical nanoparticles were synthesized from the hydrolysis and condensation of tetra- n -propylzirconate by using a continuous microwave synthesis process. The flow rate was varied from 50 to 100 mL/min in order to establish the optimum conditions required to obtain unagglomerated zirconia nanopowders. The results were compared with those obtained in batch systems. In particular as the flow rate is decreased from 100 to 50 mL/min the particle became spherical with a mean particle size of about 100 nm. [source] Kinetic Studies of Mullite Synthesis from Alumina Nanoparticles and a Preceramic PolymerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Flavio Griggio The crystallization kinetics of mullite formation in a diphasic precursor consisting of a silicone resin filled with commercial ,-alumina nanoparticles (15 nm mean particle size, specific surface area of 100 m2/g), heated in air from 1250° to 1350°C, was studied by X-ray diffraction. Transitional ,-alumina and amorphous silica from the pyrolysis of the preceramic polymer exhibited a remarkable reactivity, as demonstrated by a very low incubation time (from 500 s at 1250°C to 20 s at 1350°C), a high mullite yield (about 80 vol%, after 100 s at 1350°C), and a low activation energy for nucleation (677±60 kJ/mol). The activation energy values found were lower than those reported previously for other diphasic systems, including sol,gel precursors. Besides the high specific surface of nanosized ,-alumina particles, the low energy barrier could be attributed to the highly reactive silica deriving from the oxidation of Si,CH3 bonds in the silicone and to the homogeneous dispersion of the nanosized filler inside the preceramic polymer. Furthermore, the possibility of applying plastic shaping processing methods to the mixture of a preceramic polymer and nanosized filler makes this approach particularly valuable, in comparison, for instance, with sol,gel based alternatives. [source] Starch and fibre distribution in maize silages in relation to particle sizeJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2003I Fernandez Abstract In a first trial the particle size distribution of four maize silages was measured by two different sieving methods, dry and wet sieving. Particle size distribution was quantified by three values, mean particle size, extent of dispersion, and proportion of large particles. Wet sieving separated particles better than dry sieving and was more suitable for measuring maize silage particle size. In a second trial the particle size distribution of 10 maize hybrids grown in the same conditions was measured by wet sieving. Starch proportion in large particles varied widely between maize hybrids, from 39.7 to 82.4%, against a variation from 75.4 to 100% for cell wall proportion in the same class of particles, and these variations might be predicted by dry matter distribution. © 2003 Society of Chemical Industry [source] Effect of single-mineral filler and hybrid-mineral filler additives on the properties of polypropylene compositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2009A.K. Nurdina The present study was carried out to determine the filler characteristics and to investigate the effects of three types of mineral fillers (CaCO3, silica, and mica) and filler loadings (10,40 wt%) on the properties of polypropylene (PP) composites. The characteristics of the particulate fillers, such as mean particle size, particle size distribution, aspect ratio, shape, and degree of crystallinity were identified. In terms of mechanical properties, for all of the filled PP composites, Young's modulus increased, whereas tensile strength and strain at break decreased as the filler loading increased. However, 10 wt% of mica in a PP composite showed a tensile strength comparable with that of unfilled PP. Greater tensile strength of mica/PP composites compared to that of the other composites was observed because of lower percentages of voids and a higher aspect ratio of the filler. Mica/PP also exhibited a lower coefficient of thermal expansion (CTE) compared to that of the other composites. This difference was due to a lower degree of crystallinity of the filler and the CTE value of the mica filler. Scanning electron microscopy was used to examine the structure of fracture surfaces, and there was a gradual change in tensile fracture behavior from ductile to brittle as the filler loading increased. The nucleating ability of the fillers was studied with differential scanning calorimetry, and a drop in crystallinity of the composites was observed with the addition of mineral filler. Studies on the hybridization effect of different (silica and mica) filler ratios on the properties of PP hybrid composites showed that the addition of mica to silica-PP composites enhanced their tensile strength and modulus. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers [source] Preparation of 5-Fluorouracil-Poly(L -lactide) Microparticles Using Solution-Enhanced Dispersion by Supercritical CO2MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2006Ai-Zheng Chen Abstract Summary: 5-Fluorouracil-poly(L -lactide) (5-Fu-PLLA) microparticles have been prepared by an SEDS process. First, the 5-Fu is successfully micronized and is then used to produce the 5-Fu-PLLA microparticles. The 5-Fu-PLLA microparticles synthesized by the SEDS process exhibit a rather spherical shape and a narrow particle size distribution, where it ranges from 615 to 1,990 nm, with a mean particle size of 980 nm. The dichloromethane residue in the 5-Fu-PLLA microparticles without any further treatment is 46 ppm. The average drug load and encapsulation efficiency of the 5-Fu-PLLA microparticles are 3.05 and 17.8%, respectively. The rate of drug release from the 5-Fu-PLLA microparticles shows mainly first-order kinetics. Scanning electron spectroscopy image of 5-Fu-PLLA microparticles. [source] Characterization of Powder Beds by Thermal Conductivity: Effect of Gas Pressure on the Thermal Resistance of Particle Contact PointsPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2004Michael Shapiro Abstract The thermal conductivity of ceramic powder packed beds was measured at temperatures below 100,°C for various powder sizes and compositions and under different gas atmospheres. Measurements at low pressures (down to 10,Pa) combined with a theoretical model allowed the elucidation of geometrical and thermal resistance parameters for the contact points between granules. The gap thickness and contact point size were found to be well correlated with the mean particle size. The thermal conductivities of all powders at low pressure were found to differ at most by a factor of two, whereas the solid-phase conductivities of the powder materials differed by more than one order of magnitude. A theoretical model accounting for the size-dependence of contact point conductivity is incorporated to rationalize this trend. [source] Classification of Fine Particles in High-Speed CentrifugesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2010L. E. Spelter Abstract The classification of dispersed particles below 1,,m is a difficult task due to the high surface area-to-volume ratio. Tubular-bowl centrifuges offer high centrifugal numbers, which enable the separation and classification of fine particles, biological cells and cell debris. This work presents the classification of two fine products with a mean particle size below 1,,m. Polydisperse silica and polystyrene were split successfully into a fine and a coarse fraction by a semi-continuous tubular-bowl centrifuge. The fine fractions exhibited narrow particle size distributions. An optimization of the process could be achieved by a comprehensive understanding of the flow patterns, which are accessible with computational fluid dynamics. The axial and tangential velocity profiles were calculated for rotational speeds up to 40,000 rpm and throughputs ranging from 0.1 to 2,L/min. [source] Applying a Thermodynamic Model to the Non-Stoichiometric Precipitation of Barium SulfateCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2003L. Vicum Abstract Thermodynamic models for aqueous Ba2+ -SO42, -Na+ -Cl, -solutions are compared in their accuracy to predict ion activities in saturated and supersaturated solutions. The Pitzer and the Bromley model are employed, taking into account ion pair formation of barium sulfate. Such models are then used to describe particle nucleation and growth, and finally they are imbedded in a mechanistic mixing-precipitation model for a single feed semibatch process. The effect of the key operating parameters on the mean particle size is analyzed through simulations. The results are compared with previous experimental data, thus highlighting the significance of a proper choice of the thermodynamic model. [source] Supercritical fluid extraction of walnut kernel oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7 2006Sema Salg Abstract The objective of this study was to investigate the effects of the main process parameters on supercritical fluid extraction of walnut (Juglans regia,L.) kernel oil. The recovery of walnut kernel oil was performed in a green and high-tech separation process. CO2 and CO2 +,ethanol mixtures were used as the supercritical solvent. The extraction was carried out at operating pressures of 30, 40 and 50,MPa, operating temperatures of 313, 323 and 333,K, mean particle sizes of 1.78×10,4, 3.03×10,4, 4.78×10,4, 7.00×10,4 and 9.00×10,4,m, supercritical CO2 (SC CO2) flow rates of 1.67×10,8, 3.33×10,8, 6.67×10,8 and 13.33×10,8,m3/s and entrainer (ethanol) concentrations of 2, 4, 8 and 12,vol-%. Maximum extraction yield and oil solubility in SC CO2 obtained at 50,MPa, 333,K, 9.00×10,4,m, 3.33×10,4,m3/h were 0.65,kg oil/kg of dry sample and 37.16,g oil/kg CO2, respectively. The results obtained in this study showed that the crossover pressure effect of walnut kernel oil was at 30,MPa. At 30,MPa and 313,K, the obtained extraction yields above 4,vol-% ethanol reached the organic solvent extraction yield of 68.5,kg oil/kg dry sample. Extraction time was decreased significantly because of the higher solubility of walnut kernel oil in SC CO2 +,ethanol mixtures. [source] Multinuclear NMR characterisation and dermal delivery of fluorinated drugs in soybean-microemulsion systemsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2009Sonja Hoeller Abstract The present study evaluated the effect of different commercially available soybean lecithins in microemulsion systems in terms of microstructure transformation, physicochemical properties and transport of selected entrapped fluorinated drugs through skin. Physicochemical characterisations by particle size and polydispersity index (PDI) measurements were performed and a direct correlation with NMR self-diffusion coefficients of the individual components was found. An increase of lysophosphatidylcholine (LPC), phosphatidylethanolamine (PE) and lysophosphatidylethanolamine (LPE) in the phospholipid mixtures increased the mean particle sizes and PDI. Bicontinous microemulsion structures were proven by 1H and 31P NMR in the placebo microemulsions. Reasonable permeation of the lipophilic drugs of all microemulsions systems was confirmed in standard diffusion studies using porcine skin. This could be due to the incorporation of the drugs in the surfactant structure of the lecithin based bicontinous micro textures, as proven by 19F NMR self-diffusion studies. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2686,2695, 2009 [source] Enrichment of the thymoquinone content in volatile oil from Satureja montana using supercritical fluid extractionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2009Clara Grosso Abstract Supercritical fluid extraction (SFE) of the volatile oil from Satureja montana L. was performed under different conditions of pressure (90 and 100 bar), temperature (40 and 50°C), mean particle sizes (0.4, 0.6 and 0.8 mm) and CO2 flow rate (0.8, 1.1 and 1.3 kg/h) to understand the influence of these parameters on the composition and yield of this oil. The results were compared with those obtained for the essential oil isolated by hydrodistillation (HD). The volatile and the essential oil were analysed by GC and GC-MS. The main compounds are carvacrol (52.2,62.0% for HD vs. 41.7,64.5% for SFE), thymol (8.6,11.0% for HD vs. 6.0,11.3% for SFE), p -cymene (6.9,12.8% for HD vs. 6.0,17.8% for SFE), ,-terpinene (6.4,9.4% for HD vs. 2.3,6.0% for SFE) and ,-bisabolene (2.0,2.7% for HD vs. 2.2,3.5% for SFE). The major difference between SFE and HD was the relative amount of thymoquinone, an oxygenated monoterpene with important biological activities, which can be ten-fold higher in volatile oil (1.6,3.0 for SFE vs. 0.2% for HD). The morphology of the glandular trichomes of S. montana and the effect of the grinding process on them was also evaluated by SEM. [source] Microwave Plasma Synthesis of Nanostructured ,-Al2O3 PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2003L. Fu Nanostructured Al2O3 powders have been synthesized by combustion of aluminum powder in a microwave oxygen plasma, and characterized by X-ray diffraction and electron microscopy. The main phase is ,-Al2O3, with a small amount of ,-Al2O3. The particles are truncated octahedral in shape, with mean particle sizes of 21,24 nm. The effect of reaction chamber pressure on the phase composition and the particle size was studied. The ,-alumina content increases and the mean particle size decreases with decreasing pressure. No ,-Al2O3 appears in the final particles. Electron microscopy studies find that a particle may contain more than one phase. [source] | ||||||||||||||||||||||||||||