Effect of Emulsification Conditions on the Properties of Microspheres Prepared by a Solvent Extraction Process

Microspheres can be prepared using a hydrocarbon‐perfluorocarbon‐based solvent extraction process. The effect of changing the surfactant amount, emulsification temperature, and stirring speed on the size of microspheres was investigated. The surfactant concentration was found to greatly affect the microsphere size and size distribution. The Sauter mean diameter of the microspheres decreased exponentially as a function of surfactant concentration. The microsphere size distribution became narrower with increasing surfactant concentration. A clear correlation between the Sauter mean diameter of the microspheres and the Weber number was found. A surfactant concentration was identified at which the size of microspheres remained constant although the Weber number was changed. Finally, a lower emulsification temperature decreased the coalescence of the droplets and microspheres with smaller Sauter mean diameter were produced when using a low surfactant concentration.     

Supercritical carbon dioxide and solvent extraction of 2-acetyl-1-pyrroline from Pandan leaf: The effect of pre-treatment

Pandan (Pandanus amaryllifolius Roxb.) leaf is a source of natural flavoring widely used in South-east Asia. The major compound contributing to the characteristic flavor of Pandan is 2-acetyl-1-pyrroline (2AP). This highly volatile compound also contributes significantly to the flavor of aromatic rice such as basmati and jasmine rice. As the consumer requirement for use of natural flavors, extraction of components from natural sources has been sought. In this study, supercritical carbon dioxide (SC-CO₂) and solvent extraction of components from Pandan leaves were performed. Experimental parameters included particle size and drying method (oven and freeze drying). Results indicated that the initial value of moisture content and particle size of Pandan leaves had the greatest effect on the total yield and 2AP concentration of the extracts. Almost 80% of water in Pandan leaves can be removed by drying. Yields of supercritical extracts were 10 times lower when compared to the hexane extracts. The total yield of extracts was increased up to 50% with decreasing particle size of Pandan leaves. Extraction of coarsely ground freeze-dried Pandan leaves by SC-CO₂ obtained the highest yield (0.88 ± 0.06%) followed by oven dried (0.38 ± 0.09%) and fresh leaves (0.34 ± 0.01%). The 2AP was identified by GC-MS and analyzed by GC-FID. Supercritical and hexane extracts of pre-treated Pandan leaves were found to have a small quantity of 2AP ranging between 0.04 ± 0.01 and 0.45 ± 0.01 ppm. Grinding pre-treatment was the best method for both SC-CO₂ and hexane extractions while the freeze drying method was the best for SC-CO₂.     

Sintering behaviour and properties of zirconia ceramics prepared by pressureless sintering

Improvements in the sintering process and powder quality can lead to wider application of zirconia in ceramics. In this study, the effects of different temperatures on the stability, relative content of the tetragonal phase, and composition of Al₂O₃–ZrO₂ ceramic powders were explored using pressureless-assisted sintering. The crystallinity of the sintered Al₂O₃–ZrO₂ samples was significantly improved. The content of the tetragonal-phase ZrO₂ in sintered ceramic powders was 52.07%, 52.46%, 56.16%, 63.99%, and 64.90%, respectively, which was significantly higher than those of the raw materials. The average particle size of the sintered samples decreased from 1.07 μm to 0.17 μm with an increase in temperature, indicating that the ceramic powder particles were refined. The sample that was subjected to pressureless-assisted sintering at 1200 °C and held for 1 h exhibited the best stability and more uniform particle distribution compared to other samples. The particle size distribution data were closer to the standard line, satisfying the requirements of the normal distribution law. The results revealed that a high temperature was more favourable to the solid solution, and the formation of an Al₂O₃–ZrO₂ solid solution can diminish the influence of the volume expansion of ceramic powders on the sample properties during sintering. Therefore, the addition of the sintering aid Al₂O₃ significantly promotes the densification of the powders, and the pressureless sintering technique reduces the sintering temperature of the solid solution, thus imparting a crystalline structure and excellent mechanical properties to the material.     

制备工艺对多孔碳化硅材料性能的影响

研究了骨料粒径、添加剂种类、质量分数对陶瓷管性能的影响。采用自制装置分别测定了孔径分布、平均孔径、孔隙率和气体通量。用SEM观察其表面形貌。结果表明,使用较细的碳化硅颗粒,气体通量减小,抗弯强度增加;随着造孔剂质量分数的变化,多孔碳化硅陶瓷管的性能也有明显的不同,最佳添加量为10%左右。增加烧结结合剂的加入量,气体通量和抗弯强度均下降。     

Effect of material characteristics on the properties of blended cements containing high volumes of natural pozzolans

The effect of three different natural pozzolans from Turkish deposits on the properties of blended cements produced by intergrinding cement clinker with a high volume of natural pozzolan (55 wt.% of the cementitious material) was investigated. The particle size distribution of blended cements, setting time, heat of hydration, and compressive strength of blended cement mortars were determined. Experimental results showed that the hardness of the pozzolanic material strongly influenced the particle size distribution and the related properties of the blended cements by affecting the fineness of the components of the blended product. The early strength of the mortars was strongly affected by the particle size distribution of blended cements, whereas the strength development performance of the mortars was more related to the pozzolanic activity of the natural pozzolan present in the blended cement.     

Effects of particle size distribution and sintering temperature on properties of alumina mold material prepared by stereolithography

Alumina mold materials prepared by stereolithography usually have considerable sintering shrinkage, and their properties related to casting have been rarely studied. In this study, alumina molds materials were prepared by stereolithography, and the effects of particle size distribution and sintering temperature on the properties of the materials were investigated. Results show that the viscosity of the slurries decreases as the fraction of fine powder increases, and the particle size distribution affects the curing behaviors slightly. Sintering shrinkage increases as the fraction of fine powder or the sintering temperature increases. Although lower sintering shrinkage can be achieved by sintering at 1350 °C or 1450 °C, the mold materials sintered at lower temperatures would continue to shrink under the service temperature of 1550 °C, and thus 1550 °C is determined as the optimal sintering temperature. As the fraction of fine powder increases, the creep resistance first increases and then decreases, and specimens prepared with 0.1 fraction of fine powder exhibit the best creep resistance with the droop distance of 4.44 ± 0.45 mm. Specimens prepared with 0.1 fraction of fine powder and sintered at 1550 °C exhibit linear shrinkage of 6.36% along the X/Y direction and 11.39% along the Z direction, and have a flexural strength of 78.15 ± 3.50 MPa and porosity of 30.12 ± 0.08%. The resulting material possesses relatively low sintering shrinkage, proper mechanical strength, porosity and high-temperature properties that meet the requirements for casting purposes.     

Effect of wet screening on particle size distribution and coal properties

Wet screening is one of the methods used to remove fine material from the coal feed to gasification. Sasol Synfuels in South Africa undertook an investigation to quantify fine coal generation in the coal supply to gasification. Coal samples were wet screened in the laboratory and results compared to the normal dry screening procedure. It was found that the fines (−0.5 mm) increased almost five times when the coal was wet screened compared to dry screening. This study was subsequently initiated by Sasol Technology R&D to establish the mechanism of fine coal generation during wet screening, as well as the effect of wet screening on particle size distribution (PSD) and chemical properties of coal. Changes in the PSD and chemical properties of coal from individual coal sources used at Sasol Synfuels were compared. Composite coal samples with a predetermined PSD of all individual coal sources used at Sasol Synfuels were screened under wet and dry conditions. The PSD was again determined after screening, as well as the mineral composition (by X-ray diffraction) of the fines. Results indicated that wet screening caused clay minerals to be removed from the coal structure leading to an increase in the fines. This removal of minerals weakened the coal structure causing further size degradation of coarser fractions.     

Effect of the particle size on the viscoelastic properties of filled polyethylene

Composites of surface treated and non-treated colloidal calcium carbonate and high-density polyethylene with different filler loading were prepared. Their viscoelastic properties were studied by dynamic strain sweep and small-amplitude oscillatory shear, and compared to those of the corresponding composites of micron-sized calcite. The specific surface area of the filler enormously increases as the average particle diameter becomes smaller than 600 nm, leading to a strong tendency to agglomeration (soft flocks) and aggregation (hard clusters that need attrition to be disintegrated). In nanocomposites, more and stronger filler clusters are formed than in microcomposites due to the large contact area between the particles. The clusters have different shapes and maximum packing than the nearly spherical primary particles, thus enhance the moduli and viscosity of the composites. The obtained results indicate that the higher moduli and viscosity of the nanocomposites is not a direct consequence of the particle size but is due to the presence of more agglomerates and aggregates. Clusters that are local structures and do not represent a space-filling filler network enhance the moduli in the low frequency region more than at high frequencies and increase the storage more than the loss modulus. The presence of strong local structures in the nanocomposites leads to weak log moduli-log frequency dependence in the low frequency (terminal) region. Polymer adsorption on the particles' surface results in a transient filler-polymer network and slow dynamics of the bound polymer, which contribute to the moduli of the complex fluid. The sum of all these factors leads to gradual increase in moduli and to a shift of the crossover frequency to lower values. Above a certain filler volume fraction, the composite responds as a viscoelastic solid (storage modulus>loss modulus over the whole frequency range and both moduli are frequency independent in the terminal zone of the log-log plot).     

A study on the process for formation of spherical cement through an examination of the changes of powder properties and electrical charges of the cement and its constituent materials during surface modification

In the initial stage of surface modification treatment to form cement particles into a spherical shape, the fine cement particles below 3 μm increased and the specific surface area also increased. However, in the final stage of treatment, both the fine particles and the specific surface area decreased when compared to raw cement. These results seem to endorse a process for formation of spherical cement, namely grinding of the particles in the initial stage and then adhering and fixing the fine particles to the surfaces of larger core particles in the next stage. Clinker powder had a positive charge, whereas gypsum powder had a negative charge. The difference observed in the electrical charge proved that the attachment of gypsum particles to clinker particles was caused by the attraction of opposite charges in addition to the van der Waals interaction. Therefore, gypsum played an important role as an adhesive agent. The fluidity of clinker powder after it was treated with finely ground gypsum improved. This was because the fine gypsum particles quickly attached to the surfaces of the larger particles of clinker, and consequently, the final process for formation was accelerated.     

Effect of particle size distribution of petroleum coke on the properties of petroleum coke-oil slurry

The effect of particle size distribution of petroleum coke on the properties of petroleum coke-oil slurry (PCOS) from four Chinese petroleum coke samples, such as apparent viscosity, rheological behavior, static stability, were systematically investigated. The size and morphology of petroleum coke particle with different grinding time and the corresponding stabilizing mechanisms were analyzed by SEM and zeta potential measurements. Experiments proved the petroleum coke grinding time of 60 min is suitable for the particle distribution and stability of PCOS. Besides, the effect of the sample type and loading of petroleum coke on the properties of PCOS was studied. The factors governing the apparent viscosity and stability of slurries have been discussed. The experimental results showed that the properties of PCOS could be effectively improved, and a suitable PCOS with low viscosity and good stability could be prepared through controlling the particle size distribution and petroleum coke loading.     

Effect of quantity and size distribution of calcite filler on the quality of water borne paints

Calcite is the most widely used mineral filler in paint formulations. It provides not only a decrease in the cost of paint but also modifies some physical paint properties. Although some properties of calcite such as particle size distribution and refractive index are not comparable in quality to TiO₂, calcite can improve the distribution of TiO₂ via its interaction with TiO₂ particles. In this study, calcites of different size distributions are used as filler in the architectural waterborne, acrylic based paint recipes. The quality of paints was compared to properties based on both wet and dry paint such as viscosity, density, opacity, gloss, scrub resistance and Buchholz hardness. Examination of the results identified an optimum quantity and size distribution of calcite for the paint recipe. The second series of this study involved substitution possibilities of TiO₂ with calcite using seven different paint formulations. Phase images of the dry paint films obtained using “Atomic Force Microscopy” (AFM) showed the extent of distribution and aggregation of particles for each formulation on the paint surface. The overall experimental results revealed that the use of TiO₂ can be decreased up to 4% by replacement of calcite with an optimum size distribution that was also supported by AFM measurements.     

Effect of sample size on solvent extraction for detecting cocontinuity in polymer blends

The effect of sample size on the results of solvent extraction measurements for detecting cocontinuity in polymer blends was investigated. Poly(ethylene oxide)/polystyrene (PEO/PS) blend samples of several thicknesses were analyzed by removing the PEO phase using water extraction. The experimental degree of continuity was shown to have a linear dependence on the reciprocal of sample thickness. A model is proposed to explain this dependence and to allow the bulk or true degree of continuity to be determined. Measurement of the bulk degree of continuity is useful for understanding properties of cocontinuous polymer blends such as electrical conductivity, impact strength, or tensile strength.     

Estimation of particle size distributions from focused beam reflectance measurements based on an optical model

A popular in situ particle characterization technique, which can be applied without dilution, is the focused beam reflectance measurement (FBRM^®). The FBRM probe measures a chord length distribution (CLD) which is different from a particle size distribution (PSD). In order to compare results obtained by an FBRM probe with other measurement technologies such as laser diffraction, it is necessary to reconstruct the PSD from a measured CLD. For this reconstruction a measurement model and an inversion procedure are required. Most FBRM models presented in the literature assume that an FBRM records a geometric chord which can be deduced from a two-dimensional projection of the particle silhouette. In previous work [Kail, N., Briesen, H., Marquardt, W., 2008. Analysis of FBRM measurements by means of a 3D optical model. Powder Technology 185 (3), 211-222] it has been demonstrated that FBRM data show significant deviations from this geometric model. Consequently, an estimation of a PSD using such a geometric FBRM model will fail. A novel FBRM model is developed in this work. This model imitates the chord discrimination algorithm used in a Lasentec D600L FBRM system and takes the intensity profile of the laser beam and the optical aperture of the probe into account. The model is ideally suited for the estimation of a PSD from a measured CLD using a sequential, linear inversion routine, as proposed in this work. The novel FBRM model and the inversion procedure are evaluated using small, mono-disperse polystyrene beads, large ion-exchanger beads, and α-lactose-monohydrate particles. The applicability of the FBRM for PSD measurements is discussed on the basis of these results.     

Effect of superfine slag powder on cement properties

The particle size distribution (PSD) of the dense packing powder and that of actual cement powder was analyzed to explain the packing effect of superfine powder. The degrees of hydration of slag powders with specific surface area ranging from 300 to 800m²/kg were calculated to illustrate the enhancement of pozzolanic effect. As an examination of the analysis, blended cement mortars and pastes incorporating superfine slag powder were tested for strength and mercury intrusion, respectively. It was found that owing to the packing effect, the porosity and pore size distribution of the pastes were improved; because of the more complete hydration of the superfine slag section, the strength of the mortars increased and had good correlation with the hydration degree of the slag powder calculated.     

生物提取用磁性微球的制备及其性能

磁性微球因其自身兼具高分子微球和磁性粒子的众多特性,广泛应用在细胞分离、固定化酶、靶向药物、分析检测、免疫测定等领域。本文通过化学共沉淀法制备了Fe3O4纳米粒子,并采用分散聚合法对其包覆,得到Fe3O4/SiO2磁性微球。研究结果表明,通过上述方法制备的磁性微球可以快速、有效的提取生物中的RNA,而且最佳的聚合反应温度为80℃。     

Low-temperature synthesis of bioactive glass-ceramic microspheres: Effect of processing parameters on the size and morphology

A low-temperature method was developed to produce bioactive glass microspheres (BGMs). The microspheres were fabricated by dispersing the prepared sol in silicon oil, a process called the sol-microemulsion-gel method. The resulting microspheres were characterized by X-ray diffractometry (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Brunauer-Emmett-Teller (BET) techniques. Furthermore, the effect of various processing parameters such as reaction chamber size and the stirring rate on microspheres diameter was investigated. The results indicated that under optimized conditions, one could obtain BGMs with acceptable sphericity having a narrow size distribution. The obtained microspheres had diameters in the range of 19.3 ± 9.3 μm. The BET specific surface area was 240.33 m²/g. The results also showed that the increase in the reaction chamber size had interesting contradictory effects on BGMs diameter. The increase in the stirring rate intensified the shear forces exerted on the water-based phase and caused the generation of smaller droplets and microspheres.     

Effect of operating conditions on catechin extraction from betel nuts using supercritical CO2-methanol extraction

In this work, the effect of extraction parameters on catechin extraction from betel nuts was studied. The supercritical carbon dioxide extraction parameters were pressure, temperature, and solvent flow rate while using average particle size of 177.5 μm and 5% (v/v) methanol as modifiers. Detection and quantification of catechin were achieved using HPLC analysis. The highest amount of extract and catechin concentration were 34.00 mg extract/g sample and 565.38 ppm of catechin obtained at 30 MPa, 70°C, and 4 mL/min. The results given by optimization tools suggest the same operating conditions with less than 3% difference.     

Temperature and solvent effects on polyphenol extraction process from chestnut tree wood

Polyphenols are a group of chemical substances found in plants, characterized by the presence of more than one phenol unit or building block per molecule. Polyphenols are generally divided into hydrolysable tannins (gallic acid esters of glucose and other sugars) and phenylpropanoids, such as lignins, flavonoids, and condensed tannins.They are widely found in natural products, nowadays they are extensively used in food and beverage industry and in pharmaceutical and nutraceutical industry for their positive effects on human health.In conventional processes polyphenols are extracted from vegetable material using water as solvent in a temperature range from 40 to 90 °C.The aim of this work is to characterize chestnut tree wood in terms of total extractable polyphenols and assess the temperature and solvent type effects on the polyphenol extraction process. To this end, experimental data on equilibrium distribution of polyphenols between solid and liquid phases for different temperatures (ranging from 60 to 80 °C) and different solvent solutions (water and ethanol-water solutions) are reported. The obtained results have been correlated by means of Freundlich isotherm.Experimental data are also reported about the batch extraction kinetics of polyphenols from solid phase and analysed by a mathematical model to estimate the polyphenol diffusion coefficient inside the chestnut wood particles and the mass transfer coefficient in the liquid phase.     

萃取条件对UHMWPE冻胶纤维结构与性能的影响

以二甲苯为萃取剂,对超高相对分子质量聚乙烯(UHMWPE)冻胶纤维中的溶剂进行萃取,研究了不同萃取条件下UHMWPE冻胶纤维的结构与性能。结果表明,UHMWPE冻胶纤维的最佳萃取条件为萃取时间5 min,萃取温度50℃。随着萃取温度的升高,UHMWPE冻胶纤维的强度和模量增大,萃取温度50℃时,其结晶度最大。经萃取干燥的UHMWPE冻胶纤维截面具有微孔的网状结构。