Comparison of different flowability tests for powders for inhalation

A series of placebo powders for inhalation was characterized regarding bulk density and powder flowability using different techniques. The powders were of the ordered mixture type and were prepared by mixing a pharmaceutical carrier grade of lactose with different fractions of intermediate sized and fine (i.e., micronized) lactose. A modified Hausner Ratio was obtained by measurement of the poured and the compressed bulk densities. Other tests investigated were the angle of repose, the avalanching behaviour using the AeroFlow, and the yield strength using the Uniaxial tester. Furthermore, the relation between ordered mixture composition and flowability was examined.Of the methods investigated, the modified Hausner Ratio discriminates well between the investigated powders and seems to have the widest measuring range. It was also found that the poured and compressed bulk densities provide information about the packing of the particles in the powders. A good correlation was obtained between the modified Hausner Ratio and the angle of repose. The AeroFlow was suitable for powders with a low percentage of fine particles, but could not discriminate between the more cohesive powders. The Uniaxial tester, on the other hand, seems to be better suited for more cohesive powders.Regarding the powder composition, addition of micronized particles has a strong influence on the flowability of ordered mixtures, while intermediate sized particles have little impact on the powder flow.     

Physical and flow properties of pecan shells—Particle size and moisture effects

Pecan shells are the byproduct of the processing of pecans for human consumption. The potential use of these shells for bioenergy and other value-added applications requires information on the physical and flow properties. These properties are needed for the design of storage, processing and handling equipment. The effects of particle size and moisture content on bulk density, particle density, tap density, compressibility, angle of repose, cohesion, angle of internal friction and flowability were quantified in this study. Equilibrium moisture relations for the shells were also determined at temperatures ranging from 10 to 50 °C. The densities (bulk, particle and tap) significantly decreased and compressibility significantly increased with increases in particle size and moisture content. Increasing the moisture content reduced its flowability from free flowing (flow index of 15.77) at a moisture content of 4.2% (w.b.) to cohesive (flow index 3.14) at a moisture content of 24.6% (w.b.). The cohesive strength of pecan shells also increased with particle size (0.58 to 1.14 kPa) and with moisture content (0.36 to 1.69 kPa). An average angle of internal friction of 41.28° was obtained and was not significantly affected by moisture content and particle size. The angles of repose of pecan shells varied from 33.1 degrees to 46.3 degrees. The equilibrium moisture relation curves for the shells were sigmoidal in shape and showed that pecan shells should be stored at moisture contents of less than 18.03% (w.b.) to minimize microbial activity. The equilibrium moisture relation curves were best predicted by the modified Henderson equation.     

Powder flowability and density ratios: the impact of granules packing

The propensity of powders to flow under given circumstances (flowability) affects a large number of industrial applications. A single, reliable and widely applicable flowability test does not exist, because of the variety of both granular materials and influence of handling on the measurements results. Here we critically examined the results provided by Hausner's method, based on apparent densities ratio, with several granular materials. Major limitations appeared to be the achievement and measurement of a dense packing condition, provided by the tapped density in the Hausner's ratio. After a detailed discussion of standard and modified techniques to measure bulk density, we eventually suggest a new flowability criterion based on a novel technique to determine a high packing density. The proposed criterion is more sensitive to differences in flowability, as quantified by the repose angle. In order to investigate also the domain of cohesive powders, we developed a novel procedure to measure the repose angle of such powders. Eventually, the new criterion was able to account consistently for free-flowing and cohesive powders. It also stimulates the discussion on subtle issues involved in the determination and use of elementary powder's properties.     

The effect of surface modification of aluminum powder on its flowability, combustion and reactivity

Surface modification of aluminum powders for the purpose of flow improvement was performed and several samples were prepared. Correlations between the flowability and reactivity for these powders as well as for the initial untreated aluminum powder were established. The powders were characterized using Scanning Electron Microscope (SEM), particle size distribution, angle of repose flowability test, Constant Volume Explosion (CVE) combustion test, and Thermo-Gravimetric Analysis (TGA). The surface modification of micron-sized aluminum powders was done by: (1) dry coating nano-particles of silica, titania and carbon black onto the surface of spherical aluminum powders and (2) chemically and physically altering the surface properties of the same powders with methyltrichlorosilane. All surface modifications improved flowability of the powders. CVE measurements indicate that powders with an improved flowability exhibit improved combustion characteristics if the powder treatment does not add an inert component to aluminum. The TGA results do not show significant differences in the reactivity of various powders. Based on combined flowability and CVE characteristics, the silane modified material gave the best results followed by the powders dry coated with carbon, titania and silica, respectively.     

轻质自流耐火浇注料

探讨了影响轻质自流耐火浇注料流动性的主要因素：颗粒级配，粒径，超细粉等，通过复合使用硅灰与自制粘土质超细粉，解决了流动性与稳定性的矛盾。制备的轻质自流浇注料流动性好，物理力学性能与普通浇注料相同。     

Measuring the bulk flow properties of PVC resins

The flow characteristics of PVC resin are often judged by measuring the time required for a given amount of dry resin to flow through a standard funnel. However, considerable variation in test results have been found between laboratories though the test is conducted well within the procedural limits of ASTM 1895-69, “Apparent Density, Bulk Factor and Pourability of Plastic Materials.” An examination has been made of the effects of funnel hole size, funnel alignment, its type metal and wall surface smoothness, filling technique, static generated, and degree of vibration. It was found that six of these seven variables need critical control, while one (alignment) has no measurable effect. It is suggested that the data presented be used for the development of an improved ASTM test for measuring the flowability of PVC resins.     

Physicochemical Characterization of Whole Egg Powder Microencapsulated by Spray Drying

Physical characterization and oxidative stability of egg powder microencapsulated by spray drying were studied in this work. The wall material (gelatin, lactose, pullulan, and their mixtures) and liquid egg mixtures were prepared by homogenization at 22,000 rpm for 60 s. The spray drying was carried out at pilot-scale spray dryer (Niro Mobile Minor, Søborg, Denmark). The spray-dried egg powders were analyzed for moisture content, water activity, peroxide value, total cholesterol oxidation products (TCOPs), particle properties, and bulk properties. Using gelatin as wall material resulted in a significant increase in the moisture content and water activity of egg powder during storage and it improved flowability. Egg powders containing pullulan as wall material showed a fibrous structure and had the lowest bulk density. Adding lactose as wall material increased the oxidative stability, which was indicated with lowest peroxide value and TCOPs level of egg powder.     

Effect of powder properties on discharge characteristics of cohesive carbonaceous fuel powders from a top discharge blow tank at high pressure

Abstract

Discharge experiments of two cohesive carbonaceous fuel powders (anthracite coal and petroleum coke) were carried out in a top discharge blow tank experimental system with design pressure up to 6.4?MPa. The effects of powder properties (particle size and powder category) on the discharge characteristics (including solid discharge rate, solids loading ratio, and discharge stability) from the top discharge blow tank at high pressure were investigated. Meanwhile, shear tests with a ShearTrac II shear tester were performed to investigate the flowability of these two cohesive powders. The results indicate that there exists a near-linear relationship between major consolidation stress and flow function (FF). As particle size decreases, the values of FF decrease and powder flowability becomes worse. However, as particle size decreases, the particle suspension velocity decreases correspondingly, and the gas permeability becomes worse and gas maintain ability becomes better, which contribute to higher solid discharge rate and better discharge stability, whereas solids loading ratio may have opposite variation tendency. Compared to petroleum coke with similar particle size, anthracite coal has better flowability and can obtain higher solid discharge rate and solids loading ratio, as well as better discharge stability. During the discharge processes of petroleum coke, it was found that as the number of discharge experiment increases, the discharge stability decreases correspondingly. After petroleum coke being discharged continuously for 4–6 times, the discharge process could not start again, adhesion phenomena of petroleum coke to the wall of conveying pipelines could be observed.     

高含量β-胡萝卜素微胶囊干粉流动性的考察及其影响因素

The flowability of five kinds of microencapsulation powders,with differentβ-carotene contents and by two alternative particle-forming technologies i.e.spray-drying and starch-catching beadlet technology,was meas- ured.The actual flow properties of the five powders were compared based on bin-flow test,and three flow indexes (Hausner ratio,repose angle and flow index)were measured.It was found that the repose angle is the most suitable index to reflect the flowability of these powders for the particle properties would not be altered due to compaction or tapping during the measuring process.Particle size and particle size distribution play most important roles in the flowability of these granular materials,which was also influenced by other factors like shape,surface texture,sur- face roughness,etc.Microcapsules with wall material of gelatin and a layer of modified starch absorbed on the sur- face showed excellent flowabilities and good mechanical properties,and they are favorable for tabletting to supply β-carotene.     

Structure, anisotropy and fractals in compressed cohesive powders

Correlation functions are commonly used to characterise the microstructure of materials. The correlation function is then related to other properties or phenomenology connected to the investigated material. In this paper, we investigate the bulk microstructure in two cohesive powders — a silica powder containing spherical grains and a carbon nanotube powder, by means of Spin-echo Small-angle Neutron Scattering technique. We show that, for the silica powder, the typical size of the heterogeneities decreases with increasing strain, thus linking microscopic deformations with the macroscopic ones. Measurements also show that the compressed silica powder is isotropic in terms of its density distribution. On the compressed nanotube powder we are able to conclude that the applied uniaxial stress induces anisotropy in the density distribution. We are able to link the compressive strain with the measured anisotropy, thus creating the link between macroscopic and microscopic behaviours. Both powders are shown to have a fractal structure, and are characterised in terms of a fractal dimension.     

Effect of glidants in binary powder mixtures

The intention of this study is to investigate on a particulate level the flow properties of dry powder mixtures consisting of cornstarch and a second nanoscaled material. Special attention is paid to the question on the working mechanism of glidants. In 1974, Rumpf showed that a roughness on the surface of a smooth particle leads to a reduction of its forces of interaction with another particle. The interaction forces are reduced as the surface roughness increases the distance between the centers of gravity of the two interacting particles. Agglomerates as well as the primary particles of materials used as glidants are characterized by diameters in the lower nanometer range. In consequence they are strongly adsorbed at the surface of larger particles and act as a surface roughness. If the effect of a glidant would be due to its ability to act as a surface roughness then all nanoparticles being small enough to reduce the net interaction forces could be used as glidants almost irrespective of their chemical nature. Indeed we have been able to demonstrate that nanoparticles of titanium dioxide, aluminum oxide, silicon dioxide or of carbon black act as glidants. Mixing time directly influences the efficiency of a nanomaterial to act as a glidant. Due to increasing ratio of adhesive force to particle weight with decreasing particle radius, nanomaterials tend to aggregate and agglomerate. With increasing mixing time the size of agglomerates decreases. At the same time the number of primary particles available for adsorption on the surfaces of the cornstarch particles increases. An optimum in flow properties is achieved at a characteristic mixing time. At a further increase in mixing time, the size of agglomerates decreases and the coverage of the cornstarch particles by nanoparticles increases. Eventually cornstarch particles are obtained being completely coated with nanoparticles. The surfaces of these coated particles are smooth. Accordingly they show a poor flow behavior. The property of the nanomaterial to act as a glidant is lost.     

PVC干混料粉体流动性的影响因素

介绍了与粉体流动性有关的理论,分析了PVC树脂、CPE、碳酸钙和冷混工艺对PVC干混料粉体流动性的影响,结果表明:①乙烯法PVC树脂的粉体流动性一般优于电石法PVC树脂,且波动较小;②某些厂家的冲击改性剂CPE可改善PVC干混料的粉体流动性,并且随着CPE用量的增加,PVC干混料的粉体流动性增加;③不同生产厂家的PVC/CPE体系对PVC干混料粉体流动性的影响规律不同,应不断摸索,找出最佳组合;④随着碳酸钙用量的增加,PVC干混料的粉体流动性降低,特别是在料斗上的表现更为突出;⑤充分冷却后的PVC干混料粉体流动性较好。     

Fluidization of cohesive powders

Relatively small changes in particle size and other parameters which affect interparticle forces can transform a fine free-flowing powder into one which is cohesive. The influence of these parameters on the fluidization behaviour of fine powders has been investigated and can be readily assessed by measuring the ratio of tap to aerated bulk density.     

团聚粉料的流动性和成型性能

以3种具有不同团聚特征的氧化铝粉料为对象,用粉料剪切仪测定了粉料的流动性。以单向加压成型测定了成型过程中压力与成型体密度变化。用压汞测孔仪及扫描电镜研究了团聚体的外形和气孔结构。通过以上各种观察,讨论了3种粉料的团聚体恃征及团聚特征对粉料流动性和成型性能的关系。     

Characterization of wet powder flowability by shear cell measurements and compaction curves

Wet powders can be classified into the pendular, the funicular, and the capillary states. The boundaries between the three states depend on particle and bulk properties. The flow properties in each of these states vary with the level of saturation as both the tensile strength and the interparticle friction are a function of the amount of liquid present in the pores. In the frame of this study, it was demonstrated that wet powders can be classified based on shear cell measurements.Compaction curves are an adequate measure of wet powder flowability and its dependency on particle and bulk properties. They can be used to evaluate the risk of blocking in extrusion processes.The significance of the transition from the funicular into the capillary state is highlighted, in particular for its distinct role in improving the flowability and the extrudability.     

Relationship between particle scale capillary forces and bulk unconfined yield strength

One of the main problems in industrial applications is the handling of fine cohesive materials. This cohesion can cause hang-ups in process equipment and stop or slow down processing. Conversely, just a small quantity of cohesion in a bulk powder can prevent particle size segregation. It is obvious that understanding cohesion from a fundamental point of view is useful in describing process flow behavior. Capillary force between particles is one source of cohesion between particles. This paper presents a theory that can be used to model the cohesive behavior of bulk materials based on capillary forces between particles.     

Vaporization study of SiC and SiC–2 mol% SiO2 powder mixtures. Grain morphology changes at high vapor pressures under pumping

The heat treatment of SiC powders, SiC–2 mol% SiO₂ powder mixtures, and bimodal SiC powder mixtures has been studied with a quadrupole mass spectrometer linked by capillary tube to a special heat treatment reactor. Silica release was monitored on the CO(g) vaporized flow and the samples were analyzed by Raman spectroscopy and Scanning Electron Microscopy after the experiments. The present study showed that silica release by vaporization – first step in heating processes – is needed before any SiC growth process could start. The second step involving active SiC oxidation conditions by the remaining oxygen was conducive to the growth of “neck-like” connections between SiC grains and growth process was observed in the 1273–1600 K range. When the CO(g) release decreased as a result of higher temperatures or longer treatment times, carbon precipitation at the SiC surface was observed as the third step in the mass loss process.     

Modified solution combustion route for the preparation of plasma sprayable ceria powder

Plasma sprayable grade ceria powder was prepared by the solution combustion method. This is the first report on the application of solution combustion for the synthesis of plasma sprayable grade oxide powders. The fuels and fuel ratios used in the solution combustion were modified to achieve adequate flowability. It was found that when a mixture of fuels like glycine and ammonium acetate was used, the combustion process yielded larger agglomerates. Phase purity of the powders was confirmed by powder XRD. The morphology of the particles was determined by scanning electron microscopy.     

高抗冲聚丙烯颗粒的流动性及其抗静电性

随着气相釜中乙烯含量的增加,高抗冲聚丙烯颗粒会出现发黏、聚并等现象,严重影响其流动性及连续化生产。添加极少量惰性无机超细粉体是减少高抗冲聚丙烯颗粒间粘连的有效措施。通过冷模研究,剖析超细粉体的加入对颗粒流动性的影响,同时探讨体系静电的产生因素及其对颗粒流动性的影响。选用的超细粉体包括球形二氧化硅和层状水滑石。研究发现,相对于直接加入未改性处理的超细粉体,加入经抗静电剂改性的超细粉体后,颗粒的带电量明显减少,落下时间缩短,流动性也得到了有效提高;而且选用水滑石的效果明显优于二氧化硅。     

A molecular simulations study of the miscibility in binary mixtures of polymers and low molecular weight molecules

The miscibility behavior of binary mixtures of polymeric and low molecular weight molecules was studied using a combination of modified Flory-Huggins theory and molecular simulation techniques. Three different atomistic approaches were used to investigate the phase behavior and χ parameters of binary mixtures consisting of polymethyl methacrylate (PMMA) and 4-n-pentyl-4′-cyanobiphenyl (5CB). Binary mixtures of methyl methacrylate monomer/5CB and methyl methacrylate oligomer/5CB were also studied. As a first approach, a fast method that calculates the local interaction between a fragment of the polymer and the organic molecule and then extends it to determine the energy of mixing using an estimated coordination number was used. By using modified coordination numbers, we were able to extend this method to include cases where the polymer segment and the small molecules are slightly dissimilar in size. More detailed studies which take into account bulk effects were also carried out where the cohesive energies of the pure compounds were derived from molecular dynamics simulations and the interaction parameters were determined from the differences in the cohesive energies. The concentration and temperature dependence of the χ parameters was evaluated by calculating the energy of mixing from the differences in the cohesive energy densities of the mixed and demixed systems. The present study provides a detailed understanding of the miscibility of PMMA and 5CB as PMMA polymerizes from its monomer, and the results indicate that although methyl methacrylate and 5CB are completely miscible, 5CB is not miscible in PMMA even in small quantities.