Calibration and Testing of Samplers with Dry,Polydisperse Latex

A new method for measuring the collection efficiency of an aerosol sampler as a function of particle size has been developed, featuring the use of dry, polydisperse latex particles. Test aerosol is generated by placing a polydisperse latex powder sample into a fluidized bed of glass beads. An Aerodynamic Particle Sizer (APS) measures the particle size distribution entering and leaving the sampler's size-selector, yielding the penetration efficiency. The use of dry latex minimizes the ''phantom'' particle problem inherent with the APS by avoiding the generation of high concentrations of small particles such as those produced by nebulizers. In addition to having useful properties for determining particle size cutoff characteristics, including spherical shape, near-unit density, and white color, latex particles afford a test for the presence of particle bounce and reen trainment. A complete efficiency measurement can be made in a little over three minutes, facilitating experimentation with parameters such as sampler flow rate, which require repeated measurements. The method has been used extensively for the development and calibration of respirable and PM-2.5 samplers.     

Identification of thermal zones and population balance modelling of fluidized bed spray granulation

Air temperature measurements in a fluidized bed of glass beads top sprayed with water showed that conditions for particles growth were fulfilled only in the cold wetting zone under the nozzle which size and shape depended on operating conditions (liquid spray rate, nozzle air pressure, air temperature, and particles load). Evolution of the particle size distribution during agglomeration was modelled using population balance and representing the fluidized bed as two perfectly mixed reactors exchanging particles with particle growth only in the one corresponding to the wetting zone. The model was applied to the agglomeration of non-soluble glass beads and soluble maltodextrin particles spraying respectively an acacia gum solution (binder) and water. Among the three adjustable parameters, identified from experimental particle size distributions evolution during glass beads agglomeration, only one describing the kinetics of the size distribution evolution depended on process variables. The model allowed satisfying simulation of the evolution of the particle size distribution during maltodextrin agglomeration.     

An Atomic Force Microscopy Study of the Wetting of an Inorganic Surface by Latex Particles

Atomic Force Microscopy is used to investigate the wetting of a calcium carbonate crystal surface by latex particles when dried from dispersion. The measured particle heights are found to depend on the scanning rate and on the force of the probe tip acting on the sample. The analysis of the particle profile shows that the spreading is not governed by capillary forces. Below their glass temperature, the latex particles have weak adhesion to the crystal and are moved easily by the probe tip. This results in tip-induced organization of particles. Above their glass temperature, the particles spread on the surface and they are no longer moved by the probe tip.     

Synthesis and properties of branched organosilicon-acrylate copolymer latexes

Summary Stable organosilicon-acrylate copolymer latexes with high silicon content were prepared by seeded semibatch emulsion polymerization of butyl acrylate (BA), methyl methacrylate (MMA) with a novel branched organosilicon monomer 3-methacryloxypropyl tris(trimethylsiloxy) silane (MPTS). Monomer conversion, evolution of the particle size and its distribution were monitored by dynamic light scattering. The effects of MPTS on the polymerization kinetics, the nucleation mechanism and properties of latex were investigated. The results indicated that, in addition to micellar nucleation, a coagulative nucleation step was also observed as a result of the addition of the organosilicon monomer, accordingly, the particle number of the silicon-acrylate latexes increased, the average particle diameter decreased and the polymerization rate accordingly increased compared to those of the acrylate latexes without organosilicon monomer. Moreover, the particle size distribution presented bimodal curves, which indicated that there were large particles formed at an early stage. However, the particle size distribution curves became monomodal at the later stage, and the final latex shows a narrow particle size distribution. It was found that the properties of latex and latex film were obviously influenced by MPTS content. With increasing MPTS content, latex film glass transition temperature and water absorption ratio decreased, the degradation temperature and water contact angle were increased. Hence, the resulting latex films containing MPTS showed lower glass transition temperature and excellent water-resistance, which probably due to the incorporation of the bulky branched hydrophobic group of MPTS into the copolymer chains.     

三相流化床动力学特征的影响因素

利用电导探头测试技术,以不同粒径的玻璃珠颗粒、金精矿、金矿氰化尾渣为固相,空气为气相,不同粘度的液体为液相,对三相流化床中不同测孔的电导率进行测试和计算,系统研究了颗粒粒径(dp)、密度(r)、质量(q)、表观气速(Ug)、液体粘度(ml)等对相含率的影响. 结果表明,dp从0.05 mm增加到0.15 mm,气含率(eg)增加2%~3%,而固含率(es)减小2%~4%;其他条件相同,密度大的颗粒es和eg较小;随q增加,eg降低,es增加,玻璃珠颗粒每增加100 g,eg减小约2.5%,es增加约1.5%;随Ug增大或减小,eg和es亦随之增大或减小;随ml增大或减小,eg和es亦呈增大或减小趋势.     

A new method for evaluating the size of moving particles with a fiber optic probe

The size of solid particles moving in an equipment can be measured simultaneously with the velocity of the particles by using a small optic fiber probe. The principle of the measurement is presented on the basis of the “characteristic length”, which is the product of the particle velocity and the width of the reflected light pulse detected when each particle is illuminated by the optic fiber.The relationship between the characteristic length and the diameter of a spherical particle can be determined from model calculation and is represented by an approximate equation. The experimental data for spherical glass beads were found to conform to the model calculation. All experimental data were correlated in terms of equations similar to those by model calculation.     

Effect of particle size distribution on stress development and microstructure of particulate coatings

The role of pigment particle size distribution on stress and microstructure development was studied for coatings prepared from aqueous suspensions of ground calcium carbonate (GCC) and latex binder. Stress development was monitored using a modified beam deflection technique under controlled environment. Microstructure was characterized by scanning electron microscopy (SEM) and cryogenic SEM. For coatings containing only GCC particles and no latex, a wide particle size distribution resulted in a significant particle size gradient in the cross-sectional microstructure and irregular stress development. With latex addition, uniform microstructures were observed in coatings with either wide or narrow GCC particle size distribution. GCC/latex coatings prepared using GCC with a wide particle size distribution developed a higher stress than those prepared using GCC with a similar average particle size but a narrow particle size distribution. The higher stress is related to the particle packing that results in smaller pore sizes and larger capillary pressures that drive compaction. In coatings prepared with the same GCC particles but different latex binders, the stress and cracking behavior of the coating depends on the latex properties.     

Processing of polymer latex emulsion: Batch coagulation

A small-scale batch experiment has been developed to establish processing conditions for latex coagulation in an extruder environment—characterized by the prevailing flow field, temperature, and pressure. Our experiments have shown that the most effective processing means to control the particle size distribution and also the particle morphology is the coagulation temperature. The changes in hydrodynamics, introduced by variations in the channel depth and rotor speed, affect the average particle size to a lesser degree. The morphology of the coagulated particles and their size distribution have been found to play an important role in the latex dewatering process. By coagulating well above the glass transition temperature(s) of the polymer, an order of magnitude drop in the specific surface area of the coagulated particles has been observed.     

The influence of humidity on dry separation of granular particles based on geometrical characteristics

The influence of atmospheric humidity on dry separation of particles was experimentally investigated, making use of the difference in particle motion on an inclined wall, due to different geometrical characteristics. Using a tilted rotating cylinder with blades, glass beads with size and shape distributions were separated according to their geometrical characteristics under various levels of humidity. Fractional recovery of particles is discussed in relation to shape and size of particle and humidity. An angle of repose of the particles was also measured in order to determine the influence of adhesion force, which is closely related to humidity.Glass beads were separated predominantly based on their shape characteristics. Fractional recovery of particles changes strongly around a relative humidity of 60-70%, at which point the angle of repose also changes markedly. The influence of interaction between particles, which becomes significant for smaller particles, was found to reduce the fractional recovery and diminish the influence of humidity.     

Theoretical and experimental investigations on particle rotation speed in CFB riser

Particle rotation is a common phenomenon in gas-solid two-phase flows. The paper presents theoretical and experimental investigations on particle rotation speed in the gas-solid flow inside a cold CFB riser. The possible particle rotation speed, caused by non-homogeneous flow field and particle collision, and its variation with time were investigated. The average particle rotation speed was predicted with considerations of particle size, average particle collision velocity, particle collision rate and particle number density. It is found that particle collision is the most significant reason for particle rotation. The maximal and average rotation speed for particles with an average size of several hundred micrometers in the CFB riser under typical working condition may be several thousand revolutions per second and several hundred revolutions per second, respectively. The rotation speed of glass beads with an average size of in the upper dilute zone of a cold CFB riser was measured by using a high speed digital imaging system. The variation of particle rotation speed with time was observed, which is in accordance with the theoretical result. The average rotation speed for glass beads was statistically analyzed based on a large number of particle examples. With several factors taken into account, the experimental result is considered to agree with the theoretical one.     

Evaporation of Distilled Water in a Fluidized Bed of Various Types of Fluidizing Particles Under Reduced Pressure

An objective of this study is to continuously obtain dispersed, dry, fine powders from a dilute suspension of heat-sensitive materials at a low temperature and high drying rate. A fluidized bed under reduced pressure was used in this study and, as a first step, only distilled water (without solid powders) was used as a sample. Drying characteristics were examined for various types of fluidizing particles. The diameter of fluidizing particle varied for inert particles (glass beads). Three kinds of hygroscopic porous particles (silica gel beads; 3A, 4B, and 5D) were also used as fluidizing particles. Under reduced pressures, the maximum drying rate was found to be higher than that at atmospheric pressure, while the bed temperature became lower with an increase in the maximum drying rate (i.e., drying at lower temperature with a higher drying rate is possible under reduced pressures. As diameter of the fluidizing particle was increased, the maximum drying rate became higher, although the amount of gas required for fluidization also increased. The maximum drying rates for silica gel beads were found to be almost equal to those of glass beads, with the exception of 3A silica gel beads (having a smaller pore diameter). The bed temperature was lower for silica gel beads compared to glass beads at the same maximum drying rate (i.e., silica gel beads (hygroscopic porous particles) are superior to glass beads (inert particles) with regard to drying at low temperatures at a high drying rate).     

Particle sizing of flocculated latex particles by physisorption of nitrogen

Physisorption of nitrogen at one specific pressure is used to determine the specific surface area of a flocculated polystyrene latex by applying BET theory. Assuming that a flocculated sample of Polymer latex is composed of distinct spherical latex particles (i.e., there is no coagulation of particles), the volume–surface-average diameter can be calculated. The resulting diameters are compared to sizes obtained using a disc centrifuge sedimentometer, which fractionizes the particles by sedimentation. The diameters from both techniques were in good agreement, showing that physisorption of nitrogen, which is a simple technique, can be used to determine sizes of flocculated latex particles. This agreement also shows that the flocculation of the polystyrene latex produced separate nonporous spherical particles. When flocculation of a latex is done above its glass transition temperature, coagulation will occur. While other particle sizing techniques can produce particle size distributions, the physisorption of nitrogen only gives the volume–surface-average diameter. However, one advantage of the physisorption of nitrogen is that it covers a broad range of particle sizes compared to most other techniques. © 1994 John Wiley & Sons, Inc.     

Electron microscopic observation of uniform macroporous particles. I. effect of seed latex type and diluent

Uniform and macroporous polymer particles in the size range of 5–21 μm were prepared by a multistep seeded polymerization method. The uniform polystyrene particles in the size range of 1.9–7.5 μm were used as the seed particles in the preparation of macroporous beads. The seed particles with different sizes and molecular weights were produced by dispersion polymerization, by changing the type of dispersion medium and the initiator concentration. In the synthesis of macroporous particles, a two‐step swelling procedure was employed. The seed latexes were first swollen by a low molecular‐weight organic agent (i.e., dibutyl phthalate, DBP), then by a divinylbenzene–ethylvinylbenzene isomer mixture including an oil phase soluble initiator (i.e., benzoyl peroxide). The porous structure in the final beads was achieved by the polymerization of the monomer phase within the swollen seed particles including a mixture of linear polystyrene and DBP. The initiator concentration in the repolymerization step, the seed latex type (i.e., the diameter and the molecular weight of seed latex), DBP/seed latex, and the monomer/seed latex ratios were changed to achieve uniform polymer beads with different average sizes and pore structures. The average size, the size distribution, and the surface morphology of final beads were analyzed by Scanning Electron Microscopy. The internal structure of the beads were analyzed by Transmission Electron Microscopy. The results indicated that the average size of the final particles increased with increasing the seed latex diameter, DBP/seed latex, and monomer/seed latex ratios. The average pore size decreased with decreasing the molecular weight of the seed latex and increasing the DBP/seed latex and monomer/seed latex ratios. These tendencies were explained by the viscosity change of the porogen solution used in the repolymerization step. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2271–2290, 1999     

Simultaneous effect of particle size and solid concentration on the hydrodynamics of slurry bubble column reactors

The simultaneous effect of particle size and concentration on the total gas holdup of slurry bubble column reactors was investigated in this work. The total gas holdup was measured for air–water–glass beads systems. Three solid concentrations and three particle diameters were used. It was found that increasing particle size at high constant concentration decreases gas holdup. Moreover, increasing solid concentration decreases gas holdup and this decreasing effect is higher for larger particles. Also, solid particles have two effects on hydrodynamics, namely, changing the viscosity and density of the liquid phase as well as hindering the bubbles from rising within the column by the collision phenomenon. Therefore, a novel correcting factor was introduced to correct the gas holdup. The hindering factor considers both the collision efficiency affected by the particle size as well as the solid concentration. A novel correlation was developed to predict the experimental data of the three-phase gas holdup.     

颗粒特性对撞击分离器性能影响的实验与数值研究

颗粒-壁面撞击行为和气固相间作用对撞击分离器的性能具有重要影响。基于玻璃珠及煤粉的单颗粒撞击实验数据建立平均撞击恢复系数模型,采用非球形颗粒曳力模型对平板式撞击分离器的分离性能和气固流动开展数值研究。结果表明,采用基于实验的平均恢复系数模型以及考虑颗粒形状的曳力模型,能够准确地预测撞击式分离器的总分离效率和分级分离效率。颗粒分离过程中,Stokes数较大的颗粒对颗粒-壁面撞击模型比较敏感,Stokes数较小的颗粒对气固曳力模型比较敏感。     

Preparation and characterization of stable and high solid content St/BA emulsifier-free latexes in the presence of AMPS

Stable and high solid content (about 50 wt%) St/BA emulsifier-free latexes were successfully synthesized using emulsifier-free emulsion polymerization with the addition of a small amount of reactive emulsifier AMPS. Properties of the latexes, such as the average particle diameter and its distribution, the morphology of latex particles, and stability were investigated. Physical properties of the latex films, i.e., glass transition temperature (T _g), water resistance, and solvent resistance were investigated as well. The size of latex particles is 400–600 nm in diameter, which is larger than that prepared by conventional emulsion polymerization. And the particle size distribution is narrow and uniform. It was found that the diameter of the latex particles decreases with the increasing content of the initiator KPS and the reactive emulsifier AMPS. Compared with the film prepared by conventional emulsion polymerization, water resistant and solvent resistant of the films prepared by emulsifier-free emulsion polymerization are improved greatly.     

Magnetic effects in particle adhesion. Part III. Magnetite particles on steel and glass

The adhesion phenomena of uniform spherical magnetite particles in an aqueous environment, on steel and glass beads of the same charge sign, have been investigated as a function of the imposed magnetic field. The latter causes a substantial increase in the rate of particle uptake by steel. On glass, the initial deposition rate is low, but it is enhanced once the first layer of magnetite is formed on the beads. With increasing strength of the magnetic field, the repulsion barrier gradually diminishes, allowing particles to be attached directly to the surface. The particles thus deposited are not easily released once the field is eliminated. The energy well is sufficiently broad to permit multilayer formation of adhered particles.     

Measurement of Solid Circulation Patterns in Liquid—Solid and Gas—Liquid—Solid Fluidized Beds

Solid circulation patterns were determined by measuring collisions between tracer particles and cylindrical probes in liquid—solid and gas—liquid—solid fluidized beds. Special probes were used to obtain two‐ and three‐dimensional views of particle motion. Circulation patterns for 3 and 5 mm glass beads were studied. Mixing cells, which had been formed at low liquid velocities, grew in size and eventually merged as the liquid velocity increased. The flow patterns of smaller particles having the same density as bed particles and particles lighter than bed particles (graphite particles) with the same size were also measured.     

Influence of Clones on Relationship between Natural Rubber and Size of Rubber Particles in Latex

IAN873, Dongfang93114 and Reyan73397, created through vegetative propagation for their high yield and excellent cold resistance, are major clones planted in China. In this work, latexes with rubber particles of the same size from these clones are separated from fresh natural rubber latex, and corresponding rubber films are prepared from each latex. The structure and components of each film are measured. This indicates that the characteristics of the rubbers obtained from latexes with similar particle sizes show some resembling trends among different clones, while for specific samples, those characteristics vary depending on the clone. The molecular weight is generally highest in IAN873 and lowest in Reyan73397. Rubber chains in small rubber particles are longer, and large rubber particles show a wider molecular weight distribution. The gel content of every sample from Reyan73397 is lower than the other two clones. The nitrogen content increases with the size of rubber particles in all clones. The ester content of small rubber particles in IAN873 and Reyan73397 is almost zero. Large rubber particles have more branching points formed via esters. This study provides a new perspective on the influence of clones on the relationship between characteristics of natural rubber and the size of rubber particles in natural rubber latex.     

Particle size determination from acoustic emissions

A new method for the determination of particle size and size distribution in powders of rigid particles is described. The method is based on the fact that rigid particles when impinging upon each other emit sound signals whose features are related to the size of the particles, to the size distribution in a powder and also to the shape of the particles. The acoustic frequencies of interest lie in the ultrasonic range and audio-noise can be filtered out. So far, the size of metallic spheres and of glass beads has been measured accurately in the range 3 cm down to 50 μm diameter with less than 10 millisec required to take data for one complete size analysis. The method appears to be applicable to continuous on-line monitoring in crushing, powder processing and in mixing and blending.