Wet granule breakage in a breakage only high-hear mixer: Effect of formulation properties on breakage behaviour

Wet granule breakage can occur in the granulation process, particularly in granulators with high agitation forces, such as high-shear mixers. In this paper, the granule breakage is studied in a breakage only high-shear mixer. Granule pellets made from different formulations with precisely controlled porosity and binder saturation were placed in a high-shear mixer in which the bulk medium is a non-granulating cohesive sand mixture. After subjecting the pellets to different mixing time in the granulator, the numbers of whole pellets without breakage are counted and taken as a measure of granule breakage. The experimental results showed that binder saturation, binder viscosity and surface tension as well as the primary powder size have significant influence on granule breakage behaviour. It is postulated that granule breakage is closely related to the granule yield strength, which can be calculated from a simple equation which includes both the capillary and viscous force of the liquid bridges in the granule. The Stokes deformation number calculated from the impact velocity and the granule dynamic strength gives a good prediction of whether the granule of certain formulation will break or not. The model is completely based on the physical properties of the formulations such as binder viscosity, surface tension, binder saturation, granule porosity and particle size as well as particle shape.     

Binding mechanisms in wet iron ore green pellets with a bentonite binder

Fundamental research during the past decade has been focussed on understanding the role of viscous forces on agglomerate deformability and strength. Much of this work has been done on glass spheres using Newtonian liquids as a binder. In this work, we show the variations in plasticity and strength of magnetite iron ore green pellets with varying liquid saturations and binder dosages (viscosities). For this purpose, a new measuring instrument was built to analyze the green pellet wet compression strength, plastic deformation and breakage pattern.Industrial iron ore green pellets are over-saturated and a supporting “network” of viscous liquid is formed on the green pellet surface. At least half, probably more, of the total binding force appeared to be due to the cohesive force of the network. The other half (or less) of the total compression strength can be explained by the capillary force. Due to irregularities on green pellet surfaces, both fully developed concave pore openings and saturated areas are expected to be found at the same time.Wet green pellets started showing plastic behaviour as they became over-saturated. In over-saturated green pellets, an explosive increase in plasticity with increasing moisture content was seen, due to the contemporary increase in porosity. Plasticity is an important green pellet property in balling and should gain the status of a standard method in green pellet characterization. It is suggested that the control strategy for the balling circuits be based on plastic deformation and compression strength of green pellets instead of the rather inaccurate drop number. The results also point out the importance of knowing whether the balling process should be controlled by adjusting the moisture content (plasticity) or by adjusting the bentonite dosage (viscosity). These two operations are not interchangeable—even if they would compensate in growth rate, the green pellet properties would differ.A new green pellet growth mechanism is suggested, based on the measured over-saturation. Firstly, green pellet plasticity needs to exceed a minimum level to enable growth. This limiting plasticity defines the material-specific moisture content needed in balling. Secondly, it is suggested that the growth rate be controlled by the viscosity of the superficial water layer rather than by the mobility of the pore water.     

Micro‐Macro Breakage Behavior of Elastic‐Plastic Granulates by Compression

This paper presents the breakage behavior of a zeolite granulate in compression tests. The compression behavior of this granulate is described by means of a force‐displacement curve, the application of Hertz‐Huber contact theory, and continuum mechanics. The effects of granulate size and stressing velocity on the breakage force and contact stiffness during elastic and elastic‐plastic deformation are examined. It is shown that the zeolite granulates with elastic‐plastic behavior have viscous properties as well. The breakage probability is approximated by the Weibull distribution function. The behavior of the granulates during compression under conditions of repeated loading‐unloading was investigated.     

Modeling the breakage stage in spheronization of cylindrical paste extrudates

Spheronization of cylindrical extrudates on a rotating friction plate involves breakage and rounding. Little attention has been given to the breakage stage and quantitative modeling of this process is scarce. Two simple models are compared with experimental data obtained for the early stages of spheronization of microcrystalline cellulose/water extrudates. Tests were conducted for different times (t), rotational speeds (ω), initial loadings, and on pyramidal friction plates with different dimensions. The first model, describing the number of pellets, validated ω³t as a characteristic time scale for the breakage stage. The kinetic parameters obtained by fitting showed a systematic dependence on plate dimensions expressed as a scaled gap width. The second model, a simple population balance, described the evolution of the number and length of pellets. The pseudo rate constants provided insights into the kinetics: extrudates tended to break near the middle, while breakage of smaller pellets was slowed down by more pellet–pellet collisions.     

A stochastic model for breakage frequency of viscous drops in turbulent dispersions

In industrial liquid-liquid mass-transfer equipment, many a times the dispersed phases involved are highly viscous. The viscosity of dispersed drops influences the rate processes, especially their breakage rate. A new stochastic model for predicting the breakage frequency of viscous drops in a turbulent dispersion applying the random behavior of the turbulent fluctuations, has been proposed. It has been assumed that the correlation time of turbulent fluctuations across the viscous drops is so small compared to the time scale of drop deformation, that the turbulent fluctuation can be considered as a white-noise process.     

Studies on the influence of a flotation collector reagent on iron ore green pellet properties

The properties of iron ore green pellets with varying additions of a surface-active flotation collector reagent (Atrac) were studied by small-scale balling. The compression strength and plasticity were measured with a semi-automatic measuring device and the pressure curves were saved and subjected to further mathematical treatment. The green pellet breakage was also filmed with a high-speed camera. Adding Atrac to the pellet feed seriously damaged the quality of green pellets, even in small dosages. This is because an increasing amount of air bubbles became so strongly attached on the particle surfaces that they could not be removed during compaction by balling. The adsorption of air in green pellets was seen as an increase in porosity and a decrease in the filling degree (proportion of pores filled with water). Both the wet and dry compression strength decreased. The air bubbles behaved in wet green pellets like large, plastic particles and the plasticity increased beyond an acceptable level. Breakage started inside the green pellets, along the air bubbles, and generated multi-breakage patterns in wet as well as dry green pellets. Green pellet breakage to crumbs instead of a few distinct segments, promotes the generation of dust and fines and leads to lower bed permeability in the pelletizing machine.The results show that the decrease in iron ore green pellet wet strength in the presence of surface-active agents is not fully described by the so called Rumpf equation, where surface tension and contact angle are used as variables to describe the capillary forces. The green pellet breakage in the presence of air bubbles took place by crack propagation along pore structures rather than through the loss of the capillary forces.     

The Effects of Operating Conditions on the Milling of Microcrystalline Cellulose

There is little detailed work relating the physical process that occurs during milling to the mechanical properties and mechanism of particle breakage. Very often, the selection of an appropriate mill and subsequently the determination of its optimum operating conditions are by trial and error. This paper look into optimizing the operating conditions of a ball mill through statistical analysis and the effect of temperature on the milling behavior of a common pharmaceutical excipient, microcrystalline cellulose (MCC). In addition, the bulk milling behavior of MCC is compared to its single particle breakage behavior. In this work, milling is conducted in a Retsch single ball mill where a bed of powder is subjected to impact by a steel ball in a horizontal cylindrical container. The container is vibrated horizontally at a set frequency, causing the ball to impact on the bed of particles. It is found that the finest MCC product can be achieved by milling a 2 g batch of material using a 12 mm ball size and at a frequency of 18 Hz. Temperature is found to have insignificant effect on the extent of breakage of MCC in both bulk milling and single particle impact testing. Milling and single particle impact experiments have both shown that MCC is more susceptible to breakage with increasing strain rate. In conclusion, the single impact tests could be used successfully for predicting the bulk milling behavior of the material, as shown in the case of MCC.     

Effect of volatiles collected above fecal pellets on behavior of the rabbit,Oryctolagus cuniculus,tested in an experimental chamber

The fecal pellets of rabbits,Oryctolagus cuniculus, are coated with secretion from the anal gland, the odor from which functions as a territorial marker. The total volatiles collected from above fecal pellets and three different fractions prepared by washing the volatiles through either distilled water, 1 M sodium hydroxide, or 1 M hydrochloric acid were tested for their effect on the territorial confidence of individual animals. Tests were based on the neutral pen paradigm used in previous studies but employed a specially designed test chamber, the internal odor environment of which could be fully controlled. In the four series of bioassays a total of 140 separate tests were performed and 64 adult male rabbits were used. The results showed that the presence of the total volatiles influences the outcome of territorial competitions in pairs of male rabbits in favor of the individual from which they were derived. They were comparable with those obtained in earlier studies when fecal pellets were presented in the test pen. The effects of the different washing reagents on the total odor are illustrated by gas chromatograms, and the components most likely to be removed by the different treatments are suggested. The volatiles remaining after passing through distilled water had less effect on the rabbit's behavior than the total odor. Since the washing process not only removed water-soluble compounds but also led to a reduction in the concentrations of water-insoluble components introduced into the test chamber, either of these factors could have been responsible for the weakened effect. Fractions of the odor obtained by washing with either sodium hydroxide or hydrochloric acid did not influence the results of the tests. This suggests that the essential components of the olfactory signal include both basic and acidic compounds.     

Fracture toughness of modified polypropylene/poly(styrene‐ran‐butadiene) blends

Fracture toughness of polypropylene (PP)/poly(styrene‐ran‐butadiene) rubber (SBR) blends as a function of concentration of maleic anhydride (MA) in the maleated polypropylene (MAPP) compatibilizer was investigated under uniaxial static and impact loading conditions. The addition of MAPP to the unmodified PP/rubber blend enhanced the tensile modulus and yield stress as well as the Charpy impact strength. The maximum values were recorded at 1.0 wt% grafted MA in the compatibilizer. V‐shaped blunt‐notched specimens exhibited typical ductile behavior and no breakage of the specimens occurred during the impact fracture tests. Sharp‐notched specimens of uncompatibilized and low‐content MA blends broke in a semibrittle manner, supported by a rapid crack propagation process. Increasing MA content in the blends led to semibrittle‐to‐ductile transition characterized by stable crack propagation. Fracture mechanics experiments, supplemented by scanning electron microscopy (SEM), were also employed to obtain a better understanding of the fracture and deformation behavior. Copyright © 2005 Society of Chemical Industry     

Effect of the preparation of cellulose pellets on the dispersion of cellulose fibers into polypropylene matrix during extrusion

Cellulose fibers are rarely used for the extrusion of composites because of the problems in feeding them into the extruder and in dispersing them properly. Pelletization made it possible to feed cellulose fibers into extruder, but it reduced dramatically the fiber length. The goal of this study was to optimize the pelletization process for extrusion applications. Bleached sulfite cellulose fibers were pelletized at different moisture contents and with the optional addition of carboxymethyl cellulose (CMC). The pellets were subsequently extruded with polypropylene matrix without compatibilizer. Fiber dispersion and fiber breakage during extrusion were investigated. Pre‐blending of polymer and fiber pellets and introduction of the fibers through a side extruder were compared. CMC acted as a processing aid during pelletization, resulting in lower fiber breakage but in compact and stiff pellets. Lower moisture content also increased the compactness of the pellets. The dispersability of the fibers during extrusion decreased with increased pellets' compactness. CMC created inter‐fiber bonds, decreasing further the fibers' dispersability. The fiber length in the composites was the same regardless of the pelletization parameters. Early introduction of the fibers improved fiber dispersion. Feeding through side extruder was more stable and more reliable than pre‐blending. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Breakage probability of irregularly shaped particles

The investigation of breakage probability by compression of single particles was carried out. The spherical glass particles and irregularly shaped particles of NaCl, sugar, basalt and marble were subjected to a breakage test. The breakage test includes the compression up to breakage of 100 particles to obtain the distribution of the breakage probability depending on the breakage force or compression work. The breakage test was conducted for five particle size fractions from each individual material, at two stressing rates. Thus obtained 50 breakage force distributions and corresponding 50 breakage work distributions were fitted with log-normal distribution function.Usually, the breakage probability distribution can be found by means of stress or energy approach. The first one uses the stress to calculate the breakage probability distribution. The second approach uses the mass-related work done to break the particle. We prefer to use the breakage force and energy as essential variables. The correlation between the force and energy at their breakage points is obtained by integrating the characteristic force–displacement curve, i.e. the constitutive function of elastic–plastic mechanical behavior of the particle. The irregularly shaped particle is approximated by comparatively “large” hemispherical asperities. In terms of elastic–plastic deformation of the contacting asperities with the plate, a transition from elastic to inelastic deformation behavior was considered. Thus, one may apply the model of soft contact behavior of comparatively stiff hemispheres. Based on this model a relationship between the breakage force distributions and corresponding energy distributions was analyzed. Every tested material exhibits a linear relationship between average breakage energy and average breakage force calculated for every size fraction.For future consideration both force and energy distributions were normalized by division by average force or energy, consequently. The relationship between the fit parameters of normalized energy distribution and corresponding fit parameters of normalized force distribution was established. The mean value and standard deviation of normalized force distribution can be found from mean value and standard deviation of normalized energy distribution by means of system of two linear equations. The coefficients of those linear equations remain the same for all of the above tested materials; particle size fractions and stressing rates. As a result the simple transformation algorithm of distributions is developed. According to this algorithm the force distribution can be transformed into energy distribution and vice versa.     

Breakage of drop nucleated granules in a breakage only high shear mixer

Wet granule breakage is a significant mechanism, particularly in high shear mixer granulation. This paper presents a study of the wet breakage mechanism using a Breakage Only Granulator. Granules with varying powder and liquid binder properties were created using single drop nucleation. These granules were inserted in a Breakage Only Granulator, a high shear mixer granulator with non-granulating cohesive sand as the bulk medium. Two different impellers were used at impeller speeds of 500 and 750 rpm. An 11° beveled edge impeller was used to create both impact and shear in the granulator, and a flat plate impeller was used to minimize impact and maximize shear in the granulator. The fraction of granules which broke during the granulation process was used as a measure of granule breakage within the granulator. These results were compared with Stokes deformation numbers calculated using mean dynamic peak flow stresses measured in unconfined uni-axial compression tests. Results for the beveled edge impeller blade show increasing breakage with increasing Stokes deformation number. Significant breakage was observed at high Stokes deformation number. Increasing impeller speed increased the magnitude of breakage. The Stokes deformations number appears to be a reasonable predictor for granule breakage within the granulator. Results for the flat plate impeller show very little breakage at 500 rpm, and significant breakage for only one formulation at 750 rpm. This suggests that either impact is dominant over shear for breakage within the granulator, or that the two impeller designs give substantially different collision velocities in the granulator. The impeller speed, type and shape have a profound effect on granule breakage in high shear mixer granulators.     

COMPRESSION ANALYSIS OF DEHYDRATED AGRICULTURAL PRODUCTS

ABSTRACT

The textural properties of apple, banana, carrot and potato were experimentally determined by uniaxial compressive tests of cylindrical specimens at a constant deformation rate of 5mm/min. Compression tests were performed, following air drying, at various moisture contents ranging from 0.2 to 6 kg/kg db. The tests were performed using a universal texture testing machine and simple mathematical equations were used to correlate the maximum experimental stress and the corresponding strain to the moisture content. It was shown that the maximum stress decreases as the moisture content decreases, until a critical moisture content of 1.8 kg water/kg dry solids. Further removal of water tends to increase the maximum stress. The maximum experimental strain was found to increase as water was removed. The stress-strain data of compression test were modelled using a simple mathematical model, containing parameters such as the maximum stress (ow), the maximum strain (dim), the elastic parameter (E) and the viscoelastic exponent (p). The effect of the moisture content on the compressive behavior of dried materials was introduced through its effect on the model parameters. The shift in compression behavior at 1.8 kg water/kg solids leads to the conclusion that there is an important change of structure at this moisture content.     

Injection molding of long sisal fiber–reinforced polypropylene: Effects of compatibilizer concentration and viscosity on fiber adhesion and thermal degradation

A two‐step process was used to obtain long sisal fiber‐polypropylene (SF/PP)–reinforced thermoplastic composites, using maleic anhydride grafted polypropylene (MA‐g‐PP) as a compatibilizer. At a first stage, modified polypropylenes (mPP) were used for an extrusion impregnation process, for the preparation of composite pellets containing about 70 wt% of SF. SF/mPP pellets with a large aspect ratio were prepared by continuous extrusion impregnation of a continuous SF yarn, using a single screw extruder and an adequate impregnation die. The mPP used were MA‐g‐PP and regular polypropylene (PP), modified by reaction with different amounts of an organic peroxide. The composite pellets were thus dry blended with regular PP pellets in an injection machine hopper, and injection molded to obtain composite tensile specimens with a minimum quantity of modified polypropylene, minimum fiber breakage and thermal degradation, and excellent mechanical properties. It is shown that the fiber breakage is reduced to a minimum, even for recycled composites, due to the presence of the low‐viscosity polymer layer wetting the SF fibers. The bulk composite effective viscosity and the fiber breakage extent and thermal degradation during the injection‐molding step are found to be closely related. Blending with much less expensive mPP at the impregnation stage optimizes the amount of expensive MA‐g‐PP. POLYM. ENG. SCI., 45:613–621, 2005. © 2005 Society of Plastics Engineers     

Influences of loading rate and preloading on the mechanical properties of dry elasto‐plastic granules under compression

To ensure high quality of granular products post‐industrial operations, it is necessary to precisely define their micro–macro mechanical properties. However, such an endeavor is arduous, owing to their highly inhomogeneous, anisotropic and history‐dependent nature. In this article, we present the distributed granular micromechanical and macromechanical, energetic and breakage characteristics using statistical distributions. We describe the material behavior of elastoplastic zeolite 4AK granules under uniaxial compressive loading until primary breakage, and localized cyclic loading up to different maximum force levels, at different displacement‐controlled loading rates. The observed force‐displacement behavior had been approximated and further evaluated using well‐known contact models. The results provide the basis for a detailed analysis of the viscous behavior of zeolite 4AK granules in the moist and wet states, indicating that higher compressive loads are required at higher displacement‐controlled loading rates to realize equivalent deformation and breakage probability achieved by loads at lower displacement‐controlled loading rates. © 2014 American Institute of Chemical Engineers AIChE J 60: 4037–4050, 2014     

Unimpaired highly extensible tough chemically crosslinked hydrogel after experiencing freeze/thaw and boiling processes

A highly extensible, tough, chemically crosslinked double-network (DN) hydrogel was synthesized from acrylamide. Three samples of this hydrogel were swelled using different solutions. One swelled in water, one in an aqueous glycerol solution, and one in an aqueous sodium chloride solution. The freezing points of the hydrogel samples were determined using differential scanning calorimetry (DSC). Then, the samples underwent controlled freeze–thaw cycles, and their mechanical behavior under loading-unloading-reloading large-strain tensile deformation were analyzed. The results of these mechanical tests indicated that all the data points for deformation cycles coincided, despite the large water content of the samples. This means that no mechanical damage occurred during the deformation process. The results of hydrogel samples boiled in these solutions also showed no damage. Thus, it can be concluded that the tough chemically crosslinked DN hydrogel does not damage under large-strain tensile deformations even after experiencing harsh environmental conditions, such as freeze/thaw or boiling processes, which makes it a great candidate for applications that involve large temperature variations. The resistance of the DN hydrogel to damage is attributed to the specific molecular architecture of this hydrogel, in that the building block of this material is a loosely crosslinked polymeric network.     

Untersuchung des Prall‐ und Druckverhaltens feuchter γ‐Al2O3‐Granulate

The material behavior of dominant elastic‐plastic γ‐Al₂O₃ granules has been experimentally studied by means of quasi static compression tests and dynamic impact tests until fracture. The obtained distributions of breakage velocity and specific breakage energy are compared. Thus, velocity‐dependent influences at stressing like viscous behaviour can be derived. Additionally, the influence of particle size and moisture content are investigated.     

Convective drying of baker’s yeast pellets containing a carrier

The drying behavior of yeast pellets containing a carrier was investigated. Yeast paste was mixed with different amounts of wheat flour, a solid carrier, to obtain spherical pellets with 69, 55, and 40?wt% of water. During the drying, the pellets moisture content, surface temperature, and dimensions were measured, using a balance, an infrared camera, and a stereomicroscope, respectively. A drying kinetics model was developed and successfully challenged to the experimental results. The experimental and modeling results give insights into the phenomena taking place during the drying of yeast pellets including a carrier. These results highlight that the addition of a carrier reduces the shrinkage of the pellets and increases the drying rate. Moreover, the results seem to indicate that an osmosis process may take place inside the pellets following the addition of the carrier.     

The effect of annealing on the time-dependent behavior of isotactic polypropylene at finite strains

Four series of tensile relaxation tests are performed on isotactic polypropylene at elongations up to the necking point. In the first series of experiments, injection-molded samples are used without thermal pre-treatment. In the other series, the specimens are annealed for 24 h prior to testing at 110, 120 and 130 °C, respectively. Results of mechanical experiments are compared with DSC measurements.A constitutive model is derived for the time-dependent response of semicrystalline polymers at finite strains. A polymer is treated as an equivalent temporary network of macromolecules bridged by junctions (physical cross-links, entanglements and crystalline lamellae). At random times chains separate from their junctions and merge with new ones (the viscoelastic response), whereas junctions slip with respect to their positions in the bulk material (the viscoplastic behavior). The network is thought of as an ensemble of active meso-regions with various potential energies for detachment of chains from temporary nodes and passive meso-domains, where separation of chains is prevented by surrounding radial and tangential lamellae.Experimental data demonstrate that the content of active meso-domains increases with elongation ratio driven by the release of constrained amorphous phase induced by fragmentation of lamellae. In the sub-critical region of deformation (relatively small strains), the growth of the concentration of active meso-regions is associated with breakage of subsidiary (thin) lamellae developed at annealing. In the post-critical region (large strains), an increase in the fraction of active amorphous domains is attributed to disintegration of primary (thick) lamellae.