Sieve Fractions Research Articles

Particle size distribution of distillers dried grains with solubles (DDGS) and relationships to compositional and color properties

Eleven distillers dried grains with solubles (DDGS), processed from yellow corn, were collected from different ethanol processing plants in the US Midwest area. Particle size distribution (PSD) by mass of each sample was determined using a series of six selected US standard sieves: Nos. 8, 12, 18, 35, 60, and 100, and a pan. The original sample and sieve sized fractions were measured for surface color and contents of moisture, protein, oil, ash, and starch. Total carbohydrate (CHO) and total non-starch CHO were also calculated. Results show that there was a great variation in composition and color among DDGS from different plants. Surprisingly, a few DDGS samples contained unusually high amounts of residual starch (11.1–17.6%, dry matter basis, vs. about 5% of the rest), presumably resulting from modified processing methods. Particle size of DDGS varied greatly within a sample and PSD varied greatly among samples. The 11 samples had a mean value of 0.660 mm for the geometric mean diameter ( d gw) of particles and a mean value of 0.440 mm for the geometric standard deviation ( S gw) of particle diameters by mass. The majority had a unimodal PSD, with a mode in the size class between 0.5 and 1.0 mm. Although PSD and color parameters had little correlation with composition of whole DDGS samples, distribution of nutrients as well as color attributes correlated well with PSD. In sieved fractions, protein content, L and a color values negatively while contents of oil and total CHO positively correlated with particle size. It is highly feasible to fractionate DDGS for compositional enrichment based on particle size, while the extent of PSD can serve as an index for potential of DDGS fractionation. The above information should be a vital addition to quality and baseline data of DDGS.

Hyperquenched volcanic glass from Loihi Seamount, Hawaii

Explosive submarine basaltic eruptions, occurring in water depths of several kilometres, commonly result in the formation of layered volcaniclastic deposits. In order to quantify the cooling of such volcaniclastics, we have identified and separated two types of glassy fragments from these deposits on Loihi seamount: 1) fine (30–80 μm) limu o Pele bubble wall fragments and 2) coarser (0.8–1.2 mm) dense angular fragments. These pristine basaltic glasses have been subjected to differential scanning calorimetry (DSC) from room temperature up to temperatures above their glass transition. Heat capacity (cp, in J g−1 K−1) data reveal glassy and liquid regimes separated by clear hysteresis behaviour within the glass transition. The transient cp in the glass transition interval exhibits a deep trough before the peak, indicating very high cooling rates. It is a classic feature of so-called “hyper-quenching”, having been observed in DSC experiments on glasses produced using the splat-quench [D.B. Dingwell, P. Courtial, D. Giordano and A.R.L. Nichols, Viscosity of peridotite liquid, Earth and Planetary Science Letters 226(1–2), 127–138, 2004.], and cascade fibre-spinning [Y.Z. Yue, J.D. Christiansen and S.L. Jensen, Determination of the fictive temperature for a hyperquenched glass, Chemical Physics Letters 357(1–2), 20–24, 2002.] techniques. The trough is deepest for the limu o Pele fragments. Energy matching methods, developed for the estimation of cooling rates for such glasses, yield a rate of 105.31 K s−1 for the cooling of the fine sieve fraction of limu glass on the sea floor at Loihi. Thus, limu o Pele volcaniclastics, believed to be formed during mild submarine pyroclastic eruptions, have experienced the fastest cooling of any natural volcanic glass measured to date. Such extreme cooling rates are likely to impact on many chemical and physical aspects of the stability of these glasses on the sea floor, as well as their use as proxies for field variables of the Earth's physical state and as monitors of the efficiency of chemical lithosphere–hydrosphere exchange.

Physical properties that govern fiber separation from distillers dried grains with solubles (DDGS) using sieving and air classification

Distillers dried grains with solubles (DDGS) is a coproduct of the dry grind corn to fuel ethanol process. Recently, we showed that Elusieve process, the combination of sieving and elutriation (air flow), was effective in separating fiber from DDGS. DDGS was sieved into different fractions and the sieved fractions were air classified to separate fiber. In this study, we determine relevant physical properties and terminal velocities of fiber and nonfiber that govern fiber separation from DDGS. Particle densities were determined using a pycnometer and equivalent spherical diameters were calculated from mean particle volume, obtained as mean particle mass divided by particle density. Sphericity of fiber was calculated as the ratio of surface area of sphere having the same volume as fiber to the actual surface area of fiber. Sphericity of nonfiber was calculated from experimentally determined terminal velocities of nonfiber and using the correlation between terminal velocity and sphericity. Terminal velocities of fiber and nonfiber are the lowest air velocities at which fiber and nonfiber, respectively, were carried by air. Particle density of fiber was higher than particle density of nonfiber. It was visually observed that fiber was flat and nonfiber was not flat. Sphericity of fiber and nonfiber ranged from 0.19 to 0.47 and 0.72 to 0.92, respectively. Within each sieved fraction, fiber particles had lower or comparable equivalent spherical diameters relative to nonfiber particles. Fiber particles experienced higher drag force and aspirated at low air velocities because: (1) they had lower or comparable mass relative to nonfiber particles and (2) their shape was flatter than nonfiber particles. The difference in shapes and equivalent spherical diameters of fiber and nonfiber within each sieved fraction resulted in difference in their terminal velocities within sieved fractions. This difference in terminal velocities allows separation of fiber from DDGS. Sieving of DDGS into fractions and then blowing air through sieved fractions was effective in separating fiber.

Structure and Physicochemical Properties of Starches from Sieve Fractions of Oat Flour Compared with Whole and Pin‐Milled Flour

ABSTRACTOne oat cultivar grown in Idaho (three field sites) was pin‐milled and separated by sieving to investigate whether starch from oat bran differs from the remainder of kernel. Ground oat particles were classified into three sieve fractions: 300–850 μm, 150–300 μm and <150 μm). β‐Glucan content in sieve fractions was analyzed and starch was extracted from kernels without milling and from kernels of each sieve fraction. β‐Glucan contents of 300–850, 150–300, and <150 μm sieve fractions were 4.2, 2.3, and 0.8%, respectively. Therefore, starch in bran (300–850 μm sieve fraction) and endosperm (<150 μm sieve fraction) were separated. Starch isolated from entire kernels had significantly higher apparent and absolute amylose content than starch from the 300–850 μm sieve fraction. Starch from different sieve fractions was not significantly different in the apparent amylose, absolute amylose, amylopectin molecular weight, gyration radii, starch gelatinization, and amylose‐lipid complex thermal transition temperatures. Starch from the 150–300 μm sieve fraction had significantly lower peak, final, and setback viscosity compared with the starch isolated from the 300–850 μm and <150 μm sieve fractions. Starch removed from the oat bran fraction during β‐glucan enrichment may have different applications compared with starch obtained from other kernel compartments. Because pin‐milling decreased apparent amylose content and shortened amylopectin branch chains, its potential to alter starch structure should be considered.

Phytosterol Distribution in Fractions Obtained from Processing of Distillers Dried Grains with Solubles Using Sieving and Elutriation

ABSTRACTIn an earlier study, the combination of sieving and elutriation was effective in separating fiber from distillers dried grains with solubles (DDGS), the coproduct remaining after ethanol production from corn. To separate fiber, air was blown through sieve fractions in an elutriation column. Material carried by air to the top of the elutriation column was the lighter fraction; material that settled in the bottom was the heavier fraction. Separation of fiber from DDGS resulted in two products: 1) elusieve fiber with high neutral detergent fiber (NDF), which was obtained by combining lighter fractions; and 2) enhanced DDGS with reduced fiber (low NDF) and increased fat and increased protein contents, which was obtained by combining material remaining after separation of lighter fractions. There were no differences in phytosterol distributions (St:E, St, and FPE) among sieve categories. Phytosterol contents of oil from the lighter fractions were higher than or the same as the corresponding heavier fractions. Total phytosterol contents in elusieve fiber and enhanced DDGS were 112–142 and 226–232 mg/100 g, respectively. Phytosterol contents in elusieve fractions were compared with phytosterol contents reported in previous studies for fiber from different corn processing techniques. Phytosterol content of elusieve fiber was higher than wet‐milling endosperm fiber (71 mg/100 g). Enhanced DDGS had higher phytosterol content than dry‐milling fiber (152 mg/100 g), wet‐milling endosperm fiber (71 mg/100 g), quick fiber obtained from steeping without chemicals (215 mg/100 g), and DDGS (216 mg/100 g). Wet‐milling pericarp fiber (241 mg/100 g) and quick fiber from steeping with chemicals (275 mg/100 g) had higher phytosterol contents than elusieve fiber and enhanced DDGS. Phytosterol extraction from elusieve fiber could potentially increase revenues from elusieve process; however the increase in price of elusieve products could not be determined because estimates for the cost of the phytosterol extraction and for the value of ferulate phytosterol esters are not available.

Effects of slash and burn practices on a soil seed bank of caatinga vegetation in Northeastern Brazil

The semiarid tropical zone covers 20% of Brazil and is dominated by caatinga, a thorny deciduous savanna well adapted to seasonal water shortage and periodic drought years. This study was focused on effects of slash and burn agriculture on the soil seed bank in a Caatinga area, in Sobral, CE, Brazil. Caatinga is rich in species, called therophytes, which remain as seeds in the soil during unfavorable seasons and rely on regeneration from the soil seed bank for persistence in the environment. Although slash and burn agriculture has been intensified in the region for the past three centuries, its effects on the soil seed bank are not well known. A seedling emergence greenhouse experiment was conducted to evaluate differences in seed bank density and diversity among soil samples collected before and after an experimental burning. Soil samples were previously submitted to sequential sieving to assess fire effects on different-sized seeds. Fire significantly reduced overall seed bank density, with smaller sieving fractions being most strongly affected. Shanon′s diversity index was also lowered by fire. Combined, these results show that agricultural practices represent a serious threat to plant biodiversity conservation in the Caatinga biome.

Measurement of drug agglomerates in powder blending simulation samples by near infrared chemical imaging

This research note describes a powder blending simulation study conducted using 20-mL scintillation vials and a bench-top rotating mixer on a scale of 2 g for each sample. In order to investigate the impact of mean particle size and size distribution on blending behavior of an active pharmaceutical ingredient (API), the drug substance was separated into sieve fractions using the US standard sieves of 60, 80, 100, 200, and 325 mesh. Each of the fractions was mixed with two excipients (hydroxypropyl methylcellulose and microcrystalline cellulose) for up to 20 min. Then the blending samples were analyzed by a near infrared chemical imaging (NIR-CI) system. The NIR-CI system was able to measure API particles/domains (agglomerates) at 0.001 mm 2 and above within a 11.2 mm × 9.0 mm field of view. It was found that blends prepared with larger API particles (60–200 mesh) contain agglomerated API domains ≥0.1 mm 2. The blends prepared with finer API particles (≤325 mesh) show the characteristics of a randomized mixing. This simple and effective method can be used for evaluation of blending behavior for APIs in formulation development.

Noninvasive Characterization of Pharmaceutical Solids by Diode Laser Oxygen Spectroscopy

Characterization of solid pharmaceuticals, ranging from monitoring of solid-state reactions to understanding tablet dissolution, is of great interest for pharmaceutical science. The quality of the finished product highly depends on knowledge about the pharmaceutical materials used and the different unit operations involved in manufacturing of pharmaceuticals. Thus, availability of appropriate and reliable tools for measurements of physical and chemical properties of drug materials in situ during chemical and physical processing is a key for optimized processing. In early stages of pharmaceutical development a whole range of techniques for characterization of the solid state is available, addressing, for example, particle size and shape, density, porosity, calorimetry, thermo-mechanical properties, specific area, and crystallinity. However, most of these techniques are slow and not well suited for fast laboratory-based or process applications. Process analytical technology (PAT) is a term describing a holistic approach to pharmaceutical manufacturing based on in-depth understanding through advanced process sensors and modeling tools. In order to succeed with this, new tools are needed, e.g., with capability to directly measure physico-chemical attributes in situ of the mechanical process. In this context, tools based on spectroscopic techniques offer obvious advantages owing to their speed, compactness, versatility, and ability to perform noninvasive analysis. By employing the spectroscopic technique referred to as gas in scattering media absorption spectroscopy (GASMAS), it is possible to extract information related to gas dispersed within highly scattering (turbid) materials. In our case, the key is contrast between the sharp (GHz) absorption features of molecular oxygen located around 760 nm and the broad absorption features related to tablet bulk material. The technique is based on high-resolution diode laser absorption spectroscopy, and its main principle is illustrated in Fig. 1. Light is injected into a highly scattering sample, often utilizing optical fibers. The actual path length distribution of transmitted photons will depend on the scattering properties of the sample. Due to significant multiple scattering, the average photon path length greatly exceeds sample dimensions. For example, the average path length of photons that have traveled through a pharmaceutical tablet typically exceeds 10 cm. During passages through air-filled pores, photons in resonance with an absorption line in the A-band of molecular oxygen can be absorbed. Oxygen absorption can be distinguished from bulk absorption due to the extremely narrow absorption features (GHz) exhibited by free gases. To resolve such narrow features, high-resolution spectroscopy must be employed. The resulting absorption signal depends on both the oxygen content and the scattering properties (photons path lengths) of the sample. Indirectly, it is thus related to mechanical properties such as porosity and particle size. The GASMAS technique has previously been used to study the gas content in, for example, polystyrene foam, wheat flour, granulated salt, wood materials, fruit, and human sinuses. Gas exchange dynamics has been studied by placing samples of wood and fruit in nitrogen atmospheres and monitoring the re-invasion of oxygen. In this paper we show the potential of using GASMAS for determination of physical and structural parameters of pharmaceutical solids. We present results from a study of pharmaceutical tablets made from two different sieve fractions (particle size distributions) and with different compression forces. In addition, the prospects of a broader use of this technique for pharmaceutical analysis are discussed.

Application of Seeding as a Process Actuator in a Model Predictive Control Framework for Fed‐Batch Crystallization of Ammonium Sulphate

AbstractSeeding is discussed from the viewpoint of reproducible process actuation. Seeded experiments in a 75‐l Draft‐Tube (DT) crystallizer were performed in triplicate to verify reproducibility of the product characteristics. The seeded experiments displayed a significantly improved reproducibility of the results in comparison with the corresponding unseeded batches.Narrow sieve fractions of ground seeds were utilized as a seeding material. The seeds were suspended in a saturated solution before being fed into the crystallizer. It was found that the Crystal Size Distribution (CSD) of crystals suspended in a saturated solution changed during the time of their residence in the seeding vessel. Images taken by the Scanning Electron Microscope (SEM) confirmed that the initial change in the median size was caused by the dissolution of fines. The dissolution was subsequently accompanied by the crystal growth and attrition. An optimal residence time was found.Finally, the influence of the initial supersaturation, the seed load, and the seed size on the product quality was investigated. The experimental studies indicated that the initial supersaturation should be as high as possible yet not high enough to trigger primary nucleation. The lowest admissible sieve fraction and the corresponding minimal seed load were found. The conservatism of the used seeding model with respect to the minimal seed load was addressed.

Influence of Physical Grain Characteristics on Optimal Rotor Speed During Impact Dehulling of Oats

ABSTRACTCentral to commercial oat (Avena sativa L.) processing is impact dehulling. During impact dehulling, oats are fed into a spinning rotor that expels the grains against an impact ring. The impact frees the groat from the hulls. To optimize dehulling protocols, we examined the effects of physical grain characteristics and rotor speed on oat dehulling using an impact dehuller. We separated grain of three cultivars (Gem, CDC Dancer, Ronald) according to size by sieve fractionation (separation by width), disk fractionation (separation by length), and by gravity table (separation by density). Grains were characterized by mass, digital image analysis, and bulk density. Samples (50 g) were adjusted to 9% moisture and dehulled at four different rotor speeds. Groat percentage, dehulling efficiency, and groat breakage were measured after dehulling. In general, oats with higher bulk density dehulled more efficiently at slower rotor speeds, regardless of grain mass. Groat breakage increased with rotor speed and with grain mass. Adjusting dehulling conditions according to grain size improved groat yields over optimal dehulling conditions for unfractionated grains for some cultivars. More refined fractionation of grain according to bulk density may provide further improvement of groat yield during impact dehulling.

Solid-assisted melt disintegration (SAMD), a novel technique for metal powder production

A new process termed “solid-assisted melt disintegration (SAMD)” has been developed for the preparation of aluminum alloy powder particles. The method consists of introducing and mixing a specified amount of as-received alumina particles (in the range of +700 to 500 μm) in A356 aluminum melt at the temperature of 715 °C. Melt disintegration occurs in 10 min by kinetic energy transfer from a rotating impeller (450 rpm) to the metal via the solid atomizing medium (alumina particles). The resulting mixture of aluminum droplets and alumina particles was cooled in air and screened through 300 μm sieve to separate alumina from solidified aluminum powder particles. A356 aluminum alloy was also gas atomized by using a free-fall atomizer operating by nitrogen gas at the pressure of 1.1 MPa and the sub-300 μm of the produced powder was used as a base of comparison. The SAMD produced powders of diameter above 53 μm were mostly spherical while powders less than 53 μm showed various elongated shapes. No evidence was found for satelliting of small particles on to large ones or agglomerated particles. While gas atomized particles in the +53 μm sieve size range showed some signs of porosity, the SAMD particles were dense and did not show any signs of internal porosity in any of the sieve fractions investigated. Comparison of the microstructure of the SAMD and gas-atomized powders revealed that for the same size powder of A356 alloy, the former exhibited a coarser microstructure as a result of a slower cooling rate.

Analytical speciation as a tool to assess arsenic behaviour in soils polluted by mining

A study is performed to evaluate the occurrence of arsenic in polluted soils using acidic extractions and liquid chromatography-hydride generation-atomic fluorescence spectrometry (LC-HG-AFS) for speciation analysis. Seven soil samples were collected in an abandoned area polluted by mining in the Eastern Pyrenees (Spain), and two uncontaminated soils were taken for reference purposes. Moreover, the total arsenic content is evaluated in two different sieved fractions in order to obtain information on the possible particle-size-dependent association of arsenic with soil components. Soil samples were extracted with both phosphoric and ascorbic acids and the stabilities of the extracted species were studied. The arsenic species were determined by LC-HG-AFS. In addition, the ability of soil grinding to effect species change is also assessed. Arsenite and arsenate were found in the polluted soils, but only arsenate was found in the unpolluted soils. The quality of the results was assessed through a mass balance calculation and by analysing two soil Certified Reference Materials. Valuable information regarding arsenic occurrence in the studied soils is obtained from the speciation results. The presence of arsenite in the extracts can be attributed to arsenopyrite residues, whereas the presence of arsenate indicates release from weathered material.

Quantification of olanzapine polymorphs using powder X-ray diffraction technique

Accurate quantification of crystalline phases present in drug materials is becoming increasingly important, due to stringent regulatory concerns about polymorph characterization and control in drug substances and products. In the present study, a quantification method for polymorphic forms of olanzapine (OLZ) has been developed using powder X-ray diffraction (PXRD). Preferred orientation has been reported to be the major source of error in PXRD analysis, therefore, prior to development of a quantification method, pure polymorphic forms (I and II) of different size ranges were analyzed. Preferred orientation effect was found to decrease on using sieve fraction BSS # 120/240 for form I. In order to obtain good peak resolution in optimum time, the step time and step size were varied so as to optimize the scan rate. Among the five combinations selected, step size of 0.05° with step time of 5 s demonstrated identification of four characteristic peaks of form I in form II in 62 min. A calibration curve was constructed in the range of 0–100% (w/w) using the characteristic peak of form I at 18.48° 2 θ ( I/ I 0 78.8%). The PXRD assay was reproducible and precise and displayed a LOD of 0.40% (w/w) and LOQ of 1.22% (w/w). Validation results showed excellent correlation between actual and predicted concentrations with R 2 0.9999.

Particle-size distribution and packing fraction of geometric random packings

This paper addresses the geometric random packing and void fraction of polydisperse particles. It is demonstrated that the bimodal packing can be transformed into a continuous particle-size distribution of the power law type. It follows that a maximum packing fraction of particles is obtained when the exponent (distribution modulus) of the power law function is zero, which is to say, the cumulative finer fraction is a logarithmic function of the particle size. For maximum geometric packings composed of sieve fractions or of discretely sized particles, the distribution modulus is positive (typically 0<alpha<0.37). Furthermore, an original and exact expression is derived that predicts the packing fraction of the polydisperse power law packing, and which is governed by the distribution exponent, size width, mode of packing, and particle shape only. For a number of particle shapes and their packing modes (close, loose), these parameters are given. The analytical expression of the packing fraction is thoroughly compared with experiments reported in the literature, and good agreement is found.

Retention properties of wood residues and their potential for soil amelioration

The particle size distribution, the nutrient content and the sorption behaviour of six solid wood and ash/charcoal residues collected in three wood-processing companies in Germany and Brazil were investigated in order to elucidate the potential of these residues for the development of new products for soil amelioration. The absorption of N, P, and K by the residues and the leaching of nutrients from impregnated samples were studied in the laboratory at substrate temperatures of 20 and 300°C. The release of elements by the impregnated samples and the sorption behaviour of ash/charcoal incorporated in the soil were also studied in the field on a temperate site (Hamburg, 53°32′N 09°59′E), on a subtropical site (Ivai, 25°15′S 50°45′W), and on a tropical site (Aripuana, 10°09′S 59°26′W). Under laboratory conditions the solid wood residues absorbed 2.0–9.1% of the N, 0.1–0.4% of the P, and 1.0–8.5% of the K available in the impregnation solution. At a temperature of 20°C, selected sieve fractions of the ash/charcoal residues absorbed up to twice as much as N and up to 100 times more K than the treated wood residues. The absorption of N, P, and K to the ash/charcoal residues increased significantly at a substrate temperature of 300°C compared to a substrate temperature of 20°C. In absolute numbers, the leaching of N, P, and K from the impregnated ash/charcoal residues was in the range of the release by the impregnated solid wood residues, whilst the relative rate of nutrient leaching was strongly reduced. The field experiments confirmed the results obtained in the laboratory and indicated that ash/charcoal residues are suitable raw materials for the development of new products for soil amelioration, in particular for application under humid climate conditions.

The effect of carrier surface treatment on drug particle detachment from crystalline carriers in adhesive mixtures for inhalation

In this study, the effect of lactose carrier surface treatment on drug particle detachment during inhalation has been investigated. Crystals of marketed brands of alpha lactose monohydrate brands normally exhibit a certain surface rugosity and contain natural fines and impurities on their surface, which influence the drug-to-carrier interaction in adhesive mixtures for inhalation. Submersion treatment may change these surface characteristics. Two different sieve fractions (63–90 and 250–355 μm) were submerged in mixtures of ethanol and water (96 and 80% v/v, respectively). Microscopic observation and laser diffraction analysis revealed that neither the shape nor the size of the carrier particles was changed by the submersion treatment. However, the specific surface area and the amount of impurities appeared to decrease substantially after submersion, and the magnitude of the decrease was different for the different ethanol–water mixtures. The reduction in specific surface area was attributed particularly to the removal of the adhering lactose fines from the carrier surface. Mixtures with budesonide (in a wide range of carrier payloads) were prepared before and after treatment. Drug particle detachment from the various mixtures was studied with a sieve test and with a cascade impactor analysis at 30 and 60 l/min. Two different types of inhalers were used, one generating lift- and drag-forces (ISF inhaler) and one generating inertial forces (test inhaler), respectively. The cascade impactor and sieve test experiments showed that an increase in carrier surface smoothness results in a reduced drug particle detachment during inhalation, which was independent of the type of inhaler used. This reduction could be attributed to the removal of the adhering lactose fines which may provide shelter for the drug particles from press-on forces during mixing.

Particle size distribution analysis of sand‐sized particles by laser diffraction: an experimental investigation of instrument sensitivity and the effects of particle shape

AbstractLaser diffraction is now widely used for particle size distribution analysis of sediments and soils. The technique can be very precise, and offers advantages of speed and cost over many other methods when used to analyse mixtures of sand, silt and clay. This study presents the results of an experimental investigation that examined the sensitivity of the Beckman‐Coulter LS230 instrument to mixtures of different grain populations and differences in particle shape. The instrument was found to have high sensitivity to coarse particles in a finer matrix (detection threshold 1–2%), but much lower sensitivity to finer particles in a coarser mixture (detection threshold 12–17%). Experiments using near‐spherical ballotini showed that laser analysis provides very similar values to dry sieving for the mean, median and mode, but for a range of natural sand samples values for the mean, median and mode were offset by 8–21%, with an average of ca 15%, compared with sieving. Analysis using a Beckman‐Coulter RapidVUE instrument, which provides both size and shape information, provided support for the hypothesis that the differences between laser analysis and sieving are partly attributable to the effects of particle shape. However, an additional factor is the way in which the laser software interprets the optical diffraction data. The software predicts a high degree of log‐normality in the size distribution, such that highly skewed, truncated or bimodal samples are poorly represented. Experiments using sieved fractions of ballotini indicated that, even with near‐perfectly spherical particles, the particle size distribution predicted by the laser software includes a relatively large percentage of particles outside the sieve class limits.

Organic matter in density fractions of water-stable aggregates in silty soils: Effect of land use

The location of soil organic matter (SOM) within the soil matrix is considered a major factor determining its turnover, but quantitative information about the effects of land cover and land use on the distribution of SOM at the soil aggregate level is rare. We analyzed the effect of land cover/land use (spruce forest, grassland, wheat and maize) on the distribution of free particulate organic matter (POM) with a density <1.6 g cm −3 (free POM <1.6), occluded particulate organic matter with densities <1.6 g cm −3 (occluded POM <1.6) and 1.6–2.0 g cm −3 (occluded POM 1.6–2.0) and mineral-associated SOM (>2.0 g cm −3) in size classes of slaking-resistant aggregates (53–250, 250–1000, 1000–2000, >2000 μm) and in the sieve fraction <53 μm from silty soils by applying a combined aggregate size and density fractionation procedure. We also determined the turnover time of soil organic carbon (SOC) fractions at the aggregate level in the soil of the maize site using the 13C/ 12C isotope ratio. SOM contents were higher in the grassland soil aggregates than in those of the arable soils mainly because of greater contents of mineral-associated SOM. The contribution of occluded POM to total SOC in the A horizon aggregates was greater in the spruce soil (23–44%) than in the grassland (11%) and arable soils (19%). The mass and carbon content of both the free and occluded POM fractions were greater in the forest soil than in the grassland and arable soils. In all soils, the C/N ratios of soil fractions within each aggregate size class decreased in the following order: free POM <1.6>occluded POM <1.6–2.0>mineral-associated SOM. The mean age of SOC associated with the <53 μm mineral fraction of water-stable aggregates in the Ap horizon of the maize site varied between 63 and 69 yr in aggregates >250 μm, 76 yr in the 53–250 μm aggregate class, and 102 yr in the sieve fraction <53 μm. The mean age of SOC in the occluded POM increased with decreasing aggregate size from 20 to 30 yr in aggregates >1000 μm to 66 yr in aggregates <53 μm. Free POM had the most rapid rates of C-turnover, with residence times ranging from 10 yr in the fraction >2000 μm to 42 yr in the fraction 53–250 μm. Results indicated that SOM in slaking-resistant aggregates was not a homogeneous pool, but consisted of size/density fractions exhibiting different composition and stability. The properties of these fractions were influenced by the aggregate size. Land cover/land use were important factors controlling the amount and composition of SOM fractions at the aggregate level.

Reduced tabletability of roller compacted granules as a result of granule size enlargement

The mechanism for the frequently observed "loss of reworkability or tabletability" of dry-granulated (DG) powders was investigated in detail using microcrystalline cellulose (MCC). It was hypothesized that granule size enlargement is the primary mechanism to the phenomenon. Detrimental effects of size enlargement on tabletability of plastic materials are predictable based on the physical model of interparticulate bonding within a tablet. In absence of extensive fracture of particles/granules, larger particles/granules exhibit lower surface area available for bonding thus lower tensile strength when compressed under identical conditions. Size effects were first demonstrated using different grades of MCC powders, both whole and sieved, of different particle size distributions. Regardless grade and sieve fraction, larger particles always resulted in lower tabletability, that is, lower tensile strength at the same compaction pressure. It was subsequently shown that enlargement of granules also reduced powder tabletability regardless grade of MCC. Tabletability of sieved granules after roller compacted for one, two, and four times decreased monotonically with increasing granule size but independent of the total number of roller compaction. Moreover, tabletability of fine granules (44-106 microm) was higher than that of coarse MCC powder (Avicel PH-200). These results suggest that the primary mechanism for reduced tabletabilty of DG granules of MCC is granule size enlargement rather than "work-hardening."

Interrelationship between the severity of heat treatments and sieve fractions after impact ball milling: a mechanical test for quality control of thermally modified wood

Abstract Thermal modification processes improve the durability and dimensional stability of wood, but strength properties, especially dynamic ones, are compromised. Results from standard dynamic strength testing, such as impact bending tests, suffer from high variability and therefore require a high number of replicates. To overcome this, a new test method named high-energy multiple impact (HEMI) was developed by investigating heat-treated Picea abies Karst., Abies alba Mill. and untreated Robinia pseudoacacia L. The method is based on crushing small specimens by thousands of impacts from pounding steel balls in a heavy vibratory mill. The level of destruction was determined by sieving and analyzing the size distribution of the fragments. We calculated the resistance to impact milling (RIM) based on the mass of the size fractions. RIM shows a linear correlation with the intensity of the thermal treatment. The HEMI test method has the following advantages: small number of specimens, short time for specimen preparation, small variances, and high reproducibility of results.