A modeling approach for understanding effects of powder flow properties on tablet weight variability

In this paper we focus on the effect of cohesion and compression speed on the outcome of the compression process for both monodisperse and polydisperse granular systems. A three dimensional discrete element model (DEM) which incorporates static and dynamic friction is used in this study to simulate die filling, and the compaction and decompaction of cohesive granular system in a confined cylindrical die similar to those used in a commercial tablet press driving the pre-compressive stage. The magnitude of the cohesive force is represented in terms of a parameter K = F_cohes/mg, where K is called the bond number and is the measure of cohesiveness. Force displacement curves are used to characterize the compression and deformation properties of the materials and are obtained by measuring the force on the upper punch and the corresponding displacements in the die. Results show that a considerable more energy is needed to compress the cohesive material as compared to free flowing materials. It is found that the time required to fill the die strongly depends on the cohesion of the material. The energy for the tableting process is directly proportional to the upper punch speed.     

The effect of processing parameters on amorphous carbon nitride layer properties

Surface morphology, deposition rate (DR), bonding composition, structural, optical and electrical properties of pulsed laser deposited amorphous carbon nitride (a-CN_x) layers using camphoric carbon (C₁₀H₁₆O) target precursor as a function of substrate temperatures (STs), laser fluences (LFs) and target to substrate distances (TSDs) are reported. At fixed LF and TSD, surface roughness, particle density and particle size increase, whereas the DR decreases with higher ST. When the TSD and ST are fixed, surface roughness, particle density, deposition rate and nitrogen (N) content increase, whereas particle size decreases with higher LF. While when the LF and ST are fixed, decreasing TSD results in an increase in the irregular small particle size, particle density, surface roughness, DR and N content. The N content in a-CN_x layers is found to increase with higher ST up to 400 °C and decrease thereafter. While the increase of LF and decrease of TSD result in an increase in the N content. We found that the amorphous structure of a-CN_x layers and the ratio of sp² trihedral component to sp³ tetrahedral component are strongly dependent on ST, LF and TSD. The a-CN_x layers with high N content have relatively high electrical resistivity.     

Numerical and experimental investigation of capping mechanisms during pharmaceutical tablet compaction

Capping is a common problem in the pharmaceutical tabletting process in which catastrophic failure of the powder compact can occur. It is of great interest to the pharmaceutical industry to understand the fundamental reasons why capping occurs and how it can be avoided. Recently, a combined numerical and experimental study on pharmaceutical powder compaction revealed that cone capping, which is a typical failure mechanism during the production of flat-faced cylindrical tablets using powders of low tensile strength, is due to the formation of a narrow band with localised, intensive shear stresses running from the top edge towards the bottom centre of the tablet [C.Y. Wu, O. Ruddy, A.C. Bentham, B.C. Hancock, S.M. Best, J.A. Elliott, Modelling the mechanical behaviour of pharmaceutical powders during compaction, Powder Technology, 152 (2005)107-117.]. In this paper, the results of further studies are reported in an attempt to explore possible methods to alleviate the propensity for tablets to cap. These methods have been systematically investigated using finite element methods (FEM), and include using lubrication to reduce the die-wall friction, employing different tooling kinematics (speeds and compression profiles), making tablets with different thicknesses, and making convex tablets using punches with curved surfaces. It has been found that none of these methods could avoid the development of intensive shear bands during unloading, which implies that capping cannot necessarily be avoided using these methods. In addition, physical experiments using a compaction simulator have also been carried out, in particular, for making convex tablets with different curvatures. The tablets produced were examined using X-ray microtomography (XMT), from which the failure patterns were identified and found to be in very good agreement with the numerical analysis. The combination of experimental and numerical studies has demonstrated that: (i) capping takes place during the decompression (unloading) phase, and (ii) the intensive shear bands formed during decompression are responsible for the occurrence of capping.     

Wet granulation: the effect of shear on granule properties

This paper presents a study of the wet granulation of fine cosmetic particles using a high-shear mixer granulator on a given particle and binder system. The shear effect on granule properties is highlighted. The granules formed under different impeller speeds are divided into size classes and further examined in terms of porosity, friability and binder content.

The main result of this study is that, depending on operating conditions, the granulation of a fine powder with a given binding liquid can result in the formation of granules of very different characteristics in terms of size, porosity and friability. Mechanical energy brought to the granulation system is as important as the physicochemical characteristics of the powder–binder pair.     

Composition,processing, and properties of biphasic zirconia bioceramics: Relationship to competing strength and optical properties

A study is made of relationships between composition, processing, structure and properties of biphasic zirconia bioceramics. The focus is on zirconia compositions with different yttria dopant contents used in modern dental restorations, namely 3–5 mol% yttria stabilized zirconia (3YSZ, 4YSZ, and 5YSZ). Crystallographies and densities are surveyed, sintering conditions examined, and microstructures characterized. Strength and optical tests are conducted on each YSZ, and dependencies on sintering temperature, cubic content and grain size analyzed. Strength correlates with the amount of tetragonal zirconia (t-ZrO₂) crystals with large lattice distortions (tetragonality). YSZ translucency correlates with content of cubic zirconia (c-ZrO₂) and t-ZrO₂ with low levels of tetragonality. Consistent with literature reporting, the materials rank in decreasing order 3YSZ, 4YSZ to 5YSZ for strength but increasing order for translucency. However, for a given composition, the data suggest that the strengths of densely sintered 3YSZ and 4YSZ actually increase with translucency, although that of 5YSZ remains undiminished. These trends are in apparent contradiction to prevailing experience, and offer potential future processing routes to optimization of clinical materials.     

Study of the effects of feed frames on powder blend properties during the filling of tablet press dies

This paper studies systematically the effect of a feed frames, a device used in rotary tablet presses to drive the powders into compression dies, on the properties of the powders entering the tablet press dies. The work focused on the effect of blend composition, feed frame parameters (blade speed, residence time), and rotary die disc parameters (die disc speed, die diameter) on the flow pattern, uniformity of die filling, applied shear, and the flow properties of pharmaceutical blends. The flow pattern suggests a stratified filling of the dies and therefore, non-uniform properties of the tablets. The amount of powder entering the dies depended on blend flow properties, feed frame speed, and dies disc speed. In addition, blend properties changed significantly as the powder flowed through the feed frame. The flowability of lubricated blends improved significantly as the number of feed frame blade passes increased, decreasing in turn the RSD of the die filling weight.     

Improving mechanical properties of porous calcium phosphate scaffolds by constructing elongated gyroid structures using digital light processing

The present study reports the manufacturing of a novel type of porous calcium phosphate scaffolds with elongated gyroid structures using digital light processing (DLP), in order to offer significantly enhanced mechanical properties. In particular, solid camphor was employed as the diluent, in order to offer sufficiently low viscosity at high solid loading for conventional layer-by-layer DLP process. Four types of porous CaP scaffolds with different percent elongation (%EL = 0, 20, 40, and 60) were manufactured, and their porous structures and mechanical properties were characterized. All porous CaP scaffolds showed that CaP walls were elongated along the z-direction, while the degree of pore elongation increased with an increase in the designed %EL. Owing to the use of controlled processing parameters, such as layer thickness and exposure time for layer-by-layer photocuring process, and carefully designed debinding process, the photocured layers could be completely bonded together with high densification after sintering at 1,200 °C for 3 h. Such elongation of a gyroid structure offered significantly enhanced mechanical properties ? compressive strengths of 4.33 ± 0.26 MPa and 11.51 ± 1.75 MPa were obtained for the porous CaP scaffold with the %EL of 0 and 60, respectively.     

The effect of EVA content on the processing parameters and the mechanical properties of LDPE/ground tire rubber blends

In this work, thermoplastic elastomers were prepared based on low‐density polyethylene (LDPE) and ground tire rubber (GTR). To improve the adhesion and achieve better rubber‐like properties, ethylene vinyl acetate copolymer (EVA) was selected and used as a compatibilizer. The GTR and EVA content were varied between 0–45 and 0–20 wt%, respectively. Blends with different composition were produced from the raw materials on a twin screw extruder. Tensile and instrumented falling weight impact (IFWI) specimens were injection molded from the granulated blends. Injection pressure and the shrinkage of the IFWI specimens were measured. Besides the tensile and IFWI tests, the cut cross‐sections were inspected with a scanning electron microscope. Based on the results, it can be stated that the application of EVA as a compatibilizer is essential for even lower weight percentage to ensure the rubber‐like properties, but as the EVA content is increased, only less additional improvement can be detected. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effects of rheological properties and processing parameters on ABS thermoforming

Understanding effects of material and processing parameters on the thermoforming process is critical to the optimization of processing conditions and the development of better materials for high quality products. In this study we investigated the influence of both rheological properties and processing parameters on the part thickness distribution of a vacuum snap‐back forming process. Rheological properties included uniaxial and biaxial elongational viscosity and strain hardening and/or softening while processing parameters included friction coefficient, heat transfer coefficient, and sheet and mold temperatures. The Wagner two parameter nonlinear viscoelastic constitutive model was used to describe rheological behavior and was fit to shear and elongational experimental data. The linear viscoelastic properties along with the Wagner model were utilized for numerical simulation of the thermoforming operation. Simulations of pre‐stretched vacuum thermoforming with a relatively complex mold for a commercial refrigerator liner were conducted. The effects of nonlinear rheological behavior were determined by arbitrarily changing model parameters. This allows determination of which rheological features (i.e., elongational mode, viscosity, and strain hardening and/or softening) are most critical to the vacuum snap‐back thermoforming operation. We found that rheological and friction properties showed a predominant role over other processing parameters for uniform thickness distribution.     

高岭土性能研究及其对炮泥性能的影响

对宝钢炮泥用过的两种不同产地的200目(≤0.074 mm)高岭土SZ和SX进行了化学分析、XRD物相分析、SEM显微结构观察和粒度分布测定,以了解两种高岭土的性能差异;并对添加15%(质量分数)的两种高岭土所制备的炮泥进行了马夏值和不同温度处理后常温耐压强度的测定,以研究选用不同高岭土的炮泥的性能差异。结果表明:与SZ高岭土相比,SX高岭土的纯度更高,粒度更细,含有叶蜡石相,且其片状晶层解理完整。因此,在同样条件下,含叶蜡石相的SX高岭土可以赋予炮泥更好的可塑性,并提高炮泥的烧结强度。     

Effects of process parameters on granules properties produced in a high shear granulator

Results of a study on the influence of process parameters such as impeller speed, granulation time and binder viscosity on granule strength and properties are reported. A high shear granulator (Cyclomix manufactured by Hosokawa Micron B.V., The Netherlands) has been used to produce granules. Calcium carbonate (Durcal) was used as feed powder and aqueous polyethylene glycol (PEG) as the binder. The dried granules have been analysed for their strength, density and size distribution. The results show that increasing the granulation time has a great affect on granules strength, until an optimum time has been reached. The underlying cause is an increase in granule density. Granules are consolidated more at higher impeller speeds. Moreover, the granule size distribution seems not to be affected significantly by an increase in impeller speed. Granules produced with high binder viscosity have a considerably lower strength, wide strength distribution due to poor dispersion of binder on the powder bed. Binder addition methods have showed no considerable effect on granule strength or on granule size distribution.     

Microstructure and properties of Si3N4 foam ceramics modified by in-situ self-grown nanowires

In this study, Si₃N₄ nanowires were prepared by one-step method in Si₃N₄ foam ceramics. This was accomplished via simple and safe pre-embedded powder treatment combined with reaction sintering method. Nitriding temperature and time were determined to have influence on the production of nanowires. Under used sintering conditions with nitriding at 1400 °C for 4–6 h or at 1450 °C for 2–6 h, densely distributed nanowires were obtained in the sample, and the formed nanowires were either straight or bent. The straight nanowires were completely crystalline, while the bent nanowires had staggered crystalline-amorphous distribution at the bending position. Nanowires in the sample did not substantially affect open porosity and density of the sample. However, the analysis of typical samples with or without dense nanowires revealed that the existence of densely distributed nanowires reduced median pore diameter of windows on the pore walls from 60.7 μm to 21.4 μm and increased BET specific surface area of the sample by 46.7%. In addition, the presence of densely distributed nanowires in pores enhanced compressive strength of the sample by at least 10%.     

Free surface electrospun fibers: The combined effect of processing parameters

In this study, a free surface electrospinning experimental setup was developed based on rotating spiral copper wire electrode and used as the spinneret. The scheme was investigated by varying processing parameters including polymer solution concentration, distance between the electrode and the collector, applied voltage between the electrode, and the collector and wire electrode diameter. An average of fiber diameter ranged between 202 and 543 nm and a relative standard deviation ranged between 11.0 and 26.9% were obtained. The combined effects of processing parameters on the resulting fiber morphology were investigated. The analysis shows that in a multiple variable process like electrospinning, the interaction between the different processing parameters played an important role, rather than one parameter separately in obtaining desired nanofibers. Knowing the relative combined effects of processing parameters on fiber morphology should be useful for process control and prediction of electrospun fiber quality as it has been demonstrated in this study. POLYM. ENG. SCI., 54:189–197, 2014. © 2013 Society of Plastics Engineers     

Analysis of catalyst particle strength by impact testing: The effect of manufacturing process parameters on the particle strength

The mechanical strength of porous alumina catalyst carrier beads, used in the reforming units with continuous catalytic regeneration, was measured by impact testing. With this testing method particle strength can be measured at higher strain rates than the traditional crushing test method, hence providing a better simulation of pneumatic conveying and chute flow conditions, and also a large number of particles can be tested quickly. This is important for particles with a brittle failure mode such as the alumina particles used in this work as a wide distribution of mechanical strength usually prevails. Extensive impact testing was carried out first with an industrial sample, in order to understand the failure mechanism of this type of particles and to develop a methodology for analysing the extent of breakage by impact. Then the method was used to analyse the effect of a number of process parameters, such as filler, macroporosity and drying procedure on the particle strength with the aim of optimising the manufacturing process. The impact test results were then used to test the model of breakage behaviour of particulate solids proposed by Vogel and Peukert [Vogel and Peukert, Breakage behaviour of different materials—construction of a mastercurve for the breakage probability. Powder Technol., 129 (2003) pp. 101-110].     

Effects of processing parameters on material properties of mechanically processed polyamide

A semicrystalline polyamide polymer was processed using a new technique known as mechanical alloying. The material processed by this technique was first introduced into a high-energy ball mill and ground over long periods of time, resulting in the production of extremely fine powders. These powders were subsequently consolidated well below the materials' melting-point temperature. The effect of processing parameters including mechanical milling time, consolidation temperature, and the length of consolidation time were studied fairly extensively. The investigation shows that polyamide powders are continually refined with increasing mechanical milling time and the resulting materials have improved mechanical properties. The influence of both consolidation temperature and the length of consolidation time on material properties indicate that materials with higher density, crystallinity, hardness, strength, and ductility are produced when consolidated using higher temperatures and longer times. © 1995 John Wiley & Sons, Inc.     

The effect of processing parameters on cell structure and mechanical properties of extrusion‐foamed poly(vinyl chloride) sheets

The objective of this study was to investigate the effect of processing parameters on cell structure and mechanical properties of extrusion‐foamed poly(vinyl chloride) sheets. For this purpose, the effects of screw speed and die temperature on cell morphology, density, and mechanical properties, including tensile strength, elongation at break, flexural strength, and notched impact strength of the foam samples, were determined under the same conditions. The experimental results indicated that the extrusion‐foaming process was comparatively stable as the screw speed changed in the range of 5.5–8.5 rpm. It was also shown that the lower the die temperature, the higher the die pressure and pressure drop rate, which is conducive to uniform bubble nucleation. In addition, the lower die temperature was beneficial for bubble solidifying and shaping. Therefore, in the range of temperature allowed, the lower the die temperature, the foamed poly(vinyl chloride) sheets with better cell structure and mechanical performance can be obtained. J. VINYL ADDIT. TECHNOL., 22:377–383, 2016. © 2014 Society of Plastics Engineers     

The influence of processing parameters on the properties of melt‐spun polypropylene hollow fibers

Isotactic polypropylene hollow fibers were produced by melt spinning. Spinning speeds up to 1880 m/min were used, and sample hollowness (percentage void in cross section) ranged from 0 to 69%. The fiber samples were characterized using dynamic mechanical analysis, birefringence, tensile testing, and differential scanning calorimetry. The hollow fibers were found to have higher crystallinity, orientation, and strength than the analogous solid fibers. In general, the polymer orientation in a hollow fiber was larger than the orientation in a solid fiber, even when the spinning speed for the latter was much larger. For a fixed outer diameter, increasing the hollowness improved fiber properties. However, as hollowness was further increased, fiber properties declined slightly. At a given percentage hollowness, increased spinning speed increased modulus and tenacity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1759–1772, 2002     

Effect of down-stream processing parameters on the mechanical properties of bacterial cellulose

Bacterial cellulose (BC), a biodegradable polymer with high degree of crystallinity, produced by Gluconacetobacter xylinus, was used as reinforcement in biocomposites. The downstream process parameters involved in the preparation process of BC have important influence on its mechanical properties. The effect of some key processing parameters such as treatment temperature, drying stages, type of treatment solvent and pressure on biocellulose sheets was investigated during drying in order to modify the parameters responsible in mechanical properties. The rise in treatment temperature and drying processes of BC sheets showed about 8 and 11 % reduction in tensile strength, respectively. The addition of NaOH solutions during the treatment reduced the tensile strength of BC sheets sharply, though an increase in NaOH concentration produced treated samples with higher tensile modulus. The use of optimum NaClO solution as a cheap treatment solvent led to an increase of about 10–11 % in the mechanical properties of BC. A pressure increase during drying stage improved the tensile strength of biocellulose sheets by 7 % and resulted in highly enhanced tensile modulus of BC samples. The production process (microbial fermentation) and structural features (porous web-shaped structure) provide an ideal scenario for synthesis of BC composites. A number of schemes have been introduced to synthesize BC composites with different materials. Among these schemes, the initial addition of materials to BC culture media, the treatment of BC with solutions and suspensions, and the dissolution of BC in solvents are the most commonly used techniques.     

The effects of processing parameters on the tensile properties of weld lines in injection molded thermoplastics

Weld or knit lines result wherever two or more polymer flow fronts unite. This results in a region of a different level of molecular entanglements than the bulk material. Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. Although this phenomenon occurs in almost all the commercially important polymer processes, there has been little systematic investigation. The effects of melt temperature, mold temperature, injection speed and injection pressure on the tensile properties of commercial grades of polystyrene (GPS), high impact polystyrene (HIPS) and polypropylene (PP) are examined. The most important processing parameters seemed to be melt and mold temperature; injection speed and pressure had little effect on the tensile properties of any of the samples. A higher melt temperature increased both the strain and stress at break considerably in GPS. In HIPS increased melt temperature increased only the elongation to break substantially. Increased mold temperature improved the stress and elongation to break in GPS but not as much as melt temperature. Polypropylene showed improved weld yield strength with increased mold temperature. Under the conditions examined, injection pressure and injection speed showed no effect on the tensile properties of any of the materials investigated.     

The effect of particle size of body components on the processing parameters of semi transparent porcelain

The effect of the particle size of quartz and K- feldspar on the sintering behaviour and technical properties of semi transparent porcelain were investigated. This study was implemented by “the Factorial Experimental Design Method” to determine the effect of factors on semi vitreous porcelain production. The sintering behaviour of the samples were examined by using an optical dilatometer. The phases and their respective amounts in the microstructure were determined by way of Rietvelt X- ray diffraction (XRD) technique. Furthermore, the values such as shrinkage, water absorption, bulk density, porosity, thermal expansion, light transmission measurements were taken on the samples and the microstructures were studied by SEM. It was observed that as the particle size of quartz and K- feldspar decreased; the viscosity of the liquid phase fell down, the relative amount of secondary mullite crystals increased and the large pores were removed among the particles and the densification rate increased. Data were analysed by Minitab 13.20 software, and assessed in relation to the amount of glassy phase and its viscosity. The effect of K- feldspar particle size on the densification of porcelain is less than the change of heat treatment and quartz particle size.