Powder densification. 1. Particle-particle basis for incorporation of viscoelastic material properties (original) (raw)
Related papers
Journal of Pharmaceutical Sciences, 1998
A micromechanical model for predicting the densification of particulate matter under hydrostatic loading was developed to account for the time-dependent response of materials to applied loads. Viscoelastic material response used in the analysis was based upon a standard three-parameter rheological model. Compaction data under closed die conditions were collected using an Instron analyzer for different rates of applied load. Densification during the loading phase of PMMA/coMMA powder, a pharmaceutical polymeric coating material, was well predicted by the proposed algorithm, which contrasts with the prediction implied through a static indentation model. Secondary factors which affect compaction such as die-wall friction are also briefly discussed.
Modelling the compaction behaviour of powders: application to pharmaceutical powders
Powder Technology, 2002
Stress and density changes in axi-symmetric compaction of pharmaceutical powders are analysed numerically. Data measured in a compression cycle are used with a calibration procedure to assess the mechanical behaviour of powders in compaction based on a Drucker-Prager Cap model. This model is based on the elastic-plastic theory and takes into account the macroscopic characteristics of powders such as cohesion and global friction between particles. Moreover, a yield function is used to limit the admissible stresses in a tablet during a compaction cycle. This yield function depends on the first and second invariants of the stress tensor: pressure and stress deviation. To represent the plastic compaction mechanisms, a strain hardening function is used to expand the yield function with increasing volumetric strain. A finite element method coupled to the finite strain plasticity theory is used to calculate stress and strain changes in a tablet during compression and decompression. The die wall friction is estimated from the transmission effort to the lower punch with the modified equation of Shaxby and Evans. This model and the calibration procedure are applied to lactose powder. Mechanical properties calculated are compared to the experimental data measurements with a Jenike shear cell. The relative density distribution at the end of compaction and after the unloading is analysed. The normal pressure on the die is numerically estimated and analysed in terms of load transferred from powder to die during compaction and load restitution to tablet during decompression.
On the die compaction of powders used in pharmaceutics
Pharmaceutical development and technology, 2017
Die compaction is widely used in the compaction of pharmaceutical powders (tableting). It is well known that the powder densification is a result of particle rearrangement and particle deformation. The former is considered to be the governing mechanism of densification in an initial stage of compaction and the latter is regarded as the governing mechanism in the compaction at the higher pressure range. As a more realistic assumption, one can consider that a simultaneous performance of both the rearrangement and deformation mechanisms takes place from the beginning of compaction. To mathematically formulate this assumption, a piston equation is presented where the material relative density is given as a function of the applied pressure on the powder. From the equation, it is possible to obtain the contribution of each mechanism to the material densification at each value of the applied pressure. In the continuation, the piston equation is applied to the tabletting of some pharmaceuti...
Journal of Pharmaceutical Sciences, 1990
A model is presented which uses the hardness and elastic moduli of brittle crystals, determined using the Vickers microindentation test, to predict the uniaxial compaction behavior of compacts. A general approach first developed in the materials science field to predict the densification of particulate matter under hydrostatic loading was followed. Modifications to account for the effects of particle geometry and the closed-die loading conditions were considered. The model predicted the densification behavior of sucrose and adipic acid. It did not predict the densification of acetaminophen as well; however, the discrepancy between the experimental and predicted values may arise either from error associated with the evaluation of the elastic modulus using the microindentation test or from error in calculating the relative density of compacts which were observed to have partially laminated. The effects of error both in the hardness value and in the ratio of punch to die-wall stress on the predictive capability of the model were also discussed briefly.
Modelling the mechanical behaviour of pharmaceutical powders during compaction
Powder Technology, 2005
The mechanical behaviour of pharmaceutical powders during compaction is analysed using Finite Element Methods (FEM), in which the powder is modelled as an elastic-plastic continuum material. The Drucker-Prager Cap (DPC) model was chosen as the yield surface of the medium, which represents the failure and yield behaviours. Uniaxial compaction experiments were also carried out using a compaction simulator with an instrumented die. The objectives of these experiments were two-fold: (1) to investigate the pharmaceutical powder behaviour during compaction, for which the variation of relative density of the powder bed with applied pressure is analysed; and to calibrate the DPC model with the experimental measurements, from which realistic powder properties are generated and fed into finite element analysis (FEA). The relationship between relative density of powder bed and applied pressure is also obtained from FEA and compared with the experimental data. Good agreement between the experimental and FEA results is observed, which demonstrates that FEA can capture the major features of the powder behaviour during compaction. Furthermore, close examination of the evolution of the stress distribution during unloading reveals that there is a narrow band existing from the top edge towards the bottom centre of the tablet, in which there are localised, intensive shear stresses. It is in this band that potential failure regions, such as cracks, can initiate. This has been demonstrated with experimental evidence from X-ray microtomographical images and photography of fractured tablets. It is therefore demonstrated that FEA can predict the possible mechanism of failure, such as capping, during compaction. D
Application of Compaction Equations for Powdered Pharmaceutical Materials
Scientific Proceedings Faculty of Mechanical Engineering
The paper is focused on an analysis of the most frequently used compaction equations for powdered materials such as Heckel equation, Kawakita equation and Cooper-Eaton equation. Compacting powdered materials is accompanied by various mechanisms of densification dependent on the properties of the compressed material, which makes the equation more satisfactory for a certain group of materials and for another groups less so, or makes the equation completely unsuitable. To determine the suitability of the equation experimental measurements have to be implemented on an instrumented laboratory press. Then these obtained data are approximated by the specific compaction equation and use the regression analysis to determine the parameters describing the required material or physical properties of the compressed material.
COMPRESSION PHYSICS OF PHARMACEUTICAL POWDERS: A REVIEW
Due to various advantages such as high-precision dosing, manufacturing efficiency and patient compliance helped making tablets the most popular dosage forms among all available dosages forms. Compaction, which is an essential manufacturing step in the manufacture of tablets, mainly includes compression (i.e. reduction of volume of the powder under consideration and particle rearrangement) and consolidation (i.e., formation of interparticulate bond to facilitate stable compaction). The success of the compaction process depends not only on the physico-technical properties of drugs and excipients, but also on the instrument settings with respect to rate and magnitude of force transfer. Tablet manufacturing speed and pre/main compression force profile also have an influence on the quality of the final tablet. Mechanical aspects of tablet formation can be studied using, instrumented punches/dies, instrumented tablet punching machines, and compaction simulators. These have potential application in pharmaceutical research and development, such as studying basic compaction mechanism, various process variables, scale-up parameters, trouble shooting problems, creating compaction data library, and fingerprinting of new active pharmaceutical ingredients (APIs) or excipients. Mathematical models, forcetime, force-distance, and die-wall force parameters of tablet manufacturing are used to describe work of compaction, elasticity/plasticity, and time dependent deformation behavior of pharmaceuticals powder under consideration.
Powder Technology, 2012
The study's primary goal was to examine the possible use of single particle mechanical properties to estimate the compressibility behaviour of a tablet's excipients during compaction. Nanoindentation was utilised to measure individual mechanical properties (Young's modulus, nanoindentation hardness, energy of elastic and plastic deformation). On the bulk scale, studied excipients' compressibility was determined by Heckel and Walker models. Single particle hardness was found to provide direct information regarding an excipient's plasticity since an excellent correlation was established with the Walker model on the bulk level. A moderate correlation was obtained with the Heckel model due to its lack of fit for brittle materials. The indentation energy on a single level effectively differentiates materials in which plastic deformation dominates from those materials in which brittle fractures prevail. Elastic properties of materials can be successfully predicted by measuring the energy of elastic deformation on a single scale since an excellent correlation was observed with the bulk parameters such as energy of elastic deformation and the tablets' elastic relaxation index. We found that individual mechanical properties of a tablet's excipients greatly control the materials' deformation behaviour during tablet production despite of numerous other processes occurring during compression in the tablet die such as friction, bonding and local mechanical stress.
Particle size distribution and evolution in tablet structure during and after compaction
International journal of pharmaceutics, 2005
The objective of this study was to investigate the effect of the distribution in size of free-flowing particles for the evolution in tablet structure and tablet strength. For sucrose and sodium chloride, three powders of different size distributions were prepared by mixing predetermined quantities of particle size fractions. For paracetamol, three batches with varying particle size distributions were prepared by crystallisation. The powders were formed into tablets. Tablet porosity and tensile strength were determined directly after compaction and after short-term storage at two different relative humidities. Tablets were also formed after admixture of a lubricant (magnesium stearate) and the tablet tensile strength was determined. For the test materials used in this study, the spread in particle size had no influence on the evolution in tablet porosity and tensile strength during compression. However, the spread in particle size had a significant and complex influence on the short-...
Particuology, 2014
During the production of pharmaceutical tablets using powder compaction, certain common problems can occur, such as sticking, tearing, cutting, and lamination. In the past, the compressibility of the powder was calculated only along the axis of the device; consequently, critical areas of the material throughout the volume could not be identified. Therefore, finite element method (FEM) can be used to predict these defects in conjunction with the use of an appropriate constitutive model. This article summarizes the current research in the field of powder compaction, describes the Drucker-Prager Cap model calibration procedure and its implementation in FEM, and also examines the mechanical behavior of powder during compaction. In addition, the mechanical behavior of pharmaceutical powders in relation to changes in friction at the wall of the system is examined, and the dependence of lubrication effect on the geometry of the compaction space is also investigated. The influence of friction on the compaction process for the flat-face, flat-face radius edge, and standard convex tablets is examined while highlighting how the effects of friction change depending on the shape of these tablets.