| 1. |
- Frenning, Göran, et al.
(författare)
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An effective-medium analysis of confined compression of granular materials
- 2009
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 194:3, s. 228-232
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Tidskriftsartikel (refereegranskat)abstract
- A simplified model for confined compression of granular materials is considered, which idealizes the collection of particles as a (central) force network. Applying an effective-medium procedure, an equation with micromechanically well-defined parameters is derived, which relates the applied pressure to the engineering strain of the powder during uniaxial compression. Despite the simplicity of the model, comparison with experimental data for mm-sized spherical granules indicates that this equation is able to satisfactorily predict the overall compression profile from single-particle data.
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| 2. |
- Frenning, Göran, et al.
(författare)
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Effective Kawakita parameters for binary mixtures
- 2009
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 189:2, s. 270-275
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Tidskriftsartikel (refereegranskat)abstract
- Despite the fact that many industrial processes use mixtures of powders with different physical and mechanical properties, most fundamental studies of powder compression have focused on single-component systems. There is thus an obvious need for an improved understanding of the compression behaviour of mixtures of particulate and granular solids. In this contribution, we show that the Kawakita equation may be particularly useful in this regard. The reason for this is that the degree of compression (i.e., the ratio between the volume reduction and the initial powder volume) for sufficiently high compression pressures P is a linear function of I I P. For ideal mixtures, for which the volume of each component may be determined independently of the others, this linearity implies that effective Kawakita parameters for the mixture may be readily expressed in terms of the parameters of its components. In order to validate the proposed approach, binary mixtures of mm-sized spherical agglomerates prepared by wet granulation followed by extrusion and spheronization were investigated experimentally. Predicted and measured Kawakita parameters were generally in good agreement, indicating that the assumption of ideal mixing behaviour is valid for this type of systems.
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| 3. |
- Hellrup, Joel, et al.
(författare)
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Powder compression mechanics of spray-dried lactose nanocomposites
- 2017
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 518:1-2, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the structural impact of the nanofiller incorporation on the powder compression mechanics of spray-dried lactose. The lactose was co-spray-dried with three different nanofillers, that is, cellulose nanocrystals, sodium montmorillonite, and fumed silica, which led to lower micron sized nanocomposite particles with varying structure and morphology. The powder compression mechanics of the nanocomposites and physical mixtures of the neat spray-dried components were evaluated by a rational evaluation method with compression analysis as a tool using the Kawakita equation and the Shapiro-Konopicky-Heckel equation. Particle rearrangement dominated the initial compression profiles due to the small particle sizes of the materials. The strong contribution of particle rearrangement in the materials with fumed silica continued throughout the whole compression profile, which prohibited an in-depth material characterization. However, the lactose/cellulose nanocrystals and the lactose/sodium montmorillonite nanocomposites demonstrated increased yield pressure compared with the physical mixtures indicating increased particle hardness. This increase has likely to do with a reinforcement of the nanocomposite particles by skeleton formation of the nanoparticles. In summary, the rational evaluation applying compression analysis proved to be a valuable tool for mechanical evaluation for this type of materials unless they demonstrate particle rearrangement throughout the whole compression profile.
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| 4. |
- Jonsson, Henrik, et al.
(författare)
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An apparatus for confined triaxial testing of single particles
- 2015
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 270, s. 121-127
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Tidskriftsartikel (refereegranskat)abstract
- A novel triaxial apparatus employing overlapping rigid boundaries has been designed and constructed for experimental measurement of contact forces under confined compression of single granules in the mm-scale. The performance of the apparatus was evaluated by performing uniaxial and triaxial compression experiments on ideal elastic-plastic materials. Compression curves were compared with the fully plastic Abbott-Firestone contact model and with results from FEM simulations. The increase in contact force associated with confined conditions was observed in the compression curves from triaxial compression experiments, as supported by predictions from simulations using single particle contact models. Hence, a new method for the assessment of mechanical behaviour of single particles under confined compression can be considered as established.
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| 5. |
- Klevan, Ingvild, et al.
(författare)
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A statistical approach to evaluate the potential use of compression parameters for classification of pharmaceutical powder materials
- 2010
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Ingår i: European journal of pharmaceutics and biopharmaceutics. - : Elsevier BV. - 0939-6411 .- 1873-3441. ; 75:3, s. 425-435
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Tidskriftsartikel (refereegranskat)abstract
- The current work aims to investigate whether a multivariate statistical approach could reveal latent structures in compression data and group powders with respect to their compression behavior in a way that is consistent with an earlier proposed classification system. Seventeen pharmaceutically relevant materials, exhibiting a wide range of mechanical properties, were used as supplied, compressed, and parameters from three commonly used powder compression models (Kawakita parameters a and b(-1), the rearrangement index ab, the Shapiro f parameter and Heckel P(y)) were retrieved. Multivariate analysis of the compression parameters was done with a Principal Component Analysis (PCA). It was found that the latent structures could be divided into three main parts; the most variation was found in the direction associated with particle rearrangement, second largest variation was found in the direction described by the particle fragmentation propensity, and the least variation was found in the direction associated with the plasticity of the particles. This work demonstrates that a combination of the selected compression parameters could be utilized to find relevant differences in compression behavior for a wide range of materials, and that this information can be presented in an efficient way by applying multivariate data analysis techniques.
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| 6. |
- Klevan, Ingvild, et al.
(författare)
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On the physical interpretation of the initial bending of a Shapiro-Konopicky-Heckel compression profile
- 2009
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Ingår i: European journal of pharmaceutics and biopharmaceutics. - : Elsevier BV. - 0939-6411 .- 1873-3441. ; 71:2, s. 395-401
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the natural logarithm of the tablet porosity arc! the applied pressure is used to describe the compression behavior of a powder. Such a relationship, here referred to as a Shapiro-Konopicky-Heckel (SKH) profile, is usually divided into three regions, of which the first often is non-linear. The objective of this work was to address the question of the mechanisms controlling the compression and the bending of the first region of a SKH profile for dense particles. In this paper, the first region was described by the Shapiro General Compression Equation, from which a compression parameter was derived as a measure of the bending. The results indicate that for powders undergoing significant particle rearrangement at low applied pressures, the particle rearrangement is the major cause for the initial bending of the SKH profile. For powders showing limited particle rearrangement, the initial bending is mainly caused by the change in particle diameter due to particle fragmentation. It is concluded that the evaluation of the first region of a SKIT profile in terms of bending may be used to assess particle fragmentation. The SKH profile could hence be a useful tool to describe powder compression behavior in terms of particle fragmentation and particle deformation from one single compression analysis.
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| 7. |
- Mahmoodi, Foad, et al.
(författare)
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A comparison between two powder compaction parameters of plasticity : The effective medium A parameter and the Heckel 1/K parameter
- 2013
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 453:2, s. 295-299
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the research was to introduce a procedure to derive a powder compression parameter (EM A) representing particle yield stress using an effective medium equation and to compare the EM A parameter with the Heckel compression parameter (1/K). 16 pharmaceutical powders, including drugs and excipients, were compressed in a materials testing instrument and powder compression profiles were derived using the EM and Heckel equations. The compression profiles thus obtained could be sub-divided into regions among which one region was approximately linear and from this region, the compression parameters EM A and 1/K were calculated. A linear relationship between the EM A parameter and the 1/K parameter was obtained with a strong correlation. The slope of the plot was close to 1 (0.84) and the intercept of the plot was small in comparison to the range of parameter values obtained. The relationship between the theoretical EM A parameter and the 1/K parameter supports the interpretation of the empirical Heckel parameter as being a measure of yield stress. It is concluded that the combination of Heckel and EM equations represents a suitable procedure to derive a value of particle plasticity from powder compression data.
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| 8. |
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| 9. |
- Nordström, Josefina, et al.
(författare)
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A particle rearrangement index based on the Kawakita powder compression equation
- 2009
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 98:3, s. 1053-1063
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the effect of original particle size on the Kawakita parameters, denoted a and b, has been studied using four model materials of different compression mechanics. It was found that fine powders, possibly showing significant particle rearrangement at low compression pressures, showed low values of parameter b(-1) and high values of parameter a. It is thus proposed that the product of these parameters is an indication of the overall contribution of particle rearrangement to the compression profile. Above a critical original particle size of a powder, particle rearrangement is negligible for the overall compression profile and below this critical particle size, particle rearrangement becomes significant. A critical particle size of about 40 microm was obtained. A classification of powders into groups dependent on the incidence of particle rearrangement is discussed and it is suggested that a rearrangement index and a classification system could be used as tools to enable rational interpretations of global compression parameters.
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| 10. |
- Nordström, Josefina, et al.
(författare)
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Compressibility and tablet forming ability of bimodal granule mixtures : Experiments and DEM simulations
- 2018
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Ingår i: International Journal of Pharmaceutics. - : Elsevier. - 0378-5173 .- 1873-3476. ; 540:1-2, s. 120-131
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Tidskriftsartikel (refereegranskat)abstract
- Compressibility and tablet forming ability (compactibility) of bimodal mixtures of differently sized granules formed from microcrystalline cellulose were studied experimentally and numerically with the discrete element method (DEM). Compression data was analysed using the Kawakita equation. A multi-body contact law that accounts for contact dependence resulting from plastic incompressibility/geometric hardening was used in the DEM simulations. The experimental Kawakita a and 1/b parameters both depended non-monotonically on composition (weight fraction of large particles). For the a parameter, this dependence was explained by variations in the porosity of the initial granule beds; for the 1/b parameter, other factors were found to be of importance as well. The numerical results generally compared favourably with the experiments, demonstrating the usefulness of the DEM at high relative densities, provided that a suitable multi-particle contact model is used. For all mixtures, the tensile strength of the formed tablets increased with increasing applied pressure. The tensile strength generally decreased with increasing fraction of large particle, and this decrease was more rapid for large differences in particle size. A possible interpretation of these findings was proposed, in terms of differences in lateral support of small particles in the vicinity of large particles.
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