Analysis of densification mechanisms of dry granulated materials

International audienceDry granulation by roll compaction is a continuum manufacturing process to produce granules with improved flowability which can further be easily used in tableting process. However, the granules are non-homogeneous in density and have non-spherical shapes which impact their densification behaviour during die-compaction. The aim of this study was to investigate both the densification mechanism and the failure strength of granules of microcrystalline cellulose (MCC) and mannitol using Cooper-Eaton and Adams models. For both materials, the Cooper-Eaton approach led to the quantification of fractional volume compaction by particle rearrangement and by plastic deformation respectively to explain the difference in densification behaviour of raw material and granules. Moreover, the model showed its ability to capture the effect of granule density and granule sizes and to differentiate the densification mechanisms of MCC as a plastic material and mannitol as a brittle material. The Adams model was used to compute the failure strength of single granule from in-die compression data. The obtained results of the granules were in the range [0.6–1.43  MPa]. However, regarding the effect of granule density, the model showed mixed results indicating that the model is not representative of the studied granules which are not spherical and have a relatively wide range of sizes, nevertheless, the model was derived for near spherical particles with a narrow size distribution

Stoichiometry and particle morphology effects on the aptitude to compaction of apatitic structure powders

Symposium on Powder Science and Technology - Powders and Sintered Material, Albi, FRANCE, MAY 23-25, 2007International audienceApatitic calcium phosphates powders with Ca/P molar ratio of 1.5 to 1.8 were synthesized at 25 degrees C using the neutralization method. These powders, differing by stoichiometry and particle morphology, were compacted in similar conditions. For a similar morphology of particles, compacts of the non-stoichiometric powders have better cohesion than those of the stoichiometric hydroxyapatite (Ca-10(PO4)(6)(OH)(2): Ca/P=11.67). The lacunar structure, with deficiency of calcium (Ca10-x (HPO4)(x)(PO4)(6-x)(OH)(2-x): 1.5 <Ca/P<1.67), seems to favour the densification process and cohesion between particles during the compaction. The better tensile strength (0.79 MPa) was obtained for the powder with the lowest atomic ratio (Ca/P=1.5, x=1). The apatite powder (Ca/P = 1.78), which has a smooth and porous structure, presented the best transmission load ratio (95.5%), the lowest die-wall friction (mu=0.1) and the highest strength (3.12 MPa). These results show the importance of chemical composition and morphological properties of synthesized particles in the development of better hydroxyapatite powders for the compaction process

Relationship between single and bulk mechanical properties for zeolite ZSM5 spray-dried particles

In this work typical mechanical properties for a catalyst support material, ZSM5 (a spray-dried granular zeolite), have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy (SEM), confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Carr index. This was confirmed by bulk measurements of the particle–particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical proper-ties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test

Numerical simulation of roll compaction of aerated powders

International audiencePermeating air is known to have a negative impact on the roller compaction process, because the feed is destabilized by the flow of escaping gas, causing pressure to build-up and potentially damage compacts at release. Airflow during powder roller compaction and its effect on the rolling process are investigated in the rolling direction (1D), using an extension of the Johanson model for the solid. Fluid transport obeys Darcy's law, with permeability being a function of both material density and particle size, through the Kozeny-Carman relationship. In this modeling, the effect of the air pressure on the solid is neglected in the compaction zone. Assuming air at atmospheric pressure at the feeding angle and ignoring airflow through the gap, predictions of air pressure as a function of the rolling angle for bentonite material powder are presented and discussed. Results suggest the existence of two different stability zones within the operating conditions, where industrial systems could function without being affected by airflow effects. The model highlights the importance of the permeability/rotation speed ratio, which governs the proportion of air trapped in the compacts to the portion evacuated through the feed. We also investigate the effect of particle fragmentation during the rolling process. Finally, we provide guidelines for the scale-up of roller presses subjected to air flow issues, through a study of the effect of the system dimensions and rotation speed on the elimination of air. In spite of the lack of available experimental data, this model allows for a better understanding of how air escapes by diffusing through the material during the rolling process, and opens interesting perspectives for the mitigation of its effect on the process

Why Are International Visitors More Satisfied with the Tourism Experience? The Role of Hedonic Value, Escapism, and Psychic Distance: .

International audiencePrevious studies have consistently observed that international visitors are more satisfied with the tourism experience than their domestic counterparts. To date, however, no study has provided empirical evidence of the mechanism that could explain this phenomenon. Building on the experiential paradigm, we conducted two empirical studies (a field study and an online experiment) showing that the reason foreign (vs. domestic) visitors exhibit higher levels of satisfaction lies in the greater hedonic value that these tourists derive from their experience. Moreover, the greater hedonic value observed among international foreign visitors is due to the deeper feeling of escapism they experience by traveling abroad. We also demonstrate that this effect is explained by the concept of psychic distance, whereby going abroad leads to a greater perception of psychic distance, and subsequently escapism, hedonic value, and satisfaction with the tourism experience

A reactive local search-based algorithm for the multiple-choice multidimensional knapasck problem

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Why Are International Visitors More Satisfied with the Tourism Experience? The Role of Hedonic Value, Escapism, and Psychic Distance: .

International audiencePrevious studies have consistently observed that international visitors are more satisfied with the tourism experience than their domestic counterparts. To date, however, no study has provided empirical evidence of the mechanism that could explain this phenomenon. Building on the experiential paradigm, we conducted two empirical studies (a field study and an online experiment) showing that the reason foreign (vs. domestic) visitors exhibit higher levels of satisfaction lies in the greater hedonic value that these tourists derive from their experience. Moreover, the greater hedonic value observed among international foreign visitors is due to the deeper feeling of escapism they experience by traveling abroad. We also demonstrate that this effect is explained by the concept of psychic distance, whereby going abroad leads to a greater perception of psychic distance, and subsequently escapism, hedonic value, and satisfaction with the tourism experience

A reactive local search-based algorithm for the Multiple-choice Multi-dimensional Knapsack Problem

In this paper, we approximately solve the multiple-choice multi-dimensional knapsack problem. We propose an algorithm which is based upon reactive local search and where an explicit check for the repetition of configurations is added to the local search. The algorithm starts by an initial solution and improved by using a fast iterative procedure. Later, both deblocking and degrading procedures are introduced in order (i) to escape to local optima and, (ii) to introduce diversification in the search space. Finally, a memory list is applied in order to forbid the repetition of configurations. The performance of the proposed approaches has been evaluated on several problem instances. Encouraging results have been obtained