Radicalar probes to measure the action of energy on granular materials

International audienceMeasuring the action of energy on matter is a complex problem, especially in the case of granular materials. For example, particle size reduction by grinding generally shows poor overall energetic yields and a significant challenge in this area is to accurately estimate the energy consumed, including that stored in the particles. Fine or ultra-fine grinding processes require a lot of energy, part of which becomes internal energy and can lead to mechanochemical reactions and useful products. We studied the appearance of free radicals during the grinding of a-lactose monohydrate by means of electron spin resonance (ESR). These radicals are the same as those induced by gamma-radiation and comparison of ESR spectra intensities with those from ground products allows the determination of an `equivalent gamma-irradiation dose'. This gives a novel concept for characterizing the action of mechanical energy on matter in fine grinding by using molecular probes. This is the first example of the investigation of mechanochemical energy during the fine grinding process

Use of co-grinding as a solvent-free solid state method to synthesize dibenzophenazines

International audienceMany synthetic methods exist for dibenzoquinoxalines but only a few for dibenzophenazines and their aza derivatives and even less are `green'. Some dibenzophenazines and dibenzopyridoquinoxaline have been efficiently obtained with good to excellent yield by a very simple method which does not require use of solvent or catalyst. Solid phase synthesis using co-grinding presents thus many advantages in developing greener synthetic organic pathways. (C) 2011 Elsevier Ltd. All rights reserved

Application of a simplifying model to the breakage of different materials in an air jet mill

Cet article est paru de nouveau en 2012 dans la revue "International journal of mineral processing", special issue Comminution 2009, (ESCC 2009 - European Symposium on Comminution and Classification, Espoo, Finland, September 15-18, 2009) vol. 112-113, pp. 7-12. (L'article de référence reste celui de 2011 pour les citations bibliographiques).International audienceThis paper describes the application of a unifying `master curve' model for single impact size reduction in an air jet mill. Based on a dimensional analysis and a modified fracture mechanical theory, it enables to relate the weight percentage of broken particles under sieve cut size to the mean sieve cut size of the studied material, the net kinetic energy provided to the material, the number of impacts and a global parameter f(Mat). Altogether 11 sieve cuts of different materials are impacted in an experimental air jet mill. Minimum breakage energies are derived and are shown to vary with a power function of the sieve cut size. The simplifying model is then successfully applied and enables to derive the fMat. parameters. In our situation, the experimental data do not show a direct relationship between fMat. and the minimum breakage energy and sieve cut size for all the materials

Influence of different dry milling processes on the properties of an attapulgite clay, contribution of inverse gas chromatography

Attention, cette publication comporte un corrigendum.International audienceThe effect of dry milling processes on the surface properties of an attapulgite clay, also called palygorskite, was investigated by carrying out experiments with different types of grinding devices. Ground products were then characterized by size measurement, scanning electron microscopy, X-ray diffraction, adsorption-desorption of N-2 and inverse gas chromatography at infinite dilution (IGC-ID) as well as finite concentration conditions (IGC-PC). These analyses were performed to evaluate the changes in particle size distribution, morphology, crystallinity and surface properties of attapulgite powder, respectively. Among the tested dry grinding devices, grinding in an air jet mill (Alpine 50 AS) and a vibratory ball mill (Pulverisette 0) led to the most significant particle size reduction. SEM photomicrographs showed that a breakage of the fibrous structure took place during dry grinding. Moreover, long grinding in Pulverisette 0 resulted in the complete destruction of fibre morphology followed by agglomeration. XRD analysis showed that whatever the grinding process, the microstructure of the attapulgite was not affected. IGC confirmed that only grinding in Pulverisette 0 affected the surface properties notably. In this case, the most significant decreases were observed in the dispersive component of the surface energy (164 to 116 mJ/m(2)) and in the specific surface area obtained with the octane probe (114.5 m(2)/g to 62.6 m(2)/g) by IGC-ID and IGC-FC, respectively. At the same time, a modification of the distribution functions of the adsorption energies (DFAE), giving information about surface heterogeneity, was noticed

Electron spin resonance - thermoluminescence studies on irradiated drugs and excipients

Issu de : 12th International Meeting on Radiation Processing (IMRP-12), AVIGNON, FRANCE, MAR 25-30, 2001International audienceThe methods (ESR, TL, GPC) developed to prove whether or not a foodstuff has been irradiated can be used to get the same proof in case of an irradiation treatment of drugs, excipients and cosmetic products

Modeling the mean interaction forces between powder particles. Application to silica gel-magnesium stearate mixtures.

International audienceDry coating experiments were performed by using the Hybridizer (Nara). Large host silica gel (SG) particles (d50 = 55 μm) were coated with fine invited particles of magnesium stearate (MS, d50 = 4.6 μm) for different contents of MS in the mixture. The real MS mass fraction wI obtained after mechanical treatment has been determined thanks to calibration from TGA measurements. The surface structure and morphology of MS coatings were observed using Environmental Scanning Electron Microscopy (ESEM) and Atomic Force Microscopy (AFM) [26, 27]. AFM has been also used to measure the adhesion forces between particles. Interaction forces between the material attached to the cantilever (Magnesium Stearate MS) and the surface of the composite material (Silica Gel SG or Magnesium Stearate MS) have been determined at different surface locations. For different compositions wI of the mixture MS-SG, the numeric distribution and the mean value f of the forces fH obtained for MS-SG interactions or fI for MS-MS interactions have been established and the experimental curve showing the evolution of f versus wI has been derived. Models of ordered structures have been developed, implying morphological hypotheses concerning large spherical or cylindrical host particles H and small invited spherical I. Different types of distribution of I materials onto the surface of H have been considered: for examples a discrete monolayer –or multilayers- of monosized particles I on the H surface. The coordinence of MS particles around SG particles has been estimated to calculate the free SG surface fraction through different modelling and to obtain the mean force f versus composition wI. The theoretical force values have been compared to experimental ones. The deviations have been discussed in terms of guest particle distributions on the surface of the large host particles and morphological hypotheses

Evolution of the interaction of a new chemical entity, eflucimibe, with gamma-cyclodextrin during kneading process

International audienceThe aim of this study was to enhance the low solubility of eflucimibe, a new chemical entity which can be used as medicine to treat dyslipidemiae, by complexation with gamma-cyclodextrin. The complex was prepared using kneading method. The interaction evolution was studied during process by comparison of the semi-solid and physico-chemical states of the product. The evolution of the semi-solid state was followed by torque measurement when the evolution of physico-chemical state was studied by differential scanning calorimetry, infrared spectroscopy and by determination of the drug solubilisation profile. The interaction, which occurs during the process, is characterised by a modification of the product consistency and by a disappearance of the drug endothermic peaks, a disappearance of a drug spectral band and a widely improvement of the drug solubilisation profile. Indeed, after complete interaction, the drug quantity solubilised in specific conditions increased about 44-fold compared to those of untreated drug. Moreover, the comparison of the physico-chemical and semi-solid states during kneading process clearly shows that when the interaction takes place, a solidification of the paste occurs. The results of these works suggested that the formation of new solid phase allows an enhancement of the solubility of eflucimibe

Evaluation of the mechanical resistance of a powder-powder coating by modulated dry feed particle size analysis

Issu de : Conference on Particulate Systems Analysis, Stratford upon Avon, ENGLAND, SEP 21-23, 2005International audienceDry powder coating is a powerful method for modifying the surface properties of particles whilst retaining their essential bulk properties. The coating of a host powder by guest particles can be achieved via different means ranging from simple stirring together of the two components, to high energy impact coating in devices such as a Nara Hybridizer or Turbula Mixer. The quality of the powder coating resulting from such methods is an important parameter, which depends both on the force of the mechanical action used, and also the physicochemical interactions between the host and guest particles. Here, a method for evaluating the strength of host-guest interactions based on particle size analysis using a standard Malvern Mastersizer with dry powder feed is presented. Basically, the liberation of small guest particles from host particles can be achieved by increasing the air pressure, and the presence of liberated fine particles mixed with guest particles can be detected from differences in volume and number distributions. Complementary examination is undertaken using an environmental scanning electron microscope (ESEM). This technique has been used to evaluate the interaction strength of a coating of hydrophobic magnesium stearate on a herbal extract (Harpagophytum). It is shown that effective coating can be achieved by three different means: simple stirring, a Turbula Mixer and by using a Nara Hybridizer. The respective strength of the coatings is greater with increasing mechanical force used for the process. The method is proposed as a simple means of evaluating powder-powder coating processes

Production de particules composites par enrobage en voie sèche dans un mélangeur cyclomix et modélisation DEM

National audienceUne modélisation de l'enrobage en voie sèche selon la méthode par éléments discrets (DEM) a été développée afin de mieux comprendre les phénomènes mis en jeu. Dans ce procédé, des poudres de taille relativement grande (dites " hôtes ") sont recouvertes de particules fines (dites " invitées ") par l'application de forces mécaniques sans l'aide de solvants ni de liants hydrauliques. Dans ce travail, les matériaux choisis comme particules hôtes sont les Suglets® (des granules sphériques constituées principalement de sucre) et les particules invitées sont constituées de stéarate de magnésium (MgSt). Ces deux éléments sont introduits sous forme de poudre dans un mélangeur à fort cisaillement appelé Cyclomix. Les propriétés du produit final comme la coulabilité et la fraction massique ont été caractérisées. La variation de l'indice de coulabilité en fonction de la durée de traitement par Cyclomix pour 4 vitesses de rotation et 3 taux de remplissage différents. La coulabilité des produits a été améliorée avec une augmentation de la durée d'opération et de la vitesse de rotation. Mais le taux de remplissage ne semble pas influer sur l' amélioration de la coulabilité. Le rendement en produit, estimé par sa fraction massique, est analysé. La constante de taux d'enrobage est corrélée avec la distance de rotation obtenue par DEM. Il a été montré que l'efficacité d'enrobage peut être prévue par la simulation

Apport de l'approche numérique DEM pour la compréhension de l'évolution des propriétés physico-chimiques des particules lors de l'enrobage en voie sèche

National audienceDans cette étude, l'intérêt est porté sur l'effet des conditions opératoires sur l'enrobage en voie sèche de grosses particules " hôtes " par de fines particules " invitées " et aussi sur la modélisation de cet enrobage selon la méthode par éléments discrets (DEM) afin de mieux comprendre les phénomènes mis en jeu. Dans ce travail, les matériaux choisis comme particules hôtes sont les Suglets® (des granules sphériques constituées principalement de sucre) et les particules invitées sont en stéarate de magnésium (StMg). Ces deux éléments sont introduits en poudre dans un mélangeur de 1L à fort taux de cisaillement, le Cyclomix. Les propriétés du produit final, comme la coulabilité, la mouillabilité et le degré d'avancement du revêtement, ont été caractérisées. La variation de l'indice de coulabilité est étudiée en fonction de la durée de traitement dans le Cyclomix pour diverses vitesses de rotation, taux de remplissage et rapport de taille de particules hôte et invitée. La coulabilité des produits a été améliorée en augmentant la durée du mélange ou la vitesse de rotation, tandis que le taux de remplissage de solide ne semble pas avoir d'importance marquée. Le degré de recouvrement des particules hôtes augmente avec la durée de mélange, et la vitesse de rotation des pales. La simulation des mouvements de particules dans le mélangeur par DEM a permis d'obtenir des informations sur la position, la vitesse des particules, et d'autres paramètres énergétiques, ainsi qu'une estimation du degré de mélange à tout instant. Grâce à l'interprétation de ces mouvements de particules à l'intérieur du Cyclomix, nous pouvons expliquer les différences de comportements déduites de l'analyse des propriétés physico-chimiques (Sato et al. 2012) des produits composites obtenus. Investigations of the effect of the operation conditions on the dry coating and the motion of particles in a high shear mixer by the DEM simulation have been done. The Suglet® and the MgSt materials have been chosen as the host/invited particles, respectively. The treatment of dry coating has been carried out in the Cyclomix, high shear mixer at different rotational speeds, filling ratio of the samples and particle size ratio to observe the effect of the operation conditions on the dry coating. The properties of the products, such as the flowability, wettability and the conversion ratio have been analyzed. The flowability has been improved along with the operation time of Cyclomix. Higher speeds of rotation of the Cyclomix can improve the flowability more rapidly. However, the flowability does not seem to be sensitive to the filling ratio. To simulate the flow of host/guest particles in the mixer, the Discrete Element Method (DEM) was applied. Experimental results such as flowability and wettability can be explained with particles flows evolutions inside the Cyclomix with different rotational speed