Michèle Delalonde

The rheology of wet powders: A measuring instrument, the compresso-rheometer

In order to control the mechanical properties and granulation processes of wet powders, steps were taken to design and develop a measuring instrument, the compresso-rheometer. Initial experiments were carried out on binary associations between microcrystalline cellulose powder and varying quantities of water.

Preparation of granular systems by extrusion/spheronization: A twin product/process approach

The extrusion/ spheronization technique makes a notable contribution to the existing range of pharmaceutical forms, especially in the area of oral controlled-release product. Analysis of this technique leads the authors to make a parallel study of the influences of the aspects linked to formulation (water content) and to processing used (extruder screw speed) with the aim of optimizing the product quality. Textural variables, porosity, saturation degree and water content were monitored throughout the elaboration process. The kneading operation brings the material to a state in which porosity is linked to water content. The extrusion operation densities the material to saturation point, while spheronization is simply a shaping process which maintains the hygrotextural state. Also emphasized is the presence of solid/liquid ratios optimizing pellet quality independently of the operating variables. In parallel to this, a range of water content for which the influence of the process parameter is relevant is identified.

Fractal Law: A New Tool for Modelling Agglomeration Process

Wet agglomeration of granular materials is widely carried out in many industrial fields, such as the pharmaceutical and food industries. This process must be optimized in terms of yields and quality of the final product. A lot of studies have shown that agglomeration occurs under capillary, viscous and frictional forces and can be divided into four steps: nucleation, consolidation, growth and rupture. This general description of agglomeration does not take into account the simultaneous changes of agglomerates size, texture and saturation degree with respect to the increase in water content. The aim of this work is to propose a description of the agglomeration based on experimental observations and to take into account the aforementioned aspects to propose a model. In this study, experiments are carried out on kaolin in a low shear mixer for various operating conditions: three speeds of blade rotation, two wetting modes. The evolution of agglomerates granulometric and textural parameters is taken into account by image analysis and immersion in paraffin, respectively. This study makes it possible to highlight an increase in agglomerates size associated with a solid volume fraction reduction when there is an increase in water content. A power law connects solid volume fraction and median diameter of agglomerates making it possible to identify a fractal growth process between the grain and pasty-like scale. This well-know approach in colloidal aggregation is new in the powder agglomeration field. Fractal dimension defined this way is mainly affected by the drop size generated during wetting. These experiments highlight the weak influence of the other process parameters tested. For a wetting mode, an equation leading to the direct determination of the desired size of agglomerates with water content is proposed. Applied to agglomeration, fractal morphogenesis should become a potential tool in product engineering.

Definition of indices for the mechanical design of wet powders : application to the study of a natural polymer, microcrystalline cellulose

Abstract The formulation of a mixture for obtaining pellets by extrusion/spheronisation is based on experience and trials and not on a complete scientific understanding of the process. It has not been possible to exploit the progress made in rheology for characterizing the wet mixtures designed for use with this process. This is no doubt because of the difficulty of studying them by using existing rheometry apparatus in the traditional manner for substances possessing specific properties. For the essential conditions for conducting a conventional rheological study, i.e. the presence of a laminar flow with assumed perfect die wall adhesion, represents a difficult challenge to take up when working with heterogeneous materials whose density changes under the impact of pressure. This article is based on the use of an apparatus, the compresso-rheometer, which enables the extrusion process to be simulated on a reduced scale. It presents an original, precise study protocol resulting in mechanical characterisation through the use of two indices (visco-elasticity and plasticity) for microcrystalline cellulose/water mixtures. These new indices were established for the purpose of forecasting the behaviour of raw materials mixed with a liquid when subjected to a shaping process, and also for indirectly addressing the problems of formulation and dissolution.

Impact of Physicochemical Environment on the Super Disintegrant Functionality of Cross-Linked Carboxymethyl Sodium Starch: Insight on Formulation Precautions

The aim of this work is to improve the understanding of the physicochemical mechanisms involved in the functionality of cross-linked carboxymethyl sodium starch (CCSS) as a tablet super disintegrant (SD). The behavior and properties of this SD (medium uptake, disintegration times, particle size, and rheology) was investigated in a wetting medium of different physicochemical properties. In particular, the relative permittivity (dielectric constant) of these media was intentionally modified for evaluating its effect on CCSS properties. Results showed different swelling behaviors of CCSS particles according to the relative permittivity of the tested media and allow to propose two underlying mechanisms that explain CCSS functionality. Both the intra-particular swelling and the inter-particular repulsion are affected by the relative permittivity of the media. Finally, disintegration test performed on tablets specially formulated with mannitol (used commonly as an excipient and known to modify relative permittivity) confirmed that the functionality of CCSS and therefore the disintegration of the tablet can be altered according to the mannitol content.

A contribution to the understanding of micro-pollutant sorption mechanisms in wastewater biological processes: case of the tributyltin

Micro-pollutant fluxes distribution throughout the physical separation and biological units of wastewater treatment plants (WWTPs) are very dependent of sorption phenomena. The understanding and the control of the sorption stage is thus essential for the optimization of micro-pollutant removal in WWTPs, and particularly in biological treatments where these mechanisms influence the bioavailability towards micro-organisms. If the influence of the micro-pollutant physicochemical characteristics (e.g. K ow, pKa) on their ability to sorb on biological media (i.e. sludge) has been demonstrated, it appears that some other parameters, like the biosorbent characteristics, have to been taken into account. The aim of this study is thus to correlate the capacities of sorption of an environmentally relevant substance (tributyltin), with a thorough characterization of different types of sludge. The characterization of three biological media (raw, sonicated and flocculated activated sludges) is proposed according to various characterization parameters related to biochemical composition, aggregate size, rheological behaviour etc. The results show first that, whatever the sludge characteristics may be, the sorption mechanisms are very rapid and that an equilibrium state is reached after a few minutes. The influence of the sludge characteristics, notably the floc size and the chemical oxygen demand partition between solid and colloidal fraction, on sorption efficiency is demonstrated. A Langmuir modelling allows giving the maximum sorption capacity, as well as the binding energy for the three studied sludges, according to their physicochemical characteristics.

Spray-dried microparticulate systems containing acetaminophen.

The present work investigates the preparation and the release of acetaminophen from spray-dried microparticles. Two cellulose derivatives were tested as sustaining agents: microcrystalline cellulose (MCC) and sodium carboxymethylcellulose (NaCMC). In-vitro dissolution studies were carried out in dissolution media of different pH. With MCC, the adsorption of acetaminophen on the surface or in the pores of the polymer does not allow a significant sustained release of the drug, which completely dissolves in 1 h. Conversely, the use of NaCMC retards the release of acetaminophen over a period of 6-8 h. The drug release depends on the plasticizer used and on the pH of the dissolution medium, and the mechanism consists essentially in the diffusion of the drug through the swollen polymeric matrix. The pH dependence observed can be correlated with a lower hydrophylicity of the polymer in acidic medium, which retards gel formation.

How the nature of the compounds present in solid and liquid compartments of activated sludge impact its rheological characteristics

ABSTRACT Although the role of the solids concentration on the rheological characteristics of sludge is greatly documented in the literature, few studies focused on the impact of the nature of these solids. How the nature of solutes can modify the solid–liquid interactions and thus the rheological properties of the sludge are also slightly explored. Thus, the objective of this study is to investigate the rheological characteristics of activated sludge in relation with the nature of the compounds present in the solid and liquid phases. Rheological measurements were carried out on raw sludge and on sludge modified by mechanical actions and/or addition of solids or solutes. The rheological properties of raw and modified sludges were measured according to flow and dynamic measurements. Results demonstrated that if suspended solid concentration affected sludge rheological parameters, the nature of the solids was quite of importance. The key role of nature and molecular weight of solutes was also highlighted. The results contribute to a better knowledge of the relationship between sludge composition and its rheological properties, which is useful for the optimization of sludge mixing, pumping or aeration and also for the improvement of sludge dewatering, notably by a relevant choice of adjuvant.

An environmental application of functionalized chitosan: enhancement of the separation of the solid and liquid fractions of digestate from anaerobic digestion

Abstract A high molecular weight chitosan was chemically modified to quantitatively incorporate quaternary ammonium groups. Its efficiency was evaluated in the liquid-solid separation for various liquors, and compared with the one of a polyelectrolyte usually used for this utilization. The performance of the liquid-solid separation was estimated through the determination of two parameters measured after the screening- settling of the mixture liquor/flocculating agent: the separation efficiency (EV) and the TS removal efficiency (ETS). Apart for liquor 6, TS removal was always better after an addition of functionalized chitosan. Furthermore, whatever the type of liquor, the distribution was modified by an increased presence of high-size particles when functionalized chitosan was added. Moreover, chitosan addition tended to homogenize the size of the particles, which could facilitate the choice of the liquid-solid separation process. This homogenization was particularly observed for the liquor initially highly dispersed in size, i.e. liquors 1, 4, 6 and 8.