Prediction of solid–binder affinity in dry and aqueous systems: Work of adhesion approach vs. ideal tensile strength approach

Wet granulation process requiresthe addition of a coating agentor binder, typicallycomposed of surfactants such as hydroxypropyl-methylcellulose (HPMC), water and a small amount offiller such as stearic acid (SA). In dry granulation however, the coating agent is added to the system in the form offine solid particles. In both cases, a successful granulation requires good affinity between host and guest particles. In this study, we compare two approaches to predict the binder–substrate affinity in dry and in aqueous media, one based on the work of adhesion and the other based on the ideal tensile strength (Rowe, 1988). The novelties of this paper are four folds. First, the equations used in both approaches are generalized and rewritten as a function of the Hildebrand solubility parameter δ.δ is obtained from molecular simulations or predicted from HSPiP group contribution method. Secondly, a correlation between δ and the experimental surface tension γ is established for cellulose de-rivative (such as HPMC and ethyl cellulose). Thirdly, the concept of ideal tensile strength, originally formalized by Gardon (1967) for binary systems, is extended to ternary systems and applied for granulation in aqueous media. Fourthly, the approaches are tested for various systems and compared to experimental observations. For dry bi-nary systems, predicted adhesive and cohesive properties agree with literature experimental observations, but the work of adhesion approach performs better than the ideal tensilestrength approach. Both approaches predict thatHPMCisa good binderfor microcrystallinecellulose (MCC).The results alsoindicate that polyethyleneglycol 400(PEG400)has a good affinity with HPMC and stearic acid. For ternary aqueous systems, the results fully agree with the observations of Laboulfie et al.(2013)

Mesoscopic modeling, experimental and thermodynamic approach for the prediction of agglomerates structures in granulation processes

Wet granulation process requires the addition of a coating agent or binder, typically composed of surfactants, water, plasticizers and fillers. In dry granulation however, the coating agent is added to the system in the form of fine solid particles. Our goals are to investigate the particles behaviour and agglomeration mechanism in dry and aqueous systems at the micro and meso scales, and also, to develop predictive methodologies and theoretical tools of investigation allowing to choose the adequate binder and to formulate the right coating solution. In this study we chose materials widely used in food and pharmaceutical industries, including; coating agents such as Hydroxypropyl-methylcellulose (HPMC) and Ethyl cellulose (EC), binders such as Polyvinylpyrrolidone (PVP) and Microcrystalline cellulose (MCC), hydrophobic filler such as Stearic acid (SA) and plasticizer such as Polyethylene glycol (PEG). A successful granulation requires good affinity between host and guest particles. In this context, in the first part of this work, two approaches to predict the binder-substrate affinity in dry and in aqueous media were compared; one based on the work of adhesion and the other based on the ideal tensile strength. The concept of ideal tensile strength was extended to ternary systems and applied for granulation in aqueous media. The developed approaches were thereafter tested for various systems (composed of PVP, MCC, HPMC, SA, EC, PEG and water) and compared to experimental observations. Approaches yielded results in good agreement with the experimental observations, but the work of adhesion approach might give more accurate affinity predictions on the particles affinity than the ideal tensile strength approach. Both approaches predicted that HPMC is a good binder for MCC. Results also indicated that PEG has a good affinity with HPMC and SA. In a second part of our work, we used mesoscale simulations and experimental techniques to investigate the structure of agglomerates formed in aqueous colloidal formulations used in coating and granulation processes. For the simulations, dissipative particle dynamics (DPD) and a coarse-grained approach were used. In the DPD method, the compounds were described as a set of soft beads interacting according to the Flory-Huggins model. The repulsive interactions between the beads were evaluated using the solubility parameter (δ) as input, where, δ was calculated by all-atom molecular simulations. The mesoscale simulation results were compared to experimental results obtained by Cryogenic-SEM, particle size distribution analysis and DSC technique. According to the DPD simulations, HPMC polymer is a better stabilizing agent for SA than PVP and MCC. In addition, HPMC is able to cover the SA particle with a thick layer ant to adsorb in depth into its inner core, preventing SA agglomeration and crystal growth. But, for high amounts of SA (above 10% (w/w)), HPMC is unable to fully stabilize SA. We also found that PEG polymer diffuses inside HPMC chains thereby extending and softening the composite polymer. Experimental results presented similar trends; particle size distribution analysis showed that in the presence of HPMC, for low percentages of SA (below 10% (w/w)), the majority of SA particles are below 1 μm in diameter. SEM images revealed that HPMC surrounds SA crystals with a hatching textured film and anchors on their surface

Stearic acid crystals stabilization in aqueous polymeric dispersions

In wet granulation processes, coatings or binders generally consist of mixtures of various raw materials that confer or enhance specific properties to the final product. Typically, a coating solution is composed of water, film forming polymer (such as hydroxypropyl-methylcellulose, HPMC) and filler (such as stearic acid, SA). One of the important issues in wet granulation processes is the stability of the aqueous coating (or binder) dispersion. An unstable dispersion results in the agglomeration of the colloidal particles, thereby affecting the film coating properties and eventually the coating process. In this study, we use dissipative particle dynamics (DPD) to elucidate the structure of aqueous colloidal formulations. DPD is a coarse-grained molecular dynamics simulation method where the materials are described as a set of soft beads interacting according to the Flory–Huggins (1942) model. The DPD simulation results are compared to experimental results obtained by Cryogenic-SEM and particle size distribution analysis. It is shown from the DPD simulation results that the HPMC polymer is able to form a layer that covers SA particles and thus produces stable colloids. Microcrystalline cellulose (MCC) also covers SA agglomerate but it is not able to diffuse inside its inner core. The agglomerate structure is characterized via the density distribution and the polymer chain end-to-end distance. Experimental results show similar trends; particle size distribution analysis shows that in the presence of HPMC, the majority of SA particles are below 1 μm in diameter, also MCC is able to prevent the formation of big SA agglomerates and may be a better stabilizing agent than HPMC. SEM images reveal that HPMC surrounds SA agglomerates with a hatching textured film and anchors on their surface

Structure of aqueous colloidal formulations used in coating and agglomeration processes: Mesoscale model and experiments

In coating and agglomeration processes, the properties of the final product, such as solubility, size distribution, permeability and mechanical resistance, depend on the process parameters and the binder (or coating) solution properties. These properties include the type of solvent used, the binder composition and the affinity between its constituents. In this study, we used mesoscale simulations to investigate the structure of agglomerates formed in aqueous colloidal formulations used in coating and granulation processes. The formulations include water, a film forming polymer (Hydroxypropyl-methylcellulose, HPMC), a hydrophobic filler (Stearic acid, SA) and a plasticizer (Polyethylene glycol, PEG). For the simulations, dissipative particle dynamics (DPD) and a coarse-grained approach were used. In the DPD method, the materials are described as a set of soft beads interacting according to the Flory–Huggins model. The repulsive interactions between the beads were evaluated using the solubility parameter (δ) as input, where δ was calculated by all-atom molecular dynamics. The DPD simulation results were compared to experimental results obtained by cryogenic-SEM and particle size distribution analysis. DPD simulation results showed that the HPMC polymer is able to adsorb in depth into the inner core of SA particle and covers it with a thick layer. We also observed that the structure of HPMC-SA mixture varies under different amounts of SA. For high amounts of SA, HPMC is unable to fully stabilize SA. Affinity between the binder materials was deduced from the DPD simulations and compared with Jarray et al. (2014) theoretical affinity model. Experimental results presented similar trends; particle size distribution analysis showed that for low percentage of SA (below 10% w/w) and in the presence of HPMC, the majority of SA particles are below 1 μm in diameter. Cryogenic-SEM images reveal that SA crystals are covered and surrounded by HPMC polymer. SA crystals remain dispersed and small in size for low percentages of SA

A reliable design of Wireless Body Area Networks

International audienceIn this paper, we propose a reliable topology design and provisioning approach for Wireless Body Area Networks (named RTDP-WBAN) that takes into account the mobility of the patient while guaranteeing a reliable data delivery required to support healthcare applications' needs. To do so, we first propose a 3D coordinate system able to calculate the coordinates of relay-sensor nodes in different body postures and movements. This system uses a 3D-model of a standard human body and a specific set of node positions with stable communication links, forming a virtual backbone. Next, we investigate the optimal relay nodes positioning jointly with the reliable and cost-effective data routing for different body postures and movements. Therefore, we use an Integer Linear Programming (ILP) model, that is able to find the optimal number and locations of relay nodes and calculate the optimal data routing from sensors and relays towards the sink, minimizing both the network setup cost and the energy consumption. We solve the model in dynamic WBAN (Stand, Sit and Walk) scenarios, and compare its performance to other relaying approaches. Experiment results showed that our realistic and dynamic WBAN design approach significantly improves results obtained in the literature, in terms of reliability, energy-consumption and number of relays deployed on the body

Wet granular flow control through liquid induced cohesion

Liquid has a significant effect on the flow of wet granular assemblies. We explore the effects of liquid induced cohesion on the flow characteristics of wet granular materials. We propose a cohesion-scaling approach that enables invariant flow characteristics for different particles sizes in rotating drums. The strength of capillary forces between the particles is significantly reduced by making the glass beads hydrophobic via chemical silanization. Main results of rotating drum experiments are that liquid-induced cohesion decreases both the width of the flowing region and the velocity of the particles at the free surface, but increases the width of the creeping region as well as the dynamic angle of repose. Also, the local granular temperature in the flowing region decreases with an increase of the capillary force. The scaling methodology in the flow regimes considered (rolling and cascading regimes) yields invariant bed flow characteristics for different particle sizes.Comment: Reviewed with minor comments and resubmitted to Powder Technology. 35 pages, 20 figure

Investigation of particle properties on the holding force in a granular gripper

The granular gripper is an innovative device designed to grasp objects using the jamming properties of granular materials. However, these properties that influence its performance is still poorly understood. Moreover, to date, there is no numerical model for the granular gripper. In this paper, we combine numerical and experimental approaches to examine the effects of the mechanical properties of the grains on the grip force, with the goal to gain better insight on the influence of these properties and to improve the performance of the granular gripper. On the numerical side, a model based on Discrete Elements Method (DEM) is developed to predict the effect of the granular properties, such as the roughness, on the holding force. Two different ways of modelling the gripper system are presented and compared. The DEM model is tested for different pressures around the jamming pressure. On the experiment side, a granular gripper apparatus is mounted and used to find the relation- ship between the grains properties and the holding force. The experimental apparatus is also used to validate the DEM model. We found that grains with higher surface roughness result in a higher holding force on a cubical aluminium object. We also found agreements between the results of the exper- iments and the DEM models. Lastly, advice is given about approximating the holding force for a given gripper system and about further optimizing this system in terms of holding force, pressure and particle roughness

Polymer-plasticizer compatibility during coating formulation: A multi-scale investigation

During the formulation of solid dosage forms coating, plasticizers are added to the film forming polymer to improve the mechanical properties of the coating shell of the drug product. For the coating formulation to be successful and in order to produce flexible continuous film, the plasticizer should be compatible with the film forming polymer (i.e. high plasticizer-polymer miscibility in solid dispersion) (McGinity and Felton, 2008). This paper proposes and compares different multi-scale methods to predict the compatibility between plasticizers and film formers. The methods are based on, i) Molecule charge density using COSMO, ii) Solubility parameter calculation using Molecular dynamics, iii) Mesoscale simulation using DPD, where we propose a coarse-grain model, and iv) experimental DSC analysis for validation. The methods are tested for various blends including HPMC-PEG, MCC-PEG and PVP-PEG. The different methods showed similar results; PEG plasticizer diffuses inside HPMC and PVP polymer chains, thereby extending and softening the composite polymer. However, MCC surrounds PEG molecules without diffusing in its network, indicating low PEG-MCC compatibility. We also found that DPD simulations offer more details than the other methods on the miscibility between the compounds in aqueous solid dispersion, and can predict the amount of plasticizer that diffuse in the film forming polymer network

CO2-Expanded alkyl lactates : A physicochemical and molecular modeling study

With the perspective of finding alternative benign media for various applications, this paper presents a study of the physicochemical behavior of some members of the alkyl lactate family when expanded by CO2. Experimental and molecular modeling techniques have been used to determine and/or predict relevant physicochemical properties of these systems such as swelling, Kamlet–Taft parameters {polarity/polarizability (p*) and proticity or hydrogen-bond donator ability (a), dielectric constants and solubility parameters}. To complete the study of these properties, sigma profiles of the three lactates molecules have been obtained by performing quantum mechanical and phase equilibria calculations of CO2/alkyl lactate systems by using the Peng–Robinson equation of stat