Cohesive Powders Research Articles

Design and optimization of stirrer and mixer design for the correct mixing of pharmaceutical powders through DEM

Mixing of granular materials is an important process for pharmaceutical industries. In this study, a quantifiable calculation method was suggested to determine the final mixing degree of the mixture. Based on that, the effect of the stirrer design, rotational speed, powder density, cohesivity, material ratios, and particle movement in the chamber guided through different designs of deflectors on the final mixing quality is examined. The results show that increasing the stirring speed, generates better mixing quality. However, introducing a varying rotational speed mode improves the mixing degree specially for binary mixtures with high relative densities. The improvement of the mixing with the number of contacting blades is observed. Finally, the introduction of a simple deflector drastically enhances the mixing quality and enables the feeding into the chamber, which is key for continuous operation with cohesive powders, making the process more stable and efficient by using more of the mixing volume.

Powder-bed additive manufacturing: The effect of layer thickness on powder bed density

The effect of layer thickness (LT) on powder bed density (PBD) was experimentally studied. The effect of LT on PBD was found dependent on both the powder flowability and measurement scenario. In the measurement scenario of fixing the powder bed height, increasing LT decreased PBD of both free-flowing powders and cohesive powders. In the measurement scenario of fixing the number of powder layers, increasing LT did not significantly affect PBD of free-flowing powders but significantly decreased PBD of cohesive powders. These findings shed light on the inconsistent results in the literature and provide guidance on the design of future studies.

Arch formation mechanism and discharge process of cohesive fine powder in a vibrated silo

The arch formation mechanism and discharge process of a very cohesive fine powder (calcium carbonate) in a vibrated silo was investigated by experiments and discrete element method (DEM) simulations. An experimental setup is built to study the flow behaviors with the proposed image-based flow rate measurement method. A cohesive DEM model is used to investigate the dynamic behaviors of the powder bed. Results indicate that the arch formation depends on the vibration acceleration amplitude and is slightly affected by the frequency. The powder discharge flow rate increases with vibration acceleration amplitude and decreases with frequency. When the acceleration amplitude exceeds 15 g, the flow rate tends to stabilize. When the acceleration amplitude exceeds 1 g, there is separation and collision between the powder bed and the silo bottom. This collision leads to a significant increase in the contact force.

Movement characteristics of coal powders at bottom of coalbed methane well under jet flow

AbstractThe removal and discharge of coal powders from coalbed methane wellbore is the key to maintaining continuous production. For this reason, based on the submerged jet theory, the force and migration starting conditions of coal powder particles deposited at the bottom of the coalbed methane well are analyzed by analyzing the cohesiveness of coal powders, and a model for the starting and migration of coal powders at the bottom of the well under submerged jet conditions is established; Considering the adhesion between coal dust, the adhesion coefficient is used to characterize the adhesion between particles, a mechanical model of coal dust particles deposited at the bottom of the well is established, and the corresponding calculation formula for the outlet flow rate of the coal dust cleaning nozzle is derived. The fluid mechanics parameters of the bottom of the well coal dust cleaning under different conditions are obtained, and the numerical simulation method is used to simulate the whole process of jet flushing of the bottom of the well coal dust deposited, and the effect of the bottom of the well jet flushing of coal dust deposits is analyzed, providing a theoretical basis for the bottom of the well coal dust flushing process.

An experimental study on flow behaviour of pharmaceutical powders during suction filling

Die filling is a crucial step in the pharmaceutical tablet manufacturing process. For industrial-scale production using rotary presses, suction filling is typically employed due to its significant efficiency advantages over gravity filling. Despite its widespread use, our understanding of the suction filling process remains limited. Specifically, there is insufficient comprehension of how filling performance is influenced by factors such as suction velocity, filling velocity, and the properties of the powder materials. Building on our previous research, this study aims to further investigate the effects of powder properties and process parameters (e.g., filling velocity, suction velocity, fill depth) on suction filling behaviour. A systematic experimental investigation was conducted using a model suction filling system, considering both cohesive and free-flowing pharmaceutical powders. The effect of fill depth on suction filling of these powders was examined at different filling and suction velocities. The results demonstrate that two distinctive flow regimes for suction filling can be identified: slow filling and fast filling. These regimes are delineated by a critical filling-to-suction velocity ratio. In the slow filling regime, the filling-to-suction velocity ratio is lower than the critical ratio, meaning that the filling phase is slower than the suction phase. Conversely, the fast filling regime occurs when the filling-to-suction velocity ratio exceeds the critical ratio, implying that the filling phase is faster than the suction phase. This study reveals, for the first time, that when the powder flow pattern during suction filling is dominated by plug flow, full die fill (i.e., the fill ratio equals unity) is achieved in the slow filling regime. However, in the fast filling regime, incomplete die fill is obtained. It is also found that when plug flow prevails during fast filling, the fill ratio has an inverse correlation with the filling-to-suction velocity ratio. This study further reveals that when the plug flow assumption is valid, the filling ratio at various fill-to-suction velocity ratios can be well predicted mathematically. Furthermore, it is also found that once the powder flow pattern differs from the ideal plug flow, which could be induced by the filling conditions and powder cohesion, the fill ratio can be overpredicted.

Effect of Microscopic Properties on Flow Behavior of Industrial Cohesive Powder

The characteristics of powders on a bulk scale are heavily influenced by both the material properties and the size of their primary particles. Throughout the stages of storage and transportation in the powder processing industry, various forms of deformation and stress, such as pressure and shear, impact these materials. Recognizing the point at which a powder undergoes yielding becomes particularly significant in numerous applications. There are also times when the level of stress needed to maintain it must be understood. The measurement of powder yield and flow properties remains a challenge and is addressed in this study. As part of the European collaborative project, a number of shear experiments were performed using two shearing devices: the Schulze ring shearing device and the Anton Paar Powder Cell (APCC). These experiments have three purposes: (i) test reproducibility/consistency between two shear devices and test protocols; (ii) relate bulk behavior to microscopic particle properties, focusing on bulk density and thus the effect of cohesion between particles; and (iii) investigate the influence of the temperature of heated powders on the powder’s flow properties, which is important for industrial reactors. Interestingly, for samples with small particle sizes, bulk cohesion increases slightly, but bulk friction increases significantly because of particle interaction effects. The experimental data not only provide useful insight into the role of microscopically attractive van der Waals gravitational and/or compressive forces on the macroscopic flow behavior of bulk powders but also have industrial relevance. We also provide robust data of cohesive and attritional fine powder for silo design used for calibration and validation of silos, models, and computer simulations.

Bed Stability Control in Pulsed Fluidized-Bed Agglomeration of Instant Riceberry Powder Using an Image-Processing Technique.

The problematic cohesiveness of food powders can commonly be solved using pulsed fluidized-bed agglomeration. However, progressively larger granules may result in unstable fluidization. The aims of this research study were to investigate fluid bed expansion as affected by particle enlargement and to control its stability using an image-processing technique. Instant riceberry powder (IRP) was agglomerated using varied air pulsation frequencies (1, 2.5, and 4 Hz). Bed expansion captured by image processing revealed that expanded bed height decreased with agglomeration time. The results showed an enlargement of agglomerated IRP, expressed in D10, D50, and D90, with narrower distribution presented by span, and an improvement in bulk and reconstitution properties. The reduced Carr index (22-27%) and Hausner ratio (1.28-1.38) presented fair flowability and intermediate cohesiveness, respectively. Additionally, airflow during agglomerate growth was progressively adjusted using the image-processing method to enhance bed hydrodynamic stability, leading to improved process efficiency and product quality. This proposed approach has potential applications in the food powder manufacturing industry, particularly by enhancing the fluidization of cohesive particles with cracks and channels.

Exploration of improved, roller-based spreading strategies for cohesive powders in additive manufacturing via coupled DEM-FEM simulations

Spreading of fine (D50 ≤20μm) powders into thin layers, such as required by layer-wise additive manufacturing (AM) processes, typically requires a mechanism such as a roller that provides adequate shear and compression to overcome the cohesive forces between particles. We explore improved, roller-based spreading strategies for highly cohesive powders using an integrated discrete element-finite element (DEM-FEM) framework. We find that optimal roller-based spreading, quantified by maximum packing density and uniformity of layer thickness, relies on a combination of surface friction of the roller and roller kinematics, e.g., counter-rotation or angular oscillation, that impart sufficient kinetic energy to break cohesive bonds between powder particles. However, excess rotation speed (or shear stress) can impart excessive kinetic energy to the powder causing ejection of particles and a non-uniform layer, suggesting the existence of a process window of optimal spreading parameters. Interestingly, the identified optimal parameters for both investigated roller kinematics, i.e., angular velocity for counter-rotation as well as angular frequency and amplitude for rotational oscillation, result in a very similar range of roller surface velocities, suggesting roller surface velocity as the critical kinematic parameter. When these conditions are chosen appropriately, layers with packing fractions beyond 50% are predicted for layer thicknesses as small as ∼2 times D90 of the exemplary cohesive powder, and the layer quality is robust with respect to substrate adhesion over a 10-fold range. The latter is an important consideration given the spatially varying substrate conditions in AM due to the combination of fused/bound and bare powder regions. As compared to counter-rotation, the proposed rotational oscillation kinematics are particularly attractive because they can overcome practical issues with mechanical runout of roller mechanisms (which limit their precision).

Stirrer design for improving fluidization of cohesive powder: A time-resolved X-ray study

Stirring has been recognized in the literature as a promising technique for facilitating fluidization of cohesive powders, via inputting additional energy to counteract interparticle forces. However, the influence of operating conditions and stirrer configurations on flow behavior remains largely unknown, which impedes the practical implementation of stirred fluidization. Utilizing X-ray imaging, this research demonstrates that stirring enhances fluidization in cohesive micron-silica powder (Sauter mean diameter ▪) by collapsing the powder packing structure, and transitioning channeling beds into bubbling states. Comb-like configurations featuring fewer stirrers and blades, placed in the bottom region, have shown to be highly effective. Excessive stirring can lead to air pockets and a compacted phase of particles on the column walls, undermining the interaction between particles and stirrers. Additionally, the experiments show that maximizing the sweeping coverage, employing complex asymmetrical configurations, and avoiding tortuous gas pathways are preferable.

Developing Dry Powder Inhaler Formulations.

This section aims to provide a concise and contemporary technical perspective and reference resource covering dry powder inhaler (DPI) formulations. While DPI products are currently the leading inhaled products in terms of sales value, a number of confounding perspectives are presented to illustrate why they are considered surprisingly, and often frustratingly, poorly understood on a fundamental scientific level, and most challenging to design from first principles. At the core of this issue is the immense complexity of fine cohesive powder systems. This review emphasizes that the difficulty of successful DPI product development should not be underestimated and is best achieved with a well-coordinated team who respect the challenges and who work in parallel on device and formulation and with an appreciation of the handling environment faced by the patient. The general different DPI formulation types, which have evolved to address the challenges of aerosolizing fine cohesive drug-containing particles to create consistent and effective DPI products, are described. This section reviews the range of particle engineering processes that may produce micron-sized drug-containing particles and their subsequent assembly as either carrier-based or carrier-free compositions. The creation of such formulations is then discussed in the context of the material, bulk, interfacial and ultimately drug-delivery properties that are considered to affect formulation performance. A brief conclusion then considers the future DPI product choices, notably the issue of technology versus affordability in the evolving inhaler market.

Influence of the “Left Span” on flow and fluidization characteristics of cohesive powders

The particle size distribution (PSD) significantly influences the flow and fluidization behaviors of powders, with the left section of PSD, indicating the portion of smaller particles, exerting dominant effects. Limited research has focused on exploring the impact of the left section of PSD on powder characteristics. Therefore, three types of Group C cohesive powders with the same diameter (20 μm) but different PSDs are derived from the same material. Results demonstrate that more abundant superfine components lead to diminished flow and fluidization quality. Finer particles exhibit greater potential for retaining gas within the bed, while realizing this potential requires specific auxiliary techniques (nanoparticle modulation), to reduce powder cohesiveness. A new parameter, termed “Left Span”, is proposed to depict the left portion of PSD. Sensitivity analysis reveals that flow and fluidization properties are more responsive to “Left Span” compared to span, which encompasses both the left and right sections of PSD.

Ultrafine food powders as clean-label flow additives

The aim of this work was to demonstrate the potential of the concept of clean-label-capable flow additives. These are spray-dried food ingredients whose particle size is small enough (<10 µm) to take over the function of classic flow additives such as highly dispersed silicas. Their acceptance by customers and consumers has been declining for years, as they are primarily mineral excipients that are becoming increasingly unpopular in foods. This poses major problems for the food industry, as many food powders have poor flow properties and handling problems. The idea of clean-label flow additives is to create an alternative to meet consumer demands and industry requirements. Using four different cohesive food powders as examples, the authors demonstrate the effectiveness of this concept. For this purpose, flow additives were prepared from low-concentration solutions in a laboratory spray dryer. Dry particle coating was carried out in a tumbling mixer for 30 min, after which the flow properties of the coated powders were determined using a Schulze Ring shear tester. The results show that a significant improvement in the flowability of cohesive food powders is possible by using these spray-dried flow additives. In addition, an anti-caking effect could be observed. There is still a need for optimization in the production of such flow additives in order to increase their economy and effectiveness. Overall, the concept of clean-label flow additives shows great potential.

Optimizing the surface modification of cohesive polyethylene powders in a vibrated plasma-spouted bed: Exploring agglomerate size impact on coarser particle addition mechanism

Ultrafine polymer powders have garnered attention owing to their superior physical properties and reactivity. Nonetheless, the cohesive nature of these powders notably impedes efficient plasma surface modification, thereby limiting potential applications. The effects of optimizing the fluidization of cohesive powders on plasma treatment within a plasma-spouted bed were investigated in a prior study, wherein surface modification was significantly improved by incorporating coarser particles and vibration. However, the optimal conditions and mechanisms by which adding coarser particles to a vibrated plasma-spouted bed contributes to this enhancement remain unelucidated. This study entailed an investigation of the influence of gas flow rate, agglomerate properties, and plasma distribution in optimizing the wettability modification of ultrafine powders. Results indicate that increased gas flow rate, coarser particle size, and quantity lead to the formation of smaller, more uniform-sized agglomerates. Furthermore, the contact angle of the treated powder demonstrated a linear decrease with the reduction of average agglomerate size within a suitable gas velocity range, suggesting that enhanced exposure of the powder surface to plasma contributes to the optimization of plasma treatment. However, high-gas velocity may trigger particle entrainment and diminish surface modification, as evidenced by the limited plasma distribution primarily at the bottom of the reactor.

Cohesive properties of ice powders analogous to fresh plume deposits on Enceladus and Europa

Active jets of water vapour and ice grains discovered by the Cassini spacecraft at the South Pole of Enceladus result in the deposit of freshly erupted materials on the icy surface of the moon, potentially coming directly from its subsurface water ocean. As suggested by sporadic detection of plume activity, similar processes may be at work on Europa as well. Such fresh ice deposit areas are primary targets for future landing and sampling missions for the search of potential bio-signatures. Determining the mechanical properties of such fresh icy powder-like materials is essential to identify safe landing sites and appropriate sampling techniques. Ice surface energy or cohesion is a key parameter driving the porosity of the material, its strength, stickiness and flowability, which determine the stability of fresh surface deposits. In this work we performed an experimental study on laboratory analogues of fresh icy regolith, consisting in investigating the flowability of ice powders through a rotating drum device at several temperatures. Our experimental results show that the flowability of fresh icy deposits significantly decreases with increasing temperatures over the range of 90 to 150 K. Using a simple scaling analysis, we derive the surface energy of ice grains from the observed angle of the flowing surface inside the drum and we show that the surface energy increase by a factor of 5 to 10 between 90 K to 150 K, a behaviour not observed in any other powder material. This result indicates that the flowability of fresh icy deposits at the surface of Enceladus and Europa should significantly change depending on the local surface temperature, which can vary spatially and temporally on the same range of temperature explored here. Due to lower gravity, ice powder will behave as a more cohesive powder on Enceladus than on Europa. Higher cohesion on Enceladus may result in the formation of a very loose regolith with high porosity, making stable landing more challenging. On Europa, the reduction of ice cohesiveness with decreasing temperature should help the flow of freshly eruptive granular ice materials, potentially explaining numerous flow features observed throughout the surface.

Quantitative analysis of thin metal powder layers via transmission X-ray imaging and discrete element simulation: Blade-based spreading approaches

Spreading uniform and dense layers is of paramount importance to creating high-quality components using powder bed fusion additive manufacturing (PBF AM). Blade-like tools are often employed for spreading powder metal feedstocks, especially in laser powder bed fusion (LPBF) and electron beam melting (EBM), where powders are characterized by a D50V of 30 μm or greater. Along with variations in boundary conditions introduced by the layer-wise geometry and surface topography of the printed component, stochastic interactions between the spreading tool and powder result in spatial variations of layer quality that are still not well understood. Here, to study powder spreading under conditions representative of PBF AM, we employ a modular, mechanized apparatus to create powder layers from moderately and highly cohesive powders (nominally 15–45μm Ti–6Al–4V and 20–63μm Al–10Si–Mg, respectively) with a selection of blade-like spreading tools. Powder layer effective depth is spatially mapped using transmission X-ray imaging, and uniformity is quantified via a statistical approach. We first compare layer density, or the effective depth of powder layer, and show that blade geometries with a curved profile lead to increased material deposition. Second, this approach enables quantification of local fluctuations, or layer defect severity. For example, we observe that the primary benefit of a V-shaped rubber (compliant) blade, as compared to a 45° rigid blade, lies in enabling local deflection of the blade edge to eliminate streaking from large particles, while also increasing deposition (layer density). Additionally, we employ a custom DEM simulation to elucidate the opposing roles of particle density and surface energy with a pseudo-material approach, where the balance of inertial and cohesive forces determine macro-scale powder flowability. For each alloy density, selected to represent Ti–6Al–4V and Al–10Si–Mg, we find via simulations a critical surface energy beyond which layer density is greatly impaired when powder spreading is performed using a blade.

Quantitative analysis of thin metal powder layers via transmission X-ray imaging and discrete element simulation: Roller-based spreading approaches

A variety of tools can be used for spreading metal, ceramic, and polymer feedstocks in powder bed additive manufacturing (AM) methods. Rollers are often employed when spreading powders with limited flowability, as arises in powders comprising fine particle sizes or high surface energy materials. Here, we study roller-based powder spreading for powder bed AM using the unique combination of a purpose-built powder spreading testbed with a proven method for X-ray mapping of powder layer depth. We focus on the density and uniformity of nominally 100 μm thick layers of roller-spread Ti-6Al-4V and Al-10Si-Mg powders. Our results indicate that when rotation is too rapid, roller-applied forces including shear and medium fluid drag impede the creation of dense and uniform layers from powders of high innate flowability, or where inertial forces driven by particle density dominate cohesive forces. Roller counter-rotation augments the uniformity of cohesive powder layers, primarily though reducing the influence of particle clusters in the flowing powder, which are otherwise shown to cause deep, trench-like streaks. Companion discrete element method (DEM) simulations further contextualize the experiments through isolation of the effects of cohesion on layer attributes. Results suggest that roller motion parameters could apply a strategic level of additional shear force to the flowing powder, thereby mitigating the clumping behavior characteristic of highly cohesive feedstocks while maintaining high layer uniformity.

On predicting the performance of different silicas on key property enhancements of fine APIs, blends, and tablets

Predictive selection of silica size, type (hydrophobic/hydrophilic), and amount is addressed for achieving significant property enhancements of fine active pharmaceutical ingredients (APIs). Four models, Chen's multi-asperity particle-adhesion, total surface energy-based guest-host compatibility, dispersive surface energy-based tablet tensile strength, and stick-bounce-based silica aggregation on coated particles, are invoked. The impact on the bulk properties of four APIs cohesive API powders (∼10 μm) and 40 wt% (wt%) blends of one API, dry-coated at 50% and 100% surface area coverage (SAC) of four nano-silicas (7–20 nm), hydrophobic (R972P), hydrophilic (M5P, A200, A300) is assessed. Significant enhancements in flowability, bulk density, compactability, agglomeration reduction, and dissolution for API or blend are achieved with all silicas. The experimental and model-based outcomes demonstrate that silica performance is impacted by multiple factors, silica size and coating effectiveness being most critical. In conclusion, R972P and A200 at lower 50% SAC present two excellent choices.

FLOWABILITY PROPERTIES OF BINARY POWDER MIXTURES CONTAINING DATES POWDER (PHEONIX DACTYLIFERA) MIXED WITH LACTOSE MONOHYDRATE AND MICROCRYSTALLINE CELLULOSE BASED EXCIPIENTS

Powder flow is important in powder processing industries to obtain a quality by design product and efficient manufacturing process. Poor powder flowability can cause problems especially during high speed tableting and capsule filling processes. In this study, dates powder (DP), lactose monohydrate powder, and two types of microcrystalline-based powder excipients evaluated for their flow properties as a binary mixture. Angle of repose (AoR), Hausner ratio (HR) and Carr index (CI) were used to characterize the extent of the powder cohesion. The results show that generally, as particle size increases, values of AoR generally decreases, depicting lower flowability characteristics with decreasing binary mixture particle size. However, HR and CI flowability indicators give contrasting flowability characteristics for the binary mixture containing lactose monohydrate and dates powder.

An examining the static and dynamic mechanical characteristics of milled ramie root reinforced polyester composites

This research works discuss about the effective utilization of waste Ramie Root, that has been in reinforced polyester composites, powdered fillers that have not been treated are used. Four different composites plate were formed with compression moulding technique process consisting of 20, 30 and 40% of Powdered Ramie Root with 80, 70 and 60% unsaturated polyester resin, respectively. The maximum mechanical properties were observed for the composite with 30:70 weight volume percentages of milled ramie root synthetic reinforced polyester. The findings show that the glass transition temperature, storage modulus, and loss factors all rise when the composition of composites changes. Additionally, the powder cohesion force (bonding strength) has a greater impact on dynamic mechanical properties. Thermo-gravimetric the inclusion of Ramie Root powder caused the thermal deterioration peak of the composite to move from 370 °C to 418 °C, according to analysis (TGA) conducted under flowing oxygen. According to the measurement of water absorption, the ideal weight ratio of Fiber: Unsaturated Polyester Resin is 30:70, which modifies the fibres’ surfaces and ensures optimal adhesion between the fibre and matrix in composite materials. Scanning electron microscopic investigation is done to ascertain the fracture behaviour of the composite. As a result of their stability, high tensile strength, and bending stiffness, the produced composites can be used in light-load applications by material technologists.

A new route to apply nanometric alumina coating on powders by fluidized bed chemical vapor deposition

A new route to deposit alumina nanometric thin films on powders from the single source Aluminum Tri-Isopropoxide (ATI) precursor is developed using the Fluidized Bed Chemical Vapor Deposition (FBCVD) process. For this study, an easy-to-fluidize silica powder is used, as a first step to ultimately coat cohesive oxygen sensitive powders. The FBCVD process has been studied under mild temperature conditions (400–500 °C), without any containing oxygen co-reactant. The influence of the deposition parameters (temperature, total flow rate, precursor inlet molar fraction) on the process behavior (ATI vaporization rate, fluidized bed thermal profile, deposition yield) and on the coating characteristics (composition, thickness, morphology) is analysed in details. Results show that for all conditions tested, the fluidization is maintained and the bed remains almost isothermal all along the deposition experiments, allowing for a uniform coating of the whole particles of the bed. Continuous and conformal nanometric films are obtained, mainly formed of non-carbon contaminated alumina, containing however a small amount of hydroxyl bonds that could be due to air contamination. The proof of concept of using FBCVD from ATI to produce nanometric stoichiometric alumina coatings on powders is then demonstrated, opening the way for new applications.