Wall Friction Angle Research Articles

Flow Properties of Coarse Powders Used in Food Extrusion as a Function of Moisture Content

The extrusion processing of food powder relies heavily on its moisture content to aid in flow and proper cooking, shaping, and/or puffing. This study focused on the impact of the moisture content on the dynamic flow and shear properties of coarse food powders (corn meal, wheat farina, and granulated sugar). The dynamic flow properties explored were the specific basic flowability energy (SBFE), specific energy, stability index, and flow rate index. The shear properties were the angle of internal friction, unconfined yield strength, major principal stress, wall friction angle, flow factor (FF), and compressibility. Corn meal exhibited an increase in SBFE as the moisture content increased (6.70 mJ/g at 13.13% to 9.14 mJ/g at 19.61%) but no change in FF (4.94 to 5.11); wheat farina also showed an increase in energy requirement as the moisture increased (5.81 mJ/g at 13.73% to 9.47 mJ/g 19.57%) but a marked decrease in FF ratings (18.47 to 6.1); granulated sugar showed a decrease in energy requirements as the moisture increased (51.73 mJ/g at 0.06% moisture content to 13.58 mJ/g at 0.78% moisture content) and a decrease in FF ratings (8.53 to 3.47). Overall, upon the addition of moisture, corn meal became cohesive yet free-flowing; wheat farina became less compressible and more cohesive; and granulated sugar became more cohesive and compressible and less free-flowing.

Reduction in Powder Wall Friction by an a-C:H:Si Film

The wall friction angle is an important parameter in powder flow. In a recent study for various powders, a reduction in the wall friction angle for steel was demonstrated by the application of an a-C:H:Si film on the steel surface. This work presents the results of a study of this effect in more detail regarding the influence of the powder material, the wall normal stress and the particle size of the powder for mass median diameters from 4 µm to approximately 150 µm. The wall friction angles were measured using a Schulze ring shear tester for three different powder materials: aluminum oxide, calcium carbonate and silicon carbide. The results showed little difference with respect to powder chemistry. For the coarser powders, the reduction in the wall friction angle due to the a-C:H:Si coating was highest (10° to 12°) and rather stress-independent, while for the fine and medium-size powders the reduction was lower and stress-dependent. With increasing wall normal stress, the reduction in the wall friction angle increased. These results can be explained by the friction reduction mechanism of a-C:H:Si, which requires a certain contact pressure for superficial graphitization.

Using AI/ML to predict blending performance and process sensitivity for Continuous Direct Compression (CDC)

Utilising three artificial intelligence (AI)/machine learning (ML) tools, this study explores the prediction of fill level in inclined linear blenders at steady state by mapping a wide range of bulk powder characteristics to processing parameters. Predicting fill levels enables the calculation of blade passes (strain), known from existing literature to enhance content uniformity. We present and train three AI/ML models, each demonstrating unique predictive capabilities for fill level. These models collectively identify the following rank order of feature importance: RPM, Mixing Blade Region (MB) size, Wall Friction Angle (WFA), and Feed Rate (FR). Random Forest Regression, a machine learning algorithm that constructs a multitude of decision trees at training time and outputs the mode of the classes (classification) or mean prediction (regression) of the individual trees, develops a series of individually useful decision trees. but also allows the extraction of logic and breakpoints within the data. A novel tool which utilises smart optimisation and symbolic regression to model complex systems into simple, closed-form equations, is used to build an accurate reduced-order model. Finally, an Artificial Neural Network (ANN), though less interrogable emerges as the most accurate fill level predictor, with an r2 value of 0.97. Following training on single-component mixtures, the models are tested with a four-component powdered paracetamol formulation, mimicking an existing commercial drug product. The ANN predicts the fill level of this formulation at three RPMs (250, 350 and 450) with a mean absolute error of 1.4%. Ultimately, the modelling tools showcase a framework to better understand the interaction between process and formulation. The result of this allows for a first-time-right approach for formulation development whilst gaining process understanding from fewer experiments. Resulting in the ability to approach risk during product development whilst gaining a greater holistic understanding of the processing environment of the desired formulation.

Effect of Moisture Content on Frictional Properties of Some Selected Grains in Indonesia

The frictional property of grains is one of the most important engineering parameters in developing solid bulk handling of grains. It is necessary for designing agricultural facilities and production process activities. These properties are expressed as internal friction angle (φ) and wall friction angle (θ), which are known to be affected by the moisture content of the grains. This research investigates the effect of moisture content on the values of φ and θ of some selected grains. In the research, some indigenous Indonesian grain types, including rough rice, white rice, corn, soybean, and coffee, each in three varieties and three level of moisture contents, were used as the research samples. Those angles were measured using a self-constructed direct shear cell apparatus. Three different normal loads for each grain type were used with three replications. It is concluded that φ and θ of the tested grains increase with moisture contents with different trends of increments. The relationship of those angles with moisture contents can be expressed as linear regression equations. The slope of the regression lines for both φ and θ is significantly affected by grain type (p<0.05). For φ, coffee (Excelsa) is the most susceptible to the change in moisture content, while dent corn (Hibrida) is the least affected one. For θ, soybean (Galunggung) is the most susceptible to the change in moisture content, while rough rice (Mapan 5) is the least affected one.

Evaluating the effect of glidants on tablet sticking propensity of ketoprofen using powder rheology

Punch sticking has been a leading drawback that has challenged successful tablet manufacturing since its initial conception. Due to the capricious nature of the complication, this can arise during any phase of the development process. Even now, identifying such a problem is a prerequisite during the initial stage of development. The present study evaluated the role of Aerosil®200, talc, and Syloid®244 as glidants in varying amounts ranging from 0.0 percent to 2.0 percent w/w on tablets sticking relatively to five different metal surfaces, with ketoprofen as the model drug. Powder rheology is a predictable technique used to calculate the sticking index. The sticking index of each formulation in comparison to each metal coupon was identified by calculating the kinematic angle of internal friction and the angle of wall friction using the shear cell test and wall friction test, respectively. Interestingly, glidants were found to reduce the sticking propensity of the powder blend in a concentration-dependent manner. In addition, the compression study validated the expected sticking tendency ranking order. According to the research data, the sticking index could effectively be utilized to envisage the possibility of tablet sticking, i.e., by selecting the formulation’s excipient and their percentages or selecting appropriate punched metal surfaces in the tableting process.

Wedge-Shaped Hopper Design for Milled Woody Biomass Flow

The bioenergy industry has been challenged by unstable flow and transport of milled biomass in material handling operations. Handling issues such as hopper clogging and auger jamming are attributed to knowledge gaps between existing handling units designed for bulk solids and their suitability for milled biomass with high compressibility. This work investigates various flow behaviors of granular woody biomass in wedge-shaped hoppers. Hopper flow physical experiments and numerical simulations are conducted to study the influence of the critical material attributes and critical processing parameters on the flow pattern, arching, and throughput. The results show that (1) the preferred flow pattern, mass flow, can be achieved by controlling the material’s internal friction angle, hopper inclination, and hopper wall friction; (2) hopper arching, governed by the competing gravity-driven force against flow resistance from material internal friction and material–wall friction, can be controlled by the hopper wall friction angle and the inclination angle; and (3) flow throughput can be accurately estimated from our empirical equation with inputs of hopper outlet geometry and particle-scale to bulk-scale material attributes. This study elucidates woody biomass flow physics and provides guidance for industrial equipment design.

Flow characteristic evaluation of iron ore for design of bunkers and chutes with different liner materials

Powders and bulk solids have to be handled and stored in all industries, ranging from powders, food, and pharmaceutical substances to raw materials such as cement, coal, and iron ore, as well as dry materials such as fly ash and moist bulk solids such as filter cake and clay. All these materials must be transported, conveyed, or otherwise handled. Thus, the characterization of powders and bulk solids in terms of flow properties is critical. The objective of this paper is to establish the flow characteristics of typical Indian iron ore for the design of test rig bunkers and chutes at different moisture levels.In this paper, the effect of moisture content on the iron ore's flow properties and its interaction with various liner materials is studied. Experimental tests were carried out for various moisture levels to determine the critical levels of moisture which adversely affecting the flow properties of bulk solids. A Jenike ring shear tester (RST) is used to find flow properties like bulk density, wall yield locus, internal friction angle, and wall friction angle of iron ore when it is interacting with different liner materials, i.e. SS 304 2B, Hardox400, Sailhard, and Chromium carbide. The results shows that 11.9% is the critical moisture level. Further, based on this, conical hopper half angle and critical opening size are evaluated for the design of mass flow bunkers and chutes.

Moisture‐dependent engineering properties of underutilized browntop millet (unhulled and hulled) and characterization of milled flour

AbstractBrowntop millet is an underutilized indigenous cereal crop. It is termed as the nutricereal due to its superiority in terms of nutritional quality. The current study attempted to investigate the effect of moisture content (10%–27%) on properties such as physical, mechanical, aerodynamic, and textural properties of unhulled and hulled browntop millet to uncover the gaps in developing the efficient primary processing machinery. In addition, we investigated the impact of milling on the biochemical, functional, color, structural, and powder flow properties of browntop millet flour. The results revealed that as the moisture content increased, the principle dimensions, 1000 grain weight, terminal velocity, angle of repose, and static coefficient of friction were linearly increased. In the same moisture content range, characteristics such as true density, bulk density, porosity, and hardness displayed an inverse trend. Milling showed a substantial (p < 0.05) influence on the nutritional, functional and color parameters. FTIR spectra and X‐ray diffraction patterns demonstrated a slight change in functional groups and a slight decrease in starch crystallinity respectively. All three millet flours were cohesive. These flours, however, exhibited a positive correlation with bulk density and a negative correlation with wall friction and effective internal friction angles as the principle consolidating stress increased.Practical ApplicationMillets are a globally significant food crop with major economic influence in developing nations. They are one of the most significant drought‐resistant crops, and a good source of health‐promoting complex carbohydrates, dietary fiber, phenolic compounds, and phytochemicals. Despite of their high nutritional superiority and environmental friendliness, production and consumption have declined over the years. The significant factor contributing to this decline is the lack of machinery or equipment available to process on a commercial and residential scale after harvest. The knowledge of the measured properties will encourage researchers to develop and modernize equipment used for destoning, grading, sorting, separation, dehulling, and conveying. The measured nutritional, mineral, functional, structural, and powder flow properties of milled browntop millet fractions will help develop a new product. So that millet can be used to its full potential.

Influence of micro- and nano-bubble treatment on morphological characteristics and flow properties of spray-dried milk protein concentrate powders

This study investigated the morphological and bulk handling properties of milk protein concentrate (MPC) powders manufactured from incorporating micro- and nano-bubbles (MNB) before spray drying. Control MPC powders (C-MPC; no MNB treatment) and MNB-treated MPC powders (MNB-MPC; MPC dispersions passed through the MNB system and subsequently spray dried) were characterized in terms of particle size, shape factors, stability, variable flow rate, shear cell tests, compressibility, and wall friction. The MPC powders produced after the MNB injection process had better flowability and lower basic flow energy. Shear tests showed that C-MPC powders were more cohesive than MNB-MPC powders. The MNB-MPC powders had lower flow rate index values, lower wall friction angles, more rounded shape, and significant differences in powder compressibility compared with C-MPC powders. Overall, the results demonstrated that MNB incorporation during spray drying can produce ingredients with comparable morphological characteristics while improving the bulk powder properties.

An Improved Method of Vertical Slices to Determine Seismic Passive Earth Pressure and Its Point of Application

This paper presents a new approach for calculating seismic passive earth pressure, its point of application, and the approximate stress-state within the rupture wedge. The method of vertical slices combined with the limit-equilibrium (LE) technique was used as the framework for the analysis. While the available LE analyses used the rupture surface of predefined shapes, in this approach, the rupture surface is derived through the analysis. First, the mobilized soil behind the wall was split into thin vertical slices and the rupture plane of every slice was calculated by enforcing the Mohr–Coulomb failure criterion. Thereafter, by adding those rupture planes consecutively, starting from the wall toe, the passive rupture surface was achieved. The inclination of the rupture planes is guided by the soil friction angle, wall friction angle, seismic acceleration, and slice-interface friction angle. The distribution of slice-interface friction angle across the rupture plane was presumed to obey a power function. The exponent of the power function, the seismic passive earth pressure, and its point of application were derived concurrently by satisfying the static equilibrium conditions of the slices and applying a boundary condition. The results show that the outline of the rupture surface is guided by the slice-interface friction angle, and the shape is curvilinear for rough walls. With increasing seismic acceleration, the passive pressure decreases, and the point of application moves predominantly downward for loose sands. The obtained results were compared with those of previous numerical and experimental studies and were found to show good agreement, thus demonstrating the validity of the proposed method.

Development and exploration on flowability of solid self-nanoemulsifying drug delivery system of morin hydrate

• Solid SNEDDS of MH was prepared by physical adsorption method. • Flowability of solid SNEDDS was investigated by powder flow tester. • Solid state characterization confers transformation of crystalline to amorphous. • In vitro- In vivo studies revealed an improvement of dissolution & bioavailability. • The estimated shelf life of solid SNEDDS of MH was found to be 27.57 months. Morin hydrate (MH) is a promising flavonoid with diverse biological activities; unfortunately, it finds limited clinical application due to its low water solubility. Herein, we developed a liquid self nano-emulsifying drug delivery system ( l -SNEDDS) employing Labrafil M 1994 CS, Cremophor RH 40, and Transcutol HP. The l -SNEDDS has been solidified by physical adsorption using inert carriers, i.e., Neusilin US2 and Aerosil 200. The S-SNEDDS was thoroughly investigated for flow function (FF), effective angle of wall friction (EAWF), and effective angle of internal friction (EAIF) employing a powder flow tester (PFT). The solid-state characterizations of S-SNEDDS were performed using FTIR, DSC, PXRD, and SEM. Further, in vitro dissolution, in vivo pharmacokinetic, and shelf life estimation were performed on selected SOF-2 formulation. The SOF-2 reveals good emulsifying ability, particle size (52 ± 4.25 nm), and PDI (0.133 ± 0.06). The FF and Jenike’s classification suggests the “free-flowing” nature of S-SNEDDS prepared using Neusilin US2. Further, S-SNEDDS prepared using Neusilin US2 showed a low friction angle, i.e., EAWF and EAIF, than Aerosil 200, therefore, a better flowability. The solid-state characterization of SOF-2 demonstrated the transition of MH from crystalline to amorphous state and good compatibility between MH and Neusilin US2. Further, SOF-2 showed more dissolution than pure MH and subsequently 2.97-fold increments in its oral bioavailability. Moreover, the shelf life of SOF-2 was reported to be 27.57 months, suggesting its excellent physical and chemical stability. In brief, solidifying l -SNEDDS and investigating flow behaviors by PFT could find attention in the pharmaceutical and food industry for commercial purposes.

Effect of Moisture and Feedstock Variability on the Rheological Behavior of Corn Stover Particles

Continuous feeding, processing, and handling of biomass powders is pivotal to the economic viability of integrated biorefineries. However, current challenges associated with the operational reliability of bulk solids handling and transport greatly impact the process economics and ultimately the widespread commercialization of integrated biorefineries. In this work, we examine the effect of moisture and feedstock variability on the flow behavior of corn stover biomass particles. The total flow energy, compressibility, shear properties, and wall friction angles were measured for corn stover samples A and B containing 0%, 15%, 25%, 50%, and 75% (mass fraction) moisture contents using a FT4 powder rheometer. In general, the flowability of both A and B was reduced when moisture was present as indicated by the stability and variable flow rate, compressibility, and shear tests. The 15% moisture sample had the highest flow energy, revealing the interplay between the increased surface tension and looser packing both of which were caused by liquid bridging. The 75% moisture sample had the highest compressibility and the lowest flowability factor (ffc). The trend in wall friction angle was found to be dependent upon the surface hydrophobicity of the wall material. The wall friction angle on the hydrophilic, stainless-steel surface increased with moisture and therefore poses additional handling challenges. On the other hand, the wall friction angle on the hydrophobic polymer surfaces were the lowest for samples with intermediate moisture contents. Sample B had greater bulk density, smaller compressibility, and greater flowability than the sample A, as suggested by the compressibility and shear tests. The wall friction angle of sample B was higher than or equal to that of sample A depending on both the type and the surface roughness of the wall material.

Flowability of spray‐dried sapodilla pulp powder

AbstractThis study aimed to evaluate the influence of maltodextrin, Arabic gum, and dextrin on phenolic compounds, morphology, and flowability of sapodilla pulp powder obtained in a spray dryer. Sapodilla pulp was characterized by its moisture and total polyphenols. The carriers were individually added to the pulp at a concentration of 20% (m/m), and the samples were dried in a spray dryer. The powders were analyzed for moisture, hygroscopicity, total polyphenols, and particle morphology, and their flowability was evaluated using the Powder Flow Tester (PFT). Total polyphenols of sapodilla pulp (average of 1055.30 mg GAE in 100 g of pulp solids) were more significant than in the powders (457.06 to 635.55 mg GAE in 100 g of pulp solids). The lowest moisture (1.16%) was obtained for maltodextrin. All carriers generated nonhygroscopic powders. The particles showed a rounded shape with greater roughness in samples containing Arabic gum. The powder with dextrin resulted in better flowability characteristics, with a higher flow index and lower compressibility index, Hausner ratio, and wall friction angle. Sapodilla pulp powder was classified as cohesive, with flow indices < 3, compressibility index from 53.2 to 59.9, and Hausner ratio between 2.14 and 2.50. The carriers used influenced the characteristics of sapodilla pulp powders, the Arabic gum promoting greater protection of total polyphenols and dextrin resulting in better flowability characteristics.Practical ApplicationsThe consumption of tropical fruits has increased in recent years, especially fruits considered exotic. The sapodilla fruit has many health benefits potential, but it has a short shelf life and seasonal crop. This research provides information on the spray‐dried sapodilla pulp powder containing different drying carriers, in order to evaluate the powder flowability behavior. This evaluation was based on particle morphology, wall friction angle, and bulk and tapped densities. It is important to determine the influence of carriers on the powder in order to produce a good quality product.

Seismic Analysis of Cantilever Sheet Pile Walls with Strip Load for Any Lateral Deformation

In the present study, a new method for designing the cantilever sheet pile wall having a strip load present on the backfill is proposed in cohesionless soil. The method uses the limit-equilibrium approach by establishing the partial mobilized earth pressure diagram in static and seismic conditions. The partial mobilization of earth pressure has been taken as a function of amount and type of wall movement and associated mobilized soil–wall friction angles. Analytical expressions are derived for the cantilever sheet pile wall to determine the earth pressure, shear force, and bending moment. It is observed that the earth pressure diagram of cantilever sheet pile walls varies with the displacement at the dredge level. Furthermore, the shifting of strip load of magnitude 20 kPa away from the cantilever sheet pile walls reduces the maximum bending moment by 10% when the width of the strip load is 1.6 m. A parametric study is carried out and presented in the nondimensionalized form of bending moment, penetration depth, and location of the pivot point. The results of the present study are compared with the existing conventional solutions available in the literature.

Development and Optimization of Vitamin D3 Solid Self-Microemulsifying Drug Delivery System: Investigation of Flowability and Shelf Life.

We report herein the design of a solid self-microemulsifying drug delivery system (SMEDDS) of vitamin D3 for augmentation of its solubility and dissolution. The studies employed a 32 full factorial design by employing JMP 13.2.1, software for preparation of liquid SMEDDS. Further, the prediction profiler was utilized to optimized liquid SMEDDS-Vit.D3 (OF) formulation. The solidification of liquid SMEDDS-Vit.D3 formulation was carried out by physical adsorption over Neusilin US2 and Aerosil 200 carriers. Solid-state evaluation of SMEDDS-Vit.D3 suggested the transformation of crystalline to amorphous form of Vit.D3 which is responsible for imparting more aqueous solubility and thus enhancement in dissolution behaviour. The investigation of flow behaviours viz. flow function (FF) and effective angle of wall friction (EAWF) of solid SMEDDS-Vit.D3 was performed using powder flow tester. Solid SMEDDS-Vit.D3 prepared using Neusilin US2 showed good flow behaviour and hence was developed into tablets. The tablets showed good quality control parameters as per pharmacopeial standards. The in vitro dissolution studies demonstrated more dissolution of Vit.D3 in SMEDDS (liquid, solid, and tablet) when compared to the unprocessed drug. The shelf life (T90) of tablets was reported to be 28.12 months suggesting excellent stability of Vit.D3 in solid SMEDDS. In nutshell, our research works explore the utilization of SMEDDS for the oral delivery of Vit.D3 to gain maximum health-related benefits.

Discovery and study of abrasion behavior in granular shear flow

ABSTRACT Experiments were performed in an Couette ring shear cell with particles from the food industry of nearly spherical geometry and nominal diameters between 2.0 and 6.7 mm and with quartz grains with 2.1 to 3.3 mm diameter to examine whether rapid shear flow would give rise to an appreciable change in the granular properties. In particular, it was suspected that surface roughness would change during shearing and lead to changes in the values of the internal and wall friction angles. Measuring these angles corroborated the supposition that abrasion of the particles reduced their frictional resistance, both via the internal and wall friction angles. This demonstrates that roughness changes may occur in granular flows and should in those situations not be ignored in the theoretical descriptions.

Physical and frictional behaviors of loblolly pine residues

Size reduction of biomass feedstock produces particulate material with a non-uniform particle size distribution, and this influences its behavior during handling, storage, and transport. Therefore, this study investigated the influence of particle size on the physical and frictional behaviors of ground loblolly pine residues. Loblolly pine residues were ground and fractionated into 6 sizes using screen apertures: 1.40 mm, 1.00 mm, 0.71 mm, 0.50 mm, 0.25 mm and pan. The moisture contents of the samples were kept at 8.69% (w.b). The particle densities (1316.21–1445.81 kg/m3) of the fractions significantly increased as particle size increased from <0.25 to 1.40 mm. An increase in particle size led to an increase in flow index values (2.63–4.05) of the fractionated biomass. All the fractions were classified as cohesive except for the samples with particle sizes of 1.40 mm and 1.00 mm, which were classified as easy flowing. Cohesive strength and angle of internal friction were found to significantly decrease as particle size increased. The angles of wall friction measured on stainless steel and mild steel surfaces were found to be lower than TIVAR 88 surface.

Comparison of the compressible class of models and non-local models with the discrete element method for steady fully developed flow of cohesionless granular materials through a vertical channel

The flow of granular materials through a vertical channel is examined using the discrete element method (DEM) and the recent continuum models of Henann &amp; Kamrin (Proc. Natl Acad. Sci. USA, vol. 110, 2013, pp. 6730–6735), Barker et al. (Proc. R. Soc. Lond. A, vol. 473, 2017, p. 20160846), Schaeffer et al. (J. Fluid Mech., vol. 874, 2019, pp. 926–951) and Dsouza &amp; Nott (J. Fluid Mech., vol. 888, 2020, p. R3). The channel is bounded by walls separated by a distance $2 \, W$ in the $x$ -direction. For the DEM, periodic boundary conditions are used in the $z$ - and $y$ - (vertical) directions with no exit at the bottom of the channel. The governing equations reduce to ordinary differential equations in the $x$ -direction. There is a plug layer near the centre and a shear layer near the wall, as observed in experiments. There is a decrease in the solids fraction $\phi$ in the shear layer, except for the models of Barker et al. and Henann &amp; Kamrin. A modification of the latter gives more realistic $\phi$ profiles. The thickness of the shear layer depends on $2\,W$ and the bulk solids fraction $\bar {\phi }$ . For all the models, solutions could not be obtained for some parameter values. An example is the negative fluidity in the model of Henann &amp; Kamrin. The model of Dsouza &amp; Nott predicts much higher normal stresses, possibly because of large contributions from the non-local terms. None of the models specify a complete set of boundary conditions (b.c.). The DEM results suggest that the slip velocity and the wall friction b.c. lead to a slip length and an angle of wall friction that are independent of $2\,W$ . The models are based on extensions of the equations for slow, rate-independent flow. A model that includes collisional effects, such as kinetic theory, should be combined with the present models. A preliminary analysis of the kinetic theory model of Berzi et al. (J. Fluid Mech., vol. 885, 2020, p. A27), shows that it may have undesirable feature.

In-depth analysis of the long-term processability of materials during continuous feeding

This study determined the feasibility of long-term continuous powder feeding and its effect on the overall process performance. Additionally, quantitative relationships were established between material properties, process settings and screw feeding responses during gravimetric feeding. Twelve divergent raw materials were processed over longer periods using a GEA Compact Feeder integrated in a continuous direct compression line (ConsiGma™ CDC-50). The resulting gravimetric feeding responses were combined with the material properties and process settings into an overall PLS model. The model elucidated the impact of the material descriptors for density; powder flow; particle size; compressibility; permeability and wall friction angle on the feeding process. Furthermore, long-term processing of the materials exhibited challenges related to the processability and refill consistency where a significant impact of the compressibility and cohesive/adhesive properties of the materials was observed. Overall, this approach provided insights into the feasibility of long-term continuous feeding which is not possible through ‘short-term’ feeding trials. Additionally, throughout this study, the need for material-specific adjustments of the feeding and refill equipment was highlighted.

Assessment of Abrasion-Induced Visual Defects in Twin Screw Wet Granulation Using Wall Friction Measurements

Starting point of the presented study were abrasion effects occurring during a twin screw wet granulation (TSG) process of a new chemical entity (NCE) formulation, resulting in gray spots on the final tablets. Several actions and systematic changes of equipment and process parameter settings of TSG process were conducted which reduced the visual defect rate of the tablets, i.e., gray spots on the surface, below the specification limit. To understand the rationale and mechanism behind these improvements, correlations of defect rates and wall friction measurements using a Schulze ring shear tester were evaluated. To check the suitability of the method, a broad range of wall materials as well as powder formulations at various moisture levels were investigated with regard to their wall friction angle. As differences in wall friction angle could be detected, further experiments were conducted using wall material samples made out of different screw materials for TSG. Evaluation of these screw wall material samples gave first hints, which screw materials should be preferred in regard of friction for TSG process. In the finally presented case study, wall friction measurements were performed using the above mentioned NCE formulation with known abrasion issues at TSG processing. The results confirmed that changes which led to a reduced visual defect rate of tablets correlated with a decreased wall friction angle. The results suggest wall friction measurements as a potent tool for equipment selection and establishment of a suitable process window prior to conducting TSG experiments.Graphical abstract