Effect of particle size on powder compaction and tablet strength using limestone

Dynamic compaction of cohesive granular materials: scaling behavior and bonding structures

The compaction of cohesive granular materials is a common operation in powder-based manufacture of many products. However, the influence of particle-scale parameters such as bond strength on the packing structure and the general scaling of the compaction process are still poorly understood. We use particle dynamics simulations to analyze jammed configurations obtained by dynamic compaction of sticky particles under a fixed compressive pressure for a broad range of system parameter values. We show that relative porosity, representing the relative importance of porosity with respect to its minimum and maximum values, is a unique function of a modified cohesion number that combines adhesion force, confining pressure, and particle size, as well as contact stiffness, which is often assumed to be ineffective but is shown here to play an essential role in compaction. An asymmetric sigmoidal form based on two power laws provides an excellent fit to the data. The statistical properties of the bond network reveal self-balanced force structures and an exponential fall-off of the number of both tensile and compressive forces. Remarkably, the properties of the bond network depend on the cohesion number rather than the modified cohesion number, implying that similar bond network characteristics are compatible with a broad range of porosities mainly due to the effect of contact stiffness. We also discuss the origins of data points escaping the general scaling of porosity and show that they reflect either finite system size or rigid confining walls.

Unloading Model of Elastic-Plastic Half-Space Contacted by an Elastic Spherical Indenter

A new unloading contact model of an elastic-perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement.

Method for Determining the Coefficient of Friction Variation Pattern as a Function of Density at Low Temperatures Using the Example of Dry Ice-Steel Contact

The developments in manufacturing technologies are expected to reduce energy input without compromising product quality. Regarding the material densification process, numerical simulation methods are applied to achieve this goal. In this case, relevant material models are built using functions that describe the variation in mechanical parameters of the material in question due to its deformation. The literature review conducted for this research has revealed a shortage of experimental research methods allowing a determination of the coefficient of friction at low temperatures, approximately 200 K. This article proposes a method for determining the friction coefficient of dry ice sliding against steel. The experimental results were analysed to obtain several functions describing the variation in the coefficient of friction. These functions were then compared using goodness-of-fit indexes. Finally, two functions with similar goodness-of-fit values were chosen. The findings of this research project will complement the already available information and may be used in various research and implementation projects related to the development or improvement of currently used crystallised carbon dioxide conversion processes.

Effect of Material Properties and Variability of Mannitol on Tablet Formulation Development

PURPOSE

Using a high level of mannitol as a diluent in oral formulations can potentially result in tablet defects (e.g., chipping, cracking) during compression. This work aims to scrutinize the linkage between the mechanical properties and material attributes of mannitol and also uncover how variations between vendors and lots can lead to significant changes in the compaction performance of tablet formulations containing mannitol.

METHODS

The mechanical properties (Poisson's ratio, fracture energy) and mechanical performance (ejection force, pressure transmission ratio, residual radial die-wall stress, and tensile strength) of mannitol compacts were assessed on a compaction simulator for four lots of mannitol from two different vendors. The variation of material attributes of each lot, including particle size distribution (PSD), crystal form, primary crystal size and morphology, specific surface area (SSA), powder flow, and moisture absorption were investigated.

RESULTS

The variability of material attributes in mannitol lots, especially primary crystal size and SSA, can result in significant changes in mechanical properties and mechanical performance such as ejection force and residual radial die-wall stresses, which potentially led to chipping during compression.

CONCLUSION

The study elucidated the linkage between fundamental material attributes and mechanical properties of mannitol, highlighting their impact on tablet defects and compaction performance in compression. A comprehensive understanding of the variability in mannitol properties between vendors and lots is crucial for successful formulation development, particularly when high percentages of mannitol are included as a brittle excipient.

On the influence of raw material attributes on process behaviour and product quality in a continuous WET granulation tableting line

Continuous manufacturing of oral solids is a complex process in which critical material attributes (CMAs), formulation and critical process parameters (CPPs) play a fundamental role. However, assessing their effect on the intermediate and final product's critical quality attributes (CQAs) remains challenging. The aim of this study was to tackle this shortcoming by evaluating the influence of raw material properties and formulation composition on the processability and quality of granules and tablets on a continuous manufacturing line. Powder-to-tablet manufacturing was performed using four formulations in various process settings. Pre-blends of different drug loadings (2.5 % w/w and 25% w/w) and two BCS classes (Class I and II) were continuously processed on an integrated process line ConsiGmaTM 25, including twin screw wet granulation, fluid bed drying, milling, sieving, in-line lubrication and tableting. The liquid-to-solid ratio and the granule drying time were varied to process granules under nominal, dry and wet conditions. It was shown that the BCS class and the drug dosage influenced the processability. Intermediate quality attributes, such as the loss on drying and the particle size distribution, directly correlated with the raw material's properties and process parameters. Process settings had a profound impact on the tablet's hardness, disintegration time, wettability and porosity.

Reviewing the Impact of Powder Cohesion on Continuous Direct Compression (CDC) Performance

The pharmaceutical industry is undergoing a paradigm shift towards continuous processing from batch, where continuous direct compression (CDC) is considered to offer the most straightforward implementation amongst powder processes due to the relatively low number of unit operations or handling steps. Due to the nature of continuous processing, the bulk properties of the formulation will require sufficient flowability and tabletability in order to be processed and transported effectively to and from each unit operation. Powder cohesion presents one of the greatest obstacles to the CDC process as it inhibits powder flow. As a result, there have been many studies investigating potential manners in which to overcome the effects of cohesion with, to date, little consideration of how these controls may affect downstream unit operations. The aim of this literature review is to explore and consolidate this literature, considering the impact of powder cohesion and cohesion control measures on the three-unit operations of the CDC process (feeding, mixing, and tabletting). This review will also cover the consequences of implementing such control measures whilst highlighting subject matter which could be of value for future research to better understand how to manage cohesive powders for CDC manufacture.

Continuous measurement of die wall pressure in a rotary tablet machine

In the pharmaceutical industry, tablets are manufactured using rotary tableting machines. Recently, die wall pressure in a single-punch press was measured to understand the compaction mechanism and predict tableting failure. However, die wall pressure measurements in rotary tableting machines have not been studied. Two challenges exist in measuring die wall pressure in these machines, viz. (i) lack of space inside the machine to set up the measurement equipment and (ii) difficulty in installing wired measurement hardware because the die rotates with the rotary plate. This study aimed to continuously measure die wall pressure in a rotary tableting machine and investigate the effect of high compression speed on die wall pressure. Die wall pressure at tableting speeds of up to 140 mm/s was successfully determined using a wireless telemeter. Residual die wall pressure for plastic materials was strongly dependent on the tableting speed, although the tableting speed affected the maximum die wall pressure minimally. This novel measurement technique can be used to study the effect of tableting speed on die wall pressure, which can be applied in solving the problems of capping and lamination during tablet production.

Softer than soft: Diving into squishy granular matter

Softer than soft, squishy granular matter is composed of grains capable of significantly changing their shape (typically a deformation larger than 10%) without tearing or breaking. Because of the difficulty to test these materials experimentally and numerically, such a family of discrete systems remains largely ignored in the granular matter physics field despite being commonly found in nature and industry. Either from a numerical, experimental, or analytical point of view, the study of highly deformable granular matter involves several challenges covering, for instance: (i) the need to include a large diversity of grain rheology, (ii) the need to consider large material deformations, and (iii) analysis of the effects of large body distortion on the global scale. In this article, we propose a thorough definition of these squishy granular systems and we summarize the upcoming challenges in their study.

Numerical analysis of die filling with a forced feeder using GPU-enhanced discrete element methods

Understanding die filling behaviour of powders is critical in developing optimal formulation and processes in various industries, such as pharmaceuticals and fine chemicals. In this paper, forced die filling is analysed using a graphics processing unit (GPU) based discrete element method (DEM), for which a powder feeder equipped with a wired stirrer is considered. The influences of operating parameters, such as the initial powder bed height, the filling speed, and the stirrer speed, on the die filling performance are systematically explored. It is shown that a larger initial powder bed height leads to a higher filling ratio, which can be attributed to a higher filling intensity; while the deposited particle mass in the die is almost independent of the powder bed height, when the initial fill level is larger than a critical bed height. Additionally, the filling ratio slightly increases with the increase of stirrer speed for cases with a stirrer, while the filling ratios are lower than that without a stirrer, which is attributed to the stirrer occupying some space above the die and reducing the effective discharge area. The obtained results can provide useful information for optimising the feeder system design and the operating condition.

An update on microcrystalline cellulose in direct compression: Functionality, critical material attributes, and co-processed excipients

Microcrystalline cellulose (MCC) is one of the most popular cellulose derivatives in the pharmaceutical industry. Thanks to its outstanding tabletability, MCC is generally included in direct compression (DC) tablet formulations containing poor-tabletability active pharmaceutical ingredients. Nowadays, numerous grades of MCC from various brands are accessible for pharmaceutical manufacturers, leading to variability in MCC properties. Hence, it seems to be worthy and urgent to evaluate the influences of MCC variability on tablet quality and to identify critical material attributes (CMAs) based on the idea of Quality by Control. Besides, MCC-based co-processed excipients can effectively combine the functions of the filler, binder, disintegrant, lubricant, glidant, or flavor, and thus have drawn extensive interest. In this review, we focused specifically on the recent advances and development of MCC on DC tableting, including the functions in tablet formulations, potential CMAs, and MCC-based co-possessed excipients, therefore providing a reference for further studies.

Effects of production conditions on the properties of limestone briquettes aimed for acid soil liming

This paper presents the results of experiments performed to determine how the quantity of the binder (bentonite) and the parameters of the laboratory roll press affect the quality of the briquettes obtained from limestone powder. These experiments aim to examine the conditions in which limestone briquettes are formed and to determine their use for agricultural purposes. During the experiments various mass fractions of bentonite was added to limestone (from 1 to 10 %), while the force of roll press drums ranged from 2 to 25 kN. The briquettes have been tested by applying scanning electron microscopy (SEM), differential thermal and thermo-gravimetric (DTA/TG) analyses, X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Bentonite distribution was found to be uniform within the compact briquette structure. Formation of new compounds was not evidenced. The experiments also demonstrated that during briquetting, limestone properties remain unchanged, the changes are only physical, water solubility is not reduced, mechanical properties (impact resistance, compressive strength and abrasion resistance) are satisfactory by the transport and storage terms if the binder mass fraction is over 5% and the briquetting force exceeds 10kN and finally there is no loss due to wind dispersal during application. The only downside of the ?green? briquettes obtained is the time required for their complete disintegration if totally immersed in water.

Systematic study of paracetamol powder mixtures and granules tabletability: Key role of rheological properties and dynamic image analysis

The aim of this systematic study was to analyze the granulometric and rheological behavior of tableting mixtures in relation to tabletability by single tablet and lab-scale batch compression with an eccentric tablet machine. Three mixtures containing 33, 50, and 66% of the cohesive drug paracetamol were prepared. The high compressibility of the powder mixtures caused problems with overcompaction or lamination in the single tablet compression method; due to jamming of the material during the filling of the die, the lab-scale batch compression was impossible. Using high shear granulation, the flow properties and tabletability were adjusted. A linear relationship between the span of granules and the specific energy measured by FT4 powder rheometer was detected. In parallel, a linear relationship between conditioned bulk density and the tensile strength of the tablets at lab-scale batch tableting was noted. The combination of dynamic image analysis and powder rheometry was useful for predicting the tabletability of pharmaceutical mixtures during the single tablet (design) compression and the lab-scale batch compression.

Tableting model assessment of porosity and tensile strength using a continuous wet granulation route

This paper presents a comprehensive assessment of the most widely used tablet compaction models in a continuous wet granulation tableting process. The porosity models, tensile strength models and lubricant models are reviewed from the literature and classified based on their formulations i.e. empirical or theoretical and applications, i.e. batch or continuous. The majority of these models are empirical and were initially developed for batch tabletting process. To ascertain their effectiveness and serviceability in the continuous tableting process, a continuous powder processing line of Diamond Pilot Plant (DiPP) installed at The University of Sheffield was used to provide the quantitative data for tablet model assessment. Magnesium stearate (MgSt) is used as a lubricant to investigate its influence on the tensile strength. Whilst satisfactory predictions from the tablet models can be produced, a compromise between the model fidelity and model simplicity needs to be made for a suitable model selection. The Sonnergaard model outperforms amongst the porosity models whilst the Reynolds model produces the best goodness of fitting for two parameters fitting porosity models. An improved tensile strength model is proposed to consider the influence of powder size and porosity in the continuous tableting process.

Impact breakage of single pharmaceutical tablets in an air gun

Milling is commonly used for controlling the size distribution of granules in the pharmaceutical dry granulation process. A thorough understanding of the breakage of single compacts is crucial in unravelling the complex interactions that exist between different pharmaceutical feed materials and the mill process conditions. However, limited studies in the literature have examined the impact breakage of single pharmaceutical compacts. In this study, pharmaceutical powders including the microcrystalline MCC 101, MCC 102 and MCC DG were compressed at different pressures and tablets with different porosities and thicknesses were produced. Impact breakage tests were conducted in an air gun and the tablet impact velocities and breakage patterns were analysed using a Phantom ultrahigh-speed camera. It was observed that the tablet breakage rate and the amount of fines reduced as the tablet porosity decreased. In addition, thin tablets with low porosity exhibited semi-brittle fracture and less intense crack propagation while thick tablets with high porosity primarily disintegrated into fine fragments. Thus, this study provides a better understanding of the breakage behaviour of different pharmaceutical materials and can potentially be used to describe the breakage modes of compacts in the ribbon milling processes.

Preparation, stabilisation, isolation and tableting of valsartan nanoparticles using a semi-continuous carrier particle mediated process

This work investigated the technical feasibility of preparing, stabilizing and isolating poorly water-soluble drug nanoparticles via a small-scale antisolvent precipitation process operating in semi-continuous mode. Specifically, a novel semi-continuous process was demonstrated for the carrier particle mediated production, stabilization and isolation of valsartan nanoparticles into a solid form using montmorillonite clay particles as the carrier. The semi-continuous process operated robustly for the full duration of the experiment (~16 min) and steady-state conditions were reached after ~5 min. Nanoparticles of valsartan (51 ± 1 nm) were successfully prepared, stabilized and isolated with the help of montmorillonite (MMT) or protamine functionalized montmorillonite (PA-MMT) into the dried form by this semi-continuous route. The dissolution profile of the isolated valsartan nanocomposite solids was similar to that of valsartan nanocomposite solids produced via the corresponding laboratory scale batch mode process, indicating that the product quality (principally the nanoscale particle size and solid-state form) is retained during the semi-continuous processing of the nanoparticles. Furthermore, tablets produced via direct compression of the isolated valsartan nanocomposite solids displayed a dissolution profile comparable with that of the powdered nanocomposite material. PXRD, DSC, SSNMR and dissolution studies indicate that the valsartan nanoparticles produced via this semi-continuous process were amorphous and exhibited shelf-life stability equivalent to > 10 months.

The influence of particle size on the application of compression and compaction models for tableting

The physical characteristics of raw materials determine powder compression and compaction performance as relevant in pharmaceutical processes. For instance, the influence of initial particle size on powder compression and the resulting strength of specimen are highly complex and are still not sufficiently understood. Existing studies are often limited to materials with well-defined deformation behaviour, such as purely brittle or ductile. However, the deformation behaviour of active pharmaceutical ingredients (APIs) is often more complex. In this study, the influence of initial particle size on powder compressibility and compactibility is systematically characterized by consideration of in-die compressibility, specific energies, quick elastic recovery, tablet porosity and, tensile strength for the binder microcrystalline cellulose and three APIs. The decrease of particle size leads to an increase of the resistance against compression by trend and probably to a different contribution of the acting deformation mechanisms. The compactibility is increased with decreasing particle size because of the increasing number of bonds in a cross-sectional area of the tablet, as found by the application of the model of Rumpf. Furthermore, it is found that the model of Rumpf combined with the JKR model provides a meaningful property function to estimate tablet tensile strength.

Confined Bed Breakage of Fine Iron Ore Concentrates

High-pressure grinding rolls (HPGR) have gained great popularity in the mining industry in the last 25 years or so. One of the first successful applications of the technology has been in iron ore pressing prior to pelletization. Piston-and-die tests can provide good insights on the material response in an HPGR. This work analyzed confined bed breakage of four iron ore concentrates under different conditions. Saturation in breakage of particles contained in the top size in the tests was observed to occur at specific energies of about 2 kWh/t, whereas full saturation in breakage, with no additional increase in specific surface area of the material, occurred at energies above about 6 kWh/t. An expression was proposed to characterize the propensity of a material to break under confined bed conditions. The phenomenology involved in confined bed breakage of such materials was then analyzed in light of the results.