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Geometries for (a) straight diet and (b) tapered die with a tapering angle of 0.56°. Geometries shown are not to scale.
Source publication
In an effort to identify the origin and the evolution of damage during the compaction/ejection cycle of powder compacts, an experimental study that compares compacts in straight and tapered dies in terms of the presence and growth of microcracks was carried out using x-ray tomography and environmental scanning electron microscopy. The results prese...
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... compacts were produced using standard flat tooling and experimental data were obtained from compaction experiments using an Instron Universal testing machine 5800R IUTM (Norwood, MA). Die compaction experiments were performed using a standard straight die with a nominal diameter of 9.525 mm ( Fig. 2(a)), and a Natoli (Saint Charles, MO) single-ended tapered die with a nominal diameter and a tapering angle of 10 mm and 0.56° respectively ( Fig. 2(b)). The tapered die, due to its geometry, is expected to allow for radial expansion of the compact within the tapered region of the die. In this manner, the stresses in the vicinity of the ...
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... experiments using an Instron Universal testing machine 5800R IUTM (Norwood, MA). Die compaction experiments were performed using a standard straight die with a nominal diameter of 9.525 mm ( Fig. 2(a)), and a Natoli (Saint Charles, MO) single-ended tapered die with a nominal diameter and a tapering angle of 10 mm and 0.56° respectively ( Fig. 2(b)). The tapered die, due to its geometry, is expected to allow for radial expansion of the compact within the tapered region of the die. In this manner, the stresses in the vicinity of the die exit are ...
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... coefficient of friction were identified for microcrystalline cellulose (Avicel PH102) using a series of experiments based on the procedure explained in [42]. The geometries of the powder and punches were modeled after flat-faced cylindrical shaped compacts. The geometries of the straight and tapered die walls used in FEM simulation are shown in Fig. 2. Axisymmetric conditions effectively reduce the problem to 2-D. Fig. 5 shows a typical discretized geometry used in the compaction simulation at the beginning and end of compaction for the straight die compaction ...
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... focus our attention on the mechanical stresses in the compact when the compact is partially ejected to a specified distance past the die exit. For the tapered die, the die exit is defined as the point at which the die taper meets the die bore (point 2 in Fig. 20(b)) and is referred to as the start of taper. For the straight compact, the exit is considered to be the point at which the die bore meets the exit chamfer (point 1 in Fig. 20(a)). Fig. 20 shows the distribution of stresses in the y direction with an emphasis on tensile stresses for compacts partially ejected approximately 0.6 mm past the ...
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... partially ejected to a specified distance past the die exit. For the tapered die, the die exit is defined as the point at which the die taper meets the die bore (point 2 in Fig. 20(b)) and is referred to as the start of taper. For the straight compact, the exit is considered to be the point at which the die bore meets the exit chamfer (point 1 in Fig. 20(a)). Fig. 20 shows the distribution of stresses in the y direction with an emphasis on tensile stresses for compacts partially ejected approximately 0.6 mm past the die exit and start of taper for the straight and tapered compact respectively. It is important to note that the partial ejection distance of 0.6 mm was simply chosen for ...
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... to a specified distance past the die exit. For the tapered die, the die exit is defined as the point at which the die taper meets the die bore (point 2 in Fig. 20(b)) and is referred to as the start of taper. For the straight compact, the exit is considered to be the point at which the die bore meets the exit chamfer (point 1 in Fig. 20(a)). Fig. 20 shows the distribution of stresses in the y direction with an emphasis on tensile stresses for compacts partially ejected approximately 0.6 mm past the die exit and start of taper for the straight and tapered compact respectively. It is important to note that the partial ejection distance of 0.6 mm was simply chosen for comparison ...
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... comparison purposes only. Any other partial ejection distance produces a similar comparison of the results. A distinct difference between straight and tapered die compacts is observed close to the radial surface of the compacts. The simulation shows the presence of high intensity tensile stresses after the exit of the compact in the straight die (Fig. 20(a)); whereas the tensile stresses in the tapered compact occur at a location beyond the start of taper and are reduced (Fig. 20(b)). Fig. 20(c) shows that within the straight die there is an intense increase of the compressive stress close to the surface of the die, while immediately after the exit from the die there is a reversal of the ...
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... between straight and tapered die compacts is observed close to the radial surface of the compacts. The simulation shows the presence of high intensity tensile stresses after the exit of the compact in the straight die (Fig. 20(a)); whereas the tensile stresses in the tapered compact occur at a location beyond the start of taper and are reduced (Fig. 20(b)). Fig. 20(c) shows that within the straight die there is an intense increase of the compressive stress close to the surface of the die, while immediately after the exit from the die there is a reversal of the sign of the stress, becoming tensile. The tapered die compact shows a noticeable transition from the compressive regime to ...
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... and tapered die compacts is observed close to the radial surface of the compacts. The simulation shows the presence of high intensity tensile stresses after the exit of the compact in the straight die (Fig. 20(a)); whereas the tensile stresses in the tapered compact occur at a location beyond the start of taper and are reduced (Fig. 20(b)). Fig. 20(c) shows that within the straight die there is an intense increase of the compressive stress close to the surface of the die, while immediately after the exit from the die there is a reversal of the sign of the stress, becoming tensile. The tapered die compact shows a noticeable transition from the compressive regime to tensile regime ...
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... die wall past the start of the taper. Fig. 21 shows the distribution of shear stresses for compacts ejected to the same locations shown in Fig. 20(a & b). A marked difference is observed in the local shear stress close to the edge of the compacts for the two compaction types. For the straight die simulation, there is an excessive intensity in the shear stresses observed towards the radial edge of the compact (Fig. 21(a)), which is virtually non-existent in the tapered compact (Fig. ...
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... only a more gradual change in shear stresses for the tapered die around the start of the taper, where this figure shows the shear stress distribution along the radial edge of the two compaction types. It is instructive to focus on the details of the stress field around the exit point of the straight die. Before the exit from the die (point A in Fig. 22), the stress state in the material is highly compressive in the radial direction within a very narrow area from the surface. This point is surrounded by two highly shearing areas (B and C in Fig. 22). The area of the surface of the material just outside the die (marked D in Fig. 22) is under uniaxial tensile stress. Most importantly, ...
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... It is instructive to focus on the details of the stress field around the exit point of the straight die. Before the exit from the die (point A in Fig. 22), the stress state in the material is highly compressive in the radial direction within a very narrow area from the surface. This point is surrounded by two highly shearing areas (B and C in Fig. 22). The area of the surface of the material just outside the die (marked D in Fig. 22) is under uniaxial tensile stress. Most importantly, the area of the surface immediately beyond the die exit (marked E in Fig. 22) is under a state of intense shear. It is important to note that a point just below this point of intense shear, the state ...
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... of the straight die. Before the exit from the die (point A in Fig. 22), the stress state in the material is highly compressive in the radial direction within a very narrow area from the surface. This point is surrounded by two highly shearing areas (B and C in Fig. 22). The area of the surface of the material just outside the die (marked D in Fig. 22) is under uniaxial tensile stress. Most importantly, the area of the surface immediately beyond the die exit (marked E in Fig. 22) is under a state of intense shear. It is important to note that a point just below this point of intense shear, the state of stress is similar with a change of sign in the shear direction. As the material ...
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... in the radial direction within a very narrow area from the surface. This point is surrounded by two highly shearing areas (B and C in Fig. 22). The area of the surface of the material just outside the die (marked D in Fig. 22) is under uniaxial tensile stress. Most importantly, the area of the surface immediately beyond the die exit (marked E in Fig. 22) is under a state of intense shear. It is important to note that a point just below this point of intense shear, the state of stress is similar with a change of sign in the shear direction. As the material attempts to expand elastically, it is constrained by the part of the compact that is still inside the die. The stresses at points D ...
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... the material attempts to expand elastically, it is constrained by the part of the compact that is still inside the die. The stresses at points D and E are imposing a mixed mode I and II loading mode on the surface of the compact and tends to open the cracks that formed during unloading. It is important to note that the level of stresses shown in Fig. 22 is exaggerated from the fact that the DCP model used in the FEM simulation does not include the relaxation of the radial stresses due to microcracking that is experimentally observed (see Fig. 7). Nevertheless, the qualitative features of the prediction are still valid. It is also important to note that qualitative features in Fig. 22 ...
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... shown in Fig. 22 is exaggerated from the fact that the DCP model used in the FEM simulation does not include the relaxation of the radial stresses due to microcracking that is experimentally observed (see Fig. 7). Nevertheless, the qualitative features of the prediction are still valid. It is also important to note that qualitative features in Fig. 22 also hold for the tapered die that is ejected to a location partly beyond the start of the taper with the exception of shear stresses, which are significantly ...
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... stress occurs as a result of the changing stress state from the highly triaxial compression at the end of compaction to the biaxial stressing (radial pressing) at the end of unloading. During this transition, the radial stress is continuously decreasing as shown in the radial versus axial stress curve during compaction and unloading shown in Fig. 23(a). The high triaxiality of the stress field during compaction closes the pores and does not create any damage in the microstructure. During unloading, when the axial stress becomes sufficiently low, the formation of the cracks commences. It is suspected that the initiation of the microcracking is demarcated by the deviation from ...
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... does not create any damage in the microstructure. During unloading, when the axial stress becomes sufficiently low, the formation of the cracks commences. It is suspected that the initiation of the microcracking is demarcated by the deviation from linearity in the radial versus axial stress diagram and the axial stress versus relative density in Fig. 23(b). During the initial stage of unloading the compact behaves as a linear elastic material, but the initiation of the microcracks relieves the radial wall stress near the last half of unloading. This is consistent with the significant deviation between FEM predicted and experimentally measured values of radial wall stresses shown in Fig. ...
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... nonlinearity observed in both the radial versus axial stress and axial stress versus relative density graphs in Fig. 23 provides an indication of the extent of cracking during unloading. The deviation from linearity (highlighted area in Fig. 23(b)) indicates to some extent the amount of work that is spent to create the cracks. Although a detailed analysis of the phenomenon is lacking, the generation of microcracking during unloading depends on the ...
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... nonlinearity observed in both the radial versus axial stress and axial stress versus relative density graphs in Fig. 23 provides an indication of the extent of cracking during unloading. The deviation from linearity (highlighted area in Fig. 23(b)) indicates to some extent the amount of work that is spent to create the cracks. Although a detailed analysis of the phenomenon is lacking, the generation of microcracking during unloading depends on the maximum radial wall stress, the elastic properties that determine the stress history during unloading and the fracture toughness of ...
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... provides insight regarding the local conditions that cause it. As discussed previously, surface microcracks generated during unloading grow at the exit from the die due to shear stresses in a mode II or due to tensile stresses along the surface of the compact due to the elastic expansion of the compact upon exiting the die points (D & E in Fig. 22). The utilization of a tapered die significantly reduces the detrimental effect of the exit of the die by minimizing the level of shear and tensile stresses in the tapered region. Therefore optimization of the die exit can be beneficial for the mechanical properties of the compacts post ejection. An indirect indication of this ...
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... interaction of the die exit with the material can lead to even larger cracks and possibly full lamination. Therefore, the use of a tapered die, which essentially minimizes the interaction of the die edge with the expanding compact, can help to minimize damage and possibly prevent capping and lamination failures. An example of this can be seen in Fig. 24, which shows the x-ray projections of sodium chloride compacts in straight and tapered dies (Fig. 24(a) and (b) respectively). Ideally, the selection of the tapering angle in the tapered dies would be such that it matches a significant percent of the expansion of the compact from the die size. For materials with even lower fracture ...
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... Therefore, the use of a tapered die, which essentially minimizes the interaction of the die edge with the expanding compact, can help to minimize damage and possibly prevent capping and lamination failures. An example of this can be seen in Fig. 24, which shows the x-ray projections of sodium chloride compacts in straight and tapered dies (Fig. 24(a) and (b) respectively). Ideally, the selection of the tapering angle in the tapered dies would be such that it matches a significant percent of the expansion of the compact from the die size. For materials with even lower fracture toughness, it is possible that the unloading process can lead not just to diffuse microcracking as seen ...
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Citations
... These tablets with internal cracks were undetected by external visual examination, which is consistent with the findings of a previous report that when the part of the tablet near the edge undergoes compression pressure, the cracks initially formed at the center may stop before reaching the tablet edge [30]. These cracks in proximity to the die surface interact with the stress field from the die during ejection, leading to the extension of pre-existing micro-cracks or even delamination [31]. Thus, the possibility of such cracks within a tablet should be considered in the manufacturing process, although they are not immediately detected just after compression. ...
... The numerical results in Section 2.6 identified a mechanism that could lead to internal cracks in the BLT during the compression process. The presence of cracks within the BLT contributes to crack expansion during the ejection of the BLT from the die due to excessive friction between the edge of the BLT and the die surface, finally leading to the delamination of the tablet when ejected [31]. In this section, shear stress distribution during the ejection process was focused on understanding its contribution to delamination in BLTs, followed by a comparison with experimental results. ...
... The numerical results in Section 2.6 identified a mechanism that could lead to in cracks in the BLT during the compression process. The presence of cracks within th contributes to crack expansion during the ejection of the BLT from the die due to exc friction between the edge of the BLT and the die surface, finally leading to the dela tion of the tablet when ejected [31]. In this section, shear stress distribution duri Figure 8 shows a comparison of the ejection pressure results with different MAIN-Ps between the modeling and experimental data, as obtained from Figure 5B, to validate the FEM simulation. ...
This study aimed to evaluate the ejection pressure and the correlation of the findings with the occurrence of internal cracks within bilayer tablets (BLTs) consisting of metformin HCl (MF) and evogliptin tartrate (EG). Then, the mechanism of tablet failure was provided by the finite element method (FEM). The ejection pressure and the difference in diameter depending on MAIN-P were evaluated to understand the correlation between ejection pressure and change in the BLT internal structure. The ejection pressure and the difference in diameter increased as the MAIN-P increased, then steeply decreased from 350 MPa to 375 MPa of MAIN-P, despite there being no pattern in compaction breaking force and porosity. The mechanical integrity at the BLT interface was weakened by internal cracks, reducing ejection pressure. The stress distribution analysis during the compression revealed that crack formation caused by entrapped air located at the center of the BLT interface may not propagate due to concentrated stress, which promotes a tight bond at the edge of the BLT. Furthermore, complete delamination can occur in the ejection process due to localized and intensive shear stresses at the BLT interface. These findings indicate that the mechanisms of internal cracking and delamination were successfully confirmed by FEM simulation. Moreover, measuring ejection pressure before BLT manufacturing can prevent invisible tablet cracks without damaging the tablets.
... To identify the type of lamination, an assessment of the defect initiation (Garner et al., 2014;Yost et al., 2019), die wall pressure (Hiestand et al., 1977;Sugimori et al., 1989), tablet failure mode (Mazel et al., 2015a), the influence of processing parameters, and the effectiveness of lamination solution may be needed . While visual observations of cracks in the tablet band may identify the presence and type of lamination, internalized laminationlike defects are more difficult to detect during development. ...
... Such microcracking behavior is consistent with literature that focused on E-SEM micro graphing of tapered die compacts with relative densities of 95%. Such compacts were subjected to exhibit diffuse surface microcracking 22 . From the past figures, one can conclude that sintering at 600 °C led to larger grains sizes compared to sintering at 550 °C. ...
This research investigates the mechanical properties improvement of reinforced Al6061 using powder metallurgy (PM) route. It utilizes the nanoparticles strengthening mechanism to enhance the prepared samples’ mechanical properties. For this purpose, Silver Nano-Particles (AgNPs) with contents of 0 wt%, 1 wt%, and 2 wt% were used to reinforce the Al6061 Matrix Composition (AMC). For optimization purposes, many parameters have been considered during the research journey namely: compaction pressure, sintering temperature, dwelling time, and reinforcement contents. All samples are examined in terms of density, hardness, and compression strength. Additionally, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, mapping analysis, and XRD were used to investigate the microstructure. The experimental results revealed highest hardness values at 2 wt% AgNPs reinforced sample that was sintered at 600 °C, while the lowest was obtained at un-reinforced sample sintered at 550 °C. Furthermore, the compression strength of sample reinforced with 2 wt% AgNPs and sintered at 600 °C recorded an improvement of 25.8% of the maximum compression strength compared to the un-reinforced sample, as it reached 216 N/mm². Regarding microstructural analysis, SEM imaging and EDX played an important role in exploring and interpreting many unusual test behaviors including the formation of intermetallic bonding, minor pores formation, and reinforcement dispersion un-homogeneity.
... The fissures appearing on the samples at varying scales indicate that the reduction process may need to be performed more slowly, as the expansion of the material may be partly responsible for them. More generally, ejection cracking after uniaxial pressing is known to produce similar features [50], and during this work the highest oxide content samples were observed to be more difficult to extract from the die. The 50% CuO sample, which shows very little macroscale cracking, may have sufficient metallic Cu to retain ductility upon ejection. ...
Nanoporous metals can serve in unique functional applications due to their high surface area, and they are often made through dealloying, which removes a sacrificial element through chemical etching and leaves a nanoporous matrix of the remaining element(s). Several variations on this technique allow for a wider variety of metals and alloys to be processed, but simple, scalable, and reliable production of nanoporous devices is still not a reality using the majority of techniques and alloy systems. Oxide reduction may provide a suitable alternative, and in this work, nanoporous Cu was produced via oxide reduction in the Cu–CuO system. This method uses mechanical milling to create a metal matrix composite powder primarily composed of CuO that is reduced under hydrogen to leave pure Cu behind. It requires no harsh chemicals, and it uses modest temperatures and short reaction times. Furthermore, it is fully compatible with traditional powder metallurgy, making it readily scalable. Powder compacts were also processed to track the geometric changes associated with each composition and demonstrate that device creation is feasible, even with the basic process applied here. This work reveals important parameters associated with these materials by incorporating a wide range of milling times and compositions, with shorter milling times and higher oxide concentrations providing the finest pore sizes, the highest porosity, and the greatest simplicity.
Graphical abstract
... This proposed mechanism is supported by previous reports that using tapered dies can mitigate the tablet cracking issues because the tapered region, which has a small angle at one end of the die, allows for a gradual radial expansion of the tablet and thus reducing radial stress during ejection [26]. In this study, only straight die with a chamfer was employed and evaluated because it is widely used in tablet manufacturing. ...
... In this study, only straight die with a chamfer was employed and evaluated because it is widely used in tablet manufacturing. The mannitol lots with higher Poisson's ratio experienced a greater change of the shear stress around the die transition point during ejection, and thus had stronger tendency of chipping [26]. Herein, it was postulated that the aforementioned differences of processibility and mechanical performance of mannitol compacts may be directly attributed to the variations in material properties of mannitol observed between vendors and lots, such as PSD, crystal form, SSA, and primary crystal sizes, which will be discussed sequentially in the following section. ...
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.
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... To get intact specimen NaCl from a regular compaction a tapered die can be used which minimizes the defects produced in ejection (see Garner et al.). 13 CPM specimens have been insensitive to the unloading mode, as can be seen in Figure 7 while milled NaCl exhibits higher strength when compaction is followed by triaxial unloading, Figure 8. The results for CPM samples with and without machined holes can be seen in Figure 9 while the NaCl samples are shown in Figure 10. ...
The characterization of the green strength of powder compacts is commonly performed using bending tests and diametrical compression tests. This classic approach provides only a limited insight into the defects that limit the strength of the compact or the inherent fracture toughness of the compacted material. In this work we reexamine some early work on the reduction of strength due to a stress concentration (a hole in this case) using the modern concept of fracture mechanics. As a result of this approach, we obtain both the fracture toughness of the compact and the size of the representative defect for brittle compacts.. This methodology uses simple die shapes (round or square, with and without a hole). In addition to a broader characterization of the compact, these experiments provide interesting insight into the observation that powder compacts are less sensitive to the presence of stress concentrations (notches, holes, etc.) than the corresponding wrought parts. The work presented here is documented using experiments on pharmaceutical powders, but the concept is fully applicable to brittle metallic powder compacts.
... Depending the kind of failure, these phenomena are called capping or lamination [1]. There is a large literature on this subject, and the mechanisms that promote the failure have been proposed [2][3][4][5][6][7][8]. Nevertheless, these phenomena are still complicated to predict. ...
... Les expériences seront menées avec différents matériaux de recouvrement élastique plus ou moins important, en tant que coeur et qu'enveloppe du Tab-in-Tab. Ainsi la cause avancée pourra être confirmée, mais d'éventuels facteurs aggravants ou atténuants pourront être identifiés.En ce qui concerne les comprimés mono-couche, des études précédentes ont montré qu'il est possible d'observer du laminage en raison de la contrainte radiale résiduelle, qui crée une concentration de contrainte de cisaillement à l'éjection[100],[101]. Garner et. ...
Les comprimés Tab-in-Tab sont un type de comprimés pharmaceutiques destiné à libérer une substance active dans l’organisme, avec un délai après l’administration du comprimé, appelé lag-time, et selon une cinétique de libération définie. Ces comprimés font partie des formes pharmaceutiques à libération différée, qui servent entre autres à traiter des maladies à symptômes nocturnes. Ces caractéristiques sont obtenues grâce à une structure cœur/enveloppe, où le cœur contient la substance active. Les Tab-in-Tab sont produits par deux compressions de poudres pharmaceutiques. Premièrement, le comprimé cœur est fabriqué par compression classique en matrice, et deuxièmement une enveloppe solide est formée autour de celui-ci lors de la compression d’enrobage, réalisée avec une poudre ne contenant pas d’actif. De nombreux travaux ont étudié les moyens de contrôler le lag-time en modifiant la formulation du cœur et de l’enveloppe, avec des excipients accélérant ou retardant la libération. Cependant, assez peu de travaux ont été réalisés sur le procédé de compression d’enrobage en lui-même. Pourtant, ce procédé est très particulier par rapport à une compression simple, et pourrait être à l’origine d’une structure atypique du comprimé, avec des effets majeurs sur ses propriétés finales.Ce travail vise à étudier en détails la répartition des contraintes mécaniques se produisant pendant la compression d’enrobage, et leurs effets sur la structure de l’enveloppe et du cœur. A travers des expériences de compression d’enrobage couplées à des simulations numériques par éléments finis, il a été montré que les couches de poudre à l’aplomb du cœur se densifient fortement par rapport au reste de l’enveloppe. Il en résulte une contrainte axiale fortement concentrée sur le cœur, avec comme conséquences des modifications de ses dimensions et une diminution de sa densité relative à basse pression apparente. Cet effet est d’autant plus marqué que l’épaisseur de couche est faible, ce qui fait de ce paramètre un nouveau paramètre d’intérêt dans la conception de Tab-in-Tab. L’épaisseur de la bande, déterminée par le choix des poinçons, joue aussi un rôle sur la répartition des contraintes, et il en résulte une différence de densité entre la bande et les couches de l’enveloppe plus importante avec une faible épaisseur de bande.Cette structure hétérogène de l’enveloppe et la différence de propriétés mécaniques avec le cœur ont des conséquences sur l’issue du test diamétral, qui est le principal test de résistance mécanique réalisé sur les comprimés pharmaceutiques. En effet ce test est applicable sur des comprimés qui rompent diamétralement, mais dans le cas des Tab-in-Tab, il est montré dans ce travail, que le profil de rupture peut être de quatre types différents. Chaque profil de rupture reflète la résistance d’une zone différente et est dépendant des rigidités des différentes régions du Tab-in-Tab, ce qui a été étudié par une approche expérimentale et numérique. Ces conclusions questionnent donc l’applicabilité de ce test pour les Tab-in-Tab.Enfin, les propriétés de libération d’actif des Tab-in-Tab ont été étudiées en fonction des paramètres du procédé. Une forte dépendance à la pression de compression et aux dimensions a été montrée. En particulier un lag-time élevé est favorisé par une haute épaisseur de la bande et dans une moindre mesure de la couche. Cela montre l’intérêt de prendre en compte ces deux paramètres géométriques lors du développement. Les structures différentes dues à ces paramètres ont non seulement un effet sur le lag-time, mais aussi sur le mode d’ouverture lors du test de dissolution. Il en résulte donc une cinétique de dissolution rapide ou lente après le lag-time, selon les paramètres de fabrication des Tab-in-Tab.
... Depending the kind of failure, these phenomena are called capping or lamination [1]. There is a large literature on this subject, and the mechanisms that promote the failure 15 have been proposed [2,3,4,5,6,7,8]. Nevertheless, these phenomena are still complicated to predict. ...
Pharmaceutical tablets must meet a number of requirements and among them, the mechanical strength plays an important role. The diametral compression test is generally used to evaluate it but can generate unstable failures. Thanks to load-unload cycles applied to the tablets subjected to a DCT test, it was shown that the concept of equivalent linear elastic fracture mechanics usually, can be successfully applied to the Mode I fracture behavior. Within this framework, the equivalent elastic crack growth resistance, commonly called resistance curve (R-curve), of the studied material was obtained and revealed the development of a Fracture Process Zone (FPZ) which is symptomatic of a quasi-brittle behavior. Moreover, the cyclic loading applied during the fracture test revealed the existence of a second dissipative mechanism leading to residual crack opening which seems to be mainly caused by friction phenomenon in the FPZ.
