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R.c. Rowe - One of the best experts on this subject based on the ideXlab platform.
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the evaluation of the rheological properties of lactose microcrystalline cellulose and water mixtures by controlled stress rheometry and the relationship to the production of spherical pellets by extrusion spheronization
European Journal of Pharmaceutical Sciences, 2002Co-Authors: K A Macritchie, Jm Newton, R.c. RoweAbstract:The consistency of wet powder masses produced from two ratios (7:3 and 8:2) of α-lactose monohydrate (L) and microcrystalline cellulose (MCC) mixed with a range of water contents has been assessed with a parallel plate controlled stress rheometer. The range of water contents, which could be studied, was restricted to those, which could be extruded uniformly by a Ram Extruder. In the creep mode, the instantaneous compliance increased as the water content increased for both L:MCC ratios illustrating the increasing deformability of the mixtures with increasing water content. The derived apparent viscosity of the mixtures as a function of shear rate, increased as the water content decreased and the values for all the systems fell on a common line. This indicates that the measurements are providing a reliable assessment of the mixtures and that the change in water content and L:MCC ratio provides systems, whose change of viscosity with rate of shear is consistent at low rates of shear. The values of the storage and loss moduli obtained from oscillatory measurements, increased with a decrease in water content but this time the two ratios of L:MCC were not on a common line when related to the water content of the mixtures. There was a range of water levels over which both the values of the storage and loss moduli were approximately constant. This corresponded to the level of water, which produced the pellets of the smallest diameter and range of diameters and were of the most spherical shape when produced by a Ram Extruder and spheronization. For 8:2 L:MCC ratio, there appeared to be a value for both the storage and the loss moduli above which the wet mass could not produce good pellets. For the 7:3 L:MCC these limiting levels were not achieved before extrusion with steady state conditions could be maintained without the mass being too wet or too dry. Instead, there appeared to be minimum levels of the moduli required to ensure that the mixtures were able to produce good pellets.
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The evaluation of the rheological properties of lactose/microcrystalline cellulose and water mixtures by controlled stress rheometry and the relationship to the production of spherical pellets by extrusion/spheronization.
2002Co-Authors: K A Macritchie, J M Newto, R.c. RoweAbstract:The consistency of wet powder masses produced from two ratios (7:3 and 8:2) of alpha-lactose monohydrate (L) and microcrystalline cellulose (MCC) mixed with a range of water contents has been assessed with a parallel plate controlled stress rheometer. The range of water contents, which could be studied, was restricted to those, which could be extruded uniformly by a Ram Extruder. In the creep mode, the instantaneous compliance increased as the water content increased for both L:MCC ratios illustrating the increasing deformability of the mixtures with increasing water content. The derived apparent viscosity of the mixtures as a function of shear rate, increased as the water content decreased and the values for all the systems fell on a common line. This indicates that the measurements are providing a reliable assessment of the mixtures and that the change in water content and L:MCC ratio provides systems, whose change of viscosity with rate of shear is consistent at low rates of shear. The values of the storage and loss moduli obtained from oscillatory measurements, increased with a decrease in water content but this time the two ratios of L:MCC were not on a common line when related to the water content of the mixtures. There was a range of water levels over which both the values of the storage and loss moduli were approximately constant. This corresponded to the level of water, which produced the pellets of the smallest diameter and range of diameters and were of the most spherical shape when produced by a Ram Extruder and spheronization. For 8:2 L:MCC ratio, there appeared to be a value for both the storage and the loss moduli above which the wet mass could not produce good pellets. For the 7:3 L:MCC these limiting levels were not achieved before extrusion with steady state conditions could be maintained without the mass being too wet or too dry. Instead, there appeared to be minimum levels of the moduli required to ensure that the mixtures were able to produce good pellets
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The influence of process variables on the preparation and properties of spherical granules by the process of extrusion and spheronisation
1995Co-Authors: J M Newto, R.c. RoweAbstract:The influence of spheronisation process variables of time, load, speed of rotation and plate texture on the properties of size, shape and density of granules has been assessed with a standard extrudate produced by a cylinder Extruder. It was found that optimum conditions of load and speed of rotation existed in that too low a speed produced no significant shape changes in the extrudate, while too high a speed resulted in a size reduction of the particles. A low load appeared to give poor particle/particle interaction while a high load produced poor plate/particle interaction. Increase in the length of the die in the cylinder Extruder resulted in the inability to spheronise the extrudate under what had been previously optimum conditions of speed and load. No such loss of spheronisation performance occurred with processing of extrudate from two lengths of die of a Ram Extruder on a spheroniser with different plate textures. The granules produced, however, were significantly larger than those obtained for the same wet mass processed by the cylinder Extruder. © 1995
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the influence of moisture content on spheronization of extrudate processed by a Ram Extruder
International Journal of Pharmaceutics, 1993Co-Authors: K E Fielde, J M Newto, R.c. RoweAbstract:Abstract The presence of water is an essential feature of formulations containing mirocrystalline cellulose (MCC) for the preparation of spherical granules by the process of extrusion/spheronisation. The current work provides further proof of this observation. Formulations consisting of MCC and either a coarse (118.0 μm) or a fine grade (18.0 μm) of lactose mixed with two levels of water have been examined as they spheronise and after collection and drying. The shape changes on the plate, plus the size and shape changes, as a function of Spheronisation time, show that the mixtures containing fine particle size will form good spheres at either 33 or 37% water content, but the mixtures containing the coarse particle size will only form controlled size spheres at 33% moisture content. The results were found to be equivalent for both 1.0 and 1.5 mm extrudates. The effect can be related to the mobility of the water in the different packing structures produced by the different particle sizes of lactose.
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A comparison of the extrusion and spheronization behaviour of wet powder masses processed by a Ram Extruder and a cylinder Extruder
International Journal of Pharmaceutics, 1992Co-Authors: K.e. Fielden, Jm Newton, R.c. RoweAbstract:Abstract The preparation of spherical granules by spheronization of extrudate obtained by extrusion through either a cylinder or Ram Extruder of a mixture of macrocrystalline cellulose, lactose (with median diameter of either 18 or 117 μm) and water has been undertaken. Spheroids of a uniform size and shape could be produced from both particle size ranges of lactose if the cylinder Extruder was used but not if the Ram Extruder formed the extrudate. The differences appear to be associated with the different rates of shear and the shear stresses involved in the two extrusion processes.
Jm Newton - One of the best experts on this subject based on the ideXlab platform.
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the evaluation of modified microcrystalline cellulose for the preparation of pellets with high drug loading by extrusion spheronization
International Journal of Pharmaceutics, 2008Co-Authors: Fridrun Podczeck, P.e. Knight, Jm NewtonAbstract:The performance of microcrystalline cellulose (MCC) which had been modified by the inclusion of various levels of sodium carboxymethylcellulose (SCMC) in the wet cake prior to drying, in terms of their ability to form pellets by a standardised extrusion/spheronization process has been assessed. Initial screening of the ability of the modified MCCs to form pellets with an 80% level of lactose as a model drug identified two potential products containing 6 or 8% of SCMC (B 6 and B 8). These two products were compared with a standard grade of MCC (Avicel PH101) in terms of their ability to produce pellets with 80% of model drugs of low (ibuprofen), intermediate (lactose) and high (ascorbic acid) water solubility when subjected to a standardised extrusion/spheronization process. Also assessed was their ability to retain water with applied pressure using a pressure membrane technique and their ability to restrict water migration during extrusion with a Ram Extruder. The two new types of MCC (B 6 and B 8) were able to form good quality pellets with all three model drugs, whereas Avicel PH101 could not form pellets with this high level of ibuprofen. This improved performance was related to the ability of the new types of MCC to hold higher levels of water within their structure and restrict the migration of water in the wet mass when subjected to pressure applied during the process of preparing the pellets. There is evidence to show that the two new types of MCC can function over a wider range of water contents than Avicel PH101 and that they have an improved performance if the extrusion process is rapid and if, after incorporation of the water into the powder, the sample is stored for some time before extrusion.
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The evaluation of modified microcrystalline cellulose for the preparation of pellets with high drug loading by extrusion/spheronization
INT J PHARM, 2008Co-Authors: Jm NewtonAbstract:The performance of microcrystalline cellulose (MCC) which had been modified by the inclusion of various levels of sodium carboxymethylcellulose (SCMC) in the wet cake prior to drying, in terms of their ability to form pellets by a standardised extrusion/spheronization process has been assessed. Initial screening of the ability of the modified MCCs to form pellets with an 80% level of lactose as a model drug identified two potential products containing 6 or 8% of SCMC (B 6 and B 8). These two products were compared with a standard grade of MCC (Avicel PH101) in terms of their ability to produce pellets with 80% of model drugs of low (ibuprofen), intermediate (lactose) and high (ascorbic acid) water solubility when subjected to a standardised extrusion/spheronization process. Also assessed was their ability to retain water with applied pressure using a pressure membrane technique and their ability to restrict water migration during extrusion with a Ram Extruder. The two new types of MCC (B 6 and B 8) were able to form good quality pellets with all three model drugs, whereas Avicel PH101 could not form pellets with, this high level of ibuprofen. This improved performance was related to the ability of the new types of MCC to hold higher levels of water within their structure and restrict the migration of water in the wet mass when subjected to pressure applied during the process of preparing the pellets. There is evidence to show that the two new types of MCC can function over a wider range of water contents than Avicel PH101 and that they have an improved performance if the extrusion process is rapid and if, after incorporation of the water into the powder, the sample is stored for some time before extrusion. (c) 2007 Elsevier B.V. All rights reserved.
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the evaluation of the rheological properties of lactose microcrystalline cellulose and water mixtures by controlled stress rheometry and the relationship to the production of spherical pellets by extrusion spheronization
European Journal of Pharmaceutical Sciences, 2002Co-Authors: K A Macritchie, Jm Newton, R.c. RoweAbstract:The consistency of wet powder masses produced from two ratios (7:3 and 8:2) of α-lactose monohydrate (L) and microcrystalline cellulose (MCC) mixed with a range of water contents has been assessed with a parallel plate controlled stress rheometer. The range of water contents, which could be studied, was restricted to those, which could be extruded uniformly by a Ram Extruder. In the creep mode, the instantaneous compliance increased as the water content increased for both L:MCC ratios illustrating the increasing deformability of the mixtures with increasing water content. The derived apparent viscosity of the mixtures as a function of shear rate, increased as the water content decreased and the values for all the systems fell on a common line. This indicates that the measurements are providing a reliable assessment of the mixtures and that the change in water content and L:MCC ratio provides systems, whose change of viscosity with rate of shear is consistent at low rates of shear. The values of the storage and loss moduli obtained from oscillatory measurements, increased with a decrease in water content but this time the two ratios of L:MCC were not on a common line when related to the water content of the mixtures. There was a range of water levels over which both the values of the storage and loss moduli were approximately constant. This corresponded to the level of water, which produced the pellets of the smallest diameter and range of diameters and were of the most spherical shape when produced by a Ram Extruder and spheronization. For 8:2 L:MCC ratio, there appeared to be a value for both the storage and the loss moduli above which the wet mass could not produce good pellets. For the 7:3 L:MCC these limiting levels were not achieved before extrusion with steady state conditions could be maintained without the mass being too wet or too dry. Instead, there appeared to be minimum levels of the moduli required to ensure that the mixtures were able to produce good pellets.
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the influence of type and quantity of model drug on the extrusion spheronization of mixtures with microcrystalline cellulose i extrusion paRameters
International Journal of Pharmaceutics, 2001Co-Authors: G Tomer, Fridrun Podczeck, Jm NewtonAbstract:Five model drugs, (methyl, propyl and butyl paraben, 4-hydroxybenzoic acid and propyl gallate), similar in their chemical structure were mixed with microcrystalline cellulose and water in different proportions and forced through a Ram Extruder. The overall water movement was measured by the difference between the initial water in the formulation and the water content in the plug remaining after extrusion was completed. The differences in theoretical and practical volume occupancy of the materials inside the barrel were calculated to look for trapped air inside the barrel. The steady-state extrusion force for each formulation was recorded. All five materials demonstrated differences in behaviour during extrusion. The relationship between each of the three properties measured and both the drug-load and initial water content was examined, to establish the potential relationship that existed between the differences due to the drug models. The five drug models were divided into two sub-groups, when examining the way that they underwent extrusion. Methyl, propyl and butyl paraben formed one group while 4-hydroxybenzoic acid and propyl gallate formed the other group. Within the former group the relationship between steady-state extrusion force and the percentage of drug and water present tended to be lower than those in the latter group. For the former group these relationships were non-linear.
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the effect of water content on the porosity and liquid saturation of extruded cylinders
International Journal of Pharmaceutics, 1995Co-Authors: E Jerwanska, Göran Alderborn, Jm Newton, Christer NystromAbstract:Abstract The preparation of isodiametrical and nearly monodispersed pellets by extrusion-spheronization requires an extruded mass which shows a complex balance between deformability and its ability to break up into smaller units. The possibility of extruding the mass through an orifice is mainly related to its plasticity or deformability. Such mechanical properties of moist compacts are related to both the porosity and the degree of liquid saturation. In this study the effect of water addition has been studied in this context. Mixtures of dicalcium phosphate dihydrate (DCPD) and Avicel PH 101 (70:30%) were massed with water (moisture contents of 50, 60, 70, 80 w/w %). The masses were extruded in a Ram Extruder (25.0 mm in diameter), initially with a 10.0 mm die and then without the die. The moist extrudates were cut to isodiametrical cylinders and the porosity and the degree of liquid saturation were determined. An increased moisture content decreased the extrusion force and increased the porosity of the extrudates. The degrees of liquid saturation were similar and high for all extruded masses. It is suggested that such a nearly complete filling of the pore space with a liquid component is a prerequisite for the wet mass to yield and thus extrude. The mechanism behind the yielding process is probably an enhanced possibility for particle movement and rearrangement due to a reduced particle-particle attraction when the pore space is filled with a liquid.
Wilso J.w. - One of the best experts on this subject based on the ideXlab platform.
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Pilot scale single stage fine coal dewatering and briquetting process. Final technical report, September 1, 1995--August 31, 1996
Illinois Dept. of Energy and Natural Resources Springfield IL (United States), 1997Co-Authors: Wilso J.w., Honake R.q., Ding Y.Abstract:The primary goal of the ongoing ICCI coal preparation research project is to reduce ash and sulfur content in coal by using fine grinding and other coal cleaning processes. The ultrafine coal particles that result from the grinding and cleaning operations are difficult to dewater, and create problems in their storage, handling and transportation. The objective of this research is to combine the dewatering and briquetting processes of fine coal preparation into a single stage operation, thereby enhancing the economic viability of utilizing fine coal. A bitumen based emulsion, Orimulsion, has proven to be an effective hydrophobic binder, which helps not only with the briquetting process but also in the expulsion of water from the coal. Encouraging results from the use of a Ram Extruder briquetting device led to experimentation in the production of briquettes using a lab scale roll briquetting device. In the first quarter of this reporting year, a commercially available lab scale roll briquetting machine was employed (Komarek B-100). Further testing was conducted for the rest of the year with the use of a pilot scale model (Komarek B220-A). Briquettes were produced and evaluated by comparing results developed by adjusting various paRameters of the briquetting machines and feed material. Results further substantiate previous findings that curing time dictates both moisture content and strengths of briquettes, and slower roll speeds produce more robust briquettes. A statistical model was set up to determine the optimal range of operating paRameters. The statistical model generated from these results provided basic relationships between the roll speed and briquette form pressure
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Ultrafine coal single stage dewatering and briquetting process. Technical report, December 1, 1994--February 28, 1995
Illinois Dept. of Energy and Natural Resources Springfield IL (United States), 1996Co-Authors: Wilso J.w.Abstract:It is well known that a large portion of the pyrite particles in the coal seams of the Illinois Basin, are finely disseminated within the coal matrix. In order to liberate these micron size pyrite particles, one must use a fine grinding operation. The ultrafine coal particles that are produced are difficult to dewater and they create problems in coal transportation as well as in its storage and handling at utility plants. The objective of this research project is to combine ultrafine coal dewatering and briquetting processes into a single stage operation. This will be accomplished by the use of bitumen based emulsions for dewatering and a compaction device for briquetting. During this reporting period, two types of coal samples have been tested for use in the dewatering and briquetting processes. These tests were carried out using Orimulsion as the dewatering reagent. A Ram Extruder that can be operated continuously is used to fabricate dewatered pellets. The influence of compaction pressure, curing time, binder concentration (2% to 5%), particle size, and compacting time on the performance of coal pellets have been evaluated in terms of their water resistance and wear vulnerability
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Pilot scale single stage fine coal dewatering and briquetting process. Technical report, September 1--November 30, 1995
Missouri Univ. Rolla MO (United States). Dept. of Mining Engineering, 1995Co-Authors: Wilso J.w., Ding Y., Honake R.q.Abstract:The primary goal of the current coal preparation research is to reduce the ash and sulfur content from coal, using fine grinding and various coal cleaning processes to separate finely disseminated mineral matter and pyrite from coal. Small coal particles are produced by the grinding operation, thus the ultrafine coal becomes very difficult to dewater. In addition, the ultrafine coal also creates problems during its transportation, storage and handling at utility plants. The current research is seeking to combine ultrafine coal dewatering and briquetting processes into a single stage operation, using hydrophobic binders as coal dewatering and binding reagents with the help of a compaction device. From previous tests, it has been found that coal pellets with a moisture content of less than 15% and good wear and water resistance can be successfully fabricated at pressures of less than 6,000 psi using a lab scale Ram Extruder. The primary objective of the research described in this quarter has been to extend the lab scale ultrafine coal dewatering and briquetting process into a pilot scale operation, based on the test data obtained from earlier research. A standard roller briquetting machine was used to dewater fine coal-binder mixtures during the briquetting process. The operating paRameters, including moisture content of feed, feed rate, and roller speed, were evaluated on the basis of the performance of the briquettes. Briquettes fabricated at rates of up to 108 pellets per minute exhibited satisfactory water and wear resistance, i.e., less than 7.5% cured moisture and less than 8.3% weight loss after 6 min. of tumbling. Also, coal-binder samples with moisture contents of 40 percent have been successfully dewatered and briquetted. Briquetting of fine coal was possible under current feeding conditions, however, a better feeding system must be designed to further improve the quality of dewatered coal briquettes
J M Newto - One of the best experts on this subject based on the ideXlab platform.
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The evaluation of the rheological properties of lactose/microcrystalline cellulose and water mixtures by controlled stress rheometry and the relationship to the production of spherical pellets by extrusion/spheronization.
2002Co-Authors: K A Macritchie, J M Newto, R.c. RoweAbstract:The consistency of wet powder masses produced from two ratios (7:3 and 8:2) of alpha-lactose monohydrate (L) and microcrystalline cellulose (MCC) mixed with a range of water contents has been assessed with a parallel plate controlled stress rheometer. The range of water contents, which could be studied, was restricted to those, which could be extruded uniformly by a Ram Extruder. In the creep mode, the instantaneous compliance increased as the water content increased for both L:MCC ratios illustrating the increasing deformability of the mixtures with increasing water content. The derived apparent viscosity of the mixtures as a function of shear rate, increased as the water content decreased and the values for all the systems fell on a common line. This indicates that the measurements are providing a reliable assessment of the mixtures and that the change in water content and L:MCC ratio provides systems, whose change of viscosity with rate of shear is consistent at low rates of shear. The values of the storage and loss moduli obtained from oscillatory measurements, increased with a decrease in water content but this time the two ratios of L:MCC were not on a common line when related to the water content of the mixtures. There was a range of water levels over which both the values of the storage and loss moduli were approximately constant. This corresponded to the level of water, which produced the pellets of the smallest diameter and range of diameters and were of the most spherical shape when produced by a Ram Extruder and spheronization. For 8:2 L:MCC ratio, there appeared to be a value for both the storage and the loss moduli above which the wet mass could not produce good pellets. For the 7:3 L:MCC these limiting levels were not achieved before extrusion with steady state conditions could be maintained without the mass being too wet or too dry. Instead, there appeared to be minimum levels of the moduli required to ensure that the mixtures were able to produce good pellets
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Preparation of extruded carbamazepine and PEG 4000 as a potential rapid release dosage form,
2002Co-Authors: . Perissutti, J M Newto, F. Podczek, Rubessa F.Abstract:The aim of this research was to use a Ram Extruder to prepare directly a fast release dosage form with uniform shape and density, containing carbamazepine (C) as a water-insoluble drug and polyethylene glycol 4000 (PEG) as a low melting binder. The potential inclusion of lactose (L) as a hydrophilic filler was also considered. The temperature suitable to ensure a successful extrusion process of several formulations containing PEG in different percentages was found to be below the melting point of the PEG. The influence of composition on the extrusion process of different Ram speeds was checked by measuring the pressure at the steady state, the apparent shear rate and the apparent shear stress of a range of mixtures of drug, lactose and PEG. The physical–mechanical properties of extrudates, including tensile strength and Young’s modulus, prepared with different Ram velocities were also determined. The solid-state physical structure by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) was established. The dissolution of the extrudates and their corresponding physical mixtures were compared. The mixtures were found to be shear thinning when extruded; the tensile strength of extrudates was dependent on the composition but not the extrusion rate, while the value of Young’s modulus was strongly influenced by the rate of extrusion, but less affected by the composition of the extrudates. The results of DSC and XRD indicated that the solid structure of the extrudates corresponded to that of a physical mixture of the components, hence there had been no change in the physical form of the drug induced by extrusion. In terms of dissolution, the rate of the extrusion process did not influence the performance of the products, whereas the composition did. The extruded mixtures of an equivalent composition exhibited a more rapid release than a simple physical mixture. The addition of lactose reduced the dissolution rate. q 2002 Elsevier Science B.V. All rights reserved
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Water movement evaluation during extrusion of wet powder masses by collecting extrudate fractions.
1999Co-Authors: Tome G, J M NewtoAbstract:Water is normally the liquid of choice in extrusion/spheronisation systems. Its behaviour during the process is crucial to its success. In most extrusion formulations water moves under the pressures involved. It is important to understand how to control and limit water movement, and to understand its consequences. Five drug models were mixed with microcrystalline cellulose and with three different ratios of water and extruded at two different speeds using a Ram Extruder. Whilst extruding, the extrudates were collected to small fractions and dried to constant weight. Different paRameters were calculated to quantify the extent of water movement that occurred. The same formulations were also extruded and than spheronised to pellets, for which size and shape factor were measured. The correlation between water level and extrusion force at the same given time was calculated. It was found that at the faster speed and in the wettest formulation there was less water movement. A significant correlation was found between extrusion force and water going through the die. The extrusion/spheronisation technique was found to be tolerant to some extent of water movement during the extrusion process. Nevertheless, excessive water movement is not appropriate
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Effect of water content on tensile fracture force ana deformability of Ram extruded cylinders
1997Co-Authors: Jerwanska E, J M Newto, Alderbo G, örjesso E, Nyström CAbstract:Wetted powder masses with varying amounts of water were used to study mechanistically the extrusion process in terms of brittleness and deformability of Ram extruded cylinders. Mixtures of dicalcium phosphatedihydrate (DCPD) and Avicel PH 101 (70/30%) were massed with water (moisture contents 50, 60, 70, 80 w/w%). The masses were extruded in a Ram Extruder (25.0 mm in diameter) with a 10.0 mm diameter and 10 mm long die. The moist extrudates were cut to isodiametrical cylinders. The porosity and degree of liquid saturation were determined. The extruded, isodiametrical cylinders were glued on to small brass cylinders and connected to a material testing instrument. The force as a function of displacement was recorded during tensile testing of the extruded cylinders at a loading rate of 1 mm/min. The tensile fracture force (force at failure) and the deformability during the measurement, i.e. an inverse number of the slope of the force displacement curves, were determined. The tensile fracture force of the extruded cylinders decreased with increased porosity. At the same lime the deformability of the cylinders increased for all the extruded masses, except the one with the highest porosity
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Analysis of extrusion of some wet powder masses used in extrusion/spheronisation
1996Co-Authors: Rk Choha, J M NewtoAbstract:The extrusion flow behaviour of mixtures of lactose, microcrystalline cellulose (MCC) and water in the ratio 5:5:6 by weight has been analysed from data previously obtained by a Ram Extruder for powder and colloidal grades of MCC. The analysis followed a recent approach of examining the viscous and elastic behaviour of polymers. Results suggest that at low flow rates, mixtures containing colloidal grades of MCC have significantly higher shear viscosities than powder grades. The present analysis also shows that shear thickening of some mixtures occurs. Elongational flow was also examined together with entry flow to the die. The results of the analysis indicate that: (a) particle size of the MCC is not important, (b) the greatest extrudate distortions occur for systems having relatively low shear viscosities at low flow rates. There appears to be an optimal elasticity for the formation of satisfactory spheres in the spheronisation stage, i.e. they must neither be too elastic nor have low elasticity
D I Wilson - One of the best experts on this subject based on the ideXlab platform.
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modelling of paste Ram extrusion subject to liquid phase migration and wall friction
Chemical Engineering Science, 2017Co-Authors: M J Patel, S Blackburn, D I WilsonAbstract:Abstract Extrusion of solid-liquid particulate pastes is a well-established process in industry for continuously forming products of defined cross-sectional shape. At low extrusion velocities, the solids and liquid phases can separate due to drainage of liquid through the interparticle pores, termed liquid phase migration (LPM). The effect of wall friction, die shape and extrusion speed on LPM in a cylindrically axisymmetric Ram Extruder is investigated using a two-dimensional finite element model of paste extrusion based on soil mechanics principles (modified Cam-Clay). This extends the smooth walled model reported by Patel et al. (2007) to incorporate a simplified Tresca wall friction condition. Three die entry angles (90°, 60° and 45°) and two extrusion speeds are considered. The extrusion pressure is predicted to increase with the Tresca friction factor and the extent of LPM is predicted to increase with decreasing Ram speed (both as expected). The effects of wall friction on LPM are shown to be dictated by the die shape and Ram displacement: there are few general rules relating Extruder design and operating conditions to extent of LPM, so that finite element-based simulation is likely to be needed to predict the onset of LPM accurately.
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a comparison of screen and Ram extrusion spheronisation of simple pharmaceutical pastes based on microcrystalline cellulose
International Journal of Pharmaceutics, 2013Co-Authors: M Zhang, D I Wilson, R Ward, C Seiler, S L RoughAbstract:Abstract The performance of two laboratory-scale extrusion apparatuses used to approximate the action of an industrial screen Extruder, namely a multi-holed die Ram Extruder and a roller screen Extruder, were compared. Both devices featured short dies (Ram 2 mm, screen 1 mm) with die diameter 1 mm and hole area fraction approaching 0.25. A series of water/microcrystalline cellulose (MCC) pastes with water contents varying from 45 to 60 wt% were extruded and pellets obtained from subsequent spheronisation of the extrudates characterised in terms of size and shape. Each device exhibited a different range of processing windows for acceptable spheronised products, with the Ram apparatus being able to extrude a wider range of paste water contents than the screen device. The pellets obtained from extrusion–spheronisation (E–S) of the pastes via the screen device were in general smaller, with a wider size distribution, than those from Ram E–S. These results are attributed to the different mechanical histories experienced by the pastes in the two types of Extruder, which lead to different extrudate densities being achieved. MCC/water/calcium carbonate pastes were also tested, where the latter component represented a ‘hard’ (non-deformable) active pharmaceutical ingredient. Addition of calcium carbonate increased the stiffness of the paste, which could be countered by adjusting the water content of the deformable MCC/water matrix within the extrudability limits of the latter material.
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paste extrusion through non axisymmetric geometries insights gained by application of a liquid phase drainage criterion
Powder Technology, 2006Co-Authors: P J Martin, D I Wilson, P E BonnettAbstract:Abstract An experimental investigation has been conducted into the flow of a talc-based paste through various combinations of axisymmetric and non-axisymmetric Ram Extruder geometries. The paste flow pattern was found to be highly rate dependent for one non-axisymmetric case. The flows were modelled using the Benbow–Bridgwater approach, but this was incapable of predicting the observed flow patterns and under-predicted the extrusion pressure at low flow rates. Evidence suggested that significant liquid phase migration was occurring at low flow rates, with associated dewatering of paste in the barrel. The situation where significant liquid phase migration occurs is comparable to a drained experiment in soil mechanics. The simple, but little known, drainage criterion of Wroth and Houlsby was used to estimate the flow rates associated with drained and undrained conditions. The criterion successfully predicted the flow rate at which transition of the flow pattern was observed. Comparable experiments using a modelling clay, undrained over all flow rates, showed no transition in flow pattern. Furthermore, the drainage criterion successfully predicted the drainage state for three of four other paste flow data sets taken from the literature covering a variety of materials and geometries. It is concluded that: (i) liquid phase migration can be a significant feature of paste extrusion which can dRamatically alter the flow patterns in non-axisymmetric Extruders, and (ii) that the Wroth and Houlsby's criterion can successfully predict the drainage state of a process but is limited by the estimation of the coefficient of permeability.
