Physical processes of tableting

Effects of Pigeon Pea and Plantain Starches on the Compressional, Mechanical, and Disintegration Properties of Paracetamol Tablets

A study has been made of the effects of pigeon pea starch obtained from the plant Cajanus cajan (L) Millisp. (family Fabaceae) and plantain starch obtained from the unripe fruit of Musa paradisiaca L. (family Musaceae) on the compressional, mechanical, and disintegration properties of paracetamol tablets in comparison with official corn starch BP. Analysis of compressional properties was done by using density measurements, and the Heckel and Kawakita equations, whereas the mechanical properties of the tablets were evaluated by using tensile strength (T--a measure of bond strength) and brittle fracture index (BFI--a measure of lamination tendency). The ranking for the mean yield pressure, P(y), for the formulations containing the different starches was generally corn < pigeon pea < plantain starch while the ranking for P(k), an inverse measure of the amount of plasticity, was pigeon pea < plantain < corn starch, which indicated that formulations containing corn starch generally exhibited the fastest onset of plastic deformation, whereas those formulations containing pigeon pea starch exhibited the highest amount of plastic deformation during tableting. The tensile strength of the tablets increased with increase in concentration of the starches while the Brittle Fracture Index decreased. The ranking for T was pigeon pea > plantain > corn starch while the ranking for BFI was corn > plantain > pigeon pea starch. The bonding capacity of the formulations was in general agreement with the tensile strength results. The disintegration time (DT) of the formulation increased with concentration of plantain and corn starches but decreased with concentration of pigeon pea starch. The general ranking of DT values was plantain < pigeon pea < corn starch. Notably, formulations containing pigeon pea starch exhibited the highest bond strength and lowest brittleness, suggesting the usefulness of pigeon pea starch in producing strong tablets with minimal lamination tendency. Plantain starch, on the other hand, would be more useful where faster disintegration of tablet is desired. The results show that the starches could be useful in various formulations depending on the intended use of the tablets with the implication that the experimental starches can be developed for commercial purposes.

Comparative evaluation of the binding properties of two species of Khaya gum polymer in a paracetamol tablet formulation

A study was made of the comparative effects of polymers obtained from two species of khaya tree - Khaya senegalensis and Khaya grandifoliola - as binding agents in a paracetamol tablet formulation. The mechanical properties of the tablets were assessed using the tensile strength (T), brittle fracture index (BFI) and friability (F) of the tablets while the drug release properties of the tablets were assessed using disintegration and dissolution times. The tensile strength, disintegration and the dissolution times of tablets increased with the increase in binder concentration while F and BFI decreased. K. senegalensis gum produced tablets with stronger mechanical properties with less tendency to laminate, and longer disintegration and dissolution times than K. grandifoliola gum. The results suggest that the polymer gum from K. senegalensis will be more appropriate as a binding agent than the gum from K. grandifoliola when higher mechanical strength and slower release profiles of tablets are desired.

Influence of binder type on interacting variables acting on mechanical properties of a sulfadimidine tablet formulation

A study of the quantitative effect of type of binder (N), applied pressure (P), and granular size (G) on two mechanical properties-tensile strength (TS) and brittle fracture index (BFI) - of a sulfadimidine tablet formulation has been carried out by using a 2(3) factorial experimental design. The results obtained from this work suggest that P exhibited the largest individual effect on TS and BFI. It is also seen from this work that the nature of binders in combination affects the influence that P and G had on the TS or BFI.

Effects of plantain and corn starches on the mechanical and disintegration properties of paracetamol tablets

The effects of plantain starch obtained from the unripe fruit of the plant Musa paradisiaca L. (Musaceae) on the mechanical and disintegration properties of paracetamol tablets have been investigated in comparison with the effects of corn starch BP using a 2(3) factorial experimental design. The individual and combined effects of nature of starch binder (N), concentration of starch binder (C), and the relative density of tablet (RD) on the tensile strength (TS), brittle fracture index (BFI), and disintegration time (DT) of the tablets were investigated. The ranking of the individual effects on TS was RD > C >> N, on BFI was C >> RD > N and on DT was N > C > RD. The ranking for the interaction effects on TS and DT was N-C >> N-RD > C-RD, while that on BFI was N-C >> C-RD > N-RD. Changing nature of starch from a "low" (plantain starch) to a "high" (corn starch) level, increasing the concentration of starch binding agent from 2.5% to 10.0% wt/wt, and increasing relative density of the tablet from 0.80 to 0.90, led to increase in the values of TS and DT, but a decrease in BFI. Thus, tablets containing plantain starch had lower tensile strength and disintegration time values than those containing corn starch, but showed better ability to reduce the lamination and capping tendency in paracetamol tablet formulation. The interaction between N and C was significantly (P < .001) higher than those between N and RD and between C and RD. There is therefore the need to carefully choose the nature (N) and concentration (C) of starch used as binding agent in tablet formulations to obtain tablets of desired bond strength and disintegration properties. Furthermore, plantain starch could be useful as an alternative binding agent to cornstarch, especially where faster disintegration is required and the problems of lamination and capping are of particular concern.

Benefits of die-wall instrumentation for research and development in tabletting

Instrumented presses used in tabletting research and development are normally equipped to measure punch force and displacement. Die-wall monitoring is rare, probably because instrumentation and calibration are quite difficult. The authors critically examine the tenets of radial pressure measurement in compression physics. The theoretical background concerning axial to radial stress transmission during the different phases of the compression cycle is presented. The literature reporting on the use of radial stress measurement to assess the self-lubricating properties of materials or the effect of lubricants is reviewed. Examples of interpretation of radial pressure cycles to define the basic material behaviour are given. The influence of particle size and shape as well as that of process and formulation variables on die-wall response are also discussed. Substantial inconsistencies can be seen in the literature with respect to the interpretation of experimental data, often because of the poor reliability of results and mostly because powders are essentially not solid, isotropic bodies. There is also a distinct lack of complementary tabletting parameters that would help understanding their comparative benefits. For this reason, original data on 13 model compounds are presented together with a classification of the materials encountered in pharmaceutical tabletting, based on selected parameters. In conclusion, none of the determined parameters, including those derived from radial pressure measurement, is able, alone, to predict the material behaviour under compression. Although die-wall instrumentation contributes little to the development of improved tablet formulations, it is valuable for characterising the mechanical properties of the materials. This is particularly advantageous given that the mechanical properties account for variations in tabletting performance to a much greater extent than the magnitude of the interparticulate attractions. Nevertheless, because of the peculiar nature of powders compared to solid, isotropic bodies, there is a need to develop new models for analysing their behaviour and to put more emphasis on examination of time-dependent deformation in the later stage of the compression cycle.

Characterization of pharmaceutical solids by scanning probe microscopy

The force-displacement profiles of four well-characterized materials that represent both soft/hard and plastic/brittle materials have been obtained using a novel nanoindentation technique. Flat surfaces of acetaminophen, potassium chloride, sucrose, and sodium stearate were prepared by melting or recrystallization, and the melting points were measured. Topographic and the corresponding first derivative images were obtained both before and after indentation. The materials were indented using a 10 s loading time, followed by a 2 s hold, and ending with a 10 s unloading time thereby providing a unique force-displacement profile for each material. The loading profile of acetaminophen was discontinuous, whereas the profiles for the other three materials were smooth. The profiles were analyzed and the rank order of hardness was sucrose > acetaminophen > KCl > sodium stearate, which is consistent with the literature. The rank order of the stiffness, which is related to the modulus of elasticity, was sucrose > KCl > acetaminophen > sodium stearate. Given the flexibility and power of this approach, nanoindentation coupled with atomic force microscopy may be a useful means to characterize materials for evaluating tablet-processing conditions, perhaps at a preformulation stage.

Die wall pressure measurement for evaluation of compaction property of pharmaceutical materials

The aim of this study was to evaluate the compaction property of several pharmaceutical materials by measuring the die wall pressure. The profile of die wall force during tabletting process was measured with the compaction process analyzer (TabAll). Several compaction parameters such as maximum die wall pressure (MDP), residual die wall pressure (RDP) and pressure transmission ratio (PTR) from upper punch to lower punch were calculated. The ejection pressure (EP) of tablet compacted was also measured as a parameter for sticking property of the compacts. The profile of die wall force observed was classified to the typical two types, a small type and a large one. Partly pre-gelatinized starch (PCS), cornstarch and low substituted hydroxypropylcellulose (L-HPC) were the small type, while crystalline lactose, ascorbic acid and potassium chloride were the large type. The die wall force of crystalline lactose remarkably increased at the ejection of tablet and then capping was observed. RDP value of PCS, cornstarch, L-HPC was smaller than that of crystalline lactose, ascorbic acid, potassium chloride. As the higher pressure transmission ratio from upper punch to lower punch means a good compressing property of the powder, we proposed that RDP/MDP is a useful parameter for evaluating the compaction property of powders. Although potassium chloride which is strongly plastic deformable powder showed the highest RDP value among the powders tested, the RDP/MDP value was lower than that of crystalline lactose or ascorbic acid and the tensile strength of resultant tablet of potassium chloride was much higher than these powders.

Development and evaluation of a miniaturized procedure for determining the bonding index: a novel prototype for solid dosage formulation development

The purpose of this study was a comparative evaluation of miniaturized vs. University of Minnesota's (i.e., U of Minn. = Hiestand's) procedures for determining the tensile strength, indentation hardness, and bonding index (BI), one out of three Indices of Tableting Performance (ITP). Tableting properties of six direct compression placebo formulations were determined by using a compaction simulator and a Texture Analyser TA-XT2I, or by following the U of Minn. method, which included a specially designed triaxial compression device, a computer-controlled mechanical stress-strain analyzer, and a dynamic pendulum impact apparatus. Miniaturization of the procedures to determine the ITP, as well as the ability to differentiate between materials while operating compaction cycles more comparable to standard tablet production conditions, enabled proper evaluation of each material's inherent tableting properties. Indentation diameter calculated via an empirical equation appeared to correlate well with, and provided acceptable precision of accuracy to, the determination of indentation diameter via standard optical microscopy methods. The miniaturized and U of Minn. procedure exhibited a significant degree of correlation when comparing the BI. However, the tensile strength and indentation hardness values were somewhat different due to the use of triaxial decompression for the U of Minn. procedure vs. standard compaction profiling for the miniaturized procedure. The present direct compression placebo formulation data gathered from the miniaturized procedures and compared with the U of Minn. method for determining the ITP suggest that both techniques yield similar conclusions. However, discrimination of out-of-die compaction properties determined via the miniaturized procedures, such as tensile strength and indentation hardness, appeared to associate more precisely with changes in strain rate, thus allowing better discrimination of particle-particle interactions and ductile-to-brittle characteristics as a function of compaction speed and pressure.

The powder flow and compact mechanical properties of sucrose and three high-intensity sweeteners used in chewable tablets

The physical, flow, and mechanical properties of four common pharmaceutical sweeteners were measured to assess their relative manufacturability in solid dosage formulations. Sucrose, acesulfame potassium (Sunett), saccharin sodium, and aspartame were evaluated to determine significant differences in particle shape, size distribution, and true density. Powder flow and cohesivity as well as compact mechanical properties such as ductility, elasticity, and tensile strength were measured and found to be noticeably different. Among these sweeteners, sucrose and acesulfame potassium demonstrated excellent flowability and marginal mechanical property performance relative to over 100 commonly used pharmaceutical excipients evaluated in the authors' laboratory. Saccharin sodium and aspartame demonstrated poor flowability and superior compact strength relative to sucrose and acesulfame, despite their noticeably higher brittleness. These data suggest that careful selection of an appropriate sweetener is warranted in obtaining desirable process and tableting robustness, particularly if sweetener loading is high. Detailed descriptions of each material property and recommendations for sweetener selection in formulation development are included.

Compressional characteristics of native and pregelatinized forms of sorghum, plantain, and corn starches and the mechanical properties of their tablets

A study was made of the compressional characteristics of native and pregelatinized forms of sorghum, plantain, and corn starches and the mechanical properties of their tablets. Compressional characteristics were analyzed using density measurements and the Heckel and Kawakita plots. Pregelatinized starches exhibited more densification than native starches during die filling and at low pressures. The ranking for the mean yield pressure (Py) values for the starches was plantain < corn < sorghum, with the pregelatinized starches having lower values than the native starches. The ranking for the values of another pressure term, Pk--an inverse measure of plasticity, was corn < plantain < sorghum, but with the native starches having the lower values. For the tablets, the ranking for values of tensile strength (T) was corn > plantain > sorghum, while the ranking for the brittle fracture index (BFI) was plantain > corn > sorghum. Tablets made from pregelatinized starches had lower T and BFI values than those made from native starches. The results suggest that pregelatinization of the starches facilitated faster onset of plastic deformation but reduced the amount of plastic deformation which occurred during the compression process.

Characterization of khaya gum as a binder in a paracetamol tablet formulation

The influence of khaya gum, a binding agent obtained from Khaya grandifolia (Meliaceae family), on the bulk, compressional, and tabletting characteristics of a paracetamol tablet formulation was studied in comparison with the effects of two standard binders: polyvinylpyrrolidone (PVP; molecular weight 40,000) and gelatin. The relative ability of khaya gum to destroy any residual microbial contamination in the binder or in the formulation during tabletting was also studied using Bacillus subtilis spores as a model. Formulations containing khaya gum exhibited more densification than formulations containing PVP and gelatin during die filling, but less densification due to rearrangement at low pressures. The mean yield pressure of the formulation particles obtained from Heckel plots, and another pressure term, also inversely related to plasticity, obtained from Kawakita plots, showed dependence on the nature and concentration of the binder, with formulations containing khaya gum exhibiting the lowest and highest values respectively. The values of the pressure terms suggest that the yield pressure relates to the onset of plastic deformation during compression, while the Kawakita pressure relates to the total amount of plastic deformation occurring during the compression process. Tablets made from formulations containing khaya gum had the lowest tensile strength values but also the lowest tendency to laminate or cap, as indicated by their lowest brittleness. All the tablets had friability values < 1% at higher concentrations of the three binders. In addition, khaya gum demonstrated a comparable ability to destroy microorganisms in the formulation during tabletting as the two binders. The characterization of the formulations suggests that khaya gum can be developed into a commercial binding agent for particular tablets.

The effect of compression and decompression speed on the mechanical strength of compacts

The purpose of this work was to investigate the effect of punch speed on the compaction properties of pharmaceutical powders; in particular, to separate out differences between the effect of the compression and decompression events. Tablets were prepared using an integrated compaction research system. Various "sawtooth" punch profiles were followed to compare the effects of different punch speeds on the crushing strength of the resulting tablets. The loading and unloading speeds were varied independently of one another. In general, when the compression speed was equal to the decompression speed, the tablet crushing strength was observed to decrease as the punch velocity increased. When the compression speed was greater than or less than the decompression speed, the results varied, depending on the material undergoing compaction. Reduction of the unloading speed from 300 to 10 mm/sec for pregelatinized starch and microcrystalline cellulose produced a significant increase in crushing strength, whereas no significant increase in crushing strength was observed until the loading speed was reduced to 10 mm/sec. Reduction of the unloading speed had a similar effect on the direct compression (DC) ibuprofen, however, even greater improvement in the crushing strength was observed when the loading speed was reduced. No improvement in the DC acetaminophen tablets was observed when the unloading speed was reduced, however, a significant increase in crushing strength was produced when the rate of loading was reduced. This work showed that the strength of tablets can be improved and some tableting problems such as capping can be minimized or prevented by modifying the rates of loading/unloading.

Estimation of capping incidence by indentation fracture tests

The purpose of this study was to predict the capping tendencies of pharmaceutical powders by creating indentation fracture on compacts. Three sets of binary mixtures containing different concentrations of each ingredient were used in the study. The binary mixtures were chosen to represent plastic-plastic, plastic-brittle, and brittle-brittle combination of materials. The mixtures were tableted at different pressures and speeds on Prester, a tablet press simulator. These mixtures were also compacted on the Instron Universal Testing Machine 4502. Static indentation tests were done on these compacts at different depths until surface cracking and chipping were observed. The extent of surface cracking and chipping was observed from light microscope and scanning electron microscope images. A rank order correlation was observed between lamination susceptibility and the depth at which indentation failure occurred. It was concluded that indentation fracture tests could provide a useful estimate of lamination properties of pharmaceutical powders.

Factors influencing capping and cracking of mefenamic acid tablets

The tendency of capping and longitudinal cracks of mefenamic acid tablets was evaluated in relation to the amount of the binder, the influence of the granulation technique, and the relative humidity of the granules. Tablets made from fluidized bed granules using methylcellulose in the granulating liquid showed significantly lower capping and longitudinal cracks than tablets from conventional granules prepared by wet granulation using methylcellulose as a dry binder.

Principles and application of ultrasound in pharmaceutical powder compression

The use of ultrasound during the tableting of pharmaceutical powders is a new concept. However, in the metallurgy, plastic, and ceramic industries, ultrasound-assisted compression of materials has been known for some years. Ultrasound improves the characteristics of the compression process leading to optimized mechanical strength of the compacts without applying excessive compression force. Therefore, problems associated with high-pressure compression in tableting can be overcome and tablets may be manufactured more economically and consistently with the aid of ultrasound compared to conventional pressure processes. Although great progress in the theoretical understanding of the ultrasound-assisted powder compression process has been made since the late 1960s, the need for further research in the area of ultrasound application during pharmaceutical powder compression is essential. Further investigations on a wide range of drugs and excipients, to expand the usefulness and scope of the ultrasound-assisted technique, and to understand the complex phenomena involved in the process, are needed. In this article the principles, advantages, and limitations of the application of ultrasonic vibrations during pharmaceutical powder compression is reviewed with the hope that this article can contribute to, and stimulate research in the area.

The influence of engravings on the sticking of tablets. Investigations with an instrumented upper punch

The purpose of this study was to investigate the influence of engravings on the sticking of tablets. Therefore, an instrumented upper punch capable of measuring the pull-off force, which occurs when the punch detaches itself from the upper surface of a tablet, was equipped with small cones of different angles between the punch face and the cones' lateral face. The cones could be screwed into a threaded hole at the center of the punch face. The adhesion forces of two formulations known to stick to engravings during production increased with a greater steepness of the cones' lateral face. With microencapsulated acetylsalicylic acid, no quantitative differences could be found between the adhesion forces obtained with plain and modified punch faces, indicating that the sticking behavior of the substance was not affected by shear forces. Starch 1500 showed higher adhesion force signals in comparison to those obtained with a plain punch face. Microcrystalline cellulose, which gave no adhesion force signals with a plain punch face and did not stick to the cones, showed distinct pull-off signals. The instrumented upper punch equipped with shear cones is a valuable instrument for detecting the adhesion caused by engravings and is therefore a helpful tool for tablet formulation development and the design optimization of tablet identification.

Prediction of the Hiestand bonding indices of binary powder mixtures from single-component bonding indices

A priori predictions of the bonding indices of binary powder mixtures from the single-component indices were attempted. The binary mixtures were classified according to the mechanism of deformation of the single-components as plastic-plastic, brittle-brittle, and plastic-brittle. When the components of a binary mixture consolidated by the same mechanism (plastic-plastic and brittle-brittle mixtures), a straight line could be fit to a plot of bonding index versus composition. This linearity indicates that the bonding index can be reliably estimated by interpolation between the two single-component bonding indices. When the mixtures were such that one component was brittle while the other was plastic, a linear function did not fit the data. For these cases, a second-degree polynomial equation could be fit to a plot of bonding index versus composition. A combination of multiple linear regression and trial and error was used to generate a single generalized equation. For pairs of compounds wherein each compound has a different compaction mechanism, this new equation appears to allow satisfactory predictions of the bonding indices of mixtures with varying compositions using only the single-component bonding indices.

Mechanical properties of powders for compaction and tableting: an overview

This review provides an insight into mechanical properties that are critical to understanding powder processing for tableting. Various parameters that reflect these basic fundamental properties of powder and their evaluation by different techniques are described. Some recent examples in which these techniques are used in drug substance selection, formulation optimization or scale-up are also provided.

The effects of lag-time and dwell-time on the compaction properties of 1:1 paracetamol/microcrystalline cellulose tablets prepared by pre-compression and main compression

The effects of lag-time and dwell-time on the compaction properties of tablets compressed from a 1:1 blend of paracetamol and microcrystalline cellulose have been examined using a compaction simulator. Increases in lag-times (from 0.06 to 0.53 s) resulted in small increases in the tensile strengths of the tablets when combinations of 80 and 160 MPa were used as the compression pressures. Further increases in lag-time did not alter the tablet strengths. When combinations of 240 and 320 MPa were used for pre-compression and main compression, the effects on the tensile strengths were more complex, partly because the high elastic recoveries of the tablets resulted in greater variability in the data. Increases in lag-times from 0.06 to 0.97 s resulted in an increase of between 12 and 28% in tensile strength. Longer lag-times (1.24 or 1.52 s) did not result in further increases in tensile strength. The application of a dwell-time of 0.26 s during pre-compression or main compression pressures of 80 and 160 MPa generally led to a decrease (14-22%) in tensile strength compared with tablets where no dwell-time was used. This was because of increases in both the elastic recoveries and elastic energies. Subsequent increases in dwell-time from 0.26 to 0.9 s resulted in increases in tablet strength compared with that obtained when no dwell-time was applied. The tensile strengths of tablets made with a pre-compression of 160 MPa then a main compression of 80 MPa were 11-33% higher than those of tablets made with a pre-compression of 80 MPa then a main compression of 160 MPa. This was because higher plastic energies and more plastic deformation occurred at the higher pre-compression. Generally, the application of dwell-time resulted in greater increases in tensile strengths than lag-time, which had less effect on the compaction properties.

Effect of compression speeds on the compaction properties of a 1:1 paracetamol-microcrystalline cellulose mixture prepared by single compression and by combinations of pre-compression and main-compression

A 1:1 blend of paracetamol and microcrystalline cellulose was compacted at different compression speeds by single compression or combinations of pre- and main-compression. The tensile strengths of the tablets decreased from 0.74+/-0.01 to 0.44+/-0.05 MPa as the compression speed was increased from 78 to 390 mm/s when a single compression pressure of 80 MPa was used to compress the tablets. When combinations of pre- and main-compression of 320 and 240 MPa were used to compress the tablets, tensile strengths decreased from 3.12+/-0.67 MPa at a compression speed of 78 mm/s to 1.24+/-0.36 MPa when the compression speed was 390 mm/s. The energies of compression and the ratio of elastic to plastic energies increased with increase in compression speed. This was because the material was becoming more elastic and more energy was required for the elastic expansion leading to a reduction in the energy available for plastic deformation and bond formation which resulted in a decrease in tensile strengths. Pre-compression played a major role at high compression speeds. The tensile strengths of tablets (1.2+/-0.08 MPa) compressed with a pre-compression of 160 MPa followed by a main-compression of 80 MPa (compression speed of 390 mm/s) were similar to the tensile strengths of tablets (1.1+/-0.10 MPa) compressed using a single compression of 320 MPa at the same compression speed of 390 mm/s. Thus, combinations of lower pressures can be employed to compress the material to the same tensile strength as a high single compression.

The effect of composition on the tableting indices of binary powder mixtures

The purpose of this study was to investigate the effect of the composition of a binary powder mixture on the bonding index, the brittle fracture index, and the strain index, as defined by Hiestand. The studies involved tensile strength and dynamic indentation hardness determinations of square compacts, the solid fractions of which were 0.83. The mixtures were such that both components consolidated by plastic deformation, both components consolidated by brittle fracture, or one component was brittle while the other was plastic. The measured quantities were then used to compute the bonding index, the brittle fracture index, and the strain index. The bonding indices and tensile strengths of the individual plastic materials were greater than those of the individual brittle materials. It was concluded that the bonding indices were linearly related to composition when both materials consolidated by the same mechanism. It was further concluded that the bonding indices were related to compact composition by a second-degree polynomial equation for mixtures with one brittle and one plastic component. This latter relationship was consistent for four pairs of components.

Mechanical properties of compacts and particles that control tableting success

The use and limitations of linear-elasticity equations for describing mechanical properties of compacts is discussed; the limitations occur because compacts are porous, viscoelastic, nonhomogeneous, Mohr bodies. Awareness of these properties permits meaningful comparisons to be made. Ignoring limitations may result in unjustified conclusions. Special care during measuring mechanical properties of compacts is required. The mechanical criteria for a successful formulation are good flowability for powders and adequate strength without fracture for compacts. Interparticle attraction is spontaneous but particle contact numbers and size are limited by mechanical preclusion. Plastic deformation and fracture mechanics are controlling mechanisms with the magnitude of elastic constants having little effect on the successful processing. General compaction characteristics can be appraised by using combinations of properties, e.g., specific tableting indices.

Examination of the compaction properties of a 1:1 acetaminophen:microcrystalline cellulose mixture using precompression and main compression

The compaction properties of a 1:1 acetaminophen and microcrystalline cellulose (MCC) mixture have been studied using a compaction simulator to make tablets by single compression and by a combination of precompression and main compression. The tensile strengths of the tablets and the energies involved in the compressions were determined. The tensile strengths of the tablets increased with increases in single compression pressure from 80 to 400 MPa and as the total applied pressure increased from 80 MPa up to around 400 MPa when combinations of precompression and main compression pressures were used. The tablet porosity decreased with increase in main compression pressure while the tablet tensile strengths increased. At minimum tablet porosity, further increase in main compression pressure could no longer result in increase in tablet strengths. Tablets compressed with combinations of precompression and main compression were stronger (2.15 +/- 0.02 to 3.99 +/- 0.1 MPa) than those produced with single compression (0.73 +/- 0.01 to 3.09 +/- 0.05 MPa). The total gross energies of compression increased with an increase in pressure of both the precompression and main compression. The elastic energies during main compression increased with an increase in precompression pressure as the tablet exhibited greater elastic deformation and reduced plasticity on second compression. The increase in elastic energies during main compression may also be because elastic energy is recoverable and is independent of precompression. As the precompression pressure increased, the minimum tablet porosity was attained; hence, the plastic energy during main compression became smaller while the elastic energy increased. Thus, a combination of low precompression and main compression pressures of 160/80 MPa or 80/160 MPa are more advantageous in the tableting of the 1:1 acetaminophen:MCC than a high single compression pressure of 320 or 400 MPa.

The effect of moisture on the mechanical and powder flow properties of microcrystalline cellulose

PURPOSE

This study determined the effects of moisture on the mechanical and powder flow properties of microcrystalline cellulose.

METHODS

A variety of mechanical properties were determined as a function of solid fraction at moisture levels ranging from 0 to 12.2% and included: compaction pressure required to form a compact, dynamic indentation hardness, quasi-static indentation hardness, tensile strength, best case and worst case Bonding Index, Brittle Fracture Index, Strain Index, Compressibility Index and shear cell index.

RESULTS

Significant changes were observed as the moisture level of microcrystalline cellulose increased. The compaction pressure required to produce a compact at a solid fraction of 0.6 decreased with increasing moisture content. The permanent deformation pressure and tensile strength of compacts were observed to be relatively independent of moisture content below about 5% moisture and then decrease as the moisture content increased further. The "best case" Bonding Index was also observed to be independent of moisture content below 5% and then increase with increasing moisture. The Brittle Fracture Index and "worst case" Bonding Index, however, did not appear to be affected by changes in moisture content. Powder flow was shown to decrease with increasing moisture content.

CONCLUSIONS

These mechanical property data are consistent with the hypothesis that water acts as a plasticizer and influences the mechanical properties of microcrystalline cellulose. At moisture levels above about 5%, the material exhibits significant changes consistent with a transition from the glassy state to the rubbery state.

Thermodynamic analysis of energy dissipation by pharmaceutical tablets during stress unloading

A thermodynamic analysis of the energy transformations occurring within pharmaceutical tablets during the unloading phase of compaction was performed on Avicel, calcium phosphate, acetaminophen, and calcium oxalate. This analysis was based on viscoelastic stress data collected using an instrumented rotary press and was conducted for the purpose of determining the extent and nature of energy release, beyond that of force displacement, during this phase of compaction. The four materials investigated were selected to reflect a range of compaction properties, and the viscous vs force-displacement energy distributions were seen to be consistent with their brittle vs plastic character. Magnesium stearate, added in various concentrations up to 4% w/w, was found to act both as an internal lubricant for particle-particle slipping and as a moderator of interparticulate bonding.

The influence of thermal treatment on the physical-mechanical and dissolution properties of tablets containing poly(DL-lactic acid)

Five molecular weight grades of poly(DL-lactic acid) (PLA) were incorporated as organic and aqueous pseudolatex binders into matrix tablet formulations containing microcrystalline cellulose and the model drug theophylline. The tablets were thermally treated to temperatures above and below the glass transition temperature (Tg) of the PLA. The results of the dissolution studies showed that thermally treating the tablets to temperatures above the Tg of the PLA significantly retarded the matrix drug release compared to tablets which were not thermally treated. The retardation in drug release could be attributed to a stronger compact and a more efficient redistribution of polymer throughout the tablet matrix, based on fundamental principles of annealing. In addition, results from tablet index testing supported the dissolution results. The bonding index of the compact formulations increased after thermal treatment above the Tg of the PLA. Gel permeation chromatography and differential scanning calorimetry studies demonstrated that thermal treatment had no significant effect on the molecular weight and the glass transition temperature of (PLA) alone and in combination with other components of the tablet formulation.

Peak offset times as an indication of stress relaxation during tableting on a rotary tablet press

During powder compaction on a Manesty Betapress, peak pressures, Pmax, are reached before the punches are vertically aligned with the centres of the upper and lower compression roll support pins. The interval between the time taken to reach this alignment and the time to reach Pmax is defined as the peak offset time, t(off). The duration of t(off) depends on the ability of the compacted powder to relieve stress and is an indication of the predominant mechanisms of particle deformation during consolidation. Thus, at a given Pmax, short t(off) values are characteristic of materials that consolidate mainly by brittle fracture while longer values indicate an increase in plastic flow. On the Betapress, the decrease in stress during t(off) occurs under conditions approaching constant strain and t(off) therefore, is an indirect measure of stress relaxation. Stress relaxation, and hence t(off), decreases with increase in Pmax due to the reduction in the porosity of the compact and consequent restriction of plastic flow into the void spaces. In addition to Pmax, the effects of variables such as punch head geometry, press speed and formulation on t(off) are reported.

Effects of compaction variables on porosity and material tensile strength of convex-faced aspirin tablets

The porosity and tensile strength of convex-faced aspirin tablets formed under a compaction pressure in the range 40-320 MPa and at punch velocities in the range 0.008 to 500 mm s-1 have been determined. The material tensile strength, sigma f, was calculated from the observed fracture load, Ps, using the equation of Pitt et al (1988): sigma f = 10 Ps/pi D2(2.84 t/D - 0.126 t/W + 3.15 W/D + 0.01)-1 where D is the tablet diameter, t is the overall tablet thickness and W is the central cylinder thickness. Tablets formed at lower compaction pressures had a higher porosity and lower tensile strength than those formed at higher compaction pressures. Tablets of face curvature ratio (D/R) in the range 0.25-0.67 and a normalized cylinder length (W/D) of 0.2 had the optimum tensile strength. (R is the radius of curvature of the tablet face.) Tablets formed at high compaction rates were significantly weaker than those formed at lower compaction rates.