Relationships between flow properties,compression behaviour and mechanical characteristics of prednisone-microcrystalline cellulose tablets

Abstract

This paper describes the effects on the flow properties, as well as the changes in the compression behaviour, of microcrystalline cellulose (Avicel PH 101) incorporated with prednisone together with the mechanical properties of compacts made by direct compression from mixtures of these components.

There is a gradual degradation of the flow properties of the mixtures with increase proportions of prednisone. At the same time there is a close correlation between the parameters chosen to characterise the flow properties of the mixtures (unconfined yield stress, major consolidation stress and flow factor) and the compression work which influence the mechanical properties (crushing strength and friability) of compacts manufactured at low uniaxial compression forces.     

Relationships between flow properties, compression behaviour and mechanical characteristics of prednisone-microcrystalline cellulose tablets

This paper describes the effects on the flow properties, as well as the changes in the compression behaviour, of microcrystalline cellulose (Avicel PH 101) incorporated with prednisone together with the mechanical properties of compacts made by direct compression from mixtures of these components.

There is a gradual degradation of the flow properties of the mixtures with increase proportions of prednisone. At the same time there is a close correlation between the parameters chosen to characterise the flow properties of the mixtures (unconfined yield stress, major consolidation stress and flow factor) and the compression work which influence the mechanical properties (crushing strength and friability) of compacts manufactured at low uniaxial compression forces.     

The mechanical properties of asbestos

Stereoscan electron microscope studies and measurements of tensile strength and Young's modulus have been made on chrysotile and five naturally-occurring fibrous amphiboles. The effect of heat on the modulus and fracture mechanism has also been examined. With the exception of tremolite which has a different microstructure from the remaining amphiboles, the moduli and strengths were similar. The loss of strength which occurs when the fibrous amphiboles, and to a lesser extent, chrysotile are heated below their decomposition temperature is shown to be due to an increase in interfibrillar bonding causing the material to become notch-sensitive     

Evaluation of the effects of khaya gum on the mechanical and release properties of paracetamol tablets

A study of the comparative effects of khaya gum and two standard binding agents-polyvinylpyrrolidone (PVP) and gelatin--on crushing strength and friability, and the disintegration and dissolution characteristics of paracetamol tablets was made. The crushing strength-friability ratio (CSFR), the disintegration times, D, and the dissolution times t50, t90, and t1 (derived from the equation of Noyes and Whitney), all increased with an increase in binder concentration; however, the dissolution rate constants, k1 and k2, decreased. The ranking for the values of CSFR for tablets containing the different binders was PVP > gelatin > khaya gum. The ranking for D and the dissolution times was gelatin > khaya gum > PVP, whereas the ranking for the dissolution rate constants was PVP > khaya gum > gelatin. There were significant linear correlations between CSFR, D, t50, t90, and t1 for the tablets. There were also significant correlations between k1 and D, t50, t90, and t1, and between k2 and t90. The results suggest that khaya gum could be useful as an alternative binding agent to produce tablets with particular mechanical strength and drug release profiles.     

The mechanical properties of epoxy resins

Crack propagation in a series of epoxy resins described in Part 1 has been studied as a function of testing rate and temperature. It has been found that crack propagation is continuous at low temperatures but that as the temperature is raised the mode of propagation becomes unstable (stick/slip). Features on the fracture surfaces at the crack arrest lines have been shown to be of the same dimensions as those expected for a Dugdale plastic zone. It has been suggested that the slip process takes place by slow growth of a crack through the plastic zone followed by rapid propagation through virgin material. It has been shown that the stick/slip behaviour is due to blunting of the crack which is controlled by the yield behaviour of the resin. A unique fracture criterion has been shown to be applicable to epoxy resins which is that a critical stress of the order of three times the yield stress must be achieved at a critical distance ahead of the crack. Electron microscope replicas of the fracture surfaces have been obtained and an underlying nodular structure can be resolved. However, no direct correlation between the nodule size and fracture properties has been found.     

The mechanical properties of non-crimped fabric-based composites

The mechanical properties of composites prepared from two types of non-crimped fabric (NCF), namely biaxial, ±45° and quadriaxial with a 0°, ±45°, 90°, −45° ply sequence, are examined as a function of fabric weight and compared with those of alternative composite forms. In general, the properties of NCF laminates decrease slightly as the areal weight of the fabric increases. Laminates produced from biaxial fabrics exhibit superior properties for a given volume fraction of reinforcement than do laminates produced using woven rovings or continuous fibre prepregs, while quadriaxial NCF laminates have equivalent properties to woven roving laminates at certain orientations but, unlike woven roving laminates, retain their properties when rotated through 45°. Biaxial NCFS loaded at 45° to the fibre and quadriaxial fabrics produce composites with superior properties to those predicted using finite element and laminate analysis for idealized laminates based on the same materials.     

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.     

The mechanical properties of pressed processed wheat material

Breakfast wheatflake materials, produced by two methods, were milled and different sieve fractions reconstituted by hot pressing into bar-shaped test pieces, to reduce the geometry and structure effects of flakes. The stiffness and fracture properties of these pressed bars of different particle size in ranges <0.5 mm, 0.5–1 mm, 1–1.4 mm, 1.4–2 mm and of different water content were compared. Dynamic mechanical thermal analysis showed that the bending modulus, E, superimposed as a function of temperature in the range -40 to 140 °C. The value of E at 20 °C decreased with increasing water content corresponding to depression of the glass transition temperature. Microscopy of the test pieces revealed that starch was the continuous phase. The stiffness properties were similar in many respects to data published for pressed starch specimens. However, the energy to break samples at 7% water content (wet weight basis) was greater when a range of particle sizes was used compared to the results of narrow particle size ranges. This is consistent with published results on fracture toughness of particulate compacts. The energy to break samples increased with increasing water content.     

The structure and mechanical properties of syndiotactic polypropylene

The drawing behaviour of several syndiotactic polypropylenes is examined as a function of molecular weight and initial morphology. It is found that these materials can be drawn to a much lesser extent than comparable isotactic polypropylene. This limited drawability is attributed to the absence of an effective crystallinec-slip process, a view supported by dynamic mechanical measurements. Highest draw ratios are achieved in gel spun high molecular weight material where the degree of molecular entanglement is low enough to suppress the undesirable increase in drawing stress with extension.     

The mechanical properties of woven tape all-polypropylene composites

The creation of highly oriented, co-extruded polypropylene (PP) tapes allows the production of recyclable “all-polypropylene” (all-PP) composites, with a large temperature processing window (>30 °C) and a high volume fraction of highly oriented PP molecules (>90%). This paper describes all-PP composites made from woven tape fabrics and reports the tensile and compressive properties of these, with reference to composite processing conditions and compares these mechanical properties to those of commercial alternatives.     

The mechanical properties of ceramics from bauxite waste

This paper summarizes the development of engineering ceramics made from bauxite waste (red mud) produced in the alumina industry in Jamaica. Test specimens are fabricated from powders by sintering. For a particle size distribution of less than 75m in the starting powders and firing temperatures in the range of 1000 to 1100° C various mechanical properties are measured. These include fracture toughness (K _Ic), modulus of rupture (MOR), compression strength ( _c) and Brinell hardness. While apparent porosity varies between 40 and 48%, K _Ic is found to vary between 0.39 and 0.68 MN m^–3/2. The values are compared with those measured for commercial ceramic tiles and also with ceramics of magnesia and calcium zirconate. Within the fabrication temperature range studied the MOR ranges between 17.23 and 27.09 MN m^–2, compressive strength between 42.0 and 83.9 MN m^–2 and Brinell hardness between 26.2 and 59.9 kg mm^–2. With the aid of scanning electron microscopy and a basic knowledge of the physicochemical properties of the mud an attempt is made to explain the high strength and toughness achieved. The ready availability of raw material and the relatively low firing temperatures required for suitable engineering products should keep the production costs low for red mud ceramics.     

The mechanical properties of PVC under high pressure

The deformation properties of PVC have been studied under high pressure. Craze initiation and yield criteria have been proposed. The brittle-to-ductile transition was observed between 1×10⁷ and 2×10⁷ Pa, which is a relatively low transition pressure compared to polystyrene. Deformation in the post-yield region occurred by neck formation and subsequent drawing to produce chain orientation. When PVC was exposed to the pressure-transmitting fluid, silicon oil, a strong environmental stress cracking effect was observed.     

The measurement of transverse mechanical properties of polymer fibres

We report developments in the measurement of transverse elastic properties of a range of polymer fibres. The cylindrical fibre specimen is compressed across a diameter between a pair of parallel flat plates by a known load, while two quantities are measured; the width of the rectangular contact zone at one of the fibre-plate boundaries, and the degree of diametrical compression in the direction of the compressing force. Both measurements are used together with the relevant elastic solutions to give estimates of the transverse elastic modulus. For some fibres, plasticity is detected in the measurements of diametrical compression, and loading strategies are adopted to isolate this effect; the modulus values obtained from the two measurements are then in good agreement, provided the fibre is sufficiently large to permit accurate measurement of the contact zone. Finite-element modelling is used to show that the elastic-plastic behaviour is essentially understood and to estimate a value for yield stress. Results are presented for five fibres with diameters in the range 0.13–0.57 mm.     

The mechanical properties of elastomers in high-pressure CO2

Elastomer seals are widely used to contain high-pressure gases and can suffer from decompression damage when the contained gas is depressurized. The generally accepted mechanism for the damage is that there is a considerable degree of dissolution of the gas into the elastomer which cannot diffuse out quickly enough when the contained pressure is reduced; hence bubbles and fissures occur in the bulk of the elastomer. Attempts to model this behaviour typically assume the elastomer material properties are measured in the absence of the dissolved gas. In this study, a standard dumb-bell test piece tensometer has been developed which allows the elastomer material properties to be measured while saturated with CO2 and N2 (two gases with markedly different solubilities) at pressures of up to 4 MPa. The equipment was shown to be capable of providing accurate measurements under these conditions and various fluorocarbon, nitrile and silicone elastomers were tested. These tests showed that the high-pressure CO2 induced a slight reduction in initial modulus compared to tests in air, accompanied by a more significant loss in both strength and ultimate extension. The reduction was greater than 50% in some cases. Electron micrographs of the samples showed that the fracture surfaces were of a smoother nature for the samples tested in CO2, suggesting a mechanism of disruption of interchain forces. The implications of these results for models of decompression damage are noted.     

The mechanical properties of rubber compounds containing soft fillers

A detailed examination of failure of properties of polybutadiene containing soft elastomeric fillers has previously been described [1]. Here the effect of filler modulus and filler-matrix adhesion on tear strength is measured. Tear behaviour depends upon the level of interfacial adhesion; when high, tear strength increases with increasing filler hardness, but if interfacial adhesion is low, incorporation of fillers may result in low tear strengths. An estimate of the edge flaw size is made from the tear strength and strain energy densities at break. It was found that compounds with low interfacial adhesion generally had edge flaw sizes of the same order as the maximum filler particle size. A correlation between tear strength and tear surface morphology is made.     

The mechanical properties of carbon fibre reinforced Pyrex glass

The mechanical properties of carbon fibre reinforced Pyrex glass are discussed in terms of the volume fraction of fibre, the orientation of the fibres, fibre damage during fabrication, matrix porosity, matrix critical strain, interface properties and the mode of failure in bend tests. The stress at which matrix cracking occurs increases with fibre concentration indicating that the critical strain of the matrix increases as the fibre separation decreases. The ultimate strength of the composite is considerably greater than the stress at which the matrix begins to crack. Preliminary stress cycling experiments at stresses above that at which matrix cracks are formed suggest that propagation of these cracks is inhibited by the fibres.