The effect of temperature on the tensile strength and densification of lactose powder coated with fatty acids

Tensile strength and compression of coated pharmaceutical powders

A study has been made of the tensile strength and compression of loosely packed beds of lactose, sodium chloride and calcium phosphate powders after they had been coated with small amounts of stearic acid, polyethylene glycols and polyvinylpyrrolidones. The properties of the systems were measured over a range of temperatures. Only when the coatings were continuous and durable did they produce reductions in both tensile strength and resistance to compression. Marked changes occurred in tensile strength at temperatures 20 ° — 40 °C below the conventional melting points of the coatings. The tensile strength results have been expressed in terms of the range and magnitude of the interparticle forces which depend on the surface free energy of the coated powders and on the Brinell hardness of the coating materials employed.

Resistance to densification, tensile strength and capsule-filling performance of some pharmaceutical diluents

The purpose of this study was to compare some indicators of capsule-filling performance, as measured by tapped density under different conditions, and elucidate possible quantitative relationships between variation of capsule fill-weight (%CV) and gravitational and inter-particle forces (attractive or frictional) derived from measurements of particle size, true density, low compression and tensile strength. Five common pharmaceutical diluents (lactose, maize starch, talc, Emcocel and Avicel) were investigated and two capsule-filling methods (pouring powder and dosator nozzle) were employed. It was found that for the pouring-type method the appropriateness of Hausner's ratio (HR), Carr's compressibility index (CC%) and Kawakita's constant (alpha) as indicators of capsule fill-weight variation decreases in the order alpha > CC% > HR; the appropriateness of these indicators also decreases with increasing cylinder size and with impact velocity during tapping. For the dosator-type method the appropriateness of the indicators decreases in the order HR > CC% > alpha, the opposite of that for the pouring-type method; the appropriateness of the indicators increases with decreasing cylinder size and impact velocity. The relationship between %CV and the ratio of inter-particle attractive to gravitational forces calculated from measurements of particle size and true density (Fvdw/Wp) was more significant for the pouring-type capsule-filling method. For the dosator-type method a significant relationship (1% level) was found between %CV and the product of Fvdw/Wp and a function expressing the increase, with packing density (p(f)), in the ratio of frictional to attractive inter-particle forces derived from compression (P) and tensile-strength (T) testing, d(log(P/T))/d(p(f)). The value of tapped density in predictions of capsule-filling performance is affected by the testing conditions in a manner depending on the filling method applied. For the pouring-type method predictions can be based on the ratio of attractive (inter-particle) to gravitational forces, whereas for the dosator-type method the contribution of frictional and attractive forces should, because of packing density change, also be taken into account.

A consideration of the range and strength of interparticle forces in coated lactose powder

A study has been made of the range and strength of interparticle forces in lactose powder coated with increasing concentrations of paraffins at different temperatures. Marked changes occurred in these forces as the paraffin content was altered and the temperature increased from -10 degrees to +50 degrees C. The strength and range of interparticle forces depended on the mechanical properties of the coating materials and the surface free energy of the coated powders.

Tensile strength and compression of coated pharmaceutical powders: tablets

A study has been made of the tensile strength and compression during tableting of lactose, sodium chloride and calcium phosphate powders after they had been coated with small amounts of stearic acid, polyethylene glycols and polyvinylpyrrolidones. The properties of the systems were measured over a range of temperatures. The tensile strength and the compression behaviour depended not only on the amount and type of the coating material but also on the homologous temperature of processing. The changes in tensile strength have been explained in terms of changes in interparticle separation, changes in interparticle forces and the formation of welded bonds by the coatings. The compression results have been analysed in terms of the Heckel and the Cooper & Eaton equations.

Effects of paraffin coatings on the shearing properties of lactose

An annular shear cell has been employed to measure the shearing properties of lactose powder coated with up to 10(-4) mol g-1 of powder of a series of paraffin hydrocarbons. The angle of internal friction, delta, of the coated powders was independent of their packing density. The shearing properties of the powders depended on the concentration, the viscosity and thickness of the coating material.

Effects of paraffin coatings on the tensile strength of lactose

Measurements have been made of the tensile strength of lactose at different temperatures after coating it with up to 10(-4) mol of various paraffin hydrocarbons g-1 of powder. Providing the coating is in a liquified form, either as a result of the ambient temperature or because of the localized high pressure at the points of true contact between the particles, there is a correlation between the tensile strength of the powder and the thickness and viscosity of the coating layer.

Effect of temperature changes on the densification and compression of griseofulvin and sucrose powders

A study has been made of the effect of varying the temperature between - degree and -25 degree C on the densification and low pressure compression of griseofulvin, sucrose and mixtures of the two powders. Densification and compression of the materials were facilitated as they were cooled in the range of homologous temperatures (ratio of the experimental temperature in degree K to melting point of the material in degree K) from 0.7 to 0.5. This was attributed to a reduction in the cohesive forces operating between the particles. Values are given for the activation energies of densification and compression derived by plotting the logarithms of these properties versus the reciprocal of the absolute temperature. For both materials and their mixtures the activation energies were in the range of about 1 to 10kJ mol-1 showing that physical rather than chemical forces were operating between the particles.