New Matrix Tablet from Okra Gum: Effects of Method of Preparation and Gum Concentration on Tablet Properties

The objective of this investigation is to study the effect of methods of preparation and concentration of gum on the compressional and mechanical properties of Okra gum matrix. The compressional behavior of Okra gum matrices prepared by direct compression and wet granulations is analyzed using density measurements, Heckel and Kawakita analysis while the mechanical properties of the formulations were assessed using crushing strength (CS) and friability (FR) as well as CSFR ratio. Formulations prepared by direct compression had lower Pk values than those prepared by wet granulation while there was no significant difference between Py values of formulations prepared by direct compression and wet granulations. Therefore, formulations prepared by direct compression underwent plastic deformation more easily and rapidly than those prepared by wet granulation. The results show that DB values increased with decrease in concentration of the gum and granules undergo higher degree of fragmentation than powders. Formulations containing 90% w/w Okra gum exhibited the highest amount of total plastic deformation and gave the best packing. Tablets prepared by direct compression showed lower bond strength and higher friability values than those prepared by wet granulations. The crushing strength generally decreases with a decrease in the concentration of the gum while there was an inverse relationship between friability and gum concentration. CSFR decreases with a decrease in gum concentration and tablets prepared by wet granulations showed significantly higher values of CSFR

Mechanically induced phase transformation of zinc sulfide

Molecular dynamics （MD） simulations of the consecutive compression-decompression cycles ot hexagonal zinc sulfide （wurtzite） nanoparticles predict an irreversible phase transformation to the cubic polymorph.The phase transformation commences at the contact area between the particle and the inden- ter and proceeds with the number of compression cycles. Dislocations are visible for a particle size above 5nm. Results from wet grinding and dry powder compression experiments on a commercial wurtzite pigment agree qualitatively with MD simulation predictions. X-ray diffraction patterns reveal that the amount of cubic polymorph in the compressed samples increases with pressure applied to the powder. In comparison with powder compression, wet milling leads to a more pronounced phase transformation. This occurs because the particles are exposed to a large number of stress events by collision with the grinding media, which leads to the formation of defects and new surface crystallites by particle fracture. According to the MD simulations, phase transformation is expected to occur preferentially in surface crystallites because they experience the highest mechanical load. Because of the phase transformation, the wet ground and compressed samples exhibit a lower photo- luminescence intensity than the feed material. In comparison with powder compression, milling reduces the photoluminescence intensity more substantially. This occurs because a higher defect concentration is formed. The defects contribute to the phase transformation and photoluminescence quenching.