Direct compression method

Direct Compression. This process is relatively simple and time saving. AH the ingredients are blended and then compressed into the final tablet. This is an excellent method, but encumbered by a number of problems. Not all substances can be compressed directly, necessitating a granulation step. Likewise, the flow properties of many blends of fine, particle-sized powders are not such as to ensure even filling of the die cavities of tablet presses. In addition, air entrapment can occur. 

Direct compression is a simpler alternative tablet manufacturing method. With direct compression, tablets are compressed directly from a powder mixture of an API and appropriate excipients. Like granulation methods, this approach is also based on the required flow, compressibility, and compactibility of a formulation. Direct compression offers both time and economic advantages by eliminating intermediate granulating and drying steps. 

The formation of complex ions is an important problem for the study of the structure and properties of molten salts. Several physicochemical measurements give evidence of the presence of complex ions in melts. The most direct methods are the spectroscopic methods which obtain absorption, vibration and nuclear magnetic resonance spectra. Also, the formation of complex ions can be demonstrated, without establishing the quantitative formula of the complexes, by the variation of various physicochemical properties with the composition. These properties are electrical conductivity, viscosity, molecular refraction, diffusion and thermodynamic properties like molar volume, compressibility, heat of mixing, thermodynamic activity, surface tension. 

The measurement of particle size is a key issue in the formulation of many pharmaceutical products. Particle size distribution is known to directly influence physical properties of powders, such as dissolution rate, powder flow, bulk density, and compressibility. Conventional methods of particle size measurement include sieve analysis and laser diffractometry. ... 

There are several direct methods of measurement of yield stress. The constant stress rheometer is most frequently used to determine value in shear. Dzuy and Boger [1983, 1985] used a rotational vane viscometer. Yield stresses in compression can be calculated from the unrelaxed stress values in parallel plate geometry. Its value in elongation has been directly measured as the critical stress value below which no sample deformation was observed during 30 minutes of straining in an extensional rheometer. 

This simple and direct method (Fig. 17.4a) is usually the best choice when the column has a vapor product (77). The controller directly manipulates vapor inventory and, therefore, coliunn pressure. The equivalent method commonly used to control vacuum columns (Fig. 17.46) has the pressure controller varying the quantity of spillback to the ejector suction. The spillback control method can also be applied to pressure columns where the vapor product is compressed. 

We define the hydration number as the average number of water molecules in the first sphere about the metal ion. The residence time of these molecules is determined generally by the nature of the bonding to the metal ion. For the f-element cations, ion-dipole interactions result in fast exchange between the hydration layer and the bulk solvent. The techniques for studying the nature (number and/or structure) of the hydration shell can be classified as either direct or indirect methods. The direct methods include X-ray and neutron diffraction, luminescence and NMR (nuclear magnetic resonance) relaxation measurements. The indirect methods involve compressibility, NMR exchange and absorption spectroscopy measurements. 

For the determination of a(andhenceT ), the most direct method is arguably that based on inert gas solubiUty data. However, in view of the arduousness involved and the uncertainties in both the extrapolation procedure and the experimental solubilities, it is natural to look out for alternatives. From the various suggestions, " a convenient way is to adjust a such that the computed value of some selected thermodynamic quantity, related to repulsive forces rather than attractions. Since the low compressibility of the condensed phase is due to short-range repulsive forces, the isothermal compressibility Pr= ( 1 A7)(dV/9P)T might be a suitable candidate, in the framework of the generalized van der Waals (vdW) equation of state... 

The measurements of II versus A isotherms generally exhibit, when compressed, a sharp break in the isotherms that has been connected to the collapse of the monolayer under the given experimental conditions. The monolayer of some lipids, such as cholesterol, is found to exhibit an usual isotherm. Figure 1.39. The magnitude of II increases very little as compression takes place. In fact, the collapse state or point is the most useful molecular information from such studies. The collapse pressure is found to be a very unique property of any lipid. It is strongly dependent on the packing state of the lipid monolayer and thus provides important information about molecular interactions. It is found that this is the only direct method, which can provide information about the structure and orientation of amphiphile molecule at the surface of water. However, a steep... 

A neat direct method for studying droplet rupture and coalescence, allowing one actual visual observation of individual droplets, was developed by Parfenova et al. [38,39]. A very small droplet (about 0.3 mm in diameter) is immersed into another liquid phase and stretched under controlled conditions (see Figure 4.14). The interfacial tension and rupture force are measured at the point when the droplet assumes cylindrical shape due to deformation. This corresponds to uniaxial tension resulting from asymmetric uniaxial stretching of the film (membrane) at the interface between the polar and nonpolar phases (which can represent both the dispersed phase as well as dispersion medium). In subsequent compression of two half droplets, one measures the critical force causing coalescence,/.oai, that is, the rupture of a double-sided emulsion film. These results correspond to a symmetrical double-sided axisymmetric stretch of the membrane. 

There are basically two manufacturing methods for SCL [4]—the swelling method, in which a solid lens is first manufactured and then swollen with water, and the direct method, in which a monomer (s) that contains water or a solvent is polymerized in the lens mold. Whether it is a solid or a gel, the similarity of the manufacturing methods is shown in Fig. 1. Although frozen gel can be cut and polished (this has been done by the authors), it is not practical and is not currently used eommercially. Polymers also can be injection or compression molded to make solid lenses and then later swollen. However, these methods are not actually used. 

Figure 4.16 Schematic illustration of a cross sectional view of crystallization apparatuses to show the principle of elongational crystallization by the compression method. Z-axis is along the compressed direction. X- or i -axis is parallel to the MD. (a) Compression type apparatus.(b) Roll type apparatus. (See color insert.)...

In the SFB, it is possible to detect both attraction and repulsion between surfaces. Most of the other techniques, including surface balance, osmotic stress, and compression cell methods, cannot provide that," " as they cannot directly measure attraction between surfaces. One can also get complementary... 

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