Tablet porosity

Compression Tablet porosity (%) Percentage degradation after 3 h... 

The compaction process can be described by a variety of force (or pressure)-displacement profiles, such as force versus time, force versus tablet porosity, and force versus tablet properties (hardness, friability, dissolution, etc.). The effect of compaction speed on a variety of tablet properties can also be studied. 

Tablet porosity vs. force curve to visualize the densification process Heckel plots to quantitate the densification process and characterize materi-...

Typically, displacement measurements during compaction are used to define relationships between compaction force/pressure and the resulting tablet porosity/ density. Heckel plots have been derived from the density-pressure relationship and have been frequently presented in the literature. Fig. 18 is an example of a Heckel plot, where the tablet porosity values are plotted as a function of compaction pressure. The shape of the Heckel plot has been used to describe the type of... 

Relationships between Tablet Porosity and Compression Force or Pressure... 

MOCVD metal organic chemical vapour deposition MBE molecule beam epitaxy P value is reduced by a factor of 2.8 to take into account the tablet porosity Calculated in this work from experimental data presented in original publications... 

Keywords Ryshkewitch-Duckworth equation, compaction, tableting, surface free energy, adhesion, tablet porosity... 

The tensile strength (r) is calculated using the well-known relation that was previously introduced (Equation 16.2) and is again shown below (Equation 16.21) (Equation 16.12). Tablet porosity (f) was calculated using Equation (16.22). 

Direct evidence for the role of surface free energy in determine tablet tensile strength is limited. Two studies, however, have been performed that suggest a role of smface free energy in determining tablet tensile strength. Tablet porosity was not carefully controlled or recorded in these studies so further confirmation is likely to be desirable. 

Figures 16.1-3 show Ryshkewitch-Duckworth plots for dicalcium phosphate or lactose mixtures with sodium dodecyl sulfate as well as the Ryshkewitch-Duckworth plots for each of the pure components. As previously observed by Wu et al. [20] and Tye et al. [10] no dependence on dwell time was noted. We did note that tablets were not formed for some materials when short dwell times, comparable to production conditions, were used. Presumably, insufficient time is given for viscoelastic deformation of the materials that is, in part, responsible for adhesion. Viscoelestic recovery upon decompression may also contribute to lamination of tablets on decompression. Figures 16.1-3 and Figme 16.6 show the importance of tablet porosity to tablet tensile strength. Porosity should be considered a measure of the outcome of the tableting process.

In this paper the compaction of several common pharmaceutical excipients blended with sodium dodecyl sulfate is investigated. Furthermore, a model based on the principles of adhesion science is proposed for calculation of tablet radial tensile strength as a function of tablet porosity for powders composed of several materials. The data indicate that the model, indeed, allows for the calculation of tablet tensile strength from the Ryshkewitch-Duckworth parameters of the component materials. 

Keywords Controlled drug delivery, percolation theory, critical points, cellulose derivatives, polymeric matrices, relative particle size, tablet porosity, biodegradable polyurethane... 

In order to investigate the influence of the tablet porosity on the release behavior of inert matrix tablets, Cifuentes et al. prepared five batches containing 30% of carbamazepine and 40% of ethylcellulose (Ethocel 7 FP) as well as 5 batches containing 30% of carbamazepine and 40% of Ethocel 10 FP with 5 different porosity levels ranging from 0 to 25% [90]. Both types of matrices contained the soluble filler lactose. As it was expected, matrices prepared with both types of polymers and lower initial porosity (0-5% v/v) showed a slower release rate since these matrices were below the percolation threshold of the soluble filler plus the initial porosity. 

Previous works have explained the low values obtained for the polymer percolation threshold in hydrophilic matrices based on the contribution of the initial porosity of the tablet in order to form the gel layer that controls the drug release [13,94,95]. The results obtained by Aguilar-de-Leyva et al. do not contradict this hypothesis, since the porosity values of the previous studies correspond to the lower level (5-10%), and this study proposes that it could be an involvement of the initial porosity. Nevertheless, this new study concluded that the contribution of initial porosity to establish the gel layer would be restricted to a low range of tablet porosity [101]. Above this range, an increase in the tablet initial porosity does not affect the polymer percolation threshold. 

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