Tablet tensile strength

Tye CK, Sun C, Amid on GE. Evaluation of the effects of tableting speed on the relationship between compaction pressure, tablet tensile strength and tablet solid fraction. J Pharm Sci 2005 94(3)465-472. 

In a demonstration of the pharmaceutical advantage that can be realized through the use of a cocrystal form of a substance, it was shown that the 1 1 cocrystal of caffeine and methyl gallate exhibited significantly improved powder compaction properties [64], The compression characteristics of the cocrystal were reported to be excellent over the entire pressure range studied, with the tablet tensile strength of the cocrystal being twice that of caffeine at pressures less than 200 MPa. The superior compaction properties of the cocrystal product were attributed to the presence of slip planes in crystal structure. 

Adolfsson, A., Gustafsson, C., and Nystrom, C. (1999), Use of tablet tensile strength adjusted to surface area and mean interparticulate distance to evaluate dominating bonding mechanism, Drug Dev. Ind. Pharm., 25,753-764. 

The tableting properties of materials also depend on their deformation behavior. It is apparent that the tablet tensile strength is a strong function of the plastic work required for its formation but not a function of the elastic work recovered. Consequently, it is likely that strong and ductile interparticle functions, whose formation dissipated a significant plastic work, result in strong and tough compacts [4],... 

Table 4 Tablet tensile strengths (MPa) produced by a compression pressure of 80 MPa on an excentric press...

Vezin, W.R. Khan, K.A. Pang, H.M. Adjustment of precompression force to reduce mixing-time dependence of tablet tensile strength. J. Pharm. Pharmacol. 1983, 35, 555-558. 

Pharmaceutical tablets are made from a number of components, and each component contributes to the tablet s final properties. Therefore, it is important to study the physical properties of the individual components and their mixture rules in order to predict the mechanical properties of the final tablet. Tensile strength is one of the crucial properties that assess mechanical strength the most common method for measuring tensile strength is the diametrical compression test discussed above (110). In this section the application of the Ryshkewitch-Duckworth equation to the analysis of tensile strength of mixtures will be discussed (151,152). 

Fig. 13.3 Effect of HPMCAS level in melt-extruded solid dispersion on tablet tensile strength...

Ryshkewitch [6] and Duckworth [7] proposed an empirical equation to relate tablet tensile strength, t, to porosity of the tablet, (c = 1 - D). Thus,... 

Figure 16.10 Tablet tensile strength versus porosity for two individual components (drug compound and PEG 8000) of the formulation discussed in Figure 16.9 [23]. Circles-neat compounds. Squares - wet granulations. Dashed line - prediction using Ryshkewitch-Duckworth parameters for neat compound.

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. 

Luangtana-Anan and Fell [28] also studied the relation between surface free energy and tablet tensile strength. The correlation between the Lifshitz-van der Waals contribution to surface free energy, and tablet tensile strength is shown in Figure 16.13. 

Figure 16.12 Tablet tensile strength versus surface free energy, y. for several materials.

Figure 16.13 Tablet tensile strength versus y for several materials. Figure is drawn from data by Luangtana-Anan and Fell [28].

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. 

Here we have demonstrated the essential features of a proposed model for determining tablet tensile strength from the properties of the component materials. The dependence of the Ryshkewitch-Duckworth parameters with tablet composition is consistent with the proposed model. Furthemore, the relation between particle surface free energy and tablet tensile strength is consistent with the available data. Calculations of the type discussed can be used to improve the efficiency of the formulation process. The model presented here is a step toward achieving quality by design in the pharmaceutical industry. 

F. M. Etzler, T. Bramante, R. Deanne, S. Sienkiewicz and F. J. Chen, Tablet tensile strength An adhesion science prespective. /. Adhesion Sci. Technol. 25, 501-519(2011). 

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