Tensile strength, of compacts

The tensile strength of compacts [30] also provides useful information. Excellent specimens of square compacts are necessary to conduct the tensile testing. For this reason, a split die [31 ] (Fig. 2) is used to make compacts that are not flawed. The split die permits triaxial decompression, which relieves the stresses in the compact more uniformly in three dimensions and minimizes cracking. These specimens are then compressed with platens 0.4 times the width of the square compacts in the tensile testing apparatus. (Fig. 3). Occasionally nylon platens and side supports are used to reduce the tendency to fail in shear rather than tension. The force necessary to cause tensile failure (tensile forces are a maximum... 

Fig. 3 Schematic diagram of the tensile testing apparatus, which allows for the determination of the tensile strength of compacts of materials. (Adapted from Ref. 31 with permission of the publisher.)...

As the punch speed increases, so does the porosity of tablets and their propensity to capping and lamination. The tensile strength of compacts tends to decrease with faster speeds, especially for plastic and viscoelastic materials, such as starch, lactose, avicel, ibuprofen, or paracetamol. Such materials have the tendency to cap or laminate at higher speeds.f " ... 

Stubberud L, Arwidsson HG, Hjortsberg V, Graffner C. Water-solid interactions. Part 3. Effect of glass transition temperature, Tg and processing on tensile strength of compacts of lactose and lactose/polyvinyl pyrrolidone. Pharm Dev Technol 1996 1(2) 195-204. 

Just as metals can be ductile or brittle, so can organic materials. The Brittle Fracture Index is a measure of the brittleness of a material. It is a measure of the ability of a compact of material to relieve stress by plastic deformation. The Brittle Fracture Index (BFI) is determined [29,31] by comparing the tensile strength of a compact, stress concentrator) in it, o-T0, using the tensile test we have described. A hole in the center of the compact generally weakens a tablet. If a material is very brittle, theoretical considerations show that the tensile strength of a tablet with a hole in it will be about one-third that of a solid tablet. If, however, the material can relieve stress by plastic deformation, then the strength of the compact with a hole in it will approach that of a compact with no hole. The Brittle Fracture... 

Figure 5 Relationship between the slope of the NIR spectrum and the tensile strength of the corresponding roller compacted sample at different moisture quantities. Triangles, 3.5% diamonds, 4.6% circles, 5.7% and squares, 7.2% LOD samples.

This index describes the potential of the tablet to cap and laminate, and is related to the ability to relieve shear stresses within the compact via material flow. In Equation (1), TS equals the tensile strength of the normal tablet and TSo is measured from a tablet with a hole in its center, which simulates a defect. 

Masaki H, Akinobu O, Fukuji H. Effect of particle size of lactose on the compaction properties of powder and tensile strength of tablets. Yakuzaigaku 1986 46(l) 50-57. 

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. 

A technique generally applied to characterize and prevent the capping and lamination of a material intended to be compacted is using the brittle fracture index (BFI). The BFI was designed by Hiestand et al. [31] and measures the ability of a material to relieve stress by plastic deformation around a defect. It is obtained by applying Equation (8) and compares the tensile strength of a tablet with a hole in its center (To), which acts as a built-in stress concentrator defect, with the tensile strength of a similar tablet without a hole (T), both at the same relative density ... 

K below Tg, an amorphous drug powder formed compacts that were significantly more brittle than those formed from the crystalline form of the drug although the tensile strengths of the compacts were similar. 

McKenna, A. McCafferty, D.F. Effect of particle size on the compaction mechanism and tensile strength of tablets. J.Pharm. Pharmacol. 1982, 34, 347-351. 

As a high-speed single station press, mechanical compaction simulator will be able to plot compressibility profiles, Heckel graphs, calculate work of compaction, and virtually any other imaginable variable that is of interest to formulators. Tensile strength of tablets made on a Betapress and The Presster was similar. ... 

Pitt, K.G. Newton, J.M. Stanley, P. Effects of compaction variables on porosity and material tensile strength of convex-faced aspirin tablets. J. Pharm. Pharmacol. 1990, 42, 219-225. 

It has been shown that the tensile strength of roller compacted ribbons is reflected in the density of the compacts (59). A three point beam bending approach (69) was used to determine both tensile strengths and Young s moduli for both ribbons and uniaxial compacted surrogates for ribbons (Fig. 16) (4) which have been used to determine compaction properties when material is limiting. 

Gupta also showed that for a given set of milling conditions in a Comil the post milled particle size distribution is related to the tensile strength of the ribbon (Fig. 17). This is a key in designing and controlling a roller compaction process as will be discussed later in the monitoring section. 

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