Strength of compact

FIG. 20-79 Effect of pelleting pressure on axial crushing strength of compacted calcite particles of different sizes demonstrating existence of a critical yield pressure. Inset shows the effect of hardness on critical yield pressure. [Benhow, Enlargement and Compaction of Particulate Solids, Stanley-Wood (ed.), Butteixooiihs, 169 (1.9S3),]... 

Binders improve the strength of compacts through increased plastic deformation or chemical bonding. They may be classified as matrix type, film type, and chemical. Komarek [Chem. Eng., 74(25), 154 (1967)] provides a classification of binders and lubricants used in the tableting of various materials. 

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. 

Herrmann investigated in more detail the influence of water adsorption on the tensile and shear strengths of compacts made from barium sulfate. Figure 78 shows some results. The tensile and shear strengths were determined on compacts produced and stressed in a high vacuum and at various levels of relative humidity of the test chamber atmosphere. Since the normal relative humidity is often in a range between 60 and 80%, all conditions investigated... 

Figure 11.18 Effect of magnesium stearate mixing time on the strength of compacts.

Proctor, RR. (1948). The relationship between the foot pounds per cubic foot of compactive effort and the shear strength of compacted soils. 2 Inti. Conf. Soil Mechanics and Foundation Engineering Rotterdam 5 219-223. 

ASTM D 1075. 2011. Standard test method for effect of water on compressive strength of compacted bituminous mixtures. West Conshohocken, PA ASTM International. 

Gurrey J D (1999) What determines the bending strength of compact bone J Exp Biology, 202 2495-2503. 

ASTM D1075-96 (2000) Standard Test Method for Effect of Water on Compressive Strength of Compacted Bituminous Mixtures... 

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