Mechanical Properties of Granulates

The mechanical properties of TPS depend on the starch production temperature and water content, as weU as the quantity and type of added plasticizers and aux-ihary materials. The most notable influence on changes in mechanical properties proved to be the amounts of plasticizer and auxiUary materials. 

The most common plasticizers, such as glycerol, glycol, or sorbitol, possess hydroxy groups similar to those that appear in starch, and so are compatible with starch macrogranules. 

Mitrus [35] showed that the radial expansion index value determined for TPS granulates strongly depended on extruder working conditions. This parameter was greatly affected by extruder screw rotation and, regardless of the mixture s material composition, the expansion index of the manufactured granulates increased with higher screw rotahon speed. 

No information concerning the expansion index ofTPS is available in the professional world literature. Therefore, the results of research into this parameter can only be considered by reference to expansion indexes of other starchy products, for which it varies over a broad range from 1 to 10 or, in the case of expanded grains, even up to a factor of 17. 

Potato starch (AVEBE) Potato starch (Lornza) 

---

Kristensen, H. G., Holm, P., and Schaefer, T., Mechanical Properties of Moist Agglomerates in Relation to Granulation Mechanisms. Part I Deformability of Moist Densified Agglomerates, Powder Technology, 44 227-237 (1985)... 

Table 12 Mechanical Properties of Ibuprofen Bulk Drug and Granulations...

Blends of starch and a hydrophobic polymer make it possible to overcome the disadvantages described above. Starch compounds with Ecoflex are used to enhance hydrophobicity as well as the mechanical and thermal properties of compounded products. To obtain high quality film products, the starch has to be treated before being blended with Ecoflex . The crystalline structure of starch granules has to be destroyed because starch granules are as large as the film thickness of typical film applications and would therefore reduce the mechanical properties of the films. 

Kristensen HG, Holm P, Schaefer T. Mechanical properties of moist agglomerates in relation to granulation mechanisms Part I. Deformability of moist, densifled agglomerates. Powder Technol 1985 44 227-237. 

The physical and mechanical properties of excipients were important variables in achieving performance of the final products as well. The preferred formulation strategy for a low-dose product using dry granulation is to design a cohesive blend to... 

TABLE 6.6 Physical and Mechanical Properties of the Drug and Diluents Used in the Low-Dose Dry Granulation Formulations... 

In the particular case of protein-rich granulates (oilcakes), thermomoulding is often more suitable because it takes advantage of their cross-linking abilities (Rouilly et al 2005). The mechanical properties of these materials are lower, but the advantage is that oilcake can be used as it is, i.e., at its equilibrium moisture content, and the materials are more resistant to water. 

Typically, finer granules with lower bulk densities can be obtained when a smaller volume of liquid is added during mixing. Moreover, these granules of smaller particle size yield tablets with faster dissolution rates and lower hardness values (75). The mechanical properties of a binder film are important as well and a good tablet binder should be able to offer flexibility and plasticity and yield without rupturing in order to absorb the effects of elastic recovery (62). 

---