Powder rheometer testing

That is why, in this chapter, we present the results of our current research focused on powder flow and surface properties analysis of HA powder material by means of inverse gas chromatography (iGC) and powder rheometer testing. These are both excellent tools for characterisation of the physicochemical properties of powder materials. 

There are basically three types of shear cells available for powder testing (a) the Jenike shear cell, also known as the translational shear box (b) the annular or ring shear cell, also called the rotational shear box and (c) the rotational shear cell, which is a fixture of a powder rheometer. 

Powder and friction properties are covered in section 3.4. In ASTM D2395 [50] a test is described that measures the ability of PVC polymer to absorb plasticizer whilst remaining a free-flowing powder. The PVC polymer powder is mixed with liquid plasticizer in cither a sigma blade mixer or a planetary mixer heated at 88 C and the torque is continuously recorded by a torque rheometer. The mix passes through a sticky state before becoming dry as the plasticizer is absorbed. The change in motor drive torque with time is used to measure the time taken for this absorbtion. 

In a typical capillary rheometer, one has a temperature-controlled barrel into which the test material (usually in powder or pellet form) is packed. Directly downstream of the barrel is a cylindrical die with known length and radius. A piston is programmed to force the molten material through the die at a constant rate. A pressure transducer located near the die entry records the pressure drop. The capillary rheometer is widely employed and has been analyzed in detail (see Macosko [25], who gives a thorough discussion). The expression for the shear viscosity is... 

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