Powder rheometer

The New FT3 Powder Rheometer—Freeman Technology. Freeman, R. The Flowability of Powders, International Conference on Powder and Bulk Solids Handling, 2000. Velasco, A. Munoz-Ruiz, A.J. Perales, M.C. Munoz, N. Jimenez-Castellanos, M.R. Evaluation of an adequate method of estimating flowability according to powder characteristics. Int. J. Pharm. 1994, 103, 155-161. 

Luukkonen P. Schaefer T, Podczeck et al. Characterization of microcrystalline cellulose and silicified microcrystalline cellulose wet masses using a powder rheometer. Eur J Hiarm Sci 2001 13 143-9. 

Freeman Technology and the FT4 Powder Rheometer offer real benefits to all users of powders (5). These include ... 

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. 

Alternatives to the Jenike shear cell are the annular shear cell and the rotational shear cell, also called the powder rheometer. It has been reported (Freeman and Cooke, 2006) that powder rheometers are reliable, fast, and give results comparable to standard methods based on the Jenike shear cell. The objective of the exercise is to compare the standard Jenike method for limestone CRM 116 powder with a method using a powder rheometer. 

A rotational shear cell instrument, such as the FT4 Powder Rheometer, equipped with a 48 mm rotational shear cell and a 30 mL shear measurement vessel. A batch of reference limestone powder (CRM 116), produced and sold by the Commission of European Communities. 

The most fundamental powder properties can be determined in a powder rheometer [11]. Its principle of operation is similar to that of a rheometer for liquids, where the sample is placed in a shear cell and stress/strain relationships are measured. Design of a shear cell for a powder sample is more demanding than for a liquid sample, as an adequate contact between cell surface and powder need to be ensured. Accordingly, many shear cell configurations exist. While a powder rheometer provides very detailed information on powder properties, the interpretation of the data is also very demanding. A detailed discussion of this aspect is beyond the scope of this chapter. 

An alternative procedure, to ensure no external force is applied to the powder bed by the vaned paddle, is to place the compacted sample on a balance and when the paddle is immersed in the powder to raise the vaned head slowly until the balance reading is zero. This dynamic method of bulk powder characterisation is allied to the rheological method for measurement of the viscosity of non-Newtonian fluids and suspensions. Commercial instruments based on the WSL cohesion tester are now available in the form of the FT4 Powder Rheometer (Freeman Technology) and the Stable Micro Systems Powder Flow Analyser (Stable Micro Systems). 

Fig. 14.14 DoE results of the dynamic flow evaluation of spray dried mannitol batches with the FT powder rheometer (left). Scheme of particle-particle interactions for (a) spherical carrier particles (b) indented carrier particles (right)...

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. 

Powder rheology measurements were performed on a FT4 powder rheometer. All experiments were performed at laboratory ambient temperature (24 °C) and at a relative humidity of 43%. 

Hellen L, Yliruusi J. Process variables of instant granulator and spheroniser III. Shape and shape distributions of pellets. Int J Pharm 1993 96 217-223. Chapman SR, Rowe RC, Newton JM. Characterization of the sphericity of particles by the one plane critical stability. J Pharm Pharmacol 1988 40 503-505. Rowe RC, Sadeghnejad GR. The rheology of mcc powder/water mixes-measurement using a mixer torque rheometer. Int J Pharm 1987 38 227-229. O Connor RE, Schwartz JB. Spheronization II Drug release from drug-diluent mixtures. Drug Dev Ind Pharm 1985 11 (9-10) 1837-1857. 

Landin, M. Rowe, R.C. York, P. Characterization of wet powder masses with a mixer torque rheometer. 3. Nonlinear effects of shaft speed and sample weight. J. Pharm. Sci. 1995, 84/5, 557-560. 

Rowe, R.C. Sadeghnejad, G.R. The rheological properties of microcrystalline cellulose powder/water mixes-measurement using a mixer torque rheometer. Int. J. Pharm. 1987, 38, 227-229. 

Senouci and Smith (1988) used a simplified analysis for converging flow in a piston-driving capillary rheometer at 120-130°C and obtained ratios of uniaxial extensional viscosities to shear viscosities of maize grits and potato powder in the range of 60-3900. 

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. 

Figure 18 Typical torque rheometer trace for an unplasticized PVC powder compound.

ASTM D2396-94. Powder mix time of poly(vinyl chloride) (PVC) resins using a torque rheometer. 

If/m is the maximum packing density of the particles, which is defined as the volume fraction at which the particles touch one another, so that flow is not possible, then the actual particle volume firaction/used in injection molding is lower than/m by 5-10 vol%. This means that in a well-dispersed suspension, the particles are separated from one another by a thin layer of polymer with a thickness of about 50 nm dming the molding, so that the mixture is able to flow. Therefore, the volume fraction of particles / is determined by the particle size and distribution and the particle shape. In practice, the volume firaction of ceramic powders is determined from viscosity measurements by using a capillary rheometer. Data for the relative viscosity, i.e., the viscosity of the mixture divided by the viscosity of the unfilled polymer versus particle concentration can be well fitted by the following equation [209] ... 

Torque rheometer is used to determine mixing time of general purpose PVC. This method determines how a particular type of PVC responds to a particular type of plasticizer. The data in the standard demonstrate that the powder-mix time increases with viscosity of the plasticizer increasing and decreases with temperature of process increasing. 

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