Application Note using:
Influence of flowing agents addition on
Granular materials and fine powders are widely used in industrial applications. To control and to optimize processing methods, these materials have to be precisely characterized.
The characterization methods are related either to the properties of the grains (granulometry, morphology, chemical composition, …) and to the behaviour of the bulk powder (flowability, density, blend stability, electrostatic properties, …).
However, concerning the physical behaviour of bulk powder, most of the techniques used in R&D or quality control laboratories are based on old measurement techniques.
During the last decade, we have updated these techniques to meet the present requirements of R&D laboratories and production departments.
In particular, the measurement processes have been automatized and rigorous initialization methods have been developed to obtain reproducible and interpretable results.
Moreover, the use of image analysis techniques improves the measurements precision.
A range of measurement methods has been developed to cover all the needs of industries processing powders and granular materials.
However, in this application note, we will be focused on the GranuFlow instrument.
The GranuFlow is an improved laboratory silo compared to the ancient Hall Flow Meter (ASTM B213, ISO4490) and compared to the “Flow Through An Orifice” method described in the Pharmacopeia (USP1174).
The GranuFlow is a straightforward powder flowability measurement device composed of a silo with different apertures associated with a dedicated electronic balance to measure the flowrate.
This flowrate is computed automatically from the slope of the mass temporal evolution measured with the balance.
The aperture size is modified quickly and easily with an original rotating system.
The measurement and the result analysis are assisted by software.
The flowrate is measured for a set of aperture sizes to obtain a flow curve.
Finally, the whole flow curve is fitted with the well-known Beverloo theoretical model to obtain a flowability index (Cb, related to the powder flowability) and the minimum aperture size to obtain a flow (Dmin) (for theoretical background, user can refer to Appendix 1).
The whole measurement is performed easily, quickly and precisely.
In this paper, we used a complete set of hole diameters: 4, 8, 12, 18, 22 and 28mm.
The excipient used during this application note is called Pharmatose 200M and was provided by DFE Pharma. This is a pharmaceutical α-lactose monohydrate and it is mechanically milled. Because of its fine nature, milled lactose got a very poor flowability, but its relatively high surface area means that it is highly compactable.
Milled lactose is therefore used primarily in wet granulation applications for tablets and capsules and for spheres made by extrusion-spheronisation.
To increase the flowing behaviour of this excipient, four different flowing agents were selected: Sipernat® 500LS and 50S which are hydrophilic amorphous silica and two hydrophobic amorphous silica called Sipernat® D10 and D17. All those products were provided by the Evonik industry.
All measurements were carried out by the LRGP (Laboratoire Réactions et Génie des Procédés – University of Lorraine, Nancy, France) by Assia Saker under the guidance of Pr. Philippe Marchal and Pr. Veronique Falk.
The GranuFlow analysis were performed at 20.7°C and 34.7%RH.
The Mass Flowrate was investigated for different hole size (from 4mm to 28mm).
F is the powder flowrate (in g/s) and Cb the Beverloo parameter (in g/cm3).
Dmin is the minimum aperture size to obtain a flow (for more information about the Beverloo model, please refer to Appendix 1).
A mixture of 0.5, 1 and 2% of each flowing agent additive was studied during this application note.
Firstly, it is worth noting that the virgin Pharmatose 200M powder (without flowing agent) is unable to pass through any aperture.
Therefore no experimental results can be presented for this sample.
However, with the help of flowing agents, blends flowability can be measured with the GranuFlow. The corresponding Cb and Dmin parameters are also displayed. However, for a mass fraction of 0.5% of 500 LS and D17 flowing agents, only two holes allow the powder to flow, thus it is important to be careful about the given Cb and Dmin parameters.
Indeed, since the Beverloo Law is a fitting model, the determination of those parameters with only two points can be difficult to achieve.
The following table summarize all the calculated Cb and Dmin parameters for the Pharmatose 200M powders with flowing agents addition:
For Sipernat® 500 LS, D10 and D17 addition, the more flowing agent percentage (until 2%), the better flowability (if the Beverloo regressions with two points are not taken into account).
However, for Pharmatose 200M with Sipernat® 50S additive, a significative flowability improvement is achieved with an addition of 2% of flowing agent. Indeed, 0.5 and 1% additions yield to similar results.
The GranuFlow instrument is able to quantify powder flow ability and flowing agents addition influence easily.
The mass flow rate versus the aperture size charts can serve this purpose.
With the Beverloo model fitting available with its software, the GranuFlow can provide information on powders flowability (with the Cb parameter) and on powders cohesion (with de Dmin parameter).
All the measurements are fast (less than five minutes for one powder, with raw data and Beverloo parameters).
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