Shenyang Pharmaceutical Univeristy
LAB 18: POWDER FLOWABILITY
PHARMACEUTICS III
LABORATORY 18: Measurement of powder flowability
1. LABORATORY OBJECTIVES
a) To learn different methods for determining powder flowability and factors influencing
powder flowability.
b) To learn methods for improving powder flowability.
2. INTRODUCTION
A powder is composed of a large number of individual solid particles. A powder for
pharmaceutical applications usually has a particle size in the range of 1 μm and 10 mm.
Micromeritic properties of different powders can be distinctively different because the
particles in the powder can be different in particle shape and size, as well as the frictional
force and adhesive force between the particles. Micromeritic properties of a powder could
be divided into two main categories:
Primary properties include the properties of individual particles such as particle shape,
size, size distribution, and particle density.
Secondary properties are the properties of the powder such as powder flowability,
packability, bulk density, and compressibility/compactability.
Powder flowability is an important property which must be controlled for the
preparation of solid dosage forms. It can not only affect the preparation procedures, but
also affect the quality of the final products such as weight variation and content uniformity.
This experiment is mainly designed to investigate powder flowability and the factors
influencing this specific property.
Depending on the forces causing the flow of a powder, powder flow can be classified
as gravitational flow, vibrational flow,
compressing flow, and fluidizing flow.
Angle of repose and flow rate are the
methods
for
characterizing
gravitational flow of a powder and
can be used to assess how well a
powder will flow through a hopper,
the flow pattern in a rotary mixer and
the ease of capsule filling.
Figure 1. A measuring device for angle of repose
based on the fixing cone method.
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LAB 18: POWDER FLOWABILITY
Shenyang Pharmaceutical Univeristy
PHARMACEUTICS III
Angle of repose is the maximum angle formed between a horizontal plane and the
slope of a powder pile under a statically balanced condition. The angle of repose can be
measured by the fixing funnel method, the fixing conical bottom method, the sloping box
method, the evacuation method, and the rotating
cylinder method. The fixing cone method (also
named the residual cone method) is the most
commonly used method for measuring the angle
of repose of a powder as shown in Figure 1.
With the buffering action from the two funnels
on top of each other, the powders will fall onto
the center of a round plate with a specific
diameter. The powder flows down from the
funnel and forms a cone. When the powder
starts filling over the edge of the round plate,
stop pouring the powder and measure the angle
of repose formed between the slope of the cone
and the plate.
Flow rate of a powder is determined by
measuring the time required for a specified
Figure 2. Measuring device for flow
quantity of powder flowing out of a funnel with
rate measurement.
a specific orifice. If the powder flowability is
poor and the powder fails to produce a constant
flow from the funnel, some glass spheres with a size of 100 μm in diameter can be added
to facilitate powder flow. Measure the minimum number of glass beads needed for the
powder to flow; the larger amount of glass beads needed, the poorer is the flowability of
the powder. The measuring device is shown in Figure 2.
Compressibility (压缩度) of a powder represents powder flow properties under
vibrational conditions and can be used to assess the powder performance under different
processing conditions in a vibrational mode such as compounding, sieving, and filling. The
tapping device is shown in Figure 3.
Compressibility is calculated by using the following equation:
C
 f  0
 100%
f
where, ρf —final tapped density， ρ0 —initial bulk density. Practically, the flowability of a
powder is judged to be good when the compressibility is less than 20% ,whereas a poor
powder flowability is indicated when the compressibility value is about 40%～50%.
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LAB 18: POWDER FLOWABILITY
PHARMACEUTICS III
Figure 3. Tapping device
量筒
固定螺丝
计数器
刻度
measuring cylinder
Fixing screw
counter
scale
电机
操作按钮
电源
Electrical motor
Switch
Power source
3. METHODS
3.1 Measurement of angle of repose
3.1.1 Materials
Microcrystalline cellulose (MCC) powder, MCC spherical particle, lactose, talc,
aerosil, and magnesium stearate.
3.1.2. Sample preparation
a) Weigh 20 g of MCC powder and MCC spherical particle respectively. Measure the
angle of repose and compare the effect of shape and size of the particles on the angle
of repose.
b) Weigh three different portions of 15 g MCC powder (or lactose) and mix each
portion with 1% talc, 1% aerosol and 1% magnesium stearate, respectively. After
mixing by using the geometric dilution method, measure the angle of repose of each
sample. The lubricating efficiency of different lubricants can be compared based on
the angle of repose obtained for the samples.
c) Weigh 25 g of MCC powder and divide the powder into 5 parts with 0.2%, 1%, 2%,
5%, 10% talc added to samples respectively. After mixing, measure the angle of
repose and compare the effect of glidant concentration on the flowability of the
powder. Construct a graph with the angle of repose as the Y-axis and amount of
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LAB 18: POWDER FLOWABILITY
PHARMACEUTICS III
glidant as the X-axis.
3.1.3 Measurement procedures
Make sure that the powder falls onto the center of the round plate slowly and evenly,
resulting in the formation of a pile of powder in a cone shape. When the powder starts to
fall freely over the edge of the round plate, measure the angle of repose by a conimeter or
calculate the angle of repose using the equation, tanθ=h/r with the measurement of the
radius of the round plate (r) and the height (h) of powder cone pile.
3.2 Measurement of flow rate
3.2.1 Materials
MCC powder, MCC spheres, and starch.
3.2.2 Sample preparation
a) Weigh 15g of MCC powder, MCC spheres, and corn starch respectively.
Measure
their flow rate and determine the effect of particle shape and size on the flow rate of
different samples.
b) Glass beads with a size of 100 μm are mixed with the MCC powder or starch to
improve powder flow. Compare the number of glass beads added to achieve the
same flow rate.
3.2.3 Measurement procedures
Test materials are loaded into the device for flow rate measurement (or a triangle
funnel), open the outlet of the bottom funnel and measure the time for all the material
flowing out from the device.
3.3 Measurement of compressibility
3.3.1 Materials
MCC powder, MCC spheres, and starch
3.3.2. Sample preparation
Weigh 15 g of MCC powder, MCC beads, and starch, respectively and measure the
compressibility of these samples to compare the vibrational flowability of different
materials with different particle shapes and sizes.
3.3.3 Measurement procedures
Accurately weigh different test materials and add each material into the cylinder gently,
measure the volume, and calculate the initial bulk density. Start the tapping machine until
the volume of the material is not changing. Measure the final volume and calculate the
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Shenyang Pharmaceutical Univeristy
LAB 18: POWDER FLOWABILITY
PHARMACEUTICS III
tapped density. Compressibility is calculated using the equation shown above.
4. RESULTS AND DISCUSSION
4.1 Examine the particle size and shape of the powder under microscope and determine the
effects of these two variables on powder flowability.
4.2 Determine the influence of glidant type and amount on powder flowability.
4.3 Determine the difference in flowability for different materials.
4.4 What is the main cause for the different flowabilities determined for different
materials?
5. QUESTIONS
a) How can the particle size and shape affect powder flowability?
b) Why will a glidant reduce the powder flowability when an excessive amount is
added?
c) Which glidant is the most effective and why?
References
[1] M.J.Rhodes, Principles of powder technology, John Wiley and Sons,
Chichester-New York, 1995.
[2] D.Chulia, M.Deleuil,Y. Pourcelot. Powder technology and pharmaceutical
processes, Elservier, Amsterdam-London, 1994.
[3] Gran Alderborn, Christer Nystrm. Phamaceutical powder compaction
technology.Marcel Dekker,Inc., New York·Basel,1995.
(Fude CUI)
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