Title: Sieving
Aims:
To determine the distribution of particles size
of lactose and microcrystalline cellulose (MCC) by sieving analysis.
Introduction:
A sieve analysis is a practice or procedure used to assess the particle size distribution of a granular material. The size
distribution is often of critical importance to the way the material performs
in use. A sieve analysis can be performed on any type of non-organic or organic
granular materials including sands, crushed rock, clays, granite, feldspars,
coal, soil, a wide range of manufactured powders, grain and seeds, down to a
minimum size depending on the exact method. Being such a simple technique of
particle sizing, it is probably the most common. A sieve analysis is performed
on a sample of aggregate in a laboratory. A typical sieve analysis involves a
nested column of sieves with wire mesh cloth. A representative weighed sample is poured
into the top sieve which has the largest screen openings. Each lower sieve in
the column has smaller openings than the one above. At the base is a round pan,
called the receiver. The column is typically placed in a mechanical shaker. The
shaker shakes the column, usually for some fixed amount of time. After the
shaking is complete the material on each sieve is weighed. The weight of the
sample of each sieve is then divided by the total weight to give a percentage
retained on each sieve.
The
results of this test are used to describe the properties of the aggregate and
to see if it is appropriate for various civil engineering purposes such as
selecting the appropriate aggregate for concrete mixes and asphalt mixes as
well as sizing of water production well screens. The results of this test are
provided in graphical form to identify the type of gradation of the aggregate.
A suitable sieve size for the aggregate should be selected and placed in order
of decreasing size, from top to bottom, in a mechanical sieve shaker. A pan
should be placed underneath the nest of sieves to collect the aggregate that
passes through the smallest. The entire nest is then agitated, and the material
whose diameter is smaller than the mesh opening passes through the sieves.
After the aggregate reaches the pan, the amount of material retained in each
sieve is then weighed. In order to perform the test, a sample of the aggregate
must be obtained from the source. To prepare the sample, the aggregate should
be mixed thoroughly and be reduced to a suitable size for testing. The total
weight of the sample is also required.
Chemicals
and materials:
100g
of lactose, 100g of MCC, weighing boats, analytical balance
Procedures:
1.
100g of lactose is weighed
using analytical weighing machine.
2.
‘Sieve nests’ are prepared
with the smallest mesh above a collector tray followed by meshes get
progressively coarser towards the top of the series.
3.
100g of lactose is loaded
on the coarsest sieve.
4.
Then it is subjected to
mechanical vibration for 20 minutes.
5.
After 20 minutes, the
amount of lactose remained in each mesh of different sizes are weighed and a
graph of particle size distribution of the lactose powder is plotted.
6.
Steps 1-5 are repeated
using MCC.
Results
and calculations:
|
Size (diameter) of aperture (µm)
|
Particle size range (µm)
|
MCC
|
Lactose
|
||
|
Weight
(g)
|
Frequency
(%)
|
Weight
(g)
|
Frequency
(%)
|
||
|
<45
|
0<x≤45
|
10.3772
|
10.3772/99.1770 x 100% = 10.4633
|
5.1906
|
5.1906/99.3522 x 100% = 5.2244
|
|
45
|
45<x≤150
|
84.1925
|
84.1925/99.1770 x 100% = 84.8912
|
79.1463
|
79.1463/99.3522 x 100% = 79.6624
|
|
150
|
150<x≤300
|
4.5058
|
4.5058/99.1770 x 100% = 4.5432
|
0.1566
|
0.1566/99.3522 x 100% = 0.1576
|
|
300
|
300<x≤425
|
0.0988
|
0.0988/99.1770 x 100% = 0.0996
|
13.5843
|
13.5843/99.3522 x 100% = 13.6729
|
|
425
|
425<x≤500
|
0.0002
|
0.0002/99.1770 x 100% = 0.0002
|
0.0211
|
0.0211/99.3522 x 100% = 0.0212
|
|
500
|
>500
|
0.0025
|
0.0025/99.1770 x 100% = 0.0025
|
1.2533
|
1.2533/99.3522 x 100% = 1.2615
|
Total: 99.1770 Total: 99.3522
Graph of distribution of the particle size of
lactose and MCC
Discussion:
Based on this experiment, we can know the distribution
of particle size of lactose and also microcrystalline cellulose. Particles can
be classified into various sizes due to the pattern of particle size
distribution. Sieving can remove the oversized particles by breaking the
agglomerates or the lump in the particles. There might be some errors occur in
this experiment. One of the error is the weight of the particles remain after
vibration is not taken into the weighing boat carefully and this cause some of
the fine particles lost during the transfer from the mesh to the weighing boat
which could affect the result obtained. Supposingly, the particles should be
transfer using a paper or tissue paper rather than using the bare hands to
minimize the lost of powder formed.
From the result obtained, most of the MCC and
lactose fall in the range that less than 150 micrometer. But there are a little
bit more MCC particles that fall in that range if compared to lactose. This may
be due to the physical vibration that exerted on the particles having greater
effect on MCC compared to lactose. Different materials have different physical
properties. For example, the surface hardness of a particle molecule can
influence the reduction of size particles.
Questions:
1.
What are the overall
particle size for lactose and MCC?
The overall particle size range for MCC and
lactose is found within the range that less than 150 micrometer. There is a
small peak in the pattern of the graph of lactose that is less than 425
micrometer
2.
What are the other methods
can be used to analyze the size of a particle?
By using microscope method, coulter
counter,laser light scattering method, dynamic light scattering method and
sedimentation method.
3.
What are the importance of
particle size in a formulation?
Particle size of the active pharmaceutical ingredient and
inert excipients are to be considered in formulation as
it is influencing the proceessability, stability, bioavailability and efficacy
of drug delivery system. Reducing particle size can aid the formulation of new chemical entity’s
with poor water solubility . Conventional solid
dosage forms such as tablets are administered orally for local and systemic
action. The local activity (acid neutralizing capacity) attributed by antacid
formulations is proportional to the particle size. Particle size has a pronounced effect on the
absorption of drugs with low aqueous solubility. This was demonstrated with
tablets, capsules, suspensions and suppository dosage forms.
Conclusion:
The distribution of the size particles of lactose and MCC
can be determined through the sieving process. Different materials have
different physical properties produce different patterns of graph of
distribution of particle size. Sieving can be used to break down the lumps
contained in the particles and this will reduce the sizei of particles.
Reference:
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