SIEVING

DATE: 19 / 11 / 2015

OBJECTIVE

The objectives of the experiment are to determine the percentage of different grain sizes contained within a soil and to determine the distribution of the coarser, larger-sized particles, and the hydrometer method is used to determine the distribution of the finer particles.

INTRODUCTION

Sieves are commonly used to break down agglomerates, and determine the size and size distribution of a particular powder. Sieve nest use to determine the particle size and the size distribution of two common excipients used in table formulations, namely lactose and microcrystalline cellulose (MCC). 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 soil, a wide range of manufactured powders, grains and others, down to minimum size depending on the exact method. Being such a simple technique of particle sizing, it is probably the most common.

MATERIALS

Lactose, Microcrystalline Cellulose (MCC), five different types of sands (150 mc, 355 mc, 500 mc, 850 mc, various sizes)

APPARATUS

Microscope, sieve nest, weighing boat, spatula, balance

PROCEDURE

   Part A

1     1.   100 g of MCC was weighed.
2.      The sieve nest was prepared and arranged in descending order, from the largest diameter to the smallest, from top to bottom.
3.      The MCC was placed at the uppermost sieve and the sieving process proceeded for 10 minutes.
4.      Then, the MCC collected at every sieve was weighed and the particle size distribution was plotted in the form of histogram.
5.      Step 1-4 were repeated by using lactose.

Part B

1. 1.      Using a microscope, 5 different type of sands and powders were analysed.
2. 2.      Size and shape of the particles were analysed.
3. 3.      Shape of particle observed was sketched

RESULT :

Part A

Sieve opening (µm)	Mass of MCC retained in each sieve ( W sieve ,g)	% retained = (W sieve / W total) x 100	Cumulative % retained	% passing = 100% - cumulative % retained
426-500	2.8986	2.8986	2.8986	97.1014
356-425	0.0993	0.0993	2.9979	97.0021
151-355	0.2186	0.2186	3.2165	96.7835
46-150	4.6778	4.6778	7.8943	92.1057
45	58.8006	58.8006	66.6949	33.3051
>45	32.4071	32.4071	99.0820	0.9180

Sieve opening (µm)	Mass of lactose retained in each sieve ( W sieve ,g)	% retained = (W sieve / W total) x 100	Cumulative % retained	% passing = 100% - cumulative % retained
426-500	0.0392	0.0392	0.0392	99.9608
356-425	0.0046	0.0046	0.0483	99.9517
151-355	67.7878	67.7878	67.8361	32.1639
46-150	26.5859	26.5859	94.4220	5.578
45	4.5063	4.5063	98.9283	1.0717
>45	0.2537	0.2537	99.1775	0.8225

Part B

                                                   

Magnification: 4 x 10

Diameter:150 mc

Shapes: Irregular shape and smaller compared to 355 mc.

                                                                                                                     

Magnification:4 x 10

Diameter:355 mc

Shapes: Irregular in shape and smaller than 500mc.

Magnification: 4x10

Diameter: 500 mc

Shapes: Irregular in shape and smaller compared to 850 mc.

Magnification: 4 x10

Diameter:850 mc

Shape: Irregular in shape and large

Magnification: 4 x 10

Type: Various

Shapes: Irregular shape and various size

Magnification: 4 x 10

Type : Lactose

Shape: Fine size

Magnification: 4 x10

Type: Microcrystalline cellulose (MCC)

Shape:Fine size

DISCUSSION:

PART A

The particle-size distribution (PSD) of a powder, or granular material, or particles dispersed in fluid, is a list of values that defines the relative amount, typically by mass, of particles present according to size. PSD of a material can be used in understanding the chemical and physical properties of the materials involved. The most easily understood method of determination is sieve analysis, where powder is separated on sieves of different sizes. In this experiment, particle size distribution of lactose and microcrystalline cellulose is determined by using sieving method.

 Sieve that have diameter of aperture with 500μm will be placed above, followed by 425 µm,   355 µm, 150 µm, 45 µm and less than 45 µm. From the result obtained, the particle size distribution of MCC falls in the range of 45 µm and less than that. At the same time, particle size for lactose also falls in the range between 355 µm and 150 µm. There are many factors that lead to the outcome of the result. Lactose and MCC have two different physical properties It seems that MCC has been affected more than lactose due to the physical vibration that applied on the particles since the hardness surface of particle is the one that contribute to the reduction of particle size.

This experiment also cannot be considered accurate as the weight of lactose and MCC are not totally correct since there is still amount of powder left in the sieves after the process was carried out.  This also affects the result obtained. When transferring the powders be careful not to spill them. Wipe away any excess powders on the weighing machine using a brush before measuring. Make sure the sieves are cleaned by using brush, because if many soil particles are stuck in the openings, this will affects the result of the experiments. The electronic sieving machine also must be set up appropriately so that  no problems occur during sieving process.

 PART B

Microscope method is another excellent technique to analysing the particle size where we can directly look at the comparison of size and shape of the particles. Using a fixed magnification of 40X we analyse the 5 different types of sand with size (150 mc, 355 mc, 500 mc, 850 mc and various sizes), MCC and lactose powder. We found out that the sands have different and very angular shape. The sand with the size of 150 mc has the smallest of particle in comparison with the other sizes(355 mc, 500 mc, 850 mc), while 850 mc of sands sample has the biggest size of particle. The various size of sand sample contains different size from small to big, but have the same irregular shape. For the MCC and lactose powder, the size is very fine. This variation in shape with size affects the size distribution as determined by the microscope.

QUESTIONS:

PART A

What are the average particle size for both lactose and MCC?

It ranges from 45 µm  to 150 µm .

What are the other methods can be used to determine the size of particle?

Other methods that can be used:

-sedimentation method

-microscope method

-dynamic light scattering method

-coulter counter

-laser light scattering method

What is the importance of particle size in a pharmaceutical formulation?

Particle size affects the dissolution rate, absorption and content uniformity. All these will influence the pharmaceutical product efficacy. Therefore, particle size is very important in pharmaceutical formulation

PART B

1)      Explain in brief the various statistical methods that you can use to measure the diameter of a particle.

The projected area diameter is based on a circle of equivalent area to that of the projected image of a particle; the perimeter diameter is based on a circle having the same perimeter as the particle. Unless the particles are unsymmetrical in three dimensions then these two diameters will be independent of particle orientation. Feret’s diameter is determined rom the mean distance between two parallel tangents to the projected outline of the particle. Martin’s diameter is the mean chord length of the projected particle perimeter, which can be considered as the boundary separating equal particle areas. It is also possible to determine the equivalent sphere diameters of particles based on other actors such as volume, surface, sieve aperture and sedimentation characteristics.

CONCLUSION:

The most particle size for lactose is 355 and 150 um , while for MCC , the particle size range is 45 um and less than that .

Different particle have different size and shape. The size of particulate solids is important in achieving optimum formulation and production of efficacious medicines. Size analysis by light microscopy is carried out on two-dimensional images of particles which are generally assumed to be randomly oriented in three dimensions.

REFERENCE:

• Martin,A.N. 2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences.5th Edition. Philadelphia: Lea & Febiger