PRACTICAL 2 : SIEVING

Objective

 To determine the presence of agglomerate, particle size distribution and average size of particles

Introduction

Sieving is used to separate and break up clumps in dry powders by using sieve. Sieve is a device with meshes or perforations through which finer particles of a mixture (as of ashes, flour, or sand) of various sizes may be passed to separate them from coarser ones. 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. 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 pass through the sieves.

Apparatus

Weighing machine, sieve nest, weighing boat

Material

Lactose, microcrystalline cellulose (MCC)

Procedure

1. 100g of lactose is weighed by using weighing machine.
2. Sieve nest is prepared and arranged according to gradual increase in size of nest.
3. The lactose is put into the sieve.
4. Sieving process is started with appropriate speed for 20 minutes.
5. The product inside each sieve nest is weighed after the sieving process.
6. The particle size distribution graph is plotted with the method used
7. The process is repeated by using MCC.

Result

Bil	Size of sieve nests (micrometer)	Weight of small weighing boat (g)	Weight of small weighing boat and lactose (g)	Weight of lactose obtained (g)
1	500	1.9245	3.1778	3.1778 - 1.9245 = 1.2533
2	425	2.0941	2.1152	2.1152 - 2.0941 = 0.0211
3	300	2.1725	15.7568	15.7568 - 2.1725 = 13.5843
4	150	2.1946	2.3512	2.3512 - 2.1946 = 0.1566
5	45	3.1789	82.3252	82.3252 - 3.1789 = 79.1463
6	Base	3.2454	8.4360	8.4360 - 3.2454 = 5.1906

Bil	Size of sieve nests (micrometer)	Weight of small weighing boat (g)	Weight of small weighing boat and MCC (g)	Weight of MCC obtained (g)
1	500	2.2752	2.2777	2.2777 - 2.2752 = 0.0025
2	425	2.0370	2.0372	2.0372 – 2.0370 = 0.0002
3	300	3.1788	3.2766	3.2766 – 3.1788 =  0.0988
4	150	3.2500	7.7558	7.7558 – 3.2500 = 4.5058
5	45	5.6449	89.8374	89.8374 – 5.6449 = 84.1925
6	Base	2.7726	13.1498	13.1498 – 2.7726 = 10.3772

Graph of Weight of Sample against Size of Sieve Nests

Discussion

Sieving is an efficient tool for separating particle according to size of particles. It is used to classified and determines properties of certain sample which have larger overall particle size. From the result above, lactose has more uneven particle size distribution compared to MCC. However both of them have majority particle size distribution at 45µg which is very fine.

There are some errors occurred in this experiment. The samples are exposed to air and may absorb moisture which can affect the particle size distribution. Particle may clump together after absorbing the moisture. Some of the fine particles may form dust and lost which can affect the weight of sample at each sieve nest after sieving.

Precautions should be taken to reduce the errors occurred. The sample should weighted and poured into the sieving machine immediately to minimize the exposure to air. Besides the sieve nests should be left alone for few minutes after vigorous shaking completed to reduce the fine particles come up and diffuse in the air. The fine particles should be settled down first before open up the sieve nest for weighing purpose.

Question

1. What is the overall particle size for lactose and MCC?

Both lactose and MCC have overall particle size of 45µg.

 2.What are the alternative way to determine particle size?

The alternative ways to determine particle size are microscopy, sedimentation techniques, optical and electrical sensing zone method, laser light scattering techniques and surface area measurement techniques.

      3.What are the importance of particle size in formulation?

      The size, distribution and shape of the particles can affect bulk properties, product performance,  flowability, stability, disintegration and dissolution and appearance of the end product.

Conclusion

From this practical, we can know that there are no agglomerates present in the sample, particle size distribution and particle size can be determined by using sieving method.