Practical 2 ; Sieving

TITLE: 

Sieving

OBJECTIVE :

1. To determine the particle size distribution of the powder materials and the size of solid particles by using the ‘sieve nest’ method.

INTRODUCTION:

                Sieving is the process of classifying powders by particle size distribution. The particle size distribution is defined via the mass or volume. Sieve analysis is used to divide the particulate material into size fractions and the weight of these fractions is determined. The most common media used in sieving is test sieves which are usually round frame, in sizes that range from 3 inches to 18 inches in diameter.

                 A sieve test is performed by first assembling a stack of interlocking sieves. The sieve with the largest openings is at the top and each lower sieve will have a smaller opening than the one above it. A pre-weighed sample of the material to be tested is placed in the top sieve. The sieve stack is shaken until all the materials has either been retained on a sieve or passed through. The material retained in each sieve is weighed and compared to the weight on the other sieves. A sieve test analysis or distribution is calculated which shows the proportion of each particle size category in the sample.

PROCEDURE:

1. 100g of lactose is weighed.
2. The ‘sieve nest’ in ascending order and provided appropriate sieve size is prepared.
3. Lactose powder is put into the sieve.
4. The powder is shaken or sieved in the sieve for about 20 minutes.
5. The results obtained are weighed and the graph of powder particle size distribution is plotted.
6. The process is repeated by using microcrystalline cellulose (MCC).

RESULT:

Sieving for lactose

Diameter of the test sieve (mm)	Amount of lactose obtained after sieving for about 20 minutes (g)
12	0.01600
10	0.02680
8	0.01580
6	30.5680
5	57.4950
3	11.1636

Sieving for microcrystalline cellulose (MCC)

Diameter of the test sieve (mm)	Amount of microcrystalline cellulose obtained after sieving for about 20 minutes (g)
12	0.00350
10	0.00430
8	0.07870
6	4.94850
5	51.8688
3	42.1931

DISCUSSION:

                In this experiment, a ‘sieve nest’ is used to determine the particle size distribution of 100g of lactose and microcrystalline cellulose. After being sieved for about 20 minutes, both lactose and microcrystalline cellulose obtained in each sieves with different diameters are weighed.

                 From the results obtained, it showed that there are small amount of powder obtained in sieve with diameter 12mm which are 0.001600g lactose and 0.000350g of microcrystalline cellulose. It means that the particle size of the powders is not under the range of that size or the powder particles are might be finer than that size. Observing and weighing the other sieves with increasing magnitude of fineness and limited, varying the amount of powder obtained. For lactose, it is said to have the particle size in range of 4mm to 5mm as there is high amount of lactose powder obtained in the sieve with diameter of 5mm which is 57.4950g. For microcrystalline cellulose, it have the same size range with lactose which is at range of 4mm to 5mm.This can be proven as the amount of MCC powder obtained in sieve with diameter 5mm is the highest comparing with other sieves which is about 51.8688g.

QUESTIONS:

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

                   Sieving is one of the oldest methods of classifying powders by particle size distribution. The nest of sieves is subjected to a standardized period of agitation, and then the weight of material retained on each sieve is accurately determined. The test gives the weight percentage of powder in each sieve size range. The selected sieves should be assembled with the coarsest sieve at the top of the stack and the balance of the stack in increasing magnitude of fineness which is increasing sieve numbers with smaller openings. The size parameter involved in determining particle size distributions by analytical sieving is the length of the side of the minimum square aperture through which the particle will pass.

                     Based on both graph plotted for sieving of lactose and MCC, it can be seen that most of both lactose and MCC particles are obtained in the sieve with 5 mm diameter. It indicated that both particles are about having small and finer size which can pass all the sieves with increasing magnitude of fineness and limited until the smallest opening of sieve which is 3 mm.

2. What are the other methods that can be used to evaluate the size of a particle?

                         Other method that can be used to evaluate the size of a particle is laser light scattering or LD technique. In this latter method, the forward diffraction of laser beam by particles is used to determine their size distribution. The angle of diffraction is inversely proportional to particle size, and the intensity of the diffracted beam at any angle is measure of the number of particles with a specific cross- sectional area in the beam’s path. Two optical models are commonly used to calculate the particle size distributions which are the Fraunhofer diffraction model and the Mie theory.

                          Main advantages of LD technique for particle size distribution determination include short time of analysis, high repeatability, small size of sample needed and a wide range of fractions into which the entire range of particle sizes can be divided.

                          The main disadvantages are high cost of LD instruments and insufficient confidence in the results due to the relatively low number of LD analyses of soils as compared with the enormous number of analyses performed by the classical methods.

3. What is the importance of particle size in a formulation?

The particle size distribution of active ingredients and excipients is the most important physical characteristics of materials especially in using them to create pharmaceutical products. The size, distribution and shape of the particles can affect the bulk properties, product performance, process ability, stability and appearance of the end product. The relationship between particle size and product performance is well influenced to the dissolution, absorption rates and content uniformity. Particle size analysis is also important in order to formulate and manufacture many pharmaceutical dosage forms.

CONCLUSION:

                      In conclusion, by using ‘sieve nest’ method, the particle size distribution and size of solid particles of both powders used in this experiment which are lactose and microcrystalline cellulose is in range of 4mm to 5mm.

REFERENCE:

1. http://www.newdruginfo.com/pharmacopeia/usp28/v28230/usp28nf23s0_c786.htm
2. http://www.cscscientific.com/particle-size/sieves/