PRACTICAL 2: SIEVING

Objective:

To determine particle size distribution of powder and the size of solid particle of lactose and microcrystalline cellulose (MCC) by sieve nest.

Introduction:

Sieving is equipment that used to separate agglomeration, to obtain the distribution of size of certain powders and to determine the size of certain particles.In this experiment, lactose and microcrystalline cellulose (MCC) which are the materials that usually used in the tablets formulation are given to determine their size of particle by using sieving. Stack of sieves have been used with various kind of diameter to obtain the distribution of size particle of the materials and to separate out the different size particles of lactose and MCC.

Apparatus:

Weighing machine, stack of sieves, mechanical sieve shaker.

Materials:

Lactose, microcrystaline cellulose (MCC)

Procedures:

1. 100g of lactose is weighed by using weighing machine.
2. Sieve nests in the order of increasing size and appropriate size of sieving are prepared.
3. Lactose is poured onto the top of sieving nest.
4. The sieving machine is run for 20 minutes.
5. The weights of different sizes of lactose are weighed after the sieving process finished and a graph is plotted for the distribution of size particle of lactose.
6. Step 1-5 are repeated for MCC.

Results:

Size(diameter) of aperture (µm)	Particle size range (µm)	MCC		LACTOSE
		Weight (g)	Frequency (%)	Weight (g)	Frequency (%)
<45	0<x≤45	10.3772	10.4633	5.1906	5.2244
45	45<x≤150	84.1925	84.8912	79.1463		79.6624
150	150<x≤300	4.5058	4.5432	0.1566		0.1576
300	300<x≤425	0.0988	0.0996	13.5843		13.6729
425	425<x≤500	0.0002	0.0002	0.0211		0.0212
500	>500	0.0025	0.0025	1.2533		1.2615

   Total: 99.1770                 Total: 99.3522

 

Discussions:

In this experiment, we observe the process of sieving of two materials which are lactose and also microcrystalline cellulose. We can achieve particles according to various size range using this process. Sieving is typically used when the drug substance is close to the particle size specification, and it can be met by removing the oversized particles. Sieving can also be used to break agglomerates or "de-lump". Most sieve analyses utilize a series, stack or ‘nest’ of sieves, which has the smallest mesh at the bottom and the size of collector become progressively coarse when the collector trays come closer to the top of the stack of sieves.

When prepare a stack of sieves, the sieves having larger opening sizes (i.e lower numbers) are placed above the ones having smaller opening sizes (i.e higher numbers). So, the sieve that have diameter of aperture of 500 µm will be placed at the higher followed by 425 µm, 300 µm, 150 µm, and 45 µm. At the base is a round pan, called the receiver.

Before used the sieves, make sure the sieves are clean, if many soil particles are stuck in the openings try to poke them out using brush. Because this will affect the result of the experiments if this precaution has not been done. To start with this process, powder is put on to the coarsest sieve of the assembled stack and the nest is subjected to mechanical vibration. After a suitable time, the particles are considered to be retained on the sieve nest with according to the sieve diameter.

From the result shown, most of the MCC and lactose fall in the range that less than 150 µm. At the same time, there are more MCC particles that fall in the range of less than 150 µm. This may be due to the physical vibration that exerted on the particles having greater effect on MCC compared to lactose. This is because different materials have different physical properties which include the surface hardness of solids that will influence the reduction of size particles.

Sieve analysis has, in general, been used for decades to monitor material quality based on particle size. A sieve analysis and particle size distribution is accurate and consistent.

            However, for material that is finer than 45 µm, dry sieving can be significantly less accurate. This is because the mechanical energy required to make particles pass through an opening and the surface attraction effects between the particles themselves and between particles and the screen increase as the particle size decreases. Sieve analysis assumes that all particle will be round (spherical) or nearly so and will pass through the square openings when the particle diameter is less than the size of the square opening in the screen. For elongated and flat particles a sieve analysis will not yield reliable mass-based results, as the particle size reported will assume that the particles are spherical, where in fact an elongated particle might pass through the screen end-on, but would be prevented from doing so if it presented itself side-on.

Questions:

1. What are the average particles size of lactose and MCC?

The overall particle size range for MCC and lactose is found within less than 150µm. There are a small portion of MCC and lactose fall in the size category of between 150µm and 500µm.

 

2. Are there any other methods that can be used to determine certain particle size?

The other methods that can be used to determine particle size are microscope methods, coulter counter, laser light scattering method, dynamic light scattering method and sedimentation method.

 

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

The importance of particle size in a certain formulation is to achieve optimum production of efficacious medicines. Particle size can affect a formulation's behaviour during processing and, ultimately, its content uniformity, which is critical. Take, for example, the widespread operation of direct compression tableting; particle size can influence segregation behaviour, the ease with which powder flows through the press and the compressibility of a formulation. In turn, these factors affect the consistency of tablet weight and composition, how the press operates and the mechanical properties of the finished product. Other than that, the particle size of  medicine also influence the disintegration and dissolution rate in the body cavity which will affect the absorption and distribution of the medicine inside the body.

 

Conclusion:

Size of particles can be determined through the sieving process. Different materials have different physical properties which will affect the results of sieving. Sieving can be used to break the agglomerate and separate them from the others. Size of particles will be reduced at the same time.

Pictures:

 

 

100g of lactose and MCC that have been used in this experiment.

Mechanical sieve shaker with a stack of sieve.