INTRODUCTION
Mixing is defined as a process in which two or more components within a system are converted into one mass or mixture. Ideal Mixing indicates that different materials are thoroughly combined to produce homogenous product. Random Mixing is probabilÃty of finding same proportions of componcot in the entire mixture. Ordered Mixing yields the closest situation of the perfect mix and it is achieved by use of mechanical, adhesion or coating force.
TYPES OF MIXTURES
Mixtures can be classified as
a Positive Mixtures:
These are prepared by mixing two miscible liquids. These type of mixtures are casy to prepare.
b. Negative Mixtures:
These mixtures are prepared by mixing insoluble solids in a vehicle in case of suspension or by mixing two immiscible liquids in case of emulsion. These mixture require high degree of energy or external force.
c. Neutral Mixtures:
Some products such as Pastes, ointments etc do not mix spontaneously but after mixing they do not separate out easily. These are called neutral mixtures.
OBJECTIVES OF MIXING
Mixing can be done for the following reasons
1. Mixing is a critical process. The quality of final product depends upon the nature of mixing. Improper Mixing lead to non homogeneous products.
2 Proper Mixing lead to decrease batch cycle times and operational cost.
3. To increase the dissolution or diffusion rate
APPLICATIONS
Mixing is one of the common pharmaceutical operation. There are few examples of large scale Mixing in Pharmacy which are in practice:
a. Mixing is an intermediate step in production of tablet or capsule. Mixing of powders in different proportion prior to granulation or tabletting
b. Dry mixing of materials for direct compression into tablets.
c. Dry mixing of powders & composite powders in capsules and insufflations respectively.,
d. Blending of powders are also important in preparation of cosmetic products such as facial powder or dental powder
e. In case of potentdrugs where dose is low, mixing is critical factor. Otherwise it will affect content uniformity of tablets.
FACTORS AFFECTING MIXING OPERATION
1. Nature of the product:For effective mixing particle surface should be smooth, Rough surface of one or more components lead to increase chances of entry of active substance into the pores of another ingredient and further affect mixing.
2. Particle size:It is easier to mix powders of same particle size. Variation in particle size lead to jmproper mixing Increasing the difference in partfcle size will lead to segregation (size separation), since small particles can fall through the voids between the larger particles
3.Particle shape:The particle should be spherical in shape to achieve uniform mixing.
4. Particle charge:Some particles due to electrostatic charges exert attractive force which lead to separation.
5. Proportion of Material:It is easy to mix powders if available in equal quantities. But to mix small quantities of powders with large quantities of ingredients is difficult process.
6.Relative density:If the components have a different density, the denser material will sink through lighter material, the effect of which will depend on the relative positions of the material in the mixer.
7. Viscosity:The mixing is also affected by the viscosity. An increase in viscosity reduces the extent of mixing. More viscous particles cause poor mixing.
8. Surface tension of lfquids:The surface tension of the liquid is also an important factor affecting the mixing. High surface tension reduces the extent of mixing.
9. Temperature: The temperature also affects the mixing because the viscosity changes with the change of temperature
10. Mixer volume: The volume of the mixin g also affects the mixing phenomena. The blender volume should be such that overfilling should not be done as it decreases the mixing efficiency
11. Agitator type: The shape, size, location and type of agitator also affect the degree of mixing achieved and the time required to mix specific components.
12. Speed / rpm of the impeller: The speed of the impeller affects the homogeneity of the mixing. As mixing at less rpm is more homogeneous than at a higher rpm.
13. Mixing time: The mixing time is also very important for appropriate mixing. There is always an optimal mixing time for the specific conditions in which the mixing is taken place .
TYPE OF MIXING
SOLID-SOLID MIXING
Material having similar physical properties will be easier to form a uniform blend or mixture compared to the difference in properties, It is more difficult to achieve a good mixing of particulate solids of different Sizes and densities. material density, particle size and distribution, wettability, stickiness, particle shape / oughness are the physical properties that affect mixing proces The mechanism involved in solid solid mixing are
Convective Mixing, in which the groups of particles move from one position to another. It is also referred to as macromixing.
Shear Mixing In this, shearing forces are created within the mass of the material by the use of a stiring arm or a burst of air.
Difusive Mixing: During this mixing, gravitational forces cause the upper layers of materials to slip and random motion of the individual particles takes place on newly developed surfaces. This is also sometimes known as micromixing.
LIQUID-LIQUID MIXING
Liquid liquid Mixing require shear to form homogenous system. As compared to solid- liquid mixing. Liquid- liquid mixing is simple in operation.
Type of liquid Mixture
1. Miscible liquids: They mix with each other in all proportion. For example: Mixture of ethanol in water. Their mixing is quite easy and this type of mixing does not create any problem.
2. Partially miscible liquids: These liquids mix with each other at specific proportion. For example: Mixture of P-cresol and water. Their miscibility based on temperature and pressure.
3. Immiscible liquids: They are not miscible. For example: Vegetable oil and water mixture. They form heterogenous mixtures e.g. emulsions. A homogenous dispersion may be obtained by adding emulsifying agents.
if you have any doubts please let me now