Wednesday, May 7, 2008

emulsion in textile formulation

A lot of textile auxillaries used are in the form of emulsions. Emulsions are disperse systems consisting of two (or more) mutually insoluble or sparingly soluble liquids. The liquid present in excess is termed the closed, continuous or external phase, while the liquid dispersed in it is termed the internal or dispersed phase. The preparation of an emulsion is termed emulsification and the agents used for this purpose are termed emulsifiers. Normally the emulsions which are encountered in textile industry are oil in water (o/w) and the vice versa (w/o).

To prepare eumulsion emulsifiers are required. So what is the exact role of emulsifier? The polar (hydrophilic) aqueous phase and the polar (lipophilic) lipid or oil phase of an emulsion cannot be combined stably and homogenously without additives. The surface tension at the interface between these two phases must be reduced by the addition of emulsifiers. Emulsifiers are surface active substances that reduce the surface tension between polar and apolar phases by penetrating into the interface between the oil and the water phase. This occurs because of their amphiphilic molecular structure, i.e. they consist of both hydrophilic (polar) and lipophilic (a polar) molecular regions and are thus soluble in both the hydrophilic and the lipophilic phase.
Whether a w/o or an o/w emulsion is formed depends essentially on the stability of the emulsifier layer surrounding the droplets. If a water stable emulsifier envelope is formed around the oil droplets in a system containing water, oil and emulsifier, an o/w emulsion is produced. On the other hand the formation of an oil-stable envelope around the water droplets produces a w/o emulsion. Thus emulsifying agent should show following properties,
It should be surface active and reduce surface tension to below 10 dyne/cm
It should be adsorbed quickly around the dispersed drops as nonadherent film which will prevent coalescence
impart to the droplets an adequate electric potential so that mutual repulsion occurs
It should increase the viscosity of the emulsion
It should be effective in a reasonably low concentration
be stable
be compatible with other ingredients
be non-toxic

An emulsifier consists of water-soluble hydrophilic parts and water-insoluble, oil-soluble lipophilic parts within its.When an emulsifier is added to a mixture of water and oil, the emulsifier is arranged on the interface, anchoring its hydrophilic part into water and its lipophilic part into oil.
On the interface surface of water and air and of oil and air, the hydrophilic part and the lipophilic part are adsorbed and arranged around the interface. The emulsifier reduces the interfacial tension.That is, the force to separate the oil and water is thus weakened, resulting in the easily mixing of oil and water.

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