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Solvent Scouring Process | Advantages and Disadvantages of Solvent Scouring

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Solvent Scouring:
Solvent scouring is the treatments of fabrics in organic solvent medium to remove impurities such as lubricating oils and spin finishes. Certain organic solvents will readily dissolve oils fats and waxes and these solvents can be used to purify textiles. Removal of impurities by dissolution is called Extraction.

Suitable Solvents:
It is found that waxes are removed by solvents like chloroform, benzene, carbon tetra chloride etc. But those are not used industries because of their high cost and toxicity. Now a days widely used trichloro ethylene, perchloro ethylene etc.

Solvent Properties:
Boiling Point: Temperature at which solvent is converted from liquid to a gas.
Specific Heat: The amount of energy needed to raise one gram of solvent one degree centigrade (Calories/gram/0C).
Latent Heat of Evaporation: The amount of energy needed to vaporize one gram of solvent (Calories/gram).

Solvent Scouring Process:
There are commercial processes where textiles are cleaned with organic solvents. Fabrics processed this way are said to be "Dry Cleaned". Although not widely used as a fabric preparation step, it is an important way of removing certain difficult to remove impurities, where a small amount of residuals can cause downstream problems. Garment dry-cleaning is more prevalent.

For fabrics that do not have to be desized, solvent scouring is an effective way of removing fiber producer finishes, coning and knitting oils. Knitted fabrics made from nylon, polyester, acetate and acrylics, are particularly amenable to this method of preparation. Wool grease is effectively removed by solvent scouring. Solvent

Extractions are particularly useful in the laboratory for determining the amount of processing oils added to man-made fibers and the residual amounts of oils and waxes left by aqueous scouring. Properly controlled, fabrics can be produced with very little residual matter.
Solvent scouring process
Above figure shows a schematic of a continuous, solvent scouring range. The entire range is enclosed so the vapors are contained and not allowed to escape into the atmosphere. Recovery units are installed on the range to insure that. none of the solvent is allowed to vent to the environment. Usually carbon adsorption towers are use for this. Also a solvent distillation unit is needed to reconstitute the pure solvent and separate the removed contaminants.

The term solvent scouring is also used to describe processes where amounts of organic solvents are added to aqueous scouring formulations to assist in the removal of oils and waxes. This technique is widely used and a more in-depth discussion will be found elsewere. Organic solvents have a number of advantages that make them particularly useful for wax removal.

Advantages and Disadvantages of Solvent Scouring:
Solvents dissolve almost all oils and waxes. They have low liquid surface tensions and quickly and easily wet out and penetrate fabrics with waxes. They are much easier to evaporate than water, requiring less time and energy. On the negative side hydrocarbon solvents are flammable and present explosion hazards.

Most chlorinated solvents are proven or suspect carcinogens and some are known to contribute to atmospheric ozone depletion. Chlorinated hydrocarbons thermally decompose to form phosgene and hydrochloric acids. These decomposition by-products are corrosive to metals and also damage cellulosic fibers. Solvents are expensive so they must be recovered and purified by distillation requiring special equipment. The distillation residue becomes a solid waste disposal problem. Solvents do not aid in the removal of motes, metal ions, starch and other solvent. 
 

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