Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.7 Dry cleaning 885
the dry cleaning operation. Polar contamination, such as, salt, sugar, and most nutrition and
body excrements are not dissolved.
In the same way that water has no cleaning activity with regard to oils, fat, or grease, in
dry cleaning there is no activity with regard to salts, sugar, nutrition and body excrements.
And in the same way that water dissolves these polar substances, cleaning of textiles from
these contaminants does not pose any problems in a washing process.
To make washing active to clean oils, fat and grease from textiles, soap (detergent) has
to be added to water. To make dry cleaning active to clean salts, sugar and the like from textiles,
dry cleaning detergent has to be added to the solvent.
In washing, fresh water is used for the process. After being used, the dirty washing liquid
is drained off. In dry cleaning the solvent is stored in a tank. To be used for cleaning it is
pumped into the dry cleaning machine. After being used, the solvent is pumped back into
the storage tank. To keep the solvent clean it is constantly filtered during the cleaning time.
In addition to this, a part of the solvent is pumped into a distilling vessel after each batch to
be cleaned by distilling.
Dry cleaning solvents are recycled. The solvent consumption in modern machines is
in the range of about 1-2%perweight of the dry cleaned textiles.
14.7.1.3 Behavior of textiles in solvents and water
Fibers used for manufacturing textiles can be classified into three main groups:
• Cellulosic fibers: cotton, linen, rayon, acetate.
• Albumin fibers: wool, silk, mohair, camelhair, cashmere.
• Synthetic fibers: polyamide, polyester, acrylic.
Textiles made from cellulosic fibers and synthetics can be washed without problems.
Apparel and higher class garments are made from wool and silk. Washing very often bears a
high risk. So these kinds of textiles are typically dry cleaned.
Dependent to the relative moisture of the surrounding air fabrics absorb different
quantities of water. The higher the polarity of the the fiber, the higher is their moisture content.
The higher the swelling (% increase of fiber diameter) under moisture influence, the
higher is the tendency of shrinkage in a washing or dry cleaning process.
Table 14.7.1. Water content (%) in textile fibers dependent on relative humidity
Fiber
70
Relative humidity, %
90 max.
Swelling, %
Viscose 14.1 23.5 24.8 115
Wool 15.6 22.2 28.7 39
Silk 11.2 16.2 17.7 31
Cotton 8.1 11.8 12.9 43
Acetate 5.4 8.5 9.3 62
Polyamide 5.1 7.5 8.5 11
Acrylic 2.1 4.0 4.8 9
Polyester 0.5 0.6 0.7 0