Handbook of Solvents - George Wypych - ChemTech - Ventech!

886 Kaspar D. Hasenclever
The same absorption of water occurs if textiles are immersed in solvent in a dry cleaning
machine. If the relative humidity in the air space of the cylinder of a dry cleaning machine
is higher, textiles absorb more water. The water content of textiles in solvent is equal
to the water content of textiles in the open air if the relative humidity is the same.
If water additions are given to the dry cleaning solvent in order to intensify the cleaning
effect with regard to polar contamination, then the relative humidity in the air space of
the cylinder of the dry cleaning machine increases. As a result of this, the water content in
the dry cleaned textiles increases, too, so that swelling begins and shrinkage may occur.
Woolen fabrics are particularly sensitive to shrinkage and felting because of the scales
on the surface of the wool fiber. Not only in washing, but also in dry cleaning there is a risk
of shrinkage on woolen garments. This risk is higher when the dry cleaning process is influenced
by water addition. If the relative humidity in the air space of a dry cleaning machine is
more than 70%, shrinkage and felting may occur, if the dry cleaning solvent is
tetrachloroethylene (TCE). In hydrocarbon solvents wool is safe up to 80% relative humidity,
because of the lower density of hydrocarbons compared to TCE, which reduces mechanical
action.
14.7.1.4 Removal of soiling in dry cleaning
“Soiling” means all the contamination on textiles during their use. This contamination is of
very different sources. For cleaning purposes, the easiest way of classification of “soiling”
is by solubility of soiling components. The classification can be done by definition of four
groups:
• Pigments: Substances are insoluble in water and in solvents.
Examples are: dust, particles of stone, metal,
rubber; soot, scale of skin.
• Water soluble material: Examples are: salts, sugar, body excrements, sap
and juice.
• Polymers: Substances are insoluble in solvents but can be
soaked and swell in water. Examples are: starch,
albumin and those containing material such as
blood, milk, eggs, sauce.
• Solvent soluble material: Examples are: oil, fat, grease, wax, resins.
Table 14.7.2 Average soiling of garments (apparel) in Europe
Soil type Proportion, % Solubility Components
Pigments 50 not dust, soot, metal oxides, rub-off, pollen, aerosols
Water soluble 30 water sugar, salt, drinks, body excretions
Polymers 10 water starch, albumin, milk, food
Solvent soluble 10 solvents skin grease, resin, wax, oils, fats
In practice, the situation is not so simple as it seems to appear after this classification.
That is because soiling on garments almost always contains a mixture of different substances.
For example, a spot of motor oil on a pair of trousers consists of solvent soluble oil,
but also pigments of soot, metal oxides and other particles. The oil works as an adhesive for