Dry cleaning
Additionally, certain specialty fabrics, including silk and rayon, may also benefit from dry cleaning to prevent damage.
The ancient Greeks and Romans had some waterless methods to clean textiles, involving the use of powdered chemicals and absorbent clay (fuller's earth).
[citation needed] Modern solvent-based dry cleaning may have originated in 1821 with American entrepreneur Thomas L. Jennings.
[2] French dye-works operator Jean Baptiste Jolly[3][a] developed his own method using kerosene and gasoline to clean fabrics.
The use of highly flammable petroleum solvents caused many fires and explosions, resulting in government regulation of dry cleaners.
[citation needed] Early solvents were carbon tetrachloride and trichloroethylene (TCE), but they gradually were phased out as their adverse health effects became more known.
[citation needed] In enclosed machines, solvent extracted during the drying process is recovered and purified by distillation, so it can be reused to clean further loads or safely disposed of.
Most modern enclosed machines also incorporate a computer-controlled drying sensor, which automatically senses when all detectable traces of PCE have been removed.
These stains would otherwise only dissolve in aqueous detergent mixtures at high temperatures, potentially damaging delicate fabrics.
Water binds to these polar groups which results in the swelling and stretching of proteins within fibers during laundering.
Garments are placed in the washing or extraction chamber (referred to as the "basket" or "drum"), which constitutes the core of the machine.
[citation needed] During the wash cycle, the chamber is filled approximately one-third full of solvent and begins to rotate, agitating the clothing.
Machines using hydrocarbon solvents require a wash cycle of at least 25 minutes because of the much slower rate of solvation of solvent-soluble soils.
Modern dry cleaning machines use a closed-loop system in which the chilled air is reheated and recirculated.
In the early days of dry cleaning, large amounts of perchloroethylene were vented to the atmosphere because it was regarded as cheap and believed to be harmless.
[7] To enhance cleaning power, small amounts of detergent (0.5–1.5%) are added to the working solvent, and are essential to its functionality.
Items such as plastic pens may dissolve in the solvent bath, damaging the entire batch of textiles.
Fragile items, such as feather bedspreads or tasseled rugs or hangings, may be protected by enclosing them in a loose mesh bag.
The density of perchloroethylene is around 1.62 g/cm3 at room temperature (62% heavier than water), and the sheer weight of absorbed solvent may cause the textile to fail under typical forces during the spin extraction cycle, unless the mesh bag provides mechanical support.
Some need to be treated with spotting solvents – sometimes by steam jet or by soaking in special stain-remover liquids – before garments are washed or dry cleaned.
It is a highly effective cleaning solvent, and it is thermally stable, recyclable, and has very low toxicity and a pleasant smell.
The toxicity of tetrachloroethylene is moderate to low and reports of human injury are uncommon despite its wide usage in dry cleaning and degreasing.
[9] Tetrachloroethylene is classified as "probably carcinogenic to humans" (Group 2A) by the International Agency for Research on Cancer (IARC).
There is a possibility that it is carcinogenic to humans in long term, but the evidence is limited since most of the evaluated dry-cleaners had heavy smoking and drinking habits.
[10] The exposure to tetrachloroethylene in a typical dry cleaner is considered far below the levels required to cause any risk.
Although hydrocarbons are combustible, risk of fire or explosion can be minimized when they are used properly; a fire-suppression system may also be required.
[7] The CO2 dry cleaning process involves charging a sealed chamber which has been loaded with clothes, using gaseous carbon dioxide from a storage vessel to approximately 200 to 300 psi (14 to 21 bar) of pressure.
A separate sub-cooler reduces the temperature of the carbon dioxide by 2 to 3 °C (3.6 to 5.4 °F) below the boiling point, in an effort to prevent cavitation which could lead to premature degradation of the pump.
[citation needed] To compensate for the poor solubility and conductivity of supercritical carbon dioxide, research has focused on additives.
