Dry cleaning (or dry-cleaning) is any cleaning process for clothing and textiles
using an organic solvent rather than water. The solvent used is typically tetrachloroethylene
(perchloroethylene), abbreviated "perc" in the industry and "dry-cleaning fluid"
by the public. Dry cleaning is necessary for cleaning items that would otherwise
be damaged by water and soap or detergent. It is often used instead of hand washing
delicate fabrics, which can be excessively laborious.
Dry cleaning uses non-water-based solvents to remove soil and stains from clothes.
The potential for using petroleum-based solvents in this manner was discovered in
the mid-19th century by French dye-works owner Jean Baptiste Jolly, who noticed that
his tablecloth became cleaner after his maid spilled kerosene (paraffin) on it. He
subsequently developed a service cleaning people's clothes in this manner, which
became known as "nettoyage à sec," or "dry cleaning" in English.
Early dry cleaners used petroleum-based solvents such as gasoline and kerosene. Flammability
concerns led William Joseph Stoddard, a dry cleaner from Atlanta, to develop Stoddard
solvent as a slightly less flammable alternative to gasoline-based solvents. The
use of highly flammable petroleum solvents caused many fires and explosions, resulting
in government regulation of dry cleaners.
After World War I, dry cleaners began using chlorinated solvents. These solvents
were much less flammable than petroleum solvents and had improved cleaning power.
By the mid-1930s, the dry cleaning industry had adopted tetrachloroethylene (perchloroethylene),
colloquially called "perc," as the ideal solvent. It has excellent cleaning power
and is stable, nonflammable, and gentle to most garments. However, perc was also
the first chemical to be classified as a carcinogen by the Consumer Product Safety
Commission (a classification later withdrawn). In 1993, the California Air Resources
Board (CARB) adopted an airborne toxic control measure (ATCM) to reduce perc emissions
from dry cleaning operations. The dry cleaning industry is now[when?] beginning to
replace perc with other chemicals and/or methods. At this time, dry-cleaning was
carried-out in two different machines — one for the cleaning process itself and the
second to dry the garments.
Traditionally, the actual cleaning process was carried-out at centralized "factories";
high street cleaners shops received garments from customers, sent them to the factory,
and then had them returned to the shop, where the customer could collect them. This
was due mainly to the risk of fire or dangerous fumes created by the cleaning process.
This changed when the British dry-cleaning equipment company, Spencer, introduced
the first in-shop machines (which, like modern dry cleaning machines, both clean
and dry in one machine). Though the Spencer machines were large, they were suitably
sized and vented to be fitted into shops. In general, three models, the Spencer Minor,
Spencer Junior, and Spencer Major, were used (larger models, the Spencer Senior and
Spencer Mammoth, were intended for factory use). The cleaning and drying process
was controlled by a punch-card, which fed through the "Spencermatic" reader on the
machine. Also, Spencer introduced much smaller machines, including the Spencer Solitaire
and one simply called the Spencer Dry Cleaning Machine, for use in coin-operated
launderettes. These machines resembled coin-operated tumble dryers; to be as small
as they were, they simply filtered used perc, rather than distilling it like the
commercial Spencer machines. Solvent had to be changed far more frequently as without
distillation, it quickly became discoloured, and could cause yellowing of pale items
being cleaned. A coin-operated version of the Spencer Minor, which automatically
carried out all the distillation and solvent-cleaning operations of the standard
version was available but rarely seen, presumably due to its greater
cost and size than the other coin-operated machines.
During the 1970s and 1980s, Spencer machines were extremely popular, with virtually
every branch of Bollom possessing either a Spencer Minor or a Spencer Junior. Spencer
continued to produce machines (introducing new modular and computer controlled models,
such as the Spencer Sprint series) until the late 1980s, when the company closed.
Spencer machines may still occasionally be seen.
A dry-cleaning machine is similar to a combination of a domestic washing machine,
and clothes dryer. Garments are placed into a washing/extraction chamber (referred
to as the basket, or drum), which is the core of the machine. The washing chamber
contains a horizontal, perforated drum that rotates within an outer shell. The shell
holds the solvent while the rotating drum holds the garment load. The basket capacity
is between about 10 and 40 kg (20 to 80 lb).
During the wash cycle, the chamber is filled approximately one-third full of solvent
and begins to rotate, agitating the clothing. The solvent temperature is maintained
at 30 degrees Celsius (86 degrees Fahrenheit), as a higher temperature may damage
it. During the wash cycle, the solvent in the chamber (commonly known as the 'cage')
is passed through a filtration chamber and then fed back into the 'cage'.
This is known as the cycle and is continued for the wash duration. The solvent is
then removed and sent to a distillation unit comprising a boiler and condenser. The
condensed solvent is fed into a separator unit where any remaining water is separated
from the solvent and then fed into the 'clean solvent' tank. The ideal flow rate
is one gallon of solvent per pound of garments (roughly 8 litres of solvent per kilogram
of garments) per minute, depending on the size of the machine.
Garments are also checked for foreign objects. Items such as plastic pens will dissolve
in the solvent bath and may damage textiles beyond recovery. Some textile dyes are
"loose" (red being the main culprit), and will shed dye during solvent immersion.
These will not be included in a load along with lighter-color textiles to avoid color
transfer. The solvent used must be distilled to remove impurities that may transfer
to clothing. Garments are checked for dry-cleaning compatibility, including fasteners.
Many decorative fasteners either are not dry cleaning solvent proof or will not withstand
the mechanical action of cleaning. These will be removed and restitched after the
cleaning, or protected with a small padded protector. Fragile items, such as feather
bedspreads or tasseled rugs or hangings, may be enclosed in a loose mesh bag. The
density of perchloroethylene is around 1.7 g/cm³ at room temperature (70% heavier
than water), and the sheer weight of absorbed solvent may cause the textile to fail
under normal force during the extraction cycle unless the mesh bag provides mechanical
Many people believe that marks or stains can be removed by dry cleaning. Not every
stain can be cleaned just by dry cleaning. 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. Also, garments stored in soiled condition for
a long time (two months or more) are difficult to bring back to their original color
and texture. Natural fibers such as wool, cotton, and silk of lighter colors should
not be left in dirty or soiled condition for long amounts of time as they absorb
dirt in their texture and are unlikely to be restored to their original color and
A typical wash cycle lasts for 8–15 minutes depending on the type of garments and
degree of soiling. During the first three minutes, solvent-soluble soils dissolve
into the perchloroethylene and loose, insoluble soil comes off. It takes approximately
ten to twelve minutes after the loose soil has come off to remove the ground-in insoluble
soil from garments. 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. A dry-cleaning surfactant "soap" may also be added.
At the end of the wash cycle, the machine starts a rinse cycle wherein the garment
load is rinsed with fresh distilled solvent from the pure solvent tank. This pure
solvent rinse prevents discoloration caused by soil particles being absorbed back
onto the garment surface from the "dirty" working solvent.
After the rinse cycle, the machine begins the extraction process, which recovers
dry-cleaning solvent for reuse. Modern machines recover approximately 99.99% of the
solvent employed. The extraction cycle begins by draining the solvent from the washing
chamber and accelerating the basket to 350 to 450 rpm, causing much of the solvent
to spin free of the fabric. When no more solvent can be spun out, the machine starts
the drying cycle.
During the drying cycle, the garments are tumbled in a stream of warm air (63°C/145°F)
that circulates through the basket, evaporating any traces of solvent left after
the spin cycle. The air temperature is controlled to prevent heat damage to the garments.
The exhausted warm air from the machine then passes through a chiller unit where
solvent vapors are condensed and returned to the distilled solvent tank. Modern dry
cleaning machines use a closed-loop system in which the chilled air is reheated and
recirculated. This results in high solvent recovery rates and reduced air pollution.
In the early days of dry cleaning, large amounts of perchlorethylene were vented
to the atmosphere because it was regarded as cheap and believed to be harmless.
After the drying cycle is complete, a deodorizing (aeration) cycle cools the garments
and removes the last traces of solvent, by circulating cool outside air over the
garments and then through a vapor recovery filter made from activated carbon and
polymer resins. After the aeration cycle, the garments are clean and ready for pressing/finishing.
Working solvent from the washing chamber passes through several filtration steps
before it is returned to the washing chamber. The first step is a button trap, which
prevents small objects such as lint, fasteners, buttons, and coins from entering
the solvent pump.
Over time, a thin layer of filter cake (called muck) accumulates on the lint filter.
The muck is removed regularly (commonly once per day) and then processed to recover
solvent trapped in the muck. Many machines use "spin disc filters," which remove
the muck from the filter by centripetal force while it is back washed with solvent.
After the lint filter, the solvent passes through an absorptive cartridge filter.
This filter is made from activated clays and charcoal and removes fine insoluble
soil and non-volatile residues, along with dyes from the solvent. Finally, the solvent
passes through a polishing filter, which removes any soil not previously removed.
The clean solvent is then returned to the working solvent tank.
To enhance cleaning power, small amounts of detergent (0.5%-1.5%) are added to the
working solvent and are essential to its functionality. These detergents help dissolve
hydrophilic soils and keep soil from redepositing on garments. Depending on the machine's
design, either an anionic or a cationic detergent is used.
Since the solvent recovery is less than 100%, and because dry-cleaning does not remove
water-based stains well, entrepreneurs have developed the wet cleaning process, which
is, in essence, cold-water washing and air drying, using a computer-controlled washer
and dryer. In general, wet cleaning is regarded as being in its infancy, although
low-tech versions of it have been used for centuries.
The international GINETEX laundry symbol for dry cleaning is a circle. It may have
a letter P inside to indicate perchloroethylene solvent, or a letter F inside to
indicate a hydrocarbon solvent. A bar underneath the circle indicates that only mild
cleaning processes should be used. A crossed-out empty circle indicates that no dry
cleaning is permitted.
Cooked Powder Residue — the waste material generated by cooking down or distilling
muck. Cooked powder residue is a hazardous waste and will contain solvent, powdered
filter material (diatomite), carbon, non-volatile residues, lint, dyes, grease, soils,
and water. This material should then be disposed of in accordance with local law.
The waste sludge or solid residue from the still contains solvent, water, soils,
carbon, and other non-volatile residues. Still bottoms from chlorinated solvent dry
cleaning operations are hazardous wastes.
Perc is classified as a hazardous air contaminant by the United States Environmental
Protection Agency and must be handled as a hazardous waste. To prevent it from getting
into drinking water, dry cleaners that use perc must take special precautions against
site contamination. Landlords are becoming increasingly reluctant to allow dry cleaners
to operate in their buildings. When released into the air, perc can contribute to
smog when it reacts with other volatile organic carbon substances. California
declared perchloroethylene a toxic chemical in 1991, and its use will become illegal
in that state in 2023.
Solvents Used in Dry Cleaning
* Glycol ethers (dipropylene glycol tertiary-butyl ether) (Rynex)(Solvair) —
In many cases more effective than perchloroethylene (perc) and in all cases more
environmentally friendly. Dipropylene glycol tertiary butyl ether (DPTB) has a flashpoint
far above current industry standards, yet at the same time possesses a degree of
solvency for water-soluble stains that is at least equivalent to, and in most cases
better than, perc and the other glycol ether dry cleaning solvents presently in commercial
use. A particular advantage of the DPTB-water solutions of the Rynex product in dry
cleaning is that they do not behave like a typical mixture, but, rather, the behavior
is the same as a single substance. This permits a better-defined separation upon
azeotropic distillation at a lower boiling point and also facilitates reclamation
more effectively, at a level of 99% or greater, and also enhances purification using
conventional distillation techniques.
* Hydrocarbon — This is most like standard dry cleaning, but the processes use
hydrocarbon solvents such as Exxon-Mobil’s DF-2000 or Chevron Phillips' EcoSolv.
These petroleum-based solvents are less aggressive than perc and require a longer
cleaning cycle. While flammable, these solvents do not present a high risk of fire
or explosion when used properly. Hydrocarbon also contains volatile organic compounds
(VOCs) that contribute to smog.
* Liquid silicone (decamethylcyclopentasiloxane or D5) — gentler on garments
than Perc and does not cause color loss. Requires a license be obtained to utilize
the property of GreenEarth Cleaning. Though considerably more environmentally friendly,
the price of it is more than double that of perc, and GreenEarth charges an annual
affiliation fee. Degrades within days in the environment to silica and trace amounts
of water and CO2. Produces nontoxic, nonhazardous waste. Toxicity tests by Dow Corning
shows the solvent to increase the incidence of tumors in female rats (no effects
were seen in male rats), but further research concluded that the effects observed
in rats are not relevant to humans because the biological pathway that results in
tumor formation is unique to rats.(170.6 °F/77 °C flash point).
* Modified hydrocarbon blends (Pure Dry)
* Perchloroethylene — In use since the 1940s, perc is the most common solvent,
the "standard" for cleaning performance, and most aggressive cleaner. It can cause
color bleeding/loss, especially at higher temperatures, and may destroy special trims,
buttons, and beads on some garments. Better for oil-based stains (which account for
about 10% of stains) than more common water-soluble stains (coffee, wine, blood,
etc). Known for leaving a characteristic chemical smell on garments. Nonflammable.
* Liquid CO2 — Consumer Reports rated this method superior to conventional methods,
but the Drycleaning and Laundry Institute commented on its "fairly low cleaning ability"
in a 2007 report. Another industry certification group, America's Best Cleaners,
counts CO2 cleaners among its members. Machinery is expensive—up to $90,000 more
than a perc machine, making affordability difficult for small businesses. Some cleaners
with these machines keep traditional machines on-site for the heavier soiled textiles,
but others find plant enzymes to be equally effective and more environmentally sustainable.
CO2-cleaned clothing does not off-gas volatile compounds. CO2 cleaning is also used
for fire- and water-damage restoration due to its effectiveness in removing toxic
residues, soot and associated odors of fire.
* Wet cleaning — A system that uses water and biodegradable soap. Computer-controlled
dryers and stretching machines ensure that the fabric retains its natural size and
shape. Wet cleaning is claimed to clean a majority of "dry clean only" garments safely,
including leather, suede, most tailored woolens, silk, and rayon. (Neckties seem
to be the one exception.) Most perc cleaners use wet cleaning on some garments, but
there are only about 20 exclusive wetcleaners in the U.S.