What is Dry Cleaning
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 supposedly 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 on it. He subsequently developed a service cleaning people's clothes in this manner, which has
became known as "dry cleaning". Early dry
cleaners used petroleum-based solvents, such as petrol 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 War1, 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.
Traditionally, the actual cleaning process was carried-out in centralized factories. High street
Dry Cleaning shops received the garments from customers. They then sent them to the factory to have them
processed (cleaned and pressed), then had them returned to the shop, where the customer could collect them.
This was done mainly due to the risk of fire or dangerous fumes created by the cleaning
Modern Dry Cleaning machines are fully enclosed. In these enclosed machines, solvent recovered
during the drying process is returned, condensed and distilled, so it can be reused to clean further loads,
or safely disposed of. The majority of modern enclosed machines also incorporate a computer controlled drying
sensor, which will automatically sense when all possible traces of perc have been removed from load during
the drying process. This system ensures that only the smallest amount of perc fumes will be released when
opening the door at the end of the cycle. This is further minimized by the use of an exhaust fan causing a
lower pressure inside the cage. This means that when the door is opened the lower pressure inside the cage
causes the air outside to flow into the cage rather than the reverse.
To put the process into simple terms, 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
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 between 20 - 30 degrees Celsius.
On refrigerated machines this temperature can be further lowered to as low as 14degrees Celsius for delicate
fabrics and dyes. 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 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 re-stitched 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 1.6 g/cm³ at room temperature (60% heavier than water),
and the sheer weight of absorbed solvent may cause the textile fibre or fabric to fail under the normal
forces during the extraction cycle unless a mesh bag provides mechanical support.
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 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 finish.
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 or the new Silicone
based “Green Earth” 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) must also be added.
At the end of the wash cycle, the machine can go through a second wash cycle. In the second
wash cycle the garment load is rinsed with
fresh distilled solvent from the pure solvent tank and a detergent is added. This pure solvent wash prevents
discoloration caused by soil particles being absorbed back onto the garment surface from the "dirty" working
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 by both extraction
and evaporation processes. 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. Until this
time the cleaning is done in normal temperature, the solvent is never heated in dry cleaning process. 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 (60-63°C) 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 the high solvent recovery rates and reduced air pollution.
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.
Solvent Processing Processing
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. Modern machines
use "spin disc filters," which remove the muck from the filter by centrifugal force while it is washed with
solvent. 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 re-depositing 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
Cleaning. Fire Retardant. Leather &
Suede Cleaning. Wedding Dress Cleaning. Dry Cleaning Clothing
Alterations and Repairs.