Dry cleaning
Encyclopedia
Dry cleaning is any cleaning process for clothing
and textile
s using a chemical solvent
other than water
. The solvent used is typically tetrachloroethylene
(perchloroethylene), abbreviated "perc" in the industry and "dry-cleaning fluid" by the public. It is often used instead of hand washing delicate fabrics, which can be excessively laborious.
used ammonia
(derived from urine
) and fuller's earth
to launder their woolen toga
s. Fullonicae were very prominent industrial facilities, with at least one in every town of any notability, and frequently the largest employer in a district. These laundries obtained urine from farm animals, or from special pots situated at public latrines. The industry was so profitable that fuller's guilds were an important political constituency, and the government taxed the collection of urine.
Modern 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
on it. He subsequently developed a service cleaning people's clothes in this manner, which became known as "nettoyage à sec," or "dry cleaning".
Early dry cleaners used petroleum-based solvents, such asgasoline (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 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(a classification later withdrawn).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
adopted regulations to reduce perc emissions from dry cleaning operations. The dry cleaning industry is in the process of replacing perc with other chemicals and/or methods.
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. 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.
Machines of this era were called vented; their fumes and drying exhausts were expelled to the atmosphere, in the same way as with modern tumble dryer exhausts. This not only contributed to environmental contamination, but also much potentially reusable perc was lost to the atmosphere. Much stricter controls on solvent emissions have ensured that all dry cleaning machines in the western world are now fully enclosed, and no solvent fumes are vented to the atmosphere. In 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 the 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.
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' or 'tackle box') 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 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 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. 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/140-145°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.
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 centrifugal 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.
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.
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. A recent study conducted at Georgetown University shows Perc is retained in dry-cleaned clothes and that levels increase with repeat cleanings.
Some alternatives such as CO2 offers a solution to perc, however CO2 is inferior in removing some forms of grime.
's Dryel, allow elements of the dry cleaning process to be performed in the household using home laundry machines. Though not the complete process that would be performed by a professional dry cleaner, they allow the convenience of home laundry and work for certain types of garments.
Clothing
Clothing refers to any covering for the human body that is worn. The wearing of clothing is exclusively a human characteristic and is a feature of nearly all human societies...
and textile
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...
s using a chemical solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
other than water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. The solvent used is typically tetrachloroethylene
Tetrachloroethylene
Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...
(perchloroethylene), abbreviated "perc" in the industry and "dry-cleaning fluid" by the public. It is often used instead of hand washing delicate fabrics, which can be excessively laborious.
History
The ancient RomansRoman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
used ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
(derived from urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
) and fuller's earth
Fuller's earth
Fuller's earth is any non-plastic clay or claylike earthy material used to decolorize, filter, and purify animal, mineral, and vegetable oils and greases.-Occurrence and composition:...
to launder their woolen toga
Toga
The toga, a distinctive garment of Ancient Rome, was a cloth of perhaps 20 ft in length which was wrapped around the body and was generally worn over a tunic. The toga was made of wool, and the tunic under it often was made of linen. After the 2nd century BC, the toga was a garment worn...
s. Fullonicae were very prominent industrial facilities, with at least one in every town of any notability, and frequently the largest employer in a district. These laundries obtained urine from farm animals, or from special pots situated at public latrines. The industry was so profitable that fuller's guilds were an important political constituency, and the government taxed the collection of urine.
Modern dry cleaning uses non-water-based solvents to remove soil and stains from clothes. The potential for using petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
-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
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
on it. He subsequently developed a service cleaning people's clothes in this manner, which became known as "nettoyage à sec," or "dry cleaning".
Early dry cleaners used petroleum-based solvents, such as
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
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
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, dry cleaners began using chlorinated
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
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
Tetrachloroethylene
Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...
(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
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
by the Consumer Product Safety Commission
Consumer Product Safety Commission
The United States Consumer Product Safety Commission is an independent agency of the United States government created in 1972 through the Consumer Product Safety Act to protect "against unreasonable risks of injuries associated with consumer products." The CPSC is an independent agency that does...
(a classification later withdrawn). In 1993, the California Air Resources Board
California Air Resources Board
The California Air Resources Board, also known as CARB or ARB, is the "clean air agency" in the government of California. Established in 1967 in the Mulford-Carrell Act, combining the Bureau of Air Sanitation and the Motor Vehicle Pollution Control Board, CARB is a department within the...
adopted regulations to reduce perc emissions from dry cleaning operations. The dry cleaning industry is in the process of replacing perc with other chemicals and/or methods.
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. 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.
Machines of this era were called vented; their fumes and drying exhausts were expelled to the atmosphere, in the same way as with modern tumble dryer exhausts. This not only contributed to environmental contamination, but also much potentially reusable perc was lost to the atmosphere. Much stricter controls on solvent emissions have ensured that all dry cleaning machines in the western world are now fully enclosed, and no solvent fumes are vented to the atmosphere. In 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 the 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.
Process
Washing machine
A washing machine is a machine designed to wash laundry, such as clothing, towels and sheets...
, and clothes dryer
Clothes dryer
A clothes dryer or tumble dryer is a household appliance that is used to remove moisture from a load of clothing and other textiles, generally shortly after they are cleaned in a washing machine....
. 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' or 'tackle box') 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
Normal force
In mechanics, the normal force F_n\ is the component, perpendicular to the surface of contact, of the contact force exerted on an object by, for example, the surface of a floor or wall, preventing the object from penetrating the surface.The normal force is one of the components of the ground...
during the extraction cycle unless the 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 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
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
"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. 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/140-145°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.
Solvent processing
Working solvent from the washing chamber passes through several filtrationFiltration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
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
Filter cake
A filter cake is formed by the substances that are retained on a filter. The filter cake grows in the course of filtration, becomes "thicker" as particulate matter is being retained. With increasing layer thickness the flow resistance of the filter cake increases. After a certain time of use the...
(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 centrifugal 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
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
(0.5%-1.5%) are added to the working solvent and are essential to its functionality. These detergents help dissolve hydrophilic
Hydrophile
A hydrophile, from the Greek "water" and φιλια "love," is a molecule or other molecular entity that is attracted to, and tends to be dissolved by water. A hydrophilic molecule or portion of a molecule is one that has a tendency to interact with or be dissolved by, water and other polar substances...
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
Wet cleaning
Wet cleaning is the safest method in garment cleaning, utilizing gentle washing machine, biodegradable soaps and conditioners, and various types of pressing and re-shaping equipments that may be specialized for many different fabric and fiber types...
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.
Symbols
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 muck
Cooked Powder Residue — the waste material generated by cooking down or distilling muck. Cooked powder residue is a hazardous wasteHazardous waste
A hazardous waste is waste that poses substantial or potential threats to public health or the environment. According to the U.S. environmental laws hazardous wastes fall into two major categories: characteristic wastes and listed wastes.Characteristic hazardous wastes are materials that are known...
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.
Sludge
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.Environment
Perc is classified as carcinogenic to humans by the United States Environmental Protection AgencyUnited States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
and must be handled as a hazardous waste
Hazardous waste
A hazardous waste is waste that poses substantial or potential threats to public health or the environment. According to the U.S. environmental laws hazardous wastes fall into two major categories: characteristic wastes and listed wastes.Characteristic hazardous wastes are materials that are known...
. 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
Smog
Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...
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. A recent study conducted at Georgetown University shows Perc is retained in dry-cleaned clothes and that levels increase with repeat cleanings.
Some alternatives such as CO2 offers a solution to perc, however CO2 is inferior in removing some forms of grime.
Modern
- Glycol etherEtherEthers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
s (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. - HydrocarbonHydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
— This is most like standard dry cleaning, but the processes use hydrocarbon solvents such as Exxon-Mobil’s DF-2000 or Chevron PhillipsChevron PhillipsChevron Phillips is a chemical producer jointly owned by Chevron Corporation and ConocoPhillips. The company was formed July 1, 2000 by merging the chemicals operations of both Chevron Corporation and Phillips Petroleum Company. A 50/50 venture, the company continues to be governed by a board of...
' EcoSolv. These petroleumPetroleumPetroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
-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 siliconeSiliconeSilicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
(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 CleaningGreenEarth CleaningGreenEarth Cleaning is a patented process for drycleaning using liquid silicone , a clear, odorless, non-toxic solvent solution in a closed loop system. D5 degrades into silica and trace amounts of water and carbon dioxide within days if spilled or disposed of...
. 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. A recent study conducted at Georgetown University shows perc, classified as carcinogenic to humans by the EPA, is retained in dry-cleaned clothes and that levels increase with repeat cleanings.
- Liquid CO2Supercritical carbon dioxideSupercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.Carbon dioxide usually behaves as a gas in air at STP or as a solid called dry ice when frozen...
— Consumer ReportsConsumer ReportsConsumer Reports is an American magazine published monthly by Consumers Union since 1936. It publishes reviews and comparisons of consumer products and services based on reporting and results from its in-house testing laboratory. It also publishes cleaning and general buying guides...
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. The environmental impact is very low; Carbon dioxide is almost entirely nontoxic, it does not persist in clothing or in the environment, and its greenhouse gas potential is lower than that of many organic solvents. - Wet cleaningWet cleaningWet cleaning is the safest method in garment cleaning, utilizing gentle washing machine, biodegradable soaps and conditioners, and various types of pressing and re-shaping equipments that may be specialized for many different fabric and fiber types...
— 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 rayonRayonRayon is a manufactured regenerated cellulose fiber. Because it is produced from naturally occurring polymers, it is neither a truly synthetic fiber nor a natural fiber; it is a semi-synthetic or artificial fiber. Rayon is known by the names viscose rayon and art silk in the textile industry...
. (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.
Historical
- Carbon tetrachlorideCarbon tetrachlorideCarbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
— Highly toxic. - Trichloroethane1,1,1-TrichloroethaneThe organic compound 1,1,1-trichloroethane, also known as methyl chloroform, is a chloroalkane. This colourless, sweet-smelling liquid was once produced industrially in large quantities for use as a solvent...
— Overly aggressive and harsh. - Stoddard solvent — Very flammable and explosive, 100°F/38°C flash pointFlash pointThe flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a flash point requires an ignition source...
. - CFC-113 - Freon — Ozone destroying CFCChlorofluorocarbonA chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...
.
Home dry cleaning
Various commercial products on the marketplace today, such as Procter & GambleProcter & Gamble
Procter & Gamble is a Fortune 500 American multinational corporation headquartered in downtown Cincinnati, Ohio and manufactures a wide range of consumer goods....
's Dryel, allow elements of the dry cleaning process to be performed in the household using home laundry machines. Though not the complete process that would be performed by a professional dry cleaner, they allow the convenience of home laundry and work for certain types of garments.
External links
- Dry clean only? Article about exceptions to "dry clean only" labels.
- Hazard Summary provided by the United States Environmental Protection Agency.
- How stuff works article on how dry cleaning works.
- How stuff works article on how home dry cleaning works.
- NIOSH Safety and Health Topic: Drycleaning
- Perchloroethylene on PERC and environmental issues.
- Solvents in Europe
- Chemicals used in Dry Cleaning
- Professional Laundry Systems Wet Cleaning system - Lagoon
- http://yosemite.epa.gov/opa/admpress.nsf/0/B8D0E4D8489AD991852579190058D6C3
- http://www.georgetown.edu/story/dry-cleaning-study.html
- http://onlinelibrary.wiley.com/doi/10.1002/etc.665/abstract