Dry cleaning is a cleaning process for clothing and textiles using chemical solvents other than water. It is used for cleaning degraded fabrics in water, and soft fabrics that can not withstand rough and fall from clothes washer and dryer. Can eliminate hand-washed labor intensive.
Unlike its name, dry cleaning is not a "dry" process. Clothing is soaked in solvents other than water. Tetrachloroethylene (perchloroethylene), by industry called "perc", is the most widely used solvent. Alternative solvents are trichlorethane and petroleum spirits.
Video Dry cleaning
Histori
The use of modern dry cleaning of non-aqueous solvents for soil removal and stain from clothing was reported as early as 1855. The potential of petroleum-based solvents was recognized by French dye operator Jean Baptiste Jolly, who offered a new service known as nettoyage ÃÆ' sec - that is, dry cleaning. Flammability caused William Joseph Stoddard, a dry cleaner from Atlanta, to develop Stoddard (white spirit) solvents as a slightly more flammable alternative to gasoline-based solvents. The use of highly flammable petroleum solvents causes many fires and explosions, resulting in government regulations on dry cleaners. After World War I, dry cleaners began using chlorinated solvents. These solvents are much more flammable than petroleum solvents and have better cleaning power.
On March 3, 1821, Thomas L. Jennings became the first African-American to be granted a US patent. The patent was for the discovery of a cleaning process called "dry scouring", which is a precursor to dry cleaning.
Switch to tetrachlorethylene
In the mid-1930s, the dry cleaning industry had adopted tetrachlorethylene (perchloroethylene), or PCE for short, as a solvent. It has excellent cleaning power and is not flammable and is compatible with most clothing. Because it is stable, tetrachlorethylene is easily recycled.
Infrastructure
Traditionally, the cleaning process is done in centralized factories. Small local cleaning shops accept clothes from customers, send them to the factory, and then return them to the store for customers to pick up. This cycle minimizes the risk of fire or hazardous smoke created by the cleaning process. At this time, dry cleaning is done in two different machines - one for cleaning, and the second to remove solvents from clothing.
This era machine is described as vented ; Their dried exhausts are thrown into the atmosphere, just like many modern dry-fall dryer exhausts. This not only contributes to environmental pollution but also many reusable PCEs are lost to the atmosphere. Tighter controls on solvent emissions have ensured that all dry cleaning machines in the Western world are now completely enclosed, and no solvent smoke is released into the atmosphere. In a closed machine, the solvent obtained during the drying process is returned thick and distilled, so it can be reused to clean the charge further or disposed of safely. The majority of modern closed machines also incorporate computer-controlled drying sensors, which automatically detect when all detected PCE traces have been removed. This system ensures that only a small amount of PCE smoke is released at the end of the cycle.
Maps Dry cleaning
Mechanism
In terms of mechanism, dry cleaning selectively dissolves stains on the article. The solvents are non-polar and tend to selectively extract the compounds that cause stains. These stains would otherwise only dissolve in a mixture of aqueous detergents at high temperatures, potentially damaging fine fabrics.
Non-polar solvents are also good for some fabrics, especially natural fabrics, because the solvent does not interact with the polar group inside the fabric. Water binds these polar groups that produce swelling and stretching of proteins inside the fibers during the wash. Also, the binding of water molecules interferes with a weak attraction within the fiber, which results in the loss of the original form of fiber. After the laundry cycle, the water molecules will dry out. However, the original shape of the fiber has been distorted and this usually results in shrinkage. The non-polar solvent prevents this interaction, protecting the finer fabric.
The use of effective solvents coupled with mechanical friction from overturned effectively removes stains.
Process
The dry-cleaning machine is similar to a combination of a domestic washing machine and clothes dryer. Clothing is placed in the washing or extraction chamber (referred to as 'basket' or 'drum'), which is the core of the machine. The washing room contains a horizontal hollow drum rotating inside the outer shell. Shell holds the solvent while the rotary drum holds the garment load. The basket capacity is between about 10 and 40 kg (22 to 88 pounds).
During the washing cycle, the room filled about a third full of solvents and began to spin, poking around in clothes. The temperature of the solvent is maintained at 30 degrees Celsius (86 degrees Fahrenheit), because higher temperatures can damage it. During the washing cycle, the solvent in space (commonly known as the 'cage' or 'fishing pole') is passed through the filtration chamber and then put back into the 'enclosure'. This is known as the cycle and continued for the duration of washing. The solvent is then removed and sent to the distillation unit comprising a boiler and condenser. The thick solvent is introduced into the separating unit where any remaining water is separated from the solvent and then fed into a 'clean solvent' tank. The ideal flow rate is about 8 liters of solvent per kilogram of clothing per minute, depending on engine size.
Clothing is also checked for foreign objects. Items such as plastic pens that can dissolve in bath solvents, damage textiles. Some textile dyes are "loose" and will dip the dye during solvent immersion. Fragile items, such as bed sheets or rugs or tasseled ornaments, may be enclosed in loose bag pockets. The density of perchlorethylene is about 1.7 g/cm 3 at room temperature (70% heavier than water), and the weight of the adsorbed solvent can cause the textile to fail under normal force during the extraction cycle unless the mesh sac provides mechanical support.
Not all stains can be removed with dry cleaning. Some need to be treated with solvent spots - sometimes with steam jets or by immersion in special stain removal fluids - before the clothes are washed or cleaned dry. Also, clothes kept in dirty conditions for a long time are hard to return to their original colors and textures.
A typical wash cycle lasts for 8-15 minutes depending on the type of garment and level of dirtiness. During the first three minutes, soluble soil in solvent dissolves into perchlorethylene and loose and insoluble soil is released. It takes 10-12 minutes after loose soil has been released to remove soil in the insoluble soil of the garment. Machines using hydrocarbon solvents require a 25 minute washing cycle due to a much slower solvent-soluble solvation rate. "Dry cleaning soap" can also be added.
At the end of the washing cycle, the machine starts a rinsing cycle in which the garment load is rinsed with a fresh distilled solvent removed from the solvent tank. This pure solvent solution prevents the color change caused by soil particles being absorbed back into the garment surface of the 'dirty' work solvent.
After the rinse cycle, the engine starts the extraction process, which restores the solvent for reuse. Modern machines recover about 99.99% of the solvents used. The extraction cycle begins by draining the solvent from the washing room and accelerating the basket up to 350-450 rpm, causing many solvents to spin free of fabric. Until now, cleaning is done in normal temperature, because the solvent is never heated in the dry cleaning process. When no more solvents can be removed, the engine begins the drying cycle.
During the drying cycle, clothing is dropped in a warm air stream (60-63 ° C/140-145 ° F) that circulates through the basket, vaporizing the remaining solvent trace after the cycle of rotation. The temperature of the air is controlled to prevent heat damage to the clothing. The warm air discharged from the machine then passes through the chiller unit where the solvent vapor is condensed and returned to the distilled solvent tank. Modern dry cleaning machines use a closed-loop system in which cold air is heated and recirculated. This results in a high level of solvent recovery and reduces air pollution. In the early days of dry cleaning, large amounts of perchlorethylene are released into the atmosphere because they are considered cheap and are believed to be harmless.
After the drying cycle is over, the aeration cycles cool the clothing and eliminate further solvent footprint, by circulating the cold air outside of the clothing and then through a vapor recovery filter made from activated carbon and polymer resins. After the aeration cycle, the clothes are clean and ready to be pressed and finishing.
Solvent processing
The working solvent from the wash room goes through several filtration steps before being returned to the laundry room. The first step is the key trap, which prevents small objects such as threads, fasteners, buttons, and coins entering the solvent pump.
Over time, a thin layer of filter cake (called "dirt") accumulates on a fiber filter. The dirt is removed regularly (usually once per day) and then processed to recover the solvent trapped in the dirt. Many machines use a "spin disk filter", which removes impurities from the filter with centrifugal force when re-washed with solvent.
After the fiber filter, the solvent passes through the absorbent cartridge filter. This filter, which contains active clay and charcoal, removes both insoluble soils and non-volatile residues, along with the dye of the solvent. Finally, the solvent passes through the polishing filter, which removes the previously unused ground. The clean solution is then returned to the working solvent tank. Powder cooked residue is the name for the waste material produced by cooking down or distilling the dirt. It will contain solvent filter material, powder (diatomite), carbon, non-volatile residue, fiber, dye, fat, soil, and water. Sludge waste or solid residue of still contains solvents, water, soil, carbon, and other non-volatile residues. Used filters are another form of waste such as waste water.
To increase the cleaning power, small amounts of detergent (0.5-1.5%) are added to the solvent and are essential for their function. The detergent emulsifies the hydrophobic soil and keeps the soil from redeposit on the clothes. Depending on the machine design, either anionic or cationic detergents are used.
Symbol
The international GINETEX washing symbol for dry cleaning is a circle. It may have the letter P in it to show the perchloroethylene solvent, or the letter F to show the combustible solvent (FeuergefÃÆ'¤hrliches Schwerbenzin). A bar below the circle indicates that only a mild cleaning process is suggested. Crosses in a blank circle indicates that dry cleaning is not allowed.
Solvents are used
Perchloroethylene
Perchloroethylene (PCE, or tetrachloroethylene) has been used since the 1930s. PCE is the most common solvent, "standard" for cleaning performance. This is the most effective cleaning solvent. Thermally stable, recyclable, and have low toxicity. However, it can cause bleeding/loss of color, especially at higher temperatures. In some cases can damage trim, buttons, and special beads on some garments. It is preferable to oil-based stains (which reach about 10% of the stain) rather than the more common water-soluble stains (coffee, wine, blood, etc.). "Medium to low" tetrachlorethylene toxicity and "Human injury reports are uncommon although their use is extensive in dry cleaning and degreasing".
The state of California in California classified perchloroethylene as a toxic chemical in 1991, and its use would be illegal in the state by 2023. However, this may still be the most widely used dry cleaning solvent at present.
Hydrocarbon
Hydrocarbons are represented by products such as Exxon-Mobil DF-2000 or EcoSolv Chevron Phillips, and Pure Dry. The petroleum-based solvent is less aggressive but also less effective than PCE. Although flammable, the risk of fire or explosion can be minimized when used correctly. However hydrocarbons are pollutants. Hydrocarbons retain about 10-12% of the market.
Trichlorethylene
Trichloroethylene is more aggressive than PCE but is very rarely used. With superior degreasing properties, it is often used for industrial work clothes/cleanse overalls in the past. TCE is classified as carcinogenic to humans by the United States Environmental Protection Agency.
Supercritical CO <"supercritical_CO2"> CO 2
Supercritical CO 2 is an alternative to PCE, but lower in removing some form of impurities. Surfactant additives increase the efficacy of CO 2. Carbon dioxide is almost entirely non-toxic. The potential of greenhouse gases is also lower than that of many organic solvents.
Consumer Reports Supercritical Rating CO 2 is superior to the conventional method, but the Drycleaning and Laundry Institute commented on "fairly low cleaning ability" in the 2007 report. Supercritical CO 2 is, overall, a mild solvent which lowers its ability to aggressively attack stains.
One drawback with supercritical CO 2 is its low conductivity. As mentioned in the Mechanism section, dry cleaning uses chemical and mechanical properties to remove stains. When the solvent interacts with the surface of the fabric, friction destroys dirt. At the same time, friction also adds electric charge. The fabric is a very bad conductor and usually, this buildup is released through the solvent. This discharges do not occur in the liquid carbon dioxide and the accumulation of electrical charges on the fabric surface pulls the dirt back to the surface, which reduces poor cleaning efficiency. To compensate for the solubility and poor conductivity of supercritical carbon dioxide, research has focused on additives. For increased solubility, 2-propanol has shown an increased cleaning effect for liquid carbon dioxide as it improves the solvent's ability to dissolve polar compounds.
Machines for the supercritical use of CO 2 are expensive - up to $ 90,000 more than the PCE machines, making the price difficult for small businesses. Some cleaners with these machines keep traditional machines in place for heavier gross textiles, but others find plant enzymes as effective and more environmentally friendly.
Other solvents: niches, pops, etc.
For decades, efforts have been made to replace the PCE. These alternatives have not proven economical so far:
- Stoddard solvents - flammable and explosive flash point, 100 ° F/38 ° C
- CFC-113 (Freon-113), CFC. Now prohibited as ozone is not friendly.
- Decamethylcyclopentasiloxane ("liquid silicone"), called D5 for short. It was popularized by GreenEarth Cleaning. It's more expensive than PCE. It's degraded within a few days in the neighborhood.
- Dibutoxymethane (SolvonK4) is a bipolar solvent that removes water-based stains and oil-based stains.
- Brominated solvents (n-propyl bromide, Fabrisolv, DrySolv) are solvents with higher KB values ​​than PCE. This allows faster cleaning, but can damage some synthetic beads and beads if not used properly. Healthwise, there are reported risks associated with nPB such as numbness. Exposure to solvents in typical dry cleaners is considered far below the level required to pose a risk. Environment, this is approved by the US EPA. This is one of the more expensive solvents, but faster cleaning, lower temperature, and faster dry time.
See also
- Fabrication of fabric
- List of laundry topics
- Wet cleaning
References
External links
- Hazard Summary provided by the United States Environmental Protection Agency.
- NIOSH Safety and Health Topics: Drycleaning
Source of the article : Wikipedia
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