Editing Dry cleaning (section)

==Solvents used==
===Perchloroethylene===
[[File:Tetrachloroethylene.svg|thumb|[[Chemical structure]] of perchloroethylene]]
[[Perchloroethylene]] (PCE or perc, tetrachloroethylene) is the main solvent in dry cleaning and it has been in use since the 1930s. PCE is the most common solvent, the standard for cleaning performance. It is a highly effective cleaning solvent, and it is thermally stable, nonflammable, recyclable, and has very low toxicity and a pleasant smell. PCE is recycled by [[distillation]] at its boiling point (121&nbsp;°C). Unlike the related dry-cleaning solvent [[carbon tetrachloride]], perchloroethylene is not an [[ozone-depleting substance]].<ref>Wuebbles, D. J.; Patten, K. O.; Wang, D.; Youn, D.; Martínez-Avilés, M.; Francisco, J. S. (2011). "Three-dimensional model evaluation of the Ozone Depletion Potentials for n-propyl bromide, trichloroethylene and perchloroethylene". Atmos. Chem. Phys. Vol 11. p. 2371-2380. doi:10.5194/acp-11-2371-2011.</ref>

The solvent can cause color bleeding/loss, especially at higher temperatures. In some cases it may damage special trims, buttons and beads on some garments. It is better for oil-based stains than more common water-soluble stains.

Perchloroethylene has [[narcotic]] and [[hallucinogenic]] effects upon inhalation of high amounts. Repeated long-term skin contact with perchloroethylene may result in defatting injury. The toxicity of perchloroethylene is moderate to low and reports of human injury are uncommon despite its wide usage in dry cleaning and degreasing.<ref name="Ullman2011">{{cite book | author = E.-L. Dreher | author2 = T. R. Torkelson | author3 = K. K. Beutel | chapter = Chlorethanes and Chloroethylenes | title = Ullmann's Encyclopedia of Industrial Chemistry | year = 2011 | publisher = Wiley-VCH | location = Weinheim | doi = 10.1002/14356007.o06_o01| isbn = 978-3527306732 }}</ref> Perchloroethylene is classified as "probably carcinogenic to humans" (Group 2A) by the [[International Agency for Research on Cancer]] (IARC). There is a suspicion 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 which are known carcinogens and were exposed to many other chemicals at the workplace.<ref>{{Cite web|url=https://www.inchem.org/documents/iarc/vol63/tetrachloroethylene.html|title=Tetrachloroethylene (IARC Summary & Evaluation, Volume 63, 1995)|website=www.inchem.org|access-date=2023-09-25|archive-date=2023-03-29|archive-url=https://web.archive.org/web/20230329130254/https://www.inchem.org/documents/iarc/vol63/tetrachloroethylene.html|url-status=live}}</ref> A study published in 2011, investigated cancer rates among dry cleaners exposed to perchloroethylene for many years and laundry workers who did wet cleaning without using this chemical as the [[control group]], based on a total of more than nine thousand people, found that there was no difference in the cancer rates between the two groups: there was no significant increase in the incidence of esophageal, cervical, liver, kidney and bladder cancers, which were suspected to be caused by perchloroethylene, between the two groups.<ref>Seldén, AI; Ahlborg, G (2011). "Cancer morbidity in Swedish dry-cleaners and laundry workers: historically prospective cohort study". Int Arch Occup Environ Health. 84 (4). </ref> The exposure to perchloroethylene in a typical dry cleaner is considered far below the levels required to cause any risk.<ref>{{cite journal |pmid=19367044 |year=2009 |last1=Azimi Pirsaraei |first1=S. R. |title=Occupational exposure to perchloroethylene in dry-cleaning shops in Tehran, Iran |journal=Industrial Health |volume=47 |issue=2 |pages=155–9 |last2=Khavanin |first2=A |last3=Asilian |first3=H |last4=Soleimanian |first4=A |doi=10.2486/indhealth.47.155 |doi-access=free }}</ref>

It is estimated that 50% to 70% of dry cleaners in the US were using PCE {{as of|2012|lc=y}}.<ref name="TURI-Alt">{{cite web |title=Assessment of Alternatives to Perchloroethylene for the Dry Cleaning Industry |url=https://www.turi.org/content/download/7399/134622/file/2012%20M&P%20Report%2027%20Assessment%20of%20Safer%20Alternatives%20to%20Perchloroethylene.pdf |website=TURI: Toxics Use Reduction Institute |publisher=UMass Lowell |access-date=2023-09-23 |date=June 2012}}</ref> Alternative solvents are available, but these may require major changes in equipment, procedures, and operator training. Flammable solvents may require installation of expensive [[fire-suppression system]]s.<ref name="TURI-Alt"/>

Because PCE has been the longtime [[de facto standard|''de facto'']] solvent for dry cleaning, there is considerable interest in finding a "drop-in" substitute solvent which could be used with minimal changes to existing equipment and procedures.<ref name="TURI-Alt"/>

=== High flash hydrocarbons ===
[[File:Union K Series Dry Cleaning Machine.jpg|thumb|right|A modern dry cleaning machine for use with various solvents]]
High flash [[hydrocarbons]], characterized as having a [[flash point]] higher than {{convert|60|C}}, are considered to be safer than traditional hydrocarbon solvents.<ref name="TURI-Alt"/>{{rp|18–19}} Examples include [[Exxon-Mobil]]'s DF-2000 or [[Chevron Phillips]]' EcoSolv, and Pure Dry. These [[petroleum]]-based solvents are less aggressive but also less effective than PCE. 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. Hydrocarbons are considered to be volatile organic (VOC) pollutants.<ref name="TURI-Alt"/>{{rp|18–19}}

=== Trichloroethylene===
[[Trichloroethylene]] (TCE) is more aggressive than the chemically related PCE but is very rarely used as a stain remover today. With superior degreasing properties, it was often used for industrial workwear/overalls cleaning in the past. Trichloroethylene was introduced in 1930 but it was mostly replaced by PCE in the 1950s.<ref name=Morrison/>

Most common health hazard of TCE is its anaesthetic effects. TCE is a human [[carcinogen]] (classified as such by [[International Agency for Research on Cancer]] and [[United States Environmental Protection Agency]]), albeit a weak one.<ref>Costa, A. K.; Ivanevitch, K. M. (1984). "Chlorinated Ethylenes". Carcinogenesis. 12 (1629).</ref>

===Liquid or supercritical {{CO2}}===
[[Liquid carbon dioxide|Liquid]] or [[Supercritical CO2|supercritical {{CO2}}]] is an alternative to PCE; however, it is inferior in removing some forms of grime.<ref>{{cite web |url=http://resource.wur.nl/en/wetenschap/detail/dry-cleaning_with_co2_wins_award/ |title=Dry-cleaning with CO2 wins award [Science&#93; Resource |publisher=Resource.wur.nl |date=2010-10-12 |access-date=2013-03-14 |url-status=dead |archive-url=https://web.archive.org/web/20120312013535/http://resource.wur.nl/en/wetenschap/detail/dry-cleaning_with_co2_wins_award/ |archive-date=2012-03-12 }}</ref><ref name="TURI-Alt"/> Additive surfactants improve the efficacy of {{CO2}}.<ref>{{Cite web|url=https://www.academia.edu/1074194|title=How can we use carbon dioxide as a solvent?|location=Contemporary topics in school science|access-date=2016-08-29|last1=Mohamed|first1=Azmi|archive-date=2019-12-24|archive-url=https://web.archive.org/web/20191224163924/https://www.academia.edu/1074194|url-status=live}}</ref> [[Carbon dioxide]] is almost entirely nontoxic (but is an [[asphyxiant]] risk in high concentrations).<ref name="TURI-Alt"/>

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 {{cvt|200|to|300|psi|bar}} of pressure. This step in the process is initiated as a precaution to avoid [[thermal shock]] to the cleaning chamber. Liquid carbon dioxide is then pumped into the cleaning chamber from a separate storage vessel by a hydraulic or electrically driven pump (which preferably has dual pistons). The pump increases the pressure of the liquid carbon dioxide to approximately {{cvt|900|to|1500|psi|bar}}. A separate sub-cooler reduces the temperature of the carbon dioxide by {{convert|2|to|3|C-change}} below the boiling point, in an effort to prevent [[cavitation]] which could lead to premature degradation of the pump.<ref>{{cite web |url=https://patents.google.com/patent/US5412958A/en |title=Liquid/supercritical carbon dioxide/dry cleaning system |date=1993-12-06 |access-date=2021-01-02 |archive-date=2022-04-09 |archive-url=https://web.archive.org/web/20220409130536/https://patents.google.com/patent/US5412958A/en |url-status=live }}</ref>

''[[Consumer Reports]]'' rated {{CO2}} superior to conventional methods, but the Drycleaning and Laundry Institute commented on its "fairly low cleaning ability" in a 2007 report.<ref>Drycleaning and Laundry Institute. "The DLI White Paper: Key Information on Industry Solvents." ''The Western Cleaner & Launderer'', August 2007.</ref> {{CO2}} is a mild solvent overall, which lowers its ability to aggressively attack stains.

One deficiency with {{CO2}} is that its [[electrical conductivity]] is low. As mentioned in the Mechanisms section, dry cleaning utilizes both chemical and mechanical properties to remove stains. When solvent interacts with the fabric's surface, the friction dislocates dirt. At the same time, the friction also builds up an electrical charge. Fabrics are very poor conductors, but usually this build-up of [[static electricity]] is dissipated through the solvent. This discharge does not occur in liquid carbon dioxide, and the build-up of an electrical charge on the surface of the fabric attracts the dirt back on to the surface, diminishing the cleaning efficiency.{{citation needed|date=September 2023}}

To compensate for the poor solubility and conductivity of supercritical carbon dioxide, research has focused on additives. For increased solubility, [[2-propanol]] has shown increased cleaning effects for liquid carbon dioxide, as it increases the ability of the solvent to dissolve polar compounds.<ref>{{cite patent|title=Liquid carbon dioxide cleaning system employing a static dissipating fluid|country=US|number=5784905|pubdate=1998-07-28|url=http://www.google.ch/patents/US5784905|inventor1-last=Townsend|inventor2-last=Chao|inventor3-last=Purer|inventor1-first=Carl W.|inventor2-first=Sidney C.|inventor3-first=Edna M.}}</ref>

Machinery for use of {{CO2}} is expensive{{snd}}up to $90,000 more than a PCE machine, making affordability difficult for small businesses. Some cleaners with these machines keep traditional machines on-site for more-heavily soiled textiles, but others find plant-derived enzymes to be equally effective and more environmentally sustainable.

===Other solvents: niche and emerging===
For decades, efforts have been made to replace PCE. These alternatives have not proven popular thus far:
* [[Glycol ethers]] (also called "propylene glycol ethers") are a class of organic solvents which were introduced in the 1990s as an alternative to PCE.<ref name="TURI-Alt"/>{{rp|23–24}} These solvent mixes are flammable, but are considered comparable to high flash hydrocarbons in fire hazard. They are not considered to be carcinogenic, and have relatively benign persistence and environmental effects.<ref name="TURI-Alt"/>{{rp|23–24}}
*[[Decamethylcyclopentasiloxane]] ("siloxane" or "liquid silicone", trademarked Siloxane D5),<ref name="TURI-Alt"/>{{rp|25}} was initially popularized by GreenEarth Cleaning.<ref>{{cite web|url=https://gizmodo.com/theres-a-better-way-to-dry-clean-your-clothes-1634895806|title=There's a Better Way to Dry Clean Your Clothes|last=Tarantola|first=Andrew|website=[[Gizmodo]]|date=16 September 2014|language=en-US|access-date=2016-08-29|archive-date=2014-09-16|archive-url=https://web.archive.org/web/20140916222800/https://gizmodo.com/theres-a-better-way-to-dry-clean-your-clothes-1634895806|url-status=live}}</ref> It is more expensive than PCE.<ref name="TURI-Alt"/> It is marketed as an eco-friendly product that degrades quickly in the environment, but is controlled in the European Union due to its [[Persistent, bioaccumulative and toxic substances|persistent, bioaccumulative and toxic]] characteristics.<ref>{{Citation |title=Commission Regulation (EU) 2018/35 of 10 January 2018 amending Annex XVII to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) as regards octamethylcyclotetrasiloxane (‘D4’) and decamethylcyclopentasiloxane (‘D5’) (Text with EEA relevance. ) |date=2018-01-10 |url=http://data.europa.eu/eli/reg/2018/35/oj/eng |access-date=2023-08-10 |language=en}}</ref>
*[[Dibutoxymethane]] ([[formaldehyde]] dibutyl acetal, also referred to as "butylal", loosely referred to as "acetal", and trademarked as SolvonK4)<ref name="TURI-Alt"/>{{rp|21}} is a bipolar solvent that removes water-based stains and oil-based stains.<ref>{{cite journal|title=Occupational exposures to new dry cleaning solvents: High-flashpoint hydrocarbons and butylal |last1=Ceballos |first1=Diana M. |last2=Whittaker |first2=Stephen G. |last3=Lee |first3=Eun Gyung |last4=Roberts |first4=Jennifer |last5=Streicher |first5=Robert |last6=Nourian |first6=Fariba |last7=Gong |first7=Wei |last8=Broadwater |first8=Kendra |journal=Journal of Occupational and Environmental Hygiene |year=2016 |volume=13 |issue=10 |pages=759–769 |doi=10.1080/15459624.2016.1177648 |pmid=27105306 |pmc=5511734 }}</ref><ref name="TURI-Alt"/> Because the solvent is relatively new in cleaning applications, there has been relatively little specific research into health and environmental effects.<ref name="TURI-Alt"/>{{rp|21–22}}
*Brominated solvents ([[n-propyl bromide|''n''-propyl bromide]], Fabrisolv, DrySolv) are solvents with higher [[Kauri-butanol value|KB-value]]s than PCE. This allows faster cleaning, but can damage some synthetic beads and sequins if not used correctly. Machines used with ''n''-propyl bromide were converted PCE machines.<ref name=smith>{{Cite journal|last1=Smith|first1=Carr J|last2=Perfetti|first2=Thomas A|last3=Morford|first3=Richard G|date=2020-01-01|title=Use of 1-bromopropane (N-propyl bromide) in dry cleaning is rare and rapidly declining toward obsolescence|journal=Toxicology Research and Application|language=en|volume=4|pages=2397847320966961|doi=10.1177/2397847320966961|issn=2397-8473|doi-access=|s2cid=228978817 }}</ref> Healthwise, there are reported risks associated with nPB such as permanent numbness of nerves.<ref>[http://www.cdph.ca.gov/programs/hesis/Documents/bpropane.pdf "HAZARD EVALUATION 1-Bromopropane"] {{webarchive|url=https://web.archive.org/web/20131106024756/http://www.cdph.ca.gov/programs/hesis/Documents/bpropane.pdf |date=2013-11-06 }} July 2003. Accessed 2014-Jan-22</ref> Environmentally, it is approved by the US EPA. It is among the more expensive solvents, but it has advantages of faster cleaning, lower temperatures, and quick drying times. In 2016, the state of Massachusetts listed the solvent as a "Higher Hazard Substance" due to increased concerns about its health and environmental effects.<ref name="TURI-Bromide">{{cite web |title=Massachusetts Chemical Fact Sheet: N-propyl bromide |url=https://www.turi.org/content/download/10480/174392/file/Fact%20Sheet.%20n-Propyl%20Bromide%20October%2025%202016.pdf |website=TURI: Toxics Use Reduction Institute |publisher=UMass Lowell |access-date=2023-09-23 |date=October 2016 |archive-date=2023-11-03 |archive-url=https://web.archive.org/web/20231103111115/https://www.turi.org/content/download/10480/174392/file/Fact%20Sheet.%20n-Propyl%20Bromide%20October%2025%202016.pdf |url-status=live }}</ref>

===Obsolete solvents===
* [[Stoddard solvent]] – flammable and explosive, relatively low {{cvt|38|C}} [[flash point]] 
* [[Carbon tetrachloride]] (CCl<sub>4</sub>) was once widely used in dry cleaning as the first chlorinated solvent, but its use was abandoned after its high [[hepatotoxicity]] was discovered.
* [[1,1,1-Trichloroethane]] was also used in dry cleaning, until its use was banned due to its harmful effects on the ozone layer.
* [[CFC-113]] (Freon-113, Valclene, Arklone), a [[Chlorofluorocarbon|CFC]], is now banned as [[Ozone depletion potential|ozone-unfriendly]]. It was introduced to dry cleaning in the early 1960s. It is almost non-toxic to humans.