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Paint remover is applied to an aircraft's landing gear during an inspection looking for cracks in the aluminum

Paint stripper, or paint remover, is a chemical product designed to remove paint, finishes, and coatings while also cleaning the underlying surface.

The product's material safety data sheet provides more safety information than its product labels.

Paint can also be removed using mechanical methods (scraping or sanding) or heat (hot air, radiant heat, or steam).

Lead-based paint is banned in the United States. Removing old lead-based paint can disperse lead and cause lead poisoning, leading several US workplace and environmental regulations address removal of old paint that could contain lead.[1]

Contents

Types of chemical paint removerEdit

Chemical paint removers work only on certain types of finishes, and when multiple types of finishes may have been used on any particular surface, trial-and-error testing is typical to determine the best stripper for each application. Two basic categories of chemical paint removers are caustic and solvent.

CausticsEdit

Caustic paint removers, typically sodium hydroxide (also known as lye or caustic soda), work by breaking down the chemical bonds of the paint, usually by hydrolysis of the chain bonds of the polymers forming the paint. Caustic removers must be neutralized or the new finish will fail prematurely. In addition, several side effects and health risks must be taken into account in using caustic paint removers. Such caustic aqueous solutions are typically used by antique dealers who aim to restore old furniture by stripping off worn varnishes, for example.

SolventsEdit

Solvent paint strippers penetrate the layers of paint and break the bond between the paint and the object by swelling the paint.[2]

The principal active ingredient in common solvent paint strippers is dichloromethane, also called methylene chloride. Methylene has serious health risks including death[3] and is likely a carcinogen.[4]

Solvent strippers may also have formulations with orange oil (or other terpene solvents), n-methylpyrrolidone, esters such as dibasic esters (often dimethyl esters of shorter dicarboxylic acids, sometimes aminated, for example, adipic acid or glutamic acid), aromatic hydrocarbons, dimethylformamide, and other solvents are known as well. The formula differs according to the type of paint and the character of the underlying surface. Nitromethane is another commonly used solvent. Dimethyl sulfoxide is a less toxic alternative solvent used in some formulations.

Paint strippers come in a liquid, or a gel ("thixotropic") form that clings even to vertical surfaces.

The principle of paint strippers is penetration of the paint film by the molecules of the active ingredient, causing it to swell; this volume increase causes internal strains, which, together with the weakening of the layer's adhesion to the underlying surface, leads to separation of the layer of the paint from the substrate.

Other componentsEdit

Various co-solvents are added to the primary active ingredient. These assist with penetration into the paint and its removal and differ according to the target paint. Ethanol is suitable for shellac, methyl ethyl ketone is used for cellulose nitrate, and phenol and cresols are employed in some industrial formulas.[citation needed] Benzyl alcohol is used as well.

Activators increase the penetration rate; for dichloromethane water is suitable, other choices are amines, strong acids or strong alkalis. The activator's role is to disrupt the molecular and intermolecular bonds in the paint film and assist with weakening this. Its composition depends on the character of the paint to be removed. Mineral acids are used for epoxy resins to hydrolyze their ether bonds. Alkaline activators are usually based on sodium hydroxide. Some cosolvents double as activators. Amine activators, alkalines weaker than inorganic hydroxides, are favored when the substrate could be corroded by strong acids or bases.

Surfactants assist with wetting the surface, increasing the area of where the solvent can penetrate the paint layer. Anionic surfactants (e.g., dodecyl benzenesulfonate or sodium xylene sulfonate) are used for acidic formulas, cationic or non-ionic are suitable for alkaline formulas. Paint strippers containing surfactants are excellent brush cleaners.

Thickeners are used for thixotropic formulas to help the mixture form gel that adheres to vertical surfaces and to reduce the evaporation of the solvents, thus prolonging the time the solvent can penetrate the paint. Cellulose-based agents, e.g., hydroxypropyl cellulose, are commonly used for mixtures that are not extremely acidic or basic; under such conditions cellulose undergoes hydrolysis and loses effectiveness, so fumed silica is used for these instead. Another possibility is using waxes (usually paraffin wax or polyethylene or polypropylene derivatives), or polyacrylate gels.

Corrosion inhibitors are added to the formula to protect the underlying substrate and the paint stripper storage vessel (usually a steel can) from corrosion. Dichloromethane decomposes with time to hydrochloric acid, which readily reacts with propylene oxide or butylene oxide and therefore is removed from the solution. Chromate-based inhibitors give the mixture a characteristic yellow color. Other possibilities include polyphosphates, silicates, borates, and various antioxidants.

Sequestrants and chelating agents are used to "disarm" metal ions present in the solution, which could otherwise reduce the efficiency of other components, and assist with cleaning stains, which often contain metal compounds. The most common sequestrants used in paint strippers are EDTA, tributyl phosphate, and sodium phosphate.

Colorants may be added.

Petroleum hydroxideEdit

Petroleum hydroxide was a chemical used by the New York City Transit Authority to remove graffiti from subway trains. Graffiti vandals first started calling it "orange crush" naming it in reference to defoliant Agent Orange. They later called it "the buff".[5]

HistoryEdit

In 1977, the Transit Authority built a graffiti removal station in its Coney Island train yard, in an attempt to discourage graffiti artists. Costing the city $400,000 annually, trains were sprayed with petroleum hydroxide, after which the graffiti was buffed off. However, the removal process often failed[citation needed] to completely remove graffiti. Those in contact with the chemical experienced nausea and breathing difficulties, leading to the closing of a nearby public school. The chemical also corroded the trains, and contaminated the city's water supply, through unsafe dumping. In 1985, transit workers were awarded $6.3 million for "health problems stemming from exposure to fumes from cleaning solvents."[citation needed]

AlternativesEdit

Heat guns are an alternative to chemical paint strippers. When heated, softened paint clumps and is easier to contain. High-temperature heat guns at 1,100 °F (590 °C) or more create toxic lead fumes in lead-based paint,[6][7] but low-temperature heat guns and 400 °F (200 °C) infrared paint removers do not create lead fumes.[8] Fire is a possible hazard of using heat guns.

Steam can be used on large surfaces or items to be stripped, such as window sash, can be placed inside a steam box.[9]

See alsoEdit

ReferencesEdit

  1. ^ Beckley, Bob; Groenier, James (December 2007). "Lead-Based Paint: Planning Your Paint Removal Project". T&D Pubs. United States Forest Service. Archived from the original on 2019-02-02.
  2. ^ Active Interest Media, Inc. (May–June 2001). Old-House Journal. Active Interest Media, Inc. ISSN 0094-0178.
  3. ^ MacIsaac, J., Harrison, R., Krishnaswami, J., McNary, J., Suchard, J., Boysen-Osborn, M., Cierpich, H., Styles, L. and Shusterman, D. (2013), "Fatalities due to dichloromethane in paint strippers: A continuing problem". Am. J. Ind. Med. doi: 10.1002/ajim.22167 http://onlinelibrary.wiley.com/doi/10.1002/ajim.22167/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false accessed 6/1/2013
  4. ^ Nat. Toxicology Program (NTP) (NIH) (8 October 2011). Report on Carcinogens (12th Ed. ). DIANE Publishing. ISBN 978-1-4379-8736-2.
  5. ^ Caponi-Tabery, Gena (1999). Signifyin(g), sanctifyin' & slam dunking : a reader in African American expressive culture. Amherst: University of Massachusetts Press. p. 201. ISBN 1558491821. OCLC 40820991.
  6. ^ United States Environmental Protection Agency, Office of Pollution Prevention and Toxics, Reducing lead hazards when remodeling your home September 1997, 14. https://books.google.com/books?id=SQQUAQAAMAAJ
  7. ^ Petit, Georges, and Donald Grant. The manufacture and comparative merits of white lead and zinc white paints. London: Scott, Greenwood & Son;, 1907. 13. Print. This source states that lead vapors are given off around 400 °F (200 °C) http://www.mediafire.com/view/1xyimc3wdo3/manufacturecompa00petirich.pdf
  8. ^ Thomas, Baker, "All About Exterior Paint", "This Old House Magazine" 2012. http://www.thisoldhouse.com/toh/photos/0,,20586187_21145196,00.html
  9. ^ John, Leeke, "Getting up to speed on steam", Old-House Journal May–June 2006. 31-32. https://books.google.com/books?id=qW03wP0EynUC

External linksEdit