- Paint stripper
Paint stripper, or paint remover, is the generic name given to
solventmixtures designed to remove paintand other finishes and also to clean the underlying surface. The principal active ingredient is usually dichloromethane. Formulations with orange oil (or other terpenesolvents), N-methylpyrrolidone, esters such as dibasic esters (often dimethyl esters of shorter dicarboxylic acids, sometimes aminated, for example, adipic acidor 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. Nitromethaneis another commonly used solvent. Dimethyl sulfoxideis 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 its
swelling; this volume increase causes internal strains, which, together with the weakening of the layer's adhesionto the underlying surface, leads to separation of the layer of the paint from the substrate.
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.
Ethanolis suitable for shellac, methyl ethyl ketoneis used for cellulose nitrate, and phenoland cresols are employed in some industrial formulas. Benzyl alcoholis used as well. Activators increase the penetration rate; for dichloromethane water is suitable, other choices are amines, strong acids or strong alkalines. The activators role is to disrupt the molecular and intermolecular bonds in the paint film and assist with weakening it. Their composition depends on the character of the paint to be removed; mineral acids are used for epoxyresins to hydrolyze their etherbonds. Alkaline activators are usually based on sodium hydroxide. Some cosolvents double as activators. Amineactivators, alkalines weaker than inorganic hydroxides, are favored when the substrate could be corroded by strong acids or bases. Surfactants assist with wettingthe surface, increasing the area of where the solvent can penetrate the paint layer. Anionic surfactants (eg. dodecyl benzene sulfonateor sodium xylene sulfonate) are used for acidic formulas, cationic or nonionic are suitable for alkaline formulas.Paint strippers containing surfactants are excellent brush cleaners. Thickeners are used for thixotropicformulas to help the mixture form gelthat 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, eg. hydroxypropyl cellulose, are commonly used for mixtures that are not extremely acidic or basic; under such conditions cellulose undergoes hydrolysis and loses effectivity, so fumed silicais used for these instead. Another possibility is using waxes (usually paraffin waxor polyethyleneor polypropylenederivates), or polyacrylategels. Corrosion inhibitors are added to the formula to protect the underlying substrate and the paint stripper storage vessel (usually a tin can) from corrosion. Dichloromethane decomposes with time to hydrochloric acid, which readily reacts with propylene oxideor butylene oxideand 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 negatively impart 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. Colourants are added in order to make the substance look different from the competitors, and/or to make it easier to see to which areas the remover has been applied to.
Hot air guns are an alternative to chemical paint strippers.
* [http://www.diyinfo.org/wiki/Paint_Removal DIYinfo.org's Paint Removal Wiki] - Heaps of practical information on how to remove / strip paint around the house
* [http://aic.stanford.edu/jaic/articles/jaic32-01-005_indx.html JAIC 1993: The composition of proprietary paint strippers]
* [http://www.freepatentsonline.com/6923873.html Patent 6923873 - Paint stripping composition and method of using the same]
* [http://www.easystrip.co.nz/more_info.php] - has pictorial sequence and information on how to strip paint effectively
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