The utility properties free from methylene chloride paint strippers

Please cite as: CHEMIK 2014, 68, 5, 486–493
Introduction Various types of protective coatings are used to protect the surface of the functional elements from weather or aggressive environment. Damaged or worn old protective coating must be removed before putting a new layer. Removal paint coating is also necessary to remove the effect of vandalism (graffiti). Mechanical, thermal, chemical [1] or biochemical methods are used to remove the protective coating. Mechanical methods include: manual brushing, hammering, removal by scraping, abrasive blasting and high pressure water cleaning. So far, a significant advantage of these methods was no need for use complicated equipment. Exacerbation safety regulations and environmental protection forces introduction dust-free blasting methods, which essentiallyods and increases the cost of application. Currently mechanical methods are used only for elements to which are easily accessible. The biggest disadvantage of these methods is rapid deterioration of cleaned items. Many countries depart from classical method of sandblasting (due to the ecological aspect) and it is replaced by cleaning with a jet of water under pressure. Depending on used water pressure following methods are distinguished [2]: • Low-Pressure Water Cleaning – pressure under 34MPa – this method can be used only to remove loose coatings • High-Pressure Water Cleaning – water pressure from 34 to 70 MPa – this method can be used to remove coatings with a standard adhesion to the substrate, • High-Pressure Water Jetting – water pressure from 70 to 170 MPa – this method can be used to remove coatings with a high adhesion and special coating, • Ultra High-Pressure Water Jetting – water pressure above 170 MPa Unfortunately, this technique has limitations and can’t be used in all cases cleaning painted elements before re-painting. Thermal methods consist of burning protective layer in molten salts, burning in furnaces with or without the afterburner gases and burning in a fluidized bed. Process is carried out in two stages. In first stage process is carried out at a temperature from 350 to 450°C (treatment chamber), in second stage at a temperature from 850 to 920°C (combustion chamber). This method is allocated to remove paints, varnishes, and plastics from small, badly painted metal part [3]. Chemical methods consist of cleaning elements in alkaline solutions, acidic solutions or in organic solvent. The leaching is carried out at a temperature of 60–80°C. Currently this method is rarely used because in most cases it is only softening the coating, not its removal. As a result, there are problems with complete cleaning the element and with emerging waste. Acidic solutions to removing protective coating are mainly: fluorosulphuric acid and a mixture of concentrated nitric acid, sulphuric acid and chromic anhydride. This method is mainly used to removal old or defective imposed coating with small elements. In this method there is a problem with generated waste.
Corresponding author: Otmar Vogt, Ph.D., (Eng.), e-mail: ozvogt@.pl
Preparations based on organic solvent are the most universal. They contain mixture of organic solvent and substances such as: thickeners, evaporation retardants, emulsifiers, corrosion inhibitors and activators. These preparations function through gradual penetration of the coating, swelling and in the final step wrinkling or gradual dissolution. The most commonly used industrial chemical methods are immersion technique or spray technique in closed chamber. These techniques are often useless when the purifying detail is impossible to remove. Therefore, the gel paint remover methods are the most universal and irreplaceable to remove graffiti or renovation vertical elements which are difficult to dismantling. So far, in view on dissolving power and breakout paint from the ground of methylene chloride most preparations have been using this compound as active ingredient [4–6]. From December 6th 2011 in European Union rules that prohibit use of methylene chloride in this type of application take effect. Nowadays, new paint remover can’t contain more than 0.1% methylene chloride [7]. Biopreparations and biochemical methods are recent developments in the field of paint stripper. In recent years preparations which active ingredients obtain from bio-materials were developed. Their main ingredients are lactic acid esters and fatty acid methyl esters received from trans esterification of soybean oil [8, 9]. Such selection of components allows to ensure easy biodegradation of the preparation and its residues. Biopreparations use microorganisms to distribution breakout coating or enzymes to remove coating from clean surface [10–12]. The process is used to remove paint from steel, galvanized parts, aluminium and its alloys and plastics [11, 12]. In some solutions biopreparations also contain coagulants and flocculants that facilitate separation of solid waste from liquid phase [13]. Paint stripper components The main paint remover component is base solvent. So far DCM (methylene chloride) was an unquestionable leader in this application. Its advantages resulted with similar solubility DCM and the organic resin, fast operating time and relatively low prices, as well as lack of the effect of this substances on ozone layer [1, 4]. New European Union rules [7] caused elimination of DCM and extorted intensive search for another active substitute. In many paint stripper the base solvent is N-methylpyrrolidone (NMP) or compounds of similar structure. NMP is a highly polar solvent, miscible with water, most organic solvents and polymers used for production of paints and varnishes. They work slower than DCM but are less volatile [14–20]. Impact studies of NMP on animals have shown, that NMP is a potentially dangerous substance affecting on the reproductive system and the nervous system of mammals [21, 22]. So there is a good chance that it will share fate of DCM and will be withdrawn from use as well. In present produced preparations role of active ingredients is played by such compounds as benzyl alcohol [23], alkylene carbonates [24], carboxylic acids esters [25–27], cyclic ethers [28] and many others. Important addition to base solvent is co-solvent (e.g. low molecular weight alcohols, ethyl acetate, ethylene glycol).