A oil drain is oil hardened into a hard and dense film after exposure to air. Oil hardened through a chemical reaction in which the cross component (and hence, polymerization) by the action of oxygen (not by evaporation of water or other solvents). Drying oil is a major component of oil paint and some varnish. Some commonly used oil dryers include linseed oil, tung oil, poppy seed oil, perilla oil, and walnut oil. Its use has declined over the last few decades, as they have been replaced by alkyd resins and other binders.
Because oxidation is the key to cure in this oil, those susceptible to chemical drying are often unsuitable for cooking, and are also very susceptible to being rancid through autoksidation, a process in which fatty foods develop flavor off. Fabrics, fabrics, and paper saturated with drying oil can ignite spontaneously (on) after a few hours as heat is released during the oxidation process.
Video Drying oil
Chemical of the drying process
"Drying", hardening, or, more precisely, oil preservation is the result of autoxidation, the addition of oxygen to organic compounds and subsequent cross crosses. This process begins with an oxygen molecule (O 2 ) in the air that inserts a carbon-hydrogen (C-H) bond adjacent to one of the double bonds in an unsaturated fatty acid. The resulting hydroperoxide is susceptible to crosslinking reactions. The bond formation between the neighboring fatty acid chains, resulting in polymer tissue, is often seen by the formation of films such as skin on the sample. This polymerization produces stable films that, although somewhat elastic, do not flow or change shape easily. The derivative of diene-containing fatty acids, such as those derived from linoleic acid, is particularly susceptible to this reaction because it produces a pentadienyl radical. Monounsaturated fatty acids, such as oleic acid, are slower to dry due to less stable alical radical intermediates (ie, more slowly formed).
The early stages of the drying process can be monitored by heavy changes in the oil film. The film becomes heavier because it absorbs oxygen. Linseed oil, for example, increases weight by 17 percent. When the oxygen uptake stops, the film's weight decreases as volatile compounds evaporate. As oil age increases, a further transition takes place. A large number of the original ester bonds in the oil molecules undergo hydrolysis, releasing individual fatty acids. In the case of paints, some parts of these free fatty acids (FFAs) react with the metal in the pigment, producing a metal carboxylate. Together, the various non-cross substances associated with polymer tissue are the mobile phase. Unlike the molecules that are part of the network itself, they are capable of moving and spreading inside the film, and can be removed using heat or solvent. The mobile phase can play a role in plasticizing paint films, preventing them from becoming too fragile. The carboxyl group in the stationary phase ionized polymer becomes negatively charged and forms a complex with the metal cations present in the pigment. Native tissue, with nonpolar bonds, covalent, is replaced by ionomeric structures, which are united by ionic interactions. The structure of these ionomer networks is not well understood.
Most drying oils increase viscosity after heating in the absence of air. If oil is exposed to elevated temperatures for a long time, the oil will become an insoluble substance in the oil.
The role of metal catalyst
The drying process is accelerated by certain metal salts, especially those derived from cobalt, manganese, or iron. In technical terms, this oil drying agent is a coordination complex that functions as a homogeneous catalyst. These salts come from carboxylates of lipophilic carboxylic acids, such as naphthenic acid to make oil-soluble complexes. This catalyst accelerates the reduction of hydroperoxide intermediates. A series of additional reactions occur later. Each step generates additional free radicals, which then engage in further crosslinking. The process finally ends when the free radicals join. Polymerization occurs over several days to years and makes the film dry to the touch. The premature action of the drying agent causes skinning on the paint, this undesirable process is suppressed by the addition of an antapartum agent such as methylethyl ketone oxime, which evaporates when the paint/oil is applied to the surface.
Maps Drying oil
Constitution
Drying oil consists of a glycerol triester of fatty acids. These esters are characterized by high levels of polyunsaturated fatty acids, especially alpha-linolenic acids. One common measure of the "siccative" (oil draining) properties is the iodine number, which is an indicator of the number of double bonds in the oil. Oil with iodine numbers greater than 130 is considered drying, those with iodine quantities of 115-130 are semi-drying, and those with less than 115 iodine are not dry.
Comparison with wax and resin
Non-"dry" waxes, such as carnauba or hard-wax paste, and resins, such as resin, copal, and lacquers, consist of long, compact, but not covalent, strands of a long, comparable, spaghetti-like molecule of hydrocarbons. bond by drying oil. Thus, the wax and resin can be dissolved while the oil paint or non-dried paint is not.
Security
Fabrics, fabrics, and paper saturated with drying oils can burn spontaneously (burned) due to heat released during the curing process. This danger is greater when the material soaked in oil is folded, fastened, or stacked together, allowing heat to accumulate and accelerate the reaction. Precautions include: wetting the fabric with water and spreading it away from direct sunlight; completely seal it in water in an airtight metal container designed for such applications; or store it immersed in a solvent in a suitable sealed container. The grass soaked in flax oil is the cause of the fire that destroyed One Meridian Plaza
Although spontaneous combustion has been said to occur with a cloth soaked in a paint thinner, this is incorrect unless the drying oil is used as a diluent. However, the classical paint diluent does not include drying oil. The danger is that laps are soaked in oil-based paints, as these are oils that dried in paint (or varnish), not diluents per se unless they have been mixed with flue oil such as flaxseed.
See also
- Blown oil
- Danish Oil
- Fat above lean
- Linseed oil
- Oil paint
- Semi-dried oil
- Oil tung
- Varnish
- Wood finishing
References
Further reading
- "Autoxidation." McGraw Hill Encyclopedia. 8th ed. 1997.
- Friedman, Ann, et al. "Paint." www.worldbookonline.com. 2006. 46 Stetson St. # 5 Brookline, MA. May 10, 2006
- "The History of Oil Paints." www.cyberlipid.org. May 5, 2006 & lt; http://www.cyberlipid.org/perox/oxid0011.htm>
- van den Berg, Jorit D.J. "Mobile and Stationary Phases in Traditional Oil Paints." www.amolf.nl 2002. MOLART. May 8, 2006
- AndÃÆ' Â © s, Louis Edgar, Drying oil, boiled oil, and solid and liquid dryer . London: Scott, Greenwood & amp; Co., 1901.
External links
- Tung Oil and Linseed by Steven D. Russel
Source of the article : Wikipedia
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