乾性油：修订间差异
翻译drying oil 新条目 |
（没有差异）
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2018年6月9日 (六) 22:37的版本
| 植物油 |
|---|
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| 類型 |
| 用途 |
| 脂肪酸 |
干性油 是一种经过一段时间暴露在空气中的油 ，它会硬化形成坚硬的固体薄膜。 油通过化学反应而变硬， 在化学反应中，成分通过氧的作用(而不是通过水的蒸发或其他溶剂的蒸发)交联 (从而聚合) 。干性油是油漆和一些清漆的重要组成部分。一些常用的干燥油包括亚麻籽油、桐油、罂粟籽油、紫苏油和核桃油。过去几十年来，它们已被醇酸树脂和其他粘合剂所取代，故使用量有所下降。
由于氧气是油固化的关键，所以那些易受化学干燥影响的食物通常不适合烹饪,并且还很容易通过自动氧化变为酸败，这是脂肪食物产生异味的过程。 [1] 浸有干性油的抹布、布和纸在氧化过程中释放热量几小时后可能会自燃（点燃）。
干燥过程的化学性质
油的“干燥”、硬化，或者更确切地说，固化的油是由于自氧化作用、向有机化合物中添加氧气和随后的交联的结果。这个过程开始于空气中的一个氧分子(O2)插入到与不饱和脂肪酸中的一个双键相邻的碳-氢(C-H)键中。产生的过氧化氢容易发生交联反应。在相邻的脂肪酸链之间形成化学键，形成聚合物网络，通常可以通过样品上的皮肤状薄膜来观察。这种聚合反应产生稳定的薄膜，虽然有一定的弹性，但不容易流动或变形。含二烯的脂肪酸衍生物，例如衍生自亚油酸的衍生物，特别容易发生该反应，因为它们产生戊二烯基。单不饱和脂肪酸，如油酸，干燥较慢，因为烯丙基自由基中间体不太稳定（即形成较慢）。[2]
干燥过程的早期阶段可以通过油膜重量的变化来监测。由于吸收氧气，薄膜变得更重。.例如，亚麻油的重量增加了17%。[3]随着氧吸收的停止，膜的重量随着挥发性化合物的蒸发而降低。 作为油的产物，会发生进一步的转变。 A large number of the original ester bonds in the oil molecules undergo hydrolysis, releasing individual fatty acids. 大量的原始酯键在油分子中进行水解反应，释放单个脂肪酸。 在涂料中，这些游离脂肪酸(FFAs)的某些部分与颜料中的金属发生反应，生成金属羧酸盐。总之，与聚合物网络相关的各种非交联物质构成了流动相。 与作为网络本身的一部分的分子不同，它们能够在膜内移动和扩散，并且可以使用高温或溶剂除去。流动相可以起到塑化漆膜的作用，防止漆膜变得太脆。固定相聚合物中的羧基离子化，变为负电荷，并与颜料中存在的金属阳离子形成络合物。最初的网络，具有非极性共价键,被由离子相互作用连接在一起的离聚体取代. 这些离聚体网络的结构尚不清楚。
大多数干性油在没有空气的情况下加热后粘度迅速增加。. 如果干性油长时间地经受升高的温度，它将变成橡胶状的油不溶性物质。[3]
金属催化剂的作用
The drying process is accelerated by certain metal salts, especially derivatives of cobalt, manganese, or iron. In technical terms, these oil drying agents are coordination complexes that function as homogeneous catalysts. These salts are derived from the carboxylates of lipophilic carboxylic acids, such as naphthenic acids to make the complexes oil-soluble. These catalysts speed up the reduction of the hydroperoxide intermediates. A series of addition reactions ensues. Each step produces additional free radicals, which then engage in further crosslinking. The process finally terminates when pairs of free radicals combine. The polymerization occurs over a period of days to years and renders the film dry to the touch. Premature action of the drying agents causes skinning of the paint, this undesirable process is suppressed by the addition of antiskinning agents such as methylethyl ketone oxime, which evaporate when the paint/oil is applied to a surface.
构造
Representative triglyceride found in a drying oil. The triester is derived from three different unsaturated fatty acids, linoleic (top), alpha-linolenic (middle), and oleic acids (bottom). The order of drying rate is alpha-linolenic > linoleic > oleic acid, reflecting their degree of unsaturation.
Drying oils consist of glycerol triesters of fatty acids. These esters are characterized by high levels of polyunsaturated fatty acids, especially alpha-linolenic acid. One common measure of the "siccative" (drying) property of oils is iodine number, which is an indicator of the number of double bonds in the oil. Oils with an iodine number greater than 130 are considered drying, those with an iodine number of 115–130 are semi-drying, and those with an iodine number of less than 115 are non-drying.
Comparison to waxes and resins
Non-"drying" waxes, such as hard-film carnauba or paste wax, and resins, such as dammar, copal, and shellac, consist of long, spaghetti-like strands of hydrocarbon molecules, which interlace and compact but do not form covalent bonds in the manner of drying oils. Thus, waxes and resins are re-dissoluble whereas a cured oil varnish or paint is not.
安全
Rags, cloth, and paper saturated with drying oils may combust spontaneously (ignite) due to heat released during the curing process. This hazard is greater when oil-soaked materials are folded, bunched, or piled together, which allows heat to accumulate and accelerate the reaction. Precautions include: wetting rags with water and spreading them away from direct sunlight; closing them off completely in water inside air-tight metal containers designed for such applications; or storing them immersed in solvents in suitable closed containers. Linseed oil soaked rags were the cause of the fire that destroyed One Meridian Plaza
Although spontaneous combustion has been said to occur with rags soaked in paint thinners, this is not true unless a drying oil is used as a thinner. However, classical paint thinners do not include drying oils. The danger is due to rags soaked in oil based paints, as it is due to the drying oils in the paints (or varnishes), not thinners per se unless they have been mixed with drying oils such as linseed.
参阅
参考
- ^ Ulrich Poth, "Drying Oils and Related Products" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a09_055
- ^ Ned A. Porter, Sarah E. Caldwell, Karen A. Mills "Mechanisms of free radical oxidation of unsaturated lipids" Lipids 1995, volume 30, Pages 277-290. doi:10.1007/BF02536034
- ^ 3.0 3.1 Apps, E. A. Printing Ink Technology. London: Leonard Hill [Books] Limited. 1958: 14.
查阅
- “Autoxidation.” McGraw Hill Encyclopedia. 8th ed. 1997.
- Friedman, Ann, et al. “Painting.” www.worldbookonline.com. 2006. 46 Stetson St. #5 Brookline, MA. 10 May 2006
- “History of Oil Paint.” www.cyberlipid.org. 5 May 2006 <http://www.cyberlipid.org/perox/oxid0011.htm>
- van den Berg, Jorit D.J. “Mobile and Stationary Phases in Traditional Aged Oil Paint.” www.amolf.nl 2002. MOLART. 8 May 2006
- Andés, Louis Edgar, Drying oils, boiled oil, and solid and liquid driers. London: Scott, Greenwood & Co., 1901.
外链
- Tung and Linseed Oils by Steven D. Russel