Linseed oil drying

The oxidation of linseed oil, which takes place in drying, is attended by the generation of much heat. If the oil is exposed in thin layers on porous inflammable material, such as cotton rags or waste, spontaneous combustion may take place as the result of active oxidation. Linseed oil dries more rapidly when exposed to the air if it has been previously boiled for some hours. The process consists in heating the oil with certain oxides or salts, called driers, such as litharge, lead acetate, or borate of manganese, which probably act as catalytic agents... 

Linseed Oil Drying oil made from the flax seed. Used as a solvent in many oil-based paints. "Boiled" linseed oil can be used to protect wood from water damage. Sometimes used as a furniture polish. 

Chemical modification of the wax can improve smear resistance (5). Sihcones, which do not harm furniture finishes (6), are incorporated as film-forming ingredients in furniture pohshes. The lubricant properties of sihcones improve ease of apphcation of the pohsh and removal of insoluble soil particles. In addition, sihcones make dry films easier to buff and more water-repeUent, and provide depth of gloss, ie, abihty to reflect a coherent image as a result of a high refractive index (7). Wax-free pohshes, which have sihcones as the only film former, can be formulated to dehver smear resistance (8). Another type of film former commonly used in oil-base furniture pohshes is a mineral or vegetable oil, eg, linseed oil. 

Cobalt in Driers for Paints, Inks, and Varnishes. The cobalt soaps, eg, the oleate, naphthenate, resinate, Hnoleate, ethyUiexanoate, synthetic tertiary neodecanoate, and tall oils, are used to accelerate the natural drying process of unsaturated oils such as linseed oil and soybean oil. These oils are esters of unsaturated fatty acids and contain acids such as oleic, linoleic, and eleostearic. On exposure to air for several days a film of the acids convert from Hquid to soHd form by oxidative polymeri2ation. The incorporation of oil-soluble cobalt salts effects this drying process in hours instead of days. Soaps of manganese, lead, cerium, and vanadium are also used as driers, but none are as effective as cobalt (see Drying). 

Based on the data in Table 1, the average number of methylene groups between double bonds, ie, the functionaHty, for the typical linseed oil is 3.6 it is a drying oil. The corresponding number for soybean oil is 2.07 it is a semidrying oil. The higher the average functionaHty is above 2.2, the more rapidly a solvent-resistant, cross-linked film forms on exposure to air. 

The products of these reactions with maleic anhydride, termed maleated oils, react with polyols to give moderate mol wt derivatives that dry faster than the unmodified oils. For example, maleated, esterified soybean oil is a drying oil with a drying rate comparable to that of a bodied linseed oil with a similar viscosity. Maleated linseed oil can be converted to a water-dilutable form by hydrolysis with aqueous ammonium hydroxide to convert the anhydride groups to ammonium salts of the diacid. Such products have not found significant commercial use, but similar reactions with alkyds and epoxy esters are used on a large scale to make water-dilutable derivatives. 

Soybean oil and tall oil fatty acids are not used in paints without modification. These products, Hsted as used in paints, first must be converted to alkyds or other synthetic drying oils. Presumably significant amounts of the linseed oil Hsted under paints are also converted to alkyds or other derivatives before use. In addition to the numbers given in Table 2, relatively large amounts of the oils are reported to have been consumed by conversion into fatty acids. Some indeterrninate fraction of the fatty acids, especially tall oil fatty acids, are presumably converted into derivatives that are used like drying oils. 

A frequently cited example of protection from atmospheric corrosion is the Eiffel Tower. The narrow and, for that age, thin sections required a good priming of red lead for protection against corrosion. The top coat was linseed oil with white lead, and later coatings of ochre, iron oxide, and micaceous iron oxide were added. Since its constmction the coating has been renewed several times [29]. Modern atmospheric corrosion protection uses quick-drying nitrocellulose, synthetic resins, and reaction resins (two-component mixes). The chemist Leo Baekeland discovered the synthetic material named after him, Bakelite, in 1907. Three years later the first synthetic resin (phenol formaldehyde) proved itself in a protective paint. A new materials era had dawned. 

Leinfil-saure, /. linoleic acid, -schlichte, /. linseed-oil size, -trockenprozess, m. drying of linseed oil. 

Raw linseed oil Boiled linseed oil Stand oils Air drying Oxidative polymerisation Aliphatic hydrocarbons Fair Bad Fair Poor Poor/fair Binder for anticorrosive primers for wire-bushed steel Slow drying... 

Polyunsaturated fats can combine easily with oxygen at the points where there is a double bond between two carbon atoms. This is why they make good antioxidants they combine with the oxygen free radicals so they don t damage other molecules. It is also how oils harden, and is thus important to painters. Oil paints made with linseed oil are almost three-quarters trilinolein. They dry to form a tough plastic film that incorporates the pigments and holds them onto the surface to be painted. 

Linolenic acid is also important industrially it is the major constituent of linseed oil (approximately 47%) which is obtained from flax. The high degree of unsaturation present in this acid makes the oil an excellent drying agent for use in paints, varnishes and inks. 

Drying oils. Place 3 ml. of hnseed oil in a test-tube, add about 0-1 g. of litharge and boil the mixture gently for 10 minutes. When cold, pour a little of the product on a watch glass and spread the oil into a thin film with the aid of a small piece of paper. Pour a little of the untreated linseed oil on another watch glass and spread it out as a thin film. Compare the times taken for the films to become dry. 

---