Autoxidative drying

The alcoholysis process has lower raw material costs than the fatty acid process but higher production costs, since it is a two-step process. The decision whether to produce from oil or from fatty adds is thus largely based on the amount of od/fatty adds in the formulation (see short oil/long oil resins, discussed in Section 16.5.4). 

Variables measured at regular intervals to control and, if necessary, adjust the process are  

After reaching these specifications, potential modifications can be made, for example with silicones for better outdoor durability, or polyamides to impart thixotropy. Finally the resin is cooled, diluted in solvent and/or emulsified, and if necessary filtered. 

---

Surfactants capable of participating in autoxidative drying are of interest for the post-emulsification of alkyd resins. Ethoxylated monoethanolamides of unsaturated fatty acids are one such type of surfactant that can be chemically incorporated into the network during drying... 

A basic reaction scheme of the autoxidative drying process is depicted in Scheme 16.18. A catalyst is needed to give this reaction sufficient speed usually a cobalt(II) salt is used. The diene moieties of the linolenic acids, especially, are involved in this process. After formation of a conjugated hydroperoxide with molecular oxygen from the ambient air, the hydroperoxide decomposes into oxy-radicals that can fur-... 

Drier Mechanism. Oxidative cross-linking may also be described as an autoxidation proceeding through four basic steps induction, peroxide formation, peroxide decomposition, and polymerization (5). The metals used as driers are categorized as active or auxiUary. However, these categories are arbitrary and a considerable amount of overlap exists between them. Drier systems generally contain two or three metals but can contain as many as five or more metals to obtain the desired drying performance. 

Viscosity of drying oils also can be increased by passing air through the oil at relatively moderate temperatures, 140 to 150°C, to produce blown oils. Presumably, reactions similar to those involved in cross-linking cause autoxidative oligomeri2ation of the oil. 

Common impurities found in aldehydes are the corresponding alcohols, aldols and water from selfcondensation, and the corresponding acids formed by autoxidation. Acids can be removed by shaking with aqueous 10% sodium bicarbonate solution. The organic liquid is then washed with water. It is dried with anhydrous sodium sulfate or magnesium sulfate and then fractionally distilled. Water soluble aldehydes must be dissolved in a suitable solvent such as diethyl ether before being washed in this way. Further purification can be effected via the bisulfite derivative (see pp. 57 and 59) or the Schiff base formed with aniline or benzidine. Solid aldehydes can be dissolved in diethyl ether and purified as above. Alternatively, they can be steam distilled, then sublimed and crystallised from toluene or petroleum ether. 

Autoxidation of dimethylketene with oxygen in ether at —20°C gives the poly (peroxylactone) which as a dry solid is liable to undergo unpredictable and violent detonation. 

Clear white to yellow-pink deliquescent crystals with an odor like rotten eggs due to formation of hydrogen sulfide. Commercial material may be yellow or brick-red lumps or flakes. It is unstable and discolors upon exposure to air. It undergoes autoxidation to form polysulfur, thiosulfate, and sulfate. It absorbs carbon dioxide from the air to form sodium carbonate. Moist sodium sulfide is spontaneously flammable upon drying in air. This material is hazardous through ingestion and produces local skin/eye impacts. 

The slow spontaneous oxidation of compounds in the presence of oxygen is termed autoxidation (autooxidation). This radical process is responsible for a variety of transformations, such as the drying of paints and varnishes, the development of rancidity in foodstuff fats and oils, the perishing of rabber, air oxidation of aldehydes to acids, and the formation of peroxides in ethers. 

Lipid autoxidation in fluid milk and a number of its products has been a concern of the dairy industry for a number of years. The need for low-temperature refrigeration of butter and butter oil, and inert-gas or vacuum packing of dry whole milks to prevent or retard lipid deterioration, in addition to the loss of fluid and condensed milks as a result of oxidative deterioration, have been major problems of the industry. The autoxidation of milk lipids is not unlike that of lipids in other... 

---