Blown (air oxidised) vegetable & marine oils & paint manufacture

Many vegetable drying, semi‐drying, and non‐drying oils and also marine oils have the property of being able to absorb oxygen as such, or from the air, to varying degrees and thereby become thickened and viscous, and soluble in mineral oils, the commercial acceleration of the process being known as “blowing”, giving blown, oxidised and polymerised oils. Thus blown oils are oils that have been agitated vigorously by having a current of air or oxygen passed through them whilst in a heated state, temperatures of the order of 70/120°C being usually involved, such oils having a long history of application. The degree of oxidation of an oil and degree of reduction in unsaturation depends upon the amount of air/oxygen passed through an oil, the length of time of blowing and temperature, and is in direct proportion to the air/oil interface, and whether or not a catalyst is used. Blown oils are characterised chemically by the presence of C‐O‐C links and C‐C links, with useful terminal groups such as hydroxyl and carboxyl. The products of the air oxidation in blown oils, whilst still polymeric, etc, in nature, are quite different from those in oils whose properties have been changed by application only of heat and catalysts i.e. heat‐bodied oils, for use in resin and paint manufacture, the former oils containing hydroxy groups, etc., the films of which are less resistant to alkalies and to water. Many oils which show a tendency to “gumming” are free of this defect after blowing.