The secret of refined linseed oil and linseed oil varnish

Natural and effective: Linseed oil varnish for wood preservation (Foto@Fotolia)

How can it be that refined linseed oil still works just as well in many applications as synthetic resins? What is the secret? Answers to this can be found in the structure of linseed oil as well as in the composition of the fatty acids.

Linseed oil is based on linolenic acid and linoleic acid and has a high number of double bonds, which are broken down by an oxidative polymerization process and thus form a chemical crosslink. The resulting polymer is called linoxin and forms a weather-resistant and non-polar film. The oil itself has very good cross-linking properties with a wide variety of substrates and additives such as. B. pigments and fillers. In addition, linseed oil adheres to wood, cementitious substrates and even many metals.

Linseed oil: Particularly exciting for biobased paint systems

Linseed oil is not in competition with food or animal feed production. It is pressed from linseed and can be extracted from linseed using quick and easy extraction processes. The subsequent refining process is necessary so that the fat does not go rancid.Where does linseed grow? Flax seeds thrive very well in cold, arid regions with a large temperature gradient between summer and winter, so it is not surprising that the largest growing areas are in Eastern Europe and Canada. In comparison to synthetic paint resins, the purified, refined linseed oil, also called paint linseed oil, has both approval for direct and indirect food contact.

Although the product is 100% based on a natural raw material, there are hardly any major fluctuations in quality. Why does linseed oil need to be refined? Crude oils are often unattractive for end users due to their dark color and often slightly cloudy appearance. But also in technical applications, raw linseed oil ages quickly due to the residual water and the acid. This increases extremely and leads to poorer drying and deteriorated weather resistance and thus to faster loss of gloss and embrittlement. A clear indication of aging oil or poorer oil quality is the increase in the peroxide number. Nevertheless, "linseed oil varnish" can be produced from raw linseed oil, which is used both as a clear varnish and in highly filled systems. Linseed oil varnish as a natural wood protection has been used for many decades. Provided with so-called "siccatives", as a drying agent and other additives, linseed oil varnish is often used as a coating agent for indoor and outdoor use. After hardening, linseed oil varnish forms a water-repellent protective layer made of linoxin. This layer is called 'varnish', coming out of French 'Vernis', in German 'lacquer'. Art uses oil paints made from pigmented linseed oil and other additives that lead to the varnish layer on the canvas. Linseed oil varnish is slightly viscous and looks similar to honey.

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