linseed oil

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linseed oil
Raw material plant (noun)

Common flax ( Linum usitatissimum )

colour

gold-greenish

ingredients
Oleic acid 10-22%
Linoleic acid 12-18%
Linolenic acid 56-71%
More fatty acids 4-6% palmitic acid , 2-3% stearic acid
Other ingredients Tocopherol 110-280 mg / kg
properties
density 0.93 kg / l at 15 ° C
viscosity = 51.2 mm 2 / s (at 20 ° C)
Oxidation stability 0.3 h; 1.7 h
Melting point −13 ° C to −20 ° C
Flash point 240 ° C
Iodine number 169-192
Saponification number 187-195
Calorific value 39.33 MJ / kg
Cetane number 27.6; 32.9; 52
Manufacturing and Consumption
Production worldwide approx. 0.8 million t (status: 1992); approx. 0.88 million t (as of 2014)
Most important production countries China, Belgium , USA , Turkey
use Food, industry (for paints, floor coverings)

Blooming flax field
General chemical structure of oils such as linseed oil. R 1 , R 2 and R 3 therein are alkyl radicals (less than 10%) or alkenyl radicals (over 90%) with a mostly odd number of carbon atoms. Like other oils, linseed oil is a mixture of tri esters of glycerine .

Linseed oil (linseed oil) is a vegetable oil made from linseed , the ripe seeds of flax . Raw linseed oil (raw linseed oil) is linseed oil without the addition of other oils or other substances. In addition to the actual oil flax, other types of flax (genus Linum ) are also used to extract oil .

properties

Cold-pressed linseed oil is golden yellow, warm-pressed oil is yellowish-brown. Refined linseed oil is light to golden yellow in color. The oil smells spicy like hay, is described as herbaceous to dull and slightly roasted and can have a fishy note. Fresh, the product tastes slightly nutty and hay-like, after storage it becomes bitter and rancid. As a food, use within a few weeks is recommended. For manual and technical purposes it can often be stored for several years if it is sealed off from light and air.

Curing

Due to the high content of monounsaturated and polyunsaturated fatty acids, linseed oils harden and have been used for centuries as binders for pigments for the production of oil colors . Curing is an oxidative polymerisation process which, depending on oxygen, light, temperature, humidity and additives with catalytic properties ( siccatives ), can take days to decades. In the process, oxygen from the air is deposited on the double bond of the unsaturated fatty acids and a complex sequence of chemical reactions occurs , which results in the cross-linking of the individual molecules. The polymer end product is called Linoxyn and is u. a. the starting product of linoleum . The volume of the binder linseed oil increases through oxidation (absorption of oxygen) and decreases again during the subsequent polymerization. This type of reaction is important for the proper use of oil paints (see under paints and coatings ).

Self-ignition

Cloths, brushes, etc. soaked in linseed oil can self-ignite. Textiles that have been soiled with unsaturated oils and have not been washed out sufficiently can ignite spontaneously in the tumble dryer or when they are subsequently stored.

The self-ignition is probably caused by the autoxidation of double bonds of the α-linolenic acid with a large surface area and thus high availability of atmospheric oxygen. If the heat generated during the oxidation of the linseed oil builds up, carrier substances can also ignite at the appropriate temperatures. The risk is particularly high when working with so-called semi - oil , which consists of half linseed and turpentine oil , as the latter has a flash point of below 50 ° C, while linseed oil itself has a flash point of approx. 315 ° C ( Marcusson ) and one Boiling point above 350 ° C is rather difficult to ignite.

Textiles soaked in linseed oil should be spread out on a non-flammable surface and laid out to harden or stored under water. They can be hung up to dry outdoors. They should be kept in an airtight container or they should be incinerated in a controlled manner. Brushes can hang in raw linseed oil until they are used again.

ingredients

Linseed oil contains mostly (90% and more) unsaturated fatty acids in its triglycerides and in particular has a high proportion of the omega-3 fatty acid α-linolenic acid of 45% to 71% (also about 17% to 23.5% oleic acid and 12 % to 24% linoleic acid ). A small proportion (1–10%) of α-linolenic acid is also converted into the higher-quality omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Linseed oil contains about 1.2 mg / 100 g alpha-tocopherol and 52 mg / 100 g gamma-tocopherol in vitamin E. In addition, with 17 to 30 mg / 100 g, a relatively high value of the tocotrienol -like and lipid peroxidation- protective plastochromanol -8.

Manufacturing and storage

Linseed oil for nutrition and pharmaceutical purposes is cold-pressed with screw presses . Hot pressing with subsequent extraction with solvents and refining is used in the extraction of linseed oil for technical purposes.

As an unsaturated oil, linseed oil is very sensitive to air; it tastes bitter after a short time, while fresh linseed oil has a less pronounced taste. It should be kept cool after opening. Even when stored in the refrigerator (around 4 ° C), a bitter taste develops after a few days.

Pressing

Linseed oil hand press, exhibited in the historic Dutch windmill in Straupitz .
Hot pressed linseed oil
The dried flax seeds are rolled into flour, mixed with hot water and worked in a kneading machine until a solid, crumbly mass is formed, which is roasted while stirring. The oil is then separated from the solids in a hydraulic press. One liter of oil can be obtained from four kilograms of flaxseed. This type of linseed oil contains a high proportion of slimy and suspended matter. This raw linseed oil (not to be confused with raw linseed oil) is not suitable for craft applications. The raw linseed oil must be cleaned before use.
Cold pressed linseed oil
is obtained by pressing the flaxseed through a screw press. The linseed is pressed through a press cylinder with the help of a screw roller at low pressure. Different nozzles at the end of the outlet as well as a change in the pressing speed have an influence on the oil yield. During cold pressing, oil temperatures of a maximum of 40 ° C are reached. Suspended solids are removed before use. This can be achieved by settling the suspended solids with a sufficiently long storage period and decanting the pure oil.
Pressing with exclusion of oxygen
Since linseed oil is oxidized very quickly by the oxygen in the air even when it is cold pressed and thus becomes bitter, various pressing processes have been developed to prevent oxidation during the pressing process. This is done by using a protective atmosphere made of pure nitrogen or carbon dioxide, which keeps the oxygen in the air away from the pressed material and oil. Examples of such pressing processes are those under the trade names oxyguard and omega safe . In both processes, the oil is also protected from the effects of light and the pressing temperature is continuously monitored.
Feed linseed press cake from a screw press

During the pressing process, linseed oil and the firm linseed press cake are produced . This press residue is primarily used as high-quality feed in the winter months.

Variants for technical use

Raw linseed oil

In the original state after pressing, linseed oil is also called raw linseed oil to distinguish it from cooked linseed oil . Since no polymerization has taken place here, it is thin and hardens slowly. As a result, it penetrates particularly deep into capillary building materials such as wood, stone and ceramics. It is well suited for impregnating or priming absorbent materials, as it offers protection against moisture penetration. Curing takes place extremely slowly when there is no light. This is desirable in many cases, as the oil, which is still liquid in the deeper layers, can redistribute itself even if the surface is later deformed, cracked or damaged. Compared to non-hardening oils such as white oil and some vegetable oils , hardening oils have the advantage that the layers that have already hardened on the surface are resistant to leaching and strengthen the surface of the base material.

If pigments are added to raw linseed oil , it can be used as a glaze . When used outdoors, boiled linseed oil, linseed oil varnish or stand oil can then be coated in order to protect the pigments and the surface of the base material from weathering over the long term. However, this limits the luminosity of the pigments.

Half oil

Half oil consists of linseed oil and half of solvents such as turpentine oil , orange oil, turpentine or white spirit ( turpentine substitute ) in order to be able to penetrate even better into porous materials. Since uncooked linseed oil already has good creeping properties, the use of half oil is controversial.

Boiled linseed oil

When linseed oil is boiled down, the polymerization is started in order to achieve faster hardening. The already partially chained molecules no longer penetrate so deeply into the pores of the painting surface. This can be desirable in order to apply an opaque coating that allows the structure of the material to shine through less and offers better protection against the effects of the weather . Greater layer thicknesses can be achieved, which also results in a stronger gloss.

Occasionally, manufacturers of natural paints also use the term for raw linseed oil to which drying agents have been added.

Linseed oil varnish

The term varnish is used differently depending on the age and subject area. Linseed oil varnish is usually intended for the production of an opaque coating and is often just another name for boiled linseed oil. It can also be cooked or raw linseed oil, the desiccants (ie polymerization catalysts such as zirconium - and cobalt - salts ) were buried, to speed up the drying process.

Stand oil, sun-thickened and blown linseed oil

Stand oil or sun-thickened linseed oil is used for special purposes . To get the oxidation going, it is exposed to the sun in shallow tubs for several months and stirred over and over again so that a film does not form.

With blown linseed oil, an aerator is used, as it is used for aquariums , which prevents film formation through constant circulation.

These treatments have four goals: firstly, the consistency becomes more viscous, secondly, the linseed oil is bleached (i.e. lighter), thirdly, the subsequent hardening time is shortened and fourthly, the increase in volume during hardening is reduced, which reduces the risk of wrinkles and cracks.

Sun-thickened linseed oil is traditionally used in violin making and painting , especially in Flemish Baroque painting. When making violins, the linseed oil is thickened so much that the mass has to be turned through a meat grinder to homogenize it.

Depending on the manufacturing process and the added siccatives, it can take a few days or many weeks for the stand oil to dry completely . If in doubt, preliminary tests or the addition of drying agents are recommended.

Stand oil is very well suited for the production of weatherproof oil paints by adding pigments . It forms a more elastic film than modern paints and has little tendency to peel off. If it begins to weather after a long time, it can easily be repainted with an oil paint.

Primer, binding and coating agent

Paints

The most striking difference between modern synthetic resin paints and the traditional way of applying oil paints is the thinner layer of the paint. This means that irregularities in the subsurface are less well covered and several applications are necessary to achieve comparable abrasion resistance. On the other hand, due to the low layer thickness and the slower curing, there are fewer tensions in the paint layer, so that later cracking or peeling of oil paints is almost unknown (as long as the substrates are dry and stable). Subsequent renovation coatings for oil paints can usually also be carried out without leaching, sanding or removing the old layers of paint, which saves a lot of time. By adding natural or synthetic resins , oil paints can be given some of the properties of modern paints.

Linseed oil is the most important binder for oil paints . It dries faster than other hardening vegetable oils such as poppy seed oil , safflower oil or walnut oil , but tends to yellow. Its properties both as a binding agent and as a preservative make it the basis of linseed oil paints that have been tried and tested for centuries . The first known mentions of the use of oil-based paints for art painting can be found in manufacturing recipes from the 8th century. In the meantime, the colors are preferably made from boiled linseed oil and pigments ; depending on the application technology, they also contain thickeners such as aluminum stearates or setting accelerators .

The patina-like shining paints known from old farms are caused by the weathering of the top layer of linseed oil, which causes the pigments themselves to come to the surface. Further weathering constantly exposes new pigments. This process results in a lively shimmering surface. The constant renewal of the surface reduces the pollution caused by the growth of microorganisms and fungi. When the pigments have weathered down to the substrate, they can be painted again without the old layer of paint having to be removed or sanded beforehand.

The volume of oil paint increases through oxidation (absorption of oxygen) - in contrast to acrylic paint , the volume of which decreases when it hardens. This is why high-binder ("fat") layers of oil paint above can break up low-binder ("lean") paint layers, which leads to the formation of cracks typical of oil paints : It can be recognized by the fact that only the upper paint layer is torn and the one underneath is undamaged. This type of crack is referred to as a shrinkage crack to distinguish it from the age cracks that reach down to the painting surface (wooden panels or canvas ). Too high a proportion of binder often causes "greasiness": The paint layer throws creases as it expands, so it forms wrinkles, which can usually be observed in the darker parts of pictures because the common dark color pigments (brown earth, soot or coal) are relatively have a small particle size (around 1 µm) and thus require more binder than coarser pigment particles.

The binder requirement of a pigment is expressed by the oil number , an internationally standardized code number (ISO 787 Part 5) that describes how many grams of linseed oil are needed to turn 100 grams of a pigment into a cohesive, putty-like substance.

Wood protection

Linseed oil is a natural wood preservative and has been used for centuries for the impregnation of wood (half-timbering, windows , doors, wooden facades) and terracotta, rarely for plaster or masonry. It is water-repellent but open to vapor diffusion and, unlike other binders, penetrates deep into the wood, where it polymerizes to form a stable bond. The depth of penetration and thus the preservative effect increases with the flowability of the oil and is therefore improved by heating or the use of low-viscosity oils.

Pigments must be added to the oil for long-term protection of wooden surfaces from weathering by the sun's UV radiation. Light pigments reduce the heating of the wood when exposed to sunlight, which increases the service life of the components. Highly pigmented linseed oil paints can easily be thinned with pure linseed oil.

The combination of impregnation with raw linseed oil and a colored layer of pigmented, boiled linseed oil guarantees a long service life for wooden components such as doors, gates and windows that are exposed to the weather. Modern coating systems can quickly fail when exposed to weathering, especially on soft coniferous wood. If water penetrates into the wood underneath through fine cracks in the coating, it can only dry out very slowly due to the vapor-tight coating material. The wood begins to rot under the surface unnoticed. In contrast, the flexible oil paints are less prone to cracking and the deeply penetrating oil impregnation prevents the entry of water. The disadvantage is that the particularly exposed areas (such as the almost horizontally aligned weatherboard ) have to be checked and painted over every few years .

Wrinkles and cracks are avoided in construction and craft by applying thin layers of paint several times and curing each individual paint for about two days. A few hours after painting, any oil that has not yet been absorbed is removed with a cloth or brush and distributed. Pure, cold-pressed, raw (not boiled) linseed oil penetrates particularly deeply, which is therefore best suited for priming, but only hardens over a very long period of time and therefore cannot be used everywhere, especially since the treated surfaces are sensitive to the end during the long hardening phase for dust and contact stay.

As hard oil mixtures of curing oils with different natural resins referred. In particular, mixtures with the abrasion-resistant carnauba wax are used to treat softwood floors and stairs.

Corrosion protection

Due to its high iodine number, linseed oil is used to create a corrosion protection layer on pans made of cast or wrought iron by means of what is known as baking .

In the Middle Ages, linseed oil was used as an anti-corrosive agent for armor and weapons. It was also used in vehicle construction in the past. It is increasingly used by friends of old-timers , in the preservation of monuments or in “healthy building” as a “non-toxic type” of conservation. The oil forms a water-insoluble compound with Fe 3+ ions in the rust and, after setting (hardening), the oil also forms a crack-free coating.

The addition of lead (II, IV) oxide (Pb 3 O 4 ) to linseed oil produces red lead , a classic and effective, but toxic, corrosion and wood preservative. It was used as early as 700 BC. By the Phoenicians to preserve the ships inside and out. Lead had an anti-fouling effect on the outer layer and as a fungicide on the inside. However, the use of lead oxide is only permitted with a special permit - for restorers, for example. With modern wood and rust protection with linseed oil paint , the poisonous lead oxide is replaced by iron (III) oxide , which is non-toxic as red iron mint.

As a refreshment , linseed oil is used in seafaring to care for and preserve ropes and steel ropes , and sometimes also wood.

Decorative coatings

By the illegal production of products made of cast or wrought iron in addition to the corrosion protection is a dark surface coloration is achieved.

Linseed oil is also burned into surfaces made of copper , bronze and brass ( varnish firing ) in order to then process them artistically and decoratively.

Aluminum can by painting with linseed oil and then heating up to 400 ° C brownish patina (burnished) are.

Binder for pasty masses and plastics

Linseed oil thickens through oxidation to linoxin . It is traditionally used as a binder for wood and window putty, as well as in the manufacture of linoleum .

Other uses

food

Linseed oil (here in a small portion bowl, next to it in commercially available sales packaging in the form of a glass bottle with 250 ml content)

Among the natural sources of the essential α-linolenic acid , linseed oil is one of the few in which the proportion of omega-3 fatty acids exceeds that of omega-6 fatty acids . Others are camelina oil and the exotic chia and perilla oils . Flax belongs (together with barley , wheat, lentils and peas ) to the five earliest agricultural plants of the Eurasian cultural area in the Neolithic . Besides the later oil from hemp and poppy seeds, it is the only historical oil plant in Europe. Since the fats in cereals mainly consist of omega-6 fatty acids, the oil from flaxseed with its high content of omega-3 fatty acids is an important nutritional achievement of the Neolithic period. Omega-3 and omega-6 fatty acids should go together good ratio to each other (the DGE recommends 1: 5). Heated linseed oil contains some trans fatty acids , the physiological properties of which are the subject of special research.

In Lusatia , Saxony and Silesia in particular , linseed oil is used in dishes containing milk such as quark (→ quark with linseed oil ) with potatoes or jacket potatoes , cucumber salad or sour herring in a cream sauce. Due to the oil layer on the dairy dishes, they do not turn sour so quickly, a fact that was used intensively in the summer.

In Upper Austrian cuisine, linseed oil is used to prepare various dishes. In Austria, linseed oil is entered in the register of traditional foods .

Cosmetics

Linseed oil, the medicinal plant oil of 2005, is rich in omega-3 and omega-6 fatty acids. It has not been proven that these are absorbed by the skin. Nevertheless, there are cosmetic products that contain natural linseed oil and claim to revitalize the skin. High quality linseed oil is used for the production of natural soaps. Using clove oil and lemongrass oil , linseed oil soap is said to have a stimulating and refreshing effect.

Biofuel

Due to its low pour point, linseed oil has better cold start properties than rapeseed oil . However, the high iodine number leads to very rapid drying in air (due to atmospheric oxygen), which makes it considerably more difficult to use in the fuel system. On the other hand, linseed oil is of no practical importance for the production of biofuels .

Lusatian linseed oil

Lusatian specialty: dip rolls in linseed oil and sugar

Lusatian linseed oil is a protected name of geographical origin. The Lausitz oil mill in Hoyerswerda was founded in 1924. The cutting of linseed oil has been a traditional trade in Lusatia for a long time.

literature

  • S. Krist, G. Buchbauer, C. Klausberger: Lexicon of vegetable fats and oils. Springer, Vienna 2008, ISBN 978-3-211-75606-5 , pp. 246-250.
  • H.-U. Grimm: Linseed oil makes you happy: the blue nutritional wonder. Knaur MensSana, Munich 2012, ISBN 978-3-426-65696-9 .

Web links

Commons : Linseed Oil  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c German Society for Fat Science : Fatty acid composition of important vegetable and animal edible fats and oils. Retrieved February 11, 2020 . .
  2. ↑ Bertrand Matthäus: Which fat and oil for which purpose? Features and specifications of oils and fats. (PDF; 183 kB).
  3. ↑ a b c Bavarian State Ministry for State Development and Environmental Issues: Vegetable oil- powered combined heat and power plants. Part 1, 2002, pp. 11, 18 online (PDF; 2.12 MB), lfu.bayern.de, accessed on April 30, 2017.
  4. ↑ a b c d FNR : Biofuels Basic Data Germany. October 2008 (PDF; 526 kB).
  5. ↑ a b c Jens Schaak: Emissions from the diesel engine combustion of vegetable oils and ... Dissertation, Techn. Univ. Braunschweig, Cuvillier, 2012, ISBN 978-3-95404-173-2 , p. 364.
  6. ↑ a b S. Krist, G. Buchbauer, C. Klausberger: Lexicon of vegetable fats and oils. Springer, Vienna 2008, ISBN 978-3-211-75606-5 , pp. 246-250.
  7. ↑ Ibrahim Dincer, Calin Zamfirescu: Sustainable Energy Systems and Applications. Springer, 2011, ISBN 978-0-387-95860-6 , p. 184.
  8. ^ Forest Gregg: SVO. New Society, 2008, ISBN 978-0-86571-612-4 , p. 47.
  9. ↑ Axel Diederichsen: Lein (Linum usitatissimum L.) - the most useful, its ancestry and today's meaning. ( Memento of October 14, 2007 in the Internet Archive ) (PDF; 39 kB), pp. 4–5.
  10. ↑ FAO statistics 2014 .
  11. ↑ Michael Kundel: Fires caused by spontaneous combustion (PDF; 1.64 MB), In: Schadenprisma / Brandschutz. 3/2013, p. 3, on schadenprisma.de, accessed on September 2, 2017.
  12. ↑ Schildhauer, Peter .: Self-ignition of unsaturated vegetable oils on absorbent carriers: Investigations on the process at room temperature and new investigation methods . VdS-Schadenverhütung, Cologne 2001, ISBN 3-936050-00-7 .
  13. ↑ JT Brenna, N. Salem, AJ Sinclair, SC Cunnane: alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans. In: Prostaglandins, leukotriene, and essential fatty acids. Volume 80, Number 2-3, 2009, pp. 85-91, ISSN  0952-3278 . doi: 10.1016 / j.plefa.2009.01.004 . PMID 19269799 . (Review).
  14. ↑ Breanne M Anderson, David WL Ma: Are all n-3 polyunsaturated fatty acids created equal ?. In: Lipids in Health and Disease. 8, 2009, p. 33, doi: 10.1186 / 1476-511X-8-33 .
  15. ↑ JT Brenna: Efficiency of conversion of alpha-linolenic acid to long chain n-3 fatty acids in man. In: Current opinion in clinical nutrition and metabolic care. Volume 5, Number 2, 2002, pp. 127-132, ISSN  1363-1950 . PMID 11844977 . (Review).
  16. ↑ E. Mantzioris, MJ James, RA Gibson, LG Cleland: Dietary substitution with alpha-linolenic acid-rich vegetable oil Increases eicosapentaenoic acid Concentrations in tissues. In: The American journal of clinical nutrition. Volume 59, Number 6, 1994, pp. 1304-1309, ISSN  0002-9165 . PMID 7910999 .
  17. ↑ Gwendolyn Barcel-Coblijn, Eric J. Murphy: Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: Benefits for human health and a role in maintaining tissue n-3 fatty acid levels. In: Progress in Lipid Research. 48, 2009, pp. 355-374, doi: 10.1016 / j.plipres.2009.07.002 .
  18. ↑ Tocopherol, tocotrienol and plant sterol contents of vegetable oils and industrial fats. In: Journal of Food Composition and Analysis . 21, 2008, pp 152-161 ( de.scribd.com ( Memento of 1 February 2014 Internet Archive )).
  19. ↑ Jolanta Gruszka, Jerzy Kruk: RP-LC for Determination of Plastochromanol, Tocotrienols and Tocopherols in Plant Oils. In: Chromatographia. 04/2012; 66 (11), pp. 909-913, doi: 10.1365 / s10337-007-0416-2 .
  20. ↑ Thomas Seilnacht: Linseed oil. Retrieved November 19, 2018 .
  21. ↑ For example, the manufacturer LeinölPro according to their own information.
  22. ↑ Wolfgang Boesner (Ed.): Catalog from Boesner-Künstlerbedarf . No. (2009/2010) . Witten, S. 332 .
  23. ↑ However, this depends on the local microclimate and probably works best on surfaces that are exposed to the sun.
  24. ↑ DGE article with a ratio of 1: 5. Retrieved November 19, 2018 .
  25. ↑ O'Keefe SF, Lagarde M, Grandgirard A, Sebedio JL: Trans n-3 eicosapentaenoic and docosahexaenoic acid isomers exhibit different inhibitory effects on arachidonic acid metabolism in human platelets compared to the respective cis fatty acids. , J Lipid Res. 1990 Jul; 31 (7): 1241-6, PMID 2144870
  26. ↑ Grandgirard A, Piconneaux A, Sebedio JL, Julliard F: Trans isomers of long-chain n-3 polyunsaturated fatty acids in tissue lipid classes of rats fed with heated linseed oil. , Reprod Nutr Dev. 1998 Jan-Feb; 38 (1): 17-29, PMID 9606746
  27. ↑ linseed oil . Entry no. 108 in the register of traditional foods of the Austrian Federal Ministry of Agriculture, Regions and Tourism . Retrieved February 14, 2013.
  28. ↑ Characteristics of some vegetable oils ( Memento from September 6, 2012 in the web archive archive.today ) on inaro.de.
  29. ↑ Information about linseed oil. In: TIS - Transport Information Service. Retrieved November 19, 2018 .