Linseed oil
From Wikipedia, the free encyclopedia
Linseed oil, also known as flaxseed oil, is a colorless to
yellowish oil obtained from the dried ripe seeds of the flax plant (Linum usitatissimum, Linaceae).
The oil is obtained by pressing, sometimes followed by solvent extraction. Due to its high levels of α-Linolenic acid (a particular form of omega-3 fatty acid), it is used as a nutritional supplement.
Linseed oil is a drying oil,
meaning it can polymerize into a solid form. Due to its polymer-forming properties,
linseed oil is used on its own or blended with other oils, resins,
and solvents
as an impregnator and varnish in wood finishing,
as a pigment
binder in oil paints, as a plasticizer
and hardener in putty, and in the manufacture of linoleum.
Linseed oil use has declined over the past several decades with increased
availability of synthetic alkyd resins—which function similarly but resist yellowing.[1]
Linseed oil is an edible oil
marketed as a nutritional supplement. In parts of Europe, it is traditionally eaten with
potatoes and quark (cheese). It is regarded as a delicacy due to its hearty taste,
which spices the bland quark.[2]
Chemical
aspects
Linseed oil is a triglyceride,
like other fats. Linseed oil is distinctive in terms of fatty acid
constituents of the triglyceride, which contain an unusually large amount of α-linolenic acid, which has a distinctive reaction toward oxygen in air.
Specifically, the constituent fatty acids in a typical linseed oil are of the
following types:[3]
- The triply unsaturated α-linolenic acid (51.9-55.2%),
- The saturated acids palmitic acid (about 7%) and stearic acid (3.4-4.6%),
- The monounsaturated oleic acid
(18.5-22.6%),
- The doubly unsaturated linoleic acid (14.2-17%).
Having a high content of di- and
triunsaturated esters, linseed oil is particularly susceptible to
polymerization reactions upon exposure to oxygen in air. This polymerization,
which is called drying, results in the rigidification of the material.
The drying process can be so exothermic as to pose a fire hazard under certain
circumstances. To prevent premature drying, linseed oil-based products (oil
paints, putty) should be stored in air-tight containers.
Uses
Most applications of linseed oil
exploit its drying properties, i.e., the initial material is liquid or at least
pliable and the aged material is rigid but not brittle. The water-repelling
(hydrophobic) nature of the resulting hydrocarbon-based
material is advantageous.
Paint
binder
Linseed oil is a common carrier used
in oil paint.
It can also be used as a painting medium, making oil paints more fluid, transparent
and glossy. It is available in varieties such as cold pressed, alkali refined,
sun bleached, sun thickened, and polymerised (stand oil). The introduction of
linseed oil was a significant advance in the technology of oil painting.
Putty
Traditional glazing putty, consisting of a paste of chalk powder and linseed oil, is a
sealant for glass windows that hardens within a few weeks of application and
can then be painted over. The utility of putty is owed to the drying properties
of linseed oil.
Wood
finish
When used as a wood finish,
linseed oil dries slowly and shrinks little upon hardening. Linseed oil does
not cover the surface as varnish does, but soaks into the (visible and
microscopic) pores, leaving a shiny but not glossy surface that shows off the
grain of the wood. A linseed oil finish is easily repaired, but it provides no
significant barrier against scratching. Only wax finishes are less protective.
Liquid water penetrates a linseed oil finish in mere minutes, and water vapour
bypasses it almost completely.[4]
Garden furniture treated with linseed oil may develop mildew.
Oiled wood may be yellowish and is likely to darken with age. Because it fills
the pores, linseed oil partially protects wood from denting by compression.
Linseed oil is a traditional finish
for gun stocks, though very fine finish may require months to obtain. Several
coats of linseed oil is the traditional protective coating for the raw willow
wood of cricket
bats. Linseed oil is also often used by billiards
or pool cue-makers for cue shafts,
as a lubricant/protectant for wooden recorders, and used in place of epoxy to seal modern wooden surfboards.
It is used to coat cricket bats so that the wood retains some moisture. New
cricket bats are coated with linseed oil and knocked to perfection so they last
longer.[5]
Additionally, a luthier
may use linseed oil when reconditioning a guitar,
mandolin,
or other stringed instrument's fret board; lemon-scented mineral oil
is commonly used for cleaning, then a light amount of linseed oil (or other
drying oil) is applied to protect it from grime that might otherwise result in
accelerated deterioration of the wood.
Linoleum
Linseed oil is used to bind wood
dust, cork particles, and related materials in the manufacture of the floor
covering linoleum. After its invention in 1860 by Frederick Walton, linoleum, or "lino"[citation needed] for short, was a common form of domestic and industrial
floor covering from the 1870s until the 1970s when it was largely replaced by PVC ('vinyl') floor coverings.[6]
However, since the 1990s, linoleum is on the rise again, being considered more
environmentally sound than PVC.[7]
Linoleum has given its name to the printmaking technique linocut,
in which a relief design is cut into the smooth surface and then inked and used
to print an image. The results are similar to those obtained by woodcut
printing.
Nutritional
supplement and food
Although flax seeds contain lignans,
a class of phytoestrogens considered to have antioxidant and cancer-preventing properties,[8][9][10]
the extracted linseed oil according to some, does not contain lignans found in
flax seed,[8]
and allegedly does not have the same antioxidant properties. Some brands of
supplement have lignans added during production. Flax seed oil is easily
oxidized, and rapidly becomes rancid, with an unpleasant odor, unless refrigerated.
Even when kept under cool conditions, it has a shelf life of only a few weeks.[11][12][13]
Oil with an unpleasant or rancid odor should be discarded. Oxidation of flax
seed oil is a major commercial concern, and antioxidants may be added to prevent
rancidification.[14]
The alpha linolenic acid
(ALA) in flaxseed oil is suitable for
cooking, as it (and the lignans in flax seeds themselves) can withstand
temperatures up to 350 degrees F (176.67 C) for two hours.[15][unreliable medical source?][16]
Food-grade flaxseed oil is
cold-pressed, obtained without solvent extraction, in the absence of oxygen,
and marketed as edible flaxseed oil. Fresh, refrigerated and unprocessed,
linseed oil is used as a nutritional supplement and is a traditional European ethnic food, highly regarded
for its hearty taste. It contains the highest level of the omega-3 fatty acid ALA among vegetable oils.[17]
Regular flaxseed oil contains between 52% and 63% ALA (C18:3 n-3). Plant
breeders have developed flaxseed with both higher ALA (70%) and very low ALA content
(< 3%).[18]
The USFDA granted generally recognized as safe (GRAS) status for high alpha
linolenic flaxseed oil.[19]
According to the Flax Council of
Canada, ALA is required for normal infant development[20]
and may be beneficial for reducing inflammation leading to atherosclerosis,[21]
and for preventing heart disease and arrhythmia.[22]
However, recent well-controlled placebo
studies suggest the regular consumption of flaxseed oil may not reduce the risk
of stroke, heart disease, or cancer.[23]
Studies[24][25]
have shown a relationship between ALA and an increased risk of prostate cancer.
This risk is irrespective of source (e.g., meat, vegetable oil).[26]
Alternatively, at least one meta analysis
has found a weak protective association between dietary ALA intake and prostate
cancer risk.[27]
Nutrient
content
|
Typical
fatty acid content
|
||
|
6.0
|
4.0–6.0
|
|
|
2.5
|
2.0–3.0
|
|
|
0.5
|
0–0.5
|
|
|
-
|
0–0.5
|
|
|
19.0
|
10.0–22.0
|
|
|
-
|
0–0.6
|
|
|
24.1
|
12.0–18.0
|
|
|
47.4
|
56.0–71.0
|
|
|
Other
|
0.5
|
-
|
Per 1 tbsp (14 g)
Flax seed oil contains no
significant amounts of protein, carbohydrates, or fiber.
Additional
uses
- Animal care products
- Bicycle
maintenance as a thread fixative, rust inhibitor and lubricant
- Composition ornament
for moulded decoration
- Earthen floors
- Animal feeds
- Industrial lubricant
- Leather
treatment
- Oilcloth
- Particle Detectors[30]
- Textiles
- Wood preservation
- Cookware seasoning
Modified
linseed oils
Stand
oil
Stand oil is generated by heating
linseed oil near 300 °C for a few days in the complete absence of air. Under
these conditions, the polyunsaturated fatty esters convert to conjugated dienes, which then undergo Diels-Alder reactions, leading to crosslinking. The product, which is highly
viscous, gives highly uniform coatings that "dry" to more elastic
coatings than linseed oil itself. Soybean oil
can be treated similarly, but converts more slowly. On the other hand, tung oil
converts very quickly, being complete in minutes at 260 °C. Coatings prepared
from stand oils are less prone to yellowing than are coatings derived from the
parent oils.[31]
Boiled
linseed oil
Boiled linseed oil is used as a paint binder or as a wood finish on its own. Heating the oil
causes it to polymerize and oxidize, making it thicker and shortening its drying
time. Today, most products labeled as "boiled linseed oil" are a
combination of raw linseed oil, petroleum-based
solvent, and metallic dryers (catalysts to accelerate drying). The use of
metallic dryers makes boiled linseed oil inedible. Some products contain only
heat-treated linseed oil, without exposure to oxygen.
Heat-treated linseed oil is thicker and dries very slowly. This grade of
linseed oil is usually labeled as "polymerized" or "stand"
oil, though some types may still be labeled as "boiled".
Spontaneous
combustion
Rags soaked with linseed oil stored
in a pile are considered a fire hazard because they provide a large surface
area for oxidation of the oil, and the oil oxidizes quickly. The oxidation of
linseed oil is an exothermic reaction, which accelerates
as the temperature of the rags increases. When heat accumulation exceeds the
rate of heat dissipation into the environment, the temperature increases and
may eventually become hot enough to make the rags spontaneously combust.[32]
In 1991, One Meridian Plaza, a high rise in Philadelphia
was severely damaged and three firefighters perished in a fire caused by
linseed oil-soaked rags.[33]
In 2011, a garage in Sacramento also caught fire due to the spontaneous combustion of
linseed oil-soaked rags.[34]
The entire wiki link can be found at: https://en.wikipedia.org/wiki/Linseed_oil
1 comment:
Mostly, these days, I use linseed oil to soak into the wood floor I live on, and also the wood porch I visit a lot. Plus my dog likes to lick it a lot.
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