Even if the present invention is applicable in rela- tion to other cellulose-based products than wood the in- vention will in the following be described in connection with wood in the form of different types of lumber. De- composition of wood when used outdoors is almost exclu- sively caused by fungi and bacteria. The requirement for growth of such micro-organisms is the presence of water.

Furthermore, a suitable temperature and access to nutri- tion and oxygen are required. Prevention of decomposition can be based on the elimination of one or more of these conditions necessary for the growth of the micro- organisms. As an example there can be mentioned that if the moisture content is brought down to a value lower than about 20% biological decomposition is substantially prevented.

A number of different impregnation processes for the protection of wood are known, and these methods can in principle be divided up into techniques based on the sup- ply of a substance poisonous to the growth of the micro- organisms, and techniques whereby the wood is given hy- drofobic properties, for example by impregnation with some kind of oil. In the latter case an impregnation agent is crude linseed oil which can be c-hot-or cold- pressed type, both of which by suitable heat treatment are converted into boiled linseed oils. The use of such linseed oils is, however, associated with certain draw- backs, for example a viscosity which is unfavourably high for ease of handling, a contents of components constitut-

ing substrate for the relevant micro-organisms, unfavour- able drying properties, etc. One method used for lowering the viscosity is dilution with a solvent something which, however, is environmentally unacceptable. The use of chemical poisons is presently frequently used but should for the future be mainly prohibited for environmental reasons. Also impregnation with a combination of hydrofo- bation and toxic treatment is used, for example treatment with creosote.

The present invention has for an object to provide a processed linseed oil with properties which are substan- tially improved, mainly in connection with the use of the linseed oil for the impregnation of wood and wood prod- ucts.

Another object of the invention is to provide a pro- cess for the manufacture of such linseed oil of improved properties.

Yet an object of the invention is to provide a proc- ess, whereby the uptake of the oil by the wood or the wood product in connection with impregnation is substan- tially increased and can even reach a near 100 percent level of uptake.

In connection with extensive research and experimen- tal work it has in accordance with the invention been found that a treatment of linseed oil resulting a situa- tion that its content of free tocoferol will be less than about 100 ppm, results in substantially improved proper- ties of the linseed oil, particularly in connection with its use as an impregnating agent for wood or lumber.

These and other objects of the invention which will be clear from the following description are obtained a processed linseed oil essentially consisting of lino- lenic, linolic and oleic acids, mainly in the form of triglycerides, the linseed oil being characterized in that its content of free tocoferol is less than about 100 ppm.

It is particularly preferred that the processed lin- seed oil contains free tocoferol in a concentration less than about 75 ppm and particularly less than about 50 ppm.

Even if the processed linseed oil according to the present invention can be based on cold pressed as well as hot pressed linseed oil it is preferred to use cold- pressed linseed oil as a starting material for the lin- seed oil according to the invention.

The new process according to the invention for the manufacture of a linseed oil of the above type is charac- terized by the following steps: a) heating crude linseed oil to an increased temperature lower than the boiling point of water, b) adding a heated inorganic acid to the oil and mixing the oil, c) separation of precipitated materials, for example by sedimentation and discharge and removal of bottom de- posit formed, d) adding a heated aqueous solution of alkali to the oil and mixing the oil, e) discharge of the soap formed, and f) rinsing the oil with hot water until a clear rinsing water is obtained.

The heating in step a) above suitably takes place at a temperature lying within the range about 80 to about 99°C while avoiding that the boiling point of water will be reached.

The inorganic acid is preferably added in an amount of about 0.5 to 30% by weight based on the weight of the oil. Among suitable inorganic acids there may be men- tioned phosphoric acid, sulphuric acid and hydrochloric acid. It is preferred to use as an inorganic acid phos- phoric acid, for example thermal phosphoric acid, at a concentration of for example 80% and in a quantity of about 0.5 to about 2% by weight, particularly from about 1 to about 1.5% by weight.

The mixing in step b) suitably lasts until the reac- tion has come to a stop, which corresponds to a period of about 10 to about 30 minutes.

As alkali any suitable alkaline compound can be used, for example hydroxides of alkali or earth alkali metals, particularly sodium hydroxide or potassium hy- droxide. Particularly preferred is sodium hydroxide, also called caustic soda. The alkaline compound is suitably added in a quantity equivalent to about 2 to 5% by dry weight based on the weight of the oil. Alkali is suitably added in the form of an aqueous solution in a quantity of about 7 to 15% by weight water also this based on the weight of the oil.

For the purpose of avoiding thickening of the oil during heating the oil may in a further step be heated while adding a suitable agent, such as manganese tetrabo- rate. A suitable temperature range for the heating of the oil in this further step is from about 120 to about 140°C. In order to improve the trying properties of the processed oil a suitable catalyst can be added, for exam- ple manganese tetraborate. The agent used as a catalyst can be the same as the agent used to avoid thickening of the oil during heating.

The invention will in the following be further de- scribed with reference to non-limiting examples, wherein quantities and percentages relate to weight if not other- wise stated. In the examples abbreviations concerning the fatty acid present in the linseed oil are furthermore used. Accordingly, for example oleic acid is abbreviated C18: 1, linolic acid C18: 2 and linolenic acid C18: 3. The number following the colon thus indicates the degree of unsaturation.

EXAMPLE 1 Manufacture of processed linseed oil As a starting material in the treatment of the oil Swedish cold-pressed crude linseed oil is used. The treatment of this linseed oil takes place as follows.

The crude cold-pressed linseed oil is heated to about 90°C, and 1.2% hot 80% thermal phosphoric acid is then added to the linseed oil and mixing is carried out for about 20 minutes. The bottom deposit in the form of a black precipitate formed during this acid treatment is removed by sedimentation and discharge.

Then 3.7% 100% caustic soda dissolved in 11% heated water is added to the acid-treated linseed oil, and mix- ing then takes place for 7-10 minutes while observing the course of reaction. The soap formed in this alkali treat- ment is discharged and the linseed oil obtained is puri- fied by rinsing with 25% by volume heated water 5 to 7 times or until the rinsing water is clear and has a pH- value normal to water.

By this treatment substantially all of the no- desired components of the linseed oil have been removed, particularly its original contents of tocoferol. In order that the oil shall possess drying properties it is then heated to about 127°C for about 6 hours, about 0.02% man- ganese tetraborate being used as a catalyst, reason being that the oil shall not thicken during boiling.

In the following examples analysis of processed lin- seed oils according to the present invention prepared as described above are given and also corresponding analysis data for conventional products available on the market.

EXAMPLE 2 Analvsis of processed linseed oil accordina to the inven- tion and two commerciallv available linseed oils In the table below the designations for the linseed oils are KH. KF Eg 1382 boiled linseed oil varnish made from Swedish cold-pressed crude linseed oil from the har-

vest of 1998. The two commercially available oils FK. K Eg 1382 and AC. K Eg 1383 are linseed oils sold by Farghan- delskompaniet in Malmö, hot-pressed boiled linseed oil and Alfort & Cronholm Grosshandel AB, Stockholm, also hot-pressed boiled linseed oil, respectively.

TABLE I Fatty acid composi-FK. K Eg KH. KF Eg ACK Eg IUPAC ! tion, % 1381 1382 1383 (m) C16 : 0 5, 1 4,1 5,1 C18 : 0 3, 6 3,3 3,6 C18 : 1 18, 1 12,2 18,1 C18:2 15,6 14,8 15,7 C18 : 3 55, 9 64,1 55,9 C20 :0 0, 2 0, 1 1 C20 : 1 0, 2 0,2 0,2 C22 : 0 0, 1 0,1 0,1 C24 : 0 0, 1 0,1 0,1 C24 : 1 0, 3 0,4 0,2 . ___ Unknown 0,8 0,7 0,9 Tocoferol, ppm IUPAC 2.432 Alpha <5 <5 <5 Alpha T3 <5 <5 <5 Gamma 170 <5 168 Gamma T3 <5 <5 <5 Delta 5 <5 5 Delta T3 <5 <5 <5 Phosphorus AAS, 250 40 250 IUPAC 2.423 mg/kg (m)

As is clear from the analysis data given above the content of free tocoferol has been largely lowered to 0 in the linseed oil according to the invention. Further- more, a substantial decrease of oleic acid and an even

greater decrease of the amount of phosphorus present can be noted.

EXAMPLE 3 Analysis of processed linseed oil according to the inven- tion and three commercially available linseed oils.

In the table below the designations for the linseed oils are KH. KI Eg 1387 boiled impregnating linseed oil from the harvest of 1998. The three commercially avail- able oils BE. K. Eg 1384 is boiled linseed oil from Beck- ers, Stockholm, AL. R. Eg 1385 is Swedish cold-pressed crude linseed oil from Alcro Farg, Stockholm and EA. R. Eg 1386 is hot-pressed crude linseed oil from Eskil Akerberg AB, Malmo, respectively.

TABEL II BE. K Eg AL. R Eg EÅ. R Eg KH. KI Eg 1384 1385 1386 i Fatty acid IUPAC 2.302 (m) composition % C16:0 5,0 5,2 5,0 4,3 C18:0 3,6 3,8 3,1 3,8 C18: 1 18,0 13,5 20,8 ! C18: 2 15, 5 18,0 15,0 ! C18: 3 56, 5 58,0 54,0 61,1 C20: 0 0, 1 0, 1 0, 2 0,1 C20: 1 0,2 0,1 0,3 0,2 C22: 00, 1 0, 10, 2 0,1 C22: 1 <0, 1 <0, 1 0, 1 <0,1 C24: 0 0, 1 0,1 0, 1 0,1 iC24 : 1 0, 3 1 0, 4 0, 1 0, 3 Unknown 0, 6 0, 7 0,-9 0, 7 Tocoferol, ppm IUPAC 2.432 Alpha <5 <5 <5 <5 AlphaT3 <5 <5 <5 <5 Gamma 105 350 230 <5 GammaT3 <5 <5 <5 <5 Delta 5 5 5 <5 DeltaT3 <5 <5 <5 <5 Phosphorus 206 20 67 25 IUPAC 2. 423 (m) AAS, mg/kg

Also in this analysis report it can be noted that the processed linseed oil according to the invention is largely free from tocoferol, whereas the contents of oleic acid and phosphorus are lower than in two of the commercial oils, whereas the third commercial oil also has relatively low contents of oleic acid and phosphorus.

Tests carried out with the processed linseed oil ac- cording to the present invention show that it has sub- stantially improved properties, particularly in connec- tion with its use for the impregnation of wood and wood products. Thus, the oil according to the invention has lower viscosity and thereby improved handling, it has also by the treatment a lower contents of substances con- stituting substrates for micro-organisms, and it gives when used for impregnation of wood substantially improved resistance.

Thus, accelerated tests in fungus cellar have shown that the linseed oil according to the invention has sub- stantially improved rot-resistance compared with CCA- impregnated wood products (CCA = chromium, copper, arse- nic). The same holds for rot-resistance for impregnated rods inserted into moist earth in cellar climate of high

relative moisture and temperature. Moreover, rot- resistance tests have been carried out with impregnated rods inserted into the ground on fields with micro- organism flora and aggressive brown rot shown that im- pregnation with the processed linseed oil according to the invention results in substantially improved rot- resistance compared with both CCA-impregnation and im- pregnation with conventional linseed oils.

It should be observed that the present invention is not restricted to the specific embodiments exemplified above. Thus, modifications and changes can be carried out within the frame-work of the invention and such changes and modifications are easily understood by those skilled in the art.