WO1996038275A1

WO1996038275A1 - Method for binding oil to wood

Info

Publication number: WO1996038275A1
Application number: PCT/FI1996/000329
Authority: WO
Inventors: Pertti Viitaniemi; Saila JÄMSÄ; Leena Paajanen; Pentti Ek; Juhani Piipponen
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 1995-05-31
Filing date: 1996-05-31
Publication date: 1996-12-05
Also published as: SE9704395L; AU5823796A; SE9704395D0; FI952654A0; FI104706B; FI952654A; SE509980C2

Abstract

The invention relates to a method for binding oil to wood and to a composition used in the method. According to the invention a wood product is contacted with a composition containing a solid anhydride, vegetable oil and alcohol. The treated wood product is dried and then subjected to a heat treatment at a temperature above 150 °C in order to bind the oil. The vegetable oil used preferably comprises at least one double bond, such as linseed oil, tall oil or rapeseed oil, and the anhydride used comprises maleic anhydride, succinic anhydride or phthalic anhydride. An auxiliary solvent, i.e. a lower aliphatic alcohol is used in order to help mixing the oil with the anhydride. By means of the invention the oil is so well bound to the wood that no oil seeps out of the wood even if it is heated above 70 °C. The oil-treated products can be used for outdoor furniture and boat boards.

Description

Method for binding oil to wood

The present invention concerns a method according to the preamble of claim 1 for binding oil to wood.

The invention also relates to a composition according to the preamble of claim 11, which is suitable for oil treatment of wood.

Already for a long time, wood products have been treated with different kinds of oils in order to reduce absorption of water and to provide a water and dirt repellant surface.

The surface of wood treated with oil is often tacky, which makes the use of the wood rather uncomfortable. Depending on the application, the oil has therefore been bound to the wood so as to prevent any seeping from taking place. One way of binding oil is based on oxidation of its double bonds. Furthermore, to achieve a decreased swelling, different methods based on chemical swelling of the wood have been used. The newest methods are based on chemical reactions with the hydroxyl groups in wood by using a mixture of, e.g., maleic anhydride and glycerol.

There are considerable problems related to the known binding methods. Thus, oxidation of double bonds is a slow method and not reliable. The method does not work at all if the temperature grows too high; oil seeps out of the wood. The chemical swelling methods are usually based on water-soluble chemicals (PEG) which are rinsed off as time goes by or which are very toxic. In the anhydride methods, the anhydride is dissolved in alcohol or in another solvent which can be used to prepare a useful, non- precipitating solution together with water. The pH of this solution is very low, e.g. about 1 for a maleic anhydride-glycerol mixture. As result of the low pH (1 to 2), the strength of the wood decreases. The acidity left in the wood can influence long-term stability and cause, e.g., corrosion of iron constructions.

It is an object of the present invention to eliminate the problems related to the prior art and to provide a new solution for binding oil to wood.

The invention is based on the concept of formulating a treatment substance composition containing at least one vegetable oil, at least one anhydride and at least one alcohol which is miscible with the oil and the anhydride. The anhydride is mixed with the oil by using the alcohol as an auxiliary solvent. The wood product is impregnated with a desired amount of the composition and the oil is bound to the wood by means of heat.

More specifically, the method according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.

The composition according to the invention is characterized by what is stated in the characterizing part of claim 11.

Essential features of the invention comprise polymerizing absorbed oil in the interior parts of the wood to form a solid substance, which does not submerge to the surface of the wood even at temperatures up to 100 °C, and reducing swelling and retaining the form of compressed wood.

The vegetable oils used in the invention can be derived from annual or perennial plants. Typical oils pressed from plant seeds can be obtained, for example, from rapeseed, rubsen, sunflower, linen, soybean, cotton, peanut, pumpkin, ricinus, sesame, coconut, cocoa and almond. It is also possible to use oils produced from oil-containing fruits, such as olives. In addition to the afore-mentioned oils suitable are also raw tall oil obtained as a side product of cellulose pulping, and oils which can be separated from wood by, for example, steam distillation, such as pine oil, fore-runs of pine oil and mixtures of turpentine oil. A common feature of all the above mentioned oils is that they contain at least one double bond. Many of the vegetable oils are, however, multi- unsaturated, i.e. they contain several, usually conjugated, double bonds.

Obviously, instead of the afore-mentioned oils, synthetic oils containing at least one double bond can be used. These oils can be prepared from short- and long-chained olefins by oligomerization.

According to the invention it is possible to use compositions containing mixtures of two or more oils, at least one of which belongs to the above mentioned oils.

The vegetable oil is used together with an anhydride or a corresponding reactive substance which is capable of achieving esterification reactions in wood (esterifying component). According to an embodiment of the invention, anhydrides are used for binding oily substances to wood. The anhydrides can be aliphatic or aromatic. Pre- ferably anhydrides derived from dicarboxylic acids are used. Of the aromatic anhydrides, it is preferred to use compounds containing one benzene ring, and of the aliphatic, it is preferred to use saturated or unsaturated anhydrides containing 4 to 6 carbon atoms. These compounds are solid substances at room temperature. Particularly preferred examples are maleic anhydride, succinic anhydride, glutaric anhydride and phthalic anhydride.

The alcohol used in the invention is an aliphatic or aromatic alcohol or phenol, pre¬ ferably a lower aliphatic alcohol containing 1 to 6 carbon atoms, such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol or a pentanol or hexanol. It is required that the alcohol is miscible with the oil and the anhydride. Most of the suitable alcohols are capable of at least partially dissolving the anhydride used. Without an intermediate or auxiliary solvent the anhydride or the corresponding esterifying component and the oil do not mix with each other. Ethanol has found to be a particularly advantageous auxiliary solvent. The alcohol used in the invention contains at the most small amounts of water. Preferably absolute alcohol is used having a water content corresponding to amount of water in an azeotropic mixture of alcohol and water. Typically the concentration of the alcohol is, thus, above 90 %, preferably above 95 %.

The term "auxiliary solvent" comprises all solvents which are miscible with the other components of the compositions, in particular with the oil (oils) and the anhydride

(anhydrides). The compositions according to the invention are typically emulsions which contain an oil and an anhydride phase. At least a part of the anhydride and even of the oil can, however, be dissolved in the alcohol. For the sake of simplicity, in the following the compositions are called emulsions rather than solutions.

Within the scope of the present invention, the term "the wood product to be treated" denotes a product made of wood whose shape or properties are to be changed. Thus, it may be desired to bring the wood product into, e.g., a plastic form in order to shape it, or wood is treated in order to improve its dimensional stability, in particular its surface hardness. Typically a product to be treated according to the invention is at least reason¬ ably thick, its thickness is generally greater than about 5 mm (= massive piece of wood). It can comprise an integral piece of wood prepared from solid wood, but it can also comprise a laminar product (e.g. a chip or wood fibre board) prepared from wood veneer or chips, for instance by compressing. The wood product can also comprise a structure wherein uniform wood layers are bonded together to form a laminate. In the last-mentioned case, the term "wood product" denotes a layered or laminated product which can be impregnated either before it is formed into a product or thereafter.

The method according to the invention comprises three stages, viz. a treatment of wood pieces with a composition according to the invention; drying of the wood pieces; and heat treatment of them (in order to bind the oil component to wood by means of heat).

In the first stage the wood pieces are typically impregnated with an emulsion containing anhydride, oil and alcohol. The emulsion can also contain additives known from the use of anhydrides, such as glycerol. A mixture of the present kind is prepared by mixing together 1 to 1000 parts by weight of an anhydride, 1 to 1000 parts by weight of vegetable oil and 1 to 1000 parts by weight of alcohol. Preferred mixing ratios (indicated in the order anhydride-to-oil-to-alcohol) are the following: 1 to 20 : 1 to 100 : 1 to 100.

Preferably me wood raw material is impregnated with an emulsion of the presented kind having a weight ratio between the maleic anhydride and oil amounting to from 1:10 to 10:10. Advantageously a rather concentrated composition is used containing the afore¬ mentioned components at a concentration of about 1 to 99 weight- %, preferably about 20 to 85 % , in particular about 40 to 70 % . The amount of emulsion to be impregnated into the wood product depends on application of the wood product and on the raw material (species, density and moisture) of the wood. Usually so much substance is impregnated into the wood substance that it penetrates essentially deeper than superficially into the wood. As regards reduction of wood swelling and stabilization of compressed wood it is important that the wood product contains a large amount of oil. Thus, preferably, calculated on each cubic metre of the wood, the said composition is impregnated in an amount of at least about 20 kg, preferably about 25 to 300 kg and in particular about 30 to 140 kg. The moismre content of the wood which is to be subjected to impregnation is preferably 5 to 30 % , in particular about 6 to 7 % . The impregnation can be carried out by removing air from the wood at reduced pressure in a pressure vessel. Thereafter, liquid which is to be used for impregnation is fed into the vessel and the wood is impregnated therewith at normal pressure or, possibly, at overpressure (a method known as the vacuum-pressure-method). Alternatively the wood material is immersed into an impregnation liquid for such a long time that the composition has ample time to penetrate deep into the wood (the immersion method). When it is desired to apply the vegetable oil/anhydride only onto the surface of the wood, the impregnation can also be carried out by surface coating.

After the treatment with the oil and the modification chemical, the wood product is dried slowly at a low temperature in order to remove the auxiliary solvent and to deposit the active chemical in the wood. Drying is continued until the moisture content of the wood product is at least below 20 % , preferably even below 15 to 17 % . Drying can be carried out at room temperature, but it is preferred to carry it out at an elevated temperature which is below 100 °C. The temperature depends on the alcohol used. In particular in the case of ethanol drying is preferably carried out at a temperature in the range of 20 to 99 °C, advantageously 30 to 95 °C, typically at about 70 °C. Any known device can be used for the heat treatment such a drying oven, a heating chamber or an equivalent apparatus which can be used for drying the wood piece in the presence of steam or without it.

According to one preferred embodiment the oil-treated wood product is dried by continuously determining the interior temperature and the temperature on the surface of the wood product and by continuously maintaining the difference between them rather small. Advantageously said temperature difference is 30 °C at the most. By the term "the interior temperature of the wood" is meant the temperature which can be measured in the wood at some distance from the outer surface of it. Depending on the shape of the wood pieces the "interior temperature" is typically measured at a depth of at least about 2 to 5 cm. By the term "outer temperature" is meant the temperature on the wood surface or slightly below it. In many cases, the "outer temperature" thus essentially corresponds to ambient temperature. The temperature is gradually increased so that the temperature difference between the surface of the wood and the interior parts thereof remains constant with a deviation of about 5 °C at the most and not greater than 30 °C. Preferably the temperature difference is kept at 10 to 30 °C. This solution can be carried out by attaching at least two sensors to a test specimen, one of the sensors measuring the interior temperature of the wood and the other the surface temperature thereof. When larger amounts of lumber are to be dried more than one test piece should be equipped with sensors. On an industrial scale, it is preferred to operate the invention is such a way that, based on the measurements, a suitable heating program is determined for each group of lumber, whereby the heating program takes account of the initial moisture content on the process. ^~

After drying the oil component is bound to the wood product for instance in a heating heating chamber a temperature of at least about 150 °C, usually about 150 to 250 °C. In the case of maleic anhydride a preferred temperature range comprises 160 to 180 °C. The duration of the heat treatment is typically about 10 min to 24 h; the binding or fixing time depends, however, on the size of the piece and the components of the treatment composition. Longer or even shorter periods of time can be used. In practice, it has been found that particularly advantageous results are obtained if the temperature of the whole piece corresponds to the temperature of the oven for a time period of at least 2 hours.

In connection with the heat treatment the volatile components are evaporated, which enhances the cross-linking reactions which take place in wood. Considerably advantages are obtained by means of the invention. Thus, it is possible to bind the oil to the wood so that no seeping of the oil will occur even at high tempera¬ tures (not even at above 100 °C). Therefore the surface of a wood product according to the invention is not sticky or tacky. The treatment reduces swelling of wood even to 1/5 and it stabilizes compressed wood so that it becomes moisture proof. The pH of the used solution remains neutral.

The invention will provide a modified wood product which contains (in addition to solvent residues, if any) anhydride and vegetable oil and, possibly, reaction products thereof.

Wood products which have been treated according to the invention, which a free from seeping oil, can advantageously be used for the following applications: furniture, boat boards, wooden bridge beams, constructions in humid spaces, outdoor furniture, environmental constructions (noise barriers) etc.

In the following the invention will be examined in more detail with the aid of a working examples.

Example

The test specimens were treated as follows:

Solutions consisting of a vegetable oil, maleic anhydride and an auxiliary solvent were formulated. Their compositions are indicated in Tables 1 and 2. Pieces of wood having the dimensions 20x40x400 mm were impregnated with the solutions. After impregnation the treated samples were subjected to an intermediate drying step at 70 °C. Then, the samples were hardened at a temperature of 160 °C. The hardening time depended on the size of the sample (about 2 to 6 hours). The temperature of the whole sample was, however, the above-mentioned oven temperature for at least 2 hours.

The (thickness and lateral) swelling of the samples was determined by measuring the dimensions of the samples at absolute dryness and after immersion into water.

Pieces of wood that had been subjected to a conventional treatment with oil and drying at an increased temperature were used as controls. No anhydride had been used for the binding of the oils nor was the temperature raised above 150 °C. The samples treated with linseed oil were first kept for 3 days at 50 °C. Then, for 1 day, they were subjected to a temperature of 70 °C. As a result some 1.5 % oil (calculated on basis of the weight of the sample) seeped out of the sample. When the samples were subjected to a further treatment for 1 day at 70 °C, their weight dropped by a further 0.4 %. Control samples also comprised test specimens impregnated with linseed oil which had not been kept in a heating chamber. The weight of these changed by about 3 % at 70 °C (1 day). The surface of the test specimens was greasy.

Each of the test series according to the invention contained at least one sample which had been treated at a temperature above 150 °C but which did not contain acid anhydride.

In the following Table 1 there is indicated the swelling of birch samples impregnated according to the invention with different compositions (maleic anhydride, oil, ethanol) and immersed for 1 day and 21 days, respectively, into water.

Table 1. Swelling of wood

Thickness swelling, % Lateral swelling, %

M:O:E*

1 day 21 days 1 day 21 days

Linseed oil

(1:1:1) 0,80 1.82 1.42 3.07

(0:1:1) 2.35 7.44 2.52 7.54

Rapeseed oil

(1:1:1) 0.35 0,41 0.59 1.23

(0:1:1) 1.78 5,11 3.50 10.58

Tall oil

(1:1:1) 0.49 0,90 1.17 3.35

(1:2,5:2,5) 0.66 2,34 1.15 4.52

(1:5:6) 1.02 3,08 1.26 3.74

(0:1:1) 1.14 3,12 1.68 4.73

Control 8.52 8,89 11.53 12.51

M = maleic anhydride O = vegetable oil E = ethanol

The surface of the samples according to the invention was dry and no oil seeped out of them, not even at a temperature of 70 °C. The swelling of the samples is also very small. It clearly appears from the table that the addition of an anhydride to a treatment composition decreases swelling by over 50 %. The more anhydride the composition contained the less swelling of the wood could be noticed.

In the following Table 2 the thickness swelling of birch samples impregnated with different mixture (maleic anhydride, oil, ethanol) and then compressed by 30 % is indicated after immersion for 1 day and 21 days, respectively, in an aqueous solution. Table 2. Stabilization of compressed wood

Thickness swelling, %

M:O:E *

1 day 21 days

Linseed oil

(1:1:1) 3.42 5.79 (0:1:1) 31.11 33.71

Rapeseed oil

(1:1:1) 1.41 6.83

(0:1:1) 28.51 35.97

Tall oil

(1:1:1) 1.82 9.50 (1:2,5:2,5) 1.43 12.14 (1:5:6) 3.54 17.59 (0:1:1) 26.44 37.07

M = maleic anhydride O = vegetable oil E = ethanol

The advantageous influence on wood stabilization by anhydrides appears even more clearly from Table 2 than from Table 1.

Claims

Claims:

1. Method for binding oil to wood, characterized by

- contacting a wood product with a composition containing a solid acid anhydride, vegetable oil and alcohol and

- subjecting the wood product thus treated with said composition to a heat treatment at increased temperamre.

2. The method according to claim 1, characterized by using oil containing at least one double bond.

3. The method according to claim lor2, characterized by using a vegetable oil selected from the group consisting of rapeseed, rubsen, sunflower, linen, soybean, cotton, peanut, pumpkin, ricinus, sesame, coconut, cocoa, almond or olive oil, or raw tall oil, distilled tall oil, a fore-run of tall oil or turpentine oil or a mixture thereof.

4. The method according to claim 1,2 or 3, charaterized by using a lower - aliphatic alcohol, such as ethanol, as an aliphatic alcohol.

5. The method according to any one of claim lto4, characterized by using an anhydride selected from the grup consisting of maleic anhydride, succinic anhydride and phthalic anhydride.

6. The method according to any one of claim lto5, characterized in that, after the treatment with a composition containing anhydride, vegetable oil and alcohol, the wood product is dried at a temperamre of about 50 to 100 °C and then it is subjected to a heat treatment at a temperature above 150 °C in order to bind the oil to the wood.

7. The method according to any one of the preceding claims, characterized in that the composition contains at least a small amount of glycerol.

8. The method according to any one of the preceding claims, characterized in that the wood product is treated with the composition by impregnating the wood with the composition, by pressure impregnating the wood with the composition or by vacuum impregnation of the wood with the composition.

9. The use of an anhydride for binding vegetable oil to wood.

10. The use according to claim 9, characterized in that the anhydride and the vegetable oil are mixed with an auxiliary solvent, such as ethanol, before the mixture of vegetable oil and anhydride are contacted with wood.

11. A composition for oil treatment of wood containing

- 1 to 1000 parts by weight of a vegetable oil and

- 1 to 1000 parts by weight of an alcohol miscible therewith, characterized in that the composition further contains

- 1 to 1000 parts by weight of an anhydride.

12. The composition according to claim ll.characterized^'in that it contains

1 to 20 parts by weight of an anhydride, 1 to 100 parts by weight of a vegetable oil and 1 to 100 parts by weight of an alcohol.

13. The composition according to claim 11 or 12, characterized in that it contains linseed oil, pine oil, raw pine oil or rapeseed oil or a mixture thereof, maleic anhydride, succinic anhydride or phthalic anhydride and a lower aliphatic alcohol.

14. Modified wood product, characterized in that

- it contains acid anhydride, vegetable oil and possibly reaction products thereof, and

- essentially no vegetable oil seeps out of it.

15. Wood product according to claim 14, characterized in that it is used for indoor and outdoor furniture, boat boards, wooden bridge beams, construction in humid spaces and for environmental constructions.