EP1002630B1 - Wood treatment process - Google Patents

Abstract

Wood preservation method comprises exposing wood to hot oil at 180-260 degrees C.

Description

The invention relates to a wood treatment process in which lignocellulose-containing Materials are immersed in hot oil for a specified amount of time.

A wood treatment process of the above type is the subject of DE 1 000 592. Das Impregnation process explained in this document is used to oil or oil as quickly as possible soak other impregnating agents to change the properties of the wood. By Use of high frequency is said to soak at a temperature of the oil bath of 200 ° C in a few minutes. Resistance can be achieved by such a procedure only increase compared to wood-destroying fungi, provided that the biocides corresponding to the oil Adds funds.

Treatment of wood in hot oil, which is used to protect against rot and blue rot contains biocides, is described for example in DE 30 43 659 A1. Such means are, however, questionable for reasons of environmental protection and can lead to health problems Cause damage.

DE 29 16 677 shows that it is also known for wood protection, the wood in exposed to an autoclave under protective gas for 0.5 h to 8 h at temperatures above 180 ° C. This heat treatment is said to have good fungal resistance and dimensional stability of the wood. However, treating wood in an autoclave requires relatively expensive systems and is therefore not feasible in smaller companies. The thermal conversion of wood has over other wood preservation processes, for example the boiler pressure impregnation has the advantage that the preservative effect The heat comes about, so that there are no environmentally harmful biocidal agents must use and also lignocellulosic material that is not or poorly impregnable can compensate for the entire cross-section. A disadvantage of this type of heat treatment is however, in particular that at the required high temperatures (160-260 ° C) in a gas atmosphere due to the relatively poor heat transfer of gases and sensitivity of the entire remuneration process often an inhomogeneous remuneration with partial reduced resistance to wood-destroying fungi is achieved.

Boiler pressure impregnation is particularly widespread as a wood preservation process. there are the wood products to be protected in a boiler under a pressure of 7 - 14 bar at normal temperatures immersed in a saline solution, which is often a Chromate-copper salt-borate mixtures or other chromium-containing mixture. The Pressure impregnation has proven to be a very effective wood preservation process, however there are increasing concerns about the use of solutions containing heavy metals for reasons of environmental protection, because it cannot be excluded that these substances can be washed out of the wood over time and thereby into the ground and in reach the groundwater. There may be a hazard when performing the procedure of the persons entrusted with it and cause environmental damage from waste water. Wood preservation processes of the above type are recommended for wood products, that are exposed to the weather, for example in wooden buildings, fences or outdoors banks to be set up.

A long time ago it was reported in the literature as a heat transfer medium To use liquid metal and immerse the wood in a hot metal bath, in particular an increase in dimensional stability and resistance to wood-destroying To reach mushrooms. However, such procedures were not widely used because they were none satisfactory results.

Under the name "Royal Treatment" or "Royal Process" (similar to DE 3043659 A1), a wood preservation process has already become known in which wood is in one Oil bath with a temperature of 130 ° C to 140 ° C is immersed. This temperature will chosen to allow a better penetration of the oil into the wood and a good surface treatment to enable. However, wood preservation is a matter of prior treatment achieved with biocidal agents, since at this temperature there is still no thermal transformation of wood to the extent necessary

The reduction in viscosity due to the heating of oils has also been used for years Impregnation of tar oils practiced (e.g. DE 4112643). Heat treatments also for additional hardening of modified vegetable oils in impregnated wood (e.g. WO 96/38275) is used. However, these procedures are only applicable to wood types that are easy to drink applicable; types of wood that are difficult to soak cannot be compensated.

The invention is based on the problem of a wood treatment method with a preserving effect at the beginning to develop the type mentioned, which leads to the highest possible, uniform protective effect of the material over the entire cross-section, but not for health reasons or necessitates substances of concern for reasons of environmental protection, advantageous properties of the wood changed as little as possible and which with a the simplest possible system can be carried out.

According to the invention, this problem is solved in that for controlled, thermal Converting the duration of the oil treatment to several hours and the temperature of the Oil bath is 180 ° C to 260 °.

The method according to the invention is carried out in exactly the same way as for thermal treatment under protective gas to a preservative effect, without this for reasons of Environmentally harmful wood preservatives must be used. Because as a heat transfer medium however hot oil is used instead of protective gas, can be carried out during the implementation of the procedure work with relatively simple facilities, so that even smaller companies can apply the method according to the invention. Unlike other wood preservation processes, whose protective effect is based on the impregnation with various substances, can also use this process to process impregnable, lignocellulosic materials such as. Spruce, poplar or bamboo due to the thermal transformation over the whole Cross-section can be coated homogeneously since no substances are introduced into the material Need to become. The protective effect is achieved by thermal conversion of the lignocellulose-containing Caused substance, the oil serves as a heat exchanger and shields the to be remunerated Material before exposure to oxygen. Escaping gases prevent penetration of the oil during the thermal treatment, e.g. just a few millimeters of wood oil-soaked and can be planed off, making oil-free tempered wood products If necessary, easily soakable types of wood such as pine sapwood be impregnated by cooling the oil after the thermal treatment.

It was found that the treatment according to the invention is very homogeneous in oil and additionally For increased resistance to wood-destroying fungi there is a high dimensional stability of the wood.

Due to the good heat transfer of oils, in contrast to heat treatments in a gas atmosphere Advantages with thermal treatments of larger quantities lignocellulose-containing products achieved because at the required high temperatures more uniform treatment conditions in the entire reactor space are possible. From the Liquid tree resins and pyrolysis products are found in the vegetable oils dissolved and can be used together with the oil. In this process no water or water vapor is required for remuneration, which reduces water consumption is minimal. Material costs and equipment that arise from processes with inert gas, are also eliminated.

The necessary heating of the oil is usually possible for woodworking companies without significant additional costs, since waste wood is often generated in such companies, which can be burned to generate the required heat. The heated oil can be pumped out at the end of the treatment, as a result of which the thermal energy stored in the oil can be transferred quickly to other reactor vessels with little energy loss. According to the invention, the high oil temperatures of 180-260 ° C. do not lead to any crack formation upon contact with moist products containing lignocellulose. For example, freshly sawn, large-sized spruce scantlings with the dimensions 100x100x1350 mm ^{3 were} thermally converted in hot rapeseed oil over the entire cross-section without cracks in an oil bath.

The method according to the invention has so far been tested in practice in the case of pine and spruce wood, with improved dimensional stability and increased resistance to wood-destroying fungi being found in laboratory tests. A few hours are usually sufficient for the treatment; however, the remuneration period depends on the material moisture and the dimensions and can take several days if the values are high. A treatment time of 4.5 hours on samples with the dimensions 50x25x15 mm ³ and an initial wood moisture of 6% was tested in practice and found to be sufficient.

example

Fresh, untreated pine ( Pinus sylvestris L.) and spruce ( Picea abies L. Karst.) Were cut to the dimensions given in Table 1. For the oil heat treatment, the samples were heated with a wood moisture content of 6% at three temperatures (180 ° C, 200 ° C and 220 ° C) without pressure in an oil bath made of pressed, refined linseed oil with exclusion of oxygen. After reaching the desired temperature, the wood samples were immersed in the hot oil for 4.5 hours. The samples cooled in the oil bath for 15 minutes. Comparative samples were also treated in the drying cabinet at appropriate temperatures in an air atmosphere for 4.5 hours (no protection claim is made for the treatment in air). Dimensions of the samples Kind of exam Cracking / surface / masses Dimensions of Changes / ASE Bending modulus of elasticity / fracture impact work Resistance to C. puteana Species pine sapwood pine sapwood pine sapwood Pine sap spruce [mm ³ ] 40x70x100 20x20x10 10x10x150 15x25x50

Results:

Mass change: The mass increase WPG (Weight Percent Gain) of the oil-heat-treated samples was 50-70% (Table 2). The heat-treated samples in an air atmosphere showed mass losses depending on the treatment temperature of up to 10%. Since the oil content caused a mass increase, a possible loss of wood substance as a result of the oil heat treatment could not be determined exactly. Mass change due to treatment [%] 180 ° C oil 180 ° C air 200 ° C oil 200 ° C air 220 ° C oil 220 ° C air jaw 51, 28 -1.94 40.87 -2.93 42.14 -8.46 Spruce 18,00 -1.99 12.42 -2.86 9.97 -8.24

Cracking, surface: none of the wood samples thermally treated in oil showed cracks. The surfaces were homogeneously colored brown, in contrast to the surfaces of the air-dried samples, which showed stained discolouration due to leaking resin.

dimensional changes

The sample dimensions were reduced both by the oil heat treatment and by the heat treatment in an air atmosphere as a function of the treatment temperature, the dimensions decreasing more in the tangential direction than in the radial direction (Table 3). At 200 ° C, the dimensional changes due to the oil heat treatment in the tangential direction were somewhat larger than with the heat treatment in an air atmosphere. Dimensional changes due to treatment [%] 180 ° C oil 180 ° C air 200 ° C oil 200 ° C air 220 ° C oil 220 ° C air wheel 0.04 -0.07 -0.43 -0.62 -1.14 -1.89 tan -0.20 -0.29 -0.86 -0.74 -1.63 -2.76

Reduction of swelling and shrinkage (ASE)

The ASE improvement of samples treated at 220 ° C was of a similar order of magnitude for both types of treatment, around 40% (Table 4). The degree of improvement was dependent on the relative humidity. The ASE decreased with increasing humidity, whereby samples treated with higher temperatures showed smaller differences than samples treated with lower temperatures. ASE [%] 180 ° C oil 180 ° C air 200 ° C oil 200 ° C air 220 ° C oil 220 ° C air ASE 20/35 29 41 43 37 44 46 ASE 20/65 21 27 35 28 40 41 ASE 20/85 19 22 31 27 38 40

Flexural modulus / impact bending strength

The highest flexural modulus of elasticity for samples with an oil heat treatment were achieved at 200 ° C with more than 11000 N / mm ² (Table 5). The values for the modulus of elasticity of untreated softwood known from the literature were not reduced with either tempering method. In contrast, the fracture work decreased sharply with increasing treatment temperature, but less with oil heat treatment than with treatment in an air atmosphere (Table 6). Bending modulus of elasticity N [/ mm ² ] 180 ° C oil 180 ° C air 200 ° C oil 200 ° C air 220 ° C oil 220 ° C air controls 10259 10029 11002 9801 10162 9445 9986 Fracture work [%] 180 ° C oil 180 ° C air 200 ° C oil 200 ° C air 220 ° C oil 220 ° C air controls 82.45 62.89 59.8 50.84 50.84 37.02 100.00

Resistance to Coniophora puteana .

The resistance of spruce and pine to the brown rot fungus Coniophora puteana was increased at temperatures above 200 ° C. A significantly lower mass loss was determined for oil-heat-treated samples than for air-heat-treated samples. A mass loss of less than 2% was found for pine sapwood when using 200 ° C oil heat treatment, whereas a spike in spruce was only achieved at 220 ° C (Table 7). Untreated spruce controls, on the other hand, showed a mass loss of 48% and pine controls one of 40%. Weight loss after 19 weeks of exposure to heat-treated samples according to DIN EN 113 (fungus: Coniophora puteana ) Oil heat treatment Air-heat treatment pine sapwood Spruce pine sapwood Spruce treatment [G] [%] [G] [%] [G] [%] [G] [%] 180 ° C 1.1 13.0 1.2 15.0 2.3 25.0 2.5 31.2 200 ° C 0.1 1.9 1.1 13.1 1.0 15.8 2.2 26.7 220 ° C 0.1 2.0 0.0 0.0 0.9 11.0 0.4 5.5

Since the lignocellulose-containing material treated by the process according to the invention has increased dimensional stability, paint on the wood surface is better than untreated material.

The lignocellulose-containing material treated by the process according to the invention has due to the oil loading during later processing compared to the previously known Processed material has the advantage, among other things, that it is easier to machine edit and nails can be driven in easily. On top of that prevented by the oil from the formation of health-threatening fine dust or is at least greatly reduced. The oil loading in the process according to the invention easily adapted to the respective intended use of the products and for example for wood products to be brought into the ground are chosen higher than for those that are only exposed to weathering without earth contact.

Another advantage of the method according to the invention is that the oil after Treatment is absorbed very quickly, so that a few minutes after the treatment results in a dry surface of the wooden parts.

The resin stains that often occur during heat treatment in gas atmospheres on the Wood surface are avoided in the treatment according to the invention in an oil bath, because there the leaking resin is evenly distributed in the oil.

Linseed oil and rapeseed oil have been tried out in practice, with comparably good protective effects let achieve.

An undesirable embrittlement of the lignocellulose-containing material can be reduced if the heat treatment is carried out in an oil bath in the absence of oxygen.

In addition to the function as a heat exchanger, the oil can also function as a surface coating agent take over when the liquid bath after heat treatment cooled with the material in it and then this in a room climate air-conditioned and then heated to 60 to 180 ° C. By this cooling and Subsequent heating creates a closed, hardened surface on wooden surfaces Oil film. This also means that the brown color created by the oil can be achieved the surface is more permanent, while otherwise oiled wood surfaces in the Nature quickly fades.

It is advantageous if the oil has an initial temperature of at least 180 ° C. hereby fast energy-saving compensation is possible without causing cracking on the wooden surface of materials containing lignocellulose, also with moisture content comes about fiber saturation and larger dimensions.

Claims (7)

1. Wood treatment process with preservative effect in which materials with a lignocellulose content are dipped in hot oil for a set period, characterized in that, for controlled thermal transformation, the duration of the oil treatment is several hours and the temperature of the oil bath is 180°C to 260°C.
2. Wood treatment process according to Claim 1, characterized in that after the thermal transformation, the materials with a lignocellulose content are impregnated with the oil modified by the thermal transformation.
3. Wood treatment process according to Claim 1, characterized in that the oil has an initial temperature of at least 180°C.
4. Wood treatment process according to Claims 1, 2 or 3, characterized in that the oil used is a vegetable oil.
5. Wood treatment process according to at least one of the preceding claims, characterized in that the thermal transformation takes place in an oil bath in the absence of oxygen.
6. Wood treatment process according to at least one of the preceding claims, characterized in that the thermal transformation takes place at pressures of 2 bar to 14 bar.
7. Wood treatment process according to at least one of the preceding claims, characterized in that after completion of the thermal transformation the liquid bath is cooled, and the specimens which are then impregnated with thermally modified oil are conditioned at room temperature and are then heated to 60 to 180°C until a hardened oil film is formed in an air atmosphere.