JP5965670B2 - Process for producing heat-treated wood - Google Patents

Description

  The present invention relates to a method for producing heat-treated wood having high dimensional stability and decay resistance. More specifically, the present invention relates to a method for producing heat-treated wood characterized by heating wood in supercritical carbon dioxide.

  When using wood, in order to prevent dimensional stability caused by water or moisture, decay caused by wood-rotting fungi, or damage caused by termites, some kind of storage / modification treatment is usually applied. On the other hand, user interest in the global environment and user health is increasing year by year, and there is a growing demand for wood preservation / modification without using chemicals or organic solvents.

  In recent years, thermally modified wood (thermally modified wood, heat treated wood) has been developed as a material having excellent dimensional stability and decay resistance in European countries including Finland.

  The heat-treated wood is non-chemically treated wood that has been subjected to high-temperature treatment at 150 to 240 ° C. for several tens of hours in a nitrogen atmosphere (dry) or in water vapor (wet). Although the mechanism of its performance has not been fully clarified, the equilibrium water content of wood has been improved due to degradation during heat treatment such as decomposition of hemicellulose, the main component of wood, increase in crystallinity of cellulose, depolymerization and recombination of lignin. It is said that the rate will decrease and the dimensional stability and decay resistance will improve.

  Patent Document 1 is known as a dry heat treatment method, and Patent Document 2, Patent Document 3 and the like are known as wet heat treatment methods.

JP 56-135044 A JP-A-3-231802 Japanese National Patent Publication No. 9-502508

  However, the conventional method of heating and treating wood has many problems to be improved, such as reduction in strength of wood due to high humidity and long time treatment, and a large amount of input energy.

  The problem to be completed by the present invention is to provide a method for producing heat-treated wood with reduced strength, less input energy, and high dimensional stability and decay resistance.

  As a result of extensive research by the present inventors, it was found that the above problems can be solved by heat treating wood in supercritical carbon dioxide having excellent diffusion permeability and high density, and the present invention has been completed. It was.

The present invention is as follows.
(1) A method for producing heat-treated wood, characterized in that wood is heated under pressure in supercritical carbon dioxide.
(2) The method for producing heat-treated wood according to (1), wherein the pressure is 7.4 to 30 MPa.
(3) The method for producing heat-treated wood according to (1) or (2), wherein the heating temperature is 150 to 250 ° C.
(4) a pressure-resistant container that contains wood, an atmospheric pressure release valve provided in the pressure-resistant container, a filling container filled with carbon dioxide, and a pressure pump that pressurizes and injects fluid from the filling container to the pressure-resistant container; An apparatus for producing heat-treated wood, comprising a heater for heating the inside of the pressure vessel.

  The method for producing a heat-treated wood of the present invention can produce a heat-treated wood having high dimensional stability, reduced strength, little input energy. In addition, it has been reported that the heat resistance by the conventional method improves the decay resistance of the wood, and it is expected that the heat-treated wood produced by the present invention will also have high decay resistance.

The flowchart which shows one embodiment of the manufacturing apparatus of the heat-treated wood of this invention. The graph which shows the relationship between an equilibrium moisture content and relative humidity. The graph which shows ASE of each specimen. The graph which shows the relationship between ASE and processing time.

  The supercritical carbon dioxide used as a heating medium in the present invention is carbon dioxide having a critical point (31 ° C., 7.4 MPa) or more, and is diffusive and penetrating like a gas while having a high density like a liquid. It is a fluid with special properties that is excellent in properties and is neither gas nor liquid.

  In order to manufacture heat-treated wood, first, the wood is placed in a pressure vessel and sealed. The pressure vessel used in the present invention is not particularly limited as long as it can accommodate wood to be heat-treated and can hold supercritical carbon dioxide, but a cylindrical shape can easily withstand a supercritical high pressure state. Because it is more desirable. The material is preferably stainless steel having excellent corrosion resistance, such as SUS316.

  At this time, the tree species and shape of the wood to be processed are not particularly limited. The moisture content of wood (mass percentage of moisture relative to the wood substance) is not particularly limited, but is preferably 30% or less. Moreover, since decomposition | disassembly of hemicellulose is accelerated | stimulated by adding a small amount of water, the water of 10 g or less may be poured beforehand with respect to 1 liter of capacity | capacitance of a pressure vessel.

  Next, supercritical carbon dioxide is filled in the pressure vessel, and the temperature is raised to a predetermined temperature and pressure. Alternatively, the carbon dioxide may be brought into a supercritical state by heating the pressure vessel after the pressure filling of carbon dioxide is completed.

  The temperature and pressure conditions of supercritical carbon dioxide in the present invention are a temperature of 150 to 250 ° C., preferably 180 to 240 ° C., and a pressure of 7.4 to 30 MPa, preferably 10 to 20 MPa. After raising the temperature and pressure, the state is maintained for a while, and the wood is fully heated. The heating time is in the range of 30 minutes to 24 hours, preferably 1 to 8 hours. After the heat treatment is completed, the pressure in the pressure vessel is released and the heat-treated wood is taken out.

  For example, when a cedar heartwood (water content: about 10.7%) having dimensions of 50 mm (L) × 20 mm (R) × 20 mm (T) was heat-treated in supercritical carbon dioxide at 220 ° C./10 MPa for 1 hour, The anti-swelling ability (hereinafter abbreviated as ASE) showing the dimensional stability was 63.9%. Furthermore, the ASE when a cedar core material having a water content of about 16.7% was heat-treated in supercritical carbon dioxide at 220 ° C./10 MPa for 1 hour was 69.5%. This means that the dimensional change with respect to moisture was suppressed to less than 1/3 that of the untreated material. Although the reaction mechanism of the present invention is currently under investigation, it is presumed that heat is transferred quickly due to the high density and diffusion penetration power of supercritical carbon dioxide, and the temperature inside the wood is raised in a short time. In addition, heat treatment of wood with a high moisture content showed a higher ASE because the presence of a small amount of moisture promoted the decomposition of wood components such as hemicellulose and the presence of moisture with high thermal conductivity. It is conceivable that the time for raising the temperature to the inside has become shorter. If the present invention makes it possible to reduce the processing time and the processing temperature, it is expected that the amount of energy input can be greatly reduced. Moreover, although there is a concern that the strength of the wood may be reduced by high-temperature and long-time heat treatment, it is expected that the strength reduction can be suppressed to a minimum by shortening the treatment time.

  FIG. 1 illustrates an embodiment of a heat-treated wood production apparatus of the present invention.

  Reference numeral 1 denotes a pressure vessel in which wood is sealed, and this pressure vessel 1 is provided with an atmospheric pressure release valve 2 for reducing the internal pressure to atmospheric pressure and a back pressure valve 10 for adjusting the pressure reduction speed. . Furthermore, the pressure vessel 1 is provided with a pressure gauge 4 and a thermometer 5 for measuring the internal pressure and temperature.

  A fluid is pressurized and filled into the pressure resistant container 1 from the filling container 9 filled with carbon dioxide through the valve 8, the pressure pump 7 and the valve 6. The pressure-filled carbon dioxide is heated by the heater 3, and the wood is heated in supercritical carbon dioxide. After maintaining the supercritical state for a certain time, the valve 2 is released and the pressure in the container is reduced to atmospheric pressure.

  A cedar core material specimen (50 mm (L) × 20 mm (R) × 20 mm (T)) whose total dry mass and dimensions were measured in advance was prepared. And a specimen that was completely dried, a specimen that was conditioned for 3 weeks or more in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 64% (average moisture content: 10.7%), a temperature of 20 ° C./relative Three types of specimens (average moisture content: 16.7%) that were conditioned for 3 weeks or more in a constant temperature and humidity room with a humidity of 87% were used. The humidity-controlled specimen was measured for mass and dimensions, and the moisture content was calculated according to the following formula.

  Next, four specimens conditioned under the same conditions were put in a pressure-resistant container having a capacity of 0.9 liter and sealed. Then, carbon dioxide was filled into the container from a carbon dioxide gas cylinder, and the temperature was raised to 180, 200, 220 ° C./10 MPa to obtain supercritical carbon dioxide. The heat treatment was performed for 1 hour or 6 hours, and after the treatment, the pressure in the container was reduced to atmospheric pressure, and the specimen was taken out. And it dried under reduced pressure for 48 hours with a 60 degreeC drying machine, the mass and the dimension were measured, and mass reduction rate (WL) was calculated | required. The treated specimens were then conditioned for 3 weeks or more in a constant temperature and humidity chamber of 20 ° C / 33%, 20 ° C / 64%, and 20 ° C / 87%, respectively, and the mass and dimensions of the specimens were determined. Measurements were made to calculate the equilibrium moisture content and the anti-swelling ability (ASE) indicating dimensional stability against moisture. ASE was calculated by the following formula.

  Table 1 shows the mass reduction rate of the specimen by the heat treatment. A sample with a high treatment temperature and humidity controlled in advance had a tendency to increase the mass reduction rate. This is presumably because the decomposition reaction of the wood component is promoted as the temperature of the sample increases and the amount of water in the sample increases. In addition, the equilibrium moisture content tended to be lower as the treatment temperature was higher and the specimen was conditioned at high humidity in advance. As an example, FIG. 2 shows the equilibrium moisture content when the humidity control sample at 20 ° C./relative humidity 64% is heat-treated and then the humidity is adjusted at each relative humidity. I can see that This is presumed to be due to a decrease in moisture adsorption points due to decomposition of the wood components.

  The ASE of the heat treatment specimen is shown in FIG. Samples that were treated at a high temperature and were previously conditioned at high humidity showed higher ASE and less variation between individuals. In addition, ASE reached a maximum of about 70% when treated at 220 ° C.

  For heat treatment using a 20 ° C./64% relative humidity humidity specimen, a comparative experiment was conducted for two types of treatment times of 1 hour and 6 hours. The result is shown in FIG. By increasing the treatment time, the ASE increased and the variation among individuals also decreased. In particular, in the treatment at relatively low temperatures of 180 ° C. and 200 ° C., the effect of improving the ASE and stabilizing the quality by prolonging the treatment time was remarkable.

  From these results, heat treated wood excellent in dimensional stability can be produced by the heat treatment according to the present invention, and in particular, a high quality heat treated wood can be stably produced with a specimen having a high treatment temperature and humidity controlled in advance. It became clear.

  About a cedar heartwood specimen (100 mm (L) x 50 mm (R) x 40 mm (T)) having a specimen size larger than that of Example 1, it was adjusted for 3 weeks or more in a constant temperature and humidity chamber at a temperature of 20 ° C and a relative humidity of 65%. Two types were prepared: a wet specimen and a specimen conditioned for 3 weeks or more in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 87%. The humidity-controlled specimen was measured for mass and dimensions, and the moisture content was calculated. Then, a specimen was put in a pressure-resistant container having a capacity of 0.9 liter and sealed. Then, carbon dioxide was filled into the container from a carbon dioxide gas cylinder, and the temperature was raised to 220 ° C./10 MPa to obtain supercritical carbon dioxide. The heat treatment was performed for 1 hour, and after the treatment, the pressure in the container was reduced to atmospheric pressure, and the specimen was taken out. And it dried under reduced pressure for 48 hours with a 60 degreeC drying machine, the mass and the dimension were measured, and mass reduction rate (WL) was calculated | required. Then, the treated specimen was conditioned for 3 weeks or more in a constant temperature and humidity room where the temperature and relative humidity were 20 ° C./64%, the mass and dimensions of the specimen were measured, and the equilibrium moisture content and ASE were calculated.

  The mass reduction rate and ASE of the specimen by heat treatment are shown in Table 2, but it can be seen that the ASE values are almost the same if the treatment conditions are the same even if the specimen dimensions are increased. Moreover, the mass reduction rate shows a slightly higher value when the specimen size is larger, and it is estimated that the thermal decomposition reaction of hemicellulose and the like by the heat treatment proceeds smoothly.

  From the above results, it became clear that the heat treatment according to the present invention can be applied even when the specimen size is increased.

  Using an air-dried cedar heartwood specimen (100 mm (L) x 6 mm (R) x 6 mm (T)), the heat treatment according to the present invention and the heat treatment according to the conventional dry method are carried out, and the strength of both is compared It was. In the heat treatment according to the present invention, three air-dried specimens are sealed in a pressure-resistant container having a capacity of 0.9 liter, carbon dioxide is filled into the container from a carbon dioxide gas cylinder, and a temperature and pressure of 200 ° C./10 MPa are used. The treatment was performed for 1 hour at a temperature / pressure of 220 ° C./10 MPa. After the treatment, the pressure inside the container was reduced to atmospheric pressure, and the specimen was taken out. Heat treatment by the conventional dry method is performed by placing three air-dry specimens in a pressure-resistant container with a capacity of 0.9 liter and sealing, and replacing the air in the container with nitrogen gas at atmospheric pressure for 6 hours at 200 ° C. Alternatively, the treatment was performed at 220 ° C. for 1 hour. For strength measurement, a stress-strain diagram in the fiber direction was prepared by a two-point support centralized weighting method, and bending Young's modulus (MOE) and bending strength (MOR) were measured.

The experimental results are shown in Table 3. The MOE and MOR of the heat-treated specimen by the conventional dry method were lower than those of the untreated specimen. On the other hand, the MOE and MOR of the heat-treated specimen according to the present invention also took lower values than the untreated specimen, but were not as low as the dry method. In particular, the difference between the MOE and MOR of the untreated specimen was slight when treated at 220 ° C. for 1 hour.
From the above results, it was shown that the treatment method according to the present invention can suppress the decrease in MOE and MOR as compared with the conventional dry method. In this example, the processing method according to the present invention and the conventional method are compared under the same processing conditions. However, since the processing time is expected to be shortened by using the present invention, there is a possibility that the strength reduction can be further suppressed. is there.

  INDUSTRIAL APPLICABILITY The present invention is useful for effective utilization of forest resources because it can produce heat-treated wood with reduced strength, less energy input, and high dimensional stability and decay resistance.

DESCRIPTION OF SYMBOLS 1 Pressure-resistant container 2 Valve for atmospheric pressure release 3 Heater 4 Pressure gauge 5 Thermometer 6 Valve 7 Pressure pump 8 Valve 9 Filling container 10 Back pressure valve

Claims (1)

Heat treatment characterized by pressurizing and heating wood having an average water content of 10.7 to 16.7% in supercritical carbon dioxide at a pressurizing pressure of 7.4 to 30 MPa and a heating temperature of 150 to 250 ° C. Wood manufacturing method.

Images