Wood heat treatment method

Abstract

According to the wood heat treatment method, heat treatment, water treatment, drying and balancing are sequentially carried out on wood, heat treatment can be carried out in saturated steam / superheated steam / hot air, the moisture absorption reversibility of the wood treated through the method is effectively reduced after periodic moisture absorption and desorption circulation, and the moisture absorption reversibility of the wood is effectively improved. Meanwhile, the strength of the wood is not damaged, and the texture features and color of the wood are also reserved; in addition, the method is simple in process, free of chemical agents, environmentally friendly, low in requirement for used equipment and beneficial to industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of wood processing, in particular to a wood heat treatment method. Background Art

[0002] Wood is a renewable resource that is easy to process and has good thermal insulation properties. It is widely used in construction and interior decoration. Wood is also a porous, hygroscopic material. Its dimensional stability, mechanical strength, environmental regulation and other properties are easily affected by moisture content. Heat treatment technology is one of the commonly used and effective means of physical modification of wood. It is a modification technology that treats wood in a high temperature environment to degrade wood hemicellulose, reduce the number of hydroxyl groups, and increase crystallinity. It can effectively reduce wood hygroscopicity, improve dimensional stability, and enhance environmental visual characteristics.

[0003] Although heat treatment can reduce the hygroscopicity of wood, the hygroscopicity of heat-treated wood will undergo reversible changes after a periodic process of moisture absorption and desorption. That is, after multiple dry-wet cycles, the ability of heat-treated materials to reduce hygroscopicity will weaken, thus affecting the dimensional stability of heat-treated materials and their products during long-term use. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a wood heat treatment method, which can reduce the reversible periodic moisture absorption of the wood after heat treatment, and the process is simple and environmentally friendly.

[0005] The technical solution of the present invention to solve the above problems is as follows:

[0006] The wood heat treatment method comprises the following steps:

[0007] S1. thermally treating the wood at a temperature lower than the pyrolysis temperature of cellulose to pyrolyze at least the hemicellulose in the wood;

[0008] S2, treating the wood with water to dissolve the pyrolysis products in the wood;

[0009] S3, drying the wood;

[0010] S4, performing a balancing process on the wood.

[0011] Hemicellulose is the main bonding material between the cellulose skeleton and lignin filler in the wood cell wall. When the wood is heat treated, hemicellulose begins to undergo thermal degradation reaction first. The acetyl group in the molecular chain will first break from the main chain to form acetic acid, and a small amount of carboxyl groups on the glucuronic acid polyxylose molecule will also break to form formic acid and other substances. At the same time, some molecules in the cellulose quasi-crystalline region of the wood cell wall component are rearranged and further crystallized, resulting in an increase in the crystallinity of cellulose in the wood cell wall after high-temperature heat treatment. At the same time, the microfibrils in cellulose will aggregate with each other due to the degradation of the hemicellulose component during the high-temperature heat treatment process. The cross-sectional size of the aggregated microfibrils is larger, reducing the number of water adsorption sites on the cellulose surface that can be contacted; at the same time, lignin undergoes partial reorganization during the heat treatment process, and the changes in the cell wall matrix caused by cross-linking with cellulose also hinder the channel for water movement, thereby reducing the hygroscopicity of the wood. Then water treatment is carried out to remove the degradation products produced by the heat treatment.

[0012] Preferably, the water treatment is performed by immersing the wood in water.

[0013] Preferably, water is replaced while the wood is being water treated.

[0014] Preferably, the wood is placed in a sealed container for water treatment, so that the internal pressure of the sealed container is higher than the atmospheric pressure and maintained.

[0015] Preferably, the sealed container is subjected to pressure relief treatment, and then the air pressure inside the sealed container is made higher than the atmospheric pressure and maintained for at least one cycle. By means of pressurization and pressure relief, water and wood can be fully contacted, thereby improving the efficiency of removing degradation products.

[0016] Preferably, the water treatment temperature is 50-80° C., which will not destroy the cell structure of the wood and avoid affecting the mechanical properties of the wood.

[0017] Preferably, the water treatment time is 0.5 to 2 hours.

[0018] Preferably, the heat treatment in step S1 is performed under a steam atmosphere.

[0019] More preferably, the heat treatment in step S1 is performed under a saturated steam atmosphere.

[0020] More preferably, the heat treatment in step S1 is performed under a superheated steam atmosphere.

[0021] Preferably, the temperature during the heat treatment in step S1 is 130-160°C.

[0022] Preferably, the heat treatment in step S1 is carried out at 130-160° C. for 1-3 hours.

[0023] Preferably, in step S1, the heat treatment comprises the following steps: heating the wood to 70-90°C at a rate of 18-22°C / h, heating to 100-110°C at a rate of 8-12°C / h, keeping the temperature for 3 hours, heating to 115-120°C at a rate of 12-18°C / h, and then heating to 130-160°C at a rate of 18-22°C / h, keeping the temperature for 1-3 hours, cooling naturally to room temperature after the heat preservation, and taking out the wood. The heat treatment by heating at the above rate can prevent the wood from generating stress due to uneven moisture content inside and outside.

[0024] Preferably, in step S3, the drying temperature is 45-60° C., and the drying time is 10-18 days.

[0025] Preferably, in step S4, equilibration is performed in an atmospheric environment, and the equilibration time is 25 to 35 days.

[0026] The present invention has the following beneficial effects:

[0027] The present invention provides a wood heat treatment method, which sequentially performs heat treatment, water treatment, drying and balancing on the wood, wherein the heat treatment can be performed in saturated steam / superheated steam / hot air. After the wood treated by the above method undergoes a periodic moisture absorption and desorption cycle, its moisture absorption reversibility is effectively reduced, while the strength of the wood is not damaged and the texture characteristics and color of the wood itself are retained. In addition, the above method is simple in process, does not require chemical agents, is green and environmentally friendly, and has low requirements on the equipment used, which is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a comparison diagram of two moisture absorption and desorption cycle curves of Examples 1 to 6 and Comparative Examples 1 to 6;

[0029] Figure 2 It is a graph showing the difference in moisture absorption between two cycles of Examples 1 to 6 and Comparative Examples 1 to 6;

[0030] Figure 3 It is a graph showing the change of moisture absorption hysteresis value in moisture absorption and desorption cycles of Examples 1 to 6 and Comparative Examples 1 to 6;

[0031] In the figure: Sat represents that the treatment medium is saturated steam, Uns represents that the treatment medium is superheated steam, and Air represents that the treatment medium is hot air; 4 represents 140°C, and 6 represents 160°C; 0 represents no water treatment, and 1 represents water treatment; (1) represents the first moisture absorption and desorption cycle, and (2) represents the second moisture absorption and desorption cycle. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0035] S1. Place the air-dried mangosteen wood in a saturated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 140°C at a rate of 20°C / h, keep it at 140°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0036] S2, immersing the heat-treated mangosteen wood in 60° C. hot water at a constant temperature for 1 hour, stopping heating after 1 hour, and taking out the mangosteen wood after the water cools naturally;

[0037] S3, placing the water-treated mangosteen wood in an oven at 50° C. for low temperature drying for two weeks;

[0038] S4. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0039] The obtained heat-treated material was subjected to a dynamic vapor adsorption test. Three small samples (tangential × radial × along-grain) were randomly selected, cut into small pieces with a table saw, mixed together, and crushed into powder with a high-speed grinder. The wood powder was sieved with a 40-mesh (0.45 mm) sieve and dried in an oven at 80°C until it was absolutely dry. The dynamic vapor adsorption test was conducted using a high-precision dynamic vapor adsorption instrument (Dynamie Vapour Sorption): DVS-Intrinsic, sensitivity 0.000001g, manufactured by Surface Measurement System, UK). The sample weight weighed for each test was about 10 mg. The instrument was equipped with a high-precision microbalance with an accuracy of 0.1 μg. During the experiment, the sample weight was collected every 1 minute. When the change in the sample weight within 10 minutes was less than 0.002% of the sample weight, the sample was considered to have reached equilibrium at the relative humidity, and the test automatically entered the next stage. The relative humidity changes of the samples during the moisture absorption and desorption process are shown in Table 1. Each sample has two moisture absorption and desorption cycles (relative humidity 0% to 95% and then to 0% for one cycle). The maximum equilibrium moisture content of Example 1 in the first cycle was measured to be 18.09%, and the second cycle was 18.12%, and the two moisture absorption and desorption cycle curves of Example 1 were obtained.

[0040] Table 1 Relative humidity control method of moisture absorption-desorption cycle

[0041]

[0042] Example 2

[0043] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0044] S1. Place the air-dried mangosteen wood in a saturated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 160°C at a rate of 20°C / h, keep it at 160°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0045] S2, placing the heat-treated mangosteen wood in a sealed container, immersing it in 60°C hot water at a constant temperature for 1 hour, stopping heating after 1 hour, and maintaining the internal air pressure of the sealed container at 0.2MPa from 0 to 25 minutes, then performing pressure relief treatment, and taking out the mangosteen wood after the water cools naturally;

[0046] S3, placing the water-treated mangosteen wood in an oven at 50° C. for low temperature drying for two weeks;

[0047] S4. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0048] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Example 2 was measured to be 18.66%, and the second cycle was 17.89%, and two moisture absorption and desorption cycle curves of Example 2 were obtained.

[0049] Example 3

[0050] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0051] S1. Place the air-dried mangosteen wood in a superheated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 140°C at a rate of 20°C / h, keep it at 140°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0052] S2, immersing the heat-treated mangosteen wood in 60° C. hot water at a constant temperature for 1 hour, stopping heating after 1 hour, and taking out the mangosteen wood after the water cools naturally;

[0053] S3, placing the water-treated mangosteen wood in an oven at 50° C. for low temperature drying for two weeks;

[0054] S4. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0055] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Example 3 was measured to be 19.86%, and the second cycle was 19.51%, and two moisture absorption and desorption cycle curves of Example 3 were obtained.

[0056] Example 4

[0057] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0058] S1. Place the air-dried mangosteen wood in a superheated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 160°C at a rate of 20°C / h, keep it at 160°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0059] S2, placing the heat-treated mangosteen wood in a sealed container, immersing it in 60°C hot water at a constant temperature for 1 hour, stopping heating after 1 hour, and maintaining the internal air pressure of the sealed container at 0.2MPa from 0 to 25 minutes, then performing pressure relief treatment, and taking out the mangosteen wood after the water cools naturally;

[0060] S3, placing the water-treated mangosteen wood in an oven at 50° C. for low temperature drying for two weeks;

[0061] S4. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0062] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Example 4 was measured to be 18.41%, and the second cycle was 18.38%, and two moisture absorption and desorption cycle curves of Example 4 were obtained.

[0063] Example 5

[0064] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0065] S1. Place the air-dried mangosteen wood in an air atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 140°C at a rate of 20°C / h, keep it at 140°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0066] S2, immersing the heat-treated mangosteen wood in 60° C. hot water at a constant temperature for 1 hour, stopping heating after 1 hour, and taking out the mangosteen wood after the water cools naturally;

[0067] S3, placing the water-treated mangosteen wood in an oven at 50° C. for low temperature drying for two weeks;

[0068] S4. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0069] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Example 5 was measured to be 19.82%, and the second cycle was 19.49%, and two moisture absorption and desorption cycle curves of Example 5 were obtained.

[0070] Example 6

[0071] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0072] S1. Place the air-dried mangosteen wood in an air atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 160°C at a rate of 20°C / h, keep it at 160°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0073] S2, placing the heat-treated mangosteen wood in a sealed container, immersing it in 60°C hot water at a constant temperature for 1 hour, stopping heating after 1 hour, and maintaining the internal air pressure of the sealed container at 0.2MPa from 0 to 25 minutes, then performing pressure relief treatment, and taking out the mangosteen wood after the water cools naturally;

[0074] S3, placing the water-treated mangosteen wood in an oven at 50° C. for low temperature drying for two weeks;

[0075] S4. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0076] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Example 6 was measured to be 19.38%, and the second cycle was 19.04%, and two moisture absorption and desorption cycle curves of Example 6 were obtained.

[0077] Comparative Example 1

[0078] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0079] S1. Place the air-dried mangosteen wood in a saturated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 140°C at a rate of 20°C / h, keep it at 140°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0080] S2, placing the heat-treated mangosteen wood in an oven at 50°C for two weeks;

[0081] S3. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0082] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1. The maximum equilibrium moisture content of the first cycle of Comparative Example 1 was measured to be 16.49%, and the second cycle was 16.69%. Two moisture absorption and desorption cycle curves of Comparative Example 1 were obtained.

[0083] Comparative Example 2

[0084] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0085] S1. Place the air-dried mangosteen wood in a saturated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 160°C at a rate of 20°C / h, keep it at 160°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0086] S2, placing the heat-treated mangosteen wood in an oven at 50°C for two weeks;

[0087] S3. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0088] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Comparative Example 2 was measured to be 16.65%, and the second cycle was 16.09%, and two moisture absorption and desorption cycle curves of Comparative Example 2 were obtained.

[0089] Comparative Example 3

[0090] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0091] S1. Place the air-dried mangosteen wood in a superheated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 140°C at a rate of 20°C / h, keep it at 140°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0092] S2, placing the heat-treated mangosteen wood in an oven at 50°C for two weeks;

[0093] S3. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0094] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Comparative Example 3 was measured to be 19.64%, and the second cycle was 18.93%, and two moisture absorption and desorption cycle curves of Comparative Example 3 were obtained.

[0095] Comparative Example 4

[0096] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0097] S1. Place the air-dried mangosteen wood in a superheated steam atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 160°C at a rate of 20°C / h, keep it at 160°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0098] S2, placing the heat-treated mangosteen wood in an oven at 50°C for two weeks;

[0099] S3. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0100] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Comparative Example 4 was measured to be 18.69%, and the second cycle was 18.82%, and two moisture absorption and desorption cycle curves of Comparative Example 4 were obtained.

[0101] Comparative Example 5

[0102] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0103] S1. Place the air-dried mangosteen wood in an air atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 140°C at a rate of 20°C / h, keep it at 140°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0104] S2, placing the heat-treated mangosteen wood in an oven at 50°C for two weeks;

[0105] S3. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0106] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Comparative Example 5 was measured to be 19.54%, and the second cycle was 18.91%, and two moisture absorption and desorption cycle curves of Comparative Example 5 were obtained.

[0107] Comparative Example 6

[0108] A wood heat treatment method, using air-dried mangosteen wood with a moisture content of 11±1% as raw material, comprises the following steps:

[0109] S1. Place the air-dried mangosteen wood in an air atmosphere, heat it from 20°C to 80°C at a rate of 20°C / h, heat it to 105°C at a rate of 10°C / h, keep it at 105°C for 3h, heat it to 120°C at a rate of 15°C / h, heat it to 160°C at a rate of 20°C / h, keep it at 160°C for 2h, and naturally cool it to room temperature after the heat preservation ends;

[0110] S2, placing the heat-treated mangosteen wood in an oven at 50°C for two weeks;

[0111] S3. Place the dried mangosteen wood in a cool and ventilated atmosphere for one month for equilibrium to obtain heat-treated wood.

[0112] The obtained heat-treated material was subjected to a dynamic vapor adsorption test according to the method in Example 1, and the maximum equilibrium moisture content of the first cycle of Comparative Example 6 was measured to be 19.46%, and the second cycle was 19.06%, and two moisture absorption and desorption cycle curves of Comparative Example 6 were obtained.

[0113] Figure 1 It is a comparison chart of the moisture absorption and desorption cycle curves of the above embodiment and the comparative example. Figure 1 It can be seen that the desorption curves of the heat-treated materials in the embodiment and the comparative example are highly overlapped, and the moisture absorption curves in the second cycle are increased compared with the first cycle, which indicates that the moisture absorption of the heat-treated material increases with the increase of the moisture absorption and desorption times, that is, the heat-treated material has a reversible moisture absorption phenomenon;

[0114] Table 2 shows the total difference (au) in moisture absorption during two cycles within the full relative humidity range of the above embodiments and comparative examples.

[0115] Group Total difference in moisture absorption Sat4-1 (Example 1) 50.54 Sat6-1 (Example 2) 35.88 Uns4-1 (Example 3) 55.12 Uns6-1 (Example 4) 39.46 Air4-1 (Example 5) 34.26 Air6-1 (Example 6) 46.02 Sat4-0 (Comparative Example 1) 53.63 Sat6-0 (Comparative Example 2) 58.33 Uns4-0 (Comparative Example 3) 64.77 Uns6-0 (Comparative Example 4) 87.04 Air4-0 (Comparative Example 5) 55.09 Air6-0 (Comparative Example 6) 52.13

[0116] Figure 2 The difference diagram of moisture absorption in two cycles between the above embodiment and the comparative example is shown in Table 2 and Figure 2 It can be learned that:

[0117] Compared with the heat-treated material without water treatment, under the same other conditions, the total difference of moisture absorption in two cycles of the heat-treated material after water treatment is smaller. Water treatment helps to weaken the reversible moisture absorption of the heat-treated material caused by the moisture absorption and desorption cycle.

[0118] By comparing Examples 1 and 2, 3 and 4, and 5 and 6, it can be seen that the different heat treatment media have different moisture absorption amounts in two cycles of the heat treatment material. The total difference in moisture absorption amounts in two cycles of different heat treatment media is: superheated steam> hot air> saturated steam. Therefore, saturated steam as a heat treatment medium helps to reduce the reversible moisture absorption of the heat treatment material.

[0119] Figure 3 The graph of the moisture absorption hysteresis value change of the above-mentioned embodiment and comparative example in the moisture absorption and desorption cycle. Wood moisture absorption hysteresis means that the moisture absorption equilibrium moisture content of wood is always less than the desorption equilibrium moisture content in the process of reaching the equilibrium moisture content, so that the size of the wood is different after reaching equilibrium through moisture absorption or desorption under the same relative humidity environment. Therefore, the smaller the moisture absorption hysteresis value is, the better.

[0120] from Figure 3 It can be seen that when the heat treatment medium is saturated steam, the moisture absorption hysteresis value of the heat-treated material is smaller, which is beneficial to improving the dimensional stability of the heat-treated material;

[0121] from Figure 3 It can also be seen that during the first cycle, the moisture absorption hysteresis peak of the above embodiment mostly appears at a relative humidity of about 70%. During the second cycle, the moisture absorption hysteresis curve of the above embodiment shifts, and its peak shifts to a relative humidity of about 80%. This can provide certain recommendations for the use environment of heat treatment materials.

[0122] In summary, heat treatment is carried out in a saturated steam atmosphere and water treatment can effectively reduce the reversible moisture absorption of the heat-treated material. This method is simple, does not require chemical reagents, is green and environmentally friendly, and can be used for industrial production.

Claims

1. A wood heat treatment method comprising the following steps: S1. thermally treating the wood at a temperature lower than the pyrolysis temperature of cellulose to pyrolyze at least the hemicellulose in the wood; S2, treating the wood with water to dissolve the pyrolysis products in the wood; S3, drying the wood; S4, performing a balancing process on the wood.

2. The wood heat treatment method according to claim 1, characterized in that: The water treatment is to immerse the wood in water for treatment.

3. The wood heat treatment method according to claim 2, characterized in that: The water is replaced while the wood is being water treated.

4. The wood heat treatment method according to claim 2, characterized in that: The wood is placed in a sealed container for water treatment, and the air pressure inside the sealed container is maintained higher than the atmospheric pressure.

5. The wood heat treatment method according to claim 4, characterized in that: The closed container is subjected to pressure relief treatment, and then the internal pressure of the closed container is made higher than the atmospheric pressure and maintained, and the cycle is repeated for at least one cycle.

6. The wood heat treatment method according to any one of claims 1 to 5, characterized in that: The temperature of the water treatment is 50-80°C.

7. The wood heat treatment method according to claim 6, characterized in that: The water treatment time is 0.5 to 2 hours.

8. The wood heat treatment method according to any one of claims 1 to 5, characterized in that: The heat treatment in step S1 is performed in a steam atmosphere.

9. The wood heat treatment method according to any one of claims 1 to 5, characterized in that: The temperature during the heat treatment in step S1 is 130 to 160°C.

10. The wood heat treatment method according to claim 9, characterized in that: During the heat treatment in step S1, the temperature is kept at 130-160°C for 1-3 hours.

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