JP4686775B2 - Method for modifying wood - Google Patents

Description

  The present invention relates to a method for modifying wood by chemical reaction treatment.

  In order to eliminate the disadvantages of wood, such as dimensional changes caused by water and moisture, decay, and damage caused by termites, wood is usually modified by some chemical processing. Injection of chemicals, heating and steam treatment are also types of chemical processing, but chemical reaction treatment is also an effective treatment method.

  Many chemical reaction treatments occur when the moisture content of the wood, hemicellulose, and lignin molecules in the wood are chemically modified with chemical reaction reagents to improve dimensional stability against moisture and antiseptic / anticidal properties. Variations in the strength properties of the wood are also suppressed. Tsuji summarizes the main points of chemical reaction treatment of wood (Non-patent document 1: Kazuya Tsuji, issues and prospects in chemical processing research of wood, Journal of the Wood Society, Vol.48, No.6, p. 399-406 (2002)) as well as Non-Patent Document 2 (Wood Industry Handbook (Maruzen Co., Ltd., 2004) "Chapter 13 Chemical Processing 13.2 Chemical Modification" (p.866-871)) .

  For example, an acetylation treatment in which a hydroxyl group in wood is substituted with an acetyl group is one of chemical reaction treatments, and is widely recognized as a very effective modification method. However, there are many problems that need to be improved, such as the fact that the acetylation process takes a long time and a large amount of chemical reaction processing reagents must be used. Not reached.

  Conventional acetylation methods for wood are roughly classified into two types: liquid phase reaction and gas phase reaction. In the liquid phase treatment at the industrial level, a raw material or an air-dried wood block is vapor-dried with xylene vapor, then the wood is dried under reduced pressure, and acetic anhydride diluted with xylene is introduced into the reactor. There is a method of acetylation treatment at ˜130 ° C. and about 10 atm for 8 to 16 hours.

  Further, in the gas phase treatment, there is a method in which dried wood and acetic anhydride are put in a reactor, evacuated and decompressed, heated to 100 to 140 ° C., and reacted for 8 to 16 hours. In the case of a liquid phase reaction, even a material having a large cross-sectional shape can be processed, but a large amount of processing chemicals and organic solvents are required. After processing, unreacted chemicals must be made into waste liquid. In addition, long-time treatment is indispensable for performing sufficient acetylation treatment.

There is a method to shorten the treatment time by adding a catalyst, but it is necessary to use a catalyst harmful to human body and environment such as pyridine. On the other hand, it is possible to process with a small amount of chemicals in the gas phase reaction, but it takes some time to diffuse the vapor into the wood. It is difficult to react, and the treatment takes a long time as in the case of the liquid phase reaction.
Kazuya Tsuji, Issues and Prospects in Chemical Processing Research of Wood, Journal of the Wood Society, Vol.48, No.6, p.399-406 (2002) “Chapter 13 Chemical Processing 13.2 Chemical Modification” (p.866-871) of the Wood Industry Handbook (Maruzen Co., Ltd., 2004)

  The problem to be solved by the present invention is to provide a method for efficiently and safely performing a chemical reaction treatment for eliminating the defects of wood in a short time.

  In order to solve the above-mentioned problems, the present inventors have studied a chemical reaction treatment method using supercritical carbon dioxide having a penetration / diffusion power comparable to that of a gas while having a density as high as that of a liquid as a chemical reaction field. It came to be completed.

That is, the present invention
(1) A method for modifying wood, characterized in that acetic anhydride is used as an acetylating reagent in carbon dioxide in a supercritical state, and wood is acetylated by a non-catalytic reaction .
(2) A pressure vessel is filled with wood and an acetylating reagent, sealed, filled with carbon dioxide, heated and pressurized so that the carbon dioxide is in a supercritical state, and subjected to acetylation treatment for a predetermined time. A method for modifying wood.
(3) The wood according to (1) or (2), wherein, in the acetylation treatment, the amount of the acetylating reagent is 0.6 to 3.5 with respect to the wood 1 by weight. Reforming method.

  According to the present invention, it is possible to modify wood safely in a short time, efficiently and without using a catalyst such as pyridine.

  Carbon dioxide has a critical point of 31 ° C. and 7.4 Mpa. Carbon dioxide in a supercritical state shows a large density change, and has a penetration / diffusion power similar to that of a gas while being as dense as a liquid. In the present invention, wood is subjected to chemical reaction treatment using carbon dioxide in a supercritical state as a chemical reaction field.

  The temperature and pressure conditions for obtaining carbon dioxide in a supercritical state are not particularly limited as long as carbon dioxide is in a supercritical state, but are 31 ° C. and 7.4 Mpa or higher, preferably 100 to 130 ° C. and about 10 Mpa.

  Cellulose, hemicellulose, and lignin, which are the main constituents of wood, have a large number of hydroxyl groups, and these hydroxyl groups are substituted with acetyl groups, ester groups, and the like, and chemical reaction treatment is performed.

  Carbon dioxide in the supercritical state undergoes intense molecular motion at high density, and chemical reaction reagents such as acetylation reagents can react in small amounts and reproduce reagent-impregnated states such as liquid phase reactions. In a very short time, the reagent may reach the reaction site inside the wood and be chemically processed.

  The chemical reaction treatment in the present invention refers to acetylation treatment, oligoesterification treatment, etherification treatment, formalization treatment and the like.

  The reagent used for the acetylation treatment can include acetic anhydride, the reagent used for the oligoesterification treatment can include maleic anhydride, and the reagent used for the etherification treatment can include propylene oxide. The reagent used for the formalization treatment can include formaldehyde. The reagent for chemical reaction treatment in the present invention is not limited to these, as long as it is capable of chemically modifying cellulose, hemicellulose, or a hydroxyl group in a lignin molecule, which are main constituent components of wood.

  The reforming method of the present invention may be performed as follows.

  For example, wood and a chemical reaction treatment reagent are placed in a pressure-resistant container and sealed. The amount of the chemical reaction treatment reagent is 0.6 to 3.5, preferably 1.0 to 2.0, relative to the wood 1 by weight. Next, after deaeration by decompression, carbon dioxide is filled. What is necessary is just to heat and pressurize so that a carbon dioxide may be in a supercritical state, and to perform a chemical reaction process for predetermined time. If the pressure is reduced after the treatment, the chemical reaction treatment reagent and carbon dioxide can be easily separated and recovered and reused.

  The apparatus for carrying out the method of the present invention is not particularly limited as long as it can chemically treat wood in carbon dioxide in a supercritical state, but a batch type reaction apparatus using an autoclave can be used.

  FIG. 1 shows an embodiment of an apparatus for carrying out the method of the present invention.

  The reaction vessel 1 is pressure resistant and is made of, for example, stainless steel. The reaction vessel 1 is provided with a heater 2 for heating. Wood and chemical reaction treatment reagent are enclosed in a reaction vessel 1. The valve 5 is opened and the reaction vessel 1 is degassed by the vacuum pump 3. Next, the valves 10 and 11 are opened, and carbon dioxide is pressurized and inserted into the reaction vessel 1 from the carbon dioxide cylinder 6 through the condenser 7 and the cold water circulator 8 by the liquid feed pump 9. The head portion of the liquid feed pump 9 is cooled by cold water circulated by the cold water circulator 8. The reaction conditions are controlled so that carbon dioxide maintains a supercritical state by measuring temperature and pressure with the pressure gauge 4 and the thermometer 14. When the pressure exceeds a predetermined pressure, the pressure is adjusted by the back pressure valve 13. The reaction temperature is adjusted by turning on and off the heater 2. After the chemical reaction treatment of the wood is completed, the heater 2 is turned off, the back pressure valve 13 is gradually opened, the pressure is slowly reduced to normal pressure, and then the modified wood is taken out.

  Hereinafter, a method for modifying wood by acetylation will be described in detail as examples, but the present invention is not limited to the examples.

  The wood was acetylated by the apparatus shown in FIG.

  A cedar heartwood specimen (5 mm (L) × 20 mm (R) × 20 mm (T)) was used in the experiment. Samples were extracted in advance with ethanol / benzene mixed solution (v / v = 1: 2) for 96 hours and hot water for 7 hours, and the dry weight was measured.

  Two specimens and 3 ml of acetic anhydride were placed in a 90 ml capacity pressure vessel, sealed, degassed with a vacuum pump for 10 minutes, and then filled with carbon dioxide. Then, the temperature was adjusted to 130 ° C. and the pressure to 10.5 MPa, and the specimen was acetylated in a supercritical state. The treatment time was 5 types of 1, 3, 6, 15, and 24 hours.

  After the treatment, the dry weight of the specimen was measured again to determine the weight increase rate. The result is shown in FIG. As is apparent from FIG. 2, a weight increase rate of nearly 20% was obtained even in a short time treatment of 1 hour, and it was found that the acetylation reaction proceeded in a very short time. In addition, the weight increase rate reached 27% after 24 hours of treatment, and a value higher than or equal to the maximum value of the weight increase rate obtained by the conventional method was obtained.

  Next, in order to evaluate the dimensional stability of the acetylated wood, anti-swelling ability (hereinafter abbreviated as ASE) was measured. A specimen whose dimensions were measured in advance in a dry state was submerged in water and immersed for one week while decompressing with an aspirator. One week later, the specimen was taken out and the dimensions were measured to determine the swelling ratio of the specimen. And ASE was computed by the following formula | equation.

ASE = (D ₀ −D) / D ₀ × 100 (%)
D ₀ : Swelling rate of untreated material D: Swelling rate of treated material

  FIG. 3 shows the relationship between the rate of weight increase due to acetylation and ASE, and ASE showed a very high value of 76 to 81%. In the conventional method, the ASE is about 65 to 75% at a weight increase rate of 20% or more, but the supercritical carbon dioxide treatment showed a dimensional stability exceeding that of the conventional method. This is probably because the acetylation reaction mainly occurs on the wood surface in the conventional method, whereas the supercritical carbon dioxide treatment has a uniform reaction to the inside of the wood, so it has excellent dimensional stability. It seems that acetylated wood was obtained.

From the above results, by using supercritical carbon dioxide as the reaction field, high-performance acetylated wood can be produced in a very short time in a non-catalytic reaction using only a small amount of acetic anhydride compared to the conventional method. Became clear.
(Comparative Example 1)
Using the same cedar heartwood specimen as in Example 1, acetylation treatment by liquid phase reaction was performed. Two specimens were immersed in 100 ml of acetic anhydride and injected overnight under reduced pressure, then transferred into 100 ml of acetic anhydride heated to 120 ° C., and subjected to acetylation treatment for 1 hour or 8 hours. After the treatment, the weight increase rate and ASE were measured in the same manner as in Example 1. The results are shown in FIG. 2 and FIG. In order to obtain a weight increase rate of 20% or more, treatment for 8 hours is required, and it is also necessary to inject acetic anhydride in advance before the treatment. long. Moreover, about 50 to 100 times as much acetic anhydride as the weight of the specimen is required, which consumes a large amount of drug.
(Comparative Example 2)
Using the same cedar heartwood specimen as in Example 1, acetylation treatment by gas phase reaction was performed. Two specimens and 5 ml of acetic anhydride were placed in a 2 liter desiccator and depressurized with an aspirator for 5 minutes. Thereafter, the desiccator was placed in a dryer heated to 120 ° C. and subjected to acetylation treatment for 1 hour or 8 hours. After the treatment, the weight increase rate and ASE were measured in the same manner as in Example 1. The results are shown in FIG. 2 and FIG. It can be seen that in the gas phase reaction, acetylation does not proceed sufficiently as compared with the method of the present invention, and the treatment time is also long.

  According to the method of the present invention, wood can be chemically treated safely and efficiently in a short time, which is useful as a method for modifying wood.

The flowchart which shows one Embodiment of the apparatus for implementing this invention method. The graph which shows the relationship between the acetylation reaction time of Example 1, and a weight increase rate. The graph which shows the relationship between the weight increase rate by acetylation of Example 1, and ASE.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction container 2 Heater 3 Pressure reduction pump 4 Pressure gauge 5 Valve 6 Carbon dioxide cylinder 7 Condenser 8 Cold water circulator 9 Liquid feed pump 10, 11, 12 Valve 13 Back pressure valve 14 Thermometer

Claims (3)

A method for reforming wood, characterized in that acetic anhydride is used as an acetylating reagent in carbon dioxide in a supercritical state, and wood is acetylated by a non-catalytic reaction . Wood, which is sealed with wood and an acetylating reagent in a pressure vessel, filled with carbon dioxide, heated and pressurized so that carbon dioxide is in a supercritical state, and subjected to acetylation treatment for a predetermined time Reforming method. The method for modifying wood according to claim 1 or 2, wherein, in the acetylation treatment, the amount of the acetylating reagent is 0.6 to 3.5 with respect to the wood 1 by weight. .

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