JPH06220788A - Preparation of pulp with high yield and high degree of bleaching for paper manufacturing - Google Patents

Abstract

PURPOSE: To provide a preparation method of bleached paper pulp in high yield in which wood chips are treated with an alkaline solution of hydrogen peroxide before splitting. CONSTITUTION: Wood chips are treated with a solution of at least one reducing agent before treating with the alkaline solution of hydrogen peroxide. In the concrete, the wood chips are impregnated with the reducing agent solution, which then are heated to 60160 deg.C and compressed to extract 20% or more of the impregnated reducing agent solution. Thus obtained chips are impregnated with the alkaline solution containing hydrogen peroxide, which then are heated to 50-120 deg.C. The chips thus treated are refined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-yield bleached pulp for papermaking, which has excellent mechanical properties, and more particularly to a method for producing a chemo-co-mechanical pulp and a chemo-thermo-mechanical pulp. Pulp is produced by adding mechanical, chemical or thermal operations to wood chips separately or simultaneously. Chemical pulp is obtained by chemically defibrage or beating wood. However, the yield is generally 50%
It is the following. The yield means the dry weight of pulp with respect to the dry weight of the starting material. Mechanical pulp or high-yield pulp is produced by mechanically crushing wood chips, for example, by a crusher, a defibrator or a disc refiner. Its yield is generally above 85%, but its mechanical properties, in particular breaking strength, tear strength and breaking strength, are low. In order to improve these mechanical properties, wood chips have been heat treated with steam at a temperature of 100-140 ° C before grinding. This pulp is called thermomechanical pulp (TMP), but has low whiteness. There is also a method of treating wood chips with an acidic or alkaline sodium sulfite solution depending on the type of wood. The pulp obtained by this method is called chemo-mechanical pulp and has good mechanical properties. The strength of mechanical pulp can be significantly improved by treating wood chips with one or more chemicals simultaneously with thermal and mechanical defibration processes. This pulp is called Chemico Thermomechanical Pulp (CTMP). In this treatment method, the material is boiled nondestructively at a temperature above 100 ° C. under saturated steam pressure and in the presence of sulfites, in particular sodium sulfite Na ₂ SO ₃ or sodium hydrogen sulfite NaHSO ₃ . The advantage of this CTMP pulp is that the mechanical strength is increased and the yield is generally above 85%, in most cases at least 90%, with the same yield as when purely mechanically operated.

Pulp treated by these methods, particularly chemo-co-mechanical pulp (CMP) and chemo-co-thermo-mechanical pulp (CTMP), have excellent mechanical strength, but the bleaching degree required for paper quality still has a problem. is there. French patent 1,389,308 and European patent EP-A-29 for improving the bleaching of pulp.
No. 3,309 proposes a method in which wood chips are treated with a mixed solution of an alkali metal borohydride and sulfite with acidic or alkaline ph. The pulp obtained after defibration by this treatment method shows excellent mechanical properties and high bleaching degree, but the whiteness is not sufficient, and it is necessary to further bleach the pulp with hydrogen peroxide after crushing. . This lack of bleaching degree is especially due to the sulfite treatment. Moreover, the sulfite treatment improves the mechanical properties of refined pulp, but reduces the reactivity with hydrogen peroxide. Therefore, many problems remain for obtaining a pulp having a high bleaching degree, which has excellent mechanical properties and has a sufficient whiteness for papermaking. In order to solve this problem, European patent No.
In EP-A-239,583, wood chips are squeezed with three types of solutions before defibration: metal ion sealant solution, hydrogen peroxide stabilizer solution such as sodium silicate and magnesium salt, and alkaline solution of hydrogen peroxide. The method of processing is described. With this method, the whiteness of the pulp obtained after defibration is high, but the whiteness is not sufficient for all applications. Especially when conifers are used, the whiteness is below 80 ° ISO.
Therefore, it is generally necessary to bleach the refined pulp with hydrogen peroxide in a conventional manner, which increases production costs. Mechanical properties are improved even if hydrogen peroxide treatment is performed without sulphite treatment before defibration, but this method cannot obtain satisfactory properties in the case of softwood.

[0003]

The object of the present invention is to provide high mechanical properties (breaking strength, tearing strength, breaking strength) and high whiteness after defibration, especially for softwood of 80 ° ISO or higher. Is to provide a method for producing a high-yield pulp suitable for producing a paper having high whiteness.

[0004]

The method of the present invention is a method for producing high-yield bleached pulp for papermaking. In the method of the present invention, wood chips are treated with a solution of at least one reducing agent before defibration, It is then treated with an alkaline solution of hydrogen peroxide.
The method according to the invention comprises in particular the following steps: (a) impregnating the wood chips with a reducing agent solution, (b) heating the impregnated wood chips to 60-160 ° C., (c) pressing the wood chips. Extract at least 20% of the reducing agent solution with (d) (c)
The wood chips obtained in step (1) are impregnated with an alkaline solution containing hydrogen peroxide, and the chips impregnated in steps (e) and (d) are mixed with 50 to 120
(F) Wood chips treated as above are refined by heating to ℃.

Optionally, prior to step (d), a solution containing a chelating agent or a sequestering agent such as DTPA.
40% of (diethylenetriaminepentaacetic acid) sodium
It is also possible to add the operation of impregnating the wood chips with an aqueous solution. The lignocellulosic material which can be treated by the method of the present invention may be coniferous trees such as fir, pine and spruce, hardwood such as poplar, eucalyptus and the like, which are made into chips generally used in the pulp and paper industry. It is also possible to treat annual plants such as bagasse and straw cut into pieces of several centimeters. These chips are subjected to the preparatory treatments customary in the pulp and paper industry, such as washing, sorting and preliminary steam heating.

In the method of the present invention, the chips are first treated with a reducing agent solution (step a). This treatment is performed by impregnating the chip with the solution. This impregnation operation can be carried out using a usual method in the paper industry. Before this impregnation operation, the chips are softened by a humidification operation using steam and / or oven steaming, and then squeezed using a screw press to remove a part of the gas and / or liquid in the chips and squeezed. When the chip swells later, it is impregnated with the reducing agent solution.

A particularly suitable device for the continuous industrial impregnation of chips is the Sands-Defibrator (SU
NDS-DEFIBRATOR) plex (PREX) system, BAUER (impressor finer)
R), HYMAC conical screw presses, and any device capable of compressing and expanding chips in the presence of an impregnating solution once or several times, preferably at the highest possible compression ratio. You can In the present invention,
The tip should be swollen with the smallest possible amount of tip impregnation solution.

The reducing agent solution used in the method of the present invention contains one or more reducing agents selected from the group consisting of alkali metal sulfites, bisulfites or a mixture of sulfur dioxide and an alkaline agent such as sodium hydroxide. Contains. Also, sodium borohydride (NaBH ₄ ) can be used as it is or in the form of an alkaline solution. Further, pure sodium dithionite (Na ₂ S ₂ O ₄ ) or its zinc salt is used as it is, or an alkaline solution of sodium borohydride and sodium sulfite (Na ₂ SO ₃ ) or sodium bisulfate (Na ₂ HSO ₄ ) is used. The product obtained by the reaction with ₃ ) can also be used. It is also possible to use thiourea dioxide or formamidine sulphonic acid as reducing agent. From an economical point of view, the reducing agent is an alkali metal sulfite such as sodium sulfite, MORTON In
sodium bisulfite, an alkaline solution of sodium borohydride consisting of 12% by weight sodium borohydride and 40% by weight sodium hydroxide, marketed under the name BOROL® by the company Ternational. , Sodium dithionite, a mixture of sodium sulfite and an alkaline solution of sodium borohydride (borol, BOROL).

[0009] The reducing agent is 0.1 ~ dry weight of the chip
10% by weight, especially 0.5-6% for sodium sulfite,
In the case of sodium borohydride alkaline solution borol
0.5-1.5%, 0.5-2.5 for sodium bisulfite
% Is preferably used. The pH of the reducing solution of the present invention is selected according to the lignocellulosic material of the chip,
Be over 7 and 13 or less. It is preferably 11 to 12.8 for hardwood and 9.5 to 11 for softwood (resin wood). In order to adjust the pH of the reducing solution to the desired value, NaO
Alkali agents such as H, KOH, Na ₂ CO ₃ , K ₂ CO ₃ , MgO and CaO can be added if necessary.

In the present invention, a complexing agent or a metal ion chelating agent can be added to the reducing agent. This complexing agent or metal ion chelating agent is sodium tripolyphosphate, sodium tetrapyrophosphate, nitrilotriacetic acid,
It may be a sodium salt of ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid. It is preferred to use a 40% aqueous solution of the sodium salt of diethylenetriaminepentaacetic acid (DTPA) in an amount of 0.2-0.5% with respect to the reducing solution.

The temperature of the reducing agent solution during impregnation can be 10 to 100 ° C. This temperature is determined according to the stability of the reducing agent, but if the temperature is high, the impregnation time can be shortened, and if the temperature is low, the reducing action of the solution is continued. In most cases, the temperature is preferably 20 to 60 ° C., especially 20 to 40 when a reducing agent (borol above) obtained by mixing sodium sulfite with an alkaline solution of sodium borohydride is used.
The temperature is preferably set to ° C.

Immediately after impregnating with the reducing agent solution, the chips are
Heat to ~ 160 ° C, preferably 75-120 ° C (step b). The heating time is from 1 minute to 3 depending on the temperature and the type of wood.
Can be on time. 15-60 minutes at 90 ℃, 5 at 120 ℃
It is preferably -30 minutes. The impregnated chips are preferably transferred and heated in a steam atmosphere or in an inert atmosphere such as nitrogen or carbon dioxide under the condition that oxygen in the air does not exist. A part of the reducing agent solution after the reaction is removed by impregnating the reducing agent and pressing the heated chips with a screw press or other means. The reason for squeezing the chips is to remove the reducing solution and increase the efficiency of the overall process. It is particularly desirable to remove at least 20% of the reducing agent solution. The reducing agent solution can be removed by one or more pressing operations. It can also be washed with water after pressing. The pressing operation can be carried out at 20 to 160 ° C. A part or the whole of the reducing agent solution extracted by the pressing operation can be recycled for preparing the reducing agent solution used in the step (a).

Chips impregnated with a reducing agent solution and pressed are
It is then impregnated with an alkaline solution of hydrogen peroxide (step d). The oxidizing agent or hydrogen peroxide may be used in an amount of 0.1 to 10% by weight based on the dry weight of the chip to be treated. This amount depends on the desired whiteness, but is usually from 1 to 5% by weight. Generally, 5% by weight or more is not used for economic reasons. One or more alkaline agents such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, magnesium oxide, calcium oxide, etc. are added to the hydrogen peroxide solution so that the initial pH of the solution is 8 to 12.5. Sodium hydroxide is preferred. The optimum amount of alkaline agent depends on the type of wood and is proportional to the amount of hydrogen peroxide. The amount of alkali agent when expressed as sodium hydroxide is 0.5 to 10% by weight based on the dry weight of the chips to be treated,
It is preferably 0.5 to 6% by weight.

It is also possible to add a stabilizer of hydrogen peroxide to an alkaline solution of hydrogen peroxide to suppress decomposition of hydrogen peroxide in an alkaline medium and enhance the treatment effect. As the stabilizer, sodium silicate of 40% solution is generally used in an amount of 0.5 to 5% by weight based on the weight of dry chips, or a magnesium salt such as magnesium chloride, magnesium nitrate, magnesium carbonate or a mixed salt thereof. Is used in an amount of 0.01 to 1% magnesium, or polylactone of poly (α-hydroxyacrylic) acid is used in an amount of 0.02 to 2% by weight. It is also possible to add to the hydrogen peroxide solution one or more chelating agents and sequestering agents, for example diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, in the form of their sodium salts. These are used in amounts of 0.1 to 1% by weight, based on the dry weight of the chips to be treated. The temperature of the alkaline solution of hydrogen peroxide during impregnation is 10 to 80 ° C,
In order to suppress the decomposition of hydrogen peroxide, the temperature is preferably 40 ° C or lower.

After impregnating the chips with an alkaline solution of hydrogen peroxide, the temperature is raised to 50-120 ° C., preferably at the step (e).
Heat to 60-80 ° C for 10 minutes to 5 hours. The heating time is determined according to the type of wood, the temperature and the amount of hydrogen peroxide.
Generally, 60 ℃ for 5 hours, 70 ℃ for 2-3 hours, 90 ℃ for 1 ~
Make it 2 hours. This heating can be performed in an atmosphere of saturated steam.

After performing two kinds of treatments with a reducing agent solution and an oxidizing agent solution, the chips are passed through one or more refiners under atmospheric pressure or under a steam pressure of several bar to defibrate or raffinage. Yes (step f). Refining is usually performed in two stages. The first refining is carried out under pressure and the second refining is carried out under atmospheric pressure. The conditions for the refining operation are determined according to the required properties of paper pulp.

Refined pulp is generally neutralized with an acid to eliminate alkalinity due to treatment with an alkaline solution of hydrogen peroxide. In this neutralization operation, it is preferable to adjust the pH to 5.5 to 6 by using dilute sulfurous acid or sulfurous acid gas. The pulp is then processed in the usual way (filtration, screening, recirculation on a sieve, etc.).

[0018]

EXAMPLES The present invention and its advantages will be described below with reference to examples, but the present invention is not limited to the following examples. In the examples below, the amount of reactants is expressed in wt% relative to the dry weight of the chips. In the examples, softwood chips (fir etc.) or hardwood chips (poplar etc.) were used. These chips are manufactured in an industrial manufacturing plant of mechanical pulp for papermaking, and comply with the industrial standard. The examples were carried out in a pilot plant for producing high yield mechanical pulp. The capacity of this pilot plant is 200kg / hour, continuously operated and equipped with the following facilities: 1. Chip preparation line (storage, water washing, oven steaming at 90 ℃), 2. With filtration function A first screw impregnator equipped with a squeeze zone and an expansion zone (reactant is injected here with a metering pump), 3. a buffer container capable of ensuring a residence time of 5 to 60 minutes at a temperature of 40 to 100 ° C, 4. A second impregnator with a squeeze zone equipped with a filter and a means for injecting wash water, and an impregnating zone in which a second reactant is injected with a metering pump, 5. At a temperature of 40-100 ° C. A buffer container that can secure a residence time of 15 to 120 minutes, a double disc refiner (40 ps), a slotted HOOPER screen, and a storage container for neutralizing pulp with sulfurous acid gas. After the pulp was prepared, the obtained pulp was used for papermaking, and the whiteness and mechanical properties were measured according to the ISO standard for papermaking industry. The commercially available sodium borohydride solution used was the boron (12) sold by Molton International.
% Sodium borohydride and 40% sodium hydroxide) ®. The metal ion chelating agent used in the examples is a 40% aqueous solution of the sodium salt of DTPA (diethylenetriaminepentaacetic acid).

Example 1 Softwood chips (fir, spruce) are washed and steam-steamed with steam. This chip was treated with 5.9% sodium sulfite, 0.5% DTPA solution (40% concentration),
Impregnation is continuously carried out at a temperature of 20 ° C. with a reducing agent solution having a pH of 10.5 and containing 1.5% of the above Borol®. 60 ℃ tip
Heat for 30 minutes. The chips are squeezed at 60 ° C to remove about 0.5 liter of the reducing agent solution per 1 kg of dried chips (removal rate is about 50%). The chips are washed with 2 liters of water per kg dry weight. Then, an oxidizer solution containing 5% hydrogen peroxide, 2% sodium hydroxide, 4% sodium silicate solution (concentration 40%) and 0.5% DTPA solution (concentration 40%) was applied to the chip. Impregnate continuously at 20 ° C. The pH of this oxidant solution is 11.5. Then the impregnated chips 90
Heat at ℃ for 1 hour and refine with a double disc refiner. Then, pass the pulp through the screen, and return the pulp that did not pass through the screen to the refiner. The fined pulp has an indice d'egouttage of 70 ° SR. Neutralizing the pulp to pH 6 with sulfurous acid gas gives a paper with the following characteristics: ISO whiteness 82 ° ISO rupture strength: rupture length 4500 m eclatement strength 2.3 KPa m ² / g dechirure 80 ° I after refining from conifers by the method of the invention consisting of treatment with a reducing agent solution containing strength 5.1 mN m ² / g sodium sulfite and sodium borohydride and treatment with hydrogen peroxide
It can be seen that a pulp having a high whiteness of SO or higher is obtained.

Example 2 The procedure of Example 1 is repeated, but after impregnation with the oxidant solution
Change the heating time at ℃ from 1 hour to 2 hours. A pulp having the same mechanical properties as Example 1 but a whiteness of 83 ° ISO is obtained.

Example 3 The procedure of Example 1 was repeated, but using a reducing agent solution of 5.9
% Sodium sulfite and 0.5% DTPA solution (concentration 40
%) And pH of 9.6 are used. A pulp having the following properties is obtained: ISO whiteness 80 ° ISO Breaking strength: Breaking length 4400 m Bursting strength 2.2 KPa m ² / g Tear strength 5.4 mN m ² / g

Example 4 (Comparative Example) The procedure of Example 1 is repeated, but the treatment of the chip with the reducing agent solution is omitted. The first treatment involves impregnating the chips with a solution containing only 0.5% DTPA solution (40% concentration). A pulp with the following properties is obtained: ISO whiteness 78 ° ISO Breaking strength: Breaking length 3200 m Bursting strength 1.6 KPa m ² / g Tearing strength 5.2 mN m ² / g European patent to treat chips before grinding with hydrogen peroxide solution It can be seen that in the case where the treatment described in EP-A-239,583, that is, the reducing agent treatment is not performed, the whiteness and mechanical strength of pulp such as the pulp obtained by the method of the present invention cannot be obtained.

Example 5 Chips of hardwood (poplar, porcupine) that had been washed and steam-oven treated with 5% sodium sulfite and 1.5%
% Sodium borohydride solution (Borol®)
And a reducing agent solution having a pH of 11.5 containing 0.5% DTPA solution (concentration 40%) are continuously impregnated at 20 ° C. Heat the impregnated chips to 100 ° C for 30 minutes in a steam atmosphere. The chips are then squeezed at 60 ° C to remove 50% of the reducing solution. Wash with 2 liters of water per kg dry weight of chips. Next, the tip was treated with 5.2% hydrogen peroxide, 4% sodium hydroxide, 4% sodium silicate solution (concentration 40%),
Impregnation at 20 ° C. with an oxidant solution having a pH of 11.4 containing 0.5% DTPA solution (concentration 40%). After that, the chips are heated at 90 ° C. for 2 hours and refined with a double disc refiner under atmospheric pressure. The drainage index of refined pulp after screening is
56 ° SR. The properties of this pulp are as follows: ISO whiteness 87 ° ISO Breaking strength: Breaking length 3300 m Bursting strength 1.3 KPa m ² / g Tear strength 3.5 mN m ² / g Hardness with relatively high whiteness in this example. Wood (hardwood)
Although the chips have been treated, the process of the invention makes it possible to obtain a pulp of very high brightness after grinding.

Example 6 The procedure of Example 5 is repeated, except that a reducing agent solution having a pH of 11 containing 5% sodium sulfite and 0.5% DTPA solution (concentration 40%) is used. The properties of the resulting pulp are as follows: ISO whiteness 82.5 ° ISO breaking strength: breaking length 2900 m bursting strength 1.20 KPa m ² / g tearing strength 3.1 mN m ² / g

Example 7 (Comparative) The procedure of Example 5 is repeated, but using a solution containing only 0.5% DTPA solution (concentration 40%) in the first impregnation without the use of a reducing agent. The properties of the resulting pulp are as follows: ISO whiteness 84 ° ISO Breaking strength: Breaking length 2300 m Bursting strength 0.9 KPa m ² / g Tear strength 2.9 mN m ² / g Crushing of hardwood chips treated in this comparative example It can be seen that the brightness of the subsequently obtained pulp is considerably lower than the brightness of the same chips treated according to the inventive method of Example 5.

Example 8 Hardwood (poplar) chips are washed and steam oven treated at 90 ° C. 1% sodium borohydride solution (Borol®) and 0.5% DTPA solution (concentration
40%) and a reducing solution having a pH of 12.7 are continuously impregnated at 20 ° C. Heat the chips to 90 ° C for 15 minutes. The chips are squeezed at a temperature of 60 ° C. to remove 0.5 liter of the reducing agent solution per 1 kg of dry weight (removal rate is about 20%). The chips are then impregnated at 20 ° C. with an oxidant solution having a pH of 10.5 containing 4.25% hydrogen peroxide and 3.8% sodium hydroxide. The chips impregnated with the oxidant solution are heated to 85 ° C. for 1 hour. This is refined with a first double disc refiner and then with a second single disc refiner under atmospheric pressure. The drainage index of the refined pulp after neutralization to pH 6 with sulfurous acid gas is 62 ° SR, which shows the following characteristics: ISO whiteness 80.9 ° ISO fracture strength: fracture length 2800 m burst strength 1.25 KPa m ² / g

Example 9 The procedure of Example 8 is repeated except that 1% sodium sulfite solution as a reducing agent solution, 1% sodium borohydride solution (Borol®) and 0.5% DTPA solution (concentration 40%).
%) Is used. The pulp obtained has a drainage index of 68 ° SR and exhibits the following characteristics: ISO whiteness 81.1 ° ISO breaking strength: breaking length 3100 m breaking strength 1.36 KPa m ² / g

Example 10 The procedure of Example 8 is repeated, except that 2% sodium sulfite as a reducing agent solution, 1% sodium borohydride solution (Borol®) and 0.5% DTPA solution (concentration 40%) are used.
%) And a solution containing The pulp obtained has a drainage index of 65 ° SR and exhibits the following characteristics: ISO whiteness 81.7 ° ISO breaking strength: breaking length 3320 m breaking strength 1.38 KPa m ² / g

Example 11 (Comparative Example) The procedure of Example 8 is repeated, except that no reducing agent is added during the first impregnation treatment and a solution containing only 0.5% DTPA solution (concentration 40%) is used. Draining index of the obtained pulp is 66 ° S
The following characteristics are shown by R: ISO whiteness 79.8 ° ISO breaking strength: breaking length 2900 m bursting strength 1.21 KPa m ² / g The initial whiteness of the hardwood (poplar) chips used in Examples 8 to 11 was measured. Lower than that used in Examples 5-7. Therefore, the whiteness of the obtained pulp is lower than those of Examples 5-7. However, even in this case, it is understood that the pulp obtained after crushing by treating the wood chips first with the reducing agent and then with the oxidizing agent has an extremely high whiteness and excellent mechanical properties.

Claims (16)

[Claims] 1. A method for producing a high-yield bleached pulp for papermaking, wherein wood chips are treated with an alkaline solution of hydrogen peroxide before defibration, and at least one kind of bleached pulp is treated with the alkaline solution of hydrogen peroxide. A method comprising treating wood chips with a solution of a reducing agent. 2. The method according to claim 1, comprising the following steps: (a) impregnating wood chips with a reducing agent solution, (b) heating the impregnated wood chips to 60-160 ° C., (c) The wood chips are squeezed to extract 20% or more of the reducing agent solution, (d) the wood chips are impregnated with an alkaline solution containing hydrogen peroxide, and (e) the chips impregnated in steps (d) to 50-120. (F) Wood chips treated as above are refined by heating to ℃. 3. The reducing agent is selected from the group consisting of sodium sulfite, sodium bisulfite, sodium borohydride, zinc or sodium dithionite, thiourea dioxide and a mixture of sulfur dioxide and sodium hydroxide. The method according to Item 1 or 2. 4. The method of claim 3, wherein the reducing agent solution is prepared by mixing sodium sulfite and sodium borohydride. 5. The reducing agent is used in an amount of 0.1 to 10% of the dry weight of the chip.
The method according to any one of claims 1 to 4, which is used in a ratio of. 6. The method according to claim 1, wherein the pH of the reducing solution is 7 or more and 13 or less. 7. The method according to claim 1, wherein the reducing solution contains a chelating agent or a sequestering agent. 8. The method according to claim 1, wherein the temperature of the reducing solution is 10 to 100 ° C. 9. After impregnating wood chips with a reducing solution, 60
The method according to any one of claims 2 to 8, wherein heating is carried out at ~ 160 ° C for 1 minute to 3 hours. 10. A method of impregnating with a reducing solution and squeezing the heated chips to remove at least 20% of the reducing solution.
9. The method according to any one of 9. 11. The wood chip is impregnated with an alkaline solution of hydrogen peroxide so that the hydrogen peroxide is 0.1 to 10% by weight with respect to the dry weight of the wood chip. the method of. 12. The pH of an alkaline solution of hydrogen peroxide is 8
12. The method of claim 11, which is ~ 12.5. 13. The method according to claim 11 or 12, wherein the alkaline solution of hydrogen peroxide comprises one or more peroxide stabilizers. 14. The temperature of an alkaline solution of hydrogen peroxide is
The method according to any one of claims 11 to 13, which has a temperature of 10 to 80 ° C. 15. The method according to claim 1, wherein the wood chips impregnated with the alkaline solution of hydrogen peroxide are heated at 50 to 120 ° C. for 10 minutes to 5 hours. 16. The method according to claim 1, wherein the wood chips are impregnated with a solution of a metal ion chelating agent, then pressed and then treated with an alkaline solution of hydrogen peroxide.