ES3027193T3 - Method for producing cellulose pulp, cellulose pulp and use thereof, paper - Google Patents

Abstract

The present invention relates to an improved method for producing cellulose pulps with increased quality and applicability, particularly in terms of physical strength and resistance to draining, due to an enzymatic treatment step included in the production method, along with the addition of a carbohydrate-based polymer.

Description

DESCRIPTION

Method of producing cellulose pulp, cellulose pulp and its utilization, paper

Field of the invention

The present invention relates to an improved process for the manufacture of cellulose pulps with greater quality and applicability of said pulps, especially their physical strength properties and degree of resistance to drainage, through an enzymatic treatment step included in the process for manufacturing said cellulose pulp, concomitantly with the dosage of carbohydrate-based polymer.

Background of the invention

The quality and final characteristics of a paper are directly related to the type of cellulose fiber used in its composition. In recent years, several studies have been conducted to relate the impact of changes in cellulose fiber characteristics to the physical and mechanical properties of paper. Among these characteristics of cellulose fibers, their flexibility and number of carboxylic groups are considered important for the development of paper with physical strength without compromising its structure.

In addition to concerns about fiber quality and improving its characteristics, the paper and pulp industry faces constant challenges in addressing problems related to high industrial water consumption, which translates into high energy consumption.

The enzyme treatments described in the prior art were introduced into the cellulose fiber manufacturing process as a solution to promote a reduction in the consumption of chemicals used in the process through their action, and thus also to improve the characteristics of the effluent generated by the process. Another result of enzyme dosing in the process is a reduction in energy expenditure.

Regarding the physical strength properties of cellulose fibers, it can be stated that they are related to the amount of carboxylic groups present and the flexibility of the fibers.

The greater the amount of carboxylic groups present in the fibers and the more flexible these fibers are, the greater the physical strength, i.e., the traction that will be imparted to the paper made from them.

This is due to the increased contact area between fibers with these characteristics, which allows for an increase in the number of bonds between them. Furthermore, the increase in carboxylic groups or ligands allows for the formation of a greater number of hydrogen bonds.

Some prior art documents also mention the differentiation of the physical properties of fibers and paper through the use of enzymes in the manufacturing process. However, as already described in the prior art, increasing the physical strength of pulp through the use of enzymes often compromises its drainage. Or even when there is an improvement in the drainage capacity of the fiber, there is a deterioration in its physical strength.

Document W02003/021033 describes a process for manufacturing tissue paper on a machine, where the paper product contains cellulose fibers. An enzymatic treatment is carried out on the cellulose fibers to increase the number of reactive aldehyde groups on the surface of said fibers. The treatment described in said document consists of mixing an aqueous suspension of cellulose fibers with one or more hydrolytic enzymes, optionally in the presence of surfactants, other non-cellulase/hemicellulase enzymes, or non-hydrolytic chemical reagents, whereby aldehyde groups are formed on or near the surface of the fibers. The use of these hydrolytic enzymes, particularly cellulases, is responsible for the degradation of the fibrous cell wall, which impairs the tensile strength properties of the paper.

Gonzales et al. (2013) described an enzymatic pulp treatment procedure combined with the addition of nanofibrillated cellulose (NFC) that resulted in improved physical and mechanical properties of a pulp slurry used in papermaking. However, the results of the study showed no increase in fiber drainage.

Pommier et al. (1989) describe the enzymatic action on cellulose pulp as a "peeling effect" and suggest that the enzymes defibrillate cellulose fibers by removing molecules with a high affinity for water, but with a small contribution to the overall hydrogen bonding potential of the fibers. This reduction in pulp-water interactions allows for greater pulp drainage. However, it leads to a reduction in fiber strength and length, in addition to excessive production of fines. As a consequence, paper strength is drastically affected.

Document WO00/68500 relates to a process for manufacturing paper materials such as paper, cardboard, board or corrugated board with improved wet strength.

WO03/048449 relates to pulp bleaching processes that combine xylanase enzymes with hydrogen peroxide, peracids or a combination of both, wherein the hydrogen peroxide and peracids do not destroy the xylanase activity.

WO94/20672 relates to a process for bleaching hardwood and softwood pulp without chlorine or chlorine derivatives, which provides a pulp with high brightness, good physical strength and a low degree of brightness reversion.

WO2013/090272 relates to methods for reducing the effects of wet lapping, drying and callosity of cellulose fibers and consequently for increasing pulp drainage and strength properties in the final pulp or paper product.

Although the implementation of an enzymatic treatment step in the cellulose refining process is known from the state of the art, it is essential to develop a process in which the application of the enzyme results in an increase in the surface area of the cellulose fiber without compromising the physical properties of the treated fiber, and in which the cellulose pulp obtained has greater physical traction and tear resistance and at least the maintenance of its degree of resistance to drainage.

The present invention aims to provide cellulose pulps with improved surface properties, properties that are also observed in paper manufactured from said cellulose pulp. A first embodiment of the present invention relates to a process for producing cellulose pulp from cellulosic raw material by dosing enzymes at specific concentrations in a process step.

Brief description of the drawings

Figure 1 shows a simplified flow diagram showing the step of enzymatic treatment concomitantly with the dosage of carbohydrate-based polymer according to a preferred embodiment of the invention.

Figure 2 shows a graph illustrating an increase in fiber surface area with enzyme dosage.

Figure 3 shows graphs with test data confirming that enzymatic treatment can alter the reactivity of the fiber surface, evaluated through the zeta potential.

Figure 4 shows a graph illustrating the increase in tensile index of the pulp of the present invention compared to the reference pulp.

Figure 5 shows a graph illustrating the increase in tear index of the pulp of the present invention compared to the reference pulp.

Figure 6 shows a graph illustrating a comparison between the degree of drainage capacity of the pulp of the present invention and that of the reference pulp.

Figure 7 shows a graph demonstrating that paper made from the pulp of the present invention reproduces the increases in tensile strength exhibited by the pulp of the present invention.

Figure 8 shows the pilot papermaking machine.

Detailed description of the invention

The present invention relates to a process for the manufacture of cellulose pulp with greater quality and applicability of said pulps, especially their physical resistance properties, at least the maintenance of their resistance to drainage, through an enzymatic treatment step, concomitantly with the dosage of carbohydrate-based polymer included in the process for manufacturing said cellulose pulp.

The carbohydrate-based polymer can be selected from the group consisting of: starch, carboxymethylcellulose, guar gum, among others.

The enzymatic treatment comprises the enzyme or mixture of hydrolytic enzymes (EZ), known to a person skilled in the art and commercially available, and which can be selected from the group consisting of: α-amylase, 2 p-amylase, glucan 1,4-α-glucosidase, cellulase, endo-1,3(4)-p-glucanase, inulinase, endo-1,4-p-xylanase, oligo-1,6-glucosidase, dextranase, chitinase, polygalacturonase, lysozyme, exo-α-sialidase, α-glucosidase, p-glucosidase, α-galactosidase, p-galactosidase, α-mannosidase, p-mannosidase, p-fructofuranosidase, α,atrehalase, p-glucuronidase, endo-1,3-p-xylanase, amylo-1,6-glucosidase, hyaluronoglucosaminidase, hyaluronoglucuronidase, xylan 1,4-p-xylosidase, p-D-fucosidase, glucan endo-1,3-p-D-glucosidase, a-L-rhamnosidase, pullulanase, GDP-glucosidase, p-L-rhamnosidase, fucoidanase, glucosylceramidase, galactosylceramidase, galactosylgalactosylglucosylceramidase, sucrose a-glucosidase, a-N-acetylgalactosaminidase, a-N-acetylglucosaminidase.

The performance of the commercially available enzyme or enzyme blend (EZ) occurs on the surface area of the cellulose fiber, enhancing the adsorption capacity of fiber-modifying chemicals during the pulp manufacturing process.

However, dosing enzymes at excessive concentrations can cause them to act deeper into the fibers, which could significantly alter their physical strength and degree of resistance to drainage and even degrade the walls of said fibers.

The inventors have found greater physical strength and, surprisingly, at least the maintenance of the degree of drainage capacity of the cellulose pulp obtained by the process described here, by defining specific levels of enzymes that are dosed together with the carbohydrate-based polymer, in the step after bleaching the pulp and before drying said pulp.

Figure 1 shows the steps of the process of the present invention. The process for producing cellulose pulp comprises the steps of:

a) treating the cellulose raw material by the chemical or semi-chemical pulping process to produce brown pulp (BP);

b) bleaching the brown cellulose pulp by the bleaching sequence to obtain the white pulp;

c) adding the carbohydrate-based polymer (B), wherein the dosage of said polymer ranges from 2 to 12 kg/tonne of cellulose pulp;

c) adding the enzyme or enzyme mixture to the white suspension pulp already doped with the carbohydrate-based polymer (B), wherein the addition of the enzyme (E) or enzyme mixture is carried out according to the following conditions:

i. Reaction temperature between 40 °C and 90 °C;

ii. Reaction pH between 3.0 and 9.0 using a strong base or a strong acid for pH adjustment, controlled by pH measurement;

iii. Reaction time between 10 and 300 minutes;

iv. Enzyme quantity between 10 g of EZ and 200 g of EZ per ton of cellulose;

e) transporting the doped white suspension pulp to the reaction tower and through it before the drying machine (TMCB), and

f) drying (S) the doped white suspension pulp to obtain cellulose pulp (CL).

Figure 2 shows that dosing 50, 100, or 200 g/ton of enzyme results in an increase in fiber surface area compared to a reference sample. The reference sample is a white slurry pulp that has not been doped, i.e., it has not received a dose of the carbohydrate-based polymer and the enzyme or enzyme mixture.

Enzymatic treatment applied under controlled conditions of the kinetic variables of the reactions involved, namely temperature, pH and time, leads to greater treatment efficiency and, therefore, to a more optimized enzyme dosage for the cellulose pulp manufacturing process.

Figure 3 shows the increased reactivity of the fiber produced by the process of the present invention. Reactivity is represented by the zeta potential.

Figures 4 and 5 demonstrate the increases in physical strength of the pulp obtained by the process described in the present invention compared to the reference pulp. Furthermore, Figure 6 demonstrates the maintenance of the degree of drainage resistance of the pulp of the present invention compared to the reference pulp.

The paper obtained from the pulp of the present invention reproduces increases in physical resistance as shown in Figure 7.

Furthermore, since the dosage of the commercial enzyme or enzyme mixture takes place before the drying step of the white suspension pulp, said enzyme or enzyme mixture undergoes denaturation during said drying step, resulting in a cellulose (CL) pulp without enzyme or enzyme mixture residues, as demonstrated by the performance of the ELISA assay.

In a preferred embodiment of the present invention, the process for manufacturing cellulose pulp comprises the steps of:

a) treating the cellulose raw material by the chemical pulping process, preferably a Kraft process for making brown cellulose pulp

b) bleaching the brown cellulose pulp by a bleaching sequence comprising treatment with hot chlorine dioxide (HCD) followed by treatment with soda and peroxide (OPE), followed by treatment with chlorine dioxide

c) adding the carbohydrate-based polymer (B), the dosage of said polymer ranging from 2 to 12 kg/tonne of cellulose pulp, preferably adding from 3 to 10 kg of polymer/tonne of cellulose pulp; d) adding the enzyme or enzyme mixture to the white suspension pulp already doped with the carbohydrate-based polymer (B), wherein the addition of the enzyme (E) or enzyme mixture is carried out according to the following conditions:

i. reaction temperature between 50 and 80 °C;

ii. Reaction pH between 3.5 and 8.0, using sodium hydroxide or sulfuric acid to adjust the pH;

iii. reaction time between 30 and 120 minutes;

iv. enzyme quantity between 20 g of EZ and 100 g of EZ per ton of cellulose;

e) transporting the added white slurry pulp to the reaction tower and through it before the drying machine (TMCB); and

f) drying (S) the doped white suspension pulp to obtain cellulose pulp (CL).

In another preferred embodiment of the present invention, the cellulose pulp manufacturing process can be described as:

a) treating the cellulosic raw material by the chemical pulping process, wherein the chemical pulping is preferably a Kraft process, to manufacture brown pulp (BP);

b) bleaching the brown cellulose pulp by a bleaching sequence comprising treatment with hot chlorine dioxide (DHT) followed by treatment with soda and peroxide (OPE) followed by treatment with chlorine dioxide (D1);

c) adding the enzyme or enzyme mixture to the white suspension pulp, wherein the addition of the enzyme (E) or enzyme mixture is carried out according to the following conditions:

i. reaction temperature between 50 and 80 °C;

ii. Reaction pH between 3.5 and 8.0, using sodium hydroxide or sulfuric acid for adjustment;

iii. reaction time between 30 and 120 minutes;

iv. enzyme quantity between 20 g of EZ and 100 g of EZ per ton of cellulose;

d) adding the carbohydrate-based polymer (B), the dosage of said polymer ranging from 2 to 12 kg/tonne of cellulose pulp, preferably dosing between 3 and 10 kg of polymer/tonne of cellulose pulp; e) conveying the doped white suspension pulp to and through the reaction tower before the drying machine (TMCB); and

f) drying (S) the doped white suspension pulp to obtain cellulose pulp (CL).

The chemical pulp manufacturing process, more specifically the Kraft pulp manufacturing process, as already described in the prior art, comprises the treatment of fibers of plant origin, including the following steps:

a) digestion in which plant fibers are boiled together with sodium hydroxide and sodium sulfide to separate the brown pulp (BP) from the lignin;

b) separation of black liquor from cellulose, the black liquor must be separated from the brown pulp (BP); c) recovery boiler, the black liquor is treated until it can be burned in the recovery boiler to generate energy;

d) close the circuit by recovering sodium hydroxide, sodium sulfide and water;

e) transformation of brown cellulose pulp (BP) into bleached cellulose (CL), said transformation comprising:

i) washing the cellulose pulp with water to remove residual black liquor;

ii) pre-bleaching;

iii) bleach;

iv) drying the cellulose (CL).

In other embodiments of the present invention, step (b) of bleaching a brown cellulose pulp (BC) of the cellulose pulp manufacturing process of the present invention may be selected from the group consisting of:

1) hot dioxide treatment (DOHOT), followed by oxidative peroxide extraction (OPE) and then final dioxide treatment (D) - elemental chlorine-free product (ECF);

2) acidification step with sulfuric or hydrochloric acid (A) DO (non-hot dioxide treatment), followed by oxidative peroxide extraction (OPE), followed by another dioxide treatment (D1), followed by peroxide extraction (PE), followed by another dioxide treatment (D2) - elemental chlorine-free product (ECF);

3) hot dioxide treatment (HOT Do), followed by oxidative peroxide extraction (OPE), followed by dioxide treatment with soda neutralization, and another stage of dioxide treatment (DnD) - elemental chlorine-free product (ECF);

4) a delignification stage (O) followed by transport of the pulp to an acid tower and within it, washing, use of ozone with extraction (AZe), followed by another washing, then treatment with dioxide (d) and addition of peroxide (P) - elemental chlorine-free product (ECF);

5) a delignification stage (O), followed by acidification for 15 minutes, followed by application of ozone, followed by extraction, then washing with water, treatment with dioxide (D), washing again, addition of peroxide (P), followed by washing, and finally drying of the product without elemental chlorine (ECF);

6) a delignification stage (O), followed by an acidification stage with sulfuric or hydrochloric acid (A), followed by ozone extraction (Ze), followed by peroxide addition (P), followed by another peroxide addition (P) - product without elemental chlorine and chlorine-based compounds (TCF);

7) a delignification stage (O), using ozone extraction (aZe) followed by peroxide addition (P) followed by further addition of peroxide (P) product without elemental chlorine and chlorine-based compounds (TCF),

8) oxygen delignification (OO) to reduce the Kappa number by 35%, acidification step with sulfuric or hydrochloric acid and hot dioxide treatment (HOTDo), followed by oxidative peroxide extraction (OPE), followed by dioxide treatment (D) and final addition of peroxide (P) - elemental chlorine-free product (ECF).

In the final bleaching step, the carbohydrate-based polymer and the commercial enzyme or enzyme mixture are dosed and then transported to and through a homogenization device, which ensures maximum contact between the dosed products and the fiber. This mixture is then transferred to a mixing pump where effective mixing of the additives takes place. The pulp doped with carbohydrate-based polymers and the commercial enzyme or enzyme mixture is then pumped to a reaction tower, where the mixture remains for 10 to 300 minutes, preferably 30 to 120 minutes, at a temperature between 40 and 90 °C, preferably between 50 and 80 °C, and a pH ranging between 3.0 and 9.0, preferably between 3.5 and 8.0, using sodium hydroxide or sulfuric acid to complete the reaction.

The resulting pulp is then pumped to the drying stage. Cellulose pulp (CL) is then obtained for the paper market.

The inventors have further discovered that, contrary to the teachings of the prior art, the process described here results in a cellulose pulp (CL) with increased physical strength, i.e., tear and tensile strength, and also with at least the degree of maintenance of drainage resistance, as shown in Figures 4 to 6.

According to a preferred embodiment of the present invention, the enzymatic treatment is carried out by the action of hydrolytic enzymes, for example, cellulases, or a mixture of cellulases with other enzymes available on the market with filler materials ranging from 20 to 100 grams of enzyme per ton of cellulose.

Said enzymatic treatment (E) is carried out in a step subsequent to the bleaching process of the pulp obtained by the chemical pulp manufacturing process, and before the drying step (D) of the pulp so that it can then be used in paper manufacturing.

Preferably, the enzymatic treatment has a retention time in the range of 30 to 120 minutes, a pH in the range of 3.5 to 8.0, a temperature in the range of 50 to 80 °C, preferably when the hydrolytic enzyme is a cellulase.

The fibers used in the process of the present invention may be so-called plant fibers, preferably short fibers, more preferably eucalyptus fibers.

The cellulose pulp of the present invention, obtained by a process that includes an enzymatic treatment step, simultaneously dosing a carbohydrate-based polymer, surprisingly presents a greater surface area of the cellulose fiber without compromising the physical properties of the treated fiber, and also ensuring that the cellulose pulp obtained exhibits greater physical tensile and tear resistance and at least maintains its drainage resistance.

Examples

The following examples will further illustrate the present invention and the particular conditions and parameters described represent preferred but non-limiting embodiments of the present invention.

Example 1: Polymer preparation procedure: addition of polymer followed by addition of enzyme

For the Kraft pulping process, the carbohydrate-based polymer, specifically starch, was used at a dosage of 3 to 10 kg/ton of short-fiber cellulose pulp. Then, 30 to 50 g of EZ was added per ton of cellulose, and the reaction conditions were as follows: temperature 50 to 90 °C, pH 3.0 to 8.0, for a period of 60 to 240 minutes. The bleaching sequence used was an ECF sequence.

Example 2: Polymer preparation procedure: enzyme addition followed by polymer addition

For a Kraft pulping process, 30 to 50 g of EZ were added per ton of short-fiber cellulose, under the following reaction conditions: temperature 50 to 90 °C, pH 3.0 to 9.0, for a period of 60 to 240 minutes. A carbohydrate-based polymer, specifically starch, was then dosed at a rate of 3 to 10 kg/ton of cellulose pulp. The bleaching sequence used was an ECF sequence.

Example 3: Description of comparative tests with references.

Comparative tests to evaluate the characteristics of the cellulose pulp obtained from the process of the present invention were carried out with the concomitant addition of carbohydrate-based polymer and commercially available enzyme or enzyme mixture.

In the laboratory tests, the equipment used was a cellulose bleaching reactor with a capacity of 300 g of dry fibers and fully automatic control of the process conditions, which were adjusted to: temperature of 50 °C, pH of 7.0 and reaction time of 120 minutes. The amount of enzyme or enzyme mixture used ranged from 0 (Reference) to 50 to 200 g/tsa (Samples A, B, C and D).

The results of the laboratory tests are described in Table 1.

TABLE 1:

As the above results show, there was an improvement in the tear and tensile strength of the pulp obtained.

The comparative tests were followed by larger-scale trials, using the reactor with a dry pulp capacity of 100 kg and automatic control of the process variables. The following variables were maintained: temperature of 50°C, pH of 7.0, and reaction time of 120 minutes. The amount of enzyme or enzyme mixture used was 50 g/t.

Once again, it was possible to verify that, compared to the reference, the pulp of the present invention showed improved physical strength without compromising its drainage resistance. The results are described in Table 2.

TABLE 2

Tests were also conducted on an even larger scale, which also demonstrated improved physical strength of the pulp obtained, while maintaining the degree of drainage resistance. The enzyme or enzyme mixture used was 30 g/tsa and 50 g/tsa.

The results are shown in Table 3 below.

TABLE 3

The data are represented graphically in Figures 4, 5, and 6.

Therefore, the reproducibility of the physical strength characteristics of the pulp of the present invention has been observed from the laboratory scale to larger scales.

Example 4: Paper manufacturing process using the pulp of this invention

The pulp capacity of the present invention was evaluated on a pilot tissue paper machine.

The suspension preparation was carried out in batches, with 4.2 tons of pulp being prepared. After preparation, the suspension was sent for testing on a commercially available tissue paper machine, as shown in Figure 8.

As a result, it was observed that the physical strength results for the paper replicated the increases in physical strength observed for the pulp of the present invention. Specifically, the tensile index increased by more than 50%, as shown in Figure 7.

These improved properties—tear index and tensile index—were transferred to the resulting paper, particularly tissue paper and writing and printing paper. Furthermore, the papermaking process from the pulp thus obtained offers increased productivity and resource savings, as it ensures more efficient drainage/drying, while maintaining the degree of drainage resistance.

Claims (11)

1. Procedure for manufacturing a cellulose pulp from cellulose raw material, characterized by comprising the steps of: a) treating the cellulosic raw material by a chemical or semi-chemical pulping process to produce a brown pulp (BP); b) bleaching the brown cellulose pulp by a bleaching sequence to obtain a white suspension pulp; c) adding a carbohydrate-based polymer (B) to the white suspension pulp, wherein the carbohydrate-based polymer (B) belongs to the group consisting of starch, carboxymethylcellulose and guar gum, and wherein the dosage of said polymer ranges from 2 to 12 kg/tonne of cellulose pulp; d) adding an enzyme or enzyme mixture to the white suspension pulp with the carbohydrate-based polymer (B), wherein the addition of the enzyme (E) or enzyme mixture is carried out according to the following conditions: 1. reaction temperature between 40 and 90 °C; ii. Reaction pH between 3.0 and 9.0; iii. reaction time between 10 and 300 minutes; iv. enzyme quantity between 10 g of EZ and 200 g of EZ per ton of cellulose; e) transporting the white slurry pulp with the carbohydrate-based polymer (B) to and through the reaction tower before the drying machine (TMCB); and f) drying (S) the white suspension pulp with the carbohydrate-based polymer (B) to obtain the cellulose pulp (CL). 2. Method according to claim 1, characterized in that the cellulose raw material is a vegetable fiber. 3. Method according to claim 2, characterized in that the plant fiber is a short fiber, more preferably, eucalyptus fiber. 4. Method according to claims 1 to 3, characterized in that the pulp manufacturing process is a Kraft process. 5. Method according to claims 1 to 4, characterized in that the bleaching comprises the use of an ECF or TCF bleaching sequence. 6. Method according to claims 1 to 5, characterized in that the addition of the enzyme (E) or enzyme mixture is carried out according to the following conditions: i. reaction temperature between 50 and 80 °C; ii. Reaction pH between 3.5 and 8.0; iii. reaction time between 30 and 120 minutes; iv. enzyme quantity between 20 g of EZ and 100 g of EZ per ton of cellulose. 7. Procedure for manufacturing a cellulose pulp from cellulose raw material characterized by comprising the steps of and in that order: a) treating the cellulosic raw material by a chemical or semi-chemical pulping process to produce a brown pulp (BP); b) bleaching the brown cellulose pulp by a bleaching sequence to obtain a white suspension pulp; c) adding an enzyme or enzyme mixture to the white suspension pulp, the addition of the enzyme (E) or enzyme mixture is carried out according to the following conditions: i. reaction temperature between 40 and 90 °C; ii. Reaction pH between 3.0 and 9.0; iii. reaction time between 10 and 300 minutes; iv. enzyme quantity between 10 g of EZ and 200 g of EZ per ton of cellulose; d) adding the carbohydrate-based polymer (B), wherein the dose of said polymer ranges from 2 to 12 kg/tonne of cellulose pulp, the carbohydrate-based polymer (B) being selected from the group consisting of starch, carboxymethylcellulose and guar gum; e) transporting the white slurry pulp with the carbohydrate-based polymer (B) to and through the reaction tower before the drying machine (TMCB); and f) drying (S) the white suspension pulp with the carbohydrate-based polymer (B) to obtain the cellulose pulp (CL). 8. Method according to claim 7, characterized in that the plant fiber is a short fiber, more preferably a eucalyptus fiber. 9. Method according to claims 7 to 8, characterized in that the pulp manufacturing process is a Kraft process. 10. Method according to claims 7 to 9, characterized in that the addition of the enzyme (E) or the enzyme mixture is carried out according to the following conditions: i. reaction temperature between 50 and 80 °C; 11. Reaction pH between 3.5 and 8.0; iii. reaction time between 30 and 120 minutes; iv. enzyme quantity between 20 g of EZ and 100 g of EZ per ton of cellulose.