BRPI0619442A2 - paper and cardboard production method - Google Patents

Abstract

PAPER AND PAPERBOARD PRODUCTION METHOD. The invention relates to a method of producing paper or cardboard using a bleached cellulosic pulp containing hemi-celluloses. According to the invention, a significant part, at least 5% by weight, preferably about 8 to 30% by weight, of the hemi-celluloses is removed from the paste. The hemi-celluloses removed from a bleached pulp can then be transferred to another resulting in two pulps with variable properties, one with properties related to low hemi-cellulose content in the fiber wall and the other with properties related to high content of hemi-celluloses on the fiber surface.

Description

PAPER AND PAPER PRODUCTION METHOD

The present invention relates to a method according to the preamble of claim 1 for the production of paper and cardboard.

According to this paper or cardboard manufacturing method, a bleached cellulosic pulp is used which comprises hemicellulose in a paper or cardboard machine.

Low strength in paper meshes causes runnability problems in obtaining paper. The degree of bonding of the fiber network controls the mechanical properties of the paper. The net is not cohesive if there are few links between the fibers. Thus, the degree of bonding of the fiber web should be increased in order to improve the strength and machinability properties of the paper.

Paste xylan plays an important role in both fiber morphology and paper physical characteristics [1].

Fiber bonding in papermaking is conventionally considered primarily to be due to hydrogen bonding. Carboxylic groups are often components of hydrogen bonds. High levels of carboxylic acid groups on fiber surfaces increase the strength of inter-fiber bonds. The concentration of acid groups on the fiber surface has a greater effect on dry leaf bonding and tensile strength than the total concentration of acid groups. Uronic acid groups in hemicelluloses, for example in hardwood xylan, are the major constituents of the carboxylic group in wood. Higher xylan content in birch wood compared to, for example, eucalyptus, makes a controlled manipulation of xylan content in the fiber wall or fiber surface of the pulp favorable to the properties of birch pulp adapted for different gradations. of paper and cardboard.

During cooking some reading of the dissolved hemicellulose in the pulp fibers occurs. Adsorbed xylan is believed to contribute to the mechanical strength of the paper by increasing inter-fiber bonding [2]. Xylan also plays an important role in determining the chemical interactions between fibers, water, and a variety of chemicals used in the papermaking process.

The effects of xylan on pulp strength properties are believed to depend on the degree of xylan polymerization, the amount of xylan, its chemical structure and its distribution on the fiber wall [2]. Xylan especially located on the outer surface of the fibers is generally considered to have an important effect on fiber-fiber bonding and thus on the strength properties of the pulp.

The phenomena and effects of xylan readsorption on pulp fibers have been reviewed and discussed in some studies. These include, for example, the behavior of xylan during Kraft pulping, the mechanism and effect of conditions on xylan readsorption, the distribution of desorbed xylan and the influence of adsorbed xylan on pulp properties.

Based on the foregoing, it is an object of the present invention to provide a novel method of producing cellulose and lignocellulosic pulp.

The present invention is based on the concept of reducing the hemi-cellulose content of bleached cellulose pulp, such as bleached deciduous wood pulp, by the selective removal of an essential part of hemi-cellulose, in particular xylans, contained in bleached pulp to produce a modified pulp.

Hemi cellulose may be extracted from the bleached pulp under alkaline conditions. For the extraction of hemicellulose from birch paste, mainly an alkaline agent such as an alkali metal hydroxide or carbonate, or a hydrolytic enzyme such as xylanase may be used.

We have observed that the properties of the extracted pulp containing less hemi-cellulose are altered such that the filling and optical properties and tear strength are improved, which increases the applicability of the pulp for certain uses.

Extracted xylan can be adsorbed onto the fiber surface of other papermaking pulps, such as pulps derived from deciduous and coniferous tree chemical pastes, chemomechanical pastes and mechanical pastes. For this reason an improved bond between the fibers is achieved and the strength properties of the fibrous mixtures or papers or cardboard manufactured from them are obtained. Extracted hemi-cellulose may also be employed for the production of various chemicals such as furfural and xylitol from xylan.

Even though a large number of studies have been conducted on hemi-cellulose adsorption on fibers and its influence on pulp properties, the provision of hemi-cellulose by bleached pulp extraction and its use for resorption or other uses has been described in the art.

More specifically, the method according to the present invention is mainly characterized by what is defined in the characterizing part of claim 1.

Considerable advantages are obtained by the present invention. In this way, the feasibility of obtaining paper or cardboard is improved by the use of pastes with properties adapted to specific gradations. After obtaining the right fibrous raw material for the gradation of the paper in question and homogeneous baking in the formation of pulp, the properties of Kraft pulp fibers are mainly determined by their chemical compositions. As a rule, changes in bleached pulp compositions (cellulose and hemi-cellulose contents) result mainly from changes in the cooking process and somehow in the bleaching stages.

A more oriented chemical composition of pulp fibers, including fiber surface loading, can be obtained when adjusting hemi-cellulose in pulp fibers is conducted at a well controlled stage after flotation cooking and bleaching stages. Thus, hemi-celluloses can be taken from one bleached pulp and transferred to another resulting in two pulps with variable properties, one pulp with properties related to the low hemi-cellulose content in the fiber wall and the other pulp with related properties. with the high hemicellulose content on the fiber surface (Fig. 1). The location of hemi-celluloses in the fiber wall may be favorably influenced by this hemi-cellulose transfer.

In addition, the hemi-cellulose fraction removed from the bleached pulp may be used, for example, to produce fine chemicals such as pentose monomers or dimers, or the hemi-cellulose obtainable from pulp extraction. Bleached cellulose can be used at the wet end of the paper machine as a chemical in a similar way to starch.

In the following the invention will be discussed in more detail with reference to the accompanying drawing showing a scheme for the extraction and transfer of hemicellulose in birch pastes according to the invention.

As discussed above, the present invention relates to a method for producing paper or cardboard from bleached cellulose pulp containing hemi-celluloses. Typically, the hemicellulose composition of the bleached pulp depends on the wood species and pulping conditions. The term "hemi-celluloses" generally covers short chain polysaccharides consisting primarily of xylosyl, glucosyl, galactosil, arabinosyl or manosyl residues. Hemi celluloses are partially soluble, in particular in alkaline medium. The predominant hemi-cellulosic component in deciduous wood species is xylan or xyloglucan, which typically contain groups of glucuronic acid at position 4 of the anhydroxylose unit. As known in the art, depending on the pulping conditions, the xylan acid side chains of the pulp are not composed exclusively of 4-0-methyl-αD-glucuronic acid or αD-glucuronic acid present in native wood, but an essential part. 4-methylglycuronic acids is converted during the formation of the paste to an unsaturated derivative thereof, ie 4-deoxy-α-L-threo-4-hexenuronic acid, or hexenuronic acid (HexA), which can also be found in the paste. bleached as explained in EP 0 764 226, the content of which is incorporated herein by reference.

Other hemicelluloses present in bleached cellulose pastes include glycomanan and arabinogalactan, the latter being typically present in coniferous wood materials.

The present invention relates particularly to the treatment of bleached pulp comprising a pulp prepared by alkaline pulping of a predominantly deciduous tree feedstock, such as a bleached pulp prepared by Kraft pulping or a similar wood pulping process. of the species Birch. As known in the art, in Kraft pulping the wood raw material is cooked in an aqueous solution of sodium hydroxide and sodium sulfide, known as white liquor, to selectively dissolve lignin. Kraft pulping yield is typically 45%. Bleaching may be conducted with oxygen containing bleaching chemicals, such as ozone and peroxides, with chlorine containing chemicals such as chlorine dioxide or chlorine gas, or combinations of these bleaching chemicals. However, the present invention is not limited to the use of Kraft pulping in combination with conventional bleaching methods, but extends to any bleaching cooking combinations that produce a bleached pulp containing a significant portion of hemicelluloses.

In bleached pulp the hemi-cellulose content is up to about 25 wt.% Kiln dried material, a typical concentration in the deciduous wood bleached pulp being about 15 to 22 wt.%. According to the present invention a significant part of the hemicelluloses are removed by extraction before the pulp is used in the manufacture of paper or cardboard. By "significant part" is meant in this context a removal of preferably at least 5 wt% and less than 50 wt%, in particular about 7 to 30 wt% of the hemicelluloses present in the pulp. Typically, about 8 to 20% by weight is removed for the purpose of the present invention.

Extraction is typically conducted using an aqueous solution or dispersion of an alkaline substance or an enzyme or a mixture thereof. It is preferred to drive the extraction to a consistency of about 0.1 to 25%, preferably about 0.5 to 20%, in particular about 1 to 15%.

For extraction, an aqueous solution containing an alkaline substance, such as a substance selected from the group consisting of alkali metal or alkaline earth metal hydroxides or carbonates or mixtures thereof, may be employed. In addition to the pure chemical solutions or dispersions, various liquors or pulping solutions (e.g. bleaching or washing solutions) of the alkaline bleaching steps may also be employed. Of pulping liquors, white liquor or green liquor may be particularly mentioned.

Typically, the aqueous solution contains from 0.01 to 5M alkaline substance, a preferred concentration range being about 0.5 to 3M for alkali metal hydroxides such as sodium hydroxide.

Extraction with an aqueous solution or dispersion of an alkaline substance or a mixture of alkaline substances according to one embodiment is conducted at ambient temperature and pressure for from 1 minute to 24 hours, preferably from about 5 minutes to 12 hours, in particular about 10 minutes to 6 hours. According to another embodiment, extraction is conducted at an elevated temperature of 20 to 150 ° C for from 1 minute to 24 hours, preferably from about 5 minutes to 4 hours.

Additionally, or in place of an alkaline substance, the aqueous extraction solution may contain at least one hydrolytic enzyme capable of releasing hemicelluloses from pastes.

Examples of such enzymes are hydrolases selected from the group of hemicellulases and pectinases. One group of enzymes of particular interest comprises xylanases.

In accordance with the present invention, hemicelluloses are selectively removed from the pulp essentially without degrading. In practice, it has been observed that the extraction liquor contains only a small portion of mono- or disaccharides derived from hemicelluloses.

Although the extracted pulps exhibit interesting and valuable properties, and can be used as such to obtain specific paper and cardboard products as discussed below, the invention also provides for the use of the removed hemicelluloses. Extraction products are thus recovered and further processed. Typically, hemicelluloses are recovered as an aqueous dispersion or solution.

According to a first embodiment, hemicelluloses are contacted with cellulosic or lignocellulosic fibers under conditions that lead to their adsorption on the fibers. The fibers in which hemicelluloses are adsorbed include chemical, chemomechanical or mechanical pulp fibers used for the production of paper and cardboard products. In this embodiment, hemicelluloses taken from a first bleached pulp can thus be transferred to a second optionally also bleached pulp, resulting in two pulps with variable properties, a pulp with low hemicellulosic wall properties. fiber and the other having properties relating to high hemicelluloses content on the fiber surface. According to a particularly advantageous alternative, the same pulp can thus be used for the preparation of two qualitatively different types of paper or cardboard.

Hemi-cellulose transfer realization may be conducted by recovering the hemi-celluloses as an aqueous dispersion which is then fed as such, or optionally after concentration or dilution to a desired consistency, to a machine inbox. paper or cardboard where it is placed in contact with the fibers in the equipment. Hemi celluloses may be adsorbed on the fibers to a consistency of about 0.05 to 20%, preferably about 0.1 to 20%, in particular about 0.5 to 10%.

The adsorption of hemicelluloses on the fibers is conducted under alkaline conditions, preferably mild alkaline conditions, the pH being about 7 to 13, in particular about 7.5 to 10. It is also possible to operate under essentially neutral conditions. However, it was observed that the amount adsorbed increases slightly at increased pH.

The concentration of hemicelluloses in the aqueous dispersion or solution used for the adsorption of hemicelluloses in the fibers is preferably from about 0.1 to 50 g / l, such as from about 0.5 to 30 g / l, by weight. particularly about 1 to 20 g / l, more particularly about 1.5 to 15 g / l.

When birch pulp (or pulp of another wood species of the Birch species or another species rich in xyloglucans) is being extracted, the recovered hemi-celluloses comprise mainly xylan. Hemicelluloses in general, particularly xylan, have interesting properties when adsorbed to pulp fibers. In particular, it has been found that they may be adsorbed onto cellulosic or lignocellulosic fibers used for paper or cardboard in order to improve mechanical strength properties, including tensile strength, bonding and elasticity. These properties will be examined in more detail in connection with the examples.

The method according to the present invention generally leads to a reduction in the total yield of bleached pulp by up to 15%, preferably up to 10%, preferably about 1 to 8% by weight. Following extraction of the hemi-celluloses, the pulp can be used as a raw material for the production of various paper and cardboard products, in particular uncoated and coated paper or cardboard products having a weight of 25 to 500 g / m2 (for papers typically from about 40 to 180 g / m2, and for cartons typically from about 180 to 450 g / m2) exhibiting one or more improved whiteness properties, yellowing resistance, drainability and water retention. These properties will also be discussed in more detail below. Papers can be used, for example, as printing papers and cardboard materials, for example, as lining in FBB products. A particularly interesting application of the invention is for the production of thin papers from extracted pulp.

Extracted hemi-celluloses represent an extremely pure raw material - pure in relation to polysaccharide composition and lack of extractives, etc. - and may be used as raw material for the manufacture of chemicals. Examples of such fine chemicals include, in the case of xylan, xylitol and furfural. Xylitol is a sweetening agent with interesting properties and very diverse applications. Xylitol can be prepared from xylose in a batch process with three phase hydrogenation. It is also possible to produce xylitol from xylose by fermentation. Furfural may be prepared commercially by dehydrating pentoses such as xylose. It is the pyromucic acid aldehyde and has similar properties to benzaldehyde. The main application of furfural being as raw material for furfuryl alcohol which is again employed in the production of thermostable furan resin and furan cement.

In summary of the above:

The results show that the higher xylan content in birch wood compared to, for example, eucalyptus makes it more favorable for controlled manipulation of the xylan content in the fiber wall or fiber surface to increase the exploitation of the birch wood. Birch paste in the production of paper and cardboard. By altering the content and location of hemi-celluloses in the fibers by removing a fraction of the hemi-cellulose (xylan) from a bleached birch kraft pulp and transferring it to another, significant changes in the chemical and physical properties of the fibers are obtained. . As a result, the technical properties of the pulp and paperboard may be changed and the applicability of a bleached birch kraft pulp may be increased relative to a plurality of paper and cardboard gradations.

The usefulness of the invention manifests itself in many ways:

Alkaline extraction of a birch Kraft pulp mainly removes xylan from the pulp and increases the pulp content and pulp viscosity. The amounts of extractives are also significantly reduced which almost completely prevents yellowing. The fibers become lighter and the width and thickness of the fiber are reduced, indicating increased formation capacity and reduced fiber flocculation tendency in papermaking.

Xylan sorption on Kraft pulp fibers has an opposite but not significant effect on fiber properties such as high amount of xylan in polysulfite pulp fibers.

A reduced xylan content improves the properties of the starter paste such as drainage, filling and light mirroring. Although some properties, such as

resistance, bonding, elasticity and dimensional stability are also negatively affected to some extent by subjecting the pulp to more beating, for example to achieve a predetermined level of tensile strength, many of these changes in the properties of the pulp. paste can be offset.

Sorption of xylan in birch kraft fibers alters many of the pulp properties along the same lines as the increased amount of xylan in polysulphite fibers, but to a lesser extent. Some properties of the starting paste such as strength, bonding and elasticity are improved. By xylan sorption, significant improvement in Scott bonding can be obtained which can be increased by up to 50% at a certain level of tensile strength as compared to the original Kraft pulp or polysulfite pulp. The substantially increased surface charge by xylan sorption probably contributes to this high binding, but this is only one possibility.

According to the results obtained in connection with the present invention, the properties of bleached birch kraft pulp can be manipulated in a controlled manner by transferring xylan from one pulp to another. Exploration of these changes in a pure bleached birch pulp, for example, better bonding, will be further studied in pulp mixtures with respect to certain gradations of paper and cardboard.

The present results are in line with previous observations that after uniform baking and mild post-treatment, the properties of birch kraft pulp produced from a constant source of raw material are mainly affected by pulp yield, ie by hemi cellulose (xylan) content.

The following non-limiting examples illustrate the invention.

Folder Preparation

Cooking

Wood chips for birch paste from southeastern Finland (code Koivu-12) were used in baking experiments. The large and thin fractions were removed in a sieve with 16x32 mm and 6x6 mm openings. New samples from the accepted fraction were weighed 4.5 kg (as o.d.) for cooking and stored frozen in a refrigerator. Prior to cooking the samples were thawed at room temperature for a few days. Baking experiments were conducted in 15 liter KCL rotary autoclaves under the following conditions: Table 1

<table> table see original document page 16 </column> </row> <table>

A polysulfite liquor was prepared in KCL by oxidizing a white liquor obtained in the laboratory with the Moxy method. Analysis of liquors before and after oxidation was as follows: Table 2

<table> table see original document page 17 </column> </row> <table>

After cooking, the paste was washed with overnight deionized water, disintegrated and sieved in a flat sieve with 1.0 and 0.3 mm slots. Paste yield, sieving, kappa number, brightness and viscosity of the paste and residual alkali in the black liquor were determined. Birch cooking results are provided in Table 3.

Bleaching Experiments

Birch pastes were bleached with the OD (EO) DnD sequence to a target whiteness of + 90%.

Oxygen delignification (stage 0) was conducted in a 40 liter DELFI KLC reactor equipped with indirect oil bath heating and inverter controlled mixer. The process conditions were as follows: Table 4

<table> table see original document page 18 </column> </row> <table>

Magnesium sulfate was added to the slurry as an inhibitor in a plastic bag before heating the slurry to the reaction temperature in a microwave oven. The heated slurry was placed in the reactor, the alkali with more water was added and the slurry slurry was mixed for 30 seconds at a rate of 300 rpm. The reactor was pressurized with oxygen and the slurry was mixed for 30 seconds at a rate of 600 rpm. Throughout the reaction time the slurry was mixed after every 15 minutes for 18 seconds at a rate of 300 rpm at the balanced reaction temperature.

After the reaction, the pressure was released and dilution water was added to the slurry directly after sampling and pH determination. The 5% consistency slurry was immediately poured into a suction filter (Büchner type). After removing the water, the paste was washed twice with ten times volumes of water. Washing is completed when water no longer comes out of the cake. Finally the paste was centrifuged to a 22-25% dry matter content.

The leaf was prepared for determination of kappa number, whiteness and viscosity (Table 3). Paste yield and residual alkali in the stage 0 liquor were also determined.

ECF bleaching

After oxygen delignification, the birch pastes were bleached by the sequence D (EO) DnD using a conventional laboratory technique. Stage (EO) was conducted in a DELFI reactor in the same way as stage 0. Stage DO, D1, and D2 were performed in 18 liter KCL air bath reactors. The rotation (40 rpm) of the reaction vessel was concerned with mixing the slurry with the chemicals during the bleaching stage. After the bleaching stages the final pH and residual chemicals were determined. The paste was diluted to 5% consistency and washed in a standard manner. The paste sample was taken and acidified with SO 2 -water to a 2% consistency and a pH 4.5 sheet was prepared. Deionized water was used throughout the bleaching sequence. In stage Dlw, neutralization followed stage Dl without intermediate washing.

Table 5. Bleaching conditions

<table> table see original document page 19 </column> </row> <table> The bleaching results are shown in Table 3 above.

Extraction and precipitation experiments

The alkaline extraction of bleached birch pulp to remove hemi-celluloses (xylan) was performed by treating the pulp in a mixed plastic bottle under a nitrogen atmosphere using the following conditions:

Table 6

<table> table see original document page 20 </column> </row> <table> The extracted paste was washed with 2x1 liter H2O + 1 liter acetic acid + 2x1 liter H2O before yield determination, analysis and testing. .

In order to isolate xylan for precipitation experiments, a bleached birch sulphate pulp was extracted with alkali under the above conditions, but with a pulp charge of 300 g and alkalinity of 1.0 mol / 1. The pulp yield after extraction was 84.7%. The combined washings were acidified to pH 4-5 with concentrated acetic acid. The precipitate was separated by centrifugation. The amount of precipitate recovered was 295 g containing 15.0% dry matter with 70.7% xylose. The xylan precipitation experiments on a birch sulphate slurry were performed in a KCL Quantum Mark reactor under the following conditions:

Table 7

<table> table see original document page 21 </column> </row> <table>

The xylan precipitate was first dissolved in 200 ml 1 N NaOH (0.01 N NaOH in the last two experiments 1482 S6 and 1482 S7), and then mixed with slurry containing 1 mol / 1 NaAc. The alkalinity in the mixture was 0.1 and 0.001 mol NaOH / 1, respectively.

The mixture was poured into a reactor, where air was removed by nitrogen gas before heating for 30 minutes to temperature. In the first two experiments (1482S and 1482S2) the temperature was 120 ° C, in the last experiments it was 80 ° C. In the first two experiments, after treatment the slurry was first filtered, then washed with 2x1 liter H2O + 1 liter acetic acid + 2x1 liter H2O before yield determination, etc. In the latest experiments, the pH in the sludge after treatment was adjusted, if necessary, to about 7 with acetic acid prior to filtration and washing. In the last experiment (1482 S7) no acetic acid was used after treatment or washing. The following analysis was performed for pastes before and after treatments:

Table 8

<table> table see original document page 22 </column> </row> <table>

The results of the extraction and precipitation experiments are compiled in Tables 9 and 10. Table 9. Results of alkaline extractions of bleached birch DEDD kraft pulp

<table> table see original document page 23 </column> </row> <table> Table 10. Results of xylan precipitation from DEDD bleached birch kraft pulp.

<table> table see original document page 24 </column> </row> <table>

Beating and beating test

The bleached pastes were beaten in PFI. The original birch sulfate and polysulfite pastes were beaten at 0, 250, 500 and 1000 revolutions, all other pastes at 0 and 50 revolutions only. Beaten and non-beaten pastes were analyzed for: Table 11

<table> table see original document page 25 </column> </row> <table> The results are as follows:

Table 12. Fiber properties and technical paper of extracted birch kraft pulps with hemi-cellulose sorption.

<table> table see original document page 26 </column> </row> <table>

As can be seen from the above tables, by increasing the NaOH concentration to 1 mol / 1 about 15% of the bleached birch kraft pulp and more than 20% of the bleached birch polysulfite pulp were removed during alkaline extraction at room temperature. . The removal was mainly related to xylan, practically no cellulose was dissolved. The fact that cellulose remained intact was reflected in the increased viscosity values after alkaline extraction of the pulps, especially the polysulfite pulp. The acetone extracts were halved by alkaline extraction of the pastes.

Due to the dissolution of xylan with its uronic acid groups, the carboxylic group content of the Kraft pulp was reduced by almost 40%, while the surface charge from the carboxyl groups was reduced only minimally. Similarly, the dissolved xylan came from the fiber wall. Yellowing of the pastes was almost completely prevented by alkaline extraction of the pastes.

The merely alkaline conditions in the xylan precipitation experiments on birch kraft pulp fibers induced some effects from alkaline extraction on pulp properties. However, by increasing xylan concentration in precipitation up to 10 g / l, a 5% increase in pulp yield was obtained. Lowering the alkalinity of precipitation increased the yield.

On precipitation the content of carboxyl groups in the Kraft pulp increased by 15%, however the load by almost 70%. After xylan sorption the kraft had a charge about 40% higher than the xylan rich polysulfite pulp, although its carboxyl group content was 20% lower than that of the last pulp reflecting a xylan sorption on the fiber surface. .

In Kraft pulp the alkaline extraction resulted in a decrease in the fiber length value and increased fiber twisting, however in the beat the fibers were stretched as frequently observed in the PFI beat. Polysulfite pulp fibers were less twisted and slightly longer than Kraft pulp fibers. Although alkalinity induced its effects on fiber length and twisting in xylan precipitation, xylan sorption on the fibers somewhat increased the former and reduced the latter.

Increased alkalinity in extraction first resulted in a slight increase in cell wall thickness as well as fiber width, reflecting the alkaline swelling of the fibers. Subsequent dissolution of the materials caused the reduction of the dimensions of these fibers. Polysulfite pulp fibers

presented higher values for fiber width and cell wall thickness than Kraft pulp fibers; however the effect of xylan sorption was negligible.

Due to the weight reduction of fibers in alkaline extraction, their forming behavior in papermaking can be estimated as becoming better. Respectively, heavier fibers in xylan and polysulfite sorption pastes should have negative effects on formation. Similar estimates were made for the tendency for fiber flocculation in the paper machine inbox: reduced xylan removal and increased xylan content increased this trend.

Single fiber strength (such as zero-span tensile strength) was reduced when xylan was extracted from birch paste. Increasing the xylan content in baking increased the strength of the unheated pulp fiber, however the beating leveled the differences. The effect of xylan sorption remained negligible.

The pulp stress index after a constant beating, defining the beating capacity, was reduced with the removal of xylan as expected. Hemi-cellulose rich polysulfite pulp clearly produced a higher stress index than Kraft pulp. Although the stress index was reduced by alkalinity in xylan precipitation, increased xylan concentration increased it.

Removal of xylan by alkaline extraction improved pulp drainage and notably with polysulfite pulp than with Kraft pulp. In precipitation of xylan in birch paste, the effect of alkalinity was evident: the drainability was increased despite xylan sorption. Only in the case of reduced alkalinity to

drainability has been reduced. Water retention values behaved similarly to drainability.

A high concentration of NaOH in the alkaline extraction produced a noticeable increase in the unfilled Kraft pulp filling. Alkaline extraction increased beating demand and respectively increased density, ie reduced pulp filling to a certain stress index. On the other hand, xylan-rich polysulphite pulp, but not xylan sorption kratf pulp, had a higher fill than Kraft pulp at the same stress index.

Alkaline pulp extraction reduced fiber bonding, however at a constant level of stress index, due to increased beating demand, had a slightly improved effect on Scott bonding. The most beneficial was alkaline extraction after beating. The "easy-to-hit" polysulfite pulp further exhibited a somewhat lower Scott bond than the original Kraft pulp at a constant level of stress index. On the other hand, xylan precipitation increased Scott binding in birch kraft pulp by up to 50%. There is a clear difference in fiber bonding when xylan is situated primarily on the fiber wall such as polysulphite pulp fibers or on the surface of the fibers such as after xylan precipitation.

The modulus of elasticity, after a constant slapping of the slurry, was reduced by the alkaline slurry extraction, but increased by 10% by xylan sorption, or more by 30% by polysulfitic cooking.

Compared to certain air permeability, alkaline extraction induced reduced values for birch kraft pulp, but not for polysulphite pulp. The effect of xylan sorption practically disappeared at constant air permeability.

Xylan sorption slightly increased dimensional stability based on pulp shrinkage, while the effect of alkaline extraction was negative. At a constant stress index, polysulfite pulp presented dimensional stability 20-25% higher than Kraft pulp. By precipitation of xylan, the dimensional stability of birch kraft pulp can be improved at the level of polysulphite pulp.

The light scattering coefficient of the leaf with a constant beat was increased by alkaline extraction and reduced by xylan sorption or polysulfite cooking. The different beating behaviors of the pastes led, however, to the fact that, at a constant level of stress index, the light scattering coefficients of the kraft, polysulfite and xylan sorption pastes were equal. Alkaline extraction of the paste resulted in reduced light scattering in this comparison.

REFERENCES

1. Genco, J.M., Busayasakul, N., Medhora, H.K., Robbinds, W. "Hemicellulose retention during kraft pulping". Tappi J. 73 (1990): 4, 223-233.

2. Simonson, R. "The hemicellulose in the sulfate pulping process". Svensk Papperstidn. 74 (1971): 21,691-700.

3. Lai, Y.-Z. Chemical degradation. In: Hon, D.N.-S., Shiraishi, N. (Eds.) "Wood and Cellulose Chemistry", Mareei Decker, Inc., New York, 1991, p. 455523.

Claims (27)

Method for the production of paper or paperboard using a bleached cellulosic pulp containing hemicelluloses, characterized in that a significant part of the hemicellulose is removed before the pulp is used in the manufacture of paper or cardboard, and where the hemi - recovered celluloses are brought into contact with the chemical, chemomechanical or mechanical pulps used for the production of paper and paperboard products under conditions leading to their adsorption on cellulosic or lignocellulosic fibers; or recovered hemicelluloses are used as raw materials for the manufacture of chemicals. Method according to claim 1, characterized in that at least 5 wt.%, Preferably less than 50 wt.%, In particular about 8 to 30 wt.% Of the hemicelluloses are removed from the pulp. Method according to Claim 1 or 2, characterized in that the bleached cellulosic pulp comprises a pulp prepared by alkaline pulping of a predominantly deciduous tree feedstock. Method according to any one of claims 1 to 3, characterized in that the bleached cellulose pulp comprises a pulp prepared by birch wood Kraft pulping. Method according to any one of claims 1 to 4, characterized in that the hemicelluloses are removed by extraction using an aqueous solution or dispersion of an alkaline substance or an enzyme or mixture thereof. Method according to claim 5, characterized in that the extraction is conducted at a consistency of from about 0.1 to 25%, preferably from about 0.5 to 20%, in particular from about 1 to 15%. %. Method according to claim 4 or 5, characterized in that it comprises the use of an aqueous solution containing an alkaline substance selected from the group of alkali and alkaline earth metal hydroxides and carbonates or mixtures thereof. Method according to any one of claims 5 to 7, characterized in that the aqueous solution of an alkaline substance comprises white liquor or green liquor. Method according to any one of claims 5 to 8, characterized in that the aqueous solution contains from 0.01 to 5M of the alkaline substance. Method according to any one of claims 5 to 9, characterized in that extraction with an aqueous solution or dispersion of an alkaline substance or mixture of alkaline substances is conducted at ambient temperature and pressure for from 1 minute to 24 hours, preferably for about 5 minutes to 12 hours, in particular for about 10 minutes to 6 hours. Method according to any one of claims 5 to 9, characterized in that the extraction with an aqueous solution or dispersion of an alkaline substance or a mixture of alkaline substances is conducted at an elevated temperature of 20-150 ° C for up to 1 ° C. minute to 24 hours, preferably for about 5 minutes to 4 hours. Method according to any one of claims 5 to 11, characterized in that the aqueous solution contains at least one hydrolytic enzyme selected from the group of hemicellulases and pectinases. Method according to claim 12, characterized in that the hydrolytic enzyme comprises a xylanase. Method according to any one of the preceding claims, characterized in that the hemicelluloses are selectively removed from the pulp essentially without degradation thereof. Method according to any one of the preceding claims, characterized in that the hemicelluloses are recovered as an aqueous dispersion or solution. Method according to claim 1, characterized in that the hemi-celluloses are recovered as an aqueous dispersion which is fed to the inbox of a paper or cardboard machine where the hemi-celluloses are contacted with the fibers in the equipment. Method according to claim 1 or 16, characterized in that the hemi-celluloses are adsorbed on the fibers to a consistency of from about 0.05 to 20%, preferably from about 0.1 to 20%, in particular. from about 0.5 to 10%. Method according to claim 16 or 17, characterized in that the adsorption of hemicelluloses on the fibers is conducted under alkaline conditions, preferably at a pH of about 7 to 13, in particular at a pH of 7.5 to 10 The method according to any one of claims 1, 16 and 17, characterized in that the concentration of hemicelluloses in the dispersion or aqueous solution used for the adsorption of hemicelluloses in the fibers is from about 0.1 to 50 g. / l, preferably from about 0.5 to 30 g / l, in particular from about 1 to 20 g / l, more particularly from about 1.5 to 15 g / l. Method according to any one of claims 1 to 17, characterized in that the recovered hemicelluloses comprise mainly xylan. Method according to any one of claims 1 and 16-20, characterized in that the hemicelluloses, in particular xylan, are adsorbed on cellulosic or lignocellulosic fibers used for paper or cardboard in order to increase the mechanical strength properties. including tensile strength, bonding and elasticity. Method according to claim 21, characterized in that the hemicelluloses taken from one bleached pulp are transferred to another similar or identical pulp resulting in two pulps with variable properties, one pulp with low hemolytic properties. celluloses in the fiber wall and the other having properties relating to high content of hemicelluloses in the fiber surface. Method according to any one of claims 1 to 22, characterized in that the total yield of bleached pulp is reduced by a maximum of 15%, preferably by a maximum of 10%, preferably about 1 to 8% by weight. weight by removing hemi-celluloses. Method according to any one of claims 1 to 23, characterized in that the bleached pulp is, subsequent to the hemicellulose removal step, used as a raw material for the production of various paper and cardboard products. Method according to claim 24, characterized in that the bleached pulp is used for the production of a paper or cardboard product exhibiting one or more improved properties between whiteness, yellowing resistance, drainability and water retention. Method according to claim 24 or 25, characterized in that the bleached pulp is used for the production of thin papers. Method according to claim 1, characterized in that the xylan removed from the bleached birch paste is used as raw material for the production of xylitol or furfural.