Method for producing pulp

Abstract

A process for the production of pulp, characterized in that straw containing lignin, xylan and cellulose and suspended in an aqueous phase is subjected to a treatment to reduce the lignin content and a treatment with a xylanase to reduce the xylan content.

Description

[0001] The invention relates to a process for the production of pulp. Background of the invention

[0002] Biorefineries fulfill the task of sustainably producing materials, chemicals, and bioenergy from biomass, utilizing as many raw material components as possible. The pulp and paper industry is an example of an existing biorefinery. Traditional refining processes, based on wood, the most abundant raw material, are primarily geared towards pulp production. They require harsh reaction conditions that allow only limited utilization of byproducts, which are mainly used for energy recovery (Singh et al., 2022; Chandel et al., 2018; Steffen et al., 2024).

[0003] Newer lignocellulose biorefinery concepts aim to obtain the lignocellulosic components, such as lignin, glucose (the main component of cellulose), and xylose (the main component of xylane, a type of hemicellulose), with minimal energy expenditure in the purest possible form, in order to produce valuable chemicals. The raw material used is primarily lignocellulose from annual plants, rather than wood. The main advantage is that the lignin in lignocellulose is less condensed than in wood, allowing the extraction of lignin, which is always required in the first step, to be carried out under significantly milder conditions than in conventional pulp production (Singh et al., 2022; Chandel et al., 2018; Steffen et al., 2024).

[0004] Changes in the pulp market, driven by increased demand for "green" packaging materials and the generally sharp rise in demand for packaging paper, have led to a shortage of recycled paper, negatively impacting quality and price. This is prompting the pulp industry to search for new sources of virgin fiber. Pulp made from cereal straw, which is cheaper and more readily available, represents an alternative to fibers from recycled materials and wood pulp. In some Asian markets, where wood is less readily available, bagasse and rice straw already account for 70% of the raw materials used in the pulp industry (Steffen et al., 2024; Worku et al., 2023).

[0005] Especially in the booming packaging paper sector, it is expected that the use of fibers from straw can compensate for the reduced quality of recycled primary fibers. This, in turn, can also reduce the use of chemical additives (such as dry or wet strength additives).

[0006] Various processes are used to produce pulp from straw, which differ from the classic wood pulping processes (Kraft pulping / sulfate process, sulfite process) primarily in the use of milder conditions.

[0007] Organosolv pulping is considered to have the greatest potential for producing pulp from straw and other lignocellulosic waste from the food industry. This process involves fractionating the lignocellulosic raw material by treatment in an aqueous organic phase, with or without a catalyst (Thoresen et al., 2020).

[0008] The following are examples of organosolv processes that can also be applied to wheat straw.

[0009] In the Alcell process, an aqueous solution of ethanol (approx. 50 wt%) is used for delignification. The cooking process takes place at 190 °C and 28 bar. Since neither acids nor alkalis are added, the pH value stabilizes at 4 due to the deacetylation of the raw material. Lignin, furfural, acetic acid, and hemicellulose sugars (such as xylose) are the main byproducts of the Alcell process with wheat straw (Azadi et al., 2013).

[0010] Other organosolv processes are based on the use of organic acids such as acetic acid (Acetosolv, Acetocell, Formacell, CIMV) or formic acid (Formacell, Milox, Formico, CIMV) as solvents (Tofani et al., 2024).

[0011] The most established process for straw and other non-wood materials is pulping with sodium hydroxide (NaOH) as the active chemical. An organosolv process for the production of wood pulp with ethanol and NaOH at 170 °C was described as early as 1982 in WO 1982 / 001568 A1.

[0012] The high silicate content in, for example, wheat straw leads to problems in the treatment of black liquor and the recovery of NaOH due to the high solubility of silicate in alkaline environments. To avoid this problem, sodium carbonate can be used instead of sodium hydroxide. Pulp produced in this way has higher lignin content and is therefore less suitable for bleached papers, but rather for packaging material or in blends with recycled paper to improve mechanical properties (Steffen et al., 2024).

[0013] The so-called NACO process also uses sodium carbonate, but in addition to delignification, oxygen and a small amount of sodium hydroxide are used for activation. This results in pulps with a low lignin content (low kappa number). This process is carried out in two special reactors (so-called turbo-pulpers) operated in series at a pressure of 6–7 bar and a temperature of 130–145 °C (depending on the raw material) (Fiala et al., 1983).

[0014] The IDE process is also a sulfur-free alkaline pulping method. The process consists of three steps: impregnation, depolymerization, and extraction. In the first step, the raw material is treated with a concentrated sodium carbonate solution. The second step involves boiling in an aqueous ethanol solution for delignification. In the final step, the degraded lignin is extracted with a fresh aqueous ethanol solution. In trials with wheat straw, yields exceeding 50% are achieved, with a residual lignin content below 2% (Hultom et al., 1997).

[0015] The ASAM process (alkali sulfite anthraquinone methanol) or ASAE process (alkali sulfite anthraquinone ethanol) is carried out at pH values ​​above 13 and at 170–180 °C, with anthraquinone acting as a catalyst and sulfite as a delignifying agent (Black, 1991; EP 0538576 A1; Kirçi et al., 1994). Compared to classical sulfate pulps, the ASAE pulps of Brutia pine ( Pinus brutia Ten.) in a study by Kirçi et al. (1994) higher yields, viscosity, brightness and better strength properties.

[0016] EP 2611820 B1 describes a process for separating lignin from lignocellulosic material by digestion with alcohol (ethanol or isopropanol), water, and a base (NaOH or KOH) at a temperature below 100 °C. The mild and selective conditions of the process allow for the decoupling of lignin degradation from the simultaneous hemicellulose degradation that otherwise occurs in conventional boiling processes. Depending on the conditions, up to 93% of the lignin could be separated from the wheat straw, with only a small proportion of xylan being degraded and removed from the straw under these conditions. The resulting low residual lignin content is a prerequisite for the efficient enzymatic production of xylose from xylan and glucose from cellulose, and for the potential production of bioalcohol.

[0017] US Patent 9970038 B2 describes the extraction of carbohydrate breakdown products such as xylose or glucose from wheat straw. First, ground wheat straw was delignified in an alkaline (NaOH) aqueous isopropanol solution or in the presence of hydrogen peroxide in an alkaline aqueous ethanol solution. The pretreated wheat straw was then treated with a commercial enzyme mixture consisting of cellulases and hemicellulases (Accellerase 1000 from Genencor). The xylose present in solution was enzymatically broken down with a xylose reductase. Candida tenuis reduced to xylitol, a sugar substitute. The use of an enzyme mixture that also contains cellulases makes it impossible to obtain pulp using this method.

[0018] US Patents 9187571 B2 and 8617851 B2 propose a method to make cellulose more accessible to enzymatic or chemical modification. Unlike the methods described above, this method starts with cellulose, rather than lignocellulosic material, which is treated with a mixture of NaOH, water, and ethanol. Compared to untreated cellulose, this pretreated cellulose can be more easily depolymerized to glucose using cellulase.

[0019] The optimal solution for a pulp biorefinery would be a process that enables the production of pulp while simultaneously yielding native, sulfur-free lignin and xylan / xylose as a chemical feedstock. The simultaneous production of the three fractions (pulp, lignin, xylan / xylose) is not mentioned in the examples above.

[0020] Lignin is considered the chemical feedstock of the future, partly due to its abundance in nature—it is the second most abundant biogenic raw material after cellulose. Current applications include thermal utilization, its use as a binder and stabilizer in concrete and cement, and as a fertilizer. However, intensive research is underway on the use of lignin as a chemical feedstock, with applications such as adhesives, bioplastics, and as a basis for energy storage in battery cells being developed (Norgren & Edlund, 2014; Gaspar & Fardim, 2023).

[0021] The recovery of pure xylan or pure xylose in industrially applied pulping processes for wood pulp is very limited due to the high temperatures required. For example, larger quantities of xylose from the pre-hydrolysis liquor in the Kraft-based dissolving pulp process can practically only be recovered after complex purification procedures (Chen et al., 2018).

[0022] The lye obtained from the sulfite process contains not only xylose but also arabinose, glucose, galactose, and mannose, as well as degradation products such as acetic acid, furfural, and 5-hydroxymethylfurfural, which act as fermentation inhibitors. To convert the sugars into fermentation using... Enterococcus mundtii To be able to convert to L-lactic acid, the fermentation inhibitors must be separated using a complex process called Simulated Moving Bed Chromatography (Hoheneder et al., 2021).

[0023] Often, the xylan removed and broken down during pulp production is burned as "waste" (Puls & Saake, 2010) and is therefore not available as a chemical raw material.

[0024] The hydrolytic cleavage of xylan from wheat straw has also been described. Walker et al. (2018) used steam explosion (pressure 12 bar(g), residence time 6 min) with phosphoric acid as a catalyst to release 90% of the xylose from wheat straw into the hydrolysate, which was subsequently reduced microbially to xylitol. A disadvantage is the formation of the fermentation inhibitors furfural and 5-hydroxymethylfurfural (HMF) due to the dehydration of the pentoses and hexoses, respectively.

[0025] Agrawal et al. (2015) used a continuous reactor to pretreat wheat straw with dilute sulfuric acid at 160 °C, resulting in the hydrolysis of a large proportion of the hemicellulose. Glucose was released from the pretreated straw using commercially available cellulases, which were fermentatively treated with Saccharomyces cerevisiae was converted to ethanol. The authors showed that lignin, acetic acid, furfural, HMF and vanillin, which are released or formed during pretreatment with dilute acid, have an inhibitory effect on the cellulases used.

[0026] The additional extraction of xylan / xylose in connection with pulp production is ruled out based on the current understanding of its role in the pulp matrix. Xylan is considered a binding agent between the fibers in pulp, promoting paper strength. The prevailing theory states that the hydrogen bonds it mediates have positive effects on the strength and elasticity of cell walls in plants, thus leading to increased resistance to enzymatic degradation (Busse-Wicher et al., 2014).

[0027] The hemicelluloses (e.g., xylans) naturally occurring in pulp improve tensile strength and contribute to the formation of stronger fiber bonds. However, the pulping conditions used for pulp production lead to the removal or modification of these hemicelluloses (Puls & Saake, 2010; Schaubeder et al., 2024).

[0028] Wheat straw xylan, like softwood xylan, is arabinoxylan, with the two pentoses xylose and arabinose making up approximately 30% and 7% of the total dry matter in wheat straw, respectively (Walker et al., 2018).

[0029] In addition to the depolymerization of celluloses and hemicelluloses, chemical changes also occur during cooking and bleaching processes. For example, in the Kraft process, 4-O-methylglucuronic acid is converted to hexenuronic acid through the elimination of methanol, which can then subsequently react with bleaching agents (Henriksson et al., 2024; Schaubeder et al., 2024).

[0030] Malik et al. (2020) pretreated wheat straw using various methods: acidic (0.1 NH₂SO₄, 125 °C for 120 min), alkaline (6 wt% NaOH, 150 °C for 120 min), and hot water (150 °C for 120 min), extracting glucose, xylose, and arabinose. Pretreated and untreated wheat straw were pulped with different concentrations of NaOH (12%, 14%, and 16%) at 166 °C for 180 min. Paper sheets were subsequently produced from the different pulps and analyzed for their strength properties (tear index, tensile index, and burst index). Compared to untreated wheat straw, the tensile and burst index decreased across the board, with the greatest decrease in the acid-treated wheat straw, where almost the entire hemicellulose fraction was removed.In the case of the Tear Index, a slight increase (up to +4.3%) was observed for the pretreated wheat straw (for all three variants) at a NaOH concentration of 16%.

[0031] A study by Sjöberg et al. (2004) shows that the strength properties of paper are positively influenced by the presence of hemicelluloses on the surface of the fibers; therefore, hemicelluloses such as xylanes are used as additives in papermaking to improve mechanical properties.

[0032] Naterova et al. (1986) added maize xylans to wrapping paper, which increased the flexural strength by 172% with an addition of 2% xylan.

[0033] US 5810972 A describes the addition of highly ground xylan-rich birch pulp, xylan or galactomannan to cellulose for paper towels, which increased the tensile strength both in the machine direction (up to 84%) and across the direction of travel (up to 90%).

[0034] A study by Puls & Saake (2010) shows that the effect of arabinoxylan on paper strength depends on the refining grade and the pulp type. The higher the refining grade, the less pronounced the positive effect of arabinoxylan. The effect is greater with sulfite pulps than with sulfate pulps, and greater with softwood pulps than with hardwood pulps. When using unmodified xylans, also in combination with epichlorohydrin resin, a paper additive, the tensile index can be increased by 50–55% and the tear index by 20–25% in products with a low refining grade.

[0035] In EP 1688534 A1, the addition of arabinoxylans to a pulp during papermaking was described. This improved paper properties such as tear length, tensile strength, bulk, and appearance. The study showed that adding an arabinoxylan derived from oat hulls resulted in greater tear lengths compared to adding a 4-O-methylglucuronoxylan from birch wood or a Lenzing xylan from beech wood pulp. The arabinoxylan from oat hulls does not contain the 4-O-methylglucuronic acids found in hardwood and softwood xylans as substituents and is characterized by a longer chain length than the Lenzing xylan.

[0036] The pulps mentioned in the aforementioned patents and publications for increasing strength through the addition of xylan are all bleached wood pulps produced using conventional, harsh cooking processes such as the Kraft process (170 °C). These processes involve intensive degradation and significant chemical modification of the xylan.

[0037] The selective extraction of xylan from straw while simultaneously using the remaining biomass for pulp has never been reported because, according to current scientific opinion, this implies a loss of paper strength.

[0038] Attempts to produce pulp with sufficient strength for industrial applications or with increased strength values ​​through enzymatic extraction of xylan are not known.

[0039] However, xylanase-containing enzyme mixtures have been used to achieve various goals: for the modification of wood pulps to improve dewaterability (Blomstedt et al., 2010), for the extraction of chromophores (US 5498534 A), to improve milling (Noé et al., 2008), or for the purpose of enzyme-assisted bleaching (Viikari et al., 1994).

[0040] Most xylanases known in the literature also act as cellulases, which is undesirable in pulp production. However, there are also xylanases, such as those from Bacillus SSP-34 (Subramaniyan & Prema, 2000) or Thermomyces lanuginosus (Gomes et al., 1993) described which exhibit no or only minimal cellulase activity.

[0041] The improved bleachability is attributed to the degradation of xylans, which precipitates on the fiber surface during the boiling of Kraft pulps and blocks the removal of lignin (Viikari et al., 1993). No effects on fiber strength have been reported.

[0042] Furthermore, Viikari et al. (1993) conclude that high hemicellulose contents are advantageous for papermaking with regard to fiber-fiber bonding properties, and that removing hemicellulose does not improve these properties. Therefore, reducing the xylan content using enzymes is not recommended. a priori excluded, but rather the addition of Xylan to increase strength values ​​is recommended (see above).

[0043] The enzymatic removal of xylan from pulp and its effect on binding strength has only been investigated in a few studies, and these were conducted for purely scientific purposes. The pulps examined were bleached softwood kraft pulps, and the xylanase treatment was performed after milling.

[0044] Schaubeder et al. (2024) investigated the role of intrinsic and extrinsic xylan in a chlorine dioxide bleached (ECF) softwood kraft pulp (85% spruce, 10% pine, and 5% larch). A portion of the pulp was subjected to enzymatic degradation by endo-xylanase from Neocallimastix patriciariumThe pulp was subjected to a process in which approximately 1% of the xylan was degraded, and a second portion was enriched with beechwood xylan, resulting in an approximately 3% increase in xylan content. The tensile index of the resulting paper showed an 8% reduction for the enzyme-treated pulp, while an 8.5% increase was observed for the xylan-enriched pulp. This is consistent with the results of Sjöberg et al. (2004).

[0045] Schönberg et al. (2001) also investigated the role of xylan using spruce wood kraft pulp as an example. Treatment with xylanase degraded 0.9% of the xylan, resulting in a 23% decrease in the internal binding strength (Scottish Bond Value). Adsorption of 1.5% xylan led to a 22% increase in the Scottish Bond Value. Schaubeder et al. (2024) found a 12% decrease in the Scottish Bond Value for the xylanase-treated pulp and a 16% increase for the xylan-enriched pulp.

[0046] The use of straw for the production of pulp is becoming increasingly important; however, certain pulp products require increased strength. The present invention therefore aims to provide a pulp made from straw with increased strength. Detailed description of the invention

[0047] The problem of producing pulp is solved according to the invention by subjecting straw, which contains lignin, xylan and cellulose and is suspended in an aqueous phase, to a treatment to reduce the lignin content and to a treatment with a xylanase to reduce the xylan content.

[0048] Contrary to conventional wisdom, reducing the xylan content surprisingly produces a pulp with increased strength. Previously, those skilled in the art assumed that reducing the xylan content would decrease the strength of the pulp (see, e.g., Schaubeder et al. (2024)).

[0049] In a preferred embodiment of the inventive method, the treatment to reduce the lignin content is carried out using an alkaline aqueous solution containing ethanol.

[0050] The task of producing pulp, lignin and xylan decomposition products from straw, which contains lignin, xylan and cellulose, is characterized by the combination of measures that a) Shredded straw is treated with an aqueous solution containing a C1-C4 alcohol and having a pH between 11 and 14, causing some of the lignin contained in the straw to dissolve and yielding a lignin-containing solution and a first pulp suspended in this solution; b) the first pulp is separated from the lignin-containing solution; c) the lignin is extracted from the lignin-containing solution obtained; d) the separated first pulp is treated with an aqueous solution containing xylanase to selectively reduce the xylan content in the first pulp and dissolve xylan degradation products, yielding a second pulp suspended in the xylan degradation product-containing solution; e) the second pulp is separated from the xylan degradation product-containing solution; and f) the xylan degradation product-containing solution obtained is extracted Xylan fission products can be at least partially recovered.

[0051] The first pulp is a lignin-reduced pulp, which is subsequently referred to as "pulp 1", and the second pulp is a lignin- and xylan-reduced pulp, which is subsequently referred to as "pulp 2".

[0052] For the purposes of the present patent claims and description, pulp shall be understood to mean a fibrous mass produced from plant fibers, which consists predominantly of cellulose.

[0053] For the purposes of the present claims and description, straw shall be understood to mean dried fiber plants or parts thereof, such as wheat, rye, barley, oats, spelt, millet, buckwheat, emmer, einkorn, sorghum, rice, maize or grass-like raw materials such as miscanthus, with wheat straw being particularly preferred.

[0054] Xylan cleavage products, as defined in the present claims and description, include D-xylose, L-arabinose, xylooligosaccharides, substituted xylooligosaccharides (e.g., with arabinofuranosyl residues), uronic acids / uronates such as 4- O -Methyl-D-glucuronic acid / 4- O -Methyl-D-glucuronate and / or acetic acid / acetate to understand.

[0055] For the purposes of the present patent claims and description, strength is understood to mean the so-called Tear Index, which describes the tear strength per unit area (unit mN·m 2< ·g -1< ) ​​(Puls & Saake, 2010).

[0056] The alkaline organosolv process described here, in combination with enzymatic dexylanization, offers the unique possibility of a straw biorefinery that combines all three options for selective product recovery: 1) the recovery of a sulfur-free and, due to the mild cooking conditions, only slightly condensed, native lignin as a chemical feedstock (see EP 2611820 B1), 2) selective enzymatic recovery of xylan / xylose as a chemical feedstock, and 3) the production of a pulp with improved strength properties.

[0057] The xylan-reduced cellulose is further characterized by the fact that it was produced by treatment with a xylanase that consists either only of the backbone-cleaving enzyme. endoThe xylanases consist of 1,4-β-xylanase or additionally contain β-xylosidase and side-chain cleaving (accessory) enzymes such as α-L-arabinofuranosidase or individual mixtures thereof. The xylanases are essentially characterized by the fact that they possess no or minimal cellulase activity, so this has no influence on the strength properties of the pulp (see Table 2).

[0058] A xylanase can be used in the following ways to produce xylan cleavage products, the last of which is particularly preferred: 1. Use of only endo-1,4-β-xylanase for the separation of xylan (e.g., in the form of xylooligosaccharides), 2. Use of only endo-1,4-β-xylanase for the separation of xylan and subsequent enzymatic cleavage of the xylan cleavage products to monomers (xylose and arabinose), and 3. Use of endo-1,4-β-xylanase in combination with other xylanases for the direct production of monomers.

[0059] The xylan-reduced pulp (pulp 2) produced by the action of xylanase is, after xylan extraction, in a suspension / solution consisting of monomers (xylose and arabinose) and can be used as a chemical raw material after separation of the xylan-reduced pulp.

[0060] In contrast to the process described in US 9970038 B2, in which xylose and glucose were released from delignified wheat straw using a commercial cellulase / hemicellulase mixture, the present invention uses a cellulase-free xylanase for selective dexylanization. As a result, the xylan-degradation-containing solution according to the invention contains glucose (and galactose) only in concentrations below the limit of detection (see Example 3).

[0061] Xylanase is present either in the form of a suspension, in the homogenate and / or in the lysate of the corresponding cells that produce it, or in isolated form, with homogenates being particularly preferred.

[0062] In this context, suspension means a suspension of resting cells. These are harvested after cultivation (separated from the nutrient medium) and suspended in a suitable buffer system. Unlike fermentative processes, which also work with whole cells, the resting cellsDue to the removal of carbon sources and nutrients, cells no longer grow but serve only to convert substrates (Lin & Tao, 2017). In this context, homogenate refers to a physically and / or chemically treated suspension (e.g., treated with pressure, lysozyme, or ultrasound) in which the cell components are released from the cells. A lysate is obtained when the insoluble cell components of the homogenate are removed, for example, by filtration or centrifugation.

[0063] In another variant, the enzymes can also be modified at the N-terminus with a water-soluble polymer such as polyethylene glycol, immobilized in or on a solid matrix, or be part of a fusion protein.

[0064] The present invention further relates to a cellulose which can be produced according to one of the methods described above according to the invention.

[0065] The invention further relates to a cellulose sheet which is produced from the cellulose according to the invention by sheet formation.

[0066] The invention also relates to a cellulose sheet with a tear index of at least 4.00 mN·m 2< ·g -1< , particularly preferably of at least 4.50 mN·m 2< ·g -1< , and particularly preferably in combination with a xylan content of less than 25.0 wt%.

[0067] Furthermore, a cellulose sheet with a tear index of at least 4.00 mN·m 2< ·g -1< is preferred, particularly preferably at least 4.50 mN·m 2< ·g -1< , and a strain at break of at least 3.5%.

[0068] For the purposes of the present patent claims and description, "strain at break" is understood to be the ratio between the increase in length of a material and its original length when a tensile force is applied (unit %).

[0069] The pulp according to the invention can be used as such for the production of fiber composite materials, in particular paper, cardboard or carton, or as an additive to mixed pulps.

[0070] Regarding the tear index, it should be noted that it generally decreases with increasing refining, suggesting fiber damage during refining. To determine the optimal refining level for a given paper quality, a relationship is established between the tear index and the tensile index. However, the relevant relationship for the present invention is the connection between the xylan content of the pulp and the resulting tear index after refining.

[0071] The unmilled and lignin-reduced pulp (Table 7: Pulp 1) has a tear index of 4.61 mN·m²·g⁻¹ and loses 26% of its strength through FPI milling at 1500 rpm and 44% at 2500 rpm. The pulps after approximately 50% removal of xylan (Table 7: Pulp 2) reach the strength range of unmilled Pulp 1 again, with values ​​of 4.82 mN·m²·g⁻¹ (PFI milling at 1500 rpm) and 4.10 mN·m²·g⁻¹, respectively.

[0072] The ground lignin- and xylan-reduced pulp (pulp 2) gains 41% in tear strength (tear index) at 1500 rpm and 60% at 2500 rpm compared to the non-xylan-reduced pulp (pulp 1).

[0073] The strain at break value also increases by approximately 42% after xylanase treatment and milling at 2500 rpm compared to untreated pulp, while the burst index remains roughly the same after milling. Only the tensile index of the milled pulp decreases by 13% (PFI 1500 rpm) and 10% (PFI 2500 rpm) after xylanization.

[0074] This clearly shows that straw pulp treated with xylanase and milling, compared to pulp not treated with xylanase, experiences a significant increase in strength, measured as the Tear Index, at the expense of a slight decrease in the Tensile Index.

[0075] This positive strength effect achieved in the present invention on straw pulp has not been observed in any previously reported methods and measurements based on wood pulp. It is also neither predictable nor expected due to the high complexity of the factors determining strength.

[0076] This effect reveals that even after separating and extracting xylan from straw, a pulp can be obtained that meets market demands. The possibility of producing such pulp and simultaneously extracting xylan using specific xylanases had previously been ruled out because negative effects on the strength properties of the pulp and the paper produced from it were expected (Schönberg et al., 2001; Sjöberg et al., 2004; Schaubeder et al., 2004).

[0077] The improvement of pulp strength values ​​through xylan extraction completely contradicts the prevailing theory regarding the function of xylan in lignocellulose fiber structures. In none of the studies cited above was the influence of enzymatic xylan extraction on the tear index measured, nor was its significant increase mentioned or acknowledged (see Background of the invention).

[0078] The present invention shows that after mild organosolv digestion, at least 50% of the xylan can be obtained from the pulp, and yet a pulp with strength values ​​is produced which, after milling, exhibits significantly increased strength values ​​compared to pulp not treated with xylanase.

[0079] A direct comparison of the strength values ​​of the pulp according to the invention is not readily possible, since the pulps described in the prior art are mostly (bleached) wood kraft pulps, which differ significantly from the straw pulp obtained after the comparatively mild organosolv pulping.

[0080] Thus, the carbohydrate content in bleached softwood kraft pulp (BKSP), on which most studies on the function of xylan are based (see Background of the invention) derived from approximately 82% glucose, but only about 7% xylose and approximately 7% mannose combined (for example, Douglas fir; see Mansfield et al., 2002). Similar values ​​are reported by Oliver-Ortega et al. (2020) for a bleached Kraft softwood pulp from pine – 15% hemicellulose and 84% cellulose.

[0081] In contrast, the carbohydrate content of the unbleached, lignin-reduced pulp (pulp 1) of the process according to the invention consists of approximately 63% glucose and 32% xylose (see Table 6), which corresponds to a significantly higher xylan / hemicellulose content compared to the softwood Kraft pulps.

[0082] Furthermore, the fact that a high proportion of the xylans present in the pulp (> 50%) can be recovered enzymatically demonstrates that the mild organosolv digestion of the present invention transforms the straw lignocellulose, in the form of the resulting pulp, into a state of aggregation that exhibits sufficient ultrastructure porosity to ensure the diffusion of carbohydrate-splitting enzymes. This also leaves open the option of using the obtained pulp as a starting material for the enzymatic production of glucose. materials

[0083] Wheat straw was sourced from Derler Agrar GmbH, Birkfeld, Austria in October 2023. The chemical composition (see Methods for a description of the analytical methods) is shown in Table 1 below.

[0084] Hydrochloric acid, sulfuric acid, sodium hydroxide, sodium acetate, sodium dodecyl sulfate (SDS), zinc acetate and IPTG (isopropyl β-D-thiogalactopyranoside), L-arabinose and D-xylose were sourced from Carl Roth, acetone and D-galactose were sourced from AppliChem, ethanol was sourced from Honeywell, glycine, D-glucose, sodium thiosulfate, potassium permanganate and potassium hexacyanoferrate(II) trihydrate were sourced from Sigma-Aldrich and AZO-wheat-arabinoxylan, 4-nitrophenyl β-o-xylopyranoside, 4-nitrophenyl α-L-arabinofuranoside and AZO-CM-cellulose were sourced from Megazyme. Table 1. Chemical composition of the straw used. Components Salary [%] lignin 22,4 glucose 40,3 Xylose 22,8 Arabinose 2,5 Galactose 0,8 Extracts 2,9 ash 5,4 silicate 2,3 Other 2,8 Enzymes - Methods and analysis General information on the expression of recombinant enzymes in E. coli

[0085] For recombinant enzyme production in a EscherichiaThe coli strain was first selected to express the gene in a PCR using genomic DNA or its synthetically modified codon usage. E. coli A modified equivalent was used as a template, along with specific oligonucleotides additionally carrying recognition sequences for restriction endonucleases, and isolated from the reaction mixture. After nucleic acid digestion with the restriction enzymes Sphl and HindIII, the gene fragment encoding the target enzyme was ligated into the Sphl- and HindIII-cut backbone of the expression vector pQE70-Kan. The ligation product was then converted into chemically competent E . coli cells were transformed into Top10F' and the resulting colonies were used for plasmid isolation and restriction analysis.

[0086] The result of the cloning step was verified by restriction enzyme digestion and DNA sequencing. The resulting construct carries the target gene under the IPTG-inducible T5 promoter.

[0087] For the overexpression of the enzyme in E. coli The resulting expression plasmid was transformed into competent expression cells RB791. After 24 h incubation at 37 °C, the resulting colonies were inoculated into LB medium for expression assays.

[0088] The following day, expression cultures with an optical density (OD 550) of 0.02 were inoculated and shaken at 37 °C until an OD 550 of 0.3 was reached. The temperature was then lowered to 25 °C, and the cultures were induced with 0.1 mM IPTG when an OD 550 of 0.5 was reached. After 22 h, the cultures were harvested (separated from the medium by centrifugation into a cell pellet) and analyzed for the expression of the recombinant enzyme using SDS-gel electrophoresis and activity determination (for use in a use test or optical zymatic assay). Production of cell homogenates using Sonifier digestion

[0089] To prepare a cell suspension, the cell pellet produced according to the above procedure was weighed into a suitable container, mixed with buffer (e.g., sodium acetate buffer), and dissolved while stirring. The biomass fraction is typically 20% by mass; the remainder consists of the buffer.

[0090] A Branson Sonifier 450 was used for cell disruption. The suspension was treated three times with 15 ultrasonic pulses each (device settings: Timer = 15; Duty Cycle = 50; Output Control = 3-5).

[0091] The resulting homogenate was used directly for the reactions. Measurement of endo-1,4-β-Xvlanase activity

[0092] The activity of endo-1,4-β-xylanase was determined using the Megazyme AZO-Wheat assay. For the assay, the enzyme (E. coli cell homogenate) was diluted with 100 mM sodium acetate buffer (pH 5.5), and 200 µL of the enzyme solution was mixed with 200 µL of substrate solution (wheat arabinoxylan with Remazol Brilliant Blue R dye) and incubated for 10 min at 40 °C. The reaction was stopped by the addition of 1 mL of 95% ethanol and equilibrated for 10 min at room temperature. The reaction mixtures were then mixed again and centrifuged in a benchtop centrifuge at 1500 x g for 10 min. The supernatant was transferred to cuvettes, and the absorbance was measured at 590 nm. The activity was determined using a calibration curve. Measurement of β-Xvlosidase activity

[0093] The β-xylosidase activity was measured using the model substrate 4-nitrophenyl-β-D-xylopyranoside (O-PNPX). 890 µL of 20 mM sodium acetate buffer (pH 5.0) were placed in a 2 mL reaction vessel and heated to 30 °C in an Eppendorf thermomixer. 10 µL of the appropriately diluted enzyme solution (E. coli cell homogenate) and 100 µL of substrate solution (4 mM) were pipetted to the buffer, mixed, and incubated for 5 min at 30 °C. The reaction was stopped by adding 100 µL of 500 mM glycine-NaOH buffer, the mixture was transferred to a cuvette, and the UV absorption was measured at 405 nm. Measurement of α-L-arabinofuranosidase activity

[0094] α-L-arabinofuranosidase activity was measured using the model substrate 4-nitrophenyl-α-L-arabinofuranoside (O-PNPAF). For the assay, 890 µL of 20 mM sodium acetate buffer (pH 5.0) was mixed with 10 µL of the appropriately diluted enzyme solution (E. coli cell homogenate) and 100 µL of substrate solution (4 mM) in a 2 mL Eppendorf vial and incubated for 5 min at 30 °C. The activity was then stopped by adding 100 µL of 500 mM glycine-NaOH buffer, the sample was transferred to a cuvette, and the UV absorption was measured at 405 nm. Measurement of cellulase activity

[0095] Cellulase activity was determined using the Megazyme AZO-CM cellulose endo-1,4-beta-glucanase (cellulase) assay. To prepare the substrate solution, 2 g were mixed with Remazol Brilliant.

[0096] Blue R-stained CM-cellulose 4M was dissolved in 80 mL of boiling water with vigorous stirring. The pH was adjusted to 4.5 with 2 M sodium acetate buffer. The solution was cooled and made up to 100 mL with water. 200 µL of the enzyme solution were incubated with 200 µL of substrate solution for 10 min at 40 °C. The reaction was then stopped by the addition of 1 mL of 96% ethanol, the mixture was thoroughly mixed, equilibrated at room temperature for 10 min, and then centrifuged at 1000 x g in a benchtop centrifuge. The supernatant was transferred to a cuvette, and the absorbance was measured at 590 nm. The results were evaluated using a calibration curve. Overview of enzymes used for xylan depolymerization

[0097] Table 2. Enzyme types, donor organisms, NCBI Accession Numbers, activities and cellulase activities of the xylanases used for xylan depolymerization. enzyme Donor organism NCBI Accession No. Activity [U / g] Cellulase activity d< [U / g] endo -1,4-β-Xylanase I Bacillus subtilis WP_003231377 9500 a< 0,33 endo -1,4-β-Xylanase II Paenibacillus timonensis WP_240267768 180 a< 0,44 β-Xylosidase Geobacillus zalihae WP_060787919 37 b< 0,23 α-L-Arabinofuranosidase Bifidobacterium adolescentis WP_011742888 6,5 c< 0,24 Assay: a< AZO-Wheat-Arabinoxylan, b< 4-Nitrophenyl-β-D-xylopyranoside, c< 4-Nitrophenyl-α-L-arabinofuranoside, d< AZO-CM-Cellulose (see above)

[0098] To ensure that the xylanases used here do not exhibit cellulase activity, the enzymes were tested in a strain of Escherichia coliexpressed. E. coli This is a bacterium for which no natural strain is known to possess the ability to enzymatically cleave cellulose. For enzyme expression, gene fragments encoding the respective target enzyme were selected. Nevertheless, in the enzyme assay, the expressed enzymes of the xylanase complex show traces of cellulase activity (see Table 2).

[0099] To demonstrate that these substances have no effect on the strength of the cellulose and thus of the xylan-reduced pulp, the amount of glucose released in the filtrate of the xylan-reduced pulp after xylan extraction was measured following the addition of xylanase (see Example 3). This amount was below the limit of detection of the HPAEC method (see below) in all determinations. The xylanases used can therefore be described as "cellulase-free" in the sense that they have no effect on the breakdown of cellulose in the pulp. Analytical methods Determination of total sugar in solids / solutions by complete hydrolysis

[0100] Multiple determinations were performed. The solid (e.g., wheat straw, pulp 1, or pulp 2) was milled (Retsch Ultra Centrifugal Mill ZM 200) to obtain a homogeneous sample. 5 mg (± 0.1 mg) of the milled solid was weighed into a pressure test tube. For the total sugar determination from the solutions, 100–200 µL were pipetted into a pressure test tube and evaporated in a vacuum oven at 50 °C. The samples (solids or evaporated solutions) were stirred with 80 µL of 12 M sulfuric acid for 2 h using a magnetic stir bar on a magnetic stir plate at 300 rpm. The samples were then diluted with 2.75 mL of water and heated to 120 °C in a drying oven for 1 h. The test tubes were then cooled to room temperature and neutralized with calcium carbonate. The samples were centrifuged in a benchtop centrifuge for 5 minutes at maximum speed.The supernatant was removed, centrifuged again for 5 minutes, and further diluted if necessary. The solution was transferred to an IC vial and analyzed by HPAEC (see below). Determination of lignin content according to Klason

[0101] For the determination of Klason lignin, 500 mg of lignin were mixed with 7.5 mL of 12 MH₂SO₄ in a beaker. The mixture was stirred for 2 h at room temperature. The mixture was then transferred to an Erlenmeyer flask, the beaker was washed with hot deionized water, and the volume was increased to a total mass of 285 g. After incubation in an ultrasonic bath for 10 min, the mixture was boiled on a hot plate for 4 h, replenishing losses due to evaporation with deionized water every 30 min. The solution was then incubated overnight at room temperature. The following day, the solid was filtered through a tared glass frit and washed with hot deionized water until the wash solution was neutral. The mass of the solid (insoluble lignin fraction) was determined after drying the glass frit overnight in a vacuum drying oven. The soluble lignin fraction in the filtrate was quantified using photometry (measurement at 205 nm). Determination of the ash and silicate content in solids

[0102] To determine the ash content, 1 g of sample (wheat straw, cellulose, or lignin) was weighed into a previously annealed and tared ceramic crucible and ashed with a Bunsen burner until no more smoke was visible. The crucible was then heated overnight in a muffle furnace (575 °C). The mass of the ash was determined by weighing.

[0103] To determine the silicate content, the entire quantity of ash was placed in a beaker and mixed with 5 mL of 6 M HCl. The mixture was then heated on a hot plate (200–220 °C). After the HCl had evaporated, another 5 mL of 6 M HCl was added and evaporated again. This process was repeated (total addition: 15 mL of 6 M HCl). Subsequently, 20 mL of deionized water were added, and the solid was filtered through an ash-free filter. The filtrate was then washed with hot deionized water until it reached pH neutral. After ashing the filter, the silicate content was determined by weighing. Determination of the proportion of extractable substances by means of Soxhlet extraction

[0104] Four grams of shredded wheat straw were weighed into a pre-dried and weighed cellulose extraction pod. Extraction was carried out in a Soxhlet apparatus for two hours with 500 mL of acetone. The extraction pod was then dried overnight in a vacuum drying oven, and the proportion of extractables was determined as the mass difference. Determining the kappa number

[0105] 30 mg of a solid (e.g., cellulose) were weighed into a 50 mL Erlenmeyer flask, mixed with 14 mL of water, and stirred until a homogeneous suspension was formed. Then, 2 mL of a 0.1 N potassium permanganate solution were added. After 10 min, 400 µL of a 10% potassium permanganate solution were added, resulting in an orange-brown suspension. This was titrated with a 0.1 N sodium thiosulfate solution until a pale yellow solution was obtained. To improve visibility of the endpoint, 200 µL of starch solution were added, and the titration was continued until complete decolorization. The kappa number was calculated from the consumption of the sodium thiosulfate solution. Determination of the grind size according to Schopper-Riegler

[0106] 2 g of sample and 1 L of distilled water were placed in the container of the beating device (Frank-PTI) and beaten until the number of revolutions (30,000 revolutions) was reached.

[0107] The suspension was then transferred to the Schopper-Riegler grind tester (Frank-PTI), where it was separated using a sieve. The Schopper-Riegler value (°SR) was read on the scale of the measuring cup. Sample preparation for HPAEC analysis using Carrez precipitation

[0108] For Carrez solution I, 21.9 g of zinc acetate were dissolved in 100 mL of water. Carrez solution II was prepared by dissolving 10.6 g of potassium hexacyanoferrate(II) in 100 mL of water.

[0109] 70 µL of Carrez solution I were pipetted to 1 mL of sample (filtrate or wash solution after enzyme treatment) and incubated at 25 °C and 1000 rpm for 5 min. Then, 70 µL of Carrez solution II were added and incubated for another 5 min at 25 °C and 1000 rpm. The resulting precipitate was then separated by centrifugation in a benchtop centrifuge for 10 min at 1000 rpm. Further dilution was performed, if necessary, before HPAEC measurement. High Performance Anion Exchange Chromatography (HPAEC)

[0110] A Dionex ICS6000 system with an AS-AP autosampler was used to quantify arabinose, glucose, galactose, and xylose by HPAEC (High Performance Anion Exchange Chromatography). A Dionex CarboPac PA20-fast-4 µm column with a corresponding guard column and a NaOH gradient was used for analyte separation. The analytes were detected using a pulsed amperometric detector (PAD, gold electrode) and the "Carbo, Quad" waveform.

[0111] The following examples describe preferred variants of the method according to the invention in more detail. Example 1 Delignification of straw

[0112] 2.4 kg of chopped, sieved wheat straw (particle size 1–5 cm) were suspended in a horizontal paddle reactor (total volume: 80 L) in 7.2 L of a reaction solution consisting of 2.72 kg water, 4.03 kg ethanol, and 0.27 kg NaOH. The suspension was heated to 120 °C in the reactor (the heating time to reach 120 °C was approximately 15–20 min) and stirred for 15 min at 11 rpm. The reaction vessel was then cooled to approximately 40 °C, the suspension was emptied, and diluted to 4% density with water.

[0113] The suspension was then fiberized in the refiner (Sprout-Bauer 12" (7208-110); 0.3 mm plate spacing), whereby the fibers were mechanically processed.

[0114] The solid fraction was separated from the lignin solution using a washing press (Fischer stainless steel hydropress; 90 L working volume), and the resulting pulp was washed three times with 20 L of water using the same washing press. The lignin-reduced pulp was then washed with water through sieves (80 µm mesh size) until the pH of the washing solution was < 9 and treated with a spin dryer (Thomas Centri 776 SEK) to increase the dry matter content to approximately 30%. Finally, the lignin-reduced pulp was blended using a kneading machine (GGM Gastro PRMH20; 20 L working volume). The pulp obtained in this way with reduced lignin content is referred to below as "Pulse 1".

[0115] Table 3 below shows the dry matter, yield, kappa number, and Schopper-Riegler value of pulp 1. Table 4 below shows the sugar content and the lignin content according to Klason of pulp 1. Table 3. Characterization of cellulose 1. Wet mass of pulp [kg] Dry matter [%] Yield [%] Kappa number Schopper-Riegler value [°SR] 4,6 31,6 60 41,5 23 Table 4. Sugar content and lignin content (Klason) of pulp 1. Glucose [%] Xylose [%] Arabinose [%] Galactose [%] Klason lignin [%] 63,3 32,4 3,7 0,6 7,7

[0116] Lignin was precipitated from a portion of the lignin solution. Example 2 Lignin precipitation

[0117] 500 mL of the obtained lignin solution were transferred to a round-bottom flask. The ethanol contained in the solution was evaporated using a rotary evaporator at a water bath temperature of < 40 °C. After determining the lignin concentration (21.4 g / L) by photometry (measurement at 280 nm in 10 mM NaOH), the solution was diluted to a lignin concentration of 10 g / L with deionized water.

[0118] A duplicate determination was performed using 200 mL of the diluted lignin solution (10 g / L) in each sample. The pH of the solutions was first adjusted to < 4 with 66% H₂SO₄ while stirring. The solutions were then incubated without stirring in a water bath at 65 °C for 60 min, during which time a solid formed. Immediately after incubation, the solid was filtered off using A113 filter paper in a Büchner funnel and washed with a small amount of deionized water.

[0119] In this way, 1.4 g of solid material (70% yield) were obtained. The sugar content and lignin content (Klason) of the recovered lignin are shown in Table 4 (average from the duplicate determinations). Table 5. Sugar content and lignin content (Klason) of the precipitated lignin solid. Glucose [%] Xylose [%] Arabinose [%] Galactose [%] Klason lignin [%] <LOQ 1,6 0,7 <LOQ 91 Example 3 Enzymatic depolymerization and extraction of xylan

[0120] The xylan in pulp 1 was enzymatically depolymerized and the solution containing the xylan degradation products was separated from the solid (pulp 2).

[0121] The reaction was carried out in a spherical 1 L glass reaction vessel with a lid, heated by a magnetic stirrer and heat-on attachment, and equipped with a KPG stirrer and a stirring shaft with a crescent-shaped stirring blade. The reaction volume was 400 mL. 40 g (dry mass) of pretreated substrate (cellulose 1) was suspended in water, and the pH was adjusted to 6 (±0.2) with 1 M sulfuric acid. After stabilizing the pH, the xylanases were added in the form of E. coli -Cell homogenates (10.7 mL endo-1,4-β-Xylanase I, 10 mL endo-1,4-β-Xylanase II, 5 mL β-Xylosidase, 10 mL α-L-Arabinofuranosidase) were added.

[0122] The suspension was thoroughly mixed and incubated for 6 h at 50 °C and 50 rpm. To deactivate the enzymes, the suspension was heated to 95 °C for 15–30 min. After cooling to approximately 40 °C, the solution was separated from the solid by filtration through a Büchner funnel, and the enzyme-treated pulp was washed twice with 200 mL of water each time.

[0123] The sugar content of the substrate pulp (pulp 1), the enzyme-treated pulp (pulp 2), as well as the total sugar concentration and sugar monomer concentration of the filtrate and the washing solutions were analyzed using HPAEC.

[0124] The concentrations of monomeric pentoses obtained after enzyme treatment in the filtrate of pulp 2 averaged 2.7 g / L arabinose and 22.8 g / L xylose. The concentrations of monomeric hexoses galactose and glucose were below the limit of detection in all determinations, indicating negligible cellulase activity of the enzymes used (see Table 2 for the cellulase activities of the xylanases).

[0125] Table 6 below shows the sugar content in lignin-reduced pulp (pulp 1) and in lignin- and xylan-reduced pulp (pulp 2). The values ​​shown are the result of

[0126] Multiple determinations - Pulp 1: Mean of 16 samples (4 quadruple determinations) and Pulp 2: Mean of 10 samples (5 double determinations). Table 6. Sugar content of pulp 1 (lignin-reduced) and pulp 2 (lignin- and xylan-reduced). Arabinose [%] Galactose [%] Glucose [%] Xylose [%] Pulp 1 (Lignin-reduced) 3,70 0,63 63,29 32,43 Pulp 2 (Lignin and xylan reduced) 1,84 0,78 84,50 18,09 Percentage change [%] * Arabinose Galactose glucose Xylose -59,2 +0,5 +9,5 -54,3 * The average yield of pulp 2 (82%) was included in the calculation of the stated percentage changes.

[0127] A significant decrease in the pentoses arabinose and xylose is observed in pulp 2 (-59.2% and -54.3% compared to pulp 1, respectively), while the hexoses glucose and galactose (+0.5% and +9.5% compared to pulp 1, respectively) are enriched. The xylan content (sum of arabinose and xylose content) decreases from 36% (pulp 1) to 20% (pulp 2). Example 4 Strength values ​​of the pulp

[0128] 30 g of pulp 1 (lignin-reduced) or pulp 2 (lignin- and xylan-reduced) were milled at a solids concentration of 1.5% in water in a PFI mill according to standard ISO 5264-2:2011 at 1500 rpm and 2500 rpm (PFI 1500 or PFI 2500), and paper sheets were produced to determine the strength values. Sheet formation was carried out according to standard ISO 5269-2:2004 on a sheet forming machine from Frank-PTI.

[0129] The strength values ​​were determined according to the following standards: Tear Index (ISO 1974:2012), Strain at Break (ISO 1924-2:2009), Tensile Index (ISO 1924-2:2009), and Burst Index (ISO 2758:2014). The measurement results are shown in Table 7 below, as well as in Figures 1 (Tear Index) and 2 (Strain at Break), where ø represents the unground material, PFI 1500 represents milling at 1500 rpm, and PFI 2500 represents milling at 2500 rpm. Table 7. Strength parameters of sheets produced from pulp 1 (lignin-reduced) and pulp 2 (lignin- and xylan-reduced). PFI 1500 indicates milling with a PFI mill at 1500 rpm and PFI 2500 indicates milling at 2500 rpm. The percentages in parentheses describe the percentage change in strength values ​​after xylanase treatment. Pulp 1 Pulp 2 unground PFI 1500 PFI 2500 unground PFI 1500 PFI 2500 Tear Index [mN m 2< g -1< ] 4,61 3,42 2,57 5,34 (+16%) 4,82 (+41%) 4,10 (+60%) Strain at Break [%] 1,4 3,0 3,1 1,2 (-16%) 4,1 (+37%) 4,4 (+42%) Tensile Index [N·m·g -1< ] 33,3 74,0 81,4 22,3 (-33%) 64,6 (-13%) 73,4 (-10%) Burst index [kPa m 2< g -1< ] 1,67 4,35 4,83 1,18 (-29%) 4,50 (+3%) 4,96 (+3%) literature

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Claims

1. Process for the production of pulp, characterized by the fact that Straw containing lignin, xylan and cellulose, suspended in an aqueous phase, is subjected to treatment to reduce the lignin content and treatment with a xylanase to reduce the xylan content.

2. Method according to claim 1, characterized by the fact that The treatment to reduce the lignin content is carried out using an alkaline aqueous solution containing ethanol.

3. Method for obtaining pulp, lignin and xylan decomposition products from straw containing lignin, xylan and cellulose, characterized byThe combination of measures: a) treating shredded straw with an aqueous solution containing a C1-C4 alcohol and having a pH between 11 and 14, causing some of the lignin contained in the straw to dissolve and yielding a lignin-containing solution and a first pulp suspended in this solution; b) separating the first pulp from the lignin-containing solution; c) recovering the lignin from the resulting lignin-containing solution; d) treating the separated first pulp with an aqueous solution containing xylanase to selectively reduce the xylan content in the first pulp and dissolve xylan degradation products, yielding a second pulp suspended in the xylan degradation product-containing solution; e) separating the second pulp from the xylan degradation product-containing solution.and f) the xylan cleavage products are at least partially recovered from the obtained xylan cleavage product-containing solution.

4. Pulp obtainable by a process according to claims 1 to 3.

5. Cellulose sheet, which is produced from cellulose according to claim 4 by sheet formation.

6. Pulp sheet according to claim 5 with a xylan content below 25.0% and a tear index of at least 4.00 mN·m 2 ·G -1 .

7. Pulp sheet according to claim 6 with a tear index of at least 4.50 mN·m 2 ·G -1 .

8. Pulp sheet according to claim 6 or 7 having a strain at break of at least 3.5%.

9. Use of a pulp according to claim 4 for the production of fiber composite materials, in particular paper, cardboard or carton, or as an additive in mixed pulps.

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