Process for the production of microfibrillated cellulose from high-yield Kraft pulp, microfibrillated cellulose obtainable by said process and Kraft pulp and paper products comprising said microfibrillated cellulose

Abstract

The present invention relates to a process for the production of microfibrillated cellulose from a high-yield pulp, comprising the steps of selecting a Kraft pulp with a total lignin content of 5% to 30% by weight and defibering same to obtain a suspension of microfibrillated cellulose with a minimum fines content of 15% by weight. Other aspects of the present invention correspond to the microfibrillated cellulose obtainable by the process and the Kraft pulp and paper products comprising the microfibrillated cellulose. The process described allows the production of microfibrillated cellulose with lower energy consumption and the microfibrillated cellulose has increased suitability for papermaking, resulting in paper products with increased mechanical strength properties.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION

[0003] PROCESS FOR PRODUCTION OF MICROFIBRILLED CELLULOSE FROM HIGH-YIELD KRAFT PULP, MICROFIBRILLED CELLULOSE OBTAINED FROM THE KRAFT PULP PROCESS AND PAPER PRODUCTS COMPRISING SAID MICROFIBRILLED CELLULOSE

[0004] TECHNICAL DOMAIN

[0005] The present invention relates to a process for producing microfibrillated cellulose from high-yield Kraft pulp. Additionally, the invention relates to the microfibrillated cellulose obtained from the process, and to Kraft pulp and paper products comprising the microfibrillated cellulose obtained. The invention has application in the paper industry.

[0006] PRIOR TECHNIQUE

[0007] Microfibrillated celluloses have been the subject of increasing interest for different applications, particularly in the area of ​​pulp and paper production. They can be produced from different raw materials such as, for example, cellulosic fibers from herbaceous plants and tubers, among others, and through processes that may involve enzymatic, chemical and mechanical operations, individually or in several stages (Klem et al., Nanocelluloses: A New Family of Nature-Based Materials, Angew. Chem., Int. Ed., 2011, 50, 5438-5466). Conventionally, microfibrillated celluloses are produced from delignified and preferably bleached cellulose pulp (Osong et al., Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: A review, 2016, 23, 93-123; Klemm et al., Nanocellulose as a natural source for groundbreaking applications in materials science: Today's state, Materials Today, 2018, 7, 720-748) .

[0008] In fact, as shown in the documents mentioned below, microfibrillated cellulose production processes are carried out from conventional cellulosic raw materials, that is, cellulose pulps delignified by typical chemical cooking processes, such as Kraft or sulfite, and / or bleached, thus typically having total lignin contents of less than 5% by weight. Similarly, the documents reporting the use of microfibrillated cellulose in the production of papermaking material consider it according to its conventional definition with regard to the raw material and its properties.

[0009] Patent EP3341523B1 discloses a method of producing microfibrillated cellulose that requires fewer passes through refiners and, consequently, lower energy consumption, which involves refining, with sheets of certain dimensions, a chemical pulp of cellulose fibers.

[0010] Patent EP2494107B1 concerns a process for the production of microfibrillated cellulose with the aid of an extruder, in which at least one chemical product (among carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, calcium stearate, alcohols, surfactants and surfactants or other hydrophobic chemicals) is added to the extruder during the processing of a mixture of fibers, preferably cellulosic but which may also include cotton fibers and fibers from agricultural products, such as potatoes and cereals.

[0011] Patent application EP2196579A1 describes a method for producing microfibrillated cellulose, with lower associated energy consumption, which involves passing a suspension of a cellulose pulp in a solvent (such as water, alcohols, dimethylsulfoxide, glycerol and mixtures thereof) through an orifice of a homogenizer so that said suspension is subjected to a pressure drop. Said diameter of said orifice is 100 to 700 μm and said pressure drop has a maximum value of 100 MPa. The cellulose pulps described in the patent application relate to conventional pulps and those obtained by typical processes of their production, such as bleached, semi-bleached and unbleached pulps, by chemical processes using sulfite and sulfate.

[0012] Patent application WO2014147293A1 discloses a process for producing microfibrillated cellulose that involves, in chemical cooking, a physical / mechanical treatment, such as pressing and shearing, of an impregnated cellulosic fiber source, which treatment is applied during or after fiber impregnation or during or after fiber cooking, in which a change in the cellular structure of the fiber wall is observed, thus reducing the energy consumption involved in the production of microfibrillated cellulose. The process then continues with the typical cooking steps, for example by Kraft cooking, washing and bleaching, and further refining with enzymes or solvent and, finally, grinding of the obtained fibril. The invention describes the use of fibers from herbaceous and non-herbaceous plants and their combinations.

[0013] Patent EP2576629B1 describes a method for producing microfibrillated cellulose, said to be more efficient and economical than the prior art, which involves acid hydrolysis at a high temperature or acidification followed by washing and hydrolysis at a high temperature of a cellulosic material. The lignin content of the starting cellulosic material is less than 5% by weight. The cellulosic material is considered to be chemical pulp of hardwoods or resins, bleached or unbleached, such as Kraft pulp, sulphite and soda.

[0014] Patent EP2452014B1 describes a process for producing microfibrillated cellulose, more efficient than the prior art, which consists of processing a pulp of cellulose fibers with an enzyme and a mechanical treatment, both of which are carried out simultaneously in a single step. Bleached fibers, for example from softwoods and hardwoods, are used, since, as described in the aforementioned patent, the presence of lignin in unbleached pulps leads to greater energy consumption in the production of microfibrillated cellulose.

[0015] Patent application US20160273165A1 discloses a method for producing a paper product with improved strength and filler and fines retention, which involves adding an anionically modified microfibrillated cellulose to a fiber suspension in an amount of 0.1 to 10% by weight. Patent application EP3433428A4 describes a board with improved compressive strength involving the use of a cellulose pulp with drainability values ​​between 15 and 28 (in Schopper-Riegler values) to which is added between 1 and 5% by weight of microfibrillated cellulose and a hydrophobic additive, such as an alkylketene dimer, succinic anhydrides, rosin and a styrene maleic anhydride, or emulsions, modifications and mixtures thereof.

[0016] Patent EP2978894B1 describes a process for producing paper and cardboard with strength properties through a mixture of fibers that involves the addition, in a specific sequence, of microfibrillated cellulose, strength additives and microparticles, such as silica and bentonite, to this mixture of fibers.

[0017] One of the most widely used chemical processes industrially for the production of cellulose pulp from wood is Kraft cooking, or sulphur cooking. This chemical process consists of cooking the wood in a cooking liquor usually consisting of sodium hydroxide and sodium sulfide, at temperatures of around 140 to 180 °C, in pressurized reactors (Ek, Monica; Gellerstedt, Gõran; Henriksson, Gunnar; Pulp and Paper Chemistry and Technology Volume 2, Pulping Chemistry and Technology, 2009, De Gruyter, Berlin). This chemical cooking process typically ends with a total lignin content of less than 5% by weight. It is necessary to extend the Kraft cooking process to values ​​below 5% in order to allow processing of the pulp, either for direct paper production or for subsequent bleaching.The Kraft cooking process is one of the processes typically used to produce the raw material used in the state-of-the-art microfibrillated cellulose production processes.

[0018] The low lignin content in the starting cellulose pulps for the production of cellulose fibrils, obtained through the delignification of wood by chemical processes and through additional bleaching steps, is necessary and, as such, a condition for the application of methods for producing these cellulose fibrils that involve lower expenditure of mechanical and chemical energy, as demonstrated by Chaker and co-authors who, when evaluating the suitability of cellulose pulps for fibrillation, chose an initial pulp with a lignin content of less than 20% by weight and to which they also apply an additional bleaching step after cooking, in order to further reduce the lignin content to values ​​substantially lower than 5%, typically lower than 1%, in order to reduce the influence of the presence of lignin on the fibrillation of the cellulose pulp (Chaker et al., Key role of the hemicellulose content and the cell morphology on the nanofibri llation ef fectiveness of cellulose pulps , Cellulose , 2013 , 20 , 2863 - 2875 ) .

[0019] Thus, the state of the art shows that the methods for producing microfibrillated cellulose, from cellulosic materials conventionally used for the production of microfibrillated cellulose, understood as delignified cellulosic pulps by typical chemical cooking processes, such as Kraft or sulfites, and / or additionally bleached, include modifications to increase their efficiency and reduce associated costs, which involve the use of, for example, organic solvents, chemical treatments, such as hydrolysis, and fibrillation equipment developed for this purpose, in several stages or in combination. Cellulosic pulps with a lignin content substantially lower than 5% are also used as raw material, applying, for example, bleaching treatments to the starting cellulosic pulps.

[0020] There is therefore a need for a microfibrillated cellulose production process that exempts its input raw material from the application of various complex chemical and / or mechanical treatments aimed at reducing the lignin content of said raw material to values ​​below 5% by weight, and that also dispenses with such treatments during its conversion into microfibrillated cellulose. There is also a need for a microfibrillated cellulose production process that provides lower energy consumption, therefore lower associated costs, and that results in the production of microfibrillated cellulose that allows its application in the production of paper materials with increased strength properties, compared to microfibrillated celluloses produced by prior art production processes that use conventional cellulosic raw materials, that is, with lignin contents below 5%.

[0021] SUMMARY OF THE INVENTION

[0022] The present invention relates to a process for producing microfibrillated cellulose characterized by comprising the following steps: a) selection of a high-yield Kraft pulp with a total lignin content of 5% to 30% by weight; b) mechanical defibration of the pulp selected in step a) until a suspension of microfibrillated cellulose with a minimum fines content of 15% by weight is obtained.

[0023] In a preferred form of the invention the process further comprises and before step b) an enzymatic hydrolysis of the paste selected in step a).

[0024] In a preferred form of the invention, hardwood pulp, resinous pulp or mixtures thereof are selected in step a).

[0025] In a preferred form of the invention the pulp selected in step a) is eucalyptus pulp.

[0026] The present invention also relates to microfibrillated cellulose obtained by the process described.

[0027] In a preferred form of the invention, the microfibrillated cellulose has a minimum fines content of 15% by weight.

[0028] The present invention also relates to Kraft pulp comprising the microfibrillated cellulose described.

[0029] The present invention further relates to a paper product comprising the microfibrillated cellulose described. In a preferred form of the invention, the paper product is a containerboard, a kraftliner paper, a testliner paper, a fluting or corrugated board paper, a sack paper (sack kraft), a shopping bag paper, a flexible packaging paper (flexible packaging), a tissue paper or a printing and writing paper.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] Fig. 1 shows the microscopic observation of microfibrillated cellulose produced from (a) high yield Kraft pulp (used in the present invention) and (b) bleached Kraft pulp (used in the prior art) and from (c) commercial microfibrillated cellulose of the prior art.

[0032] The bar indicates the 100 pm scale.

[0033] Fig. 2 shows the fines percentage (based on the total length-weighted sample measured on an L&W Fiber Tester 912) of microfibrillated pulps produced at different refining energies from high-yield pulp (squares) and from unbleached pulp (diamonds) or bleached pulp (circles). The fines value for a commercial microfibrillated pulp is shown in the solid line.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] A process for producing microfibrillated cellulose (also referred to in this description as CMF, for the sake of simplicity) from a high-yield Kraft pulp is described herein, that is, within the scope of the present invention, a Kraft pulp with a total lignin content of 5% to 30% by weight, as described below, which, surprisingly, simultaneously allows the production of microfibrillated cellulose with lower energy consumption compared, for example, from a conventional Kraft pulp (to which a low lignin content is associated, that is, within the scope of the present invention, a total lignin content of less than 5% by weight), and in which the microfibrillated cellulose obtained has a papermaking suitability that provides increased mechanical strength properties to the paper products that incorporate it, in comparison with conventional solutions using microfibrillated celluloses produced through conventional cellulose pulps, that is,delignified by typical chemical cooking processes, such as Kraft or sulfito, and / or additionally bleached.

[0036] Within the scope of the present invention, a Kraft cooking process refers to Kraft cooking or sulphate cooking. This is a chemical process well known in the art that consists of cooking wood in a cooking liquor typically consisting of sodium hydroxide and sodium sulphide, at temperatures of the order of 140 to 180°C, in pressurized reactors. A conventional Kraft process is understood here as a typical chemical cooking that results in a pulp production yield of approximately 45-55%.

[0037] Within the scope of the present invention, Kraft pulp refers to pulp obtained by Kraft cooking.

[0038] Within the scope of the present invention, unbleached Kraft pulp refers to a pulp produced by the conventional Kraft process, typically with a total lignin content of less than 5% by weight. Within the scope of the present invention, bleached Kraft pulp refers to a pulp produced by the conventional Kraft process and which is further subjected to a bleaching step, with a total lignin content typically of less than 1% by weight. The bleaching step is intended to further delignification by the action of oxidizing agents, such as oxygen, chlorine dioxide and hydrogen peroxide.

[0039] Within the scope of the present invention, high-yield Kraft pulp refers to a Kraft pulp produced by a chemical Kraft cooking process with a yield greater than 60%, and the pulp thus produced has a total lignin content of 5% to 30% by weight. Accordingly, when in the present description reference is made to "high-yield Kraft pulp", it is intended to make simplified reference to a Kraft pulp comprising a total lignin content of 5% to 30% by weight.

[0040] Within the scope of the present invention, the cooking yield is calculated by the following formula: pasta mass / wood mass x 100

[0041] (weights on an absolutely dry basis)

[0042] Within the scope of the present invention, the total lignin content by weight is the sum of the insoluble lignin content (determined according to the Tappi 222 om-02 standard) and the soluble lignin content (determined according to the Tappi um 250 standard modified with the addition of borohydride for spectrophotometric measurement - Pinto P., Influence of the chemical structure of wood components on their performance in cellulose pulp production processes. Comparative study between Eucalyptus globulus and other hardwoods, Doctoral Thesis, University of Aveiro,

[0043] 2005 ) .

[0044] Within the scope of the present invention, and in accordance with ISO / TS 20477, microfibrillated cellulose refers to cellulose fibers composed of at least one elementary fiber containing crystalline, paracrystalline and amorphous regions, with an aspect ratio (length / diameter) greater than 10, and may contain longitudinal fibrils, interlacing between particles or network-type structures, and are produced by mechanical and / or chemical treatments of wood, such as enzymatic treatments.

[0045] It is therefore common in the field of the technique in question to designate microfibrillated celluloses produced exclusively by mechanical treatments as "mechanical microfibrillated celluloses" and when produced through a combination of these with enzymatic treatments as "enzymatic microfibrillated celluloses", since, being chemically constituted by the same elements as the original pulp, the intrinsic characteristics of the microfibrillated celluloses produced depend directly on the process used for their production, being impossible to characterize them through their constituents due to their heterogeneous nature. This is also expected for other production methods and depending on the raw materials involved.

[0046] Within the scope of the present invention, the percentage of fines refers to the percentage of fibrils with a length less than or equal to 0.2 mm, measured on an L&W Fiber Tester 901, relative to the average length of the entire sample. With mechanical defibration technology, it is possible to achieve 100% fines, combining modern machinery and adequate energy and time consumption. However, in industrial practice based on the current state of the art, it is common to treat the raw material until a fines level of close to 50% by weight is reached (measurement made on an L&W Fiber Tester 912, length-weighted average). Depending on the purpose of using the CMF, the level of fines to be achieved may be more or less high.

[0047] Within the scope of the present invention, microfibrillated cellulose from high-yield Kraft pulp refers to microfibrillated cellulose produced from a high-yield Kraft pulp.

[0048] Within the scope of the present invention, microfibrillated cellulose from unbleached Kraft pulp refers to microfibrillated cellulose produced from an unbleached Kraft pulp.

[0049] Within the scope of the present invention, microfibrillated cellulose from bleached Kraft pulp refers to a microfibrillated cellulose produced from bleached Kraft pulp.

[0050] Within the scope of the present invention, commercial microfibrillated cellulose refers to samples that can be acquired on the market with the characteristic of being produced from fully delignified wood pulp, after a conventional Kraft cooking (total lignin content in the cellulose fiber of the pulp produced of less than 5% by weight), followed by a bleaching process to obtain the pulp that was finally used in the production of microfibrillated cellulose by a mechanical process with an enzymatic pre-treatment. Within the scope of the present invention, retention agent refers to an additive added in the formation of the paper in order to retain fines and mineral fillers, such as, but not limited to, a linear cationic polyacrylamide.

[0051] Within the scope of the present invention, a corrugated paper (containerboard) corresponds to the paper commonly used to make cards (corrugated boards).

[0052] The top and base layer of a corrugated board is called linerboard. It is typically a two-ply product, a top layer and a base layer. Both virgin and recycled fiber are used in the production of this type of paper. In the first option, when the fiber used is predominantly virgin fiber produced chemically by the Kraft method, the product is called kraftliner. When predominantly recycled fibers are used, the product is referred to as testliner. The fluting between two liners is called fluted paperboard (fluting, or corrugated medium).

[0053] Within the scope of the present invention, tissue paper corresponds to papers used for hygienic and sanitary purposes, whether in a domestic environment or in public places.

[0054] A process for producing microfibrillated cellulose from a high-yield Kraft pulp is described herein, the latter comprising, by definition, a high lignin content, that is, within the scope of the present invention, a total lignin content of 5% to 30% by weight.

[0055] Surprisingly, the process of the invention simultaneously allows the production of microfibrillated cellulose with lower energy consumption compared to prior art processes that use conventional Kraft pulps (with a total lignin content of less than 5% by weight) and in which the microfibrillated cellulose obtained presents a papermaking suitability that provides increased mechanical resistance properties to the paper products that incorporate it, compared to conventional solutions using microfibrillated celluloses produced through conventional cellulose pulps (that is, delignified by typical chemical cooking processes, such as Kraft or sulphite, and / or bleached).

[0056] In fact, and surprisingly, the process of the present invention allows to produce microfibrillated cellulose, with the above-mentioned advantages, from Kraft pulps with high total lignin content (from 5% to 30% by weight), contrary to the practice established in the prior art that discourages the use of such pulps with high total lignin content, also commonly referred to as high-yield Kraft pulps.

[0057] The process described here consists of selecting a high-yield Kraft pulp followed by its mechanical defibration until a microfibrillated cellulose suspension is obtained. The process may also include, before the mechanical defibration step, enzymatic hydrolysis of the selected pulp. Examples

[0058] • Process for preparing micro fibrillated cellulose from high-yield eucalyptus Kraft pulp (CMF PKAR)

[0059] Example 1

[0060] In a conical refiner, high-yield eucalyptus Kraft pulp with a total lignin content of 8% was previously disintegrated and refined using the following refining parameters: rotational speed of 1230 rpm, edge length of 0.574 km / s, power of 0.918 kW, SEL (specific energy load applied by the edge of the bars) of 1.6 Ws / m, and specific energy of 350 kWh / ton. The resulting product was further refined in two stages in a disc refiner. The first stage was carried out with the following refining parameters: rotational speed of 700 rpm, edge length of 39.48 km / s, power of 5.076 kW, SEL of 0.15 Wm / s, and specific energy of 200 kWh / ton. The second phase was carried out with the following refining parameters: rotation speed 700 rpm, edge length 39.48 km / s, power 5.922 kW, SEL 0.10 Wm / s and specific energy 250 kWh / ton.Refining was carried out until a minimum fines content of 15% by weight was reached (length-weighted average, based on the total sample and determined on a L&W Fiber Tester 912 equipment).

[0061] Figure 1 shows the microscopic analysis of the obtained microfibrillated cellulose suspensions. Fibrilization after mechanical treatment and size heterogeneity within the same sample were observed. Therefore, the samples were analyzed on an L&W Fiber Tester 912 to determine particle size. Table 1 shows the length-weighted average of the fiber lengths and diameters, as well as the degree of polymerization, calculated using the Mark Houwink equation (parameters and equation defined in Henrikson et al., Cellulose Nanopaper Structures of High Toughness, Biomacromolecules 2008, 9, 1579-1585) with the intrinsic viscosity values ​​determined in samples dissolved in cupriethylenediamine solutions, according to ISO 5351:2010.

[0062] Table 1. Characterization (dimensions and degree of polymerization) of the microfibrillated celluloses produced from high-yield kraft pulp used in the present invention and comparison with the values ​​obtained in microfibrillated celluloses produced from unbleached pulp, bleached pulp and commercial microfibrillated cellulose of the prior art.

[0063] Figure 2 represents the percentage of fines (based on the total length-weighted sample measured on a L&W Fiber Tester 912) of microfibrillated cellulose produced with different refining energies.

[0064] It was possible to verify that, using the same refining energy, a higher percentage of fines was obtained with the high-yield Kraft pulp than with a Kraft pulp obtained by the conventional Kraft process (with a total lignin content of 2%), and than with the bleached pulp (with a total lignin content of less than 1%), typically used in the prior art. Thus, it was demonstrated that with the high-yield pulp, a lower amount of energy was required to produce the same amount of fines.

[0065] Example 2

[0066] High yield eucalyptus Kraft pulp, with a total lignin content of 5% by weight, was subjected to disintegration and refining as described in Example 1. The results also demonstrated that a higher percentage of fines was obtained, using the same refining energy, with this high yield Kraft pulp than with a bleached Kraft pulp obtained by the conventional Kraft process.

[0067] Example 3

[0068] High yield eucalyptus Kraft pulp with a total lignin content of 10% by weight was disintegrated and refined in a manner similar to that described in Example 1. A higher percentage of fines was obtained, for the same refining energy, with this high yield Kraft pulp compared with a bleached Kraft pulp obtained by the conventional Kraft process.

[0069] Example 4

[0070] High-yield Kraft pulp made from eucalyptus and pine in the ratio 85 / 15 by weight, respectively, with a total lignin content of 7% by weight, was subjected to disintegration and refining as described in Example 1. A higher percentage of fines was also found, using the same refining energy, with this high-yield Kraft pulp compared to a bleached Kraft pulp obtained by the conventional Kraft process. Example 5

[0071] High-yield pine Kraft pulp with a total lignin content of 30 wt.% was subjected to disintegration and refining as described in Example 1. A higher percentage of fines was also obtained with this high-yield Kraft pulp than with a bleached Kraft pulp obtained by the conventional Kraft process, in line with the previous Examples.

[0072] • Papermaking suitability of microfibrillated cellulose from high-yield Kraft pulp

[0073] After the production of CMF PKAR, its papermaking suitability was assessed according to the following examples. The CMF PKAR produced was added to a high-yield Kraft pulp (PKAR) with a total lignin content of 7% by weight. However, this lignin content of the high-yield Kraft pulp to which CMF PKAR is added is not linked to the corresponding content of the PKAR pulp used to produce the CMF PKAR. Any PKAR pulp with a total lignin content of 5% to 30% by weight can be used.

[0074] Example 6 - Comparison of the papermaking suitability of microfibrillated cellulose obtained from high-yield eucalyptus Kraft pulp (CMF PKAR) incorporated into high-yield eucalyptus Kraft pulp (PKAR) in relation to the papermaking suitability of microfibrillated cellulose obtained from bleached eucalyptus Kraft pulp (CMF PKEB) incorporated into bleached eucalyptus Kraft pulp (PKEB)

[0075] High-yield eucalyptus Kraft pulp, at a consistency of 0.64% (volume / weight), was mixed with CMF PKAR at a consistency of 0.5% (weight / weight) and 35% fines, in proportions of 5 and 10% by weight.

[0076] Bleached eucalyptus kraft pulp (PKEB) with a total lignin content of less than 1% by weight at a consistency of 0.64% (volume / weight) was mixed with CMF PKEB with a consistency of 0.5% (weight / weight) and 31, 45 or 54% fines in proportions of 5 and 10% by weight.

[0077] Isotropic laboratory sheets were prepared in a benchtop sheet former. The pastes were previously refined. The CMF suspension was added to the refined paste suspension in a beaker and subjected to magnetic stirring for 120 s, after which the mixture was poured into the sheet former, following ISO 5269-1 standard for sheet formation. Results

[0078] Structural properties and mechanical strength properties of 150 g / m sheets 2 (135 g O see dry (OD) / m 2 )

[0079] Tables 2 and 3 show the comparative results of the relative increases in mechanical strength properties compared to the references of sheets produced from PKEB pulp without CMF PKEB and sheets produced from PKAR pulp without the addition of CMF PKAR. The mechanical properties were measured according to the corresponding standards: burst index (ISO 2758:2015), tear index (ISO 1974:2012, tensile index (ISO 1924-2:2008), Scott-Bond (TAPPI 403). Table 2. Increases in strength properties (%) obtained in sheets with the incorporation of 5% CMF, compared to the references (without CMF).

[0080] Table 3. Increases in resistance properties (%) obtained in sheets with incorporation of 10% CMF, relative to references (without CMF).

[0081] An increase in burst, tear and tensile indices can be observed for PKAR pulp sheets with PKAR CMF compared to the reference (PKAR pulp sheets without CMF). This increase is also greater than the increase observed for PKEB pulp sheets with PKEB CMF compared to the corresponding reference (PKEB pulp sheets without CMF). This demonstrates the effect of obtaining increased mechanical strength properties in sheets made from PKAR pulp and PKAR CMF compared to the conventional option of adding PKEB CMF to PKEB pulp.

[0082] Increases in bursting, tearing and tensile indices for PKAR pulp sheets with CMF PKAR in relation to the reference (PKAR pulp sheets without CMF) were also observed with CMF PKAR with 15% and 50% fines by weight.

[0083] Example 7 - Comparison of the papermaking suitability of microfibrillated cellulose obtained from high-yield eucalyptus Kraft pulp (CMF PKAR) or commercial microfibrillated cellulose (commercial CMF) (white) incorporated into high-yield eucalyptus Kraft pulp (PKAR)

[0084] 135 g / m sheets were prepared 2 (OD) from high-yield eucalyptus Kraft pulp at a consistency of 0.64% (volume / weight) mixed with CMF PKAR at a consistency of 0.5% (weight / weight).

[0085] The procedure for forming the leaves was the same as in the previous example. The Results

[0086] Mechanical strength properties of 150 g / m sheets 2 ( 135 gop / m 2 )

[0087] Table 4 presents the results for the mechanical strength properties of 150 g / m sheets. 2 from PKAR pulps with different proportions of CMF PKAR and 150 g / m sheets 2from PKAR paste without addition of CMF PKAR. Additionally, a comparison with the same results obtained with the addition of white commercial CMF to PKAR paste is also presented. Table 4. Increases in strength properties (%) relative to the reference (PKAR without CMF PKAR).

[0088] The incorporation of 5 and 10% by weight of CMF PKAR 35% fines increases the mechanical strength of the sheets, such as the burst index, tear index and tensile index. The increases observed for CMF PKAR are always greater than the corresponding increases with commercial CMF.

[0089] Increases in the mechanical strength of the sheets, such as bursting index, tearing index and tensile index, were also observed with CMF PKAR with 15% and 50% fines by weight.

[0090] Example 8 - Comparison of the papermaking suitability of microfibrillated cellulose obtained from high-yield eucalyptus Kraft pulp (CMF PKAR) incorporated into high-yield eucalyptus Kraft pulp (PKAR) with and without retention agent. Sheets of 135 g / m were prepared. 2 (OD) from PKAR pulp and at a consistency of 0.64% (volume / weight) mixed with CMF PKAR at a consistency of 0.5% (weight / weight). An additional series was produced with the addition of a retention agent according to the compositions shown in Table 5. The sheet formation procedure was the same as in the previous examples.

[0091] Table 5. Compositions used in the preparation of 135 g / m sheets 2 .

[0092] Table 6 shows the comparative results for the mechanical strength properties of 150 g / m sheets. 2from pulps consisting of PKAR pulp with different proportions of CMF PKAR and 150 g / m sheets 2 from PKAR paste without addition of CMF PKAR. Two series are presented, namely in the absence and presence of a retention agent (linear cationic polyacrylamide).

[0093] Table 6. Increases in strength properties (%) relative to the reference (PKAR without CMF PKAR) in the presence and absence of retention agent.

[0094] The incorporation of 5 and 10% by weight of CMF PKAR 35% fines resulted in an increase in mechanical resistance properties in relation to the reference, both in the presence and in the absence of a retention agent (always positive results in Table 4). Additionally, it was found that in the presence of the retention agent the papermaking suitability of CMF PKAR is enhanced (increase relative to the reference without CMF greater than that observed without retention agent).

[0095] Increases in mechanical strength properties compared to the reference, both in the presence and absence of a retention agent, were also observed with CMF PKAR with 15% and 50% fines by weight.

[0096] Example 9 - Comparison of the papermaking suitability of microfibrillated cellulose obtained from high-yield eucalyptus Kraft pulp (CMF PKAR) incorporated into high-yield eucalyptus Kraft pulp (PKAR) with and without cationic starch.

[0097] 135 g / m sheets were prepared 2 (OD) from PKAR paste, with incorporated cationic starch and at a consistency of 0.64% (volume / weight) mixed with CMF PKAR at a consistency of 0.5% (weight / weight) and with a retention agent according to the compositions shown in Table 6.

[0098] The sheet formation procedure was similar to that of the previous examples. Table 7. Compositions used in sheet preparation 135 g / m 2 .

[0099] 2

[0100] Sheets 135 g / m (OD) o Results Structural properties and mechanical strength properties of 150 g / m sheets 2 ( 135 gop / m 2 )

[0101] Table 8 shows the comparative results for the mechanical strength properties of 150 g / m sheets. 2 from PKAR pulps with different proportions of CMF PKAR and 150 g / m sheets 2 from PKAR paste without addition of CMF PKAR, with and without starch and with and without retention agent.

[0102] Table 8. Increases in strength properties (%) relative to the reference (PKAR without CMF), in the presence and absence of dough starch and also in the presence of the retention agent. The use of paper additives commonly used in papermaking production, such as cationic starch and retention agents, maintains the competitive advantage of using CMF PKAR to enhance mechanical properties.

[0103] The competitive advantage of using CMF PKAR for property enhancement was also observed with CMF PKAR with 15% and 50% fines by weight.

[0104] Example 10 - Comparison of the papermaking suitability of microfibrillated cellulose obtained from high-yield eucalyptus Kraft pulp (CMF PKAR), with 35 or 41% fines, added to high-yield eucalyptus Kraft pulp (PKAR). Sheets of 135 g / m were prepared. 2 (OD) from PKAR pulp, with incorporated cationic starch and at a consistency of 0.64% (volume / weight) mixed with CMF PKAR produced with a fines content of 35 or 41%, with a consistency of 0.5% (weight / weight) in the presence and absence of a retention agent.

[0105] The procedure for forming the leaves was as in the previous examples. The Results

[0106] Mechanical strength properties of 150 g / m sheets 2 ( 135 gop / m 2 )

[0107] Tables 9 and 10 compare the increases in mechanical strength properties of PKAR pulps with the incorporation of CMF PKAR with different levels of fines in relation to the properties of sheets made from high-yield pulp without the addition of CMF PKAR. Table 9. Increases in strength properties (%) relative to the reference (PKAR without CMF), in the presence of dough starch and in the absence of the retention agent, of the strength properties of sheets with the addition of 5% CMF HYKEP with 35 or 41% of fines.

[0108] Table 10. Increases in strength properties (%) relative to the reference (PKAR without CMF), in the presence of dough starch and in the presence of the retention agent, of the strength properties of sheets with the addition of 5 or 10% of CMF PKAR with 35 or 41% of fines. With retention agent

[0109] As expected , the CMF PKAR with higher fines content had a more pronounced effect on strengths , for example with a 50 % increase in burst index when compared to the reference without CMF PKAR .

Claims

CLAIMS 1. Microfibrillated cellulose production process, characterized by comprising the following steps: a) selection of a Kraft pulp with a total lignin content of 5% to 30% by weight; b) mechanical defibration of the pulp selected in step a) until obtaining a microfibrillated cellulose suspension with a minimum fines content of 15% by weight.

2. Process according to claim 1, characterized by further comprising, between the selection and defibration steps a) and b), an enzymatic hydrolysis step of the pulp selected in step a).

3. Process according to any of the preceding claims, characterized in that in step a) the pulp is selected from the group consisting of hardwood pulp, softwood pulp and mixtures thereof.

4. Process according to claim 3, characterized in that in step a) the selected paste is eucalyptus paste.

5. Microfibrillated cellulose obtained by the process claimed in any one of claims 1 to 4.

6. Microfibrillated cellulose according to claim 5, characterized by comprising a minimum fines content of 15% by weight.

7. Kraft pulp, characterized by comprising the microfibrillated cellulose claimed in either of claims 5 and 6.

8. Paper product, characterized by comprising the microfibrillated cellulose claimed in either of claims 5 and 6.

9. Paper product according to claim 8, characterized by further comprising a retaining agent.

10. Paper product according to any one of claims 8 and 9, characterized in that it is selected from the group consisting of kraftliner paper, testliner paper, corrugated cardboard paper, bag paper, shopping bag paper, flexible packaging paper, tissue paper and printing and writing paper.