Microfibrillated cellulose production process

Abstract

The present invention relates to a process for producing microfibrillated cellulose comprising the steps of selecting a Kraft pulp with a total lignin content of 5% to 30% by weight, adding water and disintegrating the pulp, followed by fibrillation until a microfibrillated cellulose suspension with a minimum fines content of 15% by weight is obtained. Other aspects of the present invention relate to microfibrillated cellulose obtained from the process and to Kraft pulp and paper products comprising the claimed microfibrillated cellulose. The process described allows the production of microfibrillated cellulose with lower energy consumption, and the microfibrillated cellulose has increased paper-making suitability, resulting in paper products with enhanced mechanical strength properties.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION

[0003] Microfibrillated Pulp Production Process

[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 resulting microfibrillated cellulose. The invention has application in the paper industry.

[0006] PREVIOUS TECHNIQUE

[0007] Microfibrillated celluloses have been attracting increasing interest for various 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).

[0008] 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).

[0009] In fact, and as shown in the documents mentioned below, the production processes of microfibrillated cellulose are carried out using conventional cellulosic raw materials, that is, delignified cellulose pulps obtained through 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, documents reporting the use of microfibrillated cellulose in the production of paper consider it according to its conventional definition with respect to the raw material and its properties that give rise to it.

[0010] Patent EP3341523B1 discloses a method for producing microfibrillated cellulose that requires fewer passes through refiners and, consequently, lower energy consumption, involving the refining, with sheets of specific dimensions, of a chemical pulp of cellulosic fibers.

[0011] Patent EP2494107B1 relates to a process for the production of microfibrillated cellulose with the aid of an extruder, in which at least one chemical (among carboxymethylcellulose, methylcellulose, polyvinyl alcohol, calcium stearate, alcohols, surfactants and surface-active agents 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 potato and cereals.

[0012] Patent application EP2196579A1 describes a method for producing microfibrillated cellulose with lower associated energy consumption, involving the passage of a cellulose pulp suspension in a solvent (such as water, alcohols, dimethyl sulfoxide, glycerol, and mixtures thereof) through an orifice of a homogenizer so that said suspension is subjected to a pressure drop. The 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 obtained by typical production processes, such as bleached, semi-bleached, and unbleached pulps, by chemical processes using sulfites and sulfates.

[0013] 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. This treatment is applied during or after the impregnation of the fiber, or during or after the cooking of the fiber, 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 typical cooking steps, for example by Kraft cooking, washing and bleaching, and further refining with enzymes or solvent, and finally, grinding of the resulting fibril. The invention describes the use of fibers from herbaceous and non-herbaceous plants and their combinations.Patent EP2576629B1 describes a method for producing microfibrillated cellulose, said to be more efficient and economical compared to the previous technique, which involves acid hydrolysis at an elevated temperature or acidification followed by washing and hydrolysis at an elevated 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 hardwood or softwood, bleached or unbleached, such as Kraft pulp, phytosulfite pulp, and soda pulp.

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

[0015] Patent application US20160273165A1 discloses a method for producing a paper product with improved strength and retention of fillers and fines, involving the addition of an anionically modified microfibrillated cellulose to a fiber suspension in an amount of 0.1 to 10% by weight.

[0016] Patent application EP3433428A4 describes a board with improved compression resistance 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 alkyl ketene dimer, succinic anhydrides, rosins and a styrene maleic anhydride, or emulsions, modifications and mixtures thereof.

[0017] Patent EP2978894B1 describes a process for producing paper and cardboard with strength properties through a fiber mixture that involves adding, in a specific sequence, microfibrillated cellulose, strength additives, and microparticles such as silica and bentonite to this fiber mixture.

[0018] One of the most widely used chemical processes industrially for the production of cellulose pulp from wood is Kraft cooking, or sulfite cooking. This chemical process consists of cooking the wood in a cooking liquor usually composed of sodium hydroxide and sodium sulfite, 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 prolong 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 production of state-of-the-art microfibrillated cellulose.

[0019] The low lignin content in starting pulps for the production of cellulose fibrils, obtained through the deligninification of wood by chemical processes and through additional bleaching steps, is necessary and, as such, a condition for the application of production methods for these cellulose fibrils that entail lower mechanical and chemical energy expenditure, as demonstrated by Chaker and co-authors who, when evaluating the suitability of pulps for fibrillation, chose an initial pulp with a lignin content of less than 20% by weight and to which they also applied an additional bleaching step after cooking, in order to further reduce the lignin content to values ​​substantially below 5%, typically below 1%, so as to decrease the influence of the presence of lignin on the fibrillation of the 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 ) .

[0020] 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 cellulose pulps delignified by typical chemical cooking processes, such as Kraft or sulfite, and / or additionally bleached, include modifications to increase their efficiency and reduce associated costs. These modifications 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 cellulose pulps.Therefore, there is a need for a microfibrillated cellulose production process that exempts its incoming 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, and 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 state-of-the-art production processes that use conventional cellulosic raw materials, i.e., 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 Kraft pulp with a total lignin content of 5% to 30% by weight; b) addition of water to the pulp selected in step a) and mechanical disintegration thereof; c) fibrillation of the pulp resulting from step b) until obtaining a microfibrillated cellulose suspension with a minimum fines content of 15% by weight.

[0023] In a preferred embodiment of the invention, the process further comprises, between steps b) and c), an enzymatic hydrolysis of the paste selected in step a).

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

[0025] In a preferred embodiment 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 embodiment 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 described microfibrillated cellulose. The present invention also relates to a paper product comprising the described microfibrillated cellulose.

[0029] In a preferred embodiment of the invention, the paper product is a corrugated cardboard (containerboard), a kraftliner, a testliner, a fluting paper, a bag paper, a shopping bag paper, a flexible packaging paper, a tissue paper, or a printing and writing paper.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] Fig. 1 shows a 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 (c) commercial microfibrillated cellulose of the prior art.

[0032] The bar indicates the 100 pm scale.

[0033] Figure 2 shows the percentage of fines (based on the total sample, weighted by length, measured on an L&W Fiber Tester 912) of microfibrillated pulps produced with 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 solid lines. DETAILED DESCRIPTION OF THE INVENTION

[0034] This document describes a process for producing microfibrillated cellulose (also referred to in this description as MFC, for simplification purposes) from a high-yield Kraft pulp, i.e., 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 allows the production of microfibrillated cellulose with lower energy consumption compared, for example, to conventional Kraft pulp (which has a low lignin content, i.e., within the scope of the present invention, a total lignin content of less than 5% by weight), and in which the resulting microfibrillated cellulose exhibits papermaking suitability that provides increased mechanical strength properties to the paper products that incorporate it, compared to conventional solutions using microfibrillated cellulose produced from conventional cellulose pulps. ,de-lignin-fixed by typical chemical cooking processes, such as Kraft or sulfites, and / or additionally bleached.

[0035] The addition of water, disintegration and sequential fibrillation of Kraft pulp with a total lignin content of 5% to 30% by weight of the process of the present invention thus allows the production of microfibrillated cellulose with increased paper suitability, with respect to the strength properties of paper products, and in which its production involves lower energy consumption.

[0036] Within the scope of the present invention, a Kraft cooking process refers to Kraft cooking or sulfite cooking. This is a well-known chemical process in the art that consists of cooking wood in a cooking liquor usually composed of sodium hydroxide and sodium sulfite, 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 process that yields a pulp production yield of about 45-55%.

[0037] In the context of the present invention, Kraft paste refers to paste obtained by cooking Kraft paper.

[0038] Within the scope of the present invention, unbleached Kraft pulp refers to a pulp produced through the conventional Kraft process, typically with a total lignin content of less than 5% by weight.

[0039] Within the scope of the present invention, bleached Kraft pulp refers to a pulp produced through the conventional Kraft process and which is further subjected to a bleaching step, with a total lignin content typically less than 1% by weight. The purpose of the bleaching step is to continue the delignification by the action of oxidizing agents, such as oxygen, chlorine dioxide and hydrogen peroxide.

[0040] Within the scope of the present invention, high-yield Kraft pulp refers to a Kraft pulp produced through a chemical Kraft cooking process with a yield exceeding 60%, and the pulp thus produced having a total lignin content of 5% to 30% by weight. Therefore, when reference is made in this description to "high-yield Kraft pulp," it is intended to refer, in simplified terms, to a Kraft pulp comprising a total lignin content of 5% to 30% by weight. Within the scope of the present invention, the cooking yield is calculated using the following formula: pulp mass / wood mass x 100

[0041] (weights on a completely dry basis)

[0042] Within the scope of the present invention, 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 modified Tappi 250 standard with the addition of borohydride for spectrophotometric measurement - Pinto P., Influence of the chemical structure of wood components on their performance in pulp production processes. Comparative study between Eucalyptus globulus and other hardwoods, Doctoral Thesis, University of Aveiro, 2005).

[0043] 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 elemental fiber containing crystalline, paracrystalline and amorphous regions, with an aspect ratio (length / diameter) greater than 10, and may contain longitudinal fibrils, interweaving between particles or network-like structures, and are produced by mechanical wood treatments and / or chemical treatments such as, for example, enzymatic treatments.

[0044] It is therefore common in the field of this technique to refer to 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, making it 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.

[0045] In the context 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 using 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 appropriate energy and time consumption. However, in current state-of-the-art industrial practice, it is common to treat the raw material until a fines level close to 50% by weight is reached (measurement performed on an L&W Fiber Tester 912, length-weighted average). Depending on the intended use of the CMF, the level of fines to be achieved may be higher or lower.

[0046] 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.

[0047] Within the scope of the present invention, microfibrillated cellulose from unbleached Kraft pulp refers to microfibrillated cellulose produced from unbleached Kraft pulp. Within the scope of the present invention, the term "disintegration" refers to the separation of the fibers (or defibration) from the pulp. This disintegration action can be carried out by mechanical means that promote the disintegration of the pulp.

[0048] Within the scope of the present invention, the term "fibrillation" refers to a mechanical treatment of fibers in an aqueous medium, aiming to partially eliminate the primary fiber wall in order to promote partial delamination of the fiber wall, increasing the specific surface area of ​​the fiber, which allows for an increase in the number of inter-fiber connections. The person skilled in the art has at their disposal various techniques and means to promote fibrillation.

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

[0050] Within the scope of the present invention, commercial microfibrillated cellulose refers to marketable samples characterized by being produced from fully delignified wood pulp, after conventional Kraft cooking (total lignin content in the cellulose fiber of the produced pulp 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.

[0051] Within the scope of the present invention, a retention agent refers to an additive added during papermaking to retain fines and mineral fillers, such as, but not limited to, a linear cationic polyacrylamide. Within the scope of the present invention, a corrugated paper (containerboard) corresponds to the paper commonly used for making cardboard (corrugated boards).

[0052] The top and bottom layers of a corrugated board are called linerboard. It is typically a two-layer product, a top layer and a bottom layer. Virgin fiber 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 recycled fibers are predominantly used, the product is referred to as testliner. The fluting between two liners is called fluting paper (or corrugated medium).

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

[0054] This paper describes a process for producing microfibrillated cellulose from a high-yield Kraft pulp, 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 invention process 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 resulting microfibrillated cellulose exhibits papermaking suitability that provides increased mechanical strength properties to the paper products that incorporate it, compared to conventional solutions using microfibrillated celluloses produced from conventional cellulose pulps (i.e., delignified by typical chemical cooking processes, such as Kraft or sulfites, and / or bleached).

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

[0057] The process described here comprises the selection of a high-yield Kraft pulp, the addition of water, mechanical disintegration of the pulp, followed by its fibrillation until a microfibrillated cellulose suspension is obtained with a minimum fines content of 15% by weight.

[0058] The process may also include, before the fibrillation step, an enzymatic hydrolysis of the selected paste.

[0059] It was surprisingly found that the addition of water, the disintegration of the pulp, and its fibrillation contribute to the production of microfibrillated cellulose with increased paper-making suitability involving lower energy consumption. In principle, for reasons of simplicity, the addition of water at room temperature is preferred, although no influence of water temperature on the results was detected. Examples

[0060] • Process for preparing microfibrillated cellulose from high-yield eucalyptus Kraft pulp (CMF PKAR)

[0061] Example 1

[0062] A high-yield eucalyptus Kraft pulp with a total lignin content of 8% was selected.

[0063] Room temperature water was added to the selected paste until a consistency of 3% (mass / volume) was achieved, and in a conical refiner, the resulting paste was disintegrated with the following disintegration parameters: rotation speed 1230 rpm, edge length 0.574 km / s, power 0.918 kW, SEL (specific energy load applied by the edge of the bars) 1.6 Ws / m and specific energy 350 kWh / ton.

[0064] The resulting product was further fibrillated through a two-stage refining process in a disc refiner. The first stage was carried out with the following refining parameters: rotation speed 700 rpm, edge length 39.48 km / s, power 5.076 kW, SEL 0.15 Wm / s and specific energy 200 kWh / ton. The second stage 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. Fibrillation was conducted until a minimum fines content of 15% by weight was reached (length-weighted average, based on the total sample and determined on an L&W Fiber Tester 912).

[0065] Figure 1 presents the microscopic analysis of the obtained microfibrillated cellulose suspensions. It was possible to verify the fibrillation obtained after mechanical treatment and the heterogeneity of sizes within the same sample. In this sense, the samples were analyzed in an L&W Fiber Tester 912 instrument to determine the particle sizes. Table 1 presents 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 the samples dissolved in cupriethylenediamine solutions, according to ISO 5351:2010.

[0066] Table 1. Characterization (dimensions and degree of polymerization) of 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.

[0067] Figure 2 represents the percentage of fines (based on the total sample, weighted by length, measured on an L&W Fiber Tester 912) of microfibrillated cellulose produced with different refining energies. 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 bleached pulp (with a total lignin content of less than 1%), typically used in the previous technique. Thus, it was demonstrated that with the high-yield pulp, a lower amount of energy was required to produce the same quantity of fines.

[0068] Example 2

[0069] High-yield eucalyptus Kraft pulp, with a total lignin content of 5% by weight, was subjected to the addition of water, disintegration, and fibrillation as described in Example 1. The results obtained 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.

[0070] Example 3

[0071] High-yield eucalyptus Kraft pulp, with a total lignin content of 10% by weight, was subjected to the addition of water, disintegrated, and fibrillated 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 to a bleached Kraft pulp obtained by the conventional Kraft process.

[0072] Example 4

[0073] High-yield Kraft pulp made from eucalyptus and pine in a ratio of 85 / 15 by weight, respectively, with a total lignin content of 7% by weight, was subjected to the addition of water, disintegration, and fibrillation as described in Example 1. A higher percentage of fines was also observed, using the same refining energy, with this high-yield Kraft pulp compared to a bleached Kraft pulp obtained by the conventional Kraft process.

[0074] Example 5

[0075] High-yield pine Kraft pulp, with a total lignin content of 30% by weight, was subjected to the addition of water, disintegration, and fibrillation 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.

[0076] • Suitability for papermaking of microfibrillated cellulose from high-yield Kraft pulp

[0077] After the production of CMF PKAR, its papermaking suitability was assessed according to the following examples. The produced CMF PKAR 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 the CMF PKAR is added is not linked to the corresponding content of the PKAR pulp used for the production of the CMF PKAR. Any PKAR pulp with a total lignin content of 5% to 30% by weight can be used. 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)

[0078] 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.

[0079] 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 at a consistency of 0.5% (weight / weight) and 31, 45 or 54% fines, in proportions of 5 and 10% by weight.

[0080] Laboratory isotropic sheets were prepared in a benchtop sheet former. For this purpose, 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 the ISO 5269-1 standard for sheet formation. Results

[0081] Structural properties and mechanical strength properties of 150 g / m² sheets. 2 (135 dry(op) / m 2 )

[0082] Tables 2 and 3 show the comparative results of the relative increases in mechanical strength properties in relation to the reference values ​​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: bursting index (ISO 2758:2015), tear index (ISO 1974:2012), tensile index (ISO 1924-2:2008), Scott-Bond.

[0083] (TAPPI 403) .

[0084] Table 2. Increases in strength properties (%) obtained in sheets with 5% CMF incorporation, relative to the references (without CMF).

[0085] Table 3. Increases in strength properties (%) obtained in sheets with 10% CMF incorporation, relative to the references (without CMF). It is possible to verify an increase in bursting, tearing, and tensile strength indices for PKAR pulp sheets with CMF PKAR compared to the reference (PKAR pulp sheets without CMF). This increase is also greater than the increase observed for PKEB pulp sheets with CMF PKEB compared to the corresponding reference (PKEB pulp sheets without CMF).

[0086] This shows the effect of obtaining increased mechanical strength properties in sheets made of PKAR and CMF PKAR paste compared to the conventional option of adding CMF PKEB to PKEB paste.

[0087] Increased bursting, tearing, and tensile strength indices for PKAR pulp sheets with CMF PKAR compared to the reference (PKAR pulp sheets without CMF) were also observed with CMF PKAR containing 15% and 50% fines by weight.

[0088] 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)

[0089] Sheets weighing 135 g / m² were prepared. 2 (OD) from high-yield eucalyptus Kraft pulp and at a consistency of 0.64% (volume / weight) mixed with CMF PKAR at a consistency of 0.5% (weight / weight).

[0090] The procedure for forming the leaves was the same as in the previous example. Results

[0091] Mechanical strength properties of 150 g / m² sheets 2( 135 gop / m 2 )

[0092] Table 4 presents the results for the mechanical strength properties of 150 g / m² sheets. 2 from PKAR folders with different proportions of CMF PKAR and 150 g / m² sheets 2 Starting from PKAR paste without the addition of CMF PKAR. Additionally, a comparison is also presented with the same results obtained with the addition of commercial white CMF to the PKAR paste.

[0093] Table 4. Increases in strength properties (%) relative to the reference (PKAR without CMF PKAR).

[0094] The incorporation of 5 and 10% by weight of CMF PKAR 35% fines increases the mechanical resistance of the sheets, such as the bursting index, tearing index and tensile index. The increases observed for CMF PKAR are always greater than the corresponding increases with commercial CMF.

[0095] Increases in the mechanical resistance of the sheets, such as the bursting index, tear index, and tensile index, were also observed with CMF PKAR with 15% and 50% fines by weight. 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 a retaining agent.

[0096] Sheets weighing 135 g / m² were prepared. 2 (OD) from PKAR paste 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 retaining agent according to the compositions presented in Table 5.

[0097] The procedure for forming the leaves was the same as in the previous examples.

[0098] Table 5. Compositions used in the preparation of 135 g / m² sheets. 2 .

[0099] Table 6 shows the comparative results for the mechanical strength properties of 150 g / m² sheets. 2 from folders made up of PKAR pulp with different proportions of CMF PKAR and 150 g / m² sheets. 2 from PKAR paste without the addition of CMF PKAR. Two series are presented, namely in the absence and presence of a retaining agent (linear cationic polyacrylamide). Table 6. Increases in strength properties (%) relative to the reference (PKAR without CMF PKAR) in the presence and absence of a retaining agent.

[0100] The incorporation of 5 and 10% by weight of CMF PKAR 35% fines resulted in an increase in mechanical strength properties compared to the reference, both in the presence and absence of a retaining agent (results always positive in Table 4). Additionally, it was found that in the presence of the retaining agent, the papermaking suitability of CMF PKAR is enhanced (relative increase compared to the reference without CMF greater than that observed without a retaining agent).

[0101] 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. 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.

[0102] Sheets weighing 135 g / m² 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 retaining agent according to the compositions presented in Table 6.

[0103] The leaf formation procedure was similar to that of the previous examples.

[0104] Table 7. Compositions used in the preparation of 135 g / m² sheets. 2 .

[0105] 2

[0106] Sheets 135 g / m² (OD) Results

[0107] Structural properties and mechanical strength properties of 150 g / m² sheets. 2 ( 135 gop / m 2 )

[0108] Table 8 shows the comparative results for the mechanical strength properties of 150 g / m² sheets. 2 from PKAR folders with different proportions of CMF PKAR and 150 g / m² sheets 2from PKAR paste without added CMF PKAR, with and without starch, and with and without a retaining agent.

[0109] 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 retaining agent.

[0110] The use of paper additives commonly used in the production of paper material, such as cationic starch and retention agents, maintains the competitive advantage of using CMF PKAR to enhance mechanical properties.

[0111] The competitive advantage of using CMF PKAR to enhance properties was also observed with CMF PKAR containing 15% and 50% fines by weight.

[0112] 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)

[0113] Sheets weighing 135 g / m² were prepared. 2 (OD) from PKAR paste, with incorporated cationic starch and 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 retaining agent. The sheet formation procedure was in accordance with those of the previous examples. Results

[0114] Mechanical strength properties of 150 g / m² sheets 2 ( 135 gop / m 2 )

[0115] Tables 9 and 10 compare the increases in mechanical strength properties of PKAR pulps incorporating 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.

[0116] Table 9. Increases in strength properties (%) relative to the reference (PKAR without CMF), in the presence of mass starch and in the absence of the retaining agent, of the strength properties of the leaves with the addition of 5% CMF HYKEP with 35 or 41% fines.

[0117] Table 10. Increases in strength properties (%) relative to the reference (PKAR without CMF), in the presence of mass starch and in the presence of the retaining agent, of the strength properties of the leaves with the addition of 5 or 10% CMF PKAR with 35 or 41% fines.

[0118] As expected, the CMF PKAR with a higher fines content had a more pronounced effect on resistance, for example with a 50% increase in the bursting 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) addition of water to the pulp selected in step a) and mechanical disintegration thereof; c) fibrillation of the pulp resulting from step b) 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 steps b) and c), an enzymatic hydrolysis step of the paste selected in step a).

3. A 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.

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