Mechanical and chemical treatment process of cellulosic fibers in a mixer

Abstract

The present invention relates to a method for the mechanical and chemical treatment of cellulosic fibers in aqueous suspension in a mixer (1) comprising a body (10) defining a mixing chamber (11) whose wall forms a fixed compression surface (12), and at least one mixing shaft (20) positioned within the mixing chamber (11) and comprising a rotatable shaft (21), and a plurality of mixing elements (22) fixed to the shaft (21), projecting radially from the shaft, and each provided with a rotatable compression surface (23). In said method, the compression surfaces (23) of the mixing elements (22) face the compression surface (12) of the mixing chamber (11), so as to define between them compression zones (CZ) of the fiber suspension (2) circulating between the body (10) and the mixing shaft (20).The compression surfaces (23) of the mixing elements (22) have a compression profile whose radius with respect to the shaft (21) varies according to the angular position of said shaft, so as to compress the fiber suspension (2) in said compression zones (CZ) during the rotation of said mixing shaft (20).

Description

Title of the invention: Mechanical and chemical treatment process for cellulosic fibers in a mixer Technical field of the invention

[0001] The present invention relates to a mechanical and chemical treatment process for cellulosic fibers in aqueous suspension, in particular to increase the binding potential of the fibers used in the composition of paper, the generic term "paper" covering paper, paperboard, cardboard and molded cellulose. Prior state of the art

[0002] Fiber refining is one of the most important processing steps in the pulp and paper industry. This operation is the key process for adjusting the paper's strength and quality, such as its mechanical, optical, and printability properties. Depending on the level of refining, the range of paper types varies from blotting paper (unrefined) to tracing papers requiring intensive refining. When the pulp is enriched with mineral fillers, refining also improves the retention rate of these fillers in the paper and compensates for the reductions in mechanical properties caused by the fillers, such as tensile strength and / or tear resistance. Refining is therefore an essential operation.

[0003] Paper pulp, also called "pulp," is in the form of a suspension of cellulosic fibers dispersed in water. It is generally introduced into the air gap of a rotating machine such as a refiner. The air gap is the space between two opposing grooved surfaces arranged on disks or cones in relative motion. The speed differential at the periphery between the rotor (rotating part) and the stator (stationary part) is generally on the order of 20 to 25 m / s, and generates a shearing phenomenon. When the paper pulp passes through the air gap, which is approximately 100 µm to 300 µm (compared to the fiber dimensions of approximately 1 to 3 mm in length and 15 to 40 µm in diameter), the fibers are subjected to a succession of compressive and shearing forces, which induce morphological changes in their ultrastructure.Three primary effects are generally associated with these morphological transformations: hydration, fibrillation, and cutting.

[0004] The compressive forces will compress the fibers, having the technical effect of hydrating the fibers, delaminating their cell walls, softening them, and making them more flexible. The increase in fiber flexibility has the advantage of significantly increasing the bonding surface area between the fibers, which is beneficial for the final product. later for the formation of the paper sheet and its mechanical properties.

[0005] Shear forces will generate surface fibrillation by tearing pieces from the outer part of the fiber wall. They will also generate fiber cutting, as well as the tearing of surface fibrils, which will increase the fine particle content of the paper pulp.

[0006] However, the presence of fine cellulosic particles in the paper pulp is detrimental to the subsequent paper sheet formation process. They clog the screens and impair the pulp's drainage, leading to an increase in the energy required to create the vacuum under the screen, a limitation in the speed of the paper production machines, thus reducing productivity, and an increase in steam consumption during drying, resulting in a significant increase in the energy consumption required for paper drying. Furthermore, the fine particles recovered in the process water, when not recycled, generate non-recoverable waste.

[0007] US documents 4,614,304, DE 102 56 856 and DE 102 36 962 describe methods of mechanical treatment of cellulosic fibers.

[0008] The chemical modification of cellulosic fibers also represents a challenge, particularly in the field of paper manufacturing, as this modification can improve the properties of the paper. Description of the invention

[0009] The present invention aims to overcome these drawbacks (clogging of the screens, impaired drainage, increased energy associated with vacuum generation, limited speed of production machines, reduced yield, increased steam consumption and therefore increased energy required for paper drying, non-recycled fine particles, non-recoverable waste) by proposing an alternative fiber treatment process (advantageously for cellulosic fibers) that does not generate shearing, or at least so little as to be negligible, thus reducing or even eliminating the generation of fine particles and cut fibers. The invention also aims to provide such a process that is less energy-intensive, while improving the properties of the fibers and therefore intrinsically the properties of the paper, and even enabling the development of new papers.The process according to the invention makes it possible to increase the bonding potential of the fibers, but also the mechanical properties of a sheet of paper.

[0010] More specifically, for a given mechanical resistance of a sheet of paper, the present invention makes it possible to refine the cellulosic fiber, limiting, or even avoiding, the alteration of the drainability properties (°SR).

[0011] To this end, the invention relates to a mechanical and chemical treatment process of cellulosic fibers by mechanical compression and chemical modification of cellulosic fibers, the process comprising the following steps: a) in a mixer, (1) mechanical compression and chemical modification of cellulosic fibers (2), in aqueous suspension having a concentration of between 5 and 20% by weight of cellulosic fibers, in the presence of a chemical reagent to produce an aqueous composition of cellulosic fibers having chemically modified functional groups, the mixer comprising: - a body defining a mixing chamber delimited by a wall forming a fixed compression surface suitable for contacting the fiber suspension, - at least one mixing axis positioned within the mixing chamber and comprising: * a rotating movable shaft, * a plurality of mixing elements (or paddles) fixed on the shaft, projecting radially from the shaft, and each provided with a rotating movable compression surface capable of coming into contact with the fiber suspension, the mixing elements having a helical or eccentric compression profile, a process in which the compression surfaces of the mixing elements face the compression surface of the mixing chamber, so as to define, between said respective compression surfaces of the mixing elements and the mixing chamber, compression zones of the fiber suspension circulating between the body and the mixing shaft, and in which the compression surfaces of the mixing elements have a compression profile whose radius relative to the shaft varies according to the angular position of said shaft, so as to compress the fiber suspension in said compression zones during the rotation of said mixing axis (in other words, the compression profile, at a defined point of the mixing chamber, varies during each complete rotation of the mixing element), - the process exhibiting a velocity differential between at least one mixing axis and the mixing chamber of less than or equal to 15 m / s, - the mixer having a minimum distance separating at least one mixing axis from the mixing chamber of between 0.1 mm and 1 mm, - the aqueous suspension of cellulosic fibers has a residence time in the mixer of between 15 seconds and 15 minutes, b) optionally, at the mixer outlet, aging of the chemically modified cellulosic fiber suspension.

[0012] As already mentioned, the process makes it possible to reduce, or even eliminate, the generation of fine particles and cut fibers. Thus, the chemical modification taking place in the mixer is optimized insofar as the chemical reagent is not consumed by the fine elements.

[0013] Typically, the chemical modification of the cellulosic fibers results from a chemical reaction on the cellulosic fibers within the mixer during step a). This chemical reaction is advantageously chosen from oxidation, bleaching, carboxymethylation and reduction.

[0014] The helical blades are advantageously oriented at 45° to each other.

[0015] According to a particular embodiment, the mixing elements are configured so as to provide an increasing compression profile in the mixer.

[0016] Advantageously, the mixer comprises at least two mixing axes positioned in the mixing chamber, parallel to each other, the compression surfaces of the mixing elements of said mixing axes facing each other, so as to define between them additional compression zones of the fiber suspension circulating between the mixing axes.

[0017] The mixer can be easily integrated into a continuous process, for example between the pulper and the papermaking machine, after a pulp thickening step (aqueous suspension of cellulosic fibers). The presence of a thickening step is particularly suitable for processes using recycled cellulosic fiber pulp; in this case, a thickener can 1) separate the water from the pulp preparation circuit from the water from the papermaking machine and 2) feed the mixer.

[0018] Advantageously, the mixing chamber comprises at least an inlet zone, a mixing zone and an outlet zone, - the fiber suspension being introduced into the entry zone and extracted from the exit zone, - each mixing shaft comprising at least one worm screw fixed to the shaft, disposed in the inlet zone and arranged to move the fiber suspension from the inlet zone to the outlet zone through the mixing zone, - said plurality of mixing elements being arranged in the mixing zone and the exit zone being or not integrated into the mixing zone.

[0019] Advantageously, the mixing zone comprises several successive mixing sectors, - the mixing elements of each mixing axis being distributed in series, one series corresponding to one mixing sector, - the mixing elements of the same series being identical, and the mixing elements of one series to another being different in their shape and / or their thickness and / or their radius and / or their compression profile (the compression profile including the orientation of the mixing element with respect to the axis).

[0020] Advantageously, the mixing elements are made of flat or complex parts, which have a cross-section selected from the group comprising an ovoid cross-section with one lobe, an oblong cross-section with two lobes, a triangular cross-section with three lobes, a polygonal cross-section with a number of lobes corresponding to the number of angles, and a helical or eccentric compression profile. The lobe(s) may have a flattened end.

[0021] Even if the conditions of use of the mixer make it possible to limit, or even eliminate, the shearing effects of the cellulosic fibers, the helical profile and the eccentric profile are even less shearing than the flat profile and the notched profile.

[0022] Advantageously, the minimum distance between the mixing shaft(s) and the mixing chamber is between 0.1 mm and 0.6 mm, preferably between 0.15 mm and 0.6 mm, and in particular between 0.3 mm and 0.6 mm or between 0.3 mm and 0.5 mm. This minimum distance may, in particular, be between 0.15 mm and 0.4 mm. Beyond 1 mm, the mixer does not allow the cellulosic fibers to become more flexible, which is the desired effect in order to improve the properties of the cellulosic fibers.

[0023] Advantageously, the minimum distance separating two mixing axes is identical to the minimum distance separating the mixing axis(es) from the mixing enclosure.

[0024] Advantageously, when the mixer comprises at least two mixing axes positioned in the mixing chamber, the mixing axes are co-rotating, in that they rotate in the same direction of rotation.

[0025] Advantageously, when the mixer comprises at least two mixing shafts positioned in the mixing chamber, the mixing elements of two mixing shafts whose compression surfaces face each other have an identical compression profile.

[0026] The velocity differential between the periphery of the paddles (mixing elements) and the mixing chamber is less than or equal to 15 m / s. This differential can be at least 0.1 m / s, for example at least 2 m / s, particularly between 0.1 and 15 m / s. It can notably be between 0.5 and 10 m / s, particularly between 0.5 and 5 m / s, advantageously between 0.5 and 1.5 m / s. Above 15 m / s, the cellulosic fibers undergo significant shearing and are therefore shortened.

[0027] The residence time of the fiber suspension in the mixer is between 15 seconds and 15 minutes, for example between 15 seconds and 10 minutes, preferably between 15 seconds and 6 minutes, preferably between 15 seconds and 5 minutes, and more between 15 seconds and 3 minutes.

[0028] Advantageously, the residence time of the fiber suspension in the mixer and the velocity differential between the mixing shaft(s) and the chamber of Mixing allows a number of compressions of at least 500, advantageously between 500 and 5000, more advantageously between 3000 and 5000.

[0029] Advantageously, the aqueous suspension of cellulosic fibers comprises a mixture of cellulosic fibers and water, and optionally mineral fillers. During mechanical and chemical processing, the proportion of dry cellulosic fibers is between 5 and 20% by weight, advantageously between 5 and 15% by weight, and preferably between 8 and 15% by weight of the aqueous suspension. During mechanical and chemical processing, a concentration exceeding 20% ​​by weight, for example between 25 and 45% by weight, damages the cellulosic fibers and does not improve their mechanical properties, such as flexibility, which increases the bonding surface area (binding effect). Indeed, above 20% by weight, the cellulosic fibers tend to shorten and become kink-shaped and curled.Below 5% by weight, the aqueous suspension of cellulosic fibers undergoes a phase separation phenomenon in the mixer, which prevents homogeneous processing in particular.

[0030] Advantageously, the process according to the invention further comprises, prior to the mechanical and chemical treatment of the aqueous suspension of cellulosic fibers, a step of thickening said aqueous suspension of cellulosic fibers to form a paste. When necessary, this step allows the concentration of the aqueous suspension of cellulosic fibers to be increased, between 8 and 45% by dry weight of cellulosic fibers to feed the mixer, with a dilution of between 8 and 15% at the mixer inlet if the paste is highly concentrated.

[0031] In addition to the significant reduction of fine elements in the suspension during treatment, the treatment process of the invention has the advantage of minimizing waste, reducing production costs, improving the life cycle of paper, and entering into a virtuous circle favorable to the environment.

[0032] Furthermore, since the fibers are compressed by kneading, and not refined by shearing, the long softwood fibers are cut less frequently thanks to the process of the invention. Thus, to adjust tear resistance in particular, it becomes possible to reduce the proportion of softwood in the hardwood / softwood mixture intended to form the paper sheet. This results in savings on the cost of raw materials.

[0033] Another advantage of the process of the invention is that it leads to an improvement in paper recycling, insofar as the latter contains fewer fine elements, generally eliminated by the recycling process (flotation, washing in particular), further promoting the life cycle of paper. Figures

[0034] The present invention and its advantages will become more apparent from the following description of several embodiments given by way of non-limiting examples, with reference to the figures.

[0035] [Fig. 1] The [Fig. 1] is a plan view representing a mixer inserted between a pulper and a papermaking machine.

[0036] [Fig.2] The [Fig.2] is a radial section of the mixer of the [Fig.1].

[0037] [Fig.3] Fig.3 is a perspective view of two mixing axes of the mixer of the [Fig.2], equipped with shearing flat profile pallets.

[0038] [Fig.4] Fig.4 is a perspective view of another embodiment of mixing axes of [Fig.3], equipped with shear flat profile paddles.

[0039] [Fig.5] The [Fig.5] illustrates two mixing axes having a helical profile, minimizing shear.

[0040] [Fig.6] The [Fig.6] illustrates two mixing axes having a 90° flat paddle profile maximizing shear.

[0041] [Fig.7] Fig.7 illustrates two mixing axes having a paddle profile ex centrics mounted at 45°, reducing shear.

[0042] [Fig.8] Fig.8 illustrates two mixing axes having an eccentric paddle profile mounted at 90°, reducing shear.

[0043] [Fig.9] Fig.9 illustrates two pallets having a helical profile.

[0044] [Fig. 10] The [Fig. 10] illustrates two pallets having a flat profile.

[0045] [Fig. 11] The [Fig. 11] illustrates a palette having an eccentric profile.

[0046] [Fig. 12] Figure 12 shows the improvement in the mechanical properties of a sheet of paper (bursting index) depending on the additive used and the density of the paper.

[0047] Figures 1 to 11 reproduce the following nomenclature: 1: Mixer 2: Fiber Suspension 3: Pulper 4: Papermaking machine 5: Sheet of paper 10: Body 11: Mixing chamber 12: Compression surface (fixed) 13: Entrance opening 14: Exit hole 15 and 16: Inlet ports for injecting products, for example chemical reagents 20: Mixing axis 20': Mixing axis ([Fig.4]) 21: Tree 22: Mixing elements 22': Mixing elements ([Fig.4]) 23: Compression surface (mobile) 24: Lobes 24': Lobes ([Fig.4]) 25: Worm screw X: Axis of rotation ZC: Compression zones DM: Minimum distance ZE: Inlet zone ZM: Mixing zone ZS: Outlet zone

[0048] Although figures 1 to 8 show two mixing axes, the description of these figures can be generalized to mixers having a single mixing axis or more than two. Detailed description of the invention

[0049] Mechanical compression and chemical modification applied to cellulosic fibers

[0050] The process according to the invention relates to a method for the mechanical treatment and chemical modification of cellulosic fibers by mechanical compression and chemical modification of an aqueous suspension of cellulosic fibers. The invention corresponds to an intensification of the process, the chemical modification being carried out simultaneously with the mechanical compression, while controlling the shear thanks to the specific profile of the mixing elements.

[0051] Step a)

[0052] This process includes the mechanical compression and chemical modification, in a mixer, of cellulosic fibers, in aqueous suspension having a concentration of between 5 and 20% by weight of cellulosic fibers, in the presence of a chemical reagent to produce an aqueous composition of chemically modified cellulosic fibers.

[0053] In particular embodiments, the aqueous suspension of cellulosic fibers is free of hemicellulose.

[0054] Advantageously, the chemical modification of the cellulosic fibers results from a chemical reaction on the cellulosic fibers within the mixer during step a). This chemical reaction is advantageously chosen from oxidation, the Bleaching, carboxymethylation and reduction. Preferably it is an oxidation reaction.

[0055] Examples of chemical reagents include, but are not limited to, periodic acid or one of its salts, metaperiodic acid or one of its salts, 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO), azaadamantane-N-oxyl (AZADO), hydrogen peroxide, ozone, chloroacetic acid, a hypohalogenite or a hydrosulfite salt (sodium hydrosulfite, sodium bisulfite).

[0056] When the chemical reagent is TEMPO, the chemical reaction is advantageously carried out in the presence of sodium hypochlorite (NaClO) and sodium bromide (NaBr) under alkaline conditions or of sodium hypochlorite (NaClO) and sodium chlorite (NaClO2) under neutral conditions.

[0057] Preferably, the chemical reaction in step a) is an oxidation reaction, in particular a selective oxidation of the primary and secondary alcohol groups of the anhydroglucose units (AGU) of cellulose.

[0058] In this case (oxidation), the reagent is advantageously periodic acid or one of its salts, in particular sodium periodate. In these embodiments, the oxidized cellulose obtained has aldehyde functional groups.

[0059] During step a), the chemical reagent / cellulosic fiber molar ratio is advantageously between 0.1 and 1, more advantageously between 0.3 and 0.8, particularly when the chemical reagent is periodic acid or one of its salts.

[0060] With a ratio of 1, the number of moles of cellulosic fibers corresponds to the number of moles of anhydroglucose.

[0061] Thus, preferably, the oxidant / AGU molar ratio varies from 0.1 to 1, advantageously from 0.3 to 0.8. A ratio equal to 1 means one mole of reagent for 1 mole of AGU.

[0062] The chemical reaction is carried out in the mixer at a temperature advantageously between 15 and 100 °C, preferably 20 to 80 °C and even more preferably 40 to 70 °C, more advantageously 50 to 60 °C.

[0063] The chemical reagent of step a) can be added pure (in solid, liquid or gaseous form), or in solution (diluted in a solvent, preferably in water).

[0064] When the chemical reagent is added in the form of a solution, the solvent used is typically one chosen to solubilize the reagent. A person skilled in the art, based on their knowledge, will be able to select a suitable solvent. Advantageously, this is water.

[0065] The chemical reagent from step a), pure or in solution, and the cellulose fiber suspension can be introduced into the mixer separately or pre-mixed. Preferably, they are added separately.

[0066] Advantageously, the cellulose fiber suspension is diluted with the solution of reagent.

[0067] When the reagent is an oxidant, in particular a periodate salt, it is advantageously used in solution, preferably in concentrated solution.

[0068] When the chemical reagent is used in solution, it is advantageously diluted in water, preferably to obtain a concentrated solution of the chemical reagent, preferably at the limit of its solubility. In this case, the chemical reagent solution can be heated to dissolve the chemical reagent, for example, up to 100 °C, preferably between 20 and 80 °C, and even more preferably from 40 to 70 °C, more advantageously from 50 to 60 °C. A person skilled in the art will know how to adjust the temperature according to the nature of the chemical reagent, for example, up to 70 °C for periodate salts.

[0069] By “concentrated solution” is meant a solution at the limit of the solubility threshold of the chemical reagent in the solvent used, advantageously water.

[0070] According to a preferred embodiment, the chemical reagent is diluted in water, then mixed with the cellulosic fibers when they are introduced into the mixer.

[0071] The use of a chemical reagent solution in water allows the cellulosic fiber suspension to be diluted within the mixer. However, after dilution with the concentrated periodate solution, the cellulosic fiber concentration is, as already indicated, between 5 and 20% by weight in the mixer. For example, an aqueous suspension comprising 30 to 50% by weight, advantageously 35 to 40% by weight, of cellulosic fibers can be introduced into the mixer and diluted with a chemical reagent solution to achieve a concentration between 5 and 20% by weight, which corresponds to the concentration during mechanical and chemical treatment.

[0072] In some embodiments, the reagent is added continuously.

[0073] According to a preferred embodiment, the reagent is introduced into the mixer continuously immediately after or simultaneously with the cellulosic fibers. Those skilled in the art will know how to adjust the addition of the chemical reagent according to the residence time of the cellulosic fibers in the mixer.

[0074] Advantageously, the chemical reagent of step a) has a residence time in the mixer of between 15 seconds and 15 minutes. It is generally identical to the residence time of the aqueous suspension of cellulosic fibers.

[0075] The fiber / reagent mixture is left in the mixer to react for a period of 15 seconds to 15 minutes, more advantageously from 15 seconds to 6 minutes, even more advantageously from 15 seconds to 2 minutes.

[0076] Step b)

[0077] Optionally, once removed from the mixer, the cellulose fibers are left in an aging tank, advantageously for up to 72 hours. This aging time may improve the reaction yield of the step has).

[0078] Aging after step a) is advantageously carried out at a temperature ranging from 15 to 60 °C, more advantageously from 20 to 45 °C.

[0079] During step a) and / or aging, the cellulose fibers can swell by trapping water molecules.

[0080] After step b) of aging, the chemical reagent that has not reacted with the cellulosic fibers is advantageously separated from the reaction medium and recovered for possible reuse in the treatment process. For example, when the chemical reagent is a periodate salt, it can be recycled according to the process described in document NL 2030671.

[0081] The suspension from step b) comprises water and the modified cellulosic fibers. It is advantageously washed. It can also be concentrated, advantageously after washing. Washing facilitates the recycling of unused chemical reagents. The recycled chemical reagents can be reintroduced into the mixer at step a). The present invention therefore makes it possible to optimize the various chemical compounds used.

[0082] Conventionally, the washing step is typically carried out in a medium containing a solvent and / or water. In particular, the solvent is preferably water.

[0083] When cellulosic fibers are selectively oxidized, for example with a periodate salt, the modified functional groups are aldehyde functions (-CHO).

[0084] Remarkably compared to the prior art, the process according to the invention makes it possible to obtain a concentration of aldehyde functions (-CHO) of the oxidized cellulose of between 0.5 and 5 mmol / g of fibers, preferably between 1 and 4 mmol / g and even more preferably between 1.5 and 4 mmol / g.

[0085] These functions can be used for grafting molecules of interest, thus enabling the functionalization of cellulose.

[0086] In addition, these aldehyde functions can typically be converted into carboxylic acid functions by post-reaction in a second oxidation reaction.

[0087] Thus, the process can include, after the aging step b), a washing step and an optional post-chemical reaction step.

[0088] Advantageously, the chemical post-reaction is chosen from oxidation, reduction, sulfonation and amination.

[0089] In embodiments, after the post-chemical reaction step, in particular oxidation or sulfonation, the aqueous suspension of cellulosic fibers may be in the form of a gel.

[0090] Advantageously, in the case of an oxidation post-reaction, the oxidant used is chosen from hydrogen peroxide, ozone, a hypohalogenite such as hypochlorite (CIO₃), chlorite (C1O₂) or a hyposulfite salt.

[0091] These carboxylic acid functions can also be functionalized, so as to generate for example ester or amide functions.

[0092] The carboxylic acid functions can be present in acid form (-COOH) or in salt form (-COOX with X = alkali or alkaline earth metal or an ammonium).

[0093] In some embodiments, the cellulose is oxidized to directly obtain carboxylic acid functions in a single step in the mixer.

[0094] In this case, the alcohol groups of cellulose are converted directly into carboxylic acid groups, i.e. without intermediate transformation of the alcohol groups into aldehydes.

[0095] In these particular cases, the reagent used is a classic oxidant known to a person skilled in the art such as hydrogen peroxide, ozone, a hypohalogenite such as hypochlorite or a hyposulfite salt.

[0096] Advantageously, when the post-reaction is a sulfonation reaction, the reagent used is typically a bisulfite salt allowing the preparation of a modified cellulose having anionic sulfonate functions.

[0097] Uses

[0098] The invention also relates to the use of mechanically and chemically modified fibers to prepare paper pulp.

[0099] The resulting pulp can be used alone or mixed with paper pulp to form a sheet of paper.

[0100] The mechanical and chemical modification of the fibers alters their properties. Thus, the modified fibers exhibit an electrostatic charge that can vary from 0.5 to 5 meq / g, preferably from 1.0 to 4 meq / g.

[0101] These high electrostatic charge values ​​result from the intensification of the process (combination of the intimate mechanical mixing of the mixer and the chemical reaction with very efficient mixing of the products, in particular in the wall of the fibers) of the mechanical and chemical modification process which allows the increase of the charge density on the cellulose fibers.

[0102] The invention also relates to the use of modified cellulose (for example, anionic) as an additive in papermaking. In this case, preferably, 5 to 25% by weight of modified cellulose is added to an aqueous suspension of cellulose fibers (thick pulp and / or diluted paste), advantageously 10 to 25% by weight relative to the weight of the aqueous suspension of cellulose fibers. The amount of modified cellulose can be adjusted according to the desired improvement (gain) in mechanical properties.

[0103] Mixer

[0104] In the illustrated embodiments, identical elements or parts bear the same reference numbers. Furthermore, terms with a relative meaning, such as vertical, horizontal, right, left, front, back, above, below, etc., should be interpreted under normal conditions of use of the invention, as shown in the figures. The X, Y, and Z axes are defined by an orthonormal coordinate system illustrated in [Fig. 1]. Moreover, the geometric positions indicated in the description and claims, such as "perpendicular," "parallel," and "symmetric," are not limited to the strict geometric sense but extend to geometric positions that are close, i.e., that allow a certain tolerance within the technical field considered, without affecting the result obtained.This tolerance is notably introduced by the adverb "sensible", without this term necessarily being repeated before each adjective.

[0105] The mechanical treatment process according to the invention is applicable to any aqueous suspension of fibers, preferably cellulosic fibers for the paper industry, covering paper, paperboard, cardboard, and molded cellulose. The suspension may comprise a mixture of cellulosic fibers and water, and optionally mineral fillers, depending on the specifications. The proportion of dry cellulosic fibers may be significant, for example, between 5 and 20% by weight, and preferably between 8 and 15% by weight of the aqueous suspension, without these values ​​being limiting. The ratio between the fibers and the chemical reagents is specified above.

[0106] As explained below, the process of the invention has the advantage of making cellulosic fibers more flexible by compression-kneading, that is, of softening them, generating few or no fine elements and broken fibers, while chemically modifying them. The resulting improvement in mechanical properties makes it possible to reduce the paper's basis weight according to the desired objectives in terms of the paper's quality / price ratio.

[0107] Furthermore, the process of the invention also makes it possible to improve certain properties of cellulosic fibers. This advantage allows for the use of blends of fibers from, for example, hardwoods, softwoods, and other sources, and for varying the ratios from 0 to 100%, depending on the desired quality / price ratio of the paper. Since softwood fibers have a much higher production cost than hardwood fibers, they can thus represent a smaller proportion than other fibers, without compromising the paper's properties, particularly its tear resistance.

[0108] The process according to the invention generates little or no shearing, making it possible to use fibers from annual plants, which are generally sensitive to shearing.

[0109] With reference to [Fig. 1], the mechanical treatment process according to the invention consists of a compression step of the aqueous suspension of cellulosic fibers in a mixer, instead of the conventional compression and shearing step between two rotating blade surfaces. The chemical modification is carried out simultaneously with the mechanical compression treatment.

[0110] The mixer used in said process is known in fields quite different from papermaking. It is mainly used for homogenizing viscous materials, such as polymers, compositions, composites or the like, used in cosmetics, adhesives, plastics processing, chemicals, etc. It may, in particular, be a UCP-type mixer from the HASLER company.

[0111] In the present invention, the mixer 1, as shown in [Fig. 1], is fed with an aqueous suspension of cellulosic fibers 2 from a pulper 3 or any other equivalent machine. Its output feeds a papermaking machine 4 to form a sheet or a strip of paper 5. The mixer 1 can be easily integrated into a continuous process, between the pulper and the machine after a pulp thickening step, resulting in increased productivity and reduced production costs.

[0112] The mixer 1 mainly comprises: - a hermetically sealed body 10, elongated along an axis X, defining a mixing chamber 11, delimited by a peripheral wall forming a fixed compression surface 12, - said body 10 being provided with at least one inlet orifice 13 upstream, for the admission of the fiber suspension to be treated, and an outlet orifice 14 downstream of the mixing chamber 11, for receiving at least a fraction of the treated suspension, and - at least one mixing shaft 20, elongated along the X axis, positioned in the mixing chamber 10.

[0113] The mixing shaft 20 comprises: - a shaft 21 that rotates about said axis X, and - a plurality of mixing elements 22, also called "paddles", fixed to the shaft 21, projecting radially from the shaft, each delimited by a peripheral wall forming a compression surface 23 that is rotationally fixed to the shaft. The compression surface 23 is located at a non-constant radius from the axis of rotation X, which varies between a maximum and a minimum radius depending on the point considered on said wall. As will be described in more detail later in this text, the irregular profile of the compression surface of the mixing elements relative to the axis of the shaft ensures, in cooperation with another corresponding compression surface, optimal compression of the fibrous suspension, thus leading to a Satisfactory mixing.

[0114] The mixing elements 22 arranged along the shaft 21 are preferably alternated (as opposed to eclipsed, along the X axis) in that they are oriented relative to each other in different angular positions to create a variable compression profile along the mixing axis 20. Thus, as shown in Figures 5, 7 and 8, adjacent mixing elements can be offset, for example by 45° or 90°.

[0115] According to said method, the compression surfaces 23 of the mixing elements 22 which face the compression surface 12 of the mixing chamber 11 on the one hand, and said compression surface 12 of the mixing chamber 11 on the other hand, define between them compression zones ZC of the fiber suspension 2 circulating between the body 10 and the mixing axis 20. The compression zones ZC thus correspond to the volume remaining between the mixing axis 20 and the mixing chamber 11, which contains the fiber suspension 2. They are very roughly identified by ovals in [Fig.2].Thanks to the variable compression profile of the mixing elements 22, the shape, location and volume of the compression zones ZC are not constant and vary continuously with the angular position of the shaft 21, resulting in the generation of a large number of compression forces on the fiber suspension 2 during the rotation of the mixing shaft 20 during the mixing operation. Thus, the cellulosic fibers are kneaded, crushed, compressed, compressed, mixed, kneaded, but are not or very little cut or sheared because they do not undergo or very little shearing stress (the rotation speed of the paddles is low, typically in the order of 20 to 600, in particular between 20 and 350 revolutions per minute for example - rotation per minute or the acronym "rpm" in English - for a paddle diameter of about 25 mm, and therefore the shear at the wall is low, i.e. < 1 m / s for a laboratory mixer.For an industrial mixer, the diameter of the paddles can, for example, be approximately 300 mm, with a wall shear rate of approximately 6 m / s, which remains low compared to the size of the mixer and the quantity of suspension processed (approximately 2 tonnes per hour). In other words, unlike conventional refining, the process of the invention induces negligible fiber shear compared to their compression.

[0116] The mixer 1 may have more than one mixing shaft 20, and for example two mixing shafts 20 or more than two mixing shafts, positioned in the mixing chamber 11, parallel to each other. Thus, the compression surfaces 23 of the mixing elements 22, which face each other, define additional compression zones ZC for the suspension of fibers 2 circulating between the mixing shafts 20. In this case, mixing shafts 20 of identical or nearly identical structure, positioned between each other, will preferably be chosen. such that the compression profile of one of the mixing shafts matches the compression profile of the other mixing shaft, and they rotate at the same speed. In this preferred mode, it is advantageous to ensure that two facing mixing elements 22 have the same shape. The mixing shafts 20 can be co-rotating and thus rotate in the same direction, as shown in [Fig. 2] by the counter-clockwise arrows, or counter-rotating and thus rotate in opposite directions.

[0117] Figure 2 illustrates a radial section of a mixer 1 comprising two parallel mixing shafts 20 within a mixing chamber 11. Each mixing shaft 20 comprises oblong mixing elements 22. The mixing shafts 20 are angularly offset from each other, such that the two corresponding mixing elements 22 are positioned perpendicular to each other, although this relative position is not mandatory and identical for the other mixing elements 22 not shown. This means, for example, that for a given position of the mixing shafts, a first pair of facing mixing elements may be offset by 90° from each other, while a second pair of facing mixing elements may be offset by 45° from each other. The mixing shafts 20 rotate in the same direction of rotation and at the same speed.The center distance between the two shafts 21 of the mixing axes 20, as well as the profile of the compression surface 12 of the mixing chamber 11, are defined according to the geometry of the mixing elements 22, to introduce a respective minimum distance DM between the mixing axes 20 and the mixing chamber 11, and between the mixing axes 20 themselves.

[0118] The minimum distance DM, which is represented in [Fig. 2] by circles, is preferably between 0.1 mm and 0.6 mm, preferably between 0.15 mm and 0.6 mm, in particular between 0.3 mm and 0.6 mm or between 0.3 mm and 0.5 mm. This minimum distance may, in particular, be between 0.15 mm and 0.4 mm. This minimum distance DM allows, in particular, the rotation of the mixing shafts 20 in the mixing chamber 11 without conflict, while permitting, in a very limited way, the circulation of the fiber suspension 2 in these restricted spaces. The boundary zones located between the mixing shafts 20 on the one hand, and between each mixing shaft 20 and the mixing chamber 11 on the other hand, which are defined by the minimum distance DM, therefore correspond to zones of high mechanical stress for the fibrous composition.During the rotation of the mixing axes 20, these boundary zones move, so as to alternately constrain the composition within the volume of the enclosure, which ensures optimal compression of the fibrous composition in the compression zones ZC.

[0119] The mixing elements 22 can have different geometries, thicknesses and Compression profiles are determined according to the type of treatment and the degree of flexibility to be achieved, the nature and composition of the fiber suspension to be treated, and the paper manufacturer's specifications. The mixing elements 22 illustrated in [Fig. 2] are flat, oblong pieces, symmetrical with respect to two perpendicular planes passing through the axis of rotation X, and have two diametrically opposed lobes 24.

[0120] This example is by no means limiting. The mixing elements 22 may have an ovoid shape, symmetrical with respect to a plane passing through the axis of rotation X and comprising a single lobe (not shown). They may have a triangular shape, symmetrical with respect to a plane passing through the axis of rotation X and one of the vertices, and comprising three lobes (shown in [Fig. 4]). They may also have a polygonal cross-section, symmetrical or not with respect to a plane passing through the axis of rotation X, and whose number of lobes corresponds to the number of angles of the polygon (not shown). Finally, they may have a complex shape, symmetrical or not with respect to a plane passing through the axis of rotation X (not shown).

[0121] Similarly, the mixing elements 22 may include parts whose peripheral wall, i.e., the compression surface, is flat or not, and whose compression profile through the thickness of the part is variable. Thus, a succession along the shaft of parts whose thickness has a helical profile (Figures 5 and 9) leads to a helical mixing shaft forming a complete helix, each part constituting a fraction of the helix. [Fig. 11] illustrates a paddle with an eccentric profile. [Fig. 10] illustrates a paddle (2 lobes) with a flat shear profile.

[0122] Figure 3 illustrates two identical, parallel mixing axes 20, offset from each other by an angle of 90°, each provided with flat, oblong, two-lobed mixing elements 22 with a straight compression profile through its thickness, substantially identical to those shown in Figure 2. The mixing elements 22 of the same axis are angularly offset from each other by 90°, and the mixing elements 22 of the two mixing axes 20 are axially alternated to allow for their radial interlocking. The mixing elements 22 of Figures 3 and 6 have a flat profile (Figure 10), i.e., a shear profile.

[0123] Advantageously, the mixing elements with the eccentric profile have a rounded compression surface 23. In other words, according to this embodiment, the edges of the paddle are rounded (i.e., not protruding).

[0124] Figure 4 illustrates two identical parallel mixing axes 20', each provided with flat, triangular mixing elements 22' with three equidistant lobes 24', and a straight compression profile through the thickness. The mixing elements 22' on the same axis are angularly offset from each other by 30°, and the mixing elements 22' on the two mixing axes 20' are radially interlocked. The elements mixers 22 of [Fig.4] have a flat profile, i.e. shearing.

[0125] Figure 5 illustrates two identical, parallel mixing shafts, without angular offset, each equipped with helical mixing elements with two equidistant lobes and a helical compression profile through its thickness. The mixing elements (Fig. 5) of the same shaft are angularly offset from each other by 45°, and the mixing elements of the two mixing shafts are radially interlocked. The mixing elements of Figure 5 have a helical profile, i.e., less shearing, or even non-shearing. The mixing shafts of Figure 5 include, in the area where the cellulose fiber suspension is introduced, a screw conveyor.

[0126] Figure 6 illustrates two identical, parallel mixing shafts, without angular offset, each equipped with flat, two-lobed, equidistant mixing elements with a flat compression profile through its thickness. The mixing elements (Fig. 6) of the same shaft are angularly offset from each other by 90°, and the mixing elements of the two mixing shafts are radially interlocked. The mixing elements of Figure 6 have a flat, i.e., shear profile. The mixing shafts of Figure 6 include, in the area where the cellulose fiber suspension is introduced, a screw conveyor.

[0127] Figure 7 illustrates two identical, parallel mixing shafts, without angular offset, each equipped with mixing elements having an eccentric compression profile through its thickness. The mixing elements (Fig. 7) of the same shaft are angularly offset from each other by 45°, and the mixing elements of the two mixing shafts are radially interlocked. The mixing elements of Figure 7 have an eccentric profile. The mixing shafts of Figure 7 comprise, in the cellulose fiber suspension inlet zone, a screw conveyor and, in the outlet zone, a series of helical paddles.

[0128] In general, positioning the mixing elements (whatever the profile) on the same axis by offsetting them angularly from each other by 45° reduces shear compared to an offset of 90°.

[0129] Figure 8 illustrates two identical, parallel mixing shafts, without angular offset, each equipped with mixing elements having an eccentric compression profile through its thickness. The mixing elements (Fig. 8) of the same shaft are angularly offset from each other by 90°, and the mixing elements of the two mixing shafts are radially interlocked. The mixing elements of Figure 8 have an eccentric, i.e., non-shearing profile. The mixing shafts of Figure 8 comprise, in the cellulose fiber suspension inlet zone, a screw conveyor and, in the outlet zone, a series of helical paddles.

[0130] The mechanical treatment process according to the invention offers a flexible, modular, adaptable, scalable compression mixing solution, allowing for variation, Modifying and refining the fiber properties according to the paper to be manufactured. This process is also part of a research and development approach for new papers. To this end, the structure of mixer 1 and its operating parameters can be easily chosen, modified, and / or combined.

[0131] As seen above, the structure of the mixer 1 is determined by the number of mixing shafts 20 as well as by the arrangement and choice of geometry of the mixing elements 22, but not only that. The mechanical processing method may also include several steps to achieve different degrees of flexibility. These different steps can be carried out in different ways: - by a mixer 1 comprising a mixing chamber 11 and at least one mixing shaft 20 on which are mounted a series or more series of mixing elements 22 of different and appropriate structures, in which the fiber suspension 2 is rotated in a loop; - by an extended mixer 1 comprising a mixing chamber 11 and at least one mixing shaft 20 on which are mounted several series of mixing elements 22 of different and appropriate structures; - by a mixer (not shown) comprising several successive mixing chambers, connected in series, each comprising one or more mixing shafts of different and appropriate structures; or - by several successive mixers (not shown), connected in series, of different and appropriate structures.

[0132] In these different scenarios, the treated fiber suspension 2 can be extracted at each stage of the process and / or at the end of the process stages as required.

[0133] The operating parameters of the mixer 1 can also be selected, modified, and / or combined to vary the mixing characteristics. Examples of modifiable parameters include, but are not limited to, the following: - the feed rate of the mixer 1 in suspension of fibers 2, defining the mixing time; - Mixing temperature: The mixer operates at ambient temperature, but can also operate at a temperature higher or lower than ambient temperature thanks to the mixer body 10, which can consist of a double jacket (not shown) allowing the circulation of a heat transfer fluid. More specifically, the mixer is kept at ambient temperature by cooling to compensate for the temperature rise due to mixing, in order to better control the viscosity of the dough. In practice, a temperature rise of approximately +10°C to +30°C is observed, depending on the operating concentration, the rotation speed, and the residence time. Alternatively, it is possible to work at a hot temperature, in order to in particular to carry out oxidation reactions jointly with mixing (intensification of the process) or at cold, for example in the presence of soda to achieve a dissolution of cellulose; - Mixing pressure: preferably the mixing operation is carried out in a mixing chamber 11 at atmospheric pressure, but depending on the needs it could be carried out at a pressure higher or lower than atmospheric pressure. For example, it may be advantageous to work at a pressure higher than atmospheric pressure to adjust the filling speed of the feed screw (for example of the auger type as described later in this text); - the rotation speed of the mixing shaft(s) 20: this speed is preferably relatively low, for example between 20 and 600 rpm, preferably between 20 and 400 rpm or between 20 and 350 rpm; - the speed differential between the mixing axes 20 (rotating part) and the mixing chamber 11 (fixed part) is less than or equal to 15 m / s, thus producing little or no shearing phenomenon; - the direction of rotation of the mixing axes 20: co-rotating or counter-rotating; - the mixing power transmitted to the fiber suspension 2 by measuring the resisting torque of the mixing axes 20; - the mixing time: the residence time of the fiber suspension 2 in the mixing chamber 11 can be between 15 seconds and 15 minutes, preferably between 15 seconds and 10 minutes, and more preferably between 15 seconds and 5 minutes; - the minimum distance DM between the mixing axes 20 and the mixing chamber 11 by modifying the mixing elements 22; - the thickness of the mixing elements 22 to increase or decrease the compression surfaces.

[0134] The mixing tests carried out with the process of the invention revealed an unexpected and counterintuitive physical phenomenon for a person skilled in the art of papermaking: the higher the rotational speed of the mixing shafts 20 (20 to 600 rpm), the shorter the duration of the mechanical compression action on the cellulosic fibers, and the better the mixing result. A high speed limits the shearing and fibrillation of the cellulosic fibers and therefore the formation of fine particles. These conditions favor short compressions, but a high number of compressions, advantageously at least 500, more advantageously between 500 and 5000, and even more advantageously between 3000 and 5000.

[0135] In summary, the rotation speed of the mixing shafts (20 to 600 rpm) and the mixing conditions (speed differential < 20 m / s and residence time between 15 (seconds and 15 minutes) allow for short and frequent mechanical compression, which limits the damage to cellulosic fibers. Thus, the cellulosic fibers are less damaged, or even preserved, compared to long and frequent or infrequent mechanical compressions.

[0136] This phenomenon, which is neither detectable nor conceivable before implementing the process of the invention, makes it possible to further increase the performance of the mixing and the advantages of the process that result from it, such as better fiber flexibility, improved fiber content, new possible paper pulp formulations, reduced power consumption allowing significant energy savings, very little wear of moving parts allowing reduced maintenance of the mixer 1.

[0137] In the example of the mixer 1 shown in [Fig. 1], the mixing chamber 11 comprises an inlet zone ZE, a mixing zone ZM, and an outlet zone ZS, which are axially successive. The inlet zone ZE is coupled to the inlet orifice 13 and preferably comprises a worm screw 25 fixed to the corresponding shaft 21 of each mixing axis 20, for moving the fiber suspension 2 axially towards the mixing zone ZM and then towards the outlet zone ZS. The mixing zone ZM comprises the mixing elements 20 described above. The outlet zone ZS can be considered the end of the mixing zone ZM and also comprises mixing elements 20, which may or may not be the same as those of the mixing zone ZM. The ZS outlet zone communicates with the outlet port 14 which can be gravity-fed or combined with any other means of extraction.The mixer 1 may have several inlet ports 15, 16 which can be used to introduce additives, fillers, and other materials into the fiber suspension 2 during mixing. It may also have several outlet ports (not shown) which can be used to extract all or part of the fiber suspension 2 during mixing, as well as gases and other condensates generated during processing. This is particularly advantageous because the operator can recover several fractions of mixed fibers with different degrees of compression and therefore different properties depending on their respective outlet port, all during the same mixing operation.

[0138] The present invention is not limited to the embodiments described but extends to any modification and variant obvious to a person skilled in the art within the limits of the appended claims. Furthermore, the technical features of the various embodiments and variants mentioned above may be combined, in whole or in part. Examples

[0139] In the examples, the percentages are percentages by weight.

[0140] 1. Comparison between oxidized cellulosic fibers according to the process of the invention and oxidized cellulosic fibers in a conventional reactor

[0141] Example INV-1: Protocol for preparing oxidized cellulosic fibers according to the process of the invention (INV-1)

[0142] The suspension of cellulosic fibers (eucalyptus) is introduced into a mixer comprising a mixing shaft and sodium periodate to produce an aqueous suspension of cellulosic fibers having aldehyde groups.

[0143] The process has a velocity differential between the mixing axis and the mixing chamber equal to 0.5 m / s. The mixer has a minimum distance of 0.3 mm between the mixing axis and the mixing chamber. Upon exiting the mixer, the suspension of chemically modified cellulosic fibers is left to age. The mixing profile is a helical profile, with the helical paddles offset by 45°, which minimizes shear. The reaction conditions used are presented in Table 1 below.

[0144] Counterexample CE-1: Protocol for the preparation of oxidized cellulosic fibers in a conventional reactor (CE-1)

[0145] Comparative example CE-1 was carried out in a conventional reactor, from fibers modified in a conventional reactor at low concentration (2% by weight).

[0146] The reaction conditions used are presented in Table 1 below.

[0147] [Tables] Example CE-1 (conventional reactor) INV-1 (mixer + aging) Fiber concentration 2% 10% in the mixer Conditions 2 hours at 20 °C in the reactor 2 minutes at 20 °C in the mixer Reagent (quantity) Sodium periodate (ratio 1) Sodium periodate (ratio 0.6) Aging - 2 hours at 20 °C Amount of aldehyde in mmol / g 0.5 2

[0148] In Table 1, the amount of reagent in step a) corresponds to the molar ratio between the reagent (oxidant = sodium periodate) and the anhydroglucose units (AGU) of the cellulose in the fibers. The amount of aldehyde resulting from the reaction in step a) is expressed in mmol per gram of cellulose fibers.

[0149] Example INV-1 shows that the amount of aldehyde functionalizing the fibers of cellulose is 4 times more important than in the comparative example (2 vs 0.5 mmol / g).

[0150] On the other hand, the present invention makes it possible to treat suspensions having higher concentrations of cellulose fibers (10% vs 2%).

[0151] Thus, the present invention makes it possible to optimize the reaction in the mixer (INV-1 = oxidation) and, consequently, the functionalization by formation of aldehyde functions.

[0152] In summary, the process according to the invention allows for greater functionalization than conventional reactor processes, while reducing the necessary amount of chemical reagent (oxidant in example INV-1).

[0153] 2. Effect of the modified cellulosic fibers according to the invention on the properties of canons of a sheet of paper

[0154] The mixer and conditions of example INV-1 were used for examples DCC, DSC and INV-2 to INV-10.

[0155] [Tables2] Example DCC DSC Reagent for step a) (quantity) Sodium peridate (ratio 0.8) 50°C Sodium peridate (ratio 0.8) 50°C Aging (step b)) 72 hours at 20°C 72 hours at 20°C Post-reaction Sodium chlorite Sodium bisulfite

[0156] Table 2: Reaction conditions of chemically modified cellulosic fibers according to the process of the invention (sodium periodate in water solution at 110 g / L)

[0157] According to the DCC example, the aldehyde functions formed during step a) (NaIO4) react with the oxidant sodium chlorite (NaC1O2) to form dicarboxyl cellulose during the post-reaction (post-reaction: 30 g of NaC1O2 per liter of aqueous suspension at 30 g / L of cellulose fibers for 12 hours at 20°C).

[0158] According to the DSC example, the aldehyde functions formed during step a) (NaIO4) react with the sulfonant agent (NaHSO3) to form cellulose disulfonate during the post-reaction (post-reaction: 30 g of NaHSO3 per liter of aqueous suspension at 30 g / L of cellulose fibers for 12 hours at 20°C).

[0159] Modified DCC and DSC celluloses were used, as an additive, in the manufacture of a sheet of paper from an aqueous suspension of eucalyptus fibers (Table 3) having been refined, unrefined or modified in a mixer.

[0160] [Tables3] Example Composition of the fiber suspension Density (kg / nW) Bursting index (kPa.m² / g) Fibers (% by weight of dry matter) Additive (% by weight of dry matter) EC-2 EUCA (100) ISF 529 0.83 EC-3 EUCA (100) N 700 3.41 EC-4 EUCA (100) 0 kWh / t N 502 0.63 EC-5 EUCA (100) 50 kWh / t N 590 2.03 EC-6 EUCA (100) 100 kWh / t N 635 2.91 EC-7 EUCA <r3® (100) 200 kWh / t N 737 4,67 CE-8 EUCA^) (100) N 588 14 CE-9 EUCA^™5! (100) N 662 1,35 CE-10 HCÙ" (1QQ) U 699 1,4 CE-1I EUCA^ (100) N 741 1,7 INV-2 EUCA (90) DCC (10) 565 2,53 INV-3 EUCA (75) DCC (25) 600 4,61 INV-4 EUCA (97,5) DSC (2,5 ) 557 1,34 INV-5 EUCA (95) DSC (5) 590 2,03 INV-6 EUCA (90) DSC ( 10) 575 ■7 7 INV-7 EUCA (75) DSC (25) 608 5,09 INV-8 EUCA^ (94,85) DSC (5) DADMAC (0,15) 566 1,71 INV-9 EUCA^Ï! (90) DSC ( 10) 703 8,36 INV-10 EUCA^ (75) DSC (25) 696 8,4

[0161] Table 3: Burst index of paper sheets as a function of their density and composition

[0162] In Table 3: EUCA: unrefined eucalyptus fiber sheet EUCA(raf): eucalyptus fiber sheet that has been refined in a conventional double-disc refiner (kWh / t: energy in kW.h per tonne of cellulosic fibers; EC-4 at 0 kWh / t = no refining) EUCA(M): eucalyptus fiber sheet that has been mechanically modified in a mixer EUCA(dens): sheet of unrefined eucalyptus fibers, densified by wet pressing at increasing pressure DCC: dicarboxyl cellulose DSC: disulfonate cellulose DADMAC: diallyldimethylammonium chloride polymer N: no additive

[0163] The addition of DCC and DSC modified celluloses (at a rate of 2.5%, 5%, 10%, and 25%) to eucalyptus pulp (modified or unmodified by compression in the mixer) resulted in very high mechanical strengths, similar to those obtained by conventional refining in a disc refiner. Furthermore, mechanical modification of the fibers by compression and the addition of mechanically and chemically modified fibers (10% to 25% DSC) further increased burst strength.

[0164] The bonds created by the anionic fibers of DCC or DSC are electrostatic bonds that operate over greater distances than hydrogen bonds and are much stronger. Therefore, conventional refining in a disc refiner or mechanical modification by compression in a mixer develops the bond areas to create hydrogen bonds, while the presence of anionic cellulose (DSC or DCC) increases the bond strength, complementary effects as shown by the burst strength values.

[0165] Thus, the mechanically and chemically modified cellulose fibers according to the invention allow the formation of stronger bonds and, thus, multiply by 8 the bursting resistance of a standard paper (INV-9 and INV-10 vs CE-10).

[0166] In example INV-8, the paper sheet was prepared from an aqueous suspension containing, on a dry matter basis, 94.85% unrefined eucalyptus fibers and 5% fluidized DSC. Fluidized DSC is an anionic cellulose polymer solution obtained by shearing a DSC solution in water at pH 9. This anionic cellulose polymer was added in the presence of a cationic polymer (0.15% DADMAC), the role of which is to retain the dissolved anionic cellulose.

[0167] Unfluidified DSC comprises long fibers (some reaching about 300 pm) that are highly hydrated / swollen due to their very high anionicity.

[0168] The tests in Table 3 show that: - Mechanical densification by additional wet pressing of unrefined eucalyptus fibers (CE-8 to CE-11) increases density but increases mechanical strength only slightly because the fibers have not been made flexible and the bonding surface is small with only short-range hydrogen bonds in the contact areas. Conventional refining (between two discs) and kneading allow the sheet to be densified without additional wet pressing, resulting in increased mechanical strength due to improved fiber flexibility and greater contact surface to develop short-range hydrogen bonds. - The addition of highly anionic DSC fibers allows the development of new long-range bonds in the contact areas, in addition to hydrogen bonds: electrostatic bonds which are much stronger than hydrogen bonds. - The combination of mechanical modification (by kneading) and the addition of DSC fibers allows a synergistic effect: kneading develops bonding surfaces while DSC develops electrostatic bonds, and therefore the strength of the bonds.

Claims

Demands

1. A process for the mechanical and chemical treatment of cellulosic fibers by mechanical compression and chemical modification of cellulosic fibers, the process comprising the following steps: a) in a mixer (1), mechanical compression and chemical modification of cellulosic fibers (2), in aqueous suspension having a concentration of between 5 and 20% by weight of cellulosic fibers, in the presence of a chemical reagent to produce an aqueous composition of cellulosic fibers having chemically modified functional groups, the mixer (1) comprising: - a body (10) defining a mixing chamber (11) delimited by a wall forming a fixed compression surface (12) capable of coming into contact with the fiber suspension (2), - at least one mixing shaft (20) positioned in the mixing chamber (11) and comprising: * a rotating, movable shaft (21), * a plurality of mixing elements (22) fixed on the shaft (21), projecting radially from the shaft (21), and each provided with a rotationally movable compression surface (23) adapted to come into contact with the fiber suspension (2), the mixing elements (22) having a helical or eccentric compression profile, a method in which the compression surfaces (23) of the mixing elements (22) face the compression surface (12) of the mixing chamber (11), so as to define, between said respective compression surfaces (23, 12) of the mixing elements (22) and the mixing chamber (11), compression zones (CZ) of the fiber suspension (2) circulating between the body (10) and the mixing shaft (20), and in which the compression surfaces (23) of the mixing elements (22) have a compression profile whose radius with respect to the tree (21) varies according to the angular position of said tree,so as to compress the fiber suspension (2) in said compression zones (CZ) during the rotation of said mixing shaft (20), - the process having a speed differential between at least one mixing shaft (20) and the mixing chamber (11) less than or equal to, 15 m / s, - the mixer having a minimum distance (DM) separating at least one mixing axis (20) from the mixing chamber (11) of between 0.1 mm and 1 mm, - the aqueous suspension of cellulosic fibers has a residence time in the mixer of between 15 seconds and 15 minutes, b) optionally, at the mixer outlet, aging of the chemically modified cellulosic fiber suspension.

2. A treatment method according to claim 1, wherein the chemical reagent is selected from the group consisting of periodic acid or one of its salts, metaperiodic acid or one of its salts, 2,2,6,6-tetramethylpiperidine-1-oxyl, azaadamantane-N-oxyl, hydrogen peroxide, ozone, chloroacetic acid, hypohalogenite or one of their salts, hydrosulfite salts, and mixtures thereof.

3. A treatment method according to any one of the preceding claims, wherein the chemical reagent / fibre molar ratio varies from 0.1 to 1 when the chemical reagent is periodic acid or one of its salts.

4. A treatment method according to any one of the preceding claims, wherein when the chemical reagent is TEMPO the chemical reaction is carried out in the presence of sodium hypochlorite NaClO and sodium bromide NaBr at alkaline pH or of sodium hypochlorite NaClO and sodium chlorite NaClO2 at neutral pH.

5. A treatment process according to any one of the preceding claims, wherein an oxidation reaction is carried out at a temperature between 15 and 100 °C, preferably 20 to 80 °C and even more preferably 40 to 70 °C.

6. A treatment method according to any one of the preceding claims, wherein the method comprises step b) of aging in which the suspension of modified cellulosic fibers is allowed to age for up to 72 hours at a temperature of 15 to 60 °C, advantageously 20 to 45 °C.

7. A treatment process according to any one of the preceding claims, wherein the process comprises step b) of aging and, after step b) of aging, a washing step and a post-chemical reaction step.

8. Processing method according to claim 7, wherein the chemical after-reaction is selected from oxidation, sulfonation, reduction and amination.

9. Composition of modified cellulosic fibers obtained according to the process of any one of claims 1 to 8.

10. Use of a composition of cellulosic fibres according to claim 9 as an additive in the preparation of paper or cardboard.

11. A method for preparing a sheet of paper or cardboard, comprising adding a composition of cellulosic fibers according to claim 9 to a suspension of cellulosic fibers, and forming a sheet of paper or cardboard.

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