A method for producing a microfibrillated cellulose web

Abstract

The present invention relates to a method for producing a microfibrillated cellulose (MFC) web. The method comprises preparing an MFC suspension comprising water as suspension medium. A wet MFC web is formed of the MFC suspension by casting on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support. The wet MFC web formed on the non-porous support or on a paper or paperboard substrate positioned on the non-porous support is subjected to water removal by means of dewatering and / or drying to form the MFC web. Water removed from the wet MFC web by the water removal is collected into at least one water fraction. Optionally, the at least one water fraction is subjected to a purification treatment. The at least one water fraction is used as suspension medium in the preparation of the MFC suspension.

Description

[0001] A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE WEB

[0002] Technical field

[0003] The present disclosure relates to a method for producing a microfibrillated cellulose (MFC) web, such as an MFC film, involving web formation by casting on a non- porous support or on a paper or paperboard substrate positioned on the non-porous support, which method enables improved water management.

[0004] Oxygen, grease, water vapor and / or aroma barrier properties are required in many uses of paper and paperboard packaging. However, paper and paperboard substrates do not have these properties inherently. Most commonly barrier characteristics of paper and paperboard substrates are created by adding one or more barrier coatings and / or laminated barrier layers which are based on plastics or other non-renewable materials. The disadvantage with these coatings and barrier layers is their non-renewable raw material basis that can increase the carbon dioxide footprint of the material as well as make the otherwise biodegradable paper or paperboard non-biodegradable and in some cases non-recyclable.

[0005] More recently, microfibrillated cellulose (MFC) webs have been developed, in which cellulosic fibrils, provided by fibrillation of cellulose fibers, have been suspended, e.g., in water and thereafter re-organized and re-bonded together to form a web. For example, MFC webs in the form of MFC films, which are dense films with barrier properties, such as oxygen, aroma and grease barrier properties, have been developed. MFC webs, such as MFC films, are recyclable and biodegradable as well as based on renewable raw material.

[0006] One approach to produce MFC webs, such as MFC films, is to use a wet laid technique, i.e., to apply a dilute MFC suspension comprising MFC and water as suspension medium on a dewatering wire or membrane in a forming section and dewater it by vacuum, gravitation, capillary dewatering, press dewatering or a combination of these on the wire or membrane followed by drying or liquid evaporation. When this approach is utilized, most of the water of the wet MFC web is removed through the wire or membrane in the forming section. Another approach to produce MFC webs, such as MFC films, is to use a casting method in which a wet MFC web is formed by casting of an MFC suspension comprising MFC and water as suspension medium on a non-porous support, such as a plastic or metal support, and thereafter dewatering and / or drying to remove water from the wet MFC web. This type of casting method has been shown to produce MFC films with very smooth surfaces with good barrier properties, such as oxygen barrier properties and / or water vapor barrier properties. Also, a wet MFC web may be formed by the casting technique on a paper or paperboard substrate positioned on the non-porous support. However, when the wet MFC web is positioned on the non-porous support, or on a paper or paperboard substrate positioned on the non- porous support, removal of water from the wet MFC web needs to be substantially performed through the surface of the wet MFC web opposite the non-porous support, e.g., by press dewatering and / or evaporation, when this type of casting method is utilized. Thus, the management of water removed from the wet MFC web, when this type of casting method is utilized, is more complex than when a wet laid technique with a dewatering wire or membrane is utilized.

[0007] There is still a need of a method for producing an MFC web involving web formation by casting on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support, which enables improved water management.

[0008] Description of the invention

[0009] It is an object of the present invention to provide a method for producing an MFC web, such as an MFC film, involving web formation by casting on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support, which enables improved water management.

[0010] It is a further object of the present invention to provide a method for producing an MFC web, such as an MFC film, involving web formation by casting on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support, which enables improved water management as well as reduced use of fresh water in the production of the MFC web. The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0011] The invention is defined by the appended independent claim. Embodiments are set forth in the appended dependent claims and in the following description.

[0012] According to a first aspect illustrated herein, there is provided a method for producing a microfibrillated cellulose (MFC) web, wherein the method comprises the steps of: a) preparing an MFC suspension comprising between 50 weight-% to 100 weight-% MFC based on total dry weight and a suspension medium, wherein the suspension medium is water, wherein said MFC suspension has a dry content of 1-30 weight-%; b) forming a wet MFC web of said MFC suspension by casting on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support; c) subjecting said wet MFC web formed on said non-porous support or formed on said paper or paperboard substrate positioned on said non-porous support to water removal to form said MFC web, wherein the water removal comprises dewatering said wet MFC web in at least one dewatering step and / or drying said wet MFC web in at least one drying step; d) collecting water removed from said wet MFC web by said water removal into at least one water fraction; e) optionally, subjecting at least one water fraction of said at least one water fraction to a purification treatment comprising at least one purification step, and f) using water of said at least one water fraction as suspension medium in the preparation of said MFC suspension in step a).

[0013] The method according to the first aspect enables production of an MFC web involving a casting technique on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support, wherein an improved water management is obtained. By collecting water removed from the wet MFC web during the dewatering and / or drying into at least one water fraction, e.g., in a water collection arrangement, and reusing collected water in the preparation of MFC suspension to be used in the MFC web production, the water management is improved and made more efficient compared to discharge of liquid water from dewatering and evaporated water from drying. In addition, the method according to the first aspect enables reduced use of fresh water (i.e., water which has not been circulated in the production process) in the production of an MFC web involving a casting technique by the reuse of water, which has been removed from the wet MFC web during dewatering and / or drying steps, in the MFC web production. Thus, the method according to the first aspect enables a reduced water footprint of the produced MFC web.

[0014] Microfibri Hated cellulose (MFC) shall in the context of this patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm.

[0015] Various methods exist to make MFC, such as single or multiple pass refining, prehydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre-treatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp used when producing MFC may thus be native or pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by oxidation, for example 2, 2', 6,6'- tetramethylpiperidin-N-oxyl (TEMPO) mediated oxidation), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC.

[0016] MFC can be produced from wood cellulose fibers, both from hardwood and / or softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It can be made from pulp, including pulp from virgin fiber, e.g., mechanical, chemical and / or thermomechanical pulps. It can also be made from broke or recycled paper.

[0017] The term film as used herein refers generally to a thin continuous sheet formed material, such as a thin substrate with good gas, aroma and / or grease or oil barrier properties, e.g., oxygen barrier properties and / or water vapor barrier properties. Depending on the composition of the MFC suspension from which it is formed, the MFC film can also be considered as a thin paper (e.g., nanopaper or micropaper) or even as a membrane.

[0018] In step a) of the method of the first aspect, an MFC suspension comprising between 50 weight-% to 100 weight-% MFC based on total dry weight is prepared. In some embodiments, the prepared MFC suspension comprises between 60 weight-% to 100 weight-%, preferably between 70 weight-% to 100 weight-%, more preferably between 80 weight-% to 100 weight-% of MFC, based on total dry weight.

[0019] The MFC suspension prepared in step a) of the method of the first aspect has a dry content of 1-30 weight-%. In some embodiments, the prepared MFC suspension has a dry content of 1-25 weight-%, such as 1-20 weight-% or 1-15 weight-%. Preferably, the prepared MFC suspension has a dry content of 2-25 weight-%, such as 2-20 weight-% or 2-15 weight-% or 3-8 weight-%.

[0020] The MFC suspension prepared in step a) of the method of the first aspect comprises a suspension medium, which is water. Thus, the MFC suspension is an aqueous suspension. At least parts of the water of the MFC suspension is water collected from the dewatering and / or drying of step c) of the method of the first aspect and reused in step f) of the method of the first aspect.

[0021] The microfibrillated cellulose of the MFC suspension prepared in step a) of the method of the first aspect may comprise one or more fractions of microfibrillated cellulose. In some embodiments, the microfibrillated cellulose of the MFC suspension comprises one fraction of microfibrillated cellulose of a fine grade. In some embodiments, the microfibrillated cellulose of the MFC suspension comprises two or more fractions of microfibrillated cellulose of different fine grades. In some embodiments, the microfibrillated cellulose of the MFC suspension comprises one fraction of a fine grade and one fraction of a coarse grade, wherein the coarse grade for example may be an additive. Coarse MFC in this case has typically a Schopper- Riegler value of 80-100 SR°, such as 80-99 SR° or 90-99 SR° or 95-99 SR°, whereas fine MFC is fibrillated so measurement of the Schopper-Riegler value is not possible (theoretical value about or above 100 SR°) as determined by standard ISO 5267-1 .

[0022] In some embodiments, the MFC suspension prepared in step a) of the method of the first aspect comprises one or more further cellulose pulp fractions in addition to the microfibrillated cellulose, such as e.g. a cellulose pulp fraction having a Schopper- Riegler value of < 70 SR°, such as 15-70 SR° or 25-60 SR°, as determined by standard ISO 5267-1 and / or a further fraction of normal fibers. The MFC suspension may comprise, for example, 1-30 weight-%, more preferably 2-30 weight-%, most preferably 5-30 weight-%, of further cellulose pulp fraction(s), based on the total dry weight of microfibrillated cellulose and further cellulose pulp fraction(s) (i.e., based on the total dry weight of total amount of fibers in the MFC suspension).

[0023] By normal fibers is meant normal pulp fibers of a conventional length and fibrillation for papermaking. Normal fibers may include mechanical pulp, thermochemical pulp, pressure groundwood, chemical pulp such as sulphate (kraft) or sulphite pulp, dissolving pulp, recycled fiber, organosolv pulp or chemi-thermomechanical pulp (CTMP), or combinations thereof. The pulp may be bleached or unbleached. The normal fibers can be vegetable fibers, such as wood derived (e.g., hardwood or softwood) or agricultural sources including straw, bamboo, etc.

[0024] The normal fibers may have a beating degree, i.e., Schopper-Riegler value, in the range of 15 to 50 SR° or more preferably in the range of 18 to 40 SR° as determined by standard ISO 5267-1 . The normal fibers may preferably be chemical pulp, such as kraft pulp.

[0025] The normal fibers may have a mean length in the MFC suspension of 0.5 to 5 mm, preferably 1 mm to 5 mm, more preferably in the range of 2 mm to 4 mm, as determined using a FS5 fiber analyzer (Valmet). Mean fiber length as used herein refers to the mean fiber length measured according to the standard ISO 16065-2 using an FS5 fiber analyzer (Valmet).

[0026] In some embodiments, the MFC suspension prepared in step a) of the method of the first aspect comprises 1-30 weight-%, preferably 2-30 weight-%, most preferably 5- 30 weight-%, of reinforcement fibers based on the total dry weight of microfibrillated cellulose and further cellulose pulp fraction(s) (i.e., based on the total dry weight of total amount of fibers in the MFC suspension), wherein the reinforcement fibers have a mean diameter of >10 pm and a mean length of >1.5 mm, as determined using a FS5 fiber analyzer (Valmet).

[0027] Thus, besides MFC, the prepared MFC suspension may also comprise longer fibers, either hardwood or softwood fibers, preferably kraft pulp softwood fibers.

[0028] The MFC suspension prepared in step a) of the method of the first aspect may in addition to MFC and optional further pulp fraction(s) comprise any conventional paper making additives or chemicals such as film-forming agents, dispersants, fillers, pigments, wet strength chemicals, cross-linkers, plasticizers, softeners, humectants, adhesion primers, wetting agents, biocides, colorants, de-foaming chemicals, hydrophobizing chemicals such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), waxes, rosin resins, mineral additives (fillers) such as bentonite, kaolin, talcum, mica, montmorillonite, organoclays, graphene and graphene oxide, stearate, starch, silica, precipitated calcium carbonate, cationic polysaccharide, rheology modifiers, etc. These additives or chemicals may thus be process chemicals or film performance chemicals added to provide the end product web with specific properties and / or to facilitate production of the web.

[0029] In some embodiments, the prepared MFC suspension is free, or at least essentially free, of cationic flocculation and drainage chemicals.

[0030] Preferably, the prepared MFC suspension comprises no more than 50 weight-%, preferably no more than 35 weight-%, most preferably no more than 30 weight-% or no more than 25 weight-%, of additives, based on total dry weight of the MFC suspension. For example, the prepared MFC suspension may comprise 1-50 weight- % or 1-35 weight-% or 1-30 weight-% or 1-25 weight-% of additives, based on total dry weight of the MFC suspension.

[0031] In some embodiments, the prepared MFC suspension comprises a water soluble polymer that can form a network, such as a web or film, and / or improve binding between cellulose fibrils. Typical examples of such polymers are natural gums or polysaccharides or derivatives thereof such as carboxymethylated cellulose (CMC), hemicellulose, starch, or polyvinyl alcohol (PVOH) or derivatives or analogues thereof. The PVOH may be a single type of PVOH, or it can comprise a mixture of two or more types of PVOH, differing, e.g., in degree of hydrolysis or viscosity. The PVOH may, for example, have a degree of hydrolysis in the range of 80-99 mol%, preferably in the range of 88-99 mol%.

[0032] In some embodiments, the prepared MFC suspension comprises 0-30 weight-% or 0.5-20 weight-% or 3-15 weight-% of one or more humectants and / or plasticizing agents based on total dry weight, such as a sugar alcohol (e.g., sorbitol), glycol, other polyol or a combination thereof.

[0033] In some embodiments, the prepared MFC suspension comprises up to 20 weight-% of mineral fillers (regular filler or nanofiller) based on total dry weight, such as bentonite, kaolin, talcum, mica, montmorrillonite, organoclays, graphene, graphene oxide or a combination thereof.

[0034] In step b) of the method of the first aspect, a wet MFC web is formed of the MFC suspension prepared in step a). The wet MFC web is formed by casting on a non- porous support or by casting on a paper or paperboard substrate positioned on the non-porous support.

[0035] Thus, the MFC suspension may be applied directly on the surface of the non-porous support, e.g., to form a free-standing MFC web. Alternatively, the MFC suspension may be applied on a paper or paperboard substrate positioned on the surface of the non-porous support, wherein a laminate or a coated paper or paperboard substrate is formed.

[0036] Paper generally refers to a material manufactured in thin sheets from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as packaging material.

[0037] Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for boxes and other types of packaging. Paperboard can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. The MFC web can be a single or multilayer web, or single or multilayer ply. Thus, the wet MFC web formed in step b) may comprise a single wet web layer or two or more wet web layers on top of each other.

[0038] The term “casting”, when utilized in web-forming, such as film-forming, is a known term designating methods wherein a suspension is deposited by means of contact or non-contact deposition and levelling methods on a support to form a wet web. Examples of such a deposition and levelling method are curtain coating / application, slot die casting, or dosing the MFC suspension with spray or similar device and optionally leveling with, for example, a doctor-blade, rod, air knife or roll.

[0039] The non-porous support may be a metal (e.g., steel), rubber, plastic or polymer (e.g., polyurethane) support (e.g., belt or roll). In some embodiments, the non-porous support is a metal belt (i.e., a belt made of metal) such as a steel belt, a polymer belt or a coated belt with a permanent or temporary coating such as a polymer coated belt, e.g., a polymer coated steel belt. For example, the belt can be coated with controlled adhesion / releasing agents. A metal belt may be coated, e.g., with ceramic material. The non-porous support may be a continuous or endless non-porous support, such as a conveyor belt. Thus, in some embodiments the non-porous support is a continuous or endless metal belt.

[0040] In some embodiments, the non-porous support is a metal belt, such as a continuous metal belt, which is heated during web formation of step b) and / or during dewatering and / or drying of step c). The metal belt may be heated to a temperature above 30 °C, preferably such that at least the casting surface of the metal belt has a temperature between 30-150 °C, more preferably between 45-150 °C, even more preferred between 60-100 °C before or immediately after the MFC suspension is applied to the metal belt or to the paper or paperboard substrate positioned on the metal belt and the temperature of the metal belt may be kept during parts of the method for producing the MFC web, e.g., during at least some process steps for production of the MFC web, or during the complete method for producing the MFC web. By increasing the temperature of the metal belt and thus on the applied wet MFC web, it is possible to further increase the efficiency of the dewatering and / or drying of the wet MFC web. In step c) of the method of the first aspect, the wet MFC web formed on the non- porous support or formed on the paper or paperboard substrate positioned on the non-porous support is subjected to water removal to form the MFC web. Thus, in step c) the wet MFC web, or the paper or paperboard substrate provided with the wet MFC web, is positioned on the non-porous support. The MFC web formed by the water removal of step c) may be a dry MFC web. As utilized herein, a dry MFC web has a moisture content of 20 weight-% or less, preferably 10 weight-% or less, more preferably 5 weight-% or less. In some embodiments, the dry MFC web has a moisture content of 1-20 weight-%, preferably 1-10 weight-%, most preferably 1-5 weight-%. The moisture content may be measured under ambient conditions. For example, the moisture content may be measured using spectroscopy methods, such as infra-red (IR) spectroscopy, near infra-red (NIR) spectroscopy or Raman spectroscopy methods, in particular infra-red methods suitable for single side measurement. Alternatively, the dry content may be measured in order to determine the moisture content. For example, the dry content may be measured according to standard ISO 638 and the moisture content may be calculated based on the dry content measurement.

[0041] Typically, the formed MFC web (if the MFC web is formed directly on the non-porous support) or the paper or paperboard substrate provided with the MFC web (if the MFC web is formed on a paper or paperboard substrate) is wound onto a core to form a reel of the MFC web or of the paper or paperboard substrate provided with the MFC web after water removal and after release / separation from the non-porous support.

[0042] In some embodiments in which the MFC web is formed directly on the non-porous support, the formed MFC web is released, such as peeled off, from the non-porous support, after water removal, before winding the MFC web onto the core to form the reel. Thus, a reel of a free-standing continuous MFC web is formed in these embodiments. However, alternatively or additionally, a further drying of the MFC web may be performed after the release of the MFC web from the non-porous support but before or in connection with the winding of the MFC web onto the core to form the reel. The MFC web released from the non-porous support may be a dry MFC web. In some embodiments in which the MFC web is formed on a paper or paperboard substrate, the paper or paperboard substrate provided with the MFC web is separated from the non-porous support, after water removal, before winding the paper or paperboard substrate provided with the MFC web onto the core to form the reel. Thus, a reel of a continuous paper or paperboard substrate provided with an MFC web is formed in these embodiments. The MFC web on the paper or paperboard substrate may be a dry MFC web when released from the non-porous support. However, alternatively or additionally, a further drying of the MFC web may be performed after the release of the paper or paperboard substrate provided with the MFC web from the non-porous support but before or in connection with the winding onto the core to form the reel.

[0043] The water removal of step c) comprises dewatering the wet MFC web in at least one dewatering step and / or drying the wet MFC web in at least one drying step.

[0044] The dewatering and the drying, respectively, of step c) may be performed by using any methods known in the art that are suitable to dry the wet MFC web. The wet MFC web, or the paper or paperboard substrate provided with the wet MFC web, is positioned on the non-porous support during the dewatering and / or drying.

[0045] In some embodiments, the water removal of step c) comprises the dewatering of the wet MFC web in at least one dewatering step, wherein at least one dewatering step of the at least one dewatering step is or comprises a mechanical dewatering such as press dewatering, gravitational dewatering or vaccuum dewatering. Optionally, mechanical dewatering may be combined with evaporation provided by applying heat.

[0046] In some embodiments, the water removal of step c) comprises the dewatering of the wet MFC web in at least one dewatering step, wherein at least one dewatering step of the at least one dewatering step is or comprises a press dewatering step.

[0047] Each press dewatering step may comprise application of a press fabric in direct contact or indirect contact (e.g., via a separate membrane) with the wet MFC web formed on the non-porous support, or on the paper or paperboard substrate positioned on the non-porous support, and conducting the wet MFC web, or the paper or paperboard substrate provided with the wet MFC web, arranged between the press fabric and the non-porous support, through a pressing equipment to remove water from the wet MFC web by transferring water from the wet MFC web into the press fabric. With press fabric is meant a fabric that is permeable and allows water to be removed from the wet MFC web either by absorbing the water or by allowing the water to be removed through the fabric. The press fabric may be a press felt (dewatering felt). Any known suitable press fabric or press felt may be utilized. With pressing equipment is meant an equipment comprising one or more nips through which the wet MFC web, or the paper or paperboard substrate provided with the wet MFC web, is conducted and thus pressed and dewatered.

[0048] In some embodiments, the water removal of step c) comprises the dewatering comprising at least one press dewatering step including application of a press fabric, wherein the collection of water of step d) comprises collecting water removed from the wet MFC web by the at least one press dewatering step, wherein the collection of water removed from the wet MFC web by the at least one press dewatering step comprises collecting water transferred to the press fabric.

[0049] In some embodiments, the water removal of step c) comprises the drying of the wet MFC web in at least one drying step, wherein at least one drying step is or comprises a non-contact drying step and / or at least one drying step is or comprises a contact drying step. Thus, in some embodiments, the drying of step c) comprises at least one non-contact drying step and / or at least one contact drying step. Each non-contact drying step may comprise hot gas (or air) impingement drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near infrared drying or a combination thereof. Each contact drying step may comprise contacting the wet MFC web with at least one heated belt or heated roll.

[0050] In step d) of the method of the first aspect, water removed from the wet MFC web by the water removal in step c) is collected into at least one water fraction. Water removed from the wet MFC web may be collected in liquid form and / or vapor form (before condensation) and may be collected in a water collection arrangement. The water collection arrangement may comprise any suitable devices and / or arrangements for collecting water removed by dewatering and drying, respectively, in step c), and conveying removed water to a further process unit, wherein the further process unit may be a tank, treatment unit, mixing chest, etc. For example, the water collection arrangement may comprise one or more water collector devices arranged to collect water from dewatering step(s), such as one or more devices comprising one or more vacuum boxes to remove water from press felt(s) used in dewatering or comprising one or more press nips to remove water from press felt(s) used in dewatering, and / or one or more water collector devices arranged to collect water from drying step(s). Optionally, the water collection arrangement may also comprise any suitable devices or arrangements for condensation of water collected in vapor form.

[0051] Furthermore, the water collection arrangement may further comprise one or more tanks, conduits, means (e.g., pumps) for conveying the collected water to further process units, etc.

[0052] Thus, in embodiments comprising collection of water from one or more press dewatering steps, the water collection arrangement may comprise one or more devices arranged to collect water from the press fabric and one or more devices for conveying collected water to a further process unit, e.g., one or more pumps, conduits, etc.

[0053] In embodiments comprising collection of water from one or more drying steps, the water collection arrangement may comprise one or more devices arranged to collect water in vapor form and condense collected water vapor to liquid water and one or more devices for conveying collected liquid water to a further process unit, e.g., one or more pumps, conduits, etc. In some embodiments, the collection of water removed from the wet MFC web by the drying comprises condensation of water in vapor phase involving use of a heat exchanger and / or a condenser.

[0054] Thus, in some embodiments, the water removal of step c) comprises the drying of the wet MFC web, wherein the collection of water of step d) comprises collecting water removed from the wet MFC web by the drying, wherein the collection of water removed from the wet MFC web by the drying comprises condensation of water in vapor phase involving use of a heat exchanger and / or a condenser. In some embodiments, the water removal of step c) comprises dewatering the wet MFC web in at least one dewatering step and drying the wet MFC web in at least one drying step. In these embodiments, the collection of water of step d) may comprise collecting water removed by dewatering and / or collecting water removed by drying into at least one water fraction, e.g., in a water collection arrangement.

[0055] The method of the first aspect comprises the optional step e) in which at least one water fraction of the at least one water fraction is subjected to a purification treatment comprising at least one purification step. Any collected water may be subjected to any suitable purification treatment for removal of impurities of the collected water such that the collected water is suitable to be used as suspension medium in the preparation of the MFC suspension in step a). Thus, in embodiments of the method of the first aspect comprising step e), water collected into at least one water fraction, e.g., in a water collection arrangement, is provided to a purification treatment arrangement. The purification treatment arrangement may comprise any suitable devices or arrangements for purification treatment of the collected water.

[0056] In some embodiments each purification step of the purification treatment of step e) is selected from the group of: filtration, fractionation, cleaning, deaeration, centrifugation, sedimentation, sterilization, flotation and screening. For example, the filtration may be a membrane filtration / separation, such as a pressure driven method selected from microfiltration (MF), nanofiltration (NF), ultrafiltration (UF) and reverse osmosis (RO). The membrane separation can also utilize other means, such as electrically driven methods including electrodialysis or electro deionization. For example, the sterilization may be an ultraviolet (UV) treatment or a biocide treatment.

[0057] Thus, in some embodiments the method of the first aspect comprises step e), whereas in some embodiments step e) is omitted, e.g., if the purity level of the collected water is acceptable.

[0058] In some embodiments in which the method comprises step e), the method further comprises a step of subjecting at least one water fraction of the at least one water fraction to a measurement of at least one purity parameter. In these embodiments, the utilized purification treatment arrangement may further comprise a device for measurement of the at least one purity parameter. In some embodiments in which the method comprises step e), the method further comprises a step of subjecting at least one water fraction of the at least one water fraction to a measurement of at least one purity parameter, wherein step e) comprises subjecting the at least one water fraction subjected to the measurement to the purification treatment and adjusting the purification treatment of the at least one water fraction subjected to the measurement based on the at least one measured purity parameter. Thus, in these embodiments the purity of collected water is measured by measuring at least one purity parameter and the purification treatment is adjusted based on the measurement, e.g., the selection of type(s) and / or extent of purification treatment step(s) may be adjusted. In these embodiments the utilized purification treatment arrangement may further comprise one or more devices for measurement of the at least one purity parameter and adjusting the purification treatment based on the at least one measured purity parameter.

[0059] In some embodiments, the method further comprises a step of subjecting at least one water fraction of the at least one water fraction to a measurement of at least one purity parameter before the optional step e) in order to determine whether a purification treatment is needed or not. Alternatively or additionally, a measurement of at least one purity parameter may be performed between steps of the purification treatment of step e) or after the purification treatment of step e).

[0060] It is further possible to utilize, for example, an algorithm-based model such as machine learning or artificial intelligence to monitor and predict the required purification treatment solution based on incoming process parameters and / or water quality such as the at least one purity parameter. The algorithm-based model may be implemented by a control arrangement including a self-learning artificial intelligence unit based on Convolutional Neural Network.

[0061] For example, the purity parameter may be selected from the group of: total organic carbon (TOC), biochemical oxygen demand (BOD), total suspended solids, pH, electrical conductivity, color, infrared (IR) transmittance, ultraviolet (UV) / visible light transmittance, volatile fatty acids, turbidity, volatile organic content (VOC), chlorides, sulphates, phosphorous content, nitrogen content and content of particles and / or fibers and / or fibrils. In step f) of the method of the first aspect, water of the at least one water fraction (optionally purified) is used as suspension medium in the preparation of the MFC suspension in step a). In some embodiments, at least 5 weight-%, such as 5-100 weight-%, of the suspension medium of the prepared MFC suspension is reused water, i.e., water collected into the at least one water fraction. Preferably, at least 30 weight-%, most preferably at least 40 weight-%, such as 45-100% of the suspension medium of the prepared MFC suspension is reused water, i.e., water collected into the at least one water fraction.

[0062] In some embodiments, the preparation of the MFC suspension in step a) comprises the sub-steps of: providing an MFC stock suspension, and adding water of at least one water fraction of the at least one water fraction (optionally purified) as suspension medium to the MFC stock suspension in the preparation of the MFC suspension.

[0063] The MFC stock suspension is a suspension comprising MFC provided from a fibrillation treatment plant / arrangement, in which MFC is produced from cellulose fibers or pre-treated cellulose fibers. Thus, the MFC stock suspension is utilized as raw material (i.e., raw material MFC) in the preparation of the MFC suspension used in step a) of the method of the first aspect. Optional further pulp fraction(s) and conventional paper making additives or chemicals as mentioned above may also be added to the MFC stock suspension at any suitable process position.

[0064] The addition of the water of at least one water fraction of the at least one water fraction to the MFC stock suspension may be performed, e.g., in a mixing chest or dilution control unit. Thus, in these embodiments, water collected in step d) (and optionally purified in step e)) is used as suspension medium in the preparation of the MFC suspension from the MFC stock suspension in step a), wherein the prepared MFC suspension comprises between 50 weight-% to 100 weight-% MFC based on total dry weight and has a dry content of 1-30 weight-%.

[0065] In some embodiments, the preparation of the MFC suspension in step a) comprises the sub-steps of: providing pulp to a fibrillation treatment arrangement; processing the pulp in the fibrillation treatment arrangement to form an MFC stock suspension, adding water of at least one water fraction of the at least one water fraction (optionally purified) as suspension medium to the pulp during the processing to form the MFC stock suspension, and using the MFC stock suspension in the preparation of the MFC suspension.

[0066] Thus, in these embodiments, water collected in step d) (and optionally purified in step e)) is used as suspension medium in the preparation of the MFC suspension by using collected water as suspension medium in the processing of pulp to form the MFC stock suspension, from which the MFC suspension, which comprises between 50 weight-% to 100 weight-% MFC based on total dry weight and has a dry content of 1-30 weight-%, is prepared.

[0067] Typically, the pulp provided to the fibrillation treatment arrangement is pulp obtained from wood, such as hardwood and / or softwood. However, the pulp may alternatively be obtained from agricultural sources such as wheat straw, bamboo, bagasse or other non-wood cellulosic sources.

[0068] The pulp provided to the fibrillation treatment arrangement may be produced by chemical, semi-chemical, mechanical and / or thermo-mechanical pulping of cellulosic and / or lignocellulosic raw material, such as hardwood and / or softwood. For example, the pulp may be or comprise chemical pulp, such as sulfate pulp (kraft pulp), sulfite pulp or dissolving pulp, mechanical pulp, pressure groundwood (PGW), thermomechanical pulp (TMP), high temperature thermomechanical pulp (HTMP), chemi-thermomechanical pulp (CTMP), high temperature chemi-thermomechanical pulp (HTCTMP), recycled pulp, or a combination thereof. Preferably, the pulp is or comprises kraft pulp. The pulp may be bleached or unbleached.

[0069] The processing of the pulp to the MFC stock suspension may be performed in any suitable way. For example, MFC may be produced by mechanically treating the pulp in a mechanical fibrillation treatment. The mechanical fibrillation treatment may be combined with one or more pretreatments of the pulp in order to enable an easier fibrillation and, thus, a more energy efficient fibrillation process, and to enable production of MFC with different sizes and size distributions. For example, the pulp may be pretreated mechanically and / or enzymatically. The purpose of the mechanical pretreatment is to soften the cellulose fibers of the pulp and make them more accessible and reactive before subsequent treatments or pretreatments such as an enzymatic pretreatment. The purpose of the enzymatic pretreatment is primarily to hydrolyse the cellulose fibers, in particular to break internal hydrogen bonds of the cellulose fibers (i.e., to promote disintegration of cellulose fibers in later mechanical treatment stages), and increase the accessibility and activity of the cellulose fibers and, thus, facilitate the production of MFC. For wood fibers, any suitable wood-degrading enzymes which hydrolyse / degrade cellulose fibers may be utilized.

[0070] The fibrillation treatment arrangement may comprise any suitable devices for processing the pulp to the MFC stock suspension. For example, the fibrillation treatment arrangement may comprise at least one mechanical fiber treatment apparatus. Each mechanical fiber treatment apparatus may be selected from the group of refiner, homogenizer / fluidizer, defibrator, deflaker, beater, friction grinder, high shear fibrillator (such as cavitron rotor / stator system, steam explosion system or high consistency refining or milling system), disperger, ball mill and other known mechanical fiber treatment apparatuses suitable to be used in processing of pulp to MFC, or combinations thereof. The pulp may be passed one or more times through each utilized mechanical fiber treatment apparatus. Optionally, the fibrillation treatment arrangement may further comprise one or more pretreatment apparatuses, wherein each pretreatment apparatus is arranged for pretreating the pulp mechanically, enzymatically or by chemical modification. For example, the fibrillation treatment arrangement may comprise at least one mechanical fiber pretreatment apparatus. Each mechanical fiber pretreatment apparatus may be selected from the group of refiner, defibrator, deflaker, beater, shredder, ball mill, rotor-stator mixer, ultrasonic treatment device, steam explosion device and other known mechanical fiber pretreatment apparatuses suitable for pretreating the cellulose fibers mechanically.

[0071] In some embodiments of the method of the first aspect the water removal of step c) comprises the dewatering of the wet MFC web in at least one dewatering step and the collection of water of step d) comprises collecting water removed from the wet MFC web by the dewatering into a first water fraction, e.g., in a first arrangement of a water collection arrangement. In these embodiments step f) comprises using water of the first water fraction as suspension medium in the preparation of the MFC suspension in step a). Optionally, these embodiments comprise step e), wherein step e) comprises subjecting the first water fraction to the purification treatment as described above. In some of these embodiments, the method further comprises a step of subjecting the first water fraction to a measurement of at least one first purity parameter and step e) comprises adjusting the purification treatment of the first water fraction based on the at least one measured first purity parameter. The at least one first purity parameter may be selected from the group of: total organic carbon (TOC), biochemical oxygen demand (BOD), total suspended solids, pH, electrical conductivity, color, IR transmittance, UV / visible light transmittance, turbidity, volatile fatty acids, volatile organic content (VOC), chlorides, sulphates, phosphorous content, nitrogen content and content of particles and / or fibers and / or fibrils. Step c) of these embodiments may further comprise the drying of the wet MFC web in at least one drying step even though water removed by the drying is not collected.

[0072] The first arrangement may comprise any suitable devices and / or arrangements for collecting water removed by dewatering in step c) and conveying removed water to a further process unit, wherein the further process unit may be a tank, treatment unit, mixing chest, etc. as described above. Optionally, the first arrangement may also comprise any suitable devices or arrangements for condensation of water collected in vapor form. In embodiments comprising step e), water collected in the first arrangement is provided to a purification treatment arrangement. The purification treatment arrangement may comprise any suitable devices or arrangements for purification treatment of the collected water as described above.

[0073] In some embodiments of the method of the first aspect the water removal of step c) comprises the drying of the wet MFC web in at least one drying step and the collection of water of step d) comprises collecting water removed from the wet MFC web by the drying into a second water fraction, e.g., in a second arrangement of a water collection arrangement. In these embodiments step f) comprises using water of the second water fraction as suspension medium in the preparation of the MFC suspension in step a). Optionally, these embodiments comprise step e), wherein step e) comprises subjecting the second water fraction to the purification treatment as described above. In some of these embodiments, the method further comprises a step of subjecting the second water fraction to a measurement of at least one second purity parameter and step e) comprises adjusting the purification treatment of the second water fraction based on the at least one measured second purity parameter. The at least one second purity parameter may be selected from the group of: total organic carbon (TOC), biochemical oxygen demand (BOD), total suspended solids, pH, electrical conductivity, color, IR transmittance, UV / visible light transmittance, turbidity, volatile fatty acids, volatile organic content (VOC), chlorides, sulphates, phosphorous content, nitrogen content and content of particles and / or fibers and / or fibrils. Step c) of these embodiments may further comprise the dewatering of the wet MFC web in at least one dewatering step even though water removed by the dewatering is not collected.

[0074] The second arrangement may comprise any suitable devices and / or arrangements for collecting water removed by drying in step c) and conveying removed water to a further process unit, wherein the further process unit may be a tank, treatment unit, mixing chest, etc. as described above. Optionally, the second arrangement may also comprise any suitable devices or arrangements for condensation of water collected in vapor form. In embodiments comprising step e), water collected in the second arrangement is provided to a purification treatment arrangement. The purification treatment arrangement may comprise any suitable devices or arrangements for purification treatment of the collected water as described above.

[0075] In some embodiments of the method of the first aspect the water removal of step c) comprises the dewatering of the wet MFC web in at least one dewatering step and the drying of the wet MFC web in at least one drying step, and the collection of water of step d) comprises collecting water removed from the wet MFC web by the dewatering into a first water fraction, e.g., in a first arrangement as described above, and collecting water removed from the wet MFC web by the drying into a second water fraction, e.g., in a second arrangement as described above. In these embodiments step f) comprises using water of the first water fraction and the second water fraction as suspension medium in the preparation of the MFC suspension in step a). Optionally, these embodiments comprise step e), wherein step e) comprises subjecting the first water fraction and / or the second water fraction, respectively, to the purification treatment as described above. In some of these embodiments, the method) further comprises a step of subjecting the first water fraction to a measurement of at least one first purity parameter as described above and / or subjecting the second water fraction to a measurement of at least one second purity parameter as described above and step e) comprises adjusting the purification treatment of the first water fraction based on the at least one measured first purity parameter and / or adjusting the purification treatment of the second water fraction based on the at least one measured second purity parameter

[0076] In some embodiments of the method of the first aspect the water removal of step c) comprises the dewatering of the wet MFC web in at least one dewatering step and the drying of the wet MFC web in at least one drying step, and the collection of water of step d) comprises collecting water removed from the wet MFC web by the dewatering and water removed from the wet MFC web by the drying into a first water fraction, e.g., in a first arrangement of a water collection arrangement as described above. In these embodiments step f) comprises using water of the first water fraction as suspension medium in the preparation of the MFC suspension in step a). Optionally, these embodiments comprise step e), wherein step e) comprises subjecting the first water fraction to the purification treatment as described above. In some of these embodiments, the method further comprises a step of subjecting the first water fraction to a measurement of at least one first purity parameter as described above and step e) comprises adjusting the purification treatment of the first water fraction based on the at least one measured first purity parameter.

[0077] The MFC web produced in the above described embodiments of the method of the present disclosure may be an MFC film. Thus, in these embodiments, a wet MFC film is formed in step b) and an MFC film, such as a dry MFC film, is formed in step c).

[0078] In some embodiments in which the MFC web is an MFC film, a dry MFC film having an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 10 cc / m2 / 24h, preferably less than 7 cc / m2 / 24h, and more preferably less than 5 cc / m2 / 24h, is formed.

[0079] In some embodiments in which the MFC web is an MFC film, a dry MFC film having a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C, of less than 100 g / m2 / 24h, preferably less than 50 g / m2 / 24h, and more preferably less than 20 g / m2 / 24h, is formed.

[0080] In some embodiments in which the MFC web is an MFC film, a dry MFC film having a dry grammage of 2-70 g / m2, preferably 3-70 g / m2such as 4-70 g / m2or 8-70 g / m2or 10-60 g / m2or 10-50 g / m2or 15-40 g / m2, as measured according to ISO 536, is formed.

[0081] In some embodiments in which the MFC web is an MFC film, a dry MFC film having an average film thickness of 5-60 pm, preferably 10-50 pm, 15-45 pm or 20-40 pm, is formed. The average film thickness may be defined as an average thickness of the film across the entire width. Thickness of the MFC film may be measured using, as non-limiting examples, white light interferometry, laser profilometry, or optically by cutting a sample in cross-machine directional line (either cast in resin or not) and microscopic imaging (e.g., scanning electron microscopy or other applicable method) of the cut section in thickness direction.

[0082] In some embodiments in which the MFC web is an MFC film, a dry MFC film having a width of 0.3-4 m, preferably 0.5-4 m, 1 -4 m or 2-4 m, is formed.

[0083] In some embodiments in which the MFC web is an MFC film, a dry MFC film having a density of 700-1500 kg / m3, preferably 800-1500 kg / m3, most preferably 900-1500 kg / m3, as measured according to ISO 534:2011 , is formed.

[0084] In some embodiments the MFC web produced in the method of the present disclosure is an absorbent layer, a membrane, a separation medium or a prefabricate.

[0085] A free-standing MFC film provided by the method of the present disclosure may be applied to the surface of any one of a paper product and a paperboard product so as to form a laminate, such as a paper or paper-based packaging material laminate.

[0086] A free-standing MFC film, or a paper or paperboard substrate provided with an MFC film, provided by the method of the present disclosure may be utilized in a laminate together with one or more polymer layers, such as termoplastic polymer layers. For example, the one or more additional polymer layers may be constituted by any suitable polyolefin or polyester. The additional polymer layer(s) can be provided e.g. by extrusion coating, film coating or lamination or dispersion coating. Common plastic resins used in extrusion coating include polyethylene (PE), polypropylene (PP) polyethylene terephthalate (PET), polylactic acid (PLA), polyglycolic acid (PGA), polyhydroxyalkanoates (PHA) and polybutylene succinate (PBS).

[0087] A free-standing MFC film, or a paper or paperboard substrate provided with an MFC film, provided by the method of the present disclosure, may be used as a packaging material or in a packaging material, such as a food or liquid packaging material, and may be incorporated into any type of package, such as a box, bag, a wrapping film, cup, container, tray, bottle etc.

[0088] According to a second aspect illustrated herein, there is provided an MFC web such as an MFC film obtainable by the method of the first aspect. The MFC web according to the second aspect may be further defined as set out above with reference to the method of the first aspect.

[0089] Brief description of the drawings

[0090] In the following, the invention will be further illustrated by description of exemplified embodiments with reference to the accompanying drawings, wherein:

[0091] Fig. 1 shows a schematic overview of a first embodiment of the method according to the present disclosure;

[0092] Fig. 2 shows a schematic overview of a second embodiment of the method according to the present disclosure;

[0093] Fig. 3 shows a schematic overview of a third embodiment of the method according to the present disclosure; and

[0094] Fig. 4 shows a schematic overview of a fourth embodiment of the method according to the present disclosure.

[0095] Detailed description of the drawings

[0096] Fig. 1 shows a schematic overview of a first embodiment of the method according to the first aspect of the present disclosure performed in a system 1 for MFC web production. In the first embodiment illustrated in Fig. 1 , an MFC suspension 2 is prepared from an MFC stock suspension 3 including dilution of the MFC stock suspension 3 with water as suspension medium in a mixing chest 4. Optionally, one or more additives (e.g., paper making additives and / or chemicals) and / or one or more other suitable components (e.g., further pulp fraction(s)) may also be added to the MFC stock suspension 3 in the mixing chest 4 or may be added to the MFC stock suspension 3 at any other suitable position of the system 1 . The MFC stock suspension 3 is formed in a fibrillation treatment arrangement 5. The fibrillation treatment arrangement 5 comprises any suitable devices for processing pulp to MFC, i.e., to form the MFC stock suspension 3. The prepared MFC suspension 2 comprises between 50 weight-% to 100 weight-% MFC based on total dry weight and has a dry content of 1-30 weight-%. The MFC suspension 2 is conveyed to an optional machine chest 6 and further to a slot die applicator 7. A wet MFC web 8 is formed of the MFC suspension 2 by casting a layer of the MFC suspension 2 by the slot die applicator 7 on a non-porous support in the form of an endless metal belt 9. In the first embodiment illustrated in Fig. 1 , the wet MFC web 8 positioned on the metal belt 9 is subjected to water removal by dewatering in a dewatering device 10, and optionally drying in a drying device 11 , to form a dry MFC web 12. Typically, the dry MFC web 12 is wound onto a core to form a reel 13 of the dry MFC web 12. Water removed from the wet MFC web 8 by the dewatering in the dewatering device 10 is collected and provided into a first water fraction 14 by a first water collector device 15 of a first arrangement 16 of a water collection arrangement 17. In the embodiment illustrated in Fig. 1 , the water collection arrangement 17 is constituted by the first arrangement 16. The first water fraction 14 is conveyed via conduits 18 of the first arrangement 16 to an optional purification treatment arrangement 19, in which the first water fraction 14 is subjected to a purification treatment. Optionally, the first water fraction 14 may be subjected to measurement of at least one first purity parameter in a measurement device (not shown) and the purification treatment may be adjusted based on the measurement of the at least one first purity parameter. The first water fraction 14 is after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added as suspension medium to the MFC stock suspension 3 in the mixing chest 4. Additionally or alternatively, the first water fraction 14 is after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added to the pulp during processing to form the MFC stock suspension 3 in the fibrillation treatment arrangement 5. Typically, fresh water is also added as suspension medium in the mixing chest 4. If the optional purification treatment is omitted, the first water fraction 14 may be conveyed to any other process unit(s) for use as suspension medium, e.g., directly to the mixing chest 4 or the fibrillation treatment arrangement 5, in the preparation of the MFC suspension 2. Reject 20 from the purification treatment in the purification treatment arrangement 19 may be provided to sludge treatment, effluent plant and / or reuse. If the system 1 comprises the purification treatment arrangement 19, the system 1 may further comprise a control arrangement (not shown) including a self-learning artificial intelligence unit based on Convolutional Neural Network to monitor and predict the required purification treatment solution based on incoming process parameters and / or water quality such as the at least one first purity parameter.

[0097] Fig. 2 shows a schematic overview of a second embodiment of the method according to the first aspect of the present disclosure. The second embodiment differs from the first embodiment in the water management. In the second embodiment illustrated in Fig. 2, the wet MFC web 8 positioned on the metal belt 9 is subjected to water removal by drying in a drying device 11 , optionally preceded by dewatering in a dewatering device 10, to form a dry MFC web 12. Water removed from the wet MFC web 8 by the drying in the drying device 11 (i.e., evaporated water) is collected and provided into a second water fraction 21 by a second water collector device 22 of a second arrangement 23 of a water collection arrangement 17. In the embodiment illustrated in Fig. 2, the second water collector device 22 comprises a steam condenser. In the embodiment illustrated in Fig. 2, the water collection arrangement 17 is constituted by the second arrangement 23. The second water fraction 21 is conveyed via conduits 24 of the second arrangement 23 to an optional purification treatment arrangement 19, in which the second water fraction 21 is subjected to a purification treatment. Optionally, the second water fraction 21 may be subjected to measurement of at least one second purity parameter by a measurement device (not shown) and the purification treatment may be adjusted based on the measurement of the at least one second purity parameter. The second water fraction 21 is after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added as suspension medium to the MFC stock suspension 3 in the mixing chest 4. Additionally or alternatively, the second water fraction 21 is after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added to the pulp during processing to form the MFC stock suspension 3 in the fibrillation treatment arrangement 5. Typically, fresh water is also added as suspension medium in the mixing chest 4. If the optional purification treatment is omitted, the second water fraction 21 may be conveyed to any other process unit(s) for use as suspension medium, e.g., directly to the mixing chest 4 or the fibrillation treatment arrangement 5, in the preparation of the MFC suspension 2.

[0098] Fig. 3 shows a schematic overview of a third embodiment of the method according to the first aspect of the present disclosure. The third embodiment differs from the first embodiment in the water management. In the third embodiment illustrated in Fig. 3, the wet MFC web 8 is subjected to water removal by dewatering in a dewatering device 10 and drying in a drying device 11 to form a dry MFC web 12. Water removed from the wet MFC web 8 by the dewatering in the dewatering device 10 is collected and provided into a first water fraction 14 by a first water collector device 15 of a first arrangement 16 of a water collection arrangement 17. Also, water removed from the wet MFC web 8 by the drying in the drying device 11 is collected and provided into the first water fraction 14 by a second water collector device 22 of the water collection arrangement 17. Water collected by the second water collector device 22 is conveyed via conduits 24 to the first arrangement 16. In the embodiment illustrated in Fig. 3, the water collection arrangement 17 comprises the first arrangement 16, the second water collector device 22 and the conduits 24. The first water fraction 14 is conveyed via conduits 18 of the first arrangement 16 to an optional purification treatment arrangement 19, in which the first water fraction 14 is subjected to a purification treatment. Optionally, the first water fraction 14 may be subjected to measurement of at least one first purity parameter in a measurement device (not shown) and the purification treatment may be adjusted based on the measurement of the at least one first purity parameter. The first water fraction 14 is after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added as suspension medium to the MFC stock suspension 3 in the mixing chest 4. Additionally or alternatively, the first water fraction 14 is after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added to the pulp during processing to form the MFC stock suspension 3 in the fibrillation treatment arrangement 5. Typically, fresh water is also added as suspension medium in the mixing chest 4. Fig. 4 shows a schematic overview of a fourth embodiment of the method according to the first aspect of the present disclosure. The fourth embodiment differs from the first embodiment in the water management. In the fourth embodiment illustrated in Fig. 4, the wet MFC web 8 is subjected to water removal by dewatering in a dewatering device 10 and drying in a drying device 11 to form a dry MFC web 12. Water removed from the wet MFC web 8 by the dewatering in the dewatering device 10 is collected and provided into a first water fraction 14 by a first water collector device 15 of a first arrangement 16 of a water collection arrangement 17. Water removed from the wet MFC web 8 by the drying in the drying device 11 is collected and provided into a second water fraction 21 by a second water collector device 22 of a second arrangement 23 of the water collection arrangement 17. In the embodiment illustrated in Fig. 4, the water collection arrangement 17 comprises the first arrangement 16 and the second arrangement 23. The first water fraction 14 is conveyed via conduits 18 of the first arrangement 16 to an optional purification treatment arrangement 19, in which the first water fraction 14 may be subjected to a purification treatment. The second water fraction 21 is conveyed via conduits 24 of the second arrangement 23 to the optional purification treatment arrangement 19, in which the second water fraction 21 may be subjected to a purification treatment. The first water fraction 14 and the second water fraction 21 may be subjected to the same or different purification treatments in the purification treatment arrangement 19. Optionally, the first water fraction 14 may be subjected to measurement of at least one first purity parameter in a measurement device (not shown) and the purification treatment of the first water fraction 14 may be adjusted based on the measurement of the at least one first purity parameter. Optionally, the second water fraction 21 may be subjected to measurement of at least one second purity parameter in a measurement device (not shown) and the purification treatment of the second water fraction 21 may be adjusted based on the measurement of the at least one second purity parameter. The first water fraction 14 and the second water fraction 21 , respectively, are after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added as suspension medium to the MFC stock suspension 3 in the mixing chest 4. Additionally or alternatively, the first water fraction 14 and the second water fraction 21 , respectively, are after the optional purification treatment used as suspension medium in the preparation of the MFC suspension 2 by being added to the pulp during processing to form the MFC stock suspension 3 in the fibrillation treatment arrangement 5. If the optional purification treatment for one of or both of the first water fraction 14 and the second water fraction 21 is omitted, the first water fraction 14 and the second water fraction 21 , respectively, may be conveyed to any other process unit(s) for use as suspension medium in the preparation of the MFC suspension 2, e.g., directly to the mixing chest 4 or the fibrillation treatment arrangement 5.

[0099] Generally, while the products, materials, layers and processes are described in terms of “comprising” various components or steps, the products, materials, layers and processes can also “consist essentially of’ or “consist of’ the various components and steps.

[0100] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Claims

CLAIMS1 . A method for producing a microfibrillated cellulose (MFC) web, wherein the method comprises the steps of: a) preparing an MFC suspension comprising between 50 weight-% to 100 weight-% MFC based on total dry weight and a suspension medium, wherein the suspension medium is water, wherein said MFC suspension has a dry content of 1-30 weight-%; b) forming a wet MFC web of said MFC suspension by casting on a non-porous support or on a paper or paperboard substrate positioned on the non-porous support; c) subjecting said wet MFC web formed on said non-porous support or formed on said paper or paperboard substrate positioned on said non-porous support to water removal to form said MFC web, wherein the water removal comprises dewatering said wet MFC web in at least one dewatering step and / or drying said wet MFC web in at least one drying step; d) collecting water removed from said wet MFC web by said water removal into at least one water fraction; e) optionally, subjecting at least one water fraction of said at least one water fraction to a purification treatment comprising at least one purification step, and f) using water of said at least one water fraction as suspension medium in the preparation of said MFC suspension in step a).

2. The method according to claim 1 , wherein each purification step of said purification treatment of step e) is selected from the group of: filtration, fractionation, cleaning, deaeration, centrifugation, sedimentation, sterilization, flotation and screening.

3. The method according to claim 1 or 2, wherein the method further comprises a step of subjecting at least one water fraction of said at least one water fraction to a measurement of at least one purity parameter, wherein the method comprises step e), wherein step e) comprises subjecting said at least one water fraction subjected to said measurement to said purificationtreatment and adjusting said purification treatment of said at least one water fraction subjected to said measurement based on the at least one measured purity parameter.

4. The method according to claim 3, wherein said at least one purity parameter is selected from the group of: total organic carbon, biochemical oxygen demand, total suspended solids, pH, electrical conductivity, color, infrared transmittance, ultraviolet / visible light transmittance, volatile fatty acids, turbidity, volatile organic content, chlorides, sulphates, phosphorous content, nitrogen content and content of particles and / or fibers and / or fibrils.

5. The method according to any one of the preceding claims, wherein said water removal of step c) comprises said dewatering of said wet MFC web in at least one dewatering step, wherein said collection of water of step d) comprises collecting water removed from said wet MFC web by said dewatering into a first water fraction, and wherein step f) comprises using water of said first water fraction as suspension medium in the preparation of said MFC suspension in step a).

6. The method according to claim 5, wherein the method comprises step e), wherein step e) comprises subjecting said first water fraction to said purification treatment.

7. The method according to claim 6, wherein the method further comprises a step of subjecting said first water fraction to a measurement of at least one first purity parameter and wherein step e) comprises adjusting said purification treatment of said first water fraction based on the at least one measured first purity parameter.

8. The method according to claim 7, wherein said at least one first purity parameter is selected from the group of: total organic carbon, biochemical oxygen demand, total suspended solids, pH, electrical conductivity, color, infrared transmittance, ultraviolet / visible light transmittance, volatile fattyacids, turbidity, volatile organic content, chlorides, sulphates, phosphorous content, nitrogen content and content of particles and / or fibers and / or fibrils.

9. The method according to any one of the preceding claims, wherein said water removal of step c) comprises said drying of said wet MFC web in at least one drying step, wherein said collection of water of step d) comprises collecting water removed from said wet MFC web by said drying into a second water fraction, and wherein step f) comprises using water of said second water fraction as suspension medium in the preparation of said MFC suspension in step a).

10. The method according to claim 9, wherein the method comprises step e), wherein step e) comprises subjecting said second water fraction to said purification treatment.11 . The method according to claim 10, wherein the method further comprises a step of subjecting said second water fraction to a measurement of at least one second purity parameter and wherein step e) comprises adjusting said purification treatment of said second water fraction based on the at least one measured second purity parameter.

12. The method according to claim 11 , wherein said at least one second purity parameter is selected from the group of: total organic carbon, biochemical oxygen demand, total suspended solids, pH, electrical conductivity, color, infrared transmittance, ultraviolet / visible light transmittance, volatile fatty acids, turbidity, volatile organic content, chlorides, sulphates, phosphorous content, nitrogen content and content of particles and / or fibers and / or fibrils.

13. The method according to any one of claims 5-8, wherein said water removal of step c) comprises said dewatering of said wet MFC web in at least one dewatering step and said drying of said wet MFC web in at least one drying step,wherein said collection of water of step d) comprises collecting water removed from said wet MFC web by said dewatering and water removed from said wet MFC web by said drying into said first water fraction.

14. The method according to any one of the preceding claims, wherein the dewatering comprises at least one press dewatering step.

15. The method according to claim 14, wherein each press dewatering step comprises: applying a press fabric into direct or indirect contact with said wet MFC web formed on said non-porous support or on said paper or paperboard substrate positioned on said non-porous support, and conducting said wet MFC web, or said wet MFC web and said paper or paperboard substrate, arranged between said press fabric and said non-porous support, through a pressing equipment to remove water from said wet MFC web by transferring water from said wet MFC web into the press fabric.

16. The method according to claim 15, wherein the water removal of step c) comprises said dewatering comprising at least one press dewatering step, wherein said collection of water of step d) comprises collecting water removed from said wet MFC web by said at least one press dewatering step, wherein said collection of water removed from said wet MFC web by said at least one press dewatering step comprises collecting water transferred to said press fabric.

17. The method according to any one of the preceding claims, wherein said drying of step c) comprises at least one non-contact drying step.

18. The method according to claim 17, wherein each non-contact drying step comprises hot gas impingement drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near infrared drying or a combination thereof.

19. The method according to any one of the preceding claims, wherein said drying of step c) comprises at least one contact drying step.

20. The method according to claim 19, wherein each contact drying step comprises contacting said wet MFC web with at least one heated belt or heated roll.

21. The method according to any one of claims 1-20, wherein said water removal of step c) comprises said drying of said wet MFC web, wherein said collection of water of step d) comprises collecting water removed from said wet MFC web by said drying, wherein said collection of water removed from said wet MFC web by said drying comprises condensation of water in vapor phase involving use of a heat exchanger and / or a condenser.

22. The method according to any one of the preceding claims, wherein the non- porous support is a metal belt.

23. The method according to any one of the preceding claims, wherein the preparation of said MFC suspension in step a) comprises the sub-steps of: providing an MFC stock suspension, and adding water of at least one water fraction of the at least one water fraction as suspension medium to said MFC stock suspension in the preparation of said MFC suspension.

24. The method according to any one of claims 1-22, wherein the preparation of said MFC suspension in step a) comprises the sub-steps of: providing pulp to a fibrillation treatment arrangement; processing said pulp in said fibrillation treatment arrangement to form an MFC stock suspension; adding water of at least one water fraction of the at least one water fraction as suspension medium to said pulp during said processing to form said MFC stock suspension, and using the MFC stock suspension in the preparation of the MFC suspension.

25. The method according to claim 24, wherein the preparation of said MFC suspension in step a) further comprises the sub-step of:adding water of at least one water fraction of the at least one water fraction as suspension medium to said MFC stock suspension in the preparation of said MFC suspension.

26. The method according to claim 23 or 25, wherein the addition of water of at least one water fraction of the at least one water fraction as suspension medium to said MFC stock suspension is performed in a dilution control unit.

27. The method according to any one of the preceding claims, wherein said MFC web is an MFC film.

28. The method according to claim 27, wherein said MFC film has an average thickness of 5-60 pm as dry and a dry grammage of 2-70 g / m2as measured according to ISO 536.

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