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 and forming a wet MFC web from the MFC suspension by casting on a non-porous support. The wet MFC web positioned on the non-porous support is subjected to water removal by means of dewatering and / or drying to form a dry MFC web. Broke material is discharged and collected. Collected broke material is mixed with water to provide at least one broke suspension wherein at least 90 weight- % of each broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. The broke suspension(s) is / are subjected to a mechanical treatment. The broke suspension(s) is / are used in the preparation of the MFC suspension. The mechanical treatment is performed to increase the viscosity of the broke suspension(s) to at least 60% of the viscosity of the MFC suspension without the broke suspension(s).

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, which method enables improved reuse of material rejected or wasted during the production.

[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 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 and form a dry MFC web. This type of web casting method has been shown to enable production of MFC films with very smooth surfaces with good barrier properties, such as oxygen barrier properties and / or water vapor barrier properties.

[0007] There is still a need for a method for producing an MFC web on a non-porous support with a casting method, which enables improved reuse of material rejected or wasted during the production.

[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, which enables improved reuse of material rejected or wasted during the production

[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, which enables improved broke handling.

[0011] 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.

[0012] The invention is defined by the appended independent claim. Embodiments are set forth in the appended dependent claims and in the following description.

[0013] 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; b) forming a wet MFC web of said MFC suspension by casting on a non- porous support; c) subjecting said wet MFC web positioned on said non-porous support to water removal to form a dry 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) discharging and collecting broke material comprising wet broke and / or dry broke, wherein said wet broke comprises wet MFC web waste, wherein said dry broke comprises dry MFC web waste; e) subjecting collected broke material to mixing with water to provide at least one broke suspension, wherein at least 90 weight-% of each broke suspension of said at least one broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05; f) subjecting said at least one broke suspension to a mechanical treatment to increase the viscosity of said at least one broke suspension, and g) using said at least one broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that each broke suspension of said at least one broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said at least one broke suspension.

[0014] The method according to the first aspect enables the production of an MFC web, such as an MFC film, with casting technique on a non-porous support, wherein improved reuse of material rejected / wasted during production, i.e., broke material including wet broke and / or dry broke from the MFC web production, is enabled and broke handling is improved. By discharging and collecting wet broke and / or dry broke from the MFC web production, subjecting the collected wet broke and / or dry broke to mixing with water to provide at least one broke suspension, wherein at least 90 weight-% of each broke suspension of the at least one broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05, and subjecting the at least one broke suspension to a mechanical treatment to increase the viscosity as mentioned above, and using the at least one broke suspension in the preparation of the MFC suspension used for forming the MFC web, improved reuse of broke material in the MFC web production is enabled and the broke handling is improved.

[0015] 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.

[0016] 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.

[0017] 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 from a paper or paper machine or from recycled paper.

[0018] 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 or thin absorbent.

[0019] 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.

[0020] In some embodiments, the MFC suspension prepared in step a) of the method of the first aspect has a dry content of 1-30 weight-%, such as 1-25 weight-% or 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-%.

[0021] 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.

[0022] 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 .

[0023] 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 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 fractions, 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).

[0024] 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.

[0025] 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.

[0026] 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 length-weighted ISO fiber length measured according to the standard ISO 16065-2 using an FS5 fiber analyzer (Valmet).

[0027] 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).

[0028] Thus, besides MFC, the prepared MFC suspension may also comprise longer fibers, either hardwood or softwood fibers, preferably kraft pulp softwood fibers.

[0029] 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 web performance chemicals added to provide the end product web with specific properties and / or to facilitate production of the web.

[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 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, silica, graphene, graphene oxide or a combination thereof.

[0034] In step b) of the method of the first aspect, a wet MFC web, such as a wet MFC film, is formed of the MFC suspension prepared in step a). The wet MFC web is formed by casting on a non-porous support. Preferably, the MFC suspension is applied directly on the surface of the non-porous support. 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.

[0035] 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, such as a wet film. 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.

[0036] The non-porous support may be a metal (e.g., steel), rubber, plastic or polymer (e.g., polyurethane) support (e.g., belt). 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 (e.g., polytetrafluoroethylene). 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.

[0037] In some embodiments, the non-porous support is a metal belt, such as a continuous metal belt, which is heated at least 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 wet MFC web is applied to 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 dry 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 positioned on the non- porous support is subjected to water removal to form a dry MFC web. The 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 638-2 and the moisture content may be calculated based on the dry content measurement.

[0038] The dry MFC web may be separated from the non-porous support by, for example, being peeled off from the non-porous support. Typically, the dry MFC web is wound onto a core to form a reel of the dry MFC web after release / separation from the non- porous support. Thereby a reel of the dry MFC web, i.e., a free-standing dry MFC web is formed. Possibly, a further drying of the dry MFC web may be performed after the release of the dry MFC web from the non-porous support but before or in connection with the winding of the dry MFC web onto the core to form the reel.

[0039] 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.

[0040] The dewatering and the drying, respectively, of step c) may be performed by using any methods known in the art that are suitable to provide the dry MFC web. The wet MFC web is positioned on the non-porous support during the dewatering and / or drying.

[0041] 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 comprises a mechanical dewatering such as press dewatering, gravitational dewatering or vacuum dewatering. Optionally, mechanical dewatering may be combined with evaporation provided by applying heat.

[0042] 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.

[0043] Each press dewatering step may comprise application of a press fabric in direct or indirect contact (e.g., via a separate membrane) with the wet MFC web positioned on the non-porous support and conducting 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 nip through which the wet MFC web is conducted and thus pressed and dewatered.

[0044] 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.

[0045] In step d) of the method of the first aspect, broke material comprising wet broke and / or dry broke is / are discharged and collected. The wet broke comprises waste of the wet MFC web. The dry broke comprises waste of the dry MFC web. As mentioned above, the dry MFC web has a moisture content of 20 weight-% or less. Thus, the wet MFC web has a moisture content of more than 20 weight-%.

[0046] Consequently, dry broke has a moisture content of 20 weight-% or less, such as 1-20 weight-%, and wet broke has a moisture content of more than 20 weight-%, such as more than 20 weight-% and up to 99 weight-%.

[0047] Thus, wet broke may be discharged from the MFC web production in, for example, a forming section, a dewatering section and / or a drying section of an MFC web production arrangement. For example, the wet broke may comprise wet MFC web edges (e.g., longitudinal edges of the wet MFC web cut during the production) and / or waste of wet MFC web breaks (e.g., parts of the wet MFC web cut at breaks of the wet MFC web). Accordingly, wet broke may be discharged at one or more discharge points of the MFC web production arrangement.

[0048] Dry broke may be discharged from the MFC web production in, for example, sections after the drying section and / or a reeling section of the MFC web production arrangement. For example, the dry broke may comprise dry MFC web edges (e.g., longitudinal edges of the dry MFC web cut during the production or trim rejects) and / or dry MFC web breaks (e.g., parts of the dry MFC web cut at breaks of the dry MFC web) and / or reel waste (e.g., parts of the dry MFC web removed in connection with reeling or slitting or winding of the dry MFC web). Accordingly, dry broke may be discharged at one or more discharge points of the MFC web production arrangement.

[0049] In step e) of the method of the first aspect, collected broke material, i.e., collected wet broke and / or dry broke, is / are subjected to mixing with water to provide at least one broke suspension, wherein at least 90 weight-%, preferably at least 95 weight- %, of each provided broke suspension of said at least one provided broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. Accordingly, a Mesh 30 screen is utilized instead of a Mesh 200 screen in SCAN-CM 66:05. Thus, the mixing of the collected broke material with water in step e) is performed such that at least one broke suspension is provided wherein each provided broke suspension fulfills the criteria that at least 90 weight-%, preferably at least 95 weight-%, of the broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05 (i.e., the reject is 10 weight-% or less, preferably 5 weight-% or less, of the broke suspension), i.e., such that the result of the mixing of step e) is at least one broke suspension, wherein each resulting broke suspension fulfills the mentioned criteria. Accordingly, the feature that “at least 90 weight-% of each broke suspension of said at least one broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05” is a measure of how homogeneous each broke suspension is, i.e., a measure of the level of disintegration, and is not to be interpreted in a way that each broke suspension is to pass the mentioned Mesh when performing the method.

[0050] The mixing of collected broke material with water in step e) of the method of the first aspect may comprise one or more mixing steps for providing each broke suspension wherein each provided broke suspension fulfils the criteria that at least 90 weight-%, preferably at least 95 weight-%, of the broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. Water is, thus, present in all mixing steps for each broke suspension and is provided / added to at least a first mixing step (or the only mixing step). Each of the one or more mixing steps may be a low shear mixing step or a high shear mixing step. A low shear mixing step is associated with a shear rate of less than 10000 s-1, whereas a high shear mixing step is associated with a shear rate of above 10000 s-1, such as above 50000 s-1.

[0051] Depending on the re-dispersibility of the collected broke material, e.g., depending on the wet strength of the collected broke material, to be mixed with water to provide a broke suspension which fulfils the criteria that at least 90 weight-% of the broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05, one mixing step or two or more mixing steps, e.g., with different shear rates and / or performed in different devices, may be required.

[0052] The mixing of each mixing step may be performed in any suitable device. For example, each mixing step may be performed in a device selected from the group of: a pulper, a chest with an agitator, a mixer, a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser and a high pressure drop apparatus.

[0053] In some embodiments, the mixing for providing a broke suspension which fulfils the criteria that at least 90 weight-% of the broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05 comprises a first, or only, mixing step, e.g., a low shear mixing step, which may be performed in a device selected from the group of: a pulper and a chest with an agitator. In some embodiments, the mixing for providing a broke suspension which fulfils the criteria that at least 90 weight-% of the broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05 comprises a first mixing step, e.g., a low shear mixing step, which may be performed in a device selected from the group of: a pulper and a chest with an agitator, and a second mixing step, e.g., a high shear mixing step, which may be performed in a device selected from the group of a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser and a high pressure drop apparatus.

[0054] For example, discharged broke material, i.e., wet broke and / or dry broke, may be collected in a broke collection arrangement of an MFC web production arrangement in step d) of the method of the first aspect. The broke collection arrangement may comprise any suitable devices and / or arrangements for collecting, and optionally temporarily storing, discharged wet broke and / or dry broke from the production of the MFC film, e.g., from broke discharge points, and conveying collected wet broke and / or dry broke in one or more conduits to a further process unit or arrangement. For example, the broke collection arrangement may comprise one or more collection devices arranged to collect broke material from one or more broke discharge points and optionally temporarily store broke material. Each collection device may comprise a mixing device, e.g., a pulper, arranged to perform a mixing step of the mixing of collected broke material with water in step e) of the method of the first aspect.

[0055] Thus, broke material may be collected in a collection device of a broke collection arrangement in step d) of the method of the first aspect. In case the collection device comprises a mixing device for mixing collected broke material with water, the collected broke material is mixed with water in the mixing device of the collection device in a first (or only) mixing step of the mixing of step e) of the method of the first aspect. Alternatively, broke material collected in the collection device in step d) of the method of the first aspect may be conveyed and mixed with water in a separate mixing device arranged for mixing collected broke material with water in a first (or only) mixing step of the mixing of step e) of the method of the first aspect.

[0056] After the first mixing step, broke material mixed with water may be conveyed to one or more further mixing devices for performance of one or more further mixing steps of the mixing of step e). After finished mixing of step e), the provided broke suspension may be conveyed to a broke tower and may be temporarily stored in the broke tower before the mechanical treatment of step f).

[0057] In step f) of the method of the first aspect, each broke suspension provided by the mixing of step e), is subjected to a mechanical treatment to increase the viscosity of the at least one broke suspension. The mechanical treatment may comprise one or more mechanical treatment steps. For example, each mechanical treatment step may be selected from the group of: a homogenization treatment, a fluidization treatment and a fibrillation treatment. The homogenization treatment, the fluidization treatment and the fibrillation treatment, respectively, may be performed in any suitable device(s) or arrangement(s). Preferably, the homogenization treatment is a high pressure homogenization treatment (e.g., 300 bar or higher), such as performed in a high pressure homogenizer. Preferably, the fluidization treatment is a high pressure fluidization treatment (e.g., 300 bar or higher), such as performed in a high pressure microfluidizer. High pressure enables a high pressure drop resulting in fibrillation or high shearing.

[0058] The selection of a homogenization treatment, a fluidization treatment, a fibrillation treatment or a combination thereof may depend on, for example, the wet strength of the broke material of the at least one broke suspension, the film composition and additives of the broke material, the size and quality of virgin MFC used for preparing the MFC suspension, etc.

[0059] In step g) of the method of the first aspect, the at least one broke suspension subjected to the mechanical treatment of step f) is used in the preparation of the MFC suspension of step a), i.e., the at least one broke suspension is used as a component comprising MFC of the prepared MFC suspension.

[0060] The mechanical treatment of step f) is performed such that each broke suspension of the at least one broke suspension has, after the mechanical treatment, a viscosity of at least 60% of the viscosity of the MFC suspension without any inclusion of the at least one broke suspension (i.e., of the viscosity of the MFC suspension prepared in step a) with all components except for the at least one broke suspension). By increasing the viscosity of the at least one broke suspension to at least 60% of the viscosity of the MFC suspension without any inclusion of the at least one broke suspension, each broke suspension has a sufficient quality for being used in the MFC suspension without essentially impairing the barrier properties or mechanical properties of the produced MFC web.

[0061] The viscosity of the at least one broke suspension and the viscosity of the MFC suspension without any inclusion of the at least one broke suspension may be Brookfield viscosity, such as measured with Brookfield Viscometer RVDV-II+P and V-72 spindle at rotational speed of 50 rpm after 5 min at 1 .5% dry content, temperature of 23 °C, and pH 7.3-7.6. The sample preparation may be as follows: The sample for measurement may be prepared by removing air with appropriate method (if the sample contains air), e.g., by using a Flacktek SpeedMixer. The dry content may be measured by oven drying according to ISO 638-2. pH of the sample may be adjusted to 7.3-7.6 by using HCI or NaOH solution and the sample may be mixed with magnetic stirrer at 300 rpm for 1 min. The mixing with magnetic stirrer may be continued and Ultra Turrax rotor-stator mixer may be added to the suspension to mix at 10 000 rpm for 4 min. After mixing, the sample may rest for 15 min

[0062] The mixing of the broke material of step e) is performed in order to disintegrate and homogenize the broke material and obtain a broke suspension with sufficiently homogeneous consistency for performing the mechanical treatment of step f), i.e., to obtain a broke suspension which fulfils the criteria that at least 90 weight-% of the broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. Thus, the mixing of the broke material of step e) is performed in order to make sure that the broke suspension is homogeneous and reduced in size, such as to resemble the suspension used in a mixing chest during preparation of the MFC suspension or to resemble the MFC suspension used in an applicator, (e.g., obtained by low shear mixing) and that small fragments are broken apart to flocs and fiber / fibril bundles (e.g., obtained by high shear mixing). The mechanical treatment of step f) is performed in order to avoid break down fiber / fibril bundles and other aggregates of dry matter and to regain rheological properties and inter-fibril bonding ability of the MFC.

[0063] Optionally, the method of the first aspect may further comprise subjecting the at least one broke suspension to at least one purification treatment, wherein step g) comprises using the at least one broke suspension in the preparation of the MFC suspension after the at least one purification treatment. Thus, the at least one purification treatment may be performed before and / or after step f). Each of the at least one purification treatment may be selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation. Each of the at least one purification treatment may be performed in any suitable device.

[0064] The use of the at least one broke suspension in the preparation of the MFC suspension of step a) may comprise use of at least one broke suspension subjected to the mechanical treatment of step f), by addition of at least one broke suspension to an MFC stock suspension, e.g., in a mixing chest. Additionally or alternatively, the use of the at least one broke suspension in the preparation of the MFC suspension may comprise use of at least one broke suspension by addition of at least one broke suspension to pulp or pre-treated pulp and performing the mechanical treatment by co-fibrillation to form an MFC stock suspension and using the formed MFC stock suspension in the preparation of the MFC suspension.

[0065] In some embodiments, step g) of the method comprises mixing the at least one broke suspension with an MFC stock suspension and optionally water and / or one or more further components, such as one or more additives and / or other cellulose pulp fractions, e.g., in a mixing chest.

[0066] 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(s).

[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 never-dried pulp, such as 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 using 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 fibrils and, thus, facilitate the production of MFC. For wood fibers, any suitable wood-degrading enzymes which hydrolyse / degrade cellulose fibers may be utilized. Alternatively or additionally, the pulp may be pretreated by chemical modification.

[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 first embodiments, step d) comprises discharging and collecting first broke material comprising wet broke and / or dry broke and step e) comprises subjecting collected first broke material to the mixing with water to provide a first broke suspension, wherein at least 90 weight-% of said provided first broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. The wet broke and / or dry broke of the first broke material may be discharged from one or more discharge points and collected by a first collection device of a broke collection arrangement in step d). Furthermore, the collected first broke material may be mixed with water in one or more first mixing devices (i.e., in one or more mixing steps of the mixing of step e)) to provide the first broke suspension in step e). The selection of one or more mixing steps and the shear rate and mixing device used in the mixing step(s) depend on the re-dispersibility (e.g., the wet strength) of the first broke material. Optionally, the first broke suspension may be temporarily stored in a first broke tower after the mixing of step e).

[0072] Furthermore, in the first embodiments step f) comprises subjecting the first broke suspension to the mechanical treatment to increase the viscosity of the first broke suspension and step g) comprises using the first broke suspension subjected to the mechanical treatment in the preparation of the MFC suspension of step a). In the first embodiments, the mechanical treatment of step f) is performed such that the first broke suspension has, after the mechanical treatment, a viscosity of at least 60% of the viscosity of the MFC suspension without any inclusion of said first broke suspension.

[0073] In some first embodiments, step g) may comprise mixing the first broke suspension after the mechanical treatment with an MFC stock suspension and optionally water and / or one or more further components, such as one or more additives and / or cellulose pulp fractions, in the preparation of the MFC suspension of step a). For example, the mixing of step g) may be performed in a mixing chest. Thus, these embodiments may involve conveying the first broke suspension, e.g., from a mixing device used in step e) or a first broke tower, to a device for the mechanical treatment and further conveying the first broke suspension to the mixing chest after the mechanical treatment.

[0074] In some first embodiments, the mechanical treatment of step f) comprises a mechanical treatment step being a fibrillation treatment. The fibrillation treatment may be performed in a fibrillation treatment arrangement used for providing the MFC stock suspension or in a separate fibrillation device or arrangement. In these first embodiments, step g) may comprise using the first broke suspension in the preparation of the MFC suspension in step a) by mixing the first broke suspension after the fibrillation treatment with an MFC stock suspension and optionally water and / or one or more further components, such as one or more additives and / or other cellulose pulp fractions. For example, the mixing of step g) may be performed in a mixing chest. Alternatively, the mixing of the first broke suspension after the fibrillation treatment with the MFC stock suspension may be performed in a fibrillation treatment arrangement used for providing the MFC stock suspension and the MFC stock suspension may then be further mixed with water and / or one or more further components in a mixing chest.

[0075] In some first embodiments, the mechanical treatment of step f) comprises a mechanical treatment step being a fibrillation treatment, wherein the fibrillation treatment comprises subjecting the first broke suspension to co-fibrillation with pulp or pre-treated pulp to provide an MFC stock suspension and step g) comprises using the provided MFC stock suspension in the preparation of the MFC suspension. Thus, in these first embodiments, the first broke suspension is added to pulp or pre-treated pulp in the preparation of the MFC stock suspension such that the first broke suspension is co-fibrillated with the pulp or the pre-treated pulp in a fibrillation treatment arrangement in the preparation of the MFC stock suspension.

[0076] In the first embodiments, the method may further comprise subjecting the first broke suspension to at least one first purification treatment, wherein step g) comprises using the first broke suspension in the preparation of the MFC suspension after the at least one first purification treatment. Thus, the at least one first purification treatment may be performed before and / or after step f). Each of the at least one first purification treatment may be selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation. Each of the at least one first purification treatment may be performed in any suitable device.

[0077] In some first embodiments, the first broke material comprises or consists of dry broke. In some first embodiments, the first broke material comprises or consists of wet broke. In some first embodiments, the first broke material comprises or consists of wet broke and dry broke. In some first embodiments, the first broke material comprises or consists of wet broke consisting of waste of the wet MFC web being dewatered and / or partially dried. In some first embodiments, the first broke material comprises or consists of dry broke and wet broke consisting of waste of the wet MFC web being dewatered and / or partially dried.

[0078] As mentioned above, the mixing of step e) may comprise one or more mixing steps. For example, each mixing step may be performed in a device selected from the group of: a pulper, a chest with an agitator, a mixer, a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser and a high pressure drop apparatus. In first embodiments in which the broke material comprises dry broke and / or wet broke consisting of waste of the wet MFC web being dewatered and / or partially dried, it may be necessary to include at least two mixing steps in the mixing of step e). In these first embodiments, the mixing may comprise a first mixing step, e.g., a low shear mixing step, which may be performed in a device selected from the group of: a pulper and a chest with an agitator, and a second mixing step, e.g., a high shear mixing step, which may be performed in a device selected from the group of a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser and a high pressure drop apparatus.

[0079] In second embodiments, step d) comprises discharging and collecting second broke material comprising wet broke, step e) comprises subjecting collected second broke material to the mixing with water to provide a second broke suspension, wherein at least 90 weight-% of the provided second broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. The wet broke of the second broke material may be discharged from one or more discharge points and collected by a second collection device of a broke collection arrangement in step d). Furthermore, the collected second broke material may be mixed with water in one or more second mixing devices (i.e., in one or more mixing steps of the mixing of step e)) to provide the second broke suspension in step e). The selection of one or more mixing steps and the shear rate and mixing device used in the mixing step(s) depend on the redispersibility (e.g., the wet strength) of the second broke material. Optionally, the second broke suspension may be temporarily stored in a second broke tower after the mixing of step e).

[0080] In the second embodiments, step f) comprises subjecting the second broke suspension to the mechanical treatment to increase the viscosity of the second broke suspension and step g) comprises using the second broke suspension subjected to the mechanical treatment in the preparation of the MFC suspension of step a). In the second embodiments, the mechanical treatment of step f) is performed such that the second broke suspension has, after the mechanical treatment, a viscosity of at least 60% of the viscosity of the MFC suspension without any inclusion of the second broke suspension.

[0081] In some second embodiments, step g) may comprise mixing the second broke suspension after the mechanical treatment with an MFC stock suspension and optionally water and / or one or more further components, such as one or more additives and / or cellulose pulp fractions, in the preparation of the MFC suspension of step a). For example, the mixing of step g) may be performed in a mixing chest. Thus, these embodiments may involve conveying the second broke suspension, e.g., from a second mixing device used in step e) or a second broke tower, to a device for the mechanical treatment and further conveying the second broke suspension to the mixing chest after the mechanical treatment.

[0082] In the second embodiments, the method may further comprise subjecting the second broke suspension to at least one second purification treatment, wherein step g) comprises using the second broke suspension in the preparation of the MFC suspension after the at least one second purification treatment. Thus, the at least one second purification treatment may be performed before and / or after the optional step f). Each of the at least one second purification treatment may be selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation. Each of the at least one second purification treatment may be performed in any suitable device.

[0083] In some second embodiments, the second broke material consists of wet broke. In some second embodiments, the second broke material consists of wet broke consisting of waste of the wet MFC web not being subjected to dewatering or drying. In some second embodiments, the second broke material consists of wet broke consisting of waste of the wet MFC web being subjected to dewatering but not drying. In some second embodiments, the second broke material consists of wet broke consisting of waste of the wet MFC web being subjected to dewatering and partial drying.

[0084] As mentioned above, the mixing of step e) may comprise one or more mixing steps. For example, each mixing step may be performed in a device selected from the group of: a pulper, a chest with an agitator, a mixer, a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser and a high pressure drop apparatus. In second embodiments in which the broke material consists of wet broke, in particular wet broke consisting of waste of the wet MFC web not being subjected to dewatering or drying, it may be sufficient to include one mixing step in the mixing of step e). In these second embodiments, the mixing may consist of one mixing step, e.g., a low shear mixing step, which may be performed in a device selected from the group of: a pulper and a chest with an agitator.

[0085] In third embodiments, any of the above described first and second embodiments of the method of the first aspect are combined. Thus, in third embodiments, step d) comprises discharging and collecting first broke material comprising wet broke and / or dry broke and discharging and collecting second broke material comprising wet broke, and step e) comprises subjecting collected first broke material to mixing with water to provide a first broke suspension and subjecting collected second broke material to mixing with water to provide a second broke suspension. The wet broke and / or dry broke of the first broke material may be discharged from one or more discharge points and collected by a first collection device of a broke collection arrangement in step d). The wet broke of the second broke material may be discharged from one or more discharge points and collected by a second collection device of a broke collection arrangement in step d). Furthermore, the collected first broke material may be mixed with water in one or more first mixing devices to provide the first broke suspension in step e) and the collected second broke material may be mixed with water in one or more second mixing devices to provide the second broke suspension in step e). Optionally, the first broke suspension may be temporarily stored in a first broke tower after the mixing of step e) and the second broke suspension may be temporarily stored in a second broke tower after mixing of step e). Furthermore, in the third embodiments, step f) comprises subjecting the first broke suspension and the second broke suspension to a respective mechanical treatment and step g) comprises using the first broke suspension subjected to the respective mechanical treatment and the second broke suspension subjected to the respective mechanical treatment in the preparation of the MFC suspension of step a).

[0086] Thus, in the third embodiments, handling and treatment of broke material in two different broke handling systems is enabled, i.e., handling and treatment of broke material in two different ways is enabled. Accordingly, broke material with different re-dispersibility may be handled and treated differently in order to enable reuse of the broke material in the preparation of the MFC suspension. By collecting broke into different broke handling systems, the treatment of broke material with different redispersibility before use in the preparation of the MFC suspension may be targeted. Thus, unnecessary homogenization, fluidization, fibrillation and / or purification treatments may be avoided or at least reduced. For example, in some third embodiments, dry broke may be collected in a first broke collection device and wet broke may be collected in a second broke collection device. In these third embodiments, the treatment of the dry broke (and thus the first broke suspension formed by mixing the dry broke with water of step e)) and the treatment of the wet broke (and thus the second broke suspension formed by mixing the wet broke with water of step e)) may be targeted based on e.g., wet strength difference and may thus be different. For example, it might be sufficient to treat the wet broke with only one mixing step in step e) and a homogenization treatment or fluidization treatment in step f) (and optionally one or more second purification treatments), whereas it might be necessary to treat the dry broke with two mixing steps in step e) and a fibrillation treatment in step f) (and optionally one or more first purification treatments). In particular, unnecessary fibrillation of wet broke may be avoided. Also, the targeted treatment of broke with different re-dispersibility may provide a more even quality of MFC which originates from broke and is used in the preparation of the MFC suspension used in the web forming. This might in turn lead to less risks for defects in the formed web.

[0087] In some embodiments, the MFC suspension prepared in step a) comprises 2-50 weight-%, such as 2-30 weight-% or 5-30 weight-% or 2-10 weight-% or 2-6 weight- % or 3-6 weight-% of broke material, i.e., wet broke and / or dry broke based on total dry weight.

[0088] In some embodiments, the method of the first aspect further comprises a step of air removal of the broke material before the mixing with water of step e).

[0089] 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), a dry MFC film is formed in step c), the wet broke comprises wet MFC film waste and the dry broke comprises dry MFC film waste.

[0090] In some embodiments in which the MFC web is an MFC film, the dry MFC film provided in step c) of the method of the first aspect has 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.

[0091] In some embodiments in which the MFC web is an MFC film, the dry MFC film provided in step c) of the method of the first aspect has 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.

[0092] In some embodiments in which the MFC web is an MFC film, the dry MFC film has a dry grammage of 10-70 g / m2, preferably 10-60 g / m2or 10-50 g / m2or 15-40 g / m2, as measured according to ISO 536.

[0093] In some embodiments in which the MFC web is an MFC film, an average film thickness of the dry MFC film is 5-60 pm, preferably 10-50 pm, 15-45 pm or 20-40 pm. 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 nonlimiting 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.

[0094] In some embodiments in which the MFC web is an MFC film, a width of the dry MFC film is 0.3-4 m, preferably 0.5-4 m, 1-4 m or 2-4 m.

[0095] In some embodiments in which the MFC web is an MFC film, the density of the dry MFC film is 700-1500 kg / m3, preferably 800-1500 kg / m3, most preferably 900-1500 kg / m3, as measured according to ISO 534:201 1.

[0096] 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. 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.

[0097] 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.

[0098] 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.

[0099] A free-standing 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).

[0100] A free-standing 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.

[0101] 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. Brief description of the drawings

[0102] In the following, the invention will be further illustrated by description of exemplified embodiments with reference to the accompanying drawings, wherein:

[0103] Fig. 1 shows a schematic overview of a first embodiment of the method according to the present disclosure;

[0104] Fig. 2 shows a schematic overview of an alternative first embodiment of the method according to the present disclosure;

[0105] Fig. 3 shows a schematic overview of a second embodiment of the method according to the present disclosure;

[0106] Fig. 4 shows a schematic overview of a third embodiment of the method according to the present disclosure, and

[0107] Fig. 5 shows a schematic overview of an alternative third embodiment of the method according to the present disclosure.

[0108] Detailed description of the drawings

[0109] 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 film production. In the first embodiment illustrated in Fig. 1 , an MFC suspension 2 is prepared from an MFC stock suspension 3 in a mixing chest 4, wherein water may be added as suspension medium to the MFC stock suspension 3. Optionally, one or more further components, such as one or more additives (e.g., paper making additives or chemicals) and / or one or more other cellulose pulp fractions, 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 the MFC stock suspension 3. The prepared MFC suspension 2 comprises between 50 weight-% to 100 weight-% MFC based on total dry weight. The MFC suspension 2 is conveyed to an optional machine chest (not shown) and further to a slot die applicator 6. A wet MFC web 7 is formed of the MFC suspension 2 by casting a layer of the MFC suspension 2 by the slot die applicator 6 on a non-porous support in the form of an endless metal belt 8. In the first embodiment illustrated in Fig. 1 , the wet MFC web 7 is subjected to water removal by dewatering in a dewatering device 9 and drying in a drying device 10 to form a dry MFC film 11 . The dry MFC film 11 is separated from the metal belt 8 and, typically, wound onto a core to form a reel 12 of the dry MFC film 11 . First broke material 13 comprising wet broke and / or dry broke is discharged and collected by a first collector device (not shown) of a broke collection arrangement 15. The wet broke comprises wet MFC film waste and the dry broke comprises dry MFC film waste. The collected first broke material is conveyed to a first mixing arrangement 14 comprising at least one mixing device. In the first mixing arrangement 14 the first broke material 13 is subjected to mixing with water to provide a first broke suspension 16 which fulfils the criteria that at least 90 weight-% of the first broke suspension 16 passes a Mesh 30 screen according to SCAN-CM 66:05. The first mixing arrangement 14 may comprise one mixing device for performing a first mixing step, e.g., a low shear mixing step, and one mixing device for performing a second mixing step, e.g., a high shear mixing step. For example, the first mixing step may be performed in a pulper or a chest with an agitator and the second mixing step may be performed in a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser or a high pressure drop apparatus. The first broke suspension 16 is further conveyed to a first broke tower 17 from the first mixing arrangement 14 for temporary storage. The first broke suspension 16 is conveyed from the first broke tower 17 to a homogenization / fluidization device 19 and is subjected to a homogenization / fluidization treatment in the homogenization / fluidization device 19. The first broke suspension 16 subjected to the homogenization / fluidization treatment is used in the preparation of the MFC suspension 2 by mixing with the MFC stock suspension 3, and optionally water and / or one or more further components as mentioned above, in the mixing chest 4. Optionally, the first broke suspension 16 may be subjected to at least one first purification treatment in at least one first purification treatment device 18 before the mixing with the MFC stock suspension 3 in the mixing chest 4, such as before the homogenization / fluidization treatment. The homogenization / fluidization treatment is performed to increase the viscosity of the first broke suspension 16 to at least 60% of the viscosity of the MFC suspension 2 without any inclusion of the first broke suspension 16.

[0110] Fig. 2 shows a schematic overview of an alternative first embodiment of the method according to the first aspect of the present disclosure. The alternative first embodiment of Fig. 2 differs from the first embodiment of Fig. 1 in the mechanical treatment of the first broke suspension. In the first embodiment shown in Fig. 2, the first broke suspension 16 is subjected to a fibrillation treatment in the fibrillation treatment arrangement 5 and used in the preparation of the MFC suspension 2 by mixing with the MFC stock suspension 3 in the fibrillation treatment arrangement 5 after the fibrillation treatment, wherein the MFC suspension 2 subsequently is formed from the MFC stock suspension 3 in the mixing chest 4. Alternatively, the first broke suspension 16 may be mixed, after the fibrillation treatment, with the MFC stock suspension 3 in the mixing chest 4. Alternatively or additionally, the first broke suspension 16 may be subjected to co-fibrillation with pulp or pre-treated pulp in the fibrillation treatment arrangement 5 to provide the MFC stock suspension 3 and thus used in the preparation of the MFC suspension 2 by using the MFC stock suspension 3 for forming the MFC suspension 2 in the mixing chest 4. Optionally, the first broke suspension 16 may be subjected to at least one first purification treatment in at least one first purification treatment device 18 before the fibrillation or cofibrillation in the fibrillation treatment arrangement 5.

[0111] Fig. 3 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 broke handling. In the second embodiment illustrated in Fig. 3, second broke material 20 comprising wet broke is discharged and collected by a second collector device (not shown) of the broke collection arrangement 15. The collected second broke material is conveyed to a second mixing arrangement 21 comprising at least one mixing device. In the second mixing arrangement 21 the second broke material 20 is subjected to mixing with water to provide a second broke suspension 22 which fulfils the criteria that at least 90 weight-% of the second broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. For example, the second mixing arrangement 21 may comprise one mixing device, such as a pulper or a chest with an agitator, for performing one mixing step, e.g., a low shear mixing step. The second broke suspension 22 is further conveyed to a second broke tower 23 from the second mixing arrangement 21 . The second broke suspension 22 is conveyed from the second broke tower 23 to a homogenization / fluidization device 25 and is subjected to a homogenization / fluidization treatment in the homogenization / fluidization device 25. The second broke suspension 22 subjected to the homogenization / fluidization treatment is used in the preparation of the MFC suspension 2 by mixing with the MFC stock suspension 3, and optionally water and / or one or more further components as mentioned above, in the mixing chest 4. Optionally, the second broke suspension 22 may be subjected to at least one second purification treatment in at least one second purification treatment device 24 before the mixing with the MFC stock suspension 3 in the mixing chest 4, such as before the homogenization / fluidization treatment. The homogenization / fluidization treatment is performed to increase the viscosity of the second broke suspension 22 to at least 60% of the viscosity of the MFC suspension 2 without any inclusion of the second broke suspension 22.

[0112] Fig. 4 shows a schematic overview of a third embodiment of the method according to the first aspect of the present disclosure. The third embodiment of Fig. 4 is a combination of the first embodiment of Fig. 1 and the second embodiment of Fig. 3. Thus, in the third embodiment of Fig. 4, first broke material 13 comprising wet broke and / or dry broke is collected by a first collector device (not shown) of the broke collection arrangement 15 and mixed with water in the first mixing arrangement 14 to provide the first broke suspension 16. Second broke material 20 comprising wet broke is collected by a second collector device (not shown) of the broke collection arrangement 15 and mixed with water in the second mixing arrangement 21 to provide the second broke suspension 22. As mentioned above, the first broke suspension 16 is conveyed from the first mixing arrangement 14 to the first broke tower 17 and further to the homogenization / fluidization device 19 (optionally via the first purification device 18) and then to the mixing chest 4. The second broke suspension 22 is conveyed from the second mixing arrangement 21 to the second broke tower 23 and further to the homogenization / fluidization device 25 (optionally via the second purification device 24) to the mixing chest 4. The MFC suspension 2 is formed from the MFC stock suspension 3, the first broke suspension 16, the second broke suspension 22 and optionally water and / or one or more further components as mentioned above in the mixing chest 4.

[0113] Fig. 5 shows a schematic overview of an alternative third embodiment of the method according to the first aspect of the present disclosure. The alternative third embodiment of Fig. 5 differs from the third embodiment of Fig. 4 in the mechanical treatment of the first broke suspension 16. The mechanical treatment of the first broke suspension 16 of the third embodiment of Fig. 5 corresponds to the mechanical treatment of the first broke suspension 16 of the embodiment of Fig. 2. 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.

[0114] 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; b) forming a wet MFC web of said MFC suspension by casting on a non- porous support; c) subjecting said wet MFC web positioned on said non-porous support to water removal to form a dry 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) discharging and collecting broke material comprising wet broke and / or dry broke, wherein said wet broke comprises wet MFC web waste, wherein said dry broke comprises dry MFC web waste; e) subjecting collected broke material to mixing with water to provide at least one broke suspension, wherein at least 90 weight-% of each broke suspension of said at least one broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05; f) subjecting said at least one broke suspension to a mechanical treatment to increase the viscosity of said at least one broke suspension, and g) using said at least one broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that each broke suspension of said at least one broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said at least one broke suspension.

2. The method according to claim 1 , wherein each mechanical treatment step of the mechanical treatment of step f) is selected from the group of: a homogenization treatment, a fluidization treatment and a fibrillation treatment.

3. The method according to claim 1 or 2, wherein step d) comprises discharging and collecting first broke material comprising wet broke and / or dry broke, wherein step e) comprises subjecting collected first broke material to said mixing with water to provide a first broke suspension, wherein at least 90 weight-% of said first broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05, wherein step f) comprises subjecting said first broke suspension to said mechanical treatment to increase the viscosity of said first broke suspension, and wherein step g) comprises using said first broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that said first broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said first broke suspension.

4. The method according to claim 3, wherein step g) comprises mixing said first broke suspension after said mechanical treatment with an MFC stock suspension in said preparation of said MFC suspension.

5. The method according to claim 3, wherein said mechanical treatment of step f) comprises a mechanical treatment step being a fibrillation treatment which comprises subjecting said first broke suspension to co-fibrillation with pulp or pre-treated pulp to provide an MFC stock suspension and wherein step g) comprises using said MFC stock suspension in said preparation of said MFC suspension.

6. The method according to any one of claims 3-5, wherein the method further comprises subjecting said first broke suspension to at least one first purification treatment, wherein each of said at least one first purification treatment is selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation, and wherein step g) comprises using said first broke suspension in said preparation of said MFC suspension after said at least one first purification treatment.

7. The method according to any one of claims 3-6, wherein said first broke material comprises dry broke.

8. The method according to any one of claims 3-7, wherein said first broke material comprises wet broke consisting of waste of said wet MFC web being dewatered and / or partially dried.

9. The method according to any one of claims 1 -8, wherein step d) comprises discharging and collecting second broke material comprising wet broke, wherein step e) comprises subjecting collected second broke material to said mixing with water to provide a second broke suspension, wherein at least 90 weight-% of said second broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05, wherein step f) comprises subjecting said second broke suspension to said mechanical treatment to increase the viscosity of said second broke suspension, and wherein step g) comprises using said second broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that said second broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said second broke suspension.

10. The method according to claim 9, wherein step g) comprises mixing said second broke suspension after said mechanical treatment with an MFC stock suspension in said preparation of said MFC suspension.11 . The method according to claim 9 or 10, wherein the method further comprises subjecting said second broke suspension to at least one second purification treatment, wherein each of said at least one second purification treatment is selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation, and wherein step g)comprises using said second broke suspension in said preparation of said MFC suspension after said at least one second purification treatment.

12. The method according to any one of the preceding claims, wherein the method further comprises a step of air removal of said broke material before said mixing with water of step e).

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

14. The method according to any one of the preceding claims, wherein the dewatering of step c) 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 positioned on said non-porous support and conducting said wet MFC web, 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 any one of the preceding claims, wherein said drying of step c) comprises at least one non-contact drying step and / or at least one contact drying step.

17. The method according to claim 16, 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.

18. The method according to 16 or 17, wherein each contact drying step comprises contacting said wet MFC web with at least one heated belt or heated cylinder.

19. The method according to any one of the preceding claims, wherein said wet broke comprises wet MFC web edges and / or waste of wet MFC web breaks.

20. The method according to any one of the preceding claims, wherein said dry broke comprises dry MFC web edges and / or waste of dry MFC web breaks and / or reel waste.21 . The method according to any one of the preceding claims, wherein said mixing of step e) comprises one or more mixing steps.

22. The method according to claim 21 , wherein each mixing step is performed in a device selected from the group of: a pulper, a chest with an agitator, a mixer, a pump comprising rotating mixing or shearing elements, a high shear rotor-stator mixer, a deflaker, a refiner, a disperser and a high pressure drop apparatus.

23. The method according to any one of the preceding claims, wherein the method further comprises a step of separating said dry MFC web from said non-porous support and, optionally, winding said dry MFC web onto a core to form a reel of said dry MFC web.

24. The method according to any one of the preceding claims, wherein said MFC suspension prepared in step a) comprises 2-50 weight-% of said broke material based on total dry weight.

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

26. The method according to claim 25, wherein said dry MFC film has an average thickness of 5-60 pm and a dry grammage of 2-70 g / m2as measured according to ISO 536.

27. The method according to claim 25 or 26, wherein said MFC suspension prepared in step a) has a dry content of 1 -30 weight-%.

28. An MFC web obtainable by the method as claimed in any one of claims 1 -27.

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