SE2330162A1 - A method for producing a microfibrillated cellulose film, and a microfibrillated cellulose film - Google Patents

Abstract

The present invention relates to a method for producing an MFC film comprising the steps of:a) providing a pulp comprising cellulose fibers;b) processing the pulp to form an MFC suspension, comprising subjecting the cellulose fibers to at least one modification treatment, comprising a mechanical fibrillation treatment, the processing being performed at a manufacturing plant;c) conveying the suspension to a film-forming device at the manufacturing plant; d) forming a wet MFC film by providing the suspension on a support by the filmforming device,e) dewatering and/or drying the wet MFC film to a dry MFC film, andf) winding said dry MFC film or said support provided with said dry MFC film onto a core to form a reel,wherein a time period between the start of the at least one modification treatment of step b) and the start of step f) is less than 84 hours. The invention relates also to an MFC film.

Description

1 A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE FILM, AND A MICROFIBRILLATED CELLULOSE FILM Technical field The present disclosure relates to a method for producing a microfibrillated cellulose (MFC) film having a low content of bacteria and bacterial spores. ln addition, the present disclosure relates to an MFC film having a low content of bacteria and bacterial spores.

Background 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 othen/vise biodegradable paper or paperboard non-biodegradable and in some cases non-recyclable.

More recently, microfibrillated cellulose (MFC) films 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 dense film with barrier properties, such as oxygen, aroma and grease barrier properties. MFC films are recyclable and biodegradable as well as based on renewable raw material. For example, MFC films can be used in packaging applications, such as food or liquid packaging applications, as a barrier layer, either laminated to paper or paperboard, as a stand-alone film or as a coating on paper or paperboard.

MFC can be produced in a number of different ways. For example, it is possible to produce MFC by mechanically treating pulp comprising cellulose fibers in a mechanical fibrillation treatment to form a suspension comprising MFC. The mechanical fibrillation treatment may be combined with one or more pretreatments of the cellulose fibers in order to enable an easier fibrillation and, thus, a more energy 2 efficient fibrillation process, and to enable production of MFC with different sizes and size distributions. For example, the pulp may be pretreated mechanically, enzymatically or by chemical modification. ln many packaging applications, microbiological purity of the packaging materials is important. For example, in food and liquid packaging applications the microbiological purity of the packaging materials is of uttermost importance. One challenge in the production of MFC and MFC films is that the produced aqueous MFC suspension to be used for production of MFC films might be rich in nutrients, such as various sugars (e.g., monosaccharides, oligosaccharides and polysaccharides), which in combination with the aqueous environment, temperature conditions and relatively long processing times in these conditions promote microbiological growth, i.e., growth of microorganisms such as bacteria, fungi and yeasts.

A high content of microorganisms, such as bacteria, in the MFC suspension might degrade the polymers and subsequently cause high risks for product defects, spoilage, odor and taste problems, deposits, biofilms, miscoloration as well as variations in process runnability. There is also a potential risk that a high content of microorganisms in the MFC suspension implies that microorganisms may be transferred to the produced MFC film and then to converters and food or liquid packaging sites if not handled in any way. When the MFC film is used in packaging applications, migration of any microorganisms from the MFC film could result in spoilage of the packed content. This is especially critical with food and beverages that are rich in nutrients, such as sugars, and have suitable pH and temperature conditions and aqueous environment for further growth of the microbial culture.

One approach to produce a free-standing MFC film from an MFC suspension is to use a film casting method, i.e., forming a film by casting the MFC suspension on a non-porous support such as a metal or plastic support (e.g. belt) and then dewatering and/or drying the film. Casting methods have 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.

The difficulties with a potential high content of microorganisms in MFC films might be present especially when MFC films are dried by an evaporative method, as used for 3 example when casting the MFC suspension on a non-porous support and drying by evaporation. ln such methods the major share of the water present in the MFC suspension is typically removed by evaporation, leaving any microbiological impurities predominantly in the MFC film.

Drying of the MFC film in elevated temperatures can selectively deactivate at least some microorganisms such as bacteria, fungi and yeasts, but part of the bacterial growth and spores might remain in the MFC film. Also, exposing ready MFC films to high temperatures reduces the moisture content of the film, which could make it brittle and deteriorate the ductility of the film, causing potential problems in post- processing such as Iamination and converting of the Iaminates. Furthermore, subjecting the MFC suspension to a very low or high temperature might at least temporarily reduce microbiological activity, but is not always industrially applicable or economically attractive.

Another way to control microorganisms in aqueous suspensions comprising natural polymers, such as MFC suspensions, is to sterilize the manufacturing process. Cleanliness and sanitation programs are usually adopted as well as water treatment methods to reduce bacteriological counts.

Still another way to control microorganisms in aqueous suspensions comprising natural polymers, such as MFC suspensions, is to use preservatives and/or biocides such as microbiocides. The use of chemicals is usually a very effective, but expensive alternative and mostly effective when finding an optimal dosing strategy. Unfortunately, the use of preservatives and/or biocides might be limited due to national health authorities or limited impact on total population. Also, an implemented biocide program is not necessarily prepared for unexpected contaminations in the process.

Thus, there is still room for improvements of methods for producing an MFC film having a low content of microorganisms, in particular bacteria and bacterial spores.

Description of the invention lt is an object of the present disclosure to provide an improved method for producing an MFC film having a low content of bacteria and bacterial spores, which alleviates at least some of the above-mentioned problems associated with the prior art methods. lt is a further object of the present disclosure to provide an improved method for producing an MFC film having a low content of bacteria and bacterial spores without the need of using biocides or preservatives.

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.

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

According to a first aspect illustrated herein, there is provided a method for producing a microfibrillated cellulose (MFC) film, wherein the method comprises the steps of: a) providing a pulp comprising cellulose fibers, wherein the pulp has a Schopper-Riegler (SR) value in the range of 10-35 according to standard ISO 5267-1; b) processing said pulp comprising cellulose fibers to form a suspension comprising MFC, wherein the processing comprises subjecting said cellulose fibers to at least one modification treatment modifying the structure of said cellulose fibers, wherein at least one modification treatment of said at least one modification treatment is a mechanical fibrillation treatment to form said MFC, wherein the processing is performed at a manufacturing plant; c) conveying said suspension comprising MFC to a film-forming device at said manufacturing plant; d) forming a wet MFC film by providing a layer of said suspension comprising MFC on a support by said film-forming device, wherein said suspension comprising MFC comprises at least 50 weight-% of MFC based on total dry weight and has a dry solids content of at least 2 weight-% when provided on the support; e) dewatering and/or drying said wet MFC film provided on said support to a dry MFC film, and f) winding said dry MFC film or said support provided with said dry MFC film onto a core to form a ree| of said dry MFC film or of said support provided with said dry MFC film, wherein a time period between the start of the at least one modification treatment of step b) and the start of step f) is less than 84 hours, preferably less than 72 hours, more preferably less than 48 hours.

The method according to the first aspect enables production of an MFC film having a low content of bacteria and bacterial spores, such as a total bacterial count of less than 1000 CFU/g, preferably less than 500 CFU/g, more preferably less than 100 CFU/g, according to standard ISO 8784-1. lt has surprisingly been found that by integrating the MFC production with the MFC film production at the same manufacturing plant and by controlling the delay time, between the start of the production of MFC by modifying the structure of the cellulose fibers of the raw material pulp and the provision of a dry MFC film wound on a core, to be less than 84 hours, preferably less than 72 hours, more preferably less than 48 hours, in accordance with the first aspect, the content of bacteria and bacterial spores of the produced MFC film may be controlled/limited and substantially reduced compared to utilization of long-time storage and/or transportation (e.g., between different plants) of MFC suspensions before use in MFC film production. Thus, it has surprisingly been found that by producing MFC essentially according to the just-in-time principle for MFC film production at the same manufacturing plant, the content of bacteria and bacterial spores of the produced MFC film may be limited and substantially reduced. Also, the content of bacteria and bacterial spores of the produced MFC film may be limited and substantially reduced without the need of using biocides or preservatives. ln particular, the method of the first aspect is efficient in reducing difficulties with high content of bacteria and bacterial spores in MFC films formed by casting on a non- porous support and dried by an evaporative method. ln such film formation methods the major share of the water present in the MFC suspension of the wet MFC film is 6 typically removed by drying by evaporation, leaving microbiological impurities, such as bacteria and bacterial spores, predominantly in the MFC film.

Microfibrillated cellulose (MFC) shall in the context of the patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm. Various methods exist to make MFC, such as single or multiple pass refining, pre- hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pretreatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable.

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 film can also be considered as a thin paper (e.g., nanopaper or micropaper) or even as a membrane. ln step a) of the method of the first aspect, a pulp comprising cellulose fibers, preferably native cellulose fibers, is provided. The pulp provided in step a), i.e., the raw material pulp, has a Schopper-Riegler (SR) value in the range of 10-35, such as in the range of 12-30 or in the range of 14-24, as determined by standard ISO 5267- 1. Preferably, the pulp provided in step a), i.e., the raw material pulp, has a low content of bacteria and bacterial spores, such as a total bacterial count of less than 1000 CFU/g, more preferably less than 100 CFU/g, according to standard ISO 8784- 1.

The term "total bacterial count" as used herein is the number of colony-forming units (CFU) of bacteria and bacterial spores formed after incubation in plate count agar (PCA) with Ringer's solution as diluent and without addition of Tween 80 to the diluent, under the test conditions specified in standard ISO 8784-1 and reported as "as received".

Typically, the pulp provided in step a) of the method of the first aspect is pulp obtained from wood, such as hardwood and/or softwood. However, the pulp may 7 alternatively be obtained from agricultural sources such as wheat straw, bamboo, bagasse or other non-wood cellulosic sources.

The pu|p provided in step a) of the method of the first aspect may be produced by chemical, semi-chemical, mechanical and/or thermo-mechanical pulping of cellulosic or Iignocellulosic raw material, such as hardwood and/or softwood. For example, the pu|p may be or comprise chemical pulp, such as sulfate pu|p (kraft pulp), sulfite pu|p or dissolving pu|p, mechanical pu|p, thermomechanical pu|p (TMP), high temperature thermomechanical pulp (HTMP), chemi-thermomechanical pulp (CTMP), high temperature chemi-thermomechanical pu|p (HTCTMP), recycled pu|p, or a combination thereof. Preferably, the pu|p is or comprises kraft pulp. The pulp may be bleached or unbleached. ln some embodiments, the pu|p provided in step a) is dried pu|p. ln some embodiments, the pu|p provided in step a) is never-dried pu|p. ln some embodiments, the pu|p provided in step a) comprises dried pu|p and never-dried pu|p. ln step b) of the method according to the first aspect, the pu|p comprising cellulose fibers provided in step a) is processed to form a suspension comprising MFC. Thus, preferably the pu|p used for the processing in step b) (i.e., the pu|p raw material) has a low content of bacteria and bacterial spores, such as a total bacterial count of less than 1000 CFU/g, more preferably less than 100 CFU/g, according to standard ISO 8784-1. Preferably, the suspension comprising MFC comprises water as suspension medium, i.e, water may be added to the cellulose fibers during the processing in step b) and/or to the formed suspension comprising MFC. The processing of step b) comprises subjecting the cellulose fibers of the pulp to at least one modification treatment, wherein each modification treatment impacts the structure of the cellulose fibers of the pu|p so as to modify the structure of the cellulose fibers. The at least one modification treatment of step b) comprises a mechanical fibrillation treatment to fibrillate the cellulose fibers and form the MFC of the suspension, i.e., at least one modification treatment of the at least one modification treatment is a mechanical fibrillation treatment. Thus, the at least one modification treatment of step b) comprises at least a mechanical fibrillation treatment. The cellulose fibers are fibrillated during the mechanical fibrillation treatment such that MFC is formed.

The mechanical fibrillation treatment may comprise one mechanical treatment step or two or more mechanical treatment sub-steps. lf the mechanical fibrillation treatment comprises two or more mechanical treatment sub-steps, the sub-steps may be performed in the same or different devices.

The mechnical fibrillation treatment of step b) may be performed in a mechanical fiber treatment arrangement comprising 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 fibriilator (such as cavitron rotor/stator system, steam explosion system or high consistency refining or mi||ing system), disperger, ball mill and other known mechanical fiber treatment apparatuses suitable to be used in processing of the cellulose fibers to MFC, or combinations thereof. Thus, the mechanical fiber treatment arrangement may comprise one or more of the mentioned mechanical fiber treatment apparatuses. Also, the mechanical fiber treatment arrangement may comprise more than one of the same type of mechanical fiber treatment apparatus, e.g., more than one refiner, etc. Furthermore, the pulp may be passed one or more times through each utilized mechanical fiber treatment apparatus.

The term "refiner" as used herein refers to any known apparatus suitable for refining (beating) cellulose fibers/pulp. Examples of such apparatuses are refiners and beaters equipped with refining discs (disc refiners) or a refining plug in a conical housing (conical refiner), ball mills and rod mills.

The term "homogenizer" as used herein refers to any known apparatus suitable for homogenization of cellulose fibers/pulp. Examples of such apparatuses are high- pressure fluidizers, high-pressure homogenizers and micro fluidizers. The pressure utilized in the homogenizer may be, for example, 400-2500 bar. ln some embodiments, the mechanical fibrillation treatment of step b) comprises a mechanical treatment step in at least one refiner device, with one or multiple passes through each refiner device. ln some embodiments, the mechanical fibrillation treatment of step b) comprises a mechanical treatment step in at least one homogenizer, with one or multiple passes through each homogenizer. ln some embodiments, the mechanical fibrillation treatment of step b) comprises a first mechanical treatment sub-step in at least one refiner device and a second mechanical treatment sub-step in at least one homogenizer. The first mechanical treatment sub-step in at least one refiner device may include one or multiple passes through each refiner device and the second mechanical treatment sub-step in at least one homogenizer may include one or multiple passes through each homogenizer. Thus, the mechanical fibrillation treatment of step b) in these embodiments may be performed in a combination of one refiner device and one homogenizer, with one or more passes through the refiner device and one or more passes through the homogenizer. Alternatively, the mechanical fibrillation treatment of step b) in these embodiments may be performed in a combination of two or more refiner devices and one homogenizer, with one or more passes through each refiner device and one or more passes through the homogenizer. Still alternatively, the mechanical fibrillation treatment of step b) in these embodiments may be performed in a combination of one refiner device and two or more homogenizers, with one or more passes through the refiner device and one or more passes through each homogenizer. ln a further alternative, the mechanical fibrillation treatment of step b) in these embodiments may be performed in a combination of two or more refiner devices and two or more homogenizers, with one or more passes through each refiner device and one or more passes through each homogenizer. ln some embodiments, step b) comprises subjecting the cellulose fibers to one modification treatment, which is the mechanical fibrillation treatment. Thus, in these embodiments the at least one modification treatment of step b) consists of the mechanical fibrillation treatment. ln some embodiments, step b) further comprises subjecting the cellulose fibers to at least one modification treatment in the form of a pretreatment in addition to the mechancial fibrillation treatment, wherein each pretreatment is performed before the mechanical fibrillation treatment. Thus, in these embodiments the at least one modification treatment of step b) further comprises at least one modification treatment in the form of a pretreatment (i.e., at least one modification treatment of the at least one modification treatment of step b) is a pretreatment), in addition to the mechanical fibrillation treatment, wherein each pretreatment is performed before the mechanical fibrillation treatment. Each pretreatment may be an enzymatic pretreatment or a mechanical pretreatment or a combination of an enzymatic pretreatment and a mechanical pretreatment. Thus, the processing of step b) may comprise subjecting the cellulose fibers to one or more enzymatic pretreatments and/or one or more mechanical pretreatments and/or one or more combinations of an enzymatic pretreatment and a mechanical pretreatment before the mechanical fibrillation treatment.

Accordingly, the at least one modification treatment of step b) comprises the mechanical fibrillation treatment and optionally one or more enzymatic pretreatment and optionally one or more mechanical pretreatment. ln some embodiments, the processing of step b) comprises subjecting the cellulose fibers to an enzymatic pretreatment before the mechanical fibrillation treatment. ln some embodiments, the processing of step b) comprises subjecting the cellulose fibers to a mechanical pretreatment and subsequently an enzymatic pretreatment before the mechanical fibrillation treatment. ln some embodiments, the processing of step b) comprises subjecting the cellulose fibers to a mechanical pretreatment before the mechanical fibrillation treatment. ln some embodiments, the processing of step b) comprises subjecting the cellulose fibers to an enzymatic pretreatment before the mechanical fibrillation treatment, wherein the mechanical fibrillation treatment comprises a first sub-step of mechanical treatment in at least one refiner device and a second sub-step of mechanical treatment in at least one homogenizer. The first sub-step of mechanical treatment in at least one refiner device may include one or multiple passes through each refiner device and the second sub-step of mechanical treatment in at least one homogenizer may include one or multiple passes through each homogenizer. ln some embodiments, the processing of step b) comprises subjecting the cellulose fibers to a mechanical pretreatment and subsequently an enzymatic pretreatment before the mechanical fibrillation treatment, wherein the mechanical fibrillation treatment comprises a first sub-step of mechanical treatment in at least one refiner device and a second sub-step of mechanical treatment in at least one homogenizer. The first sub-step of mechanical treatment in at least one refiner device may include 11 one or multiple passes through each refiner device and the second sub-step of mechanical treatment in at least one homogenizer may include one or multiple passes through each homogenizer.

One or more different types of enzymes may be utilized in the enzymatic pretreatment. Any known suitable enzymes for hydrolysis or degradation of cellulose fibers may be utilized. Enzymes utilized may be enzymes affecting cellulose, such as cellulases, and/or enzymes affecting hemicellulose, such as xylanases. 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 fibers and, thus, facilitate the production of MFC. Accordingly, the enzymatic pretreatment may be performed in order to improve or facilitate the subsequent mechanical fibrillation treatment by decreasing fiber strength and decrease the extension of the mechanical fibrillation treatment and thus reduce the energy consumption for preparing MFC. For wood fibers, any suitable wood-degrading enzymes which hydrolyse/degrade cellulose fibers may be utilized. ln some embodiments, at least one modification treatment of the at least one modification treatment of step b) is an enzymatic pretreatment, i.e., the processing of step b) comprises subjecting the cellulose fibers to at least one enzymatic pretreatment, wherein the enzymatic pretreatment comprises treatment with one or more enzymes selected from the group of cellulases, hemicellulases and lignin- modifying enzymes. Examples of usable cellulases are cellulases of endoglucanase type, such as mono-component endoglucanase, exoglucanase, cellobiohydrolases, endo-ß-1,4-glucanase, exo-ß-1,4 cellobiohydrolase, and ß-glucosidase. Examples of usable hemicellulases are xylanase and mannanase. Typically, an enzymatic preparation comprising two or more enzymes is utilized in the enzymatic pretreatment. For example, the enzymatic preparation may comprise one main enzyme and small parts of one or more other enzymes.

The temperature used for the enzymatic pretreatment is preferably below 95 °C, such as 20-95 °C. However, the temperature to be used depends on the optimal working temperature for the used enzyme(s) as well as other parameters of the 12 treatment, such as time and pH. The time needed for the enzymatic pretreatment depends on the pulp which is treated and on the activity of the used enzyme(s) as well as the temperature and the pH of the treatment. The activity of the enzyme may be 10-1000 nkat/g. The pH during the enzymatic pretreatment is preferably 4-7, such as 4-6, but depends on the type of pulp and enzyme(s).

As mentioned above, at least one modification treatment of the at least one modification treatment of step b) may be a mechanical pretreatment, i.e. the processing of step b) may comprise subjecting the cellulose fibers to at least one mechanical pretreatment. The purpose of the mechanical pretreatment is to soften the cellulose fibers of the pulp and make them more active and reactive before subsequent treatments or pretreatments such as an enzymatic pretreatment. The mechanical pretreatment may be performed in a mechanical fiber pretreatment arrangement comprising 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. Thus, the mechanical fiber pretreatment arrangement may comprise one or more of the mentioned mechanical fiber pretreatment apparatuses. Also, the mechanical fiber pretreatment arrangement may comprise more than one of the same type of mechanical fiber pretreatment apparatus, e.g., more than one refiner, etc. Furthermore, the pulp may be passed one or more times through each utilized mechanical fiber pretreatment apparatus. ln some embodiments, the mechnical pretreatment is performed in at least one refiner, with one or multiple passes through each refiner device. ln some embodiments, the mechanical pretreatment results in a Schopper-Fšiegler (SR) value of the pulp in the range of 25-35 according to standard ISO 5267-1.

As mentioned above, the at least one modification treatment may comprise a pretreatment which is a combination of an enzymatic pretreatment and a mechanical pretreatment, i.e., a combination of an enzymatic pretreatment and a mechanical pretreatment in a single pretreatment step. For example, an enzymatic pretreatment 13 may be combined with a low shear mechanical pretreatment, such as agitation, a medium shear mechanical pretreatment or high shear pretreatment to boost the effect of the enzymatic pretreatment.

The processing of step b) may be performed so that a suspension comprising MFC having a dry solids content of at least 1weight-%, such as at least 2 weight-%, is provided, i.e., is the result after finished processing of step b). Preferably, the processing is performed so that a suspension comprising MFC having a dry solids content of 2-30 weight-%, more preferably 3-30 weight-%, most preferably 4-20 weight-%, is provided. Dilution or concentration of the suspension comprising MFC may be performed after finished mechanical fibrillation treatment. Furthermore, addition or removal of suspension medium may alternatively or additionally be performed during the processing of step b). Providing a suspension comprising MFC having a relatively high dry solids content, i.e., at least 1 weight-%, such as at least 2 weight-%, is advantageous since it reduces the need for water removal and thus energy consumption in step e) as well as volume of processes, tank pipes and pumps throughout the whole process.

The processing of step b) may be performed so that the suspension comprising MFC comprises at least 50 weight-% MFC based on total dry weight after finished processing of step b). ln some embodiments, the suspension comprising MFC comprises between 50 weight-% to 100 weight-% MFC based on total dry weight after finished processing of step b). ln some embodiments, the suspension comprising MFC 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 after finished porcessing of step b).

Preferably, the consistency of the suspension during the enzymatic pretreatment and the mechanical pretreatment, respectively, is 0.5-25 weight-% or 2-20 weight-%. Preferably, the consistency of the suspension during the mechanical fibrillation treatment is 0.5-25 weight-% or 2-20 weight-%. ln embodiments in which the processing of step b) comprises an enzymatic pretreatment, the method of the first aspect comprises preferably also a subsequent enzyme deactivation. For example, the enzymatic deactivation may be performed by 14 increasing the temperature, increasing the pH, an oxidation step, treatment with a biocide, UV treatment, radiation treatment or a combination thereof in order to denaturate the enzyme(s) after finished enzymatic pretreatment. Preferably, the enzymatic deactivation is performed before the mechanical fibrillation treatment of step b).

The processing of step b) is performed at a manufacturing plant and the suspension comprising MFC formed in step b) is conveyed, which e.g., includes pumping such as pumping via pipes and any optional intermediate devices (e.g. mixing chests) or storage tanks, to a film-forming device at the same manufacturing plant in step c) of the method of the first aspect. ln embodiments in which a mechanical fiber treatment arrangement is utilized for the mechanical fibrillation treatment, the suspension comprising MFC may be conveyed from the mechanical fiber treatment arrangement to the film-forming device in step c). Thus, the preparation of the suspension comprising MFC from the pulp and the formation of the MFC film are performed at the same manufacturing plant (site), i.e., these steps are integrated at the same manufacturing plant.

The method of the first aspect may be a continuous method, wherein all method steps a) - f) are performed continuously (i.e., in a continuous process flow). However, alternatively steps b) - f) may be performed continuously. Still alternatively, steps a) - c) may be performed batchwise, whereas the film-forming steps d) - f) may be performed continuously. Still alternatively, the mechanical fibrillation treatment of step b) and/or the optional enzymatic pretreatment of step b) and/or the optional mechanical pretreatment of step b) may be performed batchwise with the subsequent method steps being performed continuously. ln some embodiments, the method of the first aspect may be a semi-continuous method comprising at least one intermediate storage of the suspension comprising MFC produced in step b) during the conveying of the suspension comprising MFC to the film-forming device in step c). The intermediate storage may be a storage tank or container, or a feed chest feeding the film-forming device. Thus, in these embodiments the suspension comprising MFC may be produced batchwise and stored in the at least one intermediate storage.

Optionally, water and/or one or more additives and/or broke may be added to the cellulose fibers during the processing of step b) and/or to the suspension of MFC during step b) and/or to the suspension of MFC during step c). Any added water may have a total bacterial count of less than 200 CFU/ml, preferably less than 100 CFU/ml, according to standard ISO 8784-1 (adapted for measurement on liquid by leaving out e.g. the disintegration step) in order to reduce and control the amount of added microorganisms. Any added additives and any added broke, respectively, may have a total bacterial count of less than 1000 CFU/g, preferably less than 500 CFU/g, more preferably less than 100 CFU/g, according to standard ISO 8784-1 in order to reduce and control the amount of added microorganisms to the suspension comprising MFC. Water may be added in order for the suspension comprising MFC to obtain the correct consistency to be used in the film-forming of step d). Additives may be added in order to obtain the correct formulation of the suspension comprising MFC to be used in the film-forming of step d). Additives may be 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, 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 film with specific properties and/or to facilitate production of the film. Typical examples of film-forming agents are natural gums and polysaccharides or derivatives thereof such as carboxymethylated cellulose (CMC), starch, or polyvinyl alcohol (PVOH) or derivatives or analogues thereof. Typical examples of plasticizers or humectants are sorbitol, glycol, other polyol or a combination thereof. Typical examples of fillers are mineral fillers (regular fillers or nanofillers) such as bentonite, kaolin, talcum, mica, montmorillonite, organoclays, graphene, graphene oxide or a combination thereof.

The optionally added water, additives and broke, respectively, may be added to the suspension comprising MFC at any suitable position or step during the conveying of step c), e.g., in an intermediate storage tank or in a mixing chest of a mixing step.

The optionally added water, additives and broke, respectively, may be added to the 16 suspension at any suitable position or step during step b), e.g., before the mechanicai fibrillation treatment of step b) or inbetvveen sub-steps of the mechanicai fibrillation treatment of step b) or after the mechanicai fibrillation treatment. ln step d) of the method of the first aspect, a wet MFC film is formed by providing a layer of the suspension comprising MFC on a support by the film-forming device. Thus, the suspension comprising MFC conveyed to the film-forming device in step c) is provided as a layer on a support by the film-forming device in step d) to form a wet MFC film. Any known suitable film-forming device and any known suitable support may be utilized.

The term "film-forming device" as used herein refers to a device through which the suspension comprising MFC is applied/provided as a wet film on a support. The film- forming device may be any suitable device that may be utilized for applying a wet film of the suspension comprising MFC on the support. The film-forming device may comprise one unit or several units. For example, the film-forming device may be a device utilized in slot die casting, curtain coating/application or dosing of the suspension comprising MFC with spray or similar device. ln some embodiments, the wet MFC film is formed by casting on the support in step e). The term "casting", when utilized in 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 suspension comprising MFC with spray or similar device and optionally leveling with, for example, a doctor-blade, rod, air knife or roll.

The support may be a non-porous support, such as a metal (e.g., steel), rubber, plastic or polymer (e.g., polyurethane) support (e.g., belt). ln 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. 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, the non-porous support may be an endless metal belt. 17 Accordingly, in some embodiments, the wet MFC film is formed by casting on a non- porous support, such as a metal belt. ln some embodiments, the non-porous support is a metal belt, which is heated during film formation of step d) and/or during dewatering and/or drying of step e). The metal belt support 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 film is provided on the metal belt support and the temperature of the metal belt support may be kept during parts of the method for producing the MFC film, e.g., during at least some process steps for production of the dry MFC film, or during the complete method for producing the MFC film. By increasing the temperature of the metal belt support and thus on the applied wet MFC film it is possible to further increase the efficiency of the dewatering and/or drying of the wet MFC film. ln some embodiments, the support is a paper or paperboard substrate. ln these embodiments, the wet MFC film is provided on the paper or paperboard substrate. Thus, in these embodiments, a paper or paperboard substrate provided with the dry MFC film is provided after the dewatering and/or drying in step e). Thus, a coated paper or paperboard product, or a paper or paperboard laminate, is formed. ln some embodiments in which the support is a paper or paperboard substrate, a further support, such as a non-porous support, is utilized. ln these embodiments, the paper or paperboard substrate is provided on the further support and the wet MFC film is formed on the side of the paper or paperboard substrate opposite the further support. For example, the further support may be a roll with a hard or soft cover, such as a metal (e.g., steel), rubber, plastic or polyurethane cover, or a belt, such as a metal (e.g., steel), rubber, plastic or polyurethane belt, or a porous wire, felt or fabric.

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. 18 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 suspension comprising MFC comprises at least 50 weight-% MFC based on total dry weight when provided on the support in step d). ln some embodiments, the suspension comprising MFC comprises between 50 weight-% to 100 weight-% MFC based on total dry weight when provided on the support in step d). ln some embodiments, the suspension comprising MFC 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 when provided on the support in step d).

The suspension comprising MFC has a dry solids content of at least 2 weight-% when provided on the support in step d). Preferably, the suspension comprising MFC has a dry solids content of 2-30 weight-%, more preferably 3-30 weight-%, most preferably 4-20 weight-%, when provided on the support in step d). Thus, the wet MFC film has a dry solids content of at least 2 weight-%, preferably 2-30 weight-%, more preferably 3-30 weight-%, most preferably 4-20 weight-% at formation. ln step e) of the method of the first aspect, the wet MFC film is dewatered and/or dried to form a dry MFC film. The dry MFC film has a moisture content of 20 weight- % or less, preferably 10 weight-% or less, more preferably 5 weight-% or less. ln some embodiments, the dry MFC film 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. 19 The dewatering and the drying, respectively, of step e) may be performed by using any methods known in the art that are suitable to provide the dry MFC film. The wet MFC film is provided on the support during the dewatering and/or drying. ln some embodiments, step e) comprises dewatering the wet MFC film, wherein the dewatering comprises a mechanical dewatering such as press dewatering, gravitational dewatering, vaccuum dewatering or combinations thereof. The step of dewatering may imply removal of water-borne microorganisms and thus further improve the microbiological purity.

For example, the mechanical dewatering may be performed by wet pressing, i.e., by applying a press fabric in direct contact with the wet MFC film and conducting the wet MFC film, arranged between the press fabric and the support, through a pressing equipment. Optionally, mechanical dewatering may be combined with evaporation provided by applying heat or radiation. With press fabric is meant a fabric that is permeable and allows water to be removed from the wet MFC film 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 film is conducted and thus pressed and dewatered. The dewatering may be performed in one or more sub- steps, i.e., the dewatering step may comprise one or more sub-steps. ln some embodiments, step e) comprises drying the wet MFC film. The drying may be performed by contact drying, such as cylinder drying, infrared (IR) drying, near infrared (NIR) drying, microwave (MW) drying, ultra-violet (UV) drying, hot gas impingement drying such as hot air impingement drying, any other radiation drying or a combination thereof. The drying may be performed in one or more sub-steps, i.e., the drying step may comprise one or more sub-steps. ln embodiments comprising a dewatering step, the method may further include a step of pre-drying the wet MFC film before the step of dewatering. ln step f) of the method of the first aspect, the dry MFC film, or the support provided with the dry MFC film, is wound onto a core. Thereby a ree| of the dry MFC film or of the support provided with the dry MFC film is formed. ln embodiments in which the support is a non-porous support, e.g., a metal belt, step f) further comprises releasing, i.e., separating such as peeling off, the dry MFC film from the non-porous support before winding the dry MFC film onto the core to form the ree|. Thus, a ree| of a free-standing continuous dry MFC film is formed in these embodiments. ln embodiments in which the support is a paper or paperboard substrate, step f) comprises winding the paper or paperboard substrate provided with the dry MFC film onto the core to form the ree|. Thus, a ree| of a continuous paper or paperboard substrate provided with a dry MFC film is formed in these embodiments. ln embodiments in which the support is paper or paperboard substrate and in which a further support is utilized on the side of the paper or paperboard substrate opposite the side provided with MFC film, the paper or paperboard substrate is separated from the further support before being wound onto the core to form the ree|.

According to the method of the first aspect, a time period between the start of the at least one modification treatment of step b) and the start of step f) is less than 84 hours, preferably less than 72 hours, more preferably less than 48 hours.

The phrase "the start of the at least one modification treatment of step b)" is herein intended to mean the time point when an impact (e.g., mechanical or enzymatic) on the structure of the cellulose fibers of the pulp is started, i.e. when the impact of the first (or only) modification treatment of the at least one modification treatment on the cellulose fibers is started.

As mentioned above, the at least one modification treatment of step b) comprises at least one mechanical fibrillation treatment and optionally one or more enzymatic pretreatment and optionally one or more mechanical pretreatment. Thus, the phrase "the start of the at least one modification treatment of step b)" is herein intended to 21 mean the time point when the impact on the cellulose fibers of the pulp of the first (or only) modification treatment is started. ln embodiments of the method of the first aspect in which the at least one modification treatment consists of the mechanica| fibrillation treatment (i.e. in embodiments in which the processing of step b) comprises only one modification treatment, which is the mechanica| fibrillation treatment, and thus no pretreatment), the phrase "the start of the at least one modification treatment of step b)" is herein intended to mean the time point when the mechanica| fibrillation treatment of the pulp is started in step b), i.e., the time point when the mechanica| impact on the cellulose fibers of the pulp is started in the mechanica| fibrillation treatment of step b). ln embodiments of the method of the first aspect in which the at least one modification treatment comprises one or more pretreatments (i.e. in embodiments in which the processing of step b) comprises modification treatments in the form of the mechanica| fibrillation treatment and one or more pretreatments), the phrase "the start of the at least one modification treatment of step b)" is herein intended to mean the time point when the first (or only) pretreatment of the cellulose fibers of the pulp is started in step b). lf the first (or only) pretreatment of step b) is a mechanica| pretreatment, "the start of the at least one modification treatment of step b)" refers to the time point when the mechanica| impact on the cellulose fibers of the pulp is started in the mechanica| pretreatment. lf the first (or only) pretreatment of step b) is an enzymatic pretreatment, "the start of the at least one modification treatment of step b)" refers to the time point when the enzyme(s) are contacted with, such as added to, the cellulose fibers of the pulp in the enzymatic pretreatment.

The phrase "the start of step f)" is herein intended to mean the time point when the dry MFC film, or the support provided with the dry MFC film, is provided on the core to form a reel, i.e., when the dry MFC film, or the support provided with the dry MFC film, is provided on the core by being in contact with the core (applicable for the first turn) or being in contact with a previous turn of the dry MFC film, or the support provided with the dry MFC film, on the core. 22 The produced aqueous MFC suspension to be used for production of MFC films might be rich in nutrients, such as various sugars, which in combination with the aqueous environment and pH and temperature conditions promote microbiological growth, i.e., growth of microorganisms such as bacteria, fungi and yeasts. ln particular, enzymatic pretreatments and mechanica| fibrillation treatments of pulp during processing thereof to a supension comprising MFC Iiberate sugars in the water phase which facilitate the growth of microorganisms. Thus, the |imitation of the time period between the start of the at least one modification treatment of step b) and the start of step f), i.e., the time period between the time point of start of the manufacturing of the MFC and the time point of providing the final dry MFC film, to the above specified time period implies that the time period during which microorganisms may grow in the suspension comprising MFC is limited and consequently that the increase of the total bacterial count is limited by the time for growth being limited.

The |imitation of the growth of microorganisms obtained in the method of the first aspect is achieved without the need of using biocides or preservatives. Preferably, the pulp provided in step a) is free from chemically modified cellulose fibers and free from biocides, such as microbiocides, or substantially free from biocides, such as microbiocides (i.e., comprising less than 0.1 mg/g of biocides). However, in some embodiments, the |imitation of the growth of microorganisms is further improved by the method according to the first aspect further comprising a step of adding at least one biocide to the pulp during the mechanica| fibrillation treatment of step b) or to the suspension comprising MFC before the forming of the wet MFC film. Examples of biocides that may be used are sodiumhypochlorite, sodiumhypobromite, chlorine dioxide, BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin), peracetic acid, chloramine, DBNPA (2,2-dibromo-3- nitrilopropionamide), MBT (methylene bis(thiocyanate)), bronopol (2-bromo-2- nitropropane-1,3-diol), THPS (tetrakis(hydroxymethyl)phosphonium sulphate), dazomet (3,5-Dimethyl-1,3,5- thiadiazinane-2-thione) and TCMBT (2-(thiocyanomethylthio) benzothiazole). ln some embodiments, the growth of microorganisms is further limited/reduced by the method according to the first aspect further comprising a step of subjecting the suspension comprising MFC to a heat treatment at a temperature of at least 80 °C, preferably at least 90 °C, before the forming of the wet MFC film, e.g., in step b) after 23 the mechanical fibrillation treatment or between the mechanical fibrillation treatment of step b) and the film-forming of step d).

Preferably, a temperature of 35-98 °C, more preferably 30-75 °C, is utilized during the mechanical fibrillation treatment of step b) and/or during step c). ln some embodiments, the temperature is kept at a temperature of at least 60 °C, such as at a temperature of 60-98 °C or 60-75 °C, during the mechanical fibrillation treatment of step b) and/or during step c). ln some embodiments, the dry MFC film provided in step e) of the method of the first aspect has a total bacterial count of less than 1000 CFU/g, preferably less than 800 CFU/g, more preferably less than 600 CFU/g, according to standard ISO 8784-1. Thus, in these embodiments the dry MFC film has a low content of bacteria and bacterial spores. ln some embodiments, the dry MFC film provided in step e) 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. ln some embodiments, the dry MFC film provided in step e) 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. ln some embodiments, the dry MFC film has a dry grammage of 2-70 g/m2, preferably 3-70 g/m2 such as 4-70 g/m2 or 8-70 g/m2 or 10-60 g/m2 or 10-50 g/m2 or 15-40 g/m2, as measured according to ISO 536. ln some embodiments, an average film thickness of the dry MFC film is 5-60 um, preferably 10-50 um, 15-45 um or 20-40 um. 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 24 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. ln some embodiments, a width of the dry MFC film during step f) is 0.3-4 m, preferably 0.5-4 m, 1-4 m or 2-4 m. ln some embodiments, the density of the dry MFC film is 700-1500 kg/ms, preferably 800-1500 kg/ms, most preferably 900-1500 kg/ms, as measured according to ISO 534:2011. ln some embodiments, the dry MFC film is free of biocides, or substantially free of biocides (i.e., comprising less than 0.1 mg/g of biocides). ln some embodiments, the dry MFC film is free of preservatives, or substantially free of preservatives (i.e., comprising less than 0.1 mg/g of preservatives). ln some embodiments, the dry MFC film is free or substantially free of biocides and preservatives.

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

According to a third aspect illustrated herein, there is provided a paper or paperboard substrate provided with an MFC film obtainable by the method of the first aspect. The paper or paperboard susbtrate and the MFC film according to the third aspect may be further defined as set out above with reference to the method of the first aspect.

According to a fourth aspect illustrated herein, there is provided an MFC film comprising at least 50 weight-% of MFC based on total dry weight, wherein the MFC film has a total bacterial count of less than 1000 CFU/g, preferably less than 800 CFU/g, more preferably less than 600 CFU/g, and 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. ln some embodiments, the MFC film is free or substantially free of biocides. The MFC film according to the fourth aspect may be further defined as set out above with reference to the method of the first aspect.

According to a fifth aspect illustrated herein, there is provided a paper or paperboard substrate provided with an MFC film comprising at least 50 weight-% of MFC based on total dry weight, wherein the MFC film has a total bacterial count of less than 1000 CFU/g, preferably less than 800 CFU/g, more preferably less than 600 CFU/g, and 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. ln some embodiments, the MFC film is free or substantially free of biocides. The paper or paperboard susbtrate and the MFC film according to the fifth aspect may be further defined as set out above with reference to the method of the first aspect.

A free-standing MFC film according to the present disclosure can be used as such. Alternatively, it can be combined with one or more further layers, such as one or more paper or paperboard layers, into a laminate, such as a paper or paper-based packaging material laminate.

A laminate comprising a paper or paperboard substrate provided with the MFC film according to the present disclosure can be used as such. Alternatively, it can be combined with one or more further layers.

The free-standing MFC film and the laminate, respectively, according to the present disclosure may also be utilized in a laminate together with one or more polymer layers, such as thermoplastic 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).

For example, the MFC film and the laminate, respectively, of the present disclosure can be used as a packaging material or in a packaging material, such as a food or 26 liquid packaging material. For example, the MFC film and the laminate, respectively, can be part of a flexible packaging material, such as a free-standing pouch or bag, which may be opaque or translucent. Thus, the MFC film and the laminate, respectively, according to the present disclosure may be used as bag material in boxes when packaging dry food such as cereals. Furthermore, the MFC film and the laminate, respectively, according to the present disclosure may be used as a wrapping substrate, such as a flow wrap material, as a laminate material in paper, paperboard or plastics and/or as a substrate for disposable electronics. The MFC film and the laminate, respectively, may also be included in for example a closure, a lid or a label. The MFC film and the laminate, respectively, can be incorporated into any type of package, such as a box, bag, wrap, wrapping film, cup, container, tray, bottle etc.

Examples Example 1 (E1, Comparative) - Microbiological activity in fresh MFC suspension Microfibrillated cellulose (MFC) was produced from kraft pulp having an SR value of 12-15 according to standard ISO 5267-1 by enzymatic hydrolysis with an enzymatic deactivation step (94 °C, 180 min) and subsequent fluidization and microfibrillation in solids content of 4.5 weight-%. Microbial analysis was performed for an MFC sample immediately after production according to the method described below. The results indicated low microbial activity, see table 1 (E1).

Microbial analysis was performed according to method based on FDA recommendation as described in the book "Standard Methods For The Examinaton Of Dairy Products". This method includes dispersion or disintegration of sample in phosphate dilution water, plated in plate count agar (PCA) and incubated at 32 °C and 50 °C for 48 h before determining the total bacterial count. A heat activation step in 80 °C was performed for the germination of spores. Fungal colonies were analysed with yeast glucose chloramphenicol (YGC) media, incubating the samples in 25 °C for 3 days after which yeast colony count was analyzed, and for 5-7 days after which mould colony count was analyzed. The method based on FDA recommendation corresponds to standard ISO 8784-1 except for the fact that phosphate diluent is utilized instead of Ringer's diluent. 27 Example 2 (E2, Comparative) - "Aged" MFC suspension MFC produced as in Example 1 was packed in a plastic container at 4.5 wt% solids content and transported to remote location with a truck. After shipment and storage time of approximately 14 days, at 10-25 °C and without biocides or preservatives and at pH 7.4, a sample of MFC was collected for microbial analysis, which was performed as in Example 1. The results revealed high microbial activity (high total bacterial count) in the MFC suspension, see table 1 (E2).

Example 3 (E3, Comparative) - MFC film prepared from "aged" MFC suspension The MFC suspension of Example 2, which was shipped to remote location and stored for 14 days, was used to prepare a free-standing MFC film. An MFC film comprising 13 weight-% sorbitol, which was added prior to film manufacturing, and 87 weight-% MFC based on total dry weight was prepared using a cast coating method.

The furnish was cast coated on a metal belt and dried by heating the metal belt to reach final dryness of 93 to 99 %. The film was separated from the metal belt to obtain a free-standing film. The film was analyzed for microbial activity, which was performed by the method described in Example 1. Spore and bacteria count in the film was high, see table 1 (E3).

Also, OTR measurements of the produced MFC film according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C were made twice. The result of the OTR measurements were OTR values of 1.6 cc/m2/24h and 2.5 cc/m2/24h, respectively, (27.8 um and 28.0 g/m2 MFC film).

Example 4 (E4) - MFC manufacturing at MFC film cast coating plant An MFC film was produced as described in Example 3 from MFC and sorbitol, but in Example 4 the MFC suspension was transferred directly from the MFC manufacturing process to an intermediate storage vessel prior to mixing chest (sorbitol addition) and MFC film production.

The plant construction contained MFC manufacturing in batches and short transfer (short delay time) to cast coating line, enabling production of MFC film within 48 hours from start of MFC production, i.e., enabling provision of a dry MFC film within 28 48 hours from start of the enzymatic hydrolysis by adding the enzymes to the kraft pulp. No broke or dilution water were used to contaminate the process.

The microbial activity for the produced MFC film was analyzed with the method described in Exampie 1 and showed low microbial activity (E4), see table 1. This example demonstrates that MFC film production comprising a plant integrate concept and process flow setup according to the invention can provide microbiologically acceptable product without use of preservatives and biocides.

Also, OTR measurements of the produced MFC film according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C were made twice. The result of the OTR measurements were OTR values of 2.6 cc/m2/24h and 3.4 cc/m2/24h, respectively, (19.8 um and 18.9 g/m2 MFC film).

Exampie 5 (E5) - MFC film made from "fresh" thermally treated MFC Microfibrillated cellulose (MFC) was produced according to Exampie 1 with a thermal treatment step of MFC suspension prior to preparation of the suspension for cast coating. The temperature of the MFC suspension was increased to 121 °C maintained for 30 min in pH 7.0.

The thermally treated MFC was used to prepare a free standing MFC film within approximately 48 hours from start of the enzymatic hydrolysis by adding the enzymes to the kraft pulp (i.e., the time period from the addition of the enzymes to the kraft pulp to provision of a dry MFC film was approximately 48 hours). An MFC film comprising 100 weight-% of the thermally treated MFC, based on total dry weight, was prepared by casting a film on petri dish. The film was dried by heat to reach final dryness of 93 to 99 %.The film was separated from the petri dish to obtain a free-standing film.

The microbial activity of the film was analyzed to be very low, as analyzed with the method described in Exampie 1, see table 1 (E5). The manufacturing process resembles a production integrate containing MFC manufacturing and production of a thermally treated MFC and MFC film production with minimized delay between start of production of MFC and finished production of the MFC film. The result shows that high-purity MFC film can be prepared by this method. 29 The examples also demonstrate that it is possible to produce free-standing MFC film with microbial activity (total bacterial count) less than < 1000 CFU/g. Also, the examples demonstrate that it is possible to produce an MFC film with microbial activity (total bacterial count) less than < 1000 CFU/g using no biocides or preservatives. TABLE 1 Bacteria Bacteria Spores Spores Mould 32 ° 50 ° 32 ° 50 ° E1 - Fresh MFC suspension 290 63 120 9 0 (CFU/g) E2 - Aged MFC suspension (14 3520000 2200 4000 1900 4500 days) (CFU/g) E3 - Film made from aged MFC 189 34400 180 14800 9 (CFU/g) E4 - Film made with MFC plant 710 600 660 470 9 integrate (CFU/g) E5 - Film made from thermally 0 0 0 0 0 treated MFC and MFC plant integrate (CFU/g) 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. ln 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 (3)

1. A method for producing a microfibrillated cellulose (MFC) film, wherein the method comprises the steps of: a) providing a pulp comprising cellulose fibers, wherein the pulp has a Schopper-Riegler (SR) value in the range of 10-35 according to standard ISO 5267-1; b) processing said pulp comprising cellulose fibers to form a suspension comprising MFC , wherein the processing comprises subjecting said cellulose fibers to at least one modification treatment modifying the structure of said cellulose fibers, wherein at least one modification treatment of said at least one modification treatment is a mechanical fibrillation treatment to form said MFC, wherein the processing is performed at a manufacturing plant; c) conveying said suspension comprising MFC to a film-forming device at said manufacturing plant; d) forming a wet MFC film by providing a layer of said suspension comprising MFC on a support by said film-forming device, wherein said suspension comprising MFC comprises at least 50 weight-% of MFC based on total dry weight and has a dry solids content of at least 2 weight-% when provided on the support; e) dewatering and/or drying said wet MFC film provided on said support to a dry MFC film, and f) winding said dry MFC film or said support provided with said dry MFC film onto a core to form a reel of said dry MFC film or of said support provided with said dry MFC film, wherein a time period between the start of said at least one modification treatment of step b) and the start of step f) is less than 84 hours, preferably less than 72 hours, more preferably less than 48 hours.

2. The method according to claim 1, wherein said pulp is dried pulp.

3. The method according to claim 1, wherein said pulp is never-dried pulp.The method according to any one of claims 1-3, wherein said pulp provided in step a) has a total bacterial count of less than 1000 CFU/g according to standard ISO 8784- The method according to any one of the preceding claims, wherein said pulp comprises chemical pulp, mechanicai pulp, thermomechanical pulp, recycled pulp or combinations thereof. The method according to any one of the preceding claims, wherein said pulp comprises kraft pulp. The method according to any one of the preceding claims, wherein said mechanicai fibrillation treatment of step b) comprises a first sub-step of mechanicai treatment in at least one refiner device and a second sub-step of mechanicai treatment in at least one homogenizer. The method according to any one of the preceding claims, wherein at least one modification treatment of said at least one modification treatment of step b) is a pretreatment, wherein each pretreatment is an enzymatic pretreatment or a mechanicai pretreatment or a combination of an enzymatic pretreatment and a mechanicai pretreatment, wherein each pretreatment is performed before said mechanicai fibrillation treatment. The method according to claim 8, wherein at least one modification treatment of said at least one modification treatment of step b) is an enzymatic pretreatment and wherein the enzymatic pretreatment comprises treatment with one or more enzymes selected from the group of cellulases, hemicellulases and lignin-modifying enzymes. The method according to claim 8 or 9, wherein at least one modification treatment of said at least one modification treatment of step b) is an enzymatic pretreatment, wherein the method further comprises a subsequent enzyme deactivation.The method according to any one of claims 8-10, wherein at least one modification treatment of said at least one modification treatment of step b) is a mechanical pretreatment in at least one refiner device. The method according to any one of claims 8-11, wherein at least one modification treatment of said at least one modification treatment of step b) is a mechanical pretreatment and wherein at least one modification treatment of said at least one modification treatment of step b) is a subsequent enzymatic pretreatment. The method according to any one of the preceding claims, wherein a temperature of 35-98 °C is utilized during said mechanical fibrillation treatment of step b) and/or during step c). The method according to any one of the preceding claims, wherein said suspension comprising MFC is subjected to a heat treatment at a temperature of at least 80 °C, preferably at least 90 °C, before the forming of the wet MFC film. The method according to any one of the preceding claims, wherein said method is a semi-continuous method comprising at least one intermediate storage of said suspension comprising MFC produced in step b) during conveying to the film-forming device in step c). The method according to any one of the preceding claims, wherein the method further comprises adding water and/or one or more additives and/or broke to said cellulose fibers during step b) and/or to said suspension comprising MFC during step b) and/or to said suspension comprising MFC during step c), wherein said added water has a total bacterial count of less than 200 CFU/ml according to standard ISO 8784-1, wherein each of said added additives and broke has a total bacterial count of less than 1000 CFU/g according to standard ISO 8784- The method according to any one of the preceding claims, wherein said wet MFC film is formed by casting on said support in step d).The method according to claim 17, wherein said support is a non-porous suppon. The method according to claim 17 or 18, wherein said support is a metal belt, which is heated during film formation of step d) and/or during dewatering and/or drying of step e). The method according to claim 18 or 19, wherein step f) further comprises re|easing said dry MFC film from said support before winding said dry MFC film onto said core to form said reel. The method according to any one of claims 1-17, wherein said support is a paper or paperboard substrate. The method according to claim 21, wherein step f) comprises winding said paper or paperboard substrate provided with said dry MFC film onto a core to form a reel of said paper or paperboard substrate provided with said dry MFC film. The method according to any one of the preceding claims, wherein step e) comprises dewatering said wet MFC film, wherein said dewatering comprises a mechanical dewatering, gravitational dewatering and/or vacuum dewatering. The method according to any one of the preceding claims, wherein the obtained dry MFC film has a total bacterial count of less than 1000 CFU/g, preferably less than 800 CFU/g, more preferably less than 600 CFU/g, according to standard ISO 8784-1, and 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. An MFC film comprising at least 50 weight-% of MFC based on total dry weight, wherein the MFC film has a total bacterial count of less than 1000 CFU/g, preferably less than 800 CFU/g, more preferably less than 600 CFU/gaccording to standard ISO 8784-1, and 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. The MFC film according to claim 25, wherein the MFC film is free or substantially free of biocides. A paper or paperboard substrate provided with an MFC film comprising at least 50 weight-% of MFC based on total dry weight, wherein the MFC film has a total bacterial count of less than 1000 CFU/g, preferably less than 800 CFU/g, more preferably less than 600 CFU/g according to standard ISO 8784-1, and 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. A paper or paperboard substrate provided with an MFC film according to claim 27, wherein the MFC film is free or substantially free of biocides.