Microfibrillated cellulose suspension and film, and a method for producing a microfibrillated cellulose film

Abstract

The present invention relates to a microfibrillated cellulose (MFC) suspension and an MFC film comprising a film-forming component, and a method for producing the MFC film. The film-forming component consists of MFC, 7.0-13.0 weight-% of a 5 vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) based on the weight of the MFC (dry / dry), 2.0-8.0 weight-% of a sugar alcohol based on the weight of the MFC (dry / dry), and 0-5.0 weight-% of other additives based on the weight of the MFC (dry / dry), wherein a weight ratio between the PVAE and the sugar alcohol is 1.2-3.5 (dry / dry), wherein the sugar alcohol is selected from the group of: sorbitol, xylitol, 10 xylose, mannitol, mannose, hydrogenated starch hydrolysates (HSH), wood hydrolysate, hemicellulose and combinations thereof.

Description

[0001] MICROFIBRILLATED CELLULOSE SUSPENSION AND FILM, AND A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE FILM

[0002] Technical field

[0003] The present disclosure relates to a suspension comprising microfibrillated cellulose (MFC), an MFC film and a method for producing an MFC film. In addition, the present disclosure relates to a laminate comprising the MFC film and a paper or paperboard substrate, a packaging material comprising the MFC film or the laminate and use of the MFC film or the laminate in a packaging material.

[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) 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 film. MFC films are dense films with barrier properties, such as oxygen, aroma and grease barrier properties. Also, MFC films are recyclable and biodegradable as well as based on renewable raw material.

[0006] One approach to produce MFC films is to use a wet laid technique, i.e., to apply a dilute MFC suspension comprising MFC and water as suspension medium on a dewatering wire or membrane in a forming section and dewater it by vacuum, gravitation, capillary dewatering, press dewatering or a combination of these on the wire or membrane followed by drying or liquid evaporation. Another approach to produce MFC films is to use a casting method in which a wet MFC film is formed by casting of an MFC suspension comprising MFC on a non- porous support, such as a plastic or metal support, or on a paper or paperboard substrate, and thereafter dewatering and / or drying to remove water from the wet MFC film.

[0007] MFC films are known to have good oxygen barrier properties, i.e., a low oxygen transmission rate. However, in order for MFC films to additionally have good water vapor barrier properties, some additives are usually needed. For example, it is known to use polyvinyl alcohol and fillers for improving the water vapor barrier properties of MFC films. The excess use of such additives, on the other hand, may be associated with deteriorated mechanical properties of the MFC films, such as tensile strength and strain at break. Good mechanical properties are a pre-requisite especially if using an MFC film in a laminate and subjecting the laminate comprising the MFC film to converting and exposing the material to folding, creasing, stretching and / or bending.

[0008] It is also of essential importance that the MFC film or material provides good barrier performance, including water vapor barrier, with increased moisture resistance in combination with good or improved mechanical properties, without negatively impacting recyclability or repulping of the intermediate MFC film or laminate comprising the MFC film.

[0009] Thus, there is still room for improvements of the composition of MFC films.

[0010] Description of the invention

[0011] It is an object of the present invention to provide an MFC suspension comprising a film-forming component, which film-forming component comprises MFC and has a composition which, when used for forming an MFC film, eliminates or alleviates at least some of the disadvantages of the prior art MFC films. It is also an object of the present invention to provide an MFC film which elimintes or alleviates at least some of the disadvantages of the prior art MFC films.

[0012] 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.

[0013] The invention is defined by the appended independent claims. Embodiments are set forth in the appended dependent claims and in the following description.

[0014] According to a first aspect illustrated herein, there is provided a microfibrillated cellulose (MFC) suspension comprising a film-forming component and a suspension medium, wherein said film-forming component consists of MFC, 7.0-13.0 weight-% of a vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) based on the weight of the MFC (dry / dry), 2.0-8.0 weight-% of a sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-% of other additives based on the weight of the MFC (dry / dry), wherein a weight ratio between the PVAE and the sugar alcohol is 1 .2-3.5 (dry / dry), wherein said sugar alcohol is selected from the group of: sorbitol, xylitol, xylose, mannitol, mannose, hydrogenated starch hydrolysates (HSH), wood hydrolysate, hemicellulose and combinations thereof, and wherein said suspension medium is water.

[0015] According to a second aspect illustrated herein, there is provided a microfibrillated cellulose (MFC) film comprising a film-forming component, wherein said film-forming component consists of MFC, 7.0-13.0 weight-% of a vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) based on the weight of the MFC (dry / dry), 2.0-8.0 weight-% of a sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-% of other additives based on the weight of the MFC (dry / dry), wherein a weight ratio between the PVAE and the sugar alcohol is 1 .2-3.5 (dry / dry), wherein said sugar alcohol is selected from the group of: sorbitol, xylitol, xylose, mannitol, mannose, hydrogenated starch hydrolysates (HSH), wood hydrolysate, hemicellulose and combinations thereof. It has surprisingly been found that by using an MFC suspension comprising a filmforming component consisting of MFC, PVAE, a sugar alcohol and optionally other additives as specified above for producing an MFC film, production of an MFC film is enabled which has good water vapor transmission rate (WVTR) and at the same time has good mechanical properties, such as tensile strength and strain at break.

[0016] In particular, it has surprisingly been found that by using an MFC suspension comprising a film-forming component having the above specified composition, it is enabled to produce an MFC film, which has a WVTR of less than 20 g / m2 / 24h, as measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C for an average film thickness of 30 pm as measured according to standard ISO 534:2011 , which has a strain at break of 1 .5-12%, such as 1 .5-8% or 1 .5-6%, as measured according to standard ISO 1924-3:2005 in the machine direction with the exceptions that the initial distance between the grips is 20 mm, initial load is 0.1 N and tensile speed is 40 mm / min, and which has a machine direction tensile index of 60-150 Nm / g, such as 60-120 Nm / g or 60-100 Nm / g, as measured according to standard ISO 1924-3:2005 with the exceptions that the initial distance between the grips is 20 mm, initial load is 0.1 N and tensile speed is 40 mm / min.

[0017] MFC films are generally associated with good oxygen barrier properties, i.e., a low oxygen transmission rate, and good oil and grease resistance, but in order for MFC films to additionally have good water vapor barrier properties, some additives are usually needed. However, excess use of additives may be associated with deteriorated mechanical properties of the MFC films, such as tensile strength and strain at break. Generally, additives which improve the strain at break might be decreasing the tensile strength and even the water vapor barrier. Good mechanical properties are a pre-requisite especially if using an MFC film in a laminate and subjecting the laminate comprising the MFC film to converting and exposing the material to folding, creasing, stretching and / or bending. However, by using the above specified composition of the film-forming component of the MFC suspension, production of an MFC film is enabled which comprises additives providing good WVTR in combination with good mechanical properties, such as tensile strength and strain at break. 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.

[0018] 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.

[0019] MFC can be produced from wood cellulose fibers, both from hardwood and / or softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It can be made from pulp, including pulp from virgin fiber, e.g., mechanical, chemical and / or thermomechanical pulps. It can also be made from broke or recycled paper.

[0020] 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.

[0021] As mentioned above, the MFC suspension of the first aspect comprises, such as consists of, a film-forming component and a suspension medium. Preferably, the MFC suspension of the first aspect has a dry content (such as a content of the filmforming component) of 1-40 weight-%. In some embodiments, the MFC suspension has a dry content of 1-30 weight-%, such as 1-25 weight-% or 1-20 weight-% or 1-15 weight-%. Preferably, the MFC suspension has a dry content of 2-25 weight-%, such as 2-20 weight-% or 2-15 weight-% or 3-8 weight-%.

[0022] The suspension medium of the MFC suspension is water. Thus, the MFC suspension is an aqueous suspension.

[0023] As mentioned above, the film-forming component of the MFC suspension of the first aspect and of the MFC film of the second aspect consists of MFC, 7.0-13 weight-% of a vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) based on the weight of the MFC (dry / dry), 2.0-8.0 weight-% of a sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-%, preferably 0-1 .0 weight-% or 0-0.5 weight-% or 0-0.1 weight-% or 0 weight-%, of other additives based on the weight of the MFC (dry / dry). Also, the weight ratio between the PVAE and the sugar alcohol is 1 .2-3.5 (dry / dry).

[0024] In some embodiments of the MFC suspension of the first aspect and in some embodiments of the MFC film of the second aspect, the film-forming component consists of the MFC, 8.0-12.0 weight-% of the PVAE based on the weight of the MFC (dry / dry), 3.0-7.0 weight-% of the sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-%, preferably 0-1 .0 weight-% or 0-0.5 weight-% or 0-0.1 weight-% or 0 weight-%, of the other additives based on the weight of the MFC (dry / dry).

[0025] In some embodiments of the MFC suspension of the first aspect and in some embodiments of the MFC film of the second aspect, the film-forming component consists of the MFC, 8.0-12.0 weight-% of the PVAE based on the weight of the MFC (dry / dry), 4.0-6.0 weight-% of the sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-%, preferably 0-1 .0 weight-% or 0-0.5 weight-% or 0-0.1 weight-% or 0 weight-%, of the other additives based on the weight of the MFC (dry / dry).

[0026] In some embodiments of the MFC suspension of the first aspect and in some embodiments of the MFC film of the second aspect, the film-forming component consists of the MFC, 9.0-11 .0 weight-% of the PVAE based on the weight of the MFC (dry / dry), 4.0-6.0 weight-% of the sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-% preferably 0-1 .0 weight-% or 0-0.5 weight-% or 0-0.1 weight-% or 0 weight-%, of the other additives based on the weight of the MFC (dry / dry).

[0027] In some embodiments of the MFC suspension of the first aspect and in some embodiments of the MFC film of the second aspect, the film-forming component consists of the MFC, 9.0-11 .0 weight-% of the PVAE based on the weight of the MFC (dry / dry), 3.0-7.0 weight-% of the sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-% preferably 0-1 .0 weight-% or 0-0.5 weight-% or 0-0.1 weight-% or 0 weight-%, of the other additives based on the weight of the MFC (dry / dry).

[0028] The vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) may also be denoted as an ethylene modified polyvinyl alcohol.

[0029] The PVAE may have a hydrolyzation degree of 80 to 99 mol%, preferably 90 to 99 mol%, most preferably 98 to 99 mol%.

[0030] The PVAE may have a content of ethylene groups of 1 to 20 mol%, preferably 3 to 10 mol%. The degree of polymerization may be between 200 and 5000, preferably between 400 and 3000 or 700 and 1000.

[0031] The PVAE may have a viscosity of 3-30 m*Pas measured in a solution of 4 weight-% in water at 20°C and pH 5.0-7.0 according to the standard DIN 53015.

[0032] One example of a PVAE for use in the film-forming component of the MFC suspension of the first aspect and of the MFC film of the second aspect is Exceval AQ4104 (Kuraray Europe GmbH). Exceval AQ4104 has a viscosity of 3.8-4.5 m*Pas, determined at 4 weight-% and 20°C according to DIN 53015, an ethylene content of less than 10 Mol% and a degree of hydrolyzation of 98-99%.

[0033] As mentioned above, the sugar alcohol of the MFC suspension of the first aspect and of the MFC film of the second aspect is selected from the group of: sorbitol, xylitol, xylose, mannitol, mannose, hydrogenated starch hydrolysates (HSH), wood hydrolysates, hemicellulose and combinations thereof. Preferably, the sugar alcohol is sorbitol. As mentioned above, the MFC suspension of the first aspect and the MFC film of the second aspect, resepctively, comprise 0-5.0 weight-%, preferably 0-1 .0 weight-% or 0-0.5 weight-% or 0-0.1 weight-% or 0 weight-%, of other additives based on the weight of the MFC (dry / dry). The other additives may consist of one or more additive selected from the group of lubricants, preservatives, cross-linkers, defoamers and fillers.

[0034] The MFC film of the second aspect may have a moisture content of 20 weight-% or less, preferably 10 weight-% or less, more preferably 5 weight-% or less. In some embodiments, the MFC film of the second aspect 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.

[0035] The MFC of the MFC suspension of the first aspect and of the MFC film of the second 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. 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.

[0036] Preferably, the MFC film of the second aspect has a water vapor transmission rate (WVTR) of less than 20 g / m2 / 24h, preferably less than 15 g / m2 / 24h, and more preferably less than 10 g / m2 / 24h, as measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C for an average film thickness of 30 pm as measured according to standard ISO 534:2011 .

[0037] Preferably, the MFC film of the second aspect has a strain at break of 1 .5-12%, such as 1 .5-8% or 1 .5-6%, as measured according to standard ISO 1924-3:2005 in the machine direction with the exceptions that the initial distance between the grips is 20 mm, initial load is 0.1 N and tensile speed is 40 mm / min.

[0038] Preferably, the MFC film of the second aspect has a machine direction tensile index of 60-150 Nm / g, such as 60-120 Nm / g or 60-100 Nm / g, as measured according to standard ISO 1924-3:2005 with the exceptions that the initial distance between the grips is 20 mm, initial load is 0.1 N and tensile speed is 40 mm / min.

[0039] The MFC film of the second aspect may have an average thickness of 2-60 pm, preferably 5-50 pm, most preferably 10-40 pm, as measured according to standard ISO 534:2011.

[0040] In some embodiments, the MFC film of the second aspect has a width of 0.3-4 m, preferably 0.5-4 m, 1-4 m or 2-4 m.

[0041] In some embodiments, the MFC film of the second aspect has a density of 700-1500 kg / m3, preferably 800-1500 kg / m3, most preferably 900-1500 kg / m3, as measured according to ISO 534:2011 .

[0042] In some embodiments, the MFC film of the second aspect has a dry grammage of 2- 120 g / m2, preferably 2-70 g / m2or 5-60 g / m2or 10-50 g / m2, as measured according to ISO 536:2019.

[0043] The MFC film can be a single or multilayer film, or single or multilayer ply. Thus, the MFC film may comprise a single film layer or two or more film layers on top of each other.

[0044] The MFC film of the second aspect may be a free-standing film or a coating on a paper or paperboard support. Paper generally refers to a material manufactured in thin sheets from the pulp of wood or other fibrous substances comprising cellulose fibers, used for e.g., writing, drawing, or printing on, or as packaging material. Paper can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. Paper may be a single ply material, or a multiply material comprised of two or more plies.

[0045] Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for e.g., 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. Paperboard may be a single ply material, or a multiply material comprised of two or more plies. A common type of multiply paperboard is comprised of a lower density mid-ply (also sometimes referred to as “bulk ply”) sandwiched between two higher density outer plies. The lower density mid-ply may typically have a density below 750 kg / m3, preferably below 700, below 650, below 600, below 550, below 500, below 450, below 400 or below 350 kg / m3. The higher density outer plies typically have a density at least 100 kg / m3higher than the mid-ply, preferably at least 200 kg / m3higher than the mid-ply.

[0046] The paper or paperboard used in accordance with the present disclosure can be made from pulp, including pulp from virgin fiber, e.g., mechanical, semi-chemical, chemical, chemi-thermomechanical and / or thermomechanical pulps. It can also be made from broke or recycled paper or paperboard. The paper or paperboard used as a support in accordance with the present disclosure is prepared using methods known in the art.

[0047] The paper support used in accordance with the present disclosure has preferably a grammage in the range of 10-200 g / m2, more preferably in the range of 20-100 g / m2. Unless otherwise stated, the grammage is determined according to the standard ISO 536.

[0048] The paperboard support used in accordance with the present disclosure has preferably a grammage in the range of 120-600 g / m2or 120-450 g / m2, more preferably in the range of 200-500 g / m2or 180-380 g / m2. Unless otherwise stated, the grammage is determined according to the standard ISO 536.

[0049] 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. For example, the free-standing MFC film according to the present disclosure may be joined with a paper or paperboard layer using at least one tie layer. The tie layer may comprise any suitable adhesive commonly used in paper or paperboard based packaging laminates in general or adhesives used in liquid or food packaging laminates in particular.

[0050] A paper or paperboard support provided with the MFC film in the form of a coating according to the present disclosure may be utilized as such. Alternatively, it can be combined with one or more further layers.

[0051] A free-standing MFC film according to the present disclosure, or a paper or paperboard support provided with the MFC film according to the present disclosure, may be utilized in a laminate together with one or more sealing and / or liquid barrier layers, such as one or more polymer layers or 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).

[0052] A free-standing MFC film according to the present disclosure, or a paper or paperboard support provided with the MFC film according to 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.

[0053] Some examples of possible structures of a laminate comprising the MFC film (freestanding before lamination) according to the present disclosure are shown below: - A / B / C

[0054] - D / A / B / C

[0055] - A / B / C / D

[0056] - D / A / B / C / D

[0057] - D / A / B / C / D / D

[0058] - D / D / A / B / C / D / D wherein A is paper substrate or paperboard substrate, B is tie layer (adhesive layer), C is MFC film and D is sealing and / or liquid barrier such as polyolefin.

[0059] Some examples of possible structures of a laminate comprising the MFC film coated on a paper or paperboard support according to the present disclosure are shown below:

[0060] - D / A / C

[0061] - A / C / D

[0062] - D / A / C / D

[0063] - D / A / C / D / D

[0064] - D / D / A / C / D / D wherein A is paper substrate or paperboard substrate, C is MFC film and D is sealing and / or liquid barrier such as polyolefin.

[0065] According to a third aspect of the present disclosure there is provided a method for producing an MFC film according to the second aspect, wherein the method comprises the steps of: providing an MFC suspension according to the first aspect; forming a wet MFC film of the MFC suspension on a support; subjecting the wet MFC film to water removal to form the MFC film, wherein the water removal comprises dewatering and / or drying of the wet MFC film.

[0066] In some embodiments of the method of the third aspect, the support is a non-porous support, wherein the wet MFC film is formed by casting on the non-porous support and wherein the method further comprises a step of separating the MFC film from the non-porous support after the water removal.

[0067] The term “casting”, when utilized in web-forming, such as film-forming, is a known term designating methods wherein a suspension is deposited by means of contact or non-contact deposition and levelling methods on a support to form a wet web. Examples of such a deposition and levelling method are curtain coating / application, slot die casting, or dosing the MFC suspension with spray or similar device and optionally leveling with, for example, a doctor-blade, rod, air knife or roll.

[0068] The non-porous support may be a metal (e.g., steel), rubber, plastic, or polymer (e.g., polyurethane) support (e.g., belt or roll). In some embodiments, the non-porous support is a metal belt (i.e., a belt made of metal) such as a steel belt, a polymer belt, or a coated belt with a permanent or temporary coating such as a polymer coated belt, e.g., a polymer coated steel belt. For example, the belt can be coated with controlled adhesion / releasing agents (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.

[0069] In some embodiments of the method of the third aspect, the non-porous support is a metal belt, such as a continuous metal belt, which is heated during the step of film formation and / or the water removal. 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 before or immediately after the MFC suspension is applied to the metal belt and the temperature of the metal belt may be kept during parts of the method, or the complete method, for producing the MFC film. By increasing the temperature of the metal belt and thus on the applied wet MFC film, it is possible to further increase the efficiency of the dewatering and / or drying of the MFC film.

[0070] In some embodiments of the method of the third aspect, the support is a paper or paperboard support, wherein the MFC film is provided as an MFC coating by providing a wet coating dispersion on the paper or paperboard support. In some embodiments in which the support is a paper or paperboard substrate, a further support, such as a non-porous support, is utilized. In these embodiments, the paper or paperboard support is provided on the further support and the wet MFC film is formed on the side of the paper or paperboard support 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. As mentioned above, the water removal of the method of the third aspect comprises dewatering and / or drying of the wet MFC film to form the MFC film according to the second aspect. Thus, in some embodiments the water removal comprises dewatering of the MFC film, wherein the dewatering may be performed in one or more dewatering steps. In some embodiments the water removal comprises drying of the MFC film, wherein the drying may be performed in one or more drying steps. In some embodiments the water removal comprises dewatering and drying of the MFC film. As mentioned above the MFC film of the second aspect may have a moisture content of 20 weight-% or less. Thus, the water removal may be performed to obtain a moisture content of 20 weight-% or less of the MFC film.

[0071] The dewatering and the drying, respectively, may be performed by using any methods known in the art that are suitable to provide the MFC film, e.g., with a moisture content of 20 weight-% or less. The wet MFC film is provided on the support during the dewatering and / or drying.

[0072] In some embodiments, the water removal comprises dewatering the wet MFC film, wherein the dewatering comprises a mechanical dewatering such as press dewatering, gravitational dewatering, vacuum dewatering or combinations thereof.

[0073] 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.

[0074] In some embodiments, the water removal comprises drying the wet MFC film, wherein 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.

[0075] In embodiments comprising dewatering, the method may further include a step of pre-drying the wet MFC film before the dewatering.

[0076] In embodiments in which the support is a non-porous support, e.g., a metal belt, the method may further comprise a step of releasing, i.e., separating such as peeling off, the MFC film from the non-porous support before winding the MFC film onto a core to form a reel. Thus, a reel of a free-standing continuous MFC film is formed in these embodiments.

[0077] In embodiments in which the support is a paper or paperboard support, the method may further comprise winding the paper or paperboard support provided with the MFC film onto the core to form the reel. Thus, a reel of a continuous paper or paperboard support provided with an MFC film is formed in these embodiments.

[0078] According to a fourth aspect of the present disclosure there is provided a method for producing a laminate, wherein the method comprises the steps of: providing an MFC film according to the second aspect; providing a paper or paperboard support, and

[0079] - joining the paper or paperboard support with the MFC film so as to provide the laminate.

[0080] 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.

[0081] 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.

[0082] MFC was made by subjecting bleached kraft pulp to refining, enzymatic treatment refining and homogenization as described in W02007091942A1 . Polyvinyl alcohol (PVOH) was Poval 15-99 and the ethylene modified PVOH (i.e., the vinylalcohol / vinylacetate / ethylene terpolymer (PVAE)) was Exceval AQ-4104, both from Kuraray. Sorbitol was of purity 98% or more and purchased from Sigma- Aldrich.

[0083] MFC film preparation

[0084] Aqueous MFC suspensions comprising a film-forming component consisting of: 1) PVOH or ethylene modified PVOH, 2) MFC, and 3) sorbitol were prepared according to the compositions given in Tables 1 and 2 below. The respective MFC suspensions were prepared according to the following. PVOH and ethylene modified PVOH, respectively, was first dissolved into water solution according to supplier’s instructions. Then MFC was dispersed in deionized water and mixed with a Dispermill Discovery 100 dissolver with a 60 mm disc at 1000 rpm for 5 minutes. Then sorbitol was added, and the mixing was continued 5 min. Last, the PVOH solution or ethylene modified PVOH solution was added and mixed 5 min. Each respective mixture (i.e., each respective MFC suspension) was deaired with Flacktek SpeedMixer, equipped with a vacuum pump, for 30 seconds at 800 RPM, 500 mbar and 8 min at 1600 RPM, 10 mbar.

[0085] MFC films were prepared from the respective MFC suspensions using a TQC sheen applicator instrument with a 4 pm deep patterned rod. The respective MFC suspension was cast coated on a stainless-steel support, and the thickness of the coating was adjusted by using a 1 mm thick polyethylene (PE) frame. Then the support was placed on a 5 mm thick aluminum substrate on a 3 mm thick iron substrate on a hot plate. The temperature of the hot plate was kept at 100 °C through drying. After drying, the MFC film was immediately removed to avoid extra heating, and placed between two A4 papers and stored at standard conditions (23°C, 50% relative humidity) at least 2 days before further analysis. The average MFC film thickness was approximately 30 pm. The grammage of the MFC films was approximately 30 g / m2. The film composition of the prepared MFC films are shown in Table 1 and Table 2. Methods - Grammage and thickness

[0086] The grammage of the MFC films was measured according to ISO 536:2019 and the thickness of the MFC films according to ISO 534:2011 .

[0087] Methods - Tensile testing

[0088] Tensile properties of the MFC films were measured according to ISO 1924-3:2005 with the exceptions that the initial distance between the grips was 20 mm, initial load was 0.1 N and tensile speed was 40 mm / min. The samples were measured in machine direction. The results of the measurements of tensile properties are shown in Table 1 and Table 2.

[0089] Methods - Water vapor transmission rate

[0090] The water vapor transmission rate (WVTR) of the MFC films was measured with ProUmid dynamic vapor sorption (DVS) analyzer. Two pieces of each sheet (8 cm x 8 cm) were cut and used for measurements. Samples were mounted on the sample holders with bottom side (side facing substrate while drying) faced down to absorbent. Molecular sieves were used as absorbent. The measurements were performed at 23 °C and 50% relative humidity for 6 hours after which the WVTR was calculated. Measurement points were taken every 10 min and the flow rate of the gas was 0.3 m / s. Two parallels of each sample were measured, and the average was reported. The results of the WVTR measurements are shown in Table 1 and Table 2.

[0091] Conclusion

[0092] In comparison with pure MFC films (not shown here), the additives provides improved tensile strength and strain at break as well as significant improvement in WVTR values. Surprisingly, fairly low amount of sorbitol is required as well as PVAE based on the MFC content (dry / dry). The use of PVAE improves the water vapor barrier properties and tensile index, whereas the use of sorbitol provides clear improvement in strain at break. Sorbitol on its own does not offer any water vapor barrier but adding a small amount o fsorbitol to the MFC-PVAE film, the WVTR is surprisingly improved compared to MFC-PVAE film. These films have also good tensile index and strain at break, meaning that they represent an optimum recipe window.

[0093] Table 1

[0094] Table 2

Claims

CLAIMS1 . A microfibrillated cellulose (MFC) suspension comprising a film-forming component and a suspension medium, wherein said film-forming component consists of MFC, 7.0-13.0 weight-% of a vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) based on the weight of the MFC (dry / dry), 2.0-8.0 weight- % of a sugar alcohol based on the weight of the MFC (dry / dry), and 0-5.0 weight-% of other additives based on the weight of the MFC (dry / dry), wherein a weight ratio between the PVAE and the sugar alcohol is 1 .2-3.5 (dry / dry), wherein the sugar alcohol is selected from the group of: sorbitol, xylitol, xylose, mannitol, mannose, hydrogenated starch hydrolysates (HSH), wood hydrolysate, hemicellulose and combinations thereof, and wherein the suspension medium is water.

2. The MFC suspension according to claim 1 , wherein said film-forming component consists of said MFC, 8.0-12.0 weight-% of said PVAE based on the weight of said MFC (dry / dry), 3.0-7.0 weight-% of said sugar alcohol based on the weight of said MFC (dry / dry) and 0-5.0 weight-% of said other additives based on the weight of said MFC (dry / dry).

3. The MFC suspension according to claim 1 or 2, wherein said film-forming component consists of said MFC, 8.0-12.0 weight-% of said PVAE based on the weight of said MFC (dry / dry), 4.0-6.0 weight-% of said sugar alcohol based on the weight of said MFC (dry / dry) and 0-5.0 weight-% of said other additives based on the weight of said MFC (dry / dry).

4. The MFC suspension according to any one of claims 1-3, wherein said filmforming component consists of said MFC, 9.0-11 .0 weight-% of said PVAE based on the weight of said MFC (dry / dry), 4.0-6.0 weight-% of said sugar alcohol based on the weight of said MFC (dry / dry) and 0-5.0 weight-% of said other additives based on the weight of said MFC (dry / dry).

5. The MFC suspension according to any one of claims 1-4, wherein said sugar alcohol is sorbitol.

6. The MFC suspension according to any one of claims 1-5, wherein said PVAE has a hydrolyzation degree of 80 to 99 mol%, preferably 90 to 99 mol%, most preferably 98 to 99 mol%.

7. The MFC suspension according to any one of claims 1-6, wherein said PVAE has a content of ethylene groups of 1 to 20 mol%, preferably 3 to 10 mol%.

8. The MFC suspension according to any one of claims 1-7, wherein said PVAE has a viscosity of 3-30 m*Pas measured in a solution of 4 weight-%in water at 20°C and pH 5.0-7.0 according to the standard DIN 53015.

9. The MFC suspension according to any one of claims 1-8, wherein said MFC suspension has a dry content of 1-40 weight-%.

10. A microfibrillated cellulose (MFC) film comprising a film-forming component, wherein said film-forming component consists of MFC, 7.0-13.0 weight-% of a vinylalcohol / vinylacetate / ethylene terpolymer (PVAE) based on the weight of the MFC (dry / dry), 2.0-8.0 weight-% of a sugar alcohol based on the weight of the MFC (dry / dry) and 0-5.0 weight-% of other additives based on the weight of the MFC (dry / dry), wherein a weight ratio between the PVAE and the sugar alcohol is 1 .2-3.5 (dry / dry), wherein the sugar alcohol is selected from the group of: sorbitol, xylitol, xylose, mannitol, mannose, hydrogenated starch hydrolysates (HSH), wood hydrolysate, hemicellulose and combinations thereof.,11. The MFC film according to claim 10, wherein said film-forming component consists of said MFC, 8.0-12.0 weight-% of said PVAE based on the weight of said MFC (dry / dry), 3.0-7.0 weight-% of said sugar alcohol based on the weight of said MFC (dry / dry) and 0-5.0 weight-% of said other additives based on the weight of said MFC (dry / dry).

12. The MFC film according to claim 10 or 11 , wherein said film-forming component consists of said MFC, 8.0-12.0 weight-% of said PVAE based on the weight of said MFC (dry / dry), 4.0-6.0 weight-% of said sugar alcohol based on the weight of said MFC (dry / dry) and 0-5.0 weight-% of said other additives based on the weight of said MFC (dry / dry).

13. The MFC film according to any one of claims 10-12, wherein said film-forming component consists of said MFC, 9.0-11.0 weight-% of said PVAE based on the weight of said MFC (dry / dry), 4.0-6.0 weight-% of said sugar alcohol based on the weight of said MFC (dry / dry) and 0-5.0 weight-% of said other additives based on the weight of said MFC (dry / dry).

14. The MFC film according to any one of claims 10-13, wherein said sugar alcohol is sorbitol.

15. The MFC film according to any one of claims 10-14, wherein said PVAE has a hydrolyzation degree of 80 to 99 mol%, preferably 90 to 99 mol%, most preferably 98 to 99 mol%.

16. The MFC film according to any one of claims 10-15, wherein said PVAE has a content of ethylene groups of 1 to 20 mol%, preferably 3 to 10 mol%.

17. The MFC film according to any one of claims 10-16, wherein said PVAE has a viscosity of 3-30 m*Pas measured in a solution of 4 weight-%in water at 20°C and pH 5.0-7.0 according to the standard DIN 53015.

18. The MFC film according to any one of claims 10-17, wherein said MFC film has a water vapor transmission rate (WVTR) of less than 20 g / m2 / 24h, preferably less than 15 g / m2 / 24h, more preferably less than 10 g / m2 / 24, as measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C for an average film thickness of 30 pm as measured according to standard ISO 534:2011 .

19. The MFC film according to any one of claims 10-18, wherein said MFC film has a strain at break of 1 .5-12% as measured according to standard ISO 1924-3:2005 in the machine direction with the exceptions that the initial distance between the grips is 20 mm, initial load is 0.1 N and tensile speed is 40 mm / min.

20. The MFC film according to any one of claims 10-19, wherein said MFC film has a machine direction tensile index of 60-150 Nm / g as measured according to standard ISO 1924-3:2005 with the exceptions that the initial distancebetween the grips is 20 mm, initial load is 0.1 N and tensile speed is 40 mm / min.

21. The MFC film according to any one of claims 10-20, wherein said MFC film has an average thickness of 2-60 pm, preferably 5-50 pm, most preferably 10-40 pm, as measured according to standard ISO 534:2011.

22. The MFC film according to any one of claims 10-21 , wherein said MFC film has a dry grammage of 2-120 g / m2as measured according to standard ISO 536:2019.

23. The MFC film according to any one of claims 10-22, wherein said MFC film has a density of 700-1500 kg / m3as measured according to ISO 534:2011.

24. The MFC film according to any one of claims 10-23, wherein said MFC film is a free-standing film.

25. The MFC film according to any one of claims 10-23, wherein said MFC film is a coating on a paper or paperboard support.

26. A method for producing a microfibrillated cellulose (MFC) film according to any one of claims 10-25, wherein the method comprises the steps of: providing an MFC suspension according to any one of claims 1-9; forming a wet MFC film of said MFC suspension on a support; subjecting said wet MFC film to water removal to form said MFC film, wherein the water removal comprises dewatering and / or drying of said wet MFC film.

27. The method according to claim 26, wherein said support is a non-porous support, wherein said wet MFC film is formed by casting on said non-porous support and wherein said method further comprises a step of separating said MFC film from said non-porous support after said water removal.

28. The method according to claim 26, wherein said support is a paper or paperboard support, wherein said MFC film is provided as an MFC coating on said paper or paperboard support.

29. A laminate comprising a paper or paperboard support and an MFC film according to any one of claims 10-25.

30. A packaging material comprising an MFC film according to any one of claims 10-25 or a laminate according to claim 29.31 . A method of producing a laminate, wherein the method comprises the steps of: providing an MFC film according to any one of claims 10-25; providing a paper or paperboard support, and- joining said paper or paperboard support with said MFC film so as to provide said laminate.

32. Use of an MFC film according to any one of claims 10-25 or a laminate according to claim 26 as a packaging material or in a packaging material.

Images