EP3864075A1

EP3864075A1 - An oxygen barrier layer comprising microfibrillated dialdehyde cellulose

Info

Publication number: EP3864075A1
Application number: EP19872212.6A
Authority: EP
Inventors: Isabel KNÖÖS
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2018-10-08
Filing date: 2019-10-08
Publication date: 2021-08-18
Also published as: SE1851216A1; EP3864075A4; WO2020075056A1; SE543028C2

Abstract

The present invention relates to a method for manufacturing at least one fibrous barrier layer wherein the method comprises the steps of: providing a suspension comprising intermixed microfibrillated cellulose (MFC) and microfibrillated dialdehyde cellulose (DA-MFC); adding at least one inorganic pigment to said suspension and intermix to form a mixture; applying said mixture to a substrate to form a wet fibrous web; and drying said wet web on said substrate to form a fibrous barrier layer. It also relates to a fibrous barrier layer comprising microfibrillated dialdehyde cellulose, microfibrillated cellulose and at least one inorganic pigment.

Description

AN OXYGEN BARRIER LAYER COMPRISING MICROFIBRILLATED DIALDEHYDE CELLULOSE

Technical field

The present invention relates to a method for manufacturing at least one fibrous barrier layer comprising dialdehyde polysaccharide. The present invention also relates to a fibrous barrier layer, such as a barrier film, having low oxygen transmission rate at high relative humidity.

Background

Microfibrillated cellulose (MFC) is widely used to manufacture barrier films for instance in multilayer paper laminates. However, the gas barrier properties of MFC based films are dependent on the moisture or the relative humidity in the surrounding environment. Therefore, it is quite common that MFC films are coated with a polymer film to prevent moisture or water vapor to swell and disrupt the MFC film. The EP2551104A1 teaches the use of MFC and polyvinyl alcohol (PVOH) and/or polyuronic acid with improved barrier properties at higher relative humidity (RH). Another solution is to coat the film with a film that has high water fastness and/or low water vapor transmission rate. The JP2000303386A discloses e.g. latex coated on MFC film, while US2012094047A teaches the use of wood hydrolysates mixed with polysaccharides such as MFC that can be coated with a polyolefin layer. In addition to this, different chemical modification routes have been investigated to give the possibility to cross-link of fibrils with each other or fibrils with other compounds. This improves water fastness of the films but also water vapor transmission rates. Another way to decrease the moisture sensitivity of cellulose is to chemically modify the cellulose with sodium periodate to obtain dialdehyde cellulose (DAC). Thanks to being based on a renewable material, use of DAC allows for designing barrier structures with a high renewable content. By fibrillating of dialdehyde cellulose a barrier film with improved moisture resistant can be produced. This is presented e.g. in WO2015034426. A dispersion comprising microfibrillated dialdehyde cellulose (DA-MFC) can spontaneously form crosslink to a certain degree, which leads to a material with an oxygen barrier which is not deteriorated at high relative humidity as native MFC films are.

For the most demanding applications, however, the barrier

performance needs to be even better than what DA-MFC can give alone.

Summary

It is an object of the present invention to provide an improved barrier film or barrier layer comprising microfibrillated dialdehyde cellulose, which has good barrier properties at high relative humidity.

The invention is defined by the appended independent claims.

Embodiments are set forth in the appended dependent claims.

The present invention relates to a method for manufacturing at least one fibrous barrier layer wherein the method comprises the steps of:

providing a suspension comprising intermixed microfibrillated cellulose (MFC) and microfibrillated dialdehyde cellulose (DA-MFC); adding at least one inorganic pigment to said suspension and intermix to form a mixture; applying said mixture to a substrate to form a wet fibrous web; and drying said wet web on said substrate to form a fibrous barrier layer.

It is to be understood that said inorganic pigment can be mixed firstly with MFC and then DA-MFC is added to form said mixture. It is equally possible to firstly mix the inorganic pigment with DA-MFC and then MFC is added to form said mixture.

In one aspect of the invention, polyvinyl alcohol (PVOFI) is also added in addition to said at least one inorganic pigment. It is understood that“fibrous barrier layer” may refer to a film which in its turn can be laminated e.g. onto a base layer such as paper board and/or paper, and it may also refer to a layer in a multilayer structure which has been created by wet coating directly onto a substrate and subsequently dried thereon.

It has been found that addition of an inorganic pigment to a mixture comprising dialdehyde polysacharide in making of film leads to films with improved oxygen barrier function at high relative humidities compared to DA- MFC films without pigments. A preferred dialdehyde polysacharide is microfibrillated dialdehyde cellulose.

Particularly preferred inorganic pigments that promote efficient oxygen barrier function are pigments selected from the group consisting of clays and nanoclays, talcum, silicates, carbonates, alkaline earth metal carbonates and ammonium carbonate; and oxides such as transition metal oxides and other metal oxides.

According to one aspect of the invention, the PVOH to be added preferably has a degree of hydrolysis between 80-99 mol%, more preferably between 88-99 mol%. Furthermore, the PVOFI preferably has a viscosity above 5 mPaxs in a 4 % aqueous solution at 20 °C DIN 53015 / JIS K 6726.

The cellulose derivative“dialdehyde cellulose” (DAC) can be produced by chemically modifying cellulose with sodium periodate and thereby selectively cleaving the C2-C3 bond of the anhydroglucose unit (AGU) in the cellulose chain, forming two aldehyde groups at said location. The term “degree of oxidation” (D.O.) is understood to refer to the portion of the total number of anhydroglucose units that undergo said reaction (forming the two aldehydes). The degree of oxidation is given in %. The skilled person understands that the DA-MFC added in the first suspension can have different degrees of oxidation, defined as the portion of AGUs that have a dialdehyde, as explained above.

The DA-MFC used for manufacturing of the fibrous layer is

mechanically treated to obtain microfibrillated dialdehyde cellulose. The mechanical treatment may be carried out by means of a refiner, grinder, homogenizer, colloider, friction grinder, ultrasound sonicator or fluidizer. All conventional homogenizers and fluidizers available may be used, such as Gaulin homogenizer, microfluidizer, macrofluidizer or fluidizer-type

homogenizer. It is also understood that the term“microfibrillate” refers to a mechanical treatment whereby microfibrillated (cellulose) fibers are obtained.

By“oxygen transmission rate” (OTR) means a measure of the amount of oxygen gas that passes through the film over a given time period, that is: cm³/m²/24h.

According to one aspect of the invention, the dried fibrous barrier layer is a film, such as a free-standing film.

According to another aspect of the invention, the substrate is a paper or paperboard substrate and the mixture is applied onto the substrate as a coating to form said wet fibrous web, wherein after drying said fibrous barrier layer and said substrate forms two layers of a multilayer structure. The coating as such can be applied and dried in one or more layers.

According to the invention, at least one inorganic pigment is added to said suspension and intermixed to form a mixture. The at least one inorganic pigment may be a nano size or a non-nano size particles or pigments. It is herein to be understood that that“inorganic pigment in nano-scale” refers to nano size pigments such as nanoclays and nanoparticles of layered mineral silicates, for instance selected from the group comprising montmorillonite, bentonite, kaolinite, hectorite and hallyosite. It is further to be understood that “inorganic pigment not defined as nano scale” refers to non-nano size particles such as talcum, silicates, carbonates, alkaline earth metal carbonates and ammonium carbonate, and oxides, such as transition metal oxides and other metal oxides.

In one embodiment, the mixture comprises 20-90wt% of microfibrillated cellulose, 10-80wt% microfibrillated dialdehyde cellulose, 50-300 kg/ton PVOH and less than 250 kg/ton, preferably 50-150 kg/ton inorganic pigment in non-nano size, based on the total fiber weight of the mixture. In another aspect, the mixture comprises 20-90wt% of microfibri Hated cellulose, 10-80wt% microfibrillated dialdehyde cellulose, 50-300kg/ton PVOH and less than 100 kg/ton, preferably 5-50 kg/ton inorganic pigment in nano size, based on the total fiber weight of the mixture.

According to another aspect of the invention, the inorganic pigment in nano size is selected from the group comprising montmorillonite, bentonite, kaolinite, hectorite and hallyosite.

According to another aspect of the invention, the inorganic pigment is selected from the group consisting of talcum, silicates, carbonates, alkaline earth metal carbonates and ammonium carbonate, and oxides, such as transition metal oxides and other metal oxides.

According to another aspect of the invention, the dry content of the mixture applied to the substrate is between 1 -15 wt%.

According to another aspect of the invention, the fibrous barrier layer has an oxygen transmission rate in the range of from 0.1 to 100 cc/m²/24h according to ASTM F-1927, at a relative humidity of 50 % at 23°C and/or at a relative humidity of 80% at 23°C at a barrier layer thickness 10-70 pm.

According to another aspect of the invention, the substrate is a polymer or metal substrate.

According to another aspect of the invention, said method further comprises the step of pressing the film upon and/or after drying. The temperature may be increased to 70-150°C during such pressing of the film.

It is within the scope of the invention to add further additives to the mixture, including one or more of a starch, carboxymethyl cellulose, a filler, retention chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, cellulose nanocrystals or mixtures thereof.

According to another aspect of the invention, the microfibrillated dialdehyde cellulose in the suspension has an oxidation degree between 15- 50%.

Furthermore, the present invention relates to a fibrous barrier layer having an oxygen transmission rate in the range of from 0.1 to 100 cc/m²/24h according to ASTM F-1927, at a relative humidity of 50 % at 23°C and/or at a relative humidity of 80% at 23°C, and at a barrier layer thickness 10-70 pm, and wherein at least one fibrous barrier layer comprises a mixture of a dialdehyde polysaccharide and at least one inorganic pigment.

According to one aspect of the invention, said fibrous barrier layer comprises a mixture of microfibrillated dialdehyde cellulose, polyvinyl alcohol and at least one inorganic pigment.

According to one aspect of the invention, the fibrous barrier layer comprises a mixture of microfibrillated cellulose, microfibrillated dialdehyde cellulose, PVOH and at least one inorganic pigment.

According to one aspect of the invention, the fibrous barrier layer has a basis weight of less than 55 g/m², preferably between 10-50 g/m²

According to one aspect of the invention, said fibrous barrier layer is a film, preferably comprising more than one layer.

According to one aspect of the invention, the fibrous barrier layer is a multilayer film wherein at least one layer of the film is a water vapor barrier film comprising any one of polyethylene (PE), polypropylene (PP), polyamide, polyethylene terephthalate (PET), polylactic acid (PLA) or ethylene vinyl alcohol (EVOH).

It is possible to produce a film comprising more than one layer wherein at least one of the layers comprises the mixture according to the invention. It may also be possible that more than one layer of the film comprises the mixture according to the invention. It may also be possible that one or more layers of the film only comprises native microfibrillated cellulose, i.e. which does not comprise microfibrillated dialdehyde cellulose (DA-MFC). The film may comprise two, three, four, five or more layers.

The present invention further relates to a packaging material e.g. intended for food stuff comprising a base material and at least one fibrous barrier layer as described above. The base material may include, but is not limited to, paper, cardboard, paperboard, fabric, plastic, polymer film, metal, composites and the like.

The present invention further relates to the use of a fibrous barrier layer comprising a mixture of a microfibrillated dialdehyde cellulose, microfibrillated cellulose, and at least one inorganic pigment as an oxygen barrier film.

Description of Embodiments

The method according to the present invention relates to a method for manufacturing at least one layer of a barrier film having at least oxygen barrier properties, said method comprising:

providing a suspension comprising intermixed microfibrillated cellulose (MFC) and microfibrillated dialdehyde cellulose (DA-MFC);

adding at least one inorganic pigment to said suspension and intermix to form a mixture;

applying said mixture to a substrate to form a wet fibrous web; and drying said wet web on said substrate to form a fibrous barrier layer.

It is within the scope of the invention to also add an amount of polyvinyl alcohol (PVOFI) in addition to the at least one inorganic pigment.

It has been found that by providing a suspension comprising

microfibrillated dialdehyde cellulose and microfibrillated cellulose, which also comprises at least one inorganic pigment, a film can be formed which has a good oxygen barrier property at high relative humidity, such as 80% at 23°C.

The fibrous barrier layer is produced by applying said mixture to a substrate to form a fibrous web and drying said web to form at least one layer of film or coating. The drying of said web may be done in any conventional way, preferably in combination with heat treatment and increased pressure. The dry content of the at least one layer of the film after drying is preferably above 90% by weight.

Microfibrillated cellulose (MFC) or so called cellulose microfibrils (CMF) shall in the context of the present application mean a nano-scale cellulose particle fiber or fibril with at least one dimension less than 100 nm. MFC comprises partly or totally fibrillated cellulose or lignocellulose fibers. The cellulose fiber is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 to about 300 m²/g, such as from 1 to 200 m²/g or more preferably 50-200 m²/g when determined for a freeze-dried material with the BET method. The term“native MFC” refers to MFC that is made from conventional chemical, chemo-mechanical and/or mechanical pulp without further chemical treatment, e.g. said native MFC is lacking special functional groups.

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 pre-treatment steps are usually required in order to make MFC manufacturing both energy-efficient and sustainable. The cellulose fibers of the pulp to be supplied may thus be pre-treated

enzymatically or chemically. For example, 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, carboxym ethyl, aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example

"TEMPO"), 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 or NFC.

The nanofibrillar cellulose may contain some hemicelluloses; the amount is dependent on the plant source. Mechanical disintegration of the pre-treated fibers, e.g. hydrolysed, pre-swelled, or oxidized cellulose raw material is carried out with suitable equipment such as a refiner, grinder, homogenizer, colloider, friction grinder, ultrasound sonicator, single- or twin- screw extruder, fluidizer such as microfluidizer, macrofluidizer or fluidizer-type homogenizer. Depending on the MFC manufacturing method, the product might also contain fines, or nanocrystalline cellulose or e.g. other chemicals present in wood fibers or in papermaking process. The product might also contain various amounts of micron size fiber particles that have not been efficiently fibrillated. MFC can be produced from wood cellulose fibers, both from hardwood 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 is preferably 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.

The above described definition of MFC includes, but is not limited to, the proposed TAPPI standard W13021 on cellulose nano or microfibril (CMF) defining a cellulose nanofiber material containing multiple elementary fibrils with both crystalline and amorphous regions, having a high aspect ratio with width of 5-30 nm and aspect ratio usually greater than 50. Dialdehyde cellulose (DA-MFC) is typically obtained by reacting cellulose with an oxidising agent such as sodium periodate. During the periodate oxidation, selective cleavage of the C2-C3 bond of the

anhydroglucose unit (AGU) of cellulose takes place, with concurrent oxidation of the C2- and C3-OFI moieties to aldehyde moieties. In this manner, crosslinkable functional groups (aldehyde groups) are introduced to the cellulose. The microfibrillated dialdehyde cellulose in the suspension should in this context mean a dialdehyde cellulose treated in such way that it is microfibrillated. The production of the microfibrillated dialdehyde cellulose is done by treating dialdehyde cellulose for example by a homogenizer or in any other way so that fibrillation occurs to produce microfibrillated dialdehyde cellulose. The microfibrillated dialdehyde cellulose in the suspension preferably has an oxidation degree between 15-50%, preferably between 20- 40%. The degree of oxidation was determined according to the following description: after the dialdehyde cellulose reaction, the amount of C2-C3 bonds in the cellulose that are converted to dialdehydes is measured. The degree of oxidation is the amount of C2-C3 bonds that are converted compared to all C2-C3 bonds. This is measured with a method by H. Zhao and N.D. Heindel,“Determination of Degree of Substitution of Formyl Groups in Polyaldehyde Dexran by the Hydroxylamine Hydrochloride Method”, Pharmaceutical Research, vol. 8, pp. 400-402, 1991 , where the available aldehyde groups reacts with hydroxylamine hydrochloride. This forms oxime groups and releases hydrochloric acid. The hydrochloric acid is titrated with sodium hydroxide until pH 4 is reached, and the degree of oxidation is thereafter calculated from according to the formula below. The received aldehyde content is divided by two to get the value of the degree of oxidation, since an oxidized anhydroglucose unit has two aldehyde groups.

VNaO_H = the amount of sodium hydroxide needed to reach pH 4 (I) CNaOH = 0,1 mol/l

rrisampie = dry weight of the analysed DAC sample (g)

M_w = 160 g/mol, which is the molecular weight of the dialdehyde cellulose unit

The PVOH to be added to the suspension preferably has a degree of hydrolysis between 80-99 mol%, more preferably between 88-99 mol%.

Furthermore, the PVOH preferably has a viscosity above 5 mPaxs in a 4 % aqueous solution at 20 °C DIN 53015 / J IS K 6726.

Particularly preferred inorganic pigments that promote efficient oxygen barrier function are pigments selected from the group consisting of clays and nanoclays, talcum, silicates, carbonates, alkaline earth metal carbonates and ammonium carbonate and oxides, such as transition metal oxides and other metal oxides. The mixture may further comprise additives, preferably any one of a starch, carboxymethyl cellulose, a filler, retention chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, or mixtures thereof. It may be possible to add additives that will improve different properties of the mixture and/or the produced film. It may be possible to add the additive to the first suspension, the second suspension and/or to the mixture.

Examples - Bentonite as additive to DA-MFC barrier film for improving oxygen transmission rate Example 1

A reference sample was prepared, which corresponded to a film containing 75 wt% DA-MFC with a degree of oxidation of 40%, and 25 wt% MFC. To that, 250 kg PVOFI per ton dry fiber was added.

A test sample (Sample 1 ) was also prepared which corresponded to a film containing 20 wt% MFC and 80wt% DA-MFC with a degree of oxidation of 30%. To that 100 kg PVOFI per ton dry fiber and 50 kg bentonite nanoclay per ton dry fiber were added. The PVOFI grade has a viscosity of 12.5-17.5 mPa*s of a 4 % aqueous solution at 20 °C, DIN 53015 / JIS K 6726 and a hydrolysis degree of 99%.

The mixture for manufacturing the film according to Ref 1 was prepared as follows. Polyvinyl alcohol was jet cooked for 2 h at a solids content of 14%. Dialdehyde cellulose (DAC) with a degree of oxidation of 40% was mixed with MFC and PVOFI. The mixing time was 1 h. Afterwards, the mixture was run 3 passages in a Microfluidizer M-110EFI, resulting in a MFC-DA-MFC-PVOFI suspension. The solids content was 3 wt%. The suspension was deaerated in a vacuum desiccator under stirring. By adjusting the stirring speed up and down, the air bubbles were removed from the suspension. The film was then produced by rod coating the MFC-DA- MFC-PVOFI dispersion on a metal plate, which was then placed on another metal plate, pre-heated to 105°C. The estimated temperature during drying was 70 °C.

The mixture for manufacturing the film according to Sample 1 was prepared as follows. Polyvinyl alcohol was jet cooked for 2 h at a solids content of 14%. Dialdehyde cellulose (DAC) with a degree of oxidation of 30% was mixed with MFC. Afterwards, the mixture was run 3 passages in a Microfluidizer M-110EH, resulting in a MFC-DA-MFC-suspension. The solids content was 3 wt%. Said suspension, was mixed with PVOFI and Bentonite clay. The mixing time was 1 h. The solids content was 3.5 wt%. The suspension was deaerated in a vacuum desiccator under stirring. By adjusting the stirring speed up and down, the air bubbles were removed from the suspension. The film was then produced by rod coating the MFC-DA- MFC-PVOFI-bentonite dispersion on a metal plate, which was then placed on another metal plate, pre-heated to 105°C. The estimated temperature during drying was 70 °C.

The two films referred to as Ref 1 and Sample 1 were separately coated on top of a base layer consisting of a MFC. The obtained two-layered films had a thickness of 52-58 pm and a grammage of about 50 g/m²

The films referred to as Ref 1 and Sample 1 were tested with respect to the OTR at a relative humidity of 80% at 23°C and at relative humidity of 90% at 38°C according to ASTM F-1927. The results of Example 1 are shown in Table 1 below. Table 1 : OTR of barrier films in cc/m2/24h.

The results show that the DA-MFC film containing PVOH and inorganic pigment in the form of bentonite provides a better oxygen barrier at high relative humidities compared to the DA-MFC film containing only PVOFI as an additive. In this context“high relative humidity” corresponds to 80% or higher at ambient or increased temperature.

Example 2

DAC with a degree of oxidation of 40%, which had been stored in a refrigerator for 6 months, was fibrillated 3 passages in a Microfluidizer at a solids content of 1 wt%. The resulting DA-MFC was mixed with native MFC (1 wt%) in the proportion: 60/40, respectively. To this mixture of fibrillar material, the same jet-cooked PVOFI from Example 1 was added in an amount of 100 kg dry/t dry fibrillar material, giving a reference mixture: Ref. 2. To a part of this reference mixture, bentonite nanoclay, as in Example 1 , was added in an amount of 50 kg It dry fibrillar material, giving the sample mixture: Sample 2.

Both mixtures were deaerated in a vacuum desiccator according to procedure from Example 1. Films were cast in polystyrene Petri dishes with an amount of mixture corresponding to 30 g dry/m². The films were dried in 23 °C, 50% RFI for 5 days. The reference films without clay had white dots. The oxygen transmission rate was measured according to ASTM F- 1927 at 23 °C, 80% RH and at 38 °C, 90% RH, with a Mocon Ox-Tran 2/21. Before measurement, the samples were stored in 23 °C, 80% RH for 24 h to shorten the time to a steady state value when in the instrument.

The results of Example 2 are shown in Table 2.

Table 2. OTR of barrier films in cc/m2/24h.

The overrange value in the reference film is probably due to that too much crosslinking had occurred in advance within the DAC during the long storage, resulting in an uneven distribution of the components in the film, shown as visible white dots in the film. Surprisingly, the clay addition helped the material to get well dispersed despite the premature crosslinking and the film with clay had no white dots and good oxygen barrier properties at high relative humidity.

Claims

1. A method for manufacturing at least one fibrous barrier layer wherein the method comprises the steps of:

2. The method according to claim 1 , wherein suspension is mixed with polyvinyl alcohol (PVOH) in addition to said at least one inorganic pigment, to form said mixture.

3. The method according to claim 2, wherein the PVOH to be added to the suspension preferably has a degree of hydrolysis between 80-99 mol%, more preferably between 88-99 mol%.

4. The method according to any one of claims 2 or 3, wherein the PVOH preferably has a viscosity above 5 mPaxs in a 4 % aqueous solution at 20 °C DIN 53015 / JIS K 6726.

5. The method according to any one of the previous claims, wherein the dried fibrous barrier layer is a film.

6. The method according to any one of the previous claims, wherein the substrate is a paper or paperboard substrate and the mixture is applied onto the substrate as a coating to form said wet fibrous web, wherein after drying said fibrous barrier layer and said substrate forms two layers of a multilayer structure.

7. The method according to any one of claims 2-6, wherein the mixture comprises between 20-90wt% of microfibril lated cellulose, 10-80wt% microfibrillated dialdehyde cellulose, 50-300kg/ton PVOH and less than 100 kg/ton, preferably 5-50kg/ton, inorganic pigment based on the total fiber weight of the mixture, and wherein the inorganic pigment is selected from the group comprising montmorillonite, bentonite, kaolinite, hectorite and hallyosite.

8. The method according to any one of claims 2 - 6, wherein the mixture comprises 20-90wt% of microfibrillated cellulose, 10-80wt%

microfibrillated dialdehyde cellulose, 50-300kg/ton PVOH and less than 250 kg/ton inorganic pigment, preferably between 50-150 kg/ton, inorganic pigment, based on the total fiber weight of the mixture, wherein the inorganic pigment is selected from the group consisting of talcum, silicates, carbonates, alkaline earth metal carbonates and ammonium carbonate, and oxides, such as transition metal oxides and other metal oxides.

9. The method according to any one of the preceding claims wherein the dry content of the mixture applied to the substrate is between 1 -15% by weight.

10. The method according to any one of the preceding claims wherein the fibrous barrier layer has an oxygen transmission rate in the range of from 0.1 to 100 cc/m²/24h according to ASTM F-1927, at a relative humidity of 50 % at 23°C and/or at a relative humidity of 80% at 23°C with a barrier layer thickness of 10-70 pm.

11. The method according to any one of claims 1 -5, or 7-10, wherein the substrate is a polymer or metal substrate.

12. The method according to any one of the preceding claims, wherein the temperature is increased to 70-150°C during drying of the film.

13. The method according to any one of the preceding claims, wherein said method further comprises the step of pressing the film upon and/or after drying.

14. The method according to any of the preceding claims, wherein said mixture further comprises any one of a starch, carboxymethyl cellulose, a filler, retention chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, cellulose nanocrystals or mixtures thereof.

15. The method according to any of the preceding claims wherein the microfibrillated dialdehyde cellulose has an oxidation degree between 15- 50%, preferably 20-40 %.

16. A fibrous barrier layer obtainable by means of a method according to any one of claims 1 -15.

17. A fibrous barrier layer having an oxygen transmission rate in the range of from 0.1 to 100 cc/m²/24h according to ASTM F-1927, at a relative humidity of 50% at 23°C and/or at a relative humidity of 80% at 23°C, and with a barrier layer thickness of 10-70 pm, and wherein at least one fibrous barrier layer comprises a mixture of microfibrillated cellulose, microfibrillated dialdehyde cellulose and at least one inorganic pigment.

18. A fibrous barrier layer according to claim 17, further comprising

PVOH.

19. The fibrous barrier layer as claimed in any one of claims 17 - 18, comprising a basis weight of less than 55 g/m², preferably between 10-50 g/m².

20. The fibrous barrier layer as claimed in any one of the claims 17 -

19, wherein said fibrous barrier layer is a film, preferably comprising more than one layer.

21. The fibrous barrier layer as claimed in any one of the claims 17 -

20, wherein said fibrous barrier layer is a multilayer film and wherein at least one layer of the film is a water vapor barrier film comprising any one of polyethylene (PE), polypropylene (PP), polyamide, polyethylene terephthalate (PET), polylactic acid (PLA) or ethylene vinyl alcohol (EVOH).

22. A packaging material comprising a base material and at least one fibrous barrier layer as claimed in any one of claims 17-21.

23. A packaging material according to claim 22, wherein said base material is paper or paperboard.

24. Use of a fibrous barrier layer according to any one of claims 17-21 as an oxygen barrier film, wherein the film is obtainable by a method according to any one of claims 1 -15.