SE543028C2

SE543028C2 - An oxygen barrier layer comprising microfibrillated dialdehyde cellulose

Info

Publication number: SE543028C2
Application number: SE1851216A
Authority: SE
Inventors: Isabel Knöös
Original assignee: Stora Enso Oyj
Priority date: 2018-10-08
Filing date: 2018-10-08
Publication date: 2020-09-29
Also published as: EP3864075A1; WO2020075056A1; SE1851216A1; EP3864075A4

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 first suspension comprising microfibrillated dialdehyde cellulose, mixing the first suspension with at least one inorganic pigment 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 and at least one inorganic pigment.

Description

AN OXYGEN BARRIER LAYER CONIPRISING IVIICROFIBRILLATEDDIALDEHYDE CELLULOSE Technical field The present invention relates to a method for manufacturing at leastone fibrous barrier layer comprising dialdehyde polysaccharide. The presentinvention also relates to a fibrous barrier layer, such as a barrier film, having low oxygen transmission rate at high relative humidity.

Backgroundl\/licrofibrillated cellulose (l\/IFC) is widely used to manufacture barrier films for instance in multilayer paper laminates. However, the gas barrierproperties of l\/IFC based films are dependent on the moisture or the relativehumidity in the surrounding environment. Therefore, it is quite common thatl\/IFC films are coated with a polymer film to prevent moisture or water vaporto swell and disrupt the l\/IFC film. The EP2551104A1 teaches the use of l\/IFCand polyvinyl alcohol (PVOH) and/or polyuronic acid with improved barrierproperties at higher relative humidity (RH). Another solution is to coat the filmwith a film that has high water fastness and/or low water vapor transmissionrate. The JP2000303386A discloses e.g. latex coated on l\/IFC film, whileUS2012094047A teaches the use of wood hydrolysates mixed withpolysaccharides such as l\/IFC that can be coated with a polyolefin layer. lnaddition to this chemical modification, the possibility of cross-linking fibrils orfibrils and copolymers has been investigated. This improves water fastness ofthe films but also water vapor transmission rates. Another way to decreasethe moisture sensitivity of cellulose is to chemical modify the cellulose withsodium periodate to obtain dialdehyde cellulose (DAC). By fibrillating ofdialdehyde cellulose a barrier film with improved moisture resistant can beproduced. This is presented e.g. in WO2015034426. However, a dispersion comprising microfibrillated dialdehyde cellulose (DA-l\/IFC) has a tendency to 2 spontaneously crosslink to a certain degree which leads to a lowered OTR athigh humidities.

Hence, there is a need to find a way of manufacturing a barrier film which presents good gas barrier properties even at high relative humidity.

Summary lt is an object of the present invention to provide an improved barrierfilm or barrier layer comprising microfibrillated dialdehyde cellulose, which has good barrier properties at high relative humidities.

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 leastone fibrous barrier layer wherein the method comprises the steps of: providing a first suspension comprising microfibrillated dialdehyde cellulose (DA-l\/lFC); providing a second stispensšon comprisinginicrofibriliated cellulose and intermšxind with the first suspension; adding atleast one inorganic pigment to the interrnixed first and second suspensieswsand mixind to form a fnixture; freinte-g;--the-šåret--sespensietë--wåtfë--et-ieast-ene applying said mixture to a substrate toform a wet fibrous web; and drying said wet web on said substrate to form afibrous barrier layer. ln one aspect of the invention, polyvinyl alcohol (PVOH) is also addedto said first suspension in addition to said at least one inorganic pigment. lt is understood that “fibrous barrier layer” may refer to a film which inits turn can be laminated e.g. onto a base layer such as paper board and/orpaper, and it may also refer to a layer in a multilayer structure which has beencreated by wet coating directly onto a substrate and subsequently dried thereon. 3 lt has been found that addition of an inorganic pigment to a mixturecomprising microfibrillated dialdehyde cellulose (DA-l\/IFC) in making of filmleads to films with improved oxygen barrier function at high relative humiditiescompared to DA-l\/IFC films without pigments.

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

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

The cellulose derivative “dialdehyde cellulose” (DAC) can be producedby chemically modifying cellulose with sodium periodate and therebyselectively cleaving the C2-C3 bond of the anhydroglucose unit (AGU) in thecellulose chain, forming two aldehyde groups at said location. The term“degree of oxidation” (D.O.) is understood to refer to the portion of the totalnumber of anhydroglucose units that undergo said reaction (forming the twoaldehydes). The degree of oxidation is given in °/>. The skilled personunderstands that the DA-l\/IFC added in the first suspension can havedifferent degrees of oxidation, defined as the portion of AGUs that have a dialdehyde, as explained above.

The DA-l\/IFC used for manufacturing of the fibrous layer ismechanically treated to obtain microfibrillated dialdehyde cellulose. Themechanical 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 4 Gaulin homogenizer, microfluidizer, macrofluidizer or fluidizer-typehomogenizer. lt is also understood that the term “microfibrillate” refers to amechanical treatment whereby microfibrillated (cellulose) fibers are obtained.

By “oxygen transmission rate” (OTR) means a measure of the amountof 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 layeris a film.

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

According to yet another aspect of the invention, the mixture comprises70-95wt°/> microfibrillated dialdehyde cellulose, 5-30wt°/> PVOH and less than10wt% inorganic pigment based on the total dry weight of the mixture. ln another aspect, the mixture comprises 70-95wt% microfibrillateddialdehyde cellulose, 5-30wt°/> PVOH and O.5-5wt% inorganic pigment innano-scale, based on the total fiber weight of the mixture. ln another aspect, the mixture comprises 70-95wt% microfibrillateddialdehyde cellulose, 5-30wt°/> PVOH and O.5-20wt°/> inorganic pigment notdefined as nano-scale, based on the total dry weight of the mixture. lt is understood that “inorganic pigment in nano-scale” refers to nanosize pigments such as nanoclays and nanoparticles of layered mineralsilicates, for instance selected from the group comprising montmorillonite,bentonite, kaolinite, hectorite and hallyosite. lt is further understood that “inorganic pigment not defined as nanoscale” refers to non-nano size particles such as talcum, silicates, carbonates,alkaline earth metal carbonates and ammonium carbonate, and oxides, suchas transition metal oxides and other metal oxides.

According to yet another aspect of the invention, a second suspensioncomprising microfibrillated cellulose is provided, wherein said first suspension is mixed with said second suspension. The mixed first and secondsuspension containing DA-l\/IFC and l\/IFC is further mixed at least oneinorganic pigment. Also PVOH may be added to said suspension togetherwith the at least one inorganic pigment. ln one embodiment, the mixture comprises 20-45wt% of microfibrillatedcellulose, 50-75wt°/> microfibrillated di|a|dehyde cellulose, 5-30wt°/> PVOHand less than 10wt°/> inorganic pigment, based on the total fiber weight of themixture. ln another aspect, the mixture comprises 20-45wt°/> of microfibrillatedcellulose, 50-75wt°/> microfibrillated di|a|dehyde cellulose, 5-30wt°/> PVOHand 0.5-5wt°/> inorganic pigment in nano-scale, based on the total fiber weightof the mixture.

According to another aspect of the invention, the inorganic pigment innano-scale is selected from the group comprising montmorillonite, bentonite,kaolinite, hectorite and hallyosite and said mixture comprises less than 10wt°/-.~inorganic pigment, preferably between 0.5 - 5wt°/> inorganic pigment basedon the total fiber weight of the mixture.

According to another aspect of the invention, the inorganic pigment isselected from the group consisting of talcum, silicates, carbonates, alkalineearth metal carbonates and ammonium carbonate, and oxides, such astransition metal oxides and other metal oxides, and the mixture comprisesless than 25wt°/> inorganic pigment, preferably between 5-15wt°/> inorganicpigment based on the total fiber weight of the mixture.

According to another aspect of the invention, the dry content of themixture applied to the substrate is between 1-15°/> by weight.

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

According to another aspect of the invention, the substrate is a polymer or metal substrate. 6 According to another aspect of the invention, said method furthercomprises the step of pressing the film upon and/or after drying. Thetemperature may be increased to 70-150°C during such pressing of the film. lt is within the scope of the invention to add further additives to themixture, including one or more of a starch, carboxymethyl cellulose, a filler,retention chemicals, flocculation additives, deflocculating additives, drystrength additives, softeners, cellulose nanocrystals or mixtures thereof.

According to another aspect of the invention, the microfibrillateddialdehyde cellulose in the first suspension has an oxidation degree between20-50%.

Furthermore, the present invention relates to a fibrous barrier layerhaving an oxygen transmission rate in the range of from 0.1 to 100 cc/m2/24haccording to ASTM F-1927, at a relative humidity of 50 °/> at 23°C and/or at arelative humidity of 80% at 23°C, and at a barrier layer thickness 10-70 um,and wherein at least one fibrous barrier layer comprises a mixture of ainäcrofibriliated cellulose. microfibrillated dialdehyde cellulosemand at least oneinorganic pigment.

According to one aspect of the invention, said fibrous barrier layercomprises a mixture of microfibrillated dialdehyde cellulose, polyvinyl alcoholand at least one inorganic pigment.

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

According to one aspect of the invention, the fibrous barrier layer has abasis 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 afilm, preferably comprising more than one layer.

According to one aspect of the invention, the fibrous barrier layer is amultilayer film wherein at least one layer of the film is a water vapor barrierfilm comprising any one of polyethylene (PE), polypropylene (PP), polyamide,polyethylene terephthalate (PET) or ethylene vinyl alcohol (EVOH). 7 lt is possible to produce a film comprising more than one layer whereinat least one of the layers comprises the mixture according to the invention. ltmay also be possible that more than one layer of the film comprises themixture according to the invention. 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 fibrousbarrier layer as described above. The base material may include, but is notlimited to, paper, cardboard, paperboard, fabric, plastic, polymer film, metal,composites and the like.

The present invention further relates to the use of a fibrous barrierlayer comprising a mixture of a microfibrillated dialdehyde cellulose,microfibriiiateci ceiiulose, PVOH 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 formanufacturing at least one layer of a barrier film having at least oxygenbarrier properties, said method comprising:-providing a first suspension comprising microfibrillated dialdehyde cellulose;tzrovfidirio a second suspension coinprisirio rnicroiibriliatsd ceiitilose and intermixinci vvith the first suspension, yadoiiiiai ai ieasi one inorganic pigment to the interrriixed fiixst aitd secoiid susosrisions and rnixirto 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. 8 lt is within the scope of the invention to also add an amount of polyvinylalcohol (PVOH) to said first suspension, together with the at least one inorganic pigment. lt has been found that by providing a suspension of microfibrillated cellulosegig microfibrillated dialdehyde cellulose, which "aismgcomprises at least oneinorganic pigment, a film can be formed which has a good oxygen barrierproperty at high relative humidities, such as a relative humidity of 80% at23°C.

The fibrous barrier layer is produced by applying said mixture to asubstrate to form a fibrous web and drying said web to form at least one layerof film or coating. The drying of said web may be done in any conventionalway, 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. l\/licrofibrillated cellulose (l\/IFC) or so called cellulose microfibrils (Cl\/IF)shall in the context of the present application mean a nano-scale celluloseparticle fiber or fibril with at least one dimension less than 100 nm. l\/IFCcomprises partly or totally fibrillated cellulose or lignocellulose fibers. Thecellulose fiber is preferably fibrillated to such an extent that the final specificsurface area of the formed l\/IFC is from about 1 to about 300 m2/g, such asfrom 1 to 200 m2/g or more preferably 50-200 m2/g when determined for afreeze-dried material with the BET method. The term “native lVlFC” refers tol\/IFC that is made from conventional chemical, chemomechanical and/ormechanical pulp without further chemical treatment, e.g. said native l\/IFC islacking special functional groups.

Various methods exist to make MFC, such as single or multiple passrefining, pre-hydrolysis followed by refining or high shear disintegration orliberation of fibrils. One or several pre-treatment steps are usually required inorder to make l\/IFC manufacturing both energy-efficient and sustainable. The 9 cellulose fibers of the pulp to be supplied may thus be pre-treatedenzymatically or chemically. For example, the cellulose fibers may bechemically modified before fibrillation, wherein the cellulose moleculescontain functional groups other (or more) than found in the original cellulose.Such groups include, among others, carboxymethyl, aldehyde and/or carboxylgroups (cellulose obtained by N-oxyl mediated oxidation, for example"TEl\/lPO"), or quaternary ammonium (cationic cellulose). After being modifiedor oxidized in one of the above-described methods, it is easier to disintegratethe fibers into l\/IFC or NFC.

The nanofibrillar cellulose may contain some hemicelluloses; theamount is dependent on the plant source. l\/lechanical disintegration of thepre-treated fibers, e.g. hydrolysed, pre-swelled, or oxidized cellulose rawmaterial 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-typehomogenizer. Depending on the l\/IFC manufacturing method, the productmight also contain fines, or nanocrystalline cellulose or e.g. other chemicalspresent in wood fibers or in papermaking process. The product might alsocontain various amounts of micron size fiber particles that have not beenefficiently fibrillated. l\/IFC can be produced from wood cellulose fibers, both from hardwoodor softwood fibers. lt can also be made from microbial sources, agriculturalfibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fibersources. lt is preferably made from pulp including pulp from virgin fiber, e.g.mechanical, chemical and/or thermomechanical pulps. lt can also be made from broke or recycled paper.

The above described definition of l\/IFC includes, but is not limited to,the proposed TAPPI standard W13021 on cellulose nano or microfibril (Cl\/IF) 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-l\/IFC) is typically obtained by reactingcellulose with an oxidising agent such as sodium periodate. During theperiodate oxidation, selective cleavage of the C2-C3 bond of theanhydroglucose unit (AGU) of cellulose takes place, with concurrent oxidationof the C2- and C3-OH moieties to aldehyde moieties. ln this manner,crosslinkable functional groups (aldehyde groups) are introduced to thecellulose. The microfibrillated dialdehyde cellulose in the second suspensionshould in this context mean a dialdehyde cellulose treated in such way that itis microfibrillated. The production of the microfibrillated dialdehyde cellulose isdone by treating dialdehyde cellulose for example by a homogenizer or in anyother way so that fibrillation occurs to produce microfibrillated dialdehydecellulose. The microfibrillated dialdehyde cellulose in the second suspensionpreferably has an oxidation degree between 10-50°/>, preferably between 30-40°/>. The degree of oxidation was determined according to the followingdescription: after the dialdehyde cellulose reaction, the amount of C2-C3bonds in the cellulose that are converted to dialdehydes is measured. Thedegree of oxidation is the amount of C2-C3 bonds that are convertedcompared to all C2-C3 bonds. This is measured with a method by H. Zhaoand N.D. Heindel, “Determination of Degree of Substitution of Formyl Groupsin Polyaldehyde Dexran by the Hydroxylamine Hydrochloride Method”,Pharmaceutical Research, vol. 8, pp. 400-402, 1991, where the availablealdehyde groups reacts with hydroxylamine hydrochloride. This forms oximegroups and releases hydrochloric acid. The hydrochloric acid is titrated withsodium hydroxide until pH 4 is reached, and the degree of oxidation isthereafter calculated from according to the formula below. The receivedaldehyde content is divided by two to get the value of the degree of oxidation,since an oxidized anhydroglucose unit has two aldehyde groups. 11 Xí><100 D-O[%]: msampleXMw 2VNaoH = the amount of sodium hydroxide needed to reach pH 4 (I)CNaoH = 0,1 mol/Imsampie = dry weight of the analysed DAC sample (g) lVlw = 160 g/mol, which is the molecular weight of the dialdehyde cellulose unit The PVOH to be added to the first suspension preferably has a degreeof hydrolysis between 80-99 mol°/>, more preferably between 88-99 mol°/-.~.Furthermore, the PVOH preferably has a viscosity above 5 mPa>aqueous solution at 20 °C DIN 53015 / JIS K 6726.

Particularly preferred inorganic pigments that promote efficient oxygenbarrier function are pigments selected from the group consisting of clays andnanoclays, talcum, silicates, carbonates, alkaline earth metal carbonates andammonium carbonate and oxides, such as transition metal oxides and other metal oxides.

The mixture may further comprise additives, preferably any one of astarch, carboxymethyl cellulose, a filler, retention chemicals, polyvinyl alcohol,flocculation additives, deflocculating additives, dry strength additives,softeners, or mixtures thereof. lt may be possible to add additives that willimprove different properties of the mixture and/or the produced film. lt may bepossible to add the additive to the first suspension, the second suspension and/or to the mixture.

Example Bentonite as additive to DA-l\/IFC barrier film for improving oxygen transmission rate 12 A reference sample was prepared, which corresponded to a filmcontaining 75wt% DA-MFC with a degree of oxidation of 40% and 25wt%PVOH.

A test sample (Sample 1) was also prepared which corresponded to afilm containing 87wt% DA-MFC with a degree of oxidation of 40°/>, 9wt%PVOH and 4wt% bentonite. The percentages refer to the dry solids of totalfiber weight of the mixture.

The PVOH grade has a viscosity of 12.5-17.5 mPa*s of a 4 % aqueoussolution at 20 °C, DIN 53015 / JlS K 6726 and a hydrolysis degree of 99%.

The mixture for manufacturing the film according to Ref 1 wasprepared as follows. Polyvinyl alcohol was jet cooked for 2 h at a solidscontent of 14%. Dialdehyde cellulose (DAC) with a degree of oxidation of40% was mixed with 20wt% l\/IFC and 20wt% PVOH, based on the total fiberweight of the mixture. The mixing time was 1 h. Afterwards, the mixture wasrun 3 passages in a l\/licrofluidizer l\/l-110EH, resulting in a DA-l\/IFC-PVOHsuspension. The solids content was 3 wt°/-.~. The suspension was deaerated ina vacuum desiccator under stirring. By adjusting the stirring speed up anddown, the air bubbles were removed from the suspension. The film was thenproduced by rod coating the DA-l\/IFC-PVOH 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 wasprepared as follows. Polyvinyl alcohol was jet cooked for 2 h at a solidscontent of 14%. 80% of Dialdehyde cellulose (DAC) with a degree ofoxidation of 30% was mixed with 20% of MFC. Afterwards, the mixture wasrun 3 passages in a l\/licrofluidizer l\/l-110EH, resulting in a DA-l\/lFC-l\/lFC-suspension. The solids content was 3 wt°/-.~. Said suspension, seen as 100%was mixed with 10wt% PVOH and 5% of Bentonite clay. The mixing time was 1 h. The solids content was 3.5 wt°/-.~. The suspension was deaerated in a 13 vacuum desiccator under stirring. By adjusting the stirring speed up anddown, the air bubbles were removed from the suspension. The film was thenproduced by rod coating the DA-l\/IFC-PVOH-bentonite dispersion on a metalplate, 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 separatelycoated on top of a base layer consisting of a MFC. The obtained two-layeredfilms had a thickness of 52-58 um and a grammage of about 50 g/m2.

The films referred to as Ref 1 and Sample 1 were tested with respectto the OTR at a relative humidity of 80% at 23°C and at relative humidity of90% at 38°C according to ASTM F-1927. The results are shown in Table 1below.Table 1: OTR of barrier films iiiiiiiiiiii iN-àiíóiéëiiiuiiióšè iiiiiiii fiiÄdidiiiiiië iiiiiiiiiiiii iiiiiiiiiiii iiiiiiiiiii " i in top layer 23/80 38/90 Ref1 60% DA-I\/IFC + 25% PVOH 3.9 40 _, 20% l\/IFC samp|e1 7o °/, DA- 9% PVOH o.4 24 l\/lFC+17°/> l\/IFC 4% bentonite The results show that the DA-l\/IFC film containing PVOH andinorganic pigment in the form of bentonite provides a better oxygen barrier at25 high relative humidities compared to the DA-l\/IFC film containing only PVOHas an additive. ln this context “high relative humidity” corresponds to 80°/> or higher.

Claims

1. A method for manufacturing at least one fibrous barrier layer wherein themethod comprises the steps of: providing a first suspension comprising microfibrillated dialdehyde cellulose, providing a second suspension comprising microfibrillated cellulose andintermixing with the first suspension, adding at least one inorganic pigment to the intermixed first and secondsuspensions and mixing 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.

2. The method according to claim 1, comprising a further step of addingpolyvinyl 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 preferablyhas 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 PVOHpreferably has a viscosity above 5 mPaXs in a 4 % aqueous solution at 20 °C DIN53015 / 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 thesubstrate 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 Iayers of a multilayer structure.

7. The method according to any one of the previous claims, wherein the mixture comprises between 20-45wt% of microfibrillated cellulose, 50-75wt% microfibrillated dilaldehyde cellulose, 5-30wt% PVOH and less than 10wt% inorganicpigment, preferably between 0.5 - 5 wt% inorganic pigment, based on the total fiberweight 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 1-6, wherein the mixturecomprises 20-45wt% of microfibrillated cellulose, 50-75wt% microfibrillateddilaldehyde cellulose, 5-30wt% PVOH and less than 25vvt% inorganic pigment,preferably between 5-15wt% inorganic pigment, based on the total fiber weight of themixture, wherein the inorganic pigment is selected from the group consisting oftalcum, 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 thefibrous barrier layer has an oxygen transmission rate in the range of from 0.1 to 100cc/m2/24h according to ASTM F-1927, at a relative humidity of 50 % at 23°C and/orat 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 saidmixture 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 themicrofibrillated dialdehyde cellulose in the first suspension has an oxidation degreebetween 20-50%.

16. A fibrous barrier layer having an oxygen transmission rate in the range offrom 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 dialdehyde cellulose and at least one inorganic pigment. PVOH. ßšêQ The fibrous barrier layer as claimed in any one of claims 16 - 119, wherein the fibrous barrier layer has a basis weight of less than 55 g/m2, preferably between 10-50 g/m2. ﬁ2-1. The fibrous barrier layer as claimed in any one of the claims 16 - E29, wherein said fibrous barrier layer is a film, preferably comprising more than one layer. _2_(_)22. The fibrous barrier layer as claimed in any one of the claims 16 - 1224,wherein said fibrous barrier layer is a multilayer film and wherein at least one layer ofthe film is a water vapor barrier film comprising any one of polyethylene (PE),polypropylene (PP), polyamide, polyethylene terephthalate (PET) or ethylene vinylalcohol (EVOH). 212. A packaging material comprising a base material and at least one fibrous barrier layer as claimed in any one of claims 16 - ÅQZZ. 223. A packaging material according to claim 212, wherein said base material is paper or paperboard. 2§4. Use of a fibrous barrier layer according to any one of claims 16-223 as anoxygen barrier film, wherein the film is obtainable by a method according to any one of claims 1-15.