A method of preparing cellulose film comprising microfibrillated cellulose

Abstract

A METHOD FOR PREPARING A CELLULOSE FILM COMPRISING MICROFIBRILLATED CELLULOSE. A method is provided for preparing a cellulose film comprising microfibrillated cellulose (MFC), said method comprising the step of: applying an aqueous emulsion of one or more vegetable oils to the surface of a molding substrate. Improved release of the MFC film can thus be obtained.

Description

"A METHOD OF PREPARING CELLULOSE FILM COMPRISING MICROFIBRILLATED CELLULOSE" TECHNICAL FIELD

[0001] The present invention relates to a method for preparing a cellulose film comprising microfibrillated cellulose (MFC). An MFC film is also provided. BACKGROUND

[0002] It is advantageous to use hydrophilic film-forming polymers, such as poly(vinyl alcohol), to improve the barrier properties and reinforcement of cellulose films. In particular, such additives are useful for microfibrillated cellulose (MFC) films, where the bonding between fibers is weak due to the fineness of the MFC.

[0003] A problem that occurs in the manufacture of cellulose films, when molding onto a substrate, is the very high degree of adhesion between the film and the substrate that such components can provide. Even at very low dosages, the film-forming polymer can create this high adhesion, such that the cellulose film cannot be separated from the molding substrate when dry. Solutions to this problem include brushing or washing the cellulose film off the molding substrate. However, such solutions are less effective in continuous production processes, where the machine speed is high and the cellulose film needs to be separated from the molding substrate in a precise and controlled manner.

[0004] The use of fluoropolymer-based release agents, silanes, silanols, or siloxanes to separate plastic films from molding substrates is known in the optical film and plastic film industries. These Petition 870220054243, dated 06 / 21 / 2022, page 5 / 37 2 / 22 release agents are often toxic and therefore unsuitable for the production of films intended, for example, for contact with food.

[0005] There remains a need for an improvement in the release of cellulose films comprising MFC from the molding substrate. SUMMARY

[0006] Thus, in a first aspect, a method is provided for preparing a cellulose film comprising microfibrillated cellulose (MFC), said method comprising the steps of: a. provide a molding substrate having at least one surface; b. apply an aqueous emulsion of one or more vegetable oils to the said surface of the said molding substrate; c. molding a film-forming composition onto the treated surface of said molding substrate, said film-forming composition comprising the MFC and a hydrophilic film-forming polymer; d. drying the film-forming composition on the molding substrate to form a cellulose film comprising microfibrillated cellulose (MFC); and e. separate the formed cellulose film from the molding substrate.

[0007] The use of a release agent is also provided for, said release agent being an aqueous emulsion of one or more vegetable oils, in promoting the Petition 870220054243, dated 06 / 21 / 2022, page 6 / 37 3 / 22 release of a cellulose film comprising MFC and a hydrophilic film-forming polymer from the surface of a molding substrate.

[0008] In addition, a cellulose film is provided comprising microfibrillated cellulose (MFC) and a hydrophilic film-forming polymer, said cellulose film defining a surface, wherein at least one vegetable oil is present on said surface.

[0009] Further details of the invention are evident from the description and dependent claims that follow. DETAILED DISCLOSURE

[0010] It has been found that a significant improvement in the release of cellulose films containing MFC and a hydrophilic film-forming polymer from the molding substrate can be achieved by applying a thin layer of release agent, which is at least a vegetable oil, onto a surface of the molding substrate before the MFC film forms on said surface. Such a release agent allows the separation of a pure, undamaged MFC film containing a film-forming polymer from the surface of the molding substrate. In particular, this type of release agent can be substantially non-toxic, can be added during continuous production, and results in a rapid response in release properties, allowing precise control of adhesion and film release without influencing the properties of the MFC film itself (e.g., oxygen barrier properties).

[0011] In particular, even low doses of Petition 870220054243, dated 06 / 21 / 2022, page 7 / 37 4 / 22 vegetable oil release agent can provide a significant improvement in release. This is important since certain chemicals can act as a separator and therefore application in low doses is useful.

[0012] The vegetable oils used in the present invention may be approved for direct contact with food according to the FDA GRAS designation or may meet the recommendation of BfR XXXVI. The vegetable oils may be edible.

[0013] The use of the release agents of the present invention allows the adhesion of an MFC film to the molding substrate to be adjusted in a controllable manner.

[0014] A method is provided for preparing a cellulose film comprising microfibrillated cellulose (MFC); that is, an MFC film. The method comprising the general steps of: a. provide a molding substrate having at least one surface; b. apply an aqueous emulsion of one or more vegetable oils to the said surface of the said molding substrate; c. molding a film-forming composition onto the treated surface of said molding substrate, said film-forming composition comprising the MFC and a hydrophilic film-forming polymer; d. drying the film-forming composition on the molding substrate to form a cellulose film comprising microfibrillated cellulose (MFC); and Petition 870220054243, dated 06 / 21 / 2022, page 8 / 37 5 / 22 e. separate the formed cellulose film from the molding substrate.

[0015] One advantage of MFC films is that they can be transparent to visible light. Preferably, therefore, the MFC film has a transparency of more than 50%, preferably more than 65%, and most preferably more than 75%, when measured for a film with a basis weight of approximately 30 g / m2 using the DIN 53147 standard. Note that the MFC film may have high transparency to visible light, but low transparency to UV light.

[0016] The MFC film described in this document can provide an increased barrier against at least one of grease / oil, moisture, oxygen, or fragrance. The MFC film suitably has an Oxygen Transmission Rate (OTR) value of less than 5000 cm3 / m2 / 24h (23°C, 50% RH) according to ASTM D-3985, at a basis weight between 10-50 g / m2, more preferably in the range of 100-1000 cm3 / m2 / 24h. The OTR can also be less than 100 cm3 / m2 / 24h, such as 0.1100 cm3 / m2 / 24h, under these conditions.

[0017] Furthermore, at least 60%, more preferably at least 70%, or most preferably at least 80% of the tensile strength (index) of the MFC film prepared according to the invention can be maintained, compared to a reference MFC film of the same composition made without using the release agents of the invention. This is particularly relevant when the release agent is applied in small quantities and thus does not affect the tensile strength of the film. Molding substrate Petition 870220054243, dated 06 / 21 / 2022, page 9 / 37 6 / 22

[0018] The method requires a molding substrate having at least one surface. The molding substrate can be any substrate commonly used for molding fibrous suspensions. The substrate can be made of plastic or metal, or combinations thereof. In one embodiment, where the method is continuous, the molding substrate is a strip, such as a metal strip.

[0019] The surface on which the MFC (film-forming composition) film is molded may be substantially flat, or it may be textured, or it may have regions that are textured and other regions that are substantially flat. The surface may have openings to drain the liquid from the film-forming composition.

[0020] The surface (e.g., strip) onto which the film-forming composition is molded can have a length of 1-300 m and a width of 0.2-10 m. The surface can also be coated with, for example, a ceramic or plastic coating, to adjust the energy of the surface.

[0021] If the surface is textured, it may contain recesses or raised areas in a random or predetermined pattern. For example, a pattern of recesses can be created on the textured surface by etching the non-conductive or conductive channels. It is also possible to deposit material to create raised areas. One example is using laser technology to engrave the textured surface.

[0022] In one embodiment, where the molding substrate is a strip of metal, the surface may have a ground or polished finish to provide a smooth film surface. For a very smooth film surface Petition 870220054243, dated 06 / 21 / 2022, page 10 / 37 7 / 22 smooth, a mirror-quality polished metal strip can be used. A metal strip can also have a polymer coating, such as a PTFE coating. Release agent

[0023] An aqueous emulsion of one or more vegetable oils is applied to the surface of said molding substrate. As mentioned above, the use of such vegetable oil allows the separation of a pure and undamaged MFC film, containing a film-forming polymer, from the surface of the molding substrate.

[0024] Vegetable oil-based release agents are used in the tissue paper industry to modify the surface properties of the Yankee cylinder for good creping of the base tissue paper; see, for example, “Pulp and paper industry chemicals” by Pratima Bajpai (2015, ISBN 978-0-12-803408-8), and WO2011156313A1. However, creping is a different process from molding, and tissue paper generally does not comprise MFC fibers. Such release agents are not normally used in molding processes or cellulosic films comprising MFC.

[0025] Suitably, the emulsion is applied to the surface of said molding substrate in such a way that one or more vegetable oils are coated to a level of 0.1 - 500 mg / m2, preferably 0.5 - 150 mg / m2. The aqueous emulsion may comprise a small amount of vegetable oils, such as 0.01-20% by weight, preferably 0.01-10% by weight, more preferably 0.1-5% by weight of said one or more vegetable oils, while still providing good release from the molding substrate. Petition 870220054243, dated 06 / 21 / 2022, p. 11 / 37 8 / 22

[0026] One or more vegetable oils may be selected from moringa oil, palm oil, palm kernel oil, canola oil, coconut oil, soybean oil, sunflower oil, rapeseed oil, peanut oil, cottonseed oil, olive oil, linseed oil, corn oil, safflower oil, walnut oil, sesame oil, almond oil, castor oil, wild turnip oil, camelina oil, hemp oil, mustard oil, radish oil, ramtil oil, rice bran oil, tung oil, salicornia oil, jatropha oil or algae-based oil.

[0027] The aqueous emulsion of one or more vegetable oils must be of sufficiently low viscosity so that it can be sprayed or spread over the surface. The aqueous emulsion of vegetable oils should suitably have a viscosity of less than 1000 mPas, preferably less than 500 mPas, when measured according to DIN 53015 at 20°C.

[0028] The aqueous emulsion may contain stabilizers or emulsifiers. The emulsifier may be selected from a non-ionic, cationic or anionic emulsifier. The average particle size in the emulsion is 10-1000 nm or preferably 20-400 nm. Film-Forming Composition

[0029] The film-forming composition of the invention comprises MFC and a hydrophilic film-forming polymer. The composition is typically an aqueous suspension of MFC in which the hydrophilic film-forming polymer is dissolved. Preferably, the film-forming composition is an aqueous composition comprising 10-99% by weight of MFC, Petition 870220054243, dated 06 / 21 / 2022, page 12 / 37 9 / 22 preferably 50-99% by weight of MFC, more preferably 70-95% by weight of MFC, based on the total solids content of the film-forming composition.

[0030] The viscosity of the film-forming composition must be greater than 500 cP, preferably greater than 1000 cP, when measured with a Brookfield viscometer at 100 rpm at 20°C. Microfibrillated cellulose (MFC)

[0031] The present invention provides a cellulose film comprising microfibrillated cellulose (MFC). MFC, in the context of the present technology, means a nanoscale cellulose fiber or fibril with at least one dimension, preferably the diameter, less than 1000 nm. An MFC suspension may also comprise partially or wholly non-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 500 m² / g, such as from 10 to 300 m² / g or more preferably 50-200 m² / g, when determined for a solvent-exchanged and lyophilized material using the BET method. The average diameter of the MFC fibrils is 1-1000 nm, preferably 10-1000 nm. MFC can be characterized by analyzing images using high-resolution SEM or ESEM.

[0032] Preferably, the MFC content in the MFC film is at least 10% by weight, preferably 50% by weight, more preferably at least 60% by weight and most preferably at least 70% by weight, based on the total solids content. In one embodiment, the MFC film comprises at most 50% by weight, such as at most 30% by weight, Petition 870220054243, dated 06 / 21 / 2022, page 13 / 37 10 / 22 adequately at most 20% by weight, based on total solids content, of partially or totally non-fibrillated cellulose or lignocellulose fibers having an average fibril diameter greater than 1000 nm.

[0033] There are several methods for preparing MFC, such as single-pass or multi-pass refining, prehydrolysis followed by refining, or high-shear disintegration or fibril release. Typically, one or more pretreatment steps are necessary to make MFC manufacturing both energy-efficient and sustainable. The cellulose fibers from the pulp to be supplied can thus be pretreated enzymatically or chemically, for example, to reduce the amount of hemicellulose or lignin. Cellulose fibers can be chemically modified before fibrillation, whereby the cellulose molecules contain other (or more) functional groups than those found in the original cellulose. Such groups include, among others, carboxymethyl, 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 using one of the methods described above, it is easier to disintegrate the fibers into MFC.

[0034] MFC may contain some hemicelluloses; the amount depends on the plant source. Mechanical disintegration of pre-treated fibers, for example, a hydrolyzed, pre-swelled or oxidized cellulose feedstock, is carried out with suitable equipment, such as a refiner, grinder, homogenizer, colloid former, attrition grinder, ultrasonic sonicator, screw extruder. Petition 870220054243, dated 06 / 21 / 2022, page 14 / 37 11 / 22 single or double fluidizer, such as a microfluidizer, a macrofluidizer, or a fluidizer-type homogenizer. Depending on the MFC manufacturing method, the product may also contain fines or nanocrystalline cellulose or, for example, other chemicals present in wood fibers or in the papermaking process. The product may also contain varying amounts of micrometer-sized fiber particles that have not been efficiently fibrillated.

[0035] MFC can be produced from wood cellulose fibers, from both hardwood and softwood fibers. It can also be prepared from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It is preferably prepared from pulp, including virgin fiber pulp, for example, mechanical, chemical and / or thermomechanical pulps. It can also be prepared from broken or recycled paper, i.e., pre- and post-consumer waste.

[0036] MFC can be native (i.e., not chemically modified) or it can be chemically modified. Phosphorylated MFC is typically obtained by reacting cellulose fibers embedded in a solution of NH4H2PO4, water, and urea and subsequently fibrillating the fibers. One particular method involves providing a suspension of cellulose pulp fibers in water and phosphorylating the cellulose pulp fibers in said water suspension with a phosphorylating agent, followed by fibrillation using methods common in the art. Phosphorylating agents Petition 870220054243, dated 06 / 21 / 2022, page 15 / 37 Suitable 12 / 22 compounds include phosphoric acid, phosphorus pentaoxide, phosphorus oxychloride, diammonium hydrogen phosphate, and sodium dihydrogen phosphate.

[0037] The film may also include other cellulosic components. Hydrophilic film-forming polymer

[0038] The film-forming composition comprises a hydrophilic film-forming polymer. The polymer assists in the bonding of the MFC fibers of the film. The film-forming composition typically comprises 0.1–50% by weight, preferably 0.1–25% by weight, more preferably 0.1–15% by weight of said film-forming polymer, based on the total solids content of the film-forming composition. The term hydrophilic means that—when in solid form—the polymer has a contact angle with water that is less than 90 degrees, preferably less than 70 degrees.

[0039] Appropriately, the film-forming polymer is selected from poly(vinyl alcohol) (PVA), cellulose derivatives, polyacrylamide, polyethylene imine, acrylic polymers, and polyethylene glycol (PEG). The preferred film-forming polymers are polyethylene glycol (PEG) and poly(vinyl alcohol) (PVA).

[0040] Partially or fully hydrolyzed derivatives of these film-forming polymers are also potentially used. The degree of hydrolysis can be 85-99%.

[0041] Film-forming polymers - in particular, PVA - can also be derivatized with various functional groups, such as, for example, silanols or carboxylic acids. Petition 870220054243, dated 06 / 21 / 2022, page 16 / 37 13 / 22

[0042] Cellulose derivatives used as the film-forming polymer include methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, sodium carboxymethyl cellulose (NaCMC), or carboxymethyl cellulose (CMC). Cellulose derivatives may also include starch or hemicellulose, or their derivatives.

[0043] The film-forming composition may comprise one hydrophilic film-forming polymer or two or more hydrophilic film-forming polymers. In one embodiment, each hydrophilic film-forming polymer may be selected from poly(vinyl alcohol) (PVA), cellulose derivatives, polyacrylamide, polyethylene imine, acrylic polymers and polyethylene glycol (PEG), and their partially or fully hydrolyzed derivatives. Film formation

[0044] The film-forming composition described above is molded onto the treated surface of said molding substrate. Molding can occur at a speed of 10 to 500 m / min, preferably 20 to 300 m / min. The film-forming composition can have a temperature of 10 to 90°C, preferably 20 to 70°C, more preferably 20 to 60°C.

[0045] The film-forming composition is dried on the molding substrate to form a cellulose film comprising microfibrillated cellulose (MFC). In the drying step, drying and, optionally, dehydration occur. Drying can be done by evaporation, where the drying method can be impact drying, contact drying, infrared drying, Petition 870220054243, dated 06 / 21 / 2022, page 17 / 37 14 / 22 Steam drying, a combination thereof, or any other method known to a person skilled in the art. During drying, the temperature of the film-forming composition may be below 90 °C, preferably below 80 °C. A separate dewatering step may also be included, immediately after molding or after molding and drying the film to a certain dryness. Dewatering may be carried out by press dewatering, capillary dewatering, filtration, or gravity dewatering. For example, a dewatering step may be followed by evaporative drying. The aim of the drying step and the optional dewatering step is to achieve a final dryness of the cellulose film of 75-99%, more preferably 80-97%.

[0046] The cellulose film formed is then separated from the molding substrate.

[0047] The method of the present invention may comprise additional conversion steps performed on the cellulose film, such as, for example, printing, coating, lamination, etc. An additional step may be rinsing the cellulose film to remove excess aqueous emulsion from the cellulose film. Any amount of vegetable oil remaining on the MFC film may be very small, but it may be detectable by UV or UV-Vis spectroscopy. The vegetable oil can be used as a tracer chemical and / or a chemical fingerprint due to its characteristic UV spectrum. Other components

[0048] The film-forming composition used in the present method and the resulting cellulose film may comprise one or more additional components. Petition 870220054243, dated 06 / 21 / 2022, page 18 / 37 15 / 22

[0049] In one aspect, the film-forming composition comprises 0.1–30% by weight, preferably 0.1–25% by weight, more preferably 0.1–15% by weight of a filler, preferably a mineral filler, such as, for example, clay, based on the total solids content of the film-forming composition. Typical fillers may be nanoclays, bentonite, silica or silicates, calcium carbonate, talc, etc. Preferably, at least part of the filler is a plate filler. Preferably, one dimension of the filler should have an average thickness or length of 1 nm to 10 µm. If determining the particle size distribution of the fillers, for example, with light scattering techniques, the preferred particle size should be that more than 90% are less than 2 µm. Other fillers can be selected from layered silicates, metal oxides, carbon nanotubes, and metal nanoparticles.

[0050] In addition, the film-forming composition may further comprise one or more stabilizing or plasticizing agents. In one particular aspect, the plasticizer is a C1-C24 polyalcohol, preferably a C1-C12 polyalcohol, more preferably a C1-C6 polyalcohol, such as sorbitol. The film-forming composition may comprise 1-40% by weight, based on the total solids content of the film-forming composition, preferably 320% of such plasticizer. In one aspect, the film-forming composition does not comprise vegetable oils.

[0051] The film-forming composition may also contain reinforcing agents, such as cellulose derivatives, or native starch or modified starch, such as, for example Petition 870220054243, dated 06 / 21 / 2022, page 19 / 37 16 / 22 For example, cationic starch, non-ionic starch, anionic starch, or amphoteric starch. In another embodiment, the film-forming composition may also contain retention and drainage chemicals. In yet another embodiment, the film-forming composition may also contain other typical process or performance chemicals, such as fluorescent dyes or brighteners, defoamers, wet-strength resins, biocides, hydrophobic agents, barrier chemicals, plasticizers, wetting agents, etc.

[0052] In one embodiment, the aqueous emulsion of one or more vegetable oils can provide an adhesion between the cellulose film and the molding substrate of between 0.5 and 5 N / m.

[0053] In general, the invention also provides the use of an aqueous emulsion of one or more vegetable oils in promoting the release of a cellulose film, comprising MFC and a hydrophilic film-forming polymer, from the surface of a molding substrate.

[0054] A cellulose film comprising microfibrillated cellulose (MFC) and a hydrophilic film-forming polymer is also provided, said cellulose film defining a surface, wherein at least one vegetable oil is present on said surface. The cellulose film provided in this document typically has a basis weight of 10-60 g / m2 when dry. All the details provided above regarding the method of the invention are also applicable to the cellulose film itself, to the extent possible.

[0055] Preferably, cellulose film Petition 870220054243, dated 06 / 21 / 2022, page 20 / 37 The 17 / 22 defined in this document has a solids content of 75-99%, more preferably 80-97%, at the point at which it is separated from the molding substrate.

[0056] Cellulose film can be used, for example, as packaging material for food, electronics or cosmetic products.

[0057] The film may also comprise polymers such as water-soluble polymers and natural gums. Water-soluble polymers may be, for example, poly(vinyl alcohol), while natural gums may be, for example, guar gum, cellulose derivatives, hemicelluloses, and other polysaccharides. EXAMPLES Example 1 (Comparative)

[0058] A film comprising microfibrillated cellulose, poly(vinyl alcohol) and bentonite was formed by molding onto a movable steel strip, so as to obtain a wet film thickness of 740 m after dewatering and drying. The steel strip had a PTFE coating, Ra roughness of 0.9 pm and surface energy of 40-42 mN / m.

[0059] The solids content of the suspension used to prepare the film was 4.24% by weight, containing 95.76% by weight of water, 3.69% by weight of microfibrillated cellulose, 0.37% by weight of poly(vinyl alcohol) and 0.18% by weight of bentonite.

[0060] The film was dried to a final solids content of over 95% by weight and an attempt was made to separate the film from the steel strip and transfer it to a winder, as an independent film, to prepare a Petition 870220054243, dated 06 / 21 / 2022, page 21 / 37 18 / 22 continuous film reel.

[0061] The adhesion between the film and the steel strip was so high that the film could not be separated from the steel strip and the machine had to be stopped. Example 2

[0062] The MFC film formula, as given in Example 1, was formed by molding, but now with the exception that the strip was treated with an emulsion to control adhesion to the strip.

[0063] An aqueous emulsion of rapeseed oil was prepared using lecithin as an emulsifier. 6 g of soy lecithin were first dispersed in 100 g of rapeseed oil in a kitchen blender, after which 1000 g of water were added and the emulsion mixed until visibly homogeneous. The emulsion was then diluted with water to achieve a final concentration of 2% by weight of rapeseed oil.

[0064] The same steel strip molding and forming conditions as in Example 1 were used, although here the emulsion was sprayed with atomizing nozzles onto the upper surface of the moving steel strip at a rate of 82 g / min before feeding the MFC suspension onto the steel strip. The strip was moving at a speed of 4.8 m² / min. 35 g / min of emulsion were recovered from the strip surface with a rubber scraper, which continuously scrapes the strip surface to remove excess water and emulsion. 17 g / min were recovered from the coating and surfaces around the spray area. Therefore, 30 g / min was the amount of emulsion that remained on the steel strip surface, corresponding to 6.25 g / m². Considering the Petition 870220054243, dated 06 / 21 / 2022, p. 22 / 37 19 / 22 vegetable oil concentration of 2% by weight, the amount of rapeseed oil on the steel strip was therefore 125 mg / m2.

[0065] In this case, the dry film can be easily separated from the steel strip substrate and an independent film wound to prepare a continuous film reel. The effective dosage of 125 mg / m2 of rapeseed oil in emulsion form was efficient, as some residual emulsion was left on the surface of the dry film and the steel strip, respectively. Example 3

[0066] The same MFC composition was prepared as in Example 2, although the rapeseed oil concentration in the emulsion was reduced to 0.2% by weight.

[0067] Also, the dosage of 12.5 g / m2 provided a successful release of the essentially dry film from the steel strip surface, and a continuous and independent film could be rolled up. With the lowest dosage of rapeseed oil emulsion, the film and the steel strip surface showed less emulsion residue. Example 4 (Comparative)

[0068] The experiment was also repeated with a film comprising microfibrillated cellulose, poly(vinyl alcohol), bentonite, and polyethylene glycol. The wet film was molded onto a movable steel strip to obtain a wet film thickness of 690 µm after dehydration and drying. A steel strip was used as in Example 1. The suspension contained 95.66% by weight water, 3.62% by weight MFC, 0.36% by weight poly(vinyl alcohol), 0.18% by weight bentonite, and 0.18% by weight polyethylene glycol, totaling a total solids content of 4.34% by weight. Petition 870220054243, dated 06 / 21 / 2022, page 23 / 37 20 / 22

[0069] Without spraying the rapeseed oil emulsion before film molding, the adhesion was again too high to remove the film from the steel strip after drying. Example 5

[0070] The same film composition, the same molding conditions, and the same steel strip as in Example 4 were used, but now with the strip treated with rapeseed oil emulsion. The rapeseed oil emulsion was sprayed at a dosage corresponding to an effective rapeseed oil quantity of 125 mg / m2. The positive effect of the strip treatment was obvious, and the separation of the MFC film could be done without problems. Example 6

[0071] The same film composition, the same molding conditions, and the same steel strip as in Example 4 were used, but now with the strip treated with rapeseed oil emulsion. The rapeseed oil emulsion was sprayed at a dosage corresponding to an effective rapeseed oil quantity of 12.5 mg / m2. The positive effect of the strip treatment was obvious, and the separation of the MFC film could be done without problems. TABLE 1 Example No. 1 2 3 4 5 6 Suspension Water % by weight 95.76 95.76 95.76 95.66 95.66 95.66 Petition 870220054243, dated 06 / 21 / 2022, page 24 / 37 21 / 22 MFC % by weight 3.69 3.69 3.69 3.62 3.62 3.62 PVOH % by weight 0.37 0.37 0.37 0.36 0.36 0.36 Bentonite % by weight 0.18 0.18 0.18 0.18 0.18 0.18 PEG % by weight 0.18 0.18 0.18 Emulsion Rapeseed oil % by weight 2 0.2 2 0.2 Soy lecithin % by weight 0.120 0.012 0.120 0.012 Water % by weight 97.88 99.79 97.88 99.79 Steel strip Speed ​​m2 / min 4.8 4.8 4.8 4.8 4.8 4.8 Amount of emulsion g / m2 6.25 6.25 6.25 6.25 Petition 870220054243, dated 06 / 21 / 2022, page 25 / 37 22 / 22 Rapeseed oil mg / m2 125 12.5 125 12.5 Adhesion high / low high low low high low low Curling yes / no no yes yes no yes yes

[0072] Adhesion is evaluated from testing following the release of the film or blanket from the steel strip, after the drying section, before transferring to the winding. Weft adhesion can also be monitored by online imaging of weft release behavior or through, for example, spectroscopic means to analyze the residue on the metal strip. Winding is evaluated following the quality of the coils, such as tension, coil dimensions, etc. Irregular or excessively high blanket adhesion can cause problems with blanket tension and subsequently coil quality. Excessively high blanket adhesion will also lead to blanket ruptures or similar defects.

[0073] Although the present invention has been described in relation to several embodiments, these should not be considered limiting to the invention. Those skilled in the art may provide other embodiments that are included in the claims by combining various aspects and embodiments as necessary.

Claims

1. A method for preparing a cellulose film comprising microfibrillated cellulose (MFC), said method comprising the steps of: a. providing a molding substrate having at least one surface; b. applying an aqueous emulsion of one or more vegetable oils to said surface of said molding substrate; c. molding a film-forming composition onto the treated surface of said molding substrate, said film-forming composition comprising MFC and a hydrophilic film-forming polymer; d. drying the film-forming composition on the molding substrate to form a cellulose film comprising microfibrillated cellulose (MFC); and e. separating the formed cellulose film from the molding substrate.

2. The method according to claim 1, wherein said film-forming composition is an aqueous composition comprising 10-99% by weight of MFC, preferably 50-99% by weight of MFC, more preferably 70-95% by weight of MFC based on the total solids content of the film-forming composition.

3. The method according to any of the preceding claims, wherein said film-forming composition comprises 0.1 - 50% by weight, preferably 0.1 - 25% by weight, more preferably 0.1 Petition 870220054243, dated 21 / 06 / 2022, page 27 / 37 2 / 4 - 15% by weight of said film-forming polymer based on the total solids content of the film-forming composition.

4. The method according to any of the preceding claims, wherein said film-forming polymer is selected from poly(vinyl alcohol) (PVA), cellulose derivatives, polyacrylamide, polyethylene imine, acrylic polymers and polyethylene glycol (PEG), and their partially or fully hydrolyzed derivatives; preferably polyethylene glycol (PEG) and poly(vinyl alcohol) (PVA) and their partially or fully hydrolyzed derivatives.

5. The method according to any of the preceding claims, wherein said film-forming composition comprises 0.1 - 30% by weight, preferably 0.1 - 25% by weight, more preferably 0.1 - 15% by weight of a filler, preferably a mineral filler, such as, for example, clay, based on the total solids content of the film-forming composition.

6. The method according to any of the preceding claims, wherein said cellulose film has a dry basis weight of 10-60 g / m2.

7. The method according to any of the preceding claims, wherein one or more vegetable oils are applied to the surface of said molding substrate at a level of 0.1 - 500 mg / m2, preferably 0.5 - 150 mg / m2.

8. The method according to any of the preceding claims, wherein said aqueous emulsion comprises 0.01-20% by weight, preferably 0.01-10% by weight, more preferably 0.1-5% by weight of said one or more vegetable oils.

9. The method according to any of the preceding claims, wherein one or more vegetable oils are selected from moringa oil, palm oil, palm kernel oil, canola oil, coconut oil, soybean oil, sunflower oil, rapeseed oil, peanut oil, cottonseed oil, olive oil, linseed oil, corn oil, safflower oil, walnut oil, sesame oil, almond oil, castor oil, turnip oil, camelina oil, hemp oil, mustard oil, radish oil, ramtil oil, rice bran oil, tung oil, salicornia oil, jatropha oil or algae-based oil.

10. The method according to any of the preceding claims, wherein the film-forming composition further comprises one or more stabilizing and / or plasticizing agents.

11. The method according to claim 10, wherein the plasticizer is a C1-C24 polyalcohol, preferably a C1-C12 polyalcohol, more preferably a C1-C6 polyalcohol, such as sorbitol.

12. The method according to claim 5, wherein the filler is selected from layered silicates, metal oxides, carbon nanotubes and metal nanoparticles.

13. The method according to any of the preceding claims, wherein the aqueous emulsion comprises one or more emulsifiers.

14. The method according to claim 13, in Petition 870220054243, dated 06 / 21 / 2022, page 29 / 37 4 / 4, whereby the emulsifier is selected from a non-ionic, cationic or anionic emulsifier.

15. The method according to any of the preceding claims, wherein the cellulose film has a solids content of 75-99%, preferably 80-97%, at the point at which it is separated from the molding substrate.

16. The use of an aqueous emulsion of one or more vegetable oils in promoting the release of a cellulose film, comprising MFC and a hydrophilic film-forming polymer, from the surface of a molding substrate.

17. A cellulose film comprising microfibrillated cellulose (MFC) and a hydrophilic film-forming polymer, said cellulose film defining a surface, wherein at least one vegetable oil is present on said surface.

18. The cellulose film as defined in claim 17, having a solids content of 75-99%, preferably 80-97%.