Water-based adhesive for the manufacture of laminated cellulose boards comprising single layers of graphene oxide, laminated cellulose boards obtained therefrom and method for producing the same

Abstract

The present invention relates to a water-based adhesive for the manufacture of laminated cellulose boards, said adhesive comprising a single layer of graphene oxide as a glue reinforcing agent. The present invention also relates to the laminated cellulose boards obtained therefrom and the method for producing the same.

Description

Technical Field

[0001] The present invention relates to the field of water-based adhesives and in particular to a glue strengthener based on single-layer graphene oxide for such adhesives. The water-based adhesives of the present invention are suitable for producing laminated cellulose boards, such as paperboard or paper laminates (e.g. cardboard blanks). Background Art

[0002] Adhesives are substances that are widely used in many industries to produce objects and / or materials. In many cases, adhesives are essential for the correct production of objects and / or materials.

[0003] Examples of industries requiring adhesives are the paper industry and the manufacture of laminated cellulose boards. Although both industries are related to paper, they are essentially different and have different requirements regarding the adhesives used. For example, in the first industry, cellulose fibers are attached to each other, while in the second industry, paper or cardboard is attached to each other. In the paper industry, cellulose materials (e.g., wood fibers other than rags, flax, cotton linters, bagasse, etc.) are used as raw materials to produce pulp, paper, cardboard, and other cellulose-based products, and adhesives are used to bind the cellulose fibers. In the manufacture of laminated cellulose boards (e.g., cardboard), the cardboard layers are typically attached to each other using such adhesives to provide multiple layers. However, not only must the layers be attached to each other to provide a cardboard blank, but they must also be attached in such a way that the resulting cardboard blank is resistant to user handling, meteorological phenomena such as humidity, rain, and hot and cold temperatures. In other words, the cardboard blank needs to be reliable, and from this perspective, adhesives are very relevant.

[0004] Graphene has been used in many different objects and materials because, in many cases, it allows for enhanced functionality or properties of the object or material. Attempts have been disclosed in the prior art to incorporate graphene oxide into paper pulp in an attempt to improve certain paper properties, as well as into paperboard to improve the bonding properties of adhesives used in paperboard manufacturing.

[0005] For example, patent application CN106381104A discloses a water-based adhesive product, which can be used for bonding various powders, fibers, soils, etc., that is, can be used for, for example, papermaking industry. The problem to be solved is to provide a recyclable and environmentally friendly adhesive while maintaining good performance. As can be seen in the examples, the adhesive material is mainly a synthetic adhesive, such as acrylamide, methyl acrylate, potassium acrylate, N, N'-bis (acryloyl) cystamine and N, N-methylene bis acrylamide, and the synthetic adhesive can be supplemented with a polysaccharide material, in which water-soluble starch is mentioned. The water-based adhesive also includes a graphite material, which can be selected from monolayer graphite oxide, multilayer graphite oxide or flaky graphite. Specific characteristics are not specified for the graphite material, and the adhesive exemplified is only used for bonding powdered soil, and paper or cellulose fiber are not disclosed in the examples, not to mention the bonding of cellulose board.

[0006] Patent application CN108914675 discloses a method for producing weather-resistant, waterproof, and high-quality printing paper. The method comprises: preparing pulp; producing paper from the pulp; and applying an adhesive layer thereto. During the pulp preparation step, a solubilizer composition is added, comprising all of the following: graphene quantum dots, nano-silica, and nano-titanium dioxide. The graphene quantum dots are single-layer graphene oxide quantum dots prepared by microwave exfoliation. The single-layer graphene oxide quantum dots provide excellent surface modification, while the silica effectively improves the adhesion of papermaking fibers and enhances the folding resistance and mechanical properties of the paper.

[0007] Patent document EP-2886621-A1 discloses again the adhesive for making cellulose product laminates, that is, the adhesive for making laminated cellulose sheets. In a mixture of water and starch, graphene nanofilaments are added to produce the adhesive. The added nanofilaments have a diameter within the range of 1 nanometer to 100 nanometers and a length greater than 30 microns. However, such nanofilaments can not mix well with water or aqueous solutions. Therefore, the mixture is not really stable and must be used within a short period of time after the preparation, and the bonding properties of the adhesive to which the graphene nanofilaments have been added have not been significantly improved, which may be due to having reduced mixing with water.

[0008] Therefore, there remains an interest in providing adhesives that can be used to produce laminated cellulose boards that overcome the disadvantages of prior art solutions. Summary of the Invention

[0009] According to a first aspect, the present invention relates to a water-based adhesive for producing laminated cellulose boards, the water-based adhesive comprising:

[0010] 1) Water;

[0011] 2) 20.0 wt% to 40.0 wt% of starch;

[0012] 3) optionally, up to 10 wt% of at least one additional polymer selected from natural polymers or soluble synthetic polymers;

[0013] 4) a glue enhancer, the glue enhancer being included in the water-based adhesive in an amount such that the water-based adhesive comprises 0.1 wt% to 10 -7 single-layer graphene oxide in water;

[0014] 5) at least one component selected from fungicides and biocides, and / or stabilizers, gelling agents, thickening agents, antifoaming agents, tackifiers, moisture- resistant resins, and rheological agents, depending on the polymer.

[0015] According to particular embodiments, the starch can be included in the water-based adhesive in an amount of 20 wt% to 32 wt%, for example in an amount of 25 wt% to 30 wt%.

[0016] The starch can for example be one of the following: corn starch, wheat starch, potato starch, pea starch, tapioca starch, or a mixture thereof.

[0017] The starch can be chemically modified to function properly under conditions often encountered during processing or storage, such as high temperatures, high shear, low pH, freeze / thaw, and cooling.

[0018] The above at least one component 5) can for example be a mixture of borax powder and calcium hydroxide and sodium carbonate, which after dissolution in water provides caustic soda (sodium hydroxide). Sodium hydroxide promotes glue penetration into the paper and reduces gelling time. Borax powder stabilizes the glue by reacting with cooked starch and improves glue adhesion and its penetration into the paper. It further helps to provide optimal rheology. The concentration of sodium hydroxide in the adhesive can be 1.5 wt% to 3.0 wt%, and the concentration of borax in the adhesive can be 1 wt% to 2 wt%.

[0019] Other additional components 5) can for example be at least one of the following: urea-formaldehyde to improve resistance to moisture; polyvinyl alcohol or polyvinyl acetate to improve resistance to cold water; or a biocide to inhibit fungal growth.

[0020] In the water-based adhesives defined above, the natural polymer is selected from plant, protein or animal origin, in particular, it is selected from dextrin, starch or albumin, or from any polymer extracted from casein, blood, fish, soy, hide or bone. The soluble synthetic polymer is selected from polyvinyl alcohol, cellulose ethers, methylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, urea-formaldehyde blends and melamine-formaldehyde blends.

[0021] The water-based adhesive may contain only one additional polymer, or a mixture of one or more polymers.

[0022] The remainder up to 100% by weight will be water.

[0023] Monolayer graphene oxide was synthesized according to the method disclosed in EP15382123, which is incorporated herein by reference for its preparation methods. Generally speaking, the process is based on a modified Hummers method, in which the oxidation reaction and post-exfoliation process are carried out using a high-shear mixer. In this way, the graphene oxide is exfoliated simultaneously with the reaction, resulting in higher yields, oxygen content, and monolayer content than using standard stirring methods. The monolayer graphene oxide obtained by the aforementioned method is in the form of nanosheets as defined in ISO / TR 18401:2017. Therefore, the monolayer graphene oxide used to prepare the adhesive of the present invention is in the form of such nanosheets. The aforementioned ISO specification provides a definition and classification of nano-objects based on their size and shape. Nano-objects are generally described or grouped according to their dimensions that are confined to the nanoscale. Therefore, if one dimension is within the nanoscale and the other two dimensions are larger than the nanoscale, the object is referred to as a nanosheet. If two dimensions are within the nanoscale, the object is referred to as a nanofiber, including nanotubes. If all three dimensions are within the nanometer scale, the object is called a nanoparticle or quantum dot.

[0024] The moisture-proof resin may be, for example, ketone-formaldehyde, urea-formaldehyde or resorcinol.

[0025] In the water-based adhesive according to the present invention, a single-layer graphene oxide is used as an adhesive reinforcing agent. Therefore, another aspect of the present invention is the use of a single-layer graphene oxide as an adhesive reinforcing agent in a water-based adhesive for producing laminated cellulose sheets. Such a single-layer graphene oxide is in the form of a nanoplatelet as defined in ISO / TR 18401:2017.

[0026] Preferred component 5) is caustic soda and / or borax. The preferred amount of caustic soda is 1.5 to 3% by weight relative to the weight of starch, and the preferred amount of borax is 1 to 2% by weight relative to the weight of starch.

[0027] A third aspect of the present invention is a method for producing a water-based adhesive for manufacturing the laminated cellulose board of the present invention as defined above, the method comprising mixing starch, water and a gum reinforcing agent, the gum reinforcing agent being a suspension of 0.1 wt.% to 0.001 wt.% of single-layer graphene oxide in water. Such single-layer graphene oxide in water is preferably in the form of nanoplatelets as defined in ISO / TR 18401 :2017.

[0028] For example, the method comprises the steps of:

[0029] a) mixing starch into a first aqueous solution under stirring and at a temperature of 20.0 °C to 30.0 °C to obtain a first mixture comprising 20.0 wt.% to 40.0 wt.% of starch; and

[0030] b) adding a gum reinforcing agent to the first mixture under stirring, the gum reinforcing agent being a second water base comprising 0.1 wt.% to 0.001 wt.% of single-layer graphene oxide, thereby resulting in a second mixture comprising 0.1 wt.% to 10 -7 wt.% of single-layer graphene oxide.

[0031] The second mixture can be used directly as a water-based adhesive.

[0032] To reduce the cost of single-layer graphene oxide in the mixture, the concentration of single-layer graphene oxide in the second mixture can preferably be 0.001 wt.% to 10 -7 wt.%, even more preferably 10 -5 wt.% to 10 -7 wt.%. As mentioned above, the single-layer graphene oxide is preferably in the form of nanoplatelets as defined in ISO / TR 18401 :2017.

[0033] According to a further embodiment, the temperature in step a) is 24.0 °C to 26.0 °C, preferably 24.5 °C to 25.5 °C.

[0034] A further embodiment provides for stirring the first mixture in step a) for at least 20 minutes and / or stirring the second mixture in step b) for at least 10 minutes.

[0035] The adhesive can be prepared by different methods known in the art.

[0036] For example, it can be prepared by a process called "Steinhall," which provides a two-phase adhesive consisting of a starch solution made from a primary starch, called a carrier, in which uncooked raw starch (i.e., secondary starch) is suspended. The carrier is prepared by the combined action of heat and caustic soda on a starch slurry. This provides the required viscosity, thereby retaining the water required for gelatinization of the secondary starch and controlling absorption into the paper and initial adhesive strength.

[0037] Another preparation method that can be used is the "carrier-free" method. This method provides a single-phase adhesive. Most of the starch granules are partially swollen, making the mixture viscous enough to prevent sedimentation. When subjected to precise heat and alkali conditions, the starch slurry gradually swells, and boric acid is used to stop the swelling reaction at the desired viscosity.

[0038] Minocar is another process that can be used. The Minocar process is a development of the carrier-free process and provides a two-phase adhesive consisting of a primary portion in which the majority of the particles are partially swollen, in which uncooked raw starch is suspended.

[0039] Another adhesive to which the glue strengthener according to the present invention can be added is "One-Bag Mix" (OBM) starch, which is a blend of several components that form Stein-Hall glue when mixed with water. The main components are:

[0040] - pregelatinized (cooked and dried) starch, which is dissolved in water to form the primary carrier component of the glue;

[0041] - uncooked native starch, which is the secondary starch part of the glue;

[0042] - a mixture of calcium hydroxide and sodium carbonate, which forms sodium hydroxide (caustic soda) when dissolved in water;

[0043] -Borax powder.

[0044] The main reason for using OBM is its ease of use, especially when manufacturing facilities are limited.

[0045] Another method is the Stein Hall process, which provides a two-phase adhesive consisting of a starch solution made of primary starch (about 10% to 20% by weight of the total starch) in which uncooked raw starch, secondary starch (about 80% to 90% by weight of the total starch), is suspended, called a carrier. The carrier is prepared by the combined action of heat and caustic soda (about 1.4% to 3% by weight) on the starch slurry. Borax is usually added at about 1% to 2% by weight.

[0046] For example, in the manufacture of laminated cellulose sheets, the adhesive of the invention as defined or obtained above may be used.

[0047] The added monolayer of graphene oxide unexpectedly and unexpectedly enhances the adhesive properties produced by polymers such as starch, and therefore enhances the adhesive properties of the produced adhesive. Furthermore, it appears that the presence of oxygen groups in the graphene oxide allows it to disperse in the adhesive to improve its adhesive properties.

[0048] The resulting adhesive has a reduced drying time compared to the drying time of an adhesive without graphene oxide. This, in turn, leads to increased productivity, as producing objects with such an adhesive takes less time.

[0049] Furthermore, the mechanical properties of the products to which the adhesive is applied (e.g. single wallpaper boards, simple wallpaper boards, double wallpaper boards, etc.) are also improved by the adhesive. Some of the mechanical properties have been tested by FEFCO TESTING method n°9 ( https: / / find- k.ru / images / FEFCO% 209.pdf The water resistance of the adhesive of the corrugated laminated cellulose board was determined by immersion test. In addition, the dry peel test, i.e. the resistance to separation of the cellulose layers, was tested by a dynamometer. Details are provided in the examples and figures.

[0050] Besides standard laminated cellulose boards, other products can also be produced using the adhesive according to the invention, for example semi-chemical paper and plastic paper.

[0051] The main component used in the production of corrugated board is paper. Depending on the type of application and its characteristics, paper used in the production of corrugated board can be divided into two groups:

[0052] -Paper used for flat layers – liner (liner, hanging noodles).

[0053] - Paper used for the corrugated layer – fluting.

[0054] Linings – depending on their manufacturing method and component composition – belong to one of two main groups:

[0055] - Cowhide lining (kraftliner, cowhide),

[0056] - Recycled lining (testliner, imitation calfskin).

[0057] Cowhide lining - has the best strength parameters of all linings. It is made of cellulose pulp with a slight addition of recycled fibers. The outer coating is usually well glued and has a high degree of smoothness.

[0058] Outer lining (white kraft lining) is a grade of kraft lining. In most cases, the outer coating is made of bleached kraft pulp, while the base is made of unbleached virgin pulp. For higher-grade imprints, coated white kraft paper is used, with the outer coating primarily being applied with a pigmented coating color.

[0059] Recycled lining – a two-ply paper most commonly made from 100% recycled paper. Recycled lining is a combination of two layers. This construction allows for the use of kraft pulp for the outer coating and recycled fibers for the bottom layer. Due to the price relationship between expensive cellulose materials and cheaper virgin pulp, we see a continuous increase in the latter in recycled lining formulations. They are increasingly made entirely from recycled fibers. In such cases, the outer coating (top layer) is dyed to limit the color of the kraft pulp. Similar to kraft lining, recycled lining is manufactured with a white outer coating of similar whiteness. For more advanced imprints, coated recycled lining is produced, where the outer coating is most often coated with a pigmented color.

[0060] In addition to the conventional papers mentioned above, special papers with specific properties are also used. These include, among others:

[0061] - Wet Strength Paper – converted to ensure that strength properties are retained after wetting (PN-P-50000:1992),

[0062] - fat-tight paper – high resistance to penetration by fats and greases. Some of these papers are particularly resistant to penetration by the above substances (PN-P-50000:1992),

[0063] - Barrier coated paper – has a protective layer covering one or both sides of the paper, for example a polyethylene (PE) protective layer (PN-EN 26590-1:1993),

[0064] - Fireproof paper – flame retardant and / or resistant to ignition (PN-P-500000:1992).

[0065] The paper used for the fluting (fluting layer) in corrugated board is divided into two groups:

[0066] -Waste based fluting (WBF)

[0067] -Semi chemical fluting (SC).

[0068] WBF – Made exclusively from recycled fiber. To improve the mechanical properties of this type of corrugated paper, starch is added to its structure. This process is often described as gluing. It can be done "in the virgin pulp" (i.e., sizing – starch is added to the waste paper pulp), or the starch can be applied to the paper surface (surface sizing).

[0069] Semi-chemical corrugated paper contains about 70% semi-chemical pulp, which is produced from hardwood (mainly birch) in a pulping process. The remainder of the pulp consists mainly of recycled paper.

[0070] The adhesive according to the invention may also be applied to any of the papers mentioned above.

[0071] Another aspect of the present invention is a method for producing a laminated cellulose board, said method comprising the steps of:

[0072] i) providing at least two cellulose layers;

[0073] ii) applying an adhesive according to the present invention to at least a portion of a surface of one of the cellulose layers, the adhesive comprising a monolayer of graphene oxide;

[0074] iii) contacting a surface of another cellulose layer with the first cellulose layer of step ii);

[0075] iv) optionally repeating step ii) and step iii) one or more times to obtain a laminated cellulose sheet.

[0076] In the above method, step iii) may further include applying the adhesive according to any one of claims 1 to 4 to at least a portion of the surface of the other cellulose layer. That is, at least a portion of the two surfaces to be bonded to each other have already been applied with the adhesive. Methods for applying the adhesive to the cellulose layer are known in the art; a preferred method is roller coating.

[0077] According to one embodiment, the cellulose layer may be a paper layer or a paperboard layer.

[0078] The present invention also relates to a laminated cellulose board obtained by the above method.

[0079] The present invention also relates to a laminated cellulose sheet comprising at least two cellulose layers attached to each other, characterised in that the at least two cellulose layers are attached to each other with an adhesive according to the invention, ie an adhesive comprising a monolayer of graphene oxide.

[0080] In the above laminated cellulose sheet, at least one of the cellulose layers may be a corrugated layer, thereby providing a corrugated laminated cellulose sheet.

[0081] In the above laminated cellulose sheet, at least one of the cellulose layers may be a laminated paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] In order to complete the description and to provide a better understanding of the present invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the present invention, which should not be interpreted as limiting the scope of the invention, but merely as examples of how the invention may be implemented. The drawings include the following figures:

[0083] Figure 1 A corrugated laminated cellulose board comprising 5 layers is shown.

[0084] Figure 2 A corrugated laminated cellulose board comprising 3 layers is shown.

[0085] Figure 3 and Figure 4 Shown are the results of dry peel tests performed with different samples:

[0086] Figure 3 Corresponds to dry peel tests carried out with corrugated board produced using an adhesive without the glue strengthener according to the invention.

[0087] Figure 4 Corresponds to dry peel tests carried out with corrugated board produced using an adhesive comprising the glue enhancer according to the invention.

[0088] Figure 5 Schematic diagrams showing adhesives obtained by some of the different preparation methods described above.

[0089] Figure 6a and Figure 6b The steps of the above-mentioned Stein Hall method are schematically shown. DETAILED DESCRIPTION

[0090] Figure 1 Shown is a corrugated laminated cellulose board having a plurality of layers, in particular five layers numbered 25 to 29, attached to one another with an adhesive, for example an adhesive according to the invention, ie an adhesive comprising a monolayer of graphene oxide as glue reinforcement.

[0091] The corrugated laminated cellulose sheet includes: a first planar layer 25; a first corrugated layer 26 attached below the first planar layer 25; a second planar layer 27 attached below the first corrugated layer 26; a second corrugated layer 28 attached below the second planar layer 27; and a third planar layer 29 attached below the second corrugated layer 28. In this particular example, the first corrugated layer 26 has smaller flutes than the flutes of the second corrugated layer 28. This should not be considered limiting in any way, as the flutes of the different corrugated layers can be the same or different.

[0092] One of the two major surfaces of the first planar layer 25 and the third planar layer 29 (i.e., the outer lining) is attached to a major surface of the first and second corrugated layers 26 and 28, respectively, with an adhesive. Both major surfaces of each of the second planar layer 27, the first and second corrugated layers 26 and 28 are attached to a major surface of the other layer with an adhesive. Depending on the properties of the adhesive, the layers are glued together with greater or lesser adhesion. The adhesive and adhesion affect the mechanical properties of the corrugated laminated cellulose board 20, as the resistance of one layer can be enhanced by the resistance of the other layers, depending on, among other characteristics, how strongly the layers are glued together.

[0093] It is obvious that other laminated cellulose sheets, with or without corrugations, are also within the scope of the present invention, such as a corrugated laminated cellulose sheet having a first planar layer and a first corrugated layer, or a corrugated laminated cellulose sheet having a first planar layer, a first corrugated layer, and a second planar layer, or a corrugated laminated cellulose sheet having additional planar layers and / or corrugated layers, etc. Furthermore, the corrugations of the corrugated layers can be the same or different. It is also obvious that different types of paper or paperboard can be used to prepare the laminated cellulose sheet, such as, for example, semi-chemical paper, kraft paper, or plastic paper.

[0094] exist Figure 2 , a corrugated laminate cellulose board having three layers is shown, specifically comprising a first planar layer; a corrugated layer attached below the first planar layer; and a second planar layer attached below the corrugated layer.

[0095] exist Figure 3 In the figure, it is shown as reference Figure 2 The described corrugated laminated cellulose board has three layers glued with an adhesive not comprising the glue strengthener according to the invention. As can be observed, the first planar layer separates quite easily from the corrugated layer without delamination due to the weak adhesion of the layers to each other.

[0096] exist Figure 4 In the figure, it is shown as reference Figure 2The described corrugated laminated cellulose board has three layers, the layers being glued together with an adhesive comprising a glue enhancer according to the invention. As can be observed, due to the stronger adhesion resulting from the inclusion of the glue enhancer according to the invention in the adhesive used to attach the layers to each other, the first planar layer delaminated (i.e., both the planar layer and the corrugated layer broke) in this case.

[0097] Example

[0098] Hereinafter, the present invention will be further illustrated by examples and comparative examples. The examples should not be interpreted as limiting the scope of the present invention under any circumstances, but are merely illustrations of the present invention.

[0099] Example 1 : Preparation of the adhesive according to the application

[0100] The adhesive was produced by providing 1800 L of water; heating the water to a maximum of 25.0° C.; adding 550 kg of modified starch; stirring the resulting mixture for 20 minutes; adding 1.5 L of a glue strengthener, which is a solvent comprising water and 0.01 wt.% of monolayer graphene oxide, to the mixture; and stirring the resulting mixture for 10 minutes. The resulting exemplary adhesive had approximately 0.0000064 wt.% of monolayer graphene oxide.

[0101] Example 2: Dry peel test

[0102] Dry peel tests were performed on several samples of corrugated laminated cellulose board with and without the adhesive according to the invention, i.e., with and without a single layer of graphene oxide. In the dry peel test, two layers glued together were peeled apart. The average load required to separate the two layers over the length of the specimen was recorded and expressed in N.

[0103] In particular, the dry peel test was performed on a board comprising three layers, e.g. Figure 2 The three layers are as follows:

[0104] -Upper layer: Flat layer: T14; Paper type: Test, weight 140g

[0105] -Inner layer: corrugated layer, corrugated SQ15; paper type: semi-chemical, weight 150g

[0106] -Lower layer: T14; Paper type: Test, weight 140g.

[0107] Sample 1 is a corrugated laminated cellulose board according to above prepared by using a glue or adhesive that does not contain the glue enhancer according to the present invention.

[0108] Sample 2 is a corrugated laminated cellulose board according to above prepared by using a glue or adhesive comprising a glue enhancer according to the present invention.

[0109] The test results are provided in Table 1, where two rows of values ​​are represented: a first row corresponding to dry peel between the upper planar layer and the inner corrugated layer; and a second row corresponding to dry peel between the corrugated layer and the lower planar layer.

[0110] Table 1 : Comparison of the dry peel test between corrugated laminated cellulose sheets with a glue enhancer according to the application and corrugated laminated cellulose sheets without a glue enhancer according to the application. Figure 4

[0111]

[0112] In sample 2, i.e. with the glue reinforcement according to the invention, dry peeling between the upper planar layer and the corrugated layer resulted in delamination (cf. Figure 4 ). Delamination is a result of the high strength of the adhesive, with both the flat and corrugated layers breaking.

[0113] In contrast, for Sample 1, ie without the glue reinforcing agent according to the invention, the dry peel force between the upper planar layer and the corrugated layer was measured to be 7.93N.

[0114] In the dry peel test between the corrugated layer and the lower planar layer, Sample 2 required a dry peel force of 4.74 N, which was greater than the dry peel force of Sample 1 (2.13 N).

[0115] Thus, in both cases, the resistance to dry peeling of Sample 2 (containing an adhesive enhancer) was greater than that of Sample 1 (without an adhesive enhancer) (refer to Figure 3 Relative to Example 3: Determination of the water resistance of the glue: FEFCO test method #9 , delamination versus peeling without delamination).

[0116] Figure 1

[0117] In addition, the water resistance of the adhesive was tested by immersing corrugated laminated cellulose board produced with or without an adhesive containing the adhesive enhancer according to the present invention in accordance with FEFCO Test Method # 9. The water resistance of the adhesive of the corrugated board is represented by the amount of time that a predetermined combination of glue lines immersed in water resists the pulling force of a hanging weight (mass of 250 grams) in a plane perpendicular to the axis of the cellulose board at right angles to the glue lines.

[0118] In particular, according to Table 2: Comparison of the water resistance of the glue between corrugated laminated cellulose sheets with a glue enhancer according to the application and corrugated laminated cellulose sheets without a glue enhancer according to the application. As shown in , a dry peel test was performed on a board comprising five layers. The five layers listed from top to bottom are as follows:

[0119] - Upper outer plane layer: T200; Paper type: Test, grammage 200g

[0120] -First corrugated layer: small corrugated, SQ150; paper type: semi-chemical, weight 150g

[0121] -Inner layer (lining): T140; Paper type: Test, weight 140g

[0122] -Second corrugated layer: large corrugated, SQ150; paper type: semi-chemical, weight 150g

[0123] -Lower outer plane layer: T200; paper type: Test, grammage 200g.

[0124] Sample 3 is a corrugated laminated cellulose board according to above prepared by using a glue or adhesive that does not contain the glue enhancer according to the present invention.

[0125] Sample 4 is a corrugated laminated cellulose board according to above prepared by using a glue or adhesive comprising a glue enhancer according to the present invention.

[0126] It can be observed in Table 2 that Sample 4 (with an adhesive comprising a glue strengthener according to the invention) has a longer time before it breaks than Sample 3 (with an adhesive not comprising a glue strengthener). In this Table 2, the water resistance between each pair of layers is measured; in addition, the standard deviation of the times measured in the different tests is shown.

[0127] ​ ​

[0128]

[0129] "Break" in Table 1 means that the paper broke before the adhesive debonded.

[0130] In this document, the terms first, second, etc. have been used herein to describe several substances or elements, and it should be understood that these substances or elements should not be limited by these terms because these terms are only used to distinguish one substance or element from another.

[0131] In this document, the term "include / comprise" and its derivatives (such as "include / comprises", etc.) should not be understood in an exclusive sense, that is, these terms should not be interpreted as excluding the possibility that the described and defined content may include additional elements, steps, etc.

[0132] On the other hand, the present invention is obviously not limited to the specific embodiments described herein, but also includes any variants that a person skilled in the art may consider (for example, with regard to the choice of materials, dimensions, components, configurations, etc.) within the overall scope of the invention as defined in the claims.

Claims

1. A water-based adhesive for use in the manufacture of laminated cellulose boards, comprising: -water; - 20.0% to 40.0% by weight of starch as a binder component; - glue strengthener, said glue strengthener is such that said water-based adhesive contains 10 -7 The amount of the monolayer graphene oxide from wt% to 0.001 wt% comprises the monolayer graphene oxide in water.

2. Water-based adhesive according to claim 1, comprising at least one further component selected from the group consisting of fungicides and biocides, and / or stabilizers, gelling agents, thickeners, defoamers, tackifiers, moisture-proof resins, rheological agents, depending on the polymer.

3. The water-based adhesive according to claim 2, wherein the at least one additional component is a mixture of borax and NaOH, or calcium hydroxide and sodium carbonate.

4. The water-based adhesive according to claim 1, wherein the starch is corn starch, wheat starch, potato starch, pea starch, tapioca starch or a mixture thereof.

5. The water-based adhesive of claim 1, further comprising up to 10% by weight of at least one additional polymer selected from natural polymers or soluble synthetic polymers.

6. The water-based adhesive according to claim 5, wherein the at least one additional polymer is a natural polymer selected from plant origin, protein origin or animal origin.

7. The water-based adhesive according to claim 5, wherein the at least one additional polymer is selected from dextrin or albumin, or any polymer extracted from casein, blood, fish, soy, hide or bone.

8. The water-based adhesive of claim 5, wherein the at least one additional polymer is a soluble synthetic polymer selected from the group consisting of polyvinyl alcohol, cellulose ethers, methyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, urea-formaldehyde blends, and melamine-formaldehyde blends.

9. The water-based adhesive according to claim 1, wherein the single-layer graphene oxide is in the form of nanoplatelets as defined in ISO / TR 18401:2017.

10. Use of a single-layer graphene oxide as a glue reinforcing agent for a water-based adhesive comprising starch as an adhesive component for producing laminated cellulose sheets, the water-based adhesive comprising starch as an adhesive component being as defined in any one of claims 1 to 9.

11. Use of a single-layer graphene oxide according to claim 10, wherein the single-layer graphene oxide is in the form of nanosheets as defined in ISO / TR 18401:2017.

12. A method for producing a water-based adhesive as defined in any one of claims 1 to 9, comprising the steps of: a) mixing starch into water under stirring at a temperature of 20.0° C. to 30.0° C. to obtain a first mixture comprising 20.0% to 40.0% by weight of starch; and b) adding a glue enhancer to the first mixture under stirring, wherein the glue enhancer is a suspension of 0.1 wt % to 0.001 wt % of a monolayer graphene oxide in water, thereby producing a mixture comprising 10 -7 wt % to 0.001 wt % of a second mixture of monolayer graphene oxide.

13. The method of claim 12, wherein the first mixture is stirred for at least 20 minutes in step a) and the second mixture is stirred for at least 10 minutes in step b).

14. A method for producing a laminated cellulose board comprising the steps of: i) providing at least two cellulose layers; ii) applying an adhesive according to any one of claims 1 to 9 to at least a portion of a surface of a cellulose layer; iii) contacting the surface of another cellulose layer with the first cellulose layer of step ii); wherein step ii) and step iii) are performed once or repeated one or more times to obtain a laminated cellulose sheet.

15. The method according to claim 14, wherein step iii) further comprises applying an adhesive according to any one of claims 1 to 9 to at least a portion of the surface of the further cellulosic layer.

16. The method of claim 14, wherein the cellulosic layer is a paper layer or a paperboard layer.

17. A laminated cellulose sheet comprising at least two cellulose layers attached to each other, characterized in that The at least two cellulose layers are attached to each other with an adhesive according to any one of claims 1 to 9.

18. The laminated cellulose sheet of claim 17, wherein at least one of the cellulose layers is a corrugated layer.

19. The laminated cellulose sheet of claim 17, wherein at least one of the cellulose layers is a laminated paper.

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