Method for accelerating the drying of solvent-based compositions using few-layer graphene

Abstract

The invention provides a method for joining at least two objects to form a multi-layered structure, addressing the problem of slow solvent evaporation in adhesives. The method utilizes an adhesive composition comprising a polymer in a solvent, characterized by the incorporation of few-layer graphene, defined as 2 to 10 stacked carbon sheets, in a very low concentration of 0.00001 to 0.5 wt%. Applying this composition significantly accelerates solvent evaporation from the adhesive layer after joining the objects. This results in substantial industrial advantages, including increased production speed, demonstrated to be over 20%, and greater energy efficiency. The invention is particularly useful for manufacturing multi-layered products such as corrugated board, paperboard, and wood-based particle and fiber boards, overcoming a key limitation in their production processes. The use of the composition to reduce drying time is also disclosed.

Description

[0001] METHOD FOR ACCELERATING THE DRYING OF SOLVENT-BASED COMPOSITIONS USING FEW-LAYER GRAPHENE

[0002] Technical field

[0003] The present invention relates generally to the use of graphene in low amounts to improve the drying time . For instance, water-based adhesives and coatings can be improved. In particular, it relates to the use of graphene, and graphene containing products primarily to speed up drying and / or curing of the adhesive or coating and to also improve mechanical properties and water resistance of the dried adhesive or coating.

[0004] Background

[0005] Graphene, one of many two-dimensional materials, has many unique properties regarding for instance thermal and electrical conductivity as well as mechanical properties . It is thus desired to use graphene to improve performance of other materials used in manufacturing of material composites . It is of even greater relevance when fossil-based additives are exchanged for bio-based additives as bio-based alternatives often come with compromising performance .

[0006] Adhesives and binders are widely used substances to produce obj ects and / or materials . In many cases, adhesives and binders are essential for correctly producing the obj ects and / or materials . Many adhesive and binder systems are waterbased and water often needs to be evaporated in order for the adhesive or binder to form strong bonds and / or coating membranes . Evaporation of water may be quite energy and / or time demanding, thus limiting production capacity.In some applications, for example when gluing high basis weight or multi-layered paperboard, or multi-layered high basis weight corrugated board, it is of interest to speed up drying of the water-based adhesive to provide faster drying and adhesion, which will allow for higher machine speed and higher production capacity. In other applications, for example when producing high density fiber boards, or woodbased particle boards, press time may limit the productivity at a given temperature . Faster drying and early bond formation may improve productivity and / or reduce the energy demand of the process .

[0007] Graphene and other related 2D-materials have been used in many different materials because 2D-materials make it possible to enhance the functionality or properties of said obj ects or materials . A few attempts were disclosed in the prior art to incorporate graphene or graphene oxide into adhesives used to glue multilayered structures, to improve the adhesion properties of the adhesive used in its manufacture .

[0008] For instance, patent document EP 2886621 discloses an adhesive for manufacturing laminates of cellulose products . The adhesive is produced by mixing graphene nanofilaments and starch in water . The nanofilaments are described as having a diameter from 1 to 100 nanometers and a length greater than 30 micrometers . Such nanofilaments, which are described as nanotubes or nanofibers, are structurally different from the few-layer graphene sheets of the present invention and do not disperse well with water in aqueous solutions . The adhesive properties are not considerably improved, probably due to the poor dispersibility in water .US 2021 / 071048 relates to a water-based adhesive for the manufacture of laminated cellulosic boards comprising monolayer graphene oxide as a glue enhancer to reinforce the final bond. However, graphene oxide has rather poor thermal conductivity compared to graphene . Graphene oxide will not provide a strong effect on heat transfer and will thus not contribute significantly to drying speed and early bond formation .

[0009] Pinto, A. M. et al . "Dispersion of graphene nanoplatelets in poly (vinyl acetate) latex and effect on adhesive bond strength. " Polymer International 62 (2013) : 928-935. DOI : 10 . 1002 / pi . 4379 describes the dispersion of graphene nanoplatelets (GNPs) in a poly (vinyl acetate) latex adhesive to improve bond strength. The GNPs used have an average thickness of 6-8 nm, corresponding to approximately 17-24 layers, which is significantly thicker than the few-layer graphene of the present invention. This document focuses on improving mechanical shear strength, not on reducing the solvent evaporation time .

[0010] Cristof olini , L . et al . "Graphene Materials Strengthen Aqueous Polyurethane Adhesives . " ACS Omega 3 (2018 ) : 8829-8835. DOI : 10 . 1021 / acsomega . 8b01342 describes adding carboxyl-functionalized graphene platelets (GP) or graphene oxide (GO) to a commercial aqueous adhesive dispersion of thermoplastic polyurethane (TPU) . The purpose is to improve mechanical properties such as peel strength, not to accelerate solvent evaporation. The polymer system (TPU) is also different from the bio-based polymers often used in paper and board applications .WO2024138249 discloses a latex coating, in particular a paint, containing low concentrations of graphene ( 1-10 layers) to improve durability, wear resistance, and other surface properties . The primary taught use is for coating a surface, not for use as an adhesive in a method for joining two obj ects to form a multi-layered structure .

[0011] EP 3562901 discloses an aqueous primer composition for adhesive bonding in aerospace applications . The composition is a primer applied to a surface before an adhesive is used, not the adhesive itself . Furthermore, it uses a different polymer system (epoxy) and describes graphene platelets with a thickness of up to 50 nm, which is well outside the fewlayer range of the present invention.

[0012] The papers Wang, Z . et al . "Graphene nanoplatelets / epoxy composites with excellent shear properties for construction adhesives . " Composites Part B: Engineering 152 (2018 ) : 311-315. DOI : 10 . 1016 / j . compositesb . 2018 . 08 . 113 and Wang, N. et al . "Development and Characterization of Graphene Enhanced Thermal Conductive Adhesives" describe epoxy-based adhesives reinforced with graphene for use in construction and electronics, respectively. These adhesives are two-component or thermal-conductive systems where any solvent used for dispersion is removed before the adhesive is applied and cured. This process is fundamentally different from the present invention, where the solvent is evaporated from the adhesive layer after the obj ects have been joined.

[0013] It remains still a challenge, not addressed in the prior art, to efficiently remove water or other solvents from the adhesive or binder system in the curing process . This is especially true if the laminated material is thick, containsmany layers or has a high basis weight, and for binding processes on large scale board machines running thick, multilayer materials . The removal of water or other solvents used is a prerequisite for the adhesive / binder polymer component to form a strong bond.

[0014] Summary

[0015] It is an obj ect of the present invention to obviate at least one of the disadvantages with water-based or solvent-based adhesives or binder systems not yet addressed in prior art and to provide a means to improve water-based or solventbased adhesives or binders so that they dry faster and therefore form stronger early bonds and allow for the potential to run the processes faster .

[0016] In a first aspect, the invention provides a method for joining at least two obj ects to form a multi-layered structure . The method comprises the sequential steps of : providing an adhesive composition comprising a polymer dissolved in or mixed with at least one solvent, and fewlayer graphene in a concentration of 0.00001 to 0.5 wt%, wherein the few-layer graphene comprises 2 to 10 layers of stacked carbon sheets; applying the adhesive composition to at least one surface of at least one of the obj ects; bringing the at least two obj ects into contact to form the multilayered structure, such that the adhesive composition forms an adhesive layer between the obj ects; and at least partially evaporating the at least one solvent from the adhesive layer .

[0017] In a second aspect, the invention provides for the use of an adhesive composition for the purpose of reducing the solvent evaporation time in a method for joining at least two obj ects to form a multi-layered structure . The adhesive compositioncomprises a polymer, at least one solvent, and few-layer graphene comprising 2 to 10 layers of stacked carbon sheets in a concentration of 0.00001 to 0.5 wt% .

[0018] In a third aspect, the invention provides a multi-layered structure, which is either obtained by the aforementioned method or comprises at least two obj ects and an adhesive layer bonding said obj ects, wherein the adhesive layer comprises a polymer and few-layer graphene comprising 2 to 10 layers of stacked carbon sheets, and wherein the concentration of said graphene in the adhesive composition used to form the adhesive layer was between 0.00001 to 0.5 wt% .

[0019] The invention highlights significant advantages such as faster drying, curing, and improved production efficiency, making it suitable for large-scale manufacturing processes . The application provides detailed examples demonstrating reductions in drying time and enhancements in production speed, energy efficiency, and mechanical properties when using graphene-enhanced adhesives in various industrial applications . This innovation addresses challenges with traditional adhesive systems, especially when applied to thick and multi-layered materials .

[0020] Drawings

[0021] The invention is described with reference to the following drawing. Figure 1 provides a schematic illustration of the method for joining at least two obj ects to form a multilayered structure, in accordance with the sequential steps of a primary aspect of the invention. The drawing is presented in three panels, (a) , (b) , and (c) , which depict the key stages of the process .The process begins at step (a) , where an adhesive composition 20, comprising a polymer, a solvent, and well-dispersed few-layer graphene, is applied to a surface of a first obj ect or substrate 30. The application may be performed using a suitable apparatus, such as a roller 32 or a spray nozzle, to form a uniform adhesive layer on the substrate 30. This first obj ect 30 may be, for example, a sheet of paperboard or a layer of a corrugated board.

[0022] Next, in step (b) , a second obj ect or substrate 34 is brought into contact with the first substrate 30. The obj ects are positioned such that the adhesive composition 20 in one embodiment forms a continuous layer between them, preparing the assembly for bonding.

[0023] Finally, step (c) depicts the formation of the final multilayered structure 36 after the obj ects 30 and 34 have been joined. A key feature of the inventive method is illustrated here : the evaporation of the solvent occurs

[0024] essentially after the structure is assembled. This is represented by wavy arrows 38, which symbolize the at least partial evaporation of the solvent escaping from the adhesive layer 20.

[0025] This sequence is fundamentally important, as the presence of the few-layer graphene within the adhesive

[0026] layer 20 accelerates this post-joining evaporation (38 ) , thereby reducing the overall drying and curing time . This is particularly advantageous when manufacturing thick or dense multi-layered products, where trapped solvent can otherwise lead to production delays, warping, or delamination. By facilitating faster solvent removal from the confined adhesive layer, the method enables increased productionspeeds and improved energy efficiency, which is a core obj ective of the present invention.

[0027] Detailed description

[0028] Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat . It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims .

[0029] It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise .

[0030] If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains .

[0031] All percentages and ratios are calculated by weight throughout the description and the claims, unless otherwise indicated .

[0032] The inventors have unexpectedly found that a small addition of few-layer graphene to polymer composition comprising at least one solvent gives a considerably shorter drying time, i . e . a considerably higher evaporation rate of the solvent during drying of the adhesive or coating composition.The Adhesive Composition

[0033] The invention is applicable to compositions comprising a polymer and a solvent, which is intended to evaporate when they are used. In one embodiment, the composition is an adhesive composition wherein the polymer is an adhesive . In another embodiment, the composition is a coating composition wherein the polymer is a binder . Examples of such coating compositions include paints, lacquers, varnishes, clear coatings and printing inks, and photoresists .

[0034] The adhesive composition is in one embodiment made so that a graphene suspension is mixed with a polymer dissolved in or dispersed in a solvent . The graphene and the polymer are preferably dispersed in the same solvent . The same applies to a coating composition and a binder .

[0035] The Few-Layer Graphene

[0036] The few-layer graphene of the present invention is graphene with 2 to 10 layers of stacked carbon sheets . This specific morphology is critical for the inventive effect . It provides a high surface area and excellent thermal conductivity, distinguishing it from thicker graphite / graphene nanoplatelets and from non-conductive graphene oxide . It is preferably evenly distributed and well-dispersed in the composition .

[0037] Typically, a very low amount of few-layer graphene is necessary to achieve a beneficial effect on the drying time (evaporation time for the solvent) of the adhesive . The concentration is between 0.00001 to 0.5 wt% . Surprisingly, the effect has a maximum, so that the drying time increases when the amount of few layer graphene is increased over a certain value . Without wishing to be bound by any particularscientific theory, the inventor believes that the effect may have to do with heat conduction and / or adsorption of the solvent to graphene, which gives an improved evaporation of the solvent .

[0038] A particularly advantageous concentration range is from 0.005 wt% to 0.1 wt% . This range provides a "sweet spot" that maximizes the reduction in drying time and improvement in production speed without negatively impacting other properties like internal bonding, as can be seen at higher concentrations . This optimized range delivers the best balance of performance, cost-effectiveness, and

[0039] pro cess ability.

[0040] The Polymer

[0041] The polymer can be selected from a wide range of materials . Examples of adhesives include but are not limited to water soluble adhesives, water dispersible adhesives, and adhesives soluble in organic solvents .

[0042] In one embodiment, the polymer is obtained from a living organism, i . e . , it is a bio-based polymer . The advantage of using bio-based polymers is their sustainability, biodegradability, and often excellent compatibility with natural substrates like paper and wood. This makes them particularly suitable for the packaging and construction industries .

[0043] More preferably, the polymer is a polysaccharide-based polymer . Polysaccharides offer good adhesion to cellulosic materials due to their similar chemical nature (hydrogen bonding) .Even more preferably, the polymer is selected from the group consisting of starch, dextrin, and fructose . These specific polymers are widely available, cost-effective, and have been proven in the examples to work exceptionally well with the few-layer graphene to achieve the inventive effect .

[0044] • Examples of water-soluble adhesives include but are not limited to polyvinyl alcohol (PVA) adhesives, dextrin, fructose, and starch-based adhesives, and casein adhesives .

[0045] • Examples of water dispersible adhesives include but are not limited to polyvinyl acetate (PVAc) emulsions, acrylic emulsions, urea-formaldehyde emulsions, melamine-urea formaldehyde emulsions, styrene-butadiene rubber (SBR) latex, natural rubber latex, and ethylenevinyl acetate (EVA) dispersions .

[0046] • Examples of adhesives soluble in organic solvents include but are not limited to : contact adhesives (neoprene) , polyurethane adhesives, acrylic adhesives, and phenolic and formaldehyde-based adhesives .

[0047] The Solvent

[0048] In one embodiment, the solvent is water, making the composition a water-based composition. The advantage of using water as a solvent is significant, as water is inexpensive, non-toxic, non-flammable, and environmentally friendly with virtually no health hazard. This aligns with modern industrial requirements for "green chemistry. "

[0049] However, the invention is also applicable to organic solvents, including but not limited to toluene, acetone,hexane, methyl ethyl ketone, xylene, alcohols, and phenolic solvents .

[0050] The Method of Joining and The Multi-Layered Structure

[0051] The method of the invention is particularly advantageous for forming multi-layered structures from obj ects such as high basis weight paperboard, multi-layered paperboard, high basis weight corrugated board, high density fiber boards, and woodbased particle boards . These materials are thick and / or dense, meaning they trap a significant amount of water from the adhesive . The accelerated evaporation provided by the invention is therefore especially beneficial, as it directly addresses the primary rate-limiting step in their production, allowing for faster machine speeds and preventing issues like warping or delamination caused by trapped moisture .

[0052] Dispersion of Graphene

[0053] The few-layer graphene is in one embodiment well-dispersed although it is possible to add the graphene to the adhesive composition and using an ordinary stirrer to mix the adhesive composition and the graphene . The well-dispersed graphene has advantages . Well-dispersed few-layer graphene is obtained by providing few-layer graphene as a suspension in water or solvent and dispersing using a high-energy mechanical dispersion process, requiring an energy of 20 to 500 kJ / g. By using an energy in this interval the few-layer graphene becomes well dispersed. In one embodiment, the few-layer graphene is provided as a suspension in water or solvent by dispersing using a high-energy mechanical dispersion process . Such a process, which may require an energy of 20 to 500 kJ / g, is advantageous because it efficiently exfoliates and stabilizes the graphene sheets, ensuring they remainseparated and can effectively interact with the solvent to accelerate evaporation. This avoids the re-agglomeration that can plague nanomaterial-enhanced compositions and diminish their effect . Using a lower energy for the mixing also works, but is less advantageous .

[0054] Use of the Adhesive Composition

[0055] A key aspect of the invention is the use of the adhesive composition for the specific purpose of reducing the solvent evaporation time . This directly translates into the industrial advantage of increasing the production speed of a manufacturing process . As demonstrated in the examples, production speed can be increased by at least 20%, and in some cases up to 30% . This represents a substantial improvement in efficiency and throughput for commercial manufacturing lines .

[0056] The invention is applicable to compositions comprising a polymer and a solvent, the solvent is intended to evaporate when they are used.

[0057] Examples of solvents include but are not limited to water, toluene, acetone, hexane, methyl ethyl ketone, xylene, alcohols and phenolic solvents .

[0058] The adhesive composition is in one embodiment made so that a graphene suspension is mixed with a polymer dissolved in or dispersed in a solvent . The graphene and the polymer are preferably dispersed in the same solvent . An adhesive composition is in one embodiment made so that a graphene suspension is mixed with an adhesive dissolved in or dispersed in a solvent . The graphene and the adhesive arepreferably dispersed in the same solvent . The same applies to a coating composition and a binder .

[0059] The few-layer graphene is graphene with 2 to 10 layers of stacked carbon sheets .

[0060] The few-layer graphene is preferably evenly distributed and well dispersed in the composition.

[0061] Typically, a very low amount of few-layer graphene is necessary to achieve a beneficial effect on the drying time (evaporation time for the solvent) of the adhesive .

[0062] Surprisingly the effect has a maximum so that the drying time increases when the amount of few-layer graphene is increased over a certain value . The exact upper limit, lower limit, and optimum concentration of few-layer graphene in the adhesive composition varies depending on the adhesive and the solvent . Without wishing to be bound by any particular scientific theory the inventor believes that the effect may has to do with heat conduction and / or adsorption of the solvent to graphene, which gives an improved evaporation of the solvent .

[0063] The lower limit of few-layer graphene in the adhesive or binder composition is 0.00001 wt%, however also other lower limits can be used, such as 0.00005 wt%, 0.0001 wt%, 0.001 wt% and 0.005 wt% . The upper limit of few-layer graphene in the adhesive composition is 0.5 wt%, but also other upper limits are encompassed such as 0.1 wt% and 0.05 wt% . The optimum level of few-layer graphene as well as the upper limit and lower limit of few-layer graphene required for obtaining the advantageous effects depends on the system in which the graphene is added. It is easy to make routine experiments to determine the optimum drying time with the amounts of few-layer graphene from the claims as startingpoint . All upper limits and lower limits can be freely combined to arrive at many different intervals for the amount of few-layer graphene, such as 0.00001 - 0.1 wt%, 0.00001-0.05 wt%, 0.0005 - 0.1 wt%, 0.0005-0.05 wt%, 0.001 - 0.5 wt%, 0.001-0.05 wt%, 0.005 - 0.1 wt%, and 0.005-0.05 wt% .

[0064] In one embodiment, the solvent is water . Using water as solvent has many advantages since water is inexpensive and environmentally friendly with virtually no health hazard.

[0065] In one embodiment, the adhesive or binder is a polymer and wherein the polymer is dissolved in the solvent .

[0066] In one embodiment, the polymer is obtained from a living organism.

[0067] In one embodiment, the adhesive or binder is in a suspension in the solvent .

[0068] In one embodiment, the adhesive or binder is in an emulsion in the solvent .

[0069] In one embodiment, the adhesive composition comprises a rheology modifier . The rheology modifier can be any additive that helps achieve shear-thinning properties . A rheology modifier based on bio-based polymers is preferred. Examples of suitable bio-based polymers are cellulose derivatives (CMC, HEC, EHEC) , starches (potato, corn...) and gums (guar, diutan...) . The rheology modifier can also be a synthetic or fossil-based polymer system or an inorganic particle-based system. The rheology modifier may act as an adhesive by itself . It is to be understood that this invention is not limited to the particular embodiments shown here . The embodiments are provided for illustrative purposes and arenot intended to limit the scope of the invention since the scope of the present invention is limited only by the appended claims and equivalents thereof .

[0070] In one embodiment, the resulting multi-layered structure exhibits improved water resistance compared to a structure made with an adhesive without graphene .

[0071] Examples

[0072] Exampl e 1

[0073] Drying time for a water-based, bio-based adhesive was measured on an IR oven (moisture analyzers from Ohouse was used in examples 1-3) .

[0074] To starch-based adhesive from BIM Kemi was added 0.05 wt% few-layer graphene as a water-based suspension. The drying time was reduced by 49-58% across repeated tests compared to the reference adhesive with no graphene .

[0075] Exampl e 2

[0076] Drying time for a water-based, bio-based adhesive was measured on an IR oven.

[0077] To a dextrin-based adhesive from BIM Kemi was added 0.05-0.1 wt% few-layer graphene as a water-based suspension. The drying time was reduced by 40-43% compared to the reference adhesive with no graphene .

[0078] Exampl e 3

[0079] Drying time for a water-based, bio-based adhesive was measured on an IR oven.To a starch-based adhesive was added 0.05% few-layer graphene as a water-based suspension. The drying time was reduced by 24-28% compared to the reference adhesive with no graphene .

[0080] Exampl e 4

[0081] A full-scale trial was performed on a board machine producing heavy double wall BC flute . A starch-based adhesive was mixed with a graphene suspension on site ( 0.0022 g graphene containing product to 1 kg starch-based adhesive) so that the few-layer graphene concentration was 0.00001 wt% in the final product .

[0082] Changing from the reference starch-based adhesive with no graphene, to the adhesive with very low addition of graphene, affected the drying speed of the adhesive so that production speed could be increased by 20% .

[0083] Exampl e 5

[0084] A full-scale trial was performed on a board machine producing corrugated board. The water-based adhesive with starch was mixed with graphene suspension to reach 0.05 wt% few-layer graphene .

[0085] With the modified adhesive it was possible to speed up drying of the adhesive (gel point is reached earlier) and increase production speed with 30% . At the same time, it was possible to reduce process temperature and steam pressure by 20% and the consumption of adhesive could also be reduced.

[0086] Exampl e 6

[0087] Lab scale testing was performed to study the effect of fewlayer graphene on four different types of water-based adhesives : three wood-based panel adhesives and one packagingadhesive . The impact of few-layer graphene on the adhesive chemistry, curing, thermal properties, and bonding properties were characterized. The introduction of few-layer graphene in low concentration showed some positive effects on the different adhesive properties, with faster curing, increased bonding ability, and higher thermal resistance of the bond. These benefits seem to drop when the few-layer graphene content in the adhesive is too high. The threshold for when properties start deteriorating again depends on the type of adhesive . Above this threshold, the water evaporation was proved to be slower again.

[0088] Exampl e 7

[0089] A fructose-based adhesive was used for producing wood-based panels at lab scale . Particle boards were produced under various conditions : adhesive concentration, few-layer graphene content in the water-based adhesive, pressing time . MUF board was also produced as a reference, for which the adhesive system was based on melamine-urea formaldehyde .

[0090] Three-layer particle board (density 630 kg / m3) were manufactured using the adhesive formulations in a way to simulate industrial production at pilot scale . The wood particles were dried at 90°C to reach a stable moisture content <3% . The adhesive formulation was sprayed onto the wood particles . Adhesive formulations with different fewlayer graphene content were evaluated. Control boards were produced using reference melamine-urea-formaldehyde resin with no graphene .

[0091] A square board (450x450 mm2) was shaped and pre-pressed cold before hot-pressing at 200°C for 10 or 8 s / mm. The board was cooled to room temperature, cut and conditioned beforetesting in standard climate condition ( 65% rh, 20°C) before analysing .

[0092] The average density and thickness of the board were analysed in accordance with EN 323. Water-related properties were measured for samples submerged in water . Swelling and water uptake were measured after 2h and 24h following EN 317 ( 1993) . 10 samples were analysed per board. Internal bond strength was evaluated following EN 319 ( 1993) . Ten samples were analysed per board. Static bending tests determined the moduli of the board rupture and elasticity. EN 310 : 1993 was applied .

[0093] Relatively high addition of few-layer graphene in the adhesive composition ( 0.1 wt%) negatively impacts the board properties, like internal bonding ( IB) . Low ( 0.01 wt%) and medium ( 0.05 wt%) addition of graphene in the adhesive composition resulted in positive effects on water resistance and mechanical properties . This is visible for the board produced at a low press factor .

[0094] Exampl e 8

[0095] High-density fibre boards were produced following the same method as in Example 7. The control board was made using melamine-urea-formaldehyde resin. Two temperatures ( 180 and 200°C) and two press-factors ( 9 and 7 s / mm) were evaluated. Medium levels ( 0.05 wt%) of few-layer graphene added to the fructose-based adhesive gave a positive effect on mechanical properties and water resistance when pressed at a lower temperature and / or press factor . Those boards perform at a similar level as the boards pressed at optimal conditions (higher temperature and press factor) . With 0.05 wt% fewlayer graphene in the adhesive, it was possible to lowertemperature and press factor and still reach good properties . It is thus possible to save energy in the production of panels .

[0096] Exampl e 9

[0097] High-density fibre boards were produced following the same method as described in Example 7. The adhesive was MUF as in example 7 (Melamine urea formaldehyde) . The HDF boards were pressed at 200°C press temperature . HDF boards with down to 0.005 wt% few-layer graphene in the adhesive could be produced to full internal strength with press factors of 3-4 s / mm. The reference HDF boards with no graphene in the adhesive needed higher press factors (5-7 s / mm) to reach the same strength.There are also disclosed the following aspects and embodiments .

[0098] 1. A composition comprising a polymer dissolved in and / or mixed with at least one solvent, wherein the composition comprises few layer graphene in a concentration of 0.00001 to 0.5 wt% and wherein the solvent is intended to evaporate at least partially during use of the composition .

[0099] 2. The composition according to 1, wherein the composition is an adhesive composition and wherein the polymer is an adhesive .

[0100] 3. The composition according to 1, wherein the composition is a coating composition and wherein the polymer is a binder .

[0101] 4. The composition according to any one of 1-3, wherein the solvent is water .

[0102] 5. The composition according to any one of 1-4, wherein the polymer is dissolved in the solvent .

[0103] 6. The composition according to any one of 1-5, wherein the polymer is obtained from a living organism.

[0104] 7. The composition according to any one of 1-6, wherein the polymer is in a suspension in the solvent .

[0105] 8. The composition according to any one of 1-6, wherein the polymer is in an emulsion in the solvent .

[0106] 9. A method of reducing the drying time for a solvent-based composition, the method comprising the steps of a) providing a composition comprising a polymer dissolvedin or mixed with at least one solvent, and few layer graphene in a concentration of 0.00001 - 0.5 wt%, b) applying the composition to a substrate, and c) at least partially evaporating the at least one solvent .

[0107] 10. Use of an adhesive composition according to any one of 1-8, for joining at least two obj ects together .

Claims

Claims1. A method for joining at least two obj ects to form a multi-layered structure, the method comprising the following sequential steps :a . providing an adhesive composition comprising a polymer dissolved in or mixed with at least one solvent, and few-layer graphene in a concentration of 0.00001 to 0.5 wt%, wherein the few-layer graphene comprises 2 to 10 layers of stacked carbon sheets ;b . applying the adhesive composition to at least one surface of at least one of the obj ects;c . bringing the at least two obj ects into contact to form the multi-layered structure, such that the adhesive composition forms an adhesive layer between the obj ects; andd. at least partially evaporating the at least one solvent from the adhesive layer .

2. The method according to claim 1, wherein the multilayered structure is formed from obj ects selected from the group consisting of high basis weight paperboard, multi-layered paperboard, high basis weight corrugated board, high density fiber boards, and wood-based particle boards .

3. The method according to claim 1 or 2, wherein the adhesive composition is a water-based composition.

4. The method according to any one of claims 1 to 3, wherein the polymer of the adhesive composition is obtained from a living organism.

5. The method according to any one of claims 1 to 4, wherein the polymer is selected from the group consisting of starch, dextrin, and fructose .

6. The method according to any one of claims 1 to 5, wherein the polymer is a polysaccharide-based polymer .

7. The method according to any one of claims 1 to 6, wherein the few-layer graphene is provided as a suspension in water or solvent by dispersing using a high-energy mechanical dispersion process, requiring an energy of 20 to 500 kJ / g.

8. The method according to any one of claims 1 to 7, wherein the concentration of few-layer graphene is selected from the range of 0.005 wt% to 0.1 wt% .

9. The method according to any one of claims 1 to 8, wherein the resulting multi-layered structure exhibits improved water resistance compared to a structure made with an adhesive without graphene .

10. Use of an adhesive composition for the purpose of reducing the solvent evaporation time in a method for joining at least two obj ects to form a multi-layered structure, wherein the adhesive composition comprises a polymer, at least one solvent, and few-layer graphene comprising 2 to 10 layers of stacked carbon sheets in a concentration of 0.00001 to 0.5 wt% .

11. The use according to claim 10, for increasing the production speed of a manufacturing process for multi-layered structures, preferably increasing the production speed by at least 20% .12 . A multi-layered structure obtained by the method of any one of claims 1 to 9 .

13. A multi-layered structure comprising at least two obj ects and an adhesive layer bonding said obj ects, wherein the adhesive layer comprises a polymer and few- layer graphene comprising 2 to 10 layers of stacked carbon sheets, and wherein the concentration of said graphene in the adhesive composition used to form the adhesive layer was between 0.00001 to 0.5 wt% .

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