Light-weight element and method for manufacturing thereof

Abstract

The present invention concerns a light-weight element and a method for manufacturing such element. The sandwich structure comprises a first layer, a second layer, and a layer of fibrous material between the first layer and the second layer. The fibrous material comprises a three- dimensional fibre network of cellulosic and / or lignocellulosic fibres. The layer of fibrous material has been subjected to compression in the direction of the thickness.

Description

LIGHT-WEIGHT ELEMENT AND METHOD FOR MANUFACTURING THEREOFFIELD

[0001] The present application relates to multi-layered elements, particularly lightweight sandwich-structured elements.BACKGROUND

[0002] Light-weighting may be required in multiple fields as a way to reduce environmental impact and logistics costs, as well as add convenience to consumer. Lightweighting is a way to improve efficiency, for example in automotive and transportation.

[0003] Current light-weighting solutions and products are typically based on fossilbased materials, mainly plastic, or require advanced technologies, such as 3D printing.SUMMARY OF THE INVENTION

[0004] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0005] According to a first aspect of the present invention, there is provided an element with a sandwich structure, the sandwich structure comprising: a first layer, a second layer, and a layer of fibrous material between the first layer and the second layer, wherein the fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, wherein the element has a thickness extending through the layers of the sandwich structure, and wherein the layer of fibrous material has been subjected to compression in the direction of the thickness.

[0006] According to a second aspect of the present invention, there is provided a method for manufacturing an element, the method comprising: receiving a layer assembly on a mould, where the layer assembly comprises at least: a first layer, optionally a second layer, a low-density fibrous material on top of the first layer, or between the first layer and the second layer, wherein the low-density fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, sealing the mould and the layer assembly within a vacuum bag, generating a negative pressure within the vacuum bag tocompress the layer assembly, and releasing the negative pressure and unsealing the vacuum bag to obtain the element.

[0007] According to a third aspect of the present invention, there is provided an element obtained by the method according to the second aspect.

[0008] Various embodiments of the first aspect or the second aspect or the third aspect may comprise one or more features from the following bulleted list:• The element is in the form of a curved panel.• Said curved panel comprises at least one non-planar surface.• Each of the first and the second layer is made from a material selected the following list: plywood or veneer.• Each of the first layer and the second layer is made from a plurality of sheets of veneer.• The cellulosic and / or lignocellulosic fibres comprise wood pulp, such as kraft pulp.• The thickness of the layer of fibrous material is below 100 mm.• The density of the layer of fibrous material is in range 40 kg / m3- 500 kg / m3.• The density of the layer of fibrous material is in range 50 kg / m3- 100 kg / m3.• The bending strength of the layer of fibrous material is in range 3 - 20 N / mm2.• The three-dimensional fibre network comprises 2 to 20 wt-% of bicomponent fibres, calculated from the dry weight of the three-dimensional fibre network.• The layers of the sandwich structure are glued together with a wood glue.• At least a portion of the layer of fibrous material is configured to act as a thermally insulating layer.At least a portion of the layer of fibrous material is configured to act as a sound insulation layer.The generating of the negative pressure comprises generating a level of negative pressure that causes an irreversible transformation to the three-dimensional fibre network of the layer of fibrous material.• The negative pressure is -0.8 bar or less.• The compressing of the layer assembly is performed as cold pressing.• The compressing of the layer assembly is performed in a temperature below 30 °C, such as 15 to 30 °C, preferably without any external heating.• During the compressing of the layer assembly, the cellulosic and / or lignocellulosic fibres do not undergo any substantial colour change as a result of chemical reactions, such as chemical oxidation reactions.• The three-dimensional fibre network has been obtained by an air-laid process or by foam forming.• The cellulosic and / or lignocellulosic fibres comprise paper-grade baled pulp which has been dry-milled, such as hammer-milled.• The cellulosic and / or lignocellulosic fibres are substantially debonded to each other, such as non-homified.• The debonding has been achieved by treating the fibres mechanically and / or chemically.• The density of the low-density fibrous material, before the compressing step, is in range 20 kg / m3- 150 kg / m3, such as 20 kg / m3- 90 kg / m3.• The first layer, the low-density fibrous material, and the optional second layer have been glued together with a wood glue, to form the layer assembly.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIGURE 1 illustrates a light-weight element in accordance with at least some embodiments of the present invention; and

[0010] FIGURES 2A and 2B illustrate simplified examples of different phases of a manufacturing process according to the present disclosure.EMBODIMENTS

[0011] The present disclosure describes a light-weight element and a method to manufacture such an element. The element may have a sandwich structure comprising a first layer, a second layer, and a layer of low-density fibrous material between the first layer and the second layer.

[0012] An element according to the present disclosure can be formed into different shapes. The element may be in the form of a panel (or, interchangeably, a board), with a length, width, and thickness. The thickness extending in a direction through the layers of the sandwich structure. The layer of fibrous material has been subjected to compression in the direction of the thickness. An element according to the present disclosure can be formed into different shapes by the same woodworking methods as with plyboard and veneer, for example. If so desired, the element may be in the form of product that has the appearance of a plyboard from the surface. However, the elements are much lighter and more flexible compared to veneer, for example.

[0013] In embodiments, the element is in the form of a curved panel, wherein said curved panel comprises at least one non-planar surface.

[0014] In an example, the panel may comprise two non-planar surfaces, such as two curved surfaces, wherein the curvatures of said two non-planar surfaces are different. The panel may comprise an upper surface and an opposite lower surface, wherein the curvature of the upper surface is different from the curvature of the lower surface which leads to corresponding thickness variation in the panel.

[0015] Fibrous material

[0016] The low-density fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres.

[0017] In the present context, the term “fibrous material” or “fibrous cellulosic material” or “cellulosic fibres” typically refers to cellulosic and / or lignocellulosic fibres. Such fibres may be of plant origin.

[0018] Within the present disclosure, the term “cellulosic material” may refer to both or either of cellulosic and lignocellulosic materials. In some embodiments, the fibrous cellulosic and / or lignocellulosic material may be selected from bleached or unbleachedchemical pulp, such as bleached or unbleached softwood chemical pulp and / or bleached or unbleached hardwood chemical pulp, or sawdust. In some preferred embodiments, the fibrous cellulosic and / or lignocellulosic material may be selected from chemical pulp, mechanical pulp, for example chemi-thermomechanical pulp (CTMP) or bleached chemi- thermomechanical pulp (BCTMP), or non-wood pulp. In other embodiments, the fibres comprise semi-chemical pulp, thermomechanical pulp, or recycled pulp. In some embodiments, the pulp may be made from any broad-leaved tree such as a tree from the betulaceae family, for example birch or aspen, from the salicaceae family, from eucalyptus, mixed tropical hardwood or pines or from any combination of the aforementioned. The pulp may be also made from any conifer such as spruce or pine or from any combination thereof. The pulp may also be made from a combination of broad-leaved trees and conifers. In another embodiment, the pulp may be made from any annuals such as straw, common reed, reed canary grass, bamboo, sugarcane, bagasse or any grass plant.

[0019] In the present context, the term “indentation hardness” refers the to a materials capacity to withstand force or load. The indentation hardness is a measure of the total force (N) required to produce a specified indentation of a material (herein an indentation corresponding to 40 % of the initial thickness). The indentation hardness of a flexible material can be measured according to the standards ISO 2439:2008. If not otherwise indicated, the indentation hardness as referred to herein is measured using ISO 2439:2008, Method A: “Determination of the 40 % / 30 s indentation hardness index”.

[0020] In the present context, the term “fatigue” refers to a materials resistance to irreversible deformation under repeated stress. In other words, the term fatigue used to describe the materials ability to revert into its original shape after repeated force or repeated load has been applied onto the material. Fatigue can be measured as loss in thickness or loss in indentation hardness of the material. The fatigue of a flexible material can be determined by constant-load pounding according to the standard ISO 3385:2014.

[0021] In the present context, the term “compression recovery” refers to a material’s capability to revert into its initial shape after compression. It can be expressed as a percentage of the initial thickness of the material, i.e., the thickness the material reverts to after compression into a predetermined thickness, such as compression into 50 % of the initial thickness of the material.

[0022] In the present context, the term “resilient” [resilient layer, resilience] refers to the flexible and / or elastic properties of a material. A resilient layer is a flexible and / or elastic layer.

[0023] In some embodiments, the fibrous material disclosed herein comprises a three- dimensional fibre network, wherein the three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 50 wt-%, the density of the three-dimensional fibre network is in the range of 20-90 kg / m3, and the three-dimensional fibre network is arranged into a layer having a thickness in the range of 1-150 mm.

[0024] Inclusion of such a fibre network will reduce the need to employ fossil-based material.

[0025] In some embodiments, the three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 55 wt-%, such as at least 70 wt-%, for example at least 75 wt-%, at least 80 wt-%, at least 85 wt-% or at least 90 wt-%, calculated from the dry weight of the three-dimensional fibre network layer. In preferred embodiments, the three-dimensional fibre network layer may comprise, for example, 85 wt- %, 90 wt-%, 95 wt-% or 98 wt-% of the fibrous cellulosic and / or lignocellulosic fibres calculated from the dry weight of the layer. When additives are included in the fibrous network, the amount of cellulosic and / or lignocellulosic fibres in the three-dimensional fibre network may be, for example, up to 60 wt-%, 75 wt-%, 80 wt-%, 85 wt-%, 90 wt-%, 95 wt- %, 98 wt-%, 99 wt-% or 99.5 wt-%, calculated from the dry weight of the three-dimensional fibre network. The term “additive” may herein refer to all kind of components added to the three-dimensional fibre network of cellulosic and / or lignocellulosic material, and may include, for example, chemical substances or alternative materials, such as fillers. Such additives may be included in the three-dimensional network to, for example, modify the compression recovery of the material or for other functionality, such as to improve the hydrophobicity or flame-resistance of the material, or to prevent bacterial growth. One or more additives, such as a binding agent, a functionalisation agent or a modifier, may be included in the material to modify the reversible deformation, i.e., compression recovery, of the three-dimensional fibre network.

[0026] A high content of cellulosic and / or lignocellulosic fibres in the three- dimensional fibre network is advantageous as it reduces the environmental impact of the product when compared to fossil-based fibrous materials. The inclusion of cellulosic and / or lignocellulosic fibres in the above amounts also enhances the recyclability and biodegradability properties of the material, as at least half of the dry weight of the material thus is recyclable and / or biodegradable. The remainder of the three-dimensional fibre network layer can comprise or consist of one or more additives for modified reversible deformation of the fibre network and / or flexibility, i.e., fibre reversibility after compression. Such additives can be selected from, for example, binding agents, binding fibres, functional fibres, bicomponent fibres, foaming agents, functionalisation agents, or cross-linking agents, without being limited thereto. Alternatively, or additionally, other functional additives can be included, such as fire retardants or mould inhibitors, as a few examples. Any additives may be comprised in the three-dimensional fibre network in a total amount of from 0.5-50 wt-%, such as from 0.5 wt-%, 1 wt-%, 2 wt-%, 3 wt-%, 5 wt-% or 10 wt-% and up to 12 wt- %, 15 wt-%, 25 wt-%, 40 wt-% or 50 wt-%, calculated from the dry weight of the three- dimensional fibre network layer.

[0027] In some embodiments, the density of the three-dimensional fibre network is at least 30 kg / m3, such as at least 35 kg / m3, 40 kg / m3, 45 kg / m3, 50 kg / m3or 55 kg / m3and up to 65 kg / m3, 70 kg / m3, 75 kg / m3or 85 kg / m3. At the higher densities of the disclosed range, such as between 70 kg / m3and 90 kg / m3, the material is relatively rigid compared to the lower density range, such as between 20 kg / m3and 50 kg / m3. A fibrous material at the lower density range provides for a soft material, i.e., a material showing higher degree of compression when compared to the higher density range material, when being subjected to a similar load. Naturally, the intended end use of such materials can be different and enables the fibrous material to be used in a wide range of applications either alone or in combination with a material of different properties.

[0028] Within the present disclosure, the three-dimensional fibre network is arranged into a layer having a thickness in the range of 1-150 mm. Mechanical properties of the material are dependent on a combination of the thickness and density of the layer. In some embodiments, the thickness may be from 5 mm, 10 mm, 15 mm, 20 mm or 35 mm up to 70 mm, 80 mm, 100 mm, 120 mm or 150 mm. A relatively thin layer, with a thickness in the range of, for example from 1, 3 or 5 mm up to 8, 10 or 15 mm, and at a medium or high- density range, can be used either alone or in combination with a softer layer, for examplesuch that the thinner and denser layer acts as a supportive layer or a pressure distribution layer. Likewise, such relatively thin layers of low-density materials may be used either alone, for example in packaging applications, or in in combination with further layers having similar or different properties. Thicker layers, having a thickness in the range of, e.g., from 20, 30 or 50 mm up to 100, 120 or 150 mm, can likewise be used either alone or in combination with other layers.

[0029] The fibrous material according to the present disclosure can consist of a three- dimensional fibre network as described herein.

[0030] In some embodiments of the present disclosure, the fibrous material has an indentation hardness in the range of 150-1400 N, preferably 300-1300 N, even more preferably 350-1200 N, such as 450-1200 N, 800-1200 N or 600-1100 N, when determined as 40 % / 30 s indentation hardness index according to ISO 2439:2008, Method A. The above presented indentation hardness is expressed as the force (N) applied when the fibrous material is compressed 40 % from the initial thickness (mm). The disclosed ranges of indentation hardness may ensure sufficient deformability of the fibrous material for example to produce curved shapes.

[0031] In some embodiments of the present disclosure, the compression recovery, after compression into 50 % of the initial thickness of the fibrous material, is at least 70 %, preferably at least 75 %, even more preferably at least 80 %, such as at least 85 % or at least 90 % of the initial thickness of the fibrous material.

[0032] The fibrous material according to the present disclosure can show fatigue properties that are comparable with traditional fibrous materials. When measured using ISO 3385:2014 (Determination of fatigue by constant-load pounding, 80 000 cycles), the change in thickness of the fibrous material can be in the range of, for example, from -2 %, -4 %, -6 % or -8 % to -15 %, -25 % or -40 %, with respect to the initial thickness of the material. The change in indentation hardness can be, for example, from -0.2 %, -0.5 %, -1 %, -5 % or -10 % to -15 %, -30 %, -45 %, -60 % or -90 %, with respect to the initial indentation hardness of the material, when determined using the same test (ISO 3385:2014).

[0033] In further embodiments of the present disclosure, the fibres of cellulosic and / or lignocellulosic material are selected from bleached or unbleached chemical pulp, such as bleached or unbleached softwood chemical pulp and / or bleached or unbleached hardwoodchemical pulp, mechanical pulp, such as chemi-thermomechanical pulp (CTMP) or bleached chemi-thermomechanical pulp (BCTMP), recycled pulp, non-wood pulp, sawdust, regenerated fibres, or any combinations thereof. Such cellulosic and / or lignocellulosic materials can be provided as paper grade pulp, such as kraft pulp.

[0034] Preferably, the cellulosic and lignocellulosic material is a wood-derived material, even more preferably wood derived pulp. Being renewable, wood derived materials are a sustainable alternative to fossil-based materials.

[0035] The fibre length of the fibrous cellulosic material may in one example be larger than 0.5 mm, in another example less than 10 mm, such as 0.5 to 5 mm, for example 1 to 5 mm, or 1 to 2.5 mm.

[0036] The term “fibre length” refers to the distance measured along the longest dimension of the fibre.

[0037] As briefly discussed above, the three-dimensional fibre network of cellulosic material can comprise additives for modified reversible deformation of the fibre network, for improved fibre strength upon compression, modified compression recovery, improved fatigue properties and / or improved three-dimensional stability. In such embodiments, the cellulosic and / or lignocellulosic fibres of the three-dimensional network can be combined with synthetic fibres and, alternatively or additionally, treated with chemical additives, such as modifiers or binding compositions, i.e., binding agents. The product lifespan can also be extended in this manner, i.e., by improving the fatigue properties of the fibrous material.

[0038] A binding composition is a composition that allows the cellulosic and / or lignocellulosic fibres in the fibre network to bind or connect to each other, either directly by forming intra-fibre chemical bonds or by fibre interaction via the binding composition. For example, the binding composition may comprise a binding polymer. The binding polymer may comprise for example a polyester, such as polybutylene terephthalate and polyethylene terephthalate, polylactic acid, polyethylene, polypropylene or combinations thereof. Preferably, the binding agent comprises bio-based polymers, such as polylactic acid. In preferred embodiments, the binding polymer is a thermoplastic polymer. This allows for at least partial melting of the binding composition, or a thermoplastic polymer thereof, after formation of the three-dimensional network.

[0039] The binder composition may be provided for example in the form of fibres, pellets of various shapes (spherical, cylindrical, oval etc.), randomly shaped particles, uniformly shaped particles or in the form of a powder. The binding composition may thus simultaneously act as a filler. When included in the form of fibres or particles, the fibre length or the particle size of the binding composition is preferably in the same range or smaller than the fibres of the cellulosic and / or lignocellulosic material. Thus, the fibre average length or the particle average size, referring to the length of the fibre or the crosssection of a particle in its longest direction, is preferably in a range of 0.001 mm-10 mm, such as 0.02 to 5 mm, for example 1 to 5 mm, or 1-2.5 mm. In particular for pellets or powders, the average cross-section (diameter) of the particles may be in the lower range of this interval, such as from 0.001-2 mm, for example, 0.01-1 mm.

[0040] Binder compositions or additives can be applied in dry form, such as dry fibres, pellets, or powders. Alternatively, the binder composition can be applied in wet form, such as in the form of an aqueous dispersion, an aqueous suspension, or water solution. The binder composition can be added to the cellulosic and / or lignocellulosic fibres before or during the manufacture of the fibrous material, such as during formation of the fibre network. Preferably, the three-dimensional fibre network comprises less than 20 wt-%, less than 15 wt-%, or even more preferably less than 10 wt-% or less than 5 wt-% of binder composition or binder additive, calculated from the dry weight of the three-dimensional network of cellulosic and / or lignocellulosic fibres.

[0041] The binding composition or at least part of the binding composition may be formulated to melt upon heating. Preferably the melting point of such binding compositions is less than 220 °C, such as less than 200 °C, such as less than 150 °C, or in the range 60 to 220 °C.

[0042] In preferred embodiments the three-dimensional fibre network of cellulosic and / or lignocellulosic fibres comprises bicomponent fibres, such as synthetic bicomponent fibres or thermoplastic bicomponent fibres. Such bicomponent fibres can function as binding composition within the fibre network and provide for additional functionality, such as improved expected lifespan of the fibrous material. Furthermore, bicomponent fibres may act as binding agent between any adjacent layers in the fibrous material.

[0043] In embodiments, the three-dimensional fibre network comprises bicomponent fibres, such as synthetic bicomponent fibres or thermoplastic bicomponent fibres or biobased bicomponent fibres.

[0044] A bicomponent fibre is a fibre that combines two separate components, i.e., a first component and a second component, into a single filament. The components may be, for example, two separate polymers or a polymer in combination with a naturally derived component, such as a cellulosic material. The two components may be arranged in bicomponent fibres in various ways, for example side-by-side, as a sheath-core structure, as a segmented structure or as a so-called islands-in-the-sea -structure, where one component surrounds several separate sections of the other component. Preferably, the two components are polymers with different properties.

[0045] The first component may comprise a different polymer than the second component. In some embodiments, the molecular weight of the first component differs from the molecular weight of the second component. The polymers of the first component and the second component may be selected from polyesters, such as polybutylene terephthalate and polyethylene terephthalate, polylactic acid, polyethylene, polypropylene or combinations thereof. In some embodiments, both components comprise, independently from each other, a thermoplastic polymer. In some embodiments, the first component comprises cellulose and the second component comprises a thermoplastic polymer. Bicomponent fibres comprising thermoplastic polymer is herein to be understood as bicomponent fibres wherein at least one of the components comprises thermoplastic polymer.

[0046] In some embodiments, the bicomponent fibre has a sheath-core structure. A sheath-core structure refers to a structure wherein the polymer(s) used in the core-component are completely surrounded by sheath-component(s). The sheath-component may in some examples comprise a different polymer than the core-component. In other embodiments, the molecular weight of the sheath-component differs from the molecular weight of the corecomponent. The polymers for the sheath-component and the core-component may be selected from polyesters, such as polybutylene terephthalate and polyethylene terephthalate, polylactic acid, polyethylene, polypropylene or combinations thereof. In some preferred embodiments, the sheath-component is a thermoplastic polymer. The core component may comprise cellulose. In some embodiments, the core component may comprise a thermoplastic polymer.

[0047] The fibrous material may comprise a bicomponent fibre having a sheath-core structure, such as a bicomponent fibre in which the core component comprises cellulose and the sheath component comprises a thermoplastic polymer.

[0048] The melting point of at least one component of the bicomponent fibre may be less than 220 °C, such as less than 200 °C, such as less than 150 °C, or in the range 60 to 220 °C. In some preferred embodiments where the bicomponent fibres have a sheath-core structure, the melting point of the sheath-component is lower than the melting point of the core-component. Preferably, the differences between the melting point of the sheathcomponent and the melting point of the core-component enables melting of the sheathcomponent while the core-component remains in solid form. The melted sheath-component may provide for inter-fibre connections within the three-dimensional network structure, while the core component remains intact and provides structural support.

[0049] It is possible to use any bicomponent fibre arrangements that provide a similar effect in which one component of the bicomponent fibre melts, connecting the cellulosic fibres together, and the other component remains intact, providing structural support to the formed fibre network.

[0050] The fibre network of the fibrous material may comprise from 2 wt-%, 3 wt-%,5 wt-% or 10 wt-% and up to 12 wt-%, 15 wt-%, 25 wt-%, 40 wt-% or 50 wt-% of bicomponent fibres calculated from the dry weight of the fibre network, for example, 2 to 20 wt-%, such as 5 to 15 wt-%, or 3 to 10 wt-%, of bicomponent fibres calculated from the dry weight of the fibre network.

[0051] In further embodiments, the binding composition may be an expandable binding composition, such as expandable microspheres. The expansion may be activated thermally or chemically. Preferably the binding composition comprises thermally expandable components, such as thermally expandable microspheres. Such thermally expandable components can have a sheath-core structure, preferably such that the sheath structure comprises thermoplastic polymers. The core structure typically comprises hydrocarbons with low boiling points. The binding agent can thus affect mechanical properties of the three-dimensional network, as it simultaneously provides for binding properties within the three-dimensional fibre network and resilient properties caused by the hollow or cellular structure of the binding agent upon expansion, thus affecting reversable deformation of the three-dimensional fibre network.

[0052] In further preferred embodiments, the cellulosic and / or lignocellulosic fibres comprise modified cellulosic and / or lignocellulosic fibres. The fibres can be mechanically or chemically modified fibres of cellulosic material, such as structurally modified fibres, non-derivatized modified fibres, or derivatized modified fibres. The fibres can, for example be heat treated or treated mechanically, such as by grinding. Such modified cellulosic and / or lignocellulosic fibres may also include fully or partially regenerated fibres. Alternatively, or additionally, the fibre modification may include use of a compatibilizer, a cross-linking agent, alkali treatment, acid treatment, solvent treatment, or activation or reaction through chemically charged regions, such as cationization or anionization, without being limited thereto. Examples of modified cellulosic fibres that may be included for functionality are viscose fibres and hydrofobized fibres.

[0053] In a preferred embodiment, the chemically treated fibres are non-derivatized cellulosic and / or lignocellulosic fibres treated with deep-eutectic solvent (DES).

[0054] A further example of solvent treatment is treatment with alkali, such as sodium hydroxide (NaOH).

[0055] The fibrous material according to the present disclosure can contain additives. In some embodiments, the fibrous material comprises additive chemicals selected from binding agents, barrier agents, flame-retardants, foaming agents, surfactants, mould inhibitors, odour suppressing agents, blowing agents, lightweight fillers, bulk improvement agents, pigments, micro- or nanofibrillated cellulose, or combinations thereof. By the addition of additives, such as the above-mentioned chemicals, the properties of the fibrous material can be modified according to the intended use.

[0056] In some embodiment, the binding agent may include thermoplastic polymers. The binding polymer may comprise for example a polyester, such as polybutylene terephthalate and polyethylene terephthalate, polylactic acid, polyethylene, polypropylene or combinations thereof. Preferably, the binding agent comprises bio-based polymers, such as polylactic acid. Alternatively, or additionally, the binder agent may be a binder composition as disclosed herein, such as bicomponent fibres or microspheres.

[0057] In some embodiments, the barrier agent may include hydrophobic agents, polymeric barriers, sizing agents, coated fibres, and barrier resins. Such barrier agents may form a barrier on individual fibres or fibre bundles of cellulosic material, or on the three-dimensional fibre network. Herein, barrier agents are also interpreted as to include agents providing the fibres with chemical barrier properties, such as water or grease resistance, i.e., without the formation of physical barriers. Thus, the barrier agents may include hydrophobic agents, such as organosilanes, betulin, and betulinic acid, or sizes, such as styrene acrylate copolymers (SA), polyurethanes, alkylated urethanes, carboxymethylcellulose and its salts, alkyl celluloses, such as methyl cellulose and ethyl cellulose, styrene / maleic acid copolymer (SMA), di-isobutylene / maleic anhydride, aery lonitrile / acry late copolymers, a rosin, a wax, such as alkyl ketene dimer (AKD) or paraffin wax, an oil, such as alkenyl succinic anhydride (ASA), or styrene acrylate emulsion (SAE).

[0058] In some embodiments, the fibrous material may comprise at least one flame retardant, which may be selected from the following group: minerals, organohalogen compounds, organophosphorus compounds, inorganic phosphorus compounds, and organic compounds, and combinations thereof. Such a flame retardant may be comprised within the three-dimensional fibre network or in any additional layers of the fibrous material.

[0059] Examples of mineral flame-retardants include: aluminium trihydroxide (ATH), magnesium hydroxide (MDH), huntite and hydromagnesite, various hydrates, red phosphorus, and boron compounds, mostly borates.

[0060] Examples of inorganic phosphorus flame-retardants include ammonium polyphosphate (APP) and melamine polyphosphate (MPP).

[0061] Examples of organic flame-retardants include carboxylic acid and dicarboxylic acids.

[0062] In some embodiments, in particular when the three-dimensional fibre network is formed by foam assisted formation, the additive may be selected from foaming agents or surfactants known in the art, such as sodium dodecyl sulphate (SDS), polyvinyl alcohol (PVA), polyethylene glycol dodecyl ether (Brij), polyethylene glycol sorbitan monolaurate (Tween 20), PEG-6 lauramide, alkyl polyglycosides (APG), such as alkyl polyglucosides, fatty alcohol ethoxylates, alkylphenol ethyxolates, fatty acid ethyxolates, fatty amide ethyxolates, alkyl glycosides, such as alkyl glucosides, sugar based non-ionic polymers, such as sorbitan alkanoates, and combinations thereof.

[0063] In some embodiments, mould inhibitors may be added to the three-dimensional fibre network for improved antibacterial properties. Such antimicrobial properties may bederived from fibre treatment or the inclusion of mould inhibitors, such as, propionic acid and salts thereof, sorbic acid and salts thereof, methyl fumarate, and p-hydroxybenzoate compounds.

[0064] In some embodiments, the fibrous material may comprise a protective layer on at least one of its surfaces. The protective layer may comprise, for example, woven fabrics or non-woven fabrics made of natural or synthetic fibres, optionally treated with additives such as a hydrophobic agent, a fire retardant, a mould inhibitor, a binding agent, a barrier agent or combinations thereof. Preferably, the thickness of the protective layer is less than 5 mm or less than 3 mm, such as ranging from 0.1 to 2 mm, for example ranging from 0.2 to 1 mm or from 0.3 to 0.5 mm. In one embodiment, the thickness of the protective layer is 0.1 to 0.4 mm. The advantage of having such a protective layer is that it may provide structural strength, for example by protecting the three-dimensional fibrous network from being defibrillated during handling, or may serve as a functional component providing, for example, water repellent properties to the fibrous material, or binding properties between layers.

[0065] The fibrous material may, in any protective layer thereof, or within the three- dimensional fibre network, comprise one or more additive chemicals. The additive chemicals can be selected from flame-retardants, foaming agents, mould inhibitors, barrier agents, binding agents, or combinations thereof. Preferably, the amount of such additives is below 40 wt-%, as calculated from the total dry weight of the fibrous cellulosic and / or lignocellulosic material, such as below 30 wt-% below 20 wt-% or below 10 wt-% of the total dry weight of the fibrous cellulosic and / or lignocellulosic material. In some embodiments, the additive chemical may be mixed to the fibrous cellulosic and / or lignocellulosic material prior to forming the three-dimensional fibre network, such as by pretreatment of fibres or by mixing the fibres with additives. In other embodiments, the additive may be applied to the three-dimensional fibre network after forming such a network. Application after forming the three-dimensional fibre network may in some embodiments comprise spraying the additive onto the surface of the fibre network.

[0066] In further preferred embodiments of the invention, the fibrous material comprises cellulosic and / or lignocellulosic fibres in an amount of at least 50 wt-%, such as at least 60 wt-%, at least 75 wt-% or at least 80 wt-%, calculated from the total dry weight of the fibrous material. This provides for a fibrous material wherein at least half of the totalweight of the fibrous material, including any additional layers, is derived from renewable sources.

[0067] As an aspect of the present disclosure is provided a method for the manufacture of a three-dimensional fibre network. The method is suitable for the manufacture of a fibrous material according to the present disclosure, or any of the embodiments thereof. The method comprises the steps of: providing fibres of cellulosic and / or lignocellulosic material, forming the fibres of cellulosic and / or lignocellulosic material into a three- dimensional fibre network with a density within the range of 20-90 kg / m3and a total content of cellulosic and / or lignocellulosic fibres of at least 50 wt-%, calculated from the dry weight of the three-dimensional fibre network, and arranging the three-dimensional fibre network into a layer having a thickness of 1-150 mm.

[0068] In the above method, some of the steps may be performed simultaneously. In particular the steps of forming the fibres into a three-dimensional network and arranging the three-dimensional fibre network into a layer may take place in a single method step, whereby the fibre network is formed into the shape of a sheet, mat, or slab. Preferably, the method includes a step of contacting the fibres of cellulosic and / or lignocellulosic material with an additive for modified reversible deformation. Such a step is preferably carried out before the formation of the fibre network. The step of contacting the fibres with an additive may also be carried out simultaneously with the step of providing fibres of cellulosic and / or lignocellulosic material, simultaneously with the step of forming a three-dimensional fibre network, or as post-treatment after the three-dimensional fibre network has been formed.

[0069] In some embodiments, the three-dimensional fibre network may be formed from dry cellulosic and / or lignocellulosic material. In an embodiment, the three-dimensional fibre network has been obtained by a web forming method, typically on a wire, such as dry forming (dry-laid process), air-laid process or foam forming or any combination thereof, preferably by an air-laid process or by dry forming. Advantages of using a dry-laid process, in particular an air-laid process, are that the obtained fibre network is easy to handle, shows homogeneous fibre distribution, and can be directly obtained in a desired thickness. Airlaying processes also allow for uniform inclusion of dry state additives, such as thermoplastic additives, polymeric fibres, or bicomponent fibres.

[0070] In preferred embodiments of the invention, the fibres of cellulosic and / or lignocellulosic material are selected from bleached or unbleached chemical pulp, such as bleached or unbleached softwood chemical pulp and / or bleached or unbleached hardwood chemical pulp, mechanical pulp, such as chemi-thermomechanical pulp (CTMP) or bleached chemi-thermomechanical pulp (BCTMP), recycled pulp, non-wood pulp, sawdust, or any combinations thereof. Pulp is a readily available, fully biodegradable and cost-efficient material that is easy to transport. In some embodiments, the three-dimensional network, which can be applied as the fibrous material or at least a fibrous part thereof, is formed from dry cellulosic material. Such cellulosic material is preferably paper grade pulp, i.e., pulp suitable for use in paper and / or cardboard manufacture. For example, baled pulp or fluff pulp may be used as the cellulosic material, preferably baled pulp.

[0071] In some embodiments of the invention, the step of providing cellulosic and / or lignocellulosic fibres comprises dry-milling the cellulosic and / or lignocellulosic material. The inclusion of a dry-milling step, such as a hammer-milling step, in the method provides for a finely separated fibre matrix, which therefore is well suited for the formation of low- density fibre networks as disclosed herein. This pre-processing step is especially preferable when using dry-laying techniques in the formation of the three-dimensional fibre network, in particular in combination with air-laying techniques. A dry-milling, e.g., hammer-milling step can be included when baled pulp or fluff pulp is used as raw material.

[0072] In some embodiments of the invention, the step of contacting the fibres of cellulosic and / or lignocellulosic material with an additive for modified reversible deformation includes the addition of binding agent, such as binding polymers.

[0073] The cellulosic fibres can be contacted with binding agent in wet state, such as an aqueous solution or suspension of binding agent. Such binding agent can be mixed with the cellulosic fibres in wet state, such as into wet pulp, or it may be applied through other techniques known in the art, such as by spraying. Wet treatment of fibres is in particular suitable in combination with foam forming techniques. When the three-dimensional fibre network is formed using dry-forming techniques, an additional drying step can be employed for cellulosic fibres treated with additives in wet state or solvents.

[0074] The binding agent can additionally or alternatively be applied in dry state, such as by inclusion of binding composition in the form of, for example, particles, fibres, or powder. Inclusion of binding agent, i.e., binding composition, in dry state is preferredespecially when using dry-laying techniques, in particular air-laying. Within the context of the current disclosure, the term “binding agent” is used interchangeably with the term “binding composition”. In such applications, the dry state additive can be premixed with dry state lignocellulosic and / or cellulosic fibres prior to formation of the three-dimensional fibre network. Alternatively, or additionally, the additive may be applied during the formation of the three-dimensional fibre network. For example, the addition of dry state additive may be an integrated part of an air-laying process where the additive is mixed with dry pulp fibres prior to settling on a substrate, typically a wire.

[0075] Preferably, a heat treatment step is performed on the three-dimensional fibre network. Such a heat treatment step can be performed to remove any excess moisture, and in particular, to melt and / or activate any additive. When thermally reactive additives, such as additives comprising thermoplastic polymers or expandable microspheres, are included in the fibre network, the heat treatment can be carried out at a temperature above the melting point or activation point of the additive, such as temperatures up to 250 °C, up to 220 °C, up to 200 °C, up to 150 °C, or in the range 60 to 220 °C. Such a heating step may be carried out by methods known in the art, for example by heating in an oven.

[0076] The above-described method steps can likewise be employed for other additives as listed herein, such additives being provided in dry state or in wet state.

[0077] In some embodiments of the present disclosure the step of contacting the fibres of cellulosic and / or lignocellulosic material with additive for modified reversible deformation is carried out by formation and / or inclusion of bicomponent fibres, preferably bicomponent fibres comprising a thermoplastic polymer. Such bicomponent fibres may be formed by modifying cellulosic and / or lignocellulosic fibres into bicomponent fibres. Alternatively, or additionally, bicomponent fibres can be mixed with the cellulosic and / or lignocellulosic fibres prior to or during the formation of the three-dimensional fibre network.

[0078] In some embodiments of the present disclosure, the step of providing fibres of cellulosic and / or lignocellulosic material or the step of contacting the fibres of cellulosic and / or lignocellulosic material with additive for modified reversible deformation comprises chemical and / or physical modification of the fibres of cellulosic and / or lignocellulosic material. Such chemical and / or physical modification can include processes known int the art, in particular any fibre modification as disclosed herein, such as mechanical grinding,cross-linking, solvent treatment, regeneration, or modification through chemical charges, or any combination thereof.

[0079] In the method of the present disclosure, a step of contacting the fibres of cellulosic or lignocellulosic material may comprise contacting the fibres with one or more additive selected from barrier agents, flame-retardants, foaming agents, surfactants, mould inhibitors, or combinations thereof. Such additives may be added in wet form, such as in the form of aqueous solutions or dispersions. Alternatively, or additionally, additives may be contacted with the fibres in dry form, such as in the form of particles, powders, or fibres.

[0080] In preferred embodiments of the invention, the step of forming the fibres into a three-dimensional fibre network is carried out using an air-laying technique. In such methods, a step of contacting the fibres of cellulosic and / or lignocellulosic material with an additive for modified reversible deformation can be carried out in the air-laying step, such that an additive for modified reversible deformation is mixed with the cellulosic and / or lignocellulosic fibres in dry state.

[0081] As discussed above, air-laying techniques allows for the formation of a uniform fibre network. Furthermore, when using air-laying techniques, bicomponent fibres or other additives in dry state may be combined with the cellulosic and / or lignocellulosic fibres upon formation of the air-laid fibre network. In this manner, no separate mixing is required, as the cellulosic and / or lignocellulosic fibres and the additive, such as bicomponent fibres, may be contacted with each other upon web formation, i.e., by supplying the fibres and the additive from different containers to the air-laying process. This also allow for uniform inclusion of the additive in the fibre network, and in particular with respect to bicomponent fibres and / or polymer fibres it allows for such fibres to be arranged within the network in a similar manner as the cellulosic material. Such a uniform fibre distribution provides for even mechanical properties across the entire fibre network. Air-laying technology can be used in the formation of three-dimensional fibre network layers in thickness ranges as disclosed herein.

[0082] In a preferred embodiment of the method of the present disclosure, the fibres of cellulosic and / or lignocellulosic material are paper grade pulp fibres, preferably provided as baled pulp. The preferred embodiment further comprises dry-milling the pulp fibres, feeding the dry-milled pulp fibres and a dry state additive to an air-laying process, preferably from separate feed sources, forming a three-dimensional air-laid fibre network of pulp fibresand additive, and subjecting the three-dimensional fibre network to a heat-treatment step. By applying a heat treatment step the temperature of the three-dimensional fibre network can be increased to a level above the melting point, or activation point, of at least one additive or any component thereof

[0083] Paper grade pulp fibres herein refers to pulp fibres suitable for paper and / or cardboard manufacture, in particular any commercial pulp to be used in such processes. The inclusion of a dry-milling step, in particular a hammer-milling step, provides for a finely separated pulp matrix, that is well suited for air-laying. By obtaining a pulp matrix having a high degree of disintegrated, individual fibres provides for a uniform fibre distribution within the air-laid material. It also provides for the possibility to include dry state additive, in particular provided from separate feed sources as described above. Dry state additives, such as polymeric fibres, can thus be fed directly to the air-laying process, without any preliminary blending of the cellulosic fibres and additive. Thus, an even quality fibre network can be obtained in a simplified process, using currently available equipment without the need for retrofitting. The additives may further be melted or activated within the air-laid fibre network, for example by heat treatment.

[0084] In some embodiments, the step of forming the cellulosic fibres into a three- dimensional fibre network is carried out using a foam forming technique. The foam forming technique, i.e., use of foam assisted forming technology, allows for inclusion of additives in wet state without applying further drying steps prior to the formation of the fibre network. By forming the three-dimensional fibre network in wet state by foam assisted web formation, it is also possible to utilise the aqueous medium for chemical modification or additive transfer. The use of an aqueous medium can increase the chemical reactivity when compared to dry state formation, whereby different types of fibre interaction can be achieved, when compared dry-formation. Foam forming technology can be used in the formation of three- dimensional fibre network layers in the thickness ranges as disclosed herein.

[0085] In some embodiments, the three-dimensional fibre network is obtained by a foam process carried out on a wire. Such a three-dimensional fibre network can be included in or constitute a fibrous material according to the present disclosure.

[0086] In another embodiment, the three-dimensional fibre network is obtained by a mould-assisted forming method, such as by a foam-forming method in a mould.

[0087] In some embodiments, the three-dimensional fibre network is obtained by continuous web forming or by mould-assisted forming.

[0088] Such a foam formed three-dimensional fibre network can be included in or constitute a fibrous material according to the present disclosure.

[0089] It is to be understood that individual method steps as disclosed herein can be exchanged or combined with further steps. For example, any mechanical treatment, such as hammer milling or grinding, can be applied or exchanged with similar processing steps for producing a fibre matrix with a higher content of disintegrated, individualised fibres. The three-dimensional fibre network formed in the method as presented above, or any embodiment thereof, may also undergo further processing steps post formation. The fibrenetwork may, for example be coated, spray treated, moisture balanced, consolidated, heat treated, etc. The surface of the fibre network can, for example be treated such that it is non- planar, thus comprising regular or irregular patterns, which may be provided, for example, for improved airflow (breathability) of the material. Such patterns may comprise, for example, grooves or knobs. The patterns may be produced by use of pressing techniques and / or heat treatment. For additional layers, the three-dimensional fibre network may be formed in or compressed to a higher density than the ranges disclosed herein. Such materials may thus function, for example, as substrate layers or protection layers providing stability to the three-dimensional fibre network as presented herein. Likewise, the method may be applied for the production of fibre-networks with a density below the range as disclosed herein. Such low-density fibre networks may be used in combination with or as a layer of the fibrous materials as disclosed herein.

[0090] Details of the element

[0091] FIGURE 1 illustrates an example of an element 10 in accordance with at least some embodiments of the present invention. In FIGURE 1, a cross-sectional view of the element 10 along its width w is shown. The viewing direction is along length of the element 10.

[0092] The element 10 in FIGURE 1 has a sandwich structure. In this context, the term “sandwich structure” refers to a multi-layer structure with at least three layers, where at least one middle layer sandwiched between two surface layers. In FIGURE 1, the sandwich structure comprises a first layer 12, a second layer 14, and a middle layer 16 in theform of fibrous material between the first layer 12 and the second layer 14. The first layer 12 defines a first surface of the element 10. The second layer 14 defines a second surface of the element 10, opposite to the first surface. In this embodiment, the first layer 12 and second layer 14 both have planar shapes, and they define two opposite sides, a first side and a second side, respectively, for the element 10. Both the first layer 12 and the second layer 14 may be made one or more sheets of material. In some embodiments, for example, the first layer 12 and the second layer 13 may be made a plurality of sheets of veneer.

[0093] In FIGURE 1, the layer 16 of fibrous material (or, simply, the middle layer) between the first layer 12 and the second layer 14 comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, as described earlier.

[0094] As mentioned earlier, in an element according to present disclosure, the layer of low-density fibrous material has been subjected to compression in the direction of the thickness. In this context, the phrase “subjected to compression” is intended to mean that mechanical force has been applied to the opposite sides of the element such that the fibres of the middle layer have gone through an irreversible transformation. Even after compression, the fibrous material can be considered to be low-density material.

[0095] In some embodiments, the mechanical force has been provided using cold pressing. In the context of the present disclosure, the term “cold pressing” means a compression process where mechanical force has been applied without applying additional heat to the middle layer. When heat is not used, original colour of bleached pulp can be maintained, and there is no yellowing and / or burning of fibres. However, in some embodiments of the element, heat may also have been used during the compression process. In the context of the present disclosure, the term “cold pressing” is not intended to be understood as a compression process requiring active cooling during the process.

[0096] In the context of the present disclosure, the transformation is largely irreversible, meaning that once sufficiently compressed along its thickness, the middle does not revert back to its original thickness. In other words, the compression causes a permanent reduction to the thickness of the middle layer, and therefore also to the sandwich structure of the element, and the element itself. In this context, the term “thickness" is intended to be understood as a dimension extending through the layers of the sandwich structure. At a given point at a first surface, this dimension may be considered to define a shortest path to thesecond surface. In FIGURE 1, the element 10 has a uniform thickness throughout its width w.

[0097] For example, the compression recovery is preferably at least 90% after a compression phase with a 10% compression. For example, the compression recovery is preferably at least 70% after a compression phase with a 50% compression.

[0098] As mentioned earlier, an element according to the present disclosure can be formed into different shapes. For example, in FIGURE 1, the element 10 is in the form of a curved panel with an essentially U-shaped cross section. In this context, the term “panel” is intended to be understood as a sheet-like or plate-like structure. Further, the term “curved panel” is intended to be understood as a panel that has curvature, i.e., a non-flat panel. The arc length and the radius of curvature depend on the application. For example, in some applications, an arc length of the curvature (i.e., length of a curved portion) may be in few centimeters to tens of centimeters while the radius of curvature may be in a similar range. In FIGURE 1, the element 10 has two curved portion 18 along its width w. In the context of the present disclosure, a curved panel may have curvature in one direction, such as width w of the element 10 in FIGURE 1, or in more directions, such as both in width and length of the element. The curvature of the panel may be constant in a direction or it may vary. In other words, a curved panel may be considered to define a 3D shape.

[0099] For example, in FIGURE 1, both the first layer 12 and second layer 14 are made of malleable (or, interchangeably, deformable), wood-based sheets or panels, such as plywood or veneer. Typically, “wood-based material” or “wood-based panel” or “woodbased layer” refers to a material or panel or layer of which at least 50 wt-% is wood or derived from wood.

[0100] Thicknesses of the first layer 12 and the second layer 14 are such that compressing the middle layer 16 and for bending the whole sandwich structure to a desired shape without cracking or breaking has been possible with existing woodworking machinery and technologies, such as a vacuum bag press.

[0101] Other malleable materials, such as plastics or even metals (e.g., thin sheet of aluminum) may also be used in one or both of the two layers. The first layer 12 and the second layer 14 may be made from the same material or different materials. The two layers 12 and 14 may have the same thickness or different thicknesses.

[0102] The wood-based first and second layer, and the middle layer may have been joined to each other by adhesive layers, preferably directly without any further layers between the wood-based layers and the middle layer. For example, the adhesive layers may be in the form of layer of glue, such as a wood glue. In some embodiments, the adhesive layers are continuous layers covering the whole contact areas between the first layer and the middle layer and between the second layer and the middle layer. The interspace between each wood-based layer and the middle layer may consist of an adhesive layer. Other attachment methods, such as mechanical attachment means, may be used.

[0103] Applications

[0104] An element according to the present disclosure can be used in very large variety of applications. By modifying thickness and density of the middle layer, mechanical properties of the element may be tuned.

[0105] For example, in furniture applications, the thickness of the middle layer is below 100 mm, preferably in the range 10 - 50 mm. In this manner, the middle layer is well suited for further processing in a vacuum bag press, for example. Density of the middle layer may be above 40 kg / m3, below 500 kg / m3which is less dense compared to e.g., birch veneer (density ~680 kg / m3), typical use in furniture. Bending strength may be between 3-20 N / mm2which is more flexible compared to veneer (typically in the range of at least 30 N / mm2at equivalent thickness range).

[0106] In some embodiments, the element comprises functional portions or zones. These functional portions / zones may be configured to perform different desired functions, such as sound and / or thermal insulation. In some embodiments, at least a portion of the layer of fibrous material may be configured to act as a thermally insulating layer. Alternatively, or in addition, at least a portion of the layer of fibrous material may be configured to act as a sound insulation layer. The functional portion / zones may also be configured to provide additional mechanical support (in the form of a higher-density portion within the middle layer) and / or act as guides guiding flow of air or sound through the middle layer. Alternatively, or in addition, reinforcing elements, such as reinforcing bars or beams, may be added to the middle layer to provide additional mechanical support. Further, by varying the thickness and / or density of the middle layer in the direction of length and / or width of the element, various localized functional portions / zones may be formed to the element.

[0107] Manufacturing

[0108] The present disclosure further describes a method for manufacturing an element according to the present disclosure. The method is suitable to be implemented in a known woodworking process, namely vacuum bag press. For example, the method may comprise: receiving a layer assembly on a mould, sealing the mould and the layer assembly within a vacuum bag, and generating a negative pressure within the vacuum bag to compress the layer assembly.

[0109] FIGURES 2A and 2B show simplified examples of some phases of a manufacturing method according to the present disclosure. In Figure 2A, a layer assembly 24 is being received on a mould 22. The layer assembly 24 comprises at least a first layer 24a, a second layer 24b, and a low-density fibrous material 24c between the first layer 24a and the second layer 24b. The first layer 24a and the second layer 24b may be made from wood-based material, such as plywood or veneer, for example. The fibrous material 24c comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, as described above. The layer of fibrous material 24c may comprise form of one or more layers or webs of the fibrous material stacked together.

[0110] In some embodiments, the layer assembly is in the form of separate layers that are individually stacked into a loose sandwich structure on the mould 22. An adhesive layer may be provided between the layers. The first layer 24a and / or the second layer 24b of the layer assembly 24 may be formed out a plurality of sheets of material. For example, in FIGURE 2A, the first layer 24a may be formed out of a plurality (e.g., three) sheets of birch veneer to for the first layer 24a. The sheets may be oriented such that direction of woodgrain on each sheet of veneer is perpendicular to its adjacent sheets. The second layer 24b may be formed in the same or similar manner. Thicknesses of the sheets of veneer may be about 1mm (or less).

[0111] In some embodiments, the layer assembly 24 is a pre-assembled unit made of at least the first layer and low-density fibrous material stacked together. In this context, the term “pre-assembled” refers to a unit that is assembled together prior to mounting it on the mould 22. The stack layers may be held together by adhesive between the stacked layers, forexample. In some embodiments, the adhesive may be in the form of a layer of glue between the first layer and the middle layer and another layer of glue between the second layer and the middle layer. In some embodiments, in particular in embodiments intended to be woodworking processes, the glue may be wood glue, for example.

[0112] In some cases, the stack of layers may further be held together with other means, such as adhesive tape extending from top of the stack to the bottom.

[0113] The mould 22 supports the layer assembly 24 from one side. The mould 22 defines a desired three-dimensional shape for the element. The mould is configured to be suitable for vacuum bag press. To avoid air bubbles within the vacuum bag, the mould 22 is preferably made from a porous material. For example, the mould may be made from polyurethane foam.

[0114] Once the layer assembly 24 has been received on top of the mould 22, the mould 22 and the layer assembly 24 may be sealed within a vacuum bag of a vacuum bag press. In the context of the present disclosure, a vacuum bag is sealable container made from flexible material that compresses against one side of the element thereby causing a mechanical force pushing the two sides towards each other. Alternative, a vacuum bag may be formed by a combination of a rigid base and a flexible membrane that can be sealed together to form a sealed container. Figure 2A shows a membrane 26 of a vacuum bag being applied on top of the mould 22 and the layer assembly 24. The mould 22 has a rigid base that is configured to form a sealed cavity together with the membrane 26.

[0115] When the vacuum bag has been sealed a negative pressure may be generated within the vacuum bag to compress the layer assembly 24 into the desired shape. A level of negative pressure may be selected such that causes an irreversible transformation to the three-dimensional fibre network of the layer of fibrous material. In particular, the negative pressure is such that it causes an irreversible reduction of thickness of the layer of fibrous material. FIGURE 2B shows an element 10 according to the present disclosure being formed between the mould 22 and the membrane 26 of the vacuum bag. The ambient air pressure outside the vacuum bag causes a mechanical force that transforms the layer assembly into an element 10 according to the present disclosure. As shown in FIGURE 2B, the element 10 has a form that conforms with the shape of the mould 22. The element 10 in FIGURE 2B has a U-shaped cross section and the element 10 may be the same or similar as in the embodiment of FIGURE 1, for example. Angles of the curved portions of the cross sectionmay 90 degrees or 75 degrees, for example. However, the curvature of elements according to the present disclosure is not limited only to such angles. In FIGURE 2B, the element 10 has a first layer 12, a second layer 14, and a middle layer 16, corresponding those of the embodiment of FIGURE 1.

[0116] In addition to bending the layers, the mechanical force of the vacuum bag press causes the fibrous material in the layer assembly to compress, thereby reducing its thickness. In FIGURE 2B, the middle layer 16 is clearly thinner than the corresponding layer 24c in FIGURE 2A. As a result of the reduction of the thickness, the density of the middle layer increases. The density of the middle layer has a significant impact on mechanical properties of the middle layer. By controlling the amount of material in the middle layer (i.e., the original thickness of the middle layer before compression), mechanical properties of the middle layer, and thus the whole element, may be tuned. Alternatively, or in addition, the mechanical properties may be tuned by controlling the level of the negative pressure used in the compression phase.

[0117] The above-mentioned compression may be performed as cold pressing. As mentioned earlier original colour of bleached pulp can be maintained, and yellowing and / or burning of fibres can be avoid in this manner. However, it is also possible to use heat in the compression process, if deemed advantageous.

[0118] The negative pressure may be -0.3 bar or less, for example. Preferably, the negative pressure is -0.8 bar. In this context, a negative value of a negative pressures indicates amount of pressure with respect to the ambient pressure. In other words, -0.8 bar indicates an absolute pressure of 0.2 bar within the vacuum bag assuming that the ambient air pressure outside the vacuum bag is 1.0 bar. Further, the phrase “-0.8 bar or less” indicates that the pressure may be below -0.8 bar, e.g., it may be -0.9 bar.

[0119] The method may comprise a step of maintaining the negative pressure for a sufficient amount of time. The sufficient amount of time is preferably in the range of minutes and not in mere seconds. Once compression has been applied for a sufficient time, the negative pressure may be released, the vacuum bag may be unsealed, and an element according to the present disclosure may be obtained. In case of an embodiment with woodbased first and second layer as presented in FIGURE 1 , for example, the sufficient time may be 45 minutes.

[0120] The above-discussed manufacturing method is very versatile and enables production of a large variety of different light-weight composite elements. The shape of a light-weight element according to the present disclosure is not limited to U-shaped cross section, as presented in FIGURE 1. For example, FIGURE 3 shows a cross-sectional view of another embodiment of an element according to the present disclosure. Similar to FIGURE 1, the sandwich structure 30 in FIGURE 3 comprises a first layer3, a second layer 34, and a middle layer 36 in the form of fibrous material between the first layer 32 and the second layer 34. The first layer 32 defines a first surface of the element 30. The second layer 34 defines a second surface of the element 30, opposite to the first surface. The element 30 in FIGURE3 also has a curved shape. However, in contrast to FIGURE 1, the element 30 has curved portions 38a and 38b that curve to opposite directions. Thus, the element 20 has essentially a S-shaped cross section. Further, while FIGURES 1 and 3 show elements that have shapes with a constant cross section along their length, the element according to the present is not limited to only to such shapes.

[0121] As the fibrous material according to the present disclosure is highly malleable, mechanical characteristics of the element are largely determined by the characteristics of the first and second layer.

[0122] The method may in some embodiments comprise one or more steps of preprocessing that occur before receiving the layer assembly to the mould 22. For example, the first layer and / or second layer may be heated so as to soften it / them before starting the process of compressing the element into a desired shape. Further, in some embodiments where plywood or veneer is being used for the first and / or second layer, it may be desirable to soak said layer / s in order to improve their malleability.

[0123] Alternatively, or in addition, the method may also comprise one or more steps of postprocessing. Such post-processing steps take place after obtaining the element 10 from a manufacturing method as described above. For example, after obtaining the element, it may be coated (e.g., by painting it). The element may also be trimmed (e.g., by cutting away excess portions from it), or its surface may be given a finishing treatment (e.g. by sanding the surfaces), for example.

[0124] Examples

[0125] Example 1 - Formation of air-laid three-dimensional fibre network

[0126] Three-dimensional fibre networks were prepared at different densities using the same composition and the same formation technique (air-laying).

[0127] Three-dimensional fibre networks were prepared from pulp fibres (Metsa Pine). The paper grade pulp fibres were provided in the form of pulp bales and hammer- milled prior to being subjected to an air-laying process for the formation of a three- dimensional fibre network.

[0128] Bicomponent fibres comprising biobased polyethylene (Bio-PE) and recycled polyethylene terephthalate (PET) were provided. The bicomponent fibres were blended with the hammer-milled pulp fibres in the air-laying process.

[0129] The pulp fibres and the bicomponent fibres were supplied to the process from different sources and thus blended in the airspace prior to being settled into a three- dimensional fibre network. Thus, no pre-blending of the fibres was needed. The bicomponent fibres of Bio-PE and recycled PET were included in the three-dimensional fibre network in a total amount of 15 wt-%, calculated based on the dry weight of the fibre network. The air-laying process was carried out such that the thickness of the obtained mat was around 50 mm. The air-laid fibre network was subjected to thermal treatment at a temperature or 150 °C.

[0130] The obtained fibre network was a resilient and durable layer, having an uniform fibre distribution.

[0131] Example 2 - Properties of air-laid material

[0132] Two different pulp mats were produced using the technique and composition presented in Example 1. The first mat (herein referred to as sample Nl) was obtained in a density of 38 kg / m3and the second mat (herein referred to as sample N2) was obtained in a density of 67 kg / m3. The thus obtained thermally insulating fibrous materials were cut into test pieces having a size of 400 mm x 400 mm x 50 mm.

[0133] The materials were subjected to tests for determination of indentation hardness properties.

[0134] Further, each test piece was subjected to tests for determination of the indentation hardness according to ISO 2439:2008, method A. The indentation hardness is herein expressed as a force (N) by which the thermally insulating fibrous material iscompressed 40 % from the initial thickness (mm). The measurement probe used to compress the material had a diameter of 200 mm.

[0135] All tests were performed under test conditions of a temperature of 23°C and a humidity of 50 % Rh.

[0136] The results of the tests are presented in Table 1.Table 1: Test results for indentation hardness.

[0137] Examples 3 and 4 describe manufacturing of foam-formed three-dimensional fibre networks and the characterisation of their compression strength and recovery before inclusion in an element according to some embodiments of the present disclosure.

[0138] Example 3 - Foam assisted forming

[0139] Three-dimensional fibre networks were prepared in accordance to the present disclosure using foam assisted formation. The three-dimensional fibre network was prepared from pulp fibres (Metsa Strong).

[0140] The samples were prepared by soaking the pulp fibres in water overnight, whereafter the fibres were disintegrated for 1 hour. The pulp was placed in a vessel and the fibre foam was generated using a laboratory mixer. Simulsol™ SL10, which is a non-ionic non-ethoxylated surfactant prepared from glucose and fatty alcohol, was added in an amount of 1.2 g / 1. The target pulp concentration before foam generation was 4 %. The foam generation time was 3 min with a rotational speed of 3800 rpm and additional 3 min with 4500 rpm.

[0141] The fibre foam obtained was poured along with a tilted plate into a mould. After the foam generation, the foam was left to drain for about 15 min in ambient conditions. The samples were dried at 70 °C in an oven. The dried sheets were rewetted to reach a solidcontent of 50 % by spraying water on the top and the bottom surfaces. The samples were then placed in a plastic bag and the moisture content was allowed to balance for 4 h, turning the sample after 2 h. The samples were compressed between metal plates to a final thickness of around 30 mm. The thickness of the samples was changed slightly to achieve the target density of 60 kg / m3. The samples were thereafter dried at 70 °C in an oven.

[0142] The three-dimensional fibre networks thus obtained had planar surfaces with even properties, i.e., no denser or flatter regions could be observed. The properties of the fibre-networks were essentially the same over the whole cross-section of the material.

[0143] Example 4 - Properties of foam formed fibre networks

[0144] Fibre-network samples prepared in the above manner, herein referred to as samples SI and S2, were tested for compression strength and recovery.

[0145] An overview of the properties of the samples prepared are listed in Table 2.Table 2: Properties of samples prepared.

[0146] The samples were subjected to compression strength and recovery tests. The samples tested were balanced overnight in an air-conditioned laboratory room (23 °C, 50 Rh). The samples were cut into a size of 50 mm x 50 mm using a band saw.

[0147] Cyclic compression tests were carried out using a Lloyd LR10K universal tester (Lloyd Instruments Ltd, Bognor Regis, West Sussex, UK). Both compression strength as well as reversibility from the compression were determined at a degree of compression of 10 % respectively 50 %. The compression speed was 10 % of the sample thickness per minute. For a 30 mm sample, the speed was 3 mm / min for the 10 % compression and 30 mm / min for the subsequent 50 % compression. In the reversibility measurement, the thickness of the sample was determined after the sample was recovered to the thicknesswhere the initial force of 0.625 N was reached. Reversibility from the compression was determined 1 min after the compression. For each trial point, 5 parallel samples were tested.

[0148] The compression recovery after 50 % compression measured for the fibre sample SI was in the range of 79-81 %. After 10 % compression, the compression recovery of the fibre sample SI was around 97 %.

[0149] The compression strength at 50 % compression was also determined for the samples. Sample SI, made of paper grade pulp fibres, showed a compression strength of around 65-75 kPa. At 10 % compression, the compression strength was around 10 kPa.

[0150] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0151] For example, while the above embodiments mainly discuss elements according to the present disclosure in relation of a sandwich structure with three or more layers, other implementations are also possible. For example, a structure with a compressed fibrous material may be formed using a two-layer implementation. In this kind of embodiments, the second layer may be missing, and the fibrous material may be compressed between the first layer and the mould. In addition, while the above embodiments discuss elements in the form of a curved panel, non-curved implementations of the element are also possible. Further, the shape of an element according to the present disclosure is not limited to panels and board. In some embodiments, an element according to the present disclosure may take the form of a beam. For example, a curved panel as described earlier may be cut into a plurality of curved beams.

[0152] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0153] As used herein, a plurality of items, structural elements, compositionalelements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0154] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0155] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0156] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.REFERENCE SIGNS LIST10 U-shaped light-weight panel12 first layer14 second layer16 middle layer18 curved portion22 mould24 layer assembly 24a first layer of layer assembly24b second layer of layer assembly24c fibrous material layer of layer assembly26 membrane of vacuum bag30 S-shaped light-weight panel 32 first layer34 second layer36 middle layer38a, 38b curved portion

Claims

CLAIMS:

1. An element with a sandwich structure, the sandwich structure comprising:- a first layer,- a second layer, and- a layer of fibrous material between the first layer and the second layer, wherein the fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, wherein the element has a thickness extending through the layers of the sandwich structure, and wherein the layer of fibrous material has been subjected to compression in the direction of the thickness.

2. The element according to claim 1, wherein the element is in the form of a curved panel, wherein said curved panel comprises at least one non-planar surface.

3. The element according to claim 1 or 2, wherein each of the first and the second layer is made from a material selected from the following list: plywood or veneer.

4. The element according to any one of preceding claims, wherein the thickness of the layer of fibrous material is below 100 mm.

5. The element according to any one of preceding claims, wherein the density of the layer of fibrous material is in range 40 kg / m3- 500 kg / m3.

6. The element according to claim 3, wherein the bending strength of the layer of fibrous material is in range 3 - 20 N / mm2.

7. The element according to any one of preceding claims, wherein the three-dimensional fibre network comprises 2 to 20 wt-% of bicomponent fibres, calculated from the dry weight of the three-dimensional fibre network.

8. The element according to any one of preceding claims, wherein the layers of the sandwich structure have been glued together with a wood glue.

9. The element according to any one of preceding claims, wherein at least a portion of the layer of fibrous material is configured to act as a thermally insulating layer.

10. The element according to any one of preceding claims, wherein at least a portion of the layer of fibrous material is configured to act as a sound insulation layer.

11. A method for manufacturing an element, the method comprising:- receiving a layer assembly on a mould, wherein the layer assembly comprises at least: o a first layer, o optionally, a second layer, o a low-density fibrous material on top of the first layer, or between the first layer and the second layer, wherein the low-density fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres,- sealing the mould and the layer assembly within a vacuum bag,- generating a negative pressure within the vacuum bag to compress the layer assembly, and- releasing the negative pressure and unsealing the vacuum bag to obtain the element.

12. The method according to claim 11, wherein the generating of the negative pressure comprises- generating a level of negative pressure that causes an irreversible transformation to the three-dimensional fibre network of the layer of fibrous material.

13. The method according to claim 12, wherein the negative pressure is -0.8 bar or less.

14. The method according to any one of claims 11 to 13, wherein the compressing of the layer assembly is performed as cold pressing.

15. The method according to any one of claims 11 to 14, wherein during the compressing of the layer assembly, the cellulosic and / or lignocellulosic fibres do not undergo any substantial colour change, such as yellowing, as a result of chemical oxidation reactions.

16. The method according to any one of claims 11 to 15, wherein the three-dimensional fibre network comprises 2 to 20 wt-% of bicomponent fibres, calculated from the dry weight of the three-dimensional fibre network.

17. The method according to any one of claims 11 to 16, wherein the three-dimensional fibre network has been obtained by an air-laid process or by foam forming.

18. The method according to any one of claims 11 to 17, wherein the cellulosic and / or lignocellulosic fibres comprise paper-grade baled pulp which has been dry-milled, such as hammer-milled.

19. The method according to any one of claims 11 to 18, wherein the cellulosic and / or lignocellulosic fibres are substantially debonded to each other, such as non-homified.

20. The method according to any one of claims 11 to 19, wherein the debonding has been achieved by treating the fibres mechanically and / or chemically.

21. The method according to any one of claims 11 to 20, wherein each of the first and the second layer is made from a material selected the following list: plywood or veneer.

22. The method according to any one of claims 11 to 21, wherein the density of the low- density fibrous material, before the compressing step, is in range 20 kg / m3- 90 kg / m3.

23. The method according to any one of claims 11 to 22, wherein the first layer, the low- density fibrous material, and the optional second layer have been glued together with a wood glue, to form the layer assembly.

24. An element obtained by the method according to any one of claims 11 to 23.

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