Thermally insulating structure

Abstract

The present invention concerns a thermally insulating structure comprising a first layer comprising a thermally insulating fibrous material, wherein the thermally insulating fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, the three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%, the density of the three-dimensional fibre network is in the range of 15−75 kg / m3, the three-dimensional fibre network is arranged into a layer having a thickness in the range of 3−50 mm, the thermal conductivity (λ10) of the thermally insulating fibrous material is below 0.4 W / (m·K), the airflow resistivity of the thermally insulating fibrous material is below 60 kPa·s / m2.

Description

THERMALLY INSULATING STRUCTUREFIELD

[0001] The present invention belongs to the field of material technology. More specifically, it relates to the field of thermally insulating fibrous material, in particular thermally insulating materials comprising cellulosic and / or lignocellulosic fibres.BACKGROUND

[0002] Food service sector requires packaging that enables contents of the packaging to stay at constant temperature. Growth in segments like online food delivery services are driving demand for such packaging solutions. Current solutions are typically single-use isothermal plastic bags made from fossil-based plastic, such as metallized PET and PE, or re-usable cooler bags. Fibre-based alternative solutions are typically paper-based.

[0003] Since the materials currently used as thermal insulation in packaging solutions most commonly comprises elements of fossil-based materials, the packaging is typically difficult to recycle and thus contribute to a negative environmental impact when the end of the product lifespan is reached. There is thus still a need for alternative packaging materials providing thermal insulation and with lower environmental impact than fossil-based materials.

[0004] In packaging applications, thermally insulating materials are used, for example, for food transports, keeping the food either cold or hot. In such applications the packaging material becomes in close contact with the food product, which typically transfer moisture into the thermally insulating material, either through condensation due to temperature changes or through direct evaporation from hot content. It is well known that fibrous cellulosic and lignocellulosic materials are hydrophilic and absorbs moisture, thus decreasing the thermal insulation properties of the material as water has higher thermal conductivity than the dry fibres. Furthermore, in loose fibre networks, typically required to achieve good insulation properties, the accumulated moisture makes the fibres heavier and will also increase the formation of fibre bundles or lumps, in particular when pressed together by the weight of an object or by touch, whereby a more compact structure is formed. This will further decrease the thermal insulation properties, as the structure becomes morecompact, thereby reducing the void space within the network, providing insulation properties.

[0005] With increased awareness of the negative impact of fossil-based single used packaging, there is a demand for more environmental packaging solutions providing thermal insulation during transportation of goods, in particular transportation of food products.SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present invention, there is provided a thermally insulating structure comprising a first layer comprising a thermally insulating fibrous material, wherein:- the thermally insulating fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres,- the three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%- the density of the three-dimensional fibre network is in the range of 15-75 kg / m3,- the three-dimensional fibre network is arranged into a layer having a thickness in the range of 3-50 mm,- the thermal conductivity ( io) of the thermally insulating fibrous material is below 0.4 W / (nrK),- the airflow resistivity of the thermally insulating fibrous material is below 60 kPa-s / m2.

[0008] According to a second aspect of the present invention, there is provided a thermally insulated container, such as such as a thermally insulated bag or a thermally insulated box, comprising the thermally insulating structure according to any of the preceding claims.

[0009] A third aspect of the present invention concerns the use of the thermally insulated container according to the second aspect of the present invention for temporary or short-term storage of cold or hot food or beverage.

[0010] More specifically the present invention is characterized by what is stated in the independent claims. Some specific embodiments are defined in the dependent claims.

[0011] In some embodiments, the invention provides a pulp fibre based, reusable and recyclable alternative to existing fossil-based isothermal bags.

[0012] Compared to typical plastic-based isothermal packaging solutions, some embodiments of the invention allow the packaging to be used for applications that require good support, such as pastries or cakes.

[0013] Moreover, the low density thermally insulating fibrous material layer may offer benefits, such as increased comfort during carrying.

[0014] In addition to thermal insulation, the combination of paperboard and low density thermally insulating fibrous material may also provide cushioning for fragile items against external impact forces.

[0015] Thermal conductivity of the present thermally insulating fibrous material layer may be at comparable level to fossil-based alternatives, such as polyurethane and PE-based foam.

[0016] The present low density thermally insulating fibrous material may also act as a cushioning material against impact shock.

[0017] Another advantage of the invention is that the thickness, composition and density of the thermally insulating fibrous material can be easily altered for different applications, and that it can be combined with various types of second layers, for example to provide improved moisture resistance or mechanical stability. The structure comprising thermally insulating fibrous material can be provided in the form of a rollable continuous sheet, which provides for easy handling and numerous alternatives with respect to foldable structures that can be pre-cut from sheets. Such sheet materials can comprise additional layers for desired functionality. Pre-cut structures can be space efficiently transported and stored, which in turn provides sustainable alternatives to current fossil-based, thermally insulating transport solutions used for food delivery services, or kept at hand for the consumer in supermarkets and bakeries, for example.

[0018] A further advantage of the present invention is that the thermally insulating fibrous material can be recycled in both standalone form and in layered form, preferably in a paperboard recycling process.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIGURE 1 illustrates manufacturing of a thermally insulating structure according to an embodiment of the present invention.EMBODIMENTS

[0020] In the present context, the term “fibrous cellulosic material” or “cellulosic fibres” typically refers to cellulosic and / or lignocellulosic fibres. Such fibres may be of plant origin.

[0021] 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 unbleached chemical 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.

[0022] Thermal conductivity (XI 0) of the thermally insulating fibrous material is measured according to SFS-EN 12667.

[0023] Airflow resistivity of the thermally insulating fibrous material is measured according to EN SFS-29053.

[0024] 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”.

[0025] 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.

[0026] In the present context, the term ’’debonded fibres” may refer to loose fibres or defiberized fibres. Such debonding may be achieved by treating the cellulosic fibres mechanically and / or chemically.

[0027] In some embodiments, the invention described here combines paperboard with low density thermally insulating fibrous material to enable new product designs in the packaging segment. In some embodiments, complementing properties are provided, particularly thermal insulation capacity and softness of fibre foams, and stiffness of paperboard. In some embodiments, the present packaging may be produced efficiently, by applying or attaching a low density thermally insulating fibrous mat on paperboard directly from a roll prior to folding to final shape.

[0028] The present disclosure provides a thermally insulating structure, which provides for insulation and padding in packaging solutions. The structure is in particular suitable for use in short-term applications. Within the current disclosure, short-term applications refer in particular to single use applications, such as packaging material. The term short-term applications herein also includes repeated use for a limited time, such as for five to ten times.

[0029] In particular, the present disclosure concerns a thermally insulating structure comprising a first layer comprising a thermally insulating fibrous material, wherein:- the thermally insulating fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres,- the three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%- the density of the three-dimensional fibre network is in the range of 15-75 kg / m3,- the three-dimensional fibre network is arranged into a layer having a thickness in the range of 3-50 mm,- the thermal conductivity ( io) of the thermally insulating fibrous material is below 0.4 W / (nrK),- the airflow resistivity of the thermally insulating fibrous material is below 60 kPa-s / m2.

[0030] The thermally insulating structure as described above comprises a first layer comprising a thermally insulating fibrous material. The thermally insulating fibrous material comprises or consists of a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, providing the structure with insulating properties. In some embodiments, the first layer of a thermally insulating fibre material consists of a thermally of a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres as defined above.

[0031] The high content of biobased material, being at least 80 wt-% in the three- dimensional fibre network, contribute to improved recyclability and biodegradability of the structure. Said density and thickness range together provide for a flexible and rollable material, which still exhibit both a stability required of the fibrous network in use, as well as insulation properties due to the relatively low density of not more than 75 kg / m3, which allows for the inclusion of isolating void volume in the network.

[0032] In some embodiments of the thermally insulating structure, the thermal conductivity ( io) of the thermally insulating fibrous material is 0.3-0.4 W / (m-K).

[0033] In further some embodiments of the thermally insulating structure, the airflow resistivity of the thermally insulating fibrous material is 10-30 kPa-s / m2, preferably 20-30 kPa-s / m2.

[0034] In some embodiments of the thermally insulating structure, the G value of the thermally insulating fibrous material is in the range 60 - 140, after the first drop in the plate drop test. The G value is determined according to the standard ASTM-D1596.

[0035] In some embodiments of the thermally insulating structure, the indentation hardness of the thermally insulating fibrous material is 150-1400 N, preferably 300-1300 N, even more preferably 350-1200 N, as determined according to ISO 2439:2008, Method A. The above presented indentation hardness is expressed as the force (N) applied when the thermally insulating fibrous material is compressed 40 % from the initial thickness (mm). A material with an indentation hardness within the above range can withstand temporary pressure, providing a three-dimensional stability required for the material not being completely flattened under pressure, thus maintaining insulating properties and providing cushioning properties to the packaging material.

[0036] In some embodiments of the thermally insulating structure, the compression recovery, after compression into 50 % of the initial thickness of the thermally insulating fibrous material, is at least 70 %, preferably at least 75 %, even more preferably at least 80 % of the initial thickness of the thermally insulating fibrous material. A compression recovery in said ranges provides for a material that after compression can revert back to its original thickness, or at least 70 % of its original thickness. In particular in packaging applications, this is an important property, as the products to be transported temporarily will compress the insulation material. The materials capacity to spring back into its original shape ensures even insulation properties also after compression. Furthermore, a compression recovery in said range provides for cushioning properties, protecting the products from external stress under transportation, such as the weight of other products transported in the same bag. The thermal insulation properties, as well as the cushioning properties, i.e., impact or vibration damping properties of the thermally insulating structure are attributed to the three-dimensional fibre network comprising cellulosic and / or lignocellulosic fibres.

[0037] Thus, the inclusion of such a fibre network will reduce or even replace fossilbased material currently used for the purpose.

[0038] In some embodiments of the thermally insulating structure, 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, regenerated fibres, or any combination thereof.

[0039] Preferably, the cellulosic and lignocellulosic material is a wood-derived material, even more preferably wood derived pulp. Being renewable, wood derived materials, such as the above listed materials, are a sustainable alternative to fossil-based materials. Currently, such materials have not been widely employed in packaging providing thermal insulating properties, and in particular not in the food sector as packaging directed to the food delivery sector or the consumer.

[0040] In some embodiments of the thermally insulating structure, the fibres of cellulosic and / or lignocellulosic material comprise paper-grade baled pulp which has been dry-milled, such as hammer-milled.

[0041] In some embodiments of the thermally insulating structure, the fibres of cellulosic and / or lignocellulosic material are substantially debonded to each other, such as non-homified.

[0042] In some embodiments of the thermally insulating structure, the debonding has been achieved by treating the fibres mechanically and / or chemically.

[0043] 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 1-2.5 mm.

[0044] The term “fibre length” refers to the distance measured along the longest dimension of the fibre.

[0045] The three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%, preferably 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 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 network.

[0046] 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 materials. The inclusion of cellulosic and / orlignocellulosic fibres in the above amounts also enhances the recyclability and biodegradability properties of the material, as at least 80 wt.-% 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 improved mechanical stability, improved 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. Preferably, such agents or fibres are biobased and / or biodegradable, such that the entire network can be recycled or processed in a single product. In particular additives may be used to improve the mechanical stability and flexibility of the material, such that the insulating structure can be wrapped around products without being compressed, and also have a good capacity to revert into full thickness after compression, thus maintaining thermal insulation capacity. Furthermore, mechanical strength properties are needed for the material not to be teared apart, for example by sharp edges of food packaging transported in the thermal insulation material. Thus, one or more additives, such as a binding agent, a functionalisation agent or a modifier, may be included in the material to improve the mechanical stability and reversible deformation properties, i.e., compression recovery, of the three-dimensional fibre network. The mechanical stability of the material can also be improved by the addition of hydrophobation agents, as the insulating material in use will be subjected to temperature differences, whereby moisture tend to condensate on at least one surface of the insulating material. Alternatively, or additionally, other functional additives can be included. Any additives may be comprised in the three-dimensional fibre network in a total amount of from 0.5-20 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-%, or 20 wt-%, calculated from the dry weight of the three-dimensional fibre network layer. 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.

[0047] In some embodiments of the thermally insulating structure, the thermally insulating fibrous material comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%, such as at least 90 wt-%, calculated from the total dry weight of the thermally insulating fibrous material. In such embodiments, not only the three-dimensional fibre network consists mainly of cellulosic material, but the entire thermally insulating layerhave the benefit of being biobased. Thus, the thermally insulating layer can comprise, for example paper or cardboard based surfaces, giving further protection to the three- dimensional fibre network that provides for insulating properties.

[0048] In some embodiments of the thermally insulating structure, the three- dimensional fibre network comprises synthetic fibres or thermoplastic fibres or biobased fibres. In particular, such fibres can be included to alter the properties of the thermally insulating fibrous material. For example, thermoplastic fibres can be included to increase the mechanical stability or compression recovery properties, as discussed above. Biobased fibres can be included to alter the properties without reduction in biodegradability of the material. Furthermore, such additional fibres can be included to increase the mechanical stability of the material upon exposure to moisture.

[0049] The melting point of at the thermoplastic fibres can be less than 250 °C, such as less than 220 °C, such as less than 200 °C, such as less than 150 °C, or in the range 60 to 220 °C.

[0050] By heat treatment of a three-dimensional fibre network comprising thermoplastic fibres above the melting point thereof, the thermoplastic fibres can function as a binding and stabilisation agent. The melted, or partially melted fibres will provide for inter-fibre connection and increased mechanical stability upon solidification. Such thermoplastic fibres can be produced from biobased thermoplastic polymers, such as polylactic acid. When applied onto the surface of the three-dimensional fibre network, such thermoplastic fibres can also act as an adhesive.

[0051] In some embodiments of the thermally insulating structure, the three- dimensional fibre network comprises bicomponent fibres, such as synthetic bicomponent fibres or thermoplastic bicomponent fibres or biobased bicomponent fibres. Such bicomponent fibres can function as binding composition within the fibre network and provide for additional functionality, such as improved mechanical stability when subjected to pressure of moisture. Furthermore, bicomponent fibres may act as binding agent between fibres within the network or between the fibre network and any additional layers within the structure.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The three-dimensional fibre network of the thermally insulating structure 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.

[0056] The melting point of at least one component of the bicomponent fibre may be less than 250 °C, such as 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 sheath-component and the melting point of the core-component enables melting of the sheath-component while the core-component remains in solid form. By subjecting the three-dimensional fibre network to heat treatment above the melting point of the bicomponent fibre, 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.

[0057] 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. Improved structural support will in turn improve the material’s capacity to maintain its initial shape and thereby its thermal insulation properties, as the void volume of the three-dimensional fibre network maintains essentially unchanged under pressure.

[0058] The fibre network of the thermally insulating fibrous material may comprise from 2 wt-%, 3 wt-%, 5 wt-% or 10 wt-% and up to 10 wt-5, 12 wt-%, 15 wt-%, or 20 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.

[0059] In further embodiments, the thee-dimensional fibre network comprises expandable microspheres, which can function as binding composition. 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 contribute to a higher void volume within the three-dimensional network, as it simultaneously provides for binding properties within the three-dimensional fibre network and resilient properties caused by thehollow or cellular structure of the binding agent upon expansion, thus contributing to improved reversable deformation of the three-dimensional fibre network. A high void volume and improved reversable deformation contribute to improved thermal insulation properties.

[0060] 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 three-dimensional fibre network can comprise a binder composition as disclosed herein, such as bicomponent fibres or microspheres.

[0061] In some embodiments of the thermally insulating structure, 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.

[0062] In a preferred embodiment, the chemically treated fibres are non-derivatized cellulosic and / or lignocellulosic fibres treated with deep-eutectic solvent (DES).

[0063] A further example of solvent treatment is treatment with alkali, such as sodium hydroxide (NaOH).

[0064] In some embodiments of the thermally insulating structure, the thermally insulating fibrous material comprises additive chemicals selected from binding agents, barrier agents, foaming agents, surfactants, mould inhibitors, odour suppressing agents, blowing agents, lightweight fillers, bulk improvement agents, pigments, micro- or nanofibrillated cellulose, or combinations thereof. Such additives can be added to alter thestructural properties, to assist in the formation of a three-dimensional fibre network, or to alter the feel and / or visual appearance of the thermally insulating material.

[0065] In some embodiments of the thermally insulating structure, the three- dimensional fibre network is arranged into a layer having a thickness in the range 5-30 mm.

[0066] Within the present disclosure, the three-dimensional fibre network is arranged into a layer having a thickness in the range of 3-50 mm. The insulating properties are dependent on a combination of the thickness and void fraction of the layer, the latter typically corresponding to the density of the layer. A thicker layer typically provides for better insulation, in particular when the insulation material otherwise is identical. In some embodiments, the thickness may be from 5 mm, 7 mm, 10 mm, 15 mm, or 20 mm up to 8 mm, 10 mm, 15 mm, 25 mm, 35 mm, or 50 mm. A relatively thin layer, with a thickness in the range of, for example from 3 or 5 mm up to 8, 10, 15 or 20 mm is beneficial in many short time packaging applications, where a space efficient storage of the packaging is desired, still providing sufficient insulation during shorter transports, such as is typical for food home delivery applications. Thicker materials, such as from 20 mm, 25 mm or 30 mm up to 35 or 50 mm can in turn be beneficial in applications where the transport is longer, or where a larger volume of products is transported in the same packaging unit, for example a as an outer transport box for individually packed food portions. It should be noted that the above-mentioned thicknesses and uses only are provided as examples. By the use of additional layers, the properties of the structure can be further optimized according to the intended end use and desired properties of the thermally insulating structure.

[0067] In some embodiments of the thermally insulating structure, the thermally insulating layer exhibits a density gradient across its thickness. Such a structure can provide for both good mechanical stability and insulation properties. The denser part can provide rigidity to the insulating structure, while the lower density part improves the insulation properties.

[0068] The softness, i.e., compressibility, of the thermally insulating fibrous material is typically dependent on the density of the three-dimensional fibre network. When the chemical and physical composition of a fibre network is the same, a lower density will provide a softer material, i.e., a material with a higher degree of compression under the same load, than a higher density material. When providing a thermally insulating fibrous material with a density gradient, one can take advantage of these differences in properties to obtaindesired features. A more dense or harder material can be used to provide mechanical stability, for example as an outer layer, i.e., surface layers for more even distribution of the pressure that products stored in the packaging will cause onto the surface, thus preventing the softer portion from reaching a point of irreversible deformation, such as a point where fibre buckling occurs. On the other hand, the softer portion of the thermally insulating structure can, in addition to insulation, provide for cushioning properties.

[0069] In some embodiments of the thermally insulating structure, at least 70%, preferably at least 80%, even more preferably at least 90% of the total volume of the thermally insulating structure consists of said thermally insulating fibrous material or materials. In such embodiments, the majority of the thermally insulating structure is produced from biodegradable and renewable materials. Likewise, as most of the structure volume constitutes of the thermally insulating fibrous material, the total weight of the structure does not increase such that it has a negative effect on handling and transport costs. In some embodiments, the thermally insulating fibrous material consists of the three- dimensional fibre network of cellulosic and / or lignocellulosic fibres.

[0070] In some embodiments, the three-dimensional fibre network is 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-laying technique), air-laying technique or foam forming or any combination thereof.

[0071] In some embodiments, the fibres of cellulosic and / or lignocellulosic material are paper grade pulp fibres, preferably provided as baled pulp. 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.

[0072] In some embodiments of the thermally insulating structure, the first layer has been obtained by a method comprising forming the fibres of cellulosic and / or lignocellulosic material into a three-dimensional fibre network by an air-laying technique. Advantages of using an air-laying technique are that the obtained fibre network is easy to handle, shows homogeneous fibre distribution, and can be directly obtained in a desired thickness. The airlaying technique also allow for uniform inclusion of dry state additives, such as thermoplastic additives, polymeric fibres, or bicomponent fibres.

[0073] By applying an additional 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.

[0074] In some embodiments of the thermally insulating structure, the first layer has been obtained by a method comprising forming the fibres of cellulosic and / or lignocellulosic material into a three-dimensional fibre network by a foam forming technique. The foam foaming technique, i.e., foam assisted forming technology, allows for the formation of a mechanically stabile three-dimensional network without the use of binding agents, as the interaction between wet fibres forms a network of fibres .

[0075] Additionally, by forming the three-dimensional fibre network in wet state by foam assisted web formation, it is 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. Furthermore, the foam forming technique, allows for inclusion of additives in wet state without applying further drying steps prior to the formation of the fibre network.

[0076] Foam forming technology can be used in the formation of three-dimensional fibre network layers in the thickness ranges as disclosed herein.

[0077] 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 thermally insulating fibrous material as presented herein.

[0078] 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.

[0079] In some embodiments, the three-dimensional fibre network is obtained by continuous web forming or by mould-assisted forming.

[0080] Such a foam formed three-dimensional fibre network can be included in or constitute a thermally insulating structure according to the present disclosure.

[0081] If desired, 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, as no additional drying step is required when the treatment of the fibres and the formation of the three-dimensional network is carried out in a continuous process.

[0082] 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.

[0083] In other embodiments, any additive, such as a binding agent, can 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.

[0084] In some embodiments, the thermally insulating structure comprises a further layer comprising, independently of the first layer, a thermally insulating fibrous material. Such a further layer can comprise a thermally insulating fibrous material that have a composition differing from the material of the first layer or a composition being identical to that of the first layer. That is, the structure can comprise one or more layers of thermally insulating fibrous material comprising a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres, optionally in combination with a further layer comprising a thermally insulating fibrous material.

[0085] In some embodiments, the first layer and the further layer have a different composition and / or a different density. By combining layers of differing composition and / or density, the insulating properties and mechanical stability of the material can be altered, simultaneously maintaining the inclusion of biobased fibres, in particular cellulosic fibres, as high as possible. Thus, any further layer can be a layer according to the first layer of the first aspect of the present disclosure, or any other kind of thermally insulating fibrous material.

[0086] In some embodiments, the first layer and the further layer have been adhered to each other through heat treatment to at least partially melt and / or activate any binder compositions and / or bicomponent fibres within the three-dimensional fibre network, by means of adhesives, or by mechanical attachment. By heating the multilayer material, or the surfaces of individual layers, to a temperature above the melting point of a binder composition and / or a at least one component of the bicomponent fibres contained therein, the layers may be adhered to one another upon being contacted in the still melted stage. Alternatively, or additionally, adhesives, such as glues or sizing agents, can be used for adhering layers. Further possibilities include adhesion through mechanical means, such as by sewing.

[0087] When the layers are adhered together, it will minimize the risk of the layers being separated or gliding apart in the structure, thus forming portion with differing insulating properties, i.e., portion without an thermally insultation fibrous material and portions with a thicker insulation material. Such adhered layers also include releasable adhering, enabling separating the layers from each other prior to disposal of the structure.

[0088] In some embodiments, the thermally insulating structure comprises a second layer, preferably attached onto the first layer. The second can be any layer, such as a protective layer. Thus, the term second layer herein refers to a layer that is not limited to a layer comprising thermally insulating fibrous material. The thermally insulating structure can comprise one or more second layers, which can form intermediate layers or surface layers. Preferably, the second layer is attached, such as releasably attached, onto the first layer. The second layer can be attached onto one side or both sides of the first layer. In some embodiments where both sides of the first layer have a second layer attached thereto, the structure and material of the second layer can differ from each other or be identical. The addition of a second layer allows for the production of versatile packaging products. In someembodiments, the thermally insulating structure can comprise a second layer which forms an intermediate layer between two first layers. For example, a paper layer, such as a greaseproof paper layer, may form an intermediate layer between two first layers, each of the first layers comprising a thermally insulating fibrous material independently of each other.

[0089] The second 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 mould inhibitor, a binding agent, a barrier agent, an odour suppressing agent, a pigment, or combinations thereof. The thickness of the protective layer can be, for example, less than 5 mm or less than 3 mm, such as ranging from 0.01 to 2 mm, for example ranging from 0.01 to 0.09 mm or from 0.3 to 1 mm, or from 0. 5 to 2 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 layer of thermally insulating fibrous material, or binding properties between layers.

[0090] According to a second aspect of the present invention, the thermally insulating structure is a multilayer structure comprising two or more layers, including the first and second layers, such as 2, 3, 4 or 5 layers, wherein at least one layer comprises the thermally insulating fibrous material according to the present disclosure.

[0091] In some embodiments of the thermally insulating structure, the second layer comprises paper, such as kraft paper or greaseproof paper, or paperboard, such as linerboard or folding boxboard. Such a thermally insulating structure can be fully biodegradable. A thermally insulating structure comprising paper or paperboard as a second layer is can be used, for example, in the production of thermally insulating bags and thermally insulating boxes. A second layer of paper forms a thermally insulating structure that is both light and flexible. The structure can thus be tightly wrapped around the product and only takes a little space when not in use. The structure also allows for the formation of thermally insulting bags, which are easy to carry. On the other hand, a second layer of cardboard provides stability to the package, which therefore makes it suitable for the transportation of, for example, bakery products. The structure with a second layer of cardboard can be folded into boxes of various shapes, optionally with the aid of pre-cut folding lines. A second paperboard layer can also be used in combination with a relatively thick first layer, forexample comprising a three-dimensional fibre network arranged into a layer having a thickness in the range of 20-50 mm. Such a thermally insulating structure can provide for the insulation needed for longer storage times, or for a more durable construction that can be used as an outer storage box in delivery cars. Thus, the food delivery service can during the transport store several smaller packages, optionally with independent thermally insulating packaging, in one storage box providing an outer shell of thermally insulting material. When compared to traditional expanded polystyrene packaging, the storage box can be disposed with a smaller environmental impact upon becoming contaminated, for example in the transport of hot foods or beverages.

[0092] In some embodiments, the second layer comprises paperboard which is selected from the group of folding boxboard, liner board and food service board. The grammage of the paperboard may be in the range 150 to 220 g / m2, such as 180 to 200 g / m2. The paperboard may have a three-layer structure.

[0093] In some embodiments, the paper or paperboard can be provided with a barrier layer, such as a barrier film for moisture resistance. Preferably, such a barrier is biobased. The barrier may be provided as a functionalization agent onto the surface of the paper or paperboard, or as a laminate.

[0094] In some embodiments of the thermally insulating structure, the second layer comprises a plastic coating layer, such as a thermoplastic coating layer. The plastic coating can be adhered to the first layer or it can be formed as an envelope structure. For applications where there is a high risk of moisture exposure, such as when the temperature difference is large or the food to be transported is in liquid form, a plastic coating arranged as an outer layer in contact with the food packaging provides protection to an inner first layer. A plastic coating layer can prolong the total lifespan of the packaging, and upon end of life, the first and second layer can be recycled together of separated for individual recycling processes. The latter does in particular apply when the first and second layer are not adhered to each other, whilst simultaneous recycling can be preferred when biopolymers are used.

[0095] In some embodiments of the thermally insulating structure, the second layer comprises a nonwoven web. The nonwoven web can provide a protective surface onto the first layer and makes it more durable, for example through improved resistance to tear.

[0096] In some embodiments of the thermally insulating structure, the first layer and the second layer have been attached to each other by adhesive. When the first and second layers are attached to each other by adhesive, the two layers can be prevented from gliding apart, thus forming portions in the structure where the thermal insulation is impaired.

[0097] In some embodiments of the thermally insulating structure, the thermally insulating structure is recyclable in paper or paperboard recycling processes.

[0098] In some embodiments of the thermally insulating structure, the structure is in the form of a sheet or a slab. Such structures enable the production of a wide variety of products by cutting and folding. Preferably, a packaging produced from a sheet or a slab can be stored unfolded or as bags stacked on top of each other.

[0099] In particular, the “sheet” or the “slab” has two opposite planar surfaces which are generally orientated in parallel. The term “slab” or “sheet” may refer to a separate, discrete object or to a layer that forms an integral part of a larger object. In the density range as disclosed herein, i.e., densities up to 70 kg / m3and thicknesses from 3 mm up to 50 mm, the “slab” or “sheet” is typically flexible so that it can be rolled. A rollable structure can allow easier handling, for example during transportation and storage.

[0100] In some embodiments, one or both surfaces of the thermally insulating structure, particularly one or both surfaces of the first layer, may be imprinted or patterned, for example by using inkjet, gravure, flexo, laser or offset printing methods. Inkjet printing may be a suitable method for thicker structures, such as with thicknesses of at least 50 mm. Such an imprinting may reduce dustiness and dusting of the surface.

[0101] A second aspect of the present disclosure concerns a thermally insulated container, such as a thermally insulated bag or a thermally insulated box, comprising the thermally insulating structure according to the first aspect of the present disclosure or any embodiment thereof.

[0102] A third aspect of the present disclosure concerns the use of a thermally insulated container according to the second aspect of the present disclosure, or any of the embodiments thereof, for temporary or short-term storage of cold or hot food or beverage. Such products can be single use packaging, or packaging intended for home delivery of meals, beverages, confectionary or frozen food products.

[0103] Examples

[0104] In the following, non-limiting examples of the present disclosure are presented.The examples are only intended to illustrate the properties and functionality of the thermally insulating fibrous material of the present disclosure, without being restricted thereto. Thus, any method steps and compositions as presented herein can be combined with other features of the present disclosure.

[0105] Example 1 - Formation of air-laid three-dimensional fibre network

[0106] Three-dimensional fibre networks as included in the thermally insulating fibrous material of the present disclosure were prepared at different densities using the same composition and the same formation technique (air-laying).

[0107] The thermally insulating fibrous material was 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.

[0108] 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.

[0109] 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.

[0110] The obtained fibre network was a resilient and durable layer, having an uniform fibre distribution.

[0111] Example 2 - Properties of air-laid material

[0112] 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.

[0113] The materials were subjected to tests for determination of indentation hardness properties. Reference tests were performed on a reference material of polyurethane foam (herein referred to sample N3).

[0114] 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 is compressed 40 % from the initial thickness (mm). The measurement probe used to compress the material had a diameter of 200 mm.

[0115] All tests were performed under test conditions of a temperature of 23°C and a humidity of 50 % Rh.

[0116] The results of the tests are presented in Table 1.Table 1: Test results for indentation hardness.

[0117] Example 3 - Foam assisted forming

[0118] 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).

[0119] 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.

[0120] 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 solid content 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.

[0121] 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.

[0122] Example 4 - Properties of foam formed fibre networks

[0123] Three dimensional fibre-network samples prepared in the above manner, herein referred to as sample Al, were tested for compression strength and recovery. Test were also performed for a PU layer alone as reference sample (sample R3).

[0124] An overview of the properties of the samples prepared are listed in Table 2.Table 2: Properties of samples prepared.

[0125] 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.

[0126] 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 thickness where 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.

[0127] The compression recovery after 50 % compression measured for the fibre samples Al were in the range of 79-81 %. After 10 % compression, the compression recovery of the fibre samples Al was around 97 %.

[0128] The PU foam reference showed a compression recovery of around 97 % after both 50 % compression and 10 % compression.

[0129] The compression strength at 50 % compression was also determined for the samples. Sample Al, 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.

[0130] Additionally, at 10 % compression, reversibility of fibre-based foam (98.5 %) was better compared to polyurethane foam (97 %).

[0131] Example 5 - Cellulosic fibre application to paperboard or linerboard

[0132] A thermally insulated bag (thermobag) according to an embodiment of the present invention was produced by combining two fibre-based materials into one product. A low density thermally insulating fibrous material (air-laid sheet) was attached to another fibre-based material which was paperboard or linerboard or kraft paper from a roll. The manufacturing process steps are depicted in FIG. 1 and described in the following:Step 1 : Reels or sheets: In this step the fibrous materials can be inserted to the converting machine by sheets or reel. There can be multiple fibrous materials to be inserted in this step to create a multilayered structure. For example, air-laid fibres between two paperboard layers or paperboard layer on one side of the air-laid fibres. Materials could be fully or partially cut before the lamination.Step 2: Eamination / gluing: Different fibrous materials are attached together. One option is to use gluing nips, similar that is used in corrugated process or lamination process.Step 3: Cutting device: Material can be cut with rotary or flat bed die-tool. This cutting can be done partially in step 1. This allows the paperboard to be modified before step 2 lamination. This allows to create creases etc. with traditional applications.Step 4: Plank formation: Planks are manipulated to create different structures. For example, planks can be glued to create package structure. Manipulation can also be folding locking mechanism or attaching any additional parts.Step 5: Stacking: The package structures are stacked and prepared for transportation.

[0133] Example 6

[0134] Air flow resistivity and thermal conductivity of the following samples were analysed:Table 3: Samples.

[0135] Airflow resistivity of the samples was determined according to SFS-EN 29053, with three different volumetric air flows. During the measurements, the temperature was 21 °C and the ambient pressure varied in the range 738 - 761 mmHg.

[0136] Thermal conductivity of the samples was determined according to SFS-EN 12667, at an average temperature of +10 °C. The samples were dried at a temperature of +50 °C before the measurement. The test method was a one-sample-piece symmetrical method. During the test, the sample was oriented horizontally and the heat flow was oriented vertically. The analysis device was FOX 600 L 4TC (Sn 09101136).Table 4: Results.

[0137] It is to be understood that the disclosed embodiments 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.

[0138] 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.

[0139] As used herein, a plurality of items, structural elements, compositional elements, 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.

[0140] 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.

[0141] 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 bemade 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.

[0142] 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.

[0143] Unless otherwise stated herein or clear from the context, any percentages referred to herein are expressed as percent by weight based on a total weight of the respective composition.

Claims

CLAIMS1. A thermally insulating structure comprising a first layer comprising a thermally insulating fibrous material, wherein- the thermally insulating fibrous material comprises a three-dimensional fibre network of cellulosic and / or lignocellulosic fibres,- the three-dimensional fibre network comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%,- the density of the three-dimensional fibre network is in the range of 15-75 kg / m3,- the three-dimensional fibre network is arranged into a layer having a thickness in the range of 3-50 mm,- the thermal conductivity ( io) of the thermally insulating fibrous material is below 0.4 W / (m-K),- the airflow resistivity of the thermally insulating fibrous material is below 60 kPa s / m2.

2. The thermally insulating structure according to any of the preceding claims, wherein the thermal conductivity ( io) of the thermally insulating fibrous material is 0.3-0.4 W / (m-K).

3. The thermally insulating structure according to any of the preceding claims, wherein the airflow resistivity of the thermally insulating fibrous material is 10-30 kPa s / m2, preferably 20-30 kPa s / m2.

4. The thermally insulating structure according to any of the preceding claims, wherein the G value of the thermally insulating fibrous material is in the range 40 - 140, preferably 50 - 100, after the first drop in the plate drop test, as determined according to the standard ASTM- D1596.

5. The thermally insulating structure according to any of the preceding claims, wherein the indentation hardness of the thermally insulating fibrous material is 150-1400 N, preferably 300-1300 N, even more preferably 350-1200 N, as determined according to ISO 2439:2008, Method A.

6. The thermally insulating structure according to any of the preceding claims, wherein the compression recovery, after compression into 50 % of the initial thickness of the thermallyinsulating fibrous material, is at least 70 %, preferably at least 75 %, even more preferably at least 80 % of the initial thickness of the thermally insulating fibrous material.

7. The thermally insulating structure according to any of the preceding claims, wherein 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, nonwood pulp, sawdust, regenerated fibres, or any combination thereof.

8. The thermally insulating structure according to any of the preceding claims, wherein the fibres of cellulosic and / or lignocellulosic material comprise paper-grade baled pulp which has been dry-milled, such as hammer-milled.

9. The thermally insulating structure according to any of the preceding claims, wherein the fibres of cellulosic and / or lignocellulosic material are substantially debonded to each other, such as non-homified.

10. The thermally insulating structure according to any of the preceding claims, wherein the debonding has been achieved by treating the fibres mechanically and / or chemically.

11. The thermally insulating structure according to any of the preceding claims, wherein the thermally insulating fibrous material comprises cellulosic and / or lignocellulosic fibres in an amount of at least 80 wt-%, such as at least 90 wt-%, calculated from the total dry weight of the thermally insulating fibrous material.

12. The thermally insulating structure according to any of the preceding claims, wherein the three-dimensional fibre network comprises synthetic fibres or thermoplastic fibres or biobased fibres.

13. The thermally insulating structure according to any of the preceding claims, wherein the three-dimensional fibre network comprises bicomponent fibres, such as synthetic bicomponent fibres or thermoplastic bicomponent fibres or biobased bicomponent fibres.

14. The thermally insulating structure according to any of the preceding claims, wherein the cellulosic and / or lignocellulosic fibres comprise modified cellulosic and / or lignocellulosic fibres.

15. The thermally insulating structure according to any of the preceding claims, wherein the thermally insulating fibrous material comprises additive chemicals selected from binding agents, barrier agents, foaming agents, surfactants, mould inhibitors, odour suppressing agents, blowing agents, lightweight fillers, bulk improvement agents, pigments, or combinations thereof.

16. The thermally insulating structure according to any of the preceding claims, wherein the three-dimensional fibre network is arranged into a layer having a thickness in the range 5~30 mm.

17. The thermally insulating structure according to any of the preceding claims, wherein the thermally insulating layer exhibits a density gradient across its thickness.

18. The thermally insulating structure according to any of the preceding claims, wherein at least 70%, preferably at least 80%, even more preferably at least 90% of the total volume of the thermally insulating structure consists of said thermally insulating fibrous material or materials.

19. The thermally insulating structure according to any of the preceding claims, wherein the first layer has been obtained by a method comprising forming the fibres of cellulosic and / or lignocellulosic material into a three-dimensional fibre network by an air-laying technique.

20. The thermally insulating structure according to any of the preceding claims, wherein the first layer has been obtained by a method comprising forming the fibres of cellulosic and / or lignocellulosic material into a three-dimensional fibre network by a foam forming technique.

21. The thermally insulating structure according to any of the preceding claims, comprising a further layer comprising, independently of the first layer, a thermally insulating fibrous material.

22. The thermally insulating structure according to claim 18, wherein the first layer and the further layer have a different composition and / or a different density.

23. The thermally insulating structure according to claim 18 or 19, wherein the first layer and the further layer have been adhered to each other through heat treatment to at leastpartially melt and / or activate any binder compositions and / or bicomponent fibres within the three-dimensional fibre network, by means of adhesives, or by mechanical attachment.

24. The thermally insulating structure according to any of the preceding claims, comprising a second layer, preferably attached onto the first layer.

25. The thermally insulating structure according to any of the preceding claims, wherein the second layer comprises paper, such as kraft paper or greaseproof paper, or paperboard, such as linerboard or folding boxboard.

26. The thermally insulating structure according to any of the preceding claims, wherein the second layer comprises a plastic coating layer, such as a thermoplastic coating layer.

27. The thermally insulating structure according to any of the preceding claims, wherein the second layer comprises a nonwoven web.

28. The thermally insulating structure according to any of the preceding claims, wherein the first layer and the second layer have been attached to each other by adhesive.

29. The thermally insulating structure according to any of the preceding claims, wherein the thermally insulating structure is recyclable in paperboard recycling processes.

30. The thermally insulating structure according to any of the preceding claims which is in the form of a sheet or a slab.

31. The thermally insulating structure according to any of the preceding claims wherein one or both surfaces of the first layer have been imprinted or patterned, for example by using inkjet, gravure, flexo, laser or offset printing method.

32. A thermally insulated container, such as a thermally insulated bag or a thermally insulated box, comprising the thermally insulating structure according to any of the preceding claims.

33. Use of the thermally insulated container according to claim 32 for temporary or shortterm storage of cold or hot food or beverage.

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