Method for producing a resilient cellulose foam

Abstract

The present invention relates to a method for producing a resilient cellulose foam, the method comprising the steps of: providing a rigid solid cellulose foam having a first thickness; and compressing the rigid solid cellulose foam to a second thickness, wherein the second thickness is smaller than the first thickness, so as to obtain a resilient cellulose foam.

Description

[0001] METHOD FOR PRODUCING A RESILIENT CELLULOSE FOAM

[0002] Field of the invention

[0003] The present invention relates to a method for producing a resilient cellulose foam, a resilient cellulose foam comprising at least one cavity, and use of said resilient foam as a protective packaging insert.

[0004] Background

[0005] Practically all consumer goods need protective packaging to cushion the goods during storage and transportation. It is recognised that there are numerous solutions for packaging and cushioning various goods depending on the physical properties of the goods to be protected and the degree of protection required relating to its application. Examples of these protective packaging materials are polymeric foam materials for packaging, such as polyurethane foam (PU), polyethylene foams (PE), expanded polystyrene (EPS) or expanded polypropylene (EPP). Porous materials for this type of use must be stable, low-weight and easy to manufacture. Due to the increased awareness of the need to use renewable materials, it is highly motivated to replace petroleum-based polymers with polymers from renewable resources.

[0006] There are many challenges with finding foam materials from renewable sources. Many bio-based foams have higher cost of production and lower mechanical performance compared to established foams from petroleum-based sources. Biobased protective materials need to have the same characteristics and properties as petroleum-based protective materials for being the first choice over petroleum-based materials.

[0007] Low weight and good shock absorption of the bio-based foams are examples of crucial characteristics. Cellulose has shown to have a special potential, as the most abundant renewable natural polymer on earth, with its crystalline structure, and the availability of methods for preparing large volumes on an industrial scale. Cellulose- based foams, such as described in WO2023119215A1 , have excellent cushioning properties making them a suitable choice for use in protective packaging applications.

[0008] It is also of importance to be able to customize the shape and form of a foam in a protective packaging to the shape and form of the goods to be protected by the protective packaging. Some cellulose foams are rigid which means that it may be difficult to obtain a tight fit around the goods to be protected. This in turn means that the goods are not always kept in place within the protective packaging, which increases the risk of damaging the goods. It may be particularly challenging to keep objects with a smooth and slippery surface in place due to the low degree of friction between the object and the foam.

[0009] In addition, the height of a rigid cellulose foam may be reduced on e.g. an impact leading to a decrease in the cushioning ability of the foam. The reduction in height will influence the ability of the foam to continue to provide protection also after an impact.

[0010] In contrast, foams from petroleum-based materials can be made to be resilient and thus fit tightly around the goods to be protected, and also recover its original shape upon an impact.

[0011] Thus, there still exists a need for a protective packaging material that is natural, biobased and recyclable and that can fit tightly around the goods it protects as well as to be able to recover its height after an impact.

[0012] Summary of the invention

[0013] It is an object of the present invention to provide a resilient cellulose foam, which is recyclable and made from renewable sources, and which eliminates or alleviates at least some of the disadvantages of the prior art materials.

[0014] It is a further object of the present invention to provide a method for producing a resilient cellulose foam such that the foam can be used in packaging applications where it is crucial to keep the goods to be protected in place within the packaging material, and / or where it is important that the thickness of the foam is not reduced due to an impact.

[0015] The above-mentioned objects, as well as other objects as will be realized by the skilled person in light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0016] According to a first aspect, the present invention relates to a method for producing a resilient cellulose foam, the method comprising the steps of: - providing a rigid cellulose foam having a first thickness;

[0017] - compressing the rigid cellulose foam to a second thickness, wherein the second thickness is smaller than the first thickness, so as to obtain a resilient cellulose foam.

[0018] It has surprisingly been found that by compressing a rigid cellulose foam, the structure of the foam is changed such that it becomes much more resilient. The open cell structure of the rigid cellulose foam is changed when the foam is deformed during compression. The compressed foam has resilient properties such that when it is further compressed, it will to a high extent recover its (compressed) shape. Such a resilient cellulose foam is useful in packaging applications and can be provided with a cavity of a shape corresponding to an object to be protected. The resilient foam will recover its height upon an impact and it will also fit tightly around an object placed in a cavity within the foam. The rigid cellulose foam must be sufficiently compressed for the change in structure to occur and for the foam to obtain resilient properties.

[0019] Prior to compression, the cellulose foam is rigid, or substantially rigid, and has only limited, or no, resilient properties, i.e. it does not expand back to its original height upon compression below a certain degree.

[0020] According to a second aspect, the present invention relates to a resilient cellulose foam comprising at least one cavity extending into the foam from a first surface of the resilient cellulose foam. The foam according to the second aspect is obtainable by the method according to the first aspect.

[0021] The resilient cellulose foam of the present invention is provided with at least one cavity for holding an object to be protected. The resilient properties of the foam help keeping an object in place within the cavity, also when the object has a smooth and slippery surface. In a preferred embodiment, the dimensions of the cavity is in addition arranged to be slightly smaller than the corresponding dimensions of the object to be protected, and the combination of the resilient properties of the foam and the smaller dimensions will ensure that the object is kept tightly within the cavity and prevent that it falls out during for example an impact or during shipping. The resilient cellulose foam is made from renewable resources and can be redispersed in water and as a result be recyclable in regular paper recycling streams.

[0022] According to a third aspect, the present invention relates to use of the resilient cellulose foam according to the second aspect as a protective packaging insert, wherein an object to be protected is held in place in the cavity of the resilient cellulose foam. Due to the resilient properties of the foam, the object is held tightly in place within the cavity. Therefore, the resilient foam of the present invention is suitable for use for delicate and / or fragile objects where it is important that the object is kept tightly in place during e.g. transport.

[0023] Detailed description

[0024] The term “foam”, as used herein, refers to a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets. Three requirements must be met in order for foam to form. Mechanical work is needed to increase the surface area. This can occur by agitation, dispersing a large volume of gas into a liquid, or injecting a gas into a liquid. The second requirement is that a foam forming agent, typically an amphiphilic substance, a surfactant or surface-active component, must be present to decrease surface tension. Finally, the foam must form more quickly than it breaks down.

[0025] The term “cellulose foam”, as used herein, refers to a foam comprising cellulose, and other components such as thickeners, surfactants and additives. The main component of the cellulose foam is cellulose, such that cellulose constitutes at least 70 wt% of the dry content of the cellulose foam. Cellulose is in the form of fibres, and the foam can thus also be defined to be a fibrous foam or a cellulose fibre foam. The cellulose foam may be wet or solid.

[0026] The term “wet foam”, or “wet cellulose foam”, as used herein, refers to a wet foam comprising cellulose, and other components such as thickeners, surfactants and additives. Gas bubbles are present within the wet foam. The wet foam is freestanding and behaves as a viscoelastic solid. This means that the wet foam has both viscous and elastic properties. The wet foam will behave as a solid, and thus be freestanding, unless a large enough force is applied so that it starts to flow and instead behave as a viscous material. Depending on the magnitude and timescale of any applied shear stress, the wet foam can show a predominantly viscous or elastic behaviour.

[0027] The term “solid cellulose foam”, or “solid foam”, as used herein, refers to a dry porous cellulose material that has been formed from a wet cellulose foam, i.e. a foam formed material. During the drying process, a closed wet cellulose foam is transformed into an open solid cellulose foam. The network of cellulose fibres is prevented from collapsing during drying. The solid cellulose foam will as a result have a shape that to a large extent corresponds to that of the wet cellulose foam. After drying, the dry content of the solid cellulose foam is at least 95 wt% as calculated based on the total weight of the solid cellulose foam. The shape and density of the solid cellulose foam is retained also in a non-confined state. The solid cellulose foam has an open cell structure, allowing air to occupy the pores within the foam. The solid cellulose foam can also be described as a porous material or a low- density material.

[0028] The cellulose foam preferably used as a starting material in the method according to the present invention will now be described in detail.

[0029] The cellulose foam used in the present invention may comprise cellulose fibres in a range of from 71 to 95 wt%, such as from 75 to 95 wt%, based on the total dry weight of the cellulose foam.

[0030] Cellulose fibres suitable for use in the present invention can originate from wood, such as softwood or hardwood, from leaves or from fibre crops (including cotton, flax and hemp). The cellulose fibres suitable for use in the present invention can also originate from regenerated cellulose such as rayon and Lyocell. The cellulose fibres suitable for use in the present invention may include lignin or hemicellulose or both, or the cellulose fibres may be free from lignin and hemicellulose. Preferably, the cellulose fibres originate from wood, more preferably the cellulose fibres are pulp fibres obtained by pulping processes which liberates the fibres from the wood matrix. Pulp fibres can be liberated by mechanical pulping, obtaining mechanical pulp such as thermomechanical pulp (TMP) or chemical thermomechanical pulp (CTMP), or by chemical pulping such as Kraft pulp or pulps obtained by the sulphite process, soda process or organosolv pulping process. More preferably, the cellulose fibres are pulp fibres liberated by chemical pulping processes. The different characteristic of each cellulose fibre will affect the properties of the final cellulose foam. A cellulose fibre is significantly longer than it is wide. Cellulose fibres can have a mean width of 0.01 to 0.05 mm. The fibre length of softwood can be from 2.5 to 4.5 mm, while hardwood can have a fibre length from 0.7 to 1 .6 mm, and Eucalyptus from 0.7 to 1 .5 mm. However, the fibre length can vary considerably with different growing place etc. The cellulose fibres in the cellulose foam disclosed herein can have a length from 0.1 mm to 65 mm, or from 0.1 mm to 10 mm, or from 0.5 mm to 65 mm, or from 0.5 mm to 10 mm, or from 0.5 mm to 7mm. The fibre lengths may provide different mechanical characteristics to the foam. Due to the length of fibres, they can entangle with each other and impart fibre to fibre interbonds that bring strength to the foam. The aspect ratio, i.e. the ratio of the fibre length to the fibre width, of the cellulose fibres in the cellulose foam according to the present invention can be at least 10, at least 25, at least 50, at least 75, or at least 100, which provides for preservation and stabilization of the foam structure during the drying procedure, making it possible to dry the wet cellulose foam with retained shape. The aspect ratio can be up to 6500, or preferably up to 2000.

[0031] The cellulose fibres may be modified to provide different properties to the final cellulose foam. For example, phosphorylated fibres or periodate oxidized fibres could also be used when producing a cellulose foam according to the present invention.

[0032] Preferably, the cellulose fibres are selected from wood pulp, such as softwood Kraft bleached pulp, hardwood pulp, chemical-thermomechanical pulp, and from dissolving pulp, or a combination of one or more of these. More preferably the cellulose pulp fibres are from softwood pulp, chemical-thermomechanical pulp, or dissolving pulp. Most preferably the cellulose pulp fibres are from softwood pulp, such as softwood Kraft bleached pulp.

[0033] The cellulose foam used in the present invention preferably comprises cellulose fibres in a range of from 71 to 95 wt%, such as from 75 to 95 wt%, based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of from 4 to 24 wt%, such as from 5 to 20 wt%, based on the total dry weight of the cellulose foam, and at least two surfactants. The water-soluble thickener may have a molecular weight of from 80 000-250 000 g / mol, or from 83 000-197 000 g / mol. Exemplary water-soluble thickeners are selected from carboxy methyl cellulose (CMC), methyl cellulose (MC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl hydroxypropyl cellulose (MHPC), starch, xanthan, guar gum, and xyloglucan, or mixtures thereof. The fact that the thickener is water-soluble facilitates recycling of the cellulose foam.

[0034] The water-soluble thickener may improve the fibre-fibre bonding strength, primarily through hydrogen bonding, in the cellulose foam. Therefore, the amount of water- soluble thickener will influence the mechanical performance of the cellulose foam, and especially the bulk of the material. A higher content of water-soluble thickener provides for a stiffer material. Thus, the water-soluble thickener enables tailoring of the mechanical properties.

[0035] The cellulose foam may also comprise a mixture of at least two surfactants. One of the at least two surfactants is preferably a fast-acting surfactant, a suitable surfactant for this purpose is an anionic surfactant, preferably a low-molecular weight anionic surfactant. The anionic surfactant may have an apparent pKa of from 3.2 to 3.8, preferably from 3.4 to 3.6, or an apparent pKa of 3.5 in a solution having a pH of from 7 to 9, preferably a pH of 8. The low-molecular weight anionic surfactant may be selected from sodium dodecyl sulphate (SDS); potassium dodecyl sulphate, sodium laureth sulphate (SLES); sodium dodecylbenzenesulphonate; sodium cocoyl sarcosinate; sodium lauroyl sarcosinate. The low-molecular weight anionic surfactant is preferably selected from sodium dodecyl sulphate (SDS); sodium p-n-dodecylbenzenesulphonate; sodium cocoyl sarcosinate; and sodium lauroyl sarcosinate. More preferably the low-molecular weight anionic surfactant is sodium cocoyl sarcosinate. The anionic surfactant may be biodegradable.

[0036] The other one of the at least two surfactants is preferably a co-surfactant. The cosurfactant may be selected from the group comprising surfactants having an apparent pKa of at least 8, or at least 9, in a surfactant solution having pH of from 7 to 9, preferably having a pH of 8; and amphoteric betaines. The co-surfactant may have maximum apparent pKa of 10. The co-surfactant preferably has a long carbon chain, more preferably a carbon chain with 14 carbon atoms (C14). The cosurfactant may be selected from high pKa fatty acids, such as from plant derived feedstock, e.g. tetradecanoic acid (myristic acid), sodium oleate, lauric acid, palmitic acid, and stearic acid; glucose based co-surfactants with an aliphatic carbon tail, such as alkyl glycosides, alkylpolyglucosides, alkyl thio-glycosides, and alkyl maltosides; amphoteric betaines, such as cocamidopropyl betaine (CAPB), and sodium cocoiminodipropionate (CADP); polyethylene glycol sorbitan monolaurate, i.e. tween® (e.g. tween® 20, tween® 80 and tween® 85); and polyoxyethylene lauryl ethers, such as polyethylene glycol dodecyl ether, pentaethylene glycol monododecyl ether and octaethylene glycol monododecyl ether.

[0037] Thus, the at least two surfactants used in the cellulose foam preferably comprise a mixture of an anionic surfactant and a co-surfactant. The molar ratio between anionic surfactant to co-surfactant may be from 0.2:1 to 3:1 , preferably from 0.5:1 to 2:1 . The total amount of the at least two surfactants together in the cellulose foam may be 0.6-5 wt%, or 0.8-2.0 wt%, as calculated on the total weight of the cellulose foam.

[0038] The solid cellulose foam can be re-dispersed in water and as a result be recyclable in regular paper recycling streams.

[0039] The wet cellulose foam may be prepared using a method comprising the following steps: disintegrating cellulose fibres in water to obtain a slurry of cellulose fibres; adding a water-soluble thickener to the slurry to obtain a mixture of thickener and cellulose fibres in water; adding at least two surfactants to the mixture to obtain a fibre suspension; and aerating the fibre suspension to obtain a wet foam, wherein the wet cellulose foam comprises 10-38 wt% cellulose fibres, 0.5-10 wt% of the water-soluble thickener, and 0.1-2 wt% surfactants, as calculated on the total weight of the wet foam, and wherein the wet cellulose foam has a density of from 120-500 kg / m3, or from 120-400 kg / m3, and a yield stress of at least 80 Pa.

[0040] Addition of a water-soluble thickener increases the viscosity of the slurry and enables incorporation of enough air to generate a densely packed foam during aeration. Since the cellulose fibres are mixed in high concentrations a drainage step is not needed, which enables the use of a water-soluble bio-based thickener in high concentrations. Addition of a fast-acting surfactant will contribute to the formation of a cellulose foam with a high density and a high viscosity as it will quickly settle at the air-water interphase during aeration. This enables a free-standing wet cellulose foam.

[0041] Addition of a co-surfactant along with the fast-acting surfactant will further improve the properties of the cellulose foam since it will facilitate the action of the fast-acting surfactant. A co-surfactant having a suitable pKa and a long carbon chain further contributes to a stable fibre suspension and a stable wet cellulose foam.

[0042] Upon aeration the composition comprising cellulose fibres, thickener and at least two surfactants will form a highly stable wet fibre foam. The aeration may be performed by mechanical agitation, and a substantial amount of air is incorporated into the material. The formation of a foam will be promoted by the surfactants. By adjusting the stability of the wet foam with the use of thickeners and surfactant combinations, a free-standing cellulose foam can be made without the use of a cross-linker or fibrillated cellulose. A good stability of the foam prevents ripening, i.e. change in bubble size, and drainage. The obtained wet foam is free-standing and does not require a mould or a forming fabric to retain its shape upon drying. The wet foam can thus be formed into a free-standing foam that is stable enough to be dried in the absence of a supporting mould without collapsing.

[0043] The bubble size in the wet foam is typically below 100 pm. This provides for a homogenous wet foam with good stability that does not flocculate during processing. During processing, and also during the subsequent drying step, the average bubble size is maintained to a large extent and the cellulose fibres remain well dispersed. The resulting solid cellulose foam obtained by drying the wet foam will be homogenous in structure, strong, have good mechanical properties, a smooth surface and no defects.

[0044] In comparison, a wet cellulose foam with low stability has a larger average bubble size (i.e. typically above 100 pm) and the bubbles will coalesce faster during processing and drying such that larger bubbles are formed. In addition, the cellulose fibres will form clusters during processing and drying. This results in the wet foam collapsing during drying. The resulting solid cellulose foam will not have a homogenous structure and will also contain defects in the form of cavities resulting from the coalesced bubbles in the wet foam. Such a solid cellulose foam is, due to the defects, weak and has a rough surface.

[0045] In some embodiments, the yield stress of the wet cellulose foams used in the present invention may be at least 80 Pa, or at least 100 Pa, or at least 150 Pa, or from 80 to 500 Pa, or from 100 to 500 Pa, or from 150 to 500 Pa.

[0046] In some embodiments, the density of the wet cellulose foams used in the present invention may be from 70 - 600 kg / m3, or from 100 - 500 kg / m3, or from 100 - 400 kg / m3, or from 125 - 375 kg / m3, or from 140 - 375 kg / m3.

[0047] In some embodiments, the wet cellulose foam used in the present invention comprises at least 10 wt% cellulose, as calculated on the total weight of the wet cellulose foam. In some embodiments, the wet cellulose foam may comprise 10 - 40 wt%, 11 - 40 wt%, 10 - 30 wt%, 11 - 30 wt%, 10 - 20 wt%, or 11 - 20 wt% cellulose fibres, as calculated on the total weight of the wet cellulose foam.

[0048] Because of the high solid content, the wet foam does not need to be dewatered before it is dried. The foam may be dried by evaporation at room temperature or at an elevated temperature, such as a temperature of from 40°C to140°C.

[0049] After drying, the solid cellulose foam may have a density of from 10 to 80 kg / m3, or from 10 to 60 kg / m3or from 20 to 50 kg / m3. In preferred embodiments the cellulose foam comprises cellulose fibres in a range of from 71 to 95 wt%, such as from 75 to 95 wt%, based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of from 4 to 24 wt%, such as from 5 to 20 wt%, based on the total dry weight of the cellulose foam, and at least two surfactants. A wet cellulose foam having such a composition is homogenous in structure and has a good stability as discussed above. Such a wet cellulose foam can also be dried without prior dewatering.

[0050] The solid cellulose foam may after drying have a solid content in the range of from 95 to 100 wt%, preferably from 98 to 100 wt%, as calculated on the total weight of the solid cellulose foam. During drying a densified layer is formed on the outer surface of the wet cellulose foam and remain on the outer surface of the dried cellulose foam. The densified layer comprises cellulose fibres that are packed more tightly and partly oriented differently compared to the bulk. The densified layers have improved mechanical stability and strength as compared to the core of the cellulose foam. The core of the cellulose foam comprises a homogenous open-cell fibre network. The core is highly porous, and even though the densified layer has a denser structure than the core, it is still porous. The densified layer provides the cellulose foam with increased stability and mechanical strength.

[0051] The cellulose foam may be prepared by a two-step deposition such as described in WO2023119215 A1 . In a first deposition, a wet foam is deposited as discrete units on a surface and at least partially dried. During drying, a densified layer is formed on the outer surface of the discrete units. In a second deposition a wet foam, preferably having the same composition as the wet foam in the first deposition, is deposited so that it fills the spaces surrounding the discrete units of the first deposition. After drying, a solid cellulose foam comprising discrete units of foam embedded in a foam matrix is obtained. The cellulose foam may also be prepared by assembly of individually formed complimentary dry cellulose foam pieces. For example, dry foam pieces of complimentary shape, each formed from a wet foam, may be assembled to form a foam substrate of any desired shape, such as a plank.

[0052] The cellulose foam described above is the preferred cellulose foam to use in the method of the present invention and is further described in WO2023119213 A1 . Alternatively, other cellulose foams, such as those disclosed in WO2016068771 A1 , WO2016068787 A1 , and W02020011587 A1 may be used.

[0053] According to a first aspect, the first invention relates to a method for producing a resilient cellulose foam. The term “resilient” as used herein refers to a cellulose foam that can resume its shape after being bent or compressed. The resilient cellulose foam of the present invention is after removal of any applied pressure able to resume 90-100% of its thickness, regardless of compressive strain. Preferably the compressive strain is in a range of from 50% to 90%, such as 60% to 80%. The method according to the first aspect involves providing a rigid cellulose foam having a first thickness. The cellulose foam used as a starting material in the method of the present invention is rigid. The term “rigid” as used herein, refers to a solid cellulose foam that is substantially stiff and non-flexible and not possible to bend to a large extent without tearing and / or creasing the foam. When a rigid cellulose foam is compressed, it does not resume its original shape, or only resumes it to a small extent, and only when compressed to a low degree of compression.

[0054] Both the rigid cellulose foam and the resilient cellulose foam are solid cellulose foams, i.e. they are dry, when used in the present invention.

[0055] In a preferred embodiment, the rigid cellulose foam provided as a starting material in the method of the present invention has a density of 20-50 kg / m3. When compressed, such a foam is, once the pressure is removed, typically able to resume its original thickness if compressed to a low degree, for example if compressed to a thickness corresponding to 80% or more, or 90% or more, of the original thickness.

[0056] The rigid cellulose foam provided in the method according to the first aspect may have any shape, such as a block, a cube, a cylinder or any irregular shape. Preferably, the solid cellulose foam has at least one flat surface. The term “flat” as used herein refers to a level surface with no indentations or protruding portions.

[0057] In one embodiment, the rigid cellulose foam is provided in the form of a plank having a thickness in the range of from 1 to 20 cm, preferably from 1 to 10 cm, more preferably from 2 to 6 cm. The length and width dimensions of the plank are typically in the range of from 100 to 300 cm. The planks may be cut into smaller pieces but preferably having the same thickness also after cutting. In embodiments where the foam is provided in the form of a plank, the foam will have a top surface, a bottom surface and side surfaces.

[0058] The first thickness corresponds to the height of the rigid cellulose foam as provided. Preferably, the thickness of the provided rigid cellulose foam is uniform such that the value of the first thickness is the same all over the foam.

[0059] In some embodiments, the rigid cellulose foam as provided comprises a densified layer on at least one outer surface. In embodiments where the rigid cellulose foam is provided in the form of a plank, the rigid cellulose foam may comprise densified layers on at least the top surface and bottom surface, and optionally on the side surfaces. If pressure is applied to an outer surface comprising a densified layer during the compression step, the densified layer will facilitate an even distribution of the pressure, thus ensuring a uniform degree of compression of the foam. The densified layer also provides improved mechanical properties such as strength and stability to the cellulose foam.

[0060] The method according to the first aspect of the present invention further involves compressing the provided rigid cellulose foam to a second thickness so as to obtain a resilient cellulose foam. The second thickness is smaller than the first thickness. The second thickness is the thickness of the rigid cellulose foam while it is compressed to make it resilient. The second thickness may for example be less than 60% of the first thickness, or less than 50%, or less than 40%, or less than 30%, or less than 20% of the first thickness. The second thickness may for example be in a range of from 20% to 60% of the first thickness. If the rigid cellulose foam is not sufficiently compressed, a resilient foam will not be obtained. By compressing the rigid solid cellulose foam to a larger extent, i.e. so that the difference between the values of the first and second thicknesses is larger, a more resilient cellulose foam will be obtained. However, since the cushioning ability of the foam is decreased by compression there is a trade-off between resilience and cushioning ability.

[0061] The value of the second thickness needed to obtain a resilient cellulose foam depends on the density of the rigid cellulose foam as provided. It may also depend on the composition of the rigid cellulose foam and on any additives present. In addition, the temperature during compression as well as the duration of the compression may have an impact. Thus, the value of the second thickness is typically determined by observing at what degree of compression a resilient foam is obtained. Once a resilient foam is obtained, such a resilient foam is able to recover almost all its (compressed) thickness after removal of any further pressure. For example, a resilient foam of the present invention may be able to recover from 90- 100% of its thickness after removal of pressure.

[0062] In a preferred embodiment of the present invention, the density of the provided solid cellulose foam is in the range of from 20-50 kg / m3. In such embodiments, the second thickness is preferably less than 30% of the first thickness, or less than 20% of the first thickness. If the density is lower, such as from 10-20 kg / m3, the rigid foam must be compressed to a higher degree to obtain a resilient foam. For example, the second thickness may be less than 20% of the first thickness. If the density is higher, such as from 50-80 kg / m3, less compression is needed to obtain a resilient foam. For example, the second thickness may be less than 50% of the first thickness.

[0063] Once the pressure is removed, the resilient cellulose foam will typically recover some, but not all, of its original thickness. Thus, the thickness of the resilient cellulose foam is always lower than that of the provided rigid cellulose foam. The obtained resilient cellulose foam has a third thickness, wherein the third thickness is less than the first thickness, and equal to or greater than the second thickness. In some embodiments where the degree of compression is high, the obtained resilient cellulose foam may not recover any of its thickness upon removal of pressure. In such embodiments, the third thickness is equal to the second thickness.

[0064] In some embodiments the third thickness, i.e. the thickness of the obtained resilient foam after compressing and subsequent removal of pressure, is 70% or less, or 60% or less, or 50% or less, or 40% or less, of the first thickness of the rigid cellulose foam.

[0065] In a preferred embodiment where the density of the rigid cellulose foam as provided is in the range of from 20-50 kg / m3, the cellulose foam is compressed to a second thickness that is less than 30% of the first thickness. Once the pressure is removed, the foam will recover some of its thickness such that the third thickness is about 60% of the first thickness of the rigid cellulose foam.

[0066] Any suitable means may be used for compressing the rigid cellulose foam. For example, a press with a flat pressing surface, a calender or a roll may be used. In a preferred embodiment of the present invention the cellulose foam is provided with a cavity in which an object to be protected is to be placed. In such embodiments, the pressing may be carried out simultaneously with forming the cavity, e.g. by diecutting. Compressing may be carried out at room temperature or at an elevated temperature.

[0067] The compressing step involves compressing at least one delimited section of the rigid cellulose foam or the entire rigid cellulose foam to a second thickness so as to obtain a resilient cellulose foam section or a resilient cellulose foam. In preferred embodiments, the entire rigid cellulose foam as provided is compressed. Further, the degree of compression is preferably uniform such that the second thickness is the same all over the resilient cellulose foam.

[0068] In an alternative embodiment, at least one delimited section of the rigid cellulose foam is compressed so that a cellulose foam having at least one resilient section is obtained. In such embodiments, the remaining uncompressed section(s) of the cellulose foam are still rigid. It is in such embodiments preferred that the section that is to be compressed is sufficiently separated from sections that are not to be compressed, e.g. by cutting lines extending partially through the foam, prior to compressing. The resilient section of the foam must be sufficiently larger than any cavity to be formed in the resilient section of the foam, to be able to benefit from the resilient properties of the foam. The second thickness is preferably uniform, such that the degree of compression is the same all over the resilient cellulose foam section.

[0069] In preferred embodiments the resilient cellulose foam has a top surface, a bottom surface and side surfaces. The top surface and / or bottom surface are preferably flat.

[0070] The density of the cellulose foam increases due to the compression since no foam material is removed. During compression, the open cell network of the rigid cellulose foam collapses and a more compact structure is obtained. The increase in density of the resilient cellulose foam compared to the rigid cellulose foam corresponds to the decrease in thickness of the obtained resilient cellulose foam compared to the rigid cellulose foam. For example, if the third thickness is 50% of the first thickness, the density of the resilient cellulose foam is doubled compared to the rigid cellulose foam.

[0071] The rigid cellulose foam as provided has an open cell structure and a first thickness. If compressed to a second thickness below a threshold value, it will not be able to resume the first thickness once the pressure is removed, due to the rigid structure of the foam. When compression starts, the structure of the foam will change such that the original open cell structure collapses and a more compact structure is obtained. This may be due to disruption of hydrogen bonds within the fibre network, and also due to buckling of cellulose fibres in the foam which introduces flexible regions. Any thickeners present in the foam may also become more flexible after compression. At a sufficient degree of compression, the foam structure is completely deformed, and a resilient foam is obtained, having a third thickness that is smaller than the first thickness. The third thickness is typically greater than the second thickness since the foam, due to its resilient properties, can resume some of its thickness when the pressure is removed. If the resilient foam is subsequently compressed further, to a thickness smaller than the third thickness, it will expand back to the third thickness once the pressure is removed. The resilient foam is mainly resilient in the height direction, with some resilience also in other directions. The obtained resilient cellulose foam is softer than the provided rigid cellulose foam which is beneficial in several applications.

[0072] The method according to the first aspect may comprise an additional step involving forming at least one cavity in the rigid cellulose foam or in the resilient cellulose foam, the at least one cavity extending into the foam from a first surface of the rigid cellulose foam or resilient cellulose foam. The first surface is preferably the top surface of the cellulose foam. The at least one cavity extends from a first surface of the cellulose foam towards a second surface of the cellulose foam. Preferably the first surface is a top surface of the cellulose foam, and the second surface is a bottom surface of the cellulose foam. The cavity may be formed either prior to compressing, simultaneously with compressing or after compressing the rigid cellulose foam. Thus, the at least one cavity may be formed either in the rigid cellulose foam or in the resilient cellulose foam.

[0073] Any formed cavity has a height, a width and a length. The height, width and length may be uniform or may vary along the cavity. The cavity comprises walls extending from the first surface of the cellulose foam and may also comprise a bottom portion. In embodiments where the bottom portion is flat, the height of the cavity corresponds to the height of the walls of the cavity. The cavity walls extend along the circumference of the cavity and are mainly formed by the core of the cellulose foam.

[0074] The cavity may be of any desired shape. The shape and dimensions of a cavity are selected so that an object to be protected can fit into the cavity. Depending on the object to be protected, it may suffice that a bottom part of the object is placed in the cavity of the resilient foam. The shape of the cavity thus corresponds to that of the bottom part of the object. Alternatively, the entire object is placed inside the cavity.

[0075] That is particularly suitable when the object is fragile and delicate.

[0076] After compression, the resilient properties of the foam will keep the object secured in the cavity, also when the object has a smooth and slippery surface. The cavity walls consist of resilient cellulose foam. The dimensions of the cavity are preferably selected such that the extension of the cavity in the width and / or length directions is smaller than the object to be protected. In such embodiments, the smaller dimensions of the cavity in combination with the resilient properties of the foam ensures that the object is kept in place within the cavity and that the foam will be wrapped tightly around the object. Preferably, the dimensions of the cavity in both width and length direction are selected so as to be smaller than the corresponding dimension of the object to be placed in the cavity. The dimensions of the cavity in the width and / or length direction may for example be selected such that they are from 0.5 to 5 mm smaller than the object to be protected. If the cavity is made too small, it may be difficult to insert the object to be protected without causing damage to the foam.

[0077] The cavity may be formed using any suitable means, such as by cutting or by milling. Preferably, the cavity is formed by cutting, using for example die-cutting, water-jet cutting or an oscillating knife.

[0078] In some embodiments the at least one cavity is formed prior to compressing the rigid cellulose foam. Thus, the cavity is formed in the rigid cellulose foam. Depending on the forming method used, it may be easier to cut the cellulose foam before compression due to the higher stiffness of the rigid cellulose foam before compression.

[0079] In some embodiments the at least one cavity is formed simultaneously with compressing the rigid cellulose foam. When die-cutting is used to form the at least one cavity, the cellulose foam is compressed by the die-cutting tool such that a resilient foam is obtained at the same time as forming the at least one cavity in the foam. Thus, one process step can be omitted when using die-cutting. In some embodiments the at least one cavity is formed after compression of the rigid cellulose foam. Thus, in such embodiments the cavity is formed in the resilient cellulose foam.

[0080] The properties of the at least one cavity are the same regardless of when the cavity is formed. The cutting of the cellulose foam is also carried out in a similar fashion regardless if the foam is rigid or resilient. Thus, in the discussion below, the foam can be either a rigid, uncompressed, cellulose foam, or a resilient, compressed, cellulose foam, or the cellulose foam can be compressed during cutting.

[0081] In some embodiments, cutting of the cellulose foam is carried out in a direction perpendicular to the first surface of the cellulose foam such that at least a part of a wall of the cavity is perpendicular to the first surface. All parts of the cavity wall may be perpendicular to the first surface or only some parts. It is typically easier to cut in a perpendicular direction compared to cutting at an angle to the first surface and thus manufacturing is simplified.

[0082] In some embodiments, cutting is carried out at an angle to the first surface of the cellulose foam such that at least a part of a wall of the cavity is slanting. All parts of the cavity wall may be slanting or only some parts. Preferably, the walls are slanting such that the width and / or length of the cavity is larger at a bottom part of the cavity than at a top part. The top part of the cavity is located at the first surface of the cellulose foam and the bottom part of the cavity is located at the bottom of the cavity, i.e. on the opposite side from the top part. In such embodiments, an angle between the first surface of the cellulose foam and the wall of the cavity is less than 90°, such as less than 80° or less than 70° or less than 60° or less than 50°. The angle may also be different at different parts of the cavity walls. The slanting cavity walls facilitate keeping an object in place within the cavity.

[0083] In some embodiments, cutting is first carried out in a direction perpendicular to the first surface and then at an angle to the first surface such that the cavity walls are perpendicular to the first surface at the top part of the cavity but slanting further down in the cavity. The perpendicular portion of the cavity wall preferably does not extend deep into the cavity, but is only present at a top portion. For example, the perpendicular portion may be less than 20 mm, or less than 10 mm, or less than 5 mm as measured from the first surface of the cellulose foam. The perpendicular portion provides a strong lid portion to the cavity which leads to improved protective properties since the cavity will become less fragile and will break less easily.

[0084] The cavity may extend all through the cellulose foam such that the foam is cut all the way through its thickness when forming the cavity. Alternatively, the cavity may extend only partially through the foam such that a bottom portion of the cellulose foam may remain, thus forming a bottom portion of the cavity. Such a bottom portion may be flat or may have any other suitable shape depending on the object to be placed in the cavity. The cellulose foam within the cavity may in such embodiments be removed by cutting along the bottom portion of the cavity, or the foam may be further compressed and remain at the bottom portion of the cavity. Any object placed in the cavity will keep the foam compressed.

[0085] In some embodiments the cellulose foam comprises more than one cavity. The cavities may be of the same shape or may be of different shapes.

[0086] According to a second aspect, the present invention relates to a resilient cellulose foam comprising at least one cavity extending into the foam from a first surface of the resilient cellulose foam. The resilient cellulose foam of the second aspect is obtainable by the method according to the first aspect, and is further characterized as set out above with reference to the first aspect.

[0087] The cavity extends from the first surface of the resilient cellulose foam towards a second surface of the resilient cellulose foam. Preferably the first surface is a top surface of the foam and the second surface is a bottom surface of the foam. The cavity may have any suitable shape. The shape is selected in view of the object to be placed in the cavity.

[0088] In some embodiments at least a part of a wall of the cavity is perpendicular to the first surface of the resilient cellulose foam. In some embodiments, all walls of the cavity are perpendicular to the first surface of the resilient cellulose foam.

[0089] In some embodiments at least a part of a wall of the cavity is arranged such that an angle between the first surface of the resilient cellulose foam and the wall of the cavity is less than 90°, such as less than 80° or less than 70° or less than 60° or less than 50°. The angle may also be different at different parts of the cavity walls. In such embodiments, at least parts of the walls of the cavity will be slanting. The width and / or length of the cavity is in such embodiments larger at a bottom part of the cavity than at the top part of the cavity, the top part being located at the first surface of the cellulose foam. The slanting walls help securing an object to be protected in the cavity.

[0090] In some embodiments, a top portion of at least a part of the walls of the cavity is arranged perpendicular to the first surface of the resilient cellulose foam. Below the top portion, the walls of the cavity are arranged at an angle to the first surface such that the cavity walls are slanting towards the bottom portion of the cavity. In such embodiments, the perpendicular portion of the cavity wall preferably does not extend deep into the cavity, but is only present at the top part of the cavity. For example, the perpendicular portion of the cavity wall may be less than 20 mm, or less than 10 mm, or less than 5 mm as measured from the first surface of the resilient cellulose foam.

[0091] The cavity may extend all through the resilient cellulose foam such that the foam is cut all the way through its thickness when forming the cavity. In such embodiments, a bottom portion may be provided by placing the resilient cellulose foam on a substrate, such as a cardboard substrate or another cellulose foam substrate. The cavity is thus provided with a bottom portion. The resilient cellulose foam may be glued to the substrate. If cushioning is desired, it may be advantageous if the substrate is a cellulose foam substrate.

[0092] Alternatively, the cavity extends partially through the resilient cellulose foam such that the bottom portion of the cavity is formed by the foam. Such a bottom portion may be flat or may have any other suitable shape depending on the object to be placed in the cavity.

[0093] In a preferred embodiment, at least one of the width and length of the cavity is smaller than a corresponding dimension of an object to be placed in the cavity. Thus, the width and / or length of an object to be protected by the resilient cellulose foam is larger than the corresponding dimension of the cavity in the resilient cellulose foam. When the object is placed in the cavity, the foam will be pressed away from the cavity by the object. Since the foam is resilient it will strive to return to its original shape and will thus exert a force on the object which will keep the object in place within the cavity. Due to the resilient properties of the foam in combination with the smaller dimensions of the cavity compared to the object to be protected, the foam wraps around the object, keeping it tightly in place within the cavity during e.g. shipping.

[0094] The resilient cellulose foam of the second aspect is suitable for use as a protective packaging insert. It may be placed in a box or other type of package to hold an object in place inside the package.

[0095] According to a third aspect, the present invention relates to use of a resilient cellulose foam according to the second aspect as a protective packaging insert wherein an object to be protected is held in place in the cavity of the resilient cellulose foam.

[0096] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Claims

Claims1 . A method for producing a resilient cellulose foam, the method comprising the steps of:- providing a rigid cellulose foam having a first thickness; and- compressing the rigid cellulose foam to a second thickness, wherein the second thickness is smaller than the first thickness, so as to obtain a resilient cellulose foam.

2. The method according to any one of claims 1 or 2, wherein the provided rigid cellulose foam has a density in the range of from 10 to 80 kg / m3.

3. The method according to any one of the preceding claims, wherein the cellulose foam comprises cellulose fibres in a range of from 71 to 95 wt% based on the total dry weight of the cellulose foam.

4. The method according to any one of the preceding claims, wherein the cellulose foam comprises cellulose fibres in a range of from 71 to 95 wt% based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of from 4 to 24 wt% based on the total dry weight of the cellulose foam, and at least two surfactants.

5. The method according to any one of the preceding claims, wherein the second thickness is less than 60% of the first thickness.

6. The method according to any one of the preceding claims, the method comprising an additional step of:- forming at least one cavity in the rigid cellulose foam or in the resilient cellulose foam, the at least one cavity extending from a first surface of the cellulose foam, wherein the step of forming at least one cavity is carried out either prior to, simultaneously with, or after compressing the rigid solid cellulose foam.

7. The method according to claim 6, wherein the step of forming the at least one cavity involves cutting the rigid cellulose foam or the resilient cellulose foam so as to obtain the at least one cavity.

8. The method according to claim 7, wherein cutting is carried out in a direction perpendicular to the first surface of the cellulose foam such that at least a part of a wall of the cavity is perpendicular to the first surface.

9. The method according to any one of claims 6 or 7, wherein cutting is carried out at an angle to the first surface of the cellulose foam such that at least a part of a wall of the cavity is slanting.

10. The method according to claim 9, wherein cutting is carried out such that a width of the cavity and / or a length of the cavity is larger at a bottom part of the cavity than at a top part of the cavity, and wherein the top part of the cavity is located at the first surface of the cellulose foam.11 . The method according to any one of claims 7-10, wherein at least one dimension in the width and / or length direction of the cavity is selected such that it is smaller than a corresponding dimension of an object to be placed in the cavity.

12. A resilient cellulose foam comprising at least one cavity extending into the foam from a first surface of the resilient cellulose foam.

13. The resilient cellulose foam according to claim 12, wherein the resilient cellulose foam comprises cellulose fibres in a range of from 71 to 95 wt% based on the total dry weight of the resilient cellulose foam.

14. The resilient cellulose foam according to any one of claims 12 or 13, wherein the resilient cellulose foam comprises cellulose fibres in a range of from 71 to 95 wt% based on the total dry weight of the resilient cellulose foam, a water-soluble thickener in a range of from 4 to 24 wt% based on the total dry weight of the resilient cellulose foam, and at least two surfactants.

15. The resilient cellulose foam according to any one of claims 12-14, wherein at least a part of a wall of the cavity is arranged perpendicular to the first surface of the resilient cellulose foam.

16. The resilient cellulose foam according to any one of claims 12-15, wherein at least a part of a wall of the cavity is arranged such that an angle between thefirst surface of the resilient cellulose foam and the wall of the cavity is less than 90°.

17. The resilient cellulose foam according to claim 16, wherein at least one of the width and length of the cavity is larger at a bottom part of the cavity than at a top part of the cavity, wherein the top part is located at the first surface of the resilient foam.

18. The resilient cellulose foam according to any one of claims 12-17, wherein at least one dimension in the width and / or length direction of the cavity is smaller than a corresponding dimension of an object to be placed in the cavity.

19. Use of a resilient cellulose foam according to any one of claims 12-18 as a protective packaging insert, wherein an object to be protected is held in place in the cavity of the resilient cellulose foam.