Solid cellulose foam comprising individual units of cellulose foam embedded in a cellulose foam matrix

Abstract

The present invention relates to a method for producing a solid cellulose foam, the method comprising providing individual units of a first cellulose foam on a surface to obtain a first foam stack, the distance between adjacent individual units being in the range of 2 to 20 mm, depositing a second wet cellulose foam between the individual units to obtain a subsequent foam stack, and drying the second wet cellulose foam in the subsequent foam stack to obtain a solid cellulose foam in which the individual units of cellulose foam are embedded in a cellulose foam matrix. The present invention also relates to a solid cellulose foam comprising individual units of cellulose foam embedded in a cellulose foam matrix, the distance between adjacent individual units being in the range of 2 to 20 mm.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid cellulose foam and to a solid cellulose foam comprising individual units of a first foam stack embedded within the cellulose foam matrix of a subsequent foam stack. The solid cellulose foam of the present invention can be used, for example, as cushioning in packaging applications. [Background technology]

[0002] Various porous materials, such as foams, are commonly used in applications such as insulation in buildings and vehicles and packaging materials for protecting various goods during storage and transport.

[0003] Depending on the item being protected, various types of protective packaging materials can be used. Many products use lightweight cushioning materials to reduce shock and vibration. Common examples of such cushioning materials include petroleum-based polymer foams such as polyurethane, polyethylene, and expanded polystyrene. The foams used should be lightweight, stable, and easy to manufacture.

[0004] Today, there is growing interest in replacing petroleum-based polymers with polymers from renewable resources, i.e., bio-based polymers. Cellulose is of particular interest because it is the most abundant renewable natural polymer on Earth. In the case of cellulose foams, depending on the foam's composition, there is the possibility that the material can be recycled in regular recycling streams.

[0005] There are several examples of cellulose foams produced by various methods. Drying the wet foam composition is often a critical step. Because wet foams typically have low stability, molds are commonly used to prevent the foam from collapsing during drying. International Publication No. 20200011587 A1 describes a porous material produced by aerating a paste containing cellulose fibers and gluten, placing the aerated paste in a mold, and drying the molded paste. The dried porous material has the shape of the mold. International Publication No. 2015036659 A1 describes a molded fiber product produced by foaming an aqueous suspension of natural fibers combined with synthetic fibers and surfactants, feeding the resulting fiber foam into a mold, first mechanically removing some of the water, and then drying the foam by evaporating the water to produce a dry fiber product.

[0006] When cellulose foam is dried unrestrained, tension pulls the cellulose fibers, causing the foam to collapse and shrink in all directions. Drying shrinkage is an inherent property of cellulose; the expanded cellulose fibers collapse onto each other when water is removed from the system. Even with more complex drying systems combining air impingement dryers and IR dryers, shrinkage through the thickness is expected to exceed 10%. This is because the drop in water level during drying generates capillary pressure within the material, forming a meniscus between particles and resulting in interparticle attraction. Increasing the dry content of the foam, which has low water affinity or hydrophobic properties, reduces the interparticle attraction caused by capillary pressure. However, the network strength formed during drying is reduced due to a decrease in interfiber bond strength and a decrease in the average number of interfiber bonds.

[0007] To avoid or reduce shrinkage during drying, cellulose foams must be dried under tension in a frame, mold, or other similar device. The use of such restraints significantly prevents shrinkage of the foam along its width and length. However, when drying objects with large surface areas, the tension provided by the frame or mold is limited to the area closest to the mold. Typically, as shown in the prior art foam in Figure 1, the foam thickness decreases due to shrinkage in the center of the object and gradually increases toward the edges. Therefore, shrinkage during drying is problematic, especially when drying foams with large surface areas, because shrinkage can be uneven and the thickness of the dried foam can vary along the width and length of the dried foam.

[0008] Because both wet and dry foams are insulating, foam drying times are typically long, and short drying times are desirable for a cost-effective process.

[0009] Therefore, there remains a need for alternative methods for preparing cellulose foams. Furthermore, the foams produced should have high impact resistance so that they can protect heavier objects when used as packaging materials. Summary of the Invention

[0010] It is an object of the present invention to provide a solid cellulose foam that is recyclable, made from renewable resources, and that eliminates or mitigates at least some of the disadvantages of prior art materials.

[0011] It is a further object of the present invention to provide an improved method for obtaining solid cellulose foams having uniform thickness and minimal non-uniform shrinkage during drying, even when producing large foamed articles.

[0012] It is a further object of the present invention to provide a cost-effective method for obtaining solid cellulose foams with reduced drying times for the foams.

[0013] The above objectives, as well as other objectives which will be realized by those skilled in the art in light of the present disclosure, are accomplished by various aspects of the present disclosure.

[0014] The invention is defined in the independent claims. Further embodiments of the invention are defined in the dependent claims.

[0015] According to a first aspect, the present invention relates to a method for producing a solid cellulose foam, said method comprising the steps of: - providing individual units of a first cellulose foam on a surface to obtain a first cellulose foam deposit, the individual units having a distance between adjacent individual units in the range of 2 to 20 mm; - depositing a second wet cellulose foam between the individual units to obtain a subsequent foam deposit; drying the second wet cellulose foam in a subsequent foam stack to obtain a solid cellulose foam in which the individual units of cellulose foam are embedded within the cellulose foam matrix; Includes.

[0016] Surprisingly, it has been found that the non-uniform shrinkage of a wet cellulose foam object during drying can be significantly reduced by the method of the first embodiment, which involves two foam stacks instead of a single foam stack. By providing the first wet cellulose foam stack in the form of individual units, the surface area of ​​each individual unit is small enough to prevent non-uniform shrinkage along its height during drying. The dried individual units of the first cellulose foam stack support the second wet cellulose foam during drying of the subsequent foam stack, so shrinkage does not occur. Therefore, the resulting solid cellulose foam has a uniform height. By arranging the individual units relatively closely together, with the distance between adjacent individual units in the range of 2 to 20 mm, the top surface of the resulting solid cellulose foam is smooth and uniform.

[0017] It has also been surprisingly found that the method according to the first aspect reduces the drying time of the wet cellulose foam. When drying large objects of wet cellulose foam, drying is slow due to the insulating properties of the foam. Drying individual units of foam increases the surface area in contact with the air, resulting in faster drying. Because the individual units are positioned closer to each other, the overall width of the subsequent wet cellulose foam stack is reduced. This reduces the total drying time of the cellulose foam produced by the two-step deposition method of the present invention compared to a cellulose foam with the same properties but deposited using a single deposition step. The shorter drying time is advantageous from a cost perspective.

[0018] According to a second aspect, the present invention relates to a solid cellulose foam comprising individual units of cellulose foam embedded within a cellulose foam matrix, the distance between adjacent individual units being in the range of 2 to 20 mm.

[0019] The solid cellulose foam according to the second aspect has high impact resistance and excellent cushioning properties, and can be used as a packaging material in various protective packaging applications. It can also be used as a building material or as a thermal or acoustic insulator. The solid cellulose foam can also be used as a plant growth medium for hydroponic cultivation.

[0020] According to a third aspect, the present invention relates to the use of a solid cellulose foam according to the second aspect as a packaging material, a building material, a thermal or acoustic insulation material, or a hydroponic plant growing medium. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows a schematic diagram of a prior art method for depositing and drying a wet cellulose foam sheet with non-uniform shrinkage across its height. [Figure 2]1 is a schematic diagram illustrating one embodiment of a two-stage deposition method of the present invention, the method comprising: i) a first deposition of cellulose foam as individual units spaced a distance d apart from one another; ii) an intermediate drying step of drying the individual units to produce iii) free-standing individual units of cellulose foam; iv) a subsequent deposition of cellulose foam between the individual units of cellulose foam; and v) a second drying step to obtain vi) a cellulose foam material comprising the individual units of cellulose foam. [Figure 3] Schematic diagrams of solid cellulose foam sheets produced according to the methods of the present invention. Figure 3A) shows a solid cellulose foam with black densified layers on the top and bottom, similar in appearance to foam sheets produced by other techniques. Figure 3B) shows the body of material below the densified top and bottom layers, the whole containing individual units of cellulose foam (black rectangular prisms), each separated from the surrounding foam matrix by a densified cellulose layer. Figure 3C) shows one individual unit surrounded by a densified layer of cellulose, shown in black (left), and homogeneous cellulose foam within the densified layer (right). [Figure 4] This figure shows the drying time of subsequent foam stacks as a function of the distance between individual units in the first foam stack. Wet cellulose foam was deposited between dry individual units positioned at distances of 5 mm (○), 8 mm (□), 10 mm (▲), and 20 mm (●) from each other. The samples were dried and weighed at several points during drying. [Figure 5] Shown are drying curves obtained during drying of wet cellulose foam deposited in one stage (○) or in two stages, including a first foam deposit that is air-cut into individual units before drying (□) and two deposits that fill the gaps between the individual units formed during air-cutting (△). DETAILED DESCRIPTION OF THE INVENTION

[0022] The term "foam" as used herein refers to a material made by entrapping air or gas bubbles within a solid or liquid. Typically, the volume of gas is much greater than the volume of the liquid or solid, and the gas pockets are separated by thin membranes. Three requirements must be met for a foam to form. Mechanical work is required to increase the surface area. This occurs by agitation, dispersing a large amount of gas in a liquid, or injecting gas into a liquid. The second requirement is the presence of a foam-forming agent (usually an amphiphile, surfactant, or surface-active component) to reduce surface tension. Finally, the foam must form faster than it can break down.

[0023] As used herein, the term "cellulose foam" refers to a foam containing cellulose and other components such as thickeners, surfactants, and additives. The primary component of cellulose foam is cellulose, which constitutes at least 70% by weight of the dry content of the cellulose foam. Because the cellulose is in the form of fibers, the foam can also be defined as a fibrous foam or a cellulose fiber foam. The cellulose foam can be wet or solid.

[0024] As used herein, the term "wet foam" or "wet cellulose foam" refers to a wet foam containing cellulose and other ingredients such as thickeners, surfactants, and additives. Air bubbles are present within the wet foam. The wet foam is self-supporting and functions as a viscoelastic solid, meaning that the wet foam has both viscous and elastic properties. The wet foam behaves as a solid and is self-supporting unless a force large enough to cause it to begin to flow and behave like a viscous material is applied. Depending on the magnitude and time scale of the applied shear stress, the wet foam can exhibit predominantly viscous or elastic behavior.

[0025] As used herein, the terms "solid cellulose foam" or "dried cellulose foam" refer to a dried, porous cellulose material, i.e., a foam-formed material, formed from wet cellulose foam. During the drying process, the wet, closed-cell cellulose foam is converted into a closed-cell solid cellulose foam. The cellulose fiber network is prevented from collapsing during drying. As a result, the solid cellulose foam has a shape that closely matches the shape of the wet cellulose foam. The dry content of the solid cellulose foam is at least 95% by weight, calculated based on the total weight of the solid cellulose foam. The shape and density of the solid cellulose foam are maintained even in an unconstrained state. The solid cellulose foam has a closed-cell structure, with air occupying the pores within the foam. Solid cellulose foam is also referred to as a porous material or a low-density material.

[0026] The method according to the first aspect of the present invention includes using a first wet cellulose foam for the individual units of the first foam stack and a second wet cellulose foam for the individual units of the second foam stack. In some embodiments, the first and second wet cellulose foams are the same. In some embodiments, the first and second wet cellulose foams are different, such as having different compositions or different densities.

[0027] The cellulose foam used in the present invention may contain cellulose fibers in the range of 71 to 95% by weight, for example 75 to 95% by weight, based on the total dry weight of the cellulose foam.

[0028] Cellulose fibers suitable for use in the present invention can be derived from wood, such as softwoods or hardwoods, leaves, or fiber crops (including cotton, flax, and hemp). Cellulose fibers suitable for use in the present invention can also be derived from regenerated cellulose, such as rayon and lyocell. Cellulose fibers suitable for use in the present invention may contain lignin, hemicellulose, or both, or the cellulose fibers may be free of lignin and hemicellulose. Preferably, the cellulose fibers are derived from wood, and more preferably, the cellulose fibers are pulp fibers obtained by a pulping process that liberates fibers from the wood matrix. Pulp fibers can be separated by mechanical pulping, such as thermomechanical pulping (TMP) and chemical thermomechanical pulping (CTMP), or by chemical pulping, such as kraft pulp and pulps obtained by sulfite, soda, and organosolv pulping. More preferably, the cellulose fibers are pulp fibers liberated by a chemical pulping process. The different properties of each cellulose fiber affect the properties of the final cellulose foam. Cellulose fibers are much longer than they are wide. The average width of a cellulose fiber is 0.01 to 0.05 mm. The fiber length of conifers is 2.5 to 4.5 mm, that of broadleaf trees is 0.7 to 1.6 mm, and that of eucalyptus is 0.7 to 1.5 mm. However, fiber length varies greatly depending on the habitat, etc. The lengths of the cellulose fibers in the cellulose foams disclosed in the present invention are 0.1 mm to 65 mm, 0.1 mm to 10 mm, 0.5 mm to 65 mm, 0.5 mm to 10 mm, and 0.5 mm to 7 mm. The mechanical properties of the foam may vary depending on the fiber length. Because the fibers are long, they entangle with each other, forming bonds between the fibers, providing strength to the foam. The aspect ratio of the cellulose fibers in the cellulose foam according to the present invention, i.e., the ratio of fiber length to fiber width, can be at least 10, at least 25, at least 50, at least 75, or at least 100, which maintains and stabilizes the foam structure during the drying process, allowing the wet cellulose foam to dry while retaining its shape. The aspect ratio can be up to 6500, but preferably up to 2000.

[0029] Cellulose fibers can also be modified to impart different properties to the final cellulose foam, for example, phosphated or periodate oxidized fibers can also be used to make cellulose foams according to the present invention.

[0030] Preferably, the cellulose fibers are selected from wood pulps such as softwood kraft bleached pulp, hardwood pulp, chemi-thermomechanical pulp, and dissolving pulp, or a combination of one or more thereof. More preferably, the cellulose pulp fibers are derived from softwood pulp, chemi-thermomechanical pulp, or dissolving pulp. Most preferably, the cellulose pulp fibers are derived from softwood pulp, such as softwood kraft bleached pulp.

[0031] The cellulose foam used in the present invention preferably comprises 71 to 95 wt. %, for example 75 to 95 wt. %, of cellulose fibers, based on the total dry weight of the cellulose foam; 4 to 24 wt. %, for example 5 to 20 wt. %, of a water-soluble thickener, based on the total dry weight of the cellulose foam; and at least two surfactants.

[0032] The water-soluble thickener may have a molecular weight of 80,000 to 250,000 g / mol, or 83,000 to 197,000 g / mol. Exemplary water-soluble thickeners are selected from carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl hydroxypropyl cellulose (MHPC), starch, xanthan, guar gum, xyloglucan, or mixtures thereof. The water-solubility of the thickener facilitates recycling of the cellulose foam.

[0033] Water-soluble thickeners can improve the bond strength between fibers in cellulose foams, mainly through hydrogen bonding. Therefore, the amount of water-soluble thickener affects the mechanical performance of the cellulose foam, especially the bulkiness of the material. The higher the content of water-soluble thickener, the harder the material will be. Therefore, water-soluble thickeners allow for adjustment of mechanical properties.

[0034] The cellulose foam may also contain a mixture of at least two surfactants. One of the at least two surfactants is preferably a fast-acting surfactant. A surfactant suitable for this purpose is an anionic surfactant, preferably a low-molecular-weight anionic surfactant. The anionic surfactant may have an apparent pKa of 3.2 to 3.8, preferably 3.4 to 3.6, or an apparent pKa of 3.5 in a solution having a pH of 7 to 9, preferably 8. The low-molecular-weight anionic surfactant may be selected from sodium dodecyl sulfate (SDS), potassium dodecyl sulfate, sodium laureth sulfate (SLES), sodium dodecylbenzenesulfonate, sodium cocoyl sarcosinate, and sodium lauroyl sarcosinate. The low-molecular-weight anionic surfactant is preferably selected from sodium dodecyl sulfate (SDS), sodium pn-dodecylbenzenesulfonate, 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.

[0035] The other of the at least two surfactants is preferably a co-surfactant. The co-surfactant can be selected from the group consisting of surfactants having an apparent pKa of at least 8, or at least 9, in a surfactant solution having a pH of 7 to 9, preferably a pH of 8, and amphoteric betaines. The co-surfactant has a maximum apparent pKa of 10. The co-surfactant preferably has a long carbon chain, more preferably a carbon chain having 14 carbon atoms (C14). The co-surfactant may be selected from high pKa fatty acids derived from plant-derived materials, such as tetradecanoic acid (myristic acid), sodium oleate, lauric acid, palmitic acid, and stearic acid; glucose-based co-surfactants having an aliphatic carbon chain, such as alkyl glycosides, alkyl polyglucosides, alkyl thioglycosides, 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.

[0036] Therefore, 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 of the anionic surfactant to the co-surfactant is 0.2:1 to 3:1, preferably 0.5:1 to 2:1. The total amount of the at least two surfactants contained in the cellulose foam may be 0.6 to 5 wt %, or 0.8 to 2.0 wt %, calculated based on the total weight of the cellulose foam.

[0037] The solid cellulose foam can be redispersed in water, making it recyclable in the normal paper recycling stream.

[0038] The wet cellulose foam used in the present invention can be produced using a method comprising the following steps: - disintegrating cellulose fibers in water to obtain a slurry of cellulose fibers; - adding a water-soluble thickener to the slurry to obtain a mixture of thickener and cellulose fibers in water; - adding at least two surfactants to the mixture to obtain a fiber suspension; - aerating the fiber suspension to obtain a wet foam, the wet cellulose foam comprising 10-38 wt. % cellulose fibers, 0.5-10 wt. % water-soluble thickener, and 0.1-2 wt. % surfactant, calculated on the total weight of the wet foam, and the wet cellulose foam has a density of 70-600 kg / m 3 and the yield stress is at least 80 Pa.

[0039] The addition of water-soluble thickeners increases the viscosity of the slurry, allowing it to entrap enough air to produce dense foam during aeration. Because the cellulose fiber is mixed at a high concentration, no drainage step is required, and water-soluble bio-based thickeners can be used at high concentrations.

[0040] The addition of fast-acting surfactants contributes to the formation of dense, high-viscosity cellulose foams by rapidly settling at the air-water interface during aeration. This allows for self-supporting wet cellulose foams. The addition of co-surfactants along with fast-acting surfactants further enhances the properties of the cellulose foam by promoting the action of the fast-acting surfactants. Co-surfactants with appropriate pKa and long carbon chains further contribute to stable fiber suspensions and stable wet cellulose foams.

[0041] Compositions containing cellulose fibers, a thickener, and at least two surfactants form highly stable wet fibrous foams upon exposure to air. Aeration is achieved by mechanical agitation, incorporating a significant amount of air into the material. The surfactants facilitate foam formation. By using a combination of thickeners and surfactants to tailor the stability of the wet foam, free-standing cellulose foams can be produced without the use of crosslinkers or fibrillated cellulose. Good foams prevent maturation, i.e., changes in cell size and drainage. The resulting wet foams are self-supporting and do not require molds or forming cloths to maintain their shape upon drying. Therefore, the wet foams can be formed into free-standing foams stable enough to dry without a supporting mold without collapsing.

[0042] The cell size of the wet foam is typically less than 100 μm. This results in a stable, homogeneous wet foam that does not agglomerate during processing. The average cell size is largely maintained during processing and the subsequent drying step, and the cellulose fibers remain well dispersed. The resulting solid cellulose foam, obtained by drying the wet foam, has a homogeneous structure, good strength, good mechanical properties, and a smooth, defect-free surface.

[0043] In contrast, less stable wet cellulose foams have larger average cell sizes (typically greater than 100 μm), which result in faster cell aggregation and larger cell sizes during processing and drying. Furthermore, cellulose fibers form clusters during processing and drying, resulting in collapse of the wet foam during drying. The resulting solid cellulose foam does not have a homogeneous structure and contains defects in the form of voids caused by coalesced cells within the wet foam. Due to these defects, the solid cellulose foam has a weak, rough surface.

[0044] In some embodiments, the yield stress of the wet cellulose foam 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.

[0045] In some embodiments, the density of the wet cellulose foam used in the present invention is between 70 and 600 kg / m 3 , or 100 to 500 kg / m 3 , or 100 to 400 kg / m 3 , or 125 to 375 kg / m 3 , or 140 to 375 kg / m 3 may be.

[0046] In some embodiments, the wet cellulose foam used in the present invention comprises at least 10 wt.% cellulose, calculated based 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 fibers, calculated based on the total weight of the wet cellulose foam.

[0047] Due to its high solids content, the wet foam does not need to be dehydrated before drying. The foam can be dried by evaporative drying at room temperature or elevated temperatures (e.g., 40°C to 140°C). After drying, the solid cellulose foam has a yield of 10 to 80 kg / m 3 , 10~60kg / m 3 , or 20 to 50 kg / m 3In a preferred embodiment, the cellulose foam preferably contains 71 to 95 wt %, for example 75 to 95 wt %, of cellulose fibers, based on the total dry weight of the cellulose foam, 4 to 24 wt %, for example 5 to 20 wt %, of a water-soluble thickener, and at least two surfactants, based on the total dry weight of the cellulose foam. A wet cellulose foam having such a composition has a homogeneous structure and, as described above, good stability. Such a wet cellulose foam can also be dried without prior dehydration.

[0048] The solid cellulose foam may have a solids content, after drying, in the range of 95 to 100% by weight, preferably 98 to 100% by weight, calculated based on the total weight of the solid cellulose foam.

[0049] During drying, a densified layer forms on the outer surface of the wet cellulose foam and remains on the outer surface of the dried cellulose foam. The densified layer is composed of cellulose fibers that are more densely packed and partially oriented in a different direction compared to the bulk. The densified layer has improved mechanical stability and strength compared to the core of the cellulose foam. The core of the cellulose foam is composed of a homogeneous subsequent cell fiber network. The core is highly porous, and the densified layer, although having a denser structure than the core, is still porous. Therefore, the densified layer provides the cellulose foam with improved stability and mechanical strength.

[0050] The cellulose foams described above are preferred foams for use in the cellulose foam deposits of the present invention. Alternatively, other cellulose foams can be used, such as those disclosed in WO2016068771 A1, WO2016068787 A1, and WO2020011587 A1.

[0051] The method according to the first aspect includes providing individual units of a first cellulose foam on a surface to obtain a first cellulose foam deposit. The distance between adjacent individual units ranges from 2 to 20 mm, 5 to 20 mm, 2 to 15 mm, 2 to 10 mm, or 2 to 8 mm. The individual units can be provided on any suitable surface. For example, the surface can be a perforated metal tray or a conveyor belt. An outer frame can be attached to the tray to further support the deposited wet foam.

[0052] As used herein, the term "individual unit" refers to an individual three-dimensional foam unit within a solid cellulose foam. In the solid cellulose foam, the individual units are separated from adjacent individual units by a fixed distance. The spaces between the individual units within the solid cellulose foam are filled by subsequent foam depositions, embedding the individual units within the foam matrix. The individual units are distinguishable from each other and from the foam matrix.

[0053] The term "adjacent," as used herein in phrases such as "adjacent individual units," refers to individual units that are next to one another. Adjacent individual units may be aligned or offset from one another. The distance between adjacent individual units is measured from one individual unit in the first foam stack to its nearest adjacent individual unit.

[0054] In some embodiments, the individual units are obtained by providing individual units of the first wet cellulose foam on a surface and drying the first wet cellulose foam in the individual units. Thus, in one embodiment, a method according to the first aspect comprises providing individual units of the first wet cellulose foam on a surface, the distance between adjacent individual units being in the range of 2 to 20 mm, and drying the first wet cellulose foam in the individual units to obtain a first cellulose foam deposit.

[0055] The individual units can be obtained by dispensing the first wet cellulose onto a surface in individual units, followed by drying the first wet cellulose foam, which can be dispensed using any suitable means, such as by extrusion through a nozzle or by passing the wet cellulose foam over a stencil surface.

[0056] The individual units can be obtained by depositing a first wet cellulose foam on a surface, making cuts extending across the height of the first wet cellulose foam to obtain the individual units, and then drying the first wet cellulose foam. The first wet cellulose foam can be deposited in the form of a plank. The cuts can be performed with a blade or knife, by using a template, or by air cutting. During drying, the foam shrinks to a certain extent, forming gaps along the cuts. After drying, the individual units of the first wet cellulose foam deposit are separated by gaps having a distance ranging from 2 to 20 mm.

[0057] Preferably, the score lines are formed by air cutting. Air cutting uses a jet of compressed air to create cuts in the material. The compressed air is delivered through a nozzle, the movement of which is controlled by a computer. This allows for high precision in the process. Multiple nozzles can be used to speed up the process by allowing simultaneous cutting. The pressure used can range from 0.1 to 5 bar, or from 0.25 to 4 bar. To cut the wet cellulose foam into individual units, the air jet must have sufficient velocity to penetrate the height of the wet cellulose foam. The velocity of the air in the jet varies depending on parameters such as the air pressure, the nozzle size, and the density and thickness of the wet cellulose foam. As will be understood by those skilled in the art, sufficient air velocity can be achieved by selecting an air pressure appropriate for the wet cellulose foam being cut. The score lines created are typically thin, with their size varying depending on the nozzle size and air pressure. The width of the score lines typically ranges from 0.5 mm to 2.0 mm. Because the wet cellulose foam of the present invention is a soft material, it can be cut with high precision using only a jet of compressed air. The air jet does not need to contain particles such as abrasive particles.

[0058] The large number of small cells makes the wet cellulose foam stable and low in density. The wet cellulose foam used in the method of the present invention has a sufficiently high viscosity and low density to allow the formation of individual units that do not collapse before drying. Thus, each individual unit can stand on its own without collapsing before drying.

[0059] The first wet cellulose foam in an individual unit is dried prior to depositing the second wet cellulose foam in a subsequent foam stack. Drying of the wet individual unit can be accomplished by evaporation at room temperature or elevated temperatures (e.g., 40°C to 140°C). Any suitable equipment can be used. In some embodiments, the individual unit of wet cellulose foam is at least partially dried when the second wet cellulose foam of the subsequent foam stack is deposited. In some embodiments, the individual unit of wet cellulose foam is completely dried when the second wet cellulose foam of the subsequent foam stack is deposited.

[0060] Each individual unit can stand on its own without collapsing during drying. Drying of the individual units of wet cellulose foam is carried out at least until a crust, i.e., a thin densified layer of cellulose fibers, forms on the outer surface of each individual unit, e.g., on each face of each individual unit. The densified layer is a very thin layer that forms on the outermost surface of the cellulose foam during drying. While the densified layer contains cellulose fibers primarily oriented in a two-dimensional plane (x-y plane), most fibers in cellulose foam contain clusters of fibers oriented in three-dimensional space with many empty spaces between the clusters. The two-dimensional structure of the cellulose fibers in the densified layer rapidly but gradually changes to the three-dimensional structure found in the majority of cellulose foam. The thin thickness of the densified layer means that it does not substantially affect the overall density of the cellulose foam while still contributing to the excellent mechanical properties of the individual units.

[0061] When the individual units of cellulose foam fibers dry, their cores consist of a dense, homogenous fiber network, while their outer surfaces, such as the bottom, top, and sides, consist of a more densely packed fiber network, or densified layer. The densified layer formed on the surfaces of the individual units during the first cellulose foam deposition strengthens the individual units and prevents them from breaking during subsequent foam depositions in which wet cellulose foam is deposited between the individual units.

[0062] In another embodiment, the individual units can be obtained by depositing a first wet cellulose foam, drying the first wet cellulose foam, and cutting the dried first cellulose foam into individual units. The wet cellulose foam can be deposited by extrusion or casting. The dried individual units are deposited on a surface. Preferably, the wet foam is extruded into boards, planks, bars, or rods. The boards, planks, bars, or rods can be cut into individual units and placed on a surface. In this embodiment, the individual units do not have a densified layer on their surfaces because they are cut from dried foam and are not dried separately. In some applications, providing individual units without a densified layer may be advantageous because it improves inter-fiber bond strength between the cellulose fibers within the individual units and during subsequent foam deposition.

[0063] The density of the solid cellulose foam in the individual units of the present invention is between 10 and 80 kg / m 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 The dry content of solid cellulose foam in the individual units may be at least 95% by weight, calculated based on the total weight of the solid cellulose foam.

[0064] Each individual unit may have a three-dimensional shape. Preferably, all individual units in the first pile have the same shape. The individual units may have any suitable three-dimensional shape, such as a cylinder or a polyhedron. Each individual unit has a height, a width, a length, a top surface, and a bottom surface. The height of an individual unit is measured perpendicular to the surface on which the unit is placed. The width and length are measured at the top of the individual unit. For cylindrical individual units, the width corresponds to the diameter.

[0065] In some embodiments, each individual unit has the shape of a polyhedron such as a rectangular parallelepiped or cube, or a prism such as a hexagonal prism. Minor variations in the symmetry of the individual units may occur without altering the primary purpose of providing stability to the foam. For example, the cube, rectangular parallelepiped, or prism may be slightly distorted, and its opposite bases may not necessarily be perfectly parallel and overlapping. The top surface of each individual unit may be, for example, rectangular, square, diamond, octagonal, or hexagonal in shape.

[0066] Depending on the shape of the individual units, the width of the individual units may be the same or may vary throughout the height of the individual units. In some embodiments, due to shrinkage of the wet cellulose foam during drying, the width at the top of the individual units is smaller than the width at the bottom of the individual units. This means that the sidewalls of the individual units may be sloping.

[0067] The distance between adjacent individual units ranges from 2 to 20 mm, 5 to 20 mm, 2 to 15 mm, 2 to 10 mm, or 2 to 8 mm. The distance is measured vertically from the edge of the top surface of one individual unit to the edge of the top surface of an adjacent individual unit, as shown in FIG. 2. Preferably, the distance between adjacent individual units is the same throughout the entire solid cellulose. The individual units can be provided in any suitable pattern. Adjacent individual units can be positioned parallel to each other or offset from each other. For example, the individual units can be positioned in a pattern selected from a chevron pattern, a honeycomb pattern, a diamond pattern, a rib pattern, or a square pattern. In embodiments in which the width of the individual units is smaller at the top than at the bottom, the distance between adjacent individual units is greater at the top than at the bottom.

[0068] In one embodiment, the width of each individual unit is in the range of 0.9 to 1.3 times, or 0.9 to 1.2 times, or 0.9 to 1.1 times its height. When the width of each individual unit is comparable to its height, uneven shrinkage during drying of the individual units in the first foam stack is minimized.

[0069] The length of each individual unit may be approximately the same as the width, or may be significantly longer. In one embodiment, each individual unit extends along the entire length or width of the solid cellulose foam, forming a rib structure. In another embodiment, the length of each individual unit is approximately equal to its width, and multiple individual units are positioned along both the width and length of the solid cellulose foam.

[0070] A second wet cellulose foam is deposited between the individual units of the first foam deposit to obtain a subsequent foam deposit. In some embodiments, the second wet cellulose foam may be identical to the first wet cellulose foam used in the individual units. This facilitates processing and ensures that the resulting solid cellulose foam has similar properties throughout the foam. In other embodiments, the second wet cellulose foam may differ from the first wet cellulose foam, for example, in terms of composition or density. For example, the density of the first wet cellulose foam may be higher than the density of the second wet cellulose foam. The final properties of the solid cellulose foam can be customized by providing wet cellulose foams with different properties.

[0071] To avoid voids within the solid cellulose foam, it is important that the second wet cellulose foam completely fills the gaps separating the individual units of the first cellulose foam deposit. The second wet cellulose foam can be deposited using any suitable means, such as extrusion.

[0072] In one embodiment, a vacuum is applied during the deposition of the second wet cellulose foam to ensure that the gaps between adjacent individual units are completely filled with the second wet cellulose foam. In such an embodiment, the air pressure on the bottom side of the first foam stack is reduced as the second wet cellulose foam is deposited. This means that the wet cellulose foam is forced into the gap by the air pressure difference. The air pressure difference must be large enough to overcome the yield stress of the wet cellulose foam and initiate flow, and large enough to force the wet foam into the narrow gap. The vacuum must be weak to prevent the air bubbles in the wet cellulose foam from expanding and collapsing. If too much vacuum is applied, the gas in each bubble in the foam will expand with great force to occupy the volume of gas equilibrated at such a low pressure. This expansion distortion will cause the foam to fail. Vacuum-assisted deposition is facilitated by the air-impermeable nature of the wet cellulose foam and the air-permeable nature of the solid cellulose foam.

[0073] The low vacuum applied does not remove water from the wet foam, and the purpose of applying vacuum is only to facilitate gap filling, not to dehydrate the wet foam.

[0074] Instead of applying a vacuum during deposition of the second wet cellulose foam, the wet foam can be forced down into the gap by increasing air pressure, mechanical means, or by increasing the pressure within the wet foam itself.

[0075] In some embodiments, increased air pressure is applied to the top of the second wet cellulose foam, forcing the foam down into the gap.

[0076] In some embodiments, the second wet cellulose foam is mechanically pressed down into the gap using mechanical means such as a scraper or roller.

[0077] In some embodiments, the second wet cellulose foam has increased pressure. When the second wet foam is discharged from the depositor, it is pressurized, facilitating filling of the gaps between the individual units of the first deposit. Filling the gaps is even easier if paths other than lowering into the gaps are at least partially restricted. One way to partially restrict other paths is to place a pipe collar on the outlet pipe from the depositor and position the outlet pipe near the gap to be filled.

[0078] The height of each individual unit in the first foam deposit may be 0.7 to 1.0 times, or 0.7 to 0.95 times, or 0.75 to 0.9 times the height of the second wet cellulose foam in the subsequent foam deposit. In embodiments where the height of the individual units is less than the height of the surrounding foam matrix of the subsequent foam deposit, a smooth top surface of the solid cellulose foam is obtained. In such embodiments, the individual units are covered by the foam matrix and therefore not visible from the top surface of the solid cellulose foam. The surface of the subsequent wet foam deposit can be sanded to a uniform surface before drying.

[0079] The second wet cellulose foam in a subsequent foam stack is dried to obtain a solid cellulose foam in which the individual cellulose foam units are embedded in the cellulose foam matrix. The individual units are formed in the first stacking step, and the cellulose foam matrix is ​​formed in the second stacking step.

[0080] Drying of the wet cellulose foam in the subsequent deposition can be carried out by evaporation at room temperature or at elevated temperatures (e.g., 40°C to 140°C). Any suitable equipment can be used. After drying, the density of the solid cellulose foam in the cellulose foam matrix is ​​between 10 and 80 kg / m. 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3The dry content of solid cellulose foam within the cellulose foam matrix may be at least 95% by weight, calculated based on the total weight of the solid cellulose foam.

[0081] In embodiments where the wet cellulosic foam in an individual unit has been only partially dried prior to the deposition of a second wet cellulosic foam in a subsequent deposition, the individual unit is dried along with the second wet cellulosic foam. However, it is preferred to completely dry the individual unit prior to subsequent deposition.

[0082] In wet cellulose foam, resistance forces hold the cellulose fibers in place. During drying, the water level between fibers decreases, increasing capillary forces within the cellulose foam material. When the capillary forces exceed the resistance forces, the fibers slip. As the water evaporates, the resistance forces increase, causing the fibers to get stuck closer together than before drying, resulting in shrinkage of the material. At the macro level, the shape of the wet cellulose foam affects the direction and magnitude of the tension vectors that develop in the material during drying. Contact points, such as with frames or perforated molds, generate opposing tension forces, affecting the net tension. Deformations such as shrinkage occur when net tension, or the tension vector, predominates in a particular direction. Therefore, the width-to-height ratio of a wet cellulose foam pile affects the distribution of net tension within the foam as it dries; the greater the ratio, the greater the net tension that develops.

[0083] The method according to the first aspect of the present invention reduces net tension in the wet cellulose foam during drying due to the low width-to-height ratio of each individual unit. This minimizes or prevents uneven shrinkage of the wet cellulose foam across the height of the individual units. Compared to drying a large wet cellulose foam pile with a large surface area, the surface area of ​​the wet cellulose foam pile in the present invention is divided into multiple individual units, each with a relatively small surface area and a favorable width-to-height ratio. Figure 2 illustrates one embodiment of the method of the present invention, in which the wet cellulose foam is deposited onto a surface as individual units to obtain a first foam pile (i). The individual units are spaced a distance d from each other. All the individual units have the same size and shape. Because each individual unit has a low aspect ratio of height to width, uneven shrinkage of each individual unit as the foam dries is eliminated or significantly reduced (ii). When the individual units dry, they contain a core with a homogeneous fiber network and a densified outer surface (i.e., top, bottom, and sides) (iii). Next, a second layer of wet cellulose foam is deposited on the surface between the previously dried individual units (iv). As the wet foam of the subsequent layer dries (v), the individual units of the first layer already distributed on the surface reduce the width-to-height ratio of the wet cellulose foam in the subsequent layer. The tensions of the individual units interact with each other, reducing the net tension of the wet foam of the subsequent layer, suppressing the increase in tension during drying and reducing the impact of shrinkage on the overall dimensions of the resulting solid cellulose foam (iv). Thus, the method of the present invention allows for the formation of solid cellulose foam with a uniform height because uneven shrinkage in the thickness (i.e., height) direction is minimized. Furthermore, the method allows for the formation of foamed objects without the use of walled molds, meaning that very large objects, such as boards and planks for use in large constructions such as buildings and other large structures, can be produced using this method.

[0084] The solid cellulose foam obtained by a method according to one embodiment of the present invention is shown in Figure 3. The majority of the solid cellulose foam consists of individual units in the shape of a rectangular parallelepiped, surrounded by a densified layer (black), which is in turn surrounded by a foam matrix (B). The top and bottom layers of the solid cellulose foam also contain a densified layer (A). Apart from the densified layer, the foam within the individual units and the foam matrix is ​​composed of a homogeneous foam.

[0085] When drying large pieces of wet cellulose foam deposited as a single foam deposit, drying is slow due to the insulating properties of the foam. In the method according to the present invention, instead of depositing a single foam deposit, two foam deposits are provided. When drying individual units of the first foam deposit, the surface area in contact with the air increases, resulting in relatively fast drying. Therefore, the two-stage deposition method of the present invention can shorten the total drying time of the cellulose foam compared to a cellulose foam of the same size obtained by a conventional one-stage deposition method. A shorter drying time is advantageous from a cost perspective. As used herein, the term "total drying time" refers to the sum of the drying time for the first foam deposit and the drying time for each subsequent foam deposit. In the case of one-stage foam deposition, the total drying time is the time required to dry the entire wet foam.

[0086] It has been found that the drying time of a first foam deposit is typically faster than the drying time of subsequent foam deposits. By placing the individual units of the first foam deposit close to each other, as in the present invention, the width of the subsequent foam deposits is reduced, thereby shortening the drying time of the subsequent deposits and, therefore, the total drying time of the foam. Narrower width wet foam deposits dry faster than wider width wet foam deposits. By selecting a smaller distance between the individual units, the width of the subsequent foam deposits can be further reduced, further shortening the overall drying time.

[0087] The height of the solid cellulose foam can be in the range of 1 to 20 cm, 1 to 10 cm, 1 to 6 cm, or 4 to 6 cm. The width and length of the solid cellulose foam are not particularly limited, but can be in the range of 60 cm to 400 cm, for example, 100 cm to 300 cm, depending on the equipment used for production and the desired dimensions. The height of the solid cellulose foam corresponds to the height of the cellulose foam of the subsequent pile. In one example, the solid cellulose foam is a plank having a thickness of 5 cm.

[0088] The density of solid cellulose foam is 10 to 80 kg / m 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 The dry content of the solid cellulose foam may be at least 95% by weight, calculated based on the total weight of the solid cellulose foam.

[0089] The number of individual units deposited within the solid cellulose foam varies depending on the size of the solid cellulose foam being produced, the size of the individual units, the distance between adjacent individual units, and the deposition method. The two-stage deposition method of the present invention can produce foam objects with reduced non-uniform shrinkage compared to similar foam objects obtained by a single-stage deposition method. The method can also reduce drying times compared to similarly sized foams obtained by a single-stage deposition method. The method also allows for a continuous process for forming foam objects, such as open-cell webs.

[0090] The present invention provides a low-density cellulose foam comprising individual cellulose foam units with stiffer, densified cellulose fiber walls embedded within a cellulose foam matrix. By incorporating the individual units as structural elements of the solid foam, it is possible to create a stiffer foam while maintaining the same low density. The individual units comprise 30-90%, 40-90%, 50-90%, or 60-90% of the total volume of the foam material, including the individual units and the surrounding foam matrix.

[0091] By ensuring that the distance between adjacent individual units within the solid cellulose foam is in the range of 2 to 20 mm, a uniform surface is obtained without any depressions at the interface between the individual units and the foam matrix on the top or bottom of the solid cellulose foam. The cross section of the solid cellulose foam is also more homogenized. If the distance between adjacent individual units is large, depressions may form on the top and bottom surfaces of the solid cellulose foam at the interface between the individual units and the foam matrix.

[0092] In some embodiments, the density of the first foam deposit is higher than the density of the subsequent foam deposit. For example, the density of the first foam deposit can be at least 110%, such as 130%, 150%, or 200% higher than the density of the subsequent foam deposit. In one embodiment, the density of the first foam deposit can be in the range of 105-500%, 110-330%, 110-250%, 110-200%, or 150-330% higher than the density of the subsequent foam deposit.

[0093] It has been found that if the density of the first foam deposit is higher than that of subsequent foam deposits, the total drying time of the foam is reduced, allowing for a more efficient process. Additionally, the higher density regions of the foam (i.e., individual units) have different properties, such as stiffness, compared to the lower density regions (i.e., the foam matrix).

[0094] In some embodiments, the density of the individual units varies in different portions of the first foam stack. The density and properties of the final solid cellulose foam can be tailored by using individual units with different densities. For example, a solid cellulose foam with regions of different stiffness can be obtained.

[0095] The density of wet cellulose foam depends on the amount of air contained in the foam. If a low density is desired, a relatively large amount of air should be included. If a high density is desired, a relatively small amount of air should be included. The density of the wet cellulose foam directly affects the density of the solid cellulose foam after drying. Therefore, any difference in density between the wet foam of the first deposit and the wet foam of subsequent deposits will remain in the solid cellulose foam.

[0096] In some embodiments, a coating can be applied to any surface of the solid cellulose foam and / or to the first or subsequent foam deposits. The coating is preferably applied in the form of a liquid coating composition, and one or more coating layers can be applied. The coating layers can be the same or different in composition. The coating can include at least one particulate material and at least one film-forming material. The particulate material can be selected from at least one of microfibrillated cellulose (MFC), cellulose fibers, or mineral particles such as clay or calcium carbonate. In the context of this application, MFC refers to cellulose particles, fibers, or fibrils having a width or diameter of 20 nm to 1000 nm. The film-forming material can be selected from at least one of carboxymethyl cellulose (CMC), cellulose ethers, starch, polyvinyl alcohol, or synthetic latexes such as acrylic latex or styrene butadiene latex. The coating may include at least one hydrophobic agent, for example, a hydrophobic agent selected from at least one of a wax, such as beeswax or carnauba wax, an alkyl ketene dimer (AKD), or an alkyl succinic anhydride (ASA).

[0097] By applying a coating, the air permeability of the solid cellulose foam is reduced because the pores on the surface of the foam are closed by the coating. This facilitates various processing and conversion operations involving vacuum. Furthermore, depending on the type of coating, the application of the coating may change the properties of the solid cellulose foam, such as its strength and hydrophobicity. The coating is preferably applied to the surface of the foam, including the densified layer.

[0098] According to a second aspect, the present invention relates to a solid cellulose foam comprising individual units of cellulose foam embedded within a cellulose foam matrix, the distance between adjacent individual units being in the range of 2 to 20 mm. The solid cellulose foam according to the second aspect may be produced by the method according to the first aspect. The solid cellulose foam according to the second aspect may be further defined as set out above with reference to the first aspect.

[0099] According to a third aspect, the present invention relates to the use of a solid cellulose foam according to the second aspect as a packaging material, building material, thermal insulation material, soundproofing material, or hydroponic plant growing medium. The solid cellulose foam of the present invention has excellent cushioning properties that are desirable in the field of protective packaging. It also has thermal and soundproofing properties. [Example]

[0100] Example 1 Drying time, subsequent foam deposits A wet cellulose foam with a dry content of 15.8 wt% was prepared. The cellulose foam consisted of 10 wt% CMC, 1 wt% surfactant (a mixture of myristic acid and sodium cocoyl sarcosinate), and 89 wt% cellulose fiber (softwood bleached kraft pulp). All weights are based on the total weight of the foam solids. Cellulose fiber (125 g, softwood bleached kraft pulp fiber) was dissolved in 700 mL of water using a Kenwood Chef XL Titanium mixer equipped with a K-beater. After the cellulose fiber suspension was properly pulped, CMC (13.5 g) was added as a dry powder and mixed with the K-beater until a uniform mixture was obtained. A surfactant solution (20 wt%) containing a 1:1 molar ratio of sodium cocoyl sarcosinate to myristic acid was then added to the cellulose fiber / CMC solution mixture (8 ml). The mixture was then aerated using the balloon whipper of the Kenwood mixer until the required amount of air was mechanically introduced into the mixture. After mixing, the foam was collected in a 250 ml plastic cup and the density was measured (target density 188 kg / m 3 ).

[0101] Individual units of wet cellulose foam were deposited on a perforated tray and dried in a convection oven at 120°C. Individual units were 5 cm high, 5 cm wide, and 14 cm long. The distance between adjacent units was 5 mm, 8 mm, 10 mm, or 20 mm.

[0102] A second deposition of wet cellulose foam was then performed. The wet cellulose foam in this second deposition was the same foam used for the individual units. The wet foam was deposited between the individual units to create a foam matrix surrounding the individual units.

[0103] After depositing the wet cellulose foam, the samples were dried in an oven at 120 °C and weighed at multiple time points (see Figure 4). It is clear that the drying time decreases as the distance between adjacent individual units decreases.

[0104] Example 2 Drying time of foams produced by two-stage deposition 15% by weight dry content and 154 kg / m 3 A wet cellulose foam (containing 88% by weight (dry weight basis) of bleached softwood kraft pulp, 10% by weight of CMC, and a surfactant mixture of myristic acid and cocoyl sarcosine) with a density of 1000 sq ft was deposited in a wooden frame (2.1 x 24.5 x 43.5 cm) on a perforated tray. The frame was scraped to smooth the top edge and create a uniform surface. The foam was then cut using 16 air nozzles facing downward perpendicular to the foam surface. The nozzles were fixed in a row with a 20 mm spacing between each nozzle outlet. The outlet pipe of each nozzle had a diameter of 0.75 mm and was long enough to achieve a directional air beam. The nozzles were connected to pressurized air at a pressure between 1 and 1.5 bar and positioned 3 mm above the foam. The foam moved horizontally along its width at a speed of 0.2 m / s, passing under the row of nozzles to create parallel cuts in the wet foam at 20 mm intervals. The cuts were perpendicular to the sides of the foam. The foam was then rotated 90° and cut again with the same row of nozzles. For the second cut, the foam was moved along its length in the same manner as the first cut, creating parallel cuts that intersected the first cut. The cut pattern was a square grid pattern, with the cuts extending completely through the foam. Both the first and second sets of cuts were continuous and extended from one side of the wet foam to the other. The cut individual units were rectangular and completely separated from each other. The distance between adjacent individual units was 4 mm, measured from the top edge of one individual unit to the top edge of the adjacent individual unit.

[0105] The resulting first foam pile was dried in an oven at 120°C. The foam was weighed at various times during drying. The resulting drying curve is shown in Figure 5 (air cut first step 2x2 cm). The drying time for the first foam pile was 50 minutes.

[0106] After the first foam deposit dried, a second wet cellulose foam with the same composition and properties as the foam used in the first foam deposit was applied on top of each individual unit of the dried first foam deposit. A vacuum was applied from below to ensure the wet foam filled the gaps between adjacent individual units of the first foam deposit. The wet foam, still confined within the same wooden frame, was scraped to create an even surface. The resulting foam plank was dried using the same conditions as the first foam deposit. Again, the foam was weighed at several time points. The resulting drying curve is shown in Figure 5 (for subsequent fills after air cutting). The drying time for the subsequent foam deposit was 49 minutes.

[0107] The total amount of water evaporated in the two successive drying steps was 390 g. The total drying time of the foam was 99 min. After both drying steps, the density of the foam was 38 kg / m 3 It was.

[0108] Example 3 (Comparative Example) Drying time of foams produced by one-step deposition A reference foam plank with a higher foam density was made in the same frame as described in Example 2. The composition and dry content of the reference foam were the same as those described for the foam in Example 2. The wet cellulose foam used in Example 3 contained the same amount of water as that evaporated during drying of the foam in Example 2. The density of the wet cellulose foam was 206 kg / m 3 The reference plank was dried as described in Example 2 and the foam plank was weighed at several time points. The resulting drying curve is shown in Figure 5 (single-stage deposited plank). The density of the dried foam was 39 kg / m 3 The drying time was 124 minutes.

[0109] Therefore, the total time required to remove the same amount of water is shorter using two-stage deposition than using one-stage deposition.

[0110] Other modifications and variations will become apparent to those skilled in the art in view of the above detailed description of the invention, and it is evident, however, that such other modifications and variations can be made without departing from the spirit and scope of the invention.

Claims

1. 1. A method for producing a solid cellulose foam, comprising: - providing individual units of a first cellulose foam on a surface to obtain a first foam deposit, the distance between adjacent individual units being in the range of 2 to 20 mm; - depositing a second wet cellulose foam between the individual units to obtain a subsequent foam stack; drying the second wet cellulose foam in a subsequent foam stack to obtain a solid cellulose foam in which the individual units of cellulose foam are embedded within the cellulose foam matrix; A method comprising:

2. 10. The method of claim 1, wherein the discrete units are obtained by providing discrete units of the first wet cellulose foam on a surface and drying the first wet cellulose foam in the discrete units.

3. 10. The method of claim 1, wherein the individual units are obtained by extruding a first wet cellulose foam, drying the extruded first wet cellulose foam, and cutting the dried first cellulose foam into individual units.

4. 4. The method of claim 1, wherein the wet cellulose foam used in the first and subsequent foam deposits comprises at least 10 wt. % cellulose, calculated based on the total weight of the wet cellulose foam.

5. The wet cellulose foam used in the first and subsequent foam deposits has a loading of 70 to 600 kg / m ３ 4. The method according to claim 1, wherein the density is in the range of

6. 6. The method of claim 1, wherein a vacuum is applied when depositing the second wet cellulose foam between the individual units of the first foam stack.

7. A method according to any one of claims 1 to 6, wherein the width of each individual unit is in the range of 0.9 to 1.3 times its height.

8. 8. The method of any one of claims 1 to 7, wherein the height of each individual unit is 0.7 to 1.0 times the height of the wet cellulose foam in the subsequent foam pile.

9. A solid cellulose foam comprising individual units of cellulose foam embedded within a cellulose foam matrix, wherein the distance between adjacent individual units is in the range of 2 to 20 mm.

10. 10. The solid cellulose foam of claim 9, wherein the solid cellulose foam comprises at least 75% by weight of cellulose fibers, calculated based on the total weight of the foam.

11. Solid cellulose foam: 10 to 80 kg / m ３ 11. The solid cellulose foam of claim 9 or 10, having a density in the range of

12. 12. The solid cellulose foam of any one of claims 9 to 11, wherein the width of each individual unit is in the range of 0.9 to 1.3 times its height.

13. 13. The solid cellulose foam of any one of claims 9 to 12, wherein the height of each individual unit is 0.7 to 1.0 times the height of the wet cellulose foam composition in the subsequent foam stack.

14. 14. The solid cellulose foam of any one of claims 9 to 13, wherein each individual unit is surrounded by a densified layer of foam.

15. 15. Use of the solid cellulose foam of any one of claims 9 to 14 as a packaging material, building material, thermal insulation material, acoustic insulation material or as a hydroponic plant growing medium.

Images