Method for producing solid cellulose foam, solid cellulose foam and uses thereof

Abstract

The present invention relates to a method for producing a solid cellulose foam. The method includes depositing a first wet cellulose foam to obtain a first wet foam deposit, followed by providing score lines at least partially through the height of the first wet foam deposit to form pillars of wet cellulose foam. During drying of the first wet foam deposit, gaps are formed along the score lines, separating the pillars. In a subsequent deposition step, a second wet cellulose foam is deposited to obtain a subsequent wet foam deposit that fills the gaps between the pillars. After drying, a solid cellulose foam is obtained that includes the pillars of the first solid foam deposit and the subsequent solid cellulose foam deposit that fills the gaps between the pillars.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid cellulose foam, and a solid cellulose foam comprising a first solid foam deposit and a subsequent solid foam deposit. 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] Various types of protective packaging materials can be used depending on the item being protected. 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, dimensionally 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 wet foams is often a critical step. Because wet foams are typically less stable, 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 it. 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] The insulating properties of cellulose foam, both wet and dry, typically result in long drying times, which 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 parts 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 provides a method for manufacturing a gyro having a height h s , length l s , width w s 1. A method for producing a solid cellulose foam having a composition comprising: a) providing a first wet cellulose foam; b) Height h 1W , length l 1W , width w 1W depositing a first wet cellulose foam onto a surface to obtain a first wet foam deposit having a top surface and a bottom surface; c) a top surface of the first wet foam deposit with a height h of the first wet foam deposit; 1w forming pillars in the first wet foam deposit by providing score lines at least partially through the first wet foam deposit; d) drying the first wet foam deposit to obtain a first solid foam deposit including pillars separated by gaps, the gaps being formed along the score lines, the first solid foam deposit having a height h 1S , length l 1S , width w 1S drying the first wet foam deposit, the first wet foam deposit having a top surface and a bottom surface; e) providing a second wet cellulose foam; f) depositing a second wet cellulose foam to obtain a subsequent wet foam deposit that fills the gaps between the pillars in the first solid foam deposit; g) drying the second wet foam deposit to obtain a solid cellulose foam comprising pillars of the first solid foam deposit and a subsequent solid foam deposit filling the gaps between the pillars; Includes:

[0016] Surprisingly, it has been found that uneven shrinkage across the height of a wet cellulose foam object during drying can be significantly reduced by the method of the first embodiment, which involves two foam depositions instead of just one. By providing score lines in the first wet foam deposition, gaps are formed along the score lines as the wet cellulose foam dries. The surface area of ​​the pillars separated by the score lines and the resulting gaps is significantly smaller than the surface area of ​​the entire wet foam deposition before providing the score lines. The smaller surface area is advantageous in minimizing uneven shrinkage during drying. The dried pillars of the first solid foam deposition support the subsequent wet foam deposition during drying, preventing shrinkage. The method of the present invention allows for the production of lightweight, dimensionally stable solid cellulose foams. The resulting solid cellulose foams have a uniform height.

[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. When drying pillars of the first wet foam according to the present invention, the presence of the pillars significantly increases the surface area in contact with the air, resulting in faster drying. Because the pillars are positioned close to each other, the total volume of subsequent wet foam deposits 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. A shorter drying time is advantageous from a cost perspective.

[0018] According to a second aspect, the present invention provides a method for manufacturing a gyro having a height h s , length l s , width w swherein the solid cellulose foam comprises a first solid foam deposit and a subsequent solid foam deposit, the first solid foam deposit comprising pillars separated by gaps, and the gaps are filled with the subsequent solid foam deposit.

[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 hydroponic plant growth medium. Because the solid cellulose foam is made from renewable resources and can be redispersed in water, it can be recycled through standard paper recycling streams.

[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.

[0021] The cellulose foam of the present invention preferably contains cellulose fibers in the range of 71 to 95 wt % calculated based on the total weight of the solid content in the foam, a water-soluble thickener in the range of 4 to 24 wt % calculated based on the total weight of the solid content in the foam, and at least two surfactants.

[0022] Embodiments of the present invention are best understood by referring to the following description and the accompanying drawings, in which the invention is described in more detail with reference to the accompanying drawings, in which dotted objects represent wet foam and solid objects represent dry foam. [Brief explanation of the drawings]

[0023] [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 2a] Figure 2a shows a schematic top view (top) and side view (bottom) of a solid cellulose foam plate at various points during fabrication: the first wet cellulose foam is deposited (Figure 2a). [Figure 2b] Score lines are provided to form rectangular pillars during the first wet foam deposition (Figure 2b), and the score lines extend partially to the height of the first wet foam deposition. [Figure 2c] After drying, a first solid foam deposit is obtained containing pillars separated by gaps corresponding to the score lines (Figure 2c). The gaps are formed by shrinkage of the wet cellulose foam during drying. [Figure 2d] Figure 2d shows the intermediate product with the gaps between the pillars and a second layer of wet cellulose foam deposited on top of the pillars. [Figure 2e] FIG. 2e shows a solid cellulose foam comprising pillars, a first solid foam deposit including a base, and a subsequent solid foam deposit including a top portion filling the gaps between the pillars and positioned at the top ends of the pillars. [Figure 3] 10A schematically illustrates another embodiment in which score lines are provided in a zigzag pattern during a first wet foam deposition, with adjacent score lines offset from one another. A first set of score lines (dotted lines) is provided, followed by a second set of score lines (dashed lines), which are offset from the first set of score lines. The score lines create rectangular pillars. [Figure 4] 10A and 10B schematically illustrate another embodiment in which pillars extend along the length of the first wet foam deposit, giving the first solid foam deposit a ribbed appearance. [Figure 5] Shown are drying curves obtained during drying of wet cellulose foam deposited in one stage (○) or in two stages: a first foam deposit that is air-cut before drying (□) and a second deposit that fills the gaps between the pillars formed during air-cutting (△). DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] 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.

[0026] 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.

[0027] As used herein, the term "solid cellulose foam" or "solid foam" refers 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.

[0028] The cellulose foam preferably used in the first and subsequent deposition steps of the method according to the invention will now be described in detail.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The solid cellulose foam can be redispersed in water, making it recyclable in the normal paper recycling stream.

[0040] The wet cellulose foam 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 based on the total weight of the wet foam, and the wet cellulose foam has a density of 120-500 kg / m 3 , or 120 to 400 kg / m 3 and the yield stress is at least 80 Pa.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] During drying, a dense layer forms on the outer surface of the wet cellulose foam and remains on the outer surface of the dried cellulose foam. The dense layer is composed of cellulose fibers that are more densely packed and partially oriented in a different direction compared to the bulk. The dense 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 dense layer, although having a denser structure than the core, is still porous. The dense layer provides the cellulose foam with improved stability and mechanical strength.

[0052] 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.

[0053] The method according to the first aspect will now be described in more detail with reference to Figure 2. Step a) of the method according to the first aspect comprises providing a first wet cellulose foam, the details of which are further described above.

[0054] Step b) of the method according to the first aspect comprises: 1W , length l 1W , width w 1W The method includes depositing a first wet cellulose foam on a surface to obtain a first wet foam deposit 10 having a top surface 11 and a bottom surface 12. The first wet cellulose foam is deposited on a surface such as a perforated metal tray or a conveyor belt. A frame can be attached to the tray to provide additional support during deposition and drying. The first wet cellulose foam can be deposited using any suitable means, such as extrusion. The height of the first wet foam deposit 10 can range from 1 to 20 cm, 1 to 10 cm, 1 to 6 cm, or 4 to 6 cm. The width and length of the first wet foam deposit 10 are not particularly limited, but can both be in the range of 60 cm to 400 cm, e.g., 100 cm to 300 cm, depending on the equipment used for production and the desired dimensions of the solid cellulose foam 300 to be produced. The first wet cellulose foam is preferably deposited so that the first wet foam deposit 10 has the shape of a sheet or plate, as shown in the embodiment of Figure 2a. As used herein, the term "plate" refers to an object whose length and width dimensions are significantly greater than its height, and whose length may be significantly greater than its width.

[0055] The method according to the first aspect can be used in a subsequent process, in which the first wet cellulose foam is typically deposited onto a moving surface, such as a conveyor belt.

[0056] Step c) of the method according to the first embodiment comprises applying a first wet foam deposit 10 to the top surface 11 of the first wet foam deposit 10 to a height h 1wThe method includes forming pillars 15 in the first wet foam deposit 10 by providing score lines 5, 6 at least partially through the first wet foam deposit 10. The score lines 5, 6 therefore extend from the top surface 11 of the first wet foam deposit 10 toward the bottom surface 12 of the first wet foam deposit 10. The score lines 5, 6 define the outer edges of the formed pillars 15. The score depth cd of the score lines 5, 6 is measured in a direction from the top surface 11 of the first wet foam deposit 10 toward the bottom surface 12 of the first wet foam deposit 10. Preferably, the cuts are made in a direction perpendicular to the top surface 11 of the first wet foam deposit 10. In another embodiment, the cuts are made obliquely relative to the top surface 11 of the first wet foam deposit 10.

[0057] The term "pillar" as used herein refers to an individual three-dimensional protruding foam unit. Pillars can be composed of wet or solid (i.e., dry) foam. In wet cellulose foam, pillars are separated from other adjacent pillars by score lines. In solid cellulose foam, pillars are separated from other adjacent pillars by gaps. The gaps between pillars in solid cellulose foam are filled by subsequent foam deposits. In solid cellulose foam, pillars are distinct from each other and from subsequent foam deposits. All pillars in a solid cellulose foam may extend from the bottom of the foam, or the pillars may be completely separated from each other. Pillars can have any suitable shape and size. For example, pillars can have the shape of a rectangular prism with the same height, width, and length dimensions. Alternatively, pillars can have the shape of a rectangular prism with the same height and width dimensions but a significantly longer length.

[0058] The height of the pillars 15 in the first wet foam deposit 10 corresponds to the cut depth cd.

[0059] In some embodiments, the score lines 5, 6 extend beyond the height h of the first wet foam deposit 10 as measured from the top surface 11 of the first wet foam deposit 10 toward the bottom surface 12 of the first wet foam deposit 10. 1W The cut depth cd extends to a cut depth cd corresponding to at least 70%, or at least 80%, or at least 90%, or at least 95% of the height h of the first wet foam deposit 10. 1W By ensuring that the cut depth cd is at least 70% of the height h of the first wet foam deposit 10, the pillars 15 are sufficiently separated to prevent uneven shrinkage in the height direction during drying. 1W If the height of the pillars 15 is less than 70%, the pillars 15 may begin to exhibit different amounts of shrinkage in their height, with more pronounced shrinkage of the pillars 15 in the center of the first wet foam deposit 10. In this case, the height of the resulting first solid foam deposit 100 will be uneven.

[0060] In some embodiments, the score lines 5, 6 extend beyond the height h of the first wet foam deposit. 1W In such an embodiment, the cut depth cd is the height h of the first wet foam deposit 10. 1W It corresponds to 100% of the above.

[0061] In some embodiments, the score lines 5, 6 extend beyond the height h of the first wet foam deposit 10 as measured from the top surface 11 of the first wet foam deposit 10 toward the bottom surface 12 of the first wet foam deposit 10. 1W In such an embodiment, the score lines 5, 6 extend to a cut depth cd in the range of 70% to 95%, for example 80% to 95%, or 85% to 95% of the height h of the first wet foam deposit 10. 1W The score lines 5, 6 do not extend across the entire height h of the first wet foam deposit 10. 1WWhen the first wet foam deposit 10 is only partially through the hole 14, the bottom surface 12 of the first wet foam deposit 10 is coherent. The coherent bottom surface is smooth and has all of the pillars 15 attached thereto, making it easier to handle during subsequent manufacturing.

[0062] The score lines 5, 6 can be provided in any suitable pattern on the top surface 11 of the first wet foam deposit 10 to form pillars 15 of any suitable three-dimensional shape. The number of score lines 5, 6 can vary depending on the size and number of pillars 15 to be formed. The score lines 5, 6 can be successive. Preferably, the score lines 5, 6 extend from one side of the first wet foam deposit 10 across the entire top surface 11 to the opposite side of the first wet foam deposit 10. In one embodiment, the score lines 5, 6 extend along the length l of the first wet foam deposit 10. 1W and / or width w 1W In one embodiment, the score lines 5, 6 are provided along the length l of the first wet foam deposit 10. 1W Direction and width w 1W The score lines 5, 6 may be provided in both directions. The score lines 5, 6 may be provided as straight lines or in other shapes such as wavy or zigzag. Multiple score lines 5, 6 may be provided parallel to each other. The spacing between the parallel score lines 5, 6 may be the same across the entire top surface 11 of the first wet foam deposit 10 or may be different in different portions of the top surface 11. The score lines 5, 6 may intersect with other score lines 5, 6. One score line 5, 6 may be offset from an adjacent score line 5, 6.

[0063] All pillars 15 formed within the first wet foam deposit 10 may have the same shape and dimensions, or the shapes and dimensions may vary in different portions of the first wet foam deposit 10. Preferably, all pillars 15 in the first wet foam deposit 10 have the same shape and dimensions. In some embodiments, each pillar 15 has the shape of a polyhedron, such as a rectangular parallelepiped or cube, or a prism, such as a hexagonal prism. Small variations in the symmetry of the pillars 15 do not affect their primary purpose of providing stability to the solid cellulose foam 300. For example, the cube, rectangular parallelepiped, or prism may be slightly distorted, and the opposite bases may not necessarily be perfectly parallel and overlapping. The top surface of each pillar 15, separated by the score lines 5 and 6, may be, for example, rectangular, square, diamond, octagonal, or hexagonal. The score lines 5 and 6 may be provided to form pillars 15 distributed in any suitable pattern. The pattern can be selected from a honeycomb pattern, a diamond pattern, a rib pattern, or a square pattern.

[0064] In one embodiment, the width of each pillar 15 is in the range of 90% to 130%, or 90% to 120%, or 90% to 110% of its height. Having similar widths and heights for each pillar 15 minimizes uneven shrinkage along its height during drying. The width is measured at the top of each pillar 15.

[0065] One embodiment is shown in Figure 2b. The height h of the first wet foam deposit 10 1W The first set of score lines 5, 6 are provided through the length l of the first wet foam deposit 10. 1W and the second set of score lines 6 extend parallel to one another along the width w of the first wet foam deposit 10. 1W Both sets of score lines 5 and 6 have the same, even spacing. The score lines 5, 6 are spaced apart along the width w of the first wet foam 10. 1W and length l 1WThe cut lines 5 and 6 are provided along both directions of the insulating film 11 and the insulating film 12, and the cut lines 5 and 6 intersect with each other to form rectangular pillars 15. The top surface of each pillar 15 is square.

[0066] Another embodiment is shown in Figure 3. A first wet foam deposit 10 is provided with score lines 5, 6 extending in a zigzag pattern along its length. A first set of score lines 5 is provided, followed by a second set of score lines 6 offset from the first set. The top surface of the first wet foam deposit 10 is formed with a pattern of square-topped pillars 15 separated by the score lines 5, 6. The zigzag cut lines, with adjacent score lines 5, 6 offset from one another, provide a simple method for producing pillars 15 of equal dimensions. Processing is simplified because the cuts are made in only one direction (i.e., along the length of the first wet foam deposit 10).

[0067] The score lines 5, 6 can be made using any suitable method. For example, a blade or knife can be used to make the score lines 5, 6. A mold with a sharp edge can also be used. Preferably, the blade, knife, or mold is made from a low-friction material such as PTFE, nylon, or a smooth metal material to prevent the wet cellulose foam from adhering to the material.

[0068] In a preferred embodiment, the score lines 5, 6 are created using air cutting. Air cutting uses compressed air jets 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 cuts. The pressure used can range from 0.1 to 5 bar, or from 0.25 to 4 bar. The cut depth cd depends on the velocity of the air used to cut, which in turn depends on parameters such as air pressure, nozzle size, and the density of the wet cellulose foam. As will be appreciated by those skilled in the art, the desired cut depth cd can be achieved by selecting an air pressure appropriate for the wet cellulose foam being cut. The score lines 5, 6 are typically thin, and their size varies depending on the nozzle size and air pressure. The width of the score lines 5, 6 can typically range from 0.5 mm to 2.0 mm. Alternatively, the width of the score lines 5, 6 can range from 5.0 mm to 15.0 mm, e.g., from 7.0 mm to 12.0 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, without the need to include particles such as abrasive particles in the air jet.

[0069] The width of the score lines 5, 6 typically depends on the means used to form the score lines 5, 6. When score lines are formed using a knife or blade, the width of the score lines 5, 6 typically ranges from 5.0 to 15.0 mm, for example, 7.0 to 12.0 mm. Depending on the means used to form the score lines 5, 6, parameters such as the applied pressure, processing speed, and density of the wet foam must be adjusted.

[0070] The wet cellulose foam in the first pile 10 has a sufficiently high viscosity and low density to allow the wet foam to not collapse before drying, even when score lines 5, 6 are provided.

[0071] Step d) of the method according to the first embodiment comprises drying the first wet foam deposit 10 to obtain a first solid foam deposit 100 comprising pillars 115 separated by gaps 55, the gaps 55 being formed along the score lines 5, 6, the first solid foam deposit 100 having a height h 1S , length l 1S , width w 1S , has a top surface 111 and a bottom surface 112 .

[0072] Drying of the first wet foam deposit 10 can be accomplished 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 first solid foam deposit 100 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 the first solid foam deposit 100 may be at least 95% by weight, calculated based on the total weight of the first solid foam deposit 100.

[0073] During drying of the first wet foam deposit 10, the wet foam within the pillars 15 shrinks to some extent due to the absence of a frame or other constraint. As a result, gaps 55 form along the score lines 5, 6 during drying. The pillars 115 are separated by the gaps 55 after drying. After drying, the pillars 115 of the first solid foam deposit 100 conform to the pillars 15 of the first wet foam deposit 10, but are slightly reduced in all dimensions due to foam shrinkage during drying. The height h of the pillars 115 of the first solid foam deposit 100 p may be in the range of 90% to 100% of the cut depth cd, for example, 92% to 98%.

[0074] In one embodiment, as shown in Figure 2c, the pillars 115 of the first solid foam deposit 100 are all rectangular prism-shaped and have similar height, width, and length dimensions. In the embodiment shown in Figure 2c, the pillars 115 have the same width and length across the entire height of the pillars 115.

[0075] In another embodiment, each pillar 115 extends across the entire width or length of the solid cellulose foam stack 100 so as to form a rib structure, as shown in Figure 4. In the embodiment of Figure 4, the length of the pillars 115 is significantly greater than their width.

[0076] After drying, the shape of the pillars 115 may become slightly distorted such that the top and bottom of the pillars 115 have different dimensions. Due to shrinkage of the wet foam during drying, the length and width of the top of the pillars 115 may become smaller than the length and width of the bottom of the pillars 115. For example, a rectangular wet foam pillar may shrink during drying such that it has a truncated pyramidal shape after drying.

[0077] During drying of the first wet foam deposit 10, the presence of the score lines 5, 6 causes a height h 1WNon-uniform shrinkage of the cellulose foam is minimized. The formed pillars 15 are self-supporting and do not collapse during drying. During drying of the wet cellulose foam in the first wet foam deposit 10, a densified layer forms on the outer surface of the foam. This means that a densified layer forms on the outer surface of the formed pillars 115. The densified layer is a very thin layer that forms on the outermost surface of the cellulose foam during drying. The densified layer primarily contains cellulose fibers oriented in a two-dimensional plane (x-y plane), whereas the majority of 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. Because the densified layer is thin, it has little effect on the overall density of the cellulose foam, but still contributes to the excellent mechanical properties of the pillars 115. When the pillars 115 in the first solid foam deposit 100 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, i.e., a densified layer. The formation of a densified layer on the outer surface of the pillars 115 in the first foam deposit 100 strengthens the pillars 115 and prevents them from collapsing when a second wet cellulose foam is deposited between them.

[0078] As the cellulose foam of the first wet foam deposit 10 shrinks during drying, the score lines 5, 6 widen, forming gaps 55. Gaps 55 separate adjacent pillars 115 in the first solid foam deposit 100. Gaps 55 can have a uniform width (as shown in Figures 2c and 4), or gaps 55 can be wider at the top than at the bottom. The width of gaps 55, measured vertically from the top edge of one pillar 115 to the top edge of the adjacent pillar 115, can range from 2 mm to 10 mm.

[0079] Width w of first solid foam deposit 100 1S and length l 1S is the width w of the first wet foam deposit 101W and length l 1W This is because the shrinkage of the foam in the width and length directions is usually negligible when the foam dries on a surface (i.e., when there is a limit). 1S is the height h of the first wet solid foam deposit 10 1W However, any shrinkage that may occur will be uniform due to the presence of pillars 15, and the height h of first solid foam deposit 100 will be 1S is the length l of the first solid foam deposit 100 1S or width w 1S does not change along

[0080] The height h of the pillars 115 of the first solid foam deposit 100 p is the height h of the first solid foam deposit 100 1S The cut lines 5, 6 may be 70% to 100% of the height h of the first wet foam deposit 10. 1W In an embodiment where the first solid foam deposit 100 is completely penetrated, the first solid foam deposit 100 is made up of a number of pillars 115, each having a height h p is the height h of the first solid foam deposit 100 1S becomes equal to

[0081] In some embodiments, as shown in FIG. 2c, the first solid foam deposit 100 has a height h of the first solid foam deposit 100 measured from the bottom surface 112 of the first solid foam deposit 100. 1S Height h equivalent to 5 to 30%, 5 to 20%, or 5 to 15% of b , with pillars 115 extending from bottom 117. In such an embodiment, score lines 5, 6 extend beyond height h of first wet foam deposit 10. 1W The height of the dry pillar, h, extends only partially through the p and the height h of the bottom 117 b The sum of these is the height h of the first solid foam deposit 100. 1SWhen the first solid foam deposit 100 includes a bottom portion 117, the bottom surface 112 of the first solid foam deposit 100 corresponds to the bottom surface 312 of the solid cellulose foam 300. In embodiments including a bottom portion 117, the bottom surfaces 112, 312 are in contact. In contact, the bottom surfaces 112, 312 are more aesthetically pleasing than those interrupted by pillars 115 and gaps 55, and also provide a smoothness and uniformity that is desirable in many applications.

[0082] In another embodiment, drying in step d) includes at least partially drying the first wet foam deposit 10. In such an embodiment, an at least partially dried first foam deposit is formed. The first wet foam deposit must be sufficiently dry so as not to collapse during subsequent wet foam deposition. The dry content of the at least partially dried first foam deposit may be at least 75% by weight, or at least 85% by weight, calculated based on the total weight of the at least partially dried first foam deposit. In such an embodiment, the at least partially dried first foam deposit is dried together with the second wet foam deposit in a second drying step to obtain a solid (i.e., completely dried) foam deposit. The at least partially dried first foam deposit is also considered a solid foam deposit, and all characteristics described with respect to a solid first foam deposit also apply to the at least partially dried first foam deposit. By only partially drying the first wet foam deposit, the total drying time of the foam is reduced because a portion of the first wet foam deposit is drying along with the second wet foam deposit, thereby reducing the energy consumption required for the process.

[0083] Step e) of the present invention involves providing a second wet cellulose foam, the details of which are further described above. In one embodiment, the second wet cellulose foam is identical to the first wet cellulose foam used in first foam deposition 10. When the first and second wet cellulose foams are identical, manufacturing is simplified.

[0084] In other embodiments, the second wet cellulose foam differs from the first wet cellulose foam, for example, in composition or density. The final properties of the solid cellulose foam 300 can be customized by providing wet cellulose foams with different properties.

[0085] Step f) of the present invention involves depositing a second wet cellulose foam to obtain a subsequent wet foam deposit 20 that fills the gaps 55 between the pillars 115 of the first solid foam deposit 100. To avoid the presence of voids within the solid cellulose foam 300, it is important that the second wet cellulose foam completely fills the gaps 55 separating the pillars 115 of the first solid foam deposit 100. After depositing the second wet cellulose foam, the pillars 115 of the first solid foam deposit 100 become embedded in the wet cellulose foam of the subsequent deposit 20. The second wet cellulose foam can be deposited using any suitable means, such as extrusion.

[0086] In one embodiment, a vacuum is applied during the deposition of the second wet cellulose foam to ensure that the gap 55 is completely filled with the second wet foam deposit 20. In such an embodiment, the air pressure on the bottom side of the first solid foam deposit 100 is reduced as the second wet cellulose foam is deposited. This means that the wet cellulose foam is forced into the gap 55 by the air pressure differential. The air pressure differential 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 low enough to prevent the gas bubbles in the second 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. Thus, even in embodiments where the first solid foam deposit 100 comprises a coherent bottom 117, vacuum assisted deposition is possible.

[0087] The vacuum applied is so low that it does not remove water from the wet foam. The purpose of applying vacuum is only to facilitate gap filling, not to dehydrate the wet foam.

[0088] Instead of applying a vacuum during deposition of the second wet cellulose foam, the wet foam can be forced down into gap 55 by increasing air pressure, mechanical means, or by increasing the pressure within the wet foam itself.

[0089] In some embodiments, increased air pressure is applied to the top of the second wet cellulose foam, forcing the foam down into gap 55 .

[0090] In some embodiments, the second wet cellulose foam is mechanically pressed down into gap 55 using mechanical means such as a scraper or roller.

[0091] In some embodiments, the second wet foam has an increased pressure. When the second wet foam is discharged from the depositor, it is pressurized, facilitating filling of the gaps 55 between the pillars 115 of the first deposit 100. Filling the gaps 55 is even easier if paths other than down into the gaps 55 are at least partially restricted. One way to partially restrict other paths is to place a pipe collar on the exit pipe from the deposition device and position the exit pipe near the gap 55 to fill.

[0092] Subsequent wet foam deposit 20 height h 2W is the height h of the pillars 115 of the first solid foam deposit 100 p For example, the height h of the subsequent wet foam deposit 20 may be 2W is the height h of the pillars 115 of the first solid foam deposit 100 p It may be 100% to 120% of the above.

[0093] In some embodiments, the height h of the subsequent wet foam deposit 20 2W is the height h of the pillars 115 of the first solid foam deposit 100 p In such an embodiment, the top surface 311 of the solid cellulose foam 300 comprises the top surface of the pillars 115 surrounded by subsequent solid foam stacks 200 filling the gaps 55 between the pillars 115.

[0094] In some embodiments, as shown in FIG. 2d, which shows an intermediate product 30, the height h of the subsequent wet foam deposit 20 2W is the height h of the column 115 of the first solid foam deposit 100 p For example, the height h of the subsequent wet foam deposit 20 2W is the height h of the pillars 115 of the first solid foam deposit 100 pThe thickness of the pillars 115 may be 105% to 120% of the thickness of the subsequent wet foam deposit 20. The portion of the subsequent wet foam deposit 20 disposed on top of the pillars 115 forms the apex 27 of the subsequent wet foam deposit 20. Such apex 27 ensures a tight and smooth top surface 311 of the solid cellulose foam 300. In embodiments in which the subsequent wet foam deposit 20 includes apex 27, the pillars 115 are not visible from the top surface 312 of the solid cellulose foam 300.

[0095] Width of subsequent wet foam deposit 20 w 2W and length l 2W is the width w of the first solid foam deposit 100 1S and length l 1S is preferably equal to

[0096] Step g) of the method according to the first embodiment involves drying the subsequent wet foam deposit 20 to obtain a solid cellulose foam 300 comprising the pillars 115 of the first solid foam deposit 100 and a second solid foam deposit 200 filling the gaps 55 between the pillars 115. After the subsequent wet foam deposit 20 has dried, the pillars 115 of the first solid foam deposit 100 become embedded in the subsequent solid foam deposit 200. The subsequent solid foam deposit 200 completely fills the gaps between the pillars of the first solid foam deposit 100, so that no voids are present in the solid cellulose foam 300.

[0097] Subsequent drying of the wet foam deposit 20 can be accomplished 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 subsequent solid foam deposit 200 can be in the range of 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 subsequent solid foam stack 200 may be at least 95% by weight, calculated based on the total weight of the subsequent solid foam stack 200.

[0098] The pillars 115 support the second wet cellulose foam in the subsequent stack 20 during drying, allowing shrinkage to be minimized.

[0099] In wet cellulose foam, resistance forces hold the cellulose fibers in place. During drying, the water level between the fibers decreases, increasing capillary forces within the 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 material shrinkage. 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.

[0100] The method according to the first aspect of the present invention reduces the net tension in the first wet cellulose foam during drying because the pillars 15 each have a low width-to-height ratio. This minimizes or prevents uneven shrinkage of the wet cellulose foam along its height within the pillars 15. Compared to drying a large wet cellulose foam stack with a large surface area, the surface area of ​​the first wet foam stack 10 in the present invention is divided into multiple pillars 15, each with a relatively small surface area and a favorable width-to-height ratio. When the pillars 15 dry, they have a core with a homogeneous fiber network and a densified outer surface (i.e., top, bottom, and sides). Next, a second wet cellulose foam is deposited between the already dried pillars 115. As the wet foam of the subsequent stack 20 dries, the pillars 115 already distributed on the surface of the first stack 100 reduce the width-to-height ratio of the wet cellulose foam in the subsequent stack 20. The tensions of the pillars 115 interact with each other, reducing the net tension in the wet foam of the subsequent stack 20, reducing tension buildup during drying and mitigating the impact of shrinkage on the overall dimensions of the resulting solid cellulose foam 300. Thus, the method of the present invention minimizes non-uniform shrinkage in the thickness (i.e., height) direction, thereby achieving a uniform height h s Furthermore, the method allows for the formation of foamed objects without the use of walled molds, which means that very large objects such as boards and planks for use in large constructions such as buildings and other large structures can be produced by this method.

[0101] The resulting solid cellulose foam 300 has a height h s , length l s , and width w s The density of the solid cellulose foam 300 is 10 to 80 kg / m 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3The solid cellulose foam 300 may have a dry content of at least 95% by weight, calculated based on the total weight of the solid cellulose foam 300. The solid cellulose foam 300 may have a dry content of at least 95% by weight, calculated based on the total weight of the solid cellulose foam 300. In one embodiment, the solid cellulose foam 300 comprises cellulose fibers in the range of 71-95% by weight, based on the total dry weight of the solid cellulose foam 300, a water-soluble thickener in the range of 4-24% by weight, based on the total dry weight of the solid cellulose foam 300, and at least two surfactants.

[0102] Solid cellulose foam 300 height h s 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 ws and length ls of the solid cellulose foam 300 are not particularly limited, but can both 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. In a preferred embodiment, the solid cellulose foam 300 is in the form of a plate.

[0103] The size and number of pillars 115 in first solid cellulose foam stack 100 may vary depending on the size of solid cellulose foam 300 and the desired properties.

[0104] Pillar 115 height h p is a solid cellulose foam 300mm high s In some embodiments, the pillars 115 extend from the top surface 311 of the solid cellulose foam 300 to the bottom surface 312 of the solid cellulose foam 300, i.e., the height h of the pillars 115 is p is a solid cellulose foam 300mm high s In such an embodiment, the height h of the first solid foam deposit 100 is equal to 1s , the height h of the subsequent solid foam deposit 200 2s , and the height h of the solid cellulose foam 300 sare all equal. In such embodiments, the pillars 115 are visible from both the top surface 311 and the bottom surface 312 of the solid cellulose foam 300. In such embodiments, the top surface 311 of the solid cellulose foam 300 is comprised of the top surface of the first solid cellulose foam deposit 100 (i.e., the pillars) and the top surface of the subsequent solid foam deposit 200 (i.e., the gaps between the pillars). Similarly, in such embodiments, the bottom surface 312 of the solid cellulose foam 300 is comprised of the bottom surface of the first solid cellulose foam deposit 100 (i.e., the pillars) and the bottom surface of the subsequent solid foam deposit 200 (i.e., the gaps between the pillars).

[0105] In some embodiments, the height h of the pillars 115 p Solid cellulose foam 300mm high s In such an embodiment, either the top surface 311 or the bottom surface 312 of the solid cellulose foam 300, or both, are in a sealed state and the pillars 115 are not visible.

[0106] In some embodiments, the first solid foam stack 100 further comprises a base 117 extending from the bottom surface 312 of the solid cellulose foam 300, with the pillars 115 extending from the base 117. The base 117 is coherent and the pillars 115 are not visible from the bottom surface 312 of the solid cellulose foam 300. The height h of the base 117 b is the height h of the first solid foam deposit 100 1s In embodiments where first solid foam stack 100 includes bottom 117, bottom surface 312 of solid cellulose foam 300 corresponds to bottom 112 of first solid foam stack 100.

[0107] In some embodiments, the subsequent solid foam stack 200 further includes a peak 217 disposed on top of the pillar 115. The peak 217 is in close contact with the pillar 115, and the pillar 115 is not visible from the peak 311 of the solid cellulose foam 300. The height h of the peak 217 t is a solid cellulose foam 300mm highs It may be 5 to 15%, for example, 7 to 12% of the total.

[0108] In a preferred embodiment, as shown in Figure 2e, the first solid foam deposit 100 includes a bottom portion 117 and the subsequent solid foam deposit 200 includes a top portion 217. This allows both the top surface 311 and the bottom surface 312 of the solid cellulose foam 300 to be coherent and smooth. This also improves the mechanical properties of the solid cellulose foam 300 by reducing the risk of breakage or other damage along the intersection between the first solid foam deposit 100 and the subsequent solid foam deposit 200. In such an embodiment, the height h of the solid cellulose foam is s is the height h of pillar 115 p , height h of top 217 t , and the height h of the bottom 117 b is equal to the sum of

[0109] The present invention provides a low-density cellulose foam in which a first solid foam deposit 100 includes pillars 115 with stiffer-density cellulose fiber walls, and the gaps 55 between the pillars 115 are filled with a subsequent solid foam deposit 200. The incorporation of the pillars 115 as structural elements of the solid foam allows for the creation of a stiffer foam while maintaining the same low density. The cellulose foam 300 is dimensionally stable because the pillars 115 prevent the typical shrinkage behavior of cellulose foams (significant shrinkage through the thickness toward the center of the object).

[0110] In one embodiment, 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.

[0111] It has been found that if the density of the first wet foam deposit 10 is higher than the density of the subsequent wet foam deposit 20, 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., pillars 115 and optional bottom 117) have different properties, such as stiffness, compared to the lower density regions (i.e., foam in gaps 55 and optional top 217). This can be used to provide a solid cellulose foam 300 with different properties in different regions.

[0112] The density of the 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 density difference between the wet foam of the first deposit 10 and the wet foam of the subsequent deposit 20 will remain in the solid foam deposits 100, 200.

[0113] In some embodiments, a coating can be applied to any surface of the solid cellulose foam 300 and / or the first or subsequent solid foam stacks 100, 200. 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).

[0114] 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.

[0115] According to a second aspect, the present invention provides a method for manufacturing a gyro having a height h s , length l s , width w sThe present invention relates to a solid cellulose foam 300 having a structure comprising a first solid foam deposit 100 and a subsequent solid foam deposit 200, the first solid foam deposit 100 comprising pillars 115 separated by gaps 55, the gaps 55 being filled with the subsequent solid foam deposit 200. The solid cellulose foam 300 according to the second embodiment may be produced by the method according to the first embodiment. The solid cellulose foam 300 according to the second embodiment may be further defined as set out above with reference to the first embodiment.

[0116] According to a third aspect, the present invention relates to the use of the solid cellulose foam 300 according to the second aspect as a packaging or building material. The solid cellulose foam 300 of the present invention has excellent cushioning properties that are desirable in the field of protective packaging. Furthermore, it can also be used as a building material, such as a thermal or acoustic insulator.

[0117] Example Example 1 Air cutting to create foam pillars for small, thin, dry cellulose foam sheets To achieve a first deposit of wet cellulose foam in the shape of pillars, a homogeneous wet paste was prepared containing 15 wt.% cellulose pulp (softwood kraft bleached pulp) in water and a thickener (CMC). The paste was aerated with a surfactant mixture (myristic acid and sodium cocoyl sarcosinate) until the wet foam density reached 160 kg / m. 3 The wet foam was placed on a flat tray in a frame with dimensions of 43*24*2 cm and scraped to an even thickness of 2 cm using a flat scraper. The foam filled the entire frame with no voids.

[0118] 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 25 mm spacing between each nozzle outlet. The outlet pipe of each nozzle was 0.75 mm in diameter, long enough to achieve a directional air beam. The nozzles were connected to pressurized air at 0.5 bar and positioned 3 mm above the foam. The foam was moved along its width in a horizontal plane at a speed of 0.2 m / s, passing under the row of nozzles to create parallel cuts in the wet foam at 25 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, and the cuts reached more than 70% of the foam's height but did not completely cut through the foam. Both the first set of cuts and the second set of cuts were continuous and extended from one side of the wet foam to the other, thus creating a cut pillar that was rectangular in shape and connected to the bottom of the wet foam pile.

[0119] The wet foam deposit was dried in a conventional convection oven at 120°C for 2 hours. For subsequent deposits, a new batch of wet cellulose foam was prepared according to the instructions above for the wet cellulose foam used in the first deposit. The wet foam was filled into the gaps between the pillars using reduced pressure. For the first deposit, the wet foam was spread over the dry foam, and vacuum was applied from below. Because dry foam is permeable to air, this technique allowed the vacuum to draw the wet foam into all voids. The surface was scraped to remove excess foam and flatten it to the height of the frame. The wet foam from the subsequent deposits covered all pillars, leaving only a thin layer of the subsequent deposit on the top surface of the foam. Finally, the foam was dried in an oven at 120°C for 1 hour. The density of the final foam sheet was approximately 34-38 kg / m. 3 It was.

[0120] The final thickness of the foam sheet was approximately 2 cm, and no shrinkage was observed. The shrinkage percentage is calculated based on the difference in thickness between the center of the foam and near the edge of the foam.

[0121] Example 2 (Comparative Example) One-stage deposition A homogeneous wet paste containing 15% by weight of cellulose pulp (softwood kraft bleached pulp) and thickener (CMC) in water was prepared. The paste was aerated with a surfactant mixture (myristic acid and sodium cocoyl sarcosinate) to a wet foam density of 180 kg / m. 3 The mixture was aerated until

[0122] A mold with dimensions of 43*24*2 cm was filled with the wet, air-filled foam, and the surface was scraped to remove excess foam and level the surface to the frame height. Finally, the foam was dried in a conventional convection oven at 120°C for 3 hours.

[0123] The density of the dry foam is approximately 30-33 kg / m 3 A 15% shrinkage was observed in the center of the foam. The shrinkage percentage is calculated based on the difference in thickness between the center of the foam and near the edge of the foam.

[0124] Example 3 Air cutting to create foam pillars for large, thick dry foam sheets A homogeneous wet paste containing 15% by weight of cellulose pulp (softwood kraft bleached pulp) and thickener (CMC) in water was prepared. A surfactant mixture (myristic acid and sodium cocoyl sarcosinate) was added to the paste, and the resulting mixture was extruded and simultaneously aerated to a density of 160 kg / m. 3 An extruded wet foam of

[0125] The wet foam was placed on a flat tray in a frame measuring 114 x 76 x 5 cm and scraped to an even thickness of 5 cm using a flat scraper. The foam filled the entire frame without any voids. Then, slits were made in the foam using 25 air nozzles pointing downward perpendicular to the foam surface. The nozzles were fixed in a row with a 50 mm spacing between each nozzle outlet. The outlet pipe of each nozzle had a diameter of 1.0 mm and was long enough to achieve a directional air beam. The nozzles were connected to pressurized air at a pressure of 1.5 bar and positioned 5 mm above the foam.

[0126] The foam was moved across its width in a horizontal plane at a speed of 0.02 m / s and passed under a row of nozzles, creating parallel cuts in the wet foam at 50 mm intervals. The foam was then rotated 90 degrees 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. Both the first and second sets of cuts were continuous and extended from one side of the wet foam to the other. The cut pattern was a square grid, and the cuts penetrated more than 70% of the foam's height but did not cut completely through the foam. Thus, the cut pillars were rectangular and connected to the bottom of the wet foam.

[0127] The first foam deposit was dried in a conventional convection oven at 80°C for 16 hours. For subsequent deposits, a new batch of wet foam was prepared according to the above instructions for the wet foam used in the first deposit. With the aid of a slit nozzle placed in close proximity to the dry material, the wet foam was filled into the spaces between the individual units. The surface was scraped to remove excess foam and level the surface to the frame height. The wet foam from the subsequent deposits covered all pillars, so that the top surface of the foam consisted of only a thin layer of the subsequent deposit. Finally, the foam was dried in an oven at 80°C for 16 hours. The density of the final dried foam sheet was approximately 32-36 kg / m. 3The final thickness of the foam sheet was approximately 5 cm, and no shrinkage was observed. The shrinkage percentage is calculated based on the difference in thickness between the center of the foam and near the edge of the foam.

[0128] Example 4 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 1.0 mm was deposited in a wooden frame (2.1 × 24.5 × 43.5 cm) on a perforated tray. The frame was scraped to smooth the top edge and create an even surface. The foam was cut into 2 × 2 cm square pillars using an air cut. The air cut was performed as in Example 1, except that the cuts were spaced 2 cm apart instead of 2.5 cm, and an air pressure of 1 to 1.5 bar was used to ensure complete separation of the pillars. The resulting first foam pile was dried in an oven at 120 °C. The foam was weighed at multiple time points during drying. The resulting drying curve is shown in Figure 5 (first air cut step, 2 × 2 cm). The drying time for the first foam pile was 50 minutes.

[0129] 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 the dry first foam deposit. Vacuum was applied from below to ensure the wet foam filled the gaps between the pillars 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.

[0130] 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.

[0131] Example 5 (Comparative Example) Drying time of foams produced by one-step deposition A reference foam with a higher foam density was used to make a reference foam plank in the same frame as described in Example 4. The composition and dry content of the reference foam were the same as those described for the foam in Example 4. The wet cellulose foam used in Example 5 contained the same amount of water as that evaporated during drying of the foam in Example 4. The density of the wet cellulose foam was 206 kg / m 3 The reference plank was dried as described in Example 4 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.

[0132] Therefore, the total time required to remove the same amount of water is shorter using two-stage deposition than using one-stage deposition.

[0133] Example 6 Drop testing of foams manufactured using two-step or one-step deposition The dry content of the wet cellulose foam was 12 wt% (density 193 kg / m 3 Foams were prepared as described in Examples 4 and 5, except that the weight of the foam was 12 g / cm from a height of 76 cm. The solid foams were evaluated in terms of degradation upon impact. Degradation was measured at 12 g / cm from a height of 76 cm. 2 The foam was evaluated by a drop test in which a static load of 38 kg / m was dropped on the foam. Degradation was measured as the relative compression ratio after five drops. Two 20 x 20 x 2 cm test pieces were stacked on top of each other and a static load was dropped on them. The average heights of the two test pieces before and after the five drops were measured and degradation was calculated. Before the test, the sample foam pieces were conditioned at 20°C and 20% RH (relative humidity) and held at a pressure of 38 kg / m. 3 The density was obtained.

[0134] The foam produced by two-step deposition (Example 4) showed a degradation of 13%, while the foam produced by one-step deposition (Example 5) showed a degradation of 18%. Thus, the foam produced using two-step deposition had better cushioning properties.

[0135] 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. Height h ｓ , length l ｓ , width w ｓ 1. A method for producing a solid cellulose foam (300) having a) providing a first wet cellulose foam; b) Height h １Ｗ , length l １Ｗ , width w １Ｗ depositing a first wet cellulose foam on a surface to obtain a first wet foam deposit (10) having a top surface (11) and a bottom surface (12); c) a top surface (11) of the first wet foam deposit (10) having a height h of the first wet foam deposit (10); １ forming pillars (15) in the first wet foam deposit (10) by providing score lines (5, 6) at least partially through the first wet foam deposit (10); d) drying the first wet foam deposit (10) to obtain a first solid foam deposit (100) comprising pillars (115) separated by gaps (55), the gaps (55) being formed along the score lines (5, 6), the first solid foam deposit (100) having a height h １Ｓ , length l １Ｓ , width w １Ｓ、 drying a first wet foam deposit (10) having a top surface (111) and a bottom surface (112); e) providing a second wet cellulose foam; f) depositing a second wet cellulose foam to obtain a subsequent wet foam deposit (20) filling the gaps (55) between the pillars (115) in the first solid foam deposit (100); g) drying the second wet foam deposit (20) to obtain a solid cellulose foam (300) comprising the pillars (115) of the first solid foam deposit (100) and a subsequent solid foam deposit (200) filling the gaps (55) between the pillars (115); A method comprising:

2. 2. The method according to claim 1, wherein the score lines (5, 6) are made by air cutting.

3. 2. The method of claim 1, wherein the score lines (5, 6) are made using a blade or knife.

4. The score lines (5, 6) are aligned along the length l of the first wet foam deposit (10). １Ｗ and / or width w １Ｗ 4. The method according to claim 1, wherein the direction of the beam is

5. The score lines (5, 6) are measured from the top surface (11) of the first wet foam stack (10) to the bottom surface (12) of the first wet foam stack (10) to the height h of the first wet foam stack (10). １Ｗ 5. The method according to claim 1, wherein the cutting depth cd corresponds to at least 70% of the cutting depth cd.

6. The score lines (5, 6) are measured from the top surface (11) of the first wet foam stack (10) to the bottom surface (12) of the first wet foam stack (10) to the height h of the first wet foam stack (10). １Ｗ The method according to any one of claims 1 to 5, wherein the cut depth cd is in the range of 70% to 95% of the cut depth cd.

7. The first solid foam pile (100) has a height h of the first solid foam pile (100) measured from the bottom surface (112) of the first solid foam pile (100). １Ｓ Height h corresponding to a range of 5% to 30% of ｂ 7. The method of claim 6, wherein the pillars extend from the base.

8. 8. The method of claim 1, wherein a vacuum is applied during deposition of the second wet cellulose foam.

9. The height h of the subsequent wet cellulose foam pile (20) ２Ｗ is the height h of the pillars (115) of the first solid foam deposit (100). ｐ The method of any one of claims 1 to 8, wherein the

10. 10. The method of claim 1, wherein both the first wet cellulose foam and the second wet cellulose foam comprise cellulose fibers in the range of 71 to 95 wt. %, based on the total dry weight of the wet cellulose foam, a water-soluble thickener in the range of 4 to 24 wt. %, based on the total dry weight of the wet cellulose foam, and at least two surfactants.

11. Height h ｓ , length l ｓ , width w ｓ 1. A solid cellulose foam (300) having a first solid foam stack (100) and a subsequent solid foam stack (200), the first solid foam stack (100) comprising pillars (115) separated by gaps (55), the gaps (55) being filled with the subsequent solid foam stack (200).

12. Height h of pillar (115) ｐ is the height h of the solid cellulose foam (300) ｓ The solid cellulose foam (300) of claim 11, wherein the viscosity is 0.6 to 1.0 times.

13. 13. The solid cellulose foam (300) of claim 11 or 12, wherein the first solid foam stack (100) further comprises a base (117) extending from a bottom surface (312) of the solid cellulose foam (300), and the pillars (115) extend from the base (117).

14. 14. The solid cellulose foam (300) of any one of claims 11 to 13, wherein the subsequent solid foam stack (200) further comprises a peak (217) disposed on top of the pillar (115).

15. The density of the solid cellulose foam (300) is 10 to 80 kg / m ３ 15. The solid cellulose foam (300) of any one of claims 11 to 14, wherein the thickness is in the range of

16. 16. The solid cellulose foam (300) of any one of claims 11 to 15, wherein the solid cellulose foam (300) comprises cellulose fibers in the range of 71 to 95 wt. %, based on the total dry weight of the solid cellulose foam (300), a water-soluble thickener in the range of 4 to 24 wt. %, based on the total dry weight of the solid cellulose foam (300), and at least two surfactants.

17. 17. Use of the solid cellulose foam (300) according to any one of claims 11 to 16 as a packaging material, a building material, a thermal insulation material, a sound deadening material or a hydroponic plant growing medium.

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