Freestanding wet low density cellulose fiber foam

Abstract

The present invention relates to a foam composition comprising cellulose fibers, a water-soluble thickener, and a surfactant. The foam composition can be used to prepare a foam that can be dried without restraint to form a three-dimensional object.

Description

[Technical field]

[0001] The present invention relates to a foam composition comprising cellulose fibers, a water-soluble thickener, and a surfactant. The foam composition can be used to prepare a foam that can be dried without restraint to form a three-dimensional object. [Background technology]

[0002] In daily life, macro- and microporous materials are used in various forms and compositions. These materials are generally based on petroleum-derived polymers, but due to the increasing awareness of the need to use renewable materials, efforts are being made to replace petroleum-derived polymers with polymers from renewable resources. Currently, different techniques are used to produce cellulose fiber foam materials. In WO2020011587, a cellulose fiber and gluten porous material is produced by aerating a cellulose fiber paste containing cellulose fibers and gluten, placing the wet foam in a mold and drying, followed by obtaining a dried porous material with the shape of the mold and a uniform fiber network throughout. In WO2015036659, a wet fiber foam is made by mixing fibers, additives, and surfactants in water to produce a liquid air foam that is drained to a certain thickness using either mechanical work or pressure. The wet fiber foam is then consolidated using a mold by conventional drying techniques.

[0003] US Patent Publication No. 2020240080 presents a foamed structure forming composition comprising fibrous and fibrillating materials, crosslinking agents, and surfactants for the production of lightweight paperboard. US Patent No. 5,612,385 presents an aerated fiber slurry composition comprising fibrous materials, foaming agents, stabilizers, water, and a certain amount of gas. The aerated fiber slurry can be dried to form a resilient foam.

[0004] An aqueous foam composition comprising fibers, a binder system including a thickener, and a blowing agent is disclosed in US Patent No. 4,613,627. The foam can be cast or molded into a desired shape. US Patent Publication No. 2015114581 presents a foam comprising water and a surfactant, in which microfibrillated cellulose (MFC) and longer fiber length pulp are incorporated. The foam is used in the manufacture of paper or paperboard fibrous webs by applying the foam to a forming fabric, followed by dewatering and drying.

[0005] Foam forming based on traditional papermaking techniques requires the foam to be drained onto a screen or forming fabric. This limits the shape and size of the material as it flattens during draining. For efficient draining, the viscosity of the liquid must be kept reasonably low to allow efficient extraction of the water. Soluble binders are therefore limited to low concentrations and must be able to be retained on the fibers to avoid excessive losses. Draining therefore limits the number of additives that can be used in this type of process. The strength of heavyweight low density foamed paper is mainly determined by the bulk of the material. Here the main means of improving strength is to increase density with some control over fiber orientation based on draining characteristics.

[0006] High dry content technologies, such as foams made from large amounts of protein-based blowing agents (e.g., WO2020011587), impede recyclability because a large fraction of the material is not water soluble and is not easily washed out of the product. Furthermore, the stability of the wet foam is insufficient to allow the foam to dry without a mold, as the protein particles begin to aggregate, the air bubbles coalesce, and the foam gradually collapses in wet conditions. This fact makes them poor candidates for freestanding wet foam deposition.

[0007] Thus, there remains a need for alternative foam compositions that are recyclable, are already dimensionally stable in the wet state, and can be manufactured using more efficient processes. Summary of the Invention

[0008] It is an object of the present invention to provide a free-standing wet low density cellulosic fibrous foam composition that can be dried without constraint to form a three-dimensional object.

[0009] In a first aspect, the present invention provides a foam composition comprising: a) 71 to 95% by weight of cellulose fibers, calculated based on the total weight of the solids content of the composition; b) 4 to 24% by weight, calculated based on the total weight of the solids content of the composition, of a water-soluble thickener; and c) at least two surfactants; The present invention relates to a foam composition comprising:

[0010] The foam composition according to the invention may be a wet foam composition having a total solids content in the range of 12-40 wt.%, calculated on the total weight of the wet composition. The foam composition according to the invention may be a dry foam having a solids content in the range of 95-100 wt.%, calculated on the total weight of the composition.

[0011] In a further aspect, the present invention provides a method for producing a foam having a composition according to the first aspect, comprising the steps of: a) disintegrating cellulose fibers in water to obtain a cellulose fiber slurry; b) adding a water-soluble thickener to the slurry obtained in a) to obtain a mixture of thickener and cellulose fibers in water; c) adding at least two surfactants to the mixture obtained in b) to obtain a fiber suspension; and d) aerating the fiber suspension obtained in c) to obtain a wet foam. the wet foam comprises 10-38 wt. % cellulose fiber, 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 foam has a density of 140-500 kg / m 3 and the yield stress is at least 80 Pa. It concerns the method. [Brief description of the drawings]

[0012] [Figure 1a] 1a-b show the yield stress of wet foams having different solids contents as a function of wet density of the wet foam composition for wet foams formulated with different solids contents. [Figure 1b] The slope of the line graph obtained in Figure 1a is plotted against the solids content of the wet foam, where the solid line represents the yield line, i.e., the gravitational stress of a 5 cm thick specimen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In a first aspect, the present invention provides a foam composition comprising: a) 71 to 95% by weight of cellulose fibers, calculated based on the total weight of the solids content of the composition; b) 4 to 24% by weight, calculated based on the total weight of the solids content of the composition, of a water-soluble thickener; and c) at least two surfactants; The present invention relates to a foam composition comprising:

[0014] The foam composition according to the present invention may be a wet foam composition having a total solids content in the range of 12-40 wt%, or 12-25 wt%, or 13-20 wt%, calculated on the total weight of the wet composition. Such wet foam compositions have a density of 140-500 kg / m 3 , or 140-400kg / m 3 In some embodiments, the yield stress of such wet foam compositions 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. In some embodiments, the yield stress of the wet foam compositions may be from 20 to 200 Pa, or from 50 to 150 Pa, or from 70 to 150 Pa.

[0015] The foam composition according to the present invention may be a dry foam having a solids content in the range of 95-100 wt.%, or 98-100 wt.%, calculated based on the total weight of the composition. The foam composition according to the present invention may be a dry foam having a density of 10-60 kg / m 3 In some embodiments, the foam composition may be a dry foam having a density of 10 to 80 kg / m 3 It may be a dry foam.

[0016] The present invention also relates to the use of the foam composition in a solid foam.

[0017] In a further aspect, the present invention provides a method for producing a foam having a composition according to the first aspect, comprising the steps of: a) disintegrating cellulose fibers in water to obtain a cellulose fiber slurry; b) adding a water-soluble thickener to the slurry obtained in a) to obtain a mixture of thickener and cellulose fibers in water; c) adding at least two surfactants to the mixture obtained in b) to obtain a fiber suspension; and d) aerating the fiber suspension obtained in c) to obtain a wet foam. Including, The wet foam comprises 10-38 wt. % cellulose fiber, 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 foam has a viscosity of 140-500 kg / m 3 and a yield stress of at least 80 Pa, It concerns the method.

[0018] The term "foam" as used here refers to a material made by trapping bubbles of air or gas inside a solid or liquid. Usually the volume of gas is much larger than the volume of the liquid or solid, and the gas pockets are separated by thin membranes. For a foam to form, three requirements must be met. Mechanical work is required to increase the surface area. This can occur by agitation, dispersing a large amount of gas into the liquid, or injecting gas into the liquid. The second requirement is that a foam-forming agent, typically an amphiphile, surfactant, or surface-active component, must be present to reduce the surface tension. Finally, the foam must form faster than it can break.

[0019] In the present invention, the term "foam" refers to a cellulose foam having a foam composition according to the first aspect and obtainable by a method according to the further aspect. Thus, a foam according to the present invention refers to a cellulose foam comprising cellulose, a water-soluble thickener, and at least two surfactants. The main component of the foam is cellulose, which constitutes at least 70% by weight of the solids content of the cellulose foam, or 71-95% by weight of the solids content of the cellulose foam. The cellulose is in the form of fibers, and therefore the foam can also be defined as a fiber foam or a cellulose fiber foam. The foam may be wet or dry.

[0020] The term "wet foam" or "wet foam composition" as used herein refers to a wet foam comprising cellulose, a water-soluble thickener, and at least two surfactants. Gas bubbles are present within the wet foam. Wet foams are self-supporting and behave as viscoelastic solids. This means that wet foams have both viscous and elastic properties. Wet foams behave as solids and are therefore self-supporting unless sufficient force is applied that they begin to flow and behave like a viscous material. Depending on the magnitude and time scale of the applied shear stress, wet foams may exhibit predominantly viscous or elastic behavior.

[0021] The term "dry foam" or "dry foam composition" as used herein refers to a dry, solid, porous cellulosic material, i.e., foam-forming material, formed from a wet cellulosic foam. During the drying process, the closed wet cellulosic foam is converted to an open dry cellulosic foam. The network of cellulose fibers is prevented from collapsing during drying. As a result, the dry foam assumes a shape that closely matches the shape of the wet foam. The solids content of the dry foam is at least 95% by weight, calculated based on the total weight of the dry foam. The shape and density of the dry foam are retained in an unconstrained state. The dry foam has an open cell structure, allowing air to enter the pores within the foam. The dry foam may also be referred to as a solid foam, a porous material, or a low density material.

[0022] "Yield stress" as used herein refers to the amount of stress required to initiate continuous motion in the form of Newtonian flow within complex fluids such as suspensions, wet foams, and pastes. Yield stress can be measured with a viscometer fitted with an impeller geometry at controlled shear rates, where a constant rotational speed is applied to the impeller and the resulting torque is measured as a function of time. The rotational speed is typically set between 0.1 and 8 rpm. Yield stress refers to the stress required to cause continuous rotation of the impeller.

[0023] The foam according to the invention may comprise 71-95% by weight, or 75-95% by weight, of cellulose fibres, calculated on the basis of the total weight of the solids content in the composition. The cellulose fibres may be selected from wood pulp, regenerated cellulose fibres and vegetable fibres, such as fibres from bamboo, cotton, hemp, flax, jute etc. Preferably, the cellulose fibres are selected from wood pulp, such as softwood kraft bleached pulp, hardwood pulp, chemi-thermomechanical pulp, and dissolving pulp, or a combination of one or more of these. More preferably, the cellulose pulp fibres are from softwood pulp, chemi-thermomechanical pulp or dissolving pulp. Most preferably, the cellulose pulp fibres are from softwood pulp, such as softwood kraft bleached pulp. The slurry of cellulose fibres obtained in the first step a) of the process according to the invention may comprise 10-30% by weight, or 12-25% by weight, of cellulose fibres, calculated on the basis of the total weight of the slurry.

[0024] Water-soluble thickeners increase the viscosity of the liquid phase in the foam. The use of water-soluble thickeners increases the viscosity of the nanometer-sized liquid films between the bubbles, further stabilizing the system through viscous damping. Non-water-soluble thickeners, such as microfibrillated cellulose and other particle-based thickeners, do not enter the thin liquid films between the bubbles of dense foams. Water-soluble thickeners increase the shear forces during mechanical agitation while also acting as anti-agglomeration agents for solid fiber particles. In addition, increasing the viscosity minimizes the diffusion rate of the system, slowing down the rate of bubble coalescence. Water-soluble thickeners allow sufficient air to be entrapped, producing dense foams with high enough yield stress to support the weight of foams up to 5 or 10 cm thick. Another aspect of setting a high viscosity is to maintain a uniform concentration throughout the foam structure by slowing down the drainage of the liquid.

[0025] The charge density of the thickener also plays an important role in the stability of the wet foam due to ionic interactions between the various components of the system. If thickeners with low charge density are used, the cellulose fibers will adhere to the carrier board and to each other, leading to high reject rates and complicating the recycling of the material. The higher the charge density of the thickener, the higher its solubility.

[0026] Due to the high concentration of cellulose fibers mixed in, no drain step is necessary and water-soluble bio-based thickeners can be used in high concentrations. The thickener may therefore be a water-soluble thickener. Water-soluble thickeners are also advantageous when recycling the foam composition, for example in normal paper recycling streams. The thickener may be present in an amount of 4-24% by weight, or 5-20% by weight, calculated on the total weight of the solids content of the composition. The thickener may have a molecular weight of 80000-250000 g / mol, or 83000-197000 g / mol. Exemplary water-soluble thickeners are selected from carboxymethylcellulose (CMC), methylcellulose (MC), hydroxyethylcellulose (HEC), ethylhydroxyethylcellulose (EHEC), methylhydroxypropylcellulose (MHPC), starch, xanthan, guar gum, xyloglucan, or mixtures thereof. The thickening agent may be added to the slurry obtained in step (a) as a solution, such as a solution containing 4-12 wt.%, or 4-6 wt.% thickening agent. Preferably, the solution containing the thickening agent is an aqueous solution.

[0027] The foam according to the invention comprises a mixture of at least two surfactants. One of the at least two surfactants is preferably a fast-acting surfactant that settles quickly to the air-water interface during mechanical agitation, thereby contributing to the formation of a high density and high viscosity foam, thus enabling a self-supporting foam. Surfactants suitable for this purpose are anionic surfactants, preferably low molecular weight anionic surfactants. 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 a pH of 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, 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.

[0028] The other of the at least two surfactants is preferably a co-surfactant. As used herein, the term "co-surfactant" refers to a surfactant that complements another main surfactant. The co-surfactant has different properties from the main surfactant, so that the surfactant actions complement each other, thus improving the overall effectiveness of the surfactant system. The surfactant system may include multiple main surfactants and multiple co-surfactants.

[0029] The delayed-acting co-surfactant separates the charged surfactant head groups of the fast-acting surfactant precipitated at the air-water interface, thus allowing for a tighter packing of the aliphatic carbon chains, thereby improving the elastic modulus of the lipid layer formed at the air-water interface. By introducing the co-surfactant, the drainage half-life (t1 / 2) can also be improved, for example by a factor of 3 or more. A co-surfactant with a suitable pKa and a long carbon chain contributes to a stable fiber suspension and a stable wet foam. The co-surfactant can be selected from the group including surfactants with 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 can have an apparent pKa of up to 10. The co-surfactant preferably has a long carbon chain, more preferably a carbon chain with 14 carbon atoms (C14). Co-surfactants can be selected from high pKa fatty acids, such as those derived from plant-derived sources, such as tetradecanoic acid (myristic acid), sodium oleate, lauric acid, palmitic acid, and stearic acid; glucose-based co-surfactants with aliphatic carbon termini, such as alkyl glycosides, alkyl polyglucosides, alkyl thioglycosides, 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, Tween® 85), and polyoxyethylene lauryl ethers, such as polyethylene glycol dodecyl ether, pentaethylene glycol monododecyl ether, and octaethylene glycol monododecyl ether.

[0030] Thus, the at least two surfactants used in the foam composition preferably comprise a mixture of an anionic surfactant and a co-surfactant. The molar ratio of the anionic surfactant to the co-surfactant may be from 0.2:1 to 3:1, preferably from 0.5:1 to 2:1. The total amount of the at least two surfactants in the foam composition may be from 0.6 to 5 wt.%, or from 0.8 to 2.0 wt.%, calculated on the total weight of the solids content of the foam. The surfactant may be added to the mixture obtained in step (b) as a solution, for example a solution containing 3 to 25 wt.%, preferably 5 to 20 wt.% of the surfactant. The pH of the surfactant solution is preferably from 7 to 9, more preferably 8. Preferably, the solution containing the surfactant is an aqueous solution. More preferably, the solution is water. The alcohol may have a defoaming effect.

[0031] Since cellulose fibers are 20-30 microns wide, only small enough, i.e., micron-sized, bubbles can suspend individual fibers, thereby further improving the anti-agglomeration properties of the foam. Both the water-soluble thickener and the delayed-acting co-surfactant contribute to the formation of finer and more stable bubbles, and thus to the reduction of the surface roughness of the dry foam. In coarse foams, such as foams containing large bubbles or foams with a large distribution of bubble sizes, the fibers tend to aggregate, resulting in high surface roughness. The composition according to the invention, which comprises cellulose fibers, a thickener and at least two surfactants, forms a very stable wet fiber foam upon aeration. The aeration can be performed by mechanical agitation. Aeration incorporates a significant amount of air into the material, resulting in a gas volume fraction φ in the range of 0.6-0.85. The surfactants promote the formation of bubbles. Before aeration, the composition has a high viscosity and a high yield stress, such as having the consistency of a non-agglomerated paste.

[0032] By adjusting the wet foam stability using a combination of thickeners and surfactants, free-standing cellulose foams can be produced without the use of crosslinkers or fibrillated cellulose. Good foam stability prevents ripening, i.e., changes in bubble size and drainage. To form a free-standing cellulose foam, the apparent yield stress of the foam must exceed the stress exerted on the foam by gravity.

[0033] In the wet state, the foam of the composition of the present invention is considered to be a highly concentrated hydrocolloid suspension that flows when mechanical load is applied. However, below the yield stress, the foam does not flow. Thus, the wet foam prepared from the composition obtained in step d) is self-supporting and does not require a mold or forming cloth to retain its shape when dried. Thus, the composition of the present invention can be foamed into a self-supporting foam that is stable enough to dry without collapsing even in the absence of a supporting mold. As a result, objects can be formed and dried without the use of a mold.

[0034] The wet foam obtained in step d) may contain 10-38% by weight, or 10-30% by weight, or 11-30% by weight, or 12-30% by weight, or 10-20% by weight, or 11-20% by weight, or 12-20% by weight of cellulose fibers, 0.5-10% by weight, or 0.5-5% by weight, or 1-5% by weight, or 2-5% by weight, or 1-3% by weight of water-soluble thickener, and 0.1-2% by weight of surfactant, calculated on the total weight of the obtained fiber suspension. The wet foam obtained in step d) may be dried to obtain a dry cellulose foam. The wet foam produced from the composition according to the invention does not need to be dehydrated before drying due to its high solids content. The foam may be dried by evaporation at room temperature or at an elevated temperature, such as 40-140°C. The dry cellulose foam may have a mass of 10-60 kg / m 3 In one embodiment, the dry cellulose foam may have a density of 10 to 80 kg / m 3 The density of the sintered body may be 0.01 to 0.01.

[0035] The use of water-soluble thickeners and delayed-acting co-surfactants allows evaporation of water from the fiber foam without collapsing the 3D structure, avoiding or delaying fiber agglomeration. This allows for a significantly reduced surface roughness and a higher quality product after the drying and solidification step. Fiber agglomeration can be delayed by controlling the rheological profile, such as the yield stress and viscosity, of the foam particle dispersion. This involves adjusting parameters such as cell size (R), gas volume fraction (φ) and surface tension (γ). Good dispersion of fibers in the wet end of the method contributes to a reduced surface roughness as the foam dries, a finer void structure in the product sections and less density variation throughout the volume.

[0036] The wet foam can be dried into a three-dimensional object without constraint or shrinkage. Drying of the foam can be performed using a two-stage deposition method, where a first deposition of wet foam obtained in step d) is deposited as individual units on a surface and the individual units are dried; a second preparation of wet foam is prepared according to steps a)-d); a second deposition of wet foam obtained in step d) is performed by filling the wet foam between the individual units of the dry cellulose foam of the first deposition; and, the foam is dried to obtain a solid foam containing the individual units of foam embedded within the foam matrix. During the initial drying stage of the individual units, a dense fibrous layer is formed on the surface of the foam. This crust-like layer provides mechanical support during drying and helps to maintain the shape of the individual units.

[0037] The thickener can improve the fiber-fiber bond strength in the dry foam, mainly through hydrogen bonding. Thus, the amount of thickener in the foam composition affects the mechanical performance of the dry foam, especially the bulk of the material. The higher the thickener content, the harder the material. Thus, the thickener allows for tuning of the mechanical properties. Both the dry foams produced from the composition according to the invention, as well as the wet foams, can be redispersed in water, and are therefore recyclable in the normal paper recycling stream.

[0038] A further aspect of the invention is a foam produced by the method according to claim 13, the foam having a viscosity of 10 to 60 kg / m 3 The foam has a density of

[0039] The present invention will now be described with reference to the following examples, but the present invention is not limited to these examples. All documents and references mentioned herein are incorporated by reference in their entirety. EXAMPLES

[0040] material Chemicals Bleached softwood kraft pulp, bleached hardwood kraft pulp, dissolving pulp, carboxymethylcellulose (Finnfix WRM from Nouryon, Finnfix30, Finnfix150, Finnfix300, Finnfix700 from CP Kelco), sodium cocoyl sarcosinate, myristic acid, sodium N-lauroyl sarcosinate (Crodasinic LS95NT from Croda).

[0041] Example 1 Differences in the amount of thickener The effect of carboxymethyl cellulose (CMC) content on foam stability was investigated by examining samples prepared from different compositions, as shown in Table 1. Sample 1 was the most commonly used composition with a CMC content of 10 wt% in the dry foam. Softwood bleached kraft pulp (120 g) was disintegrated in water (602 g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater to produce a fiber suspension. CMC (13.5 g) was dissolved in water (256.5 g) using a Vitamixer to obtain a gel-like highly viscous solution. The gel was then added to the fiber suspension and mixed with the K-beater until a uniform paste was formed. A surfactant solution (20 wt%, 6 ml) containing sodium cocoyl sarcosinate:myristic acid in a 1:1 molar ratio was then added to the paste. The amount of total solid surfactant added was 1.2 g as shown in Table 1, which corresponds to 0.9 wt% calculated based on the total weight of the solids content of the composition. The desired amount of air (78% by volume of the total foam volume) was then mechanically introduced into the mixture using the balloon whipper of the Kenwood mixer to produce a foam of approximately 222 kg / m 3 The paste was aerated until a wet foam density of 0.1 g was obtained.

[0042] The solid foam was prepared by a two-step deposition process: In the first deposition step, the prepared wet foam was initially deposited in 12 individual units using a cylindrical mould with a diameter of 6.7 cm and a height of 5.2 cm on a flat perforated oven tray (holes 3 mm diameter) with a frame of 27 × 37 × 5 cm. The mould was only used to deposit the foam in a specific shape and dimensions and was removed before the foam was dried. The individual units were then dried in a conventional convection oven at 120 °C for 1-2 h. The wet foam produced in this way showed high stability, maintaining the deposited shape and height not only during drying but also when the mould was removed. Then, in the second deposition step, a new batch of foam was prepared in the same way as the foam used in the first deposition. The spaces between the dried individual units were filled with new wet foam to completely fill the oven frame without gaps. The surface was then scraped to remove excess foam and the surface was levelled to match the height of the frame. The foam was finally dried in an oven at 120 °C for 8 h. The density of both the dried individual units and the density of the final foam board were approximately 30 kg / m 3The final foam board thickness was approximately 5 cm.

[0043] For Samples 2, 3, and 4, the amount of CMC used was varied according to Table 1 such that the CMC content in the dry foam was 5 wt%, 15 wt%, or 20 wt%, respectively, calculated based on the total weight of the solid content of the composition. The surfactant content in the dry foam of all samples was maintained at 0.9 wt%, calculated based on the total weight of the solid content of the composition. The solid content in the wet foam was maintained at 13.5 wt%, calculated based on the total weight of the wet composition for all samples, as shown in Table 1. Similar to Sample 1, Samples 2, 3, and 4 were also prepared according to the two-stage deposition procedure described above, and the wet stability of the foam was high enough that individual units in each formulation could be dried without a mold and maintained their initial shape during drying. TIFF2024545324000002.tif132170

[0044] Example 2 Different main surfactant to co-surfactant molar ratios The effect of the molar ratio of the primary surfactant, sodium cocoyl sarcosinate, to the co-surfactant, myristic acid, was investigated by examining the formulations shown in Table 2. Sample 2 had a 1:1 molar ratio of sodium cocoyl sarcosinate to myristic acid and is the most commonly used formulation.

[0045] Softwood bleached kraft pulp (120 g) was disintegrated in water (602 g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater to produce a fiber suspension. CMC (13.5 g) was dissolved in water (256.5 g) using a Vitamixer to obtain a gel-like highly viscous solution. The gel was then added to the fiber suspension and mixed with the K-beater until a uniform paste was formed. A surfactant solution (20 wt%, 6 ml) containing sodium cocoyl sarcosinate:myristic acid in a 1:1 molar ratio was then added to the paste. The amount of total solid surfactant added was 1.2 g, as shown in Table 2, which corresponds to 0.9 wt% calculated based on the total weight of the foam solids content. The desired amount of air (78% by volume of the total foam volume) was then mechanically introduced into the mixture using the balloon whipper of the Kenwood mixer to produce a foam of approximately 222 kg / m 3 The paste was aerated to a wet foam density of 0.01g / g.

[0046] The wet foam was used to prepare a solid foam board according to the two-step deposition method described in Example 1.

[0047] The wet foam in the first lay showed high stability, so that the shape and height of the individual units in the first lay were maintained not only during drying but also when the mould was removed. For the second lay, a new batch of foam was prepared according to the above description of the foam used in the first lay. Both the density of the dried individual units and the density of the final foam board were approximately 30 kg / m 3 The final foam board thickness was approximately 5 cm.

[0048] For Samples 1 and 3, the molar ratio of sodium cocoyl sarcosinate:myristic acid was varied according to Table 2. The total surfactant content of all samples was maintained at 0.9 wt%, calculated based on the total weight of the solids content of the composition. For all samples in this example, the total solids content of the wet foam was maintained at 13.5 wt%, calculated based on the total weight of the wet composition. Similar to Sample 2, Samples 1 and 3 were also prepared according to the two-stage deposition procedure described above. Each formulation exhibited high wet foam stability, allowing individual units to be dried without a mold and to maintain their initial shape during drying. TIFF2024545324000003.tif129170

[0049] Example 3 Different Sources of Cellulosic Fiber The effect of cellulose fiber type was investigated by studying the formulations shown in Table 3. Three different foams were produced using softwood bleached kraft pulp, hardwood bleached kraft pulp, or dissolving pulp. For each of the three samples, the foam was prepared according to sample 2 described in Example 2. Each of the three different foams was produced according to the two-step lay-up method described in Example 1 for producing a solid foam board. The wet foams prepared using each of the reported fiber sources were very stable, and the individual units laid down in the first step could be dried without the use of a mold while maintaining their shape during drying. The densities of the dried individual units of samples 1, 2, and 3 as well as the density of the final dry foam board were both approximately 30 kg / m 3 The final foam board thickness for samples 1 and 3 was 5 cm. The final foam board thickness for sample 2 was 2.5 cm. TIFF2024545324000004.tif133170

[0050] Example 4 Different densities Cellulose fibers (120 g, softwood bleached kraft pulp fibers) were disintegrated in water (602 g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater. CMC (13.5 g) was dissolved in water (256.5 g) using a Vitamixer to obtain a gel-like highly viscous solution. The CMC gel was then added to the cellulose fiber suspension and mixed with a K-beater until a homogenous mixture was obtained. A surfactant solution (20 wt%, 6 ml) containing sodium cocoyl sarcosinate:myristic acid in a 1:1 molar ratio was then added to the cellulose fiber / CMC solution mixture. The amount of total solid surfactant added was 1.2 g as shown in Table 4, which corresponds to 0.9 wt% calculated based on the total weight of the solids content of the composition. The mixture was then aerated using the balloon whipper of the Kenwood mixer until the desired amount of air was mechanically introduced into the mixture (see Table 4). The wet foam was used to prepare a solid foam board according to the two-stage deposition method described in Example 1. The wet foams produced in this way showed high stability, maintaining the shape and height of the individual units when the mould was removed after the first deposition and even during drying of the first deposition. For the second step of deposition, a new batch of foam was prepared as described above for the foam used in the first deposition. The density of the dry foams calculated for a given volume gain (i.e. the volume % of the air content in the foam relative to the total volume of the foam) can be seen in Table 4. The time required to reach a low wet density of the foam (i.e. low dry density) is longer compared to the time to reach a high density of the foam.

[0051] For Samples 1, 2, 3, and 4, the total surfactant content, calculated based on the total weight of the solids content of the composition, was maintained at 0.9 wt%. For all samples in this example, the wet foam solids content (concentration), calculated based on the total weight of the wet composition, was maintained at 13.5 wt%. All samples were prepared according to the two-stage deposition procedure described above. Each formulation exhibited high wet foam stability, allowing individual units to be dried without a mold and to maintain their original shape during drying. TIFF2024545324000005.tif134170

[0052] Example 5 Various molecular weights of thickeners Cellulose fibers (softwood bleached kraft pulp fibers, 120 g) were disintegrated in water (691 g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater to produce a fiber suspension. Different molecular weight CMCs (Finnfix30, Finnfix150, Finnfix300, and Finnfix700 from CP Kelco) (6.4 g) were dissolved in water (121.2 g) using a Vitamixer to obtain a gel-like highly viscous CMC solution. The CMC gel was then added to the cellulose fiber suspension and mixed with a K-beater until a homogenous mixture was obtained. A surfactant solution (20 wt%, 6 ml) containing a 1:1 molar ratio of sodium cocoyl sarcosinate:myristic acid was then added to the cellulose fiber / CMC solution mixture. The amount of total solid surfactant added was 1.2 g, which corresponds to 0.9% of the dry foam content, as shown in Table 5. The desired amount of air (78% by volume of the total foam volume) was then mechanically introduced into the mixture using the balloon whipper of the Kenwood mixer to produce a foam with a volume of approximately 222 kg / m 3 The mixture was aerated until a wet foam density of 0.01 mm was obtained. The wet foam was used to prepare a solid foam slab according to the two-step deposition method described in Example 1. The wet foam produced by this method exhibited high stability, maintaining the deposited shape and height not only during drying but also when the mold was removed. For the second deposition, a new batch of wet foam was prepared according to the above description of the wet foam used in the first deposition.

[0053] For samples 1, 2, 3, and 4, the total surfactant content in the dry foam was maintained at 0.9%, and the wet foam dry content (concentration) was maintained at 13.5% for all samples in this example. All samples were prepared according to the two-step deposition procedure described above. Each formulation exhibited high wet foam stability, allowing individual units to be dried without a mold and retaining their initial shape during drying. For the same solution concentration, as the molecular weight of the thickener increases, the viscosity of the thickener also increases. When foams are prepared using the same concentration of high molecular weight thickener, the wet foam stability shows a positive trend, but the time required to increase the foam volume (i.e., the time to reach the same wet foam density) is longer for foams prepared using thickeners with higher molecular weight. Wet foam stability correlates with the mechanical strength of the dry foam. TIFF2024545324000006.tif138170

[0054] Example 6 Comparative Example: Sodium lauroyl sarcosinate used as a foaming agent As a comparison to the combination of sodium cocoyl sarcosinate and myristic acid, sodium N-lauroyl sarcosinate (LS95NT from Croda) was used as the sole surfactant to investigate its effect on wet foam stability. The formulation used in this case was similar to that described in Sample 2 of Example 2, except that instead of the sodium cocoyl sarcosinate-myristic acid solution, a solution of LS95NT of the same concentration was used as the foaming agent.

[0055] Softwood bleached kraft pulp (120 g) was disintegrated with water (602 g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater to produce a fibre suspension. Carboxymethylcellulose (CMC) (13.5 g) was dissolved in water (256.5 g) using a Vitamixer to obtain a gel-like highly viscous solution. The gel was then added to the fibre suspension and mixed with the K-beater until a homogenous paste was formed. A surfactant solution (20 wt%, 6 ml) containing only LS95NT was then added to the paste such that the amount of solid surfactant added was 1.2 g. The paste was then mixed using the balloon whipper of the Kenwood mixer to obtain a wet density of approximately 222 kg / m 3 The wet foam was aerated until it reached a volume of 100g. Already at this stage, differences from the wet foam prepared with sodium cocoyl sarcosinate-myristic acid were clearly observed. Although the time to reach the desired amount of foaming and increase in volume was short, as soon as the wet foam was transferred from the Kenwood bowl to the oven tray and spread, the small air bubbles coalesced into larger ones and the resulting wet foam seemed to lack stability and creaminess. Due to the continuous bursting of the air bubbles, the wet foam was not stable enough at room temperature, both when poured into the mold and when drying. This caused collapse and shrinkage during drying and a rough final surface. Therefore, the formulation was not considered suitable for either the single-step or two-step deposition technique.

[0056] Example 7 Comparative Example: Use of Small and Large Amounts of Thickener Cellulose fibres (softwood bleached kraft pulp fibres, 120g) were disintegrated in water (733g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater to produce a cellulose fibre suspension. CMC (Nouryon Finnfix WRM, 3.1g) was dissolved in water (59g) using a Vitamixer to obtain a gel-like highly viscous CMC solution. The CMC gel was then added to the cellulose fibre suspension and mixed with a K-beater until a homogenous mixture was obtained. A surfactant solution (20wt%, 6ml) containing sodium cocoyl sarcosinate:myristic acid in a 1:1 molar ratio was then added to the cellulose fibre / CMC solution mixture. The amount of total solid surfactant added was 1.2g, which corresponds to 0.9% of the dry foam content, as shown in Table 6. The desired amount of air (78%) was then mechanically introduced into the mixture using the balloon whipper of the Kenwood mixer to obtain a mass of approximately 222kg / m 3 The mixture was aerated until it reached a wet foam density of 1000g / g. The time required to reach the target density (i.e., air content of the foam) was shorter compared to the sample prepared in Example 1, but the wet foam was less stable compared to the foam prepared in Example 1. The aerated mixture was transferred to a cylindrical mold with a diameter of 6.7 cm and a height of 5.2 cm, and the prepared foam was deposited in 12 individual units on a flat perforated oven tray (holes 3 mm diameter) with a frame of 27 x 37 x 5 cm. The mold was used only to deposit the foam in a specific shape and dimension and was removed before the foam was dry. The wet foam had a low viscosity and an unstable texture, which caused the foam to collapse after the mold was removed. The individual units of foam formed using the mold gradually deteriorated. The individual units were then dried in a conventional convection oven at 120°C for 1-2 hours. The wet foam shrunk during drying. The dry foam had a lower mechanical strength compared to the foam prepared in Example 1.

[0057] Cellulose fibers (softwood bleached kraft pulp fibers, 120 g) were disintegrated in water (328 g) using a Kenwood Chef XL Titanium mixer equipped with a K-beater to produce a cellulose fiber suspension. CMC (Nouryon Finnfix WRM, 35.2 g) was dissolved in water (669.7 g) using a Vitamixer to obtain a gel-like, highly viscous CMC solution. The CMC gel was then added to the cellulose fiber suspension and mixed with a K-beater until a homogenous mixture was obtained. A surfactant solution (20 wt%, 6 ml) containing sodium cocoyl sarcosinate:myristic acid in a 1:1 molar ratio was then added to the cellulose fiber / CMC solution mixture. The amount of total solid surfactant added was 1.2 g, as shown in Table 6, which corresponds to 0.9 wt% calculated based on the total weight of the solids content of the composition. The desired amount of air (78%) was then mechanically introduced into the mixture using the balloon whipper of the Kenwood mixer to obtain a volume of approximately 222 kg / m 3 The mixture was aerated until the wet foam density reached 100%. The time required to reach the target density (i.e., air content of the foam) was longer compared to the sample prepared in Example 1, the wet foam was less stable, and cellulose fiber bundles were identified compared to the foam prepared in Example 1. The aerated mixture was then transferred to a cylindrical mold 6.7 cm in diameter and 5.2 cm in height, and the prepared foam was deposited as 12 individual units on a flat perforated oven tray (holes 3 mm diameter) with a frame of 27 x 37 x 5 cm. The mold was used only to deposit the foam in a specific shape and dimensions and was removed before the foam was dry. The wet foam developed an unstable texture, which resulted in the collapse of the foam. The individual units of the foam formed using the mold gradually deteriorated. The individual units were then dried in a conventional convection oven at 120°C for 1-2 hours. The wet foam shrunk during drying.

[0058] For samples 1 and 2, the total surfactant content in the dry foam was maintained at 0.9%, and the dry content (concentration) of the wet foam was maintained at 13.5 wt%, calculated based on the total weight of the wet composition for all samples in this example. All samples were prepared according to the two-step deposition procedure described above. Each formulation had poor wet foam stability, with individual units unable to be dried without a mold and unable to maintain their initial shape during drying. Wet foam stability showed a negative trend when foams were prepared with either low (i.e., 2.5 wt%) or high (i.e., 22.5 wt%) CMC content, calculated based on the total weight of the solids content. Increasing CMC content increased the stiffness of the foam after drying. Increasing CMC content also decreased the recyclability of the foam after drying. TIFF2024545324000007.tif115170

[0059] Example 8 Evaluation of wet foam yield stress in relation to slurry solids content. To evaluate the effect of foam solids content on yield stress, wet foam compositions with different solids contents (10%, 11%, 12.6%, 14.5%, 16.1%) were prepared. All foam compositions contained 10% CMC, 1% surfactant, and 89% cellulose fiber based on the total weight of the solids content of the foam composition. The total solids content was adjusted by the amount of water added (see Table 7). Cellulosic fiber (120 g, softwood bleached kraft pulp fiber) was disintegrated in water using a Kenwood Chef XL Titanium mixer equipped with a K beater (see Table 7 for the amount of water added). For solids contents of 14.5% and 16.1%, the above solids contents were achieved after pulping with 600 ml water, squeezing out the water, and adding thickener. CMC (13.5 g) was dissolved in water (256.5 g) using a Vitamixer to obtain a gel-like highly viscous solution. The CMC gel was then added to the dehydrated cellulose fiber suspension and mixed with a K-beater until a homogenous mixture was obtained. A surfactant solution (20 wt%, 6 ml) containing sodium cocoyl sarcosinate:myristic acid in a 1:1 molar ratio was then added in small increments (0.5 ml) to the cellulose fiber / CMC solution mixture. The mixture was then aerated using a balloon whipper on a Kenwood mixer until the desired amount of air was mechanically introduced into the mixture. After mixing, the foam was collected in a 250 ml plastic cup and the yield stress was measured using a Brookfield DVNext, 0.5 RPM blade spindle V73 and V72, and a built-in yield stress tester. The results are shown in Figure 1a-b. The solid line in Figure 1a-b represents the yield line, or gravitational stress, of a 5 cm thick foam. Below the yield line, the wet foam would be expected to behave like a viscous liquid when subjected to sufficient stress, resulting in sagging at the bottom. On the other hand, above the yield line, the wet foam behaves like a solid. It can be seen from Figure 1a that the wet foams with solids contents of 10% and 11% are below the yield line, whereas the wet foams with solids contents of 12.6%, 14.5%, or 16.1% are all above the yield line. Figure 1b shows the linear slope of the curve in Figure 1a as a function of solids content in the wet foam.The relationship between the change in yield stress and the solids content is linear. Thus, for wet foam compositions containing softwood kraft pulp, the transition from liquid to solid behavior occurs at a solids content of about 12.5%. TIFF2024545324000008.tif63170

Claims

1. 1. A foam composition comprising: a) 71 to 95% by weight of cellulose fibers, calculated based on the total weight of the solids content of the composition; b) 4 to 24% by weight of a water-soluble thickener, calculated based on the total weight of the solids content of the composition; and c) at least two surfactants 1. A foam composition comprising:

2. 2. The foam composition of claim 1, wherein one of the surfactants is an anionic surfactant having an apparent pKa of 3.2 to 3.8 in a solution having a pH of 7 to 9.

3. 3. The foam composition of claim 1, wherein one of the surfactants is a co-surfactant.

4. 4. The foam composition of claim 3, wherein the co-surfactant is selected from a surfactant having an apparent pKa of at least 8 in a solution having a pH of 7 to 9, or an amphoteric betaine.

5. 4. The foam composition of claim 3, wherein the molar ratio of anionic surfactant to cosurfactant is from 0.2:1 to 3:

1.

6. 3. The foam composition of claim 1, wherein the total amount of the at least two surfactants is 0.6 to 5 wt. %, calculated based on the total weight of the solids content of the composition.

7. 3. The foam composition of claim 1, wherein the cellulose fibers are selected from wood pulp; regenerated cellulose fibers; and vegetable fibers, preferably softwood kraft bleached pulp, chemi-thermomechanical pulp, and dissolving pulp, or a combination thereof.

8. 3. The foam composition of claim 1, which is a wet foam composition having a total solids content of 12 to 40 wt. %, calculated based on the total weight of the wet composition.

9. Density: 140 to 500 kg / m ３ 9. The foam composition of claim 8, wherein

10. 9. The foam composition of claim 8 having a yield stress of at least 80 Pa.

11. 10 to 60 kg / m ３ 3. The foam composition of claim 1, having a density of

12. 10. A method for producing the foam composition of claim 1, comprising: a) defibrating cellulose fibers in water to obtain a cellulose fiber slurry; b) adding a water-soluble thickener to the slurry obtained in a) to obtain a mixture of water-soluble thickener and cellulose fibers in water; c) adding at least two surfactants to the mixture obtained in b) to obtain a fiber suspension; d) aerating the suspension obtained in c) to obtain a wet foam. The wet foam comprises 10 to 38 wt. % cellulose fibers, 0.5 to 10 wt. % water-soluble thickener, and 0.1 to 2 wt. % surfactant, calculated based on the total weight of the wet foam, and the wet foam has a viscosity of 140 to 500 kg / m ３ and a yield stress of at least 80 Pa.

13. 13. The method of claim 12, further comprising drying the wet foam obtained in d) to obtain a dry cellulose foam.

14. 14. The method of any one of claims 12 to 13, wherein the water-soluble thickener is added to the slurry obtained in step (a) as a solution containing 4 to 12 wt% thickener.

15. The dry cellulose foam has a compressive strength of 10 to 60 kg / m ３ The method of claim 13, wherein the granular material has a density of

Images