Resilient bacterial nanocellulose foam

Abstract

This invention provides a resilient bacterial nanocellulose foam having a bio-based carbon content of at least 80% and containing 0.7 to 1.5 wt% of a biopolymer of (2,2,6,6-tetramethylpiperidin-1-oxy) (TEMPO)-oxidizing bacterial nanocellulose or a mixture of TEMPO-oxidizing bacterial nanocellulose and anionic biopolymers. The material comprises 0.1 to 2 wt% of a surfactant and 0.3 to 1.5 wt% of a crosslinking agent. The crosslinking agent may be a divalent metal ion donor, such as a metal salt (e.g., calcium or zinc salts, such as calcium carbonate or zinc carbonate, or mixtures thereof). Furthermore, 0.3 to 0.9 wt% of a pore-forming agent and 4 to 10 wt% of a resilient modifier are added to provide mechanical properties similar to commercial polyurethane foams. The resilient bacterial nanocellulose foam has a density of 30 to 182 kg / m³. 3 The tensile strength is 98 to 1195 kPa, and the resilience is 18 to 39%. The degree of polymerization of TEMPO-oxidized bacterial nanocellulose is at least 700.

Description

Technical Field

[0001] This invention relates to resilient foams made from renewable materials, and more specifically, to bacterial nanocellulose foams having mechanical properties comparable to polyurethane foams. Background Technology

[0002] Polyurethane foam is widely used in the logistics and textile industries. As a packaging material, it is primarily used to absorb impact and protect goods from damage. In addition, it is used in furniture, bedding, clothing, underwear (such as bra cups), and footwear to provide support and comfort. Notably, the impact and vibration damping properties of polyurethane foam can be used to provide cushioning and padding for wearers or products, and the resilience and compressive strength of the foam material are key parameters for these applications.

[0003] Polyurethane foam is commercially produced from carbon sources derived from petroleum products and is non-biodegradable. Some bio-based polyurethane foam products are also available on the market. For example, soybean extract has been used to manufacture polyurethane foam, in which polyols (key components involved in isocyanate amidation in polyurethane bonds) are replaced. However, given factors such as food resource scarcity, particularly in low-income countries, there remain significant concerns about the diversion of food-grade soybeans for non-commercial uses.

[0004] Isocyanates are obtained by reacting amines with toxic phosgene. Besides the toxicity of phosgene, a major drawback of isocyanate production is the use of fossil fuels to produce the amines. These amines are typically derived from benzene, toluene, ethylene, or propylene.

[0005] To reduce reliance on non-biodegradable polymers, the "OK Bio-based" certification was introduced. The highest level requires that the percentage of renewable raw materials (bio-based percentage) in the product be over 80% based on carbon content. Currently, no polyurethane foam product meets this requirement.

[0006] Therefore, there is a need in the art for a foam material made from 80% or more renewable raw materials, with mechanical properties comparable to commercial polyurethane foam. This invention fulfills this need. Summary of the Invention

[0007] This invention relates to a foam material made from bacterial nanocellulose and its preparation method. The foam material exhibits similar resilience properties to polyurethane foam and has a bio-based carbon content exceeding 80%.

[0008] On one hand, the present invention provides a resilient bacterial nanocellulose foam having a bio-based carbon content of at least 80% and containing 0.7 to 1.5 weight percent of a biopolymer of 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO)-oxidizing bacterial nanocellulose or a mixture of TEMPO-oxidizing bacterial nanocellulose and anionic biopolymers. The material comprises 0.3 to 0.9 weight percent of a pore-forming agent, 0.1 to 2 weight percent of a surfactant, and 0.3 to 1.5 weight percent of a crosslinking agent. The crosslinking agent may be a divalent metal ion donor, such as a divalent metal salt (e.g., calcium or zinc salts, such as calcium carbonate or zinc carbonate, or mixtures thereof). Furthermore, 4 to 10 weight percent of a resilient modifier is added to provide mechanical properties similar to those of commercial polyurethane foams. The resilient bacterial nanocellulose foam has a density of 30 to 182 kg / m³, a tensile strength of 98 to 1195 kPa, and a resilience of 18% to 39%. The degree of polymerization of TEMPO-oxidized bacterial nanocellulose is at least 700 to maintain the foam size, such that the resulting foam has a high shrinkage rate of less than about 30%, the nanofibers are 5 to 30 micrometers in length, have an average diameter of 30 to 50 nanometers, and contain 36% to 60% Iβ-type cellulose.

[0009] Surfactants can be polysorbate-based surfactants, sodium dodecyl sulfate, or mixtures thereof.

[0010] Modifiers that enhance resilience can be one or more of sorbitol, mannitol, xylitol, glycerin, ethylene glycol, propylene glycol, and polyethylene glycol.

[0011] TEMPO-oxidizing bacterial nanocellulose can have a nanofiber morphology with a length of 5 to 30 micrometers and an average diameter of 30 to 50 nanometers.

[0012] TEMPO oxidizing bacterial nanocellulose contains 36% to 60% Iβ-type cellulose.

[0013] Anionic biopolymers can be one or more of pectin, carboxymethyl cellulose, xanthan gum, gellan gum, and sodium alginate.

[0014] The one or more divalent metal ions can be calcium ions, zinc ions, or mixtures thereof.

[0015] Modifiers that enhance resilience can be mixed with alcohols.

[0016] The present invention also provides a method for preparing resilient bacterial nanocellulose foam, the method comprising preparing a dispersion of TEMPO-oxidized bacterial nanocellulose with a crystallinity of at least 75%, anionic biopolymer, at least one surfactant, at least one crosslinking agent and at least one modifier for enhancing resilience.

[0017] A pore-forming agent is added to the above dispersion to generate carbon dioxide and form a porous structure, and a crosslinking agent ionically crosslinks the TEMPO-oxidizing bacterial nanocellulose and anionic biopolymer.

[0018] The TEMPO-oxidized bacterial nanocellulose in this method can have a crystallinity of at least 75%.

[0019] The ratio of Iα-cellulose to Iβ-cellulose in TEMPO oxidizing bacterial nanocellulose is 40:60 to 65:35.

[0020] Anionic biopolymers can be sodium alginate, which has a viscosity in water in the range of 200-350 mPa·s.

[0021] The pore-forming agent may be gluconate-δ-lactone.

[0022] Crosslinking of TEMPO-oxidizing bacterial nanocellulose and anionic biopolymers can be achieved by chelating calcium ions in calcium carbonate with the carboxyl groups present on TEMPO-oxidizing bacterial nanocellulose and anionic biopolymers respectively.

[0023] The density of resilient bacterial nanocellulose foam is less than 182 kg / cm³. 3 The tensile strength is at least 90 kPa and the compressive strength is at least 0.5 MPa. Attached Figure Description

[0024] Figure 1A Scanning electron microscope (SEM) image of bacterial nanocellulose; Figure 1B SEM image of TEMPO-oxidized bacterial nanocellulose.

[0025] Figure 2 The hydrolysis of glucose-δ-lactone and the formation of carbon dioxide and calcium ions in the composition are illustrated schematically.

[0026] Figure 3 The ionic crosslinking between sodium alginate and TEMPO-oxidized bacterial nanocellulose described in this invention is illustrated.

[0027] Figure 4 This is an external view of the porous composite material described in this invention.

[0028] Figure 5 The appearance of the porous composite material described in Example 15 before, during, and after compression is shown.

[0029] Figures 6A-6C SEM images of the porous composite material of the present invention before compression to 80%, and after 1 hour and 24 hours, as well as images of comparative examples, are shown.

[0030] Figure 7 The appearance of a porous composite material molded using the composition described in this invention is shown. Detailed Implementation

[0031] This invention provides a foam material made from 80% or more renewable raw materials, whose mechanical properties are comparable to those of commercial polyurethane foam. In one aspect, the bio-based raw material may include bacterial nanocellulose and a second material, such as sodium alginate.

[0032] Bacterial nanocellulose is a high-purity cellulose synthesized extracellularly by certain bacterial strains, typically from the genera *Komagataeibacter* (formerly *Gluconacetobacter*), *Acetobacter*, and *Sarcina*. These bacteria produce nanocellulose in aqueous media containing a carbon source, such as glucose, sucrose, or glycerol. Among the most commonly used strains, *Komagataeibacter xylinus* (formerly *Gluconacetobacter xylinus*) is widely used due to its highly efficient cellulose synthesis capabilities. The resulting cellulose forms an interconnected network of highly crystalline fibers with diameters ranging from 20 to 100 nanometers, thus possessing unique mechanical properties, water retention capacity, and biocompatibility. Unlike plant-derived cellulose, bacterial nanocellulose does not contain lignin or hemicellulose, resulting in high purity and a uniform structure. The nanoscale size of the fibers and the hydrogen bonds between them form an extensive three-dimensional network, conferring high mechanical strength and excellent water retention capacity.

[0033] In some embodiments, the selected bacterial strains include Gluconacetobacter hansenii (ATCC 53582), Komagataeibacter xylinum (ATCC 53524), and Gluconacetobacter xylinus (ATCC 23767).

[0034] In one aspect, the bacterial nanocellulose is obtained by fermentation in the presence of a bacterial strain, culture medium, metal salt, and carbon source at a concentration of approximately 5% by volume. The culture medium may be Hestrin-Schramm (H&S) broth, comprising 5 g / L peptone, 5 g / L yeast extract, 2.7 g / L disodium hydrogen phosphate, 1.15 g / L citric acid hydrate, and deionized water. The metal salt may be magnesium sulfate (MgSO4·7H2O) or ferrous sulfate (FeSO4).

[0035] The carbon source can be one or more of glucose, fructose, and sucrose. As described below, to produce sufficient raw materials for foam production, the carbon source needs to be produced on an industrial scale. Therefore, the technology of this invention can be used with various carbon sources derived from waste.

[0036] TEMPO oxidation of bacterial nanocellulose

[0037] To enhance the functional properties of bacterial nanocellulose, the (2,2,6,6-tetramethylpiperidin-1-oxy) (TEMPO) oxidation method is widely used. This selective oxidation process introduces carboxylate functional groups onto the surface of cellulose fibers, thereby improving their hydrophilicity, colloidal stability, and reactivity. This oxidation process is carried out under mild aqueous conditions using the following reagents:

[0038] TEMPO radical catalyst

[0039] Sodium hypochlorite (NaOCl)

[0040] Sodium bromide (NaBr)

[0041] Sodium hydroxide (NaOH) is used for pH control.

[0042] In this reaction, the primary hydroxyl group at the C6 position of the cellulose glucose unit is selectively oxidized to a carboxylate group (-COO). - This process preserves the β-1,4-glycoside backbone of cellulose. The degree of oxidation can be adjusted by controlling the reaction time, pH value, and oxidant concentration.

[0043] The oxidation process alters the physicochemical properties of bacterial nanocellulose, endowing it with a high anionic charge density, enabling it to interact strongly with positively charged molecules or ions. The resulting nanocellulose exhibits improved dispersibility in aqueous solutions, facilitating its integration into composite materials, while enhanced hydrophilicity promotes water retention and gelation. The degree of oxidation provides tunable mechanical properties. By controlling crystallinity, the rigidity and structural stability of the nanocellulose can be improved compared to nanocellulose with lower crystallinity.

[0044] Notably, TEMPO-oxidized bacterial nanocellulose retains a high degree of crystallinity (typically above 75%), which differs from plant-derived TEMPO-oxidized nanofibrillated cellulose. This higher crystallinity improves its dimensional stability, making it particularly suitable for foam preparation and applications. Although TEMPO-oxidized cellulose nanofibrils derived from tree pulp have been used in other foams, their crystallinity (approximately 67%) is lower than that of TEMPO-oxidized bacterial nanocellulose, resulting in a weaker network structure and more significant dimensional shrinkage. The intense shrinkage during the shrinkage process leads to a loss of porosity, making it difficult for plant-based TEMPO-oxidized nanocellulose to maintain a low-density structure.

[0045] Despite the numerous advantages of TEMPO-oxidized bacterial nanocellulose compared to traditional plant-based cellulose nanofibers, several limitations remain in the foam preparation process. For example, TEMPO oxidation increases hydrophilicity, leading to increased water absorption and capillary-driven dimensional shrinkage during drying. Nanocellulose foams are also brittle due to their rigid hydrogen-bonded network. Consequently, their mechanical properties cannot replicate the resilience of traditional polyurethane foams.

[0046] To address the poor mechanical properties of TEMPO-oxidized bacterial nanocellulose, this invention utilizes a combination of highly crystalline TEMPO-oxidized bacterial nanocellulose and a second biopolymer (i.e., a polymer derived from renewable resources) to provide a biodegradable foam with improved dimensional stability and mechanical properties. The resulting TEMPO-oxidized bacterial nanocellulose possesses anionic carboxylate groups introduced through TEMPO oxidation, which can interact with other anionic biopolymers. The addition of ions enables ionic crosslinking, bridging the carboxylate groups between the two polymers to form a dynamically interconnected network. Examples of anionic biopolymers that can be used with TEMPO-oxidized bacterial nanocellulose include pectin, carboxymethyl cellulose, xanthan gum, gellan gum, and sodium alginate. These biopolymers can be used alone or in combination to form an interconnected network.

[0047] Use divalent metal ions, such as calcium ions (Ca). 2+ ), zinc ions (Zn) 2+ ) or other metal ions or mixtures of metal ions can crosslink polymer networks, such as Figure 3 As shown in the figure, this illustrates the combination of sodium alginate and TEMPO-oxidizing bacterial nanocellulose. Divalent metal ions can be added in the form of metal salts, such as carbonates or bicarbonates. For example, calcium ions in calcium carbonate or zinc ions in zinc carbonate.

[0048] The amount of a second biopolymer can be selected by varying the degree of carboxyl substitution to provide tunable viscosity. The viscosity of the composite biopolymer affects the final foam formation because it is related to porosity, pore size, and the foam's resilience and strength. Some biopolymers, such as xanthan gum, exhibit shear-thinning behavior, which can provide important rheological modification properties that may play a role in subsequent processing, such as foam molding or extrusion.

[0049] The combination of a rigid nanocellulose network and a flexible cross-linked second biopolymer phase produces a material that maintains structural integrity under mechanical stress while resisting brittle fracture. Specifically, the ionic cross-linking of the second biopolymer with TEMPO-oxidizing bacterial nanocellulose prevents the collapse of the porous structure by maintaining a stable three-dimensional network, thereby reducing dimensional shrinkage during drying. To further optimize the mechanical properties of the material, resilience-enhancing modifiers can further improve its flexibility and toughness, preventing the dried foam from becoming too brittle. Resilience-enhancing modifiers include sorbitol, mannitol, xylitol, glycerol, ethylene glycol, propylene glycol, or polyethylene glycol. In one embodiment, a combination of glycerol and an alcohol (e.g., ethanol) can be used.

[0050] Additionally, surfactants can be added to adjust viscosity and aid in foam stabilization. Surfactants can be selected from nonionic surfactants, anionic surfactants, or combinations thereof, depending on the desired interaction with the biopolymer matrix and processing conditions. Suitable nonionic surfactants include polysorbate-based surfactants, such as polysorbate 20 (Tween 20), polysorbate 40 (Tween 40), polysorbate 60 (Tween 60), and polysorbate 80 (Tween 80), which are ethoxylated dehydrated sorbitol esters capable of stabilizing emulsions and reducing interfacial tension. Anionic surfactants promote dispersion and wetting properties by imparting a negative surface charge to the composition. Suitable anionic surfactants include sodium dodecyl sulfate (SDS), sodium dodecyl sulfate (SLS), and sodium stearoyl lactylate (SSL). In one embodiment, a combination of polysorbate 20 (Tween 20) and sodium dodecyl sulfate can be used.

[0051] To prepare foams using TEMPO-oxidized bacterial nanocellulose or TEMPO-oxidized bacterial nanocellulose / second biopolymer composites, a pore-forming system is required. This system promotes gas generation within the biopolymer matrix, leading to expansion and the formation of a lightweight porous structure. Suitable pore-forming systems include compounds that release gas upon reaction with acids or bases, as well as pore-forming agents, such as lactone-based agents.

[0052] In some embodiments, the pore-forming agent comprises a lactone-based compound that hydrolyzes over time to release acid, thereby promoting controlled pore formation. Suitable lactone-based pore-forming agents include gluconic acid-δ-lactone (GDL). GDL is a cyclic ester that hydrolyzes in water to gluconic acid and induces a decrease in the pH of the medium.

[0053] Currently, the production of bacterial nanocellulose remains limited to specific applications, such as medical materials or wound dressings. Since bacterial nanocellulose is the main component of the bio-based foam of this invention, further development of large-scale production of bacterial nanocellulose is necessary to realize its potential as a substitute for traditional polyurethane foam. Therefore, developing efficient bioreactors, low-cost fermentation methods, and optimized processing technologies is particularly important for making the TEMPO-oxidized bacterial nanocellulose-based foam of this invention commercially viable in green packaging and environmentally friendly material applications.

[0054] To meet the production demands of foam applications, it is necessary to improve the design of bioreactors to increase bacterial nanocellulose yield, shorten processing time, and reduce production costs. The following reactor technologies hold promise for large-scale bacterial nanocellulose production:

[0055] Stirred bioreactors – traditional stirred tank reactors (STRs) are suitable for culturing cellulose-producing bacteria in a controlled environment and for optimizing stirring to balance oxygen transfer and mechanical shear.

[0056] Airlift bioreactors—these systems provide improved oxygenation without excessive shear stress, thus allowing for high-yield production of bacterial nanocellulose while minimizing fiber damage.

[0057] Rotating disc bioreactors—these systems enhance oxygen diffusion and increase cellulose productivity by providing a constantly renewed gas-liquid interface for bacterial growth, which is beneficial for industrial-scale manufacturing.

[0058] Continuous culture systems—unlike traditional batch processing, these continuous bioreactors allow for controlled harvesting and replenishment of culture media, thereby maintaining higher productivity and reducing production downtime.

[0059] The commercialization of TEMPO-oxidizing bacterial nanocellulose foam for green packaging and environmentally friendly material applications requires reducing production costs by shifting from high-purity glucose to more economically viable raw materials. Potential low-cost carbon sources include:

[0060] Agricultural waste byproducts (such as molasses, lignocellulosic hydrolysate, brewer's grains)

[0061] Food industry waste stream (e.g., fruit peels, sugarcane bagasse)

[0062] Glycerin in biodiesel production. These sources not only reduce raw material costs but also promote a circular economy by transforming industrial waste into value-added bioproducts.

[0063] In one specific foam embodiment, a TEMPO-oxidizing bacterial nanocellulose composite material is formed and crosslinked with sodium alginate to create a high-strength, highly resilient foam with properties comparable to polyurethane foam. Importantly, this resilient bacterial nanocellulose foam contains at least 80% bio-based carbon, meeting "bio-based" product certification requirements. The foam can be 0.7 to 1.5 weight percent of TEMPO-oxidizing bacterial nanocellulose biopolymer or a mixture of TEMPO-oxidizing bacterial nanocellulose and sodium alginate. The material contains 0.3 to 0.9 weight percent of a pore-forming agent, such as glucono-δ-lactone.

[0064] The material contains 0.1 to 2% by weight of a surfactant and 0.3 to 1.5% by weight of a crosslinking agent, which may be calcium carbonate, zinc carbonate, or mixtures thereof. Additionally, 4 to 10% by weight of a resilient modifier is added to provide mechanical properties similar to commercial polyurethane foam. This resilient bacterial nanocellulose foam has a density of 32 to 182 kg / m³. 3 The tensile strength is 98 to 1195 kPa, and the resilience is 18% to 39%. The degree of polymerization of the TEMPO-oxidizing bacterial nanocellulose is at least 700 to maintain the foam size, resulting in a foam height shrinkage rate of less than about "30%", the nanofiber length is 5 to 30 micrometers, the average diameter is 30 to 50 nanometers, and the Iβ-type cellulose content is 36% to 60%. The term "shrinkage rate of less than about 30%" refers to a foam shrinkage test in which the height of the cubic foam decreases by about 30% or less after drying, as described in Example 3. Example

[0065] Example 1: Formation of bacterial nanocellulose

[0066] A 5% volume percentage concentration of bacterial strain ATCC 53582 (inoculated 24 hours prior) was added to pre-autoclaved H&S broth (445 mL), 0.04% by weight of MgSO4·7H2O, 0.0005% by weight of FeSO4, and 20 g / L glucose (pH 5). The mixture was then transferred to petri dishes, exposing a surface area of ​​890 cm². 2 The bacterial nanocellulose was cultured at a volume ratio of 2 to 2 with the culture medium and statically incubated. After fermentation at 30°C for 5 days, the grown bacterial nanocellulose membrane was isolated. It was purified by washing with a 1% (w / w) sodium hydroxide aqueous solution at 90°C for 1 hour, and further washed until the pH of the wash solution was neutral. The average dry weight of the bacterial nanocellulose obtained from the three batches was 6.19 ± 0.15 g / L.

[0067] like Figure 1AAs shown, the formed bacterial nanocellulose is a nanofiber. According to SEM observation, its diameter is 46.6 nm and the fiber length exceeds 20 μm. Its composition is: Iα-cellulose accounts for 68.5%, Iβ-cellulose accounts for 23%, and the total crystallinity is 64.2%.

[0068] The degree of polymerization of bacterial nanocellulose is 724 to 747.

[0069] Example 2: TEMPO oxidation of bacterial nanocellulose

[0070] In Example 1, the bacterial nanocellulose was activated by selectively oxidizing the hydroxyl groups in the cellulose units to carboxylic acid groups using the TEMPO method. The preparation process of TEMPO-oxidized bacterial nanocellulose is as follows: 1) Homogenize the bacterial nanocellulose suspension in water; 2) Mix the bacterial nanocellulose suspension in water (0.7 wt%) with TEMPO (0.1 mmol / L) and sodium bromide (1 mmol / L); 3) Slowly add sodium hypochlorite (6 mmol / L) to the suspension, stir, and maintain the pH at 10 with sodium hydroxide; 4) Add ethanol to terminate the reaction; 5) Collect the TEMPO-oxidized bacterial nanocellulose by centrifugation and wash with ethanol and water.

[0071] The TEMPO-oxidized bacterial nanocellulose obtained from the bacterial nanocellulose obtained in Example 1 has an Iα-type cellulose content of 41.7%, an Iβ-type cellulose content of 58.3%, and an overall crystallinity of 76.8%.

[0072] The resulting TEMPO-oxidizing bacterial nanocellulose was formed in the form of nanofibers, with an average diameter of 31.5 nanometers and a length exceeding 6.4 micrometers. Figure 1B As shown, the degree of polymerization is 709.

[0073] Table 1 describes the properties of bacterial nanocellulose and TEMPO-oxidized bacterial nanocellulose in Examples 1 and 2.

[0074] Table 1: Properties of TEMPO-oxidized bacterial nanocellulose

[0075] The composition of Iα or Iβ type cellulose was determined by X-ray diffraction analysis. The degree of polymerization was determined according to the method outlined in Appendix B of the Chinese industry standard GB / T9107-2023, using copper ethylenediamine solution as the solvent, the disclosure of which is incorporated herein by reference.

[0076] Example 3: Preparation of foam based on TEMPO-oxidized bacterial nanocellulose

[0077] In Example 2, TEMPO-oxidizing bacterial nanocellulose was combined with sodium alginate to form a composite cross-linked material, which was selected as the second biopolymer.

[0078] The foam is formed from the following materials having the specific components listed in Tables 2 and 3. TEMPO oxidized bacterial nanocellulose Biopolymer: Sodium alginate (viscosity in water range of 200-350 mPa·s) Surfactants: Tween 20 and / or sodium dodecyl sulfate Modifiers that increase resilience: glycerol and ethanol Crosslinking agent: calcium carbonate Pore-forming agent: gluconate-δ-lactone

[0079] The materials in the examples were prepared into foams according to the steps outlined below. A uniform aqueous dispersion of TEMPO-oxidizing bacterial nanocellulose was preheated to 50°C, and then anionic biopolymer / sodium alginate was added until completely dissolved. A calcium carbonate crosslinking agent and surfactant (Tween 20 / polysorbate 20 or sodium dodecyl sulfate) were added to the mixture, and the mixture was stirred vigorously for 1 hour. Then, a gluconate-δ-lactone void-forming agent was added, the mixture was stirred for 15 minutes, and the mixture was placed in a mold and allowed to stand for at least 2 hours. The resulting composite material was first immersed in water, then in a mixture of glycerol and ethanol for 6 hours, and cured at 60°C until completely dry. The percentages of various components in the examples and comparative examples are listed in Tables 2 and 3.

[0080] Table 2: *Sodium dodecyl sulfate (0.1%) was used as a surfactant, an aqueous solution of glycerol (7%) and ethanol (60%) was used as a modifier to enhance resilience, glucono-delta-lactone (0.6%) was used as a pore-forming agent, and calcium carbonate (0.3%) was used as a crosslinking agent. **L / W / H = Length / Width / Height

[0081] Table 3: *Using gluconate-δ-lactone (0.6%) as a pore-forming agent and calcium carbonate (0.3%) as a crosslinking agent. **L / W / H = Length / Width / Height

[0082] Technical effects of the present invention

[0083] Figure 4-7Photographs of foams formed according to embodiments and comparative examples are shown, illustrating the technical effects of the invention, particularly those related to foam porosity, foam compression, and foam molding shape. Bacterial nanocellulose and TEMPO-oxidized bacterial nanocellulose are superior to cellulose nanofibers obtained from tree pulp. Specifically, the crystallinity of the TEMPO-oxidized bacterial nanocellulose described in this invention (76.8%) is higher than that of TEMPO-oxidized cellulose nanofibers (67.7%), and the composition of cellulose Iα and Iβ forms differs (TEMPO-oxidized bacterial nanocellulose: 41.7% and 58.3%, respectively; TEMPO-oxidized cellulose nanofibers: 62.1% and 37.9%, respectively). The percentage of cellulose Iβ in TEMPO-oxidized bacterial nanocellulose (58.3%) is higher than that in TEMPO-oxidized cellulose nanofibers (37.9%), making it more suitable for use in bio-based bacterial formulations requiring greater flexibility.

[0084] Compared to the TEMPO-oxidized cellulose nanofibers used in Comparative Example 7, the TEMPO-oxidized bacterial nanofibers in Example 8 exhibited higher crystallinity, resulting in a rigid network and reduced dimensional shrinkage during the foaming process (dimensional shrinkage of foam height was 26% vs. 37%). Therefore, a low-density porous material (30.8 kg / m³) with sufficient tensile strength, compressive strength, and resilience can be retained. 3 vs 34.0kg / m 3 Example 8 vs. Comparative Example 7).

[0085] Furthermore, the use of TEMPO-oxidized bacterial nanocellulose in this invention is superior to the use of cellulose nanofibers and bacterial nanocellulose because the dimensional shrinkage during the foaming process is very significant, as seen in Comparative Examples 5 and 6 and Example 8 (foam height shrinkage of 64% vs 26% and 44% vs 26%, respectively). Figure 4 As shown. Furthermore, significant compression deformation occurs when cellulose nanofibers and / or bacterial nanocellulose are used. Figure 6A The pores of the display material deform when compressed to 80%, while Figures 6B-6C This demonstrates that the pores in the material of the present invention exhibit good pore recovery after compression. Figure 4 The macroscopic performance comparison between the foam of the present invention and the comparative foam is shown; the comparative foam has poor macroscopic shape recovery after compression, while the foam of the present invention recovers its initial shape.

[0086] Using 1.4% sodium alginate in the composition can form a density of 73.8 kg / m³. 3Porous materials were formed. However, the use of 0.7% sodium alginate in the composition did not result in a porous material. The use of sodium alginate and a certain proportion of TEMPO-oxidizing bacterial nanocellulose in the composition facilitated the formation of a porous material with a density below 36.5 kg / m³. 3 Porous materials. Using 0.7% or 1.4% TEMPO-oxidizing bacterial nanocellulose alone did not form a foam material.

[0087] The porous material formed by using TEMPO-oxidized bacterial nanocellulose exhibits high tensile and compressive strength, as shown in Example 9, where the tensile strength is increased to 1195 kPa. However, when the mass ratio of TEMPO-oxidized bacterial nanocellulose to sodium alginate is 4:1 (compared to 1:1 in Example 8), significant compressive deformation occurs. Figure 6B The results show that the pores of the material deformed when compressed to 80%. When TEMPO-oxidized bacterial nanocellulose is properly crosslinked with sodium alginate present in the composite material, sodium alginate provides flexibility to the resulting composite material.

[0088] Surfactants, such as Tween 20 or sodium lauryl sulfate, can increase the viscosity of the cellulose dispersion, thereby promoting foaming. The advantage of using Tween 20 is that, compared to Example 8 using sodium lauryl sulfate, deformation at 80% compression is minimized (Examples 13 to 15 and...). Figure 6C The density of porous materials using Tween 20 ranges from 48 to 136 kg / m³. 3 The density of porous materials using sodium dodecyl sulfate ranges from 22.5 to 36.5 kg / m³. 3 Example 15 provides a material with excellent resilience (23.9%), maintaining minimal deformation at 80% compression. Figure 5 ).

[0089] As shown in Examples 8, 11 and 12, resilience-enhancing modifiers (e.g., glycerol and ethanol) provide resilience properties to the resulting composite materials.

[0090] The porous material described in this invention has a density and tensile strength comparable to polyurethane foam, and has higher compressive strength and resilience.

[0091] The carbon-based bio-based content of the embodiments disclosed in this invention is 100%, which complies with the EN 16785 standard.

[0092] Industrial applicability

[0093] The TEMPO-oxidized bacterial nanocellulose-based foam of this invention possesses biodegradability, renewability, and mechanical durability, making it an ideal candidate material to replace petroleum-based foams. Furthermore, these materials align with global sustainable development initiatives aimed at reducing plastic waste and promoting a circular economy.

[0094] The resilient foam exhibits mechanical properties comparable to commercially available polyurethane foam (Comparative Example 16). Therefore, the applications of this invention are similar to those of polyurethane foam, including furniture / bedding, clothing, footwear, underwear, and packaging. Specific applications of this invention include...

[0095] Clothing and footwear padding and support structures, such as foam bra cups

[0096] Protective packaging materials (alternatives to expanded polystyrene and polyurethane foam)

[0097] Biodegradable food trays and containers

[0098] cushioning and insulation materials

[0099] Single-use packaging solutions for electronic products and consumer goods

[0100] The foregoing briefly describes several embodiments of this disclosure and their detailed features. The embodiments described in this disclosure can readily serve as the basis for designing or modifying other processes and structures to achieve the same or similar purposes and / or obtain the same or similar advantages as described in the embodiments of this disclosure. Such equivalent constructions do not depart from the spirit and scope of this disclosure, and various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure.

[0101] The terms “approximately,” “substantially,” “essentially,” and “about” as used herein are used to describe and explain minute variations. When used in conjunction with an event or situation, the term can refer to a situation where the event or situation occurs precisely or approximately. The term “about” as used herein with respect to a given value or range generally means within ±10%, ±5%, ±1%, or ±0.5% of the given value or range. This range can be expressed herein as from one endpoint to another, or between two endpoints. Unless otherwise stated, all ranges disclosed in this disclosure include endpoints. The term “essentially coplanar” can refer to two surfaces located within a few micrometers (μm) along the same plane, for example, within 10 μm, 5 μm, 1 μm, or 0.5 μm along the same plane. When referring to “substantially” identical values ​​or properties, the term may refer to values ​​within ±10%, ±5%, ±1%, or ±0.5% of the average value.

Claims

1. A resilient bacterial nanocellulose foam having a bio-based carbon content of at least 80%, characterized in that, include: 0.7 to 1.5 weight percent of TEMPO-oxidizing bacterial nanocellulose and anionic biopolymers; 0.3 to 0.9% by weight of lactone-based pore-forming agent; 0.1 to 2% by weight of surfactant; 0.3 to 1.5 weight percent of a crosslinking agent selected from one or more divalent metal ion sources; and 4 to 10% by weight of a modifier that enhances resilience; The density of the resilient bacterial nanocellulose foam is 30 to 182 kg / m³. 3 ; The tensile strength of the resilient bacterial nanocellulose foam is 98 to 1195 kPa; The resilience of the aforementioned resilient bacterial nanocellulose foam is 18% to 39%; and The degree of polymerization of the TEMPO-oxidizing bacterial nanocellulose in the resilient bacterial nanocellulose foam is at least 700 to form a dimensionally stable foam.

2. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The surfactant is selected from polysorbate-based surfactants, sodium dodecyl sulfate, and mixtures thereof.

3. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The modifier for enhancing resilience is selected from one or more of sorbitol, mannitol, xylitol, glycerin, ethylene glycol, propylene glycol, and polyethylene glycol.

4. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The TEMPO-oxidizing bacterial nanocellulose is a nanofiber with a length of 5 to 30 micrometers and an average diameter of 30 to 50 nanometers.

5. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The TEMPO oxidizing bacterial nanocellulose comprises 36% to 60% Iβ-type cellulose.

6. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The anionic biopolymer is selected from one or more of pectin, carboxymethyl cellulose, xanthan gum, gellan gum, and sodium alginate.

7. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The divalent metal ion source is selected from calcium ions, zinc ions, or mixtures thereof, and the crosslinking agent is selected from calcium carbonate or zinc carbonate.

8. The resilient bacterial nanocellulose foam according to claim 1, characterized in that, The modifier that enhances resilience is mixed with alcohol.

9. A method for preparing resilient bacterial nanocellulose foam according to claim 1, characterized in that, include: A dispersion comprising TEMPO-oxidizing bacterial nanocellulose with at least 75% crystallinity, anionic biopolymer, at least one surfactant, at least one crosslinking agent, and at least one modifier to enhance resilience was prepared. A pore-forming agent is added to the dispersion to generate carbon dioxide and form a porous structure; and The TEMPO-oxidizing bacterial nanocellulose is ionically crosslinked with the anionic biopolymer.

10. The method according to claim 9, characterized in that, The TEMPO-oxidizing bacterial nanocellulose has a crystallinity of at least 75%.

11. The method according to claim 9, characterized in that, The ratio of Iα-cellulose to Iβ-cellulose in the TEMPO oxidizing bacterial nanocellulose is 40:60 to 65:

35.

12. The method according to claim 9, characterized in that, The anionic biopolymer is sodium alginate, which has a viscosity of 200-350 mPa·s in water.

13. The method according to claim 9, characterized in that, The pore-forming agent is gluconate-δ-lactone.

14. The method according to claim 9, characterized in that, The formation of the porous structure is achieved through mechanical stirring or gas expansion.

15. The method according to claim 13, characterized in that, The ionic crosslinking of the TEMPO oxidizing bacterial nanocellulose and the anionic biopolymer is achieved by chelating calcium ions in calcium carbonate with the carboxylate groups present on the TEMPO oxidizing bacterial nanocellulose and the anionic biopolymer.

16. The method according to claim 9, characterized in that, The density of the resilient bacterial nanocellulose foam is less than 182 kg / cm³. 3 .

17. The method according to claim 9, characterized in that, The resilient bacterial nanocellulose foam has a tensile strength of at least 90 kPa and a compressive strength of at least 0.5 MPa.

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