Bio-based foam materials with super resilience properties and preparation, application thereof

Abstract

The application provides a bio-based foam with super resilience and a preparation method thereof. The foam material is composed of fiber raw material, bioactive agent, bio-crosslinking agent and polyvalent metal salt, and the fiber raw material is composed of natural wood fiber and bio-based synthetic fiber. The length of the natural wood fiber is 1-3 mm, the length of the bio-based synthetic fiber is 3-6 mm, and the content of the bio-based synthetic fiber in the fiber raw material is not less than 50 wt%. The foam material significantly improves the resilience, and still maintains excellent strength and original shape after 10000-40000 times of compression, achieving unexpected technical effects. The application also provides a preparation method of the bio-based foam material, which adopts a wet foaming method with simple process, easy amplification and low cost. On this basis, the application also provides an application of the bio-based foam as a dielectric layer of a capacitive pressure sensor, which can realize contact and non-contact sensing of pressure, has wide application prospect and huge economic value.

Description

Technical Field

[0001] The present invention belongs to the field of materials and relates to cellulose composite materials, in particular to a bio-based foam material with super resilience and its application in the dielectric layer of a capacitor pressure sensor. Background Art

[0002] In fields such as wearable electronics, soft robotics, and human-machine interfaces, there is an increasing demand for pressure sensors that respond to external mechanical stimuli and provide real-time information. Demand for capacitive pressure sensors has surged in recent years. This is due to their wide response range and simple structure, consisting primarily of two conductive electrodes with a dielectric layer between them, similar to a sandwich structure. Capacitance (C) changes are driven by the dielectric constant of the dielectric layer and the size of the capacitor. Dielectric variability is the most critical factor in capacitive sensing and is typically achieved by adjusting the dielectric constant and compressibility of the dielectric layer. Therefore, the material used as the dielectric layer has a significant impact on the performance of capacitive pressure sensors. Currently, the dielectric layer of capacitive pressure sensors is mostly made of low-density, high-surface-area polymer foams such as polyolefins, polyurethanes, polyamides, and polydimethylsiloxanes. This is because their porous structure allows for the inclusion of a significant amount of air within the foam, resulting in dielectric properties similar to those of air, making them suitable for use as air substitutes in sensor dielectric layers. However, these polymer foams are non-renewable and non-biodegradable, making their replacement with biodegradable materials an inevitable trend for sustainable development.

[0003] Cellulose, the most abundant renewable biopolymer in nature, is considered an attractive candidate for the development of green and sustainable materials. Cellulose aerogels / foams, with their lighter, more uniform porous structure, have been widely used in sensing research in recent years. Cellulose aerogels are mostly prepared from wet gels via freeze-drying or supercritical drying, while cellulose-based foams are typically prepared by wet foaming with a surfactant at room temperature and atmospheric pressure, followed by molding and drying in air or an oven. Cellulose aerogels are mostly made from nanosized cellulose, such as cellulose nanocrystals, cellulose nanofibers, and bacterial cellulose. Pure nanocellulose aerogels exhibit 90% compressibility. The application of freezing technology imparts an anisotropic honeycomb structure to the aerogels, which imparts excellent mechanical strength and elasticity. Furthermore, the introduction of strong covalent bonds can impart a directional structure to aerogels, which is also an effective strategy for conferring elasticity. Due to their excellent elasticity and modifiable electrical conductivity, aerogels have been successfully applied in piezoresistive pressure sensors. However, the high price of nanofibers and the complex subsequent processing technology (the use of toxic reagents, high-cost supercritical drying technology, etc.) have greatly limited the application of pure nanocellulose aerogels.

[0004] In contrast to the excellent performance and high cost of cellulose aerogels, the cost of cellulose-based foams prepared by wet foaming with bioactive agents under normal pressure is significantly reduced. This is because: (1) the raw materials of cellulose-based foams are widely available, including waste paper fibers, pulp fibers, bamboo fibers, sugarcane bagasse, etc.; (2) the fiber sizes that can be used are larger, including nano-scale fibers, micro-scale fibers, and millimeter-scale fibers. However, it is well known that the preparation of cellulose-based foams has problems with wrinkles or deformation caused by water evaporation during the drying process, and the mechanical strength is poor and there is no resilience. Based on this, researchers have proposed solvent replacement (ethanol, acetone, etc.) or microwave-assisted drying methods to effectively solve the wrinkle or deformation problem caused by water evaporation. In addition, the improvement of the mechanical strength of cellulose-based foams is achieved by constructing a cross-linked network, making the fibers microfibrillated, introducing functional coatings, and co-assembling at the gas-liquid interface. Therefore, cellulose-based foams have also been used in the fields of antibacterial, heat insulation, flame retardancy, and sound insulation.

[0005] Currently, there are no reports on solutions to the problem that cellulose-based foam cannot recover to its original height after compression and lacks resilience, which limits its application to a certain extent. Summary of the Invention

[0006] To address the problem of the lack of resilience in cellulose-based foams in the prior art, the present invention provides a bio-based foam with superior resilience and a method for preparing the same. The preparation method utilizes a simple, easily scalable, and low-cost wet foaming process, which is not only low-cost but also significantly improves the resilience of the cellulose-based foam, overcoming technical biases and achieving unexpected technical results. Furthermore, the present application also provides the use of the bio-based foam as a dielectric layer in a capacitive pressure sensor, enabling both contact and non-contact pressure sensing, with broad application prospects and enormous economic value.

[0007] The technical solution of the present invention:

[0008] A kind of bio-based foam material with super strong resilience, the foam material is composed of fiber raw material, bioactive agent, biocrosslinking agent and polyvalent metal salt, and the fiber raw material is composed of natural wood fiber and bio-based synthetic fiber. Wherein, the length of the natural wood fiber is 1-3mm, the length of the bio-based synthetic fiber is 3-6mm, and the content of the bio-based synthetic fiber in the fiber raw material is not less than 50wt%. The natural wood fiber is one or more of softwood pulp, hardwood pulp, hemp pulp, cotton fiber, pineapple leaf fiber, banana stalk fiber, bamboo pulp and bagasse pulp. The bio-based synthetic fiber is one or more of polylactic acid (PLA) fiber, polytrimethylene terephthalate (PTT) fiber, polyhydroxy fatty acid (PHA) fiber. The applicant unexpectedly found that by adding an appropriate amount of bio-based synthetic fiber with a length of 3-6mm, the resilience of the bio-based foam material finally prepared was significantly improved, and after 10000-40000 compressions, excellent strength and original shape were still maintained, achieving unexpected technical effects. After analysis, the inventor speculates that this is because: compared with natural wood fibers, bio-based synthetic fibers have outstanding rigidity and toughness; under the aforementioned fiber length conditions, a mutually entangled structure is formed between the bio-based synthetic fibers and the natural wood fibers, so they will not be damaged during the compression process and have excellent rebound performance.

[0009] The bioactive agent has a hydrophile-lipophile balance (HLB) of 10-40 and is used in an amount of 0.1-2.0 wt% of the fiber raw material. Preferably, the bioactive agent is one or more of saponin, sulfonated lignin, amino lignin, carboxylated lignin, platycoside, and liquiritin, and is used in an amount of 0.3-1.5 wt% of the fiber raw material.

[0010] The biocrosslinking agent has a viscosity of 200±20 mPa.s (1%, 2°C); the amount of the biocrosslinking agent used is 2-20 wt% of the fiber raw material. Preferably, the biocrosslinking agent is one or more of sodium alginate, carboxylated nanocellulose, and carboxymethyl cellulose; the amount of the biocrosslinking agent used is 2-10 wt% of the fiber raw material.

[0011] The polyvalent metal salt is Ca 2+ Mg 2+ 、Mn 2+ 、Al 3+ 、Zn 2+ 、Fe 3+ and Cu 2+ The amount of the multivalent metal salt is 1-10 wt% of the fiber raw material. Preferably, the amount of the multivalent metal salt is 3-10 wt% of the fiber raw material.

[0012] The bio-based foam material described above has an oriented layered structure with interconnected macropores. Its dielectric properties are similar to those of air, and it can recover its original shape after compression deformation, exhibiting excellent resilience. This significantly improves the technical performance compared to existing cellulose-based foams. Furthermore, the bio-based foam material maintains stable performance across a wide temperature range of -20°C to 150°C and in high humidity environments, offering broad application prospects and substantial potential economic benefits.

[0013] As described above, the method for preparing a bio-based foam material employs a wet foaming and ionic crosslinking strategy to prepare a bio-based foam material with high resilience. Specifically, the method comprises the following steps:

[0014] (1) Dispersing the fiber raw materials: Appropriate amounts of natural wood fibers and bio-based synthetic fibers are dispersed in water to obtain a fiber aqueous dispersion having a fiber raw material concentration of 0.3-0.6 wt %. The fiber dispersion is stirred at a speed of 100-1000 rpm for a time of 10-30 min.

[0015] (2) Foaming: Add a bioactive agent and a biocrosslinking agent to the fiber aqueous dispersion obtained in step (1), stir at room temperature to mix evenly and fully foam, and obtain a foam mixture, i.e., a slurry. The stirring speed is 500-2000 rpm, and the stirring time is 1-5 minutes. In this step, by adding the biocrosslinking agent in advance, not only is the crosslinking agent evenly dispersed in the slurry, but it also helps foaming to a certain extent. In addition, the foaming process is carried out at room temperature and pressure, the amount of additives used is small, the cost is low, and it has good economic efficiency.

[0016] (3) Crosslinking: A polyvalent metal salt solution is added to the foam mixture obtained in step (2), and the mixture is stirred at room temperature to crosslink the mixture. The mixture is then poured into a mold, filtered to obtain a wet foam, and dried to form the bio-based foam material. In this step, the crosslinking reaction primarily occurs between the polyvalent metal ions and the previously added bio-crosslinking agent.

[0017] Wherein, the stirring speed during the mixing and cross-linking is 100-500rpm, and the stirring time is 1-5min. The filtration is normal pressure filtration for 5-10min or vacuum filtration for 1-3h. The drying and molding is hot air drying or vacuum drying; the temperature of the hot air drying is 25-100℃, and the time of the hot air drying is 5-24h; the temperature of the vacuum drying is 30-60℃, and the drying time is 1-8h. In the preparation of cellulose-based foam in the prior art, if normal pressure drying is used, the foam will shrink and the structure will be destroyed, so freeze drying must be used. In contrast, in the preparation of the bio-based foam material described in the present application, even if conventional drying methods are used, the rebound properties of the foam material are not affected at all, which also verifies the significant improvement of its performance from another aspect.

[0018] As previously mentioned, bio-based foam materials are used as dielectric layers in capacitive pressure sensors. Due to their excellent resilience and porous structure, these bio-based foam materials fully meet the requirements for dielectric layers in capacitive pressure sensors. Furthermore, compared to pure nanocellulose aerogels in existing technologies, these foams offer comparable performance, simpler preparation methods, and significantly lower costs, clearly offering a competitive advantage.

[0019] A green and environmentally friendly capacitive pressure sensor is constructed by assembling an upper conductive layer, a lower conductive layer, and an intermediate dielectric layer sandwiched between them in a sandwich configuration. The intermediate dielectric layer is the aforementioned bio-based foam material, and the upper and / or lower conductive layers are adhesive conductive copper tape. The bio-based foam material is cut into rectangles of varying sizes and laid flat on a layer of copper tape of the same size to form a capacitive pressure sensor for contact and non-contact detection.

[0020] Beneficial effects of the present invention:

[0021] (1) The present invention first provides a bio-based foam material with super-strong rebound performance. Compared with the cellulose-based foam in the prior art, the bio-based foam material has excellent rebound performance and can still maintain excellent strength and original shape after being compressed 10,000-40,000 times, achieving unexpected technical effects.

[0022] (2) The present invention also provides a method for preparing the bio-based foam material. The method uses natural wood fiber and bio-based synthetic fiber as main materials. The method is not only simple and low-cost, but also environmentally friendly and has good prospects for industrial application.

[0023] (3) In view of the excellent resilience of the aforementioned bio-based foam material, it can be used as the dielectric layer of a capacitive pressure sensor to make a capacitive pressure sensor for contact and non-contact detection, thus solving the technical problem of the non-environmentally friendly / high cost of the raw materials used as the dielectric layer in the prior art, and achieving huge economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Attachment Figure 1 This is a physical picture of the bio-based foam material prepared in Example 1 of the present invention on a plant leaf.

[0025] Attachment Figure 2 These are radial and axial computed tomography images of the bio-based foam material prepared in Example 1 of the present invention.

[0026] Attachment Figure 3 This is a stress-strain curve diagram of the bio-based foam material prepared in Example 1 of the present invention after being compressed under different deformations.

[0027] Attachment Figure 4 This is the stress-strain curve of the bio-based foam material prepared in Example 1 of the present invention after 30,000 compressions at 50% compression deformation.

[0028] Attachment Figure 5 These are the stress-strain curves of the bio-based foam material prepared in Example 1 of the present invention at different temperatures and humidities.

[0029] Attachment Figure 6 This is a graph showing the mass change of the bio-based foam material prepared in Example 1 of the present invention before and after biodegradation.

[0030] Attachment Figure 7 This is a physical picture and structural schematic diagram of a capacitive pressure sensor assembled with bio-based foam material prepared in Example 1 of the present invention.

[0031] Attachment Figure 8 This is a graph showing the relationship between the relative change in capacitance and strain of the capacitive pressure sensor according to Example 7 of the present invention.

[0032] Attachment Figure 9 This is a graph showing the relationship between the relative change in capacitance and time of the capacitive pressure sensor under contact detection according to Example 7 of the present invention.

[0033] Attachment Figure 10 This is a graph showing the relationship between the relative change in capacitance and time of the capacitive pressure sensor under non-contact detection according to Example 7 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the embodiments.

[0035] The following examples are merely examples of embodiments of the present invention and do not constitute any limitation to the present invention. Those skilled in the art will appreciate that modifications or expansions without departing from the spirit and scope of the present invention fall within the scope of protection of the present invention.

[0036] Example 1: Preparation of bio-based foam material

[0037] 2.4g of polylactic acid (PLA) fiber and 0.6g of bleached softwood pulp were placed in a 1000ml measuring cup. 597ml of water was added and stirred at room temperature for 30 minutes at 500rpm to obtain an aqueous fiber dispersion. The fiber concentration in the dispersion was 0.5wt%. Next, 24ml of a 2wt% sodium alginate solution (8wt% of the bio-based fiber) and 0.01g of saponin (0.3wt% of the bio-based fiber) were added, and stirring was continued for 2 minutes at 2000rpm to obtain a foam mixture, or slurry. Finally, 24ml of a 2wt% calcium chloride solution (8wt% of the bio-based fiber) was added, and stirring was continued for 5 minutes at 100rpm. The mixture was poured into a mold and filtered at atmospheric pressure for 1 hour to remove excess liquid and foam. The resulting bio-based foam was allowed to stand at ambient temperature for 4 hours and then dried in a 60°C oven with hot air for 12 hours to obtain a dry, superelastic green elastomeric bio-based foam. The bio-based foam material was compressed under 50% deformation, and its shape recovery rate after 10,000 consecutive compressions was as high as 98%, and after 30,000 consecutive compressions was as high as 91%.

[0038] Example 2: Preparation of bio-based foam materials

[0039] 2.1g of poly(trimethylene terephthalate) (PTT) fiber and 0.9g of bleached hardwood pulp were placed in a 1000ml measuring cup. 497ml of water was added and stirred at room temperature for 10 minutes at 1000rpm to produce an aqueous fiber dispersion. The fiber concentration in the dispersion was 0.6wt%. Next, 10ml of a 3wt% carboxymethyl cellulose solution (10wt% of the bio-based fiber) and 0.012g of sulfonated lignin (0.4wt% of the bio-based fiber) were added. Stirring was continued for 3 minutes at 1500rpm to produce a foamed mixture, i.e., a slurry. Finally, 10ml of a 3wt% aluminum sulfate solution (10wt% of the bio-based fiber) was added and stirring was continued for 1 minute at 500rpm. The mixture was poured into a mold and vacuum filtered for 5 minutes to remove excess liquid and foam. The resulting bio-based foam was then allowed to stand at ambient temperature for 4 hours and then vacuum-dried in a 60°C oven for 12 hours to obtain a dry bio-based foam material. This bio-based foam material exhibited a shape recovery rate of 96% after 10,000 consecutive compressions at 50% deformation, and a shape recovery rate of 91% after 30,000 consecutive compressions.

[0040] Example 3: Preparation of bio-based foam materials

[0041] 2.1g of polyhydroxyalkanoic acid (PHA) fiber and 0.9g of bleached bamboo pulp were placed in a 1000ml measuring cup. 747ml of water was added and stirred at room temperature for 20 minutes at 800rpm to obtain an aqueous fiber dispersion. The fiber concentration in the dispersion was 0.4wt%. Next, 10ml of a 3wt% carboxylated nanocellulose dispersion (10wt% of the bio-based fiber) and the bioactive agent platycoside (0.012g, 0.4wt% of the bio-based fiber) were added. Stirring was continued for 5 minutes at 500rpm to obtain a foam mixture, or slurry. Finally, 10ml of a 3wt% zinc chloride solution (10wt% of the bio-based fiber) was added and stirred for 2 minutes at 400rpm. The mixture was poured into a mold and filtered under atmospheric pressure for 2 hours to remove the liquid and foam. The resulting bio-based foam was allowed to stand at ambient temperature for 4 hours and then dried in a 50°C oven for 14 hours to obtain a dry bio-based foam material. The bio-based foam material was compressed under 50% deformation, and its shape recovery rate after 30,000 consecutive compressions was as high as 91%. After 40,000 consecutive compressions, its shape recovery rate was as high as 90%.

[0042] Example 4: Preparation of bio-based foam materials

[0043] 2g of polylactic acid (PLA) fiber and 1g of bleached softwood pulp were placed in a 1000ml measuring cup. 797ml of water was added and stirred at room temperature for 20 minutes at 400rpm to obtain an aqueous fiber dispersion. The fiber concentration in the dispersion was 0.38wt%. Next, 24ml of a 2wt% sodium alginate solution (8wt% of the bio-based fiber) and 0.01g of sodium lauryl sulfate (0.3wt% of the bio-based fiber) as a foaming agent were added. Stirring was continued for 3 minutes at 1500rpm to obtain a foam mixture, or slurry. Finally, 24ml of a 2wt% ferric chloride solution (8wt% of the bio-based fiber) was added and stirred for 3 minutes at 300rpm. The mixture was poured into a mold and vacuum filtered for 10 minutes to remove excess liquid and foam. The resulting bio-based foam was allowed to stand at ambient temperature for 4 hours and then dried in a 60°C oven for 12 hours to obtain a dry bio-based foam material. The bio-based foam material was compressed under 50% deformation, and its shape recovery rate after 15,000 consecutive compressions was as high as 93%. After 30,000 consecutive compressions, its shape recovery rate was as high as 92%.

[0044] Example 5: Preparation of bio-based foam materials

[0045] 1.5g of polyhydroxyalkanoic acid (PHA) fiber and 1.5g of bleached hardwood pulp were placed in a 1000ml measuring cup. 663ml of water was added and stirred at room temperature for 30 minutes at 100rpm to obtain an aqueous fiber dispersion. The fiber concentration in the dispersion was 0.45wt%. Next, 10ml of a 3wt% carboxymethyl cellulose solution (representing 10wt% of the bio-based fiber) and 0.012g of amino-lignin (representing 0.4wt% of the bio-based fiber) were added, and stirring was continued at 1000rpm for 4 minutes to obtain a foam mixture, i.e., a slurry. Finally, 10ml of a 3wt% copper chloride solution (representing 10wt% of the bio-based fiber) was added, and stirring was continued at 100rpm for 5 minutes. The mixture was poured into a mold and filtered at atmospheric pressure for 3 hours to remove excess liquid and foam. The resulting bio-based foam was allowed to stand at ambient temperature for 4 hours and then vacuum-dried in a 60°C oven for 12 hours to obtain a dry bio-based foam material. The bio-based foam material was compressed under 50% deformation, and its shape recovery rate after 30,000 consecutive compressions was as high as 93%. After 40,000 consecutive compressions, its shape recovery rate was as high as 90%.

[0046] Example 6: Characterization of the bio-based foam materials prepared in Examples 1-5

[0047] The bio-based foam materials prepared in Examples 1-5 were characterized, and the results were basically consistent. The bio-based foam material prepared in Example 1 is used as an example for detailed description.

[0048] Attachment Figure 1 This is a photo of the bio-based foam material prepared in Example 1 of the present invention on a plant leaf. This can intuitively illustrate that it has the characteristics of low density and ultra-lightness.

[0049] Attachment Figure 2 The radial and axial computed tomography images of the bio-based foam material prepared in Example 1 of the present invention are shown. Figure 2 It can be seen that the bio-based foam material exhibits different structures in the radial and axial directions, indicating that it has an anisotropic structure.

[0050] Attachment Figure 3 The stress-strain curves of the bio-based foam material prepared in Example 1 after different deformation compressions are shown. Figure 3 It can be seen that the foam can be compressed to a deformation of 90%, indicating its excellent compressibility.

[0051] Attachment Figure 4 This is the stress-strain curve of the bio-based foam material prepared in Example 1 of the present invention after 30,000 compressions at 50% compression deformation. Figure 4 It can be seen that the bio-based foam material has a compressive strength of 13 kPa. It can recover to its original shape after one compression and can still maintain 91% of its initial height after 30,000 compressions, which shows that the bio-based foam material has excellent resilience.

[0052] Attachment Figure 5 The stress-strain curves of the bio-based foam material prepared in Example 1 of the present invention at different temperatures and humidities are shown below. Figure 5 It can be seen that the bio-based foam material still has excellent resilience in an environment with a temperature of up to 150°C or a humidity of up to 95%, which shows that it has excellent temperature and humidity stability.

[0053] Attachment Figure 6 The mass of the bio-based foam material prepared in Example 1 of the present invention before and after biodegradation. Figure 6 It can be seen that the weight of the bio-based foam material is reduced by 85% of the initial weight after 50 days of composting, and it has excellent biodegradability and is an environmentally friendly bio-based material.

[0054] In summary, the bio-based foam materials prepared in Examples 1-5 can not only be compressed to a 90% deformation, but also retain 91% of their initial height after 30,000 compression cycles at a 50% deformation, demonstrating excellent compressibility and resilience, yielding unexpected technical benefits compared to existing technologies. Furthermore, these bio-based foam materials exhibit excellent temperature and humidity stability, as well as excellent biodegradability, demonstrating broad industrial application prospects and significant economic value.

[0055] Example 7: Application of bio-based foam material as dielectric layer

[0056] The bio-based foam material prepared in Examples 1-5 was used to prepare a capacitive pressure sensor. The structural design and physical diagram of the capacitive pressure sensor are shown in Figure 7 .like Figure 7 As shown, the capacitive pressure sensor has a three-dimensional sandwich structure, comprising an upper conductive layer, a lower conductive layer, and an intermediate dielectric layer sandwiched between the upper and lower conductive layers. The intermediate dielectric layer utilizes the bio-based foam material prepared in Examples 1-5, while the upper and lower conductive layers utilize self-adhesive conductive copper tape. Sensing performance tests of the aforementioned capacitive pressure sensors yielded consistent results. The following description uses a capacitive pressure sensor using the bio-based foam material prepared in Example 1 as an example.

[0057] The real-time change of capacitance of capacitive pressure sensor was tested by Tonghui LCR impedance meter (TH2830). The results are shown in Figure 8 、 Figure 9 and Figure 10 Attached Figure 8 The graph is a graph showing the relationship between the relative change in capacitance and strain of the capacitive pressure sensor of the present invention. Figure 8 It can be seen from the graph that the prepared capacitive sensor has a stable signal output during the cyclic detection process. Figure 9 This is a graph showing the relationship between the relative change in capacitance and time of the capacitive pressure sensor of the present invention under contact detection. Figure 9 It can be seen that the prepared capacitive sensor has excellent stability during contact pressing, can detect a wide range of pressure from 0 to 80 kPa, and has different sensitivities in the pressure ranges of 0 to 21.7 kPa, 21.7 to 51.5 kPa, and 51.5 to 80 kPa. Figure 10 The graph is a graph showing the relationship between the relative change in capacitance and time of the capacitive pressure sensor of the present invention under non-contact detection. Figure 10 It can be seen that the prepared capacitive sensor also senses signals when the tweezers are suspended in the air, and can be used for non-contact detection.

[0058] In summary, the capacitive sensors using the bio-based foam materials prepared in Examples 1-5 as dielectric layers are not only stable and reusable, with adjustable dielectric layer thickness, but can also be used for contact and non-contact detection, and have good application prospects.

[0059] Comparative Example 1:

[0060] Unlike Example 1, no bio-based crosslinker or multivalent metal salt was added. The resulting bio-based foam had no compressive strength and collapsed instantly when subjected to 50% strain compression, demonstrating that the ionic crosslinking effect of the bio-crosslinker contributes to the foam's mechanical strength.

[0061] Comparative Example 2:

[0062] Unlike Example 1, no natural wood fiber is added. The prepared bio-based foam has a compressive strength of 8.7 kPa. Although it is significantly improved compared to the bio-based foam prepared in Comparative Example 1, it will still collapse when subjected to 50% strain compression. The shape recovery rate of the foam after 10,000 continuous compressions is 87%. The shape recovery rate after 30,000 continuous compressions is 82%. The compressive strength of the bio-based foam prepared in Example 1 is 13 kPa. It can not only be compressed to 90% deformation, but also maintain 91% of its initial height after 30,000 compressions under 50% compression deformation. This shows that the use of only bio-based synthetic fibers not only reduces the resilience, but also the compressive strength is insufficient, which cannot meet the application requirements. It also shows that in the bio-based foams prepared in Examples 1-5 of the present application, natural wood fibers play a reinforcing role in the internal network of the foam. The synergistic effect of natural wood fibers and bio-based synthetic fibers makes the foam have higher mechanical properties. There is no relevant report in the prior art, which produces unexpected technical effects.

[0063] Comparative Example 3:

[0064] Unlike Example 1, no bio-based synthetic fibers were added, resulting in a bio-based foam, equivalent to the cellulose-based foam known in the prior art. This cellulose-based foam not only undergoes significant shrinkage after drying and cannot maintain its wet shape, but also fails to recover to its original height after compression, lacking resilience.

[0065] In summary, Examples 1-5 of the present application provide methods for preparing bio-based foam materials. These processes are characterized by low energy consumption, simple operation, and environmental friendliness. Furthermore, the bio-based foam materials prepared using the aforementioned methods not only possess a directional layered structure and interconnected macropores, but also exhibit dielectric properties similar to those of air. Furthermore, they exhibit excellent resilience, with a rebound height retention rate exceeding 90% after 10,000 to 40,000 compression cycles. These materials exhibit stable performance over a wide temperature range of -20°C to 150°C and in environments with a relative humidity of 0-100%, demonstrating broad application prospects. Based on these excellent properties, capacitive pressure sensors prepared using these bio-based foam materials exhibit advantages such as high stability, a wide detection range, and the ability to implement both contact and non-contact detection.

Claims

1. A bio-based foam material with super-strong resilience, characterized by: The foam material is composed of a fiber raw material, a bioactive agent, a biocrosslinking agent and a multivalent metal salt, wherein the fiber raw material is composed of natural wood fiber and bio-based synthetic fiber; wherein the length of the natural wood fiber is 1-3 mm, the length of the bio-based synthetic fiber is 3-6 mm, and the content of the bio-based synthetic fiber in the fiber raw material is not less than 50 wt%; the amount of the bioactive agent is 0.1-2.0 wt% of the fiber raw material, and the amount of the biocrosslinking agent is 2-20 wt% of the fiber raw material. wt%, the amount of the multivalent metal salt is 1-10wt% of the fiber raw material; the bio-based synthetic fiber is one or more of polylactic acid (PLA) fiber, polytrimethylene terephthalate (PTT) fiber, and polyhydroxy fatty acid (PHA) fiber; the bioactive agent is one or more of saponin, sulfonated lignin, amino lignin, carboxylated lignin, platycoside, and liquiritin; the biocrosslinking agent is one or more of sodium alginate, carboxylated nanocellulose, and carboxymethyl cellulose; the multivalent metal salt is Ca 2+ Mg 2+ 、Mn 2+ 、Al 3+ 、Zn 2+ 、Fe 3+ and Cu 2+ One or more inorganic salts.

2. The bio-based foam material according to claim 1, characterized in that: The hydrophile-lipophile balance value of the bioactive agent ( HLB ) is 10-40; the viscosity of the biocrosslinking agent at a concentration of 1wt% and a temperature of 2°C is 200±20 mPa.s, the amount of the bioactive agent is 0.3-1.5wt% of the fiber raw material, the amount of the biocrosslinking agent is 2-10 wt% of the fiber raw material, and the amount of the multivalent metal salt is 3-10wt% of the fiber raw material.

3. The bio-based foam material according to claim 1 or 2, characterized in that: The natural wood fiber is one or more of softwood pulp, hardwood pulp, hemp pulp, cotton fiber, pineapple leaf fiber, banana stem fiber, bamboo pulp and bagasse pulp.

4. The method for preparing a bio-based foam material according to any one of claims 1 to 3, wherein: The method comprises the following steps: (1) dispersing fiber raw materials: taking an appropriate amount of natural wood fiber and bio-based synthetic fiber, dispersing them in water to obtain a fiber water dispersion, wherein the concentration of the fiber raw materials in the dispersion is 0.3-0.6 wt %; (2) foaming: adding a bioactive agent and a biocrosslinking agent to the fiber water dispersion obtained in step (1), stirring at room temperature to mix uniformly and fully foam, and obtaining a foam mixture; (3) crosslinking: adding a polyvalent metal salt solution to the foam mixture obtained in step (2), stirring at room temperature to mix and crosslink, and then pouring it into a mold, filtering to obtain wet foam, and drying and molding to obtain the bio-based foam material.

5. The preparation method according to claim 4, characterized in that: The stirring speed during the fiber decomposition and dispersion in step (1) is 100-1000 rpm, and the stirring time is 10-30 min; the stirring speed during the foaming in step (2) is 500-2000 rpm, and the stirring time is 1-5 min; the stirring speed during the mixing and cross-linking in step (3) is 100-500 rpm, and the stirring time is 1-5 min.

6. The preparation method according to claim 4 or 5, characterized in that: The filtration is atmospheric pressure filtration for 1-3 hours or vacuum filtration for 5-10 minutes; the drying and molding is hot air drying or vacuum drying, wherein the hot air drying temperature is 25-100°C and the drying time is 5-24 hours; the vacuum drying temperature is 30-60°C and the drying time is 1-8 hours.

7. Use of the bio-based foam material according to any one of claims 1 to 3 as a dielectric layer of a capacitive pressure sensor.

8. A green and environmentally friendly capacitive pressure sensor, characterized by: The sensor is composed of an upper conductive layer, a lower conductive layer and an intermediate dielectric layer sandwiched between the upper conductive layer and the lower conductive layer; the intermediate dielectric layer is the bio-based foam material according to any one of claims 1 to 3.

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