Preparation method of copper-coated fiber conductive network in plant fiber sponge

Abstract

The invention relates to a preparation method of a copper-coated fiber conductive network in plant fiber sponge, and relates to the technical field of lightweight porous plant fiber conductive materials, and the preparation method comprises the following steps: S1, pulping; s2, foaming; s3, molding and drying; s4, preparing copper paste; s5, dipping reduction; and S6, wrapping and modifying. According to the preparation method of the copper-coated fiber conductive network in the plant fiber sponge, the adopted plant cellulose material is rich in active functional groups such as hydroxyl groups and the like, and can generate strong interaction with amino groups and hydroxyl groups in 2-amino-2-methyl-1-propanol solvent molecules, including hydrogen bond association and even potential covalent bonding; the interface interaction of the molecular level obviously enhances the binding force between the plant fiber skeleton and the subsequent in-situ generated copper nanoparticles, and effectively inhibits the falling or agglomeration phenomenon of the metal particles in the use process, thereby constructing a continuous and through conductive network with a stable structure. Wide application prospects are realized in the fields of flexible electronics, electromagnetic shielding, intelligent sensing, wearable devices and the like.

Description

Technical Field

[0001] This invention relates to the field of lightweight porous plant fiber conductive materials, specifically a method for preparing a copper-coated fiber conductive network in a plant fiber sponge. Background Technology

[0002] Biomass polymer composites (BPCs) are renewable, non-conductive, and environmentally friendly materials composed of cellulose, hemicellulose, and lignin. They possess a hierarchical porous structure with distinct layers and an ordered composition. By modifying their conductivity, BPCs can be prepared into conductive porous carbonaceous materials, which can enhance their application value, broaden their application fields, alleviate environmental pollution and resource shortages, reduce carbon emissions, and contribute to achieving "carbon neutrality."

[0003] Currently, conductive porous BPCs can be prepared through processes such as high-temperature carbonization and in-situ coating modification of conductive functional units. However, due to the high anisotropy of the structure, high-temperature carbonization can easily lead to material shrinkage, resulting in deterioration of mechanical properties (such as resilience), response time (such as piezoresistive sensitivity), and interfacial bonding performance (conductivity) of conductive units.

[0004] This invention involves soaking and drying PFS with Cu-AMP slurry, and then using an in-situ reduction growth method to reduce copper formate on the fiber surface to form CuNPs, which are then stacked to form a continuous conductive layer, thus realizing the preparation of a copper-coated plant fiber conductive network. Since the AMP surface is rich in hydroxyl and amino groups, it can form hydrogen bonds or covalent bonds with the fiber, strengthening the bond between the plant fiber molecular chains and metal particles at the interface, thereby forming a good interface structure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a copper-coated fiber conductive network in plant fiber sponges. This method has advantages such as simple process, green and renewable raw materials, uniform copper distribution, high conductivity, complete porous structure, good flexibility, and strong interfacial bonding. It solves the problems of easy detachment of conductive fillers, high contact resistance, and poor stability in traditional physical mixing methods, as well as the shrinkage, embrittlement, loss of resilience, and discontinuity of the conductive network caused by high-temperature carbonization methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a copper-coated fiber conductive network in a plant fiber sponge, comprising the following steps: S1 Pulping: Plant fiber pulp is obtained by pulping plant fiber as raw material. S2 foaming: Add binder and foaming agent to plant fiber slurry in sequence, and stir to foam it; S3 Molding and Drying: After the plant fiber slurry reaches the foaming volume ratio, it is transferred to a mold for drying to obtain plant fiber porous sponge (PFS). S4 copper paste: Cu-AMP paste is obtained by physical ball milling using Cu(HCOO)2 as raw material and 2-amino-2-methyl-1-propanol (AMP) as solvent. S5 Impregnation and Reduction: PFS is immersed in Cu-AMP slurry and subjected to thermal reduction treatment under N2 atmosphere to obtain PFS@Cu composite conductive material.

[0007] S6 encapsulation modification: PFS@Cu composite conductive material is immersed in an organic elastomer solution, removed and dried to obtain conductive PFS@Cu sponge.

[0008] Furthermore, the plant fiber in step S1 is at least one of wood fiber, bamboo fiber, hemp fiber, crop straw fiber, and recycled pulp.

[0009] Furthermore, the pulping process described in step S1 is a physical-mechanical method, which includes beating and refining; the concentration of plant fiber pulp in step S1 is 1-15 wt%.

[0010] Furthermore, the adhesive mentioned in step S2 is at least one of polyvinyl acetate, polyvinyl alcohol, polyurethane, urea-formaldehyde resin, and phenolic resin; the foaming agent mentioned in step S2 is at least one of higher fatty acid salts, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and rosin soap.

[0011] Furthermore, the amount of adhesive added in step S2 is 1-30 wt% of plant fiber; the amount of foaming agent added in step S2 is 0.5-10 wt% of plant fiber.

[0012] Furthermore, in step S3, the foaming volume ratio is 4-15 times; the time for pouring into the mold and letting it stand and drain is 3-30 minutes; the drying temperature is 80-100℃, and the drying time is 5-20 hours.

[0013] Furthermore, the ball milling speed of the physical ball milling method described in step S4 is 200-600 r / min, and the ball milling time is 2-6 h; the Cu-AMP slurry concentration is 5-30 wt%.

[0014] Furthermore, the number of immersions in step S5 is 1-3 times; the thermal reduction temperature is 30-200℃; the PFS@Cu composite conductive material in step S5 is used for flexible electronic devices and sensors; and the conductivity of the PFS@Cu composite conductive material in step S5 is 0.01-100S / cm.

[0015] Furthermore, the organic elastomer solution mentioned in step S6 is at least one of thermoplastic polyurethane (TPU), polyurethane, polydimethylsiloxane (PDMS), thermoplastic polyolefin elastomer (TPE-O), 1,2-polybutadiene thermoplastic elastomer, and trans-polyisoprene thermoplastic elastomer.

[0016] Furthermore, the compressive strain of the conductive PFS@Cu sponge described in step S6 is 5%-99%.

[0017] Compared with the prior art, the technical solution of this application has the following beneficial effects: 1. The preparation method of copper-coated fiber conductive network in plant fiber sponge: The plant cellulose material used is rich in a large number of active functional groups such as hydroxyl groups, which can interact strongly with the amino and hydroxyl groups in the 2-amino-2-methyl-1-propanol (AMP) solvent molecule, including hydrogen bonding and even potential covalent bonding. This molecular-level interfacial interaction significantly enhances the binding force between the plant fiber skeleton and the subsequently generated in-situ copper nanoparticles (CuNPs), effectively inhibiting the shedding or aggregation of metal particles during use, thereby constructing a structurally stable and continuously connected conductive network.

[0018] 2. The method for preparing the copper-coated fiber conductive network in this plant fiber sponge involves constructing a Cu-AMP precursor slurry with extremely low organic component content. This allows for the loading of a high-concentration copper source within a limited volume, resulting in a functional slurry with significantly increased copper content. During the subsequent thermal reduction process, the byproducts generated from the decomposition of copper formate in the AMP system exhibit good volatility, preventing the accumulation of carbides or other insulating impurities within the material and avoiding conductivity degradation due to residues. Crucially, the reduction reaction simultaneously releases hydrogen gas, further enhancing the local reduction environment under a nitrogen protective atmosphere. This effectively suppresses the oxidation tendency of copper nanoparticles at high temperatures, ensuring that the final product possesses a high-purity metallic copper phase and excellent intrinsic conductivity.

[0019] 3. The preparation method of the copper-coated fiber conductive network in the plant fiber sponge uses natural plant fibers, copper formate, and AMP solvent—all of which are widely available, low in cost, and environmentally friendly, conforming to the development concept of green chemistry and circular economy. Furthermore, the entire preparation process is simple and efficient, requiring no complex equipment or harsh reaction conditions. The conductive network can be constructed simply through conventional ball milling, impregnation, and mild heat treatment, exhibiting good repeatability and large-scale production potential. It also shows good universality for different types of plant fibers. The obtained PFS@Cu composite material not only has low density and good flexibility but also exhibits excellent and stable conductivity, showing broad application prospects in flexible electronics, electromagnetic shielding, smart sensing, and wearable devices. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Please refer to Figure 1 A method for preparing a copper-coated fiber conductive network in a plant fiber sponge is disclosed. The preparation process involves taking wood fiber raw materials, crushing them with a pulverizer, adding deionized water, and mechanically stirring to prepare a uniform plant fiber slurry with a solid content of 10 wt%. Then, 20 wt% polyvinyl acetate (based on the weight of the plant fiber) is added to the slurry as a binder, and 1 wt% sodium dodecylbenzenesulfonate is added as a foaming agent. The mixture is stirred at high speed at room temperature until the system is fully foamed, achieving a foam volume ratio of 8 times. The resulting foam is slowly transferred to a mold with dimensions of 200 mm × 150 mm × 50 mm, allowed to stand and drain for 5 minutes, and then dried in a 95°C forced-air drying oven for 6 hours to obtain a lightweight porous plant fiber composite material (PFS).

[0023] Copper formate [Cu(HCOO)2] and 2-amino-2-methyl-1-propanol (AMP) were mixed in a certain proportion and placed in a ball mill jar. The mixture was ball milled at 300 r / min for 2 h to obtain a uniform and stable Cu-AMP slurry. The PFS sample was completely immersed in the slurry. After one immersion, the sample was removed and placed in a tube furnace for thermal reduction treatment under a nitrogen protective atmosphere. During this process, copper formate decomposed and reduced in situ on the fiber surface to generate copper nanoparticles (CuNPs), forming a continuous conductive network. Finally, PFS@Cu composite conductive material was obtained. The obtained material has a complete structure, good conductivity, and significantly reduced volume resistivity.

[0024] Finally, the PFS@Cu composite conductive material was impregnated with a 20wt% thermoplastic polyurethane (TPU) solution, removed and dried at 90°C to obtain conductive PFS@Cu sponge.

[0025] Additionally, the thermal reduction process in the above embodiments is as follows: The PFS soaking slurry was placed in a tube furnace. Under a nitrogen protective atmosphere, the temperature was raised from 30°C to 110°C in 5 minutes and held for 20 minutes. Then, it was raised to 140°C in 2 minutes and held for 20 minutes. Finally, it was raised to 195°C in 5 minutes and held for 2 hours for thermal reduction treatment.

[0026] In summary, this embodiment successfully constructed a continuous copper nano-conductive network in situ on the surface of a plant fiber sponge by a single impregnation of Cu-AMP slurry followed by thermal reduction treatment. While maintaining the lightweight and porous structure of the material, it achieved a low volume resistivity, making it suitable for basic application scenarios that balance conductivity and structural integrity.

[0027] Example 2: Plant fiber pulp and PFS sponge were prepared using the same method as in Example 1, wherein the concentration of plant fiber pulp was still 10wt%, the amount of binder (polyvinyl acetate) added was 20wt% of the mass of plant fiber, the amount of foaming agent (sodium dodecylbenzenesulfonate) added was 1wt%, the foaming ratio was 8 times, and the drying conditions were 95℃ / 6h.

[0028] The Cu-AMP slurry was also prepared using a physical ball milling method at 300 r / min for 2 h. The difference was that the PFS sample was repeatedly immersed in the Cu-AMP slurry twice, with each immersion followed by natural draining before the next immersion. The sample was then subjected to thermal reduction treatment in a nitrogen atmosphere. The high temperature promoted more thorough decomposition of copper formate and the crystallization growth of copper nanoparticles. Simultaneously, the two immersions increased the copper loading in the fiber network, resulting in a PFS@Cu composite material with higher copper coverage and lower resistivity. Subsequently, it was impregnated with a 20 wt% thermoplastic polyurethane (TPU) solution to obtain a conductive PFS@Cu sponge, suitable for applications requiring high conductivity.

[0029] Additionally, the thermal reduction process in the above embodiments is as follows: The PFS soaking slurry was placed in a tube furnace. Under a nitrogen protective atmosphere, the temperature was raised from 30°C to 110°C in 5 minutes and held for 20 minutes. Then, it was raised to 140°C in 2 minutes and held for 20 minutes. Finally, it was raised to 195°C in 5 minutes and held for 2 hours for thermal reduction treatment.

[0030] In summary, this embodiment employs a two-stage impregnation combined with thermal reduction treatment, which significantly increases the copper loading and constructs a denser conductive pathway. The resulting PFS@Cu composite material exhibits lower resistivity while maintaining the material's lightweight and porous structure, making it particularly suitable for cutting-edge applications such as flexible electronics and wearable devices that require a balance between mechanical resilience and stable conductivity.

[0031] Example 3: The preparation process of PFS sponge is the same as in Example 1: 10wt% pulp is made from wood fiber, 20wt% polyvinyl acetate and 1wt% sodium dodecylbenzenesulfonate are added, foamed to 8 times the volume, molded and dried at 95℃ for 6 hours.

[0032] The Cu-AMP slurry preparation parameters were kept consistent (ball milling at 300 r / min for 2 h). In this embodiment, the PFS sample was continuously immersed in the Cu-AMP slurry three times, with each immersion followed by natural air drying to achieve deep penetration and uniform distribution of the copper precursor in the porous network. Subsequently, a thermal reduction treatment was performed under nitrogen protection. Multiple impregnations increased the enrichment of the precursor within the fiber, effectively generating a continuous copper conductive network. However, the porosity of the PFS@Cu material obtained under these conditions was reduced. Subsequent impregnation with a 20 wt% thermoplastic polyurethane (TPU) solution resulted in a significant decrease in the flexibility of the conductive PFS@Cu sponge, making it suitable for electronic devices requiring high conductivity.

[0033] Additionally, the thermal reduction process in the above embodiments is as follows: The PFS soaking slurry was placed in a tube furnace. Under a nitrogen protective atmosphere, the temperature was raised from 30°C to 110°C in 5 minutes and held for 20 minutes. Then, it was raised to 140°C in 2 minutes and held for 20 minutes. Finally, it was raised to 195°C in 5 minutes and held for 2 hours for thermal reduction treatment.

[0034] In summary, this embodiment achieves deep penetration and uniform distribution of copper precursor in a three-dimensional network under low thermal stress through three impregnations combined with thermal reduction treatment, effectively improving the conductivity of the sponge. However, the porosity of the sponge's porous structure is significantly reduced, making it suitable for electromagnetic shielding or high-sensitivity sensing applications with stringent requirements for high conductivity.

[0035] Comparison of Examples:

[0036] The table visually demonstrates that by adjusting the number of impregnation cycles, targeted optimization can be achieved between conductivity, flexibility, and structural integrity, highlighting the flexibility and application adaptability of the process of this invention.

[0037] Comparative experiment Experimental setup: The sample of this invention (Example 2): PFS was impregnated twice with Cu-AMP slurry and then encapsulated with TPU.

[0038] Comparative Example 1 (Physical Mixing Method): Commercial micron-sized copper powder (particle size ~5μm) was mixed with ethanol, soaked and adsorbed onto the surface of PFS, and then encapsulated with TPU to form a shape without chemical bonding or in-situ reduction.

[0039] Comparative Example 2 (High-Temperature Carbonization Method): PFS was carbonized at 800℃ for 2 hours in an inert atmosphere to form a conductive carbon skeleton (without metallic copper or TPU encapsulation).

[0040] All samples were uniformly sized (30mm × 30mm × 10mm) and tested under the same conditions.

[0041] Performance comparison data

[0042] Results Analysis Conductivity advantage: The resistivity of the sample of this invention (0.25 Ω·cm) is significantly lower than that of the physically adsorbed sample (20.6 Ω·cm) and the carbonized sample (4300 Ω·cm), indicating that the in-situ generated copper nanonetwork has high continuity and low contact resistance. In contrast, due to the lack of effective interfacial connection, there are a large number of insulating gaps between copper particles in the physically adsorbed sample. Although the carbonized sample has a certain conductivity, its conductivity is limited due to the low degree of graphitization.

[0043] Excellent resilience: PFS@Cu and physically adsorbed samples still maintain a 95% resilience rate after multiple compressions, which is much higher than that of carbonized samples (45%). High-temperature carbonization leads to pyrolysis of cellulose and embrittlement of the skeleton. This invention constructs a conductive layer at low temperature, which completely preserves the flexible three-dimensional network of PFS.

[0044] Outstanding interfacial stability: Peeling tests show that the interfacial bonding force of this invention reaches 1.8 N / cm, which is 6 times that of the physically adsorbed sample (0.3 N / cm), proving that CuNPs are firmly anchored to the fiber surface through hydrogen bonding / coordination. Furthermore, after 5000 cycles, the resistance only increases by 1%, while the resistance of the physically adsorbed sample surges by 40% due to the detachment of copper from the plant fiber interface, and the resistance of the carbonized sample surges by 80% due to skeletal embrittlement, highlighting the advantages of this invention in terms of structural durability.

[0045] in conclusion Comparative experimental data fully demonstrate that this invention, through low-temperature in-situ reduction of Cu-AMP precursor, constructs a copper-coated conductive network with high conductivity, high stability, and strong interfacial bonding while retaining the porous and flexible structure of plant fiber sponge. Its comprehensive performance is significantly better than that of traditional physical adsorption or high-temperature carbonization routes, demonstrating outstanding technological advancement and application value.

[0046] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a copper-coated fiber conductive network in a plant fiber sponge, characterized in that: Includes the following steps: S1 Pulping: Plant fiber pulp is obtained by pulping plant fiber as raw material. S2 foaming: Add binder and foaming agent to plant fiber slurry in sequence, and stir to foam it; S3 Molding and Drying: After the plant fiber slurry reaches the foaming volume ratio, it is transferred to a mold for drying to obtain plant fiber porous sponge (PFS). S4 copper paste: Cu-AMP paste is obtained by physical ball milling using Cu(HCOO)2 as raw material and 2-amino-2-methyl-1-propanol (AMP) as solvent. S5 Impregnation and Reduction: PFS is immersed in Cu-AMP slurry and subjected to thermal reduction treatment under N2 atmosphere to obtain PFS@Cu composite conductive material; S6 encapsulation modification: PFS@Cu composite conductive material is immersed in an organic elastomer solution, removed and dried to obtain conductive PFS@Cu sponge.

2. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The plant fiber in step S1 is at least one of wood fiber, bamboo fiber, hemp fiber, crop straw fiber, and recycled pulp.

3. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The pulping process described in step S1 is a physical-mechanical method, which includes beating and refining; the concentration of plant fiber pulp in step S1 is 1-15 wt%.

4. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The adhesive mentioned in step S2 is at least one of polyvinyl acetate, polyvinyl alcohol, polyurethane, urea-formaldehyde resin, and phenolic resin; the foaming agent mentioned in step S2 is at least one of higher fatty acid salts, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and rosin soap.

5. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The amount of adhesive added in step S2 is 1-30 wt% of plant fiber; the amount of foaming agent added in step S2 is 0.5-10 wt% of plant fiber.

6. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The foaming volume ratio in step S3 is 4-15 times; the time for pouring into the mold and letting it stand and drain is 3-30 min; the drying temperature is 80-100℃ and the drying time is 5-20 h.

7. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The ball milling method described in step S4 has a ball milling speed of 200-600 r / min and a ball milling time of 2-6 h; the Cu-AMP slurry concentration is 5-30 wt%.

8. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The number of immersions in step S5 is 1-3 times; the thermal reduction temperature is 30-200℃; the PFS@Cu composite conductive material in step S5 is used for flexible electronic devices and sensors; and the conductivity of the PFS@Cu composite conductive material in step S5 is 0.01-100S / cm.

9. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The organic elastomer solution mentioned in step S6 is at least one of thermoplastic polyurethane (TPU), polyurethane, polydimethylsiloxane (PDMS), thermoplastic polyolefin elastomer (TPE-O), 1,2-polybutadiene thermoplastic elastomer, and trans-polyisoprene thermoplastic elastomer.

10. The method for preparing a copper-coated fiber conductive network in a plant fiber sponge according to claim 1, characterized in that: The compressive strain of the conductive PFS@Cu sponge described in step S6 is 5%-99%.

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