Negative Poisson's ratio structure-based triboelectric sensing yarn and preparation method thereof

Abstract

The invention discloses a triboelectric sensing yarn based on a negative Poisson's ratio structure and a preparation method of the triboelectric sensing yarn. The triboelectric sensing yarn is constructed on the basis of a friction nano-generator principle and used for wearable intelligent fabric and human motion mechanical energy real-time collection. The negative Poisson's ratio triboelectric sensing yarn comprises a positive friction layer, a negative friction layer and a conductive electrode layer, the conductive electrode layer is arranged in the positive / negative friction layer through a coaxial wet spinning method, the positive friction layer is wound on the surface of the negative friction layer through spiral twisting, and a negative Poisson's ratio structure is formed. During stretching, the helical angle of the positive friction layer is reduced to cause radial expansion, the negative friction layer and the positive friction layer are driven to move along a composite path of axial separation and radial sliding, finally, the positions of the core layer and the winding layer are exchanged, and mechanical deformation energy is converted into continuous charges through geometric coupling to be output. The design utilizes the negative Poisson's ratio effect to synergistically optimize the separation path and the contact area of the triboelectric layer, and can be used for preparing the flexible electronic sensing fabric.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy collection, and in particular relates to a triboelectric sensing yarn based on a negative Poisson's ratio structure and a preparation method thereof. Background Art

[0002] With the continued growth in demand for health monitoring, wearable sensor technology has become a research hotspot in the fields of smart clothing, medical monitoring, and sports protection. Traditional sensors mostly exist in the form of external electronic devices. The contradiction between their rigid structure and wearing comfort limits their deep integration with textiles. As a response, smart yarns with sensing functions are gradually becoming the core carrier for the development of new smart clothing. The key lies in achieving the unity of autonomous energy supply and flexible deformation. However, existing sensing yarns generally face technical bottlenecks such as low mechanical energy conversion efficiency and insufficient environmental adaptability, making it difficult to meet the needs of stable energy supply and multi-dimensional perception under dynamic human activities.

[0003] With its self-powered characteristics and high mechanical energy conversion efficiency, friction nanogenerators provide new ideas for the development of smart sensing yarns. Based on the coupling effect of contact electrification and electrostatic induction, this technology can directly convert the low-frequency mechanical energy generated by human movement into electrical energy. However, traditional triboelectric fabrics are limited to planar contact modes. Under complex deformations such as bending and stretching, insufficient separation of the friction interface is prone to occur, resulting in a significant attenuation of charge transfer efficiency. In addition, existing fibrous triboelectric devices mostly use a positive Poisson's ratio structure. The lateral contraction effect under the action of external force exacerbates the contact mismatch between the friction layers, making it difficult to coordinately optimize energy conversion performance and mechanical durability.

[0004] In recent years, negative Poisson's ratio materials have attracted attention due to their unique mechanical response characteristics. When the material is subjected to axial stretching, the negative Poisson's ratio lateral expansion effect can simultaneously increase the effective contact area of the friction interface. This characteristic provides a theoretical possibility for solving the problems of low energy capture efficiency and poor fatigue resistance of traditional triboelectric yarns. However, existing technologies still face the dual challenges of material system and structural design: on the one hand, traditional preparation processes make it difficult to achieve precise mechanical coupling of core-shell structures, and the difference in modulus between functional layers can easily cause interfacial delamination; on the other hand, it is difficult to balance the biocompatibility and environmental stability of the material, which restricts its practical application in wearable scenarios. In this context, the development of new triboelectric sensing yarns that combine efficient energy conversion, adaptive deformation and wearing comfort has become a technical direction that urgently needs breakthroughs in this field. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a triboelectric sensing yarn based on a negative Poisson's ratio structure and its preparation method. Conventional triboelectric yarns experience a sharp drop in power generation efficiency when stretched due to a reduction in contact area. This present invention overcomes this limitation through its unique negative Poisson's ratio structural design. The yarn utilizes an "inner-outer synergistic" architecture: an inner conductive core composed of polyvinyl chloride and silver nanowires ensures efficient charge collection; an outer biocompatible friction layer, constructed from collagen and polyvinyl alcohol composite fibers, is spirally wound to form a spring-like structure. This spiral winding process imparts a negative Poisson's ratio to the yarn. When stretched, the yarn expands laterally, dynamically increasing the contact area between the inner and outer layers as the amount of stretch increases, significantly improving triboelectric power generation efficiency. Therefore, this triboelectric yarn with a negative Poisson's ratio structure is suitable for applications requiring frequent deformation, such as smart fabrics and sports monitoring, enabling efficient collection of body mechanical energy. This addresses the energy supply challenge faced by flexible electronic devices under tensile deformation.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A triboelectric sensing yarn based on a negative Poisson's ratio structure includes a core layer and a winding layer: The core layer and the winding layer are formed into a core-shell structure through coaxial wet spinning, and are wound with a spiral angle of 30°~60° through a spiral twisting process to form a spiral structure with negative Poisson's ratio characteristics. When stretched, the radial expansion effect of the spiral structure drives the increase of the contact area between the friction layers, realizing the conversion of mechanical energy into electrical energy.

[0007] Core layer: a negative triboelectric layer formed by compounding polyvinyl chloride and the first conductive filler; Wrapping layer: A positive triboelectric layer formed by a composite of collagen aggregates, polyvinyl alcohol and a second conductive filler.

[0008] Furthermore, the first conductive filler and the second conductive filler are independently selected from at least one of metal nanowires, carbon nanotubes, and conductive polymers, and the volume proportion of the conductive filler is 3% to 7%.

[0009] Furthermore, the collagen aggregates are extracted from any one of the following biological sources: mammalian dermis collagen, fish scale collagen, poultry skin collagen and animal tendon collagen.

[0010] Furthermore, the diameter ratio of the core layer to the winding layer is 1.5:1 to 2.5:1, and the elastic modulus of the core layer is 20%-50% higher than that of the winding layer.

[0011] Furthermore, when the axial stretching rate of the negative Poisson's ratio structure reaches 20%-50%, its transverse diameter expansion rate is 5%-15% (initial diameter reference before stretching). The negative Poisson's ratio effect is achieved through the synergistic effect of the spiral twisting angle (30°~60°) and the difference in elastic modulus of the core layer / winding layer (20%-50%).

[0012] Furthermore, the radial expansion energy generated by the spiral structure during axial stretching can drive the contact area between the core layer and the winding layer to increase by 20%-50% (based on the initial contact area), thereby achieving dynamic coupling enhancement of the negative Poisson's ratio effect and the triboelectric effect.

[0013] A method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure comprises the following steps: (1) Preparation of core layer: Dissolve modified polyvinyl chloride (degree of polymerization 1300-1500) in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 10%-20%, and add 0.1%-0.5% epoxy soybean oil as a plasticizer; after the polyvinyl chloride is completely dissolved, add 0.01%-0.1% fluorosilane coupling agent in 2-3 times with an interval of 10-15 minutes each time, and stir mechanically at 800-1200 r / min at 50-60°C for 20-30 minutes; degas by ultrasonic treatment for 30-60 minutes. The fibers were extruded through a coaxial spinneret into a gradient ethanol coagulation bath (ethanol concentration of 50%-60% and temperature of 25-28°C in the first zone and 70%-80% in the second zone) with 3%-7% conductive filler (silver nanowires: diameter 20-80 nm; carbon nanotubes: diameter 5-10 nm; or polyaniline nanofibers: diameter 50-150 nm). The extrusion rate was controlled at 0.5-1.5 mL / min and the pinhole diameter was 0.15-0.75 mm. The fibers were wet-pre-stretched 1.5-3 times in the coagulation bath (stretching rate 5-10 mm / s) and then transferred to a 40-50°C deionized water bath for 3-5 washes to remove the solvent. The fibers were then dried in a hot air circulation drying oven at 70-90°C for 1-2 hours and finally wound onto a bobbin to obtain the core yarn. (2) Preparation of winding layer: 2%~6% cross-linked collagen aggregates were dispersed in deionized water at 45~55℃, and mechanically stirred at 800~1500r / min for 1~2 hours until completely dissolved; 14%~18% polyvinyl alcohol solution was added, and stirring was continued at 50~60℃ for 1.5~2.5 hours to form a homogeneous spinning solution; 0.05%~0.1% boric acid was added to the spinning solution and stirring was continued for 20 minutes, and then the solution was transferred to a defoaming kettle for vacuum degassing (-0.08~-0.1 MPa, 60 minutes), and the pH of the spinning solution was adjusted to 5.5~6.5; and 3%~7% conductive fillers (silver nanowires: diameter 20~80 nm; or carbon nanotubes: diameter 5~10 nm; or polyaniline nanofibers: diameter 50~150 The mixed solution (1000 nm) was extruded into a graded coagulation bath through a coaxial spinneret. The first coagulation bath was an aqueous solution containing 3%-5% sodium sulfate and 1%-3% glutaraldehyde (30-35°C). A thin stream of the stock solution was extruded from the spinneret (needle hole diameter 0.1-0.3 mm) to achieve preliminary crosslinking. The second coagulation bath was an ethanol-water mixture containing 28%-32% saturated sodium sulfate and 0.5%-1.5% glutaraldehyde (40-45°C), which achieved in situ covalent crosslinking between collagen and polyvinyl alcohol. After wet stretching by a guide roller group (1.5-2.5 times), the nascent fibers were placed in a phosphate buffer solution (pH 7.4, 50°C) containing 0.1%-0.3% boric acid for wet heat stretching, and an intermittent heat cycle (50°C / 10 s→room temperature / 20 s, 3-5 times); then washed in three baths (deionized water, 45-50°C) to remove inorganic salts; finally dried by humidity gradient (first stage: 60%-70% humidity, 60-70°C for 1-2 hours; second stage: 20%-30% humidity, 80-90°C for 1-1.5 hours) and then wound to obtain the wrapped yarn; (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compositely wound with a helical angle of 30°~60° through a precision twisting machine, and the linear speed ratio is controlled to be 1:1.2 to 1:1.8 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the helical structure (angle deviation <±2°); the twisted composite yarn is placed in a heat treatment box at 80~120℃, axial prestress (0.3~0.8 N) is applied and kept warm for 30~60 minutes to obtain a negative Poisson's ratio yarn.

[0014] Compared with the prior art, the effective benefits of the present invention are: (1) The negative Poisson's ratio structured triboelectric sensing yarn prepared by the present invention has negative Poisson characteristics. The negative Poisson's ratio structure is constructed through a spiral winding process, which converts axial tensile deformation into radial expansion, thereby achieving dynamic coupling enhancement of the negative Poisson's ratio effect and the triboelectric effect.

[0015] (2) The negative Poisson's ratio structured triboelectric sensing yarn prepared by the present invention is biocompatible and uses a collagen-based composite material as the positive triboelectric layer. Combined with a conductive core layer packaging design, it ensures high output performance while meeting the safety requirements of wearable devices for human contact.

[0016] (3) The negative Poisson's ratio structured triboelectric sensing yarn prepared by the present invention has high energy collection efficiency and can dynamically control the friction contact area, thus overcoming the charge dilution problem caused by the attenuation of the contact area during stretching of traditional triboelectric yarns and significantly improving the energy conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of the present invention Figure 2 This is a cross-sectional structural diagram of the present invention Figure 3 Schematic diagram of the negative Poisson's ratio effect stretching of the present invention Figure 4 The open circuit voltage of the present invention under 30% strain condition Among them, 1-conductive filler layer, 2-polyvinyl chloride layer, 3-collagen aggregate / polyvinyl alcohol layer DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] like Figure 1 As shown, a triboelectric sensing yarn based on a negative Poisson's ratio structure includes a core layer composed of polyvinyl chloride / conductive filler yarn; and a winding layer formed of collagen aggregates / polyvinyl alcohol / electrical filler yarn.

[0020] like Figure 2 As shown, a negative Poisson's ratio spiral structure is formed by spiral twisting, and the winding layer is wrapped around the outside of the core layer.

[0021] like Figure 3 As shown, the radial spacing of the triboelectric sensing yarn based on the negative Poisson's ratio structure after stretching is d3>d2>d1.

[0022] like Figure 4 As shown, the open circuit voltage of the triboelectric sensing yarn based on the negative Poisson's ratio structure is 1.25 V under 30% tensile strain. Example

[0023] (1) Preparation of core layer: Dissolve modified polyvinyl chloride (degree of polymerization 1300) in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 10%, and add 0.1% epoxy soybean oil as a plasticizer; after the polyvinyl chloride is completely dissolved, add 0.01% fluorosilane coupling agent in two gradients, each with an interval of 15 minutes, and mechanically stir at 800 r / min at 50°C for 30 minutes; degas by ultrasonic treatment for 30 minutes. A 3% silver nanowire ethanol dispersion (diameter 20-80 nm) was extruded through a coaxial spinneret into a gradient ethanol coagulation bath (ethanol concentration 50% and temperature 25°C in the first zone; ethanol concentration 70% in the second zone), with an extrusion rate of 0.5 mL / min and a pinhole diameter of 0.15 mm. The fiber was pre-stretched 1.5 times in the wet state (stretching rate 5 mm / s) in the coagulation bath, and then transferred to a 40°C deionized water bath for three times to wash with solvent; treated in a 70°C hot air circulation drying oven for 1 hour, and finally wound onto a bobbin to obtain the core yarn.

[0024] (2) Preparation of winding layer: 2% cross-linked collagen aggregates were dispersed in 45℃ deionized water and mechanically stirred at 800 r / min for 1 hour until completely dissolved; 14% polyvinyl alcohol solution was added and continued to stir at 50℃ for 1.5 hours to form a homogeneous spinning solution; 0.05% boric acid was added to the spinning solution and continued to stir for 20 minutes, then transferred to a defoaming kettle for vacuum degassing (-0.08MPa, 60 minutes), and the pH of the spinning solution was adjusted to 5.5; the mixed solution was extruded into a graded coagulation bath through a coaxial spinneret with 3% silver nanowire ethanol dispersion (diameter 20~80 nm). The first-level coagulation bath was an aqueous solution containing 3% sodium sulfate and 1% glutaraldehyde (30℃), and the spinneret extruded a thin stream of the stock solution (needle hole diameter 0.1 The initial cross-linking was achieved using a secondary coagulation bath consisting of an ethanol-water mixture containing 28% saturated sodium sulfate and 0.5% glutaraldehyde (40°C), achieving in situ covalent cross-linking between collagen and polyvinyl alcohol. The spun fibers were wet-stretched (1.5x) by a guide roller assembly before being wet-stretched in a phosphate buffer solution (pH 7.4, 50°C) containing 0.1% boric acid. Intermittent thermal cycling (50°C / 10 s to room temperature / 20 s, three times) was applied simultaneously. The fibers were then washed in three baths (deionized water, 45°C) to remove inorganic salts. Finally, they were dried using a humidity gradient (first stage: 60% humidity, 60°C for 1 hour; second stage: 20% humidity, 80°C for 1 hour) before being wound to obtain the wound yarn.

[0025] (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compositely wound with a 30° spiral angle through a precision twisting machine, and the linear speed ratio is controlled to be 1:1.2 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the spiral structure (angle deviation <±2°); the twisted composite yarn is placed in an 80°C heat treatment box, axial prestress (0.3 N) is applied and kept warm for 30 minutes to obtain a negative Poisson's ratio yarn. Example

[0026] (1) Preparation of core layer: Modified polyvinyl chloride (degree of polymerization 1400) was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 15%, and 0.3% epoxy soybean oil was added as a plasticizer; after the polyvinyl chloride was completely dissolved, 0.05% fluorosilane coupling agent was added in three gradients, with an interval of 10 minutes each time, and mechanically stirred at 1000 r / min at 55°C for 25 minutes; degassing was carried out by ultrasonic treatment for 45 minutes. A 5% ethanol dispersion of carbon nanotubes (diameter 5-10 nm) was extruded through a coaxial spinneret into a gradient ethanol coagulation bath (ethanol concentration 55% and temperature 27°C in the first zone; ethanol concentration 75% in the second zone), with an extrusion rate of 1 mL / min and a pinhole diameter of 0.4 mm. The fiber was pre-stretched twice in the wet state (stretching rate 7 mm / s) in the coagulation bath, then transferred to a 45°C deionized water bath for four washes with solvent; treated in an 80°C hot air circulation drying oven for 2 hours, and finally wound onto a bobbin to obtain the core yarn.

[0027] (2) Preparation of winding layer: 4% cross-linked collagen aggregates were dispersed in 50℃ deionized water and mechanically stirred at 1200 r / min for 2 hours until completely dissolved; 16% polyvinyl alcohol solution was added and continued to stir at 55℃ for 2 hours to form a homogeneous spinning solution; 0.08% boric acid was added to the spinning solution and continued to stir for 20 minutes, then transferred to a defoaming kettle for vacuum degassing (-0.09 MPa, 60 minutes), and the pH of the spinning solution was adjusted to 6; the mixed solution was extruded into a graded coagulation bath through a coaxial spinneret with 5% carbon nanotube ethanol dispersion (diameter 5~10nm). The first-level coagulation bath was an aqueous solution containing 4% sodium sulfate and 2% glutaraldehyde (33℃), and the spinneret extruded a thin stream of the stock solution (needle hole diameter 0.2 The initial cross-linking was achieved using a secondary coagulation bath consisting of an ethanol-water mixture containing 30% saturated sodium sulfate and 1% glutaraldehyde (45°C), which achieved in situ covalent cross-linking between collagen and polyvinyl alcohol. The spun fibers were wet-stretched (2x) by a guide roller assembly before being wet-stretched in a phosphate buffer solution (pH 7.4, 50°C) containing 0.2% boric acid. Intermittent thermal cycling (50°C / 10 s to room temperature / 20 s, four times) was applied simultaneously. The fibers were then washed in three baths (deionized water, 50°C) to remove inorganic salts. Finally, a humidity gradient drying process (first stage: 65% humidity, 65°C for 1 hour; second stage: 25% humidity, 85°C for 1 hour) was used before winding to obtain the wrapped yarn.

[0028] (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compositely wound at a 45° helical angle through a precision twisting machine, and the linear speed ratio is controlled to be 1:1.5 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the helical structure (angle deviation <±2°); the twisted composite yarn is placed in a 100°C heat treatment box, axial prestress (0.5N) is applied and kept warm for 45 minutes to obtain a negative Poisson's ratio yarn. Example

[0029] (1) Preparation of core layer: Modified polyvinyl chloride (DP 1500) was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 20%, and 0.5% epoxidized soybean oil was added as a plasticizer. After the polyvinyl chloride was completely dissolved, 0.1% fluorosilane coupling agent was added in three gradients, with an interval of 10 minutes each time, and mechanically stirred at 1200 r / min at 60°C for 20 minutes. Degassing was carried out by ultrasonic treatment for 60 minutes. A 7% polyaniline nanofiber N-methylpyrrolidone dispersion (diameter 50-150 nm) was extruded through a coaxial spinneret into a gradient ethanol coagulation bath (ethanol concentration 60% and temperature 28°C in the first zone; ethanol concentration 80% in the second zone), with an extrusion rate of 1.5 mL / min and a pinhole diameter of 0.75 mm. The fibers were wet-pre-stretched 3 times in the coagulation bath (stretching rate 10 mm / s) and then transferred to a 50°C deionized water bath for 5 washes with solvent. The fibers were treated in a 90°C hot air circulation drying oven for 2 hours and finally wound onto a bobbin to obtain the core yarn.

[0030] (2) Preparation of winding layer: 6% cross-linked collagen aggregates were dispersed in 55℃ deionized water and mechanically stirred at 1500 r / min for 2 hours until completely dissolved; 18% polyvinyl alcohol solution was added and continued to stir at 60℃ for 2.5 hours to form a homogeneous spinning solution; 0.1% boric acid was added to the spinning solution and continued to stir for 20 minutes, then transferred to a defoaming kettle for vacuum degassing (-0.1MPa, 60 minutes), and the pH of the spinning solution was adjusted to 6.5; the mixed solution was extruded into a graded coagulation bath through a coaxial spinneret with 7% polyaniline nanofiber N-methylpyrrolidone dispersion (diameter 50~150nm). The first-level coagulation bath was an aqueous solution containing 5% sodium sulfate and 3% glutaraldehyde (35℃), and the spinneret extruded a thin stream of the solution (needle hole diameter 0.3 The initial cross-linking was achieved in a secondary coagulation bath consisting of an ethanol-water mixture containing 32% saturated sodium sulfate and 1.5% glutaraldehyde (45°C), achieving in situ covalent cross-linking between collagen and polyvinyl alcohol. The spun fibers were wet-stretched (2.5 times) by a guide roller group before being wet-stretched in a phosphate buffer solution (pH 7.4, 50°C) containing 0.3% boric acid. Intermittent thermal cycling (50°C / 10 s to room temperature / 20 s, 5 times) was applied simultaneously. The fibers were then washed in three baths (deionized water, 50°C) to remove inorganic salts. Finally, a humidity gradient drying process (first stage: 70% humidity, 70°C for 2 hours; second stage: 30% humidity, 90°C for 1.5 hours) was used before winding to obtain the wrapped yarn.

[0031] (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compositely wound at a 60° helical angle through a precision twisting machine, and the linear speed ratio is controlled to be 1:1.8 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the helical structure (angle deviation <±2°); the twisted composite yarn is placed in a 120°C heat treatment box, axial prestress (0.8N) is applied and kept warm for 60 minutes to obtain a negative Poisson's ratio yarn.

Claims

1. A triboelectric sensing yarn based on a negative Poisson's ratio structure, comprising a core layer and a winding layer, characterized in that: The core layer and the winding layer are coaxially wet-spun to form a core-shell structure, and then twisted at a helical angle of 30° to 60° through a spiral twisting process to form a helical structure with negative Poisson's ratio characteristics. The core layer is a negative triboelectric layer formed by compounding polyvinyl chloride and a first conductive filler; The winding layer is a positive triboelectric layer formed by a composite of collagen aggregates, polyvinyl alcohol and a second conductive filler; The diameter ratio of the core layer to the winding layer is 1.5:1 to 2.5:1, and the elastic modulus of the core layer is 20%-50% higher than that of the winding layer.

2. The triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that: The first conductive filler and the second conductive filler are independently selected from one of metal nanowires, carbon nanotubes, and conductive polymers, and the volume proportion of the conductive filler is 3% to 7%.

3. The triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that: The collagen aggregate is extracted from any one of the following biological sources: mammalian dermis collagen, fish scale collagen, avian skin collagen and animal tendon collagen.

4. A method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure, characterized in that: The following steps are involved: (1) Core layer preparation: Modified polyvinyl chloride with a degree of polymerization of 1300-1500 was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 10%-20%, and 0.1%-0.5% epoxy soybean oil was added as a plasticizer. After the polyvinyl chloride was completely dissolved, 0.01%-0.1% of a fluorosilane coupling agent was added in 2-3 gradient steps, with an interval of 10-15 minutes between each step, and mechanical stirring was carried out at 800-1200 r / min at 50-60°C for 20-30 minutes. After ultrasonic treatment for 30-60 minutes for degassing, the solution was extruded with 3%-7% of a conductive filler through a coaxial spinneret into a gradient ethanol coagulation bath, with an extrusion rate of 0.5-1.5 mL / min and a pinhole diameter of 0.15-0.75 mm. The fiber was pre-stretched in the coagulation bath by 1.5-3 times the wet state (stretching rate 5-10 mm / s), then transferred to a 40-50°C deionized water bath for 3-5 times for cleaning with solvent; treated in a 70-90°C hot air circulation drying oven for 1-2 hours, and finally wound onto a bobbin to obtain a core yarn; (2) Preparation of winding layer: 2%~6% cross-linked collagen aggregates were dispersed in deionized water at 45~55℃, and mechanically stirred at 800~1500 r / min for 1~2 hours until completely dissolved; 14%~18% polyvinyl alcohol solution was added, and stirring was continued at 50~60℃ for 1.5~2.5 hours to form a homogeneous spinning solution; boric acid with a spinning solution content of 0.05%~0.1% was added and stirring was continued for 20 minutes, and then transferred to a defoaming kettle for vacuum degassing (-0.08~-0.1 MPa, 60 minutes), and the pH of the spinning solution was adjusted to 5.5~6.5; the mixed solution was extruded into a graded coagulation bath through a coaxial spinneret with 3%~7% conductive filler. The first-level coagulation bath was an aqueous solution containing 3%~5% sodium sulfate and 1%~3% glutaraldehyde (30~35℃), and the spinneret extruded a thin stream of the stock solution (needle hole diameter 0.1~0.3 The initial crosslinking was achieved by a secondary coagulation bath consisting of an ethanol-water mixture containing 28%-32% saturated sodium sulfate and 0.5%-1.5% glutaraldehyde (40-45°C), achieving in situ covalent crosslinking between collagen and polyvinyl alcohol. The spun fibers were wet-stretched by a guide roller assembly (1.5-2.5 times) and then wet-stretched in a phosphate buffer solution (pH 7.4, 50°C) containing 0.1%-0.3% boric acid. Intermittent heat cycles (50°C / 10s to room temperature / 20s, 3-5 times) were applied simultaneously. The fibers were then washed in three baths (deionized water, 45-50°C) to remove inorganic salts. Finally, the fibers were dried using a humidity gradient and wound to obtain the wrapped yarn. (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compositely wound with a helical angle of 30°~60° through a precision twisting machine, and the linear speed ratio is controlled to be 1:1.2 to 1:1.8 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the helical structure (angle deviation <±2°); the twisted composite yarn is placed in a heat treatment box at 80~120℃, axial prestress (0.3~0.8 N) is applied and kept warm for 30~60 minutes to obtain a negative Poisson's ratio yarn.

5. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that: The conductive filler is silver nanowire, carbon nanotube or polyaniline nanofiber, the diameter of the silver nanowire is 20-80nm; the diameter of the carbon nanotube is 5-10nm; the diameter of the polyaniline nanofiber is 50-150nm.

6. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that: The ethanol concentration in the first gradient zone of the gradient ethanol coagulation bath is 50%-60% and the temperature is 25-28° C.; the ethanol concentration in the second gradient zone is 70%-80%.

7. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that: The first gradient stage of the humidity gradient drying is 60% to 70% humidity, 60 to 70° C., and drying for 1 to 2 hours; the second gradient stage is 20% to 30% humidity, 80 to 90° C., and drying for 1 to 1.5 hours.

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