A core-sheath structure strain sensing fiber resistant to temperature interference and its preparation method

Abstract

The present invention provides a temperature-resistant core-sheath strain sensing fiber and a preparation method thereof, relating to the field of composite material technology. The fiber comprises a flexible core layer and a conductive shell layer coated on the flexible core layer; the flexible core layer is made from a mixture of thermoplastic polyurethane and dimethyl sulfide (DMF); and the conductive shell layer is made from a mixture of thermoplastic polyurethane, DMF, silver nanowires, and multi-walled carbon nanotubes, wherein the mass ratio of the silver nanowires to the multi-walled carbon nanotubes is (0.12-0.15):(0.05-0.1). By regulating the silver nanowires with a positive temperature coefficient of resistance and the multi-walled carbon nanotubes with a negative temperature coefficient of resistance, excellent temperature resistance is achieved over a wide temperature range (0°C-60°C), with a temperature coefficient of resistance reaching 300 ppm / °C. The core-sheath structure also imparts excellent elasticity to the fiber. Wet spinning enables continuous production, with high efficiency and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a core-sheath structure strain sensing fiber resistant to temperature interference and a preparation method thereof. Background Art

[0002] The rigid structure of traditional strain sensors limits their application on complex surfaces and in dynamic environments. Temperature-dependent changes in the material's physical properties, such as resistance, capacitance, and dielectric constant, can cause sensor output drift, affecting measurement accuracy. This drift is particularly pronounced in environments with large temperature fluctuations and may even cause sensor failure.

[0003] While flexible fiber-based strain sensors offer excellent flexibility and weavability, adapting to complex surfaces and dynamic environments, they lack robustness against temperature fluctuations. Flexible materials typically have high thermal expansion coefficients and low thermal conductivity, which can easily induce thermal stress in temperature-stable environments, leading to increased measurement errors. Furthermore, the complex and costly fabrication process for flexible fiber-based strain sensors limits their widespread adoption in practical applications.

[0004] Bai et al. proposed a flexible strain sensor based on thermoplastic polyurethane (TPU) and liquid metal, achieving ultrahigh sensitivity and a large sensing range. However, the TPU substrate has poor air permeability, making it uncomfortable to wear for a long time. Zhu et al. prepared highly stretchable GNP / CNT / silicone elastomer fibers by regulating carbon nanotubes (CNTs) and graphene nanosheets (GNPs) with negative and positive temperature coefficients. The fibers have a near-zero TCR (1.14 × 10 −4 ℃), but this requires precise control of the ratio and the membrane structure has poor air permeability. Ma et al. prepared a 3D MXene / reduced graphene oxide aerogel, which buffers thermal stress through its porous structure. Therefore, the fibers prepared in the existing technology have low mechanical strength, poor temperature resistance, and are difficult to prepare continuously.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a core-sheath structure strain sensing fiber that is resistant to temperature interference. By regulating the silver nanowires with positive resistance temperature coefficient and the multi-walled carbon nanotube materials with negative resistance temperature coefficient, the fiber achieves excellent resistance to temperature interference in a wide temperature range (0℃~60℃) and has excellent elasticity.

[0007] The present invention also provides a method for preparing the temperature-resistant core-sheath structure strain sensing fiber. The preparation method is simple and optimizes some parameters in the experimental process, enabling continuous preparation, improving preparation efficiency, and reducing preparation costs.

[0008] In order to achieve the purpose of the present invention, the present invention provides a core-sheath structure strain sensing fiber with resistance to temperature interference, the fiber comprising: a flexible core layer and a conductive shell layer coated outside the flexible core layer;

[0009] Wherein, the flexible core layer is made by mixing thermoplastic polyurethane and DMF;

[0010] The conductive shell layer is prepared by mixing thermoplastic polyurethane, DMF, silver nanowires and multi-walled carbon nanotubes, wherein the mass ratio of the silver nanowires to the multi-walled carbon nanotubes is (0.12-0.15): (0.05-0.1).

[0011] Furthermore, the mass ratio of the silver nanowires to the multi-walled carbon nanotubes is 0.125:0.08.

[0012] Furthermore, the mass ratio of thermoplastic polyurethane to DMF in the flexible core layer is 1:(2-5); the mass ratio of thermoplastic polyurethane to DMF in the conductive shell layer is 1:(6-7).

[0013] Furthermore, the mass ratio of thermoplastic polyurethane to DMF in the flexible core layer is 1:4; and the mass ratio of thermoplastic polyurethane to DMF in the conductive shell layer is 1:6.3.

[0014] Furthermore, the concentration of DMF in the flexible core layer is 10 wt %; and the concentration of DMF in the conductive shell layer is 20 wt %.

[0015] The present invention also provides a method for preparing a core-sheath structure strain sensing fiber resistant to temperature interference, comprising the following steps:

[0016] S1, mixing thermoplastic polyurethane and DMF at a constant temperature and stirring until fully dissolved to obtain a core layer spinning solution;

[0017] S2, mixing thermoplastic polyurethane and DMF at a constant temperature and stirring until fully dissolved to obtain a mixture for later use;

[0018] S3, dissolving the silver nanowires in anhydrous ethanol to obtain an ethanol dispersion of the silver nanowires;

[0019] S4, adding the ethanol dispersion of the silver nanowires to the mixture, magnetically stirring for 2-3 hours and then ultrasonically shaking, then adding the multi-walled carbon nanotubes, and continuing to stir to obtain a suspension;

[0020] S5. Use coaxial wet spinning and control the flow rates of the suspension and the core layer spinning solution. After being extruded through a coaxial needle, the suspension enters an ionized water coagulation bath for coagulation. After coagulation, the suspension is stretched and dried to obtain the product.

[0021] Furthermore, the flow rate ratio of the suspension and the core layer spinning solution is (1-3.5):1.

[0022] Furthermore, the flow rate ratio of the suspension and the core layer spinning solution is 1.5:1.

[0023] Furthermore, the drying temperature is 40°C-70°C.

[0024] Furthermore, the method for preparing the temperature-resistant core-sheath structure strain sensing fiber is characterized in that the drying temperature is 60°C.

[0025] The embodiments of the present invention have the following technical effects:

[0026] Silver nanowire / multi-walled carbon nanotube composite fibers were prepared via wet spinning. By manipulating the positive temperature coefficient of resistance (TCR) of the silver nanowires and the negative temperature coefficient of resistance (TCR) of the multi-walled carbon nanotubes, the fibers achieved excellent temperature resistance over a wide temperature range (0°C-60°C), achieving a TCR of 300 ppm / °C. The core-sheath structure also imparts excellent elasticity to the fibers. Wet spinning enables continuous production, high efficiency, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 : Schematic diagram of coaxial wet spinning;

[0029] Figure 2 : Electron micrograph of fiber cross section;

[0030] Figure 3 : Stress-strain curves of conductors prepared with different spinning solution ratios;

[0031] Figure 4 :(a) Relative resistance change of 0.125 g AgNWs and 0.08 g MWCNTs composite wire under cyclic strain of 5%, 10%, 20% and 50%;

[0032] (b) Response time and recovery time of AgNWs / MWCNTs wires;

[0033] Figure 5 : Durability test of 0.125 g AgNWs and 0.08 g MWCNTs composite wires after 4000 stretching cycles at 20% strain;

[0034] Figure 6 : Relationship curves between relative resistance change rate and temperature change of wires prepared with different spinning solution ratios. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0036] In the first aspect, the present invention provides a core-sheath structure strain sensing fiber that is resistant to temperature interference. By regulating the silver nanowires with positive resistance temperature coefficient and the multi-walled carbon nanotube materials with negative resistance temperature coefficient, the fiber achieves excellent resistance to temperature interference in a wide temperature range (0℃~60℃) and has excellent elasticity.

[0037] In some embodiments, a flexible core layer and a conductive shell layer coated outside the flexible core layer;

[0038] Wherein, the flexible core layer is made by mixing thermoplastic polyurethane and DMF;

[0039] The conductive shell layer is prepared by mixing thermoplastic polyurethane, DMF, silver nanowires and multi-walled carbon nanotubes, wherein the mass ratio of the silver nanowires to the multi-walled carbon nanotubes is (0.12-0.15): (0.05-0.1).

[0040] In the present invention, by adding silver nanowires and multi-walled carbon nanotubes to the conductive shell, the positive temperature coefficient of resistance and the negative temperature coefficient of resistance can be regulated, and the finally prepared material can have excellent resistance to temperature interference.

[0041] The present invention also defines the ratio and dosage of silver nanowires and multi-walled carbon nanotubes. By limiting the dosage of the two, the resistance change of the two is approximately equal, resulting in a material with excellent strain sensing performance and resistance to temperature interference. At the same time, insufficient silver nanowires can easily lead to high resistance and delayed response; while insufficient multi-walled carbon nanotubes can result in poor mechanical strength and durability of a single silver nanowire, making it prone to breakage under strain.

[0042] In some embodiments, the mass ratio of silver nanowires to multi-walled carbon nanotubes is 0.125:0.08.

[0043] By precisely controlling the mass ratio of silver nanowires to multi-walled carbon nanotubes, the positive / negative TCR can be offset, achieving near-zero drift over a wide temperature range. It also combines high-sensitivity strain sensing with high elasticity and fatigue resistance, achieving the optimal balance point for achieving the triple goals of conductivity, temperature drift suppression, and mechanical strength.

[0044] In some embodiments, the mass ratio of thermoplastic polyurethane to DMF in the flexible core layer is 1:(2-5); the mass ratio of thermoplastic polyurethane to DMF in the conductive shell layer is 1:(6-7).

[0045] In some embodiments, the mass ratio of thermoplastic polyurethane to DMF in the flexible core layer is 1:4; and the mass ratio of thermoplastic polyurethane to DMF in the conductive shell layer is 1:6.3.

[0046] In some embodiments, the concentration of DMF in the flexible core layer is 10 wt %; and the concentration of DMF in the conductive shell layer is 20 wt %.

[0047] The present invention also limits the amount of DMF and thermoplastic polyurethane used in the conductive shell and flexible core layer, based on a comprehensive consideration of material functional requirements, spinning process stability, and structural performance optimization. This limited amount of DMF and thermoplastic polyurethane in the flexible core layer allows the TPU molecular chains in the core layer to fold and precipitate rapidly, forming a loose, porous structure while imparting high resilience to the fiber. Furthermore, it prevents excessive core shrinkage that could lead to cracking or delamination of the shell layer. It also allows low-viscosity solutions to more easily pass through the coaxial needle core channel, forming a stable laminar flow with the high-viscosity shell solution, avoiding turbulence and structural unevenness.

[0048] In the shell layer, the slightly higher concentration of DMF dissolves a larger amount of TPU, resulting in a higher viscosity solution. This high viscosity provides greater resistance, making it difficult for the silver nanowires and multi-walled carbon nanotubes to settle in the solution, thereby effectively preventing their agglomeration and maintaining the dispersion stability of the conductive filler. Furthermore, this high-solids solution allows the TPU molecular chains to slowly cross-link during solidification, forming a dense coating structure, ensuring sufficient contact between the silver nanowires and multi-walled carbon nanotubes, thereby constructing a continuous conductive path and improving strain sensing stability. This concentration limit can resolve the conflicting requirements of "high elasticity" and "high conductivity" in traditional flexible sensors, while also meeting the needs of continuous production.

[0049] If the amount of core layer and shell layer is swapped, it will lead to slow solidification and fiber deformation, reduced elasticity and other properties of the finished fiber.

[0050] In a second aspect, the present invention further provides a method for preparing a core-sheath structure strain sensing fiber that is resistant to temperature interference, comprising the following steps:

[0051] S1, mixing thermoplastic polyurethane and DMF at a constant temperature and stirring until fully dissolved to obtain a core layer spinning solution;

[0052] S2, mixing thermoplastic polyurethane and DMF at a constant temperature and stirring until fully dissolved to obtain a mixture for later use;

[0053] S3, dissolving the silver nanowires in anhydrous ethanol to obtain an ethanol dispersion of the silver nanowires;

[0054] S4, adding the ethanol dispersion of the silver nanowires to the mixture, magnetically stirring for 2-3 hours and then ultrasonically shaking, then adding the multi-walled carbon nanotubes, and continuing to stir to obtain a suspension;

[0055] S5. Use coaxial wet spinning and control the flow rates of the suspension and the core layer spinning solution. After being extruded through a coaxial needle, the suspension enters an ionized water coagulation bath for coagulation. After coagulation, the suspension is stretched and dried to obtain the product.

[0056] In some embodiments, the flow rate ratio of the suspension and the core layer spinning solution is (1-3.5):1.

[0057] In some embodiments, the ratio of the flow rate of the suspension to the flow rate of the core layer spinning solution is 1.5:1.

[0058] In some embodiments, the drying temperature is 40°C-70°C.

[0059] In some embodiments, the drying temperature is 60°C.

[0060] By limiting the flow rate, the two can form a stable laminar flow, avoiding the vortex caused by high velocity differences (the shear force of the shell fluid is much greater than that of the core fluid), which can lead to stratification or uneven thickness; or the incomplete shell coating caused by low velocity differences (the core fluid presses against the shell fluid), which can partially eliminate the conductive network. This ratio allows the shell and core layers to be extruded smoothly, forming a complete and uniform concentric circle structure while ensuring a moderate shell thickness. Furthermore, it effectively prevents yarn breakage, improves spinning efficiency, and enables continuous production, ensuring the quality of the finished product and the efficiency of the production process.

[0061] The following is elaborated with reference to specific embodiments:

[0062] Example 1: Fiber Preparation

[0063] (1) Preparation of core spinning solution: First, weigh 3.5 g of thermoplastic polyurethane elastomer (TPU) and add it to a sample bottle. Use a pipette to draw 15 mL of DMF (concentration of 10 wt%) and add it. After marking, place it on a constant temperature magnetic stirrer to fully dissolve the TPU.

[0064] (2) Preparation of shell spinning solution: First, weigh 1.5 g of thermoplastic polyurethane elastomer and add it to a sample bottle. Use a pipette to draw 10 mL of DMF (concentration of 20 wt%) and add it. Prepare multiple groups in the same way. After marking, place them on a constant temperature magnetic stirrer to fully dissolve the TPU. After 2-3 hours, take two sample bottles as control groups: one group adds 5 mL of 25 mg / mL anhydrous ethanol dispersion of silver nanowires; the other group adds 0.1 g of multi-walled carbon nanotubes. Add 5 mL of anhydrous ethanol dispersion of silver nanowires to each of the other sample bottles. After magnetic stirring for 2-3 hours, ultrasonic vibration is performed for 15 minutes. The sample bottle was then taken out and 0.04 g, 0.05 g, 0.06 g, 0.07 g, 0.08 g, 0.09 g, 0.10 g, 0.11 g, and 0.12 g of multi-walled carbon nanotubes were added, respectively, and then magnetically stirred for 2-3 h until the mixture was uniform. A series of AgNWs / MWCNTs suspensions with different concentration ratios were prepared, and the naming method is shown in Table 1.

[0065] Table 1: Nomenclature of silver nanowires and multi-walled carbon nanotubes at different dosages

[0066]

[0067] (3) Coaxial wet spinning: Spinning device such as Figure 1 As shown, a 17G-22G coaxial needle was used to pour the prepared shell and core spinning solutions into 20 mL syringes, respectively. The two ports of the syringe and needle were connected respectively. The injection flow rate was controlled by a syringe pump, and the control flow rate was 10 mL / h for the core layer and 15 mL / h for the shell layer. The spinning solution was extruded through the coaxial needle and then coagulated in a deionized water coagulation bath. After coagulation, it was stretched and dried at 60°C to obtain core-sheath fibers. The obtained fiber cross-section electron micrograph is shown in FIG. Figure 2 shown.

[0068] Example 2: Mechanical properties test

[0069] The mechanical properties of the core-sheath fibers prepared with different concentration ratios of AgNWs / MWCNTs were tested. The experimental results are as follows: Figure 3 shown.

[0070] Figure 3Stress-strain curves were obtained for conductors made from pure MWCNTs spinning solutions, pure AgNWs spinning solutions, and composite spinning solutions with varying mass ratios. The data show that the stress of the composites was significantly higher than that of pure AgNWs after the addition of MWCNTs. For example, samples 1-7 exhibited significantly higher stress values ​​at the same strain, indicating that the addition of MWCNTs enhanced the material's deformation resistance. In contrast, pure AgNWs experienced the lowest stress values ​​at the same strain. Furthermore, the samples containing MWCNTs maintained stress at higher strains, suggesting that the MWCNTs may have enhanced the material's toughness or ductility. Further analysis, in comparison with the other curves, suggests that pure MWCNTs may be brittle when spun, whereas the composites of MWCNTs and AgNWs fully exploit the advantages of the MWCNTs' high strength and the AgNWs' high conductivity and ductility, resulting in a composite with superior overall performance.

[0071] The experimental results show that the addition of MWCNTs significantly improves the mechanical properties of the composite material, and this improvement becomes more pronounced with increasing MWCNT content. Although pure AgNWs have good ductility and stretchability, their strength is relatively low, and the addition of MWCNTs effectively compensates for this deficiency.

[0072] Example 3: Strain sensing performance test

[0073] The strain sensing performance of the core-sheath fibers prepared with different concentration ratios of AgNWs / MWCNTs was tested. The experimental results are shown in Figure 2. Figure 4 、 Figure 5 shown.

[0074] Figure 4 (a) The relative resistance of a 0.125 g AgNWs / 0.08 g MWCNTs composite conductor changes over time under different strain conditions (5%, 10%, 20%, and 50%). The magnitude of the resistance change in the composite conductor increases significantly with increasing strain. At 5% strain, the resistance change is minimal, and the curve fluctuates gently, indicating that the material has good elasticity and stability within this strain range. When the strain increases to 10% and 20%, the resistance change increases, demonstrating that the material's resistance sensitivity is significantly enhanced within this strain range, making it suitable for detecting moderate strain changes. At 50% strain, the resistance change is the largest, and the curve fluctuates dramatically, indicating that the material has high sensitivity under large strains. These results demonstrate that the resistance change of the composite conductor can be effectively controlled by adjusting the strain, enabling precise detection across different strain ranges. This property gives the composite material significant potential for application in temperature-resistant strain sensors, which can produce varying resistance responses depending on the strain, thereby improving sensor sensitivity and accuracy.

[0075] Figure 4 (b) shows that the response and recovery time of the wire are 51 ms and 127 ms, respectively. This indicates that the composite material has excellent performance in strain sensing and provides strong data support for practical applications.

[0076] Figure 5 The resistivity change of a 0.125 g AgNWs and 0.08 g MWCNTs composite wire after 4000 stretching cycles at 20% strain and 1 s per cycle. The two insets show the resistivity change during the initial five stretching cycles and the final five stretching cycles, respectively. Overall observation and comparison of the two detailed images show that the resistivity changes of the composite wire are essentially consistent. This demonstrates the high strain stability of the composite wire during the stretching cycles.

[0077] Example 4: Temperature Interference Resistance Test

[0078] The temperature interference resistance of the core-sheath fibers prepared with different concentration ratios of AgNWs / MWCNTs was tested. The experimental results are as follows: Figure 6 shown.

[0079] Figure 6 The graph shows the resistance change rate versus temperature for seven groups of samples. A comprehensive analysis shows that the relative resistance change rates of samples 1-5, 1-6, and 1-7 are relatively stable under temperature fluctuations. In particular, sample 1-5 has a resistance change rate that is almost zero, demonstrating excellent resistance to temperature interference. In contrast, the resistance changes of samples 1-1 and 1-2, made from pure carbon nanotubes and silver nanowires, are more sensitive to temperature and exhibit weaker resistance to interference. The data indicates that the optimal ratio of AgNWs to MWCNTs in sample 1-5 allows the positive and negative temperature coefficient materials to effectively compensate for each other.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A core-sheath structure strain sensing fiber resistant to temperature interference, characterized in that: The fiber comprises: a flexible core layer and a conductive shell layer wrapped around the flexible core layer; Wherein, the flexible core layer is made by mixing thermoplastic polyurethane and DMF; The conductive shell layer is prepared by mixing thermoplastic polyurethane, DMF, silver nanowires and multi-walled carbon nanotubes, wherein the mass ratio of silver nanowires to multi-walled carbon nanotubes is (0.12-0.15): (0.05-0.1); The mass ratio of thermoplastic polyurethane to DMF in the flexible core layer is 1:(2-5); The mass ratio of thermoplastic polyurethane to DMF in the conductive shell is 1:(6-7).

2. The temperature-interference-resistant core-sheath structure strain sensing fiber according to claim 1, characterized in that: The mass ratio of silver nanowires to multi-walled carbon nanotubes is 0.125:0.

08.

3. The temperature-interference-resistant core-sheath strain sensing fiber according to claim 1, characterized in that: The mass ratio of thermoplastic polyurethane to DMF in the flexible core layer is 1:4; the mass ratio of thermoplastic polyurethane to DMF in the conductive shell layer is 1:6.

3.

4. The temperature-interference-resistant core-sheath structure strain sensing fiber according to claim 1, characterized in that: The concentration of DMF in the flexible core layer is 10 wt %; the concentration of DMF in the conductive shell layer is 20 wt %.

5. A method for preparing a temperature-interference-resistant core-sheath strain sensing fiber according to any one of claims 1 to 4, characterized in that: The steps include: S1, mixing thermoplastic polyurethane and DMF at a constant temperature and stirring until fully dissolved to obtain a core layer spinning solution; S2, mixing thermoplastic polyurethane and DMF at a constant temperature and stirring until fully dissolved to obtain a mixture for later use; S3, dissolving the silver nanowires in anhydrous ethanol to obtain an ethanol dispersion of the silver nanowires; S4, adding the ethanol dispersion of the silver nanowires to the mixture, magnetically stirring for 2-3 hours and then ultrasonically shaking, then adding the multi-walled carbon nanotubes, and continuing to stir to obtain a suspension; S5. Use coaxial wet spinning and control the flow rates of the suspension and the core layer spinning solution. After being extruded through a coaxial needle, the suspension enters an ionized water coagulation bath for coagulation. After coagulation, the suspension is stretched and dried to obtain the product.

6. The method for preparing a temperature-interference-resistant core-sheath structure strain sensing fiber according to claim 5, characterized in that: The flow rate ratio of the suspension and the core layer spinning solution is (1-3.5):

1.

7. The method for preparing a temperature-interference-resistant core-sheath structure strain sensing fiber according to claim 6, characterized in that: The flow rate ratio of the suspension and the core layer spinning solution is 1.5:

1.

8. The method for preparing a temperature-interference-resistant core-sheath structure strain sensing fiber according to claim 7, characterized in that: The drying temperature is 40°C-70°C.

9. The method for preparing a core-sheath structure strain sensing fiber resistant to temperature interference according to claim 8, characterized in that: The drying temperature is 60°C.

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