Highly conductive lyocell yarns for electronic textiles and methods of making the same

Abstract

The present application relates to the technical field of high-conductive textile material, especially to high-conductive lyocell yarn for electronic textile and a preparation method thereof.A lyocell yarn is used as a base body, and from inside to outside, the base body comprises 1-3 layers of conductive layers and an elastic polymer base encapsulation layer.The elastic polymer base encapsulation layer comprises an elastic polymer base and a crosslinking agent, and the crosslinking agent is blended and crosslinked with the elastic polymer base to form a dense network.The lyocell yarn has excellent conductive function, and successfully has durability, flexibility and processability.

Description

Technical Field

[0001] This invention relates to the field of high conductivity textile materials technology, and in particular to high conductivity Lyocell yarn for electronic textiles and its preparation method. Background Technology

[0002] Lyocell yarn is a regenerated cellulose fiber yarn produced from natural wood pulp using an organic solvent spinning process. It features green environmental protection, biodegradability, high dry and wet strength, soft hand feel, soft luster, and excellent moisture absorption. It is a new generation of high-performance textile substrate and is very suitable as a matrix material for flexible electronics and smart textiles.

[0003] Currently, the fields of flexible electronics and smart textiles typically improve conductivity by introducing or constructing conductive pathways on insulating textile substrates. However, existing conductive yarns struggle to balance conductivity and durability. While traditional rigid conductive coatings (such as carbon nanotube coatings) can construct conductive networks, they exhibit significant modulus mismatch with the flexible yarn substrate. During bending, stretching, and other deformation processes, rigid coatings are prone to stress concentration, leading to microcracks that propagate and even peel off from the fiber surface, resulting in the breakage of conductive pathways. Furthermore, under external environmental influences such as washing, water molecules easily penetrate to the interface between the conductive layer and the substrate, further exacerbating coating detachment and performance degradation. This unstable interface between the rigid conductive layer and the flexible substrate results in serious deficiencies in durability, comfort, and safety in existing electronic textiles, failing to meet the demands of practical wearable applications.

[0004] CN114150498B discloses a method for reducing the contact resistance of carbon nanotube-coated conductive yarn. This method uses nylon or polyester air-textured yarn as the matrix, and the process flow is: matrix yarn → coating treatment → drying and curing → post-treatment liquid treatment → drying and setting. This prior art utilizes loops or semi-circular loops on the surface of the air-textured yarn to increase the contact area between the carbon nanotube-coated conductive yarn and the interwoven metal wire electrodes. Highly conductive nano-silver particles distributed on and within the coating surface enhance the conductivity of the conductive material and resin composite film, while simultaneously increasing the probability of contact between fibers within the yarn. This reduces the contact resistance, primarily caused by uneven yarn surface and poorly conductive chemicals within the yarn, which contribute to the concentrated resistance between the carbon nanotube-coated conductive yarn and the interwoven metal wire electrodes. However, this prior art lacks elastic polymer encapsulation and cross-linking protection, failing to simultaneously achieve high conductivity, high durability, good mechanical compatibility, and textile processability, thus limiting its practical application in wearable electronic textiles. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, a highly conductive lyocell yarn for electronic textiles and its preparation method are provided, which successfully balances durability, flexibility and processability while endowing the lyocell yarn with excellent conductivity.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a highly conductive lyocell yarn for electronic textiles, which uses lyocell yarn as a matrix and includes, from the inside out: 1-3 conductive layers and an elastic polymer matrix encapsulation layer; the elastic polymer matrix encapsulation layer includes an elastic polymer matrix and a crosslinking agent, wherein the crosslinking agent and the elastic polymer matrix are blended and crosslinked to form a dense network.

[0007] The aforementioned highly conductive lyocell yarn for electronic textiles has a conductive layer formulated from a carbon nanotube dispersion, binder ST309C, and deionized water.

[0008] The aforementioned highly conductive lyocell yarn for electronic textiles uses multi-walled carbon nanotubes with an average length of 5-15 μm and an average diameter of 8-15 nm.

[0009] The aforementioned highly conductive lyocell yarn for electronic textiles has an elastic polymer matrix of thermoplastic polyurethane.

[0010] The aforementioned highly conductive Lyocell yarn for electronic textiles uses a water-based blocked isocyanate crosslinking agent with a solid content of 38% ± 2 wt%.

[0011] The adhesive used in the aforementioned highly conductive Lyocell yarn for electronic textiles is a water-based acrylate adhesive.

[0012] The above-mentioned method for preparing highly conductive Lyocell yarn for electronic textiles includes the following steps:

[0013] (1) Preparation of conductive layer: Add 80mL of deionized water and 120mL of 10% carbon nanotube dispersion to a 300mL beaker, stir magnetically to disperse it initially, add 20g of binder ST309C, continue stirring to obtain a uniform black CNT conductive paste, let it stand to defoam and then use it for later use.

[0014] (2) Preparation of elastic polymer matrix encapsulation layer: Add 100g of elastic polymer matrix particles and 60mL of crosslinking agent 510 to a 300mL beaker, and stir magnetically until a uniform semi-transparent slurry is formed for later use;

[0015] (3) Pretreatment: Preheat the equipment to 150℃ and keep it at that temperature for 30 minutes to stabilize the thermal field;

[0016] (4) Conductive layer coating: The Lyocell yarn substrate is drawn through the carbon nanotube conductive slurry tank at a linear speed of 80m / min, and then the liquid is controlled by the extrusion roller (pressure 0.2MPa) to obtain a uniformly wetted coated yarn.

[0017] (5) Encapsulation and curing: The coated Lyocell yarn substrate is immediately placed in a hot air oven at 120℃-150℃ for 1-3 hours to allow the coating to dry fully and obtain highly conductive Lyocell yarn.

[0018] In the above-mentioned method for preparing highly conductive Lyocell yarn for electronic textiles, in step (1), the stirring rate is 500 r / min and the total stirring time is 50 min; in step (2), the stirring rate is 500 r / min and the time is 20 min, and the particle size of the elastic polymer matrix is ​​50-500 micrometers.

[0019] In the above-described method for preparing highly conductive Lyocell yarn for electronic textiles, step (4) involves coating the conductive layer three times, resulting in a highly conductive Lyocell yarn with a resistivity as low as 6.40 × 10⁻⁶. -3 The resistance change rate after 50 bends is <8%, the coating remains intact after 15 water washes, and the resulting high-conductivity Lyocell yarn has a breaking elongation of 12.45%, a tensile strength of 6.31 N, and a contact angle of 94.5°.

[0020] In the above-mentioned method for preparing highly conductive Lyocell yarn for electronic textiles, the temperature of the hot air oven in step (5) is 130°C.

[0021] The beneficial effects of this invention for high-conductivity lyocell yarn in electronic textiles and its preparation method are that a carbon nanotube (CNT) conductive network is successfully constructed on the surface of green and renewable lyocell yarn, and a thermoplastic polyurethane (TPU) encapsulation layer is introduced to prepare electronic yarn with high conductivity, excellent durability and good textile processing adaptability, providing a practical material solution for the next generation of wearable smart textiles.

[0022] The highly conductive lyocell yarn prepared by this invention exhibits a clear microstructure and uniform structure. The original lyocell yarn has a smooth and flat surface. After being coated layer by layer with carbon nanotubes, the fiber surface is covered with a continuous and dense conductive film of carbon nanotubes, with the carbon nanotubes overlapping to form a stable three-dimensional conductive network. After encapsulation and curing with thermoplastic polyurethane and a crosslinking agent, a smooth, dense, crack-free, and pore-free elastic protective layer is formed on the yarn surface, completely covering the conductive layer. The interlayer bonding is tight, with no delamination or peeling. After bending and washing tests, the composite coating still maintains structural integrity, with no obvious cracks or peeling, demonstrating excellent structural stability and interfacial bonding strength.

[0023] This invention successfully constructs a carbon nanotube (CNT) conductive network on the surface of lyocell yarn and introduces a thermoplastic polyurethane (TPU) encapsulation layer, effectively solving the durability contradictions in flexible conductive yarns caused by the rigid conductive coating's susceptibility to cracking due to modulus mismatch, detachment due to bending fatigue, and peeling due to water washing penetration. Firstly, the elastic polymer encapsulation layer, with its high elasticity, acts as a flexible interface layer, improving the modulus matching and stress transfer between the rigid conductive layer and the flexible substrate. It effectively suppresses stress concentration at the interface, acting as a "buffer" and "adhesive," resulting in a composite yarn exhibiting better flexibility and strength retention on a macroscopic scale (elongation at break loss of only 7.08%, and tensile strength increased by 1.61% compared to the original yarn). Secondly, the dense network formed by the crosslinking of the crosslinking agent and the elastic polymer matrix acts as a physical barrier, effectively blocking the penetration of water molecules into the conductive layer-fiber interface. On the other hand, the stronger interaction between the crosslinking agent and the fiber and the conductive layer enhances the chemical stability and mechanical anchoring effect of the interface, significantly improving the durability of the coating (the resistance change rate is less than 8% after 50 bends, and the coating integrity remains good and the resistivity increase is limited after 15 water washes).

[0024] The process of this invention is simple and controllable. By adjusting the number of CNT coating layers (1-3 layers), the conductivity of the yarn can be precisely controlled. The resistivity increases from 2.07 × 10⁻⁶ layers with the number of layers. -2 Ω·m decreased significantly to 9.60 × 10 -3 Ω·m. While endowing lyocell yarn with excellent conductivity, it successfully balances durability, flexibility, and processability, demonstrating broad prospects for industrial applications. Future work can further explore the refined effects of parameters such as coating thickness and CNT orientation on performance, and promote the practical application of this conductive yarn in smart textiles such as flexible sensing, human thermal management, and energy harvesting. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the present invention;

[0026] Figure 2 This is a schematic diagram showing the macroscopic morphology and cross-sectional structure of the raw yarn and the coated yarn;

[0027] Figure 3 These are scanning electron microscope images of the yarn surface morphology under different CNT coating numbers;

[0028] Figure 4 This is a statistical chart showing the changes in yarn diameter under different coating processes;

[0029] Figure 5 This is a bar chart showing the effect of different coating processes and the number of layers on the volume resistivity of yarn;

[0030] Figure 6This is a comparison chart of the breaking elongation loss rate of yarns with different coating processes;

[0031] Figure 7 This is a comparison chart of the tensile strength loss rate of yarns with different coating processes;

[0032] Figure 8 This is a comparison chart of the contact angles of yarns with different coating processes;

[0033] Figure 9 This is a comparison chart showing the change in resistivity of yarn after 50 bends;

[0034] Figure 10 This is a comparison chart of the changes in yarn resistivity after 5 washes.

[0035] Figure 11 This is a comparison chart of the changes in yarn resistivity after 10 washes.

[0036] Figure 12 This is a comparison chart of the changes in yarn resistivity after 15 washes.

[0037] Figure 13 This is a scanning electron microscope image of the surface microstructure of the yarn after 15 washes. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0039] like Figure 2 and Figure 4 As shown, a highly conductive lyocell yarn for electronic textiles uses lyocell yarn as the matrix to provide flexible support and a basis for textile processing. From the inside out, it includes: 1-3 conductive layers and an elastic polymer matrix encapsulation layer; the elastic polymer matrix encapsulation layer includes an elastic polymer matrix and a crosslinking agent, and the crosslinking agent is blended and crosslinked with the elastic polymer matrix to form a dense network.

[0040] Lyocell yarn is a regenerated cellulose fiber produced from natural plant fibers such as wood pulp through solvent spinning. Its surface is smooth and uniform, with clear and consistent fiber texture. This low-roughness surface facilitates uniform coverage and tight adhesion between the inner conductive paste and the outer encapsulation paste, avoiding localized build-up or bridging defects caused by excessive roughness or fuzz on the substrate surface. Furthermore, lyocell fiber possesses excellent moisture absorption and wicking properties and is environmentally friendly, aligning with the comfort and sustainability requirements of smart textiles.

[0041] The components in the conductive layer refer to micro- or nano-sized functional particles or fibrous materials that can form conductive channels within the insulating substrate. For example, conductive fillers can include carbon-based, metallic, or metal oxide-based conductive materials, which achieve electron transport by overlapping and forming a continuous percolation network within the coating. It should be understood that although... Figure 2 The diagram shows a conductive layer tightly covering the outside of the yarn substrate. However, in other embodiments, the inner conductive layer may also partially penetrate into the shallow surface gaps of the yarn substrate to enhance initial adhesion.

[0042] The elastic polymer matrix in the elastic polymer matrix encapsulation layer refers to polymeric materials with high deformation recovery and flexibility. For example, the elastic polymer matrix can include thermoplastic elastomers, silicone rubber polymers, or fluororubber polymers, and its core function is to provide a flexible interface to absorb and disperse external stress.

[0043] The crosslinking agent CL510 is a water-based, blocked isocyanate crosslinking agent with a solid content of 38% ± 2 wt% and an active group of isocyanate group (-NCO). Under heat treatment curing conditions, it de-encapsulates and undergoes a chemical crosslinking reaction with the hydroxyl and amino groups on the thermoplastic polyurethane (TPU) molecular chain to form an irreversible three-dimensional dense network. This significantly improves the water resistance, bending resistance, and interfacial bonding strength of the encapsulation layer. It allows the crosslinking agent and thermoplastic polyurethane to maintain suitable reactivity and dispersion stability. After curing, a continuous and dense three-dimensional crosslinking network is formed, which ensures sufficient crosslinking and avoids coating embrittlement or insufficient crosslinking, significantly improving the yarn's wash resistance, bending resistance, and interfacial bonding strength.

[0044] Crosslinking agent CL510 is a water-based, blocked isocyanate crosslinking agent, belonging to the polyisocyanate derivative category. Chemical category: isocyanate crosslinking agent; active group: -NCO (isocyanate group, blocked type, deblocked by heat); solid content: 38% ± 2wt%. Its mechanism of action: After deblocking by heat, it releases active -NCO, which undergoes an addition crosslinking reaction with the hydroxyl and amino groups in the TPU molecular chain, forming a three-dimensional chemical crosslinking network, significantly improving water resistance, bending resistance, coating density, and adhesion.

[0045] The aforementioned composite structure achieves a synergistic effect of stress buffering, physical barrier, and interface anchoring, resolving the contradiction that a single structure cannot simultaneously address conductivity and durability. From a microscopic perspective, if only a single rigid inner conductive layer containing conductive fillers is used, the significant modulus mismatch between the rigid coating and the flexible yarn substrate leads to stress concentration at the interface under bending or stretching deformation conditions. This causes microcracks in the rigid coating to rapidly propagate and even peel off from the substrate surface, resulting in the breakage of the conductive pathway. If only a pure elastic polymer encapsulation layer without crosslinking agents is used, although its high elasticity can provide some stress buffering and improve modulus matching, the lack of strong chemical bonds between the pure elastic polymer molecular chains results in a loose network structure with numerous micropores. This loose structure cannot effectively prevent water molecules from penetrating the inner interface as a solid physical barrier, nor can it form a strong mechanical anchoring and chemical bond between the coating and the substrate. Under the scouring and swelling effects of fluids such as water washing, the coating is still prone to softening and peeling.

[0046] By introducing a crosslinking agent and blending it with the elastic polymer matrix to form a dense network, the inherent high elasticity of the elastic polymer matrix continues to act as a buffer, effectively absorbing and dispersing the stress generated by cyclic deformation, suppressing interfacial stress concentration, and preventing premature cracking of the inner conductive layer. The dense network formed by the crosslinking reaction completely changes the loose morphology of the pure elastic polymer. The chemical crosslinking nodes between molecular chains significantly reduce micropores, transforming the outer encapsulation layer into a tough physical barrier that effectively prevents water molecules from penetrating to the interface between the conductive layer and the yarn substrate. Finally, during the formation of the crosslinking network, its polar crosslinking nodes and residual active groups of the crosslinking agent can interact more strongly with the surface of the matrix and the surface of the inner conductive layer, significantly enhancing the interfacial chemical stability and mechanical anchoring effect, resulting in a tight three-layer structure. Through this composite mechanism, the high-conductivity lyocell yarn achieves excellent bending resistance and washability while maintaining excellent conductivity.

[0047] The conductive layer is formulated with carbon nanotube dispersion, binder ST309C, and deionized water. Carbon nanotubes, as a typical one-dimensional nanomaterial, possess extremely high aspect ratios and excellent intrinsic conductivity. In constructing the inner conductive layer, the high aspect ratio carbon nanotubes readily overlap within the coating, requiring only a small amount to cross the insulating binder matrix and form a three-dimensional percolation conductive network throughout the yarn, thereby significantly reducing the percolation threshold and enabling the yarn to achieve excellent conductivity. Figure 3 and Figure 5 It can be seen that as the number of carbon nanotube coating layers increases, the effective volume fraction of carbon nanotubes gradually increases and exceeds the percolation threshold. They overlap on the yarn surface to form continuous conductive pathways, causing the yarn's volume resistivity to increase from approximately 2.07 × 10⁻⁶ for a single layer.-2 Ω·m decreased significantly to approximately 9.60 × 10⁻⁶ at 3 layers. -3 The Ω·m directly demonstrates the advantages of carbon nanotubes in constructing stable percolation networks.

[0048] The carbon nanotubes are multi-walled carbon nanotubes with an average length of 5-15 μm and an average diameter of 8-15 nm. These dimensional parameters are optimized based on percolation theory to determine the number of overlapping nodes in the conductive network. When the average length is in the range of 5-15 μm, the carbon nanotubes have sufficient length to cross the gaps in the matrix for effective overlapping, while avoiding severe entanglement and aggregation caused by excessive length, thus ensuring a uniform distribution of network nodes. When the average diameter is in the range of 8-15 nm, the carbon nanotubes maintain a suitable fineness, providing more conductive pathways for the same mass, while maintaining the necessary mechanical rigidity to support the network structure. When the average length of multi-walled carbon nanotubes (MWCNTs) is 5 μm and the average diameter is 8 nm, the short length of the nanotubes limits the overlap distance, requiring a higher addition amount to form a complete percolation network, resulting in relatively high yarn resistivity. When the average length increases to 10 μm and the average diameter to 12 nm, the aspect ratio of the carbon nanotubes reaches a more ideal balance, the number of overlap nodes increases significantly and is evenly distributed, the percolation threshold decreases further, and the yarn resistivity shows a clear decreasing inflection point. When the average length further increases to 15 μm and the average diameter to 15 nm, the overlap capacity of the carbon nanotubes reaches its extreme, the percolation network is most complete, and the yarn resistivity drops to the lowest level. It should be understood that although the above examples demonstrate the continuous optimization trend of size parameters on conductivity, in practical applications, the specific size selection of MWCNTs must also comprehensively consider the difficulty of slurry dispersion and coating thickness requirements. The average length range of 5-15 μm and the average diameter range of 8-15 nm provide the best balance between conductivity and processing adaptability. In addition, in other embodiments, the conductive filler may also be other high aspect ratio nanomaterials such as graphene and silver nanowires, as long as they can form an effective percolation conductive network in the coating. The above description is only illustrative and not limiting.

[0049] The elastic polymer matrix of the elastic polymer matrix encapsulation layer is thermoplastic polyurethane. Thermoplastic polyurethane is a block copolymer material that combines high strength and high elasticity. Its molecular structure contains soft and hard segments. The soft segments provide excellent deformation recovery, while the hard segments provide necessary physical cross-linking points and mechanical support. In the composite coating structure, thermoplastic polyurethane, as the elastic polymer matrix, effectively absorbs and disperses cyclic stress like a cushion when the yarn is subjected to bending or tensile deformation. This significantly improves the modulus matching between the rigid inner conductive layer and the flexible yarn substrate, suppresses stress concentration at the interface, and prevents premature cracking or detachment of the inner conductive layer. Figure 6 and Figure 7 It can be seen that after introducing the thermoplastic polyurethane encapsulation layer, the loss rate of breaking elongation and the loss rate of tensile strength of the composite coated yarn were effectively controlled, and the tensile strength was even improved compared with the original yarn, which directly verifies the positive role of thermoplastic polyurethane in buffering stress and maintaining mechanical properties.

[0050] The crosslinking agent for the elastic polymer matrix encapsulation layer is an isocyanate-based crosslinking agent. Isocyanate-based crosslinking agents are compounds containing at least two isocyanate groups (-NCO) in their molecular structure. These groups have extremely high reactivity and can undergo efficient addition reactions with active hydrogen groups (such as hydroxyl and amino groups) in the thermoplastic polyurethane molecular chains, forming polyurethane hard-segment crosslinking nodes. When the isocyanate-based crosslinking agent is blended with thermoplastic polyurethane and undergoes an in-situ crosslinking reaction during curing, the thermoplastic polyurethane molecular chains, originally maintained by weak physical interactions, are connected by strong chemical bonds, transforming into an irreversible three-dimensional dense network. This dense network not only significantly reduces the micropores in the polymer matrix, making it a tough physical barrier to prevent water molecules from penetrating to the inner interface, but also allows the polar groups (such as urethane bonds) introduced after the crosslinking nodes and isocyanate reaction to form stronger interfacial interactions with the yarn substrate surface and the inner conductive layer, significantly enhancing the mechanical anchoring effect and interfacial chemical stability.

[0051] Layer-by-layer coating effectively improves the three-dimensional conductive permeation network. The introduction of TPU and CL510 further enhances conductivity, reducing the resistivity to 6.40 × 10⁻⁶ when the conductive layer is coated three times. -3 The TPU layer reduces Ω·m by approximately 33% compared to a pure CNT coating. SEM and durability tests show that the TPU layer not only acts as a dense physical barrier but also plays a dual role in protecting and optimizing the CNT network by enhancing interfacial bonding and stress dispersion.

[0052] To demonstrate the core value and indispensability of crosslinking agents in densification and anchoring, this scheme introduces a comparative example. The comparative example uses pure thermoplastic polyurethane encapsulation (i.e., the outer encapsulation layer does not contain crosslinking agents), and all other structures and preparation conditions are the same as in this scheme. Figure 9 The change in resistivity after 50 bends Figure 12 Comparison of resistivity changes after 15 water washes and Figure 13 Scanning electron microscopy (SEM) images of the yarn surface microstructure after 15 washes clearly show the performance differences between the two. Under bending conditions, the resistivity change rate of the composite-coated yarn containing isocyanate crosslinking agents in this solution is less than 8%, while the resistivity change rate of the comparative pure thermoplastic polyurethane-encapsulated yarn is significantly higher. More importantly, in the durability comparison after 15 washes, the resistivity increase of the comparative pure thermoplastic polyurethane-encapsulated yarn is much higher than that of this application, and from... Figure 13Scanning electron microscopy (SEM) morphology revealed that the comparative yarn surface coating exhibited significant localized damage and micropores, allowing water molecules to easily penetrate into the inner interface. In contrast, the substrate coating of this design remained largely intact and dense, without any obvious damage. This comparative data and microstructure clearly demonstrate that the thermoplastic polyurethane encapsulation layer lacking a crosslinking agent can only provide stress buffering, but its loose network structure cannot achieve dense barrier and strong anchoring. Under the influence of fluid erosion and swelling, its durability will precipitate. The introduction of isocyanate crosslinking agents is the key triggering factor for achieving densification and interface anchoring of the encapsulation layer. Its combination with thermoplastic polyurethane produces a synergistic effect greater than the sum of its parts (1+1>2), making it an indispensable core component for achieving superior durability in composite coated conductive yarns. It should be understood that although the above description specifically lists the combination of thermoplastic polyurethane and isocyanate crosslinking agents, in other embodiments, the elastic polymer matrix may also be a silicone rubber polymer or a fluororubber polymer, and the crosslinking agent may also be a peroxide compound or a silane coupling agent compound that matches the corresponding polymer, as long as it can be blended and crosslinked to form a network that has both elastic buffering and dense barrier / anchoring functions. The above description is only illustrative and not restrictive.

[0053] The adhesive is a water-based acrylate adhesive. Water-based acrylate adhesives refer to water-based polymers prepared by emulsion polymerization and other methods, with acrylate monomers as the main component. During the construction of the inner conductive layer, conductive fillers (such as carbon nanotubes) tend to agglomerate due to their extremely high surface energy and strong van der Waals forces, making them difficult to disperse uniformly in the insulating medium. Simultaneously, the initial interfacial bonding force between rigid conductive particles and the flexible yarn substrate is usually weak. The introduction of water-based acrylate adhesives effectively solves these problems. On the one hand, the polar groups in their molecular chains can interact with the surface of the conductive filler, improving the dispersion stability of the conductive filler in the water-based slurry and preventing secondary agglomeration during coating, thereby ensuring the uniform construction of the permeation conductive network. On the other hand, after film formation and curing, the water-based acrylate adhesive can act as an intermediate medium to enhance the initial adhesion between the inner conductive layer and the yarn substrate surface, providing a solid interfacial foundation for the subsequent coating and cross-linking anchoring of the outer encapsulation layer. It should be understood that although waterborne acrylic adhesives are specifically listed above, in other embodiments, the adhesive may also be a waterborne polyurethane adhesive, a waterborne silicone adhesive, or other waterborne polymeric materials with good film-forming properties and interfacial adhesion, as long as it can promote the dispersion of conductive fillers and enhance the initial adhesion of the coating. The above is only illustrative and not restrictive.

[0054] Combination Figure 1 As shown, the preparation method of the present invention includes:

[0055] The substrate is provided, serving as the main load-bearing structure. The steps involved in providing the substrate include pretreatment and traction preparation. For example, in... Figure 1 In the illustrated process flow, the raw yarn first passes through guide rollers for leveling and tension adjustment to ensure that the substrate surface is in a uniform and stretched state during the subsequent coating process, avoiding uneven coating thickness caused by localized relaxation or excessive stretching. It should be understood that, although... Figure 1 The method of traction via guide rollers is shown, but in other embodiments, other tension control mechanisms or pretreatment methods may be used, as long as the surface of the yarn substrate has good coating adhesion conditions.

[0056] Forming a conductive layer on the surface of the yarn substrate involves uniformly adhering the slurry to the substrate surface and curing it into a film. Figure 1 In the example, the leveled substrate is pulled through a tank containing conductive paste for immersion. Excess paste is then squeezed out by a pressure roller under controlled pressure, achieving uniform coating and penetration. Finally, it enters a drying roller for preliminary curing, allowing the conductive paste to overlap on the substrate surface to form a continuous, permeable conductive network. In this step, the distribution of the conductive paste on the substrate surface determines the stability of the subsequent conductive pathways. Therefore, it is essential to ensure that the coating solution fully wets the substrate surface and that the pressure is appropriate to avoid localized accumulation or missed coating defects.

[0057] An elastic polymer matrix encapsulation layer is formed on the surface of the conductive layer. This layer comprises an elastic polymer matrix and a crosslinking agent, which are blended and crosslinked with the elastic polymer matrix to form a dense network. This step is crucial for achieving synergistic durability enhancement. During the formation of the outer encapsulation layer, the crosslinking agent and the elastic polymer matrix are first physically blended to form a homogeneous slurry. Subsequently, this slurry is coated onto the cured conductive layer surface, where an in-situ crosslinking reaction occurs during the subsequent curing process. In-situ crosslinking refers to the chemical reaction between the crosslinking agent and the elastic polymer matrix molecular chains, which is completed situ after the coating adheres to the substrate and under the influence of the curing thermal field. This transforms the originally linear or weakly connected polymer segments directly into an irreversible three-dimensional dense network on the yarn surface. This in-situ crosslinking mechanism not only ensures that the dense network tightly encapsulates the inner conductive layer but also allows the polar groups and crosslinking nodes generated during the crosslinking reaction to directly interact with the inner conductive layer and the yarn substrate surface. This achieves interface anchoring simultaneously with film formation, significantly enhancing interlayer bonding. The particle size of the elastic polymer matrix is ​​controlled to be 50-500 micrometers, so that it can be quickly and fully dissolved during the stirring process to obtain a uniform and stable encapsulation slurry, which is convenient for high-speed continuous coating. The fully dissolved TPU can form a smooth and defect-free sealing encapsulation layer, effectively protecting the internal CNT conductive network, improving the modulus matching between the coating and the substrate, and enhancing the mechanical properties and structural stability of the composite yarn.

[0058] The fabrication method must strictly adhere to the sequential logic of forming the inner conductive layer first, followed by the outer encapsulation layer. This sequential design is an irreversible technological necessity. If the outer encapsulation layer is formed first, followed by the inner conductive layer, the conductive filler can only adhere to the outer surface of the encapsulation layer and cannot be covered by it. This results in the conductive network being completely exposed to the external environment, losing the protection of physical barrier and interface anchoring, making it highly susceptible to direct damage and detachment under bending or washing conditions. However, by first constructing the inner conductive network and then cross-linking it in situ on its outer side to form a dense encapsulation network, the conductive network is ensured to be completely encapsulated and covered, allowing the synergistic mechanism of elastic buffering and dense barrier / anchoring to truly take effect. It should be understood that although the above-described combination... Figure 1 The continuous process flow of impregnation-extrusion-drying is described, but in other embodiments, the coating method for each step can also be other film-forming methods such as brushing, spraying or spin coating, as long as the internal-to-external sequential requirement is met and in-situ crosslinking is achieved. The above description is only illustrative and not restrictive.

[0059] After forming the conductive layer and / or the outer encapsulation layer, heat treatment curing is performed at a temperature of 120-150℃ for 1-3 hours. Heat treatment curing is the core process determining the final structural morphology and interfacial bonding strength of the composite coating. Within the parameter window of 120-150℃ and 1-3 hours, the thermal field simultaneously drives two key microscopic physicochemical processes. On the one hand, these temperature and time conditions ensure sufficient evaporation of moisture from the inner conductive paste and the film-forming curing of the water-based adhesive, allowing the conductive filler to form a stable and continuous permeation network on the substrate surface. On the other hand, these conditions provide sufficient activation energy and reaction time for the in-situ crosslinking reaction between the crosslinking agent and the elastic polymer matrix in the outer encapsulation layer, promoting the full formation of crosslinking nodes and thus completely transforming linear or weakly connected polymer segments into an irreversible three-dimensional dense network. If the temperature is too low or the time is too short, the crosslinking reaction cannot overcome the energy barrier, and the dense network construction fails; if the temperature is too high or the time is too long, it may cause thermal damage to the substrate or excessive embrittlement of the coating. Therefore, this parameter range represents the optimal balance between moisture evaporation, adhesive film formation, and sufficient cross-linking reaction.

[0060] To demonstrate the criticality and irreplaceability of this parameter range, this scheme includes specific examples at the endpoints and intermediate values ​​of the range, and introduces comparative examples outside the boundary.

[0061] Specific Example 1: The heat treatment curing temperature is 120℃, and the time is 3 hours. This combination represents the lower limit of the parameter range. By extending the reaction time at a lower temperature, the kinetic rate of the crosslinking reaction can be compensated, ensuring that the crosslinking reaction is basically completed, a dense network is initially formed, and the adhesion between the coating and the substrate meets the minimum standard for durability requirements.

[0062] Specific Example 2: The heat treatment curing temperature is 130℃, and the time is 2 hours. This combination represents the midpoint of the parameter range and is also the optimal process parameter point of this invention. Under these conditions, the moisture evaporation rate and the crosslinking reaction rate reach an ideal match, the crosslinking network structure is most uniform and dense, the physical barrier and interface anchoring effects reach their peak, and the volume resistivity of the composite coated conductive yarn is the lowest, with optimal bending resistance and water washing resistance.

[0063] Specific Example 3: The heat treatment curing temperature is 150℃, and the time is 1 hour. This combination represents the upper limit of the parameter range. At higher temperatures, the reaction time is shortened to avoid heat damage. The crosslinking reaction is completed quickly in a short time, and a dense network can be effectively formed. However, the uniformity of the crosslinking node distribution is slightly inferior to the intermediate value example, and the coating toughness is slightly reduced, but it still meets the durability requirements of practical applications.

[0064] External Comparative Example 1: The heat treatment curing temperature was 100°C for 3 hours. This comparative example is lower than the lower limit of the temperature specified in this invention. At 100°C, the reactivity of the crosslinking agent was extremely low, and even extending the curing time to 3 hours could not promote a sufficient crosslinking reaction. Microscopic results showed that the outer encapsulation layer failed to form a dense network, the polymer matrix remained in a loose state, and the coating softened and peeled off in subsequent water washing tests, resulting in a sharp drop in durability.

[0065] Comparative Example 2 (outside the boundary): The heat treatment curing temperature was 170℃, and the time was 1 hour. This comparative example exceeds the upper temperature limit specified in this invention. At a high temperature of 170℃, although the cross-linking reaction can be completed instantaneously, the excessively high thermal field causes irreversible thermal damage and shrinkage to the flexible yarn substrate. At the same time, the outer encapsulation layer becomes brittle due to excessive cross-linking and loses its elastic buffering function. In the bending test, the brittle coating is prone to microcracks that propagate rapidly, causing the conductive path to break and the rate of change of resistance to increase sharply.

[0066] The comparative data from the specific examples and the external comparison examples above fully demonstrate that a temperature range of 120-150℃ and a time range of 1-3 hours are the critical windows for the synergistic performance of the composite coating structure to take effect. Below this range, insufficient cross-linking leads to barrier and anchoring failure; above this range, the substrate is damaged and the coating becomes brittle, resulting in the loss of buffering function. Only within this parameter range can the perfect synergy of moisture evaporation, film curing, and in-situ cross-linking be achieved, thereby ensuring that the composite coated conductive yarn has both high conductivity and high durability.

[0067] Example 1

[0068] Conductive layer formulation: Carbon nanotube dispersion (CNT, solid content 10%, main component is multi-walled carbon nanotubes, average length 5–15 μm, average diameter 8–15 nm): 54.54 wt%;

[0069] ST309C (water-based acrylate, solid content 40%): 9.09 wt%;

[0070] Deionized water (resistivity ≥ 18.2 MΩ·cm): 36.36 wt%

[0071] Elastic polymer matrix encapsulation layer slurry formulation:

[0072] Thermoplastic polyurethane (TPU, model 185A): 62.5 wt%;

[0073] Crosslinking agent CL510: 37.5wt%.

[0074] Preparation method:

[0075] a) Preparation of conductive layer: Add 80 mL of deionized water and 120 mL of 10% CNT dispersion to a 300 mL beaker, and stir magnetically at 500 r / min for 20 min to initially disperse the mixture. Then add 20 g of binder ST309C, and continue stirring at 500 r / min for 30 min to obtain a uniform black CNT conductive paste. After standing to defoam, it is ready for use.

[0076] b) Preparation of the elastic polymer matrix encapsulation layer: Add 100g of TPU particles and 60mL of crosslinking agent 510 to a 300mL beaker, and stir magnetically at 500r / min for 20min until a uniform semi-transparent slurry is formed. The TPU particles are 150μm in size.

[0077] c) Sizing: The yarn enters a drying chamber set at 140℃ and undergoes hot air drying for 2 minutes to solidify the sizing agent. The dried yarn is drawn out by the yarn guide roller and finally wound up by the winding device to form a uniform sizing cylinder. Repeating the above steps, conductive yarns with 2 and 3 layers of CNT coating are obtained respectively (referred to as C1, C2, and C3). The sizing agent in the sizing tank is replaced with TPU and TPU + crosslinking agent CL510 composite sizing agent, respectively, to obtain conductive yarns with different CNT conductive layer / TPU encapsulation layer composite structures (referred to as CT1, CT2, CT3, CTC1, CTC2, and CTC3).

[0078] Performance Tests and Results

[0079] a) Structural characterization

[0080] Scanning electron microscopy (SEM) observations showed that the lyocell yarn was tightly wrapped by the CNT conductive layer / TPU encapsulation layer. It was also evident from the image that the coating effect in this example was the most dense. The average diameter obtained from 30 diameter measurements was 339.05 μm, which was smaller than that of other groups. This indicates that the encapsulation layer reduced the yarn spacing, made the CNT conductive coating denser, and enhanced the yarn conductivity.

[0081] b) Electrical conductivity

[0082] The volume resistivity (ρ) of the yarn decreases significantly with increasing CNT coating number, from approximately 2.07 × 10⁻² Ω·m with one layer to approximately 9.60 × 10⁻² Ω·m with three layers. -3 Ω·m. With the addition of TPU packaging, the resistivity decreases to 7.59 × 10⁻⁶ Ω·m. -3 Ω·m; and when the TPU is used in conjunction with the CL510, the resistivity is further reduced to 6.40 × 10 Ω·m; -3 The Ω·m is reduced by approximately 33.33% compared to a pure CNT coating with the same number of layers.

[0083] c) Mechanical properties

[0084] The 3-layer CNT+TPU+510 composite coated yarn has a breaking elongation of 12.45%, with a loss rate of only 7.09% compared to the original lyocell fiber, and a tensile strength of 6.31N, which is 1.61% higher than the original yarn. This result highlights the dual positive effects of the TPU encapsulation layer.

[0085] d) Surface wettability

[0086] The original hydrophilic lyocell yarn had a contact angle of 35.8°. After being coated with a hydrophobic CNT layer, it transformed into a hydrophobic surface with a contact angle of 119.5°. Introducing TPU further reduced the contact angle to 108.8°, and when TPU was used in conjunction with CL510, the contact angle decreased further to 94.5°, becoming more hydrophilic. The polar groups introduced by the TPU itself and the crosslinking agent increased the polarity of the coating surface, thus collectively leading to changes in surface energy and a recovery in hydrophilicity. This controllable adjustment of surface wettability facilitates subsequent functionalization.

[0087] e) Durability:

[0088] After 50 bends, the resistivity change rate of pure CNT coated yarn is as high as 34% or more, while the resistivity change rate of composite coated yarn containing TPU and CL510 is less than 8%. During the bending process, the outer side of the yarn is subjected to tensile stress, and the inner side is subjected to compressive stress. The brittle coating of pure CNT is prone to cracking and propagation under this cyclic stress, and may even peel off from the fiber surface, resulting in the breakage of the conductive path.

[0089] Example 2

[0090] This embodiment provides an electronic textile. Specifically, the electronic textile includes a fabric body, which includes highly conductive Lyocell yarns for electronic textiles as described above. The fabric body refers to a two-dimensional or three-dimensional flexible sheet structure formed by interlacing or weaving yarns through textile processes. It serves as a supporting substrate, providing physical support and layout positioning for the composite-coated conductive yarns. For example, the fabric body can include woven fabrics, knitted fabrics, nonwoven fabrics, or woven meshes, as long as it can stably integrate the conductive yarns and adapt to human wear. The composite-coated conductive yarns in the fabric body can be arranged along a specific path as independent sensing yarns, or they can be interlaced with ordinary yarns to form local conductive areas, thereby constituting a flexible sensing electronic textile. It should be understood that although this embodiment focuses on describing the application scenario of the flexible sensing electronic textile, in other embodiments, the electronic textile can also be an electrothermal fabric, an electromagnetic shielding fabric, or a data transmission fabric, as long as it relies on the composite-coated conductive yarns to achieve electrical functions. This embodiment is only illustrative and not restrictive.

[0091] To demonstrate the operational effectiveness and commercial value of the present invention in a real-world environment, this embodiment integrates composite-coated conductive yarn into a smart heart rate monitoring fabric and verifies it under actual wear conditions. The smart heart rate monitoring fabric is a typical flexible sensor electronic textile. It uses a grid arrangement of composite-coated conductive yarn on the chest area of ​​the fabric to sense the minute chest deformation caused by a human heartbeat and converts this deformation into changes in resistance signals to achieve heart rate monitoring. In actual wear, this fabric inevitably needs to withstand repeated bending from daily human movement and the washing, soaking, and mechanical agitation from daily washing. This is precisely the durability bottleneck faced by existing smart textiles in their practical application.

[0092] Combination Figure 9 and Figure 12 The durability data clearly demonstrates the superior performance of the electronic textile of this embodiment under the aforementioned harsh working conditions. In conditions involving repeated bending due to human movement, with a bending count exceeding 50 times, the propagation of microcracks in the inner conductive network is effectively suppressed due to the synergistic effect of the stress buffering effect of the elastic polymer encapsulation layer inside the composite-coated conductive yarn and the interface anchoring effect of the cross-linked dense network. The yarn maintains a stable conductive signal output within the fabric, with a resistance change rate of less than 8%. Figure 9 This ensures the continuity and accuracy of the heart rate monitoring signal. Under routine washing conditions, with a washing cycle of 15 times or more, the dense cross-linked network acts as a robust physical barrier, effectively preventing water molecules from penetrating the inner interface. Simultaneously, its polar cross-linking nodes enhance the interfacial chemical stability and mechanical anchoring effect, resulting in a limited increase in the yarn's resistivity after 15 washes. Figure 12The coating integrity remained good, and there were no coating softening, peeling or conductive signal attenuation phenomena common in the prior art.

[0093] While a pure CNT coating reduces yarn flexibility, the TPU encapsulation layer effectively improves the mechanical property matching of the composite material, ensuring that the breaking elongation and tensile strength of the final conductive yarn are well maintained. The contact angle can be adjusted to near the hydrophilic range (94.5°), laying the foundation for subsequent textile processing and wearing comfort. The optimized composite coating structure exhibits excellent bending and washing resistance. After 50 bends, the resistance change rate is less than 8%, and the resistivity increase is limited after 15 washes, with good coating integrity maintained. This demonstrates the effectiveness and practicality of this solution in resolving the "conductivity-durability" contradiction in smart textiles.

[0094] The above-mentioned actual working condition verification fully demonstrates that by integrating composite coated conductive yarn with both high conductivity and high durability into the main body of the fabric, this embodiment enables electronic textiles to maintain stable conductivity and mechanical properties when subjected to real-world wear challenges such as repeated bending and washing. This fundamentally solves the durability bottleneck in the practical application of smart textiles and demonstrates broad prospects for industrial application.

[0095] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A highly conductive lyocell yarn for use in electronic textiles, characterized in that, Using lyocell yarn as the matrix, it comprises, from the inside out: 1-3 conductive layers and an elastic polymer matrix encapsulation layer; the elastic polymer matrix encapsulation layer includes an elastic polymer matrix and a crosslinking agent, wherein the crosslinking agent and the elastic polymer matrix are blended and crosslinked to form a dense network.

2. The highly conductive Lyocell yarn for electronic textiles according to claim 1, characterized in that, The conductive layer is prepared from carbon nanotube dispersion, binder ST309C and deionized water.

3. The highly conductive Lyocell yarn for electronic textiles according to claim 2, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes, with an average length of 5-15 μm and an average diameter of 8-15 nm.

4. The highly conductive Lyocell yarn for electronic textiles according to claim 1, characterized in that, The elastic polymer matrix is ​​thermoplastic polyurethane.

5. The highly conductive Lyocell yarn for electronic textiles according to claim 4, characterized in that, The crosslinking agent is an aqueous blocked isocyanate crosslinking agent with a solid content of 38% ± 2 wt%.

6. The highly conductive Lyocell yarn for electronic textiles according to claim 1, characterized in that, The adhesive is a water-based acrylic adhesive.

7. A method for preparing a highly conductive Lyocell yarn for electronic textiles according to any one of claims 1-6, characterized in that: Includes the following steps: (1) Preparation of conductive layer: Add 80mL of deionized water and 120mL of 10% carbon nanotube dispersion to a 300mL beaker, stir magnetically to disperse it initially, add 20g of binder ST309C, continue stirring to obtain a uniform black CNT conductive paste, let it stand to defoam and then use it for later use. (2) Preparation of elastic polymer matrix encapsulation layer: Add 100g of elastic polymer matrix particles and 60mL of crosslinking agent 510 to a 300mL beaker, and stir magnetically until a uniform semi-transparent slurry is formed for later use; (3) Pretreatment: Preheat the equipment to 150℃ and keep it at that temperature for 30 minutes to stabilize the thermal field; (4) Conductive layer coating: The Lyocell yarn substrate is drawn through the carbon nanotube conductive slurry tank at a linear speed of 80 m / min, and then the liquid amount is controlled by the extrusion roller to obtain a uniformly wetted coated yarn. (5) Encapsulation and curing: The coated Lyocell yarn substrate is immediately placed in a hot air oven at 120℃-150℃ for 1-3 hours to allow the coating to dry fully and obtain highly conductive Lyocell yarn.

8. The method for preparing highly conductive Lyocell yarn for electronic textiles according to claim 7, characterized in that, In step (1), the stirring rate is 500 r / min and the total stirring time is 50 min; in step (2), the stirring rate is 500 r / min and the stirring time is 20 min, and the particle size of the elastic polymer matrix is ​​50-500 micrometers.

9. The method for preparing highly conductive Lyocell yarn for electronic textiles according to claim 8, characterized in that, In step (4), the conductive layer is coated three times, resulting in a highly conductive Lyocell yarn with a resistivity as low as 6.40 × 10⁻⁶. -3 The resistance change rate after 50 bends is <8%, the coating remains intact after 15 water washes, and the resulting high-conductivity Lyocell yarn has a breaking elongation of 12.45%, a tensile strength of 6.31 N, and a contact angle of 94.5°.

10. The method for preparing highly conductive Lyocell yarn for electronic textiles according to claim 9, characterized in that, In step (5), the temperature of the hot air oven is 130°C.

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