A method for preparing super-strong and super-tough polyurethane conductive fibers by wet spinning-freeze drying and application

Abstract

This invention discloses a method and its application for preparing ultra-strong and ultra-tough polyurethane conductive fibers via wet spinning and freeze-drying. The method first synthesizes a prepolymer using polytrimethylene ether glycol and dicyclohexylmethane-4,4'-diisocyanate as raw materials. Then, innovatively, it employs bio-based 2,5-furandicarboxyhydrazide (FDHA) and the ionic liquid chain extender 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide for synergistic chain extension, simultaneously constructing a strong hydrogen bond network and ionic conductive channels within the polymer chain. Subsequently, metal ions are introduced into the polyurethane spinning solution to promote microphase separation. After wet spinning and freeze-drying, fibers with a uniform porous structure are finally obtained. This invention, through a combination of molecular design and process technology, solves the problem of the difficulty in synergistically improving the strength, toughness, elasticity, and conductivity of traditional polyurethane fibers. The resulting fibers possess high strength, high toughness, good conductivity, and stable strain sensing capabilities.

Description

Technical Field

[0001] This invention belongs to the field of high-performance functional fiber technology, specifically relating to an ultra-strong and ultra-tough polyurethane conductive fiber and its preparation method. More specifically, it relates to a polyurethane fiber that is prepared by a combination of wet spinning and freeze drying processes, possessing ultra-strong mechanical properties, high toughness, and stable conductivity. It can be widely used in related technical fields such as flexible electronics, national defense, aerospace, humanoid robots, and intelligent sensing. Background Technology

[0002] Polyurethane fibers, due to their excellent elasticity, abrasion resistance, and flexibility, have been widely used in textiles, medical devices, and sports equipment. However, traditional polyurethane fibers still have shortcomings in terms of mechanical strength, toughness, and electrical conductivity, making it difficult to meet the high requirements for comprehensive material performance in smart sensing textiles for motion monitoring, human-computer interaction, and personal protection. Currently, imparting electrical conductivity to polyurethane fibers typically involves blending with conductive fillers (such as carbon nanotubes, graphene, and metal nanowires). However, this method easily leads to uneven filler dispersion and weak interfacial bonding, making the fibers prone to structural damage during tensile deformation, thus affecting electrical stability and mechanical properties. Simultaneously, conventional fiber forming processes (such as melt spinning) struggle to construct multi-level micro / nano structures within the fiber, limiting the simultaneous improvement of fiber strength and toughness.

[0003] In existing technologies, although some studies have explored the use of wet spinning to prepare porous fibers to improve certain properties, it is often difficult to precisely control the microphase separation structure and pore morphology within the fibers, resulting in a trade-off between mechanical properties and functional attributes. Furthermore, the preparation of intrinsically conductive polyurethane materials typically relies on the synthesis of conjugated polymers or ionically conductive polymers, a complex process that often leads to unsatisfactory mechanical properties and spinnability.

[0004] Based on the above analysis, developing a method for preparing polyurethane fibers that can simultaneously achieve high strength, high toughness, stable conductivity, and controllable structure has significant scientific and application value. Summary of the Invention

[0005] To overcome the shortcomings of the existing technologies, this invention aims to provide a polyurethane conductive fiber preparation route that combines molecular structure design with innovative molding processes. This route offers superior performance, a mild and feasible process, and the ability to be mass-produced. It can simultaneously achieve ultra-strong mechanical properties, high toughness, and stable conductivity, thus meeting the practical application needs of high-performance functional fibers in fields such as flexible electronics and national defense.

[0006] To achieve its objectives, the present invention employs the following technical solution: This invention discloses a method for preparing ultra-strong and ultra-tough polyurethane conductive fibers via wet spinning and freeze-drying. The method is characterized by promoting microphase separation of polyurethane segments through the complexation of metal ions with the polyurethane segments, followed by wet spinning and freeze-drying to ultimately form polyurethane conductive fibers with a uniform pore structure, ultra-strong mechanical properties, high toughness, and stable conductivity. The method specifically includes the following steps: (1) Preparation of prepolymer: First, the polytrimethylene ether glycol is vacuum dehydrated to remove moisture from the raw material to avoid affecting the subsequent polymerization reaction; then, under heating conditions and nitrogen atmosphere protection, dicyclohexylmethane-4,4'-diisocyanate, solvent N,N-dimethylacetamide and catalyst are added to the dehydrated polytrimethylene ether glycol, and after stirring evenly, the reaction is carried out for a period of time until the system reaches the preset degree of polymerization to obtain polyurethane prepolymer.

[0007] (2) Synergistic chain extension to prepare intrinsically conductive polyurethane: Two synergistic chain extenders are added to the prepolymer generated in step (1) at the same time: bio-based 2,5-furandicarboxyhydrazide (FDHA) containing abundant hydrogen bond sites and aromatic heterocyclic structure, and 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]) containing anionic and cationic groups; wherein, FDHA can provide a wide range of hydrogen bond networks and π-π stacking interactions for the material after polymerization, thereby improving the mechanical strength and thermal stability of the material, and [DiHEIm][Tf2N] can provide intrinsic conductivity for the material after polymerization; the chain extension reaction is carried out under heating conditions, and the solvent in the system is removed by drying after the reaction is completed, thus obtaining a polyurethane material with intrinsic conductivity.

[0008] (3) Preparation of spinning solution and complexation with metal ions: The intrinsically conductive polyurethane material obtained in step (2) is dissolved in a suitable solvent to prepare a polyurethane spinning solution; then metal ions are added to the spinning solution, and the metal ions and polyurethane material are thoroughly stirred and mixed so that the metal ions and polyurethane segments form a complexation effect, further promoting the microphase separation of polyurethane segments, and obtaining a polyurethane spinning solution with metal ion complexation.

[0009] (4) Wet spinning and freeze drying: The polyurethane spinning solution with metal ion complexation obtained in step (3) is loaded into the spinning device and squeezed into the coagulation bath at a uniform speed through the spinning needle. After coagulation, nascent polyurethane fibers are obtained. Then, the nascent polyurethane fibers are freeze-dried to avoid pore collapse caused by conventional drying, and finally, ultra-strong and ultra-tough polyurethane conductive fibers with uniform pore structure are obtained.

[0010] To further optimize the technical effects of this invention and achieve the best match between performance and process, the process parameters for each step have been optimized as follows: Preferably, in step (1): the temperature of the vacuum dehydration treatment is 100~140 ℃, and the dehydration time is 1~6 h; the prepolymerization reaction temperature under heating conditions is 60~140 ℃, and the reaction time is 1~12 h; more preferably, the vacuum dehydration is carried out at 110~130 ℃ for 2~4 h, and the prepolymerization reaction is carried out at 80~100 ℃ for 4~8 h. These preferred parameters can ensure sufficient dehydration and complete prepolymerization reaction, while avoiding the degradation of raw materials or the occurrence of side reactions.

[0011] Preferably, in step (2), the chain extension reaction temperature is 30~90 ℃ and the reaction time is 1~12 h; more preferably, the chain extension reaction temperature is 50~80 ℃, which can ensure that the two chain extenders work together fully and achieve a preliminary balance between intrinsic conductivity and mechanical properties.

[0012] Preferably, in step (3): the concentration of the polyurethane spinning solution is 10~40 wt%, more preferably 20~30 wt%. This concentration range can take into account both the fluidity and molding stability of the spinning solution, avoiding the problem that the fiber structure is loose due to too low a concentration and that it is difficult to spin due to too high a concentration; the amount of metal ions added is 1~5 wt% of the mass of the intrinsically conductive polyurethane material, more preferably 2~3 wt%. This amount of addition can achieve the best complexation effect between metal ions and polyurethane segments, effectively promote microphase separation, and at the same time avoid excessive metal ions becoming material defects.

[0013] Preferably, in step (4), the freeze-drying time is 12~72 h, more preferably 24~36 h. This time can ensure that the moisture inside the fiber is completely sublimated, forming a uniform and interconnected pore structure, giving full play to the stress dispersion effect of the pores, and improving the fiber toughness.

[0014] Preferably, in steps (1) and (2), the molar ratios of the raw materials are as follows: the molar ratio of polytrimethylene ether glycol to dicyclohexylmethane-4,4'-diisocyanate is 1:1~4, the molar ratio of polytrimethylene ether glycol to chain extender FDHA is 1:0.25~2, and the molar ratio of polytrimethylene ether glycol to chain extender [DiHEIm][Tf2N] is 1:0.25~2. More preferably, the molar ratio of polytrimethylene ether glycol to dicyclohexylmethane-4,4'-diisocyanate is 1:2~3, the molar ratio of polytrimethylene ether glycol to chain extender FDHA is 1:0.5~1, and the molar ratio of polytrimethylene ether glycol to chain extender [DiHEIm][Tf2N] is 1:0.5~1. This preferred ratio achieves the optimal synergistic effect of fiber strength and conductivity.

[0015] Preferably, the catalyst is one of dibutyltin dilaurate, stannous octoate, tetrabutyl titanate, bismuth neodecanoate, triethylenediamine, and trimethylbenzylamine; more preferably, it is one of stannous octoate, tetrabutyl titanate, and triethylenediamine. This type of catalyst can efficiently catalyze the prepolymerization and chain extension reaction without adversely affecting the final properties of the fiber.

[0016] Preferably, the metal ion is one of sodium chloride, zinc chloride, magnesium chloride, aluminum chloride, copper chloride, and ferric chloride; more preferably, it is one of zinc chloride, magnesium chloride, and ferric chloride. This type of metal ion has the best complexation effect with polyurethane segments, the most significant promoting effect on microphase separation, and can effectively improve the mechanical properties and electrical conductivity stability of the fiber.

[0017] The ultra-strong and ultra-tough polyurethane conductive fiber prepared by the above technical solution of the present invention has high strength, high toughness, good conductivity and stable strain sensing capability. It can be widely used in flexible electronics, national defense and military industry, aerospace and humanoid robot fields. It is also suitable for intelligent sensing textiles, motion monitoring, human-computer interaction and personal protection and other related fields, and has broad application prospects.

[0018] The synthesis route of polyurethane in this invention is as follows: Compared with the prior art, the beneficial effects of the present invention are reflected in: This invention utilizes molecular design and process innovation to prepare polyurethane fibers possessing superior strength, toughness, conductivity, and porosity. The core of this invention lies in the synergistic polymerization of bio-based 2,5-furandicarboxyhydrazide and ionic liquid chain extenders. This simultaneously constructs strong hydrogen bond networks, π-π stacking interactions, and mobile ion channels within the molecular chain, achieving a combination of high strength, high thermal stability, and intrinsic conductivity. Furthermore, the introduction of metal ion complexation effectively promotes microphase separation of polyurethane segments, enhancing intermolecular forces and order. Combining wet spinning and freeze-drying processes, a uniform and controllable multi-level porous structure is formed within the fiber. This structure not only reduces fiber density but also simultaneously improves the material's toughness, elasticity, and deformability through pore wall bearing and stress dispersion mechanisms, solving the problem of traditional conductive fibers struggling to balance strength and toughness while exhibiting poor conductivity. The resulting fibers demonstrate excellent comprehensive properties: high strength, high toughness, stable strain sensing capability, and good flexibility. The preparation process is mild, structurally controllable, easily scaled up, and utilizes some bio-based raw materials, aligning with green chemistry principles. This fiber has significant application value in the field of intelligent sensing textiles, and is especially suitable for high-dynamic, high-reliability motion monitoring, human-computer interaction, and personal protective equipment. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Figure 1 The chemical structure diagram and 1H NMR spectrum of sample 43 prepared for example are shown.

[0020] Figure 2 The infrared spectrum of sample 43 prepared in the example is shown.

[0021] Figure 3 The image shown is a scanning electron microscope (SEM) image of sample 43 prepared in the example. Detailed Implementation

[0022] The preparation method of the ultra-strong and ultra-tough polyurethane conductive fiber of the present invention will be described in detail below with reference to specific embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0023] Example 1 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Place 1 mol of polytrimethylene ether glycol in a reaction vessel and perform vacuum dehydration treatment for 4 h at 100 ℃ (corresponding to sample 1), 120 ℃ (corresponding to sample 2), and 140 ℃ (corresponding to sample 3) to completely remove the moisture from the raw materials. After dehydration, place the reaction vessel under a nitrogen atmosphere and add 3 mol of dicyclohexylmethane-4,4'-diisocyanate, 50 mL of N,N-dimethylacetamide (DMAc), and stannous octoate catalyst (addition amount is 0.1 wt% of the final total polyurethane). After stirring evenly, perform prepolymerization reaction at 100 ℃ for 6 h to obtain polyurethane prepolymer.

[0024] (2) Cool the above prepolymer to 60 °C, add 1 mol of chain extender 2,5-furandicarboxyhydrazide (FDHA) and 1 mol of 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]), and add an appropriate amount of solvent N,N-dimethylacetamide according to the viscosity of the reaction system. Continue the reaction for 8 h to complete the chain extension. After the reaction is completed, dry at 60 °C for 24 h to remove the solvent in the system and obtain the intrinsic conductive polyurethane material.

[0025] (3) Dissolve the obtained intrinsically conductive polyurethane material in N,N-dimethylacetamide to prepare a polyurethane spinning solution with a concentration of 20 wt%; add magnesium chloride with a mass fraction of 2 wt% (relative to the polyurethane material) to the spinning solution, stir and mix thoroughly to form a complex with the polyurethane chain segments to obtain a polyurethane spinning solution with metal ion complex.

[0026] (4) The polyurethane spinning solution complexed with the above metal ions is loaded into a needle tube and squeezed into the coagulation bath water at a uniform speed through the spinning needle. The nascent polyurethane fiber is then solidified and formed. The nascent polyurethane fiber is placed in a freeze-drying device and freeze-dried at -40℃ for 36 h to finally obtain a super-strong and super-tough polyurethane conductive fiber with a uniform pore structure.

[0027] Example 2 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) 1 mol of polytrimethylene ether glycol was placed in a reaction vessel and vacuum dehydrated at 130 °C for 1 h (corresponding to sample 4), 3 h (corresponding to sample 5), and 6 h (corresponding to sample 6). After dehydration, the reaction vessel was placed under a nitrogen atmosphere and 3 mol of dicyclohexylmethane-4,4'-diisocyanate, 50 mL of N,N-dimethylacetamide (DMAc) and stannous octoate catalyst (added amount is 0.1 wt% of the final total polyurethane) were added. After stirring evenly, the prepolymerization reaction was carried out at 100 °C for 6 h to obtain polyurethane prepolymer.

[0028] (2) Same as in Example 1.

[0029] (3) Same as in Example 1.

[0030] (4) Same as in Example 1.

[0031] Example 3 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) 1 mol of polytrimethylene ether glycol was placed in a reaction vessel and vacuum dehydrated at 130 °C for 4 h. After dehydration, the reaction vessel was placed under a nitrogen atmosphere and 3 mol of dicyclohexylmethane-4,4'-diisocyanate, 50 mL of N,N-dimethylacetamide (DMAc) and stannous octoate catalyst (added at 0.1 wt% of the total final polyurethane amount) were added. After stirring evenly, the prepolymerization reaction was carried out at 60 °C (corresponding to sample 7) and 120 °C (corresponding to sample 8) for 6 h to obtain polyurethane prepolymer.

[0032] (2) Same as in Example 1.

[0033] (3) Same as in Example 1.

[0034] (4) Same as in Example 1.

[0035] Example 4 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) 1 mol of polytrimethylene ether glycol was placed in a reaction vessel and vacuum dehydrated at 130 °C for 4 h. After dehydration, the reaction vessel was placed under a nitrogen atmosphere and 3 mol of dicyclohexylmethane-4,4'-diisocyanate, 50 mL of N,N-dimethylacetamide (DMAc) and stannous octoate catalyst (added at 0.1 wt% of the total final polyurethane amount) were added. After stirring evenly, the prepolymerization reaction was carried out at 100 °C for 1 h (corresponding to sample 9) and 12 h (corresponding to sample 10) to obtain polyurethane prepolymer.

[0036] (2) Same as in Example 1.

[0037] (3) Same as in Example 1.

[0038] (4) Same as in Example 1.

[0039] Table 1. Strength, elongation at break, and electrical conductivity tests of samples obtained in Examples 1-4 (Note: The test methods for strength and elongation at break are based on GB / T 14344-2022, and the test methods for electrical conductivity are based on GB / T 14342-2015.) Example 5 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0040] (2) Cool the above prepolymer to 30 °C (corresponding to sample 11), 50 °C (corresponding to sample 12), and 90 °C (corresponding to sample 13), and add 1 mol of chain extender 2,5-furandicarboxyhydrazide (FDHA) and 1 mol of 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]). Depending on the viscosity of the reaction system, add an appropriate amount of solvent N,N-dimethylacetamide and continue the reaction for 8 h to complete the chain extension. After the reaction is completed, dry at 60 °C for 24 h to remove the solvent in the system and obtain the intrinsically conductive polyurethane material.

[0041] (3) Same as in Example 1.

[0042] (4) Same as in Example 1.

[0043] Example 6 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0044] (2) Cool the above prepolymer to 60 °C, add 1 mol of chain extender 2,5-furandicarboxyhydrazide (FDHA) and 1 mol of 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]), and add an appropriate amount of solvent N,N-dimethylacetamide according to the viscosity of the reaction system. Continue the reaction for 1 h (corresponding to sample 14) or 12 h (corresponding to sample 15) to complete the chain extension. After the reaction is completed, dry at 60 °C for 24 h to remove the solvent in the system and obtain the intrinsic conductive polyurethane material.

[0045] (3) Same as in Example 1.

[0046] (4) Same as in Example 1.

[0047] Table 2. Strength, elongation at break, and electrical conductivity tests of samples obtained in Examples 5 and 6 (Note: The test methods for strength and elongation at break are based on GB / T 14344-2022, and the test methods for electrical conductivity are based on GB / T 14342-2015.) Example 7 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) 1 mol of polytrimethylene ether glycol was placed in a reaction vessel and vacuum dehydrated at 130 °C for 4 h to completely remove the moisture from the raw materials. After dehydration, the reaction vessel was placed under a nitrogen atmosphere and dicyclohexylmethane-4,4'-diisocyanate (HMDI), 50 mL of N,N-dimethylacetamide (DMAc), and stannous octoate catalyst (added at 0.1 wt% of the final total polyurethane amount) were added. After stirring evenly, the prepolymerization reaction was carried out at 100 °C for 6 h to obtain the polyurethane prepolymer. The amount of HMDI was adjusted to 1 mol (corresponding to sample 16), 2 mol (corresponding to sample 17), or 4 mol (corresponding to sample 18).

[0048] (2) Same as in Example 1.

[0049] (3) Same as in Example 1.

[0050] (4) Same as in Example 1.

[0051] Example 8 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0052] (2) The prepolymer was cooled to 60 °C, and chain extender 2,5-furandicarboxyhydrazide (FDHA) and 1 mol of 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]) were added. Depending on the viscosity of the reaction system, an appropriate amount of solvent N,N-dimethylacetamide was added, and the reaction was continued for 8 h to complete the chain extension. After the reaction was completed, the system was dried at 60 °C for 24 h to remove the solvent and obtain the intrinsically conductive polyurethane material. The amount of FDHA was adjusted to 0.25 mol (corresponding to sample 19), 0.5 mol (corresponding to sample 20), 1.5 mol (corresponding to sample 21), or 2 mol (corresponding to sample 22).

[0053] (3) Same as in Example 1.

[0054] (4) Same as in Example 1.

[0055] Example 9 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0056] (2) Cool the prepolymer to 60 °C, add 1 mol of chain extender 2,5-furandicarboxyhydrazide (FDHA) and 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]), and add an appropriate amount of solvent N,N-dimethylacetamide according to the viscosity of the reaction system. Continue the reaction for 8 h to complete the chain extension. After the reaction is completed, dry at 60 °C for 24 h to remove the solvent in the system and obtain the intrinsically conductive polyurethane material. Adjust the amount of [DiHEIm][Tf2N] to 0.25 mol (corresponding to sample 23), 0.75 mol (corresponding to sample 24), 1.5 mol (corresponding to sample 25) or 2 mol (corresponding to sample 26).

[0057] (3) Same as in Example 1.

[0058] (4) Same as in Example 1.

[0059] Example 10 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) 1 mol of polytrimethylene ether glycol was placed in a reaction vessel and vacuum dehydrated at 130 °C for 4 h to completely remove the moisture from the raw materials. After dehydration, the reaction vessel was placed under a nitrogen atmosphere and 3 mol of dicyclohexylmethane-4,4'-diisocyanate (HMDI), 50 mL of N,N-dimethylacetamide (DMAc), and a catalyst (0.1 wt% of the final total polyurethane amount) were added. After stirring evenly, the prepolymerization reaction was carried out at 100 °C for 6 h to obtain the polyurethane prepolymer. The catalyst type was adjusted to be dibutyltin dilaurate (corresponding to sample 27), tetrabutyl titanate (corresponding to sample 28), bismuth neodecanoate (corresponding to sample 29), triethylenediamine (corresponding to sample 30), or trimethylbenzylamine (corresponding to sample 31).

[0060] (2) Same as in Example 1.

[0061] (3) Same as in Example 1.

[0062] (4) Same as in Example 1.

[0063] Table 3. Strength, elongation at break, and electrical conductivity tests of samples obtained in Examples 7-10 (Note: The test methods for strength and elongation at break are based on GB / T 14344-2022, and the test methods for electrical conductivity are based on GB / T 14342-2015.) Example 11 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0064] (2) Same as in Example 1.

[0065] (3) Dissolve the obtained intrinsically conductive polyurethane material in N,N-dimethylacetamide to prepare a polyurethane spinning solution with a concentration of 10 wt% (corresponding to sample 32) or 40 wt% (corresponding to sample 33); add 2 wt% (relative to the polyurethane material) of magnesium chloride to the spinning solution and stir thoroughly to form a complex with the polyurethane chain segments to obtain a polyurethane spinning solution with metal ion complex.

[0066] (4) Same as in Example 1.

[0067] Example 12 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0068] (2) Same as in Example 1.

[0069] (3) Dissolve the obtained intrinsically conductive polyurethane material in N,N-dimethylacetamide to prepare a polyurethane spinning solution with a concentration of 20 wt%; add a metal salt with a mass fraction of 2 wt% (relative to the polyurethane material) to the spinning solution, stir and mix thoroughly to form a complex with the polyurethane chain segments, and obtain a polyurethane spinning solution with metal ion complex.

[0070] The metal salts selected were sodium chloride (corresponding to sample 34), zinc chloride (corresponding to sample 35), aluminum chloride (corresponding to sample 36), copper chloride (corresponding to sample 37), and ferric chloride (corresponding to sample 38).

[0071] (4) Same as in Example 1.

[0072] Example 13 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0073] (2) Same as in Example 1.

[0074] (3) Dissolve the obtained intrinsically conductive polyurethane material in N,N-dimethylacetamide to prepare a polyurethane spinning solution with a concentration of 10 wt% (corresponding to sample 32) or 40 wt% (corresponding to sample 33); add magnesium chloride with a mass fraction of 1 wt% (corresponding to sample 39) or 5 wt% (corresponding to sample 40) (relative to the polyurethane material) to the spinning solution, stir and mix thoroughly to form a complex with the polyurethane chain segments, and obtain a polyurethane spinning solution with metal ion complex.

[0075] (4) Same as in Example 1.

[0076] Example 14 In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Same as in Example 1, except that the vacuum dehydration treatment temperature is 130 °C and the time is 4 h.

[0077] (2) Same as in Example 1.

[0078] (3) Same as in Example 1.

[0079] (4) The polyurethane spinning solution complexed with the above metal ions is loaded into a needle tube and squeezed into the coagulation bath water at a uniform speed through the spinning needle to solidify and form nascent polyurethane fibers; the nascent polyurethane fibers are placed in a freeze-drying device and freeze-dried at -40℃ for 12 h (corresponding to sample 41) or 72 h (corresponding to sample 42) to finally obtain super-strong and super-tough polyurethane conductive fibers with uniform pore structure.

[0080] Example 15 (Optimal Conditions) In this embodiment, polyurethane conductive fibers are prepared according to the following steps: (1) Place 1 mol of polytrimethylene ether glycol in a reaction vessel and dehydrate it under vacuum at 130 °C for 4 h to completely remove the moisture from the raw materials. After dehydration, place the reaction vessel under a nitrogen atmosphere and add 3 mol of dicyclohexylmethane-4,4'-diisocyanate, 50 mL of N,N-dimethylacetamide (DMAc) and stannous octoate catalyst (0.1 wt% of the total final polyurethane). After stirring evenly, carry out a prepolymerization reaction at 100 °C for 6 h to obtain the polyurethane prepolymer.

[0081] (2) Cool the above prepolymer to 60 °C, add 1 mol of chain extender 2,5-furandicarboxyhydrazide (FDHA) and 1 mol of 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]), and add an appropriate amount of solvent N,N-dimethylacetamide according to the viscosity of the reaction system. Continue the reaction for 8 h to complete the chain extension. After the reaction is completed, dry at 60 °C for 24 h to remove the solvent in the system and obtain the intrinsic conductive polyurethane material.

[0082] (3) Dissolve the obtained intrinsically conductive polyurethane material in N,N-dimethylacetamide to prepare a polyurethane spinning solution with a concentration of 20 wt%; add magnesium chloride with a mass fraction of 2 wt% (relative to the polyurethane material) to the spinning solution, stir and mix thoroughly to form a complex with the polyurethane chain segments to obtain a polyurethane spinning solution with metal ion complex.

[0083] (4) The polyurethane spinning solution with metal ions complexed above is loaded into a needle tube and squeezed into the coagulation bath water at a uniform speed through the spinning needle. The nascent polyurethane fiber is obtained by coagulation and molding. The nascent polyurethane fiber is placed in a freeze-drying device and freeze-dried at -40℃ for 36 h to finally obtain a super-strong and super-tough polyurethane conductive fiber with a uniform pore structure (corresponding to sample 43).

[0084] Comparative Example 1 This comparative example prepared polyurethane conductive fibers according to the following steps: (1) 1 mol of polytrimethylene ether glycol was placed in a reaction vessel and vacuum dehydrated at 130 °C for 4 h. After dehydration, the reaction vessel was placed under a nitrogen atmosphere and 3 mol of dicyclohexylmethane-4,4'-diisocyanate, 50 mL of N,N-dimethylacetamide (DMAc) and stannous octoate catalyst (added at 0.1 wt% of the total final polyurethane amount) were added. After stirring evenly, the prepolymerization reaction was carried out at 100 °C for 6 h to obtain polyurethane prepolymer.

[0085] (2) Cool the above prepolymer to 60°C and add 2 mol of chain extender 1,3-di(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide ([DiHEIm][Tf2N]). Depending on the viscosity of the reaction system, add an appropriate amount of solvent N,N-dimethylacetamide and continue the reaction for 8 h to complete the chain extension. After the reaction is completed, dry at 60°C for 24 h to remove the solvent in the system and obtain the intrinsically conductive polyurethane material.

[0086] (3) Dissolve the obtained intrinsically conductive polyurethane material in N,N-dimethylacetamide to prepare a polyurethane spinning solution with a concentration of 20 wt%; add magnesium chloride with a mass fraction of 2 wt% (relative to the polyurethane material) to the spinning solution, stir and mix thoroughly to form a complex with the polyurethane chain segments to obtain a polyurethane spinning solution with metal ion complex.

[0087] (4) The polyurethane spinning solution complexed with the above metal ions is loaded into a needle tube and squeezed into the coagulation bath water at a uniform speed through the spinning needle. The nascent polyurethane fiber is then solidified and formed. The nascent polyurethane fiber is placed in a freeze-drying device and freeze-dried at -40℃ for 36 h to finally obtain polyurethane conductive fiber.

[0088] Comparative Example 2 This comparative example prepares polyurethane conductive fibers using the same steps as comparative example 1, except that the chain extender added in step (2) is 2 mol 2,5-furandicarboxyhydrazide.

[0089] Comparative Example 3 This comparative example prepares polyurethane conductive fibers using the same steps as comparative example 1, except that the chain extender added in step (2) is 2 mol polytetrahydrofuran diol.

[0090] Table 4. Variables for Examples 11-13 and Comparative Examples 1-3: Strength, Elongation at Break, and Conductivity Tests (Note: The test methods for strength and elongation at break are based on GB / T 14344-2022, and the test methods for electrical conductivity are based on GB / T 14342-2015.) This invention systematically investigates the influence of various process parameters on the mechanical properties (strength, elongation at break) and electrical properties (conductivity) of polyurethane conductive fibers through a series of embodiments and comparative experiments, and further demonstrates the strain sensing application performance of the final product. The experimental data from Examples 1-14 and Comparative Examples 1-3 are comprehensively analyzed as follows: 1. The Influence of Dewatering Process Parameters on Fiber Properties Experimental results show that the fibers prepared under vacuum dehydration conditions of 130℃ and 4h for polytrimethylene ether glycol (PO3G) exhibit the best overall performance, with sample 43 achieving a strength of 52.75 MPa, an elongation at break of 1414.58%, and an electrical conductivity of 2.08 × 10⁻⁶ MPa. -4 S·cm -1 If the dehydration temperature is too low or the dehydration time is too short, the moisture in the raw material will not be removed sufficiently, which will interfere with the smooth progress of subsequent prepolymerization and chain extension reactions, ultimately leading to a significant decrease in fiber performance. If the dehydration temperature is too high or the dehydration time is too long, the effect on improving fiber performance will be limited, and it may even cause the raw material to degrade, thereby damaging the mechanical and electrical properties of the fiber.

[0091] 2. Influence of prepolymerization process parameters on fiber properties The optimal conditions for the prepolymerization reaction are a prepolymerization temperature of 100℃ and a prepolymerization time of 6 hours. If the prepolymerization temperature is too low, the reactivity is insufficient, leading to incomplete prepolymerization and severe deterioration of the fiber's mechanical and electrical properties. If the prepolymerization temperature is too high, side reactions are easily triggered, damaging the polymer chain structure and affecting the overall fiber performance. Regarding the prepolymerization time, 1 hour is severely insufficient to form a stable prepolymer structure. Extending the prepolymerization time to 6 hours significantly improves fiber performance. Further extending the prepolymerization time results in a gradual improvement in fiber performance, indicating that 6 hours is sufficient for complete prepolymerization.

[0092] 3. The Influence of Chain Extension Process Parameters on Fiber Properties The optimal temperature for the chain extension reaction is 60℃, at which the fiber's strength, toughness, and electrical conductivity all reach their peak values. If the chain extension temperature is too low (30~50℃), the reactivity is insufficient, the chain extension reaction is incomplete, and the fiber performance is poor. If the chain extension temperature is too high, side reactions may occur, or the ionic liquid chain extender may decompose, resulting in a significant decrease in the fiber's mechanical properties. An extension time of 8 hours is ideal, at which point excellent overall fiber performance can be obtained. If the chain extension time is too short, the reaction is incomplete, and the fiber performance is poor. Extending the chain extension time to 12 hours results in fiber performance that is essentially equivalent to that of 8 hours, indicating that 8 hours is sufficient for a complete chain extension reaction.

[0093] 4. The effect of raw material ratio on fiber properties (1) Dosage of 2,5-furandicarboxyhydrazide (FDHA): With the increase of FDHA dosage, the fiber strength showed a significant upward trend, but the elongation at break dropped sharply after the molar ratio of FDHA to PO3G exceeded 1:1. This is because the strong hydrogen bonds and aromatic heterocyclic structures in the FDHA molecule can effectively enhance the material stiffness and improve the fiber strength, but excessive FDHA will destroy the flexibility of the polymer chain segments, resulting in a decrease in fiber elasticity and toughness. In summary, a good balance between fiber strength and toughness can be achieved when the molar ratio of FDHA to PO3G is controlled between 0.5:1 and 1:1.

[0094] (2) Dosage of ionic liquid chain extender ([DiHEIm][Tf2N]): With the increase of the dosage of ionic liquid chain extender, the conductivity of the material shows a monotonically increasing trend, from 0.89×10 -4 S·cm -1 Increased to 5.01×10 -4 S·cm -1 The reason is that the addition of ionic liquid provides more mobile ions to the fiber, improving its conductivity. The mechanical properties of the fiber (strength, elongation at break) reach their optimal level when the amount of ionic liquid is 1~1.5 mol. When the amount exceeds 1.5 mol, the excessive ionic liquid may disrupt the microphase separation structure of the polyurethane chain segments, leading to a decrease in the fiber's mechanical properties. This indicates that there is a certain trade-off between the fiber's conductivity and mechanical properties, and the amount of ionic liquid can be adjusted according to the actual application requirements.

[0095] (3) Dosage of dicyclohexylmethane-4,4'-diisocyanate (HMDI): Based on experimental data, when the molar ratio of HMDI to PO3G is controlled at 2~3 mol, the overall performance of the fiber is better. When the molar ratio is 3 mol, the toughness and conductivity of the fiber are more prominent.

[0096] 5. The effect of catalyst type on fiber properties Different types of catalysts have significantly different effects on the overall properties of fibers. Among them, fibers prepared with organotin catalysts (stannous octoate, dibutyltin dilaurate) and titanate catalysts (tetrabutyl titanate) exhibit better overall properties, with stannous octoate showing the best catalytic effect, effectively promoting the smooth progress of prepolymerization and chain extension reactions, and endowing the fibers with excellent mechanical and electrical properties. Fibers prepared with bismuth catalysts (bismuth neodecanoate) and amine catalysts (triethylenediamine, trimethylbenzylamine) show poor performance in terms of toughness or strength, failing to meet the requirements for ultra-strong and ultra-tough performance.

[0097] 6. Effects of spinning solution concentration and metal ion parameters on fiber properties (1) Spinning solution concentration: When the polyurethane spinning solution concentration is 20 wt%, the fiber has the best overall performance. Too low a concentration (10 wt%) will result in a non-dense structure and reduced strength after fiber forming. Too high a concentration (30~40 wt%) will result in excessive viscosity of the spinning solution, which will affect the spinning forming effect and destroy the internal pore structure of the fiber, leading to a decrease in the mechanical and electrical properties of the fiber.

[0098] (2) Types and amounts of metal ions: When 2 wt% of magnesium chloride, ferric chloride, copper chloride, and zinc chloride were added to the spinning solution, the fibers all exhibited good overall performance. Among them, magnesium chloride showed a balanced and outstanding performance in improving fiber strength and conductivity, making it the optimal metal ion choice. There is an optimal value (2 wt%) for the amount of metal ions added. When the amount added is too low (1 wt%), the complexation effect between the metal ions and the polyurethane segments is insufficient, and it is impossible to effectively induce the microphase separation of the polyurethane segments, resulting in poor fiber performance. When the amount added is too high (3~5 wt%), excessive metal ions will destroy the polymer bulk structure, becoming defect points inside the fiber, leading to a decrease in fiber mechanical properties.

[0099] 7. Comparative Experimental Analysis Comparative Example 1 (using only ionic liquid chain extenders): The prepared fibers had extremely low strength (only 12.36 MPa), although they had the highest electrical conductivity (6.62 × 10⁻⁶ MPa). -4 S·cm -1 However, lacking the strong hydrogen bond network and π-π stacking effect provided by FDHA, the mechanical properties of the material are severely insufficient and it has no practical application value, indicating that a single ionic liquid chain extender cannot achieve a synergistic improvement in fiber strength, toughness and conductivity.

[0100] Comparative Example 2 (using only FDHA chain extender): The prepared fiber has extremely high strength and toughness (strength 68.51 MPa, elongation at break 1563.62%), but electrical conductivity is 0, which confirms the key enhancing effect of FDHA on the mechanical properties of the fiber, and also shows that ionic liquid chain extender is a necessary component to endow the fiber with intrinsic conductivity.

[0101] Comparative Example 3 (using common chain extender polytetrahydrofuran diol): The prepared fibers had extremely poor strength and toughness (strength 8.91 MPa, elongation at break 195.36%), and no electrical conductivity.

[0102] This result contrasts sharply with the embodiments of the present invention, highlighting the crucial necessity of the synergistic effect of FDHA (responsible for toughening) and ionic liquid chain extender (responsible for conductivity) in the present invention. Both are indispensable and together achieve the synergistic performance of polyurethane conductive fibers in terms of ultra-strong and ultra-toughness and stable conductivity.

[0103] Figure 1The diagram shows the chemical structure and 1H NMR spectrum of sample 43. This polyurethane uses polytrimethylene ether glycol (PO3G) as the soft segment and dicyclohexylmethane-4,4'-diisocyanate (HMDI) as the hard segment linking unit, and is prepared through synergistic chain extension of FDHA and [DiHEIm][Tf2N]. The structure clearly reveals the chemical composition of the polyurethane segments and the connection mode between each unit, directly confirming that FDHA and [DiHEIm][Tf2N] have been successfully integrated into the polymer backbone. This achieves the simultaneous construction of a strong hydrogen bond network (FDHA) and ion-conducting channels (ionic liquid), providing a clear molecular structural basis for the subsequent superior mechanical properties and stable electrical conductivity exhibited by the fiber.

[0104] Figure 2 The infrared spectrum of sample 43 clearly shows the absorption peaks of various characteristic functional groups in the polyurethane molecular chain: the NH stretching vibration peak confirms the formation of urethane bonds, and the peak broadening and redshift characteristics directly indicate the presence of strong hydrogen bond interactions provided by FDHA within the material; the C=O stretching vibration peak corresponds to the urethane carbonyl group, and its absorption characteristics further verify the successful reaction between the prepolymer and the chain extender; the COC stretching vibration peak corresponds to the ether bond structure of the soft segment of polytrimethylene ether glycol, proving that the soft segment is completely retained in the polymer chain.

[0105] Figure 3 The image shows the cross-sectional microstructure of sample 43. As shown, the fiber exhibits a uniform and well-developed hierarchical porous structure, consisting of centrally radiating macropores and densely packed micropores around the periphery. This unique porous structure is the core structural basis for the fiber of this invention to achieve a synergistic effect of "high strength, high toughness, and stable conductivity".

Claims

1. A method for preparing ultra-strong and ultra-tough polyurethane conductive fibers by wet spinning-freeze drying, characterized in that, The method involves complexing polyurethane segments with metal ions to promote microphase separation of polyurethane segments, followed by wet spinning and freeze-drying to ultimately form polyurethane conductive fibers with a uniform pore structure. The method specifically includes the following steps: (1) Polytrimethylene ether glycol is subjected to vacuum dehydration treatment, and then dicyclohexylmethane-4,4'-diisocyanate, N,N-dimethylacetamide and catalyst are added to the dehydrated polytrimethylene ether glycol under heating and nitrogen atmosphere. The reaction is carried out until the system reaches the preset degree of polymerization to obtain polyurethane prepolymer. (2) Add bio-based 2,5-furandicarboxyhydrazide and ionic liquid 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide as synergistic chain extenders to the prepolymer obtained in step (1), carry out chain extension reaction under heating conditions, and dry to remove solvent after the reaction to obtain intrinsically conductive polyurethane material. (3) The intrinsically conductive polyurethane material obtained in step (2) is prepared into a polyurethane spinning solution, and then metal ions are added to the spinning solution and mixed thoroughly with the polyurethane material to form a polyurethane spinning solution with metal ion complexation. (4) The polyurethane spinning solution with metal ion complexation obtained in step (3) is squeezed into the coagulation bath through a spinning needle to form nascent polyurethane fiber; the nascent polyurethane fiber is freeze-dried to obtain super-strong and super-tough polyurethane conductive fiber with uniform pore structure.

2. The preparation method according to claim 1, characterized in that, In step (1): the temperature of the vacuum dehydration treatment is 100~140 ℃ and the dehydration time is 1~6 h; the heating temperature is 60~140 ℃ and the reaction time is 1~12 h.

3. The preparation method according to claim 1, characterized in that, In step (2), the chain extension reaction is carried out at a temperature of 30~90 ℃ and for a reaction time of 1~12 h.

4. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the polyurethane spinning solution is 10-40 wt%, and the amount of metal ions added is 1-5 wt% of the intrinsically conductive polyurethane material.

5. The preparation method according to claim 1, characterized in that, In step (4), the freeze-drying time is 12~72 h.

6. The preparation method according to claim 1, characterized in that, In steps (1) and (2), the molar ratios of the raw materials are as follows: the molar ratio of polytrimethylene ether glycol to dicyclohexylmethane-4,4'-diisocyanate is 1:1~4; the molar ratio of polytrimethylene ether glycol to bio-based 2,5-furandicarboxyhydrazide is 1:0.25~2; and the molar ratio of polytrimethylene ether glycol to 1,3-bis(2-hydroxyethyl)imidazolium bis(trifluoromethanesulfonyl)imide is 1:0.25~2.

7. The preparation method according to claim 1, characterized in that, The catalyst is selected from one of dibutyltin dilaurate, stannous octoate, tetrabutyl titanate, bismuth neodecanoate, triethylenediamine, and trimethylbenzylamine.

8. The preparation method according to claim 1, characterized in that, The metal ion is selected from one of sodium chloride, zinc chloride, magnesium chloride, aluminum chloride, copper chloride, and ferric chloride.

9. A super-strong and super-tough polyurethane conductive fiber obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the ultra-strong and ultra-tough polyurethane conductive fiber as described in claim 9 in the fields of flexible electronics, national defense and military industry, aerospace or humanoid robots.

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