Highly elastic polyurethane fiber and its spinning process

Abstract

The present application relates to the technical field of polyurethane fiber preparation, in particular to a high-elasticity polyurethane fiber and a spinning process thereof.The present application overcomes the technical problem in the prior art that polyurethane fibers cannot simultaneously have high strength elasticity and long-term anti-aging effect.The present application uses polytetrahydrofuran ether glycol and polycarbonate glycol as soft segments, 4,4'-diphenyl methane diisocyanate as hard segment basis, and through step-by-step reaction, covalently bonds modified nanocrystals, diamine containing dynamic disulfide bond and active amine with hindered amine structure to the polyurethane macromolecular main chain;and combines a dry spinning forming process of three-temperature-zone gradient drying.The polyurethane fiber obtained by the present application forms endogenous anti-oxidation defense, dynamic stress self-adaptive dissipation and multi-functional group enhancement, prevents the migration and precipitation of anti-aging agents, and at the same time improves the ultimate tensile resilience, realizes excellent ultraviolet resistance and water washing yellowing resistance, and meets the application requirements of high-end high-speed weaving.

Description

Technical Field

[0001] This invention relates to the field of polyurethane fiber preparation technology, specifically to a high-elasticity polyurethane fiber and its spinning process. Background Technology

[0002] In the field of high-end textile manufacturing, the performance of elastic yarns directly determines the quality and lifespan of fabrics. Taking air-jet weaving as an example, during the ultra-high-speed weft insertion process, the yarn needs to withstand extremely high-frequency alternating tension and intense mechanical friction. If the initial modulus of polyurethane fibers is insufficient or their fatigue resistance is poor, breakage, stress relaxation, and uneven tension are likely to occur during weaving, seriously affecting the smoothness of the fabric surface. In applications such as sports compression garments and medical compression protective clothing, not only is a durable high-elasticity wrapping feel required, but the fabric also faces more stringent weather resistance challenges, including erosion from human sweat, exposure to high-intensity ultraviolet radiation outdoors, and frequent daily washing.

[0003] However, existing single-component polyurethane fibers struggle to balance elasticity and long-lasting anti-aging properties. Traditional polyurethane elastomers typically use polytetrahydrofuran ether diol as the soft segment. While this structure imparts good resilience to the fiber, the ether bonds in its main chain are highly susceptible to photo-oxidative and thermo-oxidative degradation. Furthermore, to improve aging resistance, the conventional approach is to physically add antioxidants and UV absorbers to the spinning solution. However, these small-molecule additives are prone to leaching and loss during spinning, dyeing, and especially long-term washing of the fabric, leading to a significant decrease in anti-aging efficacy. Existing technologies attempt to graft high-molecular-weight hindered amines and other anti-aging groups onto the polyurethane main chain through chemical copolymerization. However, the significant steric hindrance effect disrupts the originally regular hydrogen bond network of the polyurethane hard segment microregions. This loosening of the molecular chain directly leads to a deterioration in the degree of fiber phase separation, macroscopically manifested as a decrease in initial fiber strength and severe irreversible plastic deformation after repeated stretching.

[0004] In summary, existing technologies have effectively improved the strength of polyurethane fibers by adding modified substances and optimizing the spinning process. However, there is still a technical problem that the high strength and elasticity of polyurethane fibers cannot be simultaneously achieved with long-term anti-aging properties.

[0005] Therefore, a highly elastic polyurethane fiber and its spinning process are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a high-elasticity polyurethane fiber and its spinning process. This invention overcomes the technical problem in existing polyurethane fibers that cannot simultaneously achieve high strength and elasticity while maintaining long-term anti-aging properties. This invention uses polytetrahydrofuran ether diol and polycarbonate diol as soft segments, and 4,4'-diphenylmethane diisocyanate as the hard segment base. Through a stepwise reaction, modified nanocrystals, diamines containing dynamic disulfide bonds, and active amines with hindered amine structures are covalently bonded to the polyurethane macromolecular backbone. This is combined with a dry spinning process using a three-temperature gradient drying method. The polyurethane fiber obtained by this invention exhibits endogenous antioxidant defense, dynamic stress adaptive dissipation, and multifunctional group reinforcement, preventing the migration and precipitation of antioxidants. While improving ultimate tensile resilience, it also achieves excellent UV resistance and anti-yellowing properties after washing, meeting the application requirements of high-end high-speed weaving.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a spinning process for highly elastic polyurethane fibers, comprising the following preparation steps: 72-78 parts by weight of polytetrahydrofuran ether diol and 22-28 parts by weight of polycarbonate diol are placed in a vacuum drying oven and dried at 100°C for 10 hours to obtain dried raw materials. These are then added to a reaction vessel, followed by the addition of 20.2-21.8 parts by weight of 4,4'-diphenylmethane diisocyanate. The mixture is stirred and reacted at a constant temperature of 80-90°C for 90-150 minutes under nitrogen protection. The temperature is then lowered to 40-50°C, and N,N-dimethylacetamide is added to obtain a prepolymer solution with a solid content of 40%-50%. 1.2-2.3 parts by weight of modified nanocrystals are pre-dispersed in 15-25 parts by weight of N,N-dimethylacetamide, and the mixture is then stirred at 5... Under pressure of 0-100 MPa, and with cooling in an ice-water bath (controlling the system temperature to below 25℃), homogenize by circulation for 20-40 min to obtain a mixture; add 0.45-0.75 parts of 2,2'-dithiodiethylamine and 0.55-1.15 parts of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine to the mixture, and stir at 300-500 rpm for 10-20 min to obtain a homogeneous mixture; slowly add the mixture dropwise to the prepolymer solution, setting the stirring speed to 600-1000 rpm, controlling the dropwise addition time to 20-40 min, and keep stirring at the temperature for 45 min to obtain a chain-extended system; ethyl... 1.45-1.75 parts of diamine and 0.1-0.2 parts of diethylamine are dissolved in 10-20 parts of N,N-dimethylacetamide. The mixture is shear-dropped into the first-stage chain extension system at 1200-1800 r / min. The second-stage chain extension is added over 10-20 min, with the maximum system temperature controlled to not exceed 45℃. The mixture is stirred at this temperature for 30 min, at which point the isocyanate absorption peak disappears on infrared monitoring. N,N-dimethylacetamide is then added to adjust the solid content to 30%-35%, and the mixture is aged at 35-45℃ for 20-30 h. The mixture is then filtered through a 200-300 mesh metal filter and degassed under a vacuum of -0.08 to -0.10 MPa for 4-8 h to obtain a viscous solution at 40℃. The spinning solution has a temperature of 800-1200 Pa·s. During the spinning process, a slightly positive pressure nitrogen gas circulation is maintained in the channel to ensure that the solvent vapor concentration is less than 25% of the lower explosive limit. The spinning solution is heated to 65-75℃ and extruded through a spinneret into a three-temperature zone channel. The upper zone temperature is set at 320-340℃, the middle zone at 235-255℃, and the lower zone at 155-175℃. Then, it is wound by a downward-flowing hot air flow, with the side air temperature at 200-240℃ and the side air velocity at 0.3-0.8 m / s. The winding speed is 700-900 m / min, the winding stretch ratio is 1.1-1.3, and the winding temperature is 40-60℃. The polyurethane fiber is then obtained by winding.

[0008] In this invention, when the molar ratio R of isocyanate groups to hydroxyl groups is less than 1.61, the prepolymer has a large molecular weight and high viscosity, and is prone to local gelation during cooling and dilution; when the R value is greater than 1.74, there is too much residual free -NCO, and the crosslinking density of the subsequent chain extension reaction is too high, resulting in a hard fiber modulus and a decrease in elongation at break.

[0009] In this invention, the soft segment glycol is a composite of polycarbonate glycol and polyether glycol. Utilizing the high cohesive energy and stable carbonate bonds of polycarbonate, it effectively compensates for the chemical defects of pure ethers, which are prone to photo-oxidative degradation. This achieves a synergistic interaction between weather resistance and basic mechanical strength at the molecular skeleton level. The functionalized main chain extender N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine chemically bonds its hindered amine structure to the polyurea microregions of the polyurethane main chain, preventing the easy migration of traditional physical blending additives during washing or at high temperatures, thus achieving long-lasting antioxidant performance and water resistance. Furthermore, this invention introduces 2,2'-dithiodiethylamine for polymerization, endowing the hard segment of the polyurethane with dynamic covalent disulfide bonds. When the fiber is under high strain tension, these disulfide bonds can effectively dissipate the locally concentrated huge stress through a stimulated dynamic fracture and recombination mechanism, preventing irreversible physical damage to the hard segment microregion network. The process employs a stepwise mixing and chain extension technique. Utilizing the differences in steric hindrance and reactivity among various amines, and through time difference and temperature control, amines with high steric hindrance and low reactivity are preferentially allowed to fully react and anchor with the prepolymer molecular chain ends under mild, low-shear conditions. Subsequently, highly reactive ethylenediamine is used for end-capping to complete the molecular weight increase, preventing the high-reactivity monomer from reacting too quickly, which could lead to the inability to graft the modified material and localized gelation of the original solution. In this invention, a three-temperature-zone gradient drying spinning process is used. The high temperature in the upper zone instantly vaporizes the polar solvent on the fiber surface to form a dense surface layer. The stable temperature in the middle zone, combined with the mechanical stretching force of the winding, promotes the high axial orientation of the matrix macromolecular chain segments and rigid nanofibers. The mild cooling in the lower zone provides an energy thermodynamic window for the rearrangement of dynamic disulfide bonds, allowing the residual internal stress generated by stretching to be eliminated before the macromolecular chain is finally solidified.

[0010] Preferably, the preparation of modified nanocrystals includes the following steps: dispersing 10 parts of cellulose nanocrystals in 400-600 parts of anhydrous N,N-dimethylformamide, sonicating at 400-600W for 20-40 min, adding 5 parts of 3-aminopropyltriethoxysilane, stirring and reacting at 75-85℃ under nitrogen protection for 10-14 h, centrifuging at 7000-9000 r / min for 10-20 min after reaction, washing alternately with anhydrous ethanol and deionized water 5 times, and freeze-drying under vacuum at -45 to -55℃ for 40-50 h to obtain modified nanocrystals; the finished product is a white to slightly yellow fluffy freeze-dried powder with an amino grafting rate of 2 mmol / g and a Zeta potential of 30 mV to 45 mV.

[0011] Modified nanocrystals utilize their own rigid, non-deformable geometric structure and surface-grafted amino groups as multifunctional cross-linking centers to capture and fix the loosely structured hard molecular chains due to the introduction of hindered amine steric groups during the reaction. Through the induced orientation crystallization mechanism at the microscopic interface, the elastic modulus of the matrix material is improved. At the same time, the introduction of cellulose effectively improves the aging resistance and mechanical strength of the fiber material.

[0012] The present invention also provides a highly elastic polyurethane fiber, the raw materials for which include polytetrahydrofuran ether diol, polycarbonate diol, 4,4'-diphenylmethane diisocyanate, modified nanocrystals, 2,2'-dithiodiethylamine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine and ethylenediamine.

[0013] Two 2.0 g samples of polyurethane fiber prepared in Example 1 and Comparative Example 3 of this invention were chopped and placed in a Soxhlet extractor. Using N,N-dimethylacetamide as a good solvent, extraction was performed continuously at 30°C for 48 h to fully dissolve and wash away free polymer chains that did not participate in micro-crosslinking or chemical bonding. After extraction, the insoluble gel / residue was centrifuged and washed three times alternately with anhydrous ethanol and deionized water. It was then freeze-dried under vacuum at -50°C for 24 h to obtain the extraction residue. The dried extraction residue was ultrasonically dispersed in anhydrous ethanol to form a uniform suspension with a concentration of 0.01 wt%. This suspension was then added dropwise onto an ultrathin carbon film copper grid using a microsyringe. After air-drying, its microstructure was observed using a transmission electron microscope with an accelerating voltage of 200 kV. Specifically, as shown... Figure 1 As shown; the dried extraction residue was mixed with fully dried KBr powder at a mass ratio of 1:100, thoroughly ground and compressed into tablets under infrared lamp irradiation, and the samples were analyzed using a Fourier transform infrared spectrometer at 4000-4000 cm⁻¹. -1 The scanning test was conducted within the wavenumber range, with a resolution set to 4cm. -1 A total of 32 scans were performed, and the test results are as follows: Figure 2 As shown.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the prior art, pure ether-based polyurethane soft segments are prone to ether bond breakage under long-term ultraviolet irradiation, leading to fiber pulverization and a decrease in mechanical strength. This invention uses a composite of polycarbonate diol and polytetrahydrofuran ether diol as the soft segment matrix. By introducing carbonate bonds with high cohesive energy and stable chemical properties, a tough defensive skeleton is constructed at the molecular level. This not only retains the excellent low-temperature flexibility imparted by the polyether segments, but also overcomes the technical bottleneck of photo-oxidative degradation, enabling the fiber to maintain high mechanical integrity even after long-term exposure to harsh outdoor environments.

[0015] 2. Conventional physical blending anti-aging agents tend to migrate to the surface and be lost during subsequent dyeing and finishing processes or frequent daily washing, leading to a rapid loss of the fabric's anti-aging function. This invention uses active amine monomers with hindered amine structures as main chain extenders to participate in polymerization, achieving durable antioxidant, yellowing-resistant, and wash-resistant properties. This chemical bonding mechanism directly incorporates hindered amine groups into the polyurea micro-network of the polyurethane hard segment, avoiding the release of anti-aging groups and endowing the fiber with an intrinsic antioxidant barrier, ensuring that the anti-aging defense performance remains stable after repeated high-temperature washing and mechanical friction.

[0016] 3. When existing elastic fibers are subjected to high-frequency tensile loads in practical applications, their traditional physical hydrogen bond network is prone to irreversible slippage and breakage, leading to fiber stress relaxation and permanent plastic deformation. This invention uses a diamine chain extender containing dynamic covalent disulfide bonds to crosslink with a macromolecular prepolymer, which improves the fiber's fatigue resistance and high elastic recovery ability under high strain conditions. The introduced disulfide bonds can be activated by mechanical force in stress concentration areas, dissipating destructive energy through a dynamic fracture and recombination mechanism. In addition, the macromolecular network completes adaptive rearrangement of the structure under deformation, giving the fiber the ability to rebound after multiple repeated deformations.

[0017] 4. Existing technologies inevitably weaken the regularity of hard-segment hydrogen bonds when introducing steric hindrance anti-aging groups, leading to loosening of molecular chains and deterioration of phase separation, resulting in a decrease in the initial modulus and strength of the fiber. This invention uses modified nanocrystals combined with stepwise mixing chain extension and multi-temperature gradient molding processes to strengthen the microscopic phase separation structure of the polymer and improve its structural stability. Stepwise chain extension transforms rigid nanocrystals into multifunctional crosslinking centers. Under the thermodynamic action of gradient drying, the rigid core induces the surrounding loose macromolecules to crystallize in a highly oriented manner along the fiber axis, avoiding mechanical damage caused by modification and achieving a balance between high elasticity and high strength. Attached Figure Description

[0018] Figure 1Transmission electron microscope images of the residues after extraction with a good solvent for Example 1 and Comparative Example 3; where (a) is Example 1; (b) is Comparative Example 3; Figure 2 Fourier transform infrared spectra of the residues after extraction with a good solvent in Example 1 and Comparative Example 3; Figure 3 The change rate of tensile strength of polyurethane fibers obtained in Embodiment 1 and Comparative Examples 1-7 of the present invention before and after ultraviolet aging and before and after heat setting. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The polytetrahydrofuran ether glycol used in this invention has a number-average molecular weight of 2000, a hydroxyl value of 56 mgKOH / g, a functionality of 2.0, and is a white waxy solid at room temperature; the polycarbonate glycol has a number-average molecular weight of 2000, a hydroxyl value of 56 mgKOH / g, and a viscosity of approximately 3000 mPa·s at 60°C; the cellulose nanocrystals have a length of 100-200 nm, a diameter of 5-20 nm, and a crystallinity >70%.

[0021] Please see Figures 1 to 3 This invention provides a high-elasticity polyurethane fiber and its spinning process, the technical solution of which is as follows: Example 1 Ten parts of cellulose nanocrystals were dispersed in 500 parts of anhydrous N,N-dimethylformamide and sonicated at 500W for 30 min. Five parts of 3-aminopropyltriethoxysilane were added and the mixture was stirred and reacted at 80℃ under nitrogen protection for 12 h. After the reaction, the mixture was centrifuged at 8000 r / min for 20 min and washed 5 times alternately with anhydrous ethanol and deionized water. The modified nanocrystals were obtained by vacuum freeze-drying at -50℃ for 40 h.

[0022] 75 parts of polytetrahydrofuran ether glycol and 25 parts of polycarbonate glycol were placed in a vacuum drying oven and dried at 100℃ for 10 h to obtain dried raw materials. These materials were then added to a reaction vessel, followed by 21.3 parts of 4,4'-diphenylmethane diisocyanate. The mixture was stirred at 85℃ for 120 min under nitrogen protection, and the NCO mass fraction was measured to be 2.44%. The mixture was then cooled to 40℃ and N,N-dimethylacetamide was added to obtain a prepolymer solution with a solid content of 45%. 1.5 parts of modified nanocrystals were pre-dispersed in 20 parts of N,N-dimethylacetamide and homogenized under 60 MPa pressure for 30 min to obtain a mixed solution. 0.6 parts of 2,2'-dithiodiethylamine and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)- 0.8 parts of 1,6-hexanediamine were stirred at 400 rpm for 15 minutes to obtain a homogeneous mixture. This mixture was then slowly added dropwise to the prepolymer solution at 800 rpm for 30 minutes. The mixture was then kept at this temperature and stirred for 45 minutes to obtain a first-stage chain-extended system, at which point the NCO mass fraction decreased to 1.87%. 1.6 parts of ethylenediamine and 0.15 parts of diethylamine were dissolved in 15 parts of N,N-dimethylacetamide and sheared dropwise at 1500 rpm to obtain a second-stage chain-extended system. The second-stage chain-extended system was added dropwise within 15 minutes, with the maximum system temperature controlled to not exceed 45°C. The mixture was kept at this temperature and stirred for 30 minutes. At this point, the residual NCO mass fraction was ≤0.05%, and the free amine value was ≤1.0%. mgKOH / g was added, and N,N-dimethylacetamide was added to adjust the solid content to 35%, then the mixture was aged at 40℃ for 25h. After filtration through a 300-mesh metal filter, the mixture was degassed under a vacuum of -0.095MPa for 6h to obtain the spinning solution. The spinning solution was heated to 70℃ and extruded through a spinneret into a three-temperature zone channel. The upper zone temperature was set at 330℃, the middle zone at 245℃, and the lower zone at 165℃. Then, hot air was blown from top to bottom, with a side blowing temperature of 220℃ and a side blowing speed of 0.5m / s. The winding speed was set at 800m / min, the winding stretch ratio was controlled at 1.2, and the winding temperature was set at 50℃. Finally, polyurethane fibers were obtained by winding.

[0023] Examples 2-5 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0024] Table 1. Parameter variations in Examples 1-5 Comparative Example 1 is the same as Example 1, except that 1,4-butanediol is used instead of amine chain extenders (including ethylenediamine, 2,2'-dithiodiethylamine and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine), while the rest of the process remains the same.

[0025] Comparative Example 2 is the same as Example 1, except that instead of using the three-temperature zone solution dry spinning process, a melt extrusion spinning process is used. Specifically, the solid content is not adjusted by N,N-dimethylacetamide, and the product is directly dried and then melted at 220°C. The screw extrusion speed is set to 150 r / min, and the product is directly wound after being cooled by air side blowing. The rest of the process remains unchanged.

[0026] Comparative Example 3 is the same as Example 1, except that no modified nanocrystals are added, while the rest of the process remains unchanged.

[0027] Comparative Example 4 is the same as Example 1, except that 2,2'-dithiodiethylamine is not added, but is replaced with ethylenediamine in equal molar amounts, while the rest of the process remains unchanged.

[0028] Comparative Example 5 is the same as Example 1, except that instead of using stepwise mixing chain extender, the amine chain extender is mixed and added dropwise to the prepolymer solution at one time, while the rest of the process remains the same.

[0029] Comparative Example 6 is the same as Example 1, except that the soft segment diol is 100 parts of polytetrahydrofuran ether diol and no polycarbonate diol is added, while the rest of the process remains the same.

[0030] Comparative Example 7 is the same as Example 1, except that N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine is not added, and its equimolar amount is replaced with ethylenediamine, while the rest of the process remains unchanged.

[0031] Combination Figure 1 As can be seen, the extraction residue of Example 1(a) exhibits a clear high aspect ratio rigid rod-like structure (corresponding to modified cellulose nanocrystals) under transmission electron microscopy. At the same time, a blurry polymer halo is clearly wrapped on the surface of the structure, which verifies that the modified nanocrystals use the amino groups grafted on their surface as multifunctional cross-linking centers to fix the polyurethane hard segment molecular chains. Even under the reflux of good solvent N,N-dimethylacetamide, the macromolecular chains tightly bonded to the interface cannot be detached. On the contrary, since no modified nanocrystals were added to Comparative Example 3, it lacks an indeformable rigid geometric structure as the core of the micro-interface cross-linking network. Its resistance to dissolution in good solvent is extremely poor. The remaining trace extract only shows an irregular, loose amorphous aggregate outline (b) under transmission electron microscopy and cannot maintain a stable multidimensional network morphology. Combination Figure 2 The spectral data, the extraction residue of Example 1 at 1055 cm⁻¹ -1 The vicinity exhibits a strong characteristic absorption peak belonging to the COC framework of cellulose nanocrystals; additionally, at 1705 cm⁻¹... -1 (Corresponding to the C=O stretching vibration of the carbamate / urea bond), 1530cm -1 (NH bending vibration) and 2920cm-1 At the (CH asymmetric stretching vibration) location, the characteristic peak of polyurethane is retained; while in Comparative Example 3, due to the complete dissolution and loss of its components, very little residue is missing at 1055 cm⁻¹. -1 The intensity of the characteristic peaks of nearby rigid particles, as well as the characteristic peaks related to polyurethane, also decreased.

[0032] Experimental Example 1: Mechanical Property Testing The polyurethane fibers prepared in Examples 1-5 and Comparative Examples 1-5 were subjected to mechanical property tests. Breaking strength, elongation at break, stress at 300% elongation, and elastic recovery at 300% elongation were tested according to FZ / T50006-2013 using a constant-speed elongation single-yarn tensile tester. The initial gauge length of the sample was set to 50 mm, and the stretching speed was 500 mm / min. When testing the breaking index, the fiber was stretched until breakage, and the maximum strength and elongation at break were recorded. When testing the elongation at 300%, the fiber was stretched to 300% elongation and then held at that point. Hold the clamp for 1 minute and record the stress value at this time. Then, return the clamp to its original position at the original speed and measure the residual elongation of the fiber that failed to recover to calculate the recovery rate. Perform multiple tensile fatigue plastic deformation rate tests according to FZ / T50006-2013. Specifically, on a single yarn strength tester, set the gauge length to 50 mm and perform 5 consecutive cycles of reciprocating tension at a speed of 500 mm / min between 0% and 300% elongation. After the 5th unloading, measure the permanent residual elongation of the fiber and calculate its percentage relative to the initial gauge length. The test results are shown in Table 2.

[0033] Table 2 Test results of the examples and comparative examples As shown in Table 2, the mechanical properties of the polyurethane fibers obtained in the comparative examples, through adjustments to the components and processes, differed significantly from those in the examples. In Comparative Example 1, 1,4-butanediol was used to replace the amine chain extender. The reaction of the polyol with isocyanate to form urethane bonds resulted in a lower hydrogen bond density and cohesive energy compared to the polyurea structure. This led to weak physical crosslinking points in the hard segment micro-regions, making the molecular chains prone to irreversible slippage under high strain, thus reducing the overall mechanical properties. In Comparative Example 2, melt extrusion spinning was used. The high-temperature melting environment caused partial thermal degradation of the chain extender containing dynamic disulfide bonds and hindered amine structures. Furthermore, the high viscosity melt hindered the uniform dispersion and orientation of the modified nanocrystals, resulting in residual thermal stress and microscopic defects within the fibers, manifesting as reduced elongation at break and poorer fatigue resistance. In Comparative Example 3, no modified nanocrystals were added, and the polyurethane matrix lacked its own rigid geometric structure and surface... The grafted amino groups, acting as multifunctional crosslinking centers, cannot capture and fix the loosened hard-segment molecular chains caused by the introduction of hindered amine steric hindrance groups during the reaction. The lack of an interface-induced orientation crystallization mechanism results in insufficient support for the matrix's elastic modulus. In Comparative Example 4, the polyurethane hard-segment network lacks dynamic covalent disulfide bonds. When the fiber is under high-strain repeated stretching, it cannot effectively dissipate the locally concentrated large stress through the stimulated dynamic fracture and recombination mechanism. Irreversible physical damage occurs in the hard-segment micro-network, leading to an increase in the plastic deformation rate during repeated tensile fatigue and a decrease in elastic recovery. In Comparative Example 5, the lack of stepwise mixing and chain extension prevents the use of the differences in steric hindrance and reactivity of various amine substances for time and temperature control. This results in the highly reactive ethylenediamine reacting too quickly, preventing the steric hindrance amine monomers from being effectively anchored and easily causing localized gelation of the original solution. This disrupts the uniformity of the macromolecular chains, leading to a significant decrease in various mechanical properties of the fiber.

[0034] Experiment Example 2: Anti-aging Performance Test The polyurethane fibers prepared in Examples 1-5 and Comparative Examples 1-7 were subjected to anti-aging performance tests. According to GB / T16422.3-2022, the polyurethane fiber samples were laid flat in an ultraviolet aging test chamber using a UVA-340 fluorescent lamp with an irradiance of 0.76 W / (m²·nm). The ultraviolet irradiation stage temperature was set at 60℃±3℃ for 8 hours, and the condensation stage temperature was set at 50℃±3℃ for 4 hours. This cycle of "8 hours of irradiation + 4 hours of condensation" was repeated continuously for 12 hours until a total cumulative time of 200 hours was reached. After conditioning the samples under standard atmospheric conditions, their aging tensile strength was tested according to FZ / T50006-2013, and the percentage of initial strength was calculated. The washing procedure followed GB / T8629-2017, and the yellowing evaluation followed GB / T8629-2017. According to B / T17644-2008, a type A standard washing machine was used to perform 50 consecutive standard washing and drying cycles on polyurethane fiber samples. Before and after washing, the yellowing index of the fiber surface was measured using a spectrophotometer. The polyurethane fiber samples were placed in a 190°C hot air drying oven under tension-free conditions for 1 minute, then cooled to room temperature and conditioned before being tested for breaking strength again. The retention rate from the initial strength was calculated. According to GB / T6505-2017, the initial fiber length (L0) was first measured. The sample was then immersed in boiling water at 100°C for 30 minutes under tension-free conditions. After being removed, naturally dried, and conditioned, the residual length (L1) was measured again, and the boiling water shrinkage rate was calculated using the formula (L0-L1) / L0×100%. The changes in breaking strength before and after UV aging and heat setting in Examples 1 and Comparative Examples 1-7 of this invention are as follows: Figure 3 As shown in the figure; the test results are shown in Table 3.

[0035] Table 3. Test results of the examples and comparative examples As shown in Table 3, the polyurethane fibers obtained in the comparative examples, through adjustments to the components and processes, exhibited significantly different anti-aging and thermal stability compared to the examples. In Comparative Example 1, due to the low hydrogen bond dissociation temperature of the urethane bonds, the hard segment hydrogen bonds were destroyed under the 190℃ heat setting environment, resulting in a significant decrease in strength retention. Furthermore, the weak physical cross-linking network could not resist the relaxation of molecular chains under boiling water conditions, leading to a significant increase in boiling water shrinkage. In Comparative Example 2, the high-temperature melt environment caused thermal degradation of some hindered amines and sulfur-containing structures, reducing the strength retention after UV aging. Simultaneously, the high viscosity melt... During cooling and solidification, the orientation of the internal macromolecules cannot be effectively relaxed, resulting in extremely high internal thermal residual stress and increased boiling water shrinkage. In Comparative Example 3, the lack of rigid nanoparticles' physical pinning and crystallization-inducing effect on the hard segment phase at the microscopic level means that the free volume expansion of the polymer network during high-temperature heat setting cannot be effectively suppressed, leading to thermal damage to the phase separation structure and a lower strength retention rate after heat setting compared to the Example. In Comparative Example 4, no chain extender containing dynamic disulfide bonds was added. Although the fiber exhibited weather resistance, the loss of the reversible rearrangement mechanism of dynamic covalent bonds in the macromolecular network resulted in increased stretching during the spinning and winding stage. Residual internal stress cannot be released through disulfide bond exchange in the lower channel zone and winding stage. The frozen internal stress is released under the thermal stimulation of boiling water, leading to an increase in boiling water shrinkage. In Comparative Example 5, the one-time addition leads to disordered competition among monomers with large differences in reactivity. The sterically hindered chain extender cannot be uniformly grafted onto the main chain, resulting in scattered distribution and even local agglomeration. This reduces the efficiency of ultraviolet absorption and free radical capture, decreases the UV aging strength retention rate, and increases the yellowing index. In Comparative Example 6, polytetrahydrofuran ether glycol is used entirely. The ether bonds in the soft segments of pure polyether are prone to photo-oxidative degradation, resulting in high strength degradation after 200 hours. Under ultraviolet irradiation, a large number of ether bonds in the main chain break, resulting in a significant decrease in strength retention. Furthermore, degradation products cause a sharp increase in the yellowing index after washing. In Comparative Example 7, the polymer molecules lack a chemical defense barrier that captures free radicals. When the material faces high-intensity ultraviolet radiation and a thermo-oxidative environment, the generated photo-oxidative free radicals undergo chain transfer and amplification reactions within the matrix, destroying the polyurethane polymer backbone. This leads to a significant decrease in strength retention after ultraviolet aging. At the same time, the matrix, which has lost its anti-aging protection, is prone to oxidation and discoloration during repeated washing, resulting in an increase in the yellowing index. This makes it unsuitable for long-term anti-aging outdoor applications.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A spinning process for highly elastic polyurethane fibers, characterized in that, The preparation process includes the following steps: Dried polytetrahydrofuran ether diol and polycarbonate diol are added to a reaction vessel, and 4,4'-diphenylmethane diisocyanate is added at a molar ratio of isocyanate groups to hydroxyl groups of 1.61-1.74:

1. The mixture is stirred at a constant temperature and the reaction is carried out. The solution is diluted with N,N-dimethylacetamide to obtain a prepolymer solution. Modified nanocrystals, 2,2'-dithiodiethylamine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine and ethylenediamine are mixed stepwise for chain extension, cured, filtered, and degassed under vacuum to obtain a spinning solution. The solution is then passed through a three-temperature zone tunnel and wound with a downward-flowing hot air stream to obtain the polyurethane fiber. The modified nanocrystals are obtained by reacting cellulose nanocrystals with 3-aminopropyltriethoxysilane and then freeze-drying.

2. The spinning process of the high-elasticity polyurethane fiber according to claim 1, characterized in that, The preparation of the prepolymer solution includes the following steps: 72-78 parts of the polytetrahydrofuran ether diol and 22-28 parts of the polycarbonate diol are dried and added to a reaction vessel, 20.2-21.8 parts of the 4,4'-diphenylmethane diisocyanate are added, and the mixture is stirred and reacted under nitrogen protection. After cooling, the N,N-dimethylacetamide is added and stirred to obtain the prepolymer solution; wherein the number average molecular weight of the polytetrahydrofuran ether diol is 2000; and the number average molecular weight of the polycarbonate diol is 2000.

3. The spinning process of the high-elasticity polyurethane fiber according to claim 1, characterized in that, The stepwise mixing and chain extension includes the following steps: 1.2-2.3 parts of the modified nanocrystals are pre-dispersed in N,N-dimethylacetamide and homogenized to obtain a mixture; 0.45-0.75 parts of 2,2'-dithiodiethylamine and 0.55-1.15 parts of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine are added to the mixture and mixed evenly; the mixture is added dropwise to the prepolymer solution at a time controlled at 20-40 min, and stirred at a constant temperature to obtain a first-stage chain extension system; 1.45-1.75 parts of ethylenediamine and diethylamine are dissolved in N,N-dimethylacetamide and added dropwise to the first-stage chain extension system at a time controlled at 10-20 min, stirred at a constant temperature, and after adjusting the solid content, the mixture is matured, filtered, and degassed to obtain the spinning solution.

4. The spinning process of the high-elasticity polyurethane fiber according to claim 1, characterized in that, The preparation of the polyurethane fiber includes the following steps: heating the spinning solution, extruding it through a spinneret into a three-temperature zone channel, setting the upper zone temperature to 320-340℃, the middle zone temperature to 235-255℃, and the lower zone temperature to 155-175℃, then passing it through a top-down flow of hot air, with a winding stretch ratio of 1.1-1.3 and a winding temperature of 40-60℃, and finally winding it to obtain the polyurethane fiber.

5. The spinning process of the high-elasticity polyurethane fiber according to claim 1, characterized in that, The preparation of the modified nanocrystals includes the following steps: Cellulose nanocrystals were dispersed in anhydrous N,N-dimethylformamide, sonicated, and then 3-aminopropyltriethoxysilane was added. The mixture was stirred and reacted under nitrogen protection, separated, centrifuged, washed, and then freeze-dried under vacuum to obtain the modified nanocrystals.

6. A highly elastic polyurethane fiber, characterized in that, The raw materials for preparation include polytetrahydrofuran ether diol, polycarbonate diol, 4,4'-diphenylmethane diisocyanate, modified nanocrystals, 2,2'-dithiodiethylamine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine, and ethylenediamine; the polyurethane fiber is prepared by any one of the spinning methods of claims 1-5.

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