A core-shell structure bimodal thermal regulating color-changing fiber and a preparation method thereof

Abstract

The application discloses a kind of core-shell structure double-mode thermal regulation color-changing fiber and preparation method thereof, belong to functional fiber material technical field.The application utilizes thermoplastic polyurethane base spinning solution, and prepares shell layer spinning solution containing thermochromic microcapsule and core layer spinning solution containing nano-aluminum oxide;By coaxial wet spinning technology, core layer spinning solution and shell layer spinning solution are extruded simultaneously, after forming in coagulation bath, drafting, washing and drying, core-shell structure fiber is obtained.The thermochromic microcapsule in the shell layer of the fiber can reversibly regulate solar wave reflectivity according to environmental temperature change, the nano-aluminum oxide in the core layer provides higher mid-infrared emissivity to realize radiation heat dissipation, and both realize physical isolation and functional synergy through core-shell structure.The fiber can realize "low-temperature heat preservation, high-temperature heat dissipation" self-adaptive double-mode thermal regulation without external energy input, and preparation process can be continuously carried out.

Description

Technical Field

[0001] This invention relates to the field of functional fiber materials technology, and in particular to a core-shell structured bimodal thermochromic fiber and its preparation method. Background Technology

[0002] The basic principle of passive radiative cooling technology is to utilize the high infrared emissivity of materials in the "atmospheric window" band (8-13 μm) to output heat in the form of thermal radiation, thereby achieving passive cooling without the need for refrigerant or external energy input. Integrating radiative cooling into textiles overcomes the limitations of traditional clothing that relies solely on heat conduction and convection for heat dissipation, achieving effective thermal management without the need for external energy.

[0003] However, existing radiation-cooling textiles typically employ a static optical design, with their solar reflectivity and mid-infrared emissivity remaining fixed after fabrication. This static characteristic presents certain limitations in practical applications: when ambient temperature and light levels change, such as in environments with large diurnal temperature variations or cold conditions, their continuous infrared radiation heat dissipation characteristics may lead to an excessive drop in human body surface temperature, resulting in an "overcooling" effect; or under hot conditions, they cannot dynamically adjust to "radiate" heat, causing heat accumulation and resulting in a stuffy, hot feeling, affecting wearing comfort.

[0004] Existing technologies have also attempted to dynamically couple radiative cooling mechanisms with solar heating mechanisms to achieve switching of thermal regulation modes based on environmental conditions. However, existing technologies still have certain shortcomings: Optical transmittance can be adjusted by changing the pore size or interlayer spacing of fabrics through mechanical deformation structures. However, mechanical deformation structures usually involve complex microfabrication processes, and the reliability and durability of the system need further verification. Moreover, the control process often depends on human intervention or external driving. When thermochromic materials and inorganic radiation-cooling fillers are simply blended in the same fiber matrix, problems such as agglomeration, delamination, and spinneret blockage can easily occur during the spinning process due to differences in density, particle size, and surface chemical properties, affecting the continuous preparation and performance uniformity of the fiber. At the same time, the random distribution of the two functional materials in the fiber cross section may cause mutual interference in their respective response spectral bands, thus limiting the overall thermal management effect.

[0005] Therefore, how to endow textiles with the ability to adaptively adjust to changes in ambient temperature, achieve the synergistic effect of thermochromic and radiative cooling functions, and produce composite fiber materials that can be mass-produced through conventional spinning processes remains a problem to be solved in this field. Summary of the Invention

[0006] This invention proposes a core-shell structured dual-mode thermochromic fiber and its preparation method to solve the problems of existing textiles using static optical design, where reflectivity and mid-infrared emissivity are fixed and cannot be automatically adjusted; to solve the problem of mutual interference between thermochromic materials and radiation-cooling materials; and to solve the problems of existing dynamic control technologies relying on external stimuli or having complex processes.

[0007] The technical solution of this invention lies in the following: A coaxial wet spinning process is employed to simultaneously extrude a shell spinning solution containing thermochromic microcapsules (TM) and a core spinning solution containing nano-alumina (Al2O3). After coagulation bath molding, a composite fiber with a core-shell structure is obtained. The TM in the shell layer endows the fiber with the ability to reversibly regulate the reflectivity of solar light bands with temperature changes, while the Al2O3 in the core layer endows it with a high mid-infrared emissivity for radiative heat dissipation. The two components achieve physical isolation and functional synergy through the core-shell structure, enabling the fiber to autonomously switch between "low-temperature insulation" and "high-temperature heat dissipation" thermal regulation modes according to the ambient temperature without the need for external energy input.

[0008] The specific solution of the present invention is as follows: A method for preparing core-shell structured bimodal thermochromic fibers includes the following steps: Preparation of basic spinning solution: Thermoplastic polyurethane (TPU) is dissolved in N,N-dimethylformamide (DMF) to obtain TPU / DMF basic spinning solution; Preparation of shell spinning solution: 1-3 μm thermochromic microcapsules (TM) are dispersed in the base spinning solution to obtain TM / TPU / DMF shell spinning solution, wherein the mass ratio of thermochromic microcapsules (TM) to TPU is 10:100 to 14:100. Preparation of core spinning solution: 300-500 nm nano-alumina (Al2O3) particles are dispersed in another part of the base spinning solution to obtain Al2O3 / TPU / DMF core spinning solution, wherein the mass ratio of nano-alumina (Al2O3) particles to TPU is 10:100 to 16:100. Extrusion of core-shell structured fibers: The core spinning solution and the shell spinning solution are simultaneously extruded through the inner and outer channels of a coaxial wet spinning spinneret to form a composite spinning solution flow with a core-shell structure. Coagulation bath forming and post-treatment: The extruded composite spinning solution is introduced into a deionized water coagulation bath for phase separation forming to obtain nascent fibers; the nascent fibers are then subjected to post-treatment including drawing, washing, and drying to obtain core-shell structured bimodal thermochromic fibers. The extrusion flow rate ratio of the core spinning solution to the shell spinning solution is 2:3, and the ratio of the shell thickness to the fiber cross-sectional diameter is 0.125 to 0.25.

[0009] Furthermore, the preparation of the basic spinning solution includes: TPU particles with a molecular weight of 200 kDa were added to N,N-dimethylformamide (DMF) solvent at a mass percentage of 20 wt%. The mixture was heated in a water bath at 60-80°C and stirred continuously at a speed of 300-500 r / min for 1-2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

[0010] Furthermore, the preparation of the shell spinning solution includes: Thermochromic microcapsule TM powder of 1-3 μm was added to the TPU / DMF base spinning solution. It was first dispersed by mechanical stirring for 1-2 hours, and then transferred to an ultrasonic cleaner for ultrasonic dispersion under ice water bath conditions for 30-60 minutes. After that, it was placed in a vacuum degassing box for static degassing for 1-2 hours to obtain a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0011] Furthermore, the preparation of the shell spinning solution includes: The temperature range of the ice-water bath is 0-5°C, and the phase transition initiation temperature of the thermochromic microcapsule (TM) is 30°C.

[0012] Furthermore, the preparation of the core spinning solution includes: Nano-alumina (Al2O3) particles of 300-500 nm are added to the TPU / DMF base spinning solution at a set ratio and initially dispersed by mechanical stirring for 1-2 hours. Then, the solution is transferred to an ultrasonic cleaner and ultrasonically dispersed for 45-60 minutes under ice-water bath conditions. After vacuum static degassing treatment, a uniform and stable Al2O3 / TPU / DMF core spinning solution is obtained.

[0013] Furthermore, the extrusion of the core-shell structured fibers includes: The degassed core spinning solution and shell spinning solution were respectively loaded into two syringes equipped with micro-injection pumps, and the core spinning solution and shell spinning solution were continuously extruded at a set flow rate ratio; the extrusion flow rate of the core spinning solution was set to 10 mL / h, and the extrusion flow rate of the shell spinning solution was set to 15 mL / h.

[0014] Furthermore, the coagulation bath molding and post-treatment include: After the nascent fibers are separated and formed in a deionized water coagulation bath at 20-25°C, they are continuously drawn in a water bath by guide rollers, with a draw ratio of 2-4 times. The nascent fibers collected by take-up rollers are immersed in the coagulation bath and left to stand for 12-24 hours, and the coagulation bath is replaced every 8 hours to extract and remove residual N,N-dimethylformamide solvent.

[0015] A core-shell structured bimodal thermochromic fiber, the fiber comprising a shell layer and a core layer, the shell layer covering the outer periphery of the core layer; The shell comprises a thermoplastic polyurethane (TPU) matrix and thermochromic microcapsules (TM) with a particle size of 1-3 μm dispersed therein. The thermochromic microcapsules are used to undergo reversible color changes at different temperatures to adjust the reflectivity of the fiber in the solar radiation band. The mass ratio of the thermochromic microcapsules (TM) to TPU is 10:100 to 14:100. The core layer comprises a thermoplastic polyurethane (TPU) matrix and nano-alumina (Al2O3) particles with a particle size of 300-500 nm dispersed therein. The nano-alumina is used to adjust the emissivity of the fiber in the infrared band (8-13 μm) in the atmospheric window. The mass ratio of the nano-alumina (Al2O3) particles to TPU is 10:100 to 16:100.

[0016] Furthermore, the ratio of the shell thickness to the fiber cross-sectional diameter ranges from 0.125 to 0.25.

[0017] Furthermore, after the fiber is heated to the phase transition temperature at room temperature (26°C), the thermal response time for the phase change from dark to light is 8-10 s, and the thermal response time for the phase change from light to dark is 10-12 s after heating is stopped.

[0018] The present invention has the following technical effects: This invention encapsulates thermochromic microcapsules within a fiber shell and fills the fiber core with nano-alumina, which has high infrared emission. In low-temperature environments, the thermochromic microcapsules in the shell are dark, maintaining a low reflectivity in the solar spectrum, thus aiding heat absorption. In high-temperature environments, the microcapsules in the shell transform into a light color, increasing solar reflectivity and reducing heat absorption, while the high mid-infrared emissivity provided by the alumina core dissipates the absorbed heat. Compared to the excessive cooling at low temperatures and the stuffy, hot feeling at high temperatures of traditional radiative cooling fibers, the fiber of this invention achieves an environmentally adaptive dual-mode thermal regulation function, improving wearing comfort.

[0019] This invention utilizes coaxial wet spinning technology to confine thermochromic microcapsules and nano-alumina in the shell and core layers, respectively, achieving spatial physical isolation and reducing direct contact and mutual interference between the two particles. The core-shell structure design improves the dispersion stability and spinnability of the spinning solution, enhances the compatibility of the two functional materials during spinning, and facilitates continuous production. Within the specified extrusion flow rate ratio and shell thickness ratio range, the core and shell layers form a continuous coating structure, balancing continuous spinning and dual-band thermal conditioning. Attached Figure Description

[0020] Figure 1 This is a SEM image of a core-shell structured dual-mode thermochromic fiber in one embodiment of the present invention, wherein (a) is the surface morphology of the fiber; and (b) is the cross-sectional morphology of the fiber. Figure 2 This is a reflectance spectrum before and after color change in one embodiment of the present invention; Figure 3 This is an atmospheric window emissivity map in one embodiment of the present invention; Figure 4 The phase transition temperature of TM obtained by testing in one embodiment of the present invention; Figure 5 This is a schematic diagram of the dark state of the core-shell structure dual-mode thermo-regulated color-changing fiber in one embodiment of the present invention; Figure 6 This is a schematic diagram of the light-colored state of the core-shell structure dual-mode thermo-regulated color-changing fiber in one embodiment of the present invention. Detailed Implementation

[0021] 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.

[0022] This invention provides a method for preparing core-shell structured bimodal thermochromic fibers, comprising the following steps: Preparation of S1 basic spinning solution: Thermoplastic polyurethane (TPU, with a molecular weight of 200 kDa) particles were dried in an 80°C vacuum oven for 4 hours. The dried TPU particles were added to N,N-dimethylformamide (DMF) solvent at a set mass percentage of 20 wt%. Under water bath heating conditions of 60-80°C, the mixture was continuously stirred with a mechanical stirrer at a speed of 300-500 r / min for 1-2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

[0023] Preparation of S2 shell spinning solution: Thermochromic microcapsules (TM, 1-3 μm) powder in a predetermined mass ratio were added to the TPU / DMF base spinning solution prepared in step S1. Initial dispersion was achieved by mechanical stirring for 1-2 hours, followed by ultrasonic dispersion in an ultrasonic cleaner under ice-water bath conditions for 30-60 minutes to break down microcapsule aggregates. Finally, the solution was placed in a vacuum degassing chamber for 1-2 hours to degas, resulting in a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0024] In the shell TM / TPU / DMF spinning solution, the mass ratio of thermochromic microcapsules (TM) to TPU is 10:100 to 14:100.

[0025] The temperature range of the ice-water bath is 0-5°C to prevent the local heat released by high-frequency ultrasound from accelerating solvent evaporation.

[0026] like Figure 4 As shown, the heat flux curve of the thermochromic microcapsule (TM) deflects downwards near 30°C, indicating that 30°C is the initial threshold for the phase transition of TM. At 30°C, TM undergoes a phase transition, turning a lighter color. Further thermal regulation occurs, and TM reaches its heat flux peak at 34.75°C, at which point the color change is relatively complete. In the cooling state, also around 30°C, the color begins to darken, and a heat flux peak occurs at 25°C, at which point TM reverts to its darker state.

[0027] Preparation of S3 core spinning solution: Nano-alumina (Al2O3, with a size of 300-500 nm) particles were added to another portion of the TPU / DMF base spinning solution prepared in step S1 according to a set ratio. The solution was initially dispersed by mechanical stirring for 1-2 hours, and then transferred to an ultrasonic cleaner for ultrasonic dispersion under ice-water bath conditions (temperature range 0-5°C) for 45-60 minutes. After vacuum settling and degassing, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0028] In the Al2O3 / TPU / DMF core spinning solution, the mass ratio of nano-alumina (Al2O3) particles to TPU is 10:100 to 16:100.

[0029] Extrusion of S4 core-shell structured fibers: The deaerated core spinning solution and shell spinning solution are respectively loaded into two syringes equipped with micro-injection pumps, and tightly connected to the corresponding interfaces of the coaxial wet spinning spinneret using silicone tubing. The injection pumps are adjusted to continuously extrude the core spinning solution and shell spinning solution at a set flow rate ratio.

[0030] The extrusion flow rate of the core spinning solution was set to 10 mL / h, and the extrusion flow rate of the shell spinning solution was set to 15 mL / h.

[0031] S5 Coagulation Bath Forming and Post-treatment: After the nascent fibers undergo dual-diffusion phase separation and forming in the coagulation bath, they are continuously drawn in a water bath via guide rollers and collected by take-up rollers. The nascent fibers collected by the take-up rollers are immersed in the coagulation bath and allowed to stand to extract and remove residual N,N-dimethylformamide solvent. Finally, the washed fibers are dried in a vacuum oven at 50-60°C for 12-24 hours to obtain core-shell structured bimodal thermochromic fibers.

[0032] The coagulation bath is made of deionized water and the temperature is controlled at 20-25°C.

[0033] The draw ratio of the nascent fibers is controlled at 2-4 times.

[0034] The nascent fibers are left to stand in the coagulation bath for 12-24 hours, and the coagulation bath is replaced every 8 hours. The final product is as follows: Figure 1 The core-shell structured dual-mode thermochromic fiber shown.

[0035] Verification was performed using the above methods in various embodiments. Example 1

[0036] Preparation of S11 basic spinning solution: Thermoplastic polyurethane (TPU) particles were dried in an 80°C vacuum oven for 4 hours. The dried TPU particles were added to N,N-dimethylformamide (DMF) solvent at a set mass percentage of 20 wt%. Under the heating condition of a 60°C water bath, the mixture was continuously stirred at a speed of 400 r / min for 2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

[0037] Preparation of S12 shell spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, wherein the mass ratio of TM to TPU was 14:100 to prepare the shell spinning solution. The solution was first initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber for 1 hour to obtain a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0038] Preparation of S13 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a specific ratio of 12:100 (Al2O3:TPU mass ratio). The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0039] Extrusion of S14 core-shell structured fibers: The deaerated core spinning solution and shell spinning solution are respectively loaded into two syringes equipped with micro-injection pumps, and tightly connected to the corresponding interfaces of the coaxial wet spinning spinneret using silicone tubing. The injection pumps are adjusted to extrude the spinning solutions at the set flow rate ratio.

[0040] S15 Coagulation Bath Forming and Post-treatment: The extruded nascent fibers are directly fed into a 25°C deionized water coagulation bath for dual-diffusion phase separation forming. After forming in the coagulation bath, the nascent fibers are continuously drawn in a water bath via guide rollers, with the draw ratio controlled at 3 times, and collected by take-up rollers. The nascent fibers collected by the take-up rollers are immersed in room temperature deionized water and left to stand for 24 hours (with the deionized water replaced every 8 hours) to extract and remove residual DMF solvent. Finally, the washed fibers are placed in a 60°C vacuum oven and dried for 12 hours to obtain the core-shell structured dual-mode thermochromic fiber described in this embodiment.

[0041] To verify the effect of different TM addition amounts on product performance, Examples 2 to 6 were based on Example 1, with other conditions remaining unchanged except for the TM addition amount. The specific methods for each example are as follows: Example 2

[0042] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S22 shell spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, so that the mass ratio of TM to TPU was 6:100 to prepare the shell spinning solution. The solution was first initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber and allowed to stand for 1 hour to degas, resulting in a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0043] Example 3

[0044] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S32 shell spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, so that the mass ratio of TM to TPU was 8:100 to prepare the shell spinning solution. The solution was first initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber for 1 hour to obtain a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0045] Example 4

[0046] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S42 shell spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, so that the mass ratio of TM to TPU was 10:100 to prepare the shell spinning solution. The solution was first initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber and allowed to stand for 1 hour to degas, resulting in a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0047] Example 5

[0048] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S52 shell spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, so that the mass ratio of TM to TPU was 12:100 to prepare the shell spinning solution. The solution was first initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber for 1 hour to obtain a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0049] Example 6

[0050] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S62 shell spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, so that the mass ratio of TM to TPU was 16:100 to prepare the shell spinning solution. The solution was first initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber for 1 hour to obtain a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

[0051] To verify the thermal regulation performance of the present invention, spinning state, solar reflectivity, and fiber surface temperature performance at high and low temperatures were tested for Examples 1 to 6 under different TM addition amounts. The performance testing methods used are as follows: Thermal regulation performance test: The obtained core-shell fibers were woven into block-shaped fabric samples and laid flat on a thermally insulating foam sample stage (to block unnecessary downward heat loss). The test setup was then subjected to 1000 W / m². 2 Under the sunlight simulator, different initial ambient temperatures (low temperature 18°C, high temperature 26°C) were set. Using a T-type thermocouple connected to a multi-channel temperature tester, the temperature change curve of the fabric-covered area was monitored and recorded in real time. The temperature measured at 5 minutes was recorded to compare and characterize the adaptive thermal regulation effect of the fiber.

[0052] Optical and infrared emissivity testing: such as Figure 2 , Figure 3 As shown, the spectral reflectance (ρ) of the sample in the solar radiation band (300-2500 nm) was measured using a UV-Vis-NIR spectrophotometer; the reflectance (ρ) and transmittance (τ) of the sample in the mid-infrared band (8-13 µm) were measured using a Fourier transform infrared spectrometer (FTIR). According to Kirchhoff's law, the radiative emissivity (ε) of an object in thermodynamic equilibrium is equal to its absorptivity (α). The mid-infrared emissivity of the material was calculated using the formula ε = 1 - τ - ρ.

[0053] Yarn breakage rate test: A micro injection pump (TYD01-01-CE) equipped with a drafting and winding device was used. The linear speed of the take-up roller was set to 1 m / min. The target total length of continuous fiber produced in a single test was set to 10 meters. At a speed of 1 m / min, a single uninterrupted test was conducted for 10 minutes.

[0054] Each experimental group underwent 10 independent parallel replicate experiments, and the final result was the arithmetic mean.

[0055] The test results are shown in the table below:

[0056] 1. Influence on "spinning state" When the mass ratio of TM to TPU is between 6:100 and 14:100: TM microcapsules can be uniformly dispersed in TPU / DMF spinning solution, the system is stable, and the extrusion through coaxial wet spinning spinneret is smooth. After solidification, the fiber surface is smooth, the internal structure is continuous, the yarn breakage rate is low, and it remains relatively stable.

[0057] When the mass ratio of TM to TPU is 16:100: due to the excessively high number density of TM microcapsules, the particles agglomerate, causing physical blockage during extrusion; at the same time, the agglomerates also become stress concentration points, causing jet breakage during extrusion, and the yarn breakage rate fluctuates up to 8 times / ten meters, affecting continuous spinning.

[0058] 2. Impact on "solar reflectivity" (color-changing performance) Thermochromic microcapsules (TM) exhibit a dark color at low temperatures and a light color at high temperatures.

[0059] Under low-temperature conditions, when the mass ratio of TM to TPU is between 6:100 and 8:100, the reflectivity in the solar radiation band is relatively high. This is because if the amount of TM microcapsules added is too low, it cannot adequately cover the base color. The TPU / DMF matrix itself is translucent or light-colored, and alumina is light-colored. When the microcapsules are insufficient, the intrinsic reflection contribution of the matrix dominates, resulting in a higher overall reflectivity.

[0060] When the mass ratio of TM to TPU reaches 10:100 to 14:100, the TM microcapsules form a continuous and dense shell, effectively masking the matrix color. At this time, the reflectivity is mainly determined by the dark state of the microcapsules, so the value remains stable at a low level.

[0061] Therefore, it can be seen that by configuring an appropriate amount of thermochromic microcapsules (TM) in the shell layer, the present invention can reduce the reflectivity of solar light bands at low temperatures and better absorb heat.

[0062] 3. Effect on "fiber surface temperature" When the mass ratio of TM to TPU is between 10:100 and 14:100, the fiber temperature is at a comfortable human body temperature under low-temperature conditions. However, when the mass ratio of TM to TPU is lower than 8:100, the temperature is lower, resulting in a supercooling effect. Under high-temperature conditions, the fiber temperature is below 40℃, indicating that it has a heat dissipation effect at high temperatures.

[0063] In summary, the preferred addition range of microcapsules obtained through the test experiments in Examples 1-6 is 10:100 to 14:100.

[0064] To verify the effect of different alumina (Al2O3) addition amounts on the thermal regulation performance of the product, Examples 7 to 12 were based on Example 1, with other conditions remaining unchanged except for the amount of nano-alumina (Al2O3) added. The specific methods for each example are as follows: Example 7

[0065] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S73 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 6:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0066] Example 8

[0067] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S83 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 8:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0068] Example 9

[0069] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S93 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 10:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0070] Example 10

[0071] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S103 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 14:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0072] Example 11

[0073] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S113 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 16:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0074] Example 12

[0075] The steps that are the same as in Example 1 will not be repeated; only the steps that are different will be described: Preparation of S123 core spinning solution: Nano-alumina (Al2O3) particles were added to another prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 18:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF core spinning solution was obtained.

[0076] To verify the thermal regulation performance of the present invention, spinning state, mid-infrared emissivity, and fiber surface temperature performance at high temperatures were tested for Examples 1 and 7 to 12 under different alumina (Al2O3) addition amounts. The performance testing methods used were the same as described above, and the test results are shown in the table below:

[0077] 1. Influence on "spinning state" When the mass ratio of Al2O3 to TPU is 6:100 to 16:100, the nano-Al2O3 particles can be uniformly dispersed in the TPU / DMF spinning solution, and the system remains stable. Extrusion through a coaxial wet spinning spinneret is smooth, and the fiber structure remains intact after solidification, resulting in a low yarn breakage rate and relatively stable performance.

[0078] When the mass ratio of Al2O3 to TPU is 18:100: the number density of nano Al2O3 particles is too high, causing the particles to agglomerate and causing physical blockage during extrusion; at the same time, the agglomerates form stress concentration points in the spinning solution, causing jet breakage during extrusion, and the yarn breakage rate fluctuates up to 10 times / ten meters, affecting continuous spinning.

[0079] 2. Impact on "Mid-infrared emissivity" When the mass ratio of Al2O3 to TPU is 6:100 to 8:100, the mid-infrared emissivity is below 80%, indicating that when the addition amount is too low, the volume fraction of Al2O3 particles in the core layer is insufficient, and an effective radiative heat dissipation network cannot be formed. Most of the core layer volume is occupied by the TPU matrix, resulting in a low overall mid-infrared emissivity.

[0080] When the mass ratio of Al2O3 to TPU is 10:100 to 16:100, the Al2O3 particles form a relatively complete and uniform distribution in the core layer, and the mid-infrared emissivity is stable at over 80%, exhibiting good heat dissipation capabilities.

[0081] 3. Effect on "fiber surface temperature" When the mass ratio of Al2O3 to TPU is 10:100 to 16:100, the surface temperature of the fiber is close to the human body's comfortable temperature at high temperatures. However, when the mass ratio of Al2O3 to TPU is 6:100 to 8:100, the surface temperature of the fiber exceeds 40°C at high temperatures.

[0082] The test results from Examples 1 and 7-12 show that adding an appropriate amount of nano-alumina (Al2O3) to the core layer endows the fiber with a high mid-infrared emissivity (>80%), meeting the requirements for radiative heat dissipation under high-temperature environments. When the mass ratio of Al2O3 to TPU is low (6:100 to 8:100), the mid-infrared emissivity decreases, and the heat dissipation capacity at high temperatures weakens; when the mass ratio of Al2O3 to TPU is too high (18:100), the spinning system agglomerates, resulting in a high yarn breakage rate, which in turn affects the normal operation of the spinning process. Experiments revealed that the optimal addition range of Al2O3 is 10:100 to 16:100.

[0083] To verify the role of the "core-shell structure" of this invention in structural design and overall performance, four single-layer structures were compared, as follows: Comparative Example 1 Preparation of D11 basic spinning solution: Thermoplastic polyurethane (TPU) particles were added to N,N-dimethylformamide (DMF) solvent at a set mass percentage of 20 wt%. Under the conditions of water bath heating at 60-80°C, the mixture was continuously stirred with a mechanical stirrer at a speed of 300-500 r / min for 1-2 hours until the TPU was completely dissolved. Finally, the mixture was placed in a vacuum degassing box and allowed to stand for degassing for 1 hour to obtain a uniform and transparent TPU / DMF basic spinning solution. Extrusion of D12 TPU fibers: The deaerated spinning solution is loaded into a syringe equipped with a micro-injection pump, and a silicone tube is tightly connected to the corresponding interface of the coaxial spinning spinneret. The injection pump is adjusted to continuously extrude the spinning solution at the set flow rate ratio; D13 Coagulation Bath Forming and Post-treatment: After the nascent fibers are formed in the coagulation bath, they are continuously drawn in a water bath via guide rollers. The nascent fibers collected by the take-up rollers are immersed in the coagulation bath and allowed to stand to extract and remove residual N,N-dimethylformamide solvent. Finally, the washed fibers are dried in a vacuum oven at 60°C for 12-24 hours to obtain comparative TPU fibers.

[0084] Comparative Example 2 Preparation of D21 basic spinning solution: Thermoplastic polyurethane (TPU) particles were dried in an 80°C vacuum oven for 4 hours. The dried TPU particles were added to N,N-dimethylformamide (DMF) solvent at a set mass percentage of 20 wt%. Under the conditions of heating in a water bath at 60°C, the mixture was continuously stirred at a speed of 400 r / min for 2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

[0085] Preparation of D22 Al2O3 / TPU / DMF spinning solution: Nano-alumina (Al2O3) particles were added to the prepared TPU / DMF base spinning solution in a certain proportion, making the mass ratio of Al2O3 to TPU 12:100. The solution was initially dispersed by mechanical stirring for 1 hour, and then transferred to an ultrasonic cleaner for ultrasonic dispersion under ice-water bath conditions for 60 minutes. After vacuum settling and degassing for 1 hour, a uniform and stable Al2O3 / TPU / DMF spinning solution was obtained.

[0086] Extrusion of D23 Al2O3 / TPU / DMF fibers: The deaerated Al2O3 / TPU / DMF spinning solution is loaded into a syringe equipped with a micro-injection pump, and tightly connected to the corresponding interface of the coaxial spinning spinneret using a silicone tubing. The injection pump is adjusted to extrude the spinning solution at the set flow rate ratio.

[0087] D24 Coagulation Bath Molding and Post-treatment: The extruded mixed fluid directly enters a 25°C deionized water coagulation bath for dual-diffusion phase separation molding. After the nascent fibers are formed in the coagulation bath, they are continuously drawn in a water bath via guide rollers, with the draw ratio controlled at 3 times, and collected by take-up rollers. The nascent fibers collected by the take-up rollers are immersed in room temperature deionized water and left to stand for 24 hours (with the deionized water replaced every 8 hours) to extract and remove residual DMF solvent. Finally, the washed fibers are dried in a 60°C vacuum oven for 12 hours to obtain comparative Al2O3 / TPU monolayer fibers.

[0088] Comparative Example 3 Preparation of D31 basic spinning solution: Thermoplastic polyurethane (TPU) particles were dried in an 80°C vacuum oven for 4 hours. The dried TPU particles were added to N,N-dimethylformamide (DMF) solvent at a set mass percentage of 20 wt%. Under a water bath heating condition of 60°C, the mixture was continuously stirred at a speed of 400 r / min for 2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

[0089] Preparation of D32 TM / TPU / DMF spinning solution: Thermochromic microcapsules (TM) were added to the TPU / DMF base spinning solution prepared above, making the mass ratio of TM to TPU 14:100. The solution was first mechanically stirred for 1 hour to initially disperse it, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 45 minutes under ice-water bath conditions. Finally, it was placed in a vacuum degassing chamber and allowed to stand for 1 hour to degas, resulting in a uniformly dispersed and bubble-free TM / TPU / DMF spinning solution.

[0090] Extrusion of D33 TM / TPU / DMF fibers: The deaerated TM / TPU / DMF spinning solution is loaded into a syringe equipped with a micro-injection pump, and a silicone tube is tightly connected to the corresponding interface of the coaxial spinning spinneret. The injection pump is adjusted to extrude the spinning solution at the set flow rate ratio.

[0091] D34 Coagulation Bath Molding and Post-treatment: The extruded mixed fluid is directly fed into a 25°C deionized water coagulation bath for dual-diffusion phase separation molding. After the nascent fibers are formed in the coagulation bath, they are continuously drawn in a water bath via guide rollers, with the draw ratio controlled at 3 times, and collected by take-up rollers. The nascent fibers collected by the take-up rollers are immersed in room temperature deionized water and left to stand for 24 hours (the deionized water is changed every 8 hours) to extract and remove residual DMF solvent. Finally, the washed fibers are dried in a 60°C vacuum oven for 12 hours to obtain comparative TM / TPU monolayer fibers.

[0092] Comparative Example 4 Preparation of D41 basic spinning solution: Thermoplastic polyurethane (TPU) particles were dried in an 80°C vacuum oven for 4 hours. The dried TPU particles were added to N,N-dimethylformamide (DMF) solvent at a set mass percentage of 20 wt%. Under a water bath heating condition of 60°C, the mixture was continuously stirred at a speed of 400 r / min for 2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

[0093] Preparation of D42 TM / Al2O3 / TPU / DMF blend spinning solution: Thermochromic microcapsules (TM) and nano-alumina (Al2O3) particles were added to the prepared TPU / DMF base spinning solution in a specific ratio, where the mass ratio of TM to TPU was 14:100 and the mass ratio of Al2O3 to TPU was 12:100. The solution was initially dispersed by mechanical stirring for 1 hour, then transferred to an ultrasonic cleaner and ultrasonically dispersed for 60 minutes under ice-water bath conditions. After vacuum settling and degassing for 1 hour, a uniform and stable TM / Al2O3 / TPU / DMF blend spinning solution was obtained.

[0094] Extrusion of D43™ / Al2O3 / TPU / DMF blended fibers: The deaerated spinning solution is loaded into a syringe equipped with a micro-injection pump, and a silicone tube is tightly connected to the corresponding interface of the coaxial spinning spinneret. The injection pump is adjusted to extrude the spinning solution at the set flow rate ratio.

[0095] D44 Coagulation Bath Molding and Post-treatment: The extruded mixed fluid is directly fed into a 25°C deionized water coagulation bath for dual-diffusion phase separation molding. After molding in the coagulation bath, the nascent fibers are continuously drawn in a water bath via guide rollers, with the draw ratio controlled at 3 times, and collected by take-up rollers. The nascent fibers collected by the take-up rollers are immersed in room temperature deionized water and left to stand for 24 hours (with the deionized water replaced every 8 hours) to extract and remove residual DMF solvent. Finally, the washed fibers are dried in a 60°C vacuum oven for 12 hours to obtain the comparative TM / Al2O3 / TPU / DMF blended fibers.

[0096] To verify the effect of the core-shell structure of the present invention on thermal regulation performance, the spinning state, solar reflectivity, mid-infrared emissivity, and fiber surface temperature performance at high and low temperatures were tested for Examples 1 and Comparative Examples 1 to 4. The performance testing methods used were the same as described above, and the test results are shown in the table below:

[0097] Comparative Example 1: Pure TPU fiber, without any added Al2O3 or TM, just pure polyurethane fiber.

[0098] Test results: At high temperatures: Lacking Al2O3 with high infrared emissivity, it cannot effectively dissipate heat; at the same time, lacking the color-changing function of TM, its reflectivity in the solar spectrum remains unchanged at high and low temperatures, and it cannot respond to changes in ambient temperature to change its color and reflectivity in the solar spectrum. Therefore, it will absorb a lot of heat in high-temperature environments, resulting in a stuffy feeling; in low-temperature environments, it lacks a heating mechanism, and the fiber surface temperature cannot adaptively adjust according to the ambient temperature.

[0099] Comparative Example 2: Pure Al2O3 radiation-cooling fiber ("overcooling" at low temperature) Preparation characteristics: Only Al2O3 was added, and it was uniformly mixed throughout the fiber without core-shell separation.

[0100] Test results: Al2O3 endows the fiber with good mid-infrared emissivity, enabling it to effectively radiate heat dissipation in high-temperature environments. However, the reflectivity of the solar spectrum remains unchanged at both high and low temperatures. In low-temperature environments, it still "radiates" heat away, resulting in a low fiber surface temperature and causing "overcooling".

[0101] Comparative Example 3: Pure TM color-changing fiber (suffocatingly hot under high temperature) Preparation characteristics: Only TM is added, and it is uniformly mixed throughout the fiber without core-shell separation.

[0102] Test results: TM's color-changing function has a low reflectivity in the solar wavelength range at low temperatures, which can absorb some of the sunlight and play a role in heat preservation.

[0103] However, TM can only adjust the absorption and reflection of sunlight in the wavelength range, but it cannot increase the mid-infrared emissivity of the fiber. Therefore, in high-temperature environments, even if the color is changed to reduce heat absorption, the heat will still accumulate because it cannot efficiently "radiate" its own heat, resulting in "sultry and hot" conditions (up to 42.4℃).

[0104] Comparative Example 4: In Comparative Example 4, when Al2O3 and TM were blended to produce single-layer fibers, the yarn breakage rate was relatively high (9 times / ten meters). This was due to the size difference of the particles, which caused agglomeration and stratification in the spinning solution, affecting the spinning process.

[0105] The comparative experiments described above demonstrate that this invention places the TM material, which responds to the solar radiation band, in the outer shell, and the Al2O3 material, responsible for high emission in the mid-infrared band, in the core. This not only achieves physical isolation in terms of spatial structure but also ensures that the two materials do not interfere with each other in terms of spectral response bands. This allows the two materials to perform photothermal conversion and radiative heat dissipation functions separately within the same fiber.

[0106] This invention produces a core-shell structured bimodal thermoregulatory color-changing fiber with an optimized Al2O3 core layer and TM shell. This fiber exhibits a wide range of reflectivity regulation across solar wavelengths and high mid-infrared emissivity. It overcomes the shortcomings of conventional fibers (insufficient thermoregulation), the "overcooling" defects of pure radiative cooling fibers at low temperatures, and the problem of pure color-changing fibers becoming hot and stuffy at high temperatures. The resulting core-shell structured bimodal thermoregulatory color-changing fiber exhibits high mid-infrared emissivity and strong radiative heat dissipation; its surface temperature is closer to comfortable body temperature during low and high temperature switching, demonstrating good adaptive thermal management performance.

[0107] To verify the influence of different specifications of coaxial spinning needles on the spinning process and fiber properties, based on the spinning method and experimental testing methods of Example 1, Examples 1 to 17 were conducted by changing the needle specifications to adjust the total diameter and shell thickness of the fiber. The specific test results are shown in the table below:

[0108] The Influence of Needle Specifications on Spinning State In Example 13, when the outer needle specification was 18G and the inner needle specification was 22G, the yarn breakage rate was relatively high (9 times / ten meters). In Example 17, when the outer needle specification was 19G and the inner needle specification was 24G, the yarn breakage rate was also relatively high (10 times / ten meters). This is because the inner diameter is larger, resulting in a relatively larger extrusion flow rate of the core spinning solution at the same injection pump flow rate. At this time, the core flow rate is too large relative to the shell flow rate, causing the shell to easily break and failing to form a complete coating structure. When the outer needle specification is 18G and the inner needle specification is 23G, 24G, or 25G, the core flow rate decreases, and the ratio of the core flow rate to the shell flow rate becomes more reasonable. The two fluids can form a stable concentric composite jet at the outlet, resulting in a lower yarn breakage rate and enabling continuous spinning.

[0109] Further comparison of the ratio of shell thickness to fiber cross-sectional diameter shows that when the ratio in Examples 13 and 17 is less than 0.1, the yarn breakage rate increases, affecting the spinning process; when the ratio is between 0.125 and 0.25, continuous spinning is possible, and the effect on fiber thermal regulation performance is relatively small.

[0110] The test results above show that the fiber retains a good thermal regulation effect when the core-shell size is enlarged or reduced, thus the fiber has good practicality.

[0111] To verify the thermal response time of the core-shell structured dual-mode thermochromic fiber of this invention, a heat transfer test was conducted using the fiber prepared in Example 1 at room temperature (26°C). The fiber was tightly wound onto a transparent glass slide, placed on a heating stage, and heated to 30°C. The color change time of the fiber was recorded. After removing the heating stage, the time required for the fiber to return to its original color was recorded.

[0112]

[0113] The test results show that the initial state of the fiber sample is as follows: Figure 5 The color shown is dark; after heating for 8-10 seconds, it changes from a dark phase to a dark phase. Figure 6 The light-colored area is shown in the figure; after heating is stopped, the light-colored area that underwent a phase transition returns to its initial dark state after 10-12 s. These results indicate that the core-shell structured bimodal thermochromic fiber prepared in this invention can complete the optical state switching from dark to light within 8-10 s under the above test conditions, and complete the reversible recovery from light to dark within 10-12 s, exhibiting a short dynamic thermal response time and environmental adaptability.

[0114] The embodiments provided above are not intended to limit the scope of the present invention, nor are the described steps intended to limit the order of execution. The above descriptions are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing core-shell structured dual-mode thermochromic fiber, characterized in that, Includes the following steps: Preparation of basic spinning solution: Thermoplastic polyurethane (TPU) is dissolved in N,N-dimethylformamide (DMF) to obtain TPU / DMF basic spinning solution; Preparation of shell spinning solution: 1-3 μm thermochromic microcapsules (TM) are dispersed in the base spinning solution to obtain TM / TPU / DMF shell spinning solution, wherein the mass ratio of the thermochromic microcapsules (TM) to the TPU is 10:100 to 14:100; Preparation of core spinning solution: 300-500 nm nano-alumina (Al2O3) particles are dispersed in another part of the base spinning solution to obtain Al2O3 / TPU / DMF core spinning solution, wherein the mass ratio of nano-alumina (Al2O3) particles to TPU is 10:100 to 16:

100. Extrusion of core-shell structured fibers: The core spinning solution and the shell spinning solution are simultaneously extruded through the inner and outer channels of a coaxial wet spinning spinneret to form a composite spinning solution flow with a core-shell structure. Coagulation bath molding and post-treatment: The extruded composite spinning liquid is introduced into a deionized water coagulation bath for phase separation molding to obtain nascent fibers; the nascent fibers are subjected to post-treatment including stretching, washing and drying to obtain core-shell structured bimodal thermochromic fibers, and the ratio of the shell thickness to the fiber cross-sectional diameter of the obtained fibers is 0.125 to 0.

25.

2. The preparation method according to claim 1, characterized in that, The preparation of the basic spinning solution includes: TPU particles with a molecular weight of 200 kDa were added to N,N-dimethylformamide (DMF) solvent at a mass percentage of 20 wt%. The mixture was heated in a water bath at 60-80°C and stirred continuously at a speed of 300-500 r / min for 1-2 hours until the TPU was completely dissolved, resulting in a uniform and transparent TPU / DMF basic spinning solution.

3. The preparation method according to claim 1, characterized in that, The preparation of the shell spinning solution includes: Thermochromic microcapsule TM powder of 1-3 μm was added to the TPU / DMF base spinning solution. It was first dispersed by mechanical stirring for 1-2 hours, and then transferred to an ultrasonic cleaner for ultrasonic dispersion under ice water bath conditions for 30-60 minutes. After that, it was placed in a vacuum degassing box for static degassing for 1-2 hours to obtain a uniformly dispersed and bubble-free TM / TPU / DMF shell spinning solution.

4. The preparation method according to claim 3, characterized in that, The preparation of the shell spinning solution includes: The temperature range of the ice-water bath is 0-5°C, and the phase transition initiation temperature of the thermochromic microcapsule (TM) is 30°C.

5. The preparation method according to claim 1, characterized in that, The preparation of the core spinning solution includes: Nano-alumina (Al2O3) particles of 300-500 nm are added to the TPU / DMF base spinning solution at a set ratio and initially dispersed by mechanical stirring for 1-2 hours. Then, the solution is transferred to an ultrasonic cleaner and ultrasonically dispersed for 45-60 minutes under ice-water bath conditions. After vacuum static degassing treatment, a uniform and stable Al2O3 / TPU / DMF core spinning solution is obtained.

6. The preparation method according to claim 1, characterized in that, The extrusion of the core-shell structured fibers includes: The degassed core spinning solution and shell spinning solution were respectively loaded into two syringes equipped with micro-injection pumps, and the core spinning solution and shell spinning solution were continuously extruded at a set flow rate ratio; the extrusion flow rate of the core spinning solution was set to 10 mL / h, and the extrusion flow rate of the shell spinning solution was set to 15 mL / h.

7. The preparation method according to claim 1, characterized in that, The coagulation bath molding and post-treatment include: After the nascent fibers are separated and formed in a deionized water coagulation bath at 20-25°C, they are continuously drawn in a water bath by guide rollers, with a draw ratio of 2-4 times. The nascent fibers collected by take-up rollers are immersed in the coagulation bath and left to stand for 12-24 hours, and the coagulation bath is replaced every 8 hours to extract and remove residual N,N-dimethylformamide solvent.

8. A core-shell structured bimodal thermochromic fiber, characterized in that, The fiber includes a shell and a core, with the shell covering the periphery of the core. The shell comprises a thermoplastic polyurethane (TPU) matrix and thermochromic microcapsules (TM) with a particle size of 1-3 μm dispersed therein. The thermochromic microcapsules are used to undergo reversible color changes at different temperatures to adjust the reflectivity of the fiber in the solar radiation band. The mass ratio of the thermochromic microcapsules (TM) to TPU is 10:100 to 14:

100. The core layer comprises a thermoplastic polyurethane (TPU) matrix and nano-alumina (Al2O3) particles with a particle size of 300-500 nm dispersed therein. The nano-alumina is used to adjust the emissivity of the fiber in the infrared band (8-13 μm) in the atmospheric window. The mass ratio of the nano-alumina (Al2O3) particles to TPU is 10:100 to 16:

100.

9. The fiber according to claim 8, characterized in that, The ratio of the shell thickness to the fiber cross-sectional diameter ranges from 0.125 to 0.

25.

10. The fiber according to claim 8, characterized in that, When the fiber is heated to the phase transition temperature at room temperature (26°C), the thermal response time for the phase change from dark to light is 8-10 s, and the thermal response time for the phase change from light to dark is 10-12 s after heating is stopped.

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