Phase change fiber with structural damage visualization function and preparation method thereof

Abstract

This invention belongs to the field of phase change fiber structural damage identification technology, and relates to a phase change fiber with structural damage visualization function and its preparation method. The phase change fiber has a three-layer coaxial structure. The core layer is composed of a solid-liquid phase change material and a thixotropic agent, exhibiting a gel-like state in a static state and fluidity under shear stress. The middle layer is composed of a polymer and functionalized filler, the functionalized filler being a porous adsorbent filler loaded with indicator dyes. The outer layer is an optical shielding layer containing transparent colored pigments, which selectively absorb and attenuate the background color output wavelength of the indicator dyes under visible light illumination. First, a nascent fiber composed of the core and middle layers is prepared using a coaxial wet spinning process. Then, the outer layer is coated onto the surface of the nascent fiber to form the product. The phase change fiber with structural damage visualization function of this invention can achieve intuitive monitoring under natural light conditions, and the preparation method is simple.

Description

Technical Field

[0001] This invention belongs to the field of phase change fiber structural damage identification technology, and relates to a phase change fiber with structural damage visualization function and its preparation method. Background Technology

[0002] Phase change fibers (PCFs) have shown great application potential in the fields of smart textiles, wearable devices, and thermal management of components due to their excellent latent heat storage and temperature regulation properties. However, solid-liquid PCFs are highly susceptible to liquid leakage during the endothermic melting stage, leading to a significant decrease in latent heat storage performance. Leaked liquid substances can even pollute the surrounding environment, severely restricting the reliability and safety of PCFs.

[0003] Current research on phase change fibers mainly focuses on improving the loading capacity of the core phase change material and the stability of the outer encapsulation. For example, core-sheath structure fibers prepared using coaxial wet spinning technology achieve high enthalpy and leak-proof performance through polymer coating of the sheath. However, when microcracks develop due to mechanical fatigue during long-term service, these fibers are difficult to detect with the naked eye in time, and the problem often only becomes apparent after a large amount of core material leakage or a significant decline in energy storage function. Traditional core-sheath structure phase change fibers, such as those described in CN202311267840.X and CN202310878877.X, disclose process routes for preparing core-sheath structure phase change fibers using coaxial wet spinning. The focus is on improving the loading capacity, encapsulation stability, leak-proof capability, and enthalpy of the core phase change material (such as paraffin wax, octadecane, etc.). The sheath is usually a single polymer (such as polyacrylonitrile, polyurethane, etc.), or functional particles are introduced into the sheath to achieve additional functions such as photothermal and electrothermal effects. While these coaxial phase change fibers focus on improving encapsulation efficiency and enthalpy, microcracks caused by mechanical fatigue in the outer layer during long-term service are invisible to the naked eye. Before these microcracks develop into obvious breaks, users find it difficult to promptly determine whether the core layer has experienced minor leakage or thermal performance degradation. In practice, these issues are often not discovered until a large amount of core material leaks out, staining clothing or the energy storage function fails significantly, leading to insufficient safety and reliability.

[0004] To address these shortcomings, researchers have developed intelligent monitoring technologies, such as grafting aggregated fluorescent groups onto the molecular chains of phase change materials, utilizing the enhanced fluorescence after leakage to achieve a tracing effect. However, this method relies on ultraviolet light excitation, resulting in weak signals under natural light, and the fluorescence intensity is easily affected by the phase state and distribution of the leaked material, making it unable to stably and intuitively reflect damage. Furthermore, it struggles to distinguish between fiber structural rupture and normal internal migration, failing to meet the practical application requirements for visual identification of damage location, extent, and type.

[0005] For example, Reference 1 (Cellulose nanofiber encapsulated PEG phase change composites containing AIE-gen for monitoring leak process[J]. Composites Part A, 2023) describes a method that chemically grafts aggregation-induced emission (AIE) fluorescent groups (ZPP) onto PEG molecular chains to obtain PEG-ZPP, which is then physically blended with pure PEG to form a fluorescent phase change composite system. This system is then introduced into a cellulose nanofiber aerogel framework using vacuum impregnation to form a composite phase change material. Its working principle utilizes the significant fluorescence enhancement of AIE groups after leakage and solidification aggregation, using the overall fluorescence intensity change as a leak indication signal under ultraviolet light (UV 365nm) excitation. However, it has the following drawbacks:

[0006] (1) The equipment is highly dependent and cannot achieve "direct visual alarm under natural light": the visibility of leakage is enhanced by fluorescence, and the clear effect is often based on external conditions such as UV irradiation / dark environment; under ordinary natural light or indoor white light conditions, the signal is easy to become weak or not conspicuous enough. Therefore, in actual use, it is often necessary to match the equipment such as UV light source to reliably identify it, and the application scenarios are limited.

[0007] (2) The signal is greatly affected by the phase state or morphology: The AIE luminescence mechanism is closely related to whether the molecules are in an aggregated state and whether the local concentration is high enough. In actual leakage, the phase change material is often in a state of melting flow, diffusion, etc. The degree of local aggregation and concentration will change with time and circumstances, resulting in random fluctuations in fluorescence / display intensity. It is difficult to ensure that a clear signal is presented stably and continuously at different temperatures and different leakage stages.

[0008] (3) It is difficult to accurately judge the characteristics of fiber structure damage. Existing technology can only trace the leakage of phase change material, but it cannot distinguish between the normal migration of internal components and structural rupture.

[0009] Therefore, it is of great significance to study a phase change fiber with structural damage visualization function that can be directly identified by the naked eye under natural light and can reliably judge structural damage, as well as its preparation method, in order to solve the problems existing in the prior art. Summary of the Invention

[0010] The purpose of this invention is to solve the problems existing in the prior art and to provide a phase change fiber with structural damage visualization function and its preparation method.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A phase change fiber with structural damage visualization function has a three-layer coaxial structure, consisting of a core layer, an intermediate layer and an outer layer from the inside out.

[0013] The core layer is a thixotropic phase change material fluid, composed of solid-liquid phase change material and thixotropic agent. It is gel-like in a static state and has fluidity under shear stress.

[0014] The intermediate layer is composed of a polymer and a functionalized filler, wherein the functionalized filler is a porous adsorbent filler loaded with indicator dyes;

[0015] The outer layer is an optical shielding layer containing transparent colored pigments, which selectively absorb and attenuate the background color output band of the indicator dye under visible light illumination.

[0016] The present invention features an outer colored optical shielding layer to shield weak background signals caused by non-outer layer structural damage, such as internal material migration and penetration. When the fiber undergoes structural rupture and the outer layer fails at the break, the internal color signal is released and presents a high-contrast visual change, achieving a threshold-triggered visual recognition effect, while also providing both anti-background interference and high-contrast visual alarm.

[0017] As a preferred technical solution:

[0018] As described above, a phase change fiber with structural damage visualization function, wherein the solid-liquid phase change material is an alkane-based phase change material with the structural formula C0. n H 2n+2 , where n ranges from 14 to 20.

[0019] As described above, a phase change fiber with structural damage visualization function is provided, wherein the thixotropic agent is one or more of the following: hydrophobic fumed silica, organically modified bentonite, organic montmorillonite, attapulgite, hydrophobically modified cellulose nanocrystals, and carbon nanotubes, and the thixotropic agent accounts for 5-15% of the mass percentage of the core layer. These thixotropic agent materials all have the following characteristics: 1. They possess micro / nanoscale feature sizes and have high specific surface area or large aspect ratio; 2. Their surfaces all possess hydrophobic / lipophilic properties (e.g., using hydrophobic grades or undergoing organic modification), enabling excellent compatibility and dispersion with non-polar straight-chain alkane phase change materials.

[0020] The phase change fiber with structural damage visualization function as described above, wherein the polymer is one or more of thermoplastic polyurethane, polyacrylonitrile, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene), polymethyl methacrylate, polyethersulfone, polysulfone, polyvinyl chloride and cellulose acetate.

[0021] The porous adsorbent filler is composed of hydrophilic fumed silica, mesoporous carbon, metal-organic frameworks (MOFs), porous zeolite, or porous starch, with a mass fraction of 5-20% relative to the polymer. When fumed silica is used as a core layer thixotropic agent, its key characteristics are hydrophobicity and high specific surface area; hydrophobic fumed silica must be selected to ensure good dispersibility in nonpolar phase-change alkanes, thereby constructing a stable gel network. When fumed silica is used as an intermediate layer porous adsorbent, its key characteristics are hydrophilicity, high specific surface area, and high porosity; hydrophilic fumed silica must be selected, utilizing its abundant silanol groups and extremely high specific surface area to achieve efficient adsorption and loading of indicator dyes.

[0022] The indicator dye is Nile Red, Coumarin 6, or Lumogen F Red 305, and the loading of the indicator dye relative to the porous adsorbent filler is 0.3~2.0wt%, specifically: Nile Red 0.5~1.0wt%, Coumarin 6 1.0~2.0wt%, and Lumogen F Red 305 0.3~1.0wt%.

[0023] As described above, in a phase change fiber with structural damage visualization function, the optical shielding layer is made of water-based polyurethane, silicone rubber, or acrylic resin.

[0024] The outer layer has a thickness of 2~10μm and an average transmittance of 35~70% in the visible light band.

[0025] The core layer has a diameter of 200~340μm, and the intermediate layer has a radial thickness of 15~65μm.

[0026] As described above, in a phase change fiber with structural damage visualization capabilities, the indicator dye and the transparent colored pigment satisfy one of the following matching relationships:

[0027] a. Yellow-purple system: The indicator dye is Nile Red, and the transparent colored pigment is a purple transparent pigment (such as Pigment Violet 23), with the transparent colored pigment accounting for 1.0~1.5% of the outer layer by mass.

[0028] b. Green-Red System: The indicator dye is coumarin 6, and the transparent colored pigment is a red or magenta transparent pigment (such as Pigment Red 122), wherein the transparent colored pigment accounts for 1.0~2.0% of the mass percentage of the outer layer;

[0029] c. Red-green system: The indicator dye is Lumogen F Red 305, and the transparent colored pigment is a green transparent pigment (such as Pigment Green 7). The transparent colored pigment accounts for 1.5~3.0% of the mass percentage of the outer layer.

[0030] Under visible light illumination, background coloration originates from the selective absorption of a portion of the incident white light by the indicator dye. The remaining spectrum, unabsorbed, is reflected or transmitted through the fiber into the human eye, thus macroscopically presenting the corresponding color. This invention introduces a transparent colored pigment into the outer layer to form an optical shield, further selectively absorbing and attenuating the corresponding wavelength of the background coloration, ensuring that the weak coloration when the structure is intact is below the threshold for visual recognition. The degree of attenuation is determined by the coverage area and content of the pigment absorption band, as well as the coating thickness. When the fiber breaks, the outer layer fails at the fracture point, exposing the leaked material in the middle layer, thereby creating a high-contrast, visible color-changing alarm at the fracture point.

[0031] This invention aims to achieve a threshold-triggered visual recognition effect: when the fiber structure is intact, the outer layer selectively attenuates the background color signal, reducing it below the visual recognition threshold; when the fiber undergoes structural breakage, causing the outer layer to fail at the fracture point, the internal color signal is released, exhibiting a high-contrast visual change. This requires the absorption band of the outer layer's transparent colored pigment to match the actual background color band of the indicator dye in the target medium, and the content of the transparent colored pigment and the coating thickness to fall within the usable window. All three systems mentioned above can meet this requirement, ensuring a stable achievement of the "integrity suppression, breakage manifestation" effect.

[0032] The present invention also provides a method for preparing a phase change fiber with structural damage visualization function as described in any of the preceding claims. First, a nascent fiber composed of the core layer and the intermediate layer is prepared by coaxial wet spinning process. Then, the outer layer is formed by coating the surface of the nascent fiber to obtain the phase change fiber with structural damage visualization function.

[0033] As a preferred technical solution:

[0034] The specific steps of the preparation method of phase change fiber with structural damage visualization function as described above are as follows:

[0035] S1: The solid-liquid phase change material is heated to a molten state and kept at that temperature. The thixotropic agent is added, and the material is prepared by ultrasonic treatment and / or high-speed shear dispersion to obtain a core-layer thixotropic fluid with shear-thinning properties.

[0036] S2: Prepare a homogeneous mixture containing the polymer, the porous adsorbent filler and the indicator dye as an intermediate layer spinning solution;

[0037] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, extruded into the coagulation bath for solidification and molding, and then washed and dried to obtain the nascent fiber.

[0038] S4: Coating liquid is applied to the surface of the nascent fiber and cured to form the outer layer; the coating liquid is an aqueous polyurethane, silicone rubber or acrylic resin solution containing the transparent colored pigment.

[0039] The preparation method of phase change fiber with structural damage visualization function as described above, the preparation process of the intermediate layer spinning solution in step S2 includes the following steps:

[0040] S21: Preparation of composite powder: The indicator dye is dissolved in ethanol to prepare a dye solution. The dried porous adsorbent packing is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying, so that the indicator dye is adsorbed on the surface or in the pores of the porous adsorbent packing to obtain composite powder.

[0041] S22: Temporary coating treatment: Polyvinyl alcohol and / or sodium alginate are dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of polyvinyl alcohol and / or sodium alginate on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then pulverized, ground, and sieved to obtain a coated composite powder.

[0042] S23: Spinning solution blending: The polymer is dissolved in an organic solvent to obtain a homogeneous solution, and then the coated composite powder is dispersed in the homogeneous solution to obtain an intermediate layer spinning solution; the mass fraction of the polymer in the homogeneous solution is 15~20%, and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, and acetone.

[0043] In the preparation method of phase change fiber with structural damage visualization function as described above, the specific process parameters in steps S3 and S4 are as follows:

[0044] The inner diameter of the outer channel needle is 0.86~1.05mm, the inner diameter of the inner channel needle is 0.27~0.40mm, and the outer diameter of the inner channel needle is 0.55~0.70mm.

[0045] The extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.15~1:1;

[0046] The coagulation bath is deionized water or a mixture of deionized water and ethanol, and the coagulation bath temperature is 30~45℃.

[0047] The nascent fibers are washed with water in or after step S3 to dissolve and remove the temporary coating layer formed by the coated composite powder.

[0048] The solid content of the coating liquid is 40-100%;

[0049] The curing method in step S4 is either room temperature drying curing or heating curing at 60~100℃.

[0050] Invention principle:

[0051] To address the lack of visual alarm for leakage in traditional coaxial phase change fibers, this invention introduces a functional system for visually identifying structural damage into the coaxial fiber structure. Specifically, an intermediate layer, namely a polymer composite layer, is set outside the core layer, in which porous adsorbent filler is dispersed and loaded with an indicator dye. An optical shielding layer containing a specific transparent colored pigment is set on the outermost layer. This indicator dye has a color response to changes in the microenvironment. When a small amount of phase change material in the core layer migrates, it can produce a weak background color. The spectral absorption band of the transparent colored pigment in the outer layer matches the color spectrum, thereby selectively absorbing and attenuating it under visible light. This shields the weak background signal caused by internal material migration, penetration, and other non-outer layer structural damage, preventing slight changes from being directly observed.

[0052] This invention does not rely on UV excitation to "amplify the signal," but rather designs the display logic through a three-layer coaxial structure and an outer optical shield: such as Figure 3 As shown, when the fiber structure is intact, even if the core phase change material undergoes internal migration and infiltration, resulting in weak background color rendering of the intermediate layer dye, the outer colored optical shielding layer will selectively absorb and attenuate the output wavelength of this background color rendering, making the background color rendering lower than the visual recognition threshold, thus remaining invisible or extremely difficult to detect in appearance; for example Figure 4 As shown, when the fiber undergoes structural rupture, the outer layer is damaged or fails at the fracture point, releasing the optical confinement. This allows the intermediate color-developing unit and the core layer's leaks to be directly exposed in the fracture area, exhibiting a high-contrast, visible color change. This allows for direct observation under natural light or indoor white light conditions without the need for additional UV equipment. Ultimately, without altering the main structure of the coaxial fiber energy storage encapsulation, a direct alarm for structural damage and leakage risks during fiber service is achieved.

[0053] The signal strength of existing AIE (Advanced Ion Transformation) technologies is easily affected by factors such as whether the material accumulates and whether the local concentration reaches a threshold, making it difficult to guarantee a stable and continuous clear signal at different temperatures and leakage stages. In contrast, the visualization recognition result of this invention is primarily determined by the integrity of the outer optical shield: in an intact state, the background signal is suppressed; during rupture, a significant color change occurs in the leakage area, resulting in a stable and visible high-contrast signal. Therefore, even if the phase change material is in a molten, flowing, or diffused state, this invention can maintain the stability and consistency of the display effect through a threshold triggering mechanism. Regardless of whether the leakage caused by rupture is minute or large, as long as a fracture defect is formed and the outer layer fails at that point, a visual alarm can be triggered, thereby improving the selectivity and reliability of the recognition.

[0054] Beneficial effects:

[0055] (1) The phase change fiber of the present invention has a structural damage visualization function, which has high latent heat storage density, toughness and visualization damage identification ability, and can realize intuitive monitoring under natural light environment.

[0056] (2) A method for preparing phase change fiber with structural damage visualization function of the present invention is to set an outer colored optical shielding layer on the structure to shield the weak background signal generated by non-outer structural damage such as internal material migration and penetration; when the structure breaks and the core material leaks out and breaks through the shielding layer, a significant color change occurs, realizing the threshold-triggered visualization recognition effect, taking into account both anti-background interference and high-contrast visualization alarm.

[0057] (3) The present invention provides a method for preparing phase change fiber with structural damage visualization function. Existing technologies mostly use AIE fluorescence tracing to achieve leakage display. Clear high-contrast signals can usually be obtained in UV excitation / dark environment. The visibility under natural white light conditions is insufficient or unstable, and its signal is related to the aggregation state and local concentration. Melting flow and diffusion during the leakage process can easily lead to display fluctuations. In contrast, the present invention can characterize the visual alarm effect caused by structural failure through ΔE* under white light conditions, and achieves a more stable and selective structural failure visual alarm effect without the need for external excitation equipment. Attached Figure Description

[0058] Figure 1 A schematic diagram of the radial cross-section structure of a phase change fiber with structural damage visualization capabilities;

[0059] Figure 2 A schematic diagram of the axial cross-sectional structure of a phase change fiber with structural damage visualization capabilities after fabrication.

[0060] Figure 3This diagram illustrates the optical shielding and background color suppression principle of phase change fibers with structural damage visualization capabilities after thermal cycling while maintaining structural integrity. The dashed arrows in the diagram represent weak background color signals shielded by the outer layer.

[0061] Figure 4 This diagram illustrates the material leakage and high-contrast visualization alarm principle of phase change fibers with structural damage visualization capabilities when structural fracture occurs. The dashed arrows in the diagram represent weak background color signals shielded by the outer layer, while the solid arrows at the fracture point represent leaked dye color signals. Color changes are indicated by differences in symbols and signal positions.

[0062] Among them, 1 is the outer layer, 2 is the middle layer, and 3 is the core layer. Detailed Implementation

[0063] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0064] The testing methods involved in the performance indicators of this invention are as follows:

[0065] (1) Color difference ΔE*: Measurements were taken in a windowless room with fixed lighting and a fixed test position. Multiple fiber samples were tightly and seamlessly wound and fixed onto a matte white substrate using a parallel winding method, forming a pure fiber test area with a coverage area larger than the measurement aperture. A colorimeter with a 3mm measurement aperture, a D65 light source, a 10° observer angle, and a D / 8 SCI measurement geometry was used. Five measurements were taken along the fiber length for each condition, and the average value was recorded. The colorimeter established a standard based on the reference sample and directly output the color difference ΔE* according to CIE76.

[0066] This invention can be quantitatively characterized using two sets of ΔE*:

[0067] Background suppression in intact state: Using initially intact fibers as the standard, fibers that maintain structural integrity after thermal cycling from 0 to 50°C are tested. A ΔE* of ≤2.3 indicates that even if background coloration occurs due to migration and penetration within the phase change material, it remains below the visually perceptible threshold under natural white light and is not visible. Rupture-triggered alarm: Using the unruptured area as the standard, the ruptured / leaking area is tested. A ΔE* of ≥6 indicates that structural rupture leads to leakage of the core material, breaking through the outer layer's suppression, resulting in a significant visible color change alarm. Furthermore, for the case of 2.3 < ΔE* < 6, a visual warning is defined, indicating a visually perceptible change in appearance, but the contrast has not yet reached a strong alarm level. Literature and industry practice generally consider ΔE* in the order of approximately 1 to 2.3 to be close to the just-perceptible difference (JND). Therefore, ΔE* ≤ 2.3 is used as the criterion for an intact state that is imperceptible or extremely difficult to detect by the naked eye; while ΔE* ≥ 6 corresponds to a significantly visible difference and can be used as the criterion for a significantly visible alarm.

[0068] (2) Latent heat storage density: The latent heat storage density was quantitatively tested using a differential scanning calorimeter (DSC). The specific test conditions and parameter settings were as follows: Under a nitrogen (N2) atmosphere, the gas flow rate was kept constant at 200 mL / min; 5-10 mg of dried fiber sample was accurately weighed and placed in a standard aluminum sealed crucible. The specific temperature program for the test was as follows: First, the sample was heated to 80 °C at a heating rate of 10 °C / min to completely eliminate the thermal history of the sample; then, the sample was cooled to 0 °C at a cooling rate of 10 °C / min; finally, it was heated to 80 °C again at a heating rate of 10 °C / min. The heat flow curves of the complete cooling and heating cycles after eliminating the thermal history were extracted, and the area integration of the exothermic crystallization peak and the endothermic melting peak in the curves was performed using the instrument's matching analysis software to calculate the crystallization enthalpy (ΔH) of the sample. c ) and enthalpy of fusion (ΔH) m The unit is J / g. In specific embodiments, the enthalpy of fusion is used as a quantitative indicator to characterize the latent heat storage density of the fiber.

[0069] The sources of some of the materials in this invention are as follows:

[0070] Hydrophobic fumed silica: Manufacturer: Evonik, Brand: AEROSIL R972.

[0071] Organic modified bentonite: Manufacturer: Zhejiang Huatai New Materials, Grade: BP-186.

[0072] Organomontmorillonite: Manufacturer: Zhejiang Fenghong New Materials, Brand: DK2.

[0073] Attapulgite clay: Manufacturer: Changzhou Dingbang, Grade: C608.

[0074] Hydrophobically modified cellulose nanocrystals: hydrophobic nanocellulose dry powder, with a diameter of 3~5nm and a length of 300~1000nm.

[0075] Carbon nanotubes: Manufacturer: Shenzhen Suiheng Technology, 99% carbon nanotubes, inner diameter 3~5nm, outer diameter 8~15nm, length 8~14μm.

[0076] Thermoplastic polyurethane: Manufacturer: BASF, Grade: 1170A.

[0077] Polyacrylonitrile: Manufacturer: Guangzhou Zhongxin Plastics, molecular weight 150,000.

[0078] Polyvinylidene fluoride: Manufacturer: San-Ai-F, Grade: FR904.

[0079] Poly(vinylidene fluoride-hexafluoropropylene): Manufacturer: Arkema, Brand: Flex2801.

[0080] Polymethyl methacrylate: Manufacturer: Wanhua Chemical, Brand: ACRYPLAS® HD01A.

[0081] Polyethersulfone: Manufacturer: BASF, Grade: E 6020 P.

[0082] Polysulfone: Manufacturer: Solvay, Grade: P-1700.

[0083] Polyvinyl chloride: Manufacturer: Zhongtai Chemical, Grade: SG-5.

[0084] Cellulose acetate: Manufacturer: EASTMAN, Brand: CA-398-3.

[0085] Hydrophilic fumed silica: Manufacturer: Evonik, Brand: AEROSIL 200.

[0086] Mesoporous carbon: Manufacturer: Jiangsu Xianfeng Nano, Grade: CMK-3.

[0087] Metal-organic framework (MOFs) (ZIF-8 type MOF): Manufacturer: Jiangsu Xianfeng Nano, Grade: XFF28-1.

[0088] Porous zeolite: Manufacturer: Sinopharm Group, Brand: Molecular sieve 13X.

[0089] Porous starch: Manufacturer: AkzoNobel, Brand: DRY FLO® PC.

[0090] Polyvinyl alcohol: Manufacturer: Anhui Wanwei High-tech, Grade: PVA 17-88.

[0091] Sodium alginate: Manufacturer: Shanghai McLean, Brand: S817372.

[0092] Waterborne polyurethane: Manufacturer: Covestro, Brand: Impranil® DLN-SD.

[0093] Silicone rubber: Manufacturer: Dow, Brand: SYLGARD 184.

[0094] Acrylic resin: Manufacturer: Badifu, Brand: RS-2788.

[0095] Example 1

[0096] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0097] S1: Octadecylene was heated to a molten state and held at that temperature. Hydrophobic fumed silica was added, and the mixture was ultrasonically treated at 400W for 30 minutes to prepare a core-layer thixotropic fluid. The hydrophobic fumed silica accounted for 8% of the mass of the core layer.

[0098] S2: Preparation of intermediate layer spinning solution;

[0099] S21: Preparation of composite powder: Nile red is dissolved in ethanol to prepare a dye solution. The dye solution is used to pre-wet dry hydrophilic fumed silica to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying at 60°C, so that Nile red is adsorbed on the surface of hydrophilic fumed silica to obtain composite powder.

[0100] The mass-to-volume ratio of Nile Red to ethanol was 1 mg:1 mL; the loading of Nile Red relative to hydrophilic fumed silica was 0.8 wt%.

[0101] S22: Temporary coating treatment: Polyvinyl alcohol is dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of polyvinyl alcohol on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then crushed, ground and sieved to obtain a coated composite powder.

[0102] The mass fraction of polyvinyl alcohol in the coating solution is 3%;

[0103] S23: Spinning solution blending: Thermoplastic polyurethane is dissolved in N,N-dimethylformamide to obtain a homogeneous solution, and then the coated composite powder is dispersed in the homogeneous solution to obtain an intermediate layer spinning solution;

[0104] The mass fraction of thermoplastic polyurethane in the homogeneous solution is 20%; the mass fraction of hydrophilic fumed silica relative to thermoplastic polyurethane is 10%.

[0105] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, extruded into deionized water at 30°C for solidification and molding, and then washed and dried to obtain nascent fibers.

[0106] The outer channel needle has an inner diameter of 0.86 mm, the inner channel needle has an inner diameter of 0.3 mm, and the inner channel needle has an outer diameter of 0.6 mm; the extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 1:1.

[0107] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0108] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and the outer layer is formed by drying and curing at room temperature; the coating liquid is an aqueous polyurethane solution containing pigment Violet 23; the solid content of the coating liquid is 40%; and the mass percentage of pigment Violet 23 in the outer layer is 1%.

[0109] like Figures 1-2 As shown, the final phase change fiber with structural damage visualization function has a three-layer coaxial structure, consisting of a core layer 3, an intermediate layer 2, and an outer layer 1 from the inside out. The outer layer 1 is an optical shielding layer containing pigment violet 23, with a thickness of 2 μm and an average transmittance of 70% in the visible light band. The core layer 3 is gel-like in a static state and exhibits fluidity under shear stress. The diameter of the core layer 3 is 290 μm. The radial thickness of the intermediate layer 2 is 15 μm. Pigment violet 23 has a selective absorption and attenuation effect on Nile red dissolved in n-octadecane in the background color output band under visible light illumination. The latent heat storage density of the phase change fiber with structural damage visualization function is 157.5 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 1.1 (≤2.3, not visible); the ΔE* after 100 thermal cycles at 0~50℃ is 1.9 (still ≤2.3, structurally intact and background not visible); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 5.6; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 16.5 (≥6, significantly visible alarm).

[0110] Example 2

[0111] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0112] S1: Heating n-pentadecane to a molten state and holding at that temperature, adding organically modified bentonite, and then shearing at 3000 rpm for 30 min yielded a core-layer thixotropic fluid; the organically modified bentonite accounted for 5% of the core-layer mass.

[0113] S2: Preparation of intermediate layer spinning solution;

[0114] S21: Preparation of composite powder: Nile red is dissolved in ethanol to prepare a dye solution. The dried mesoporous carbon is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying at 60°C, so that Nile red is adsorbed in the pores of the mesoporous carbon to obtain composite powder.

[0115] The mass-to-volume ratio of Nile Red to ethanol was 0.4 mg:1 mL; the loading of Nile Red relative to mesoporous carbon was 1 wt%.

[0116] S22: Temporary coating treatment: Sodium alginate is dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of sodium alginate on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then crushed, ground and sieved to obtain a coated composite powder.

[0117] The mass fraction of sodium alginate in the coating solution is 1%;

[0118] S23: Spinning solution blending: Polyacrylonitrile is dissolved in dimethyl sulfoxide to obtain a homogeneous solution, and then the coated composite powder is dispersed in the homogeneous solution to obtain an intermediate layer spinning solution;

[0119] The homogeneous solution contains 18% polyacrylonitrile by mass; the mesoporous carbon contains 8% mesoporous carbon by mass relative to polyacrylonitrile.

[0120] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, and extruded into a 32°C coagulation bath for solidification and molding. After washing and drying, nascent fibers are obtained.

[0121] The outer channel needle has an inner diameter of 0.86 mm, the inner channel needle has an inner diameter of 0.27 mm, and the inner channel needle has an outer diameter of 0.55 mm. The extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 1:1. The coagulation bath is a mixture of deionized water and ethanol with a volume ratio of 8:2.

[0122] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0123] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and then cured by heating at 80°C to form an outer layer; the coating liquid is an organosilicon rubber containing pigment Violet 23; the solid content of the coating liquid is 100%; and the mass percentage of pigment Violet 23 in the outer layer is 1.5%.

[0124] The resulting phase change fiber with structural damage visualization capabilities has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out. The outer layer is an optical shielding layer containing pigment violet 23, with a thickness of 5 μm and an average transmittance of 55% in the visible light band. The core layer is gel-like in a static state but exhibits fluidity under shear stress. The core layer has a diameter of 250 μm. The radial thickness of the middle layer is 21 μm. Pigment violet 23 selectively absorbs and attenuates Nile red dissolved in n-pentadecane in the background color output band under visible light illumination. The fiber possesses structural damage visualization capabilities. The latent heat storage density of the phase change fiber with damage visualization function is 128.6 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 0.8 (≤2.3, not visible); the ΔE* after 100 thermal cycles at 0~50℃ is 1.6 (still ≤2.3, structurally intact and background not visible); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 4.6; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 14.2 (≥6, significantly visible alarm).

[0125] Example 3

[0126] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0127] S1: Hexadecane was heated to a molten state and held at that temperature. Organomontmorillonite was added, and the mixture was subjected to high-speed shearing at 3500 rpm for 20 min to prepare a core-layer thixotropic fluid. The organomontmorillonite accounted for 7.50% of the mass of the core layer.

[0128] S2: Preparation of intermediate layer spinning solution;

[0129] S21: Preparation of composite powder: Coumarin 6 is dissolved in ethanol to prepare a dye solution. The dry metal-organic framework material is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying at 60°C, so that coumarin 6 is adsorbed on the surface of the metal-organic framework material to obtain composite powder.

[0130] The mass-to-volume ratio of coumarin 6 to ethanol was 0.2 mg:1 mL; the loading of coumarin 6 relative to the metal-organic framework material was 1 wt%.

[0131] S22: Temporary coating treatment: Polyvinyl alcohol is dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of polyvinyl alcohol on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then crushed, ground and sieved to obtain a coated composite powder.

[0132] The mass fraction of polyvinyl alcohol in the coating solution is 2%;

[0133] S23: Spinning solution blending: A mixture of polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene) in a mass ratio of 1:1 is dissolved in N-methylpyrrolidone to obtain a homogeneous solution. Then, the coated composite powder is dispersed in the homogeneous solution to obtain an intermediate layer spinning solution.

[0134] The mass fraction of polyvinylidene fluoride (PVDF) and poly(PVDF-hexafluoropropylene) mixture in the homogeneous solution is 15%; the mass fraction of metal-organic framework material relative to PVDF and poly(PVDF-hexafluoropropylene) mixture is 10%.

[0135] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, and extruded into deionized water at 35°C for solidification and molding. After washing and drying, nascent fibers are obtained.

[0136] The outer channel needle has an inner diameter of 0.86 mm, the inner channel needle has an inner diameter of 0.3 mm, and the inner channel needle has an outer diameter of 0.6 mm; the extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.5:1.

[0137] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0138] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and then cured by heating at 80°C to form an outer layer; the coating liquid is an acrylic resin containing Pigment Red 122; the solid content of the coating liquid is 50%; Pigment Red 122 accounts for 2% of the mass percentage of the outer layer.

[0139] The resulting phase change fiber with structural damage visualization capabilities has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out. The outer layer is an optical shielding layer containing Pigment Red 122, with a thickness of 4.5 μm and an average transmittance of 52% in the visible light band. The core layer is gel-like in a static state but exhibits fluidity under shear stress; the core layer has a diameter of 280 μm. The radial thickness of the middle layer is 26 μm. Pigment Red 122 selectively absorbs and attenuates coumarin 6 dissolved in n-hexadecane in the background color output band under visible light illumination. The latent heat storage density of the phase change fiber with structural damage visualization function is 115.3 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 0.9 (≤2.3, not visible); the ΔE* after 100 thermal cycles at 0~50℃ is 1.7 (still ≤2.3, structurally intact and background not visible); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 4.2; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 13.6 (≥6, significantly visible alarm).

[0140] Example 4

[0141] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0142] S1: Tetradecane was heated to a molten state and held at that temperature. Attapulgite was added, and the mixture was subjected to high-speed shearing at 2500 rpm for 15 min and ultrasonic treatment at 400 W for 15 min to prepare a thixotropic fluid for the core layer. The mass percentage of attapulgite in the core layer was 10%.

[0143] S2: Preparation of intermediate layer spinning solution;

[0144] S21: Preparation of composite powder: Coumarin 6 is dissolved in ethanol to prepare a dye solution. The dry porous zeolite is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying at 60°C, so that coumarin 6 is adsorbed on the surface of the porous zeolite to obtain composite powder.

[0145] The mass-to-volume ratio of coumarin 6 to ethanol was 0.2 mg:1 mL; the loading of coumarin 6 relative to porous zeolite was 2 wt%.

[0146] S22: Temporary coating treatment: Polyvinyl alcohol is dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of polyvinyl alcohol on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then crushed, ground and sieved to obtain a coated composite powder.

[0147] The mass fraction of polyvinyl alcohol in the coating solution is 1.5%;

[0148] S23: Spinning solution blending: Polymethyl methacrylate is dissolved in N,N-dimethylacetamide to obtain a homogeneous solution, and then the coated composite powder is dispersed in the homogeneous solution to obtain the intermediate layer spinning solution;

[0149] The mass fraction of polymethyl methacrylate in the homogeneous solution was 18%; the mass fraction of porous zeolite relative to polymethyl methacrylate was 12%.

[0150] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, extruded into deionized water at 38°C for solidification and molding, and then washed and dried to obtain nascent fibers.

[0151] The outer channel needle has an inner diameter of 1.05 mm, the inner channel needle has an inner diameter of 0.3 mm, and the inner channel needle has an outer diameter of 0.6 mm; the extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.25:1.

[0152] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0153] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and then cured by heating at 60°C to form an outer layer; the coating liquid is an aqueous polyurethane solution containing pigment red 122; the solid content of the coating liquid is 40%; and the pigment red 122 accounts for 1% of the mass percentage of the outer layer.

[0154] The resulting phase change fiber with structural damage visualization capabilities has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out. The outer layer is an optical shielding layer containing Pigment Red 122, with a thickness of 2.5 μm and an average transmittance of 65% in the visible light band. The core layer is gel-like in a static state but exhibits fluidity under shear stress. The core layer has a diameter of 270 μm. The radial thickness of the middle layer is 38 μm. Pigment Red 122 selectively absorbs and attenuates coumarin 6 dissolved in n-tetradecane in the background color output band under visible light illumination. The latent heat storage density of the phase change fiber with structural damage visualization function is 92.4 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 1 (≤2.3, not visible); the ΔE* after 100 thermal cycles at 0~50℃ is 1.8 (still ≤2.3, structurally intact and background not visible); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 5; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 15.5 (≥6, significantly visible alarm).

[0155] Example 5

[0156] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0157] S1: Heating n-nonadecane to a molten state and holding at that temperature, adding hydrophobically modified cellulose nanocrystals, and then subjecting the mixture to high-speed shearing at 2000 rpm for 10 min and ultrasonic treatment at 400 W for 30 min, yielded a core-layer thixotropic fluid; the hydrophobically modified cellulose nanocrystals accounted for 15% of the mass of the core layer.

[0158] S2: Preparation of intermediate layer spinning solution;

[0159] S21: Preparation of composite powder: Lumogen F Red 305 is dissolved in ethanol to prepare a dye solution. The dried porous starch is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying at 60°C, so that Lumogen F Red 305 is adsorbed in the pores of the porous starch to obtain composite powder.

[0160] The mass-to-volume ratio of Lumogen F Red 305 to ethanol was 0.3 mg:1 mL; the loading of Lumogen F Red 305 relative to porous starch was 0.3 wt%.

[0161] S22: Temporary coating treatment: Sodium alginate is dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of sodium alginate on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then crushed, ground and sieved to obtain a coated composite powder.

[0162] The mass fraction of sodium alginate in the coating solution is 1%;

[0163] S23: Spinning solution blending: Dissolve a mixture of polyethersulfone and polysulfone in N-methylpyrrolidone at a mass ratio of 1:1 to obtain a homogeneous solution, and then disperse the coated composite powder in the homogeneous solution to obtain an intermediate layer spinning solution.

[0164] The homogeneous solution contains 20% polyethersulfone and polysulfone mixture by mass; the porous starch contains 15% of the polyethersulfone and polysulfone mixture by mass.

[0165] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, extruded into deionized water at 40°C for solidification and molding, and then washed and dried to obtain nascent fibers.

[0166] The outer channel needle has an inner diameter of 1.05 mm, the inner channel needle has an inner diameter of 0.4 mm, and the inner channel needle has an outer diameter of 0.7 mm; the extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.2:1.

[0167] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0168] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and then cured by heating at 100°C to form an outer layer; the coating liquid is an organosilicon rubber containing pigment green 7; the solid content of the coating liquid is 100%; and the pigment green 7 accounts for 1.5% of the mass percentage of the outer layer.

[0169] The resulting phase change fiber with structural damage visualization capabilities has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out. The outer layer is an optical shielding layer containing pigment green 7, with a thickness of 6.3 μm and an average transmittance of 50% in the visible light band. The core layer is gel-like in a static state but exhibits fluidity under shear stress. The core layer has a diameter of 340 μm. The radial thickness of the middle layer is 47 μm. Pigment green 7 is effective against Lumogen FRed dissolved in n-nonadecane. 305 exhibits selective absorption and attenuation in the background color output band under visible light illumination; the latent heat storage density of the phase change fiber with structural damage visualization function is 97.7 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 0.6 (≤2.3, not visible); the ΔE* after 100 thermal cycling treatments at 0~50℃ is 1.4 (still ≤2.3, structurally intact and not visible against the background); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 3.8; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 12.4 (≥6, significantly visible alarm).

[0170] Example 6

[0171] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0172] S1: Eicosane was heated to a molten state and held at that temperature. Carbon nanotubes were added, and the mixture was subjected to high-speed shearing at 2500 rpm for 15 min and ultrasonic treatment at 400 W for 40 min to prepare a thixotropic fluid with a core layer. The carbon nanotubes accounted for 11% of the mass of the core layer.

[0173] S2: Preparation of intermediate layer spinning solution;

[0174] S21: Preparation of composite powder: Lumogen F Red 305 was dissolved in ethanol to prepare a dye solution. The dye solution was used to pre-wet dry hydrophilic fumed silica to form a dye-adsorbent slurry. Then, the ethanol was removed by heating and drying at 60°C, so that Lumogen F Red 305 was adsorbed on the surface of hydrophilic fumed silica to obtain composite powder.

[0175] The mass-to-volume ratio of Lumogen F Red 305 to ethanol was 0.5 mg:1 mL; the loading of Lumogen F Red 305 relative to hydrophilic fumed silica was 1 wt%.

[0176] S22: Temporary coating treatment: A coating solution is obtained by dissolving a mixture of polyvinyl alcohol and sodium alginate in deionized water at a mass ratio of 1:1. The composite powder is then added to the coating solution and mixed and dispersed to form a coating on the outer surface of the composite powder by the mixture of polyvinyl alcohol and sodium alginate. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then pulverized, ground, and sieved to obtain the coated composite powder.

[0177] The mass fraction of the mixture of polyvinyl alcohol and sodium alginate in the coating solution is 2%;

[0178] S23: Spinning solution blending: Polyvinyl chloride is dissolved in tetrahydrofuran to obtain a homogeneous solution, and then the coated composite powder is dispersed in the homogeneous solution to obtain an intermediate layer spinning solution;

[0179] The homogeneous solution contains 18% polyvinyl chloride by mass; the hydrophilic fumed silica by mass relative to polyvinyl chloride is 8%.

[0180] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, and extruded into a 45°C coagulation bath for solidification and molding. After washing and drying, nascent fibers are obtained.

[0181] The outer channel needle has an inner diameter of 0.86 mm, the inner channel needle has an inner diameter of 0.3 mm, and the inner channel needle has an outer diameter of 0.6 mm; the extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.25:1; the coagulation bath is a mixture of deionized water and ethanol with a volume ratio of 7:3.

[0182] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0183] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and then cured by heating at 60°C to form an outer layer; the coating liquid is an acrylic resin solution containing pigment green 7; the solid content of the coating liquid is 50%; and pigment green 7 accounts for 3% of the mass percentage of the outer layer.

[0184] The resulting phase change fiber with structural damage visualization capabilities has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out. The outer layer is an optical shielding layer containing pigment green 7, with a thickness of 10 μm and an average transmittance of 35% in the visible light band. The core layer is gel-like in a static state but exhibits fluidity under shear stress. The core layer has a diameter of 260 μm. The radial thickness of the middle layer is 32 μm. Pigment green 7 is effective against Lumogen F dissolved in n-eicosane. Red305 exhibits selective absorption and attenuation in the background color output band under visible light illumination; the latent heat storage density of the phase change fiber with structural damage visualization function is 88.7 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 0.4 (≤2.3, invisible); the ΔE* after 100 thermal cycling treatments at 0~50℃ is 1.2 (still ≤2.3, structurally intact and invisible to the background); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 3.1; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 11.6 (≥6, significantly visible alarm).

[0185] Example 7

[0186] A method for preparing phase change fibers with structural damage visualization capabilities, comprising the following specific steps:

[0187] S1: Heptadecane was heated to a molten state and held at that temperature. A mixture of hydrophobically modified cellulose nanocrystals and carbon nanotubes in a mass ratio of 1:1 was added. After high-speed shearing at 3000 rpm for 20 min and ultrasonic treatment at 400 W for 45 min, a thixotropic fluid with a core layer was prepared. The mass percentage of the hydrophobically modified cellulose nanocrystals and carbon nanotubes mixture in the core layer was 10%.

[0188] S2: Preparation of intermediate layer spinning solution;

[0189] S21: Preparation of composite powder: Nile red is dissolved in ethanol to prepare a dye solution. The dried porous zeolite is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying at 60°C, so that Nile red is adsorbed in the pores of the porous zeolite to obtain composite powder.

[0190] The mass-to-volume ratio of Nile Red to ethanol was 0.6 mg:1 mL; the loading of Nile Red relative to porous zeolite was 0.5 wt%.

[0191] S22: Temporary coating treatment: Sodium alginate is dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of sodium alginate on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then crushed, ground and sieved to obtain a coated composite powder.

[0192] The mass fraction of sodium alginate in the coating solution is 1%;

[0193] S23: Spinning solution blending: Dissolve cellulose acetate in a mixed solvent of N,N-dimethylacetamide and acetone in a mass ratio of 8:2 to obtain a homogeneous solution, and then disperse the coated composite powder in the homogeneous solution to obtain the intermediate layer spinning solution.

[0194] The homogeneous solution contains 20% cellulose acetate by mass; the porous zeolite contains 20% cellulose acetate by mass.

[0195] S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, and extruded into deionized water at 42°C for solidification and molding. After washing and drying, nascent fibers are obtained.

[0196] The outer channel needle has an inner diameter of 1.05 mm, the inner channel needle has an inner diameter of 0.4 mm, and the inner channel needle has an outer diameter of 0.7 mm; the extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.15:1.

[0197] S4: Wash the nascent fibers with water to dissolve and remove the temporary coating layer formed by the coated composite powder;

[0198] S5: A coating liquid is applied to the surface of the nascent fibers after washing, and the outer layer is formed by drying and curing at room temperature; the coating liquid is an aqueous polyurethane solution containing pigment Violet 23; the solid content of the coating liquid is 40%; and the mass percentage of pigment Violet 23 in the outer layer is 1.2%.

[0199] The resulting phase change fiber with structural damage visualization capabilities has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out. The outer layer is an optical shielding layer containing pigment violet 23, with a thickness of 2.2 μm and an average transmittance of 68% in the visible light band. The core layer is gel-like in a static state but exhibits fluidity under shear stress; the core layer has a diameter of 200 μm. The radial thickness of the middle layer is 65 μm. Pigment violet 23 selectively absorbs and attenuates Nile red dissolved in n-heptadecane in the background color output band under visible light illumination. The fiber possesses a three-layer coaxial structure with structural damage visualization capabilities. The latent heat storage density of the phase change fiber with structural damage visualization function is 54.8 J / g; the initial ΔE* of the phase change fiber with structural damage visualization function is 0.7 (≤2.3, not visible); the ΔE* after 100 thermal cycles at 0~50℃ is 1.5 (still ≤2.3, structurally intact and background not visible); when the fiber has minor damage / minor leakage (visible warning stage), the ΔE* of the leakage / breakage area is 4.8; when the fiber has obvious structural rupture and significant leakage, the ΔE* of the leakage / breakage area is 14.5 (≥6, significantly visible alarm).

Claims

1. A phase change fiber with structural damage visualization function, characterized in that: It has a three-layer coaxial structure, consisting of a core layer, a middle layer, and an outer layer from the inside out; The core layer is composed of a solid-liquid phase change material and a thixotropic agent. It is gel-like in a static state and has fluidity under shear stress. The intermediate layer is composed of a polymer and a functionalized filler, wherein the functionalized filler is a porous adsorbent filler loaded with indicator dyes; The outer layer is an optical shielding layer containing transparent colored pigments. The transparent colored pigments have a selective absorption and attenuation effect on the background color output band of the indicator dye under visible light illumination. The optical shielding layer is made of water-based polyurethane, silicone rubber, or acrylic resin. The outer layer has a thickness of 2~10μm and an average transmittance of 35~70% in the visible light band. The core layer has a diameter of 200~340μm, and the intermediate layer has a radial thickness of 15~65μm; The indicator dye is Nile Red, Coumarin 6, or Lumogen F Red 305; The indicator dye and the transparent colored pigment satisfy one of the following matching relationships: a. The indicator dye is Nile Red, the transparent colored pigment is a purple transparent pigment, and the transparent colored pigment accounts for 1.0~1.5% of the mass percentage of the outer layer; b. The indicator dye is coumarin 6, and the transparent colored pigment is a red or magenta transparent pigment, wherein the transparent colored pigment accounts for 1.0~2.0% of the mass percentage of the outer layer; c. The indicator dye is Lumogen F Red 305, the transparent colored pigment is a green transparent pigment, and the transparent colored pigment accounts for 1.5~3.0% of the mass percentage of the outer layer.

2. The phase change fiber with structural damage visualization function according to claim 1, characterized in that, The solid-liquid phase change material is an alkane-based phase change material with the structural formula C0. n H 2n+2 , where n ranges from 14 to 20.

3. A phase change fiber with structural damage visualization function according to claim 1, characterized in that, The thixotropic agent is one or more of hydrophobic fumed silica, organic modified bentonite, organic montmorillonite, attapulgite, hydrophobic modified cellulose nanocrystals, and carbon nanotubes, and the thixotropic agent accounts for 5-15% of the mass percentage of the core layer.

4. A phase change fiber with structural damage visualization function according to claim 1, characterized in that, The polymer is one or more of thermoplastic polyurethane, polyacrylonitrile, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene), polymethyl methacrylate, polyethersulfone, polysulfone, polyvinyl chloride and cellulose acetate. The porous adsorbent packing material is hydrophilic fumed silica, mesoporous carbon, metal-organic framework material, porous zeolite, or porous starch, and the mass fraction of the porous adsorbent packing material relative to the polymer is 5-20%. The indicator dye is loaded at a rate of 0.3 to 2.0 wt% relative to the porous adsorbent packing.

5. A method for preparing a phase change fiber with structural damage visualization function as described in any one of claims 1 to 4, characterized in that: First, a nascent fiber composed of the core layer and the intermediate layer is prepared using a coaxial wet spinning process. Then, the outer layer is formed by coating the surface of the nascent fiber to obtain the phase change fiber with structural damage visualization function.

6. The method for preparing a phase change fiber with structural damage visualization function according to claim 5, characterized in that, The specific steps are as follows: S1: The solid-liquid phase change material is heated to a molten state and kept at that temperature. The thixotropic agent is added, and the core layer thixotropic fluid is prepared by ultrasonic treatment and / or high-speed shear dispersion. S2: Prepare a homogeneous mixture containing the polymer, the porous adsorbent filler and the indicator dye as an intermediate layer spinning solution; S3: The core layer thixotropic fluid and the intermediate layer spinning solution are respectively introduced into the inner and outer channels of the coaxial spinneret, extruded into the coagulation bath for solidification and molding, and then washed and dried to obtain the nascent fiber. S4: Coating liquid is applied to the surface of the nascent fiber and cured to form the outer layer; the coating liquid is an aqueous polyurethane, silicone rubber or acrylic resin solution containing the transparent colored pigment.

7. The method for preparing a phase change fiber with structural damage visualization function according to claim 6, characterized in that, The preparation process of the intermediate layer spinning solution in step S2 includes the following steps: S21: Preparation of composite powder: The indicator dye is dissolved in ethanol to prepare a dye solution. The dried porous adsorbent packing is pre-wetted with the dye solution to form a dye-adsorbent slurry. Then, the ethanol is removed by heating and drying, so that the indicator dye is adsorbed on the surface or in the pores of the porous adsorbent packing to obtain composite powder. S22: Temporary coating treatment: Polyvinyl alcohol and / or sodium alginate are dissolved in deionized water to obtain a coating solution. The composite powder is added to the coating solution and mixed and dispersed to form a coating of polyvinyl alcohol and / or sodium alginate on the outer surface of the composite powder. The resulting product is then dried to remove moisture and obtain a solid product. The obtained solid product is then pulverized, ground, and sieved to obtain coated composite powder. S23: Spinning solution blending: The polymer is dissolved in an organic solvent to obtain a homogeneous solution, and then the coated composite powder is dispersed in the homogeneous solution to obtain an intermediate layer spinning solution; the mass fraction of the polymer in the homogeneous solution is 15~20%, and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, and acetone; The nascent fibers are washed with water in or after step S3 to dissolve and remove the temporary coating layer formed by the coated composite powder.

8. The method for preparing a phase change fiber with structural damage visualization function according to claim 7, characterized in that, The specific process parameters in steps S3 and S4 are as follows: The inner diameter of the outer channel needle is 0.86~1.05mm, the inner diameter of the inner channel needle is 0.27~0.40mm, and the outer diameter of the inner channel needle is 0.55~0.70mm. The extrusion flow rate ratio of the core layer thixotropic fluid to the intermediate layer spinning solution is 0.15~1:1; The coagulation bath is deionized water or a mixture of deionized water and ethanol, and the coagulation bath temperature is 30~45℃. The solid content of the coating liquid is 40-100%; The curing method in step S4 is either room temperature drying curing or heating curing at 60~100℃.

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