Radiation cooling and phase change energy storage dual functional composite fiber and preparation method thereof

Abstract

This application relates to the fields of functional polymer materials and textiles, and discloses a dual-functional composite fiber for radiation cooling and phase change energy storage, as well as its preparation method. The composite fiber has a sheath-core structure. The sheath material comprises surface-modified optical powder and polyethylene terephthalate, with epoxy groups grafted onto the powder surface. The core material comprises homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer, and phase change microcapsules. By introducing ethylene-octene copolymer into the core layer for physical buffering, and by forming transphase boundary covalent bonds at the sheath-core interface through the reaction of maleic anhydride groups, epoxy groups, and polyester terminal hydroxyl groups, this invention improves the shear resistance of the phase change microcapsules during spinning and enhances the interfacial bonding between the sheath and core layers. The composite fiber of this invention possesses good spinning continuity, mechanical strength, and washability, while simultaneously achieving dual thermal management through passive radiation cooling and phase change temperature control.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials and textile technology, specifically to a dual-functional composite fiber with radiation cooling and phase change energy storage and its preparation method. Background Technology

[0002] With increasing demands for thermal comfort, smart textile materials with thermal management functions have become a research hotspot. Currently, the two main approaches to achieving fabric temperature regulation are introducing phase change materials into the fiber matrix to absorb or release heat, or adding specific inorganic powders to reflect sunlight and radiate heat outwards. To meet more complex environmental adaptation needs, combining phase change energy storage and radiative cooling functions into the same fiber has become a research direction for development in this field.

[0003] In actual production, melt spinning is a common method for preparing composite fibers. When preparing phase change fibers, the phase change material usually needs to be pre-encapsulated in microcapsules to prevent leakage. Due to the high processing temperature and intense hydrodynamic shearing within the spinning equipment, the shell of the phase change microcapsule is prone to rupture during extrusion and drawing. Once the microcapsule is damaged, the internal phase change core material will leak out and may vaporize. This not only reduces the energy storage capacity of the final product but also causes melt stream breakage, affecting the continuity of the spinning process.

[0004] On the other hand, when inorganic powders are added to the polymer matrix to achieve radiative cooling, the powders tend to agglomerate within the matrix due to the difference in surface properties between inorganic particles and organic polymers, leading to a decrease in fiber spinnability and mechanical strength. When a core-sheath composite spinning process is used to place functional powders and phase change microcapsules in different layers, insufficient interfacial compatibility between different types of polymer matrices often results in weak physical bonding between the sheath and core layers. This makes the fibers prone to sheath peeling or functional powder detachment during subsequent textile processing and routine washing, making it difficult to maintain long-term thermal management performance. Summary of the Invention

[0005] The technical problem solved by this invention is that the phase change microcapsules of existing phase change energy storage composite fibers are easily sheared and broken during melt spinning, resulting in energy storage failure. Furthermore, the addition of inorganic functional powders often leads to poor fiber spinnability, weak core-sheath interface bonding, and insufficient water washability.

[0006] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a dual-functional composite fiber for radiation cooling and phase change energy storage, employing the following technical solution: A dual-functional composite fiber for radiation cooling and phase change energy storage, having a sheath-core structure.

[0007] The sheath of the composite fiber is made from raw materials containing surface-modified optical powder and polyethylene terephthalate.

[0008] Based on the total mass of the sheath material, the mass fraction of the surface-modified optical powder is 12wt% to 18wt%, with the balance being polyethylene terephthalate.

[0009] The surface of the surface-modified optical powder is grafted with epoxy groups.

[0010] The core layer of the composite fiber is made from raw materials including homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and phase change microcapsules.

[0011] Based on the total mass of the core layer raw materials, the mass fractions of each component are as follows: homopolymer polypropylene 50.5% to 57.0%, maleic anhydride-grafted polypropylene 2.5% to 3.1%, ethylene-octene copolymer 4.0% to 5.0%, and phase change microcapsules 35.0% to 42.0%. The mass ratio of sheath material to core material in the composite fiber is 60 to 70:30 to 40.

[0012] By adopting the above technical solution, due to the use of a core layer polymer blend structure with a specific mass ratio and a sheath inorganic powder system containing epoxy groups, the fiber generates a synergistic effect during the molding process. Therefore, it is beneficial to obtain composite fibers with higher spinning stability, higher mechanical strength and better water resistance.

[0013] The specific mechanism is mainly reflected in the following aspects: during the core layer component melting and mixing stage, the ethylene-octene copolymer is dispersed as an elastomer in the continuous phase of homopolymer polypropylene and preferentially coats the surface of the phase change microcapsules.

[0014] Under the strong shear field of extrusion and spinning, the ethylene-octene copolymer undergoes a certain degree of deformation, thereby absorbing the hydrodynamic stress applied to the microcapsule shell, maintaining the structural integrity of the phase change microcapsule, and reducing the risk of leakage of the internal phase change material.

[0015] Simultaneously, when the two high-temperature melts converge within the coaxial spinneret, the maleic anhydride groups carried by the maleic anhydride-grafted polypropylene in the core matrix undergo ring-opening and esterification with the hydroxyl groups at the ends of the polyethylene terephthalate (PET) molecular chains in the sheath. Furthermore, the surface-modified optical powder dispersed in the sheath also undergoes ring-opening addition of its surface epoxy groups, forming covalent bonds with the terminal hydroxyl groups of the PET matrix.

[0016] Through the above chemical reactions, a cross-phase chemical bonding network is constructed in the interface region between the sheath and the core layer. This not only helps to alleviate stress concentration caused by inorganic powder agglomeration, but also improves the fiber's breaking strength and structural stability after multiple water washings.

[0017] Preferably, the surface-modified optical powder is prepared by... - (2,3-epoxypropoxy)propyltrimethoxysilane surface-modified mixed inorganic powder.

[0018] The mixed inorganic powder is composed of nano-silica, rutile titanium dioxide and hexagonal boron nitride, and the mass ratio of nano-silica, rutile titanium dioxide and hexagonal boron nitride is 25 to 30: 40 to 50: 20 to 30.

[0019] By adopting the above technical solution, titanium dioxide provides high reflectivity in the ultraviolet and visible light bands, while silicon dioxide and hexagonal boron nitride provide corresponding high emissivity in the mid-infrared band of the atmospheric window. The three inorganic particles generate a synergistic optical response to assist in achieving passive radiative cooling.

[0020] Meanwhile, the grafting of silane coupling agents improves the dispersibility of inorganic powders in the polyester matrix, and to a certain extent maintains the continuity of the spinning process.

[0021] Preferably, the phase change microcapsule comprises a melamine resin shell and a paraffinic phase change core material encapsulated within the shell. The paraffinic phase change core material is composed of a mixture of n-octadecane and n-nonadecane in a 1:1 mass ratio.

[0022] The dry basis mass ratio of the paraffin phase change core material to the melamine resin shell is 2.0 to 3.0 to 1.

[0023] By adopting the above technical solution, the combination of n-octadecane and n-nonadecanane can provide a phase transition range that is more compatible with the temperature of the human body surface, and the highly cross-linked network formed by melamine resin helps the microcapsules withstand the heat load during the subsequent spinning process.

[0024] Preferably, the monofilament linear density of the bifunctional composite fiber is between 1.8 dtex and 3.5 dtex. By adopting the above technical solution and controlling the monofilament linear density within this range, the fiber can generally have suitable textile processing suitability and yarn softness.

[0025] Secondly, the present invention provides a method for preparing a dual-functional composite fiber of radiation cooling and phase change energy storage, employing the following technical solution: A method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage includes the following steps: Steps for preparing sheath material: Polyethylene terephthalate chips with a moisture content of less than 30 ppm were premixed with surface-modified optical powder to prepare sheath material.

[0026] Preparation steps of core layer raw materials: Homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and phase change microcapsules are mixed and dried until the moisture content is less than 50 ppm to obtain core layer raw materials.

[0027] Composite spinning steps: The sheath layer material and the core layer material are separately fed into a twin-screw extruder for melt extrusion. After metering, they are fed into the composite spinning box, where the two melt streams converge and are extruded into a fine melt stream within the coaxial spinneret cavity. Drawing and setting steps: The extruded melt stream is cooled by side blowing air, oiled and bundled, and then subjected to multi-stage hot drawing. It is subsequently set by a hot plate and wound up to obtain the bifunctional composite fiber.

[0028] By adopting the above technical solutions, positioning the radiation cooling functional powder in the sheath layer helps to optimize the photothermal exchange efficiency with the external environment. Encapsulating the phase change energy storage microcapsules in the core layer aims to provide better slow-release temperature control capabilities. Side-blowing cooling and multi-stage stretching processes promote the orientation and crystallization of macromolecular chains along the fiber axis, thereby constructing a spatially isolated distribution and playing a dual thermal management function.

[0029] Preferably, the surface of the mixed inorganic powder is pre-modified in the step of preparing the sheath material.

[0030] The modification method involves ultrasonically dispersing nano-silica, rutile titanium dioxide, and hexagonal boron nitride in a mixed solvent of anhydrous ethanol and water, adjusting the pH to 4.5 to 5.0 with glacial acetic acid, and slowly adding 1.0 wt% to 2.0 wt% of the total inorganic powder mass. -(2,3-epoxypropoxy)propyltrimethoxysilane was refluxed at 60°C to 70°C for 2 to 4 hours, and then centrifuged, washed, dried and pulverized.

[0031] By adopting the above technical solution, the methoxy group of the silane coupling agent is hydrolyzed into an active silanol group under weakly acidic conditions, and then condensed and dehydrated with the hydroxyl groups on the surface of the inorganic powder, thereby introducing epoxy groups into the powder surface.

[0032] Preferably, phase change microcapsules are prepared in advance during the preparation of the core layer raw materials. The preparation method involves mixing melamine and formaldehyde aqueous solution at a molar ratio of 1:2.5 to 3.0, and reacting them in a water bath at a pH of 8.5 to 9.0 and a temperature of 70°C to 75°C to obtain a melamine resin prepolymer solution. Molten paraffin phase change core material is added to an aqueous solution of styrene-maleic anhydride copolymer with a mass fraction of 1 wt% to 3 wt%, and emulsified to form an oil-in-water emulsion. The melamine resin prepolymer solution was added dropwise to the emulsion, the pH of the system was adjusted to 4.0 to 4.5, and then the temperature was raised to 80°C to 90°C and kept at a constant temperature for 2 to 3 hours for curing. After cooling, filtration, washing and drying were performed.

[0033] By adopting the above technical solution, the emulsifying effect of styrene-maleic anhydride copolymer is used to control the size of paraffin droplets. After adjusting the acidity, the melamine resin prepolymer undergoes a cross-linking and polycondensation reaction at the oil-water interface to form a relatively dense microcapsule shell.

[0034] Preferably, in the step of preparing the sheath material, the polyethylene terephthalate chips are pre-dried under vacuum at 120°C for 12 to 14 hours. In the step of preparing the core material, the core material is pre-dried at 85°C for 4 hours.

[0035] By adopting the above technical solution, residual moisture in the raw materials is deeply removed, and the hydrolysis and chain scission reaction of polyethylene terephthalate during high-temperature melting is avoided as much as possible, thereby maintaining the molecular weight of the polymer and the activity of the terminal hydroxyl groups.

[0036] Preferably, in the composite spinning step, the temperature of each section of the twin-screw extruder for extruding the sheath material is 190°C to 265°C. The temperature of each section of the twin-screw extruder for extruding core layer raw materials is 135℃ to 195℃. The sheath melt channel outlet diameter of the coaxial spinneret is 0.45 mm, and the core melt channel outlet diameter is 0.30 mm.

[0037] By adopting the above technical solution, two independent temperature control systems are set up to address the difference in melting points between the sheath polyester and the core polypropylene matrix, so that the core extrusion temperature is kept in a lower range. This helps to reduce the thermal load on the phase change microcapsules and reduce the probability of shell cracking caused by excessive gasification of the core material inside the microcapsules.

[0038] Preferably, in the stretching and setting step, the side-blowing air temperature is 17°C to 19°C, and the air velocity is 0.35m / s to 0.55m / s; The total draw ratio of the multi-stage hot drawing is 3.2 to 3.8 times; the hot plate setting temperature is 110℃; The winding speed is 2600m / min to 3200m / min.

[0039] By adopting the above technical solution, the solidification rate of the melt stream and the orientation of the polymer chains are controlled, so that the molecular chains at the sheath-core interface can complete the conformation adjustment and undergo certain chemical cross-linking within a suitable temperature range. The hot plate shaping operation helps to eliminate the internal stress of the fiber macromolecules and improve the dimensional stability of the finished composite fiber.

[0040] This invention provides a dual-functional composite fiber for radiation cooling and phase change energy storage, and its preparation method. It possesses the following beneficial effects: 1. This invention adds an ethylene-octene copolymer to the core layer, dispersing and coating it on the surface of phase change microcapsules. During melt extrusion and spinning, the ethylene-octene copolymer absorbs hydrodynamic stress, reducing the shear force on the microcapsules. Combined with the independent temperature control design of the twin-screw extruder, this reduces core layer heating, decreases the risk of microcapsule rupture and core material leakage, and improves the stability of the spinning process.

[0041] 2. This invention constructs a chemical cross-linking network at the interface between the sheath and core layers of the composite fiber. The maleic anhydride-grafted polypropylene in the core layer and the epoxy groups on the surface of the surface-modified optical powder in the sheath layer can both undergo ring-opening reactions with the terminal hydroxyl groups of polyethylene terephthalate during spinning to form covalent bonds. This cross-phase interfacial chemical bonding improves the interfacial bonding force between the sheath and core layers, thereby increasing the fiber's breaking strength and washability.

[0042] 3. This invention achieves the superposition of radiative cooling and phase change energy storage functions by arranging inorganic functional powders and phase change microcapsules in the sheath and core layers of composite fibers, respectively. The titanium dioxide, silicon dioxide, and hexagonal boron nitride in the sheath layer generate a synergistic response, optimizing the fiber's photothermal exchange efficiency in the ultraviolet, visible, and mid-infrared bands; while the phase change microcapsules encapsulated in the core layer provide sustained-release temperature control capabilities, thus achieving a better dual thermal management effect. Attached Figure Description

[0043] Figure 1 The following are infrared spectra of the powder and fiber interface of the present invention; wherein, (a) is the infrared spectrum of the unmodified optical powder and the modified optical powder of Preparation Example 4, and (b) is the infrared spectrum of the composite fiber core-sheath interface of Comparative Example 2 and Example 1. Figure 2 The figures show the thermal performance test results of the microcapsules and composite fibers of the present invention; wherein, (a) is a thermogravimetric analysis (TGA) mass loss curve, and (b) is a differential scanning calorimetry (DSC) heat flow curve. Figure 3 The image shows the passive radiation cooling optical performance spectrum of the composite fiber fabric of the present invention; wherein, (a) is the solar reflectance curve in the 0.3-2.5μm band, and (b) is the mid-infrared emissivity curve in the 8-13μm band. Figure 4 Figure 1 shows the mechanical and spinning stability test results of the composite fiber of the present invention; wherein, (a) is the stress-strain curve of the single filament of the composite fiber, and (b) is the curve showing the cumulative number of broken ends during 24 hours of continuous spinning. Figure 5The figures show the test results of the composite fiber's water resistance and mechanical durability according to the present invention; wherein, (a) is a curve showing the change of phase change melting enthalpy with the number of water washes, and (b) is a curve showing the change of single filament breaking strength with the number of water washes. Figure 6 This is a time-temperature variation curve of the composite fiber fabric of the present invention under an all-weather photothermal simulation environment. Detailed Implementation

[0044] 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.

[0045] The following are specific embodiments of the present invention, which, in conjunction with the examples, provide a further detailed description of the technical solution of the present invention. It should be noted that the following examples are merely for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0046] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0047] Polyethylene terephthalate, CAS No. 25038-59-9, intrinsic viscosity 0.65 dL / g, melting point 255℃, spinning grade chips.

[0048] Homopolymer polypropylene, CAS No. 9003-07-0, isotacticity 97%, melt flow rate 25 g / 10 min (230℃, 2.16 kg), spinning grade chips.

[0049] Maleic anhydride-grafted polypropylene, CAS No. 25722-45-6, maleic anhydride grafting rate 1.0wt%, melt index 50g / 10min (190℃, 2.16kg).

[0050] Ethylene-octene copolymer, CAS No. 26221-73-8, octene mass fraction 25%, density 0.87 g / cm3.

[0051] n-Octadecane, CAS No. 593-45-3, melting point 28.2℃, latent heat of phase change 235J / g.

[0052] n-Nicotinane, CAS No. 629-92-5, melting point 32.1℃, latent heat of phase change 228J / g.

[0053] Nano-silica, CAS No. 112945-52-5, average particle size 50nm.

[0054] Rutile titanium dioxide, CAS No. 1317-80-2, average particle size 250nm.

[0055] Hexagonal boron nitride, CAS No. 10043-11-5, flake diameter 0.5 mm .

[0056] -(2,3-epoxypropoxy)propyltrimethoxysilane, CAS No. 2530-83-8.

[0057] Preparation Example 1: This preparation example provides a method for preparing melamine resin-encapsulated paraffin phase change microcapsules, including the following steps: Melamine and 37% formaldehyde aqueous solution were mixed at a molar ratio of 1:2.8, deionized water was added, the pH was adjusted to 8.8 with triethanolamine, and the mixture was stirred in a water bath at 72°C for 50 minutes to obtain a transparent melamine resin prepolymer solution.

[0058] Octadecyl and nonadecane were mixed at a mass ratio of 1:1 and heated to 50°C to melt and serve as the core material. The core material was added to an aqueous solution containing 2 wt% styrene-maleic anhydride copolymer at a dry basis mass ratio of 2.5:1 to melamine resin prepolymer. The mixture was then emulsified at 7000 r / min for 35 min using a high-shear emulsifier to form a paraffin oil-in-water emulsion.

[0059] The melamine resin prepolymer solution was added dropwise to the paraffin emulsion. The rotation speed was reduced to 400 r / min. The pH of the system was slowly adjusted to 4.2 with 10% citric acid solution. Then, the temperature was increased to 85℃ at a rate of 0.5℃ / min and the system was kept at a constant temperature for 2.5 h to cure.

[0060] After the reaction was completed, the microcapsules were obtained by cooling, filtration, washing with deionized water multiple times, and vacuum drying at 60°C.

[0061] Preparation Example 2: This preparation example provides a method for preparing melamine resin-encapsulated paraffin phase change microcapsules, including the following steps: Melamine and 37% formaldehyde aqueous solution were mixed at a molar ratio of 1:2.5, deionized water was added, the pH was adjusted to 8.5 with triethanolamine, and the mixture was stirred in a water bath at 70°C for 45 minutes to obtain a transparent melamine resin prepolymer solution.

[0062] Octadecyl and nonadecane were mixed at a mass ratio of 1:1 and heated to 50°C to melt and serve as the core material. The core material was added to an aqueous solution containing 1 wt% styrene-maleic anhydride copolymer at a dry mass ratio of 2:1 to the melamine resin prepolymer. The mixture was then emulsified at 6000 r / min for 30 min using a high-shear emulsifier to form a paraffin oil-in-water emulsion.

[0063] The melamine resin prepolymer solution was added dropwise to the paraffin emulsion. The rotation speed was reduced to 300 r / min. The pH of the system was slowly adjusted to 4.0 with 10% citric acid solution. Then, the system was heated to 80°C at a heating rate of 0.5°C / min and cured at a constant temperature for 2 hours.

[0064] After the reaction was completed, the microcapsules were obtained by cooling, filtration, washing with deionized water multiple times, and vacuum drying at 60°C.

[0065] Preparation Example 3: This preparation example provides a method for preparing melamine resin-encapsulated paraffin phase change microcapsules, including the following steps: Melamine and 37% formaldehyde aqueous solution were mixed at a molar ratio of 1:3.0, deionized water was added, the pH was adjusted to 9.0 with triethanolamine, and the mixture was stirred in a water bath at 75°C for 60 minutes to obtain a transparent melamine resin prepolymer solution.

[0066] Octadecyl and nonadecane were mixed at a mass ratio of 1:1 and heated to 50°C to melt and serve as the core material. The core material was added to an aqueous solution containing 3 wt% styrene-maleic anhydride copolymer at a dry mass ratio of 3:1 to the melamine resin prepolymer. The mixture was then emulsified at 8000 r / min for 40 min using a high-shear emulsifier to form a paraffin oil-in-water emulsion.

[0067] The melamine resin prepolymer solution was added dropwise to the paraffin emulsion. The rotation speed was reduced to 500 r / min. The pH of the system was slowly adjusted to 4.5 with 10% citric acid solution. Then, the temperature was increased to 90℃ at a rate of 0.5℃ / min and the system was kept at a constant temperature for 3 hours to cure.

[0068] After the reaction was completed, the microcapsules were obtained by cooling, filtration, washing with deionized water multiple times, and vacuum drying at 60°C.

[0069] Preparation Example 4: This preparation example provides a surface modification method for radiation-cooled optical powder, including the following steps: Nano-silica, rutile titanium dioxide, and hexagonal boron nitride were added to a reaction vessel containing a mixture of anhydrous ethanol and water (volume ratio 9:1) at a mass ratio of 25:45:30, and ultrasonically dispersed for 30 min.

[0070] Adjust the pH to 4.8 with glacial acetic acid, and add it dropwise slowly. -(2,3-epoxypropoxy)propyltrimethoxysilane, the amount of which added is 1.5 wt% of the total mass of the inorganic powder.

[0071] The reaction was mechanically stirred and refluxed at 65°C for 3 hours. The reaction product was centrifuged, washed, dried in a vacuum drying oven at 80°C for 12 hours, pulverized, and sieved to obtain surface-modified optical powder.

[0072] Preparation Example 5: This preparation example provides a surface modification method for radiation-cooled optical powder, including the following steps: Nano-silica, rutile titanium dioxide, and hexagonal boron nitride were added to a reaction vessel containing a mixture of anhydrous ethanol and water (volume ratio 9:1) at a mass ratio of 30:50:20, and ultrasonically dispersed for 30 min.

[0073] Adjust the pH to 4.5 with glacial acetic acid, and add it dropwise slowly. -(2,3-epoxypropoxy)propyltrimethoxysilane, the amount of which added is 1.0 wt% of the total mass of the inorganic powder.

[0074] The reaction was mechanically stirred and refluxed at 60℃ for 2 hours. The reaction product was centrifuged, washed, dried in a vacuum drying oven at 80℃ for 12 hours, pulverized and sieved to obtain surface-modified optical powder.

[0075] Preparation Example 6: This preparation example provides a surface modification method for radiation-cooled optical powder, including the following steps: Nano-silica, rutile titanium dioxide, and hexagonal boron nitride were added to a reaction vessel containing a mixture of anhydrous ethanol and water (volume ratio 9:1) at a mass ratio of 30:40:30, and ultrasonically dispersed for 30 min.

[0076] Adjust the pH to 5.0 with glacial acetic acid, and add it dropwise slowly. -(2,3-epoxypropoxy)propyltrimethoxysilane, the amount of which added is 2.0 wt% of the total mass of the inorganic powder.

[0077] The reaction was mechanically stirred and refluxed at 70°C for 4 hours. The reaction product was centrifuged, washed, dried in a vacuum drying oven at 80°C for 12 hours, pulverized, and sieved to obtain surface-modified optical powder.

[0078] Example 1: This embodiment provides a dual-functional composite fiber for radiation cooling and phase change energy storage, and its preparation method, including the following steps: Polyethylene terephthalate chips were vacuum dried at 120°C for 12 hours to reduce their moisture content to less than 30 ppm. They were then premixed with the surface-modified optical powder obtained in Preparation Example 4 at room temperature for 15 minutes in a high-speed mixer to obtain the sheath material, wherein the modified optical powder accounted for 15 wt% of the total mass of the sheath material.

[0079] Homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer, and the phase change microcapsules obtained in Preparation Example 1 were mixed in a mass ratio of 55.5:2.5:4.0:38.0 (at this time, the compatibilizer accounted for about 4.0 wt% of the total mass of the carrier, and the elastomer accounted for about 6.5 wt% of the carrier). The mixture was pre-dried at a low temperature of 85°C for 4 hours, and the moisture content was controlled to be below 50 ppm to obtain the core layer raw material.

[0080] The sheath material is fed into a five-stage temperature-controlled twin-screw extruder with temperatures of 190℃, 252℃, 262℃, 260℃, and 258℃ in each stage. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the sheath material is adjusted to 6.5 kg / h through online weighing calibration. The core layer material is simultaneously fed into a gradient temperature-controlled twin-screw extruder with temperatures of 135℃, 175℃, 192℃, 190℃, and 188℃ in each section. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the core layer material is adjusted to 3.5 kg / h through online weighing calibration.

[0081] The mass ratio of raw materials for the sheath layer to the core layer is controlled at 65:35. The two melts are extruded by converging in the inner cavity of the coaxial spinneret. The outlet diameter of the sheath layer melt channel is 0.45 mm, and the outlet diameter of the core layer melt channel is 0.30 mm.

[0082] The extruded melt stream enters the side blowing window, with a blowing temperature of 18℃ and a wind speed of 0.45m / s.

[0083] After being oiled and bundled with an oiling rate of 0.8%, the fiber bundles enter a multi-stage drawing process. The speed of the first-stage guide roller is 857 m / min. The fiber bundles pass through a first-stage drawing heat plate at 78°C and a second-stage drawing heat plate at 92°C. The total drawing ratio is set to 3.5 times. The speed of the final-stage drawing roller is 3000 m / min. The fiber bundles are then set on a 110°C setting heat plate and wound up by a winding machine at a speed of 3000 m / min to produce a bifunctional composite fiber with a monofilament linear density of 2.5 dtex.

[0084] Example 2: This embodiment provides a dual-functional composite fiber for radiation cooling and phase change energy storage, and its preparation method, including the following steps: Polyethylene terephthalate chips were vacuum dried at 120°C for 14 hours to reduce their moisture content to less than 30 ppm. They were then premixed with the surface-modified optical powder obtained in Preparation Example 5 at room temperature for 15 minutes in a high-speed mixer to obtain the sheath material, wherein the modified optical powder accounted for 12 wt% of the total mass of the sheath material.

[0085] Homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and the phase change microcapsules obtained in Preparation Example 2 were mixed in a mass ratio of 57.0:3.0:5.0:35.0 (composite agent accounts for 4.6 wt% of the carrier and elastomer accounts for 7.7 wt% of the carrier), and pre-dried at 85°C for 4 h to control the moisture content to be below 50 ppm, thus obtaining the core layer raw material.

[0086] The sheath material is fed into a five-stage temperature-controlled twin-screw extruder with temperatures of 190℃, 250℃, 260℃, 258℃, and 256℃ respectively. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the sheath material is adjusted to 7.0 kg / h through online weighing calibration. The core layer material is simultaneously fed into a gradient temperature-controlled twin-screw extruder with temperatures of 135℃, 170℃, 190℃, 188℃, and 185℃ in each section. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the core layer material is adjusted to 3.0 kg / h through online weighing calibration.

[0087] The raw material feeding ratio of the skin layer to the core layer is controlled at 70:30. The two melts are extruded by converging in the inner cavity of the coaxial spinneret. The skin layer has an orifice diameter of 0.45 mm and the core layer has an inner orifice diameter of 0.30 mm.

[0088] The extruded melt stream enters the side blowing window, with a blowing temperature of 17℃ and a wind speed of 0.35m / s.

[0089] After being oiled and bundled with an oiling rate of 0.6%, the fiber bundles enter a multi-stage drawing process. The speed of the first-stage guide roller is 813 m / min. The fiber bundles pass through a 75°C first-stage drawing plate and a 90°C second-stage drawing plate. The total drawing ratio is set to 3.2 times. The speed of the final-stage drawing roller is 2600 m / min. The fiber bundles are then shaped on a 110°C setting plate and wound up by a winding machine at a speed of 2600 m / min to produce a bifunctional composite fiber with a monofilament linear density of 3.5 dtex.

[0090] Example 3: This embodiment provides a dual-functional composite fiber for radiation cooling and phase change energy storage, and its preparation method, including the following steps: Polyethylene terephthalate chips were vacuum dried at 120°C for 12 hours to reduce their moisture content to less than 30 ppm. They were then premixed with the surface-modified optical powder obtained in Preparation Example 6 at room temperature for 15 minutes in a high-speed mixer to obtain the sheath material, wherein the modified optical powder accounted for 18 wt% of the total mass of the sheath material.

[0091] Homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and the phase change microcapsules obtained in Preparation Example 3 were mixed in a mass ratio of 50.5:2.9:4.6:42.0 (composite agent accounts for 5.0 wt% of the carrier and elastomer accounts for 7.9 wt% of the carrier), and pre-dried at 85°C for 4 hours to control the moisture content to be below 50 ppm, thus obtaining the core layer raw material.

[0092] The sheath material is fed into a five-stage temperature-controlled twin-screw extruder with temperatures of 190℃, 255℃, 265℃, 262℃, and 260℃ in each stage. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the sheath material is adjusted to 6.0 kg / h through online weighing calibration. The core layer material is simultaneously fed into a gradient temperature-controlled twin-screw extruder with temperatures of 135℃, 180℃, 195℃, 192℃, and 190℃ in each section. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the core layer material is adjusted to 4.0 kg / h through online weighing calibration.

[0093] The raw material feeding ratio of the skin layer to the core layer is controlled at 60:40. The two melts are extruded by converging in the inner cavity of the coaxial spinneret. The skin layer has an orifice diameter of 0.45 mm and the core layer has an inner orifice diameter of 0.30 mm.

[0094] The extruded melt stream enters the side blowing window, with a blowing temperature of 19℃ and a wind speed of 0.55m / s.

[0095] After being oiled and bundled with an oiling rate of 0.9%, the fiber bundles enter a multi-stage drawing process. The speed of the first-stage guide roller is 842 m / min. The fiber bundles pass through an 80°C first drawing heat plate and a 95°C second drawing heat plate. The total drawing ratio is set to 3.8 times. The speed of the final drawing roller is 3200 m / min. The fiber bundles are then shaped on a 110°C setting heat plate and wound up by a winding machine at a speed of 3200 m / min to produce a bifunctional composite fiber with a monofilament linear density of 1.8 dtex.

[0096] Example 4: This embodiment provides a dual-functional composite fiber for radiation cooling and phase change energy storage, and its preparation method, including the following steps: Polyethylene terephthalate chips were vacuum dried at 120°C for 12 hours to reduce their moisture content to less than 30 ppm. They were then premixed with the surface-modified optical powder obtained in Preparation Example 4 at room temperature for 15 minutes in a high-speed mixer to obtain the sheath material, wherein the modified optical powder accounted for 15 wt% of the total mass of the sheath material.

[0097] Homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and the phase change microcapsules obtained in Preparation Example 1 were mixed in a mass ratio of 53.9:3.1:5.0:38.0 (composite agent accounts for 5.0 wt% of the carrier and elastomer accounts for 8.0 wt% of the carrier), and pre-dried at 85°C for 4 hours to control the moisture content to be below 50 ppm, thus obtaining the core layer raw material.

[0098] The sheath material is fed into a five-stage temperature-controlled twin-screw extruder with temperatures of 190℃, 252℃, 262℃, 260℃, and 258℃ in each stage. It is then metered and fed into the composite spinning box by a gear pump. The mass flow rate of the sheath material is adjusted to 6.5 kg / h through online weighing calibration. The core material is simultaneously fed into a gradient temperature-controlled twin-screw extruder, with temperatures of 135℃, 175℃, 192℃, 190℃, and 188℃ in each section. It is then metered and fed into the composite spinning box by a gear pump with a displacement of 0.6 mL / r and a rotation speed of 14 r / min.

[0099] The feed ratio of the skin layer to the core layer is controlled at 65:35. The two melt streams converge and are extruded within the coaxial spinneret cavity. The skin layer has an orifice diameter of 0.45 mm, and the core layer has an orifice diameter of 0.30 mm. The extruded melt stream enters the side blowing window, with a blowing temperature of 18℃ and a wind speed of 0.45 m / s.

[0100] After being oiled and bundled with an oiling rate of 0.8%, the fiber bundles enter a multi-stage drawing process. The speed of the first-stage guide roller is 842 m / min. The fiber bundles pass through a 78°C first-stage drawing heat plate and a 92°C second-stage drawing heat plate. The total drawing ratio is set to 3.8 times. The speed of the final-stage drawing roller is 3200 m / min. The fiber bundles are then shaped on a 110°C setting heat plate and wound up by a winding machine at a speed of 3200 m / min to produce a bifunctional composite fiber with a monofilament linear density of 2.0 dtex.

[0101] Comparative Example 1: The difference compared to Example 1 is that the optical powder was not subjected to... -(2,3-epoxypropoxy)propyltrimethoxysilane surface modification is directly mixed with polyethylene terephthalate; maleic anhydride-grafted polypropylene and ethylene-octene copolymer are not added to the core layer raw material, and the mass fraction of homopolymer polypropylene is adjusted accordingly to 62.0; all other parts are the same.

[0102] Comparative Example 2: Compared with Example 1, the difference is that maleic anhydride-grafted polypropylene is not added to the core layer raw material, and the mass fraction of homopolymer polypropylene is adjusted to 58.0 accordingly, while the rest are the same.

[0103] Comparative Example 3: Compared with Example 1, the difference is that ethylene-octene copolymer is not added to the core layer raw material, and the mass fraction of homopolymer polypropylene is adjusted to 59.5, while the rest are the same.

[0104] Comparative Example 4: The difference compared to Example 1 is that the optical powder was not subjected to... Surface-modified with (2,3-epoxypropoxy)propyltrimethoxysilane, directly mixed with polyethylene terephthalate, with all other properties remaining the same.

[0105] Comparative Example 5: Compared with Example 1, the difference is that phase change microcapsules are not added to the core layer raw material, and the mass fraction of homopolymer polypropylene is adjusted to 93.5, while the rest are the same.

[0106] Comparative Example 6: Compared with Example 1, the difference is that no surface-modified optical powder is added to the sheath material, the mass fraction of polyethylene terephthalate is adjusted to 100%, and the rest are the same.

[0107] Test Example 1: Comparative Test of Surface Modification and Interfacial Chemical Environment 1. Weigh 2 mg each of unmodified optical powder (mixed with nano-silica, rutile titanium dioxide and hexagonal boron nitride in a mass ratio of 25:45:30) and the surface-modified optical powder prepared in Preparation Example 4. Grind them evenly with 200 mg of dry potassium bromide powder in an agate mortar. Press them into transparent sheets using a tablet press under a pressure of 10 MPa as powder infrared test samples.

[0108] 2. Take the bifunctional composite fibers prepared in Example 1 and Comparative Example 2, freeze them in liquid nitrogen for 5 minutes, and then take them out. Use a micro slicer to mechanically peel them along the fiber axis to expose the interface area between the sheath layer and the core layer. Cut a sample with a length of about 5 mm as the interface infrared attenuation total reflection test sample.

[0109] 3. Place the powder tablet sample in the optical path of a Fourier transform infrared spectrometer (test range 4000-400cm-1, resolution 4cm-1, number of scans 32) for transmission mode scanning to obtain infrared spectral data of unmodified and modified powders.

[0110] 4. Place the prepared fiber interface sample tightly against the surface of the germanium crystal on the attenuated total reflection accessory of the infrared spectrometer, adjust the pressure knob to make the sample and crystal in close contact, and scan under the same test parameters to collect infrared spectral data at the interface.

[0111] Baseline correction and smoothing were performed on all obtained spectral data, and the positions and absorbance information of key characteristic peaks were extracted.

[0112] The relative absorbance of epoxy groups in the powder sample is based on the 800 ppm value in the powder spectrum. The nearby stable absorption peaks were used as internal standards for normalization calculations. The relative absorbance of carbonyl and epoxy groups in the fiber interface sample was measured using PET aromatic rings at 1505 nm. The nearby absorption peaks were used as internal standards for normalization calculations.

[0113] Powder samples and interface samples were tested using different modes and internal standard systems, and their relative absorbance was compared only between samples of the same type.

[0114] Table 1. Data on characteristic absorption peaks in infrared spectra

[0115] According to Table 1 and Figure 1 The data shows that the infrared spectrum of the modified optical powder obtained in Example 4 is at 908.7 cm⁻¹. - The characteristic absorption peak of the epoxy group appeared at ¹, with a relative absorbance of 0.14, while the unmodified powder showed no obvious absorption at this point, indicating that the optical powder surface was introduced with an organosilicon structure containing epoxy groups after treatment with the silane coupling agent.

[0116] Infrared spectroscopy of the interface in Example 1 showed that, compared to Comparative Example 2 (which did not contain maleic anhydride-grafted polypropylene), the carbonyl characteristic peak decreased from 1719.1. Offset to 1726.8 Furthermore, the relative absorbance increased from 0.83 to 0.95.

[0117] Since the main difference between Example 1 and Comparative Example 2 is whether the core layer contains maleic anhydride-grafted polypropylene, the changes in the carbonyl peak position and relative absorbance indicate that the chemical environment of the carbonyl group at the core-skin interface changes after the addition of maleic anhydride-grafted polypropylene.

[0118] Based on the reaction characteristics of maleic anhydride groups being able to undergo ring-opening esterification with the terminal hydroxyl groups of PET, it can be inferred that the high-temperature shear conditions of composite spinning promoted the interfacial esterification reaction.

[0119] This chemical bonding across the phase interface is beneficial for improving the interfacial compatibility of the composite fiber sheath-core structure and reducing the tendency for interfacial delamination.

[0120] A faint epoxy characteristic peak (902.1) still exists at the interface. This indicates that some of the epoxy groups located on the powder surface are still retained after composite spinning.

[0121] Test Example 2: Verification Test of Heat Resistance and Phase Change Range of Phase Change Energy Storage Microcapsules 1. Weigh out uncoated n-octadecane and n-nonadecanane mixture (mass ratio 1:1) to prepare phase change microcapsules prepared in Example 1, bifunctional composite fibers prepared in Example 1, and bifunctional composite fibers prepared in Comparative Example 3. Prepare thermogravimetric analysis (TGA) samples and differential scanning calorimetry (DSC) samples for each sample; wherein, the mass of the TGA sample is 5 mg and the mass of the DSC sample is 8 mg.

[0122] 2. Place the thermogravimetric analysis test sample in an alumina crucible and put it into a thermogravimetric analyzer. Under nitrogen atmosphere protection (gas flow rate 50 mL / min), heat from 30℃ to 600℃ at a heating rate of 10℃ / min. Continuously record the mass loss curve of the sample as a function of temperature. The temperature at which the sample mass loss reaches 5% is taken as the initial thermal decomposition temperature.

[0123] 3. Place the differential scanning calorimetry (DSC) sample in a standard aluminum crucible, seal it, and place it in the DSC instrument. Under a nitrogen atmosphere (gas flow rate 50 mL / min), first heat to 80 °C at a rate of 10 °C / min and hold at that temperature for 5 min to eliminate thermal history; The temperature was then cooled to 0°C at a rate of 5°C / min, and the exothermic crystallization curve was recorded. The temperature was then heated to 80°C at a rate of 5°C / min, and the endothermic melting curve was recorded.

[0124] The latent heat enthalpy of phase transition is calculated by integrating the phase transition peak using the instrument's built-in software.

[0125] Table 2 Thermal properties of microcapsules and composite fibers

[0126] According to Table 2 and Figure 2 According to the data, the initial thermal decomposition temperature of uncoated mixed paraffin is only 148.6℃, and it is prone to volatilization loss or decreased thermal stability under melt spinning temperature conditions. The initial thermal decomposition temperature of the phase change microcapsules prepared in Example 1 was increased to 312.4℃, indicating that the highly cross-linked network constructed by the melamine-formaldehyde resin shell material endowed the microcapsules with good thermal stability, providing a thermally stable basis for their short-time thermal processing in the core layer melt extrusion and composite spinning box.

[0127] Differential scanning calorimetry data showed that the peak melting phase transition temperature of the composite fiber in Example 1 was 29.6℃, and the melting enthalpy reached 20.3J / g.

[0128] Based on the fact that the phase change microcapsules account for 38% of the core layer mass, the core layer accounts for 35% of the composite fiber mass, and the microcapsule melting enthalpy is 162.8 J / g, the theoretical melting enthalpy of the composite fiber in Example 1 is approximately 21.7 J / g, and its actual melting enthalpy is approximately 93.8% of the theoretical value, indicating that the phase change microcapsules retain most of the energy storage capacity after composite spinning.

[0129] In contrast, the melting enthalpy of the composite fiber in Comparative Example 3 was only 8.7 J / g, which was significantly lower than that in Example 1.

[0130] Based on the differences in core layer components, it can be seen that Comparative Example 3 lacks the ethylene-octene copolymer elastomer component. Under the high temperature and high shear action of twin-screw extrusion and spinneret micropores, the microcapsules lack an elastic buffer structure, causing some microcapsules to suffer shell damage, deformation, or core material migration. Molten paraffin may leak and evaporate during the processing, resulting in a decrease in the latent heat of phase change after filamentation.

[0131] The data from Example 1 demonstrate that the elastic buffer structure formed by the ethylene-octene copolymer in the polypropylene matrix can reduce the degree of mechanical damage to the microcapsules during the spinning process, which is beneficial to maintaining the integrity of the microcapsules and their phase change core material.

[0132] Test Example 3: Spectral Characterization Test of Optical Performance of Passive Radiation Cooling 1. The bifunctional composite fibers prepared in Example 1 and Comparative Example 6 (without surface-modified optical powder in the sheath) were knitted into single-sided plain knitted fabrics with an areal density of 150 g / m2 using a circular knitting machine under the same process parameters. The fabrics were then conditioned for 24 hours in a standard environment with a temperature of 20°C and a relative humidity of 65% to serve as samples for optical performance testing.

[0133] 2. Lay the sample flat and fix it on the integrating sphere test port of the UV-Vis-NIR spectrophotometer, and use a polytetrafluoroethylene standard white plate as a baseline reference.

[0134] Set the scanning wavelength range to 0.3. Up to 2.5 The data sampling interval was 1 nm. The spectral reflectance of the sample in the solar band was recorded, and the AM1.5 standard solar spectrum was used as the weight. The average solar reflectance in the 0.3–2.5 μm band was calculated according to the following formula: ; The ultraviolet band is selected from 0.3 to 0.4. The visible light band is taken as 0.4–0.78. The near-infrared band is selected from 0.78 to 2.5. .

[0135] 3. Transfer the sample to a Fourier transform infrared spectrometer equipped with a gold-plated integrating sphere.

[0136] Set the spectral scan range to 2.5. Up to 15 The resolution is 4 The number of scans was accumulated to 64, and the hemispherical reflectance curve and hemispherical transmittance curve of the sample were recorded respectively.

[0137] According to Kirchhoff's law of thermal radiation, =1- - Calculate the spectral emissivity of the sample, where R(λ) is the spectral reflectivity. This represents spectral transmittance. As of 8 Up to 13

[0138] The average mid-infrared emissivity was calculated using data from the atmospheric transparency window band and the 300K blackbody radiation spectrum as a weight.

[0139] Table 3 Optical Performance Data of Composite Fiber Fabrics

[0140] According to Table 3 and Figure 3 The data ranges from 0.3 to 2.5. In the full solar radiation band, the average reflectance of the fabric in Example 1 reached 91.1%, which is significantly higher than the 55.6% of Comparative Example 6.

[0141] This difference indicates that the high-refractive-index titanium dioxide, low-refractive-index silicon dioxide, and layered hexagonal boron nitride dispersed in the sheath polyethylene terephthalate form a multi-scale light scattering system composed of particles with different refractive indices, particle sizes, and morphologies.

[0142] This system enhances the fiber's ability to reflect sunlight of different wavelengths through Mie scattering, Rayleigh scattering, and multiple scattering at the particle-polymer interface, thereby reducing the absorption and photothermal conversion of solar radiation in the fiber and the object it covers.

[0143] In 8-13 In the atmospheric transparency window band, the average emissivity of the fabric in Example 1 reached 94.6%, which is 16.2 percentage points higher than that in Comparative Example 6.

[0144] This enhancement in infrared emissivity originates from the Si-O bonds, Ti-O bonds, and the lattice vibrational resonance bands of hexagonal boron nitride in the inorganic powder. The molecular vibrational modes of these chemical bonds are in the range of 8-13. The region generates strong resonant absorption and emission, giving the fiber a high thermal radiation capability in this band.

[0145] In practical applications with an open sky view, this spectral characteristic is beneficial for fibers to radiate heat to the cold sky through atmospheric transparent windows.

[0146] The comparison of the two sets of data verifies that the composite optical powder added to the sheath is an indispensable structural basis for realizing the passive radiation cooling mechanism.

[0147] Test Example 4: Comparative Test of Industrial Spinnability and Macroscopic Mechanical Properties 1. The spinning forming sections of Examples 1 to 4, Comparative Example 1 and Comparative Example 4 were selected as test objects.

[0148] 2. Each group of raw materials is continuously run on a composite spinning machine for 24 hours according to the extrusion temperature, feeding ratio, cooling conditions, drawing conditions and winding conditions specified in the corresponding examples or comparative examples.

[0149] The online monitoring system configured at the winding machine end records the total number of yarn breaks and the total length of filaments during the spinning process, and calculates the yarn breakage rate index.

[0150] 3. After winding, the fiber cake is placed in a constant temperature and humidity environment of 20℃ and 65% for 24 hours to condition it. Thirty monofilaments are randomly selected from different parts of each group of fiber cakes as mechanical test samples.

[0151] 4. Using an electronic monofilament tensile tester, set the initial distance between the upper and lower clamps to 20 mm, and maintain a constant tensile speed of 20 mm / min. Stretch the specimen axially until it fractures. Record the load and displacement data at fracture, calculate the fracture strength and elongation at fracture, and take the arithmetic mean of 30 tests as the final result.

[0152] Table 4. Data on continuous spinning and mechanical properties of composite fibers

[0153] According to Table 4 and Figure 4 The data show that the composite fibers of Examples 1 to 4 exhibited a breakage rate of 0.87 to 1.48 times / 10,000 meters and a breaking elongation of 24.9% to 29.3%, indicating that each example has good continuous filamentation stability and adaptability to subsequent drawing processing under its corresponding process conditions.

[0154] In Comparative Example 1, maleic anhydride-grafted polypropylene and ethylene-octene copolymer were removed, and the inorganic powder was not modified. Its tensile strength was reduced to 1.35 cN / dtex, and the breakage rate reached 18.73 times / 10,000 meters.

[0155] The decline in these mechanical properties is mainly related to the poor compatibility between polyethylene terephthalate and homopolymer polypropylene. The stretching process can easily cause microcracks and relative slippage at the sheath-core interface. Meanwhile, the lack of an elastic buffer structure formed by ethylene-octene copolymers will also increase stress concentration in the microcapsules and the surrounding matrix in the core layer.

[0156] Comparative Example 4 only changed the surface state of the powder without coating it with silane coupling agent. Its breakage rate was 8.26 times / 10,000 meters and its tensile strength was 2.14 cN / dtex.

[0157] Based on the surface characteristics analysis of inorganic powders, unmodified nanoparticles have high surface energy and generate secondary agglomeration in polymer melts. These agglomerates form stress concentration points inside the fibers.

[0158] When an axial tensile load is applied, the stress around the micro-aggregates cannot be effectively transferred and dissipated, causing the fibers to undergo macroscopic fracture at a low stretching ratio.

[0159] The data from Example 1 show that surface modification of silane coupling agents helps reduce the agglomeration tendency of powders and improve their dispersion uniformity in the matrix. At the same time, the esterification bonding that may form at the sheath-core interface improves the interfacial bonding strength.

[0160] The above-mentioned effects collectively improve the molding stability and macroscopic mechanical properties of composite fibers.

[0161] Test Example 5: Comparison Test of Washability and Enthalpy Retention Rate The bifunctional composite fibers prepared in Example 1, Comparative Example 2 and Comparative Example 3 were selected and woven into plain weave fabrics with an areal density of 150 g / m2 under the same parameters as test objects.

[0162] Referring to the household washing and drying procedures for textile testing as specified in the national standard GB / T8629, each fabric sample was placed in a standard drum washing machine for 50 consecutive washing cycles.

[0163] Each washing cycle uses a standard washing program at 40℃, adds the prescribed amount of standard detergent, and uses the same quality of standard washable fabrics to adjust the total washing load to 2.0kg. After each wash and rinse cycle, allow the fabric to air dry at room temperature before starting the next wash cycle.

[0164] An independent parallel sample was taken for testing every 10 washing cycles.

[0165] Composite fibers were extracted from the fabric before (0 washes) and after washing, and their melting phase transition peaks were tested using a differential scanning calorimeter (heating and cooling rate 5℃ / min, nitrogen atmosphere). The latent heat enthalpy of phase transition was obtained by integrating the peak area.

[0166] Monofilaments were extracted from the fabric before washing and after 50 washes, and axial tensile tests were performed using an electronic monofilament tensile tester at a tensile speed of 20 mm / min. The breaking strength of the monofilaments was recorded.

[0167] Table 5. Thermal and mechanical data of composite fibers before and after washing.

[0168] According to Table 5 and Figure 5 According to the data, after 50 water washing cycles, Example 1 showed a melting enthalpy retention rate of 95.1% and a fracture strength retention rate of 96.5%, demonstrating good structural durability.

[0169] Comparative Example 2, due to the absence of maleic anhydride-grafted polypropylene, had an initial tensile strength of only 1.42 cN / dtex. After 50 washes, the tensile strength decreased to 0.68 cN / dtex, and the enthalpy of fusion decreased from 19.0 J / g to 7.3 J / g.

[0170] The data changes indicate that when there is a lack of interfacial covalent bonding between the polar polyethylene terephthalate sheath and the non-polar polypropylene core, the repeated mechanical rubbing force and water shear force generated by the washing machine drum will cause macroscopic slippage and peeling at the sheath-core interface.

[0171] After the outer layer is damaged, the core matrix is ​​directly exposed and some components are lost, resulting in the simultaneous loss of energy storage capacity and mechanical load-bearing capacity.

[0172] Comparative Example 3, without the addition of ethylene-octene copolymer, had an initial melting enthalpy of only 8.7 J / g, which decreased to 6.4 J / g after washing with water.

[0173] This confirms that phase change microcapsules suffer significant mechanical damage during the spinning and extrusion stage when a buffer network constructed from elastomers is lacking.

[0174] The remaining incomplete capsule shells are unable to withstand the continuous action of surfactants and mechanical forces during subsequent washing. The free paraffin phase change material inside may migrate and be lost with the washing liquid under the emulsification of detergent and mechanical rubbing, leading to a further decrease in latent heat performance.

[0175] The data from Example 1 demonstrate that the interfacial compatibilization effect formed by maleic anhydride-grafted polypropylene and the elastic buffering effect formed by ethylene-octene copolymer are beneficial to improving the structural stability and phase change enthalpy retention rate of composite fibers under repeated washing conditions.

[0176] Test Example 6: Comparative Test of Simulated Temperature Control During a Single-Cycle Daytime Warming-Nighttime Cooling The bifunctional composite fibers prepared in Examples 1, 5, and 6 were selected and woven into plain weave fabrics with an areal density of 150 g / m² under the same textile process parameters as the test objects for macroscopic temperature control. Meanwhile, commercially available ordinary polyethylene terephthalate (PET) pure spun fabric was selected as a blank control sample.

[0177] A simulated human microenvironment testing device was constructed within a sealed, temperature-controlled simulation chamber to evaluate the ability of different fabrics to regulate temperature fluctuations in a closed microenvironment under controlled light heating and ambient cooling conditions. This test is not directly used to characterize fabrics under open-sky conditions.

[0178] The main body of the device is a hollow polyurethane insulating foam box with an open top. A high-precision thermocouple temperature sensor is fixed at the center of the bottom surface inside the box. Test fabric is covered and fixed to the top opening of the foam box to ensure a tight seal with no air gaps.

[0179] A daytime high-temperature exposure simulation test was conducted. The artificial sun lamp (xenon lamp source, radiation power density set to 800W / m²) on the top of the simulation chamber was turned on, and the ambient temperature inside the chamber was simultaneously adjusted to rise uniformly from 20°C to 35°C within one hour and remain constant. The temperature change curve of the microenvironment inside the foam box was recorded from 0 to 4 hours, and the highest peak temperature during the exposure period was extracted.

[0180] A nighttime, dark-free cooling simulation test was conducted. At the end of the fourth hour of the daytime test, the artificial sun lamps were turned off, and the cabin cooling system was activated, causing the ambient temperature inside the cabin to drop from 35°C to 15°C within 30 minutes and remain constant. The temperature change curves of the microenvironment inside the foam box were continuously recorded over 4 to 8 hours, and the lowest trough temperature during the cooling period was extracted.

[0181] Table 6. Microenvironmental temperature data of composite fiber fabrics under simulated conditions.

[0182] According to Table 6 and Figure 6 According to the data, during the daytime heatwave, the temperature under ordinary PET fabric rapidly rises to 42.6℃.

[0183] Comparative Example 6 shows that the fabric has insufficient ability to reflect sunlight and radiate heat due to the lack of sheath-layer passive radiation cooling powder.

[0184] In the early stages of exposure to direct sunlight, the phase change material in the core layer absorbs some of the heat, mitigating the temperature rise. However, as the heat continues to accumulate, the latent heat of the solid-liquid phase change in the phase change microcapsules is exhausted, the fabric loses its temperature control ability, and the maximum temperature of the microenvironment soars to 39.8℃.

[0185] Comparative Example 5, without the addition of a phase change material core layer, relied solely on the radiative cooling effect of the sheath layer to control the highest daytime temperature at 33.4℃; However, when entering the dark and cooling phase at night, the fabric's radiative cooling effect continues to radiate heat to the outside in the cold environment without heat source input, causing the microenvironment temperature to drop to 14.7℃, which is lower than the ambient base temperature, resulting in obvious overcooling.

[0186] Example 1: The fabric maintains a maximum temperature of 31.5°C during the day and a minimum temperature of 22.8°C at night, with a maximum temperature difference of only 8.7°C between day and night.

[0187] Data verified the structural partitioning synergistic temperature control mechanism of the present invention: the dielectric micro-nano scattering system of the sheath layer blocked a large amount of external heat energy during the day through high reflection and high infrared radiation, thus delaying the depletion of the latent heat of the core phase change material. The core phase change microcapsules absorb heat and suppress the temperature rise when the ambient temperature reaches the phase change range, and release latent heat through a liquid-solid phase change when the temperature drops at night.

[0188] The closed-loop combination of photothermal and thermodynamic mechanisms eliminates the undercooling defects caused by a single refrigeration technology and the latent heat saturation failure problem caused by a single phase change technology.

[0189] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dual-functional composite fiber for radiation cooling and phase change energy storage, having a sheath-core structure, characterized in that, The sheath of the composite fiber is made from a raw material comprising surface-modified optical powder and polyethylene terephthalate; Based on the total mass of the sheath material, the mass fraction of the surface-modified optical powder is 12wt% to 18wt%, with the remainder being polyethylene terephthalate; the surface of the surface-modified optical powder is grafted with epoxy groups. The core layer of the composite fiber is made from raw materials including homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and phase change microcapsules. Based on the total mass of the core layer raw materials, the mass fraction of each component is as follows: homopolymer polypropylene 50.5%–57.0%, maleic anhydride grafted polypropylene 2.5%–3.1%, ethylene-octene copolymer 4.0%–5.0%, and phase change microcapsules 35.0%–42.0%; in the composite fiber, the mass ratio of sheath material to core layer material is (60–70):(30–40).

2. The dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 1, characterized in that, The surface-modified optical powder is prepared by... -(2,3-epoxypropoxy)propyltrimethoxysilane surface-modified mixed inorganic powder; The mixed inorganic powder is composed of nano-silica, rutile titanium dioxide and hexagonal boron nitride, and the mass ratio of nano-silica, rutile titanium dioxide and hexagonal boron nitride is (25-30): (40-50): (20-30).

3. The dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 1, characterized in that, The phase change microcapsule includes a melamine resin shell and a paraffin phase change core material encapsulated inside the shell. The paraffin phase change core material is composed of n-octadecane and n-nonadecane mixed in a mass ratio of 1:1; the dry basis mass ratio of the paraffin phase change core material to the melamine resin shell is (2.0~3.0):

1.

4. The dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 1, characterized in that, The monofilament linear density of the bifunctional composite fiber is 1.8 dtex to 3.5 dtex.

5. A method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage, comprising the dual-functional composite fiber for radiation cooling and phase change energy storage according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of sheath material: Polyethylene terephthalate chips with a moisture content of less than 30 ppm are premixed with the surface-modified optical powder to obtain sheath material; S2. Preparation of core layer raw materials: Homopolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-octene copolymer and phase change microcapsules are mixed and dried until the moisture content is less than 50 ppm to obtain the core layer raw materials. S3. Composite spinning: The sheath material and the core material are respectively fed into a twin-screw extruder for melt extrusion. After metering, they are fed into the composite spinning box, so that the two melts are merged and extruded in the inner cavity of the coaxial spinneret to form a melt stream. S4. Stretching and shaping: The extruded melt stream is cooled by side blowing, oiled and bundled, and then subjected to multi-stage hot stretching. It is then shaped and wound up by a hot plate to obtain the bifunctional composite fiber.

6. The method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 5, characterized in that, In step S1, the surface-modified optical powder is obtained by pre-modifying the mixed inorganic powder. The method is as follows: Nano-silica, rutile titanium dioxide, and hexagonal boron nitride were ultrasonically dispersed in a mixed solvent of anhydrous ethanol and water. The pH was adjusted to 4.5–5.0 with glacial acetic acid, and the solution was slowly added dropwise at a rate of 1.0 wt%–2.0 wt% of the total inorganic powder mass. -(2,3-epoxypropoxy)propyltrimethoxysilane was refluxed at 60℃~70℃ for 2h~4h, and then centrifuged, washed, dried and pulverized.

7. The method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 5, characterized in that, In step S2, the phase change microcapsules are prepared in advance by the following method: Melamine and formaldehyde aqueous solution were mixed at a molar ratio of 1:(2.5-3.0) and reacted in a water bath at a pH of 8.5-9.0 and a temperature of 70℃-75℃ to obtain a melamine resin prepolymer solution. Molten paraffin phase change core material is added to an aqueous solution of styrene-maleic anhydride copolymer with a mass fraction of 1wt% to 3wt%, and emulsified to form an oil-in-water emulsion. The melamine resin prepolymer solution was added dropwise to the emulsion, the pH of the system was adjusted to 4.0-4.5, and then the temperature was raised to 80℃-90℃ and kept at a constant temperature for 2-3 hours for curing reaction. After cooling, filtration, washing and drying were performed.

8. The method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 5, characterized in that, In step S1, the polyethylene terephthalate chips are pre-dried under vacuum at 120°C for 12-14 hours. In step S2, the core layer raw material is pre-dried at 85°C for 4 hours.

9. The method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 5, characterized in that, In step S3, the temperature of each section of the twin-screw extruder that extrudes the sheath material is 190°C to 265°C. The temperature of each section of the twin-screw extruder extrudes the core layer material is 135℃~195℃; The sheath melt channel outlet diameter of the coaxial spinneret is 0.45 mm, and the core melt channel outlet diameter is 0.30 mm.

10. The method for preparing a dual-functional composite fiber for radiation cooling and phase change energy storage according to claim 5, characterized in that, In step S4, the side-blowing air temperature is 17℃~19℃, and the wind speed is 0.35m / s~0.55m / s; The total draw ratio of the multi-stage hot drawing is 3.2 to 3.8 times; the hot plate setting temperature is 110℃. The winding speed is 2600m / min to 3200m / min.

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