Preparation method of coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling

Abstract

The present application relates to a kind of coaxial cellulose-based aerogel fiber fabric preparation methods for daytime radiation refrigeration, it is characterized in that, coaxial fiber includes with pure cellulose as core, skin layer includes hollow silica and low concentration cellulose, hollow silica is uniformly dispersed in cellulose;Specific steps include: S1, adjustable hollow silica preparation of particle size;S2, hollow silica / cellulose mixed spinning solution preparation;S3, cellulose dissolves;S4, coaxial wet spinning;S5, multi-step solvent replacement;S6, continuous normal pressure drying;S7, fiber weaving;The aerogel fiber fabric prepared by weaving can effectively scatter sunlight, improve solar reflectance (>92%), and enhance emissivity (>96%) in atmospheric transparent window;The preparation method is green and environmentally friendly, simple operation, can realize the continuous, large-scale production of cellulose-based aerogel fiber, and the coaxial aerogel fiber fabric prepared can exhibit excellent radiation refrigeration performance during the day.

Description

Technical Field

[0001] This invention relates to the field of radiation cooling materials technology, and in particular to a method for preparing coaxial cellulose-based aerogel fiber fabric for daytime radiation cooling. Background Technology

[0002] Passive radiative cooling materials, with their ultra-high solar reflectivity (0.3–2.5 μm) and selective emission of thermal radiation into the cold outer space through atmospheric transparency windows (8–13 μm), offer a promising candidate for efficient cooling of buildings and people without consuming any energy. Furthermore, the development of passive radiative cooling fabrics can enable textiles to protect the human body in hot weather.

[0003] Cellulose fibers are among the most abundant biological resources in nature, possessing numerous hydroxyl functional groups and carbon-oxygen bonds, giving them high emissivity within the "atmospheric window." However, pure cellulose fibers exhibit low solar reflectivity under direct sunlight, resulting in limited cooling efficiency. Further introduction of nanomaterials can regulate the micro / nano structure of cellulose fibers, enhancing their reflectivity in the visible-near-infrared band, thereby suppressing solar energy absorption and achieving broadband light management capabilities. Patent 202210426528.X discloses a method of depositing inorganic cooling materials such as magnesium oxide or magnesium hydroxide onto the surface of cellulose acetate fabric using a coating method. However, these inorganic particle coatings affect the softness of passively radiatively cooled fiber fabrics, and the coating material inevitably faces the problem of functional particle shedding during repeated washing and friction. To address this challenge, another strategy is to prepare fibers through random blending and spinning of micro / nano particles. However, when the material surface temperature is lower than the ambient temperature, it easily absorbs heat from the surrounding environment through convection heat transfer, leading to an increase in the material surface temperature and reducing the cooling effect.

[0004] Cellulose aerogel fibers possess sufficient refractive index (n~1.5) to enhance optical path difference, thereby inducing high solar reflection. Their high porosity results in low thermal conductivity, offering a novel approach to combating parasitic heat transfer from the surrounding environment. Cost-effective large-scale radiative cooling can be achieved through multi-scale structural design and randomly dispersed nanoparticles. However, the high porosity and weak interfacial bonding of composite aerogel fibers also lead to deterioration in their mechanical properties, posing a significant obstacle to the practical application of composite functional aerogel fibers. Furthermore, large-scale fiber manufacturing faces substantial challenges. There is an urgent need to develop relatively low-cost, simple, and continuously scalable cellulose composite aerogel fiber preparation technologies to produce cellulose aerogel fibers with well-defined microstructures for daytime radiative cooling. Summary of the Invention

[0005] To address the above deficiencies, the present invention provides a method for preparing coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling, comprising the following steps:

[0007] S1. Water, anhydrous ethanol, hexadecyltrimethylammonium bromide, ammonia and tetraethyl orthosilicate are mixed and hydrolyzed to obtain solid silica microspheres; the solid silica microspheres are washed with anhydrous ethanol and water by centrifugation, and the template is removed by stirring and etching; the microspheres are washed alternately with anhydrous ethanol and water by centrifugation and dried to obtain hollow silica microspheres.

[0008] S2. Disperse the hollow silica microspheres from S1 in a cellulose solution to form a mixture; mix cellulose in the mixture, centrifuge to degas, and obtain a hollow silica / cellulose mixed spinning solution.

[0009] S3. Disperse pure cellulose in a cellulose solution, centrifuge to degas, and form a pure cellulose solution.

[0010] S4. The hollow silica / cellulose mixed spinning solution of S2 is filled into the coaxial needle sheath, and the pure cellulose solution of S3 is filled into the core. The sheath / core layer solution is uniformly injected into a coagulation bath containing tert-butanol citrate at a certain flow rate, and gel fiber is obtained by coaxial wet spinning.

[0011] S5. The gel fibers from S4 are sequentially introduced into an alcohol dehydrating agent displacement tank and a short-chain alkane solution displacement tank, and dried under normal pressure to obtain coaxial cellulose aerogel fibers.

[0012] S6. The coaxial cellulose aerogel fibers of S5 are processed into cellulose-based aerogel fiber fabrics by weaving.

[0013] In a preferred embodiment of the present invention, in S1, the mass ratio of water to anhydrous ethanol is in the range of 1:0.5~3, the mass ratio of hexadecyltrimethylammonium bromide, ammonia and tetraethyl orthosilicate is in the range of 0.5~0.7:3~5:3~5, and the mass ratio of water to tetraethyl orthosilicate is in the range of 6~10:1~3.

[0014] In a preferred embodiment of the present invention, in step S1, the hollow silica microspheres have a particle size of 200-1200 nm and a hollow diameter of 100-800 nm.

[0015] In a preferred embodiment of the present invention, the solvent in the cellulose dissolving solution is one of sodium sulfonate solution, tetrabutylammonium hydroxide / urea solution, alkali / urea solution, N-methylmorpholine N-oxide solution, or 1-allyl-3-methylimidazolium chloride ion liquid, and the cellulose is one of bamboo pulp, cotton pulp, or wood pulp.

[0016] In a preferred embodiment of the present invention, in step S2, the solid content in the hollow silica / cellulose mixed spinning solution is 3-5 wt%; the mass ratio of hollow silica to cellulose is 1:9-3:7.

[0017] In a preferred embodiment of the present invention, in step S3, the cellulose content in the pure cellulose solution is 7-9 wt%.

[0018] In a preferred embodiment of the present invention, in step S4, the core flow rate of the coaxial wet spinning is 30~50 μL. - 1 min -1 The sheath flow rate is 50~100 μL. -1 min -1 The coaxial outer needle size is 15~18G, and the inner needle size is 20~23G; the extrusion speed of the nascent gel fiber is 20~40m / h.

[0019] In a preferred embodiment of the present invention, in step S5, the alcohol dehydrating agent is at least one of ethanol, ethylene glycol, tert-butanol, and isopropanol; the short-chain alkane is at least one of n-pentane, n-hexane, n-heptane, and n-octane; and the replacement time is 20-60 min.

[0020] In a preferred embodiment of the present invention, in step S6, the coverage factor of the woven aerogel fiber fabric is 0.7 to 0.9.

[0021] In a preferred embodiment of the present invention, in step S1, a hydrolysis reaction is carried out at 30-40°C for 20-30 hours to obtain solid silica microspheres, and the centrifugation speed is 4000-8000 r / min.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The hollow silica prepared by this invention has abundant hydroxyl groups on its surface. Even a high proportion of hollow microparticles can be uniformly dispersed in cellulose solution. At the same time, the hollow microspheres provide more pores and store more still air, which can significantly improve the overall thermal insulation performance of aerogel fibers and reduce thermal conductivity.

[0024] 2. The coaxial cellulose-based aerogel fiber prepared by this invention uses cellulose as the base material for both the outer and core layers, exhibiting excellent interfacial bonding properties, sustainability, and environmental friendliness. The resulting fibers possess a large specific surface area and pore volume, with a porosity of 80-93%.

[0025] 3. The coaxial cellulose-based aerogel fiber core layer prepared by this invention has a high cellulose concentration, resulting in a denser aerogel structure that provides good mechanical support for the aerogel fiber. The outer layer contains hollow silica functional particles, which have poor interfacial bonding with the low-concentration fiber. The fiber is prone to stress concentration and breakage during stretching. The core layer mainly bears most of the stress and improves the mechanical strength of the entire composite fiber, with mechanical properties 1.8 times higher than those of composite fibers without a coaxial structure.

[0026] 4. The aerogel fiber drying method employed in this invention enables rapid drying under normal pressure. This novel drying method primarily utilizes the low surface tension of short-chain alkanes, allowing for rapid solvent removal at high temperatures. This method increases the skeletal strength of the gel network, preventing excessive shrinkage, deformation, and structural damage during drying, resulting in aerogel fibers with high porosity and low density. Furthermore, this method is simple to operate, safe, and reliable, enabling continuous production of aerogel fibers. It is significantly faster than traditional freeze-drying or supercritical CO2 technologies and avoids the need for sealed equipment under high pressure or vacuum conditions. This technology can meet the needs of continuous, large-scale production of aerogel fibers.

[0027] 5. The coaxial cellulose-based aerogel fibers prepared by this invention have good solar reflectivity (>92%) and atmospheric window emissivity (>96%), while also having low thermal conductivity (<0.66 W / m²). -1 K -1 This can prevent parasitic heat from reducing the efficiency of radiative cooling.

[0028] 6. The core layer of this invention uses bamboo pulp cellulose, whose high crystallinity and complex microstructure provide excellent mechanical strength and low thermal conductivity, ensuring that the fiber is not easily broken during stretching and effectively preventing heat conduction. The sheath layer uses wood pulp cellulose, whose lower crystallinity and ease of modification allow it to combine with nanoparticles such as hollow silica microspheres, significantly enhancing light scattering and reflection properties and improving solar reflectivity. This combination of core and sheath layers optimizes daytime radiative cooling through synergistic effects of mechanical, optical, and thermal management, while maintaining good flexibility and breathability. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 Flowchart of the preparation process of coaxial cellulose-based aerogel fibers of the present invention;

[0031] Figure 2 This is a microscopic morphology image of the surface of coaxial cellulose-based aerogel fibers in Example 1 of the present invention;

[0032] Figure 3 This is a cross-sectional microstructure of the coaxial cellulose-based aerogel fiber of Example 1 of the present invention;

[0033] Figure 4 This is a comparison chart of solar reflectance and mid-infrared emissivity curves between Embodiment 2 and Comparative Example 1 of the present invention;

[0034] Figure 5 This is the radiative cooling performance of Embodiment 2 of the present invention under direct sunlight.

[0035] In the diagram: 1-Core spinning solution; 2-Sheath spinning solution; 3-Coaxial needle; 4-Traction roller; 5-Coagulation bath; 6-Alcohol dehydrating agent; 7-Short-chain alkanes; 8-High-temperature drying channel; 9-Collecting roller. Detailed Implementation

[0036] like Figure 1 As shown, the present invention provides a method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiation cooling, comprising the following steps:

[0037] S1. Water, anhydrous ethanol, hexadecyltrimethylammonium bromide, ammonia and tetraethyl orthosilicate are mixed and hydrolyzed to obtain solid silica microspheres; the solid silica microspheres are washed with anhydrous ethanol and water by centrifugation, and the template is removed by stirring and etching; the microspheres are washed alternately with anhydrous ethanol and water by centrifugation and dried to obtain hollow silica microspheres.

[0038] S2. Disperse the hollow silica microspheres from S1 in a cellulose solution to form a mixture; mix cellulose in the mixture, centrifuge to degas, and obtain a hollow silica / cellulose mixed spinning solution.

[0039] S3. Disperse pure cellulose in a cellulose solution, centrifuge to degas, and form a pure cellulose solution.

[0040] S4. The hollow silica / cellulose mixed spinning solution of S2 is filled into the coaxial needle sheath, and the pure cellulose solution of S3 is filled into the core. The sheath / core layer solution is uniformly injected into a coagulation bath containing tert-butanol citrate at a certain flow rate, and gel fiber is obtained by coaxial wet spinning.

[0041] S5. The gel fibers from S4 are sequentially introduced into an alcohol dehydrating agent displacement tank and a short-chain alkane solution displacement tank, and dried under normal pressure to obtain coaxial cellulose aerogel fibers.

[0042] S6. The coaxial cellulose aerogel fibers of S5 are processed into cellulose-based aerogel fiber fabrics by weaving.

[0043] In some specific implementations, the cellulose in S2 is selected as wood pulp cellulose, and the cellulose in S3 is selected as bamboo pulp cellulose;

[0044] The preparation method of wood pulp cellulose includes: cutting eucalyptus wood into small sections of 1-3 mm, removing impurities by mechanical screening and air separation, cooking in 10-15% NaOH solution at 150-200℃ for 2-3 hours, then bleaching with 2-3% hydrogen peroxide for 0.5-1 hours, and then dissolving in tetrabutylammonium hydroxide / urea solution (TBAH / urea / water = 2:2:3), controlling the dissolution temperature at 30-40℃ and the time at 1-2 hours, and finally centrifuging and degassing (4000 r / min, 10 minutes) to obtain bamboo pulp cellulose with a crystallinity of 40-50% and a degree of polymerization of 1000-1500.

[0045] The preparation method of bamboo pulp cellulose includes: cutting moso bamboo into small sections of 1-3 mm, removing impurities by mechanical screening and air separation, cooking in 150-200℃ with 15-20% NaOH solution for 2-3 hours, then bleaching with 2-3% hydrogen peroxide for 0.5-1 hours, and then dissolving in tetrabutylammonium hydroxide / urea solution (TBAH / urea / water = 2:2:3), controlling the dissolution temperature at 30-40℃ and the time at 1-2 hours, and finally centrifuging and degassing (5000 r / min, 15 minutes) to obtain bamboo pulp cellulose with a crystallinity of 65-75% and a degree of polymerization of 1200-1600.

[0046] In some specific implementations, in S1, the mass ratio of water to anhydrous ethanol ranges from 1:0.5 to 3, the mass ratio of hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate ranges from 0.5 to 0.7:3 to 5:3 to 5, and the mass ratio of water to tetraethyl orthosilicate ranges from 6 to 10:1 to 3.

[0047] In some specific implementations, in S1, the hollow silica microspheres have a particle size of 200~1200nm and a hollow diameter of 100~800nm.

[0048] In some specific implementations, the solvent in the cellulose dissolving solution is one of sodium sulfonate solution, tetrabutylammonium hydroxide / urea solution, alkali / urea solution, N-methylmorpholine N-oxide solution, or 1-allyl-3-methylimidazolium chloride ion liquid, and the cellulose is one of bamboo pulp, cotton pulp, or wood pulp.

[0049] In some specific implementations, in S2, the solid content in the hollow silica / cellulose mixed spinning solution is 3~5wt%; the mass ratio of the mixed solution to cellulose is 1:9~3:7.

[0050] In some specific implementations, in S3, the cellulose content in the pure cellulose solution is 7-9 wt%.

[0051] In some specific implementations, in S4, the core flow rate of the coaxial wet spinning is 30~50 μL. -1 min -1 The sheath flow rate is 50~100 μL. -1 min -1 The coaxial outer needle size is 15~18G, and the inner needle size is 20~23G; the extrusion speed of the nascent gel fiber is 20~40m / h.

[0052] In some specific implementations, in S5, the alcohol dehydrating agent is at least one of ethanol, ethylene glycol, tert-butanol, and isopropanol; the short-chain alkane is at least one of n-pentane, n-hexane, n-heptane, and n-octane; and the replacement time is 20-60 min.

[0053] In some specific implementations, in S6, the coverage factor of the woven aerogel fiber fabric is 0.7 to 0.9.

[0054] In some specific implementations, in S1, a hydrolysis reaction is carried out at 30~40℃ for 20~30h to obtain silica solid microspheres, and the centrifugation speed is 4000~8000r / min.

[0055] like Figures 2-4 As shown, the specific embodiments of the present invention will be further described below with reference to the examples, but the present invention is not limited to the scope of the examples described.

[0056] The following examples

[0057] The wood pulp cellulose is selected from bamboo pulp cellulose with a crystallinity of 50% and a degree of polymerization of 1200 prepared by the above process; the bamboo pulp cellulose is selected from bamboo pulp cellulose with a crystallinity of 70% and a degree of polymerization of 1500. Example 1

[0058] The present invention provides a method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling, comprising the following:

[0059] S1. a) Water and anhydrous ethanol were uniformly mixed at a mass ratio of 1:2, and then hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate were added sequentially in a mass ratio of 0.64:4:4. The mixture was hydrolyzed at 35°C for 24 h to obtain solid silica microspheres; b) The microspheres after the reaction were washed twice each with anhydrous ethanol and water by centrifugation. The centrifuged silica was dispersed in water at 70°C and etched by stirring for 48 h to remove the hexadecyltrimethylammonium bromide template; c) The etched silica was washed alternately with anhydrous ethanol and water by centrifugation, and dried to obtain hollow silica microspheres with a diameter of 1000 nm.

[0060] S2. Disperse the 2g of hollow silica synthesized above in 140ml of a mixed solution of tetrabutylammonium hydroxide / urea / water with a mass ratio of 2:2:3. Disperse the solution by ultrasonication at room temperature. Then add 4g of wood pulp cellulose to the above mixture, dissolve it completely, and centrifuge to degas it to obtain a mixed spinning solution containing hollow silica.

[0061] S3. Disperse 8g of pure bamboo pulp cellulose in 100ml of a mixed solution of tetrabutylammonium hydroxide / urea / water with a mass ratio of 2:2:3, stir thoroughly, dissolve, and then centrifuge to remove gas.

[0062] S4. Coaxial needles are used to spin gel fibers. The outer needle is model 17G and the inner needle is model 19G. The needle sheath is filled with a hollow silica / cellulose mixed spinning solution, and the core is filled with a pure cellulose solution. The flow rate of the solution in the sheath is 80 μL-1 min-1, and the flow rate of the solution in the core is 40 μL. -1 min -1 The extruded spinning solution is evenly injected into a coagulation bath containing tert-butanol in a mass ratio of 1:2:3.

[0063] S5. To remove residual alkaline solvents and salts, the gel fibers are sequentially introduced into a fresh ethanol dehydrating agent replacement tank and a hexane solution replacement tank, with each solvent replacing for 50 minutes.

[0064] S6. After displacement, coaxial cellulose wet gel fibers are quickly passed through a high-temperature drying tank at 120~220℃ and collected by a collecting roller to obtain coaxial cellulose aerogel fibers.

[0065] S7. The coaxial cellulose aerogel fiber is processed into a fabric by weaving, and the fabric coverage factor is 0.9.

[0066] The obtained coaxial cellulose-based aerogel fibers have a diameter of 500 μm, and the core layer diameter accounts for 60% of the total fiber diameter. Example 2

[0067] This embodiment is basically the same as Embodiment 1, except that: S4 is as follows: gel fibers are spun using coaxial needles, with the outer needle model being 17G and the inner needle model being 21G; the needle sheath is filled with a hollow silica / cellulose mixed spinning solution, and the core is filled with a pure cellulose solution, with a sheath solution flow rate of 90 μL. -1 min -1 Core solution flow rate 20 μL -1 min -1 The extruded spinning solution is evenly injected into a coagulation bath containing tert-butanol in a mass ratio of 1:2:3.

[0068] The obtained coaxial cellulose-based aerogel fiber has a diameter of 500 μm, and the core layer diameter accounts for 40% of the total fiber diameter. The obtained coaxial aerogel fiber has poorer tensile properties, but better thermal insulation properties and lower thermal conductivity. Example 3

[0069] This embodiment is basically the same as Example 1, except that the hollow silica used has a size of 800 nm. In S1, a) water and anhydrous ethanol are mixed uniformly at a mass ratio of 1:1, and then hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate are added sequentially in a mass ratio of 0.64:4:4. The mixture is hydrolyzed at 35°C for 24 h to obtain solid silica microspheres; b) the microspheres after the reaction are washed twice each with anhydrous ethanol and water by centrifugation. The centrifuged silica is dispersed in water at 70°C and etched by stirring for 48 h to remove the hexadecyltrimethylammonium bromide template; c) the etched silica is washed alternately with anhydrous ethanol and water by centrifugation, and after drying, hollow silica microspheres with a diameter of 800 nm are obtained. Example 4

[0070] This embodiment is basically the same as Example 1, except that the hollow silica used has a size of 1200 nm. In S1, a) water and anhydrous ethanol are mixed uniformly at a mass ratio of 1:3, and then hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate are added sequentially in a mass ratio of 0.64:4:4. The mixture is hydrolyzed at 35°C for 24 h to obtain solid silica microspheres; b) the microspheres after the reaction are washed twice each with anhydrous ethanol and water by centrifugation. The centrifuged silica is dispersed in water at 70°C and etched by stirring for 48 h to remove the hexadecyltrimethylammonium bromide template; c) the etched silica is washed alternately with anhydrous ethanol and water by centrifugation, and after drying, hollow silica microspheres with a diameter of 1200 nm are obtained. Example 5

[0071] This embodiment is basically the same as Example 1, except that the hollow silica used has a size of 900 nm. In S1, a) water and anhydrous ethanol are mixed uniformly at a mass ratio of 1:1.5, and then hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate are added sequentially in a mass ratio of 0.64:4:4. The mixture is hydrolyzed at 35 °C for 24 h to obtain solid silica microspheres; b) the microspheres after the reaction are washed twice each with anhydrous ethanol and water by centrifugation. The centrifuged silica is dispersed in water at 70 °C and etched by stirring for 48 h to remove the hexadecyltrimethylammonium bromide template; c) the etched silica is washed alternately with anhydrous ethanol and water by centrifugation, and dried to obtain hollow silica microspheres with a diameter of 900 nm. Example 6

[0072] This embodiment is basically the same as Example 1, except that the hollow silica used has a size of 700 nm. In S1, a) water and anhydrous ethanol are mixed uniformly at a mass ratio of 1:0.5, and then hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate are added sequentially in a mass ratio of 0.64:4:4. The mixture is hydrolyzed at 35 °C for 24 h to obtain solid silica microspheres; b) the microspheres after the reaction are washed twice each with anhydrous ethanol and water by centrifugation. The centrifuged silica is dispersed in water at 70 °C and etched by stirring for 48 h to remove the hexadecyltrimethylammonium bromide template; c) the etched silica is washed alternately with anhydrous ethanol and water by centrifugation, and after drying, hollow silica microspheres with a diameter of 700 nm are obtained. Example 7

[0073] This embodiment is basically the same as that of embodiment 1, except that the cellulose in S2 is bamboo pulp cellulose. Example 8

[0074] This embodiment is basically the same as that of embodiment 1, except that the cellulose in S3 is wood pulp cellulose. Comparative Example 1

[0075] This comparative example is basically the same as Example 1, except that: S4 is: a standard needle of model 17G is used to spin gel fibers instead of a coaxial needle; the needle is filled with a hollow silica / cellulose mixed spinning solution, the core is filled with a pure cellulose solution, and the spinning solution flow rate is 100 μL. -1 min -1 The extruded spinning solution is evenly injected into a coagulation bath containing tert-butanol in a mass ratio of 1:2:3.

[0076] The obtained cellulose-based composite aerogel fiber has a diameter of 500 μm. The homogeneous composite aerogel fiber is filled with the most silica particles, resulting in the worst tensile properties, but the best thermal insulation properties and the lowest thermal conductivity. Comparative Example 2

[0077] This comparative example is basically the same as Example 1, except that: S4 is: a standard needle of model 17G is used to spin gel fibers instead of a coaxial needle; the needle is filled with pure cellulose solution, and the flow rate of the spinning solution is 100 μL. -1 min -1 The extruded spinning solution is evenly injected into a coagulation bath containing tert-butanol in a mass ratio of 1:2:3.

[0078] The obtained cellulose-based aerogel fibers have a diameter of 500 μm. The pure cellulose aerogel fibers have the densest internal three-dimensional network and no silica particles, resulting in the best tensile properties but the worst thermal insulation properties and the highest thermal conductivity.

[0079] The test results of porosity, density, fracture strength, elongation at break, and thermal conductivity of Examples 1-8 and Comparative Examples 1-2 are shown in Table 1.

[0080] Table 1: Test data of Examples 1-8 and Comparative Examples 1-2

[0081] Porosity (%) <![CDATA[Density (g / cm 3 ).]]> Fracture strength (MPa) Elongation at break (%) <![CDATA[Thermal conductivity (Wm -1 K -1 )]]> Example 1 87.55 0.19 18.5 14.7 0.62 Example 2 86.12 0.21 19.3 17.5 0.64 Example 3 86.36 0.21 19.5 16.1 0.63 Example 4 85.20 0.22 17.8 13.2 0.65 Example 5 84.85 0.23 17.2 12.6 0.66 Example 6 83.90 0.24 16.5 11.9 0.67 Example 7 86.15 0.20 18.9 15.6 0.66 Example 8 86.03 0.21 16.3 12.5 0.59 Comparative Example 1 89.14 0.17 10.5 7.1 0.51 Comparative Example 2 83.43 0.25 23.3 24.5 0.68

[0082] The fibers obtained in Example 1 have a high porosity (87.55%) and a low density (0.19 g / cm³). 3 It has moderate breaking strength and elongation at break, and relatively low thermal conductivity (0.62 W / m²). -1 K -1 This indicates that it has good overall performance.

[0083] Compared to Example 1, Example 2 changed the type of coaxial needle and the flow rate of the spinning solution, resulting in a decrease in the proportion of core diameter to total fiber diameter (40%). Although the thermal insulation performance was better (slightly lower thermal conductivity), the tensile properties deteriorated due to the reduction in core cellulose, leading to a decrease in the overall fiber strength.

[0084] Example 3 used a smaller hollow silica size (800 nm). Although the fiber properties were basically the same as those in Example 1, the reflectivity decreased and the radiation cooling performance was reduced. This shows that the size of the hollow silica has a significant impact on the optical properties of the fiber.

[0085] Example 4 further increased the size of the hollow silica (1200 nm), resulting in increased spacing between the hollow silica particles inside the fiber, which affected the fiber's thermal insulation performance. Although the fiber porosity remained high, the increased size of the hollow silica particles led to increased air convection inside the fiber, resulting in a slight increase in thermal conductivity (0.65 W / m²). -1 K -1Meanwhile, the larger hollow silica particles weaken the mechanical properties of the fiber to some extent, and the breaking strength and breaking elongation are lower than in Example 1.

[0086] Example 5 further reduced the size of the hollow silica (900 nm), falling between that of Examples 3 and 4. Hollow silica particles of this size form a relatively uniform distribution within the fiber, ensuring both the fiber's thermal insulation performance and, to some extent, maintaining its mechanical properties. However, compared to Example 1, its porosity and density decreased slightly, while its thermal conductivity increased slightly (0.66 W / m²). -1 K -1 This is due to the fine-tuning of the internal structure of the fiber caused by the change in the size of the hollow silica particles.

[0087] Example 6 further reduced the size of the hollow silica (700 nm). While this helped increase the number and density of hollow silica particles inside the fiber, thereby improving the fiber's thermal insulation performance, the excessively small particle size also led to a decrease in the fiber's mechanical properties. This is because small particles are more likely to agglomerate or accumulate inside the fiber, affecting the fiber's uniformity and strength. Therefore, the fiber of Example 6 performed poorly in terms of breaking strength and elongation at break, while its thermal conductivity also increased (0.67 W / m²). -1 K -1 This is due to the combined effect of the unevenness of the internal structure of the fiber and the decline in mechanical properties.

[0088] Comparative Example 1 did not use a coaxial needle, but instead used a regular needle to spin gel fibers. Although the resulting fibers had the highest porosity and the lowest thermal conductivity, they had the worst tensile properties, which was due to the inhomogeneity of the fiber's internal structure.

[0089] Comparative Example 2 also did not use a coaxial needle and was not filled with hollow silica particles. The pure cellulose aerogel fiber obtained had the densest internal three-dimensional network and the best tensile properties, but the worst thermal insulation performance and the highest thermal conductivity. This indicates that the filling of hollow silica particles has a significant impact on the thermal insulation performance of the fiber.

[0090] like Figure 5 As shown, cellulose aerogel fibers have good solar reflectivity to enhance the optical path difference, thereby causing high solar reflection, while high porosity produces low thermal conductivity, which can avoid parasitic heat from reducing the radiative cooling efficiency under direct sunlight.

[0091] In Example 1, bamboo pulp cellulose with high crystallinity (70%) is used in the core layer of the coaxial fiber. It contains numerous microfibers and nanoscale pores, enhancing the fiber's mechanical properties and providing more stress dispersion paths during stretching, thus preventing breakage caused by stress concentration. The high degree of polymerization of bamboo pulp cellulose (1200-1600) means its molecular chains are longer, contributing to the formation of a stable network and further reducing heat conduction paths, thus enhancing the insulation effect. In Example 1, wood pulp cellulose has lower crystallinity (50%), with relatively loose molecular chain arrangement and a more disordered structure. This lower crystallinity gives wood pulp cellulose better light scattering properties in the visible and near-infrared bands. When light shines on the fiber surface, the disordered molecular structure scatters the light in multiple directions, increasing light reflectivity, especially showing a significant reflection effect on visible and near-infrared light from sunlight. Wood pulp cellulose has many surface active sites, making it easy to chemically react or physically adsorb with other functional materials (such as hollow silica microspheres). By introducing nanoparticles such as hollow silica microspheres, light scattering and reflection properties can be further enhanced. Hollow silica microspheres themselves have a low refractive index and a large specific surface area, which can effectively scatter and reflect sunlight, especially in the visible and near-infrared bands, significantly improving solar reflectivity.

[0092] In Example 7, the entire fiber is composed of bamboo pulp cellulose. Although the strength is guaranteed with a breaking strength of 18.9 MPa, its low light scattering ability and reflectivity will lead to increased absorption of sunlight, affecting the effect of daytime radiative cooling.

[0093] In Example 8, the entire fiber is wood pulp cellulose, and its thermal conductivity is relatively low (0.59 W / m²). -1 K -1 However, wood pulp cellulose has a low degree of polymerization, short molecular chains, and insufficient strength, making the fibers prone to breakage during stretching.

[0094] In summary, the above analysis shows that Example 1 exhibits excellent overall performance in terms of porosity, density, tensile strength, elongation at break, and thermal conductivity. While other examples offer improvements or optimizations in certain aspects, these often come at the cost of other performance characteristics. Therefore, the method for preparing coaxial cellulose-based aerogel fibers provided in Example 1 demonstrates the best balance in terms of various performance indicators.

[0095] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling, characterized in that, Includes the following steps: S1. Water, anhydrous ethanol, hexadecyltrimethylammonium bromide, ammonia and tetraethyl orthosilicate are mixed and hydrolyzed to obtain solid silica microspheres; the solid silica microspheres are washed with anhydrous ethanol and water by centrifugation, and the template is removed by stirring and etching; the microspheres are washed alternately with anhydrous ethanol and water by centrifugation and dried to obtain hollow silica microspheres. S2. Disperse the hollow silica microspheres from S1 in a cellulose solution to form a mixture; mix cellulose in the mixture, centrifuge and degas to obtain a hollow silica / cellulose mixed spinning solution, wherein the cellulose is selected as wood pulp cellulose; S3. Disperse pure cellulose in a cellulose solution, centrifuge to degas, and form a pure cellulose solution. The cellulose selected is bamboo pulp cellulose. S4. The hollow silica / cellulose mixed spinning solution of S2 is filled into the coaxial needle sheath, and the pure cellulose solution of S3 is filled into the core. The sheath / core layer solution is uniformly injected into a coagulation bath containing tert-butanol citrate at a certain flow rate, and gel fiber is obtained by coaxial wet spinning. S5. The gel fibers from S4 are sequentially introduced into an alcohol dehydrating agent displacement tank and a short-chain alkane solution displacement tank, and dried under normal pressure to obtain coaxial cellulose aerogel fibers. S6. The coaxial cellulose aerogel fibers of S5 are processed into cellulose-based aerogel fiber fabrics by weaving.

2. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In S1, the mass ratio of water to anhydrous ethanol is in the range of 1:0.5~3, the mass ratio of hexadecyltrimethylammonium bromide, ammonia and tetraethyl orthosilicate is in the range of 0.5~0.7:3~5:3~5, and the mass ratio of water to tetraethyl orthosilicate is in the range of 6~10:1~3.

3. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In S1, the hollow silica microspheres have a particle size of 200~1200nm and a hollow diameter of 100~800nm.

4. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: The solvent in the cellulose dissolving solution is one of sodium sulfonate solution, tetrabutylammonium hydroxide / urea solution, alkali / urea solution, N-methylmorpholine N-oxide solution, or 1-allyl-3-methylimidazolium chloride ion liquid, and the cellulose is one of bamboo pulp, cotton pulp, or wood pulp.

5. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In S2, the solid content in the hollow silica / cellulose mixed spinning solution is 3~5wt%; the mass ratio of hollow silica to cellulose is 1:9~3:

7.

6. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In S3, the cellulose content in the pure cellulose solution is 7-9 wt%.

7. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In step S4, the core flow rate of the coaxial wet spinning is 30~50 μL. -1 min -1 The sheath flow rate is 50~100 μL. -1 min -1 The coaxial outer needle size is 15~18G, and the inner needle size is 20~23G; the extrusion speed of the nascent gel fiber is 20~40m / h.

8. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In step S5, the alcohol dehydrating agent is at least one of ethanol, ethylene glycol, tert-butanol, and isopropanol; the short-chain alkane is at least one of n-pentane, n-hexane, n-heptane, and n-octane; and the replacement time is 20-60 min.

9. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiative cooling according to claim 1, characterized in that: In S6, the coverage factor of the woven aerogel fiber fabric is 0.7 to 0.

9.

10. The method for preparing a coaxial cellulose-based aerogel fiber fabric for daytime radiation cooling according to claim 1, characterized in that: In S1, a hydrolysis reaction is carried out at 30~40℃ for 20~30h to obtain silica solid microspheres, and the centrifugation speed is 4000~8000r / min.

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