A method for producing a porous fiber having a nano-cellulose fibril stabilized bubble structure

Abstract

The application discloses a preparation method of a porous fiber with a nanocellulose fibril stable bubble structure. The method comprises the following steps: adding a nanocellulose fibril dispersion liquid and a foaming aid into a polymer solution to mix, performing dispersion treatment on the mixed liquid to obtain a spinning solution; injecting a gas into the spinning solution and performing stirring to obtain a bubble type spinning solution; and performing wet spinning on the bubble type spinning solution to obtain a porous fiber. The diameter of the nanocellulose fibril is less than 10 nm, and the length is more than 500 nm. The porous fiber prepared by the method has an elliptical internal closed pore structure and high strength. Compared with a traditional solid fiber, the porous fiber has lower bulk density and heat conduction efficiency due to the existence of the internal closed pore structure, thereby having better warm-keeping performance, and the internal closed pore structure provides more possibilities for functional modification such as phase change capsule coating, nanoparticle loading and drug loading.

Description

Technical Field

[0001] This application relates to the field of fiber materials engineering, and in particular to a method for preparing porous fibers with a stable bubble structure of nanocellulose filaments. Background Technology

[0002] Porous fibers are fibrous materials containing numerous pores, exhibiting significant characteristics such as high air permeability, low density, and excellent adsorption properties. Due to their unique structure and properties, they are widely used in building sound insulation, automotive interiors, wound dressings, thermal clothing, and lightweight insulation materials. Although porous fibers represent a material with immense potential, their development and application still face challenges such as high production costs, complex processing procedures, and low mechanical strength. These issues result in fabrics or clothing made from porous fibers requiring special care, being difficult to process, and exhibiting insufficient durability in practical applications.

[0003] Therefore, there is an urgent need to develop a new type of closed-cell porous fiber material with high thermal insulation, waterproofing and lightweight properties to overcome the above-mentioned problems of traditional porous fibers and promote the development of the fiber industry. Summary of the Invention

[0004] In view of the shortcomings in the preparation and application of porous fibers mentioned above, the purpose of this application is to provide a method for preparing porous fibers with a stable bubble structure of nanocellulose filaments. The preparation method of this application has a simple process flow, low production cost, and can achieve continuous preparation. The prepared porous fibers have a unique internal closed-pore structure and high strength.

[0005] The purpose of this application is achieved through the following technical solution.

[0006] A first aspect of this application provides a method for preparing porous fibers with a stable bubble structure of nanocellulose filaments, comprising the following steps:

[0007] (1) Add nanocellulose fiber dispersion and foaming agent to the polymer solution and mix. The mixture is then dispersed to obtain a spinning solution.

[0008] (2) Inject gas into the spinning solution and stir to obtain a bubble-type spinning solution;

[0009] (3) The bubble-type spinning solution is wet-spun to obtain porous fibers.

[0010] In any embodiment of this application, in step (1), the polymer is at least one selected from polyvinyl alcohol, chitosan, alginate, gelatin, agar, polyethylene oxide, polyacrylic acid, sodium polyacrylate, polyacrylamide, and poly(N-isopropylacrylamide). Specifically, the average molecular weight of polyvinyl alcohol is between 60,000 and 90,000; the viscosity of chitosan is between 100 and 800 mPa·s; the alginate is sodium alginate with an average molecular weight between 200,000 and 400,000; the average molecular weight of polyethylene oxide is between 10,000 and 100,000; the average molecular weight of sodium polyacrylate is between 4,000 and 5,000; the average molecular weight of polyacrylamide is between 10,000,000 and 20,000,000; and the average molecular weight of poly(N-isopropylacrylamide) is between 20,000 and 50,000. This application preferably uses a mixture of multiple polymers, such as a mixture of three, four, or five of the following polymers: polyvinyl alcohol, chitosan, alginate, gelatin, agar, polyethylene oxide, polyacrylic acid, sodium polyacrylate, polyacrylamide, and N-isopropylacrylamide. In the case of a mixture of multiple polymers, the content of each component is such that the main polymer accounts for 60-90%, and the other polymers account for 10-40%, resulting in a polymer solution with a viscosity in the range of 1000-10000 mPa·s. The main polymer can be polyvinyl alcohol, chitosan, alginate, gelatin, polyacrylic acid, etc., and the other polymers can be agar, polyethylene oxide, sodium polyacrylate, polyacrylamide, polyN-isopropylacrylamide, etc.

[0011] In any embodiment of this application, in step (1), the mass percentage concentration of the polymer in the polymer solution is 0.5% to 40%, preferably 1% to 30%.

[0012] In any embodiment of this application, the polymer solution in step (1) is prepared by adding the polymer and a co-solvent to deionized water and stirring until the polymer is completely dissolved. The co-solvent is at least one selected from methanol, ethanol, isopropanol, aminoethanol, acetone, acetic acid, and surfactants. The volume percentage concentration of the co-solvent in the polymer solution is 0.1–2%, preferably 0.5–1%. During the stirring and dissolution, the dissolution temperature is 30–99°C, preferably 35–95°C. During the stirring and dissolution, the dissolution time is 0.5–24 h, preferably 1–12 h. The dissolution time can be appropriately determined according to the dissolution status of the polymer; stirring and dissolving until the polymer is completely dissolved is sufficient, i.e., stirring and dissolving until the solution is a transparent liquid state indicates that the polymer is completely dissolved.

[0013] In any embodiment of this application, in step (1), the diameter of the nanocellulose filaments is less than 10 nm and the length is more than 500 nm. Preferably, this application uses a high aspect ratio of nanocellulose filaments to ensure improved stability and viscosity in the spinning solution, thereby allowing air bubbles to remain in the spinning solution for a longer period of time. If the aspect ratio of the nanocellulose filaments is too small, the nanocellulose filaments will not be able to provide skeletal support; if the aspect ratio is too large, the viscosity of the spinning solution will be too high, thereby increasing the risk of clogging the spinneret during spinning and causing uneven fiber formation during spinning. Therefore, in this application, the aspect ratio of the nanocellulose filaments is set between 40:1 and 3000:1, preferably between 40:1 and 2000:1.

[0014] In any embodiment of this application, in step (1), the raw material for the nanocellulose filaments is trees, plant stalks, recycled clothing, etc., preferably trees and plant stalks. In this application, nanocellulose filaments of a specified size can be prepared using conventional methods in the art. It should be noted that even if the size of the hydrophobically modified nanocellulose filaments conforms to the specified size of this application, they are not applicable to this application due to their hydrophobicity.

[0015] In any embodiment of this application, in step (1), the foaming agent is at least one of alkyl glycoside, fatty alcohol polyoxyethylene ether, lauramide propyl betaine, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, quaternary ammonium salt, etc.

[0016] In any embodiment of this application, in step (1), the solid-liquid mass ratio of the polymer solution, the nanocellulose fiber dispersion, and the foaming agent is 100:(3-60):(0-15), preferably 100:(5-60):(1-15).

[0017] In any embodiment of this application, in step (1), the concentration of the nanocellulose fiber dispersion is 0.02-30%, preferably 0.1-25%.

[0018] In any embodiment of this application, in step (1), the nanocellulose filaments are added to deionized water and subjected to ultrasonic treatment to obtain a nanocellulose filament dispersion. The ultrasonic treatment has an ultrasonic frequency of 5 to 100 kHz, a power range of 50 to 700 W, and a treatment time of 1 to 60 min, preferably 10 to 80 kHz, a power range of 100 to 600 W, and a treatment time of 5 to 60 min.

[0019] In any embodiment of this application, in step (1), the dispersion process is an ultrasonic process, wherein the ultrasonic frequency is 5 to 100 kHz, the power range is 50 to 700 W, the processing time is 1 to 60 min, preferably 10 to 80 kHz, the power range is 100 to 600 W, and the processing time is 5 to 60 min.

[0020] In any embodiment of this application, in step (1), a functional filler is further added to the polymer solution. The functional filler is at least one of the following: polyvinylpyrrolidone, polyethyleneimine, cationic starch, waterborne polyurethane, epichlorohydrin, polyamide epichlorohydrin, epoxy resin, sodium silicate, silicone resin, glutaraldehyde, carbon black, graphene, carbon nanotubes, paraffin wax, polyethylene glycol, nano zinc oxide, nano silver, nano titanium dioxide, nano silica, and fatty acids. The solid-liquid mass ratio of the polymer solution, nanocellulose fiber dispersion, foaming agent, and functional filler is 100:(3-60):(0-15):(0-15), preferably 100:(5-60):(1-15):(1-15). In this application, adding an appropriate amount of functional filler can improve the properties of porous fibers, such as increasing their mechanical strength, heat resistance, electrical conductivity, heat storage capacity, photocatalytic effect, antibacterial properties, or other desired functional characteristics. The type and amount of functional fillers added can be adjusted according to specific application scenarios to ensure the excellent performance of porous fibers in different application scenarios.

[0021] In any embodiment of this application, in step (2), the gas is at least one of nitrogen, carbon dioxide, helium, air, and argon.

[0022] In any embodiment of this application, in step (2), the stirring speed is 1000-10000 rpm / min and the processing time is 1-90 min, preferably 1500-10000 rpm / min and 5-90 min.

[0023] In this application, the nanocellulose filaments form a network structure in the spinning solution obtained in step (1), which can increase the stability and viscosity of the spinning solution, allowing bubbles to remain in the spinning solution for a long time, and also improve the strength of the fiber skeleton. Furthermore, injecting gas into the spinning solution obtained in step (1) for foaming can reduce the permeation and escape of gas in the fiber, and maintain the stability of the porous fiber morphology.

[0024] In any embodiment of this application, in step (3), the bubble-type spinning solution is extruded through a spinneret into a coagulation bath, so that the extruded fiber coagulates in the coagulation bath to form nascent fiber. The nascent fiber is then subjected to a stretching treatment to improve fiber strength, followed by appropriate washing to remove residual impurities, and finally dried to obtain porous fiber.

[0025] In any embodiment of this application, the orifice diameter of the spinneret is 50-3000 μm, preferably 50-2000 μm, and the extrusion speed of the bubble-type spinning solution through the spinneret is 0.1-30 mL / min, preferably 0.5-30 mL / min.

[0026] In any embodiment of this application, the coagulation bath is at least one selected from saturated sodium sulfate solution, sodium hydroxide solution, calcium chloride solution, methanol solution, ethanol solution, and sodium hydroxide-ethanol solution. The temperature of the coagulation bath is -30 to 50°C, preferably -20 to 50°C, and the coagulation time is 10 to 70 seconds, preferably 20 to 70 seconds. The methanol solution, ethanol solution, and sodium hydroxide-ethanol solution are low-temperature solution systems, with the low temperature being -30 to 10°C, preferably -20 to 5°C.

[0027] In any embodiment of this application, during the stretching process, the stretching ratio of the nascent fiber is 2 to 10 times, preferably 4 to 10 times, and the stretching temperature is 25 to 200°C, preferably 30 to 200°C.

[0028] In any embodiment of this application, during the washing process, the stretched fibers are placed in a washing solution for washing, wherein the washing solution is at least one of deionized water, methanol, ethanol, etc.

[0029] In any embodiment of this application, during the drying process, the washed fibers are dried at a drying temperature of 50–200°C, preferably 60–200°C, for a drying time of 1–20 min.

[0030] The beneficial effects of this application are:

[0031] First, the spinning method of this application has a simple process flow, low production cost, and can achieve continuous production, exhibiting high stability and repeatability. Furthermore, with appropriate adjustments to existing wet spinning equipment, this method can directly utilize these devices to produce porous fibers, fully leveraging existing production conditions and reducing additional equipment investment.

[0032] Secondly, this application employs high aspect ratio nanocellulose filaments, combining the abundant hydrogen bonding and electrostatic interactions of the nanocellulose filaments to form a stable three-dimensional physical network structure in the spinning solution. On one hand, this increases the viscosity and stability of the spinning solution, preventing bubble floating and dissipation, thus ensuring bubble retention during the transformation of the bubble-type spinning solution into porous fibers. On the other hand, the high aspect ratio of the nanocellulose filaments improves the dispersibility of various components in the spinning solution, ensuring uniformity during the spinning process. Furthermore, the high aspect ratio and abundant hydroxyl groups of the nanocellulose filaments enhance the interactions between polymer molecular chains, avoiding the phenomena of non-solidification and low strength during the initial fiber formation process, improving the fiber solidification and forming ability, and simultaneously giving the obtained fibers better pore size stability and mechanical strength. Further, in the spinning solution containing the three-dimensional physical network structure of nanocellulose filaments, gas is injected for foaming, reducing gas permeation and escape from the fibers and maintaining the stability of the porous fiber morphology.

[0033] The porous fibers prepared by the method of this application possess an elliptical internal closed-pore structure and high strength. Compared with traditional solid fibers, the porous fibers of this application exhibit lower bulk density and lower thermal conductivity due to the presence of their internal closed-pore structure, thus providing better thermal insulation performance. Furthermore, the unique internal closed-pore structure of the porous fibers of this application offers more possibilities for functional modifications such as phase change capsule encapsulation, nanoparticle loading, and drug loading. Attached Figure Description

[0034] Figure 1 This is a SEM image of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 1.

[0035] Figure 2 The stress-strain curve is shown for the porous fiber with a stable bubble structure of nanocellulose filaments in Example 1.

[0036] Figure 3 This is a SEM image of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 2.

[0037] Figure 4 The stress-strain curve is shown for the porous fiber with a stable bubble structure of nanocellulose filaments in Example 2.

[0038] Figure 5 This is a SEM image of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 3.

[0039] Figure 6 The stress-strain curve is shown for the porous fiber with a stable bubble structure of nanocellulose filaments in Example 3.

[0040] Figure 7This is a DSC diagram of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 3. Detailed Implementation

[0041] To make the technical solution of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0042] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the reagents used can be purchased from chemical or biological reagent companies.

[0043] Materials used in the following embodiments:

[0044] Nanocellulose filaments: derived from trees or straw, with a diameter of 4–10 nm and a length of 500–2000 nm, prepared using conventional methods in the field.

[0045] Polyvinyl alcohol: Average molecular weight: 76,000, Model P: 1799, Manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.

[0046] Chitosan: Viscosity: 200-600 mPa·s; Manufacturer: Sinopharm Chemical Reagent Co., Ltd.

[0047] Polyacrylic acid: Viscosity: ≤2000mPa·s, Manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.

[0048] Polyacrylamide: Average molecular weight: 15,000,000; Manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.

[0049] Poly(N-isopropylacrylamide): Average molecular weight: 40,000; Manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.

[0050] Sodium polyacrylate: Average molecular weight: 5100, Manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.

[0051] Sodium alginate: Average molecular weight: 300,000; Manufacturer: Qingdao Mingyue Seaweed Group Co., Ltd.

[0052] Polyethylene oxide: Average molecular weight: 100,000, Manufacturer: Sinopharm Chemical Reagent Co., Ltd.

[0053] Example 1

[0054] 1. Preparation of polymer solution: Deionized water, polyvinyl alcohol, chitosan, polyacrylic acid, polyacrylamide, and acetic acid were mixed in the proportions of 790 mL, 150 g, 40 g, 5 g, 5 g, and 10 mL, respectively. The mixture was then stirred at 95°C for 3 hours to completely dissolve the polymer, resulting in a polymer solution with a mass percentage concentration of 20%.

[0055] 2. Preparation of spinning solution: An appropriate amount of nanocellulose filaments (10 nm in diameter and 600 nm in length) were added to deionized water and ultrasonically dispersed for 10 min to obtain a nanocellulose filament dispersion with a mass percentage concentration of 10%. Deionized water, the above polymer solution, the ultrasonically dispersed nanocellulose filament dispersion, alkyl glycosides, fatty alcohol polyoxyethylene ether, epichlorohydrin, and nano zinc oxide were mixed in a ratio of 230 mL, 650 g, 100 g, 5 g, 5 g, 5 g, and 5 g, respectively, and ultrasonically dispersed for 30 min to obtain a spinning solution with a concentration of 16%. The ultrasonic frequency used in the ultrasonic dispersion was 60 kHz, and the ultrasonic power range was 300 W. The concentration of the spinning solution refers to the mass percentage concentration of all substances in the spinning solution except water.

[0056] 3. Foaming treatment of spinning solution: The spinning solution was placed in a glove box and nitrogen gas was introduced for 30 minutes to purge the air. Then, the spinning solution was stirred while nitrogen gas was being introduced to obtain a bubble-type spinning solution. The stirring speed was 8000 rpm / min and the stirring time was 30 minutes.

[0057] 4. Preparation of composite porous fibers: The bubble-type spinning solution is placed in a spinning drum for wet spinning. Specifically, the bubble-type spinning solution is extruded through a porous spinneret into a coagulation bath for coagulation to obtain nascent fibers. The nascent fibers are then drawn, washed, and dried to obtain porous fibers with a stable bubble structure of nanocellulose filaments. The spinneret orifice diameter is 600 μm, the extrusion speed is 10 mL / min, the coagulation bath is a 2% sodium hydroxide ethanol solution, the coagulation bath temperature is -10℃, and the coagulation time is 60 s. The nascent fiber draw ratio is 4 times, the draw temperature is 30℃, the washing solution is deionized water, the drying temperature is 90℃, and the drying time is 5 min.

[0058] Example 2

[0059] 1. Preparation of polymer solution: Deionized water, polyvinyl alcohol, sodium polyacrylate, polyacrylamide, poly(N-isopropylacrylamide), and acetone were mixed in the proportions of 780 mL, 160 g, 20 g, 15 g, 5 g, and 20 g, respectively. The mixture was then stirred at 95 °C for 2 h to completely dissolve the polymer, resulting in a polymer solution with a polymer concentration of 20% (m / m).

[0060] 2. Preparation of spinning solution: An appropriate amount of nanocellulose filaments (8 nm in diameter and 800 nm in length) were added to deionized water and ultrasonically dispersed for 15 min to obtain nanocellulose filaments with a mass percentage concentration of 12%. Deionized water, the above polymer solution, the ultrasonically dispersed nanocellulose filament dispersion, sodium dodecyl sulfate, quaternary ammonium salt, nano-titanium dioxide, and nano-silica were mixed in a ratio of 300 mL, 600 g, 50 g, 5 g, 5 g, 20 g, and 20 g, respectively, and ultrasonically dispersed for 30 min to obtain a spinning solution with a concentration of 17.6%. The ultrasonic frequency used in the ultrasonic dispersion treatment was 40 kHz, and the ultrasonic power range was 500 W.

[0061] 3. Foaming treatment of spinning solution: The spinning solution was placed in a glove box and air was introduced for 5 minutes. Then, the spinning solution was stirred while air was being introduced to obtain a bubble-type spinning solution. The stirring speed was 6000 rpm / min and the stirring time was 50 minutes.

[0062] 4. Preparation of composite porous fibers: A bubble-type spinning solution is placed in a spinning drum for wet spinning. Specifically, the bubble-type spinning solution is extruded through a porous spinneret into a coagulation bath for coagulation, yielding nascent fibers. These nascent fibers are then drawn, washed, and dried to obtain porous fibers with a stable bubble structure of nanocellulose filaments. The spinneret orifice diameter is 800 μm, the extrusion speed is 15 mL / min, the coagulation bath is a saturated sodium sulfate solution, the coagulation bath temperature is 25℃, and the coagulation time is 120 s; the draw ratio is 5 times, the draw temperature is 50℃, the washing solution is deionized water, the drying temperature is 110℃, and the drying time is 3 min.

[0063] Example 3

[0064] 1. Preparation of polymer solution: Deionized water, polyvinyl alcohol, sodium alginate, gelatin, polyethylene oxide, and sodium polyacrylate were mixed in the proportions of 800 mL, 170 g, 10 g, 10 g, 5 g, and 5 g, respectively. The mixture was then stirred at 90 °C for 3 h to completely dissolve the polymer, resulting in a polymer solution with a polymer concentration of 20% (m / m).

[0065] 2. Preparation of spinning solution: An appropriate amount of nanocellulose filaments (5 nm in diameter and 1000 nm in length) were added to deionized water and ultrasonically dispersed for 5 min to obtain a nanocellulose filament dispersion with a mass percentage concentration of 8%. Deionized water, the above polymer solution, the ultrasonically dispersed nanocellulose filament dispersion, alkyl glycosides, fatty alcohol polyoxyethylene ethers, glutaraldehyde, and paraffin were mixed in a ratio of 160 mL, 600 g, 200 g, 5 g, 5 g, 10 g, and 20 g, respectively, and ultrasonically dispersed for 40 min to obtain a spinning solution with a concentration of 17.6%. The ultrasonic frequency used in the ultrasonic dispersion treatment was 40 kHz, and the ultrasonic power range was 500 W.

[0066] 3. Foaming treatment of spinning solution: The spinning solution was placed in a glove box and carbon dioxide was introduced for 30 minutes to purge the air. Then, the spinning solution was stirred while carbon dioxide was continued to be introduced to obtain a bubble-type spinning solution. The stirring speed was 7000 rpm / min and the foaming time was 40 minutes.

[0067] 4. Preparation of composite porous fibers: The bubble-type spinning solution is placed in a spinning drum for wet spinning. Specifically, the bubble-type spinning solution is extruded through a porous spinneret into a coagulation bath for coagulation to obtain nascent fibers. These nascent fibers are then drawn, washed, and dried to obtain porous fibers with a stable bubble structure of nanocellulose filaments. The spinneret orifice diameter is 500 μm, the extrusion speed is 5 mL / min, the coagulation bath is a 6% calcium chloride aqueous solution, the coagulation bath temperature is 0℃, and the coagulation time is 60 s; the draw ratio is 5 times, the draw temperature is 50℃, the washing solution is deionized water, the drying temperature is 100℃, and the drying time is 10 min.

[0068] Example 4

[0069] Figures 1 to 7 The paper shows the physical structure, mechanical properties, and functional test results of the porous fibers obtained according to Examples 1 to 3.

[0070] Figure 1 This is a SEM image of a cross-section of a porous fiber with a stable bubble structure of nanocellulose filaments from Example 1. Figure 1 As can be seen from the analysis of the porous fiber structure, a large number of closed-cell structures are found inside. The pores in the fiber are closed elliptical pores (indicated by arrows), with a pore width of 20-35 μm and a length of 50-65 μm. The overall structure of the porous fiber is intact, effectively ensuring the lightweight and thermal insulation performance of the porous material.

[0071] Figure 2 The stress-strain curve of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 1 is shown below. Figure 2 As can be seen, when the stress reaches 49.2 MPa, the porous fiber breaks, with a breaking elongation of 6.3%, indicating good mechanical properties.

[0072] Figure 3 This is a SEM image of a cross-section of a porous fiber with a stable bubble structure of nanocellulose filaments in Example 2. Figure 3 As can be seen from the analysis of the porous fiber structure, a large number of closed-cell structures are found inside. The pores in the fiber are closed elliptical pores (indicated by arrows), with a pore width of 25-40 μm and a length of 50-70 μm. The overall structure of the porous fiber is intact, effectively ensuring the lightweight and thermal insulation performance of the porous material.

[0073] Figure 4 The stress-strain curve of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 2 is shown below. Figure 4 As can be seen, when the stress reaches 40.5 MPa, the porous fiber breaks, with a breaking elongation of 11%, indicating good mechanical properties.

[0074] Figure 5 This is a SEM image of a cross-section of a porous fiber with a stable bubble structure of nanocellulose filaments in Example 3. Figure 3 As can be seen from the analysis of the porous fiber structure, a large number of closed-cell structures are found inside. The pores in the fiber are closed elliptical pores (indicated by arrows), with a pore width of 20-40 μm and a length of 50-70 μm. The overall structure of the porous fiber is intact, effectively ensuring the lightweight and thermal insulation performance of the porous material.

[0075] Figure 6 The stress-strain curve of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 3 is shown below. Figure 6 As can be seen, when the stress reaches 28.2 MPa, the porous fiber breaks, with a breaking elongation of 5.1%.

[0076] Figure 7 This is a DSC image of the porous fiber with a stable bubble structure of nanocellulose filaments in Example 3. Figure 4As can be seen, the melting peak of paraffin in the composite porous fiber is at 29.3℃, and the enthalpy of melting is 9.14 J / g. The composite porous fiber of this application has a high enthalpy of melting, indicating its superior ability to store phase change particles. Furthermore, the unique closed-cell elliptical pore structure of the composite porous fiber further enhances its heat storage and insulation performance. These pore structures not only help to effectively encapsulate phase change materials but also provide the fiber with better thermal management capabilities, thus making it excellent in heat preservation. This advantage makes the composite porous fiber more promising than traditional phase change fibers in thermal energy storage and temperature regulation applications.

Claims

1. A method for preparing porous fibers with a stable bubble structure of nanocellulose filaments, characterized in that, Includes the following steps: (1) Add nanocellulose fiber dispersion and foaming agent to polymer solution and mix. The mixture is then dispersed to obtain spinning solution. (2) Inject gas into the spinning solution and stir to obtain a bubble-type spinning solution; (3) The bubble-type spinning solution is wet-spun to obtain porous fibers; In step (3), the wet spinning includes the following steps: the bubble-type spinning solution is extruded through a spinneret into a coagulation bath, and the extruded fibers are coagulated in the coagulation bath to form nascent fibers. The nascent fibers are then stretched, washed, and dried to form porous fibers. The spinneret has an orifice diameter of 50~3000 μm, and the extrusion speed of the bubble-type spinning solution through the spinneret is 0.1~30 mL / min; and / or, The coagulation bath is at least one selected from saturated sodium sulfate solution, sodium hydroxide solution, calcium chloride solution, methanol solution, ethanol solution, and sodium hydroxide-ethanol solution; the temperature of the coagulation bath is -30~50℃, and the coagulation time is 10~70 s; and / or, In the drawing process, the draw ratio of the nascent fibers is 2 to 10 times, and the drawing temperature is 25 to 200°C; and / or, In the washing process, the drawn fibers are placed in a washing solution, wherein the washing solution is at least one selected from deionized water, methanol, and ethanol; and / or, In the drying process, the washed fibers are dried at a drying temperature of 50~200℃ for a drying time of 1~20 min. The aspect ratio of the nanocellulose filaments is 40:1 to 3000:

1.

2. The preparation method according to claim 1, characterized in that, In step (1), The polymer in the polymer solution is at least one of polyvinyl alcohol, chitosan, alginate, gelatin, agar, polyethylene oxide, polyacrylic acid, sodium polyacrylate, polyacrylamide, and poly(N-isopropylacrylamide); and / or, The polymer in the polymer solution has a mass percentage concentration of 0.5% to 40%.

3. The preparation method according to claim 1, characterized in that, The polymer solution described in step (1) is prepared by adding the polymer and co-solvent to deionized water and stirring until the polymer is completely dissolved.

4. The preparation method according to claim 3, characterized in that, The co-solvent is at least one selected from methanol, ethanol, isopropanol, aminoethanol, acetone, formic acid, acetic acid, and surfactant; and / or, The co-solvent has a volume percentage concentration of 0.1% to 2% in the polymer solution; and / or, During the stirring and dissolving process, the dissolution temperature is 30~99℃; and / or, During the stirring and dissolving process, the dissolution time is 0.5 to 24 hours.

5. The preparation method according to claim 1, characterized in that, In step (1), the diameter of the nanocellulose filaments is less than 10 nm and the length is more than 500 nm.

6. The preparation method according to claim 1, characterized in that, In step (1) The raw materials for the nanocellulose filaments are trees, plant straw, recycled clothing; and / or, The foaming agent is at least one selected from alkyl glycosides, fatty alcohol polyoxyethylene ethers, lauramide propyl betaine, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and quaternary ammonium salts; and / or, The solid-liquid mass ratio of the polymer solution, the nanocellulose fiber dispersion, and the foaming agent is 100:(3~60):(0~15); and / or, The percentage mass concentration of the nanocellulose fibers in the nanocellulose fiber dispersion is 0.02~30%; and / or, The nanocellulose filaments are added to deionized water and subjected to ultrasonic treatment to obtain a nanocellulose filament dispersion. The ultrasonic treatment is performed at a frequency of 5–100 kHz, a power of 50–700 W, and a treatment time of 1–60 min; and / or, The dispersion treatment is ultrasonic treatment, in which the ultrasonic frequency is 5~100 kHz, the power is 50~700 W, and the treatment time is 1~60 min.

7. The preparation method according to claim 1, characterized in that, In step (1), a functional filler is also added to the polymer solution. The functional filler is at least one of polyvinylpyrrolidone, polyethyleneimine, cationic starch, waterborne polyurethane, epichlorohydrin, polyamide epichlorohydrin, epoxy resin, sodium silicate, silicone resin, glutaraldehyde, carbon black, graphene, carbon nanotubes, paraffin wax, polyethylene glycol, nano zinc oxide, nano silver, nano titanium dioxide, nano silica, and fatty acids. The solid-liquid mass ratio of the polymer solution, nanocellulose fiber dispersion, foaming agent, and functional filler is 100:(3~60):(0~15):(0~15).

8. The preparation method according to claim 1, characterized in that, In step (2), The gas is at least one selected from nitrogen, carbon dioxide, helium, air, and argon; and / or, During the stirring process, the stirring speed is 1000~10000 rpm, and the processing time is 1~90 min.

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