Cellulose-based composite heating fiber, its preparation method and application

Abstract

The present invention relates to a cellulose-based composite heating fiber and its preparation method and application. The cellulose-based composite heating fiber includes: a core composed of regenerated cellulose and a shell composed of a nanocellulose / functional material composite. The cellulose-based composite heating fiber obtained by the method of the present invention has higher structural integrity and stronger interfacial bonding ability, and at the same time meets excellent mechanical properties, photothermal properties and electrothermal properties, and has application value in the preparation of wearable devices, heating blankets or physiotherapy devices.

Description

Technical Field

[0001] This application belongs to the fields of functional fibers, cellulose materials, composite fibers, functional fabrics, and thermal management materials, and specifically relates to a cellulose-based composite heating fiber and its preparation method and application. Background Art

[0002] Cellulose-based composite heating fibers are a new type of functional material formed by compounding functional materials with a cellulose matrix, and have received extensive attention in recent years in the fields of intelligent textiles, healthcare, and thermal management. Cellulose is a natural polymer material with a wide source, low price, and environmental friendliness. Due to its excellent biocompatibility, biodegradability, and mechanical properties, cellulose has been widely used in many fields. In the aspect of functional material compounding, common heating materials include carbon-based materials (such as graphene, carbon nanotubes), metal nanoparticles (such as silver, gold), and conductive polymers (such as polypyrrole, polyaniline), etc. These materials generate heat through different mechanisms (such as electrothermal effect, photothermal effect). Cellulose-based composite heating fibers can generate heat under the stimulation of an external electric field or light, and have good flexibility and mechanical properties, and can be widely used in smart clothing, heating blankets, and physiotherapy devices. In addition, cellulose-based composite heating fibers also have significant advantages in terms of environmental protection and sustainable development, because their main raw materials come from renewable resources, and can be degraded or recycled after the end of their service life.

[0003] There are mainly two preparation methods for cellulose-based composite heating fibers: one is to dissolve cellulose with a solvent and then compound it with a heating material, and prepare composite fibers through wet spinning technology; the other is to prepare cellulose into nanofibrillated cellulose, and then mix it evenly with a heating material to obtain a composite dispersion, and finally prepare composite fibers through wet spinning technology. However, there are still the following technical problems in the existing technology: functional materials such as carbon nanotubes are prone to aggregation, resulting in poor interfacial properties with the cellulose matrix. If functional groups are introduced on the surface of the heating material or physical adsorption and coating are carried out, the compatibility and stability between it and the dispersion solvent can be improved, but the steps are cumbersome and the method is complex. Carbon nanotubes themselves are brittle, and most carbon nanotube dispersions have poor spinnability. Therefore, the limit content ratio of carbon nanotubes is small, the conductivity is limited, and the mechanical strength of the fibers is low. Composite conductive fibers have problems such as single drive conversion, low thermal conversion efficiency, and long thermal response time.

[0004] Therefore, there is still a need to develop a new fabric fiber with improved heating performance and its preparation method to solve some or all of the above technical problems. Summary of the Invention

[0005] Technical Objectives

[0006] The technical objective of the present invention is to provide a cellulose-based composite heating fiber with improved mechanical properties and heating performance, as well as a preparation method and application thereof.

[0007] Technical solution

[0008] On the one hand, the present invention provides a method for preparing a cellulose-based composite heating fiber, comprising the following steps:

[0009] S1: Preparation of spinning solution

[0010] S1-1: Preparation of cellulose spinning solution

[0011] Completely dissolve the cellulose raw material in a cellulose solvent, and optionally add an auxiliary agent according to the dissolution situation and solid content requirement to obtain a cellulose spinning solution;

[0012] S1-2: Preparation of nano-cellulose / functional material composite spinning solution

[0013] Mix and disperse nano-cellulose and a functional material in deionized water to obtain a nano-cellulose / functional material composite spinning solution.

[0014] S2: Wet spinning

[0015] Using a spinning solution extrusion device equipped with a barrel and a coaxial spinning needle with an inner and outer double layer, extrude the cellulose spinning solution from the inner layer of the coaxial spinning needle, and extrude the nano-cellulose / functional material composite spinning solution from the outer layer of the needle. By controlling the extrusion speeds of the inner and outer layer spinning solutions, the two spinning solutions are extruded simultaneously. After passing through an air gap with a height of 2-8 cm, they enter the coagulation bath, and a wet composite fiber is obtained through a solvent exchange process;

[0016] S3: Solvent exchange and drying

[0017] Place the wet composite fiber obtained in S2 in the solvent of the coagulation bath and let it stand for more than 24 h, or wind and move it through the coagulation bath multiple times, so that the wet composite fiber undergoes sufficient solvent exchange with the solvent of the coagulation bath. Then, continuously dry or intermittently dry it in an oven, and finally wind it around a bobbin to obtain a cellulose-based composite heating fiber, which includes a core composed of regenerated cellulose and a shell composed of a nano-cellulose / functional material composite.

[0018] In the specific embodiment, in step S1-1, the cellulose raw material is pre-prepared in the following manner: shredded into small pieces by a paper shredder and then broken by a high-strength cutter to facilitate the subsequent acceleration of the dissolution process. The dissolution conditions (temperature, rotation speed, dissolution time, additive dosage, etc.) are adjusted according to the dissolution concentration and dissolution characteristics, thereby improving the spinnability. The cellulose solvent gradually destroys the hydrogen bond network of cellulose, enabling the cellulose raw material to be completely dissolved in the cellulose solvent to obtain a cellulose spinning solution. The inner-layer cellulose spinning solution can endow excellent mechanical strength to the fibers well, and at the same time, the fluidity of the outer-layer nanofibrillated cellulose / functional material composite spinning solution can drive the flow of the high-viscosity cellulose spinning solution in the inner layer, enabling the inner and outer layers to be spun simultaneously to form a continuous spinning process.

[0019] In the specific embodiment, in step S1-1, the cellulose solvent is selected from one or more of ionic liquids and N-methylmorpholine N-oxide (NMMO) solutions.

[0020] In the specific embodiment, the ionic liquid is selected from one of superbase ionic liquids, imidazolium ionic liquids, pyridinium ionic liquids, and choline-based ionic liquids. For example, the ionic liquid is 1-allyl-3-methylimidazolium chloride or N-allylpyridinium chloride.

[0021] The concentration of the NMMO solution is 60-80%.

[0022] In the specific embodiment, in step S1-1, the cellulose raw material is selected from one or more of cotton, dissolving pulp, purified cotton, and chemical wood pulp, in powder form or cotton form, and the degree of polymerization is 400-1500.

[0023] In the specific embodiment, in step S1-1, the additive is selected from one or more of absolute ethanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC).

[0024] In the specific embodiment, in step S1-1, the cellulose raw material and the cellulose solvent are mixed in a mass ratio of 1:50-1:15, the mass ratio of the cellulose solvent to the additive dosage is 1:0-1:1, and the total concentration of the cellulose spinning solution is 2-10 wt%.

[0025] In the specific embodiment, in step S1-1, the conditions for dissolving the cellulose raw material are: stirring at 60-100 °C at a rotation speed of 100-800 rpm for 1-5 h until the cellulose raw material is completely dissolved in the cellulose solvent.

[0026] In a specific embodiment, in step S1-2, the nanocellulose is selected from one or more of unmodified cellulose nanofibrils, TEMPO-oxidized cellulose nanofibrils, and carboxymethylated cellulose nanofibrils.

[0027] In a specific embodiment, in step S1-2, the functional material is selected from one of carbon nanotubes, graphene, and MXene.

[0028] In a specific embodiment, in step S1-2, the nanocellulose, the functional material, and deionized water are kept under high-shear conditions of 300-1000 rpm for 30 min-2 h to be completely and uniformly dispersed in the deionized water.

[0029] In a specific embodiment, in step S1-2, the nanocellulose and the functional material are mixed at a mass ratio of 1:0.1-1:10, and the total concentration of the nanocellulose / functional material composite spinning solution is 0.5 wt%-5 wt%.

[0030] In a specific embodiment, in step S2, the air gap height is 3-8 cm, preferably 4 cm or 5 cm. When the fiber passes through the air gap stage, the dissolved cellulose inside exists in molecular form. Due to the interaction between the cellulose solvent and the water in the outer spinning solution, the water in the outer layer gradually enters the inside for solvent replacement, causing a regeneration process inside to form regenerated cellulose. Part of the nanocellulose in the outer spinning solution is also exchanged into the inner layer with the water. At this time, the cellulose chains not only form strong intermolecular interactions with each other, but also interact with the nanocellulose on their contact surfaces. At the same time, due to the good dispersion between the functional material and the nanocellulose, a small part of the functional material also enters the inner layer, which is the first-stage solvent exchange process.

[0031] In a specific embodiment, in step S2, the cellulose spinning solution prepared in S1-1 is used as the inner spinning solution, and the nanocellulose / functional material composite spinning solution prepared in S1-2 is used as the outer spinning solution.

[0032] In a specific embodiment, in step S2, a feeding device is used to control the extrusion speed of the inner and outer spinning solutions. Among them, the feeding device can be a gear pump, a vacuum pump, a peristaltic pump, an injection pump, etc., and the feeding device can be selected according to the total amount of the spinning solution.

[0033] In a specific embodiment, in step S2, the spinning needles (inner and outer double layers) are each one of 10G-32G, and the inner and outer needle specifications can be selected respectively according to the fiber diameter size required for actual production and the ratio of the inner and outer diameters.

[0034] In a specific embodiment, in step S2, the extrusion speed is 0.06 - 0.4 ml / min, which is selected according to the rheological properties and solid content of different spinning solutions.

[0035] In a specific embodiment, in step S2, the extrusion temperature is 25 - 100 °C, and its temperature can be controlled by the temperature adjustment device of the barrel. The extrusion temperature is selected according to the rheological properties of the spinning solution.

[0036] In a specific embodiment, in step S2, the solvent of the coagulation bath is selected from one of ethanol, methanol, isopropanol, ethylene glycol, and n-butanol.

[0037] In a specific embodiment, in step S2, the solvent exchange is a two-stage solvent exchange as follows: The first-stage solvent exchange process is a process in which the cellulose dissolved in the inner-layer spinning solution is subjected to solvent replacement with the water in the outer-layer spinning solution; The second-stage solvent exchange process is a process in which the cellulose solvent that has been exchanged to the outer layer is replaced into the coagulation bath, and the water in the fiber is also continuously replaced into the coagulation bath. After passing through the air gap (i.e., the first-stage solvent exchange process), the second-stage solvent exchange is then carried out. The cellulose solvent that has been exchanged to the outer layer is replaced into the coagulation bath, and the water in the fiber is also continuously replaced into the coagulation bath, so that partial chimerism actually occurs at the interface between the inner and outer layers of the regenerated fiber, enabling the components of the inner and outer layers of the fiber to solidify and form simultaneously, making the core-shell fiber more tightly combined. The tightly connected interface between the core and the shell prevents the shedding of the outer shell, thus being more conducive to the formation of a stable structure of the composite fiber. When all the cellulose solvent and water are replaced into the coagulation bath, a stable gel-like fiber is formed. In addition, the smaller surface tension of the coagulation bath makes the fiber surface rough and porous, and this rough structure can increase the contact surface of the fiber, contributing to improving the photothermal performance, thereby promoting the composite fiber to have high orientation, high conductivity, and high light absorption.

[0038] In a specific embodiment, in step S3, continuous drying is carried out by an on-line device or intermittent drying in an oven.

[0039] On the other hand, the present invention provides a cellulose-based composite heating fiber, and the cellulose-based composite heating fiber includes:

[0040] A core composed of regenerated cellulose; and

[0041] A shell composed of a nanocellulose / functional material composite.

[0042] In a specific embodiment, the regenerated cellulose is formed by dissolution and regeneration of one or more cellulose raw materials selected from cotton, dissolving pulp, purified cotton, and chemical wood pulp.

[0043] In a specific embodiment, in the nanocellulose / functional material composite, the nanocellulose is selected from one or more of unmodified cellulose nanofibrils, TEMPO-oxidized cellulose nanofibrils, and carboxymethylated cellulose nanofibrils; the functional material is selected from one of carbon nanotubes, graphene, and MXene.

[0044] In a specific embodiment, the cellulose-based composite heating fiber is prepared by the above method.

[0045] The cellulose-based composite heating fiber of the present invention has good mechanical properties. It can not only be stretched with a rubber band, but also withstand a certain degree of bending and swinging, and can lift a heavy object (200 g) 2000 times its own weight. At the same time, due to the addition of the functional material in the outer layer, the cellulose-based composite heating fiber of the present invention is endowed with excellent electrothermal properties. It can quickly reach 195°C under a 6V voltage, has good electrothermal responsiveness and recyclability. In addition, the rough surface structure of the cellulose-based composite heating fiber of the present invention endows it with good photothermal properties. Under the light power density conditions of 100 mW / cm 2 , 200 mW / cm 2 and 300 mW / cm 2 , the cellulose-based composite heating fiber can rise from room temperature to 40°C, 49°C, and 73°C within 180 s.

[0046] On the other hand, a product of the present invention comprises at least the above-mentioned cellulose-based composite heating fiber.

[0047] In a specific embodiment, the product is a wearable device, a heating blanket, or a physiotherapy device.

[0048] In a specific embodiment, the product is clothing, shoes, or hats.

[0049] Beneficial Effects

[0050] 1. The cellulose-based composite heating fiber of the present invention is prepared by two-stage solvent replacement with air and a coagulation bath, optimizing the wet coaxial spinning process and structural design. Compared with the fibers prepared by traditional dip coating or spraying, the core-shell structured fiber obtains higher structural integrity and stronger interfacial bonding ability only by physical methods. Its preparation method is simple and feasible, has the potential for continuous production, and is expected to be industrially produced.

[0051] 2. The cellulose-based composite heating fiber designed by the present invention not only retains the high strength and excellent toughness of regenerated cellulose, but also overcomes the disadvantage of poor spinnability of regenerated cellulose. The outer layer introduces nanocellulose and functional materials, endowing the fiber with electrothermal and photothermal properties. The prepared fiber simultaneously meets excellent mechanical properties, photothermal properties, and electrothermal properties. Description of the Drawings

[0052] Figure 1 Show the SEM image of the side surface of the composite heating fiber prepared in Example 1 of the present invention.

[0053] Figure 2 Show the SEM image of the transverse cross-section of the composite heating fiber prepared in Example 1 of the present invention.

[0054] Figure 3 Show the SEM image of the outer layer structure of the composite heating fiber prepared in Example 1 of the present invention.

[0055] Figure 4 Show the stretching diagram of the composite heating fiber prepared in Example 1 of the present invention and a rubber band.

[0056] Figure 5 Show the swinging (a) and bending (b) diagrams of the composite heating fiber prepared in Example 1 of the present invention.

[0057] Figure 6 Show the diagram of the composite heating fiber prepared in Example 1 of the present invention lifting a 200 g weight.

[0058] Figure 7 Show the temperature change curve diagram of the composite heating fiber prepared in Example 2 of the present invention under different voltages.

[0059] Figure 8 Show the temperature change curve diagram of the composite heating fiber prepared in Example 2 of the present invention under a 6V voltage in five cycles.

[0060] Figure 9 Show the temperature change curve diagram of the composite heating fiber prepared in Example 3 of the present invention under different light intensities.

[0061] Figure 10 Is the rheological diagram of the spinning solutions prepared in Example 2 and Comparative Example 1 of the present invention.

[0062] Figure 11 Show the fiber photograph prepared in Comparative Example 1 of the present invention.

[0063] Figure 12 Show the fiber photograph prepared in Comparative Example 2 of the present invention.

[0064] Figure 13 Show the fiber photograph prepared in Comparative Example 3 of the present invention.

[0065] Figure 14 Show the fiber photograph prepared in Comparative Example 4 of the present invention. Detailed Description of the Invention

[0066] The technical solutions of the present application will be described in detail below through embodiments so that those skilled in the art can better understand the present invention. However, these embodiments are not used to limit the scope of the present application.

[0067] Term

[0068] In the present application, the ranges shown in numbers are intended to include all integers and decimal values between the lower and upper limits within the range.

[0069] Example 1

[0070] (S)1 Preparation of spinning solution:

[0071] (S1-1) Preparation of cellulose spinning solution: First, the refined cotton with a polymerization degree of 600 is shredded into small pieces by a paper shredder, and then broken into cotton-like by a high-strength cutting machine. Then, the refined cotton and N-methylmorpholine oxide (NMMO) solution are mixed at a mass ratio of 1:20 and dissolved at 100 °C and 200 rmp for at least 2 h. Finally, a cellulose spinning solution with a concentration of 5% is obtained.

[0072] (S1-2) Preparation of nanofibrillated cellulose / functional material composite spinning solution: According to the mass ratio of carboxymethylated cellulose nanofibrils: graphene of 6:1, it is added to deionized water to make the total concentration 1.2%. It is kept for 30 min under the condition of high-speed shearing at 500 rpm to be completely and uniformly dispersed in deionized water.

[0073] (S2) Wet spinning: Using a spinning solution extrusion device equipped with a barrel and a coaxial spinning needle (inner and outer double layers), the cellulose spinning solution prepared in (S1-1) is used as the inner layer, and the nanofibrillated cellulose / functional material composite spinning solution prepared in (S1-2) is used as the outer layer for wet spinning. The inner and outer needles of the coaxial spinning are 21G (outer diameter 0.81 mm, inner diameter 0.51 mm) and 16G (outer diameter 1.65 mm, inner diameter 1.19 mm) respectively. The spinning speeds of the inner and outer layer injection pumps are 0.07 ml / min and 0.35 ml / min respectively. The temperature of the inner layer is controlled at 70 °C by the temperature control device of the barrel so that the inner and outer layer spinning solutions are extruded simultaneously. The distance between the syringe and the surface of the anhydrous ethanol coagulation bath is 5 cm, and the fiber enters the coagulation bath after passing through an air gap.

[0074] (S3) Solvent exchange and drying: The wet composite fiber obtained in (S2) is wound and moved through a n-butanol coagulation bath to make the wet composite fiber fully exchange solvents with the solvent in the coagulation bath, and then dried intermittently through an oven. Finally, it is wound on a bobbin to obtain a cellulose-based composite heating fiber, which structurally includes a core composed of regenerated cellulose and a shell composed of nanofibrillated cellulose / functional material composite.

[0075] SEM observations were carried out on the cellulose-based composite heating fibers prepared above, and a series of mechanical property tests were conducted. The results are as follows. Figure 1 and Figure 2 respectively show the SEM images of the side surface and cross-section of the cellulose-based composite heating fibers prepared in Example 1. Figure 3 shows the SEM image of the outer layer of the cellulose-based composite heating fibers. It can be clearly seen that the fibers exhibit a rough and porous core-shell structure with tight connections at the interface. The inner layer is a solid and dense structure, and the outer layer is highly oriented and arranged along the fiber formation direction ( Figure 2 and Figure 3 ). The excellent mechanical strength of cellulose is well imparted to the cellulose-based composite heating fibers. The fibers can not only be stretched with a rubber band ( Figure 4 ), but also withstand a certain degree of swinging and bending ( Figure 5 ). At the same time, it can lift a heavy object equivalent to 2000 times its own weight (200 g) without breaking ( Figure 6 ).

[0076] Example 2

[0077] (S1) Preparation of the spinning solution:

[0078] (S1-1) Preparation of the cellulose spinning solution: First, dissolve wood pulp with a polymerization degree of 800 is shredded into small pieces by a paper shredder, and then broken into cotton-like by a high-strength cutter. Then, the dissolved wood pulp and 1-allyl-3-methylimidazolium chloride are mixed at a mass ratio of 1:25 and placed at 80 °C and 100 rmp for at least 2 h. Then, a dimethyl sulfoxide solution with a mass ratio of 1:1 to the ionic liquid is added and reacted at 80 °C and 100 rmp for at least 4 h. Finally, a cellulose spinning solution with a concentration of 4% is obtained.

[0079] (S1-2) Preparation of the nanofibrillated cellulose / functional material composite spinning solution: The mass ratio of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxide) oxidized cellulose nanofibrils to carbon nanotubes is 7:1, and it is added to deionized water to make the total concentration 1%. It is kept under high-speed shearing conditions of 500 rpm for 30 min to be completely and uniformly dispersed in deionized water.

[0080] (S2) Wet spinning: Using a spinning solution extrusion device equipped with a barrel and a coaxial spinning needle (inner and outer double layers), the cellulose spinning solution prepared in (S1-1) is used as the inner layer, and the nanofibrillated cellulose / functional material composite spinning solution prepared in (S1-2) is used as the outer layer for wet spinning. The inner and outer needles of the coaxial spinning are 21G (outer diameter 0.81 mm, inner diameter 0.51 mm) and 16G (outer diameter 1.65 mm, inner diameter 1.19 mm) respectively. The spinning speeds of the inner and outer layer vacuum pumps are 0.09 ml / min and 0.28 ml / min respectively. The temperature of the inner layer is controlled at 60 °C by the temperature control device of the barrel, so that the inner and outer layer spinning solutions are extruded simultaneously. The distance between the syringe and the surface of the absolute ethanol coagulation bath is 4 cm, and the fiber enters the coagulation bath after passing through an air gap.

[0081] (S3) Solvent exchange and drying: The wet composite fiber obtained in (S2) is placed in an absolute ethanol coagulation bath with a liquid level sufficient to submerge the fiber and left standing for more than 24 h, so that the wet composite fiber undergoes sufficient solvent exchange with the solvent in the coagulation bath. Then, it is continuously dried through an online device and finally wound on a bobbin to obtain the cellulose-based composite heating fiber.

[0082] The electrothermal performance of the obtained cellulose-based composite heating fiber is tested as follows: Cut a 1.5 cm long composite fiber, use a voltage controller (WPS3010B) to control the voltage at both ends of the sample, and use an infrared thermal imager (fotric325Pro) to measure the real-time temperature of the fiber and collect data.

[0083] The results are as Figure 7 shown. Figure 7 It shows the temperature of the fiber in this example under different voltages. When the voltage is 2V and 6V, the temperature can reach about 40 and 195 °C respectively. And under the cyclic application and release of 6V voltage for 5 cycles, the fiber shows fast electrothermal responsiveness and recyclability ( Figure 8 ). The above results confirm that through the structural design of the cellulose-based composite heating fiber, the fiber has excellent electrothermal performance, which is of great significance for fields such as human thermal management and medical care. The fiber has a unique core-shell structure. The cellulose rich in the inner and outer layers endows the fiber with good mechanical properties. The functional material in the outer layer forms a porous conductive network on the outer layer of the fiber, making the fiber conductive, and thus endowing it with good electrothermal performance.

[0084] Example 3

[0085] (S1) Preparation of spinning solution:

[0086] (S1-1) Preparation of cellulose spinning solution: First, chemically pulped wood with a degree of polymerization of 1000 is shredded into small pieces by a paper shredder, and then broken into cotton-like by a high-strength cutting machine. Then, the chemically pulped wood and N-propenylpyridinium chloride are mixed at a mass ratio of 1:20 and dissolved at 90 °C and 150 rmp for at least 3 h. Then, a dimethyl sulfoxide solution with a mass ratio of 1:0.5 to the ionic liquid is added and reacted at 90 °C and 150 rmp for at least 5 h. Finally, a cellulose spinning solution with a concentration of 3.3% is obtained.

[0087] (S1-2) Preparation of nano-cellulose / functional material composite spinning solution: According to the mass ratio of TEMPO-oxidized cellulose nanofibrils to carbon nanotubes of 9:1, it is added to deionized water to make the total concentration 2%. It is kept under high-speed shearing conditions of 600 rpm for 30 min to be completely and evenly dispersed in deionized water.

[0088] Steps (S2) and (S3) are the same as those in Example 2.

[0089] The photothermal performance of the obtained cellulose-based composite heating fiber is tested: The spectral radiometer (CEL-NP2000.CeAulight·China) is placed at the illumination center of a xenon lamp (CEL-HXUV300,CeAulight·China) with an AM·1.5·G filter to measure the illumination intensity. Then, 1.5 cm of the composite fiber is intercepted and cross-overlapped and placed at the illumination center, and an infrared thermal imager (fotric325Pro) is used to measure the real-time temperature of the fiber and collect data.

[0090] The results are as Figure 9 shown. At power densities of 100 mW / cm 2 , 200 mW / cm 2 and 300 mW / cm 2 , the temperature of the fiber rises from 30 °C to about 40 °C, 49 °C and 73 °C within 180 s respectively. The above results confirm that by optimizing the spinning process and structural design, using the rough and porous surface structure of the fiber, the contact area with photothermal is effectively increased, providing more photon absorption cross-sections for the fiber, thus showing strong photothermal performance.

[0091] Comparative Example 1

[0092] (S1) Preparation of spinning solution:

[0093] Preparation of cellulose spinning solution: First, the dissolved wood pulp with a degree of polymerization of 800 is shredded into small pieces by a paper shredder, and then broken into cotton-like by a high-strength cutting machine. Then, the dissolved wood pulp and 1-allyl-3-methylimidazolium chloride are mixed at a mass ratio of 1:25 and dissolved at 80 °C and 100 rmp for at least 2 h. Then, a dimethyl sulfoxide solution with a mass ratio of 1:1 to the ionic liquid is added and reacted at 80 °C and 100 rmp for at least 4 h. Finally, a cellulose spinning solution with a concentration of 4% is obtained.

[0094] (S2) Wet spinning: Using the cellulose spinning solution prepared in (S1) alone as the spinning solution, wet spinning is carried out using a spinning solution extrusion device equipped with a barrel and a spinning needle. The spinning needle is 21G (outer diameter 0.81 mm, inner diameter 0.51 mm), the spinning speed of the vacuum pump is 0.09 ml / min, and its temperature is controlled at 60 °C using the temperature control device of the barrel. The syringe is 5 cm from the surface of the anhydrous ethanol coagulation bath, and the fiber enters the coagulation bath after passing through an air gap.

[0095] Wet spinning requires the spinning solution to have good rheological properties for smooth extrusion. The wet spinning behaviors in Example 2 and Comparative Example 1 above were evaluated, and the results are as follows.

[0096] Figure 10 It shows that the nanocellulose / functional material composite spinning solution in Example 2 exhibits shear thinning behavior, showing good fluidity, which is beneficial to improving spinnability. However, the same cellulose spinning solution in Example 2 and Comparative Example 1 does not have shear thinning behavior, has a high viscosity, and is difficult to carry out wet spinning. Although the subsequent wet spinning process is exactly the same as that in Example 2, continuous fibers cannot be achieved in Comparative Example 1 ( Figure 11 ), which is because the lack of the high-rheology nanocellulose / functional material composite spinning solution in the outer layer fails to drive the cellulose spinning solution in the inner layer to effectively carry out wet spinning, indicating the importance of the outer layer design for the construction of core-shell structured fibers.

[0097] Comparative Example 2

[0098] (S1) Preparation of spinning solution:

[0099] Preparation of nanocellulose / functional material composite spinning solution: According to the mass ratio of TEMPO-oxidized cellulose nanofibrils: carbon nanotubes of 7:1, add to deionized water to make the total concentration 1%. Keep it under high-speed shearing conditions of 500 rpm for 30 min to be completely and uniformly dispersed in deionized water.

[0100] (S2) Wet spinning: Using the nanofibrillated cellulose / functional material composite spinning solution prepared in (S1) alone as the spinning solution, wet spinning is carried out using a spinning solution extrusion device equipped with a barrel and a spinning needle. The spinning needle is 16G (outer diameter 1.65 mm, inner diameter 1.19 mm), and the spinning speed of the vacuum pump is 0.28 ml / min. The distance between the syringe and the surface of the absolute ethanol coagulation bath is 6 cm, and the fiber enters the coagulation bath after passing through an air gap.

[0101] The wet spinning behavior in Comparative Example 2 was evaluated, and the results are as follows.

[0102] Although the nanofibrillated cellulose / functional material composite spinning solution in Comparative Example 2 has good rheological properties, and the subsequent wet spinning process is exactly the same as that in Example 2, continuous spinning cannot be carried out alone, and the fiber is extremely easy to break in the coagulation bath due to lack of good mechanical properties ( Figure 12 ).

[0103] In Example 2, the inner cellulose spinning solution endows the cellulose-based composite heating fiber with excellent mechanical properties, combined with the high electrothermal and photothermal properties of the outer nanofibrillated cellulose / functional material composite spinning solution.

[0104] Comparative Example 3

[0105] (S1) The preparation of the spinning solution is exactly the same as that in Example 2.

[0106] (S2) The wet spinning is the same as that in Example 2, except that the distance between the syringe outlet and the coagulation bath is adjusted to zero, and the fiber directly enters the absolute ethanol coagulation bath without passing through an air gap.

[0107] The wet spinning behavior in Comparative Example 3 was evaluated, and the results are as follows. The fiber spun by wet spinning with the same spinning solution as in Example 2 did not pass through the air gap stage but directly entered the absolute ethanol coagulation bath after coming out of the syringe, that is, the first-stage solvent exchange process was missing, and only the second-stage solvent exchange process was present. From Figure 13 It can be seen that after the fiber in Comparative Example 3 enters the coagulation bath, the cellulose spinning solution and the nanofibrillated cellulose / functional material composite spinning solution are immediately divided into two parts and cannot form a complete single fiber. This confirms the necessity of the first-stage solvent exchange process for spinning.

[0108] Comparative Example 4

[0109] (S1) The preparation of the spinning solution is exactly the same as that in Example 2.

[0110] (S2) The wet spinning is the same as that in Example 2, except that the distance between the syringe and the surface of the absolute ethanol coagulation bath is adjusted to 15 cm, and the fiber enters the coagulation bath after passing through a longer air gap.

[0111] The wet spinning behavior in Comparative Example 4 was evaluated, and the results are as follows.

[0112] From Figure 14 It can be seen that the fibers in Comparative Example 4 showed a beaded shape. This is because the air gap height was too high, that is, the first-stage solvent exchange process was long, the rheological properties of the inner and outer layers differed greatly, and due to the gravitational force, the outer-layer nanofibrillated cellulose / functional material composite spinning solution could not drive the flow of the high-viscosity cellulose spinning solution in the inner layer in time, thus forming beaded fibers. Through Comparative Example 3 and Comparative Example 4, it can be proved the importance of the two-stage solvent exchange process in this design for the continuous spinning of cellulose-based composite heat-generating fibers.

Claims

1. A method for preparing a cellulose-based composite heating fiber, comprising the following steps: S1: Spinning solution preparation S1-1: Preparation of cellulose spinning solution The cellulose raw material is completely dissolved in a cellulose solvent, and an auxiliary agent is optionally added to obtain a cellulose spinning solution; S1-2: Preparation of nanocellulose / functional material composite spinning solution The nanocellulose and the functional material are mixed and dispersed in deionized water to obtain a nanocellulose / functional material composite spinning solution. S2: Wet spinning A spinning solution extrusion device equipped with a barrel and a coaxial spinning needle with inner and outer double layers is used to extrude a cellulose spinning solution from the inner layer of the coaxial spinning needle, and a nanocellulose / functional material composite spinning solution is extruded from the outer layer of the needle. The extrusion speeds of the inner and outer spinning solutions are controlled so that the two spinning solutions are extruded simultaneously, and after passing through an air gap with a height of 2-8 cm, they enter a coagulation bath, and wet composite fibers are obtained through a solvent exchange process. S3: Solvent exchange and drying The wet composite fiber obtained in S2 is placed in the solvent of the coagulation bath and allowed to stand for more than 24 hours, or is wound and moved through the coagulation bath multiple times to allow sufficient solvent exchange to occur between the wet composite fiber and the solvent of the coagulation bath, followed by continuous drying or intermittent drying in an oven, and finally wound on a wire roller to obtain a cellulose-based composite heat-generating fiber, which includes a core composed of regenerated cellulose and a shell composed of a nanocellulose / functional material composite material.

2. The method according to claim 1, wherein: In step S1-1, The cellulose solvent is selected from one or more of an ionic liquid and an N-methylmorpholine oxide (NMMO) solution, wherein the ionic liquid is selected from one of a superbase ionic liquid, an imidazolyl ionic liquid, a pyridyl ionic liquid and a choline ionic liquid; and / or The cellulose raw material is selected from one or more of cotton, dissolving wood pulp, refined cotton, and chemical wood pulp; and / or The auxiliary agent is selected from one or more of anhydrous ethanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N,N-dimethylacetamide (DMAC); and / or The cellulose raw material and the cellulose solvent are mixed in a mass ratio of 1:50-1:15, the mass ratio of the cellulose solvent to the auxiliary agent is 1:0-1:1, and the total concentration of the cellulose spinning solution is 2-10wt%; and / or The conditions for dissolving the cellulose raw material are: stirring at 60-100° C. and 100-800 rpm for 1-5 hours until the cellulose raw material is completely dissolved in the cellulose solvent.

3. The method according to claim 2, wherein: The ionic liquid is 1-allyl-3-methylimidazolium chloride or N-allylpyridinium chloride.

4. The method according to claim 1, wherein: In step S1-2, The nanocellulose is selected from one or more of unmodified cellulose nanofibrils, TEMPO-oxidized cellulose nanofibrils and carboxymethylated cellulose nanofibrils; and / or The functional material is selected from one of carbon nanotubes, graphene and MXene; and / or The nanocellulose, functional material and deionized water are kept under high-speed shearing conditions of 300-1000 rpm for 30 min-2 h to be completely and evenly dispersed in the deionized water; and / or The nanocellulose and the functional material are mixed in a mass ratio of 1:0.1-1:10, and the total concentration of the nanocellulose / functional material composite spinning solution is 0.5wt%-5wt%.

5. The method according to claim 1, wherein: In step S2, The air gap height is 3-8 cm; and / or The extrusion speed of the inner and outer spinning solutions is controlled by a feeding device, wherein the feeding device is a gear pump, a vacuum pump, a peristaltic pump, or a syringe pump; and / or The spinning needle with inner and outer double layers is one of 10G-32G; and / or The extrusion speed is 0.06-0.4 ml / min; and / or The extrusion temperature is 25-100°C; and / or The solvent of the coagulation bath is selected from one of ethanol, methanol, isopropanol, ethylene glycol and n-butanol.

6. The method according to claim 5, wherein: In step S2, the air gap height is 4 cm or 5 cm.

7. The method according to claim 1, wherein: In step S3, continuous drying is performed by online equipment or intermittent drying in an oven.

8. A cellulose-based composite heat-generating fiber prepared by the method according to any one of claims 1 to 7, the cellulose-based composite heat-generating fiber comprising: a core composed of regenerated cellulose; and Shell composed of nanocellulose / functional material composites.

9. A product comprising at least the cellulose-based composite heat-generating fiber according to claim 8.

10. The article of claim 9, which is a wearable device, a heating blanket, or a physiotherapy device.

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