Cellulose-based moisture generator with wettability gradient structure and preparation method of cellulose-based moisture generator

Abstract

The invention provides a cellulose-based moisture generator with a wettability gradient structure and a preparation method thereof, and the cellulose-based moisture generator based on the wettability gradient structure comprises a negative electrode layer, an active layer and a positive electrode layer which are connected in sequence, the active layer comprises a mixed fiber paper layer and a cellulose acetate nano porous fiber membrane layer, and the mixed fiber paper layer comprises plant fibers and cellulose acetate fibers; the mixed fiber paper layer is connected with the negative electrode layer, and the cellulose acetate nano-porous fiber membrane layer is connected with the positive electrode layer. Different types of degradable cellulose fiber materials are used, and the wettability gradient in which the aperture gradient and the functional group gradient cooperate with each other is constructed, so that the output power, the output stability and the sustainability of the cellulose-based moisture generator are improved.

Description

Technical Field

[0001] The present invention belongs to the field of biomass energy, and particularly relates to a cellulose-based moisture generator with a wettability gradient structure and a preparation method thereof. Background Art

[0002] With the increasing emphasis on global sustainable development and environmental protection, the development of green energy has become one of the key issues in the global energy industry. Various different power generation technologies have been widely studied and applied by researchers, including solar energy, wind energy, hydropower, biomass energy, thermoelectricity, piezoelectricity, and triboelectricity, etc., to reduce the dependence on traditional fossil fuels and achieve a cleaner and more sustainable energy future. Moist-electric generation, as an emerging technology in the field of green energy, can convert the kinetic energy of water evaporation or water diffusion in the atmosphere into electrical energy. The moist-electric generation technology has good flexibility and can be applied to different scales and scenarios, including personal wearable devices, outdoor environments, building surfaces, etc. This flexibility makes moist-electric generation have broad application prospects in the fields of wearable devices, Internet of Things, outdoor sensors, etc. At the same time, with the continuous development of materials science, nanotechnology, and energy conversion technology, the efficiency and stability of moist-electric generation are expected to be improved, promoting the commercial application of the technology.

[0003] Cellulose, as the most abundant, non-toxic, renewable, and sustainable biomass-based polymer material on the earth, is the most attractive green and sustainable material in the 21st century. The cellulose surface has abundant hydrophilic groups (such as -OH) and has a strong adsorption capacity for water molecules, which can be used to construct a green and sustainable moisture generator. The principle of traditional paper-based moisture generators is based on the hygroscopic properties of paper materials. When the moisture in the environment comes into contact with the paper material, the paper will absorb the water in the moisture, resulting in an increase in the humidity of the paper. The moist paper can become an electrolyte, enabling the movement of charges on the fiber surface and generating a potential difference and current. Patent document CN115411971A discloses a cellulose-based moisture absorption and evaporation integrated power generation device, which absorbs and evaporates water by constructing four layers of a double electrode layer, a cellulose moisture absorption layer, and a cellulose evaporation layer. The humidity gradient depends on the added hygroscopic agent and evaporation material, and there are disadvantages such as difficult gradient control and complex processes. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a cellulose-based moisture generator with a wettability gradient structure and a preparation method thereof. The cellulose-based moisture generator is a cellulose-based composite membrane based on the gradient coordination of functional groups and pore size gradient, and has a high output voltage and sustainability.

[0005] The present invention is realized through the following technical solutions:

[0006] A cellulose-based moisture generator based on a wettability gradient structure, comprising a negative electrode layer, an active layer, and a positive electrode layer connected in sequence. The active layer includes a mixed fiber paper layer and a cellulose acetate nanoporous fiber membrane layer. The mixed fiber paper layer includes plant fibers and cellulose acetate fibers. The mixed fiber paper layer is connected to the negative electrode layer, and the cellulose acetate nanoporous fiber membrane layer is connected to the positive electrode layer.

[0007] Preferably, there is a pore size gradient inside the cellulose acetate nanoporous fiber membrane layer, and the pore size gradually decreases from the side of the cellulose acetate nanoporous fiber membrane layer close to the mixed fiber paper layer to the other side.

[0008] Preferably, there are nano-scale pore structures on the surface and inside of the fibers in the cellulose acetate nanoporous fiber membrane layer.

[0009] Preferably, the negative electrode layer is a copper mesh electrode, and the positive electrode layer is a double-conductive copper foil electrode.

[0010] Preferably, in the mixed fiber paper layer, the mass of cellulose acetate accounts for 30% - 70% of the mass of the mixed fiber paper layer.

[0011] Preferably, the plant fibers include hardwood fibers and softwood fibers.

[0012] The preparation method of the cellulose-based moisture generator based on the wettability gradient structure includes:

[0013] (1) Mix plant fiber slurry and cellulose acetate short fibers, add sodium dodecylbenzenesulfonate, and carry out beating to obtain a mixed fiber slurry. Filter and form the mixed fiber slurry to obtain a mixed fiber paper layer.

[0014] (2) Mix cellulose acetate powder, acetone, dichloromethane, and N,N-dimethylformamide to obtain a spinning solution. Paste a silicon oil paper and the mixed fiber paper layer prepared in step (1) on the roller receiver of an electrospinning machine in sequence, and carry out electrospinning to prepare a cellulose acetate nanoporous fiber membrane layer on the mixed fiber paper layer to obtain a cellulose-based composite membrane with a wettability gradient structure.

[0015] (3) Paste the negative electrode layer and the positive electrode layer on both sides of the cellulose-based composite membrane respectively, and connect the positive and negative electrodes of a multimeter or the working electrode and the auxiliary electrode of an electrochemical workstation to the negative electrode layer and the positive electrode layer respectively to prepare a moisture generator.

[0016] Preferably, during the electrospinning process, continuously adjust and increase the voltage value as the electrospinning progresses, and the voltage adjustment range is 14 kV - 20 kV.

[0017] Preferably, the electrospinning process is carried out under the condition of relative environmental humidity of 75% - 90%.

[0018] A respiratory sensor is obtained by encapsulating the above-mentioned moisture generator with epoxy resin.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The active layer of the cellulose-based moisture generator of the present invention is a bilayer structure formed by a mixed fiber paper layer and a cellulose acetate nanoporous fiber membrane layer. This bilayer structure is used to provide mobile ions and is responsible for the adsorption, diffusion, and evaporation channels of moisture. Among them, from the highly wettable mixed fiber paper layer to the low-wettable cellulose acetate nanoporous fiber layer, there is a pore size gradient and a functional group gradient in which the fiber pore size and hydroxyl group content decrease from large to small. The pore size gradient cooperates with the functional group gradient to promote the unidirectional diffusion of ions during the directional transport of moisture, forming a diffusion current and enhancing the electrical output. That is, the present invention uses different types of degradable cellulose fiber materials to improve the output power, output stability, and sustainability of the cellulose-based moisture generator by constructing a wettability gradient in which the pore size gradient and the functional group gradient cooperate with each other. The output voltage of the cellulose-based moisture generator with the wettability gradient structure of the present invention has stability and sustainability. Tested with a multimeter, a single drop of water can achieve an open-circuit voltage of 615 mV and last for more than 48 hours. Compared with other reported paper-based moisture generators, its performance is very superior. By connecting 4 cellulose-based moisture generator units in series, a voltage of about 2.4 V is achieved, successfully lighting up a light-emitting diode.

[0021] Furthermore, the cellulose acetate nanoporous fiber membrane layer of the present invention has a pore size gradient in the thickness direction, which can further enable the directional diffusion of moisture.

[0022] Furthermore, the fibers in the cellulose acetate nanoporous fiber membrane layer of the present invention itself have a nanoporous structure, which improves the porosity and is more conducive to the diffusion of moisture.

[0023] The preparation method of the cellulose-based composite membrane with the wettability gradient structure of the present invention adopts the paper-making technology to prepare the mixed fiber paper layer and the electrospinning technology to prepare the cellulose acetate nanoporous fiber membrane layer. The pore size of the mixed fiber paper layer obtained by the paper-making technology is larger, while the pore size formed by the cross of fibers in the cellulose acetate nanoporous fiber membrane layer obtained by electrospinning is smaller. Thus, the bilayer structure formed by the mixed fiber paper layer and the cellulose acetate nanoporous fiber membrane layer has a pore size gradient, and at the same time, the cellulose acetate content in the two layers is different, making it have a functional group gradient. Therefore, the bilayer structure formed by the mixed fiber paper layer and the cellulose acetate nanoporous fiber membrane layer has a pore size gradient and a functional group gradient, and the pore size gradient cooperates with the functional group gradient to promote the unidirectional diffusion of ions during the directional transport of moisture.

[0024] Furthermore, during the electrospinning process of the present invention, the voltage value is continuously adjusted and increased, so that the diameter of the obtained fibers is continuously reduced, and the pore size formed between the fibers is continuously reduced, enabling the cellulose acetate nanoporous fiber membrane layer to have a pore size gradient in the thickness direction, which can further enable the directional diffusion of moisture.

[0025] Furthermore, the electrospinning process of the present invention is carried out under the condition of an environmental relative humidity of 75% - 90%. The combination of electrospinning and the breath figure method makes the fibers in the prepared cellulose acetate nanoporous fiber membrane layer have a nanoporous structure itself, improving the porosity and being more conducive to moisture diffusion. Moreover, the combination of electrospinning and the breath figure method enables the thickness, porosity, fiber diameter, and wettability of the nanofibers in the cellulose acetate nanoporous fiber membrane layer to be effectively regulated by the spinning process and environmental humidity. Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of a cellulose-based moisture generator based on a wettability gradient structure of the present invention.

[0027] Figure 2 It is the surface morphology (SEM image) of the active layer in a cellulose-based moisture generator based on a wettability gradient structure of the present invention: a and b are the upper and lower surfaces of the cellulose acetate fiber @ plant fiber composite paper (CA@Cell); c is the cellulose acetate fiber; (d - f) are electrospun cellulose acetate nanoporous fibers (CA-NPFs); g - i are the cross-sections of the CA@Cell / CA-NPFs bilayer membrane.

[0028] Figure 3 It is the fiber morphology (SEM image) of the electrospun cellulose acetate nanoporous fiber layer (CA-NPFs) in a cellulose-based moisture generator based on a wettability gradient structure of the present invention: a1 and a2 are the wrinkled cellulose acetate fibers in the low-humidity environment (40% RH) of Comparative Example 1; b1 and b2 are the porous cellulose acetate fibers in the environment with a relative humidity of 75% in Example 1; c1 and c2 are the porous cellulose acetate fibers in the environment with a relative humidity of 90% in Example 4.

[0029] Figure 4 It is the pore size distribution of the mixed fiber paper layer (CA@Cell), the electrospun cellulose acetate nanoporous fiber layer (CA-NPFs), and the cellulose-based composite membrane in the active layer of a cellulose-based moisture generator based on a wettability gradient structure of the present invention.

[0030] Figure 5The surface wettability (contact angle) of the active layer in a cellulose-based moisture generator with a wettability gradient structure according to the present invention: (a) shows the change in the water contact angle during the wetting process of the highly wettable mixed fiber paper layer; (b) shows the change in the water contact angle during the wetting process of the upper surface of the low wettability cellulose acetate nanoporous fiber layer; (c) shows the change in the water contact angle during the wetting process of the lower surface of the low wettability cellulose acetate nanoporous fiber layer.

[0031] Figure 6 The liquid directional transport phenomenon and mechanism of the active layer of a cellulose-based moisture generator with a wettability gradient structure according to the present invention.

[0032] Figure 7 The directional sweat absorption effect of the active layer of a cellulose-based moisture generator with a wettability gradient structure according to the present invention.

[0033] Figure 8 The series voltage increase diagram of a cellulose-based moisture generator with a wettability gradient structure according to the present invention.

[0034] Figure 9 The open circuit voltage of the cellulose-based moisture generator under extreme conditions: (a) high temperature (70 °C); (b) cold (-3 °C).

[0035] Figure 10 A cellulose-based moisture generator with a wettability gradient structure according to the present invention is applied to a respiratory sensor for sensing oral and nasal breathing patterns. Detailed implementation mode

[0036] To further understand the present invention, the present invention will be described below in conjunction with embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not used to limit the claims of the present invention.

[0037] The cellulose-based moisture generator with a wettability gradient structure according to the present invention includes an active layer and an asymmetric electrode layer. The asymmetric electrode layer includes a negative electrode layer and a positive electrode layer. The active layer is located between the negative electrode layer and the positive electrode layer, forming a sandwich structure; the active layer is a cellulose-based composite film with a wettability gradient, including a mixed fiber paper layer (cellulose acetate fiber @ plant fiber, CA @ Cell) and a cellulose acetate nanoporous fiber membrane layer (CA-NPFs). The cellulose-based moisture generator forms an increasing interlayer humidity gradient along the thickness direction from the negative electrode layer to the positive electrode layer.

[0038] Among them, the mixed fiber paper layer is a high wettability layer, which is prepared by a wet forming technology; the cellulose acetate nanoporous fiber membrane layer is a low wettability layer, which is prepared by an electrospinning technology combined with a breath figure method in a high humidity closed environment. The active layer presents a gradient characteristic in terms of surface wettability and pore size distribution, so that the distribution and penetration process of moisture inside the material show a gradient change. When moisture contacts the active layer, it diffuses from the high wettability region to the low wettability region, effectively guiding the directional diffusion of moisture along the thickness direction. An electrical signal is generated during the directional diffusion of the liquid along the thickness direction and is directly guided to the electrode systems on the upper and lower surfaces.

[0039] In the embodiment of the present invention, there is a pore size gradient inside the cellulose acetate nanoporous fiber membrane layer, and the pore size gradually decreases from the side of the cellulose acetate nanoporous fiber membrane layer close to the mixed fiber paper layer to the other side. There are nano-scale pore structures on the surface and inside of the fibers in the cellulose acetate nanoporous fiber membrane layer.

[0040] In the embodiment of the present invention, the negative electrode layer is preferably a copper mesh electrode, and the positive electrode layer is preferably a double-conductive copper foil electrode.

[0041] The asymmetric electrode layers are distributed on the upper and lower sides of the active layer to achieve comprehensive energy collection and utilization. The negative electrode layer is located on the upper surface of the CA@Cell layer of the active layer, while the positive electrode layer is located on the lower surface of the CA-NPFs of the active layer, forming a complete asymmetric electrode system. In the asymmetric electrode layer, a decreasing humidity gradient is formed from the negative electrode layer to the positive electrode layer direction; due to the asymmetric structure of the two electrode layers on both sides, the humidity on the negative electrode layer side is higher, which helps to maximize the absorption and transmission efficiency of moisture; while the airtight positive electrode layer maintains a low humidity; the humidity gradient formed by the asymmetric electrode layer cooperates with the wettability gradient of the active layer to promote the diffusion of ions in the moving direction during the moisture penetration process, and improve the magnitude and stability of the output voltage.

[0042] The preparation method of the cellulose-based moisture generator with the wettability gradient structure of the present invention includes the following steps:

[0043] (1) Prepare the high wettability mixed fiber paper layer (CA@Cell):

[0044] Mix a variety of fibers in a certain proportion, including two plant fiber slurries of hardwood fiber and softwood fiber and cellulose acetate short fibers, and add sodium dodecylbenzenesulfonate, and carry out pulp foaming and beating to obtain a mixed fiber pulp. Pour the beaten mixed fiber pulp into a rapid sheet former, and use bubble homogenization to fully mix and filter and form to obtain a mixed fiber paper layer.

[0045] (2) Prepare the low wettability cellulose acetate nanoporous fiber layer (CA-NPFs):

[0046] Using cellulose acetate powder as the raw material, acetone, dichloromethane (DCM), and N,N-dimethylformamide (DMF) are added, and stirred thoroughly until dissolved. After degassing and standing by, a spinning solution is obtained. The silicone oil paper is pasted on the roller receiver of the electrospinning machine, and the mixed fiber paper layer (CA@Cell) prepared in step (1) is pasted on the roller receiver, and electrospinning is carried out to obtain a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) on the roller receiver. After the electrospinning is completed, the electrospinning membrane on the roller receiver is peeled off and naturally dried at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient structure.

[0047] During the electrospinning process, by adjusting the voltage to 14 kV to 20 kV and using different voltages at different stages, a gradient pore size can be formed within the cellulose acetate nanoporous fiber membrane layer. For example, at 0, 3, 6, and 9 h, the voltages are adjusted to 14 kV, 16 kV, 18 kV, and 20 kV respectively. As the electrospinning proceeds and the voltage continuously increases, the pore size within the cellulose acetate nanoporous fiber membrane layer continuously decreases.

[0048] During the electrospinning process, by controlling the relative humidity of the environment inside the device (75% - 90%), a nanoporous structure is formed on the surface and inside of the cellulose acetate nanoporous fiber, endowing the material with a higher porosity and specific surface area, and increasing its air permeability.

[0049] (3) Assembly of the moisture generator

[0050] The negative electrode layer and the positive electrode layer are respectively pasted on the upper surface of the mixed fiber paper layer and the lower surface of the low-wettability cellulose acetate nanoporous fiber layer to form an asymmetric electrode structure. Then, the positive and negative electrodes of the multimeter or the working electrode and the auxiliary electrode of the electrochemical workstation are respectively connected to the negative electrode layer and the positive electrode layer to obtain the CA@Cell / CA-NPFs moisture generator.

[0051] In step (1) of the present invention, the cellulose acetate short fibers are added at 30% - 70% of the absolute dry mass of all fibers after being sheared at high speed by a high-speed grinding machine, and the addition concentration of sodium dodecylbenzenesulfonate is 0.1 g / L - 0.4 g / L.

[0052] In step (2) of the present invention, the mass concentration of the spinning solution is controlled at 12 wt.% - 16 wt.%, and the volume ratio of N,N-dimethylformamide, acetone, and dichloromethane is 3:4:8; during the spinning process, the spinning rate is 0.001 - 0.010 mm / s, and the receiving distance is 12 - 15 cm.

[0053] In step (3) of the present invention, the negative electrode layer is a copper mesh electrode with a copper mesh area of 0.25 cm 2 ~16 cm 2 , a pore size of 10 - 200 mesh, and a thickness of 0.2 mm; it is wiped clean with ethanol degreasing cotton and then rinsed with deionized water, and dried in an oven at 60 °C for 30 min; in addition, the positive electrode layer is a double-sided conductive copper foil electrode with a size of 0.25 cm 2 ~16 cm 2 , and a thickness of 0.06 mm.

[0054] Example 1

[0055] Example 1 provides a cellulose-based moisture generator based on a wettability gradient structure, and its structural schematic diagram is as shown in Figure 1 . The moisture generator is assembled in a sandwich structure by an active layer and an asymmetric electrode layer; the active layer is a cellulose-based composite membrane with a wettability gradient structure, which is a bilayer structure, including a mixed fiber paper layer and a cellulose acetate nanoporous fiber membrane layer. This cellulose-based composite membrane is used to provide mobile ions and is responsible for the adsorption, diffusion, and evaporation channels of moisture; the negative electrode layer of the asymmetric electrode layer is an active copper mesh electrode, and the positive electrode layer is a double-sided conductive copper foil electrode. In the cellulose-based composite membrane, there is a gradient of hydroxyl functional groups from more to less and a gradient of pore sizes from large to small from the mixed fiber paper layer to the cellulose acetate nanoporous fiber membrane layer. In addition, the cellulose acetate nanoporous fiber membrane layer has a gradient of pore sizes from large to small along the Z direction, and the side with a larger pore size is compounded with the mixed fiber paper layer. The synergistic effect of the pore size gradient and the hydroxyl functional group gradient realizes the wettability gradient structure in the Z direction of the cellulose-based composite membrane.

[0056] It can be seen from Figure 1 that the moisture generator consists of three parts, a copper mesh electrode as the negative electrode layer, a cellulose-based composite membrane with a wettability gradient structure as the active layer, and a double-sided conductive copper foil electrode as the positive electrode layer. The overall device is in a sandwich structure, and the preparation and assembly process is simple and reliable.

[0057] This example also provides a preparation method for a cellulose-based moisture generator based on a wettability gradient structure, and the specific steps are as follows:

[0058] (1) Preparation of the highly wettable mixed fiber paper layer (CA@Cell)

[0059] The standard basis weight of the paper is 60 g / m 2, the hardwood fibers and softwood fibers are soaked and defibrated with water, and further beaten to obtain a plant fiber pulp. The beating degree of the plant fiber pulp is 40°SR, and the mass ratio of the hardwood fiber pulp to the softwood fiber pulp is 3:1. The plant fiber pulp is mixed with short cellulose acetate fibers. Based on the total mass of the absolute dry mass of the plant fiber pulp and the mass of the cellulose acetate short fibers, the cellulose acetate short fibers account for 40% of the total mass. The cellulose acetate short fibers are added after being sheared by a high-speed grinder at high speed for 2 minutes, and sodium dodecylbenzenesulfonate is added and foamed and defibrated in a pulp defibrator for 8000 revolutions. A certain volume of water is injected into the pulp storage cylinder of the paper former, and the defibrated mixed fiber pulp is poured into the rapid paper former, and bubble homogenization is used for sufficient mixing and water filtration to form a mixed fiber paper layer. The added sodium dodecylbenzenesulfonate is mainly used as a surfactant with a concentration of 0.2 g / L, aiming to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the evenness of the interweaving between fibers in the mixed fiber paper layer.

[0060] (2) Preparation of low wettability cellulose acetate nanoporous fiber layer (CA-NPFs)

[0061] Using cellulose acetate powder (degree of substitution DS = 2.37) as raw material, prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM = 3:4:8), stir fully for 24 h until dissolved, and let it stand for 2 h after degassing for use. Cut the silicone oil paper into a suitable shape and paste it on the roller receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the roller receiver of the electrospinning machine. During the electrospinning process, a 5 mL syringe and a 19G stainless steel single-tube flat-head needle are used, the internal temperature of the equipment is controlled at 25 °C, and the spinning voltage (14 kV - 20 kV), spinning rate (0.005 mm / s), receiving distance (12 cm) and environmental relative humidity RH% are controlled at 75%. These conditions ensure the acquisition of a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) on the roller receiver. In addition, during the electrospinning process, the spinning voltage is gradually adjusted in stages. At 0, 3, 6, and 9 h, the voltages are adjusted to 14 kV, 16 kV, 18 kV, and 20 kV in sequence, aiming to achieve a pore size gradient in the thickness direction. After the electrospinning is completed, the electrospinning membrane on the roller receiver is peeled off and naturally dried at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0062] Consisting of Figure 2It is known that the active layer is composed of a highly wettable mixed fiber paper layer and a low wettable cellulose acetate nanoporous fiber membrane layer; among them, the SEM images (a, b) of the mixed fiber paper layer show that the plant fibers and cellulose acetate short fibers are intertwined tightly and evenly. The SEM images (d - f) of the electrospun cellulose acetate nanoporous fibers show that the fibers are intertwined with each other to form a micron - scale porous structure, and the combination of the breath figure method and electrospinning technology under a high - humidity environment can form microscopic nano - pores on the surface and inside of the cellulose acetate nanofibers. The combination of the two gives the active layer a higher porosity and specific surface area, and increases its air permeability. In addition, the cross - section SEM images (g - i) of the active layer show that there is an interweaving between the highly wettable mixed fiber paper layer and the low wettable cellulose acetate nanoporous fiber layer, and the physical picture is as Figure 6 shown in A. Further, the mercury intrusion method is used to measure the pore size distribution of the mixed fiber paper layer, the cellulose acetate nanoporous fiber membrane layer and the composite membrane, as Figure 4 shown. Through comparison, it can be found that the pore size of the mixed fiber paper layer has the highest relative abundance at 91μm and 24μm, which is mainly the micron - porous structure formed by the interweaving of plant fibers and cellulose acetate fibers; the pore size of the cellulose acetate nanoporous fiber membrane layer has the highest relative abundance at 90μm, 6μm, 3μm and 9nm, which proves the existence of a gradient pore size distribution inside the cellulose acetate nanoporous fiber membrane layer and the existence of a nanoporous structure on the fiber surface; the pore size distribution of the cellulose composite membrane has changed significantly, and the pore size has the highest relative abundance at 91μm, 24μm and 3.5μm, which proves that the cellulose composite membrane has a gradient pore size distribution. The reasons for the change in pore size after compounding are mainly the following aspects: (1) Stable lamination caused by solvent evaporation; (2) The tight interweaving of the fibers between the mixed fiber paper layer and the cellulose acetate nanoporous fiber membrane layer; (3) Hydrogen - bond interaction between the hydroxyl and ester groups on the surface of cellulose acetate fibers and the hydroxyl groups on the surface of plant fibers, forming a stable hydrogen - bond network. As Figure 6 shown in A, when the composite material is bent or folded, the mixed fiber paper and the cellulose acetate nanoporous fiber membrane layer are tightly combined without delamination.

[0063] From Figure 5 shown, a, b and c are respectively the contact - angle change diagrams of the wetting process of the mixed fiber paper layer and the cellulose acetate nanoporous fiber membrane layer. The mixed fiber paper layer realizes full - process wetting within 0.122s. Due to the gradient porous structure, the cellulose acetate nanoporous fiber membrane layer realizes a gradient wettability structure. The wetting time of its upper surface is 25.06s, and the wetting time of its lower surface is 1s, showing a wettability gradient structure perpendicular to the device structure direction. As Figure 6As shown in Figure B, when a liquid is dropped onto the mixed fiber paper layer with high wettability, the liquid is quickly absorbed and diffused; when the liquid is dropped onto the cellulose acetate nanoporous fiber membrane with low wettability, the liquid diffusion rate is slower. Due to the capillary effect of the underlying mixed fiber paper layer, once the moisture contacts the fiber surface of the high-wettability mixed fiber paper layer due to gravity, the liquid will be quickly absorbed; further simulating anti-gravity absorption, the liquid can be spontaneously pumped to the hydrophilic layer; this pressure difference is mainly affected by the asymmetric wettability in the active layer of the wettability gradient structure, and the mechanism of liquid directional transport is analyzed according to the Laplace pressure difference, as Figure 6 shown in Figure C. Further, 50 μL of sweat was dropped on the arm, and the CA@Cell layer and the CA@Cell / CA-NPFs double-layer membrane were respectively attached to the arm. The sides close to the skin were the CA@Cell layer and the CA-NPFs layer respectively. A humidity moisture meter was used to measure the water content on both sides after the sweat was absorbed, and it can be obtained that the CA@Cell layer always has a higher water content. The CA-NPFs layer can quickly recover to dryness, keeping the skin free of sweat accumulation and refreshing( Figure 7 ).

[0064] Example 2

[0065] This example provides a preparation method of a cellulose-based moisture generator based on a wettability gradient structure. The specific steps are as follows:

[0066] (1) Preparation of the high-wettability mixed fiber paper layer (CA@Cell)

[0067] The standard grammage of the paper is 60 g / m 2 , the broad-leaved wood fibers and softwood fibers are soaked and defibrated with water, and further beaten to obtain a plant fiber pulp. The beating degree of the plant fiber pulp is 40°SR, and the mass ratio of the broad-leaved wood fiber pulp to the softwood fiber pulp is 3:1; the plant fiber pulp is mixed with cellulose acetate short fibers. Based on the total mass of the absolute dry mass of the plant fiber pulp and the mass of the cellulose acetate short fibers, the cellulose acetate short fibers account for 30% of the total mass. The cellulose acetate short fibers are added after being sheared by a high-speed grinder for 2 minutes, and sodium dodecylbenzenesulfonate is added, and foamed and defibrated in a pulp defibrator at 8000 r; a certain volume of water is injected into the pulp storage cylinder of the paper former, and the defibrated mixed fiber pulp is poured into the rapid paper former, and bubble homogenization is used for full mixing, water filtration and forming to obtain a mixed fiber paper layer. The added sodium dodecylbenzenesulfonate is mainly used as a surfactant, and the concentration is 0.2 g / L. The purpose is to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the interweaving uniformity between the fibers in the mixed fiber paper layer.

[0068] (2) Preparation of the low-wettability cellulose acetate nanoporous fiber layer (CA-NPFs)

[0069] Using cellulose acetate powder (degree of substitution DS = 2.37) as the raw material, a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM = 3:4:8) was prepared, stirred thoroughly for 24 h until dissolved, and left to stand for 2 h after degassing for later use. The silicone oil paper was cut into a suitable shape and pasted on the roller receiver, and the mixed fiber paper layer (CA@Cell) prepared in step (1) was pasted on the roller receiver of the electrospinning machine. During the electrospinning process, a 5 mL syringe and a 19G stainless steel single-tube flat-head needle were used, the internal temperature of the equipment was controlled at 25 °C, and the spinning voltage (14 kV - 20 kV), the spinning rate (0.005 mm / s), the receiving distance (12 cm), and the relative humidity RH% of the environment were controlled at 75%. These conditions ensured the acquisition of a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) on the roller receiver. Additionally, during the spinning process, the spinning voltage was gradually adjusted in stages. The voltages were adjusted to 14 kV, 16 kV, 18 kV, and 20 kV at 0, 3, 6, and 9 h respectively, with the aim of achieving a pore size gradient along the thickness direction. After the electrospinning was completed, the electrospun membrane on the roller receiver was peeled off and naturally dried at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0070] Example 3

[0071] This example provides a preparation method of a cellulose-based moisture generator based on a wettability gradient structure, and the specific steps are as follows:

[0072] (1) Preparation of a highly wettable mixed fiber paper layer (CA@Cell)

[0073] The standard grammage of the paper is 60 g / m 2, soaking and decomposing the hardwood fiber and the softwood fiber in water, and further beating to obtain the plant fiber pulp, the beating degree of the plant fiber pulp is 40°SR, and the mass ratio of the hardwood fiber pulp to the softwood fiber pulp is 3:1; the plant fiber pulp is mixed with cellulose acetate staple fibers, and the cellulose acetate staple fibers account for 70% of the total mass based on the total mass of the absolute dry mass of the plant fiber pulp and the mass of the cellulose acetate staple fibers, and the cellulose acetate staple fibers are added after the cellulose acetate fibers are sheared at high speed by a high-speed mill for 2 minutes, and sodium dodecylbenzene sulfonate is added, and the cellulose acetate fibers are foamed and decompressed in a pulp decompressor for 8000r; a certain volume of water is injected into the pulp storage cylinder of the paper sheet former, and the decompressed mixed fiber pulp is poured into the rapid paper sheet former, and the mixed fiber pulp is fully mixed by bubble homogenization, and the mixed fiber paper layer is obtained by filtering the water. The added sodium dodecylbenzene sulfonate is mainly used as a surfactant with a concentration of 0.2 g / L, the purpose of which is to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the interweaving uniformity between the fibers in the mixed fiber paper layer.

[0074] (2) Preparation of low-wettability cellulose acetate nanoporous fiber layers (CA-NPFs)

[0075] Cellulose acetate powder (substitution degree DS = 2.37) was used as raw material to prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM =3:4:8), stir thoroughly for 24 hours until dissolved, degas and stand for 2 hours for standby. Cut the silicone oil paper into a suitable shape and paste it on the drum receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the drum receiver of the electrospinning machine. During the electrospinning process, a 5mL syringe and a 19G stainless steel single-tube flat-head needle were used, the internal temperature of the equipment was controlled at 25°C, the spinning voltage (14kV~20kV), the spinning rate (0.005mm / s), the receiving distance (12cm) and the relative humidity RH% of the environment were controlled at 75%. These conditions ensure that a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) is obtained on the drum receiver. In addition, during the spinning process, the spinning voltage is adjusted step by step, and the voltage is adjusted to 14kV, 16kV, 18kV, and 20kV at 0, 3, 6, and 9h respectively, in order to achieve a pore size gradient along the thickness direction. After the electrospinning is completed, the electrospun membrane on the drum receiver is peeled off and dried naturally at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0076] When the mass of cellulose acetate fibers in the highly wettable mixed fiber paper layer accounts for 70% of the total mass, the CA-NPFs layer and the CA@Cell layer can still be tightly combined and do not delaminate after bending. However, the increase in the proportion of cellulose acetate fibers will cause a decrease in the number of hydroxyl groups, resulting in a decrease in the wettability of the CA@Cell layer, which will affect the collection of moisture and the conversion of electrical energy during the moisture power generation process.

[0077] Example 4

[0078] This Example 4 provides a cellulose-based moisture generator based on a wettability gradient structure, and its structural schematic diagram is as Figure 1 shown. This moisture generator is assembled in a sandwich structure by an active layer and an asymmetric electrode layer; the active layer is a cellulose-based composite membrane with a wettability gradient structure, which is a bilayer structure, including a composite fiber paper layer and a cellulose acetate nanoporous fiber membrane. This cellulose-based composite membrane is used to provide mobile ions and is responsible for the adsorption, diffusion, and evaporation channels of moisture; the negative electrode layer of the asymmetric electrode layer is an active copper mesh electrode, and the positive electrode layer is a double-conductive copper foil electrode. In the cellulose-based composite membrane, there is a gradient of hydroxyl functional groups from more to less and a gradient of pore sizes from large to small from the mixed fiber paper layer to the cellulose acetate nanoporous fiber membrane layer. In addition, there is a gradient of pore sizes from large to small along the Z direction in the cellulose acetate nanoporous fiber membrane layer, and the side with a larger pore size is compounded with the mixed fiber paper layer. The synergistic effect of the pore size gradient and the hydroxyl functional group gradient realizes the wettability gradient structure in the Z direction of the cellulose-based composite membrane.

[0079] It can be seen from Figure 1 that the moisture generator consists of three parts, the copper mesh electrode as the negative electrode layer, the cellulose-based composite membrane with a wettability gradient structure as the active layer, and the double-conductive copper foil electrode as the positive electrode layer. The overall device is in a sandwich structure, and the preparation and assembly processes are simple and reliable.

[0080] This example also provides a preparation method for a cellulose-based moisture generator based on a wettability gradient structure. The specific steps are as follows:

[0081] (1) Preparation of the highly wettable mixed fiber paper layer (CA@Cell)

[0082] The standard basis weight of the paper is 60 g / m 2, soak and defibrate hardwood fibers and softwood fibers with water, and further beat them to obtain a plant fiber pulp. The beating degree of the plant fiber pulp is 40°SR, and the mass ratio of the hardwood fiber pulp to the softwood fiber pulp is 3:1. Mix the plant fiber pulp with short cellulose acetate fibers. Based on the total mass of the absolute dry mass of the plant fiber pulp and the mass of the cellulose acetate short fibers, the cellulose acetate short fibers account for 40% of the total mass. The cellulose acetate short fibers are added after being sheared by a high-speed grinder for 2 minutes, and sodium dodecylbenzenesulfonate is added, and foaming and defibrating are carried out in a pulp defibrator at 8000 r. Inject a certain volume of water into the pulp storage cylinder of the paper sheet former, pour the defibrated mixed fiber pulp into the rapid paper sheet former, and use bubble homogenization to fully mix and filter water to form a mixed fiber paper layer. The added sodium dodecylbenzenesulfonate is mainly used as a surfactant with a concentration of 0.2 g / L, aiming to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the evenness of the interweaving between fibers in the mixed fiber paper layer.

[0083] (2) Preparation of low wettability cellulose acetate nanoporous fiber layer (CA-NPFs)

[0084] Using cellulose acetate powder (degree of substitution DS = 2.37) as raw material, prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM = 3:4:8), stir fully for 24 h until dissolved, and let it stand for 2 h after degassing for later use. Cut the silicone oil paper into a suitable shape and paste it on the roller receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the roller receiver of the electrospinning machine. During the electrospinning process, use a 5 mL syringe and a 19G stainless steel single-tube flat-head needle, control the internal temperature of the equipment at 25 °C, and control the spinning voltage (14 kV - 20 kV), spinning rate (0.005 mm / s), receiving distance (12 cm) and environmental relative humidity RH% at 90%. These conditions ensure that a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) is obtained on the roller receiver. In addition, during the electrospinning process, gradually adjust the spinning voltage stage by stage. At 0, 3, 6, and 9 h, the voltages are adjusted to 14 kV, 16 kV, 18 kV, and 20 kV in sequence, aiming to achieve a pore size gradient along the thickness direction. After the electrospinning is completed, peel off the electrospinning membrane on the roller receiver and dry it naturally at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0085] The adjustment of the relative humidity inside the electrospinning equipment will directly affect the pore structure on the surface of cellulose acetate fibers. Compared with Example 1, in this Example 4, the environmental relative humidity is changed to 90%, fromFigure 3 As can be seen from b1 and b2 in the figure, the cellulose acetate nanoporous fibers prepared in Example 1 have many nano-porous structures. According to Figure 3 As can be seen from c1 and c2 in the figure, under the high humidity conditions of Example 4, the pore structure on the fiber surface decreases. In a high humidity environment, water vapor may adsorb and accumulate on the fiber surface to form a water film, resulting in a reduction in surface pores. In addition, the increase in moisture in the air will cause the solvent evaporation rate to slow down, which will make it difficult for the solvent to evaporate quickly during the fiber formation process, resulting in the densification and reduction of the fiber surface structure.

[0086] Example 5

[0087] Example 5 of the present invention provides a cellulose-based moisture generator based on a wettability gradient structure, and its structural schematic diagram is as shown in Figure 1 the figure. The moisture generator is assembled by an active layer and an asymmetric electrode layer in a sandwich structure; the active layer is a cellulose-based composite membrane with a wettability gradient structure, including a composite fiber paper layer and a cellulose acetate nanoporous fiber membrane. The cellulose-based composite membrane is used to provide mobile ions and is responsible for the adsorption diffusion and evaporation channels of moisture; the negative electrode layer of the asymmetric electrode layer is an active copper mesh electrode, and the positive electrode layer is a double-conductive copper foil electrode. In the cellulose-based composite membrane, there is a gradient of hydroxyl functional groups from more to less and a gradient of pore sizes from large to small from the mixed fiber paper layer to the cellulose acetate nanoporous fiber membrane layer. In addition, the cellulose acetate nanoporous fiber membrane layer has a gradient of pore sizes from large to small along the Z direction, and the side with a larger pore size is compounded with the mixed fiber paper layer. The synergistic effect of the pore size gradient and the hydroxyl functional group gradient realizes the wettability gradient structure in the Z direction of the cellulose-based composite membrane.

[0088] It can be seen from Figure 1 that the moisture generator is composed of three parts, the copper mesh electrode as the negative electrode layer, the cellulose-based composite membrane with a wettability gradient structure as the active layer, and the double-conductive copper foil electrode as the positive electrode layer. The overall device is in a sandwich structure, and the preparation and assembly process are simple and reliable.

[0089] Example 5 of the present invention also provides a preparation method of a cellulose-based moisture generator based on a wettability gradient structure, and the specific steps are as follows:

[0090] (1) Preparation of a highly wettable mixed fiber paper layer (CA@Cell)

[0091] The standard basis weight of the paper is 60 g / m 2, soaking and decomposing the hardwood fiber and the softwood fiber in water, and further beating to obtain the plant fiber pulp, the beating degree of the plant fiber pulp is 40°SR, and the mass ratio of the hardwood fiber pulp to the softwood fiber pulp is 3:1; the plant fiber pulp is mixed with cellulose acetate staple fibers, and the cellulose acetate staple fibers account for 40% of the total mass based on the total mass of the absolute dry mass of the plant fiber pulp and the mass of the cellulose acetate staple fibers, and the cellulose acetate staple fibers are added after the cellulose acetate fibers are sheared at high speed by a high-speed mill for 2 minutes, and sodium dodecylbenzene sulfonate is added, and the cellulose acetate fibers are foamed and decompressed in a pulp decompressor for 8000r; a certain volume of water is injected into the pulp storage cylinder of the paper sheet former, and the decompressed mixed fiber pulp is poured into the rapid paper sheet former, and the mixed fiber pulp is fully mixed by bubble homogenization, and the mixed fiber paper layer is obtained by filtering the water. The added sodium dodecylbenzene sulfonate is mainly used as a surfactant with a concentration of 0.2 g / L, the purpose of which is to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the interweaving uniformity between the fibers in the mixed fiber paper layer.

[0092] (2) Preparation of low-wettability cellulose acetate nanoporous fiber layers (CA-NPFs)

[0093] Cellulose acetate powder (substitution degree DS = 2.37) was used as raw material to prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM =3:4:8), stir thoroughly for 24 hours until dissolved, degas and stand for 2 hours for standby. Cut the silicone oil paper into a suitable shape and paste it on the drum receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the drum receiver of the electrospinning machine. During the electrospinning process, a 5mL syringe and a 19G stainless steel single-tube flat-head needle were used, the internal temperature of the equipment was controlled at 25°C, the spinning voltage (14kV~20kV), the spinning rate (0.005mm / s), the receiving distance (12cm) and the relative humidity RH% of the environment were controlled at 80%. These conditions ensure that a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) is obtained on the drum receiver. In addition, during the spinning process, the spinning voltage is gradually adjusted in stages, and the voltage is adjusted to 14kV, 16kV, 18kV, and 20kV at 0, 3, 6, and 9h respectively, in order to achieve a pore size gradient along the thickness direction. After the electrospinning is completed, the electrospun membrane on the drum receiver is peeled off and dried naturally at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0094] (3) Assembly of wet gas generator

[0095] The cellulose-based composite film with a wettability gradient prepared in steps (1) and (2) was cut into 1 cm * 2 cm. The copper mesh electrode and the double-conductor copper foil electrode were cut into the same shape and respectively pasted on the upper surface of the highly wettable mixed fiber paper layer and the lower surface of the low-wettable cellulose acetate nanoporous fiber layer to form an asymmetric electrode structure. Then, the positive and negative electrodes of the multimeter or the working electrode and the auxiliary electrode of the electrochemical workstation were respectively connected to the copper mesh electrode and the double-conductor copper foil electrode to prepare the CA@Cell / CA-NPFs moisture generator. The pore density of the copper mesh is a square porous copper foam of 90 ppi, with a thickness of 0.2 mm; the size of the double-conductor copper foil electrode is 1 cm * 2 cm, with a thickness of 0.06 mm; finally, the assembled device was placed in a constant temperature and humidity environment to dry, with a temperature of 20 °C and a relative humidity of 35%.

[0096] (4) Preparation of the respiration sensor

[0097] After obtaining the moisture generator through steps (1), (2), and (3), the side of the moisture generator was sealed with natural epoxy resin and placed in a normal temperature and dry environment for 24 hours to obtain a self-powered respiration sensor. The prepared self-powered respiration sensor was connected to an electrochemical workstation (Shanghai Chenhua CHI760E), and the electrochemical workstation was adjusted to the Open Circuit potential-Time mode to measure the output voltage of the respiration sensor during the respiration process. The device was placed 2 cm away from the mouth and nose of the tester, and the tester was made to breathe in different modes to observe the voltage output curve of the device.

[0098] From Figure 8 As shown, the output voltage of the cellulose-based moisture generator is a DC voltage. The output voltage of a single moisture generator unit is 615 mV - 630 mV; the output voltage after two moisture generator units are connected in series is about 1.3 V; the output voltage after three moisture generator units are connected in series is about 1.8 V; the output voltage after four moisture generator units are connected in series is about 2.4 V, and the LED light-emitting diode was successfully lit. During the 1-hour electrical output test, the output voltage of the moisture generator remained stable without obvious attenuation, indicating that the moisture generator can continuously provide electrical energy for microelectronic devices. Under extreme conditions, the moisture generator can still maintain a certain output voltage. As Figure 9 shown, the output voltage of the moisture generator at -3 °C is 523 mV, and the output voltage of the moisture generator at 70 °C is 400 mV, proving the wide environmental applicability of the moisture generator.

[0099] From Figure 10 As shown, when the self-powered respiration sensor is in the intense mouth breathing and gentle nasal breathing modes, the moisture content in the mouth breathing is higher, and its V ocThe voltage value is significantly greater than that for soothing nasal breathing, and the oral and nasal breathing patterns can be clearly distinguished. Therefore, the self-powered breathing sensor can be used as a breathing pattern detection device to detect the corresponding electrical signals under different humidities and different breathing frequencies. All these detections only require a single self-powered breathing sensor without an additional power supply device.

[0100] Comparative Example 1

[0101] This comparative example provides a preparation method of a cellulose-based moisture generator based on a wettability gradient structure. The specific steps are as follows:

[0102] (1) The preparation method of the highly wettable mixed fiber paper layer (CA@Cell) is the same as that in Example 1.

[0103] (2) Preparation of the low wettability cellulose acetate nanoporous fiber layer (CA-NPFs)

[0104] Using cellulose acetate powder (degree of substitution DS = 2.37) as the raw material, prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM = 3:4:8), stir well for 24 h until dissolved, defoam and let stand for 2 h for use. Cut the silicone oil paper into a suitable shape and paste it on the drum receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the drum receiver of the electrospinning machine. During the electrospinning process, use a 5 mL syringe and a 19G stainless steel single tube flat head needle. The internal temperature of the electrospinning equipment is controlled at 25 °C. Adjust the spinning voltage (14 kV - 20 kV), spinning rate (0.005 mm / s), receiving distance (12 cm), and the environmental relative humidity RH% is controlled at 40%. These conditions ensure that a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) is obtained on the drum receiver. Additionally, during the spinning process, gradually adjust the spinning voltage at 0, 3, 6, and 9 h in stages, which are 14 kV, 16 kV, 18 kV, and 20 kV respectively, aiming to achieve a pore size gradient along the thickness direction. After the electrospinning is completed, peel off the electrospinning membrane on the drum receiver and dry it naturally at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0105] Compared with Example 1, in this comparative example, the environmental relative humidity is changed to 40%. Figure 3As shown in a1 and a2, the SEM image of the cellulose acetate nanoporous fiber layer shows that the fibers are intertwined with each other to form a micron-scale porous structure. However, in an environment with a relative humidity of 40%, nano-pores do not form on the surface of the cellulose acetate nanofibers, but rather a dense wrinkled structure along the fiber direction is presented. The reason for this fiber morphology may be that the solvent evaporation rate in the cellulose acetate spinning solution is too fast in a dry environment, causing the cellulose acetate molecules to rapidly arrange and solidify into filaments without sufficient time to interact with water molecules, resulting in a wrinkled structure on the fiber surface instead of an obvious porous structure.

[0106] Comparative Example 2

[0107] This example provides a preparation method of a cellulose-based moisture generator based on a wettability gradient structure, and the specific steps are as follows:

[0108] (1) Preparation of a highly wettable mixed fiber paper layer (CA@Cell)

[0109] The standard grammage of the paper is 60 g / m 2 , soak the hardwood fibers and softwood fibers in water for defibration, and further beat them to obtain a plant fiber slurry. The beating degree of the plant fiber slurry is 40°SR, and the mass ratio of the hardwood fiber slurry to the softwood fiber slurry is 3:1; mix the plant fiber slurry with cellulose acetate short fibers. Based on the total mass of the absolute dry mass of the plant fiber slurry and the mass of the cellulose acetate short fibers, the cellulose acetate short fibers account for 20% of the total mass. The cellulose acetate short fibers are added after the cellulose acetate fibers are sheared by a high-speed grinder for 2 minutes, and sodium dodecylbenzenesulfonate is added, and foaming and defibration are carried out in a pulp defibrator at 8000 r; inject a certain volume of water into the pulp storage cylinder of the paper former, pour the defibrated mixed fiber slurry into the rapid paper former, and use bubble homogenization to fully mix and filter water to form a mixed fiber paper layer. The added sodium dodecylbenzenesulfonate is mainly used as a surfactant with a concentration of 0.2 g / L, aiming to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the interweaving uniformity between the fibers in the mixed fiber paper layer.

[0110] (2) Preparation of a low wettability cellulose acetate nanoporous fiber layer (CA-NPFs)

[0111] Using cellulose acetate powder (degree of substitution DS = 2.37) as the raw material, prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM=3:4:8), stir thoroughly for 24 hours until dissolved, degas and stand for 2 hours for standby. Cut the silicone oil paper into a suitable shape and paste it on the drum receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the drum receiver of the electrospinning machine. During the electrospinning process, a 5mL syringe and a 19G stainless steel single-tube flat-head needle were used, the internal temperature of the equipment was controlled at 25°C, the spinning voltage (14kV~20kV), the spinning rate (0.005mm / s), the receiving distance (12cm) and the relative humidity RH% of the environment were controlled at 75%. These conditions ensure that a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) is obtained on the drum receiver. In addition, during the spinning process, the spinning voltage is adjusted step by step, and the voltage is adjusted to 14kV, 16kV, 18kV, and 20kV at 0, 3, 6, and 9h respectively, in order to achieve a pore size gradient along the thickness direction. After the electrospinning is completed, the electrospun membrane on the drum receiver is peeled off and dried naturally at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0112] Cellulose acetate fiber is relatively soft, which makes it have good plasticity and adaptability in the fields of textile and paper manufacturing. This softness can greatly improve the overall flexibility and bending performance of mixed fiber paper. Compared with Example 1, the addition ratio of cellulose acetate fiber in the mixed fiber paper in this comparative example 2 was changed to 20%, and the hardness of the paper increased, the flexibility decreased, and the feel became worse. In addition, after being compounded with cellulose acetate nanoporous fiber membrane, obvious layer separation phenomenon occurred during bending and folding, which is not conducive to the assembly and design of wet gas power generation device.

[0113] Comparative Example 3

[0114] This embodiment provides a method for preparing a cellulose-based moisture generator based on a wettability gradient structure, and the specific steps are as follows:

[0115] (1) Preparation of high wettability mixed fiber paper layer (CA@Cell)

[0116] The standard basis weight of paper is 60g / m 2, soaking and decomposing the hardwood fiber and the softwood fiber in water, and further beating to obtain the plant fiber pulp, the beating degree of the plant fiber pulp is 40°SR, and the mass ratio of the hardwood fiber pulp to the softwood fiber pulp is 3:1; the plant fiber pulp is mixed with cellulose acetate short fibers, and the cellulose acetate short fibers account for 80% of the total mass based on the total mass of the absolute dry mass of the plant fiber pulp and the mass of the cellulose acetate short fibers, and the cellulose acetate short fibers are added after the cellulose acetate fibers are sheared at high speed by a high-speed mill for 2 minutes, and sodium dodecylbenzene sulfonate is added, and the cellulose acetate fibers are foamed and decompressed in a pulp decompressor for 8000r; a certain volume of water is injected into the pulp storage cylinder of the paper sheet former, and the decompressed mixed fiber pulp is poured into the rapid paper sheet former, and the mixed fiber pulp is fully mixed by bubble homogenization, and the mixed fiber paper layer is obtained by filtering the water. The added sodium dodecylbenzene sulfonate is mainly used as a surfactant with a concentration of 0.2 g / L, the purpose of which is to solve the agglomeration phenomenon of cellulose acetate fibers in the mixed fiber paper layer and improve the interweaving uniformity between the fibers in the mixed fiber paper layer.

[0117] (2) Preparation of low-wettability cellulose acetate nanoporous fiber layers (CA-NPFs)

[0118] Cellulose acetate powder (substitution degree DS = 2.37) was used as raw material to prepare a 12 wt.% cellulose acetate / acetone / dichloromethane / N,N-dimethylformamide spinning solution (V DMF :V 丙酮 :V DCM =3:4:8), stir thoroughly for 24 hours until dissolved, degas and stand for 2 hours for standby. Cut the silicone oil paper into a suitable shape and paste it on the drum receiver, and paste the mixed fiber paper layer (CA@Cell) prepared in step (1) on the drum receiver of the electrospinning machine. During the electrospinning process, a 5mL syringe and a 19G stainless steel single-tube flat-head needle were used, the internal temperature of the equipment was controlled at 25°C, the spinning voltage (14kV~20kV), the spinning rate (0.005mm / s), the receiving distance (12cm) and the relative humidity RH% of the environment were controlled at 75%. These conditions ensure that a uniform cellulose acetate nanoporous fiber membrane layer (CA-NPFs) is obtained on the drum receiver. In addition, during the spinning process, the spinning voltage is adjusted step by step, and the voltage is adjusted to 14kV, 16kV, 18kV, and 20kV at 0, 3, 6, and 9h respectively, in order to achieve a pore size gradient along the thickness direction. After the electrospinning is completed, the electrospun membrane on the drum receiver is peeled off and dried naturally at room temperature to finally obtain a cellulose-based composite membrane with a wettability gradient.

[0119] Cellulose acetate fiber has a certain degree of hydrophobicity. This is mainly because the acetic acid groups in its molecular structure replace some of the hydroxyl groups, resulting in a decrease in the hydrophilicity of cellulose acetate fiber. Compared with Example 1, in this Comparative Example 3, the addition ratio of cellulose acetate fiber in the mixed fiber paper is changed to 80%. During the beating process, agglomeration occurs between cellulose acetate fibers, resulting in uneven fiber arrangement during the paper forming process. In addition, the high proportion of cellulose acetate fiber reduces the interweaving and connection between the two different fibers, and the fiber network structure is unstable. The surface and interior of the paper are relatively loose, which may lead to a decrease in the mechanical properties and durability of the material.

[0120] The cellulose-based moisture generator, preparation method and application based on the wettability gradient structure according to the present invention; by regulating the electrospinning parameters, the pore size gradient distribution of the cellulose acetate nanofiber layer is regulated, and then a plant fiber paper layer with high wettability is attached to the cellulose acetate nanoporous fiber layer as the active layer to provide a large number of movable ions; finally, an asymmetric electrode layer is constructed by using a copper mesh electrode and a double-conductor copper foil. After assembling the positive electrode, the active layer and the negative electrode in a sandwich structure, a cellulose-based moisture generator with a wettability gradient structure is finally prepared. This moisture generator can obtain energy from air moisture and convert it into electrical energy in an environment with different humidity and temperature all day long. Its main principle is that moisture moves directionally along the humidity gradient inside the wettability gradient porous material, and charge separation and movement occur on the microscopic surface where the material contacts the moisture, so that electrical output is manifested on both sides with a humidity difference. The porous characteristics ensure the moisture circulation path and the performance stability of the device.

[0121] The present invention can be placed in an environment with simulated human sweat. The high-wettability area of the moisture diffusion layer absorbs the sweat in its surrounding environment, and converts the chemical energy generated during the directional transmission of the sweat to the low-wettability area into electrical energy, and can be applied to the human body for practical applications. The present invention has a simple structure, convenient operation and low cost. The prepared device can convert the energy during the spontaneous evaporation of the collected water or liquid into electrical energy, and can be applied to the instant power supply of electronic devices.

Claims

1. A cellulose-based moisture generator based on a wettability gradient structure, characterized in that, It includes a negative electrode layer, an active layer, and a positive electrode layer connected in sequence. The active layer includes a mixed fiber paper layer and a cellulose acetate nanoporous fiber membrane layer. The mixed fiber paper layer includes plant fibers and cellulose acetate fibers. The mixed fiber paper layer is connected to the negative electrode layer, and the cellulose acetate nanoporous fiber membrane layer is connected to the positive electrode layer.

2. The cellulose-based moisture generator based on the wettability gradient structure according to claim 1, wherein There is a pore size gradient inside the cellulose acetate nanoporous fiber membrane layer, and the pore size gradually decreases from the side of the cellulose acetate nanoporous fiber membrane layer close to the mixed fiber paper layer to the other side.

3. The cellulose-based moisture generator based on the wettability gradient structure according to claim 1, characterized in that, There are nanoscale pore structures on the surface and inside the fibers in the cellulose acetate nanoporous fiber membrane layer.

4. The cellulose-based moisture generator based on the wettability gradient structure according to claim 1, characterized in that, The negative electrode layer is a copper mesh electrode, and the positive electrode layer is a double-conductive copper foil electrode.

5. The cellulose-based moisture generator based on the wettability gradient structure according to claim 1, wherein In the mixed fiber paper layer, the mass of cellulose acetate accounts for 30% - 70% of the mass of the mixed fiber paper layer.

6. The cellulose-based moisture generator based on the wettability gradient structure according to claim 1, wherein The plant fibers include hardwood fibers and softwood fibers.

7. The preparation method of the cellulose-based moisture generator based on the wettability gradient structure according to any one of claims 1 to 6, characterized in that It includes: (1) Mix plant fiber pulp and cellulose acetate short fibers, add sodium dodecylbenzenesulfonate, and perform beating to obtain a mixed fiber pulp. Filter and form the mixed fiber pulp to obtain a mixed fiber paper layer. (2) Mix cellulose acetate powder, acetone, dichloromethane, and N,N-dimethylformamide to obtain a spinning solution. Paste a silicon oil paper and the mixed fiber paper layer prepared in step (1) on the roller receiver of an electrospinning machine in sequence, perform electrospinning, and prepare a cellulose acetate nanoporous fiber membrane layer on the mixed fiber paper layer to obtain a cellulose-based composite membrane with a wettability gradient structure. (3) Attach the negative electrode layer and the positive electrode layer to both sides of the cellulose-based composite membrane respectively, and connect the positive and negative electrodes of a multimeter or the working electrode and the auxiliary electrode of an electrochemical workstation to the negative electrode layer and the positive electrode layer respectively to prepare a moisture generator.

8. The preparation method of the cellulose-based moisture generator based on the wettability gradient structure according to claim 7, wherein, During the electrospinning process, continuously adjust and increase the voltage value as the electrospinning progresses. The voltage adjustment range is 14 kV - 20 kV.

9. The preparation method of the cellulose-based moisture generator based on the wettability gradient structure according to claim 7, characterized in that, The electrospinning process is carried out under the condition of an environmental relative humidity of 75% - 90%.

10. A respiratory sensor, characterized in that, It is obtained by encapsulating the moisture generator according to any one of claims 1 - 6 with epoxy resin.

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