WO2024174521A1 - Preparation method for cellulose-based moisture-sensing color-changing material - Google Patents

Abstract

The present invention belongs to the field of bio-based material preparation, and provides a preparation method for a cellulose-based moisture-sensing color-changing material. The preparation method comprises: dissolving a softwood kraft pulp serving as a starting material in a composite ionic liquid dissolving system, the composite ionic liquid dissolving system comprising an ionic liquid, a hydrogen bond ligand, a reinforcing agent, and a residence agent; after a cellulose is dissolved, preparing cellulose materials in different forms by means of an extruder or a film making device; then entering a coagulating bath for regeneration; in a washing process, dipping the obtained cellulose wet material into an aqueous cobalt chloride solution with a proper concentration; and then drying to obtain the cellulose-based moisture-sensing material. Under the condition that the production process is not increased, the present invention endows the cellulose with moisture-sensing color-changing performance; meanwhile, the strength is enhanced, and the cost is reduced.

Description

Preparation method of cellulose-based moisture-sensitive color-changing material

This application claims the priority of the Chinese patent application filed with the China Patent Office on February 24, 2023, with application number CN202310181983.2 and invention name “A method for preparing a cellulose-based hygroscopic color-changing material”, the entire contents of which are incorporated by reference into this application.

Technical Field

The invention belongs to the field of bio-based material preparation, and relates to a method for preparing a cellulose-based moisture-sensitive color-changing material.

Background Art

The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

Hygrochromic materials refer to materials whose structure changes after absorbing water, thereby changing the material's absorption spectrum, causing the material's color to change. Materials that show different colors under different humidity levels have the advantages of being observable with the naked eye and responding quickly. At this stage, hygrochromic materials are mostly organic compounds and synthetic compounds, which have the disadvantages of being difficult to degrade, high cost, and complex preparation process.

Cellulose is a natural polymer that exists in large quantities in nature. It is naturally degradable and can be sustainably regenerated. Cellulose-based materials have many advantages such as light weight, good air permeability, environmental friendliness, and wide sources. Cellulose is a polymer composed of β-D-pyranose glucose groups connected by 1,4-β-glycosidic bonds. There are many hydroxyl groups and hydrogen bonds between molecules, so it has good water absorption and swelling capacity, which makes cellulose a good choice for the preparation of humidity sensors. At the same time, the degradability, renewability and biofriendliness of cellulose also make it a good choice to replace fossil raw materials. The cellulose-based humidity sensing materials prepared at this stage have disadvantages such as low strength and low sensitivity, which restricts the application and development of cellulose-based humidity sensing materials.

Summary of the invention

In order to overcome the above shortcomings, the present invention provides a method for preparing a cellulose-based moisture-sensitive color-changing material. Coniferous wood kraft pulp is used as a raw material and dissolved in a composite ionic liquid system, and then cellulose materials in different states are prepared by an extruder or a film-making device, and then enter a coagulation bath for regeneration. During the washing process, the obtained cellulose wet material is immersed in a cobalt chloride aqueous solution of appropriate concentration, and then dried to obtain the cellulose-based moisture-sensitive material.

In order to achieve the above object, the present invention adopts the following technical solution:

The first aspect of the present invention provides a method for preparing a cellulose-based hygroscopic color-changing material, comprising:

The pulp and the composite ionic liquid dissolving system are mixed in vacuum at 60 to 75° C. for 20 to 30 minutes to dissolve the cellulose and obtain a cellulose solution;

regenerating the cellulose solution to obtain a cellulose wet material;

The wet cellulose material is immersed in a cobalt chloride aqueous solution with a concentration of 2wt% to 25wt% for 10 to 60s, and dried to obtain the cellulose-based moisture-sensitive color-changing material;

The composite ionic liquid dissolution system comprises: an ionic liquid, a hydrogen bonding ligand, a reinforcing agent, and a resident agent.

The amount of hydrogen bonding ligand is 0.5-5% of the ionic liquid, the amount of strengthening agent is 0.5-10% of the ionic liquid, and the amount of resident agent is 0.5-5% of the ionic liquid, calculated by mole fraction.

The research in this application found that: the composite ionic liquid dissolution system composed of ionic liquid, hydrogen bonding ligand, enhancer and resident agent system is used to prepare cellulose material. The system has low viscosity and good dissolution effect, which can increase the mass fraction of cellulose dissolved in the system; the composite ionic liquid dissolution system is low in price, recyclable and has good feasibility.

The regenerated cellulose material has a smooth surface, few structural defects and high material strength. Based on this material, the cellulose-based moisture-sensitive material can be directly prepared by the impregnation method, which is simple and low-cost.

The second aspect of the present invention provides a cellulose-based humidity-sensitive color-changing material prepared by the above method, wherein the color-changing material changes from blue to red as the humidity increases from 0% to 97% RH.

The natural cellulose material is dissolved in the composite ionic liquid dissolution system to form a cellulose solution, which is then regenerated in a coagulation bath. During the regeneration process, the cellulose material is modified to obtain a cellulose material that changes color in response to humidity, including cellulose fibers, cellulose films, cellulose gels, etc. The cellulose material that changes color in response to humidity can be adjusted according to the humidity to be detected, and can be applied to humidity detection and characterization in multiple fields such as electronics, medicine, materials, and energy, such as breathing detection, diaper detection, and sealed food detection. It has a wide range of applications and broad application prospects.

The third aspect of the present invention provides the application of the above-mentioned cellulose-based hygrochromic material in the fields of electronics, medicine, materials and energy.

Beneficial Effects of the Invention

(1) The present invention dissolves softwood kraft pulp through a composite ionic liquid dissolving system, so that during the regeneration process of cellulose, cellulose and hydrogen bond ligands, reinforcing agents, resident agents, etc. are combined to enhance the physical strength of the cellulose material.

(2) The cellulose-based hygroscopic color-changing material prepared by the present invention has the advantages of high sensitivity, obvious color-changing effect, high strength, high elongation, good softness, etc., and can be extended to a variety of raw materials, such as hardwood kraft pulp, cotton pulp, bamboo pulp, coniferous wood dissolving pulp, etc.

(3) The cellulose-based humidity-sensitive color-changing material prepared by the present invention has a controllable humidity sensitivity range, and can accurately detect humidity in different ranges through simple process adjustments according to usage requirements. The color can change from blue to red, and the change is obvious, which is easy to observe.

(4) The treatment method of the present invention is simple, highly practical, easy to promote, and the material is degradable, which is convenient for industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their description are used to explain the present invention, and do not constitute improper limitations on the present invention.

FIG1 shows the color changes of the comparative sample at 11% RH, 33% RH, 67% RH and 97% RH humidity;

FIG2 shows the color change of the sample of Example 2 at 11% RH, 33% RH, 67% RH and 97% RH humidity;

FIG3 shows the color change of the sample of Example 3 at 11% RH, 33% RH, 67% RH and 97% RH humidity;

FIG4 shows the viscosity of the cellulose solutions of the comparative example sample and the sample of Example 3;

FIG5 is a SEM image of a fiber cross section of a comparative example sample (left) and an example 3 sample (right);

FIG6 is an infrared spectrum of the comparative example sample, the sample of Example 1 and the sample of Example 3.

DETAILED DESCRIPTION

It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

As introduced in the background technology, most of the current moisture-sensitive materials are non-degradable compounds and the preparation process is complicated, and the bio-based moisture-sensitive materials have low strength and poor sensitivity. Therefore, the present invention proposes that the present invention provides a method for preparing a cellulose-based moisture-sensitive color-changing material. After coniferous wood sulfate pulp is dissolved in a composite ionic liquid dissolution system as a raw material, cellulose materials in different states are prepared by an extruder or a film-making device, and then immersed in a coagulation bath for regeneration. During the washing process, the obtained cellulose wet material is immersed in an aqueous solution of cobalt chloride at an appropriate concentration, and dried to obtain a cellulose-based moisture-sensitive color-changing material, thereby obtaining a high-efficiency and low-cost cellulose-based moisture-sensitive color-changing material, and the material is degradable.

The experiment includes the following detailed steps:

The ionic liquid, the hydrogen bonding ligand, the reinforcing agent and the resident agent are compounded to synthesize a composite ionic liquid dissolving system;

The softwood kraft pulp and the composite ionic liquid dissolving system are mixed in a high-speed mixer under vacuum at 60-75° C. for 20-30 minutes until the cellulose is dissolved to obtain a cellulose solution.

The cellulose solution is poured into an extruder with a metering device for spinning or film-making. The cellulose solution passes through a spinning head and enters a coagulation bath to obtain cellulose wet fibers or cellulose wet films.

The obtained wet cellulose material is washed, immersed in a cobalt chloride aqueous solution for 10 to 60 seconds, dried and curled to obtain a cellulose-based moisture-sensitive color-changing material.

In some embodiments, the dissolution system mixing step is: taking a hydrogen bonding ligand, a reinforcing agent and a resident agent and mixing them in an ionic liquid, heating and stirring to mix them evenly, and heating the composite ionic liquid dissolution system to 60-75° C. for standby use. The amount of the hydrogen bonding ligand is 0.5-5% (molar fraction) of the ionic liquid, the amount of the reinforcing agent is 0.5-10% (molar fraction) of the ionic liquid, and the amount of the resident agent is 0.5-5% (molar fraction) of the ionic liquid.

In some embodiments, the softwood kraft pulp is a debonded and dispersed pulp with a moisture content of about 10%.

The present application does not impose any particular limitation on the moisture content of the pulp. In some embodiments, the moisture content of the softwood kraft pulp is between 6% and 15%, which can effectively shorten the dissolution time of cellulose in the system.

In some embodiments, the amount of softwood kraft pulp is 8-15% (mass fraction) of the dissolving system. The softwood kraft pulp and the composite ionic liquid dissolving system are premixed and then added to a 1L kneading machine for Dissolve with a stirring speed of 100 rpm and a temperature of 70-80°C. The dissolution time is generally 30-60 minutes.

In some embodiments, the dissolved cellulose solution is poured into an extruder for spinning or film making, the screw aspect ratio is 20:1-30:1, the screw speed is 50-60 revolutions per minute, the spinning extruder is a vertical single-hole spinning head made of brass with a diameter of 0.6 mm to 0.8 mm, the film-making mold is a double-piece nozzle made of alloy with a gap of 0.1 mm to 1 mm, and the extrusion method is dry-jet wet spinning;

This application does not impose any special restrictions on the extruder speed, spinning head aperture and film-making die gap, which only affect the fiber and film morphology;

In some embodiments, the extruded cellulose solution falls vertically into a coagulation bath, the air gap is 10 mm to 30 mm, the concentration of the composite ionic liquid dissolving system in the coagulation bath is 0% to 20%, and the temperature is 20 to 30° C.;

The present application does not impose any particular limitation on the concentration of the coagulation bath. In some embodiments, the concentration of the coagulation bath has a certain influence on the strength of the regenerated fiber. As the concentration of the coagulation bath increases, the fiber strength increases, and after increasing to a certain extent, it begins to decrease.

In some embodiments, the coagulation bath is an aqueous solution system consisting of water and 1-allyl-3-methylimidazolium chloride, and the mass ratio of water to 1-allyl-3-methylimidazolium chloride is 9:1 or 8:2.

In some embodiments, the coagulated cellulose-based material enters a washing tank to remove the complex ionic liquid.

In some embodiments, the cellulose-based material after immersion and washing enters an impregnation tank, the cobalt chloride concentration in the impregnation tank is 2% to 25% (mass fraction), the impregnation time is 10 to 60 seconds, and the material is dried and curled to obtain a cellulose-based moisture-sensitive color-changing material.

Another embodiment of the present invention provides a method for preparing a cellulose hygroscopic color-changing material obtained by the above method.

The cellulose-based humidity-sensitive color-changing material provided by the invention can display red or blue at different humidity levels.

The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

Comparative Example:

(1) Take 150 g of 1-allyl-3-methylimidazolium chloride (water content: 0.72%), mix well, and heat the system to 80° C. for later use.

(2) The softwood kraft pulp is dispersed and the moisture content is about 9.7%.

(3) 15.21 g of softwood kraft pulp and the dissolving system were premixed and added to a 500 ml kneader for dissolution at a stirring speed of 60 rpm, a temperature of 75° C., and a dissolution time of 30 min.

(4) the dissolved cellulose solution is poured into an extruder for spinning, the screw aspect ratio is 27:1, the screw speed is 60 rpm, the extrusion head is a vertical single-hole spinning head made of brass with a diameter of 0.6 mm, and the extrusion method is dry-jet wet spinning;

(5) The cellulose solution extruded from the spinning head falls vertically into a coagulation bath with an air gap of 15 mm. The coagulation bath uses water and the coagulation bath temperature is 25 °C.

(6) The coagulated fiber enters a washing tank to remove the ionic liquid. The length of the washing tank is 1 m. The washing liquid is distilled water. The temperature of the washing tank is 60°C.

(7) The obtained wet cellulose material is placed in an impregnation tank with a length of 0.5 m. The impregnation liquid is distilled water. The temperature of the impregnation tank is 25° C. and the impregnation time is 30 s.

(8) After the impregnation treatment, the cellulose material is dried by hot air (120°C, 2 min). The dried fibers are curled onto a take-up reel, and the speed ratio between the take-up reel line speed and the extrusion speed is 1:1.

Example 1

A method for preparing a cellulose-based moisture-sensitive color-changing material, the specific steps are as follows:

(1) 1.86 g of triethylene glycol, 3.96 g of choline chloride, and 0.8 g of nano-silicon dioxide were added to 159.32 g of 1-allyl-3-methylimidazolium chloride (water content 0.47%) which was slowly stirred, and then ultrasonically vibrated for 10 min after high-speed mixing. At the same time, the system was heated to 70° C. for standby use.

(2) 17.15 g of softwood kraft pulp (moisture content 9.8%) and the composite ionic liquid system were premixed and then vacuum stirred at a stirring speed of 60 rpm, a temperature of 70° C., and a dissolution time of 30 min.

(3) The dissolved cellulose solution was poured into an extruder with a screw length-to-diameter ratio of 23:1 and a screw speed of 56 rpm. 20 g of the extruded solution was placed in a square mold with a size of 10 cm × 10 cm and made of glass. A film scraper was used to smooth the surface of the solution.

(4) The square mold is placed horizontally in a coagulation bath with an air gap of 15 mm. The coagulation bath is water and the coagulation bath temperature is 25 °C.

(5) The coagulated cellulose membrane enters a washing tank to remove the ionic liquid. The length of the washing tank is 1 m. The washing liquid is distilled water. The temperature of the washing tank is 60°C.

(6) The obtained wet cellulose membrane is placed in an immersion tank with a length of 0.5 m. The immersion liquid is a 2.5% (mass fraction) cobalt chloride solution. The immersion tank temperature is 25° C. and the immersion time is 30 s.

(7) After the impregnation treatment, the cellulose film is dried by hot air (120°C, 2 min), and the stretching ratio of all four sides during drying is 1:1.

Example 2

A method for preparing a cellulose-based moisture-sensitive color-changing material, the specific steps are as follows:

(1) Take 2.12 g of triethylene glycol, 4.05 g of choline chloride, and 1.08 g of nanocellulose fibrils and add them to 150.34 g of 1-allyl-3-methylimidazolium chloride (water content 0.47%) and 12.29 g of 1-butyl-3-methylimidazolium chloride which are slowly stirred, mix well, and heat the system to 70° C. for use.

(2) 18.47 g of softwood kraft pulp (moisture content 9.8%) and the composite ionic liquid system were premixed and then vacuum stirred at a stirring speed of 80 rpm, a temperature of 70° C., and a dissolution time of 30 min.

(3) the dissolved cellulose solution was poured into a single screw extruder for spinning, the screw aspect ratio was 26:1, the screw speed was 60 rpm, the five temperature zones from the feed port to the extrusion port were 90°C, 170°C, 165°C, 130°C, and 120°C, the extrusion head was a vertical single-hole spinning head made of brass with a diameter of 0.7 mm, and the extrusion method was dry-jet wet spinning;

(4) the cellulose solution extruded from the spinning head falls vertically into a coagulation bath with an air gap of 20 mm. The coagulation bath adopts an aqueous solution system consisting of water/1-allyl-3-methylimidazolium chloride, the mass ratio of water to 1-allyl-3-methylimidazolium chloride is 9:1, and the coagulation bath temperature is 25°C;

(5) The coagulated fiber enters a washing tank to remove the ionic liquid. The washing tank is 1 m long, the washing liquid is distilled water, and the temperature of the warm washing tank is 60°C.

(6) The obtained wet cellulose membrane is placed in an immersion tank with a length of 0.5 m. The immersion liquid is a 2.5% (mass fraction) cobalt chloride solution. The immersion tank temperature is 25° C. and the immersion time is 30 s.

(7) After impregnation, the fiber is dried by hot air (120°C, 2 min). The dried fiber is curled onto a take-up reel. The speed ratio of the take-up reel linear speed to the extrusion speed is 1.1:1.

Example 3

A method for preparing a cellulose-based moisture-sensitive color-changing material, the specific steps are as follows:

(1) 2.86 g of urea, 3.98 g of choline chloride and 0.4 g of nanocellulose were added to 158.32 g of 1-allyl-3-methylimidazolium chloride (water content 0.47%) which was slowly stirred, and stirred at high speed at 80° C. for 15 min. Meanwhile, the system was heated to 70° C. for standby use.

(2) 16.93 g of softwood kraft pulp (moisture content 9.8%) and the composite ionic liquid system were premixed and then vacuum stirred at a stirring speed of 60 rpm, a temperature of 70° C., and a dissolution time of 30 min.

(3) the dissolved cellulose solution was poured into a single screw extruder for spinning, the screw aspect ratio was 26:1, the screw speed was 50 rpm, the five temperature zones from the feed port to the extrusion port were 85°C, 170°C, 165°C, 130°C, and 120°C, the extrusion head was a vertical single-hole spinning head made of brass with a diameter of 0.6 mm, and the extrusion method was dry-jet wet spinning;

(4) the cellulose solution extruded from the spinning head falls vertically into a coagulation bath with an air gap of 10 mm. The coagulation bath adopts an aqueous solution system consisting of water/1-allyl-3-methylimidazolium chloride, the mass ratio of water to 1-allyl-3-methylimidazolium chloride is 8:2, and the coagulation bath temperature is 30°C;

(5) The coagulated fiber enters a washing tank to remove the ionic liquid. The washing tank is 1 m long, the washing liquid is distilled water, and the temperature of the warm washing tank is 60°C.

(6) The obtained wet cellulose membrane is placed in an immersion tank with a length of 0.5 m. The immersion liquid is a 5.0% (mass fraction) cobalt chloride solution. The immersion tank temperature is 30° C. and the immersion time is 25 s.

(7) After impregnation, the fiber is dried by hot air (120°C, 2 min). The dried fiber is curled onto a take-up reel. The speed ratio of the take-up reel linear speed to the extrusion speed is 1.1:1.

Experimental test:

The performance of the cellulose-based humidity-sensitive color-changing materials prepared in the comparative example and Examples 1-3 was tested, and the specific testing method was as follows:

Humidity color change test: Prepare 100 ml of solution in a 250 ml wide-mouth reagent bottle at relative humidity of 11%, 33%, 67%, 87% and 97%, place the cellulose-based humidity color change material 5 cm above the liquid surface, and observe its color change after standing for 5 minutes.

Humidity sensing electrical response test. A relative humidity environment of 11%, 33%, 67%, 87% and 97% of 100ml solution was prepared in a 250ml wide-mouth reagent bottle, and the electrodes of the electrochemical workstation were clamped at both ends of the cellulose-based humidity sensing color-changing material, with a spacing of 1cm. The cellulose-based humidity sensing material was placed 5cm above the liquid surface, and the change in resistance was recorded using an electrochemical workstation (produced by Shanghai Chenhua Company, model CHI760E) and a computer.

Breaking strength and breaking elongation: The instrument used is a texture analyzer produced by Stable Microsystems, model PL/CEL5, and the test method refers to GBT14337-2008). The results are shown in Table 1.

The viscosity of the cellulose/ionic liquid solution was measured using an ES-G2 rotational rheometer (TA Instruments, New Castle, USA) with a parallel plate of 20 mm in diameter. The gap for all measurements was 1 mm. The shear rate range was 0.1 to 100 s ^-1 , and the scanning angular frequency (w) was 6.28 rad/s.

Scanning electron microscope measurement (SEM) and energy spectrum measurement (EDS). SEM test uses Schottky field emission electron gun; resolution: 0.9nm@15Kv (secondary electron image); 2.0nm@30Kv (backscattered electron image); electron optical path is electron beam in the tube without cross optical path, acceleration voltage: 200v-30kv; probe beam current: 1pA-100nA, stability better than 0.2%/h; magnification: 8×～100,000×; objective lens uses electromagnetic/electrostatic composite lens; detector: In-BeamSE and SE secondary electron detector, backscattered detector, EDS spectrometer. EDS energy spectrum model: Xplore30, energy spectrum analysis working distance: 15mm; sample stage travel: X＝125mm; Y＝125mm; Z＝50mm; T＝-60°to60°; R＝360°(continuously adjustable). Before the sample test, a gold spraying station was used to spray gold on the fiber surface and cross section to increase conductivity.

Infrared analysis Fourier transform infrared (FTIR) spectra of regenerated cellulose fibers were recorded using an ALPHA FTIR spectrophotometer (Bruker Corporation, Billerica, MA, USA) in attenuated total reflectance (ATR) mode with a diamond-ZnSe crystal probe. The wavelength range was 500–4000 cm ^-1 with a resolution of 4 cm ^-1 . Ten fibers were closely arranged and placed under the probe for testing, with at least three replicates for each sample. All spectra were air-corrected, water vapor-corrected, automatically baseline-corrected, and smoothed using MONIC 9.0 software without ATR correction.

Table 1 Performance of cellulose-based humidity-sensitive color-changing materials prepared in comparative examples and examples 1 to 3

Figures 1 to 3 show the color changes of the samples prepared in the comparative example, Example 2, and Example 3 at 11% RH, 33% RH, 67% RH, and 97% RH, respectively. As shown in Figures 1 to 3 and Table 1, Compared with the comparative example, the cellulose fibers treated with cobalt chloride impregnation showed different colors at different humidity, wherein the color of the comparative example sample did not change at 11% RH, 33% RH, 67% RH and 97% RH humidity (as shown in Figure 1). The color of the sample in Example 2 at 11% RH was dark blue, light blue at 33% RH, purple at 67% RH, and red at 97% RH (as shown in Figure 2). The sample in Example 3 was ink blue at 11% RH, dark blue at 33% RH, light blue at 67% RH, and red at 97% RH (as shown in Figure 3). As the relative humidity increases, the cellulose material gradually changes from blue to red. The humidity response time of Example 1 is 367s, the humidity response time of Example 2 is 380s, and the humidity response time of Example 3 is 248s. All implementation cases have good color change response and electrical response.

It can be concluded from the data in Table 1 that the strength of the regenerated fiber impregnated with cobalt chloride after adding choline chloride and polyol is greatly improved compared with the strength of the regenerated cellulose fiber without addition. The breaking strength of the comparative example is 58.43MPa, and the elongation at break is 15.23%; the breaking strength of Example 1 is 153.32MPa, which is increased by 162.40%, and the elongation at break is 10.34%; the breaking strength of Example 2 is 150.36MPa, which is increased by 157.16%, and the elongation at break is 8.73%; the breaking strength of Example 3 is 132.37MPa, which is increased by 126.54%, and the elongation at break is 4.23%. The method for preparing cellulose-based hygrochromic material of the present invention can also improve the strength of cellulose materials.

FIG4 shows the viscosity of the cellulose solutions of the comparative sample and the sample of Example 3; as can be seen from FIG4 , the viscosity of the cellulose solution of Example 3 is significantly lower than that of the comparative example, and the cellulose material is prepared by using a composite ionic liquid dissolution system consisting of an ionic liquid, a hydrogen bonding ligand, a reinforcing agent and a resident agent system. The system has low viscosity and good dissolution effect, and can increase the mass fraction of cellulose dissolved in the system.

Figure 5 shows the SEM images of the cross-sections of the samples of the comparative example and Example 3. The interior of the comparative example sample shows a macroporous structure with inconsistent pore sizes and shapes. The diameter of the pore structure of the cross-section of the hygroscopic color-changing cellulose fiber prepared by the composite ionic liquid dissolution system is significantly smaller, and the pores are arranged regularly. The cellulose structure inside the fiber prepared by the patent is arranged more closely and evenly through the cross-section SEM image, thereby improving the strength of the regenerated cellulose fiber.

FIG6 is an infrared spectrum of the comparative example sample, the sample of Example 1 and the sample of Example 3. As can be seen from FIG6, choline chloride as a resident agent can participate in the preparation of cellulose-based hygrochromic materials. The peak between wavelengths 2920 and 2885 cm ^-1 is considered to be the characteristic peak of -CH and _CH2 stretching bonds of cellulose. The characteristic wavelengths of the samples of Example 1 and Example 3 change at this location, where -CH The stretching bond blue shifts, and the -CH ₂ stretching bond red shifts. The -CH ₂ bending bond of the samples of Example 1 and Example 3 shifts slightly at 1425 cm ^-1 . This treatment changes the chemical environment of the hydroxymethyl group connected to C6 in the glucose unit, proving the presence of the resident agent choline chloride in the cellulose material.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (14)

A method for preparing a cellulose-based moisture-sensitive color-changing material, comprising: The pulp and the composite ionic liquid dissolving system are mixed in vacuum at 60 to 75° C. for 20 to 30 minutes to dissolve the cellulose and obtain a cellulose solution; regenerating the cellulose solution to obtain a cellulose wet material; The wet cellulose material is immersed in a cobalt chloride aqueous solution with a concentration of 2wt% to 25wt% for 10 to 60s, and dried to obtain the cellulose-based moisture-sensitive color-changing material; The composite ionic liquid dissolution system comprises: an ionic liquid, a hydrogen bonding ligand, a reinforcing agent, and a resident agent; In terms of molar fraction, the amount of the hydrogen bonding ligand is 0.5-5% of the ionic liquid, the amount of the reinforcing agent is 0.5-10% of the ionic liquid, and the amount of the resident agent is 0.5-5% of the ionic liquid. The method for preparing a cellulose-based humidity-sensitive color-changing material according to claim 1, wherein the ionic liquid is an imidazole ionic liquid. The method for preparing a cellulose-based humidity-sensitive color-changing material as described in claim 2 is characterized in that the ionic liquid is selected from at least one of 1-allyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate. The method for preparing a cellulose-based humidity-sensitive color-changing material as described in claim 1 is characterized in that the hydrogen bonding ligand is a hydrogen bonding donor selected from at least one of urea, ethylene glycol and glycerol. The method for preparing a cellulose-based hygroscopic color-changing material according to claim 1, wherein the reinforcing agent is at least one of nanocellulose fibrils, nanocellulose fibers and nanosilicon dioxide. The method for preparing a cellulose-based humidity-sensitive color-changing material according to claim 1, wherein the resident agent is choline chloride. The method for preparing a cellulose-based humidity-sensitive color-changing material as described in claim 1 is characterized in that the preparation steps of the composite ionic liquid dissolution system are: taking a hydrogen bonding ligand, a reinforcing agent and a resident agent and mixing them in an ionic liquid, heating and stirring to mix them evenly, and heating the composite ionic liquid dissolution system to 60-75°C. The method for preparing a cellulose-based hygroscopic color-changing material according to claim 1, wherein the amount of the pulp used is 8 to 15 wt % of the composite ionic liquid dissolution system. The method for preparing a cellulose-based hygroscopic color-changing material as described in claim 1 is characterized in that the dissolved cellulose solution is poured into an extruder for spinning or film-making; the extruder has a screw aspect ratio of 20:1 to 30:1, a screw speed of 50 to 60 revolutions per minute, a spinning extruder head is a vertical single-hole spinning head made of brass with a diameter of 0.6 mm to 0.8 mm, a film-making mold is a double-piece nozzle made of alloy with a gap of 0.1 mm to 1 mm, and the extrusion method is dry-wet spinning. The method for preparing a cellulose-based hygroscopic color-changing material as described in claim 9 is characterized in that the extruded cellulose solution falls vertically into a coagulation bath, the air gap is 10 mm to 30 mm, the concentration of the composite ionic liquid dissolving system in the coagulation bath is 0% to 20%, and the temperature is 20 to 30°C. The method for preparing a cellulose-based moisture-sensitive color-changing material as described in claim 1 is characterized in that the pulp is coniferous wood kraft pulp, hardwood wood kraft pulp, cotton pulp, bamboo pulp or coniferous wood dissolving pulp. A cellulose-based hygroscopic color-changing material prepared by the preparation method according to any one of claims 1 to 11. Application of the cellulose-based hygrochromic material described in claim 12 in the fields of electronics, medicine, materials, and energy. The use according to claim 13 is characterized in that the cellulose-based hygroscopic color-changing material is used for humidity detection.