Composite fiber with humidity discoloration-sensing dual-mode response

Abstract

The invention discloses a composite fiber with humidity discoloration-sensing dual-mode response, and belongs to the technical field of intelligent materials. According to the invention, the fibrous humidity sensor based on the ion conductor and the color-changing fiber based on the cobalt ion coordination compound are combined, so that a humidity color-changing and sensing dual-mode response mechanism is innovatively realized, and the composite fiber with humidity color-changing and sensing dual-mode response is obtained. The composite fiber has excellent mechanical properties, so that the composite fiber can bear various kinds of stretching and bending in daily use. In addition, the composite fiber shows high sensitivity, and the sensitivity can be visually shown through color change; the performance is stable, and the consistent sensing and color changing effects can still be kept even after multiple times of recycling. Besides, the preparation process is relatively simple, complex equipment and harsh conditions are not needed, and the material is expected to be widely applied to multiple fields of flexible electronics, intelligent textiles, environment monitoring and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a composite fiber with humidity color-changing-sensing dual-mode response, and belongs to the technical field of intelligent materials. BACKGROUND

[0002] Humidity is an important reference index in the environment, and it has been widely used in industrial, agricultural production, aerospace, electronics, meteorology and other fields in recent decades. With the rapid development of flexible electronics and smart textiles, the demand for environmentally friendly humidity sensors in health monitoring (such as respiratory rate and wound exudate monitoring), environmental detection (such as atmospheric humidity and food packaging) is increasingly urgent. However, the current mainstream humidity sensors are mostly based on high polymer materials or rigid semiconductor elements, which have poor biocompatibility, are not degradable, and lack flexibility, which cannot meet the requirements of comfort, safety and sustainability of wearable devices.

[0003] Although some studies have tried to use bacterial cellulose (BC), sodium alginate and other bio-based materials to construct humidity sensors, there are still significant technical bottlenecks: first, the mechanical properties and functional characteristics of the materials are difficult to balance, pure bacterial cellulose has low fiber strength and is easy to break, and pure sodium alginate has high strength but poor toughness; second, the sensing function is single, most sensors can only realize resistance or capacitance output, and lack intuitive visual feedback mechanism; third, the preparation process is polluting, traditional spinning coagulation bath often contains toxic organic solvents or heavy metal ions that are difficult to recover, which violates the green manufacturing concept.

[0004] In recent years, humidity-responsive materials based on natural biopolymers have become a research hotspot due to their biocompatibility, environmental friendliness and rich functional groups. Their technical development mainly evolves along the following two directions: 1. Fiber-like humidity sensor based on ion conductor This kind of technology mainly uses the principle of change of ion conductivity after hydrophilic biopolymers (such as chitosan, sodium alginate, gelatin, etc.) absorb water. By designing the microstructure of the material to optimize the ion transport path, the sensing performance can be greatly improved. Among them, a recently reported ultra-micro fiber humidity sensor (Adv. Mater. 2024, 10.1002 / adma.202411558) is innovative in that it constructs nearly parallel ion channels through a special spinning process, realizes efficient "water-electricity" conversion, and achieves fast response and high sensitivity. However, such sensors usually only provide single electrical signal (such as resistance or impedance) output, which has limitations in applications that require intuitive, qualitative or redundant judgment.

[0005] 2. Color-changing fiber based on cobalt ion coordination compound To achieve intuitive visual feedback, developing color-changing materials based on the characteristics of specific metal ion (such as cobalt ion) coordination environment changing with humidity is an effective approach. In the sodium alginate cobalt color-changing artificial muscle (Chem. Eng. J. 2024, 10.1016 / j.cej.2024.150520), sodium alginate and cobalt chloride are directly used to form a hydrogel fiber through ion cross-linking, which can undergo reversible color change under humidity stimulation, accompanied by significant mechanical deformation.

[0006] Although the above research has made progress, it still faces severe challenges to integrate humidity-sensitive electrical signals and reliable visual color-changing signals into a single, durable device, especially for wearable applications: Insufficient mechanical performance and durability: Taking the "sodium alginate-cobalt chloride" ion cross-linking system as an example, the hydrogel or fiber materials formed generally have inherent shortcomings such as high brittleness and poor flexibility. Under the action of repeated humidity cycles or external mechanical stress (such as bending and stretching), the material is prone to structural damage, functional degradation, or even rupture, making it difficult to meet the requirements of wearable devices for material durability and long-term stability.

[0007] Low functional integration, limited application: Most existing technologies focus on single signal mode (either resistance change or color change) output. For example, cobalt alginate fibers can only provide color change, lacking precise and quantifiable electrical signal output; while some ion conductor humidity sensors can only output electrical signals, unable to provide intuitive visual feedback. This single functionality greatly limits its application in scenarios requiring dual verification or specific scenarios.

[0008] Weak environmental stability and anti-interference ability: Traditional biopolymer-based materials often lack performance retention ability in complex environments (such as sweat infiltration and temperature fluctuations), and the signal is prone to drift, limiting its practical application.

[0009] Therefore, there is an urgent need in the art for an innovative material system or structural design that can significantly improve the mechanical strength, flexibility, and environmental durability of the material while inheriting the biocompatibility of the biopolymer matrix and the sensitive color-changing characteristics of the "sodium alginate-cobalt ion" system, and successfully integrate stable resistance-type sensing and visual color-changing response into one, thereby providing a solution for the next generation of high-performance, wearable smart humidity sensors and feedback devices. SUMMARY

[0010] [TECHNICAL PROBLEM] The purpose of the present application is to overcome the above technical limitations and develop a new type of smart humidity sensing material with excellent mechanical properties, dual-mode response characteristics, and green manufacturing throughout the process.

[0011] [Technical Solution] The first objective of this invention is to provide a method for preparing a composite fiber with a humidity-changing color-sensing dual-mode response, the method comprising the following steps: S1. Preparation of composite spinning solution: Mix tricarboxylated oxidized bacterial cellulose suspension with sodium alginate sol at a mass ratio, so that sodium alginate sol accounts for 55-65% of the total mass, and obtain composite spinning solution by stirring and degassing. S2. Wet spinning: The composite spinning solution is injected into a cobalt chloride coagulation bath through an injection pump and solidified to obtain composite fibers.

[0012] In one embodiment of the present invention, in step S1, the tricarboxylated oxidizing bacterial cellulose is dispersed in water at a mass fraction of 2-2.5 wt%.

[0013] In one embodiment of the present invention, in step S1, the sodium alginate sol is dispersed in water at a mass fraction of 3-5 wt%.

[0014] In one embodiment of the present invention, in step S1, the sodium alginate sol is prepared by the following steps: dispersing sodium alginate powder in water, stirring and degassing.

[0015] In one embodiment of the present invention, the stirring speed is 600~1000 rpm.

[0016] In one embodiment of the present invention, the degassing conditions are as follows: the sol is placed under a vacuum of -0.09 to -0.095 MPa for 20 to 30 minutes.

[0017] In one embodiment of the present invention, in step S1, the tricarboxylated oxidizing bacterial cellulose suspension is prepared by the following steps: dispersing tricarboxylated oxidizing bacterial cellulose in water, homogenizing, and sonicating.

[0018] In one embodiment of the present invention, the homogenization conditions are: homogenization at 300-500 rpm for 10-20 min.

[0019] In one embodiment of the present invention, the ultrasound conditions are: ultrasonic treatment at a power of 100~250 W for 15 min under ice water bath conditions.

[0020] In one embodiment of the present invention, the preparation method of the tricarboxylated oxidizing bacterial cellulose is as follows: 2,2,6,6-tetramethylpiperidine-1-oxy free radical, sodium periodate, and sodium bromide are added to water, ultrasonically dispersed, and then bacterial cellulose is added to obtain a mixed solution; sodium hypochlorite is added to the mixed solution, the pH is maintained at 10.5±0.5, and after reacting for 6~8 h, ethanol is added, washed, centrifuged, and freeze-dried to obtain tricarboxylated oxidizing bacterial cellulose.

[0021] In one embodiment of the present invention, in step S1, the mixture is stirred at 5~15°C and at a speed of 600~1000 rpm for 1~2 h.

[0022] In one embodiment of the present invention, in step S1, the degassing is carried out for 20 to 60 minutes under a vacuum degree not lower than -0.09 to -0.095 MPa.

[0023] In one embodiment of the present invention, in step S2, the composite spinning solution is extruded through a 20G needle with a length of 150~200 mm.

[0024] In one embodiment of the present invention, the extrusion speed is 10~30 mL / min.

[0025] In one embodiment of the present invention, the concentration of cobalt chloride is 0.1~0.5 M.

[0026] A second objective of this invention is to provide a composite fiber with a humidity-changing color-sensing dual-mode response prepared according to the above method.

[0027] A third objective of this invention is to provide a smart textile comprising the aforementioned humidity-sensitive dual-mode response composite fiber.

[0028] A fourth objective of this invention is to provide the application of the composite fiber in the preparation of humidity monitoring sensors or textile products with humidity visualization functions.

[0029] [Beneficial Effects] 1. Innovatively implemented a dual-mode response mechanism. The prepared composite fiber (color-changing sensing yarn) breaks through the limitation of traditional humidity sensors that can only output electrical signals, simultaneously realizing a dual response of quantitative resistance detection and qualitative / semi-quantitative color visualization. This dual-mode output greatly improves the reliability and practicality of the humidity sensor, allowing users to read accurate data through precision instruments or make quick judgments by observing color with the naked eye, significantly expanding its application scenarios.

[0030] 2. It possesses both excellent mechanical properties and environmentally friendly characteristics. The reinforcing effect of tricarboxylated bacterial cellulose nanofiber networks and Co 2+ The ion coordination crosslinking results in fibers with significantly better mechanical properties than pure sodium alginate fibers, with a tensile strength of 1.77 cN and an elongation at break of less than 10%, meeting the requirements of wearable devices for material flexibility and durability.

[0031] The entire preparation process uses water as a solvent, the raw materials (bacterial cellulose, sodium alginate) are derived from renewable biomass, and the coagulation bath can be recycled. The whole process is green and environmentally friendly, perfectly meeting the requirements of the "dual carbon" strategy for the sustainable development of the materials industry.

[0032] 3. High sensitivity, rapid response, and stable performance. The composite fiber (color-changing sensing yarn) exhibits high sensitivity over a wide humidity range of 11%-90%, with a response / recovery time as fast as 1.2 seconds / 1.5 seconds, enabling it to accurately capture rapid humidity fluctuations. It also exhibits the highest sensitivity (approximately 13.75 mV / %RH) in the medium humidity region (40~70% RH).

[0033] After repeated cyclic testing, the performance degradation of its electrical signal and color change was less than 5%, demonstrating excellent long-term working stability and durability, and ensuring reliability in practical applications.

[0034] 4. The preparation process is simple and has the potential for large-scale production. The wet spinning process employed is mature and simple, facilitating its transition from laboratory to industrial applications. By adjusting the composition of the spinning solution and process parameters, continuous filaments with uniform properties can be stably and efficiently produced, laying a solid technological foundation for the commercial application of smart textiles.

[0035] In summary, this invention not only provides a high-performance, multifunctional intelligent sensing material, but also incorporates the concept of green manufacturing from source to end, offering an effective and innovative path to solve the current technical bottlenecks of flexible sensors in terms of functional integration, mechanical performance, and environmental compatibility. Attached Figure Description

[0036] Figure 1 Determination of the color-changing properties of color-changing sensing yarn; Figure 2 Steady-state rheological curves of spinning solution at different concentrations; Figure 3 Stress / strain curves of tricarboxylic acid bacterial cellulose / sodium alginate fiber with different concentration ratios; Figure 4 IV curves of tricarboxylic acid bacterial cellulose / sodium alginate cellulose at different concentration ratios; Figure 5IV curves of tricarboxylic acid bacterial cellulose / sodium alginate fiber under different humidity conditions; Figure 6 WAXS image of ordered fibers extruded by a 150mm long needle; Figure 7 WAXS image of disordered fibers extruded by a 6.5mm short needle; Figure 8 IV curves of fibers extruded with long and short needles at 44% RH; Figure 9 Observing the internal structure of the color-changing sensing yarn using a scanning electron microscope; Figure 10 Sensitivity curves of color-changing sensor yarn under different humidity levels; Figure 11 Testing the long-term stability of color-changing sensing yarn under different humidity levels. Detailed Implementation

[0037] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0038] The raw materials involved in the following examples are: Fermentation medium: 0.3 wt% tryptone, 0.5 wt% yeast extract, 2.5 wt% mannitol, 1 g / L citric acid, balance water, pH 6.0.

[0039] Glucosamine acetate ( Komeigatacter xylinum (ATCC 10245) 2,2,6,6-Tetramethylpiperidine-1-oxygen radical (TEMPO): CAS#: 2564-83-2; Sodium periodate (NaIO4): CAS#: 7790-28-5; Sodium bromide (NaBr): CAS#: 7647-15-6; Sodium hypochlorite (NaClO): CAS#: 7681-52-9; Sodium alginate: CAS#: 9005-38-3, the particle size of the powder is 150 mesh; Cobalt chloride hexahydrate (CoCl2·6H2O): CAS#: 7791-13-1, 0.1 M cobalt chloride hexahydrate was prepared by using water as a solvent.

[0040] Example 1: Preparation of Tricarboxylated Bacterial Cellulose 1. Preparation of bacterial cellulose hydrogels (static culture method): Acetobacter xylodis ATCC 10245 was inoculated into the fermentation medium and cultured at 30℃ for 24 h to obtain the activated solution; 5 mL of activation solution was inoculated into a culture dish containing 50 mL of fermentation medium and incubated at 30 °C for 14 days to obtain BC nanofiber membranes. After the BC nanofiber membrane was removed, it was immersed in a 0.1 mol / L NaOH aqueous solution and then bathed in an 80℃ water bath for 12 h to remove nutrients and live bacteria. The treated bacterial cellulose membrane was removed and rinsed with deionized water until the pH reached 7.0 to obtain the treated bacterial cellulose membrane.

[0041] 2. Purification and freeze-drying of bacterial cellulose: Remove the bacterial cellulose membrane from step 1, rinse the surface with deionized water, add an appropriate amount of deionized water, and then pulverize and homogenize at 300 rpm for 10 min to form a homogeneous slurry. Filter the slurry through a 100-mesh filter, collect the filter cake, and wash the filter cake repeatedly with distilled water three times until the washing liquid is neutral. The washed filter cake was pre-frozen in an ultra-low temperature freezer at -80℃ for 12 hours, and then transferred to a freeze dryer and dried for 48 hours under conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain freeze-dried bacterial cellulose.

[0042] 3. Preparation of tricarboxylic acid-oxidizing bacterial cellulose: 2.5 mmol of 2,2,6,6-tetramethylpiperidine-1-ox free radical (TEMPO, 0.39 g), 12.5 mmol of sodium periodate (NaIO4, 2.67 g) and 40 mmol of sodium bromide (NaBr, 4.12 g) were added to 200 mL of deionized water and sonicated for 10 min to completely dissolve the free radical, resulting in a mixed oxidizing solution. Add 2 g (dry weight) of lyophilized bacterial cellulose obtained in step 2 to the mixed oxidation solution and disperse it thoroughly. Add 40 mmol of sodium hypochlorite (NaClO, 3 g) dropwise at room temperature to initiate the reaction. Control the pH of the reaction solution to be maintained at 10.5±0.5. After 6 h of reaction, add 100 mL of ethanol to terminate the reaction. The reaction product was washed continuously by centrifugation with deionized water until the supernatant was neutral. The reaction product was pre-frozen in an ultra-low temperature freezer at -80℃ for 12 h, and then transferred to a freeze dryer and dried for 48 h under conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain freeze-dried tricarboxylated oxidized bacterial cellulose.

[0043] Example 2: Preparation of Tricarboxylated Bacterial Cellulose / Sodium Alginate Spinning Solution 1. Pretreatment of tricarboxylated bacterial cellulose: The freeze-dried tricarboxylated oxidized bacterial cellulose prepared in Example 1 was redispersed in deionized water at a mass fraction of 2 wt%, and homogenized at 300 rpm for 10 min using a high-speed homogenizer to obtain a preliminarily dispersed suspension. The suspension was ultrasonically treated at 150 W for 15 min under ice-water bath conditions to obtain a uniform, stable, and particle-free tricarboxylated bacterial cellulose suspension.

[0044] 2. Preparation of sodium alginate sol: Sodium alginate powder was dispersed in deionized water at a mass fraction of 4 wt%, and stirred at 800 rpm until a uniform sol was formed. The sol was placed in a sealable container, a vacuum pump was connected, and the system pressure was reduced to -0.09 MPa and maintained for 20 minutes. Under this negative pressure condition, the bubbles in the sol were encouraged to rise rapidly to the surface and burst. The completion of degassing was determined by observing that no more dense bubbles were emerging from the surface and that the solution volume no longer expanded significantly. Finally, a uniform, pale yellow sodium alginate sol was obtained.

[0045] 3. Preparation of composite spinning solution: The tricarboxylated oxidizing bacterial cellulose suspension prepared in step 1 and the sodium alginate sol prepared in step 2 were mixed such that the sodium alginate sol accounted for 60% of the total mass of the mixture and the tricarboxylated oxidizing bacterial cellulose suspension accounted for 40% of the total mass. According to the calculation, the dry matter mass ratio of tricarboxylated oxidizing bacterial cellulose to sodium alginate was 1:3. Place the mixture at 10°C and stir at 600 rpm for 60 min; The stirred and mixed solution was transferred to a vacuum dryer and degassed under a vacuum of -0.09 MPa or higher for 30 min until no more bubbles overflowed from the liquid surface, resulting in a homogeneous, bubble-free preliminary composite spinning solution.

[0046] Example 3: Preparation and performance testing of tricarboxylated oxidized bacterial cellulose / sodium alginate color-changing sensing yarn 1. Preparation of tricarboxylic acid oxidized bacterial cellulose / sodium alginate color-changing sensing yarn: The composite spinning solution prepared in Example 2 was transferred into a syringe equipped with a 20G needle (outer diameter 0.9 mm, inner diameter 0.6 mm, length 150 mm) and fixed to an injection pump device. Under the uniform drive of the injection pump, the composite spinning solution was injected at a rate of 10 mL / min. -1The tricarboxylated bacterial cellulose / sodium alginate color-changing sensing yarn was prepared by extruding the yarn into a cobalt chloride (CoCl2) coagulation bath with a concentration of 0.1 M at a certain rate.

[0047] 2. Determination of color-changing properties: The absorbance in the wavelength range of 200–800 nm was measured using a UV-Vis spectrophotometer (Lambda 950, Perkin Elmer, USA).

[0048] The results are as follows Figure 1 As shown, in the dry state, the material exhibits strong absorption at approximately 550–600 nm, corresponding to a bluish-purple appearance; after absorbing moisture, the absorption band shifts significantly to around 680–700 nm, and the appearance changes to pink or light blue. This color change is mainly due to the transformation of the coordination structure of cobalt ions: when dry, Co… 2+ In a low-coordination state, it absorbs shorter wavelengths of light; in a wet state, water molecules coordinate to form [Co(H2O)6]. 2+ The absorption band of hydrated ions red-shifts, and the macroscopic color changes accordingly. This phenomenon directly confirms that the color-changing sensing yarn prepared in step 1 has a rapid humidity-response color-changing ability, and the change is reversible, indicating that it can be used as both a visual humidity indicator material and an electrical sensing material.

[0049] 3. Tensile strength test Using an electronic single-fiber tensile testing machine (YG004), the color-changing sensing yarn prepared in step 1 was subjected to tensile testing at a specification length of 1 cm and a strain rate of 10 mm / min, with a sample length of 5 cm. Its tensile strength and elongation at break were 1.75 cN / dtex and 8%, respectively.

[0050] 4. Sensitivity Measurement The sensitivity change of the color-changing sensing yarn under different humidity levels was obtained through the following system testing and data processing methods: The two ends of the color-changing sensing yarn prepared in step 1 were connected to a high-impedance source meter (Keithley 2450) and set to open-circuit voltage measurement mode to accurately capture its self-generated potential. The color-changing sensing yarn was placed in a humidity-controlled sealed cavity, and the humidity was continuously adjusted at a constant rate within the range of 11% to 91% RH using a standard humidity generator. At the same time, a calibrated digital humidity sensor was used to synchronously monitor the actual relative humidity value inside the cavity. The source meter and the humidity acquisition system were synchronized via a computer, recording voltage and relative humidity in parallel at a frequency of at least one data point per minute to form a complete voltage-humidity (V-RH) dynamic response curve.

[0051] After obtaining the continuous response curve, the sensitivity of different humidity ranges was quantitatively calculated using a piecewise linear fitting method. Specifically, based on the significant changes in the curve trend, the entire humidity range was divided into three characteristic ranges: low humidity (e.g., 11–40% RH), medium humidity (40–70% RH), and high humidity (70–91% RH). Linear regression analysis was performed on voltage and humidity data within each range, with voltage denoted as V (mV) and relative humidity as H (%RH). The linear equation is V = kH + b. The slope of the regression line (ΔV / ΔRH) is the sensitivity for that humidity range, denoted in mV / %RH.

[0052] This method can effectively quantify the differences in response efficiency of color-changing sensing yarn under different humidity environments, revealing the transformation characteristics of its moisture adsorption and ion conduction mechanisms with humidity changes. Test results show that the color-changing sensing yarn prepared in step 1 exhibits the highest sensitivity (approximately 13.75 mV / %RH) in the medium humidity range, which also meets the needs of color-changing sensing yarn for daily use. Figure 10 ).

[0053] 5. Repeated loop test The self-powered voltage output cycle stability test of the color-changing sensing yarn prepared in step 1 was performed using a source meter (Keithley 2450) in open-circuit voltage mode.

[0054] The two ends of the color-changing sensing yarn prepared in step 1 were directly connected to the high-resistance input terminals of the source meter. It was then placed in two constant humidity environments controlled by a saturated salt solution: 75% RH and 11% RH. Each humidity condition was maintained for approximately 300 seconds, constituting a complete cycle. Throughout the test, the source meter continuously recorded the open-circuit voltage value, and multiple cycles were repeated to examine its output stability and repeatability. This test method aims to directly evaluate the ability of the color-changing sensing yarn to convert the ambient humidity gradient into a stable electrical output and its durability as a self-powered sensor under conditions without an external power supply.

[0055] Test results show that the voltage output of the color-changing sensing yarn prepared in step 1 responds significantly to changes in ambient humidity and exhibits good cyclic reversibility. Figure 11 The performance degradation of both electrical signals and color changes is less than 5%.

[0056] 6. Conductivity test The tricarboxylated oxidizing bacterial cellulose / sodium alginate color-changing sensing yarn prepared in step 1 was connected to an electrochemical workstation (model CHI660e), and the IV curve was tested by controlling humidity with a nitrogen atmosphere. The scan rate was set to 100 mV / s, and the scan interval was set to... 1 to 1 V.

[0057] Example 4: Preparation of Tricarboxylated Oxidized Bacterial Cellulose / Sodium Alginate Color-Changing Sensing Yarn 1. Pretreatment of tricarboxylated bacterial cellulose: The tricarboxylated oxidizing bacterial cellulose prepared in Example 1 was redispersed in deionized water at a mass fraction of 2 wt%. First, it was homogenized at 500 rpm for 15 min using a high-speed homogenizer to obtain a preliminarily dispersed suspension. The suspension was then subjected to ultrasonic treatment at 150 W for 15 min in an ice-water bath to obtain a uniform, stable, and particle-free tricarboxylated bacterial cellulose suspension.

[0058] 2. Preparation of sodium alginate sol: Sodium alginate powder was dispersed in deionized water at a mass fraction of 4 wt%, and stirred at 800 rpm until a uniform sol was formed. The sol was placed in a sealable container, a vacuum pump was connected, and the system pressure was reduced to -0.09 MPa and maintained for 20 min to obtain a uniform, pale yellow sodium alginate sol.

[0059] 3. Preparation of composite spinning solution: The tricarboxylated oxidizing bacterial cellulose suspension prepared in step 1 and the sodium alginate sol prepared in step 2 were mixed at a mass ratio of 2:3 to obtain a mixture; wherein, the sodium alginate sol accounted for 60% of the total mass of the mixture. Place the mixture at 15°C and stir at 800 rpm for 60 min; The stirred and mixed solution was transferred to a vacuum dryer and degassed under a vacuum of -0.09 MPa or higher for 30 min until no more bubbles overflowed from the liquid surface, resulting in a homogeneous, bubble-free preliminary composite spinning solution.

[0060] 4. Preparation of color-changing sensing yarn: The composite spinning solution prepared in step 3 was transferred into a syringe equipped with a 20G needle (outer diameter 0.9 mm, inner diameter 0.6 mm, length 150 mm) and fixed to the syringe pump device. Under the uniform drive of the syringe pump, the composite spinning solution was dispensed at a rate of 10 mL / min. -1 The tricarboxylated bacterial cellulose / sodium alginate color-changing sensing yarn was prepared by extruding the yarn into a coagulation bath with a concentration of 0.3 M cobalt chloride (CoCl2) at a certain rate.

[0061] Example 5: Preparation of Tricarboxylated Oxidized Bacterial Cellulose / Sodium Alginate Color-Changing Sensing Yarn 1. Pretreatment of tricarboxylated bacterial cellulose: The tricarboxylated oxidizing bacterial cellulose prepared in Example 1 was redispersed in deionized water at a mass fraction of 2 wt%. First, it was homogenized for 10 min at 300 rpm using a high-speed homogenizer to obtain a preliminarily dispersed suspension. The suspension was ultrasonically treated at 150 W for 15 min under ice-water bath conditions to obtain a homogeneous, stable, and particle-free tricarboxylated bacterial cellulose suspension.

[0062] 2. Preparation of sodium alginate sol: Sodium alginate powder was dispersed in deionized water at a mass fraction of 4 wt%, and stirred at 800 rpm until a uniform sol was formed. The sol was placed in a sealable container, a vacuum pump was connected, and the system pressure was reduced to -0.09 MPa and maintained for 30 min to obtain a uniform, pale yellow sodium alginate sol.

[0063] 3. Preparation of composite spinning solution: The tricarboxylated oxidizing bacterial cellulose suspension prepared in step 1 and the sodium alginate sol prepared in step 2 were mixed at a mass ratio of 2:3 to obtain a mixture; wherein, the sodium alginate sol accounted for 60% of the total mass of the mixture. Place the mixture at 10°C and stir at 800 rpm for 30 min; The stirred and mixed solution was transferred to a vacuum dryer and degassed under a vacuum of -0.09 MPa or higher for 30 min until no more bubbles overflowed from the liquid surface, resulting in a homogeneous, bubble-free preliminary composite spinning solution.

[0064] 4. Preparation of color-changing sensing yarn: The composite spinning solution prepared in step 3 was transferred into a syringe equipped with a 20G needle (outer diameter 0.9 mm, inner diameter 0.6 mm, length 150 mm) and fixed to the syringe pump device. Under the uniform drive of the syringe pump, the composite spinning solution was dispensed at a rate of 10 mL / min. -1 The tricarboxylated bacterial cellulose / sodium alginate color-changing sensing yarn was prepared by extruding the yarn into a coagulation bath with a concentration of 0.3 M cobalt chloride (CoCl2) at a certain rate.

[0065] Example 6: Effect of Tricarboxylated Oxidizing Bacterial Cellulose / Sodium Alginate Spinning Solution Ratio on Color-Changing Sensing Yarn This embodiment illustrates the effect of the mass ratio of tricarboxylated oxidized bacterial cellulose to sodium alginate in the composite spinning solution on the preparation and performance of color-changing sensing yarn. The specific steps are as follows: 1. Preparation of composite spinning solutions with different ratios: Except for the following parameters, the remaining steps are the same as in Example 2: In preparing the composite spinning solution, the mass percentage of sodium alginate sol in the mixed system (the sum of the total mass of sodium alginate sol and tricarboxylated oxidizing bacterial cellulose suspension) was controlled to be 30%, 40%, 50%, 60% and 70%, respectively, thus obtaining five composite spinning solutions with different ratios.

[0066] Subsequently, referring to the color-changing sensing yarn preparation method of Example 3, the prepared composite spinning solutions with different ratios were used to prepare color-changing sensing yarns, resulting in color-changing sensing yarns with different mass percentages of sodium alginate sol.

[0067] 2. Performance Testing: The color-changing sensing yarn samples prepared in step 1 were characterized and compared in terms of forming properties (observing fiber continuity, surface morphology, and diameter uniformity), mechanical properties (such as breaking strength and elongation at break), and electrical properties (such as conductivity). (1) Forming properties When the mass percentage of sodium alginate sol is 50%, the viscosity of the spinning solution is less than 50 mPa·s (@100 s). -1 Due to insufficient cohesion, the extruded filaments frequently break in the coagulation bath due to their weak tensile strength, resulting in a fiber formation success rate of less than 60% and a fiber diameter variation coefficient exceeding 25%.

[0068] When the mass percentage of sodium alginate sol is 70%, the zero-shear viscosity of the spinning solution exceeds 10,000 mPa·s, and the extrusion pressure needs to be higher than 0.8 MPa, which leads to unstable extruded streams and periodic "sharkskin" or breakage phenomena. The extrusion process becomes clogged in less than 10 minutes, resulting in poor spinnability.

[0069] When the mass percentage of sodium alginate sol is 60%, the spinning solution at a spinning shear rate (100 s⁻¹) -1 The viscosity is stable in the range of 80~120 mPa·s, the extrusion pressure is maintained at 0.3~0.4 MPa, the fine stream is uniform and stable, the fiber breakage rate is less than 5% during the forming process, the obtained fiber diameter is uniform, the coefficient of variation is less than 8%, and continuous spinning for more than 30 minutes without breakage can be achieved.

[0070] Test results show that a 50% formulation leads to molding failure due to excessively thin consistency, a 70% formulation leads to extrusion failure due to excessively high viscosity, while a 60% formulation achieves the optimal balance between viscosity, spinnability, and molding stability, and is therefore identified as the optimal process window for preparing high-performance fibers in this system. Fibers obtained under this formulation exhibit the best overall performance in subsequent tests of mechanical strength (>1.2 cN / dtex) and electrical response.

[0071] Therefore, the mass ratio of tricarboxylated oxidizing bacterial cellulose suspension to sodium alginate sol directly regulates the extrudability and formability of the spinning solution. Test results show that: When the mass percentage is below 50%, the spinning solution is too thin and the cross-linking network strength is insufficient, leading to forming failure. When the mass percentage reaches 70%, the spinning solution is too viscous, leading to extrusion failure. At a mass percentage of 60%, the spinning solution achieves the best balance between viscosity, cross-linking density, and process stability, proving to be the optimal ratio for preparing high-performance color-changing sensor yarns in this system. The yarn prepared under this ratio also exhibits the best overall performance in mechanical and electrical property tests.

[0072] (2) Rheological properties The steady-state shear viscosity of composite spinning solutions with sodium alginate mass percentages of 50%, 60%, and 70% at 25°C was tested using a rotational rheometer (model Physica MCR301, Anton Paar, Austria).

[0073] The results are as follows Figure 2 As shown, all systems exhibit typical shear-thinning behavior. At low shear rates, the zero-shear viscosity of the composite spinning solution with 70% sodium alginate sol mass percentage is significantly higher than that of the composite spinning solutions with 50% and 60% sodium alginate sol mass percentage, indicating that it has the highest molecular chain entanglement density and the worst flowability. The viscosity curve of the composite spinning solution with 60% sodium alginate sol mass percentage falls between the two, indicating that it has moderate rheological properties, which can ensure the smoothness of the extrusion process (avoiding high viscosity clogging at 70% mass percentage) and have sufficient chain entanglement to maintain the stability of the extruded stream (overcoming the problem of easy breakage caused by excessively low viscosity at 50% concentration).

[0074] (3) Mechanical properties Tensile tests were conducted using an electronic single-fiber tensile testing machine (YG004) at a strain rate of 10 mm / min and a sample length of 5 cm for fibers containing 30%, 40%, 50%, 60%, and 70% sodium alginate sol by mass.

[0075] The results are as follows Figure 3As shown, the breaking strength of the color-changing sensing yarn initially increased and then stabilized with increasing sodium alginate concentration. The color-changing sensing yarns with 30% and 40% sodium alginate sol had lower strengths (<2 cN / dtex), while the strength of the yarn with 50% sodium alginate sol increased. The breaking strengths of both the color-changing sensing yarns with 60% and 70% sodium alginate sol reached high levels (>6 cN / dtex), and their values ​​were close, indicating that a sufficiently dense and robust ionic cross-linking network could be formed at a sodium alginate sol concentration of 60%, allowing the mechanical properties to plateau. The breaking elongation decreased slightly with increasing concentration, but the fiber with 60% sodium alginate sol still maintained approximately 5% extensibility, demonstrating good toughness.

[0076] (4) Electrical conductivity Color-changing sensing yarns with varying mass percentages of the constructed sodium alginate sol were connected to an electrochemical workstation (model CHI660e), and the IV curves were tested by controlling humidity using a humidity and nitrogen atmosphere. The scan rate was set to 100 mV / s, and the scan interval was set to... 1 to 1 V.

[0077] The results are as follows Figure 4 5. The IV curves of all color-changing sensing yarns are approximately linear, indicating that their conductivity conforms to Ohm's law. Figure 4 The color-changing sensing yarn with a sodium alginate sol content of 30% exhibits the steepest slope, indicating the lowest resistance and best conductivity. This is attributed to its porous structure, which facilitates ion migration. As the sodium alginate sol content increases, the curve slope gradually decreases, indicating a decline in conductivity. The color-changing sensing yarn with a sodium alginate sol content of 70% shows the most significant conductivity degradation. While the conductivity of the color-changing sensing yarn with a sodium alginate sol content of 60% is lower than that of the 30% content, it is significantly better than that of the 70% content, demonstrating that it achieves high mechanical strength without excessively sacrificing charge transport capabilities.

[0078] like Figure 5It is clearly observed that, under a fixed voltage, the current flowing through the color-changing sensing yarn increases significantly with increasing ambient humidity. For example, at 1.0 V, the current is approximately -5 μA at 11% RH, while at 91% RH, the current increases to approximately -18 μA, a change of more than three times. All curves maintain good linearity under different humidity levels, and the current shows a clear positive correlation with the humidity level. This indicates that the color-changing sensing yarn with a sodium alginate sol content of 60% can effectively convert changes in ambient humidity into measurable changes in resistance (or conductivity), exhibiting excellent humidity response characteristics. The mechanism lies in the fact that the adsorption of water molecules alters the concentration and mobility of ion carriers within the fiber.

[0079] Based on the above performance analyses, it can be seen that: While color-changing sensing yarn with 30% sodium alginate by mass has extremely high conductivity, its inherently weak mechanical properties cannot meet the basic requirements for material durability in practical applications.

[0080] Although the color-changing sensing yarn with 70% sodium alginate by mass has excellent mechanical properties, its severe degradation of electrical properties causes it to lose its core value as a functional conductive material.

[0081] Therefore, the color-changing sensing yarn prepared with a mass percentage ratio of 40:60 for tricarboxylated oxidizing bacterial cellulose suspension and sodium alginate sol achieves an optimal balance between mechanical properties and acceptable conductivity without significant loss. This ratio avoids the structural weaknesses at low concentrations while preventing the blockage of conductive pathways at high concentrations. The resulting color-changing sensing yarn possesses both high mechanical strength and good sensing activity, laying a reliable material foundation for its practical applications in flexible electronics and smart textiles.

[0082] Table 1

[0083] Comparative Example 1 This embodiment illustrates the effect of needle length on the preparation and performance of color-changing sensor yarn. The specific steps are as follows: Replace the needle of the syringe with a 20G needle (outer diameter 0.9 mm, inner diameter 0.6 mm, length 150 mm) with a short needle with a length of 6.5 mm, and the rest of the steps are the same as in Example 3.

[0084] The results are as follows Figure 6 , 7 As shown, for color-changing sensing yarn prepared with long needles, its two-dimensional WAXS plot exhibits a strong scattering intensity signal in the horizontal direction, but no signal in the vertical direction. In contrast, color-changing sensing yarn prepared with short needles is almost flat at all angles. From... Figure 8As can be seen, under the same humidity conditions, the I-V curves show that the conductivity of the long-needle-oriented fibers is significantly higher than that of the short-needle-disordered fibers, indicating that the near-parallel ion channels can achieve faster carrier transport. The results clearly confirm that the 6.5 mm short needle cannot enable the fibers to form an effective high-orientation structure. This microstructural defect directly hinders the efficient directional flow of ions within the fiber, ultimately degrading its conductivity and color change performance during the sensing process.

[0085] Using a scanning electron microscope (e.g.) Figure 9 (As shown) Further observation was made of the regularity of the internal structure of the color-changing sensing yarn material prepared by long needle spinning. The ordered fibers obtained by long needle wet spinning have a high degree of orderliness. The tricarboxylic acid oxidizing bacterial cellulose filaments are arranged in almost the same direction, proving the successful construction of near-parallel ion channels. Effective ion migration can be achieved through near-parallel nanofluidic ion channels.

[0086] The highly oriented color-changing sensing yarn, prepared using 150 mm long needles, exhibits high ionic conductivity. Under external stimuli (such as stretching), its resistance changes sensitively and the signal is strong, effectively driving subsequent color-changing units, enabling the sensor to demonstrate high sensitivity, fast response, and significant color contrast.

[0087] Low-orientation color-changing sensing yarns prepared with 6.5 mm short needles have low intrinsic ionic conductivity, which hinders ion flow, resulting in weak signals and slow responses in the entire sensing circuit. Even when stimulation is applied, an effective ion flow cannot be formed inside to trigger a sufficient color change, ultimately leading to insensitive conductive sensing performance and weak or even non-existent color change performance.

[0088] This comparative experiment clearly demonstrates that the needle length directly determines the micro-orientation of the fiber by controlling the shear flow field during the spinning process. A short needle of 6.5 mm cannot provide the flow field conditions required to form a highly oriented structure, leading to disorder in the fiber structure and fundamentally limiting the directional migration ability of ions. This ultimately becomes a bottleneck restricting its advanced applications (such as high-performance conductive sensing and color change). Therefore, selecting a needle of sufficient length (e.g., 150 mm) is a necessary process condition for obtaining high-performance functional fibers.

[0089] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a composite fiber with a humidity-changing color-sensing dual-mode response, characterized in that, The method steps are as follows: S1. Preparation of composite spinning solution: Tricarboxylated oxidizing bacterial cellulose suspension and sodium alginate sol are mixed in a mass ratio so that sodium alginate accounts for 55-65% of the total dry matter mass of the two. The composite spinning solution is obtained by stirring and degassing. S2. Wet spinning: The composite spinning solution is injected into a cobalt chloride coagulation bath through an injection pump and solidified to obtain composite fibers.

2. The method according to claim 1, characterized in that, In step S1, the sodium alginate sol is prepared by the following steps: dispersing sodium alginate powder into a solution at a solid content of 3-5 wt%, stirring and degassing; Optionally, the degassing conditions are as follows: the sol is placed under a vacuum of -0.09 to -0.095 MPa for 20 to 30 minutes.

3. The method according to claim 1, characterized in that, In step S1, the preparation method of the tricarboxylated oxidizing bacterial cellulose suspension is as follows: the tricarboxylated oxidizing bacterial cellulose is dispersed in water at a solid content of 2~2.5 wt%, homogenized, and then sonicated. Optionally, the preparation method of the tricarboxylated oxidizing bacterial cellulose is as follows: 2,2,6,6-tetramethylpiperidine-1-oxy free radical, sodium periodate, and sodium bromide are added to water, ultrasonically dispersed, and then bacterial cellulose is added to obtain a mixed solution; sodium hypochlorite is added to the mixed solution to maintain the pH at 10.5±0.5, and after reacting for 6~8 h, ethanol is added, washed, centrifuged, and freeze-dried to obtain tricarboxylated oxidizing bacterial cellulose.

4. The method according to claim 1, characterized in that, In step S1, the mixing is carried out at 10~20℃ and stirred at a speed of 600~1000 rpm for 1~2 h; the degassing is carried out under a vacuum degree of not less than -0.09~-0.09 MPa for 20~60 min.

5. The method according to claim 1, characterized in that, In step S2, the composite spinning solution is extruded through a 20G needle with a length of 150~200 mm.

6. The method according to claim 5, characterized in that, The extrusion speed is 10~30 mL / min.

7. The method according to claim 1, characterized in that, The concentration of cobalt chloride is 0.1~0.5 M.

8. The composite fiber prepared by any one of the methods described in claims 1 to 7.

9. A smart textile, characterized in that, It includes the composite fiber as described in claim 8.

10. The application of the composite fiber of claim 8 in the preparation of a humidity monitoring sensor or a textile product with humidity visualization function.

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