Ultra-high strength ultra-sensitive moisture-responsive fiber and preparation method thereof

Abstract

The present invention belongs to the field of nanomaterial technology, and in particular relates to an ultra-high strength and ultra-sensitive moisture-responsive fiber and a preparation method thereof. The present invention prepares natural ultra-strong, high-humidity-responsive bacterial cellulose (BC) fibers by culturing Bacillus xylosaccharis. First, the cellulose tubes biosynthesized by Bacillus xylosaccharis have the advantages of high purity, high crystallinity, large aspect ratio, and good mechanical and thermal properties, and are ideal raw materials with almost no structural defects. Afterwards, we developed a novel, simple and effective tension-assisted twisting technology (TAT) to manufacture fibers. Finally, we prepared an environmentally friendly, ultra-high strength, ultra-sensitive moisture-responsive, high-performance multifunctional fiber with a low-cost, simple and effective method, achieving excellent mechanical properties and sensitive humidity drive.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and in particular relates to an ultra-high strength ultra-sensitive moisture-responsive fiber and a preparation method thereof. Background Art

[0002] Currently, high-performance fibers are used in many fields, such as construction, medical treatment, automobile manufacturing, energy transmission, wearable electronic devices, and even aerospace. To date, most of these fibers are made from synthetic polymers extracted from petroleum through spinning processes, such as polypropylene fibers, polyolefin fibers, polyethylene fibers, nylon fibers, and poly(ethylene terephthalate) fibers. The preparation process of these materials is complex, the equipment required is expensive, and their inherent non-renewable nature and environmental pollution greatly limit their use. At the same time, although these synthetic fibers can meet certain strength requirements, they still have disadvantages such as poor mechanical properties and insufficient functionality.

[0003] Although the wet-responsive color-changing fiber invented by patent CN112962164A also has wet response, it uses synthetic chemical fibers prepared by chemical synthesis methods, which are non-degradable and non-regenerable, not conducive to environmental protection, and the production process will cause pollution. The intelligent wet-responsive compact fabric invented by patent CN112869948A can only shrink the fiber mesh surface and cannot achieve a large degree of wet response with a single fiber, which greatly limits its application space. The humidity sensing material invented by patent CN105891266A is a humidity sensing material based on lithium bromide / polyvinyl alcohol / barium titanate prepared by using a mixed solution of barium acetate, ethanol, acetic acid, deionized water, butyl titanate, polyvinyl pyrrolidone, polyvinyl alcohol and lithium bromide. Its preparation process is too complicated, and the required reagents are all toxic and harmful, which does not make use of its large-scale production. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing ultra-high strength and ultra-sensitive moisture-responsive fibers. The method has a simple preparation process and low preparation cost. The high-performance fibers prepared have both ultra-high strength and ultra-sensitive moisture responsiveness. The raw materials are green and the product advantages are outstanding.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A method for preparing ultra-high strength ultra-sensitive moisture-responsive fiber, the method comprising the following steps:

[0007] S1. Cultivation of cellulose hydrogel tubes using Bacillus xylosus

[0008] The culture medium containing live Taonella mepensis bacteria was injected into the hollow silicone tube, and the two ends of the silicone tube were clamped. The tube was incubated at 30°C ± 5°C for 3-5 days, and the synthesized cellulose hydrogel tube (TB) was removed from the silicone tube.

[0009] S2. Purification of cellulose hydrogel tubes

[0010] Soak TB in 0.1-0.5 M sodium hydroxide solution for more than 24 h, then wash with water;

[0011] Repeat soaking and washing at least three times to remove culture medium components and attached bacteria;

[0012] Finally, the TB was washed thoroughly with water until the pH of the washing solution was neutral;

[0013] S3. Conversion of cellulose hydrogel tubes into bacterial cellulose fibers via tension-assisted twisting

[0014] Under a constant strain of 5-30%, 10-30 cm long wet TB hydrogel tubes were twisted with a twist parameter range of 1-10 twists / cm, and then the twisted material under tension was fixed in shape and dried at room temperature to obtain the finished cellulose fiber (MF).

[0015] The present invention prepares natural ultra-strong, highly humidity-responsive bacterial cellulose (BC) fibers by culturing Bacillus xylosaccharis. First, the cellulose tubes biosynthesized by Bacillus xylosaccharis have the advantages of high purity, high crystallinity, large aspect ratio, and good mechanical and thermal properties, making them ideal raw materials with almost no structural defects. Subsequently, we developed a novel, simple and effective tension-assisted twisting technology (TAT) to manufacture the fibers. Ultimately, we prepared an environmentally friendly, ultra-high-strength, ultra-sensitive humidity-responsive, high-performance multifunctional fiber using a low-cost, simple and effective method, achieving excellent mechanical properties and sensitive humidity actuation.

[0016] The fibers produced by this invention can be effectively driven by steam, are environmentally friendly, readily available at low cost, and exhibit significant responsiveness. The fibers produced by this invention exhibit extremely high tensile strength, reaching 1057.1 MPa, a leader among natural fibers. They also exhibit excellent wet responsiveness, with a wet-induced rotational speed of up to 884 rpm / m. The entire preparation process does not involve chemical reagents, making it environmentally friendly and pollution-free, facilitating large-scale production.

[0017] Preferably, the culture medium in S1 is HS culture medium, containing 25.0 g / L glucose, 2.5 g / L Na2HPO4, 1.15 g / L citric acid, 5.0 g / L yeast extract, and 5.0 g / L peptone. The HS culture medium is sterilized at 121°C for 20 min until use.

[0018] Preferably, the size of the hollow silicone tube in S1 is 10-30 cm long and 2 mm-10 mm in diameter.

[0019] Preferably, the sodium hydroxide solution in S1 is 0.3M.

[0020] Preferably, the size of the hollow silicone tube in S1 is 10-30 cm long and 2 mm in diameter.

[0021] Preferably, the specific method of S3 is: while applying tension to both ends of the fiber to increase its length by 20-30%, twist the wet TB by 8-10 twists / cm, and then fix the two ends with clips to fix the shape of the material twisted under tension and dry it at room temperature to obtain a finished cellulose fiber (MF). The optimal process parameters are when the length increases by 30%, because the maximum increase in the length of the fiber is 30%, which is the limit of our hydrogel tube, and it will usually break if stretched further. The longer the stretch, the better the orientation of the microscopic fiber bundle, which is more conducive to the increase of macroscopic mechanical strength. Therefore, 30% is a balance point, which not only ensures high orientation, but also ensures that the material is not broken.

[0022] An ultra-high-strength ultra-sensitive moisture-responsive fiber prepared by the preparation method of the present invention.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention uses a silicone tube as a mold. By injecting culture medium into the silicone tube, the bacterial cellulose is cultured in Bacillus xylosus to synthesize bacterial cellulose, resulting in a bacterial cellulose hydrogel tube with a perfect fiber structure. Furthermore, the tension-assisted twisting technique (TAT) and room-temperature drying are used to prepare a functional fiber with ultra-high strength and ultra-sensitive moisture response. The maximum tensile strength reaches 1057 MPa, and the humidity-activated speed reaches 884 rpm / m.

[0025] 2. The fiber preparation method of the present invention is simple and easy to implement, offering a low-cost, convenient, and effective physical processing method, unlike existing treatment methods that involve chemical treatment. Furthermore, the resulting fiber achieves both high strength and high humidity responsiveness, offering broad application prospects in intelligent materials such as next-generation green sensors, remote actuators, and soft robotics. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The appearance and morphology of TB and MF described in the present invention, including the appearance of unpurified wet TB (a), wet (top) and dry (bottom) TB (b), from left to right: TB8, TB6, TB4, and TB2; the appearance of prepared MF (c), from left to right: MF8, MF6, MF4, and MF2; SEM observation of the morphological distribution of MF2 before purification (d), after purification (e), and after purification (g); digital photos of MF2 (g), from left to right: MF2, MF4, MF6, and MF8; ductility and flexibility of MF2 (h), and a demonstration of the use of MF2 as a sewing thread (i);

[0027] Figure 2 are the FTIR (a), XRD (b), TGA (c) and DTG (d) curves of TB2 and MF described in the present invention;

[0028] Figure 3 are electron microscope images of MF at different magnifications;

[0029] Figure 4 Schematic diagram of the process for preparing MF by TAT and the structural differences between MF2 and MF8;

[0030] Figure 5 TB2 (a), MF2 (b), MF4 (c), MF6 (d), MF8 (e) and their corresponding Hermann order parameters (f) determined by SAXS;

[0031] Figure 6 are SEM images of MF cross sections at different magnifications;

[0032] Figure 7 Mechanical properties of MF, including (a) tensile tests of TB2 and MF2, and (b) tensile stress comparison between MF2 and other types of MF; (c) ratio of the liftable weight of MF to the MF's own weight; (d) digital photo showing that MF8 can lift more than 4.6 kg of water. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail below through specific examples. It should be understood that the implementation of the present invention is not limited to the following examples, and any form of modification and / or change made to the present invention will fall within the scope of protection of the present invention.

[0034] In the present invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. The methods in the following examples are all conventional methods in the art unless otherwise specified.

[0035] The cellulose-synthesizing bacterium, Taonella mepensis xylosus (strain number: CICC 10529), was purchased from the China Industrial Culture Collection (CICC). Hestrin Schramm medium (HS) contained 25.0 g / L glucose, 2.5 g / L Na₂HPO₄, 1.15 g / L citric acid, 5.0 g / L yeast extract, and 5.0 g / L peptone. HS medium was sterilized at 121°C for 20 min until use.

[0036] Chemicals such as sodium hydroxide were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

[0037] All reagents in the following examples were of analytical grade and were used directly without further treatment.

[0038] Twisting is a conventional technology in the field of fiber preparation. The so-called stress twisting is to apply a certain force to the twisting process so that the length of the twisted fiber is maintained at a certain length, which is conducive to the stretching and orientation of the fiber to become consistent. The tension-assisted twisting technology is to apply force to both ends of our wet TB hydrogel tube to stretch it by 1-30%, twist it like a rag, so that our fiber material becomes similar to a twist, and fix the two ends with clips, and self-ignite and dry it to fix this twist-like microscopic morphology. The specific technical parameters are: when tension is applied to both ends of the wet TB hydrogel tube to increase its length by 1-30%, the wet TB hydrogel tube is twisted with 1-10 twists / cm, and then the two ends are fixed with clips to fix the shape of the material twisted under tension and dry it at room temperature to obtain a finished cellulose fiber (MF).

[0039] Example 1

[0040] A method for preparing ultra-high strength ultra-sensitive moisture-responsive fiber, the method comprising the following steps:

[0041] 1. Prepare 1 liter of solid culture medium. The formula is as follows: add 20.0g glucose, 5.0g yeast extract, K2HPO4

[0042] Add 1.0g of MgSO4, 15.0g of MgSO4, 5ml of anhydrous ethanol, 1.0L of distilled water, and 25g of agar to a 2-liter beaker and stir to dissolve. Seal tightly with heat-resistant tissue culture film and a rubber band.

[0043] 2. Prepare 2.5 liters of liquid culture medium. The recipe is as follows: Prepare 2.5 liters of HS medium by adding 62.5 g glucose, 6.25 g disodium hydrogen phosphate, 2.875 g citric acid, 12.5 g yeast extract, and 12.5 g peptone to a large beaker and stirring. Prepare 10 bottles, each containing 250 ml. Seal tightly with heat-resistant tissue culture film and a rubber band.

[0044] 3. Sterilize the above culture medium in an autoclave at 121°C for 20 minutes. Bring the temperature below 70°C. After sterilization, pour 1 liter of the solid medium into 40 Petri dishes, 25 ml per dish, and cool to room temperature.

[0045] 4. To revive the bacteria, inoculate one solid culture with 200 μl of the Bacillus xylosus suspension, and inoculate two solid cultures separately. Place the culture in an incubator at 30°C.

[0046] 5. Subculture. One day later, inoculate onto new solid medium. This is considered one subculture. Place in a 30°C incubator for a total of three subcultures.

[0047] 6. Transfer the culture to the liquid culture. Wait until hyphae grow. Sterilize the tube and pipette tip with alcohol for 30 minutes. Begin filling a 20cm long silicone tubing. Clamp both ends of the tubing with clamps and place in a 30°C incubator.

[0048] 7. After three days, take the silicone tube out of the incubator, squeeze out the cellulose hydrogel tube (TB) from the silicone tube, and soak it in 0.2 mol / L NaOH solution for 24 hours, then wash it with deionized water until it is neutral.

[0049] 8. The fibers were prepared using tension-assisted twisting technology (TAT). A 20 cm long wet cellulose tube was twisted 200 times (10 twists / cm) under a constant strain of 30%, and then dried at room temperature to obtain a finished fiber.

[0050] Example 2

[0051] A method for preparing an ultra-high strength ultra-sensitive moisture-responsive fiber according to Example 1 is as follows:

[0052] 1. Biosynthesis of cellulose hydrogel tubes (TB)

[0053] Three colonies (Taonella mepensis) grown on a Mueller-Hinton agar plate were transferred to 250 mL Erlenmeyer flasks filled with 200 mL of HS medium. After static incubation at 30°C for 4 days, the HS medium containing live bacteria was injected into 20 cm long hollow silicone tubes with diameters of 2 mm, 4 mm, 6 mm, and 8 mm, respectively. The silicone tubes were clamped at both ends and placed in a 30°C incubator for 3 days. The silicone tubes were then removed and the synthetic cellulose hydrogel tubes (TBs) were removed from the silicone tubes. The TBs were soaked in 0.3 M sodium hydroxide solution for 1 day and then washed with deionized water. These two steps were repeated three times to remove the culture medium components and attached bacteria. Finally, the TBs were thoroughly washed with deionized water until the pH of the washing solution was neutral. The TBs with 2 mm, 4 mm, 6 mm, and 8 mm silicone tubes were named TB2, TB4, TB6, and TB8, respectively.

[0054] 2. Preparation of film materials using tension-assisted twisting technology (TAT)

[0055] A TB with a length of 20 cm was twisted 200 times (10 turns / cm) under a constant strain of 30%. This method is defined as tension-assisted twisting technology (TAT). Figure 4 The stretched and twisted matrix materials were dried at room temperature overnight to obtain dry matrix materials, which were named MF2, MF4, MF6 and MF8, corresponding to their starting materials TB2, TB4, TB6 and TB8.

[0056] The surface and cross-sectional morphologies of the samples were analyzed using a Hitachi S-4800 field emission scanning electron microscope (SEM). The crystal structure analysis of the samples was measured using an XPert Professional Materials Research Diffractometer equipped with an X-ray accelerator detector at 30 mA and 40 kV using monochromatic CuKα radiation, and the crystallinity index of the samples was determined and calculated using a previously reported method (Zhao & Li, 2020). FTIR spectra were measured using a PerkinElmer Spectra 2000 Fourier transform infrared spectrometer (Waltham, MA, USA) equipped with an ATR system and a Ghost MKII Golden Gate (Criston Ridge, GA, USA). TGA data were acquired using a metetdo TGA / SDTA 851e in combination with STARe software. The tensile properties of the samples were measured using an Instlon 4411 mechanical tester equipped with a 500-N load cell (Instron Ltd.). Small-angle X-ray scattering (SAXS) measurements were performed using a CuKα beam through The alignment was performed. In addition, SAXS studies were performed at 40 kV and 30 mA, and scattered x-rays were detected using a two-dimensional detector (column 100 K, Dectris). The degree of alignment was quantified by analyzing the two-dimensional SAXS data and calculating the Hermann order parameters using a previously reported method (BarhoumiMeddeb, A., Chae, I., Han, A., Kim, SH, & Ounaies, Z. (2020). Magnetic field effects on cellulose nanocrystal ordering in a non-aqueous solvent. Cellulose, 27(14), 7901-7910).

[0057] The above-mentioned products were further tested:

[0058] 2.1 Preparation and characterization of defect-free cellulose hydrogel tubes (TBs)

[0059] As is well known, Xylosaccharomyces cerevisiae is aerobic and readily synthesizes cellulose at the liquid-air interface. The present invention uses a silicon tube with good air permeability as a template to prepare a cellulose hydrogel tube (TB). When the silicon tube filled with HS culture medium and bacteria is cultured at 30°C, Xylosaccharomyces cerevisiae tends to synthesize cellulose nanofibers along the inner surface of the silicon tube, forming a layer of cellulose hydrogel, ultimately producing a light yellow TB ( Figure 1 a). SEM images of TB2 obtained without further purification show that Xylella fastidiosa is a typical rod-shaped Bacillus that uses glucose in HS medium to synthesize cellulose nanofibers through the cellulose synthesis terminal complex along the longitudinal direction of the cell surface ( Figure 1 d). The wet TB obtained was purified by continuous NaOH treatment to remove bacteria and residual culture medium, and it was in a hollow tube shape and could even be well preserved after drying ( Figure 1 b). The inner diameter of the silica tube determines the size of the cellulose tube, and we found that this also affects the thickness of the cellulose tube.

[0060] As shown in Table 1, the hydrogel thickness of wet and dry TB increased with the increase of the inner diameter of the silicon tube, which should be due to the richer culture medium, larger liquid-air interface and more available oxygen. SEM observation of dry TB2 confirmed that the diameter of cellulose nanofibers was 24.58 ± 2.57 nm, further woven into a network structure with random fiber orientation ( Figure 1 e). No visible breaks in the cellulose nanofiber network were observed in the SEM images of TB2, indicating that they are very long nanofibers with a large aspect ratio.

[0061] Table 1. Size, density and mechanical properties of TB and MF

[0062]

[0063]

[0064] TB2 was proved to be very pure cellulose, with the same characteristic peaks of pure cellulose in the FTIR spectrum ( Figure 2 a):3334cm -1 and 2900cm -1 Originated from -OH stretching and CH symmetric stretching, 1161 cm -1 and 1110cm -1 Produced by CO antisymmetric bridge stretching and C-OH skeletal vibration, 1054 cm -1 and 1031cm -1 The results are attributed to the skeletal vibration of the COC pyranose ring. In addition, TB2 has a typical Iβ cellulose isoform, and its diffraction pattern shows that the 2θ is 14.7°, 16.8° and 22.8°, respectively, generated from the planes (1i0), (110) and (200) ( Figure 2 b). The calculated crystallinity index of TB2 is 90.3%, which is consistent with the high crystallinity of BC nanofibers observed previously, which is 84-90%. The pure and highly crystalline BC nanofibers also showed good thermal stability, with an onset degradation temperature of 245°C and a peak degradation temperature of 347°C ( Figure 2 c and d).

[0065] We have found that the mechanical properties of TB are diameter-dependent. In general, the tensile stress and strain of TB decrease with increasing diameter, indicating that the material is weaker and more brittle (Table 1). TB2 exhibits a tensile stress of 237.7 MPa, significantly higher than the 18.6–24.8 MPa of other TBs. During the drying process, the smallest hollow channels within TB2 are more likely to collapse, and the increased direct contact within the tubular hydrogel wall self-reinforces its structure, resulting in a higher tensile stress for TB2 than for other TBs. Overall, the resulting TB exhibits high purity, uniform thickness, high crystallinity, a well-aligned three-dimensional fiber network, and distinct mechanical and thermal properties, making it an ideal raw material for the fabrication of high-performance MF.

[0066] 2.2 Preparation of MF by tension-assisted twisting technology (TAT)

[0067] The obtained wet TB with a length of 20 cm was twisted 200 times (10 turns / cm) under a constant strain of 30%, which is defined as the stretch-assisted twisting (TAT) technique. The twisted material under tension was then dried overnight at room temperature to obtain the following: Figure 1MF shown in c and g. MF exhibits great flexibility and ductility and can even be used as sewing thread ( Figure 1 h and i).

[0068] In order to understand the mechanism of TAT process, the physicochemical changes of cellulose nanofibers during MF preparation were comprehensively studied, taking MF2 as an example. Figure 4 As shown in the figure, dry TB2 shrinks due to water evaporation during the drying process, and the surface has a ribbon-like wrinkled structure, but the network structure formed by the interweaving of cellulose nanofibers in wet TB2 is well preserved. Compared with TB2, MF2 is rod-shaped, with a smoother surface and a denser network structure. During the TAT process, the water in the TB2 network is squeezed out, which will greatly reduce the hydration state of the cellulose nanofibers ( Figure 4 ). In addition, the loss of water molecules brings the cellulose nanofibers closer together, allowing for direct contact, thereby removing larger interfiber voids / pores and densifying the network. The density of MF2 is 1.375 g / cm 3 , close to the theoretical density of pure cellulose Iα unit cell 1.582g / cm 3 , confirming the denseness of the cellulose nanofiber network in MF2. In addition to the physical interaction, there are also intramolecular interactions between the densely arranged cellulose nanofibers. Figure 2 As shown in a, the FTIR spectrum of MF2 is almost the same as that of TB2, indicating that MF2 is still high-purity cellulose and no chemical reaction occurs between cellulose nanofibers during the TAT process. -1 and 2900cm -1 A more obvious peak appeared at the MF2 site, which indicated that more hydrogen bonds were formed between the cellulose nanofibers during the preparation process of MF2.

[0069] Another obvious morphological change of MF2 compared with TB2 is the alignment of cellulose nanofibers with a uniform offset angle of 45° ( Figure 3 This was further confirmed by SAXS analysis. The elliptical shape of TB2 determined by SAXS indicated that the cellulose nanofibers were isotropically arranged, and the Hermann order parameter was calculated to be 0.48 ( Figure 5 a and f). During TB2 biosynthesis, bacteria tend to synthesize cellulose nanofibers on the surface of the silica tubes, which are randomly arranged and correspond to relatively low Hermann order parameters. Compared with TB2, the corresponding MF2 exhibits a strong diffraction pattern with high anisotropy along the MF axis, confirming a highly oriented network of cellulose nanofibers, corresponding to a much higher Hermann order parameter of 0.76 ( Figure 5b and f). When treated with TAT, the tension applied to TB2 drives the cellulose nanofibers to stretch along the tensile axis, resulting in a good alignment of the cellulose nanofibers and further assembly into bundled cellulose nanofibers. This results in a dense and compact structure of MF. The cross section of MF2 can also be observed by SEM, showing a typical multilayer structure ( Figure 5 During the TAT process, the hydrogel walls of TB2 twist layer by layer and then assemble to form this unique network ( Figure 4 ).

[0070] When the same TAT method was applied to other TBs, the FTIR spectra, XRD diffraction patterns, and TGA degradation of all MFs confirmed that the obtained MFs with different diameters had similar chemical properties, crystal structures, and thermal stability to MF2 ( Figure 2 ). However, their morphologies are completely different. Figure 3 As shown in Figure 2, as the diameter of the TB increases, the corresponding MF surface becomes coarser and a distinct wrinkled structure is observed. In particular, MF8 exhibits a curled shape. These observed differences are likely due to the different behaviors of BC nanofibers during TAT treatment. Fibers prepared from small-diameter TB, such as MF2, tend to stretch and align along the axial direction under unstable tension, forming a weak S-chirality helical structure in a bundle-like and self-twisting manner, which is reflected in the smooth surface helical angle of MF2 ( Figure 3 However, when the TB is twisted with increasing diameter, for example MF8, in addition to the twisted fibers mentioned above, the TB8 tubular will self-fold with the first and then twisted Z chiral helix MF, which is indicated by its fluctuating wrinkled surface ( Figure 4 With the formation of twisted MF8 and helical MF8, gaps or spaces are inevitably generated between the wrinkled stripes, which reduces the density and makes the network loose, which shows that the density of MF8 is lower than that of other MFs (Table 1). The self-coiling of MF has a negative impact on the arrangement of BC nanofibers, which can be seen from the disordered arrangement of BC nanofibers ( Figure 4 ), the deformed ellipse of the two-dimensional SAXS diffraction pattern and the lower Hermann order parameter of MF8 can be seen.

[0071] 2.3MF's excellent mechanical properties

[0072] TB2 has the highest tensile stress of all TBs measured by tensile tests, which is 237.7 MPa, significantly higher than the 18.6-24.8 MPa of the other tests (Table 1). After twisting the TB into MF, the tensile stress of the MF increased more than that of the corresponding TB. However, it is obvious that the tensile stress of the MF decreases with the increase of its diameter, which is closely related to the looser network and less nanofiber arrangement in the MF with larger diameter discussed in Section 3.2. Among all MFs, MF2 has the highest tensile stress of 1057.1 MPa ( Figure 7 a). Although MF8 has the lowest tensile stress among all MFs, it can still lift 4.6kg of water, which is 122348 times the weight of MF8 ( Figure 7 d). As the MF gets thinner, the ratio of the liftable weight to the MF's own weight becomes incredible, with the highest value for MF2 being 342444 ( Figure 7 c), which is consistent with the observation that the tensile stress increases with decreasing MF diameter.

[0073] Existing literature studies have focused on preparing ultra-strong nanofibers from cellulose through different preparation strategies. The mechanical properties of MF2 are compared with other bacterial cellulose-based MFs reported in the literature, as shown in Table 2, which shows that the tensile stress obtained by MF2 in the present invention has set a new record.

[0074] Table 2 Comparison of mechanical properties of MF2 and other bacterial cellulose-based MFs reported in the literature

[0075]

[0076] In addition, MF2 is also stronger than most cellulose-based matrices, including natural cellulose matrices (cotton, ramie, coconut silk, and sisal), regenerated cellulose matrices, and nanocellulose-based MF (softwood and hardwood) ( Figure 7 b and Table 4).

[0077] Table 4 Deduced MF speed

[0078]

[0079] In addition, MF2 also outperformed common natural matrix materials such as protein-based wool and silk nanofibers and PET-based synthetic matrix materials, confirming that a new type of ultra-strong matrix material was achieved using cellulose as raw material through the TAT method developed in the present invention (Table 3).

[0080] Table 3 Comparison of mechanical properties of MF2 and other biopolymer-based MFs reported in the literature

[0081]

[0082]

[0083] In summary, the reason why MF2 can achieve ultra-high mechanical strength can be attributed to the following reasons ( Figure 3 ): (1) Excellent chemical and crystal structures of cellulose. The present invention shows that cellulose has high purity, high degree of polymerization (14,000-16,000), and high crystallinity (90.3%), making it an ideal material for preparing high-performance MF; (2) Defect-free fibrillar cellulose nanofiber network. In TB, the width of cellulose nanofibers is 20-30nm, no breakpoints are observed in scanning electron microscope images, and they are long with a huge aspect ratio. These extremely long cellulose nanofibers further interweave to form a mesh network with good network integrity, which gives TB good mechanical and thermal properties; (3) TAT treatment can greatly reduce the gaps in the MF network, allowing the cellulose nanofibers to be fully stretched and arranged along the MF axis, so that the cellulose nanofibers are close to each other, forming a densely packed bundle structure, and forming strong intrafiber hydrogen bonds between the cellulose nanofibers, thereby strengthening the MF network; (4) In addition to the good alignment of cellulose nanofibers, the self-folding and coiling of TB nanofibers induce the tubular cellulose wall to assemble layer by layer to form a multilayer structure, which further strengthens the network.

[0084] Furthermore, cellulose nanofibers, with their excellent hygroscopic properties, experience a large volume expansion upon absorbing water molecules, which leads to the release of stored tension in the MF network and results in extremely fast torsional rotations, with a peak speed of up to 884 rpm. Leveraging this excellent humidity-responsive property, we have successfully implemented MFs as advanced actuators, such as remote rain indicators, smart switches, and smart curtains.

[0085] The above is merely a preferred embodiment of the present invention. Based on the above-mentioned concepts, those skilled in the art may make various modifications and variations. For example, variations such as the diameter of the silicone tube mold for fiber production, the ratio and amount of solid culture medium and liquid culture medium, and the twisting method and degree are all within the spirit of the present invention. However, such variations and modifications are inherent to the present invention.

[0086] It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing ultra-high strength ultra-sensitive moisture-responsive fiber, characterized in that The method comprises the following steps: S1. Cultivation of cellulose hydrogel tubes using Bacillus xylosus will carry Xylella fastidiosa ( Komagataeibacter xylinus ) The culture medium of live bacteria was injected into a hollow silicone tube with a diameter of 2 mm. The two ends of the silicone tube were clamped and cultured at 30℃±5℃ for 3-5 days. The synthetic cellulose hydrogel tube TB was removed from the silicone tube. The strain number of the xylosaccharinobacterium is CICC 10529; The culture medium is HS medium, containing 25.0 g / L glucose, 2.5 g / L Na2HPO4, 1.15 g / L citric acid, 5.0 g / L yeast extract, and 5.0 g / L peptone; S2. Purification of cellulose hydrogel tubes TB was soaked in 0.3 M sodium hydroxide solution for more than 24 h and then washed with water; Repeat soaking and washing at least three times to remove culture medium components and attached bacteria; Finally, the TB was washed thoroughly with water until the pH of the washing solution was neutral; S3. Conversion of cellulose hydrogel tubes into bacterial cellulose fibers via tension-assisted twisting While applying tension at both ends of the fiber to increase its length by 20-30%, 10-30 cm long wet TB is twisted with 8-10 twists / cm, and then the two ends are fixed with clips. The twisted material under tension is fixed in shape and dried at room temperature to obtain a finished cellulose fiber.

2. The preparation method according to claim 1, wherein: The HS medium described in S1 was sterilized at 121°C for 20 min until use.

3. The preparation method according to claim 1, wherein: The size of the hollow silicone tube S1 is 10-30 cm long.

4. An ultra-high strength and ultra-sensitive moisture-responsive fiber prepared by the preparation method according to claim 1.

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