Preparation and application of nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber

Abstract

The invention belongs to the field of new materials, and particularly relates to preparation and application of nano-silver / dialdehyde chitosan / cellulose composite aerogel fibers. The preparation method of the composite aerogel fiber comprises the following steps: (1) adding sodium periodate and ethylene glycol into a chitosan acetic acid aqueous solution, dialyzing a reaction solution, and freeze-drying to obtain dialdehyde chitosan; (2) mixing pulp powder with the dialdehyde chitosan prepared in the step (1), adding ionic liquid for dissolving to obtain a dialdehyde chitosan / cellulose solution, and performing spinning treatment to obtain composite aerogel fibers; and (3) adding the composite aerogel fiber obtained in the step (2) and a silver nitrate solution into an alkaline solution, and carrying out pre-freezing and freeze-drying treatment to obtain the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber. The composite aerogel fiber has excellent mechanical properties, thermal stability, heat insulation performance, hydrophobicity and photothermal conversion capability, so that the composite aerogel fiber has application potential in hydrophobic textiles and heat insulation textiles.

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and particularly relates to the preparation and application of a nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber. Background Art

[0002] With the increasing urgency of the global demand for sustainable development, the development of new materials with high performance, environmental friendliness and multifunctionality has become the core topic in the field of materials science. In this context, bio-based polymer materials have attracted much attention due to their remarkable advantages such as renewability, biodegradability and low toxicity. Among them, cellulose and chitosan, as representatives of natural polysaccharides, are considered ideal matrices for constructing green functional materials. However, single-component natural polymer materials often have difficulty meeting the requirements of high-end applications due to their functional limitations (such as weak antibacterial properties and insufficient mechanical properties). It is worth noting that in recent years, through multi-component composite and structural design strategies, combined with nanotechnology to endow materials with multifunctional properties, has become an important way to break through the application bottleneck of natural polymers. Under this development trend, the research and development of nano-silver (AgNPs) / dialdehyde chitosan (DCS) / cellulose composite aerogel fibers not only provides new ideas for the development of high-performance bio-based materials, but also shows broad prospects in the fields of environmental governance, biomedicine and smart wearable devices.

[0003] As the most abundant natural polymer in nature, cellulose has excellent mechanical strength, processability and biocompatibility, but its chemical inertness and single functionality limit its application in the fields of antibacterial and catalysis. Chitosan, as the deacetylation product of chitin, is widely used in drug carriers and wound dressings due to its cationic properties, antibacterial activity and biodegradability. However, its poor mechanical properties and easy swelling defects still need to be improved urgently. Chitosan molecules have hydroxyl and amino groups on their molecular chains, which have active chemical properties. Therefore, it can be easily modified through molecular design. Selectively oxidizing the hydroxyl and amino groups on the chitosan molecular chain with sodium periodate to introduce dialdehyde groups not only retains the antibacterial and biocompatible properties of chitosan, but also endows it with high reactivity (such as Schiff base reaction with amino groups) and enhanced stability. The reducibility of the aldehyde groups of DCS can be used to in-situ reduce and stabilize metal nanoparticles (such as AgNPs), thus providing an ideal platform for constructing multifunctional composite materials.

[0004] AgNPs have become key additives for enhancing material functionality due to their broad-spectrum antibacterial properties, surface plasmon resonance effects, and catalytic activity. However, the problems of easy aggregation and poor chemical stability of AgNPs lead to a decrease in their activity, and traditional loading methods (such as physical mixing) often result in the detachment of nanoparticles due to weak interfacial binding forces. In addition, the preparation processes of existing AgNPs composite materials mostly rely on toxic reducing agents (such as sodium borohydride) or organic solvents, which do not conform to the principles of green chemistry. Therefore, how to stably load AgNPs onto biobased materials through green and efficient methods and achieve functional synergy remains a difficult point in current research.

[0005] Although previous studies have reported the preparation of AgNPs / chitosan or cellulose composite materials, their application in the field of aerogel fibers still faces many challenges: First, the structural stability is insufficient, and the porous structure of the aerogel easily leads to uneven distribution or detachment of AgNPs; Second, the interfacial compatibility is poor, and the polarity difference between cellulose and chitosan leads to phase separation, directly affecting the mechanical properties and functional expression of the composite material; Finally, the preparation process is complex, and most methods require multiple-step chemical modification or high-temperature treatment, with high energy consumption and difficulty in scaling up.

[0006] To address the above problems, this study proposes an innovative "one-pot" green preparation strategy: using dialdehyde chitosan (DCS) as a reducing agent, controllably synthesizing AgNPs in an aqueous phase through the reducibility of its aldehyde groups, and finally preparing composite aerogel fibers with a porous structure through freeze-drying technology. Summary of the Invention

[0007] Aiming at the problems and deficiencies in the existing technology, the purpose of the present invention is to provide a preparation and application of silver nanoparticles / dialdehyde chitosan / cellulose composite aerogel fibers.

[0008] To achieve the purpose of the invention, the technical solutions adopted by the present invention are as follows:

[0009] In the first aspect, the present invention provides a preparation method of silver nanoparticles / dialdehyde chitosan / cellulose composite aerogel fibers, comprising the following steps:

[0010] (1) Add sodium periodate to an aqueous acetic acid solution of chitosan, stir and react at 20 - 60 °C for 2 - 6 h, then add 1 - 5 ml of ethylene glycol to terminate the reaction, dialyze the reaction solution, and freeze-dry to obtain dialdehyde chitosan;

[0011] (2) Mix pulp powder with the dialdehyde chitosan prepared in step (1) to obtain a mixture, add the mixture to an ionic liquid, stir and dissolve to obtain a dialdehyde chitosan / cellulose solution; subject the dialdehyde chitosan / cellulose solution to spinning treatment to obtain composite aerogel fibers; wherein, when performing spinning treatment, water is used as the coagulation bath.

[0012] (3) Add the composite aerogel fiber obtained in step (2) and silver nitrate solution to the alkaline solution, stir and react at 20-60 °C for 0.5-2 h. After the reaction, subject the reaction system to pre-freezing and freeze-drying treatments to obtain the silver nanometer / dialdehyde chitosan / cellulose composite aerogel fiber.

[0013] Preferably, in step (1), the temperature of the stirring reaction is 50 °C and the time of the stirring reaction is 4 h; in step (3), the temperature of the stirring reaction is 40 °C and the time of the stirring reaction is 2 h.

[0014] Preferably, in step (3), the alkaline solution is ammonia water and the dosage of the ammonia water is 1-5 ml; more preferably, the dosage of the ammonia water is 5 ml.

[0015] Preferably, in step (1), the mass ratio of sodium periodate to chitosan is 0.5-2:1.

[0016] More preferably, the mass ratio of sodium periodate to chitosan is 1:1.

[0017] Preferably, in step (1), the mass concentration of chitosan in the chitosan acetic acid aqueous solution is 0.01-0.05 g / ml.

[0018] More preferably, the mass concentration of chitosan in the chitosan acetic acid aqueous solution is 0.02 g / ml.

[0019] Preferably, in step (2), by mass percentage, the content of pulp powder in the mixture is 80%-95%, and the content of dialdehyde chitosan is 5%-20%.

[0020] Preferably, in step (3), the mass ratio of the composite aerogel fiber to the silver nitrate solution is 1:20-50.

[0021] More preferably, the mass ratio of the composite aerogel fiber to the silver nitrate solution is 1:40.

[0022] Preferably, in step (3), the mass concentration of the silver nitrate solution is 0.05-0.2 g / ml.

[0023] More preferably, the mass concentration of the silver nitrate solution is 0.1 g / ml.

[0024] Preferably, in step (3), the temperature of the pre-freezing is -10--40 °C and the time of the pre-freezing is 6-12 h.

[0025] More preferably, the temperature of the pre-freezing is -20 °C and the time of the pre-freezing is 12 h.

[0026] Preferably, in step (3), the temperature of the freeze-drying is -30 to -50 °C, and the time of the freeze-drying is 12 to 24 h.

[0027] More preferably, the temperature of the freeze-drying is -40 °C, and the time of the freeze-drying is 12 h.

[0028] Preferably, in step (2), the stirring temperature is 50 to 100 °C, and the stirring time is 0.5 to 2 h.

[0029] More preferably, the stirring temperature is 90 °C, and the stirring time is 1 h.

[0030] Preferably, in step (2), the ionic liquid is 1-ethyl-3-methylimidazolium acetate (EmimOAc). Preferably, in step (2), the spinning treatment includes the following steps: Pour the obtained cellulose solution into a dry spinning can, transfer the spinning can to a vacuum drying oven, and perform degassing treatment under certain pressure and temperature. Install the spinning can on the spinning frame, turn on the oil-free silent air compressor, and set the spinning temperature to 70 °C. Open the air jet valve, adjust the spinning pressure, and start spinning. The spinning solution is stretched through the air gap and then enters the coagulation bath filled with water to regenerate aerogel fibers, and then enters the second coagulation bath (water) after being stretched by a drawing machine to obtain aerogel fibers.

[0031] In the second aspect, the present invention provides a nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber prepared by the method described in the first aspect.

[0032] In the third aspect, the present invention provides the application of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber described in the second aspect in hydrophobic textiles and heat-insulating textiles.

[0033] Compared with the prior art, the positive and beneficial effects achieved by the present invention are as follows:

[0034] 1. The present invention proposes an innovative "one-pot" green preparation strategy to prepare a nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber with high porosity and high specific surface area (the preparation process is as Figure 1 shown). Cellulose is used as the aerogel matrix, and sodium periodate is used to selectively oxidize the hydroxyl and amino groups on the chitosan molecular chain to introduce dialdehyde groups, which not only retains the antibacterial and biocompatible properties of chitosan, but also endows it with high reactivity and high stability, and can be used as a reducing agent and chelating agent for AgNPs; AgNO3 penetrates into the pores inside the aerogel fiber, and under the action of dialdehyde chitosan, Ag +It was in-situ reduced to AgNPs. Due to the chelation between dialdehyde chitosan and AgNPs, AgNPs can be firmly fixed inside the aerogel fiber. Finally, highly porous and high specific surface area silver nanocomposite / dialdehyde chitosan / cellulose aerogel fibers were obtained by freeze-drying.

[0035] 2. The silver nanocomposite / dialdehyde chitosan / cellulose composite aerogel fiber has excellent mechanical properties (tensile strength 7.6 MPa, elongation at break 43.0%), thermal stability (decomposition temperature > 250 °C), and heat insulation performance (thermal conductivity 0.0521 W / (m·K)). The introduction of AgNPs endows the fiber with hydrophobicity (water contact angle 141°) and photothermal conversion ability (temperature reaches 100 °C under near-infrared light), showing broad application prospects in hydrophobic textiles and heat-insulating textiles. Brief Description of the Drawings

[0036] Figure 1 It is a preparation flow chart of silver nanocomposite / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7;

[0037] Figure 2 It is a polarized light micrograph of cellulose in the pulp powder prepared in Example 2 and dialdehyde chitosan (DCS) prepared in Example 1 in ionic liquid EmimOAc at 90 °C for different times. Among them, (a, b) are polarized light micrographs of cellulose in the pulp powder in ionic liquid EmimOAc at 90 °C for different times; (c, d, e) are polarized light micrographs of DCS in ionic liquid EmimOAc at 90 °C for different times;

[0038] Figure 3 It is a Fourier transform infrared spectroscopy diagram of silver nanocomposite / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2, chitosan (CS), dialdehyde chitosan (DCS) prepared in Example 1, and silver nanocomposite / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7. In the figure, ACCA is ACCA20 prepared in Example 7;

[0039] Figure 4 It is an ultraviolet-visible absorption spectrum of dialdehyde chitosan (DCS) reducing silver nanocomposite prepared in Example 14. The photo in the figure is a digital photo of AgNPs stored in deionized water for 1 month;

[0040] Figure 5 It is an XRD spectrum of silver nanocomposite / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2, dialdehyde chitosan (DCS) prepared in Example 1, and silver nanocomposite / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7. In the figure, ACCA is ACCA20 prepared in Example 7;

[0041] Figure 6 Cross-sectional SEM images and EDS spectra of the nano-silver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7; a1, a2 are cross-sectional SEM images of CE; b1, b2 are cross-sectional SEM images of ACCA05; c1, c2 are cross-sectional SEM images of ACCA10;

[0042] d1, d2 are cross-sectional SEM images of ACCA20; (e) surface morphology of ACCA20; (f - j) EDS spectra of different elements on the surface of ACCA20 fibers;

[0043] Figure 7 TG curves and DTG curves of the nano-silver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7, where (a) TG curves of CE, ACCA05, ACCA10, ACCA20; (b) DTG curves of CE, ACCA05, ACCA10, ACCA20;

[0044] Figure 8 Mechanical property analysis diagrams of the nano-silver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7, where (a) digital photo of ACCA20 bearing a 100 g weight; (b) stress-strain curves of CE, ACCA05, ACCA10, ACCA20; (c) elongation at break of CE, ACCA05, ACCA10, ACCA20; (d) tensile strength of CE, ACCA05, ACCA10, ACCA20;

[0045] Figure 9 Density and porosity diagrams of the nano-silver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7;

[0046] Figure 10 N2 adsorption-desorption isotherm curve and pore size distribution diagram of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7, where (a) N2 adsorption-desorption isotherm curve; (b) pore size distribution curve of ACCA20 obtained based on the desorption of the isotherm;

[0047] Figure 11 Thermal insulation performance diagrams of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7 at different temperatures. Among them, (a) the thermal insulation mechanism of the composite aerogel fiber; (b) the temperature changes of ACCA20 and cellulose cotton fabric on a hot stage at 130 °C; (c) the temperature changes of 1, 2, and 3 layers of ACCA20 on a hot stage at 70 °C; (d) the temperature changes of 1, 2, and 3 layers of ACCA20 on a hot stage at 100 °C; (e) the temperature changes of 1, 2, and 3 layers of ACCA20 on a hot stage at 130 °C; (f) the temperature difference between different layers of ACCA20 and the hot stage at different heating temperatures;

[0048] Figure 12 Thermal conductivities of the nano-silver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7;

[0049] Figure 13 Photothermal performance analysis diagrams of the dialdehyde chitosan / cellulose composite aerogel fiber (denoted as CE-CS) prepared in Example 4 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7; (a) Schematic diagram of the photothermal simulation of ACCA20; (b) Photothermal temperature curve of CE-CS; (c) Photothermal temperature curve of ACCA20; (d) Photothermal cycle images of ACCA20 with and without light illumination; (e) Photothermal mechanism of ACCA20;

[0050] Figure 14 Water contact angle images of the dialdehyde chitosan / cellulose composite aerogel fiber (CE-CS) prepared in Example 4 and the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7, where (a) water contact angle image of CE-CS; (b) water contact angle image of ACCA20. Detailed implementation manners

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] Example 1:

[0053] The preparation of dialdehyde chitosan is carried out according to the following specific steps:

[0054] Add 200 ml of 1% aqueous acetic acid solution to chitosan and stir at 30 °C for 2 h to obtain a uniform aqueous chitosan acetate solution; add sodium periodate to the aqueous chitosan acetate solution, stir and react at 50 °C for 4 h, then add 5 ml of ethylene glycol to terminate the reaction. Place the reaction solution in a dialysis bag (the molecular weight cut-off of the dialysis bag is 3500 Da) and dialyze with deionized water for 7 days. Subsequently, freeze-dry the dialyzed solution to obtain powdery dialdehyde chitosan (DCS); the mass ratio of sodium periodate to chitosan is 1:1; the mass concentration of chitosan in the aqueous chitosan acetate solution is 0.02 g / ml.

[0055] Example 2:

[0056] Preparation of composite aerogel fiber, the specific steps are as follows:

[0057] (1) Cut the pulp board into pieces, wash with deionized water to remove impurities, and then place it in a drying oven to dry at 50 °C for 12 h to obtain pulp powder;

[0058] (2) Mix the pulp powder with the dialdehyde chitosan prepared in Example 1 to obtain 1.2 g of a mixture. Add the mixture to 18.8 g of ionic liquid, seal and stir at 90 °C for 1 h to obtain a dialdehyde chitosan / cellulose solution; the content of pulp powder in the mixture is 95%, and the content of dialdehyde chitosan is 5%;

[0059] (3) Pour the obtained dialdehyde chitosan / cellulose solution into a dry spinning can (the diameter of the spinneret is 1 mm), transfer the spinning can to a vacuum drying oven, and perform degassing treatment at a pressure of -0.1 MPa and a temperature of 90 °C to eliminate the internal bubbles of the solution. After cleaning the coagulation bath, add a certain amount of deionized water to the bath to submerge the pulley. Install the spinning can on the spinning frame, turn on the oil-free silent air compressor, set the distance between the spinning can and the coagulation bath liquid surface to 30 mm, and set the spinning temperature to 70 °C. Open the jet valve, adjust the spinning pressure to 0.1 MPa, and start spinning. The spinning solution is stretched through the air gap and then enters the coagulation bath of deionized water to regenerate the composite aerogel fiber, and then enters the second coagulation bath (deionized water) after being stretched by a drafting machine to obtain the composite aerogel fiber.

[0060] Example 3:

[0061] The content of Example 3 is basically the same as that of Example 2, and the difference is that in step (2), the content of pulp powder in the mixture is 90%, and the content of dialdehyde chitosan is 10%.

[0062] Example 4:

[0063] The content of Example 4 is basically the same as that of Example 2, and the difference lies in that: in step (2), the mass content of pulp powder in the mixture is 80%, and the mass content of dialdehyde chitosan is 20%.

[0064] Example 5:

[0065] Preparation of silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA05), the specific steps are as follows:

[0066] Add 40 ml of silver nitrate solution and 5 ml of ammonia water to the composite aerogel fiber obtained in Example 2, heat at 40 °C for 2 h to obtain a composite aerogel fiber. The obtained composite aerogel fiber is pre-frozen at -20 °C for 12 h, and then freeze-dried at -40 °C for 12 h to obtain silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA05). The mass ratio of the composite aerogel fiber to the silver nitrate solution is 1:40; the mass concentration of the silver nitrate solution is 0.1 g / ml.

[0067] Example 6:

[0068] Preparation of silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA10), the specific steps are as follows:

[0069] Add 40 ml of silver nitrate solution and 5 ml of ammonia water to the composite aerogel fiber obtained in Example 3, heat at 40 °C for 2 h to obtain a composite aerogel fiber. The obtained composite aerogel fiber is pre-frozen at -20 °C for 12 h, and then freeze-dried at -40 °C for 12 h to obtain silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA10). The mass ratio of the composite aerogel fiber to the silver nitrate solution is 1:40; the mass concentration of the silver nitrate solution is 0.1 g / ml.

[0070] Example 7:

[0071] Preparation of silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20), the specific steps are as follows:

[0072] Add 40 ml of silver nitrate solution and 5 ml of ammonia water to the composite aerogel fiber obtained in Example 4, heat at 40 °C for 2 h to obtain a composite aerogel fiber. The obtained composite aerogel fiber is pre-frozen at -20 °C for 12 h, and then freeze-dried at -40 °C for 12 h to obtain silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20). The mass ratio of the composite aerogel fiber to the silver nitrate solution is 1:40; the mass concentration of the silver nitrate solution is 0.1 g / ml.

[0073] Example 8:

[0074] The content of Example 8 is basically the same as that of Example 1, except that: the heating temperature is 20°C and the heating time is 2 h; the mass ratio of sodium periodate to chitosan is 0.5∶1; the mass concentration of chitosan in the chitosan acetic acid aqueous solution is 0.01 g / ml.

[0075] Example 9:

[0076] The content of Example 9 is basically the same as that of Example 1, except that: the heating temperature is 60°C and the heating time is 6 h; the mass ratio of sodium periodate to chitosan is 2∶1; the mass concentration of chitosan in the chitosan acetic acid aqueous solution is 0.05 g / ml.

[0077] Example 10:

[0078] The content of Example 10 is basically the same as that of Example 2, except that: in step (2), the stirring temperature is 50°C and the stirring time is 0.5 h.

[0079] Example 11:

[0080] The content of Example 11 is basically the same as that of Example 2, except that: in step (2), the stirring temperature is 100°C and the stirring time is 2 h.

[0081] Example 12:

[0082] The content of Example 12 is basically the same as that of Example 5, except that: the heating temperature is 20°C and the reaction time is 0.5 h; the pre-freezing temperature is -10°C and the pre-freezing time is 6 h; the mass ratio of the composite aerogel fiber to the silver nitrate solution is 1∶20; the mass concentration of the silver nitrate solution is 0.05 g / ml.

[0083] Example 13:

[0084] The content of Example 13 is basically the same as that of Example 5, except that: the heating temperature is 60°C and the heating time is 1 h; the pre-freezing temperature is -40°C and the pre-freezing time is 8 h; the mass ratio of the composite aerogel fiber to the silver nitrate solution is 1∶50; the mass concentration of the silver nitrate solution is 0.2 g / ml.

[0085] Comparative Example 1:

[0086] The preparation of the aerogel fiber is specifically carried out according to the following steps:

[0087] (1) Cut the pulp board into pieces, wash it with deionized water to remove impurities, and then put it into a drying oven to dry at 50°C for 12 h to obtain pulp powder;

[0088] (2) Add 1.2 g of pulp powder to 18.8 g of EmimOAc, seal it, and stir at 90 °C for 1 h to obtain a uniform cellulose solution;

[0089] (3) Pour the obtained cellulose solution into a dry spinning can (the diameter of the spinneret is 1 mm), transfer the spinning can to a vacuum drying oven, and perform degassing treatment at a pressure of -0.1 MPa and a temperature of 90 °C to eliminate the internal bubbles in the solution. After cleaning the coagulation bath, add a certain amount of deionized water to the bath to submerge the pulley. Install the spinning can on the spinning frame, turn on the oil-free silent air compressor, set the distance between the spinning can and the coagulation bath liquid surface to 30 mm, and set the spinning temperature to 70 °C. Open the air jet valve, adjust the spinning pressure to 0.1 MPa, and start spinning. The spinning solution is stretched through the air gap and then enters the deionized water coagulation bath to regenerate aerogel fibers, and then enters the second coagulation bath (deionized water) after being stretched by a drafting machine to obtain aerogel fibers.

[0090] Comparative Example 2:

[0091] Preparation of silver nanowire / cellulose composite aerogel fibers (CE), the specific steps are as follows:

[0092] Add 40 ml of silver nitrate solution and 5 ml of ammonia water to the aerogel fibers obtained in Comparative Example 1, heat at 40 °C for 2 h, pre-freeze the reaction system at -20 °C for 12 h after the reaction ends, and then freeze-dry at -40 °C for 12 h to obtain silver nanowire / cellulose composite aerogel fibers (CE). The mass ratio of the composite aerogel fibers to the silver nitrate solution is 1:40; the mass concentration of the silver nitrate solution is 0.1 g / ml.

[0093] Characterization and performance testing of silver nanowire / dialdehyde chitosan / cellulose composite aerogel fibers

[0094] (1) Structural analysis of silver nanowire / dialdehyde chitosan / cellulose composite aerogel fibers

[0095] To evaluate the dissolution ability of cellulose in the pulp powder prepared in Example 2 and dialdehyde chitosan (DCS) prepared in Example 1 in the ionic liquid EmimOAc, a polarized light microscope was used to observe their dissolution behavior. From Figure 2 It can be seen that bright cellulose can be observed without heating. When heated at 90 °C for 30 minutes, the field of view becomes completely dark, indicating that the cellulose has completely dissolved in the ionic liquid; when DCS is not heated, bright DCS can be observed. When DCS is heated at 90 °C for 15 minutes, the field of view becomes dark, indicating that it dissolves slowly. When heated for 30 min, the bright area completely disappears, indicating that DCS has completely dissolved. The above results show that EmimOAc has good dissolution ability for both cellulose and DCS, providing a technical basis for the subsequent spinning process.

[0096] Fourier transform infrared spectra of chitosan (CS), nano silver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2, dialdehyde chitosan (DCS) prepared in Example 1, and nano silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7 are as follows Figure 3 shown. From Figure 3 it can be seen that in the infrared spectrum of CS, the characteristic peak at 1650 cm -1 corresponds to the stretching vibration of C=O in the residual acetyl group, the one at 1550 cm -1 corresponds to the bending vibration of N-H in amide II band, and the characteristic peak at 1380 cm -1 corresponds to the stretching vibration of C-N. Compared with CS, a new peak appears at 1749 cm -1 in DCS, which belongs to the characteristic absorption peak of C=O in the aldehyde group, indicating the successful preparation of DCS; the characteristic peak at 3400 cm -1 corresponds to the stretching vibration peak of O-H (N-H) of cellulose and chitosan, and the characteristic peak at 2919 cm -1 is the stretching vibration absorption peak of C-H. At the same time, the above absorption peaks all appear in the infrared spectrum of ACCA20, indicating that DCS has been successfully introduced into cellulose.

[0097] Due to their extremely high specific surface area and surface free energy, nanomaterials are often in a thermodynamically metastable state. This property leads to strong interactions between nanoscale particles, resulting in particle aggregation. Research shows that the active groups in the dialdehyde chitosan molecule can coordinate with the surface of nanoparticles, regulate the surface energy of the particles by changing the interfacial properties, and thus enhance the stability of the nano-dispersion system. The specific steps for dialdehyde chitosan to reduce nano silver are as follows: Take 0.01 g of the dialdehyde chitosan (DCS) sample in Example 1, disperse it in water, add 1 ml of silver nitrate solution and 0.1 ml of ammonia water, mix well, and heat at 40 °C for 2 h to obtain a dialdehyde chitosan / nano silver (DCS-Ag) dispersion. Digital photos of DCS-Ag kept at room temperature for 2 months and the corresponding ultraviolet-visible absorption spectra are as follows Figure 4 shown. From the Figure 4 digital photos, it can be seen that the DCS-Ag system is in a stable state and has an obvious Tyndall phenomenon; from the Figure 4 ultraviolet-visible absorption spectra, it can be known that the characteristic peak at 415 nm is the surface plasmon resonance peak of nano silver, confirming the successful preparation of a stable DCS / AgNPs dispersion system.

[0098] XRD detection was performed on the nanosilver / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2, the dialdehyde chitosan (DCS) prepared in Example 1, and the nanosilver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7. The detection results are as follows: Figure 5 As shown. Figure 5 It can be seen that CE showed a characteristic peak of cellulose II at 2θ=21.8°, corresponding to the (020) crystal plane of regenerated cellulose, and DCS showed a crystal diffraction peak of chitosan at 2θ=21.5°. ACCA20 showed a composite diffraction peak of cellulose and chitosan at 2θ=21.8°, indicating the successful composite of dialdehyde chitosan and cellulose. The crystal diffraction peaks of silver in ACCA20 were 2θ=38°, 44° and 64°, corresponding to the (111), (200) and (220) crystal planes of silver, respectively, indicating that nanosilver was firmly fixed on chitosan through the chelation of aldehyde and amino groups and successfully composited with cellulose.

[0099] (2) Micromorphology analysis of nanosilver / dialdehyde chitosan / cellulose composite aerogel fibers

[0100] The nanosilver / cellulose composite aerogel fibers (CE) prepared in Comparative Example 2 and the nanosilver / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7 were subjected to cross-sectional SEM detection and EDS energy spectrum analysis. The results are as follows: Figure 6 As shown. Figure 6 From a1 to d2, it can be seen that the composite aerogel fibers have a relatively obvious skin-core structure, which is caused by the inconsistent shrinkage of the surface and the inside during liquid nitrogen brittle fracture. In addition, several fibers have large diameters, indicating that the collapse of the aerogel structure is not obvious during freeze-drying. Figure 6 As shown in a2, b2, c2, and d2, several composite aerogel fibers have large pores and high porosity, forming a three-dimensional network structure composed of cellulose chains, which further verifies the successful preparation of composite aerogel fibers. As shown in Figures b2, c2, and d2, when the proportion of dialdehyde chitosan is increased, the internal skeleton density of the composite aerogel fiber gradually decreases. This is due to the reduction in the content of the cellulose matrix. When sodium periodate oxidizes chitosan, it destroys the β-1,4 glycosidic bond, resulting in the generation of DCS with a smaller molecular weight. These DCS will not participate in the chain entanglement with the cellulose molecular chain due to their short molecular chains, which will reduce the internal skeleton density of the aerogel to a certain extent. Figure 6 e is the surface morphology of ACCA20. Different from the cross-sectional morphology, its surface is relatively dense. The reason is that during the fiber forming process, the surface is first in contact with the coagulation bath, and the fiber surface gels rapidly, resulting in a denser surface structure.

[0101] Figure 6 Images f - j are EDS spectra analysis images of different elements on the surface of ACCA20 fibers. As Figure 6 shown in f and 6g, it can be clearly seen that Ag is attached to the surface of ACCA20 fibers and is small in size, further indicating the successful synthesis of silver nanoparticles on the aerogel fibers; from Figure 6 h - j, it can be known that ACCA20 contains elements C, O, and N.

[0102] (3) Thermal stability analysis of silver nanoparticle / dialdehyde chitosan / cellulose composite aerogel fibers

[0103] The thermal stability of the composite aerogel fibers was analyzed by thermogravimetric analysis. Figure 7 TG curves and DTG curves are for the silver nanoparticle / cellulose composite aerogel fibers (CE) prepared in Comparative Example 2 and the silver nanoparticle / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 - 7. Figure 7 a) The TG curve can be divided into three stages: The first stage is from room temperature to about 150 °C. In this stage, mainly the loss of free water in the fiber occurs, and the mass change is small; the second stage is the decomposition of organic substances such as cellulose and chitosan in the composite fiber. Obvious mass loss starts from around 250 °C, and the organic substances are gradually decomposed into gases such as water, CO, and CO2. The mass change in this stage is large; the third stage is the carbonization stage of the organic substances. When the temperature exceeds 350 °C, the mass loss rate of the sample reaches 60% - 70%. This stage corresponds to the further cracking of the organic substances, generating gases and a small amount of solid carbon, and this stage is also a process of slow weight loss. For ACCA10 and ACCA20, the mass loss rate at 600 °C is significantly lower than that of CE and ACCA05 ( Figure 7 a), which is due to the Ag reduced by DCS remaining in the solid, resulting in an increase in the remaining mass. From Figure 7 b, it can be seen that the positions of the weight loss peaks of ACCA05, ACCA10, and ACCA20 do not change significantly compared with CE, indicating that the introduction of DCS and Ag does not affect the thermal stability of the composite fibers. At the same time, the thermal decomposition temperature of all fibers is above 250 °C, which can meet the stable use of fibers or fabrics in most environments.

[0104] (4) Mechanical property analysis of silver nanoparticle / dialdehyde chitosan / cellulose composite aerogel fibers

[0105] For heat-insulating fabrics, composite fibers need to have a large porosity to obtain good heat-insulating performance. However, this will cause problems such as increased structural defects and reduced mechanical strength, which is not conducive to the production and manufacturing of textiles. Therefore, it is crucial to maintain the balance between thermal stability and mechanical properties. The mechanical properties of the silver nanoparticles / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the silver nanoparticles / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7 were analyzed, as Figure 8 shown. As Figure 8 shown in a, ACCA20 has good tensile strength and can withstand a 100 g weight without breaking. As Figure 8 shown in b - d, several composite aerogel fibers all have good mechanical properties. The maximum tensile strength of CE reaches 12.5 MPa, and the elongation at break reaches 52.0%. Although the strength and elongation at break of the composite aerogel fibers both decrease with the increase in the DCS content, ACCA20 can still maintain a tensile strength of 7.6 MPa and an elongation at break of 43.0%, which reflects the excellent mechanical properties of cellulose as the matrix. Through SEM cross-section analysis, since the density of the composite aerogel fiber skeleton decreases with the increase in the DCS ratio, it shows that the introduction of DCS and AgNPs will weaken the density of hydrogen bonds in the cellulose chain, resulting in a decrease in mechanical properties.

[0106] (5) Porosity and specific surface area analysis of silver nanoparticles / dialdehyde chitosan / cellulose composite aerogel fibers

[0107] Generally, for heat-insulating fabrics, fibers need to have a large porosity to obtain excellent heat-insulating performance. The density and porosity of the silver nanoparticles / cellulose composite aerogel fiber (CE) prepared in Comparative Example 2 and the silver nanoparticles / dialdehyde chitosan / cellulose composite aerogel fibers (ACCA05, ACCA10, ACCA20) prepared in Examples 5 to 7 were analyzed, as Figure 9 shown. As Figure 9 shown, the density of CE is 0.085 g / cm 3 , which is much smaller than the density of dry fibers (about 1 g / cm 3 ). In addition, with the increase in the DCS ratio, the density of the composite aerogel fibers gradually increases, while the porosity changes little. This is because when the DCS content increases, the content of reduced silver nanoparticles also increases accordingly. Therefore, the density of the composite aerogel fibers gradually increases, but the volume of the composite aerogel fibers changes little, so it will not affect its porosity.

[0108] The BET method was used to further study the specific surface area and pore size distribution of ACCA20 prepared in Example 7, and the results are shown in Figure 10. As Figure 10As shown in Figure a, the N2 adsorption and desorption isotherms of ACCA20 conform to the type-IV isotherm and have an obvious hysteresis loop, indicating that the prepared composite aerogel fiber has a mesoporous structure; the specific surface area of ACCA20 is as high as 129 m 2 / g. The pore size distribution curve obtained based on the desorption of the isotherm is shown in Figure 10 Figure b. The most probable pore size of ACCA20 within the mesoporous range is 22 nm. These results indicate that the prepared ACCA20 has a smaller pore size and a larger specific surface area.

[0109] (6) Thermal insulation performance analysis of nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber

[0110] The thermal insulation performance of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7 was detected at different temperatures. The specific detection method was as follows: The composite aerogel fiber sample was woven into a fabric and fixed on a heating platform, and a thermal imaging camera (FLIR ONE PRO, USA) was used to record the temperature changes during the heating and cooling processes of the fabric surface, and near-infrared images were obtained by taking pictures at certain time intervals. The thermal insulation performance was detected by performing a heating / cooling cycle by turning the heating platform on / off, and the experimental results are shown in Figure 11 Figure.

[0111] Figure 11 Figure a shows the thermal insulation mechanism of the composite aerogel fiber. The composite aerogel fiber has a high porosity, and heat conduction mainly depends on the vibration of the material skeleton (phonon transfer). The high porosity significantly reduces the proportion of the solid skeleton, thereby greatly reducing the solid-state thermal conductivity; at the same time, most of the pores inside the composite aerogel fiber are nanoscale (<100 nm), resulting in the mean free path (molecular collision spacing) of gas molecules (such as air) being much larger than the pore size. At this time, the collision frequency of gas molecules with the pore wall is much higher than the intermolecular collision, and it is difficult for gas molecules to transfer heat through free movement, significantly reducing gas convection heat transfer and gas thermal conductivity. To visually evaluate the thermal insulation performance of ACCA20, the temperature difference (|ΔT|) between the surface temperature of ACCA20 and the cellulose cotton fabric and the surface temperature of the hot stage was calculated. As shown in Figure 11 Figure b, the thermal insulation performance of ACCA20 is much higher than that of the cellulose cotton fabric. The ΔT of the cellulose cotton fabric is only 14.7 °C when heated on a 130 °C hot stage, while the ΔT of ACCA20 can reach 33.1 °C, which is 2.3 times that of the cellulose cotton fabric, showing excellent thermal insulation performance. Figure 11 Figures c to e are the time-temperature curves of the surface temperature of 1, 2, and 3 layers of ACCA20 simply stacked and the hot stage at different temperatures. From Figure 11It can be seen from c to 11e that the ΔT of the single-layer ACCA20 on a hot stage at 70 °C is 14.9 °C. When the hot stage temperature rises to 100 °C and 130 °C respectively, the ΔT of the single-layer ACCA20 increases to 22.5 °C and 34.1 °C. From Figure 11 e, it can be seen that when the hot stage temperature is 130 °C, increasing the number of ACCA20 layers can effectively enhance its heat insulation performance. When the number of ACCA20 layers increases from a single layer to three layers, its ΔT also increases from 34.1 °C to 55.1 °C. From Figure 11 f, it can be seen that the more the number of ACCA20 layers, the lower the heat transfer rate and the greater the temperature difference. Moreover, this heat insulation performance is more obvious at high temperatures. Therefore, the heat insulation of any object's contact surface can be adjusted by further changing the number of fabric layers within a certain temperature range to regulate the overall heat insulation performance.

[0112] The thermal conductivity of the ACCA20 fiber was further measured using a thermal conductivity meter ( Figure 12 ), and it can be seen from Figure 12 that the thermal conductivity of ACCA20 is 0.0521 W / (m·K), which is much lower than that of CE at high temperature and dry conditions. This shows that the relatively high porosity of ACCA20 is the key to its excellent heat insulation performance. Generally, the heat flux through an object is proportional to the temperature difference across the object. The thermal conductivity of composite aerogel fibers also shows an increasing trend. Heat transfer is mainly achieved through three basic methods: conduction, convection, and radiation. The increase in temperature leads to an acceleration of molecular thermal motion, which promotes heat conduction in the solid skeleton and convective heat transfer in the pores. Radiative heat transfer between pore walls also increases at higher temperatures. However, high-porosity composite aerogel fibers and textiles can block all three heat transfer methods. Gas thermal conduction is the heat transfer method of most low-density composite aerogel fibers under environmental conditions. Gas conduction mainly depends on the pore diameter and mean free path of air molecules in the porous structure. If the pore diameter is smaller than the mean free path of air molecules (<50 nm), the so-called Knudsen effect occurs, and gas thermal conduction will be significantly reduced, thereby reducing the thermal conductivity. In addition, the large number of pore walls in composite aerogel fibers increases the interfacial thermal resistance and limits the propagation of thermal radiation in the fibers. Moreover, convective heat transfer requires the gas to be transported along the temperature gradient within the material. Therefore, when the pore diameter of the insulating material is small enough (<1 mm), the contribution of convection can be ignored. Although the diameter of ACCA20 is small, textiles based on ACCA20 still have good heat insulation performance over a wide temperature range, making it have great potential in the field of personal thermal management.

[0113] (7) Photothermal performance analysis of silver nanowire / dialdehyde chitosan / cellulose composite aerogel fiber

[0114] The solar spectrum is mainly composed of ultraviolet light (280 - 400 nm), visible light (400 - 760 nm), and near-infrared radiation (NIR) light (760 - 2500 nm), accounting for 3%, 44%, and 53% of solar energy respectively. One of the key strategies to improve the photothermal conversion efficiency is to broaden the absorption band. As is well known, noble metal nanostructures have the localized surface plasmon resonance (LSPR) effect, endowing them with excellent photothermal conversion capabilities. The random and wide size distribution of AgNPs can generate a series of plasmon resonances at different optical wavelengths, and the plasmon near-field coupling effect can be excited from the gaps (less than 10 nm) between adjacent metal nanoparticles, thus showing extremely high absorption efficiency for near-infrared light. The photothermal properties of the silver nanometer / bisaldehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7 were analyzed and characterized, and compared with CE-CS at the same time. The results are as Figure 13 shown. Among them, Figure 13 a is the schematic diagram of the photothermal simulation of ACCA20. As can be seen from Figure 13 b and 13c, under the irradiation of near-infrared light, the maximum temperature of ACCA20 can reach above 100 °C, significantly higher than the temperature of CE-CS (34 °C). As can be seen from Figure 13 c, at the starting stage, the temperature of ACCA20 rises sharply and then enters the equilibrium state with the temperature remaining stable; when the near-infrared lamp is turned off, the temperature of ACCA20 drops sharply and quickly returns to near room temperature, indicating that ACCA20 has very excellent near-infrared response ability and good photothermal conversion efficiency. Figure 13 d shows the temperature change of ACCA20 with / without near-infrared light irradiation. The results show that ACCA20 has very excellent photothermal stability performance. Combining with the high-temperature heat insulation performance of ACCA20, it has great application potential in personal thermal management.

[0115] (8) Water contact angle analysis of silver nanometer / bisaldehyde chitosan / cellulose composite aerogel fiber

[0116] Cellulose aerogel fiber is easy to absorb moisture, which in turn affects its nano-porous structure. Hydrophobicity can inhibit the reproduction of bacteria and prevent the growth of bacteria. The water contact angle of the silver nanometer / bisaldehyde chitosan / cellulose composite aerogel fiber (ACCA20) prepared in Example 7 was detected. The detection results are as Figure 14 shown. As can be seen from Figure 14 a, CE-CS has a small water contact angle (θ = 47°), and the water droplet is completely absorbed by the fabric within 45 s. This is because there are a large number of oxygen-containing groups in cellulose and bisaldehyde chitosan, endowing the cellulose-based fabric with very excellent hydrophilicity and water absorption. However, due to the loose structure inside the aerogel, the structure is very easy to collapse when contacting water, thus affecting the performance of the composite aerogel fiber. As shown in Figure 14As shown in Fig. b, ACCA20 has a very large water contact angle (θ = 141°) and can still maintain 140° after stabilization, showing good hydrophobic properties. This is because the nano-scale silver particles make the fiber surface rougher, reducing the actual contact area between water and the composite aerogel fiber, similar to the hydrophobic effect caused by the micro-nano multi-level structure in the "lotus leaf effect".

[0117] The above embodiments are specific implementation manners of the present invention, but the implementation manners of the present invention are not limited by the above embodiments. Any combination, change, modification, substitution, or simplification that does not exceed the design idea of the present invention falls within the protection scope of the present invention.

Claims

1. A preparation method of a nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber, characterized in that, It includes the following steps: (1) Sodium periodate is added to the aqueous solution of chitosan acetate, and the mixture is stirred and reacted at 20 - 60 °C for 2 - 6 h. Then, 1 - 5 ml of ethylene glycol is added to terminate the reaction. The reaction solution is dialyzed and then freeze-dried to obtain dialdehyde chitosan; (2) The pulp powder is mixed with the dialdehyde chitosan prepared in step (1) to obtain a mixture. The mixture is added to an ionic liquid and stirred to dissolve to obtain a dialdehyde chitosan / cellulose solution; The dialdehyde chitosan / cellulose solution is subjected to spinning treatment to obtain composite aerogel fibers; Among them, when performing the spinning treatment, water is used as the coagulation bath; (3) The composite aerogel fibers obtained in step (2) and a silver nitrate solution are added to an alkaline solution, and the mixture is stirred and reacted at 20 - 60 °C for 0.5 - 2 h. After the reaction ends, the reaction system is subjected to pre-freezing and freeze-drying treatments to obtain silver nano / dialdehyde chitosan / cellulose composite aerogel fibers.

2. The preparation method of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber according to claim 1, characterized in that, In step (1), the mass ratio of the sodium periodate to the chitosan is 0.5 - 2:

1.

3. The preparation method of the nano silver / dialdehyde chitosan / cellulose composite aerogel fiber according to claim 2, characterized in that, In step (1), the mass concentration of the chitosan in the aqueous solution of chitosan acetate is 0.01 - 0.05 g / ml.

4. The preparation method of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber according to claim 1, wherein In step (2), by mass percentage, the content of the pulp powder in the mixture is 80% - 95%, and the content of the dialdehyde chitosan is 5% - 20%.

5. The preparation method of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber according to claim 1, wherein, In step (3), the mass ratio of the composite aerogel fibers to the silver nitrate solution is 1:20 - 50.

6. The preparation method of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber according to claim 5, characterized in that, In step (3), the mass concentration of the silver nitrate solution is 0.05 - 0.2 g / ml.

7. The preparation method of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber according to any one of claims 5 or 6, characterized in that, In step (3), the temperature of the pre-freezing is -10 - -40 °C, and the time of the pre-freezing is 6 - 12 h.

8. The preparation method of the nano-silver / dialdehyde chitosan / cellulose composite aerogel fiber according to claim 1, wherein In step (2), the stirring temperature is 50 - 100 °C, and the stirring time is 0.5 - 2 h.

9. Silver nano / dialdehyde chitosan / cellulose composite aerogel fibers prepared by using the method according to any one of claims 1 - 8.

10. Application of the silver nano / dialdehyde chitosan / cellulose composite aerogel fibers according to claim 9 in hydrophobic textiles and heat-insulating textiles.

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