CN111620667A

CN111620667A - Aerogel fiber, preparation method and application thereof

Info

Publication number: CN111620667A
Application number: CN202010323700.XA
Authority: CN
Inventors: 周剑; 范俊呈; 易明松
Original assignee: Hunan Bondzer Technology Co ltd; Zeiridium Foshan Industrial Technology Co ltd; Green Intelligent Manufacturing Research Institute Xiangtan University Foshan
Current assignee: Hunan Bondzer Technology Co ltd; Zeiridium Foshan Industrial Technology Co ltd
Priority date: 2020-04-22
Filing date: 2020-04-22
Publication date: 2020-09-04
Anticipated expiration: 2040-04-22
Also published as: CN111620667B

Abstract

The invention relates to aerogel fibers, a preparation method and application thereof. The aerogel fiber comprises an aerogel core layer and a polymer coating layer, the polymer coating layer is of a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer. According to the aerogel fiber provided by the technical scheme of the invention, the polymer coating layer with the porous structure plays a role in protecting the aerogel core layer positioned on the inner side, so that the integrity of the aerogel can be protected from being damaged by external force, and the wide application is facilitated. In addition, the invention also relates to a preparation method of the aerogel fiber and application of the aerogel fiber in building thermal insulation materials, wearable equipment and water-soluble coatings.

Description

Aerogel fiber, preparation method and application thereof

Technical Field

The invention relates to the technical field of aerogel, in particular to aerogel fiber and a preparation method and application thereof.

Background

Aerogels are the least dense materials with densities approaching that of air, and are also porous materials with porosities in excess of 99%, and therefore these properties are the most unique properties in many potential applications.

Biz website recently issued a research report titled "global aerogel market applications (oil and gas, construction, automotive and aerospace, healthcare, high performance coatings, chemical, electronic and other), morphology, species, process type and region — global to 2026 predictions". The 2016 global aerogel market value is reported to be about $ 5.129 billion, and with a 31.8% composite annual growth rate of 2017-2026, the 2026 global aerogel market value is expected to reach $ 80.837 billion.

Aerogel materials are an ideal alternative to insulation materials, being less expensive and readily available than other insulation materials, driving the need for such materials in a variety of end-user applications and industries. Increased globalization and urbanization have led to the development of infrastructure in developed and developing countries, another key factor driving the growth of the global aerogel market. The increasing demand for aerogels has driven the growth of the global aerogel market due to their light diffusing, thermal insulating, and high surface area properties in architectural applications. Furthermore, advances and innovations in materials, increased awareness of product benefits, and the use of aerogels in new application areas are expected to promote growth in the global aerogel market over the projected period. A major and growing trend in the market is the increased awareness of global warming and the increasing need for more environmentally friendly and efficient insulation materials in the construction field, especially in developing countries.

While the most interesting and commercially available aerogel is silica aerogel, interest has expanded to include aerogels based on carbon, organic materials, metals and metal oxides. The ability to shape the aerogel into the desired shape and size is critical to the application of the aerogel. However, aerogels are easily damaged by external forces due to their typically low tensile strength and young's modulus, making them brittle, and difficult to use alone or in combination with other flexible, stretchable, conformable materials (e.g., textiles).

Disclosure of Invention

Based on this, there is a need to provide an aerogel fiber, a method for preparing the same, and applications thereof, aiming at the problem of how to protect the integrity of the aerogel from being damaged by external force.

An aerogel fiber, the aerogel fiber includes an aerogel core layer and a polymer coating layer, the polymer coating layer is a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer.

According to the aerogel fiber provided by the technical scheme of the invention, the polymer coating layer with the porous structure plays a role in protecting the aerogel core layer positioned on the inner side, so that the integrity of the aerogel can be protected from being damaged by external force, and the wide application is facilitated.

In one embodiment, the material of the aerogel core layer is selected from at least one of conductive polymer and nanocellulose;

the conductive polymer is at least one selected from a mixture of poly (3, 4-ethylenedioxythiophene) and sodium polystyrene sulfonate, polypyrrole and polyaniline;

the nano-cellulose contains a conductive material, and the conductive material is selected from at least one of conductive metal particles, conductive metal nanowires, carbon nanotubes and graphene.

In one embodiment, the polymer coating layer is made of at least one material selected from cellulose acetate and elastomer.

In one embodiment, the elastomer is at least one selected from PU, TPU, TPE and fluororubber.

A method of preparing aerogel fibers, comprising the steps of:

preparing hollow fibers containing liquid inside by adopting coaxial wet spinning;

removing the liquid in the hollow fibers to obtain a hollow fiber template; and

injecting an aerogel precursor solution into the hollow fiber template, freezing, and then freeze-drying to form aerogel so as to obtain aerogel fibers; the aerogel fiber comprises an aerogel core layer and a polymer coating layer, wherein the polymer coating layer is of a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer.

The preparation method of the aerogel fiber has simple process and can continuously produce a large amount of coaxial fibers.

In one embodiment, the operation of removing the liquid from the interior of the hollow fibers is:

freezing the hollow fiber, and then freeze-drying; or air dried at room temperature.

In one embodiment, the hollow fiber adopts cellulose acetate as a main body spinning polymer, polyacrylic acid with the molecular weight of 4000kDa is added into the cellulose acetate, dimethylacetamide is used as a solvent, and water is filled in the central channel;

extruding a mixed solution of cellulose acetate, polyacrylic acid and dimethylacetamide into a water bath, wherein the mass fraction of the cellulose acetate and the polyacrylic acid in the mixed solution is 16 wt%, and the mass ratio of the cellulose acetate to the polyacrylic acid is 23: 2; immersing the spun hollow fiber in water for 15 hours to remove residual dimethylacetamide while keeping the core filled with water; freezing the water-filled hollow fiber at-20 ℃ for 15h, and then freeze-drying the water-filled hollow fiber at-50 ℃ for 2d to obtain a hollow fiber template;

injecting 0.7 wt% of nano-cellulose aqueous solution into the hollow fiber template at 300 mu l/min, freezing at-20 ℃ for 15h, and freeze-drying at-50 ℃ for 2d to form continuous aerogel in the core layer.

In one embodiment, the polymer coating layer is made of an elastomer, an aerogel precursor solution is injected into the hollow fiber template, and the hollow fiber template is subjected to freezing treatment, and then the operation of freeze-drying to form the aerogel is as follows:

pre-stretching the hollow fiber template, injecting an aerogel precursor solution in the pre-stretching process or after the pre-stretching is completed, freezing, releasing the pre-strain applied to the hollow fiber template after freeze drying, and performing heat treatment on the hollow fiber to obtain the aerogel fiber.

In one embodiment, the polymer coating layer is made of a porous thermoplastic elastomer, and the aerogel core layer is made of nanocellulose; the preparation method of the aerogel fiber comprises the following steps:

firstly, carrying out wet spinning to obtain a hollow shell of the thermoplastic elastomer, wherein the solution used by the shell is a mixture of the thermoplastic elastomer doped with dichloromethane and lignin, and an internal channel is filled with ethanol;

adding lignin particles with the average particle size of 2-50 microns into the thermoplastic elastomer, wherein the lignin is attached to the thermoplastic elastomer in a dispersing way; in dichloromethane, the mass fraction of the thermoplastic elastomer is 38.5%, and the mass ratio of the thermoplastic elastomer to the lignin is 2: 3, wet spinning in a coagulating bath of ethanol, and filling ethanol into the hollow channel in the fiber tube product; then soaking the spun hollow fiber in water for 1h to remove lignin, thereby generating a hole structure; then transferring the mixture into an ethanol tank for placing;

air-drying the tube core of the hollow fiber for 10min at room temperature, fixing one end of the hollow fiber on a metal frame, inserting a needle head of 27G type into the other end of the hollow fiber, applying a pulling force to one end with the needle head after fixing one end of the hollow fiber, and fixing the hollow fiber on the metal frame, wherein the deformation amount of the hollow fiber reaches 100%; then injecting a conductive polymer solution dispersion system into the stretched hollow fiber, wherein the conductive polymer solution dispersion system is a solution dispersion system formed by mixing PEDOT and PSS or a solution dispersion system formed by mixing PEDOT, PSS and CNF, and the mass fraction of solute in the conductive polymer solution dispersion system is 0.7%; then transferring the mixture to liquid nitrogen to store for five minutes at a temperature of-193 ℃, and then freeze-drying the mixture for 2 days at a temperature of-50 ℃; and releasing the pre-strain applied to the hollow fibers, and carrying out methanol steam annealing on the hollow fibers to obtain the aerogel fibers.

A method of preparing aerogel fibers, comprising the steps of:

preparing fibers containing liquid inside by adopting coaxial wet spinning, wherein the outer layer solution of the coaxial wet spinning is a polymer coating layer precursor solution, and the inner layer solution is an aerogel precursor solution;

Freezing the fibers containing liquid in the fibers, and then freeze-drying the fibers to form aerogel in the fibers to obtain aerogel fibers; the aerogel fiber comprises an aerogel core layer and a polymer coating layer, wherein the polymer coating layer is of a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer.

Application of the aerogel fiber in building thermal insulation materials, wearable equipment and water-soluble coatings.

Drawings

FIG. 1(a) is a schematic illustration of the mechanism of thermal insulation of a polymer coating in an aerogel fiber according to an embodiment of the present invention;

FIG. 1(b) is a schematic diagram of the thermal insulation mechanism of aerogel fibers according to one embodiment of the present invention;

FIG. 2 is a flow chart of a method of making aerogel fibers according to one embodiment of the present disclosure;

FIG. 3 is a flow chart of a method of making aerogel fibers according to another embodiment of the present invention;

FIG. 4 is a photograph of rice straw in example 1;

FIG. 5(a) is a scanning electron micrograph of a cellulose fiber in example 1;

FIG. 5(b) is a transmission electron micrograph of the cellulose fiber of example 1;

FIG. 5(c) is an image of the cellulose fiber of example 1 under an atomic force microscope;

FIG. 6(a) is a first photograph of a hollow fiber template in example 1;

FIG. 6(b) is a second photograph of the hollow fiber template of example 1;

FIG. 6(c) is a first photograph of aerogel fibers of example 1;

FIG. 6(d) is a second photograph of aerogel fibers of example 1;

FIGS. 7(a) to 7(d) are sectional scanning electron micrographs of the hollow fiber template in example 1;

FIG. 7(e) is a scanning electron micrograph of the inner surface of the hollow fiber template in example 1;

FIG. 7(f) is a scanning electron micrograph of the outer surface of the hollow fiber template in example 1;

FIG. 7(g) is a cross-sectional scanning electron micrograph of the coaxial aerogel fibers of example 1;

FIG. 7(h) is a scanning electron micrograph of an aerogel of coaxial aerogel fibers of example 1;

FIGS. 7(i) -7 (j) are enlarged SEM images of the outer fibers of the coaxial aerogel fibers of example 1;

FIG. 7(k) is a scanning electron micrograph of the inner surface of the coaxial aerogel fibers of example 1;

FIG. 7(l) is a scanning electron micrograph of the outer surface of the coaxial aerogel fibers of example 1;

FIG. 8(a) is the temperature difference (| T |) between the fiber surface (Tf) and the hot stage (Th) and the single layer hollow fiber and the single layer coaxial fiber in experiment one of example 1;

fig. 8(b) is a thermal image of a monolayer of hollow fibers and a monolayer of coaxial fibers corresponding to example 1 at Th 150 ℃ in experiment one;

FIG. 8(c) is the temperature difference (| T |) of two layers of hollow fibers and two layers of coaxial fiber mats Tf and Th to Th in example 1 experiment one;

fig. 8(d) is a thermal image of two layers of hollow fibers and two layers of coaxial fibers at Th 150 ℃ for example 1 experiment one;

FIG. 8(e) is the temperature difference between Tf and Th (| T |) for 2mm thick CA boards and 1.8mm thick cotton fabric in experiment one of example 1;

fig. 8(f) is a thermal image of CA plaques and cotton fabric at Th 150 ℃ in experiment one of example 1;

fig. 8(g) is the temperature difference (| Δ T |) of the 5 middle layer hollow fibers and 5 coaxial fibers Tf and the cold substrate (Ts) in experiment two of example 1;

fig. 8(h) is a corresponding thermal image of 5 layers of hollow fibers and 5 layers of coaxial fibers at Ts ═ 15 ℃ for experiment two of example 1.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The aerogel fiber of an embodiment includes an aerogel core layer and a polymer coating layer, where the polymer coating layer is a porous structure, and the polymer coating layer is coated outside the aerogel core layer.

Wherein the porous structure is a three-dimensional network solid structure formed by a plurality of holes. The holes that make up the structure have the following characteristics: the shape of the holes can be regular holes or irregular holes; the holes can be separated from each other or communicated with each other; the distribution of the holes can be either uniform or random.

The aerogel fiber is tubular, the aerogel core layer is positioned inside, the polymer coating layer is positioned outside, and the polymer coating layer is of a porous structure. On one hand, the aerogel core layer positioned on the inner side can be protected, so that the integrity of the aerogel can be protected from being damaged by external force, and the wide application is facilitated; on the other hand, the heat insulation material can play an important heat insulation role.

Preferably, the material of the aerogel core layer is selected from at least one of conductive polymers and nano-Cellulose (CNF).

Wherein, when the material of aerogel sandwich layer is electrically conductive polymer, antistatic function and heating function can be realized to the aerogel fibre.

The inventor of the invention can successfully obtain the nano-cellulose by coupling a TEMPO oxidation method and a mechanical separation method by using straws as raw materials and preparing the nano-cellulose into the aerogel. CNF extracted from straw is an elongated nanofiber (about 2nm thick, 1 μm long) with very high aspect ratio and specific surface area. The amphiphilic nano cellulose surface can be self-assembled into unique aerogel with ultra-low density (2-8mg cm)^-3) Ultra-high porosity (>99.5%), high specific surface area (123 m)²g^-1) And 0.37cm³g^-1Pore volume. These properties enable the application of CNF aerogels in the field of thermal insulation. Furthermore, cellulose is one of the least thermally conductive materials, the honeycomb structure of CNF aerogels limits the circulation of air, making it a good inhibitor of convection, while its low transparency to infrared radiation inhibits the transmission of radiation. These CNF aerogels have excellent insulating potential, coupled with their unique elasticity and biocompatibility, and are particularly attractive for wearable insulating materials.

Preferably, the conductive polymer is at least one selected from a mixture of poly 3, 4-ethylenedioxythiophene (PEDOT) and sodium polystyrene sulfonate (PSS), polypyrrole and polyaniline.

Preferably, the nanocellulose contains a conductive material, and the conductive material is selected from at least one of conductive metal particles, conductive metal nanowires, carbon nanotubes and graphene.

The conductive material is introduced into the aerogel fiber, so that the porous aerogel fiber can realize two functions of passive heat insulation and active heating. The conductive aerogel fiber is coated by the polymer coating layer, so that short circuit can be prevented, and the safe operation of the device can be ensured.

Preferably, the material of the polymer coating layer is at least one selected from cellulose acetate and elastomer. Of course, the main material of the polymer coating layer may contain a small amount of other performance-improving substances. For example, when the main material of the polymer coating layer is cellulose acetate, polyacrylic acid (PAA) with a molecular weight of 4000kDa may be further included to improve spinnability.

When the polymer coating layer is made of elastomer, the aerogel core layer in the elastic polymer coating layer has a compressible structure, so that the aerogel core layer has reversible tensile elasticity. The stretchable aerogel fiber can be used as an insulator in a wearable textile or applied to a fiber heater, and has good application prospect.

Preferably, the material of the elastomer is at least one selected from PU, TPU, TPE and fluororubber.

Referring to fig. 1(a) and 1(b), the main material of the polymer coating layer 110 in the aerogel fiber according to an embodiment of the present invention is Cellulose Acetate (CA), the CA further contains polyacrylic acid (PAA) with a molecular weight of 4000kDa, and the material of the aerogel core layer is CNF. The aerogel fibers of the present embodiment are heated by the external heat source 200, and the heat insulation mechanism of the aerogel fibers of the present embodiment is analyzed as follows:

wherein the individual polymer coating layers 110 are hollow fibers having a thermal conductivity λ_hollowIs shown as

λ_hollow＝λ_conv1+λ_cond1+λ_rad1

Wherein λ is_conv1Is convective heat transfer, λ_cond1Is the heat conduction of hollow fibers through gas (air) and solid (CA), lambda_rad1Is radiative heat transfer. The porous structure in the hollow fiber (with a high porosity of 63%) is key to reducing the overall thermal conductivity. First, the close connection of sub-micron pores (133 + -49 nm) around the micro-pores several tens of microns wide can significantly reduce the thermal convection lambda_conv1. Secondly, the submicron pore size is similar to the size of the average free path (70nm) of gas molecules in air. Since air conducts heat much less than a solid, the heat conduction in the hollow fibers is λ_cond1And is also greatly reduced. Finally, the inclusion of a large number of solid-gas interfaces in white CA greatly reduces the infrared radiation (λ)_rad1). These graded porous structures have several ways of impeding heat transfer, which is evident in comparison to transparent CA foil. The common hollow fiber can be used independently or combined with the solid fiber, and the purpose of heat insulation and heat preservation is achieved through air in the hollow core body. In addition, the multi-scale pore hollow fiber has the advantages of lighter weight, more porosity, heat insulation performance and the like compared with the common hollow fiber, and can be used as a forming template formed by core layer aerogel. Thermal conductivity (λ) of core aerogel_aerogel) Can be expressed as:

λ_aerogel＝λ_cond2+λ_conv2+λ_rad2

wherein λ cond2 conducts heat through gas (air) and solid (CNF) in the aerogel. λ conv2 and λ rad2 are convective and radiative heat transfer, respectively. The CNF aerogel, as a core layer 120 of coaxial fibers, further inhibits the heat transfer mechanism in several respects. The tightly coupled honeycomb aerogel-shut network structure and 10-100 μm voids in the CNF aerogel suppress convection by suppressing air circulation. The ultra-high porosity of CNF aerogels means that more than 99.5% of its internal volume is air. Aerogel honeycomb networks, consisting of highly crystalline CNFs self-assembled walls, are able to effectively block infrared radiation compared to optically transparent polymer films and even silica aerogels. CA/PAA hollow fibers provide several key roles for the CNF aerogel core layer. The hollow fibers provide an interior space and a compatible surface for filling with the aqueous CNF aerogel precursor. The multi-scale pore structure of the coating layer allows the water vapor diffusion formed by the aerogel to be pumped out in vacuum, and provides a precondition for the formation of the aerogel. And the multi-scale porous structure in the polymer cladding helps to suppress air convection. In addition, the infrared reflection porous membrane of the CNF aerogel surrounding coating layer achieves the minimum infrared emissivity, and effectively inhibits radiation heat loss.

It is clear that the superior thermal insulation effect of the coaxial aerogel fibers (λ fiber) is due to the porous aerogel core layer 120 and the porous CA/PAA coating layer 110 with synergistic thermal insulation properties. Theoretically, the heat insulating properties of the coaxial fibers can be further improved by engineering the microstructure of the core layer 120 and the cladding layer 110. For example, reducing the pore size of the cladding below the air mean free path (<70nm) allows the formation of closed cell structures in all parts of the fiber, or reduces the pore size of the core aerogel. However, the volume ratio of aerogel core and CA/PAA cladding may also need to be adjusted to balance density, porosity, and specific desired insulation properties.

The novel fibrous thermal insulation material consisting of the multi-scale porous CA/PAA coating layer and the CNF aerogel core layer in the embodiment of the invention is a new-generation aerogel material and is also a latest representative of fibrous aerogels. The wet-spun hollow CA/PAA fibers provide a porous outer membrane for the aerogel core layer, which is not only beneficial to the formation of CNF aerogel in the aerogel core layer, but also plays a role in protecting and enhancing the mechanical strength of the aerogel core layer. The coaxial fiber has unique high porosity (85%), low density (0.2 g/cm)³) And high specific tensile strength (23.5 +/-2.5 MPa g cm)^-3) The heat insulation material can effectively play a heat insulation role in a working temperature range of-20 ℃ to 150 ℃. The porous sheath of coaxial fibers and the CNF aerogel core layer play a critical role in achieving good thermal insulation performance. Most importantly, the structural formation method of the porous skin-core coaxial fiber opens up completely new possibilities for the formation of continuous fibers of aerogel under different diameters and has expandability. The development and concept of these porous coaxial aerogel fibers proved to be a breakthrough in bio-based insulation, which could potentially drastically alter the sustainable energy-saving solutions for wearable devices and building structures.

The aerogel fibers of the present invention have at least the following advantages:

(1) aerogel fibers have low density (linear density)<1.10mg cm^-1Density of<0.2g cm^-3) High porosity: (>90％)。

(2) The fiber diameter is adjustable (158.3 +/-10.2 mu m, 588.3 +/-19.3 mu m and 1191.4 +/-60.6 mu m).

(3) The specific strength and the specific modulus of the fiber are high (23.5 +/-2.5 MPa g cm)^-3,987.0±106.0MPa g cm^-3)。

(4) Compared with the block aerogel, the fibrous aerogel has good flexibility and certain stretchability (the breaking elongation is 6.1 +/-1.0%).

(5) The surface hydrophilicity and hydrophobicity can be adjusted, namely, the cellulose acetate with the hydrophobic surface can form hydrophilic cellulose through deacetylation.

(6) Since aerogel thermal conductivity is the smallest of the insulation materials, fewer and thinner aerogel fiber materials are used.

(7) The use mode is nimble, and continuous aerogel long fiber can form chopped strand or aerogel capsule through the eager grain process, and chopped strand or aerogel capsule accessible accuse temperature encapsulation at both ends in the eager grain process.

Referring to fig. 2, a method for preparing aerogel fibers according to an embodiment of the present invention includes the following steps:

and S10, preparing the hollow fiber containing the liquid inside by adopting a coaxial wet spinning method.

The operation of preparing the hollow fiber containing liquid inside by adopting coaxial wet spinning comprises the following steps:

the main spinning polymer and a solvent are mixed to form an outer layer solution, liquid is used as an inner layer solution, wet spinning is carried out in a liquid bath, and then impurities are removed to obtain the hollow fiber containing liquid inside.

Wherein the impurities are solvents or other substances doped in the host spinning polymer.

And S20, removing the liquid in the hollow fibers to obtain the hollow fiber template.

Preferably, the operation of removing the liquid inside the hollow fibers is:

freezing the hollow fiber, and then freeze-drying; or air dried at room temperature. Different removal modes can be selected according to different liquids. For example, when the liquid inside the hollow fibers is water, the hollow fibers may be subjected to a freezing process, followed by lyophilization to remove the water; when the liquid inside the hollow fibers is ethanol, it can be directly air-dried at room temperature to remove the ethanol.

S30, injecting the aerogel precursor solution into the hollow fiber template, freezing, and then freeze-drying to form aerogel so as to obtain aerogel fibers; the aerogel fiber comprises an aerogel core layer and a polymer coating layer, the polymer coating layer is of a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer.

Preferably, the material of the polymer coating layer is an elastomer, the aerogel precursor solution is injected into the hollow fiber template, and the hollow fiber template is subjected to freezing treatment, and then the operation of freeze-drying to form the aerogel is as follows:

Elastic aerogel fibers can be prepared by the present embodiment.

In one embodiment, the main material of the polymer coating layer in the aerogel fiber is Cellulose Acetate (CA), and the material of the aerogel core layer is CNF. The method for preparing the aerogel fiber according to the embodiment includes the steps of:

and (3) carrying out wet spinning by adopting spinning equipment, wherein the spinning nozzle consists of coaxial inner and outer channels. In the wet spinning process, the hollow fiber firstly adopts Cellulose Acetate (CA) as a main body to spin a polymer, and polyacrylic acid (PAA) with the molecular weight of 4000kDa is added into the CA to improve the spinnability of the hollow fiber. Dimethylacetamide (DMAc) was used as a solvent and water filled the central channel.

16 wt% CA/PAA (23:2w/w) dissolved in DMAc is extruded into a water bath, the DMAc can be extracted from water inside and outside the hollow fiber, and phase change can be simultaneously carried out on the inner wall and the outer wall of the fiber. The spun hollow fiber was immersed in water for 15h to remove residual DMAc while keeping the core full of water. The water-filled hollow fibers are frozen (freezing conditions: -20 ℃, 15h), and then freeze-dried (freeze-drying conditions: -50 ℃, 2d) in a freeze-dryer into hollow fiber templates to pour aqueous solution for aerogel and form aerogel precursors.

An aqueous solution of CNF (0.7 wt%) was injected into the hollow fiber template at 300. mu.l/min, followed by freezing (freezing conditions: -20 ℃, 15h), followed by freeze-drying (freeze-drying conditions: -50 ℃, 2d) to form a continuous aerogel in the core layer. The aerogel core is strong enough to be drawn from the coaxial fibers.

In another embodiment, the polymer coating layer in the aerogel fiber is made of porous thermoplastic elastomer (TPE), and the aerogel core layer is made of CNF. The method for preparing the aerogel fiber according to the embodiment includes the steps of:

and wet spinning is carried out by adopting spinning equipment, wherein a spinning nozzle consists of coaxial inner and outer channels which are respectively a No. 21 standard needle and a No. 15 standard needle.

The hollow TPE shell is obtained by wet spinning, the solution used for the shell is TPE/lignin doped with Dichloromethane (DCM), and the inner channel is filled with ethanol. Highly dense lignin particles with the average particle size of 2-50 mu m are added into the TPE, and the lignin is attached to the TPE in a dispersing way. In DCM, TPE mass fraction was 38.5% and lignin was (2: 3w/w), wet spinning was carried out in a coagulating bath of ethanol and the hollow channels in the fiber tube article were filled with ethanol. The DCM of the outer hollow fiber is then extracted by ethanol, inducing phase transition of the shell, thus achieving sustainable single strand wet spinning, and finally obtaining TPE/lignin strands of about 3m length. Thereafter, the spun hollow fiber was soaked in water for 1 hour to remove lignin, thereby generating a porous structure. And then transferring the aerogel fibers into an ethanol tank for placing, and waiting for preparing the aerogel fibers.

Air-drying the tube core of the thermoplastic elastomer hollow fiber at room temperature for 10min, fixing one end of the thermoplastic elastomer hollow fiber on a metal frame, inserting a needle head of 27G into the other end of the fiber, applying a pulling force to the end with the needle head after fixing one end of the fiber, and fixing the end with the needle head on the metal frame, wherein the deformation amount of the end reaches 100%; then injecting a conductive polymer solution dispersion system into the stretched hollow thermoplastic elastomer fiber, wherein the conductive polymer solution dispersion system is a solution dispersion system formed by mixing PEDOT and PSS or a solution dispersion system formed by mixing PEDOT, PSS and CNF, and the mass fraction of solute in the conductive polymer solution dispersion system is 0.7%; then transferring the mixture to liquid nitrogen to store for five minutes at a temperature of-193 ℃, and then freeze-drying the mixture for 2 days at a temperature of-50 ℃; the pre-strain applied to the fibers was released and the fibers were steam annealed with methanol to give aerogel fibers.

In the above preparation method, the conductive polymer solution dispersion system is an aqueous solution of conductive polymer. When the conductive polymer solution dispersion system is a mixed solution dispersion system of PEDOT and PSS, the solutes are PEDOT and PSS; when the conductive polymer solution dispersion system is a solution dispersion system mixed by PEDOT, PSS and CNF, the solutes are PEDOT, PSS and CNF.

It should be noted that the preparation method of the aerogel fiber is a two-step method, and the preparation method of the aerogel fiber of the present invention may also be a one-step method.

Referring to fig. 3, a method for preparing aerogel fibers according to another embodiment of the present invention includes the following steps:

s100, preparing the fiber containing liquid inside by adopting coaxial wet spinning, wherein the outer layer solution of the coaxial wet spinning is a polymer coating layer precursor solution, and the inner layer solution is an aerogel precursor solution.

S200, freezing the fiber containing liquid in the fiber, and then freeze-drying to form aerogel in the fiber to obtain aerogel fiber; the aerogel fiber comprises an aerogel core layer and a polymer coating layer, the polymer coating layer is of a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer.

In one embodiment, the spinning nozzle is comprised of coaxial inner and outer channels. The outer layer solution of the fiber takes Cellulose Acetate (CA) as a main spinning polymer and acetone (acetone) as a solvent; the fiber inner layer solution was a CNF aqueous solution (CNF concentration 0.5 wt%). The two solutions are extruded into a coaxial needle head which is inverted in a water bath through an inner pipeline and an outer pipeline to finish the solidification process of the cellulose acetate at the outer layer of the fiber. The fiber can be continuously collected at the speed of 1-2 m/s, and the potential of large-scale production is preliminarily proved. The resulting fibres, which are liquid inside, are then rapidly frozen in liquid nitrogen and then de-iced by a freeze-drying process (conditions: 2d, -50 ℃) to form a continuous aerogel in the core layer. The method simplifies the manufacturing process in the two-step method, and can continuously produce a large amount of coaxial fibers; while the diameter of the fibers can be easily controlled by controlling the collection speed.

Use of an aerogel fiber of an embodiment in building insulation, wearable devices, and water-soluble coatings.

The aerogel fiber of the invention can be widely applied to the temperature range of-50 ℃ to 150 ℃ when being used as a heat insulation material. Three applications can be mainly formed:

(1) continuous long fiber aerogel fibers: the continuous long fiber can be woven into fabrics formed at will, and can be mainly applied to building heat-insulating materials and aerogel cold-resisting clothes. And can also be used for heat insulation in the fields of petroleum, natural gas, building, automobiles, aerospace and the like.

(2) Chopped aerogel fibers: the chopped aerogel fibers (with the length less than 1mm) with the two sealed ends can be added into the water-soluble coating slurry to form the heat-insulating coating.

(3) Aerogel capsules: the chopped aerogel fibers (with the length of less than 1mm) with two ends packaged can be added with other materials with the need of increasing the heat preservation effect to form the aerogel capsule heat-insulation reinforced composite material. The inner and outer materials of the aerogel capsule can be controlled. The inner material is a water-soluble or water-dispersible material and the outer material is an elastic and non-elastic material.

The aerogel fiber is an efficient heat-insulating material, has the advantages of health, safety, environmental protection, low heat-insulating thickness, long acting, construction convenience and the like, can replace the heat-insulating material widely used in the industries of metallurgy, energy, electric power, chemical industry, building, clothing and the like at the temperature of between 50 ℃ below zero and 150 ℃, and can be used for building heat insulation, heating pipeline heat insulation and the like.

When the aerogel fiber is used for wearable equipment, the aerogel fiber has at least the following advantages:

(1) the continuous fibrous structure can be woven, can combine with traditional textile technology, realizes the aerogel fabric of arbitrary shape, according to the object of using the very easy adjustment fabric's shape.

(2) The preparation process is green and environment-friendly, and the energy consumption is low. The aerogel fiber product is environment-friendly and reliable, can be converted into a biocompatible material under certain conditions, and can be degraded.

(3) Aerogel fibers can be directly made into clothing without encapsulation.

The aerogel fibers and the methods for making the same according to the present invention are further described below with reference to specific examples.

The apparatus used in the following examples included: a centrifuge of Vitamix 5200 type, Vita-Mix Corporation, Shanghai Tokyo technology Co., Ltd; a rotary evaporator with the model number of Buchi rotavapor R-114; a wet spinning machine, model number Fusion 200syringe pumps, manufactured by Chemyx inc; syringe pump, model Fusion 200syringe pumps, manufactured by Chemyx inc; a Freeze dryer, model number Free Zone 1.0LBenchtop Freeze Dry System, Labconco, Kansas City, MO; mechanical testing machine model 5944, Instron Corporation.

The raw materials used in the following examples included: PEDOT/PSS solution, model number Clevios PH 1000, manufacturer HC Starck, Inc; TPE, styrene mass fraction is 22%; lignin, alkali basic, Mw ═ 10,000; dichloromethane, manufacturer Sigma Aldrich; ethanol, Fisher Chemical, manufacturer.

Example 1

Preparation of cellulose fibers (CNFs): cellulose from 1g of rice straw (as shown in FIG. 4) was decomposed by centrifugation and dialyzed against an alkaline solution of 0.016g TEMPO/0.1g NaBr/5mmol NaClO at pH 10.0. Mixing and stirring speed is 37,00rpm, and time is 30 min; the centrifugation speed was 5,000rpm for 15 min. The centrifuged supernatant was rotary-evaporated to 0.7 wt% in a rotary evaporator and stored at 4 ℃ for further use.

Preparation of CA/PAA coated aerogel fibers:

in the wet spinning process, the hollow fiber firstly adopts Cellulose Acetate (CA) as a main body to spin a polymer, polyacrylic acid (PAA) with the molecular weight of 4000kDa is added into the CA, dimethylacetamide (DMAc) is used as a solvent, and water is filled in a central channel.

16 wt% CA/PAA (23:2w/w) dissolved in DMAc is extruded into a water bath, the DMAc can be extracted from water inside and outside the hollow fiber, and phase change can be simultaneously carried out on the inner wall and the outer wall of the fiber. The spun hollow fiber was immersed in water for 15h to remove residual DMAc while keeping the core full of water. The water-filled hollow fibers were frozen (freezing conditions: -20 ℃ C., 15 hours) and then lyophilized in a lyophilizer (lyophilizing conditions: -50 ℃ C., 2d) into hollow fiber templates.

An aqueous CNF solution (0.7 wt%) was injected into the hollow fiber template at 300. mu.l/min, followed by freezing (freezing condition: -20 ℃, 15h), followed by freeze-drying (freeze-drying condition: -50 ℃, 2d) to form a continuous aerogel in the core layer, to obtain the aerogel fiber of example 1.

Scanning Electron Microscopy (SEM) characterization of the raw material of cellulose fibers (CNFs) in example 1 gave fig. 5 (a). As can be seen from FIG. 5(a), the rice straw has multiple layers of porosity.

Transmission Electron Microscopy (TEM) characterization and Atomic Force Microscopy (AFM) characterization were performed on the cellulose fibers (CNFs) in example 1 to obtain fig. 5(b) and 5 (c). As can be seen from fig. 5(b) and 5(c), the aspect ratio of the cellulose fiber is high.

The hollow fiber template and the aerogel fiber in example 1 were photographed, respectively, to obtain fig. 6(a) to 6 (d). As can be seen from fig. 6(a) and 6(b), the hollow fiber template has a hollow structure inside. As can be seen in fig. 6(c) and 6(d), the aerogel core is strong enough to be pulled out of the coaxial fibers.

Scanning electron microscopy was performed on the hollow fiber template in example 1 to obtain FIGS. 7(a) to 7 (f). SEM results show that the cross section of the CA/PAA hollow fiber has an average outer diameter of 992.7 +/-46.6 mu m and an average wall thickness of 155.7 +/-21.2 mu m. As can be seen from fig. 7(a) to 7(d), the wall surface features dual concentric porous structure layers, the cross section of the hollow fiber template is microporous, and the periphery is a submicron pore structure and a nanometer pore structure. This is due to phase separation caused by water exposed inside and outside the hollow fibers during immersion precipitation and coagulation. The porous structure is believed to be formed by a combination of phase separation and phase transfer during phase transition of CA/PAA (polymer), DMAc (solvent) and water (coagulant). The pores on the walls of the hollow fibers are large, with a width varying from a few microns to tens of microns (average: 14.5. + -. 13.1 μm) for the two inner and outer layers. Further enlargement of the hollow fiber walls showed additional porous morphology consisting of sub-micron pore mean diameter 133 + -49 nm and smaller intra-nanopore (24.8 + -5.2 nm) and outer (25.8 + -5.0 nm) surfaces. As can be seen from fig. 7(e) and 7(f), the inner and outer surfaces of the hollow fiber template have a nanopore structure. Clearly, the outer and inner surfaces of the cladding of these multi-scale porous structures, i.e., micropores tens of microns wide, submicron pore wall thicknesses, and smaller nanopores, provide prerequisites for aerogel formation.

Scanning electron microscopy characterization was performed on the coaxial aerogel fibers of example 1 to obtain fig. 7(g) to 7 (l). The coaxial fibers have an outer diameter of 846.2 + -18.6 μm and a wall thickness of 118.9 + -14.9 μm, are smaller than the original hollow fibers, and are highly porous aerogel CNF, comprising an average pore size of 41.8 + -24.1 μm. The bilayer pores also remain unchanged over the range of wall thicknesses from a few microns to tens of microns. The average diameter of the nano-pores in the coaxial fiber coating layer is 138.2 +/-55.2 nm, which is equivalent to that of a hollow fiber (133 +/-49 nm). Further, the average diameters of the pores on the inner and outer surfaces of the coaxial fiber were 26.0. + -. 4.7 and 25.3. + -. 4.2nm, respectively. As can be seen from fig. 7(g) and 7(h), the cross-section shows the porous cladding and the porous core structure, where the cellular CNF aerogel and the multi-scale porous cladding are visible. As can be seen in fig. 7(i) and 7(j), the coaxial fibers have similar submicron and nanoporous structures as the outer layer of the hollow fiber template. As can be seen from fig. 7(k) and 7(l), the inner and outer surfaces of the coaxial fiber are both of a nanopore structure.

The hollow fiber template and aerogel fibers of example 1 were tested for thermal insulation performance:

experiment one, 10 fibers were closely aligned, unidirectionally aligned, formed into a single aerogel mat about 1mm thick on a hot table, and infrared images were captured during heating at 30 to 150 ℃. The absolute temperature difference (| Δ T |) between the fiber surface (Tf) and the hot stage is plotted against the hot stage temperature (Th), yielding fig. 8(a) to 8 (f). The higher the | Δ T | the better the insulation performance.

Fig. 8(a) shows that at any given Th, the single-layer coaxial fiber mat consistently has a higher | Δ T | than the single-layer hollow fiber mat. When Th reached 150 ℃, the coaxial fiber mat temperature was 125 ℃ and the hollow fiber mat temperature was 130 ℃, indicating that the thermal insulation performance of the coaxial fiber mat was superior to that of the hollow fiber mat. In the case of two layers of fiber mat, both types of fiber | Δ T | are doubled at the same Th, the double layer increases in | Δ T | more than the single layer due to the reduced thermal convection. The | Δ T | for the coaxial and hollow fiber mats at Th 150 ℃ were 54 ℃ and 41 ℃, respectively. Coaxial aerogel fibers have proven to have significantly better insulation properties than hollow core optical fibers, which may be associated with the CNF aerogel in the core layer. The convective heat transfer hollow fibers have a large hollow core (711.4 + -23.3 μm) to facilitate sufficient fluid movement. In contrast, a CNF aerogel core with an average pore diameter of 41.8 + -24.1 μm, greatly reduces the flow and may eventually no longer convect. Furthermore, the infrared radiative heat transfer of the cell walls in CNF aerogel networks is greatly reduced compared to hollow fibers. The temperature of the 2mm thick double-layered coaxial fiber mat was 96 ℃ at a hot-stage temperature of 150 ℃, which was much lower than that of the hollow fiber mat (fig. 8(c) and 8 (d)). The coaxial fiber mat is also much better than the other two cellulose material classes at the same thickness, with the temperature of the hot stage at 150 ℃ the temperature of the single layer transparent CA sheet (thickness: 2mm) and the three layer porous cotton (thickness: 1.8mm) rose to 133 ℃ and 118 ℃ respectively (FIG. 8 (e)). While the thermal insulation performance of the three-layer porous cotton fabric is superior to that of the monolithic non-porous transparent CA, the porosity of the cotton fabric is lower than that of the hollow and coaxial fibers (63% and 85%, respectively).

Experiment two, to simulate a cold environment, we placed a 5-ply fiber mat on top of a polystyrene substrate, under which was placed 3cm thick dry ice (as shown in fig. 8 (g)).

As can be seen from fig. 8(g) and 8(h), the hollow fiber mat where the | Δ T | of the 5-layer coaxial fiber mat was reduced to 10 ℃ at-15 ℃ substrate temperature (Ts), which was higher than 4 ℃, again demonstrates the superior thermal insulation performance of the coaxial aerogel fibers over the hollow fiber mat in cold environments.

Thus, the layered coaxial fiber mat has good thermal insulation properties in both high and low temperature external environments.

Example 2

Preparation of cellulose fibers (CNFs): 1g of rice straw cellulose was decomposed by centrifugation and dialyzed against an alkaline solution containing 0.016g of TEMPO/0.1g of NaBr/5mmol of NaClO at pH 10.0. Mixing and stirring speed is 37,00rpm, and time is 30 min; the centrifugation speed was 5,000rpm for 15 min. The centrifuged supernatant was rotary-evaporated to 0.7 wt% in a rotary evaporator and stored at 4 ℃ for further use.

Preparing an aerogel precursor solution: to 2.0g of distilled water was added 5.5g of PEDOT/PSS solution (mass fraction: 1.1 wt%), and stirred at high speed for 30min until uniformly dispersed, thereby obtaining a PEDOT/PSS dispersion system having a mass fraction of 0.7%. In order to obtain a PEDOT/PSS/CNF dispersion system with the mass fraction of 0.7 wt%, a PEDOT/PSS solution and a CNF solution with the same mass of 5.5g are added, the mass fractions of the PEDOT/PSS solution and the CNF solution are both 0.7 wt%, and the mixture is stirred at a high speed for 30min until the mixture is uniformly dispersed.

Preparing TPE coated conductive aerogel fibers:

1.5g TPE was mixed with 6g DCM solution and stirred for 1h, after which 2.25g lignin was added and stirred at high speed for 2 h. Filling a 10ml thin tube with ethanol (tube core material) and TPE/lignin/DCM (shell material) in stainless steel needles of inner tube (size 21G) and outer tube (size 15G) at 600 μ l/min^-1And 200. mu.l.min^-1Speed extrusion into an ethanol coagulation bath, the fiber will be continuously spun in the ethanol coagulation bath at room temperature, and then the spun fiber is soaked in water to remove lignin. And then soaking the fibers in an ethanol solution to prepare the hollow TPE fibers containing liquid inside.

The tube cores of the TPE hollow fibers (containing ethanol) were air dried at room temperature for 10 min. Then one end of the TPE hollow fiber is fixed on the metal frame, and a needle with the model number of 27G is inserted into the other end of the hollow fiber. After the end is fixed, the end with the needle is pulled to make the deformation amount reach 100% and fixed on the metal frame. Then, a prepared PEDOT/PSS/CNF solution dispersion system (mass fraction is 0.7%) is injected into the stretched hollow TPE fiber, the fiber is transferred to liquid nitrogen (minus 193 ℃, 5min) for storage for five minutes, and then the fiber is frozen and dried (minus 50 ℃, 2d) to form continuous conductive aerogel in a tube core. Finally, the pre-strain applied to the fibers was released and the fibers were steam annealed with methanol for 3 hours to yield the TPE coated aerogel fibers of example 2 with high tensile and conductivity.

Example 3

Example 3 differs from example 2 in that: the conductive polymer solution dispersion system is a solution dispersion system formed by mixing PEDOT and PSS.

And (3) characterization:

1. SEM scans of the cross-section were made and the internal and external surfaces of the hollow fibers were observed under vacuum (Quattro S) and all samples were gold-sprayed (thickness about 3-5nm) before observation. The inner and outer surface pore diameters of 30 pores were measured by Image J software, and the average value thereof was taken. Cross-sectional dimension measurement of fibers fiber density ρ f was calculated from SEM images and their mass measurements (by a balance with 0.1mg resolution). Porosity index P of fiber_fThe calculation method comprises the following steps: p_f＝1-ρ_f/ρ_b，ρ_bIs cellulose with a bulk density of 1.3g/cm³。

2. A universal test machine model 5566Instron was used, with a constant strain rate of 5% min^-1The mechanical behavior of the hollow TPE fiber and the TPE-coated conductive aerogel fiber was tested. The fiber samples were 3cm in length and were coated with epoxy adhesive at each end to prevent damage to the fibers during clamping. Data for tensile strength, young's modulus and elongation were collected for at least 10 samples per formulation and their mean and standard deviation were reported.

3. Handling of the samples was controlled by a 5566Instron machine. The loading and unloading of the sample are controlled by a 5944 type mechanical testing machine, the fiber is firstly placed on a paper frame, the two ends of the fiber with the length of 3cm are connected with copper wires, the copper wires are firstly coated with conductive silver epoxy resin, and then coated with epoxy resin glue for electrode protection. The resistance change of the fiber was monitored using a 1252B digital multimeter.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The aerogel fiber is characterized by comprising an aerogel core layer and a polymer coating layer, wherein the polymer coating layer is of a porous structure, and the polymer coating layer is coated on the outer side of the aerogel core layer.

2. The aerogel fiber according to claim 1, wherein the material of the aerogel core layer is at least one selected from the group consisting of conductive polymers and nanocellulose;

3. The aerogel fiber according to claim 1, wherein the polymer coating layer is made of at least one material selected from the group consisting of cellulose acetate and elastomer.

4. The aerogel fiber of claim 3, wherein the elastomer is at least one selected from the group consisting of PU, TPU, TPE, and fluororubber.

5. The preparation method of the aerogel fiber is characterized by comprising the following steps of:

removing the liquid in the hollow fibers to obtain a hollow fiber template; and

6. The method for preparing aerogel fibers according to claim 5, wherein the operation of removing the liquid inside the hollow fibers is:

7. The method for preparing aerogel fiber according to claim 5, wherein the hollow fiber is a spinning polymer using cellulose acetate as a main body, polyacrylic acid having a molecular weight of 4000kDa is added to the cellulose acetate, dimethylacetamide is used as a solvent, and water is filled in the central channel;

extruding a mixed solution of the cellulose acetate, the polyacrylic acid and the dimethylacetamide into a water bath, wherein the mass fraction of the cellulose acetate and the polyacrylic acid in the mixed solution is 16 wt%, and the mass ratio of the cellulose acetate to the polyacrylic acid is 23: 2; immersing the spun hollow fiber in water for 15 hours to remove residual dimethylacetamide while keeping the core filled with water; freezing the water-filled hollow fiber at-20 ℃ for 15h, and then freeze-drying the water-filled hollow fiber at-50 ℃ for 2d to obtain a hollow fiber template;

8. The method for preparing aerogel fiber according to claim 5, wherein the polymer coating layer is made of elastomer, the aerogel precursor solution is injected into the hollow fiber template, and the hollow fiber template is frozen, and then the hollow fiber template is freeze-dried to form aerogel by the following operations:

9. The method for preparing aerogel fibers according to claim 8, wherein the polymer coating layer is made of a porous thermoplastic elastomer, and the aerogel core layer is made of nanocellulose; the preparation method of the aerogel fiber comprises the following steps:

10. The preparation method of the aerogel fiber is characterized by comprising the following steps of:

preparing fibers containing liquid inside by adopting coaxial wet spinning, wherein the outer layer solution of the coaxial wet spinning is a polymer coating layer precursor solution, and the inner layer solution is an aerogel precursor solution; and

11. Use of the aerogel fiber of any of claims 1-4 in building insulation, wearable devices, and water-soluble coatings.