Bacterial cellulose / polyurethane composite aerogel fiber and its preparation method and application

Abstract

The present invention discloses a bacterial cellulose / polyurethane composite aerogel fiber and its preparation method and application, belonging to the technical field of aerogel fibers. The above-mentioned bacterial cellulose / polyurethane composite aerogel fiber is prepared by spinning a spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer. The preparation method includes: (1) preparing a spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer; (2) obtaining the fiber by wet spinning the spinning solution, solvent replacement and freeze-drying. In order to solve the defects of large brittleness and low mechanical strength of existing aerogel fibers, the present invention adds a thermoplastic polyurethane elastomer to the bacterial cellulose aerogel to protect the gel skeleton, which can effectively enhance the mechanical strength of the aerogel fiber and endow the aerogel fiber with good flexibility. The composite aerogel fiber has a porous structure, good flexibility, tensile properties and excellent heat insulation properties. Moreover, the present invention adopts the wet spinning technology, which has a simple process and low requirements for equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of bacterial cellulose aerogel fibers, and particularly relates to a bacterial cellulose / polyurethane composite aerogel fiber and its preparation method and application. Background Art

[0002] Aerogel is a lightweight nanoporous material with a basic three-dimensional nano-network skeleton, and has excellent properties such as a high specific surface area, a high porosity, a low density, and a low thermal conductivity. Because of the low density and low thermal conductivity of aerogel, preparing it into a one-dimensional fiber material and applying it to high-performance textile materials has good application prospects. However, due to the high brittleness, low mechanical strength, and difficult forming of aerogel materials, its partial development and application are restricted.

[0003] With the development of aerogel fibers, it is particularly important to ensure their mechanical properties on the basis of fiber forming and prepare lightweight, flexible, and warm aerogel fibers. Bacterial cellulose aerogel fibers have good flexibility and heat insulation properties, but the gel skeleton has low strength and poor tensile properties. Therefore, selecting a suitable reinforcing material to prepare composite aerogel fibers can obtain composite aerogel fibers with good mechanical strength, flexibility, and outstanding heat insulation properties. Summary of the Invention

[0004] Object of the Invention: To solve the technical problems existing in the prior art, the present invention aims to provide a bacterial cellulose / polyurethane composite aerogel fiber with excellent mechanical properties, good heat preservation performance, and a simple preparation process. Moreover, the present invention also provides a preparation method and an application of the bacterial cellulose / polyurethane composite aerogel fiber.

[0005] Technical Solution: The bacterial cellulose / polyurethane composite aerogel fiber described in the present invention is prepared by spinning a spinning solution containing bacterial cellulose and a thermoplastic polyurethane elastomer.

[0006] Furthermore, the mass ratio of the bacterial cellulose to the thermoplastic polyurethane elastomer is 1 - 5:1, preferably 2 - 5:1. Because the addition of thermoplastic polyurethane will affect the strength of the aerogel skeleton, controlling the addition amount can enhance its mechanical properties while reducing the impact on the gel skeleton.

[0007] Furthermore, the thermoplastic polyurethane elastomer is a polyether-based thermoplastic polyurethane elastomer. Compared with a polyester-based thermoplastic polyurethane elastomer, the polyether-based thermoplastic polyurethane elastomer has high strength, hydrolysis resistance, high resilience, and good low-temperature resistance, and can maintain good properties after freeze-drying.

[0008] The preparation method of the bacterial cellulose / polyurethane composite aerogel fiber described in the present invention includes the following steps:

[0009] (1) Prepare a spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer;

[0010] (2) The spinning solution prepared in step (1) is subjected to wet spinning, solvent replacement, and freeze-drying to obtain bacterial cellulose / polyurethane composite aerogel fibers.

[0011] Furthermore, in step (1), the method for preparing the spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer is as follows: The activated bacterial cellulose nanofibers are fully dissolved in a solvent, and then thermoplastic polyurethane elastomer is added and mixed evenly to obtain the solution.

[0012] Furthermore, in step (1), the conditions for the activation treatment are: soaking in an ethylenediamine solution with a mass concentration of 10-30% for 4-8 h; the conditions for the full dissolution are: first stirring at 90-110 °C for 5-7 h, cooling for 10-14 h, and then stirring at 90-110 °C for 20-40 min; the conditions for the uniform mixing are: stirring at 40-60 °C for 10-14 h.

[0013] Furthermore, in step (1), the solvent consists of N,N-dimethylacetamide and lithium chloride; the mass ratio of N,N-dimethylacetamide to lithium chloride is 10-12:1.

[0014] Furthermore, in step (1), in the spinning solution, the mass fraction of bacterial cellulose nanofibers is 1.5-3.0 wt%, and the mass fraction of thermoplastic polyurethane elastomer is 0.5-1.5 wt%. This is because bacterial cellulose is relatively difficult to dissolve, and the masses of bacterial cellulose and thermoplastic polyurethane elastomer are adjusted while the total mass remains unchanged. Also, since the addition of thermoplastic polyurethane elastomer will affect the strength of the aerogel gel skeleton, in order to enhance the mechanical strength of the aerogel fibers and maintain the strength of the gel skeleton, the maximum added mass of thermoplastic polyurethane elastomer is selected as 1.5 wt%.

[0015] Further, in step (2), the wet spinning process is to extrude the spinning solution from the needle using an injection pump and enter the water coagulation bath. During this process, double diffusion occurs between the spinning solution and the coagulation bath, resulting in phase separation. The spinning solution rapidly solidifies and forms a shape. Bacterial cellulose forms a three-dimensional gel network through hydrogen bonds, and thermoplastic polyurethane solidifies and adheres to the gel skeleton during the diffusion process of the solvent in the spinning solution, obtaining continuous and uniform bacterial cellulose / thermoplastic polyurethane hydrogel fibers. The specific parameters are as follows: the needle is 0.41 mm, the spinning speed is 20 - 30 ml / h, the coagulation bath is a water coagulation bath, and the immersion time in the coagulation bath is 10 - 14 h to ensure complete contact between the spinning solution and water and complete formation of the gel structure; the solvent used for solvent replacement is a mixed solution of tert-butanol and water, with a volume ratio of tert-butanol to water of 2:3, and the replacement time is 80 - 100 min. The water in the gel is exchanged with tert-butanol to reduce the surface tension between the solvent in the gel fiber and the aerogel fiber and prevent damage to the gel structure during subsequent freeze-drying; the parameters for freeze-drying are: at a pressure of 2 - 8 Pa and a temperature of -55°C to -45°C, freeze-dry for 20 - 30 h.

[0016] Application of the bacterial cellulose / polyurethane composite aerogel fiber described in the present invention in the field of thermal insulation.

[0017] Principle of the invention: Bacterial cellulose is a linear polymer with β-1,4-linked glucopyranose residues identical to those of plant cellulose. It forms nanofibrils into nanofiber bundles, and the celluloses are intertwined with each other to form a fine network structure, having excellent properties such as biodegradability, biocompatibility, adaptability, non-toxicity, hydrophilicity, and high water retention.

[0018] Thermoplastic polyurethane elastomer has become one of the important thermoplastic elastomer materials due to its excellent properties and wide applications. Its molecules are basically linear, with no or very few chemical crosslinks. There are many physical crosslinks formed by hydrogen bonds between the linear polyurethane molecular chains, and the hydrogen bonds play a strengthening role in its morphology, thus endowing many excellent properties, such as high modulus, high strength, excellent wear resistance, chemical resistance, hydrolysis resistance, high and low temperature resistance, and mildew resistance.

[0019] The aerogel fibers prepared from bacterial cellulose have good thermal insulation properties, but the problems of poor mechanical properties and high brittleness of the aerogel fibers themselves are still difficult to overcome. The present invention adds the organic reinforcing material thermoplastic polyurethane elastomer to endow the aerogel fibers with good flexibility and tensile properties while maintaining the strength of the gel skeleton of the aerogel fibers.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0021] (1) The composite aerogel fiber prepared by blending bacterial cellulose with thermoplastic polyurethane elastomer in the present invention has a three-dimensional network skeleton and a porous structure, with stable structure, excellent mechanical properties and good heat insulation performance.

[0022] (2) The present invention adopts the wet spinning technology, which has a simple process and low requirements for equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Scanning electron micrographs of the aerogel fibers prepared in Example 1 - Example 2 and Comparative Example 1 - Comparative Example 2 of the present invention (a - c are the surfaces of the aerogel fibers prepared in Comparative Example 2, d - e are the cross-sections of the aerogel fibers prepared in Comparative Example 2, f - h are the surfaces of the aerogel fibers prepared in Example 1, i - j are the cross-sections of the aerogel fibers prepared in Example 1, k - m are the surfaces of the aerogel fibers prepared in Example 2, n - o are the cross-sections of the aerogel fibers prepared in Example 2, p - r are the surfaces of the aerogel fibers prepared in Comparative Example 1, s - t are the cross-sections of the aerogel fibers prepared in Comparative Example 1);

[0024] Figure 2 Stress-strain curves of the aerogel fibers prepared in Example 1 - Example 2 and Comparative Example 1 - Comparative Example 2 of the present invention;

[0025] Figure 3 Curves showing the change of the aerogel fibers prepared in Example 1 - Example 2 and Comparative Example 1 - Comparative Example 3 of the present invention with the temperature of the hot stage. DETAILED DESCRIPTION OF THE INVENTION

[0026] Next, the present invention will be further described in conjunction with specific examples and drawings.

[0027] Sources of main experimental materials:

[0028] Bacterial cellulose hydrogel blocks (BC) were purchased from Guilin Qihong Technology Co., Ltd., and polyether-based thermoplastic polyurethane elastomers (TPU) were purchased from Guilin Qihong Technology Co., Ltd.

[0029] Example 1: The bacterial cellulose / polyurethane composite aerogel fiber provided by the present invention was prepared by spinning a spinning solution containing bacterial cellulose and polyether-based thermoplastic polyurethane elastomer. The mass ratio of bacterial cellulose to polyether-based thermoplastic polyurethane elastomer was 5:1. The preparation method includes the following steps:

[0030] (1) Prepare bacterial cellulose hydrogel blocks into nanofibers using a mechanical method, and activate them in an ethylenediamine solution with a mass concentration of 10%. Then dissolve 2.5 wt% of the activated bacterial cellulose nanofibers in a mixed solution of 96 mL of N,N-dimethylacetamide and 8 g of lithium chloride. Heat at 90 °C, stir at a speed of 900 rpm, and heat for 6 h; after cooling for 12 h, heat and stir again under the same conditions for 30 min, and cool to obtain a homogeneous solution; add 0.5 wt% of polyether-based thermoplastic polyurethane elastomer, heat at 50 °C, and stir at 500 rpm for 12 h to obtain a spinning solution;

[0031] (2) Use a pressure pump to extrude the spinning solution through a 0.41-mm needle at a speed of 20 ml / h into a water coagulation bath. After soaking for 10 h, place the hydrogel fibers in an exchange bath with a volume ratio of tert-butanol to water of 2:3 for solvent replacement for 80 min. Finally, perform freeze-drying at -45 °C and 2 Pa for 24 h to obtain bacterial cellulose / polyurethane composite aerogel fibers.

[0032] Example 2: The bacterial cellulose / polyurethane composite aerogel fibers provided by the present invention are prepared by spinning a spinning solution containing bacterial cellulose and polyether-based thermoplastic polyurethane elastomer. The mass ratio of bacterial cellulose to polyether-based thermoplastic polyurethane elastomer is 2:1. The preparation method includes the following steps:

[0033] (1) Prepare bacterial cellulose hydrogel blocks into nanofibers using a mechanical method, and activate them in an ethylenediamine solution with a mass concentration of 10%. Then dissolve 2.0 wt% of the activated bacterial cellulose nanofibers in a mixed solution of 96 ml of N,N-dimethylacetamide and 8 g of lithium chloride. Heat at 100 °C, stir at a speed of 900 rpm, and heat for 6 h; after cooling for 12 h, heat and stir again under the same conditions for 30 min, and cool to obtain a homogeneous solution; add 1.0 wt% of thermoplastic polyurethane elastomer, heat at 50 °C, and stir at 500 rpm for 12 h to obtain a spinning solution.

[0034] (2) Use a pressure pump to extrude the spinning solution through a 0.41-mm needle at a speed of 25 ml / h into a water coagulation bath. After soaking for 12 h, place the hydrogel fibers in an exchange bath with a volume ratio of tert-butanol to water of 2:3 for solvent replacement for 90 min. Finally, perform freeze-drying at -50 °C and 4 Pa for 24 h to obtain bacterial cellulose / polyurethane composite aerogel fibers.

[0035] Comparative Example 1: The bacterial cellulose / polyurethane composite aerogel fibers described in the present invention are prepared by spinning a spinning solution containing bacterial cellulose and polyether-based thermoplastic polyurethane elastomer. The mass ratio of bacterial cellulose to polyether-based thermoplastic polyurethane elastomer is 1:1. The preparation method includes the following steps:

[0036] (1) The bacterial cellulose hydrogel blocks were prepared into nanofibers by mechanical method, and then activated in an ethylenediamine solution with a mass concentration of 10%. Then, 1.5 wt% of the activated bacterial cellulose nanofibers were dissolved in a mixed solution of 96 ml of N,N-dimethylacetamide and 8 g of lithium chloride. The heating temperature was 110 °C, the stirring speed was 900 rpm, and the heating time was 6 h. After cooling for 12 h, it was heated and stirred again under the same conditions for 30 min, and then cooled to obtain a homogeneous solution. 1.5 wt% of thermoplastic polyurethane elastomer was added, heated at 50 °C, and stirred at 500 rpm for 12 h to obtain a spinning solution.

[0037] (2) The spinning solution was extruded through a 0.41-mm needle at a speed of 30 ml / h using a pressure pump and entered a water coagulation bath. After soaking for 14 h, the hydrogel fibers were placed in an exchange bath with a volume ratio of tert-butanol to water of 2:3 for solvent replacement for 100 min. Finally, freeze-drying was carried out at -55 °C and 6 Pa for 24 h to obtain bacterial cellulose / thermoplastic polyurethane composite aerogel fibers.

[0038] Comparative Example 2: The preparation method of the bacterial cellulose aerogel fibers provided in this comparative example includes the following steps:

[0039] (1) The bacterial cellulose hydrogel blocks were prepared into nanofibers by mechanical method, and then activated in an ethylenediamine solution with a mass concentration of 10%. Then, 3.0 wt% of the activated bacterial cellulose nanofibers were dissolved in a mixed solution of 96 ml of N,N-dimethylacetamide and 8 g of lithium chloride. The heating temperature was 100 °C, the stirring speed was 900 rpm, and the heating time was 6 h. After cooling for 12 h, it was heated and stirred again under the same conditions for 30 min, and then cooled to obtain a homogeneous spinning solution.

[0040] (2) The spinning solution was extruded through a 0.41-mm needle at a speed of 25 ml / h using a pressure pump and entered a water coagulation bath. After soaking for 12 h, the hydrogel fibers were placed in an exchange bath with a volume ratio of tert-butanol to water of 2:3 for solvent replacement for 90 min. Finally, freeze-drying was carried out at -50 °C and 8 Pa for 24 h to obtain bacterial cellulose aerogel fibers.

[0041] Comparative Example 3: Commercially available conventional cotton threads with the same diameter were provided in this comparative example.

[0042] The aerogel fibers obtained in the above examples and comparative examples were characterized by scanning electron microscopy, tensile property testing, and heat insulation property testing according to the following methods respectively.

[0043] The surface and cross-section microtopography of the aerogel fibers were observed using a scanning electron microscope (SU1510 scanning electron microscope, Hitachi, Ltd., Japan). To observe the cross-section of the sample, it was first fractured in liquid nitrogen and then sputter-coated with gold. The test voltage was 5 kV. The tensile properties of the aerogel fibers were tested using a single-filament strength tester (ZB-802 single-filament strength tester, Jiangsu Zhengrui Taibang Electronic Technology Co., Ltd.). The tensile speed was 10 mm / min, the gauge length was 10 mm, and 10 groups of tests were performed for each sample, and the average value was taken. The thermal insulation performance was visually tested using an infrared thermal imager (FOTRIC 240M infrared thermal imager, Shanghai Thermo Imaging Technology Co., Ltd.). 20-cm-long cotton fibers, BC aerogel fibers, and BC / TPU composite aerogel fibers were placed on a heating table for heating, and infrared thermal imaging pictures were taken at a distance of 20 cm using the infrared thermal imager.

[0044] The aerogel fibers were obtained through scanning electron microscopy tests Figure 1 ((a-c, f-h, k-m, and p-r are the surface images of Comparative Example 2, Example 1, Example 2, and Comparative Example 1, respectively, and d and e, i and j, n and o, s and t are the cross-section images of Comparative Example 2, Example 1, Example 2, and Comparative Example 1, respectively). It can be Figure 1 seen that the surface of the aerogel fibers has a certain orientation structure. When the spinning solution is vertically extruded from the needle tip, it is affected by gravity traction and solidifies into a nascent fiber in a stretched state in the coagulation bath, and the BC molecular chains are oriented to a certain extent, which is beneficial to improving the mechanical properties of the fibers. The SEM pictures of the fiber cross-section show that the prepared aerogel fibers have a porous structure. The average diameter of the aerogel fibers is about (0.20 ± 0.02) mm.

[0045] Table 1 Tensile property tests of aerogel fibers prepared in Examples 1-2 and Comparative Examples 1-2

[0046] Breaking strength (MPa) Elongation at break (%) Elastic modulus (MPa) Example 1 16.47 28.12 406.67±19.35 Example 2 24.69 38.54 436.52±25.74 Comparative example 1 11.68 19.46 112.72±16.44 Comparative example 2 13.43 31.16 47.61±3.59

[0047] Table 1 and Figure 2Tensile property test data for Examples 1-2 and Comparative Examples 1-2. When a tensile stress is applied to the sample until it fractures, the deformation of the fiber is mainly the stretching of molecular chains and the stretching and orientation of macromolecules in the amorphous region by overcoming the secondary valence bonds. The addition of TPU alleviates the tensile effect on the gel skeleton, but the -OH groups in BC can form polyurethane bonds with the -NCO groups of TPU. As the TPU content increases, the number of polyurethane bonds also increases, but a connection is formed between TPU and the gel skeleton, and the tensile properties will be affected. The mechanical properties of Examples 1 and 2 are improved compared to Comparative Example 2. The fracture strength and elongation at break of Example 2 reach 24.69 Mpa and 38.54%, respectively, and the breaking strength is almost twice that of Comparative Example 2. However, in Comparative Example 1, the mechanical properties of the fiber may be unsatisfactory due to the decrease in the amount of BC used and the resulting decrease in the strength of the gel skeleton. Table 1 shows that the addition of TPU material enhances the elastic modulus of the aerogel fiber, but excessive addition will lead to a decrease in the strength of the gel network of the composite material and a corresponding decrease in the elastic modulus.

[0048] The data obtained by observing the temperature changes of Examples 1-2 and Comparative Examples 1-3 from 40°C to 100°C with a hot stage heating through infrared thermal imaging are Figure 3 . The temperature of the cotton thread rises by 15.05°C, the temperature of Comparative Example 2 rises by 10.82°C, the temperature of Example 1 rises by 11.23°C, the temperature of Example 2 rises by 12.16°C, and the temperature of Comparative Example 1 rises by 13.00°C. As the amount of thermoplastic polyurethane elastomer increases, the temperature rise of the bacterial cellulose aerogel fiber increases and the heat insulation performance decreases, but it is still better than that of the cotton thread. This is because the nano-scale pore size (<50 nm) of the aerogel is lower than the mean free path of air molecules (about 70 nm), and the internal gas molecules lose their ability to flow freely, reducing heat convection and heat conduction. In addition, the gel skeleton of the aerogel is a three-dimensional nano-structure, which increases the heat transfer path through the gel skeleton, thus effectively restricting heat conduction.

Claims

1. A bacterial cellulose / polyurethane composite aerogel fiber, characterized in that, The composite aerogel fiber is prepared by spinning a spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer; the preparation method of the spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer is as follows: the activated bacterial cellulose nanofibers are fully dissolved in a solvent, and then the thermoplastic polyurethane elastomer is added and mixed evenly to obtain; the conditions of the activation treatment are: soaking in an ethylenediamine solution with a mass concentration of 10-30% for 4-8 h; the thermoplastic polyurethane elastomer is a polyether-based thermoplastic polyurethane elastomer.

2. The composite aerogel fiber according to claim 1, wherein, The mass ratio of the bacterial cellulose to the thermoplastic polyurethane elastomer is 1-5:

1.

3. A method for preparing the bacterial cellulose / polyurethane composite aerogel fiber according to claim 1, characterized in that, It includes the following steps: (1) Prepare a spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer; (2) The spinning solution obtained in step (1) is subjected to wet spinning, solvent replacement and freeze-drying to obtain bacterial cellulose / polyurethane composite aerogel fibers.

4. The preparation method according to claim 3, characterized in that, In step (1), the preparation method of the spinning solution containing bacterial cellulose and thermoplastic polyurethane elastomer is as follows: the activated bacterial cellulose nanofibers are fully dissolved in a solvent, and then the thermoplastic polyurethane elastomer is added and mixed evenly to obtain.

5. The preparation method according to claim 4, characterized in that, The conditions of the activation treatment are: soaking in an ethylenediamine solution with a mass concentration of 10-30% for 4-8 h; the conditions for full dissolution are: first stirring at 90-110 °C for 5-7 h, cooling for 10-14 h and then stirring at 90-110 °C for 20-40 min; the conditions for uniform mixing are: stirring at 40-60 °C for 10-14 h.

6. The preparation method according to claim 4, characterized in that, The solvent consists of N,N-dimethylacetamide and lithium chloride; the mass ratio of N,N-dimethylacetamide to lithium chloride is 10-12:

1.

7. The preparation method according to claim 3, wherein In step (1), in the spinning solution, the mass fraction of the bacterial cellulose nanofibers is 1.5-3.0 wt%, and the mass fraction of the thermoplastic polyurethane elastomer is 0.5-1.5 wt%.

8. The preparation method according to claim 3, wherein In step (2), the parameters of the wet spinning are: the spinning speed is 20-30 ml / h, the coagulation bath is a water coagulation bath, and the soaking time in the coagulation bath is 10-14 h; the solvent used for the solvent replacement is a mixed solution of tert-butanol and water, and the replacement time is 80-100 min; the parameters of the freeze-drying are: freeze-drying at a pressure of 2-10 Pa and a temperature of -55 °C to -45 °C for 20-30 h.

9. Use of the bacterial cellulose / polyurethane composite aerogel fiber according to claim 1 in the field of thermal insulation.

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