Method for preparing cellulose nanofiber from fine components of bamboo pulp, cellulose nanofiber and application

Abstract

The invention relates to the field of bamboo resource utilization, and discloses a method for preparing cellulose nanofibers from fine components of bamboo pulp, the cellulose nanofibers and application of the cellulose nanofibers. The preparation method comprises the following steps: adding fine components of bamboo pulp into an acidic sodium chlorite solution for pretreatment to obtain a fiber raw material; adding the fiber raw material into anhydride for reaction; and washing and dispersing residues obtained by the reaction, and then carrying out mechanical treatment to obtain the cellulose nanofibers. The method provided by the invention is high in production efficiency and relatively low in energy consumption, the length-diameter ratio of the prepared cellulose nanofiber can reach 800-2000, and the problems that resources such as fine fibers and parenchyma cells are wasted after chemical pulping of bamboos, and the prepared cellulose nanofiber is poor in dispersity and stability and the like are solved.

Description

Technical Field

[0001] The present invention relates to the field of bamboo resource utilization, and more specifically, to a method for preparing cellulose nanofibers from bamboo pulp fine components, the cellulose nanofibers and applications. Background Art

[0002] Bamboo has a cellulose content of 50% to 60%, long fibers and high strength, making it an important raw material in the field of pulping and papermaking. However, during the pulping process, small fibers and small thin-walled cells are often discarded due to their adverse effects on cooking and pulp properties.

[0003] The size of fine fibers is about tens to hundreds of microns, and they are squeezed, crushed, and separated between fiber bundles during the cooking process. However, as a representative thin-walled cell tissue volume ratio can account for 50.3%, containing a higher level of cellulose. Compared with bamboo fibers, thin-walled cells have thinner cell walls, and the microfibril angle is large, about 40°~50°, and the degree of lignification is low. In addition, there are small holes on the surface of some miscellaneous cells. The presence of small holes may be beneficial to the input of external energy to a certain extent. These reasons lead to the easy peeling and dispersion between the wall layers of the miscellaneous cells. Based on the characteristic advantages of the above fine components, it is very suitable for the preparation of cellulose nanofibers (CNF).

[0004] At present, the preparation methods of CNF include mechanical method, chemical method, chemical mechanical method, etc., which not only face high energy consumption, chemical pollution and complex operation in the preparation process, but also the prepared CNF has a small aspect ratio, poor stability and limited application range. The mechanical method of preparing CNF directly treats the fiber dispersion liquid with the help of high-pressure homogenizer, microjet homogenizer, ball mill or disc mill and ultrasonic crushing equipment. Although this type of method is mature, it has the disadvantages of high equipment cost, high energy consumption, large material loss and complex equipment operation. In the field of CNF preparation, more and more studies combine pretreatment with mechanical method. The purpose of this is to reduce the stubbornness of lignocellulose before mechanical treatment, so as to reduce the energy consumption of mechanical treatment. The common pretreatment methods of chemical method are TEMPO-mediated oxidation pretreatment and bio-enzyme pretreatment. Chemical pretreatment reduces the stubbornness of lignocellulose, and combined with simple mechanical treatment, chemically modified CNF with a high aspect ratio can be produced. Although the chemical method can effectively improve the chemical properties of cellulose and reduce the stubbornness of fiber, it involves complex chemical reactions and expensive reagents and is not suitable for large-scale production.

[0005] In addition, although bamboo is a high-quality fiber source with a high cellulose content, byproducts such as fine fibers and thin-walled cells produced during the chemical pulping process of bamboo pulp are usually not effectively utilized due to their small size, and become resources discarded during the pulping process. Therefore, how to make full use of the fine components in bamboo pulp to prepare high-performance, low-energy-consuming, and high-aspect-ratio cellulose nanofibers is still a difficult problem in current technology. In the prior art, there is no public method for preparing cellulose nanofibers (CNF) using bamboo pulp fine components as raw materials by pretreatment combined with mechanical methods. Summary of the invention

[0006] The present invention provides a method for preparing cellulose nanofibers from bamboo pulp fine components to overcome the problems described in the prior art that fine components such as fine fibers and miscellaneous cells after bamboo chemical pulping cannot be utilized as resources, and the prepared cellulose nanofibers have poor dispersibility and stability.

[0007] Another object of the present invention is to provide a cellulose nanofiber;

[0008] Another object of the present invention is to provide an application of cellulose nanofibers.

[0009] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0010] A method for preparing cellulose nanofibers from bamboo pulp fine components comprises the following steps:

[0011] S1, adding the bamboo pulp fine component to an acidic sodium chlorite solution for pretreatment to obtain a delignified fine component;

[0012] S2, adding the delignified fine component to anhydride for reaction, wherein the reaction ratio of the delignified fine component to the anhydride is not less than 1:10;

[0013] S3, washing the residue obtained by the reaction, and dispersing it through mechanical treatment to obtain cellulose nanofibers.

[0014] Furthermore, the bamboo pulp fine components are collected by screening the bamboo pulp through a 100-200 mesh sieve.

[0015] Preferably, the sieving is performed by a Paul fiber sieving screen.

[0016] Preferably, the bamboo pulp fine components include fine fibers and miscellaneous cells.

[0017] Furthermore, the concentration of the acidic sodium chlorite solution is 1 to 5 wt.%, and the pH value is 3.5 to 4.5.

[0018] Furthermore, the pretreatment temperature is 70-100° C., and the treatment time is 1-3 hours each time.

[0019] Preferably, the acidic sodium chlorite solution of the same concentration is replaced after each treatment, and the treatment is performed 2 to 4 times to remove the residual lignin in the fine components of the bamboo pulp.

[0020] Preferably, after the pretreatment, the fiber is washed with deionized water until it becomes neutral, and then freeze-dried to remove residual water to obtain the fiber raw material, which is then dried and stored for later use.

[0021] Further, add acid anhydride and react at 70-100° C. for 2-5 hours.

[0022] Preferably, the reaction is carried out under stirring.

[0023] Preferably, the acid anhydride comprises at least one of succinic anhydride, maleic anhydride or phthalic anhydride.

[0024] Preferably, the anhydride is prepared at 70-100°C.

[0025] Furthermore, the reaction ratio of the delignified fine components and the acid anhydride is 1:10-40.

[0026] Further, the residue is washed to a pH of 2.5 to 3.0, then adjusted to a pH of 11.0 to 13.0, and washed again to neutrality.

[0027] Furthermore, the dispersion method is mechanical treatment, including high-pressure homogenization, ultrasonic crushing and stirring.

[0028] Preferably, the parameters of the high-pressure homogenization are: working pressure 1000-1500 bar, the number of times the slurry passes through the high-pressure homogenizer cavity is 5-15 times; the parameters of the ultrasonic crushing are: ultrasonic power 1000-1800 W, ultrasonic time 10-30 min; the parameters of the mechanical treatment of the mixer are: 1500-7000 rpm, stirring time 10-30 min.

[0029] A cellulose nanofiber is prepared by the method for preparing cellulose nanofiber from bamboo pulp fine components, and the aspect ratio of the cellulose nanofiber is 800-2000.

[0030] Preferably, the obtained cellulose nanofibers have a diameter of 2 to 5 nm and a length of about 2 to 4 μm.

[0031] An application of the cellulose nanofiber includes applications in the fields of papermaking, filter materials, food, barrier materials, solar cells, cosmetics, and medicine.

[0032] The present invention aims at the problem of waste of fine fibers and miscellaneous cells generated during the chemical pulping process of bamboo, and proposes an innovative method for preparing cellulose nanofibers (CNF) to achieve high-value utilization of bamboo pulp fine components. The method uses a one-step esterification modification to graft carboxyl groups with ester bonds onto the cellulose surface of bamboo pulp fine components, increase the electrostatic repulsion between fibers, and promote fiber swelling and dispersion. Esterification modification significantly improves the dispersibility of the fibers while reducing the energy consumption required for subsequent mechanical treatment. The introduced carboxyl groups also give the fibers stronger hydrophilicity and chemical stability, further improving the dispersibility and stability of cellulose nanofibers, ensuring uniform distribution of the fibers and high-quality products.

[0033] Subsequently, simple mechanical methods such as high-pressure homogenization, ultrasonic crushing and wall-breaking treatment are used to effectively convert bamboo pulp fine components into high-quality cellulose nanofibers. Compared with traditional methods, the technical solution of the present invention has the significant advantages of low energy consumption, simple operation, large aspect ratio and good stability. The present invention not only makes full use of the fine components after bamboo chemical pulping, but also can prepare satisfactory CNF at 70-100°C through low temperature and low energy consumption treatment conditions, and the modified reagents used have little impact on the environment and are recyclable.

[0034] The cellulose nanofibers prepared by the present invention have high carboxyl content, large aspect ratio, excellent stability and good dispersibility. Compared with the traditional preparation methods (such as the pure mechanical method with high energy consumption and expensive equipment, the TEMPO oxidation method with high cost and great environmental pollution, and the aspect ratio of CNF is small), the present invention can not only ensure that the fiber diameter is about 3nm, but also realize CNF with an aspect ratio of more than 1000. In addition, the yield of the method is higher than 90%, ensuring efficient resource utilization. The prepared cellulose nanofibers have a diameter of 2 to 5nm and an aspect ratio of 800 to 2000, and have a wide range of application potential, especially in the fields of food packaging, filter materials and medical materials.

[0035] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0036] (1) Efficient use of bamboo pulp fine components. The present invention rationally utilizes the structural characteristics of bamboo pulp fine components and adopts a one-step esterification modification combined with mechanical treatment to successfully convert the originally discarded fine fibers and miscellaneous cells in bamboo pulp into high-quality cellulose nanofibers with a yield of more than 90%. This not only realizes the high added value utilization of bamboo pulping waste, but also expands its application scope.

[0037] (2) Low energy consumption and low temperature processing. The present invention can be processed under low temperature and low energy consumption conditions, significantly reducing energy consumption while ensuring the high quality of CNF. Under 70-100°C conditions, esterification modification and mechanical treatment can effectively prepare high-quality cellulose nanofibers, significantly reducing energy consumption, and without the need for high temperature or expensive equipment, which is suitable for large-scale production.

[0038] (3) Cellulose nanofibers have excellent performance. The carboxyl groups introduced by esterification modification during the preparation process of the present invention effectively enhance the electrostatic repulsion between the fibers, so that the fibers can maintain good dispersion and stability without stratification. The obtained CNF has a nanoscale fine structure with a diameter of 2 to 5 nm, a length of about 2 to 4 μm, and an aspect ratio of 800 to 2000. It can be used in papermaking, filter materials, barrier materials, solar cells, cosmetics and other industries.

[0039] (4) Excellent stability. The CNF dispersion prepared by the present invention has excellent stability and still does not show stratification after being stored for several months, thus avoiding the problem of large-scale agglomeration of the CNF dispersion during storage, providing great convenience for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The actual picture (A) and scanning electron microscope picture (B) of bamboo fine fibers and miscellaneous cells;

[0041] Figure 2 Transmission electron microscopy (A) and atomic force microscopy (B) images of CNF;

[0042] Figure 3 is the diameter distribution diagram of CNF;

[0043] Figure 4 (A) is a real picture of the CNF dispersion and (B) is a real picture of the CNF dispersion after being placed for three months. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0045] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0046] Example 1

[0047] A method for preparing cellulose nanofibers using bamboo pulp fine components comprises the following steps:

[0048] (1) Screening the bamboo pulp treated with chemical cooking with a Paul fiber grading screen to collect materials with a mesh size of 100 to 120, i.e., the bamboo pulp fine fraction;

[0049] (2) Chemical refining pretreatment: The bamboo pulp fine components obtained in step (1) are added to a 1 wt.% acidic sodium chlorite solution (pH 3.5) and treated at 70°C for 1 h. This process is repeated 4 times. After delignification is completed, the bamboo pulp is washed with deionized water to neutrality and then freeze-dried into powder for later use.

[0050] (3) 1 g of the powder purified in step (2) was added to 20 g of succinic anhydride and reacted at 70° C. for 3 h;

[0051] (4) After the reaction in step (2) is completed, centrifuge and wash with deionized water to adjust the pH to 3.0, then add sodium hydroxide solution to adjust the pH to 11.0, and then thoroughly wash with deionized water until neutral;

[0052] (5) The washed material in step (4) was redispersed in water and passed through a high-pressure homogenizer cavity for 5 times at a working pressure of 1500 bar to obtain a dispersion of cellulose nanofibers.

[0053] Example 2

[0054] A method for preparing cellulose nanofibers using bamboo pulp fine components comprises the following steps:

[0055] (1) Screening the bamboo pulp treated with chemical cooking with a Paul fiber grading screen to collect materials with a mesh size of 120 to 160, i.e., the bamboo pulp fine fraction;

[0056] (2) Chemical refining pretreatment: The bamboo pulp fine fraction obtained in step (1) is added to a 3 wt.% acidic sodium chlorite solution (pH 4.0) and treated at 80°C for 2 h. This process is repeated 3 times. After delignification is completed, it is washed with deionized water to neutrality and then freeze-dried into powder for later use.

[0057] (3) 1 g of the powder purified in step (2) was added to 10 g of succinic anhydride and reacted at 80° C. for 3 h;

[0058] (4) After the reaction in step (2) is completed, centrifuge and wash with deionized water to adjust the pH to 2.5, then add sodium hydroxide solution to adjust the pH to 11.0, and then thoroughly wash with deionized water until neutral;

[0059] (5) The washed material in step (4) is redispersed in water and treated at an ultrasonic power of 1800 W for 15 min to obtain a dispersion of cellulose nanofibers.

[0060] Example 3

[0061] A method for preparing cellulose nanofibers using bamboo pulp fine components comprises the following steps:

[0062] (1) Screening the bamboo pulp treated with chemical cooking with a Paul fiber grading screen to collect materials with a mesh size of 160 to 200, which is the bamboo pulp fine fraction;

[0063] (2) Chemical refining pretreatment: The bamboo pulp fine fraction obtained in step (1) is added to a 5 wt.% acidic sodium chlorite solution (pH 4.0) and treated at 80°C for 2 h. This process is repeated 3 times. After delignification is completed, it is washed with deionized water to neutrality and then freeze-dried into powder for later use.

[0064] (3) 1 g of the powder purified in step (2) was added to 40 g of phthalic anhydride and reacted at 90° C. for 3 h;

[0065] (4) After the reaction in step (2) is completed, centrifuge and wash with deionized water to adjust the pH to 2.5, then add sodium hydroxide solution to adjust the pH to 12.0, and then thoroughly wash with deionized water until neutral;

[0066] (5) The washed material in step (4) was redispersed in water and passed through a high-pressure homogenizer chamber 10 times at 1000 bar.

[0067] Example 4

[0068] A method for preparing cellulose nanofibers using bamboo pulp fine components comprises the following steps:

[0069] (1) Screening the bamboo pulp treated with chemical cooking with a Paul fiber grading screen, collecting the material passing through a 200-mesh screen, which is the bamboo pulp fine component;

[0070] (2) Chemical refining pretreatment: The bamboo pulp fine fraction obtained in step (1) is added to a 5 wt.% acidic sodium chlorite solution (pH 4.5) and treated at 100°C for 3 h. This process is repeated twice. After delignification is completed, it is washed with deionized water to neutrality and then freeze-dried into powder for later use.

[0071] (3) 1 g of the powder purified in step (2) was added to 20 g of maleic anhydride and reacted at 100° C. for 5 h;

[0072] (4) After the reaction in step (2) is completed, centrifuge and wash with deionized water to adjust the pH to 2.0, then add sodium hydroxide solution to adjust the pH to 13.0, and then thoroughly wash with deionized water until neutral;

[0073] (5) The washed material in step (4) was redispersed in water and mechanically treated with a kitchen blender for 30 min to obtain a CNF dispersion, wherein the speed of the kitchen blender was adjusted to level 6 (5500-7000 rpm).

[0074] Comparative Example 1

[0075] A method for preparing cellulose nanofibers using bamboo pulp fine components comprises the following steps:

[0076] (1) Screening the bamboo pulp treated with chemical cooking with a Paul fiber grading screen, collecting the material passing through a 200-mesh screen, which is the bamboo pulp fine component;

[0077] (2) Chemical refining pretreatment: The bamboo pulp fine fraction obtained in step (1) is added to a 5 wt.% acidic sodium chlorite solution (pH 4.5) and treated at 100°C for 3 h. This process is repeated twice. After delignification is completed, it is washed with deionized water to neutrality and then freeze-dried into powder for later use.

[0078] (3) 1 g of the powder purified in step (2) was added to 5 g of maleic anhydride and reacted at 60° C. for 0.5 h;

[0079] (4) After the reaction in step (2) is completed, centrifuge and wash with deionized water to adjust the pH to 2.0, then add sodium hydroxide solution to adjust the pH to 13.0, and then thoroughly wash with deionized water until neutral;

[0080] (5) The washed material in step (4) was redispersed in water and mechanically treated with a kitchen blender for 10 min to obtain a CNF dispersion, wherein the speed of the kitchen blender was adjusted to level 6 (5500-7000 rpm).

[0081] Comparative Example 2

[0082] A method for preparing cellulose nanofibers using bamboo pulp fine components comprises the following steps:

[0083] (1) Screening the bamboo pulp treated with chemical cooking with a Paul fiber grading screen, collecting the material passing through a 200-mesh screen, which is the bamboo pulp fine component;

[0084] (2) Chemical refining pretreatment: The bamboo pulp fine fraction obtained in step (1) is added to a 5 wt.% acidic sodium chlorite solution (pH 4.5) and treated at 100°C for 3 h. This process is repeated twice. After delignification is completed, it is washed with deionized water to neutrality and then freeze-dried into powder for later use.

[0085] (3) Take 1 g of the powder after the purification treatment in step (2) and redisperse it in water, and mechanically treat it with a kitchen blender for 30 min to obtain a CNF dispersion, wherein the speed of the kitchen blender is adjusted to level 6 (5500-7000 rpm).

[0086] Analysis

[0087] Figure 1 A is a fine component of bamboo pulp after chemical refining pretreatment to remove lignin, which is in the form of white powder, indicating that the lignin in the bamboo pulp has been effectively removed after treatment with acidic sodium chlorite solution, thereby improving the purity of the remaining cellulose. The removal of lignin is crucial to the preparation of cellulose nanofibers, because the residual lignin will affect the stability and dispersibility of the fiber and the quality of the final product. Figure 1 B is a scanning electron microscope image, which shows that the morphology of bamboo pulp fine components is very complex, including rectangular, square, spherical and other miscellaneous cells and fibrous fine fibers. The cell wall structure of this type of miscellaneous cells is relatively loose, the wall layer is thinner than bamboo fiber and the degree of lignification is lower, which is easy to fibrillate. Figure 2 The prepared TEM and AFM images are shown in Figure 2. Figure 2 A) It can be clearly seen in the image that the size of the prepared CNF is relatively uniform, the dispersion state is good, and the length is long (more than 2 μm), indicating that the method of the present invention has successfully prepared cellulose nanofibers with a high aspect ratio and meets the requirements of high-performance CNF. The nanoscale scale of CNF is further verified by AFM scanning, showing the surface roughness and morphology of the fiber. Figure 2 B shows that the surface of CNF is very smooth, which indicates that its surface treatment is relatively uniform, which helps to further improve the stability and application performance of CNF.

[0088] Figure 3 The graph shows the distribution of CNF diameters in a column. According to statistics, the average diameter of CNF is 3.36 nm, indicating that the size of the prepared cellulose nanofibers is very small. The smaller diameter gives CNF a larger specific surface area, which is beneficial for its application in high-performance materials (such as filter materials, food packaging materials, medical materials, etc.). This graph shows the stability and consistency of the preparation process, further proving the effectiveness of the method of the present invention in controlling the size of CNF.

[0089] Figure 4 A is a real picture of the CNF dispersion just prepared. The dispersion is uniform and transparent, showing a good dispersion state without obvious stratification or precipitation. Figure 4 B is a real picture of the CNF dispersion after being stored for three months. The dispersion remains uniform and transparent after being stored for several months, without stratification or sedimentation, which proves that the CNF dispersion prepared by the present invention has significant stability.

[0090] Comparative Example 1 and Comparative Example 2 did not finally obtain a uniformly dispersed CNF dispersion, and the obtained CNF dispersion was stratified 10 minutes after the preparation was completed. In Comparative Example 1, since the amount of maleic anhydride directly affects the degree of surface modification of the fiber, 5g of maleic anhydride is not enough to effectively modify the fiber surface of 1g of bamboo pulp fine components. When the esterification reaction is incomplete, the content of carboxyl groups on the fiber surface is low, resulting in insufficient electrostatic repulsion between the fibers and poor dispersibility, which easily leads to stratification. In addition, the time and energy of mechanical treatment in Comparative Example 1 are insufficient, and the raw materials cannot be effectively fiberized and dispersed. In Comparative Example 2, since maleic anhydride is not used for chemical modification but mechanical treatment is directly performed, the raw materials cannot be fiberized and dispersed under the input of limited mechanical treatment energy, which proves the necessity of anhydride modification. The insufficient energy of mechanical treatment leads to aggregation between fibers, and the bamboo pulp fine components cannot be effectively converted into nano-scale fibers, thereby affecting the dispersibility and stability of the final CNF.

[0091] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing cellulose nanofibers from bamboo pulp fine components, characterized in that: The following steps are involved: S1, adding the bamboo pulp fine component to an acidic sodium chlorite solution for pretreatment to obtain a delignified fine component; S2, adding the delignified fine component to anhydride for reaction, wherein the reaction ratio of the delignified fine component to the anhydride is not less than 1:10; S3, washing the residue obtained by the reaction, and dispersing it through mechanical treatment to obtain cellulose nanofibers.

2. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: The bamboo pulp fine components are collected by screening the bamboo pulp through a 100-200 mesh screen.

3. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: The acidic sodium chlorite solution has a concentration of 1 to 5 wt.%, and a pH value of 3.5 to 4.

5.

4. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: The pretreatment temperature is 70-100°C, and the treatment time is 1-3 hours each time.

5. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: Add acid anhydride and react at 70-100°C for 2-5 hours.

6. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: The reaction ratio of the delignified fine components and the acid anhydride is 1:10-40.

7. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: The residue is washed to a pH of 2.5 to 3.0, then adjusted to a pH of 11.0 to 13.0, and washed again to neutrality.

8. The method for preparing cellulose nanofibers from bamboo pulp fine components according to claim 1, characterized in that: The dispersion method is mechanical treatment, including high-pressure homogenization, ultrasonic crushing and stirring.

9. A cellulose nanofiber, characterized in that: The cellulose nanofiber is prepared by the method for preparing cellulose nanofibers from bamboo pulp fine components according to any one of claims 1 to 8, and the aspect ratio of the cellulose nanofibers is 800 to 2000.

10. An application of the cellulose nanofiber according to claim 9, characterized in that: Applications include papermaking, filtration materials, food, barrier materials, solar cells, cosmetics, and medicine.

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