Method for preparing nano cellulose

Abstract

The invention discloses a method for preparing nano cellulose, and belongs to the technical field of biomass-based nano material preparation. The preparation method comprises the following steps: reacting strong chaetoceros with a sodium hydroxide solution at 80-110 DEG C for 100 minutes, cooling the reaction solution to room temperature, adding a hydrogen peroxide solution to react at 80 DEG C for 30 minutes, cooling the reaction solution to room temperature, performing post-treatment to obtain strong chaetoceros cellulose, dispersing the strong chaetoceros cellulose in a 57% sulfuric acid solution, performing acidolysis at 40 DEG C for 45 minutes, and performing filtration to obtain the strong chaetoceros cellulose. And carrying out post-treatment to obtain the nano cellulose. The method disclosed by the invention has the beneficial effects that the nano cellulose with high length-diameter ratio and high crystallinity is prepared by taking waste green tide algae, namely chaetoceros, as a raw material and utilizing the characteristics of almost no lignin and slender fibers of the waste green tide algae, and a relatively mild and simple method, so that a new idea is provided for the preparation of the nano cellulose; the method has important significance on innovative development and utilization of algae waste.

Description

Technical Field

[0001] The invention relates to a method for preparing nanocellulose, in particular to a method for preparing nanocellulose with high aspect ratio and high crystallinity by taking hardy algae as raw material, belonging to the technical field of biomass-based nanomaterial preparation. Background Art

[0002] At present, nanocellulose is mainly prepared from terrestrial wood fiber biomass through chemical acid hydrolysis, mechanical homogenization or enzymatic method. However, most wood fiber biomass contains more lignin and shorter fiber length, which makes the preparation process of nanocellulose complicated and the prepared nanocellulose has a smaller aspect ratio and lower crystallinity. Therefore, it is urgent to develop a method that is simple to operate and can prepare nanocellulose with high aspect ratio and high crystallinity. Summary of the invention

[0003] In order to solve the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing nanocellulose with high aspect ratio and high crystallinity by using strong sclerophyll algae which contains almost no lignin and has slender fibers as raw material, which is simple to operate and has mild reaction conditions.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing nanocellulose comprises the following steps: (1) The strong chaete algae and a sodium hydroxide solution with a mass percentage concentration of 2% to 5% were fully mixed and reacted at 80°C to 110°C for 100 minutes, wherein the amount ratio of the strong chaete algae to the sodium hydroxide solution was 1 g: 30 mL; (2) After the reaction is completed, the reaction solution is cooled to room temperature, and then a hydrogen peroxide solution with a mass percentage concentration of 2% to 5% is added, and the reaction is carried out at 80°C for 30 minutes, wherein the amount of hydrogen peroxide solution used is 10 mL / 1 g of Ribes robusta; (3) After the reaction is completed, the reaction solution is cooled to room temperature, and then the reaction solution is filtered to retain the filter cake, the filter cake is washed with water, and finally the filter cake is dried to obtain strong chaete algae cellulose; (4) The cellulose of the strong chaete algae was uniformly dispersed in a sulfuric acid solution with a mass percentage concentration of 57%, and placed in a constant temperature water bath at 40°C for acid hydrolysis. After 45 minutes, ice-cold distilled water was added to dilute the reaction solution to stop the acid hydrolysis reaction. The dosage ratio of the cellulose of the strong chaete algae to the sulfuric acid solution was 1 g: 20 mL. (5) The reaction solution is placed in a centrifuge for centrifugation, the precipitate is retained and centrifuged and washed until neutral to obtain a suspension, and the suspension is dried to obtain nanocellulose.

[0005] Preferably, in step (3), the filter cake is washed with deionized water.

[0006] Preferably, in step (4), stirring is performed continuously during the acid hydrolysis process.

[0007] Preferably, in step (5), the centrifugation conditions are: centrifugation at 3000 rpm for 20 min, three times in total; and deionized water is used for centrifugal washing.

[0008] The present invention is beneficial in that: (1) The present invention uses the waste green tide algae - strong hair algae as raw material, and takes advantage of its characteristics of almost no lignin and slender fibers to prepare nanocellulose with a high aspect ratio and high crystallinity in a relatively mild and simple method, which provides a new idea for the preparation of nanocellulose and is of great significance to the innovative development and utilization of algae waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is the SEM morphology of the nanocellulose prepared in Example 6; Figure 2 is the AFM morphology image of the nanocellulose prepared in Example 6; Figure 3 is a height diagram of the nanocellulose prepared in Example 6; Figure 4 is the aspect ratio distribution diagram of the nanocellulose prepared in Example 6; Figure 5 is a crystal structure diagram of nanocellulose prepared in Example 6; Figure 6 This is the Zeta potential diagram of the nanocellulose prepared in Example 6. DETAILED DESCRIPTION

[0010] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0011] 1. Extracting cellulose from strong sclerophyll algae

[0012] Example 1

[0013] 20g of strong sclerochaete algae was fully mixed with 600mL of 2% sodium hydroxide solution (the mass ratio of sodium hydroxide to water was 1:49) and reacted at 80°C for 100min. After the reaction was completed, the reaction solution was cooled to room temperature, and then 200mL of 2% hydrogen peroxide solution (the mass ratio of hydrogen peroxide to water was 1:49) was added and reacted at 80°C for 30min. After the reaction was completed, the reaction solution was cooled to room temperature, and then the reaction solution was filtered, the filter cake was retained, the filter cake was washed with deionized water, and finally the filter cake was dried to obtain strong sclerochaete algae cellulose with a yield of 12.6g and a yield of 63.0%.

[0014] After testing, the purity of the strong sclerophyll algae cellulose was 52.2%.

[0015] Example 2

[0016] 20g of strong sclerochaete algae was fully mixed with 600mL of 2% sodium hydroxide solution by mass, and reacted at 80°C for 100min. After the reaction was completed, the reaction solution was cooled to room temperature, and then 200mL of 4% hydrogen peroxide solution by mass (the mass ratio of hydrogen peroxide to water was 1:24) was added, and the reaction was carried out at 80°C for 30min. After the reaction was completed, the reaction solution was cooled to room temperature, and then the reaction solution was filtered, the filter cake was retained, the filter cake was washed with deionized water, and finally the filter cake was dried to obtain strong sclerochaete algae cellulose, with a yield of 10.5g and a yield of 52.5%.

[0017] After testing, the purity of the strong sclerophyll algae cellulose was 64.1%.

[0018] Example 3

[0019] 20g of strong sclerochaete algae was fully mixed with 600mL of 4% sodium hydroxide solution (the mass ratio of sodium hydroxide to water was 1:24) and reacted at 80°C for 100min. After the reaction was completed, the reaction solution was cooled to room temperature, and then 200mL of 2% hydrogen peroxide solution was added and reacted at 80°C for 30min. After the reaction was completed, the reaction solution was cooled to room temperature, and then the reaction solution was filtered, the filter cake was retained, the filter cake was washed with deionized water, and finally the filter cake was dried to obtain strong sclerochaete algae cellulose with a yield of 9.8g and a yield of 49.0%.

[0020] After testing, the purity of the strong sclerophyll algae cellulose was 68.4%.

[0021] Example 4

[0022] 20g of strong sclerochaete algae was fully mixed with 600mL of 4% sodium hydroxide solution by mass, and reacted at 80°C for 100min. After the reaction was completed, the reaction solution was cooled to room temperature, and then 200mL of 3% hydrogen peroxide solution by mass (the mass ratio of hydrogen peroxide to water was 3:97) was added, and the reaction was carried out at 80°C for 30min. After the reaction was completed, the reaction solution was cooled to room temperature, and then the reaction solution was filtered, the filter cake was retained, the filter cake was washed with deionized water, and finally the filter cake was dried to obtain strong sclerochaete algae cellulose, with a yield of 7.6g and a yield of 38.0%.

[0023] After testing, the purity of the strong sclerophyll algae cellulose was 94%.

[0024] Example 5

[0025] 20g of strong sclerochaete algae was fully mixed with 600mL of 5% sodium hydroxide solution (the mass ratio of sodium hydroxide to water was 1:19) and reacted at 110°C for 100min. After the reaction was completed, the reaction solution was cooled to room temperature, and then 200mL of 5% hydrogen peroxide solution (the mass ratio of hydrogen peroxide to water was 1:19) was added and reacted at 80°C for 30min. After the reaction was completed, the reaction solution was cooled to room temperature, and then the reaction solution was filtered, the filter cake was retained, the filter cake was washed with deionized water, and finally the filter cake was dried to obtain strong sclerochaete algae cellulose with a yield of 5.8g and a yield of 29.0%.

[0026] After testing, the purity of the strong sclerophyll algae cellulose was 96.2%.

[0027] It can be seen from Examples 1 to 5 that as the extraction conditions become more severe (i.e., the mass percentage concentrations of sodium hydroxide and hydrogen peroxide become higher and higher), the purity of the cellulose of the strong sclerophyll algae becomes higher and higher, while the yield becomes lower and lower. This is mainly because in addition to cellulose (accounting for about 36% by mass), the strong sclerophyll algae also contains non-cellulose substances such as hemicellulose, lipids and pigments. The strong sclerophyll algae can be treated with sodium hydroxide and hydrogen peroxide to remove non-cellulose substances such as hemicellulose, lipids and pigments. As the mass percentage concentrations of sodium hydroxide and hydrogen peroxide increase, the removal rate of non-cellulose substances such as hemicellulose, lipids and pigments becomes higher and higher, making the purity of cellulose higher and higher, while the yield of cellulose decreases accordingly (Examples 1 to 4). When the mass percentage concentrations of sodium hydroxide and hydrogen peroxide continue to increase (Example 5), in addition to the removal of non-cellulose substances such as hemicellulose, lipids and pigments, the cellulose will also be degraded, resulting in only a small increase in the purity of cellulose, while the yield is significantly reduced.

[0028] 2. Preparation of nanocellulose using strong Chaetodon cellulose.

[0029] Example 6

[0030] 1 g of the strong sclerophyll cellulose prepared in Example 4 was uniformly dispersed in 20 mL of a 57% sulfuric acid solution (the mass ratio of sulfuric acid to water was 57:43), and placed in a constant temperature water bath at 40°C for acid hydrolysis. The mixture was stirred continuously during the acid hydrolysis process. After 45 minutes, 200 mL of iced distilled water was added to dilute the reaction solution to stop the acid hydrolysis reaction. The reaction solution was then placed in a centrifuge and centrifuged at 3000 rpm for 20 minutes. The reaction solution was centrifuged three times in total, and the precipitate was retained and washed with deionized water until neutral to obtain a suspension. The suspension was dried to obtain cellulose.

[0031] After testing, the SEM morphology of the cellulose prepared in this example is as follows: Figure 1 As shown in the AFM morphology Figure 2As shown. Figure 1 and Figure 2 It can be seen that the cellulose prepared in this example is in the form of long filaments, with a length mainly distributed in the range of 5 mm to 20 mm and a diameter mainly distributed in the range of 5 nm to 20 nm, and is nano-scale cellulose.

[0032] After testing, the height of the cellulose prepared in this example is as follows Figure 3 As shown in the figure, the aspect ratio distribution diagram is as follows Figure 4 As shown. Figure 3 and Figure 4 It can be seen that the cellulose height prepared in this example is mainly concentrated in the range of 5nm to 20nm ( Figure 3 ), the aspect ratio is mainly concentrated in the range of 900 to 1500 ( Figure 4 ).

[0033] After testing, the crystalline structure of the cellulose prepared in this example is as shown in Figure 5 As shown. Figure 5 Calculation shows that the crystallinity of the cellulose prepared in this embodiment is as high as 78%.

[0034] After testing, the Zeta potential diagram of the cellulose prepared in this example is as follows: Figure 6 As shown. Figure 6 It can be seen that the Zeta potential of the cellulose prepared in this example is concentrated in the range of -10 mV to -45 mV, with an average value of -26.658 mV.

[0035] The above results show that the cellulose prepared in this example has both high aspect ratio and high crystallinity characteristics and good dispersibility.

[0036] Comparative Example 1 1g of the strong sclerophyll cellulose prepared in Example 4 was evenly dispersed in 20mL of a 50% sulfuric acid solution (the mass ratio of sulfuric acid to water was 1:1), and placed in a constant temperature water bath at 45°C for acid hydrolysis. Stirring was continued during the acid hydrolysis process. After 35 minutes, 200mL of iced distilled water was added to dilute the reaction solution to stop the acid hydrolysis reaction. The reaction solution was then placed in a centrifuge and centrifuged at 3000rpm for 20 minutes, three times in total, and the precipitate was retained and centrifuged and washed with deionized water until neutral. Finally, the cellulose flocculated into a mass, and a suspension was not obtained. This is mainly because: the acid hydrolysis conditions are too mild, and the large-sized strong sclerophyll cellulose cannot be acid hydrolyzed to form nano-scale cellulose.

[0037] Comparative Example 2 1 g of the strong chaeta cellulose prepared in Example 4 was evenly dispersed in 20 mL of a 64% sulfuric acid solution (the mass ratio of sulfuric acid to water was 16:9), and placed in a constant temperature water bath at 55°C for acid hydrolysis. The mixture was stirred continuously during the acid hydrolysis process. After 45 minutes, a burnt substance appeared in the reaction solution (the strong chaeta cellulose was corroded by sulfuric acid), and the reaction stopped (failed).

[0038] It can be seen from Example 6, Comparative Example 1 and Comparative Example 2 that the concentration of sulfuric acid, acid hydrolysis temperature and acid hydrolysis time will affect the formation of nanocellulose.

[0039] It should be noted that the above embodiments 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 impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing nanocellulose, characterized in that: The following steps are involved: (1) The strong chaete algae and a sodium hydroxide solution with a mass percentage concentration of 2% to 5% were fully mixed and reacted at 80°C to 110°C for 100 minutes, wherein the amount ratio of the strong chaete algae to the sodium hydroxide solution was 1 g: 30 mL; (2) After the reaction is completed, the reaction solution is cooled to room temperature, and then a hydrogen peroxide solution with a mass percentage concentration of 2% to 5% is added, and the reaction is carried out at 80°C for 30 minutes, wherein the amount of hydrogen peroxide solution used is 10 mL / 1 g of Ribes robusta; (3) After the reaction is completed, the reaction solution is cooled to room temperature, and then the reaction solution is filtered to retain the filter cake, the filter cake is washed with water, and finally the filter cake is dried to obtain strong chaete algae cellulose; (4) The cellulose of the strong chaete algae was uniformly dispersed in a sulfuric acid solution with a mass percentage concentration of 57%, and placed in a constant temperature water bath at 40°C for acid hydrolysis. After 45 minutes, ice-cold distilled water was added to dilute the reaction solution to stop the acid hydrolysis reaction. The dosage ratio of the cellulose of the strong chaete algae to the sulfuric acid solution was 1 g: 20 mL. (5) The reaction solution is placed in a centrifuge for centrifugation, the precipitate is retained and centrifuged and washed until neutral to obtain a suspension, and the suspension is dried to obtain nanocellulose.

2. The method according to claim 1, characterized in that: In step (3), the filter cake is washed with deionized water.

3. The method according to claim 1, characterized in that In step (4), stirring is continued during the acid hydrolysis process.

4. The method according to claim 1, characterized in that In step (5), the centrifugation conditions are: centrifugation at 3000 rpm for 20 min, for a total of three centrifugations.

5. The method according to claim 1, characterized in that In step (5), the centrifugal washing is performed with deionized water.

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