Method for preparing nanocellulose from giant rice straw

Abstract

The invention provides a method for preparing nano cellulose from giant rice straw. Giant rice straw is used as a raw material, and the giant rice straw nanocellulose is efficiently prepared in a short time through four steps of powder preparation through pretreatment, alkali treatment, bleaching and stirring by a high-speed homogenizer. According to the method for preparing the giant rice straw nanocellulose, the raw materials are wide in source, the cost is low, the technological process is short in time consumption, and batch extraction can be achieved. The problem of waste of the giant rice straw is solved, the additional value is increased, and the environment is protected. A new raw material for preparing the nano cellulose is developed, and the development of the biomass energy industry is promoted.

Description

Technical Field

[0001] The invention belongs to the field of textile materials, and specifically relates to a method for preparing nanocellulose from giant rice straws. Background Art

[0002] Giant rice plants are 1.8 to 2.2 meters tall and produce 700 to 900 kilograms per mu, more than 1.5 times the yield of existing rice. However, as giant rice is widely planted, the recycling of giant rice straw has attracted attention.

[0003] Giant rice straw is thick and long, and has higher cellulose content than ordinary rice straw. Nanocellulose has the advantages of small diameter, large specific surface area, and strong adsorption, and is widely used in wastewater treatment, energy, textiles and other fields to achieve high value-added materials.

[0004] Many scholars have studied other methods of extracting nanocellulose from straws. For example, Song Ting et al. used corn straw as raw material and adopted the ejection steam flash explosion method to prepare corn straw nanocellulose with small particle size and good water solubility. The time required was 35 hours and the cellulose content was 45.88%. Zhao Yanjiao et al. used rice straw as raw material and used TEMPO to prepare cellulose nano whiskers. The preparation time was 26 hours, but it was time-consuming. Fatma et al. used garlic straw to prepare nanocellulose crystals. First, chemical alkaline extraction was used for purification, bleaching, and acid hydrolysis to prepare nanocellulose crystals. It took 14.67 hours and was time-consuming. Therefore, the development of an efficient and time-saving process for preparing giant rice straw nanocellulose is of great significance for environmental protection and increasing added value.

[0005] The present invention aims to overcome the shortcomings of the existing process and provide a method for extracting nanocellulose from giant rice straw in batches with low cost and short time consumption using discarded giant rice straw as raw materials. The present invention provides the possibility of developing giant rice straw and increasing its added value, and promotes the industrial development of nanocellulose and biomass energy. Summary of the invention

[0006] In view of this, the invention aims to provide a method for preparing nanocellulose by extracting giant rice straw in batches with short time consumption and low cost. By developing giant rice straw, the waste of straw resources can be solved and its added value can be increased. At the same time, a new raw material for preparing nanocellulose is provided, which promotes the new development of biomass energy.

[0007] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0008] A method for preparing nanocellulose from giant rice straw, the method comprising the following steps:

[0009] Step 1 is giant rice straw pretreatment:

[0010] The giant rice straw is cut into appropriate lengths for crushing and filtering.

[0011] Step 2 is alkali treatment:

[0012] The pre-treated giant rice straw powder is immersed in alkali solution and heated. After heating, it is filtered out and washed with warm water.

[0013] Step 3 is bleaching:

[0014] The alkali-treated giant rice straw powder is immersed in a hydrogen peroxide solution for bleaching, and after bleaching, it is filtered out, washed with warm water and dried.

[0015] Step 4 is stirring with a high-speed homogenizer:

[0016] The bleached giant rice straw powder is stirred by a high-speed homogenizer to obtain a nanocellulose suspension, which is then freeze-dried to obtain nanocellulose.

[0017] In the above technical solution, further, in step 1, the giant rice straw pretreatment method is: cut the giant rice straw into small segments of about 3 cm, crush it twice with a grinder, each time for 3 minutes, and then filter the powder twice with a 60-mesh sieve to obtain giant rice straw powder below 280 μm.

[0018] In the above technical solution, further, in step 2, the bath ratio of giant rice straw powder and alkali solution is 1:10-1:35 (g / ml), the concentration of sodium hydroxide is 1-1.5%, the heating time is 1-5h, the heating temperature is 60-100°C, and after the end, it is filtered out and washed with warm water at about 40°C.

[0019] In the above technical scheme, further, in step 3, the bath ratio of giant rice straw powder and hydrogen peroxide solution is 1:20 (g / ml), the concentration of hydrogen peroxide is 4-7%, the heating time is 30-90 minutes, the heating temperature is 40-90°C, the pH is 8-11, and after the end, it is filtered out, washed with warm water at about 40°C and dried.

[0020] In the above technical solution, further, in step 4, a high-speed homogenizer is used for stirring, and stirring is performed at 1600 rpm for 20 minutes to obtain a giant rice straw nanocellulose suspension with a concentration of 1%, and freeze-dried at -60°C for 72 hours to obtain giant rice straw nanocellulose.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The method described in the invention provides a new solution to the problem of giant rice straw disposal, with low raw material cost and increased added value of giant rice straw.

[0023] (2) The method described in the invention develops a method for preparing nanocellulose from giant rice straw, thereby promoting the development of nanocellulose and biomass energy industries.

[0024] (3) The process of the present invention is time-saving and can be used to mass-produce giant rice straw nanocellulose. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of preparing nanocellulose from giant rice straw in Example 1.

[0026] Figure 2A This is a morphological picture of the giant rice straw powder of Example 1.

[0027] Figure 2B This is the morphology of giant rice straw nanocellulose in Example 1.

[0028] Figure 3 is the XRD pattern of giant rice straw powder and nanocellulose in Example 1.

[0029] Figure 4 This is the transmission electron microscope image and diameter size distribution diagram of giant rice straw nanocellulose in Example 1. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with embodiments.

[0031] Example 1

[0032] A method for preparing nanocellulose from giant rice straw comprises the following steps:

[0033] Step 1 is giant rice straw pretreatment:

[0034] The giant rice straw was cut into small pieces of about 3 cm, crushed twice with a high-speed multifunctional crusher, each time for 3 min, and then the powder was filtered twice with a 60-mesh sieve to obtain giant rice straw powder below 280 μm, the composition of which is shown in Table 1.

[0035] Step 2 is alkali treatment:

[0036] The pretreated giant rice straw powder was immersed in an alkali solution and heated, the bath ratio of giant rice straw powder to alkali solution was 1:20 (g / ml), and then placed in a 1.25% NaOH solution at 70°C for 2 hours for alkali treatment. After the treatment, it was filtered out and washed with warm water at about 40°C.

[0037] Step 3 is bleaching:

[0038] The giant rice straw powder treated with alkali was immersed in a hydrogen peroxide solution and heated. The bath ratio of giant rice straw powder to hydrogen peroxide solution was 1:20 (g / m1). Sodium hydroxide was added to adjust the pH to 10. The concentration of hydrogen peroxide was 6%. The heating time was 60 minutes and the heating temperature was 80°C. Hydrogen peroxide will accelerate the bleaching effect as the temperature and concentration increase, causing the whiteness value to increase continuously. In an alkaline environment, hydrogen peroxide ionization is enhanced to produce more hydrogen peroxide ions (HOO - ), oxidize and remove colored substances, and inhibit the catalytic decomposition of hydrogen peroxide. Then filter out, wash with warm water at about 40℃ and dry.

[0039] Step 4 is stirring with a high-speed homogenizer:

[0040] The bleached giant rice straw powder was stirred using a high-speed homogenizer at 1600 rpm for 20 min to obtain a giant rice straw nanocellulose suspension with a concentration of 1%, which was freeze-dried at -60°C for 72 h to obtain giant rice straw nanocellulose. The performance parameters of Example 1 are shown in Table 2.

[0041] Example 2

[0042] A method for preparing nanocellulose from giant rice straw comprises the following steps:

[0043] Step 1 is giant rice straw pretreatment:

[0044] The giant rice straw was cut into small pieces of about 3 cm, crushed twice with a grinder, each time for 3 min, and then the powder was filtered twice with a 60-mesh sieve to obtain giant rice straw powder with a size of less than 280 μm. The composition is shown in Table 1.

[0045] Step 2 is alkali treatment:

[0046] The pretreated giant rice straw powder was immersed in an alkali solution and heated, the bath ratio of giant rice straw powder to alkali solution was 1:20 (g / ml), and then placed in a 1.25% NaOH solution at 70°C for 2 hours for alkali treatment. After the treatment, it was filtered out and washed with warm water at about 40°C.

[0047] Step 3 is bleaching:

[0048] The alkali-treated giant rice straw powder was immersed in a hydrogen peroxide solution and heated, the bath ratio of the giant rice straw powder to the hydrogen peroxide solution was 1:20 (g / ml), sodium hydroxide was added to adjust the pH to 10, the hydrogen peroxide concentration was 5.5%, the heating time was 60 minutes, and the heating temperature was 40° C. After the end, it was filtered out, washed with warm water at about 40° C. and dried.

[0049] Step 4 is stirring with a high-speed homogenizer:

[0050] The bleached giant rice straw powder was stirred using a high-speed homogenizer at 1600 rpm for 20 min to obtain a giant rice straw nanocellulose suspension with a concentration of 1%, which was freeze-dried at -60°C for 72 h to obtain giant rice straw nanocellulose. The performance parameters of Example 2 are shown in Table 2.

[0051] Table 1 Composition of giant rice straw powder

[0052] Element Cellulose Hemicellulose Lignin Pectin Water soluble Waxy Giant Rice Straw Powder 38.62％ 26.18％ 17.12％ 3.84％ 5.12％ 9.12％

[0053] Table 2 Performance parameters of the embodiment

[0054]

[0055] As shown in Table 2, the degumming rate of giant rice straw powder in Example 1 is 78.20%. The high degumming rate is because the high temperature alkaline conditions have a puffing effect on the fiber, which can react with the hemicellulose, pectin, and lignin components in the powder to oxidize them and dissolve them into small molecules before removal, thereby achieving the purpose of degumming. The increase in temperature and concentration will accelerate its bleaching effect, causing the whiteness value to continue to increase, so Example 1 has a better bleaching effect. At the same time, the alkaline environment enhances the ionization of hydrogen peroxide, generating more hydrogen peroxide ions (HOO - ), oxidative removal of colored substances, and inhibition of catalytic decomposition of hydrogen peroxide. However, the yield of nanocellulose is low, because the high hydrolysis temperature will destroy more amorphous cellulose regions, remove more colloids, and increase the cellulose content, which is also the reason for the high degumming rate in Example 1.

[0056] As shown in Table 2, the nanocellulose yield of Example 2 is 42.98% and the degumming rate is 63.87%. When the hydrogen peroxide concentration and temperature are low, the hemicellulose, pectin, and lignin in the giant rice straw powder do not react fully with the solution, resulting in a low degumming rate, so the nanocellulose yield is high. At the same time, low hydrogen peroxide concentration and temperature will also lead to low bleaching efficiency and yellowish whiteness.

[0057] The degumming process of Example 1 and Example 2 takes 3 hours, which is shorter than 35 hours by Song Ting et al., 26 hours by Zhao Yanjiao et al., and 14.67 hours by Fatma et al.

[0058] Therefore, embodiment 1 was selected based on the comprehensive whiteness and degumming rate. The preparation process adopted in embodiment 1 is as follows Figure 1 As shown in Figure 1, using giant rice straw as raw material, through four steps of pretreatment to prepare powder, alkali treatment, bleaching and high-speed homogenizer stirring, giant rice straw nanocellulose is prepared in a short time and efficiently. The morphology of nanocellulose prepared from giant rice straw powder is shown in Figure 1. Figure 2A and 2BAs shown. The surface of giant rice straw powder is relatively smooth and flat, with a compact structure and some colloid components. During the drying process of giant rice straw nanocellulose, the hydrogen bonding between the hydroxyl groups on the cellulose surface enhances the attraction between the fibers, and then self-assembles to form cellulose flakes. The surface of nanocellulose has a wrinkled structure and fewer lumps. Due to the destruction of the cell wall structure during the alkaline hydrogen peroxide bleaching process, the surface becomes rough due to the aggregation of cellulose molecules, and the hemicellulose and lignin coated on the surface are degraded, exposing the cellulose.

[0059] Combined XRD of giant rice straw powder and giant rice straw nanocellulose ( Figure 3 ) analysis, the curve shows two typical characteristic peaks at 16.3° and 22.2°, corresponding to the cellulose I structure. This shows that after treatment, the crystal structure and cellulose type of giant rice straw have not changed. Compared with giant rice straw powder (45.63%), giant rice straw nanocellulose has a higher crystallinity index (63.07%). This shows that after the giant rice straw powder is degummed, the colloid components in the straw are greatly degraded, the amorphous area of ​​the straw is further removed, the cellulose content is increased, and the crystallinity of the straw is improved.

[0060] Transmission electron microscopy images and diameter size distribution of giant rice straw nanocellulose ( Figure 4 ) It can be seen that the high-speed homogenizer stirring can break the structure of the bundled fibers in the giant rice straw powder, so that the single fibers are released, and the fibers finally reach the nanometer level. From the diameter size distribution diagram, it can be seen that about 87% of the nanocellulose has a diameter concentrated between 10 and 40nm, and about 6% exceeds 50nm or is less than 10nm, with good size distribution and nano effect.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing nanocellulose from giant rice straw, characterized in that: Using discarded giant rice straw as raw material, nanocellulose is extracted from giant rice straw through pretreatment, alkali treatment, bleaching and high-speed homogenizer stirring.

2. The preparation method according to claim 1, characterized in that The method comprises the following steps: Step 1 is the pretreatment of giant rice straw: the giant rice straw is cut into small pieces of about 3 cm, crushed twice with a crusher, each time for 3 minutes, and then the powder is filtered twice with a 60-mesh sieve to obtain giant rice straw powder below 280 μm; Step 2 is alkali treatment: the bath ratio of giant rice straw powder and alkali solution is 1:10-1:35 (g / ml), the concentration of sodium hydroxide is 1-1.5%, the heating time is 1-5 hours, the heating temperature is 60-100°C, after the end, filter out and wash with warm water at about 40°C; Step 3 is bleaching: the bath ratio of giant rice straw powder and hydrogen peroxide solution is 1:20 (g / ml), the concentration of hydrogen peroxide is 4-7%, the heating time is 30-90 minutes, the heating temperature is 40-90° C., the pH is 8-11, after the end, filter out, wash with warm water at about 40° C. and dry; Step 4 is stirring with a high-speed homogenizer: stirring with a high-speed homogenizer at 1600 rpm for 20 min to obtain a giant rice straw nanocellulose suspension with a concentration of 1%, and freeze-drying at -60°C for 72 h to obtain giant rice straw nanocellulose.

3. The preparation method according to claim 2, characterized in that: In step 2, the bath ratio of giant rice straw powder and alkali solution is 1:20 (g / ml), the concentration of sodium hydroxide is 1.25%, the heating time is 2h, and the heating temperature is 70°C.

4. The preparation method according to claim 2, characterized in that: In step 3, the concentration of hydrogen peroxide is 6%, the heating time is 60 min, the heating temperature is 80° C., and the pH is 10.

Images