CN105713100A - Method for rapidly preparing cellulose nanocrystalline - Google Patents

Abstract

A method for rapidly preparing cellulose nanocrystals, the invention relates to a method for preparing cellulose nanocrystals. The invention aims to solve the problems of using concentrated acid to pollute the environment, long preparation period, low yield and low thermal stability of products existing in the prior preparation of cellulose nanocrystals. Method: 1. preparation of treatment agent; 2. pretreatment of biomass fiber; 3. separation and cleaning; The invention is used for a method for rapidly preparing cellulose nanocrystals.

Description

A method for rapidly preparing cellulose nanocrystals

technical field

The invention relates to a method for preparing cellulose nanocrystals.

Background technique

Natural cellulose has been used as an engineering material for thousands of years, and this use is still continuing today, such as forest products, paper and fabrics. With the development of science and technology and social needs, the traditional use of natural cellulose cannot fully meet the requirements of modern society for high performance and low cost of cellulose-based products. Therefore, how to research and develop next-generation cellulose-based products and engineering applications has attracted widespread attention. With the development of nanotechnology, the research on extracting nanoscale cellulose from natural cellulose fibers by destroying the hierarchical structure continues to deepen. Due to its high specific surface area, size effect and quantum effect, nanocellulose provides objective conditions for it to be used as a building block for next-generation cellulose-based products.

Cellulose nanocrystals are an ideal reinforcement material for composites due to their excellent mechanical properties. The tensile strength (7.5GPa～7.7GPa) and axial elastic modulus (110GPa～220GPa) of cellulose nanocrystals can even be comparable to or higher than traditional reinforcing fibers (Kevlar fibers and carbon fibers, etc.). However, the density of cellulose nanocrystals is only 1.6 g/cm ³ . In addition, cellulose nanocrystals also have high specific surface area and low thermal expansion coefficient. The large number of hydroxyl groups on the surface of cellulose nanocrystals facilitates its grafting reaction, which can then be applied to strengthen various composite materials.

Cellulose nanocrystals can be obtained from a variety of raw materials, including wood, plants, tunicates, algae, and bacteria. However, the preparation methods of cellulose nanocrystals are mainly concentrated acid hydrolysis, and there are also some physical methods or organic solvent methods. These methods mainly have problems such as relatively large equipment corrosion, environmental pollution, long period and low yield, and low thermal stability of the obtained cellulose nanocrystal product.

The deep eutectic solvent is an environmentally friendly green solvent, and its components are hydrogen bond supply/donation systems composed of degradable quaternary ammonium salts and organic acids or alcohols. This low-cost solvent currently shows good potential in the fields of organic reactions, organic extraction, electrochemical reactions, and enzymatic reactions.

Contents of the invention

The purpose of the present invention is to solve the problems of using concentrated acid to pollute the environment in the existing preparation of cellulose nanocrystals, long preparation period, low yield and low thermal stability of products, and to provide a method for rapidly preparing cellulose nanocrystals method.

A method for rapidly preparing cellulose nanocrystals, specifically carried out according to the following steps:

1. Prepare the treatment agent: under the condition of temperature of 60°C-90°C, distill the deep eutectic solvent under reduced pressure and stir for 0.5h-2h to obtain the treatment agent;

The deep eutectic solvent is a mixture of hydrogen bond acceptors and hydrogen bond donors; the molar ratio of the hydrogen bond acceptors and hydrogen bond donors is 1:(1～10);

The hydrogen bond acceptor is a quaternary ammonium salt; the hydrogen bond donor is an amide, carboxylic acid or polyol;

2. Biomass fiber pretreatment: Mix biomass fiber with a treatment agent to obtain a mixture, and then heat the mixture by microwave. The condition of microwave heat treatment is to treat it for 0.5min to 10min at a temperature of 70°C to 100°C. , to obtain a mixed solution containing biomass fiber insoluble matter;

The mass ratio of the biomass fiber to the treatment agent is (0.1～0.8):10;

3. Separation and cleaning: use the cleaning solution to dilute the mixed solution containing biomass fiber insoluble matter, then filter and separate, and then clean the insoluble matter to obtain biomass fiber insoluble matter;

The cleaning solution is a mixed solution of an organic solvent and water; the volume ratio of the organic solvent to water is (1-9):1;

4. Mechanical treatment: mix the biomass fiber insolubles with water to obtain an aqueous solution of biomass fiber insolubles with a mass percentage of 0.05% to 2%, and perform mechanical treatment on the aqueous solution of biomass fiber insolubles to complete a rapid Method for preparing cellulose nanocrystals.

The beneficial effects of the present invention: 1. The preparation efficiency is high, and the preparation time can be shortened to tens of minutes compared with the traditional preparation method. 2. The solvents used are non-toxic, non-polluting, and environmentally friendly; 3. The nanocellulose prepared by the present invention has good thermal stability, and the maximum thermal degradation rate can reach 353.9 ° C. It is type I cellulose, and the crystallinity can reach 84%. The shape is similar to the nanocrystal prepared by the traditional method, and the yield is high (60%-70%).

Invention principle: The preparation principle of cellulose nanocrystals is to first destroy the non-crystalline region of cellulose and reduce the hydrogen bond force between cellulose molecular chains; prime nanocrystals. The traditional method of preparing cellulose nanocrystals uses concentrated acid to destroy the non-crystalline region of cellulose, and then uses mechanical methods (ultrasonic, homogeneous, etc.) to obtain cellulose nanocrystals; there are also direct high-intensity mechanical treatments to obtain cellulose nanocrystals; Liquid or organic solvents to destroy the non-crystalline region of cellulose is also a new method of preparing cellulose nanocrystals in recent years. However, the yield and thermal stability of cellulose nanocrystals obtained by the concentrated acid method are low, and often need to be treated by dialysis, which has a long cycle, and there are also problems that the acid waste liquid is corroded and difficult to recycle; the cost of ionic liquids is also due to the Its preparation process is complicated and high. The deep eutectic solvent is composed of hydrogen bond donors/acceptors. There are a large number of hydrogen bonds in the solvent, and the presence of halogen ions helps to destroy the amorphous region of cellulose; It has a good bonus effect, speeds up and improves efficiency. In addition, the raw materials constituting the deep eutectic solvent are non-toxic and pollution-free, the cost is also low, and the preparation method is simple and easy to recycle.

The invention is used for a method for rapidly preparing cellulose nanocrystals.

Description of drawings

Fig. 1 is the SEM electron micrograph of the 50000 times magnification of the cellulose nanocrystal prepared in embodiment one;

Fig. 2 is the TEM electron micrograph of the cellulose nanocrystal that embodiment one prepares;

Fig. 3 is the X-ray diffraction figure of the cellulose nanocrystal prepared in embodiment one;

Fig. 4 is the thermogravimetric analysis figure of the cellulose nanocrystal that embodiment one prepares, and 1 is DTG curve, and 2 is weight percentage curve;

FIG. 5 is a TEM electron micrograph of the cellulose nanocrystals prepared in Example 2.

detailed description

Embodiment 1: A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out according to the following steps:

1. Prepare the treatment agent: under the condition of temperature of 60°C-90°C, distill the deep eutectic solvent under reduced pressure and stir for 0.5h-2h to obtain the treatment agent;

The deep eutectic solvent is a mixture of hydrogen bond acceptors and hydrogen bond donors; the molar ratio of the hydrogen bond acceptors and hydrogen bond donors is 1:(1～10);

The hydrogen bond acceptor is a quaternary ammonium salt; the hydrogen bond donor is an amide, carboxylic acid or polyol;

2. Biomass fiber pretreatment: Mix biomass fiber with a treatment agent to obtain a mixture, and then heat the mixture by microwave. The condition of microwave heat treatment is to treat it for 0.5min to 10min at a temperature of 70°C to 100°C. , to obtain a mixed solution containing biomass fiber insoluble matter;

The mass ratio of the biomass fiber to the treatment agent is (0.1～0.8):10;

3. Separation and cleaning: use the cleaning solution to dilute the mixed solution containing biomass fiber insoluble matter, then filter and separate, and then clean the insoluble matter to obtain biomass fiber insoluble matter;

The cleaning solution is a mixed solution of an organic solvent and water; the volume ratio of the organic solvent to water is (1-9):1;

4. Mechanical treatment: mix the biomass fiber insolubles with water to obtain an aqueous solution of biomass fiber insolubles with a mass percentage of 0.05% to 2%, and perform mechanical treatment on the aqueous solution of biomass fiber insolubles to complete a rapid Method for preparing cellulose nanocrystals.

The beneficial effects of this embodiment are: 1. The preparation efficiency is high. Compared with the traditional preparation method, the preparation time can be shortened to tens of minutes. 2. The solvents used are non-toxic, non-polluting, and environmentally friendly; 3. The nanocellulose prepared in this embodiment has good thermal stability, and the maximum thermal degradation rate can reach 353.9°C. It is type I cellulose, and the crystallinity can reach 84%. , the shape is similar to the nanocrystal prepared by the traditional method, and the yield is high (60%-70%).

In this specific embodiment, a deep eutectic solvent is used in combination with microwave heating to pretreat cotton fibers, and then ultrasonic treatment is used to obtain cellulose nanocrystals. Its key lies in 1, deep eutectic solvent is a kind of nontoxic and pollution-free green solvent, non-volatile, and synthetic method is simple; In addition, deep eutectic solvent has dissolving characteristic to non-cellulose component, and the deep eutectic solvent Hydrogen bond acceptors and halide ions can well weaken the force between cellulose molecular chains, thereby achieving the destruction of the amorphous region. 2. Microwave heating is used to take advantage of the ion-rich characteristics of the solvent, which greatly accelerates the experimental efficiency and shortens the reaction time. 3. Mechanical treatment is a treatment method that is easy to scale up and has practical significance.

Specific embodiment two: the difference between this embodiment and specific embodiment one is that the quaternary ammonium salt described in step one is choline chloride, choline bromide, choline iodide or betaine; The carboxylic acid is oxalic acid, malic acid, formic acid or lactic acid; the amide described in step one is urea or thiourea; the polyhydric alcohol described in step one is a trihydric alcohol. Others are the same as in the first embodiment.

Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that the biomass fiber described in step 2 is cotton fiber, pulp fiber, wood fiber, bamboo fiber, hemp fiber, straw fiber, Grass plant fiber or algae plant fiber. Others are the same as in the first or second embodiment.

Embodiment 4: This embodiment differs from Embodiments 1 to 3 in that the power of the microwave heating treatment described in step 2 is 800W-1000W. Others are the same as the specific embodiments 1 to 3.

Embodiment 5: The difference between this embodiment and one of Embodiments 1 to 4 is that the mechanical treatment described in step 4 is ultrasonic treatment, homogenization treatment or grinding treatment;

When the mechanical treatment is ultrasonic treatment, it is specifically carried out according to the following steps: under the condition of ultrasonic power 800W-1200W, the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05%-2% is ultrasonically treated for 5 minutes ~60min;

When the mechanical treatment is homogeneous treatment, it is specifically carried out according to the following steps: under the condition of working pressure of 200bar to 500bar, the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05% to 2% is passed through the homogeneous The homogenization machine is used for 5 to 20 times of homogenization, and the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05% to 2% per 100mL is 30s to 70s each time;

When the mechanical treatment is grinding, it is specifically carried out according to the following steps: under the condition that the rotating speed is 1000rpm～1500rpm, the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05%～2% is placed in the grinding machine Medium grinding for 3min to 10min. Others are the same as the specific embodiments 1 to 4.

Embodiment 6: The difference between this embodiment and one of Embodiments 1 to 5 is that in step 2, the mixture is subjected to microwave heating treatment for 3 minutes at a temperature of 70° C. Others are the same as those in Embodiments 1 to 5.

Embodiment 7: This embodiment differs from Embodiment 1 to Embodiment 6 in that: in step 2, the mixture is subjected to microwave heating treatment for 1 min at a temperature of 80° C. Others are the same as those in Embodiments 1 to 6.

Embodiment 8: This embodiment is different from one of Embodiments 1 to 7 in that: in step 2, the mixture is subjected to microwave heating treatment for 1 min at a temperature of 90° C. Others are the same as those in Embodiments 1 to 7.

Embodiment 9: This embodiment is different from Embodiment 1 to Embodiment 8 in that: in step 2, the mixture is subjected to microwave heating treatment for 30 s at a temperature of 100° C. Others are the same as those in Embodiments 1 to 8.

Embodiment 10: This embodiment is different from Embodiment 1 to Embodiment 9 in that: the organic solvent described in step 3 is acetone, methanol or ethanol. Others are the same as the specific embodiments 1 to 9.

Adopt the following examples to verify the beneficial effects of the present invention:

Embodiment one:

A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out in accordance with the following steps:

1. Preparation of the cotton fiber treatment agent: under the condition of temperature of 80°C, the deep eutectic solvent was distilled under reduced pressure and stirred for 1 hour to obtain the cotton fiber treatment agent;

Described deep eutectic solvent is the mixture of choline chloride and oxalic acid; The mol ratio of described choline chloride and oxalic acid is 1:1;

2. Cotton fiber pretreatment: mix cotton fiber with a cotton fiber treatment agent to obtain a mixture, and carry out microwave heating treatment on the mixture. The condition of microwave heating treatment is to treat for 1 min at a temperature of 80° C. to obtain insoluble cotton fiber mixed solution of substances;

The mass ratio of described cotton fiber and cotton fiber treatment agent is 0.3:10;

3. Separation and cleaning: dilute the mixed solution containing cotton fiber insolubles with cleaning solution, then filter and separate, then clean the insolubles to obtain cotton fiber insolubles;

The cleaning solution is a mixture of acetone and water; the volume ratio of the acetone and water is 1:1;

Four. Mechanical treatment: the cotton fiber insolubles are mixed with water to obtain an aqueous solution of 0.5% cotton fiber insolubles by mass percentage. Under the condition of ultrasonic power 1200W, the aqueous solution of 0.5% cotton fiber insolubles is processed Ultrasonic treatment for 30 min to obtain cellulose nanocrystals.

Figure 1 is a 50,000-fold SEM image of the cellulose nanocrystals prepared in Example 1. It can be seen from the figure that the microscopic size of the cellulose nanocrystals is very uniform and uniform in size.

Fig. 2 is the TEM electron micrograph of the cellulose nanocrystal prepared in Example 1. It can be seen from the figure that under the electron microscope, most cellulose fibers obtain cellulose nanocrystals after ultrasonic treatment, and no larger cellulose is found, indicating that in the Under the action of microwave at 80℃, the deep eutectic solvent has a greater effect on the intermolecular hydrogen bonds in the non-crystalline region of cotton cellulose fibers.

3 is an X-ray diffraction pattern of the cellulose nanocrystals prepared in Example 1. It can be seen from the figure that the crystal form of the cellulose nanocrystals is cellulose type I.

Fig. 4 is the thermogravimetric analysis figure of the cellulose nanocrystal prepared in embodiment one, and 1 is DTG curve, and 2 is weight percentage curve; As can be seen from the figure, the maximum heat release rate of the cellulose nanocrystal prepared in the present embodiment is 353.9 ℃, good thermal stability.

The yield of the cellulose nanocrystals prepared in this example is shown in Table 1, and the yield is 74.16% by dividing the mass of the obtained cellulose nanocrystals by the mass of the raw material.

Embodiment two:

A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out in accordance with the following steps:

1. Preparation of poplar fiber treatment agent: under the condition of temperature of 80°C, the deep eutectic solvent was distilled under reduced pressure and stirred for 1 hour to obtain poplar fiber treatment agent;

Described deep eutectic solvent is the mixture of choline chloride and oxalic acid; The mol ratio of described choline chloride and oxalic acid is 1:1;

2. Poplar fiber pretreatment: mix poplar fiber with poplar fiber treatment agent to obtain a mixture, and carry out microwave heating treatment on the mixture. The condition of microwave heating treatment is to process 3 minutes at a temperature of 80° C. to obtain a mixture containing Mixed solution of poplar fiber insoluble matter;

The mass ratio of described poplar fiber and poplar fiber treatment agent is 0.5:10;

3. Separation and cleaning: use the cleaning solution to dilute the mixed solution containing poplar fiber insolubles, then filter and separate, and then clean the insolubles to obtain poplar fiber insolubles;

The cleaning solution is a mixture of acetone and water; the volume ratio of the acetone and water is 1:1;

Four, mechanical treatment: the insoluble matter of poplar fiber is mixed with water, obtains the aqueous solution of the poplar fiber insoluble matter of 0.5% by mass percentage, under the condition of ultrasonic power 1200W, the poplar fiber insoluble matter of 0.5% by mass percentage The aqueous solution of the product was ultrasonically treated for 30 min to obtain cellulose nanocrystals.

Fig. 5 is the TEM electron micrograph of the cellulose nanocrystal prepared in embodiment two, as can be seen from the figure under the electron microscope, the poplar fiber insoluble matter obtains the cellulose nanocrystal after ultrasonic treatment, and the size is relatively uniform; for the cellulose prepared in the present embodiment The nanocrystals were tested by X-ray diffraction, which proved that the obtained cellulose nanocrystals were type I cellulose, and the maximum thermal degradation rate temperature was 350.7°C.

Embodiment three:

A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out in accordance with the following steps:

1. Preparation of the cotton fiber treatment agent: under the condition of temperature of 80°C, the deep eutectic solvent was distilled under reduced pressure and stirred for 1 hour to obtain the cotton fiber treatment agent;

Described deep eutectic solvent is the mixture of choline chloride and oxalic acid; The mol ratio of described choline chloride and oxalic acid is 1:1;

2. Cotton fiber pretreatment: Cotton fiber is mixed with cotton fiber treatment agent to obtain a mixture, and the mixture is subjected to microwave heating treatment. The condition of microwave heating treatment is to treat 3 minutes at a temperature of 70° C. to obtain insoluble cotton fiber mixed solution of substances;

The mass ratio of described cotton fiber and cotton fiber treatment agent is 0.3:10;

3. Separation and cleaning: dilute the mixed solution containing cotton fiber insolubles with cleaning solution, then filter and separate, then clean the insolubles to obtain cotton fiber insolubles;

The cleaning solution is a mixture of acetone and water; the volume ratio of the acetone and water is 1:1;

Four. Mechanical treatment: the cotton fiber insolubles are mixed with water to obtain an aqueous solution of 0.5% cotton fiber insolubles by mass percentage. Under the condition of ultrasonic power 1200W, the aqueous solution of 0.5% cotton fiber insolubles is processed Ultrasonic treatment for 30 min to obtain cellulose nanocrystals.

The cellulose nanocrystals obtained in this embodiment were observed under a transmission electron microscope and found that the insoluble matter of most cotton fibers was obtained through ultrasonic treatment to obtain cellulose nanocrystals, but there were some larger insoluble matter of cotton cellulose, which was due to the low processing temperature. , the weakening effect on the cellulose molecular chains of cotton fibers is small. It was found by scanning electron microscopy that the microscopic size of the cellulose nanocrystals was very uniform and uniform in size. X-ray diffraction test was performed on the cellulose nanocrystals prepared in this example, and the crystal form of the cellulose nanocrystals was cellulose type I. The maximum thermal degradation rate temperature of the cellulose nanocrystals prepared in this example is 352.7° C., and the thermal stability is good.

The yield of the cellulose nanocrystals prepared in this example is shown in Table 1, and the yield is 75.93% by dividing the mass of the obtained cellulose nanocrystals by the mass of the raw material.

Embodiment four:

A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out in accordance with the following steps:

1. Preparation of the cotton fiber treatment agent: under the condition of temperature of 80°C, the deep eutectic solvent was distilled under reduced pressure and stirred for 1 hour to obtain the cotton fiber treatment agent;

Described deep eutectic solvent is the mixture of choline chloride and oxalic acid; The mol ratio of described choline chloride and oxalic acid is 1:1;

2. Cotton fiber pretreatment: mix cotton fiber with a cotton fiber treatment agent to obtain a mixture, and carry out microwave heating treatment on the mixture. The condition of microwave heating treatment is to treat for 1 min at a temperature of 90° C. to obtain insoluble cotton fiber mixed solution of substances;

The mass ratio of described cotton fiber and cotton fiber treatment agent is 0.3:10;

3. Separation and cleaning: dilute the mixed solution containing cotton fiber insolubles with cleaning solution, then filter and separate, then clean the insolubles to obtain cotton fiber insolubles;

The cleaning solution is a mixture of acetone and water; the volume ratio of the acetone and water is 1:1;

Four. Mechanical treatment: the cotton fiber insolubles are mixed with water to obtain an aqueous solution of 0.5% cotton fiber insolubles by mass percentage. Under the condition of ultrasonic power 1200W, the aqueous solution of 0.5% cotton fiber insolubles is processed Ultrasonic treatment for 30 minutes to obtain cellulose nanocrystals.

The microscopic size of the cellulose nanocrystals prepared in this embodiment is very uniform, and the size is uniform. The crystal form of the prepared cellulose nanocrystals is also type I cellulose. The maximum thermal degradation rate temperature of the prepared cellulose nanocrystals is 352.6 ℃, and the thermal stability is good.

The yield of the cellulose nanocrystals prepared in this example is shown in Table 1, and the yield is 62.35% by dividing the mass of the obtained cellulose nanocrystals by the mass of the raw material. This is different from Example 1 or 3. As the temperature increases, the deep eutectic solvent not only acts on the non-crystalline region of cellulose, but also has a certain effect on the crystalline region, resulting in a decrease in crystallinity compared to Example 2. was 81.90%, and the thermal stability decreased to 352.6°C.

Embodiment five:

A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out in accordance with the following steps:

1. Preparation of the cotton fiber treatment agent: under the condition of temperature of 80°C, the deep eutectic solvent was distilled under reduced pressure and stirred for 1 hour to obtain the cotton fiber treatment agent;

Described deep eutectic solvent is the mixture of choline chloride and oxalic acid; The mol ratio of described choline chloride and oxalic acid is 1:1;

2. Cotton fiber pretreatment: mix cotton fiber with a cotton fiber treatment agent to obtain a mixture, and carry out microwave heating treatment on the mixture. The condition of microwave heating treatment is to treat for 1 min at a temperature of 100° C. to obtain insoluble cotton fiber mixed solution of substances;

The mass ratio of described cotton fiber and cotton fiber treatment agent is 0.3:10;

3. Separation and cleaning: dilute the mixed solution containing cotton fiber insolubles with cleaning solution, then filter and separate, then clean the insolubles to obtain cotton fiber insolubles;

The cleaning solution is a mixture of acetone and water; the volume ratio of the acetone and water is 1:1;

Four. Mechanical treatment: the cotton fiber insolubles are mixed with water to obtain an aqueous solution of 0.5% cotton fiber insolubles by mass percentage. Under the condition of ultrasonic power 1200W, the aqueous solution of 0.5% cotton fiber insolubles is processed Ultrasonic treatment for 30 minutes to obtain cellulose nanocrystals.

The microscopic size of the cellulose nanocrystals prepared in this embodiment is very uniform, and the size is uniform. The cellulose nanocrystals prepared in this example were tested by a TEM electron microscope, and most of the insoluble matter of cotton fibers were mechanically processed to obtain cellulose nanocrystals, which was similar to the TEM electron microscope image in Example 4. The crystal form of cellulose nanocrystal is cellulose type I. The maximum thermal degradation rate temperature of the prepared cellulose nanocrystals is 349.4°C, and the thermal stability is good.

The yield of the cellulose nanocrystals prepared in this example is shown in Table 1. By dividing the mass of the obtained cellulose nanocrystals by the mass of the raw material, the yield is 57.80%. The above description further increases the microwave heating temperature, and the deep eutectic solvent has a certain degradation effect on cotton cellulose, resulting in a decrease in its thermal stability to 349.4°C and a decrease in crystallinity to 80.70%.

The above shows that if the temperature is too low (70° C.), the effect of the deep eutectic solvent on the cotton cellulose will be weak, and there will be some unfibrillated cellulose fibers in the cellulose nanocrystals obtained by ultrasound. As the temperature increased to 80°C, the degree of fibrillation of the prepared cellulose nanocrystals was higher, and the thermal stability reached the maximum. As the temperature continues to rise, the deep eutectic solvent not only acts on the non-crystalline region of cellulose, but also has a greater effect on the crystalline region of cellulose, resulting in a decrease in the yield and thermal stability of the obtained cellulose nanocrystals.

Table 1 embodiment one, three to six prepare the productive rate of cellulose nanocrystal

Example three one Four Fives temperature/℃ 70 80 90 100 Yield/% 75.93 74.16 62.35 57.80 Crystallinity/% 84.25 82.03 81.90 80.70

Embodiment six:

A method for rapidly preparing cellulose nanocrystals described in this embodiment is specifically carried out in accordance with the following steps:

1. Preparation of the cotton fiber treatment agent: under the condition of temperature of 80°C, the deep eutectic solvent was distilled under reduced pressure and stirred for 1 hour to obtain the cotton fiber treatment agent;

Described deep eutectic solvent is the mixture of choline chloride and oxalic acid; The mol ratio of described choline chloride and oxalic acid is 1:1;

2. Cotton fiber pretreatment: mix cotton fiber with a cotton fiber treatment agent to obtain a mixture, and carry out microwave heating treatment on the mixture. The condition of microwave heating treatment is to treat for 30 seconds at a temperature of 100° C. to obtain insoluble cotton fiber mixed solution of substances;

The mass ratio of described cotton fiber and cotton fiber treatment agent is 0.3:10;

3. Separation and cleaning: dilute the mixed solution containing cotton fiber insolubles with cleaning solution, then filter and separate, then clean the insolubles to obtain cotton fiber insolubles;

The cleaning solution is a mixture of acetone and water; the volume ratio of the acetone and water is 1:1;

Four, mechanical treatment: the clear cotton fiber insolubles are mixed with water to obtain an aqueous solution of 0.5% cotton fiber insolubles by mass percentage, and under the condition of ultrasonic power 1200W, the aqueous solution of 0.5% cotton fiber insolubles Ultrasonic treatment was performed for 30 min to obtain cellulose nanocrystals.

The microscopic size of the cellulose nanocrystals prepared in Example 5 is very uniform, and the size is uniform. The TEM electron microscope images of the prepared cellulose nanocrystals show that most of the insoluble matter of cotton fibers are mechanically processed to obtain cellulose nanocrystals.

Among many cellulose-rich raw materials, the cellulose content of cotton is the highest, which also causes the hydrogen bond between the cotton cellulose molecular chains to be very strong, and then it is difficult to prepare nanocellulose with cotton, so embodiment one, 3 to 6 use cotton with the strongest hydrogen bond force as a representative to prepare cellulose nanocrystals. In order to shorten the time, the ultra-fast pretreatment of 30 s adopted in Example 6 resulted in better morphology and size of the obtained cellulose nanocrystals. In general, the use of deep eutectic solvents to treat cellulose fibers can well weaken the hydrogen bond force in the non-crystalline region of cellulose, achieve the purpose of cutting off the non-crystalline region, and then promote mechanical treatment to obtain cellulose nanocrystals.

Claims (9)

1. A method for preparing cellulose nanocrystals rapidly is characterized in that a method for rapidly preparing cellulose nanocrystals is carried out according to the following steps: 1. Prepare the treatment agent: under the condition of temperature of 60°C-90°C, distill the deep eutectic solvent under reduced pressure and stir for 0.5h-2h to obtain the treatment agent; The deep eutectic solvent is a mixture of hydrogen bond acceptors and hydrogen bond donors; the molar ratio of the hydrogen bond acceptors and hydrogen bond donors is 1:(1～10); The hydrogen bond acceptor is a quaternary ammonium salt; the hydrogen bond donor is an amide, carboxylic acid or polyol; 2. Biomass fiber pretreatment: Mix biomass fiber with a treatment agent to obtain a mixture, and then heat the mixture by microwave. The condition of microwave heat treatment is to treat it for 0.5min to 10min at a temperature of 70°C to 100°C. , to obtain a mixed solution containing biomass fiber insoluble matter; The mass ratio of the biomass fiber to the treatment agent is (0.1～0.8):10; 3. Separation and cleaning: use the cleaning solution to dilute the mixed solution containing biomass fiber insoluble matter, then filter and separate, and then clean the insoluble matter to obtain biomass fiber insoluble matter; The cleaning solution is a mixed solution of an organic solvent and water; the volume ratio of the organic solvent to water is (1-9):1; 4. Mechanical treatment: mix the biomass fiber insolubles with water to obtain an aqueous solution of biomass fiber insolubles with a mass percentage of 0.05% to 2%, and perform mechanical treatment on the aqueous solution of biomass fiber insolubles to complete a rapid Method for preparing cellulose nanocrystals. 2. a kind of method for rapidly preparing cellulose nanocrystal according to claim 1 is characterized in that the quaternary ammonium salt described in step 1 is choline chloride, choline bromide, choline iodide or betaine ; The carboxylic acid described in step one is oxalic acid, malic acid, formic acid or lactic acid; the amide described in step one is urea or thiourea; the polyol described in step one is trihydric alcohol. 3. a kind of method for rapidly preparing cellulose nanocrystal according to claim 1 is characterized in that the biomass fiber described in step 2 is cotton fiber, pulp fiber, wood fiber, bamboo fiber, hemp fiber, straw class fiber, grass fiber or algae fiber. 4. A method for rapidly preparing cellulose nanocrystals according to claim 1, characterized in that the power of the microwave heating treatment described in step 2 is 800W-1000W. 5. A kind of method for rapidly preparing cellulose nanocrystal according to claim 1, is characterized in that the mechanical treatment described in step 4 is ultrasonic treatment, homogeneous treatment or grinding treatment; When the mechanical treatment is ultrasonic treatment, it is specifically carried out according to the following steps: under the condition of ultrasonic power 800W-1200W, the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05%-2% is ultrasonically treated for 5 minutes ~60min; When the mechanical treatment is homogeneous treatment, it is specifically carried out according to the following steps: under the condition of working pressure of 200bar to 500bar, the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05% to 2% is passed through the homogeneous The homogenization machine is used for 5 to 20 times of homogenization, and the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05% to 2% per 100mL is 30s to 70s each time; When the mechanical treatment is grinding, it is specifically carried out according to the following steps: under the condition that the rotating speed is 1000rpm～1500rpm, the aqueous solution of biomass fiber insoluble matter with a mass percentage of 0.05%～2% is placed in the grinder Medium grinding for 3min to 10min. 6. A method for rapidly preparing cellulose nanocrystals according to claim 1, characterized in that in step 2, the mixture is subjected to microwave heat treatment for 3 minutes at a temperature of 70° C. 7. A method for rapidly preparing cellulose nanocrystals according to claim 1, characterized in that in step 2, the mixture is subjected to microwave heating treatment for 1 min at a temperature of 80°C. 8. A method for rapidly preparing cellulose nanocrystals according to claim 1, characterized in that in step 2, the mixture is subjected to microwave heating treatment for 1 min at a temperature of 90° C. 9. A method for rapidly preparing cellulose nanocrystals according to claim 1, characterized in that in step 2, the mixture is subjected to microwave heating treatment for 30 s at a temperature of 100° C.