KR102509908B1 - Manufacturing method of redispersible cellulose nanofibrils in aqueous solution - Google Patents

Abstract

This application relates to a method for preparing cellulose nanofibrils that can be redispersed in an aqueous solution. First, the dietary fiber raw material is beaten and then nano-homogenized to obtain a CNF suspension, and after adjusting the pH of the prepared CNF suspension, a certain amount of potassium chloride is added and dried. In the method of the present application, a mechanical method is adopted to produce CNF, and the yield is relatively high. In the method of the present application, the CNF suspension after adjusting the pH and adding salt is vacuum-dried and then easily redispersed in an aqueous solution, and has good properties such as stability after redispersion, and this method is suitable for storing and transporting cellulose nanofibrils The cost can be reduced and the work is simple, so it is suitable for large-scale production. This provided a new idea and a new method for high-value utilization of cellulose, and a new method for the preparation of aqueous solution redispersible CNF.

Description

Manufacturing method of redispersible cellulose nanofibrils in aqueous solution

This application was filed with the Chinese Intellectual Property Office on June 27, 2019, with the application number 201910567064.2, and claims the priority of a Chinese patent application titled "Method for producing redispersible cellulose nanofibrils in aqueous solution", The entire contents of which are hereby incorporated into this application by reference.

This application belongs to the field of cellulose, and specifically relates to a method for preparing, drying and redispersing nanocellulose in an aqueous solution.

Cellulose, as an abundant, renewable and biodegradable natural polymer, has enormous application prospects in the production of household chemicals and in industries such as paper, food, printing, cosmetics, oil well drilling and pharmaceuticals. At the same time, cellulose nanofibrils (CNF) have very broad application prospects due to their excellent properties such as nanoscale, high specific surface area, high aspect ratio, low density, recyclability and degradability. However, since CNF has a high specific surface area and a large amount of hydroxyl groups are contained on the surface, it causes irreversible recombination in the drying process and recombination of CNF (film or powder) in the non-polar matrix during compounding; In the drying process, additional hydrogen bonds are formed between the amorphous parts of CNF, leading to irreversible polymerization formation, and at the same time, these hydrogen bonds formed in the drying process do not “break” after redispersion.

To ensure that CNF does not form irreversible clusters or membrane structures during drying, it must be suspended in water. These problems limit the industrial-scale production and large-scale commercial application of CNF in transportation, storage and composite materials.

There was an article on how to increase the redispersibility of nanocellulose by way of denaturation, and many chemical reagents such as isopropyl alcohol, sodium hydroxide, and acetic acid were used in the treatment process. These reagents not only change and affect the properties of CNF itself, but also do not effectively maintain the original performance and pollute the environment.

In order to overcome the above problems, the present invention provides a method for producing redispersible cellulose nanofibrils in an aqueous solution. This method combines the effects of vacuum drying, pH, and temperature on the deprotonation of CNF, and significantly improves the redispersibility of CNF aqueous solution by adding salt and then drying to prepare CNF that is easy to redisperse in aqueous solution. As a method, at the same time, the application requirements of different solids after the non-chemically modified cellulose nanofibrils are redispersed in an aqueous solution are achieved, and the application of CNF after redispersion in an aqueous solution is more convenient.

In order to achieve the above technical objectives, the technical solutions used in this application are as follows:

In the method for producing redispersible cellulose nanofibrils in an aqueous solution,

Beating and nanohomogenizing the pulp to form a CNF suspension;

After adjusting the pH value of the CNF suspension to 3-4, the pH value of the CNF suspension is adjusted to 7-8;

adding potassium chloride to the CNF suspension having a pH value of 7-8, mixing uniformly, and vacuum drying to form dried CNF;

and dispersing the dried CNF in an aqueous solution to obtain it.

Results of the study of the present application: Acid-base adjustment of the pH value of the CNF suspension is beneficial to the deprotonation of cellulose, ^- forming CNF. When adding potassium chloride, it is easy to form K ^+_- CNF, and in the drying process, this structure limits the formation of hydrogen bonds and lowers the degree of keratinization of CNF, making it easy to redisperse after drying.

Result of research of the present application: In the manufacturing method of CNF, since the drying temperature, pressure, etc. greatly affect the performance of the CNF suspension after redispersion in an aqueous solution, in some embodiments, the beating has a rotational speed of 400 to 800 rpm. Use a fiber separator.

In some embodiments, the degree of beating after the beating is 50-100 mL.

Since the high-pressure micro-jet nanohomogenization can make the particles of the medium extremely fine, and the product after homogenization has advantages such as non-sedimentation, high colloidal quality, and high stability, in some embodiments, the conditions of the nanohomogenization are at 200 to 400 bar , The CNF suspension prepared by passing through a 200 μm chamber 10 to 15 times and sequentially passing through 200 μm and 87 μm chambers 10 to 30 times at 1000 to 1500 bar has excellent dispersibility.

Results of the study of the present application: Since the use of monovalent potassium salt as a hydrogen bond blocking agent in the vacuum drying process can effectively improve the water solubility of CSF, in some embodiments, the amount of potassium chloride added is controlled to an ionic strength of 5 to 15 mM, Water solubility and redispersibility were effectively improved.

Results of research on the present application: In the current method of drying cellulose nanofibrils, different drying methods have different treatment temperatures, which greatly affects the action and effect of potassium chloride. In some examples, the vacuum drying pressure is -15 to - 10 "Hg, temperature is 40 ~ 60 ℃, drying time is 2 ~ 3 days. The relatively mild drying temperature and pressure conditions of vacuum drying are not only advantageous for redispersing CNF in aqueous solution after drying, but also CNF in aqueous solution. stability after re-dispersion is improved, etc. In some embodiments, the rotational speed of the re-dispersion is 10000-20000 rpm, and the time is 15-90 s.

The present application also provides aqueous solution redispersible nanocellulose nanofibrils prepared by any of the above methods. This method can make CNF have better redispersibility in aqueous solution without denaturation treatment, and at the same time has the advantages of being green, pollution-free, low cost, and simple operation.

The present application also provides cellulose nanofibrils redispersible in the aqueous solution having a particle diameter of 500 to 2500 nm, preferably 610 to 2300 nm, more preferably 610 to 1990 nm, still more preferably 610 to 1480 nm, and most preferably 610 to 1100 nm And, in the embodiment of the present invention, specifically preferably 1100 ~ 2300nm, 1100 ~ 1900nm, 710 ~ 1480nm and 610 ~ 1100nm; After re-dispersion in aqueous solution, TSI was 0.0~0.25.

This application also provides applications of the redispersible nanocellulose nanofibrils in the aqueous solution in the fields of chemicals, papermaking, food, printing, cosmetics, oil well drilling or pharmaceuticals.

Advantageous effects of the present application are as follows:

(1) CNF is produced by a mechanical method, and the obtained CNF has a high yield.

(2) Using vacuum drying, the drying temperature is more favorable to the further formation of K ⁺ ~ ^- CNF, and more favorable to redispersion after drying.

(3) In the drying process, monovalent potassium salt is used as a hydrogen bond blocking agent, so the cost is low and the effect is good.

(4) A plan was provided to solve the transportation and storage problems of CNF.

(5) The operation method of this application is simple, low-cost, and universal, so it is easy to scale production.

The drawings in the specification, which form a part of this application, are used for further understanding of this application, and the exemplary embodiments of this application and their descriptions are used to explain this application, and do not constitute inappropriate limitations of this application. don't
1 is a process flow diagram of Example 1 of the present application.
2 is a particle size distribution diagram of CNF after redispersion in aqueous solutions obtained in Examples 1, 2, 3, and 4 of the present application, where 1%, 0.5%, 0.25%, and 0.125% are sequentially redispersed in aqueous solutions of Examples 1 to 4 It corresponds to the mass fraction of CNF when
Figure 3 is a graph of the stability index (TSI) of redispersion in CNF aqueous solutions of different mass fractions after adding and drying salts in Examples 1, 2, 3 and 4 of the present application. Here, 1%, 0.5%, 0.25%, and 0.125% sequentially correspond to the mass fraction of CNF when redispersed in an aqueous solution in Examples 1 to 4.
4 is a scanning electron micrograph of CNF after drying by adding salt in Example 1 of the present application.
5 is a scanning electron micrograph of CNF redispersed in an aqueous solution after adding salt and drying in Example 1 of the present application.

It should be pointed out that the following detailed description is all illustrative, and is intended to explain a further step in the present application. Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is only for describing specific implementations and is not intended to limit the exemplary implementations according to the present invention. For example, as used herein, singular expressions include plural expressions, unless the context clearly dictates otherwise, and also when the terms “comprising” and/or “comprising” are used herein, It should be understood that it indicates the presence of features, steps, operations, devices, components, and/or combinations thereof.

As described in the background technology, the conventional technology for producing redispersible cellulose nanofibrils in aqueous solution has a problem in that the cellulose nanofibrils are modified to various degrees and it is difficult to maintain the original performance. Therefore, the present invention proposes a method for preparing redispersible cellulose nanofibrils (CNF) in an aqueous solution. Perform the following steps:

(1) Refining treatment: The pulp disintegrated by the fiber separator is beaten through the beating machine.

(2) Nanohomogenization: Under room temperature, the pulp treated by the beating machine is first processed by a 200 μm chamber and then sequentially passed through a 200 μm and 87 μm chamber to be homogenized.

(3) pH adjustment: After adjusting the pH of the CNF suspension to acidic with a hydrochloric acid solution, adjust to alkaline with a sodium hydroxide solution.

(4) Addition of potassium chloride: A certain amount of potassium chloride is added to the pH-adjusted CNF suspension.

(5) Drying treatment: The CNF suspension to which potassium chloride is added is placed in a vacuum drying oven and dried.

(6) Mechanical redispersion: The dried CNF was redispersed in water through a mixer, and the stability was measured by multiple light scatterers.

Preferably, in step (1), the rotational speed of the fiber separator is 400-800 rpm, and the degree of beating after beating is 50-200 mL.

Preferably, the pulp beaten in step (2) passes through a 200 μm chamber 10 to 15 times at 200 to 400 bar, and then passes through 200 μm and 87 μm chambers 15 to 30 times at 1000 to 1500 bar sequentially.

Preferably, in step (3), the pH of the prepared CNF suspension is adjusted to 3-4 with a 0.05-0.2 M hydrochloric acid solution, and then the pH is adjusted to 7-8 with a 0.05-0.2 M potassium hydroxide solution.

Preferably, potassium chloride is added to the CNF suspension in step (4) to control the ionic strength to 5-15 mM.

Preferably, the vacuum drying pressure in step (5) is -15 to -10 "Hg, the temperature is 40 to 60 ° C, and the drying time is 2 to 3 days.

Preferably, in step (6), cutting is performed for 15 to 90 seconds at a rotational speed of 10000 to 20000 rpm during mechanical redispersion.

One aspect of the present invention also provides a method for producing cellulose nanofibrils redispersible in an aqueous solution by adjusting the pH, adding a salt, adjusting the temperature and drying, and including the following steps:

(1) Beat the pulp to a certain degree of beating using a beating device.

(2) Prepare a CNF suspension from the pulp prepared in step (1) with a high-pressure micro-jet nanohomogenizer.

(3) Adjust the pH value of the CNF suspension obtained in step (2).

(4) A certain amount of potassium chloride is added to the CNF suspension in step (3).

(5) Vacuum-dry the CNF suspension in step (4) to obtain dried CNF.

(6) Disperse the CNF obtained in step (5) with a mixer according to different mass fractions.

Preferably, the beating treatment in step (1) is to beat the bleached hardwood pulp to 100-150 mL of CSF (Canadian Standard Beating).

Preferably, in step (2), the homogeneous pressure is 200-400 bar, 10-15 passes through the 200 μm chamber, and 10-30 passes through the 200 μm and 87 μm chambers sequentially at 1000-1500 bar.

Preferably, in step (3), the pH of the CNF suspension is adjusted to 3-4, and then the pH is adjusted to 7-8.

Preferably, the amount of potassium chloride added in step (4) maintains the ionic strength at 5 to 15 mM.

Preferably, the vacuum drying conditions in step (5) are -15 ~ -10 "Hg vacuum pressure, 40 ~ 60 ℃ temperature, and 2 ~ 3 days.

Preferably, in step (6), when re-dispersing with a mixer, the rotational speed is 10000 to 20000 rpm, and shearing is performed for 15 to 90 seconds.

Principle explanation: Adjusting the pH of the CNF suspension favors the deprotonation of cellulose, forming ^CNF . It is easy to form K ⁺ - ^- CNF after adding potassium chloride, and this structure limits the formation of hydrogen bonds in the drying process, reduces the degree of CNF keratinization, and makes it easy to redisperse after drying.

The following describes the technical solution of the present application through specific examples.

Example 1

1. Refining, put the pulp disintegrated by the fiber separator into the Valli refiner with a pulp concentration of 10% and beat until the CSF becomes 100mL.

2. Nanohomogenization treatment, using high-pressure micro-jet nanohomogenizer. Treatment conditions were: 10 passes through a 200 μm chamber at 200 bar, followed by 15 passes through 200 μm and 87 μm chambers sequentially at 1200 bar.

3. pH adjustment, first, the pH of the CNF suspension was adjusted to 3 with hydrochloric acid, and then the pH was adjusted to 8 by adding sodium hydroxide dropwise.

4. Potassium chloride was added to the CNF suspension to maintain an ionic strength of 10 mM.

5. Drying treatment, a vacuum drying oven was used. Treatment conditions: drying at −15" Hg, 60° C. for 2 days (see FIG. 4 for scanning electron micrograph).

6. Re-dispersion, dispersion conditions are: CNF 1%, shear at 10000 rpm for 15 seconds. (See FIG. 5 for scanning electron micrographs).

The particle diameter of the redispersed particles prepared in this example is 1100 to 2300 nm (see FIG. 2), and the TSI after redispersion in aqueous solution is 0.0 to 0.05 (see FIG. 3).

Example 2

1. Refining: Put the pulp disaggregated by the fiber separator into the Valli refiner with a pulp concentration of 20% and beat until the CSF becomes 50mL.

2. Nano homogenizer treatment, use high-pressure micro jet nano homogenizer. Treatment conditions were: 15 passes through a 200 μm chamber at 300 bar, followed by 25 passes through 200 μm and 87 μm chambers sequentially at 1000 bar.

3. pH adjustment, first, the pH of the CNF suspension was adjusted to 4 with hydrochloric acid, and then the pH was adjusted to 8 by adding sodium hydroxide dropwise.

4. Potassium chloride was added to the CNF suspension to maintain the ionic strength at 15 mM.

5. Drying treatment, drying by vacuum drying oven. Treatment conditions: -10" Hg, dried at 55 °C for 3 days.

6. Re-dispersion, dispersion conditions are: CNF 0.5%, shear at 11000 rpm for 30 seconds.

The particle size of the redispersed particles prepared in this example is 1100 to 1990 nm (see FIG. 2), and the TSI after redispersion in aqueous solution is 0.0 to 0.05 (see FIG. 3).

Example 3

1. Refining, put the pulp disintegrated by the fiber separator into the Valli refiner with a pulp concentration of 15% and beat it until the CSF becomes 80mL.

2. Nano homogenizer treatment, using high-pressure micro jet nano homogenizer. Treatment conditions were: 10 passes through a 200 μm chamber at 400 bar, followed by 30 passes through 200 μm and 87 μm chambers sequentially at 1500 bar.

3. pH adjustment, first, the pH of the CNF suspension was adjusted to 3.5 with hydrochloric acid, and then the pH was adjusted to 7.5 by dropwise addition of sodium hydroxide.

4. Drying treatment, drying by vacuum drying oven. Treatment conditions: drying at -13 "Hg, 50°C for 3 days.

5. Potassium chloride was added to the CNF suspension to maintain an ionic strength of 8 mM.

6. Re-dispersion, dispersion conditions are: CNF 0.25%, shear at 12000 rpm for 60 seconds.

The particle diameter of the redispersed particles prepared in this example is 710 to 1480 nm (see FIG. 2), and the TSI after redispersion in aqueous solution is 0.0 to 0.05 (see FIG. 3).

Example 4

1. Refining, put the pulp disintegrated by the fiber separator into the Valli refiner with a pulp concentration of 10% and beat until the CSF becomes 150mL.

2. Nano homogenizer treatment, use high-pressure micro jet nano homogenizer. Treatment conditions were: 13 passes through a 200 μm chamber at 250 bar, followed by 20 passes through 200 μm and 87 μm chambers sequentially at 1000 bar.

3. pH adjustment, first, the pH of the CNF suspension was adjusted to 4 with hydrochloric acid, and then the pH was adjusted to 8 by adding sodium hydroxide dropwise.

4. Potassium chloride was added to the CNF suspension to maintain an ionic strength of 15 mM.

5. Drying treatment, drying by vacuum drying oven. Processing conditions: -15 "Hg, drying for 2 days at 50°C.

6. Redispersion, dispersion conditions are: CNF 0.125%, shear at 15000 rpm for 40 seconds.

The particle size of the redispersed particles prepared in this example is 610 to 1100 nm (see FIG. 2), and the TSI after redispersion in aqueous solution is 0.0 to 0.25 (see FIG. 3).

Result: The particle diameter of the CNF prepared in the above example was between 500 and 2500 nm, and the presence of potassium chloride had a good effect in maintaining the stability of the redispersed CNF suspension. After vacuum drying the CNF suspension, it is redispersed in an arbitrary mass fraction of 0.25 ~ 1%, and all properties such as stability are good. This revolutionized the application requirements of various solid contents after redispersion of the non-denaturing aqueous solution of cellulose nanofibrils (see Fig. 3), and also showed the great influence of the drying method on the production of aqueous redispersible CNF.

Finally, it should be explained that the above description is merely a preferred embodiment of the present invention, not limiting the present invention, and the present invention has been described in detail with reference to the foregoing embodiments, but the ordinary knowledge in the art Those who have it can still modify or equally replace some of the technical solutions described in the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall all be included in the protection scope of the present application. In the above, specific embodiments of the present invention have been described with reference to the accompanying drawings, but the protection scope of the present invention is not limited, and those skilled in the art, based on the technical solution of the present invention, can be made by those skilled in the art without creative work. It should be understood that various modifications or variations of the present invention still fall within the protection scope of the present invention.

Claims (10)

Beating and nanohomogenizing the pulp to form a CNF suspension;
After adjusting the pH value of the CNF suspension to 3-4, the pH value of the CNF suspension was adjusted to 7-8;
adding potassium chloride to the CNF suspension having a pH value of 7 to 8, mixing uniformly, and vacuum drying to form dried CNF;
The vacuum drying has a pressure of -15 to -10 "Hg, a temperature of 40 to 60 ° C, and a drying time of 2 to 3 days;
A method for producing redispersible cellulose nanofibrils in an aqueous solution, comprising the step of dispersing the dried CNF in an aqueous solution again.
According to claim 1,
The beating is a method for producing redispersible cellulose nanofibrils in an aqueous solution, characterized in that using a fiber separator and a rotational speed of 400 to 800 rpm.
According to claim 1,
A method for producing redispersible cellulose nanofibrils in an aqueous solution, characterized in that the CSF after the beating is 50 to 100 mL.
According to claim 1,
The conditions of the nanohomogenization are redispersible in an aqueous solution, characterized in that at 200 to 400 bar, passing through a 200 μm chamber 10 to 15 times, and at 1000 to 1500 bar, sequentially passing through 200 μm and 87 μm chambers 10 to 30 times. Method for producing cellulose nanofibrils.
According to claim 1,
Method for producing redispersible cellulose nanofibrils in an aqueous solution, characterized in that the addition amount of potassium chloride is controlled to an ionic strength of 5 to 15 mM.
delete According to claim 1,
Method for producing redispersible cellulose nanofibrils in an aqueous solution, characterized in that the rotational speed of the redispersion is 10000 to 20000 rpm and the time is 15 to 90s.
Cellulose nanofibrils redispersible in an aqueous solution prepared by the method according to any one of claims 1 to 5 and 7.
According to claim 8,
Cellulose nanofibrils redispersible in an aqueous solution, characterized in that the particle size of the redispersible cellulose nanofibrils in the aqueous solution is 500 to 2500 nm, and the TSI is 0.0 to 0.25 after redispersion in the aqueous solution.
Cellulose nanofibrils redispersible in an aqueous solution according to claim 8 are redispersible in an aqueous solution, characterized in that they are utilized in any one of the fields of chemicals, paper, food, printing, cosmetics, oil well drilling or pharmaceuticals. .

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