CN106883301A - Method for simultaneously preparing cellulose nanocrystals and cellulose nanofibers - Google Patents

Abstract

The invention relates to a method for simultaneously preparing cellulose nanocrystals and cellulose nanofibers, which comprises the following steps: 1) carrying out micro-nano wet grinding treatment on the cellulose with low polymerization degree; 2) and carrying out centrifugal separation on the mixed solution after the grinding treatment to obtain supernatant in which the cellulose nanocrystals are dispersed and lower sediment containing the cellulose nanofibers. According to the method, the cellulose with low polymerization degree is directly ground, the cellulose nanocrystal and the cellulose nanofiber can be obtained simultaneously after centrifugation, other post-treatments are not needed, the operation process is simple, and the operation method is green and environment-friendly.

Description

A method for simultaneously preparing cellulose nanocrystals and cellulose nanofibers

technical field

The invention relates to the field of polymer materials. In particular, it relates to a method for simultaneously preparing cellulose nanocrystals and nanocellulose.

Background technique

Cellulose has a wide range of sources in nature, abundant reserves, low price, renewable, degradable, and good biocompatibility. Under the background of the depletion of earth resources and the urgent need to protect the environment, people are increasingly researching and utilizing cellulose, especially cellulose products with high added value. Nanocellulose is an important high-performance material, which has many excellent properties, such as large aspect ratio, high mechanical properties, low thermal expansion coefficient, etc., making it have a wide range of application prospects in the field of materials.

Nanocellulose can be divided into cellulose nanocrystals and cellulose nanofibers, the main difference between which is the length. Nowadays, there are many methods for preparing cellulose nanocrystals and cellulose nanofibers, such as acid hydrolysis of concentrated sulfuric acid to prepare cellulose nanocrystals, high-pressure homogenization method to prepare cellulose nanofibers, TEMPO oxidation to prepare modified cellulose nanofibers, etc. , and the above methods all have certain shortcomings. For example, when using the concentrated acid acid hydrolysis method, a large amount of acid will be used and post-treatment is required. Not only the cycle is long, but also a large amount of waste acid will be produced, which will cause a certain burden on the environment. The improved methods based on this method also require post-treatment to remove acid or additives. For example, patent CN 102558367 requires subsequent treatment to remove acid, and patent CN105777913 requires subsequent treatment to remove additives. The high-pressure homogenization method has the disadvantage of high cost, and the TEMPO oxidation method has the disadvantages of complex and uncontrollable methods. Most importantly, the above methods can only obtain cellulose nanocrystals or cellulose nanofibers, but cannot obtain cellulose nanocrystals and cellulose nanofibers at the same time, which invisibly wastes raw materials and further increases costs. Therefore, it is very necessary to solve the problems of complex process, post-treatment, and inability to simultaneously obtain cellulose nanocrystals and cellulose nanofibers in the traditional method for preparing nanofibers. It is very necessary to invent a method that is simple and easy, does not require post-treatment, and can simultaneously obtain cellulose nanocrystals and cellulose nanofibers.

Contents of the invention

The purpose of the present invention is to provide a method that is simple and easy, does not require post-treatment, and can simultaneously obtain cellulose nanocrystals and cellulose nanofibers. Including the following steps:

1) The cellulose with a low degree of polymerization is subjected to micro-nano level wet grinding treatment;

2) centrifuging the ground mixed solution to obtain a supernatant liquid in which cellulose nanocrystals are dispersed and a lower precipitate containing cellulose nanofibers.

In the method of the present invention, in the process of grinding the cellulose, the cellulose with a smaller degree of polymerization is selected, and centrifuged after grinding to obtain the supernatant containing cellulose nanocrystals and the cellulose nanofiber containing cellulose. Precipitation, the obtained supernatant and precipitation can be used directly, and can also be used after removing water; the method prepares two products through one operation method, simplifies the preparation process, and the preparation method is green and environmentally friendly.

Preferably, the degree of polymerization of the cellulose with a low degree of polymerization is less than 600, and more preferably, the degree of polymerization of the cellulose is 150-550. The applicant found in research that only cellulose with a lower degree of polymerization can be ground to obtain cellulose nanocrystals and cellulose nanofibers, and the effect is better when the degree of polymerization is 150-550.

Preferably, the cellulose with the degree of polymerization is one or more of microcrystalline cellulose, cellulose CF11, cotton linter cellulose, cotton pulp cellulose, and pulp cellulose; further preferably microcrystalline cellulose, fiber Prime CF11 or cotton linter cellulose; above-mentioned several celluloses adopt the method of the present invention to have better effect after treatment.

Preferably, during the wet grinding process, the mass ratio of the cellulose to water is controlled to be 2-8:100. If it is lower than 2, the mechanical force is too large and the heat is generated too much, which will make the fiber oxidized and blackened. If it is higher than 8, the viscosity of the system will be too large, and the size of the obtained nanocrystals and nanofibers will be uneven.

Preferably, the wet grinding is carried out in a planetary ball mill, a vibration ball mill or a disc mill;

Preferably, during the ball milling process using a planetary ball mill, the rotating speed is 150-500rpm, and the ball milling time is 30-480min; the amplitude of the vibratory ball mill is ≤5mm, the frequency is 47.8Hz, and the vibration time is 120-480min; The rotating speed is 500-2000rpm, and the time is 120-480min. The planetary ball mill is further preferred, and the size and performance of the product after being ground by the planetary ball mill are more uniform.

Preferably, during the centrifugation process, the rotational speed is maintained at 3000-10000 rpm for 3-10 minutes. This centrifugation condition enables the separation of cellulose nanocrystals and cellulose nanofibers.

Preferably, before grinding the cellulose with a low degree of polymerization, an operation of swelling the cellulose with a low degree of polymerization is also included. The soaking and swelling treatment can make the fibers swell, weaken the hydrogen bond interaction between the fibers, facilitate the subsequent defibrillation, and shorten the grinding time.

Preferably, the swelling treatment is: adding the cellulose with a low degree of polymerization to an alkali solution or a salt solution containing a halogen, soaking at room temperature for 4 to 12 hours, and then washing to remove the alkali solution or a salt solution containing a halogen solution to obtain swollen cellulose.

Preferably, the alkali solution is one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide with a mass fraction of alkali of 2 to 8%; at this concentration, the cellulose can be fully swollen and not destroyed. The original crystalline form of cellulose.

And/or the halogen-containing salt solution is one or more of lithium bromide, lithium chloride, and zinc chloride solutions with a mass fraction of 5-20%. Swelling with a solution of this concentration ensures that the cellulose is fully swollen without wasting the saline solution.

Preferably, the method of the present invention comprises the steps of:

1) Add microcrystalline cellulose, cellulose CF11, cotton linter cellulose, cotton pulp cellulose, or pulp cellulose into an alkaline solution or a halogen-containing salt solution, soak at room temperature for 4 to 12 hours, and wash to remove all Alkaline solution or salt solution containing halogen to obtain swollen cellulose;

2) mixing the swelled cellulose with water at a ratio of 2 to 8:100 and placing it in a planetary ball mill, controlling the speed of the planetary ball mill to 150 to 500 rpm for 30 to 480 minutes;

3) Centrifuge the mixed solution after ball milling. During the centrifugation process, control the rotational speed at 4000-8000 rpm for 3-10 minutes; obtain the supernatant liquid dispersed with cellulose nanocrystals and the lower precipitate containing cellulose nanofibers .

The method of the present invention has the following beneficial effects:

1) The method of the present invention, by selecting cellulose with a smaller molecular weight, directly grinds the cellulose with a smaller molecular weight, and can obtain both cellulose nanocrystals and cellulose nanofibers through this physical treatment. This kind of product is easy to operate and environmentally friendly. It solves the problems that the traditional concentrated acid hydrolysis method uses a large amount of acid, requires a long time for post-treatment, and produces a large amount of waste acid, which is a burden on the environment.

2) The surface of the cellulose nanocrystal prepared by the present invention is all hydroxyl groups, and no other groups are introduced, which is beneficial to subsequent modification and chemical reaction.

3) The method of the present invention can simultaneously obtain cellulose nanocrystals and cellulose nanofibers without any other post-treatment, and the operation process is simple.

4) The physical state of the nanocellulose and nanocrystal obtained in the present invention is good, wherein the diameter of the cellulose nanocrystal is 3-12 nm, the length is 120-400 nm, and the aspect ratio is 19.7-62.4. The diameter of the cellulose nanofiber is 3-12nm, the length is greater than 500nm, and the aspect ratio is greater than 100.

Description of drawings

Fig. 1 is the transmission electron micrograph of the cellulose nanocrystal that concrete embodiment 1 prepares;

Fig. 2 is the transmission electron micrograph of the cellulose nanofiber prepared by specific example 1;

Fig. 3 is the transmission electron micrograph of the cellulose nanocrystal that concrete embodiment 2 prepares;

FIG. 4 is a transmission electron micrograph of cellulose nanofibers prepared in Example 2.

detailed description

The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

Example 1

(1) Weigh 1.10g of CF 11 (the degree of polymerization is 200) and mix it with water until the total mass is 23.10g. The mixture of cellulose and water was added into a 50mL zirconia ball mill jar, placed on a planetary ball mill, and milled for 360min at a speed of 300rpm.

(2) The ball-milling mixture obtained in step (2) is centrifuged at a speed of 4000 rpm, and the centrifugation time is 5 min. Obtain the supernatant that is dispersed with cellulose nanocrystal and the lower part that contains cellulose nanofiber precipitate (its micrograph is shown in Figure 1 and Figure 2), after drying, the mass ratio of nanocrystal and nanofiber is 1:6.

Example 2

(1) Weigh 1.10 g of microcrystalline cellulose (polymerization degree is 262), add to 30 mL of 8% NaOH solution, soak at room temperature for 4 h, add water to filter and wash until the pH of the filtrate reaches 7.

(2) Continue adding water to the hydrous cellulose obtained after washing in step (1), until the total mass is 23.10 g. The mixture of cellulose and water was added into a 50mL zirconia ball mill jar, placed on a planetary ball mill, and milled for 480min at a speed of 300rpm.

(3) The ball-milling mixture obtained in step (2) is centrifuged at a speed of 4000 rpm, and the centrifugation time is 5 min. A supernatant liquid dispersed with cellulose nanocrystals and a lower precipitate containing cellulose nanofibers were obtained (micrographs thereof as shown in Figures 3 and 4). After drying, the mass ratio of nanocrystals and nanofibers was 2:3.

Example 3

(1) Weigh 0.44g microcrystalline cellulose (polymerization degree is 262), add to 30mL 2% NaOH aqueous solution, soak at room temperature for 8h, add water to filter and wash until the pH of the filtrate reaches 7.

(2) Continue adding water to the hydrous cellulose obtained after washing in step (1), until the total mass is 22.44 g. The mixture of cellulose and water was added into a 50mL zirconia ball mill jar, placed on a planetary ball mill, and ball milled for 60min at a speed of 300rpm.

(3) The ball-milling mixture obtained in step (2) is subjected to centrifugation at a rotation speed of 8000 rpm and a centrifugation time of 3 min. A supernatant liquid dispersed with cellulose nanocrystals and a lower precipitate containing cellulose nanofibers were obtained. After drying, the mass ratio of nanocrystals and nanofibers was 1:19.

Example 4

(1) Weigh 1.96g CF11 (polymerization degree is 200), add to 30mL 8% NaOH solution, soak at room temperature for 12h, add water to filter and wash until the pH of the filtrate reaches 7.

(2) Continue adding water to the hydrous cellulose obtained after washing in step (1), until the total mass is 23.96 g. The mixture of cellulose and water was added into a 50mL zirconia ball mill jar, placed on a planetary ball mill, and milled for 180min at a speed of 300rpm.

(3) The ball-milling mixture obtained in step (2) is subjected to centrifugation at a speed of 8000 rpm and a centrifugation time of 10 min. A supernatant liquid containing cellulose nanocrystals and a lower precipitate containing cellulose nanofibers were obtained.

Example 5

(1) Weigh 0.88g cotton linter cellulose (polymerization degree is 453), add to 30mL 20% LiCl solution, soak at room temperature for 8h, add water and filter until the pH of the filtrate reaches 7.

(2) Continue adding water to the hydrous cellulose obtained after washing in step (1), until the total mass is 22.88 g. The mixture was added into a 50mL zirconia ball mill jar, placed on a planetary ball mill, and ball milled for 120min at a speed of 300rpm.

(3) The ball-milling mixture obtained in step (2) is subjected to centrifugation at a speed of 6000 rpm and a centrifugation time of 5 min. A supernatant liquid in which cellulose nanocrystals were dispersed and a lower precipitate containing cellulose nanofibers were obtained.

Example 6

(1) Weigh 15g microcrystalline cellulose (polymerization degree is 262), add to 50mL 8% KOH aqueous solution, soak at room temperature for 12h, add water to filter and wash until the pH of the filtrate reaches 7.

(2) Continue to add water to the aqueous cellulose obtained after washing in step (1) until the total mass is 315 g, and add the mixture to a disk mill for 480 min, and the speed of the disk mill is 1800 rpm.

(3) The ball-milling mixture obtained in step (2) is centrifuged at a speed of 10,000 rpm, and the centrifugation time is 5 min. A supernatant liquid in which cellulose nanocrystals were dispersed and a lower precipitate containing cellulose nanofibers were obtained.

Example 7

(1) Weigh 10g of CF11 (the degree of polymerization is 200), add it into 50mL of 10% LiBr aqueous solution, soak at room temperature for 10h, add water to filter and wash until the pH of the filtrate reaches 7.

(2) Continue adding water to the hydrous cellulose obtained after washing in step (1), until the total mass is 210 g. The mixture was added to a resonance ball mill, and ball milled for 240 min with a vibration frequency of 47.8 Hz.

(3) The ball-milling mixture obtained in step (2) is centrifuged at a speed of 10,000 rpm, and the centrifugation time is 5 min. A supernatant liquid in which cellulose nanocrystals were dispersed and a lower precipitate containing cellulose nanofibers were obtained.

Although, the present invention has been described in detail with general description, specific implementation and test above, but on the basis of the present invention, some modifications or improvements can be made to it, which will be obvious to those skilled in the art . Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (9)

1. a kind of at the same prepare Cellulose nanocrystal and cellulose nano-fibrous method, it is characterised in that comprise the following steps：

1) cellulose of low polymerization degree is carried out the wet grinding treatment of micro/nano level；

2) mixed liquor after the milled processed is centrifuged, obtains being dispersed with the supernatant of Cellulose nanocrystal and contain There is cellulose nano-fibrous bottom to precipitate.

2. method according to claim 1, it is characterised in that the degree of polymerization of the low polymerization degree cellulose is less than 600；It is excellent Selection of land, the degree of polymerization is 150~550.

3. method according to claim 1 and 2, it is characterised in that the low polymerization degree cellulose is microcrystalline cellulose, fibre One or several in dimension element CF11, cotton linters cellulose, cotton pulp cellulose, paper cellulose.

4. the method according to any one of claims 1 to 3, it is characterised in that during wet grinding, control is described Cellulose is 2~8 with the mass ratio of water:100.

5. the method according to claim 1 or 4, it is characterised in that the wet grinding is in planetary ball mill, vibrating ball Carried out in grinding machine or mill；

Preferably, during ball milling is carried out using planetary ball mill, rotating speed is 150~500rpm, and Ball-milling Time is 30 ~480min；Amplitude≤the 5mm of oscillatory type ball mill, frequency is 45~50Hz, and time of vibration is 120~480min；Mill Rotating speed is 500~2000rpm, and the time is 120~480min.

6. method according to claim 1 or 5, it is characterised in that during the centrifugal treating, keep rotating speed 3000 ~10000rpm, the time is 3~10min.

7. method according to claim 1 and 2, it is characterised in that be ground in the cellulose to the low polymerization degree Before processing, also carries out the operation of swelling treatment including the cellulose to the low polymerization degree；Preferably, the swelling treatment is： During the cellulose of the low polymerization degree is added into aqueous slkali or salting liquid containing halogen, after soaking 4~12h at normal temperatures, Washing removes the aqueous slkali or the salting liquid containing halogen, obtain it is swelling after cellulose.

8. method according to claim 7, it is characterised in that the aqueous slkali is hydrogen that the mass fraction of alkali is 2~8% One or several in lithia, NaOH, potassium hydroxide；

And/or the salting liquid containing halogen is in lithium bromide, lithium chloride, liquor zinci chloridi that mass fraction is 5~20% One or several.

9. the method according to any one of claim 1~8, it is characterised in that comprise the following steps：

1) microcrystalline cellulose, cellulose CF11, cotton linters cellulose, cotton pulp cellulose or paper cellulose are added to alkali soluble In liquid or the salting liquid containing halogen, 4~12h is soaked at normal temperatures, washing removes the aqueous slkali or the salt containing halogen is molten Liquid, obtain it is swelling after cellulose；

2) cellulose after the swelling treatment and water are pressed 2~8:It is placed in planetary ball mill after 100 mixing, control is described Planetary ball mill rotating speed is 150~500rpm, and the time is 60~480min；

3) mixed liquor after ball milling is centrifuged, in centrifugal process, controls rotating speed for 4000~8000rpm, the time is 3 ~10min；Obtain being dispersed with the supernatant of Cellulose nanocrystal and precipitated containing cellulose nano-fibrous bottom.