CN113307888A

CN113307888A - Carboxyl nano-cellulose and preparation method thereof

Info

Publication number: CN113307888A
Application number: CN202110645344.8A
Authority: CN
Inventors: 王晓映; 王守娟; 孔凡功
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2021-06-10
Filing date: 2021-06-10
Publication date: 2021-08-27
Also published as: AU2021105286A4

Abstract

The invention relates to a carboxyl nano-cellulose and a preparation method thereof, and the preparation method comprises the following steps: (1) soaking cellulose in water at normal temperature and normal pressure overnight, and adding sodium hydroxide solution after stirring uniformly; (2) adding a halogen-substituted carboxyl compound, continuously stirring, then dropwise adding an acidic solution to adjust the pH to be neutral, and desalting after the reaction is ended; or directly removing the sodium hydroxide solution and the halogen substituted carboxyl compound by suction filtration to terminate the reaction; (3) and after the reaction is finished, mechanically grinding by ultrasonic treatment, homogenization and the like to obtain the carboxyl nano cellulose. The method provided by the invention can carry out reaction at room temperature, and an organic solvent is not required to be added in the reaction process, so that the convention that the organic solvent is required to be added in the cellulose carboxylation process is broken, the energy consumption for preparing the nano-cellulose is reduced, and the cost for environmental treatment in the nano-cellulose preparation process is saved.

Description

Carboxyl nano-cellulose and preparation method thereof

Technical Field

The invention relates to carboxyl nanocellulose and a preparation method thereof, in particular to a method for preparing the carboxyl nanocellulose in a water phase at normal temperature and normal pressure, and belongs to the technical field of preparation of the carboxyl nanocellulose.

Background

Cellulose is a natural renewable resource with abundant reserves, carboxyl is introduced into the surface of the cellulose, on one hand, the hydrogen bond effect among cellulose molecules is destroyed, and the time and energy consumption of mechanical treatment (ultrasonic treatment, homogenization and the like) in the preparation process of the nano cellulose are reduced; on the other hand, the cellulose surface is provided with active connecting groups for subsequent modification. The TEMPO oxidation method is simple and convenient to operate, reaction conditions are mild, the TEMPO oxidation method is the most common preparation method of carboxyl nanocellulose, but the treatment efficiency of the TEMPO oxidation method on a cellulose crystallization area is low.

Disclosure of Invention

Aiming at the problems, the invention provides carboxyl nano-cellulose and a preparation method thereof, the invention utilizes the change of a high-concentration sodium hydroxide solution to the crystalline structure of the cellulose to reduce the crystallinity of the cellulose, and simultaneously the sodium hydroxide solution also provides an alkaline condition for a grafting reaction to promote the grafting reaction of a halogen-substituted carboxyl compound on the surface of the cellulose; the grafting reaction of the halogen-substituted carboxyl compound can also increase the steric hindrance and the charge repulsion of the secondary aggregation of the cellulose fibers, reduce the hydrogen bond effect among the cellulose fibers, promote the further dispersion of the cellulose fibers, inhibit the secondary aggregation of the cellulose fibers, and still maintain the good dispersibility of the cellulose after the sodium hydroxide solution and the halogen-substituted carboxyl compound are removed. Finally, the carboxylated nano-cellulose is obtained through simple mechanical treatment (such as ultrasonic treatment, homogenization and the like). The technical scheme of the invention is as follows:

a preparation method of carboxyl nanocellulose comprises the following steps:

(1) soaking cellulose in water at normal temperature and normal pressure overnight, wherein the addition amount of the cellulose is 0.5-5% (g/mL), adding a sodium hydroxide solution after uniformly stirring, wherein the concentration of the sodium hydroxide solution is 7-15% (g/mL), and continuously stirring; the sodium hydroxide solution has the functions of promoting the dissolution or swelling of the cellulose, changing the crystalline structure of the cellulose, promoting the amorphous arrangement of the cellulose fibers, and simultaneously enabling hydroxyl groups on the surfaces of the cellulose fibers to have negative charges so as to provide conditions for the subsequent grafting reaction of the halogen-substituted carboxyl compound on the surfaces of the cellulose fibers.

(2) Adding halogen-substituted carboxyl compounds for multiple times, continuously stirring in the adding process to promote dispersion and reaction of the cellulose fibers, wherein the adding amount of the halogen-substituted carboxyl compounds is 25-100% of the amount of sodium hydroxide solution substances, continuously stirring after dropwise adding the halogen-substituted carboxyl compounds, then dropwise adding an acidic solution to adjust the pH to be neutral, and desalting after the reaction is ended; or directly removing the sodium hydroxide solution and the halogen-substituted carboxyl compound by suction filtration to terminate the reaction, and then washing impurities remaining on the surface of the cellulose with pure water until the conductivity is not more than 50 muS/cm. The halogen-substituted carboxyl compound can remove halogen in sodium hydroxide solution, and carbon with positive charges is exposed; hydrogen in hydroxyl on the surface of the cellulose fiber is removed under the action of sodium hydroxide, oxygen with negative charges is formed on the surface of the fiber, carbon with positive charges is combined with the oxygen with negative charges, ether bonds are formed between halogen-substituted carboxyl compounds and cellulose molecules, and then the halogen-substituted carboxyl compounds are crosslinked on the surface of the cellulose fiber. The combination of the halogen-substituted carboxyl compound on the surface of the cellulose fiber not only improves the negative charge carried by the surface of the fiber and increases the electrostatic repulsion among the fibers, but also promotes the dispersion of the fiber and increases the steric hindrance of the secondary aggregation of the fiber. Preferably, the halogen-substituted carboxyl compound is selected from any one of a bromine-substituted carboxyl compound, a chlorine-substituted carboxyl compound, or an iodine-substituted carboxyl compound; the acid solution is selected from any one of hydrochloric acid and acetic acid.

(3) After the reaction is finished, the carboxyl nano-cellulose can be obtained by mechanical grinding treatment such as ultrasonic treatment, homogenization and the like.

Further, the cellulose in the step (1) is natural cellulose or cellulose obtained by artificial treatment; preferred natural celluloses are selected from lignocellulose or bacterial cellulose; the cellulose obtained by manual treatment is microcrystalline cellulose.

Further, the cellulose is added in an amount of 1% (g/mL) in the step (1), and the concentration of the sodium hydroxide solution is 8% (g/mL).

Further, the halogen-substituted carboxyl compound is added in the step (2) in an amount of 70% of the amount of the sodium hydroxide solution substance.

The invention also comprises carboxyl nanocellulose obtained by the preparation method.

Compared with the prior art, the invention has the following advantages:

(1) the reaction is carried out under the conditions of normal temperature, normal pressure and water phase, the common practice that an organic solvent is required to be added in the cellulose carboxylation process and the cellulose carboxylation is carried out under the heating condition is broken, the cost of the cellulose carboxylation is reduced, and the preparation method is more energy-saving and environment-friendly;

(2) the implementation of the carboxylation process, on one hand, carboxyl with higher reactivity is grafted to the surface of cellulose; on the other hand, the dispersion of cellulose fibers is promoted, and the secondary aggregation of the fibers is inhibited, which reduces the cost of mechanical treatment in the preparation process of the nano-cellulose.

Drawings

FIG. 1 is an infrared spectrum of a halogen-substituted carboxyl compound before and after grafting on a cellulose surface in the preparation process of the present invention;

FIG. 2 is a diagram showing the change of the crystalline structure of cellulose detected by X-ray diffraction before and after grafting of a halogen-substituted carboxyl compound on the surface of cellulose in the present invention.

Detailed Description

The invention will be further described with reference to specific embodiments, and the advantages and features of the invention will become apparent as the description proceeds. The examples are illustrative only and do not limit the scope of the present invention in any way. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, and that such changes and modifications may be made without departing from the spirit and scope of the invention.

Example 1: carboxyl nano-cellulose and preparation method thereof

The method comprises the following steps:

(1) soaking 0.5% (g/mL) of bacterial cellulose in pure water at normal temperature and pressure overnight, uniformly stirring, adding a sodium hydroxide solution to ensure that the concentration of the sodium hydroxide solution is finally 8% (g/mL), and continuously stirring;

(2) then adding bromoacetic acid for multiple times while stirring, wherein the total amount of the bromoacetic acid is 70 percent of the amount of the sodium hydroxide substance, continuously stirring overnight, dropwise adding a hydrochloric acid solution to adjust the pH value to be neutral, and desalting after the reaction is ended:

(3) and (3) ultrasonically treating the desalted solution to obtain the carboxyl nano cellulose.

Example 2: carboxyl nano-cellulose and preparation method thereof

The method comprises the following steps:

(1) soaking 2% (g/mL) microcrystalline cellulose in pure water at normal temperature and normal pressure overnight, stirring uniformly, and adding sodium hydroxide to ensure that the concentration of the sodium hydroxide solution is 12% (g/mL) at last;

(2) adding chloroacetic acid for multiple times, wherein the dropwise adding amount is 70% of the amount of the sodium hydroxide substance, stirring while adding, continuing to stir for 1 hour after the dropwise adding is finished, then performing suction filtration in a polytetrafluoroethylene funnel, and removing the sodium hydroxide and chloroacetic acid remained on the surface of the cellulose through multiple water washes until the conductivity is not more than 50 mu S/cm;

(3) ball milling to obtain carboxyl group nanometer cellulose.

Example 3: carboxyl nano-cellulose and preparation method thereof

The method comprises the following steps:

(1) soaking 0.5% (g/mL) eucalyptus pulp in pure water at normal temperature and pressure overnight, stirring, and adding sodium hydroxide solution to make the concentration of the sodium hydroxide solution to be 9% (g/mL);

(2) adding iodoacetic acid for multiple times, wherein the addition amount is 50% of the amount of the sodium hydroxide substance, continuously stirring for 2 hours, dropwise adding an acetic acid solution to adjust the pH to be neutral, and desalting after the reaction is ended;

(3) and performing ultrasonic treatment to obtain the carboxyl nanocellulose.

Example 4: carboxyl nano-cellulose and preparation method thereof

The method comprises the following steps:

(1) soaking 4% (g/mL) microcrystalline cellulose at normal temperature and pressure overnight, stirring well, adding sodium hydroxide solution to make the concentration of the sodium hydroxide solution be 8% (g/mL);

(2) adding bromoacetic acid for multiple times, wherein the dropping amount is 100 percent of the amount of the sodium hydroxide substance, and continuously stirring for 5 hours;

(2) dropwise adding hydrochloric acid solution to adjust the pH to be neutral, and desalting after the reaction is ended;

(3) homogenizing to obtain carboxyl nanometer cellulose.

Test examples

According to infrared spectrum detection, the halogen-substituted carboxyl compound is successfully grafted to the surface of the cellulose fiber in the experimental process of the invention, as shown in figure 1; the crystallinity of the cellulose was reduced by about 20% after the carboxylation treatment as measured by X-ray diffraction, as shown in FIG. 2. This experimental result shows that the carboxyl compound substituted by halogen can be grafted on the surface of the cellulose fiber in the sodium hydroxide solution system, and the reaction can be carried out at normal temperature and pressure. The invention realizes the grafting of the halogen-substituted carboxyl compound and the cellulose in a pure water phase system, avoids the use of an organic solvent, has mild reaction conditions and is a green method for realizing the carboxylation of the cellulose. Meanwhile, the method of the invention also breaks the hydrogen bond function among cellulose fibers in the implementation process, promotes the dispersion of the cellulose, and reduces the energy consumption in the process of preparing the nano cellulose by a mechanical method.

Claims

1. The preparation method of the carboxyl nanocellulose is characterized by comprising the following steps:

(1) soaking cellulose in water at normal temperature and normal pressure overnight, wherein the addition amount of the cellulose is 0.5-5% (g/mL), adding a sodium hydroxide solution after uniformly stirring, wherein the concentration of the sodium hydroxide solution is 7-15% (g/mL), and continuously stirring;

(2) adding halogen-substituted carboxyl compounds for multiple times, continuously stirring in the adding process to promote dispersion and reaction of the cellulose fibers, wherein the adding amount of the halogen-substituted carboxyl compounds is 25-100% of the amount of sodium hydroxide solution substances, continuously stirring after dropwise adding the halogen-substituted carboxyl compounds, then dropwise adding an acidic solution to adjust the pH to be neutral, and desalting after the reaction is ended; or directly removing the sodium hydroxide solution and the halogen-substituted carboxyl compound by suction filtration to terminate the reaction, and then cleaning impurities remained on the surface of the cellulose by using pure water until the conductivity is not more than 50 mu S/cm;

(3) and after the reaction is finished, mechanically grinding by ultrasonic treatment, homogenization and the like to obtain the carboxyl nano cellulose.

2. The method according to claim 1, wherein the cellulose in the step (1) is natural cellulose or cellulose obtained by artificial treatment.

3. The method according to claim 2, wherein the natural cellulose is selected from the group consisting of lignocellulose or bacterial cellulose; the cellulose obtained by manual treatment is microcrystalline cellulose.

4. The method according to claim 1, wherein the cellulose is added in an amount of 1% (g/mL) and the sodium hydroxide solution is added in an amount of 8% (g/mL) in the step (1).

5. The method according to claim 1, wherein the halogen-substituted carboxyl compound is added in an amount of 50% of the amount of the sodium hydroxide solution substance in the step (2).

6. The method according to claim 1, wherein the halogen-substituted carboxyl compound in the step (2) is selected from any one of a bromine-substituted carboxyl compound, a chlorine-substituted carboxyl compound and an iodine-substituted carboxyl compound.

7. The method according to claim 1, wherein the acidic solution in step (2) is selected from any one of hydrochloric acid and acetic acid.

8. Carboxyl nanocellulose obtained by the production method according to any one of claims 1 to 7.