CN111363064A - Preparation method of carboxymethyl chitosan with high substitution degree and high molecular weight - Google Patents

Abstract

The invention relates to a preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight. The chitosan is dissolved in a strong alkali solution to obtain a chitosan-strong alkali solution, and the After the strong alkali content in the chitosan-strong alkali solution is increased to 35-45wt% by supplementing the strong alkali solution under the condition of ℃, chloroacetic acid is added, and the carboxymethyl substitution is carried out under the condition that the temperature is 40-100 ℃ The carboxymethyl chitosan with high degree of substitution and high molecular weight is obtained by the reaction, and the preparation method performs carboxymethylation reaction under homogeneous conditions, which increases the probability of sodium hydroxide infiltrating the chitosan molecule. The process is simple and the conditions are mild. The substitution degree of carboxymethyl chitosan is significantly improved; the substitution degree of the prepared high substitution degree and high molecular weight carboxymethyl chitosan is 1.0～1.8, and the viscosity average molecular weight is 9.0×10 ⁵ ～11.0×10 ⁵ g /mol, high degree of substitution and high molecular weight, very promising application.

Description

A kind of preparation method of high substitution degree and high molecular weight carboxymethyl chitosan

technical field

The invention belongs to the technical field of preparation of carboxymethyl chitosan, and relates to a preparation method of carboxymethyl chitosan with high substitution degree and high molecular weight.

Background technique

Carboxymethyl chitosan is a carboxymethylated modified chitosan derivative with good water solubility, film-forming properties, gas selective permeability, moisturizing properties, promoting epithelial cell growth, and delaying cell aging. , Promote skin ulcer wound healing, inhibit superficial epidermal cell fungal growth and other excellent effects, it has been used in daily chemicals such as hair care and skin care, medicine and fruit and vegetable preservation. Carboxymethyl chitosan is a water-soluble amphoteric polyelectrolyte, which can also be used as a flocculant in water treatment, a metal ion chelating agent, etc. to purify water. Carboxymethyl chitosan is the most studied and applied chitosan derivative in recent years. one of the things.

At present, carboxymethyl chitosan is mainly prepared from swollen chitosan by carboxymethyl substitution reaction of chloroacetic acid in an alkaline environment. The preparation process of carboxymethyl chitosan is essentially chitosan C _3. Part or all of the hydroxyl group at _C6 position and the primary amino group at _C2 undergo carboxymethyl substitution reaction. However, the interaction of intramolecular and intermolecular hydrogen bonds of chitosan makes chitosan form a highly crystalline and ordered structure of microfiber network, which is staggered by ordered crystalline regions and disordered amorphous regions. The crystalline region of chitosan is regular, straight, and tightly arranged in three-dimensional space, while the amorphous region is formed by the random coiling and intertwining of loose molecular chains. During the carboxymethylation process In chitosan, the semi-crystalline structure of chitosan seriously hinders the entry of OH ^- into the chitosan molecule, making it unable to form an alkalinity center well, which greatly affects the degree of carboxymethylation reaction. In order to improve the effect of carboxymethylation reaction, it is necessary to add a swelling agent (isopropanol, etc.) to promote the swelling of chitosan molecules, and increase the concentration of hydroxide, so that hydroxide can better enter the interior of chitosan molecules. The formation of more alkalization centers and the increase of the reaction temperature are conducive to the carboxymethyl substitution reaction of chloroacetic acid on chitosan in an alkaline environment.

However, the chitosan powder is directly reacted under the conditions of high concentration of alkali and high temperature. Due to the high alkali concentration and the high reaction temperature, although it promotes the carboxymethylation of chitosan, it also destroys the carboxymethyl chitosan. The carbon chain skeleton of the sugar causes the molecular chain to break, which leads to a decrease in the molecular weight of the prepared carboxymethyl chitosan, and when the amount of alkali is too large, it will increase the incidence of side reactions and reduce the utilization rate of chloroacetic acid. At the same time, when using a swelling agent to swell chitosan, if the dosage is too small, the swelling ratio will be too small, and the swelling cannot be carried out. It is impossible to take into account the high degree of substitution and high molecular weight of carboxymethyl chitosan at the same time. The degree of substitution of carboxymethyl chitosan greatly affects its water-solubility and other functional applications, and its molecular weight will directly affect its mechanical properties. The current low molecular weight and low molecular weight of carboxymethyl chitosan The degree of substitution has seriously affected the application of carboxymethyl chitosan in various fields.

Therefore, it is of great practical significance to develop a preparation method that can take into account the high substitution degree and high molecular weight of carboxymethyl chitosan.

SUMMARY OF THE INVENTION

The invention provides a preparation method of carboxymethyl chitosan with high substitution degree and high molecular weight, and aims to solve the problem that the high substitution degree of carboxymethyl chitosan cannot be taken into account when preparing carboxymethyl chitosan in the prior art and high molecular weight problems.

For achieving the above object, the scheme that the present invention adopts is as follows:

A method for preparing carboxymethyl chitosan with high degree of substitution and high molecular weight. The chitosan-strong alkali solution is obtained by dissolving chitosan in a low-concentration strong alkali solution. The content of the strong alkali in the chitosan-strong alkali solution is increased to 35-45wt% by adding a high-concentration strong alkali solution under the conditions of The carboxymethyl chitosan with high degree of substitution and high molecular weight can be obtained by radical substitution reaction.

In the present invention, the strong alkali content in the chitosan-strong alkali solution is increased by supplementing the strong alkali solution to better enter the interior of the chitosan to form an alkalization center, such as adding strong alkali solid directly to the chitosan-strong alkali solution. , the strong alkali solid dissolves and releases heat, which will make the chitosan-strong alkali solution gel rapidly, and the rapid gelation will make the chitosan-strong alkali solution solid, which is not fluid and is not conducive to the formation of a homogeneous state. To make chloroacetic acid better participate in the substitution reaction, in addition, the present invention specially controls the temperature of supplementing the strong alkaline solution to be 0～10 ℃, the purpose is to avoid the gelation of the system, the fluidity is weakened, and then the carboxymethyl substitution reaction is produced. adverse effects.

In the present invention, chitosan is dissolved in a low-concentration strong alkali solution to obtain a chitosan-strong alkali solution. At this time, the system is a homogeneous system (solution state), the microfibrillar structure and crystal region are destroyed, and the molecular chain arrangement becomes Confusion, the spacing becomes larger, OH ^- is more likely to penetrate to form an alkalization center, chloroacetic acid can better react with the alkaline active center, and improve the degree of substitution of carboxymethyl chitosan. Since the system is a homogeneous system at this time, no need Excessive alkali concentration, chloroacetic acid content and reaction temperature, and no need for additional swelling agents, the reaction conditions are milder, avoiding the excessive temperature that makes carboxymethyl chitosan glycosidic bonds break and affect the carboxymethyl chitosan. viscosity average molecular weight, in addition to the random distribution of the carboxymethyl groups along the carboxymethyl chitosan chain after the homogeneous carboxymethyl substitution reaction, compared to the heterogeneous carboxymethyl substitution reaction resulting in chitosan C ₃ , C The hydroxyl group on the ₆ position and the primary amino group on C ₂ are substituted and the block distribution of the carboxymethyl group, the carboxymethyl chitosan prepared by the present invention has a higher degree of substitution, and the distribution of the substitution group is more uniform ;

Wherein, the carboxymethyl chitosan preparation reaction equation is as follows:

In the present invention, the strong alkali solution is added in two steps, the concentration of the strong alkali solution added in the first step is relatively low, the purpose is to dissolve the chitosan under freezing conditions and become a homogeneous state, and the strong alkali solution added in the second step has a lower concentration. The concentration of the alkali solution is relatively high, and the addition of a high-concentration strong alkali solution is to achieve the best concentration of the carboxymethyl substitution reaction, because the concentration of the strong alkali solution is related to the number of alkalization centers formed. The higher the concentration, the easier it is to form alkalization. In the center, the higher the degree of reaction, and the range of 35-45wt% is a suitable range of strong alkali solution that is conducive to the carboxymethyl substitution reaction. Compared with one-step addition, two-step addition can effectively prevent the solution temperature from being high. Chitosan- The strong alkali solution gels rapidly and has no fluidity, which is not conducive to the carboxymethyl substitution reaction.

As the preferred technical solution:

The above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, the process of dissolving is: adding chitosan powder to strong alkali solution a with strong alkali content of 15-25wt% After the dispersion liquid is obtained in the medium, freeze for 4-7 hours under the temperature condition of -T °C, T is less than 35, filter or centrifuge the undissolved part to obtain the chitosan-strong alkali solution, the present invention improves the chitosan by reducing the freezing temperature. Dissolved amount, under low temperature conditions, the solvent molecular clusters can destroy the intermolecular hydrogen bonds of chitosan, and at the same time form new hydrogen bonds with the molecular chain, resulting in the dissolution of chitosan, and the dissolution is an exothermic process, low temperature conditions can promote chitosan dissolve. Increasing the strong alkali content of strong alkali solution a will reduce its freezing point, which can further weaken or break the links between the molecular chains of chitosan, thereby destroying its crystallization properties and affecting the dissolution of chitosan. Therefore, it is necessary to comprehensively consider the content of strong alkali. and freezing temperature. The invention destroys the microfibrillar structure and crystal region in the chitosan through low temperature treatment, so that the arrangement of the molecular chains becomes disordered, and the distance between the molecular chains becomes larger, thereby reducing the difficulty of OH- infiltrating into the chitosan.

In the above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, the average particle size of the chitosan powder is 50-80 meshes, and the degree of deacetylation is 70-90%. The chitosan powder of the present invention is not limited to this, and it is only taken as an example here.

In the above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, the content of chitosan powder in the dispersion liquid is 2-7wt%. If the content of chitosan powder is too large, the mass fraction of chitosan after dissolution will be too high, and the viscosity of the freeze-thaw solution will be too large, which will hinder the uniform mixing with high-concentration and strong alkali solution; Methyl chitosan is less, resulting in a waste of cost.

The above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, the method used to increase the strong alkali content in the chitosan-strong alkali solution to 35-45wt% is: The strong alkali solution b is supplemented in the chitosan-strong alkali solution, and the strong alkali corresponding to the strong alkali solution a and the strong alkali solution b are the same or different.

The preparation method of a kind of high substitution degree and high molecular weight carboxymethyl chitosan as above, strong base solution a or strong base solution b are NaOH solution or KOH solution, more preferably, strong base solution a and strong base The corresponding strong bases of solution b are the same, all of which are KOH. At the same concentration, the ability of KOH solution to dissolve chitosan powder is stronger than that of NaOH solution.

The above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, the mass addition of the chloroacetic acid is 2-10 times the mass addition of the chitosan; the carboxymethyl substitution The reaction is heated by microwave, specifically in a microwave reactor, and the power of the microwave reactor during the carboxymethyl substitution reaction is 450-810W, or the carboxymethyl substitution reaction is heated by an oil bath, specifically in an oil bath in the heater. The heating mode of the carboxymethyl substitution reaction is not limited to this, only two possible heating modes are listed here, and other feasible heating modes are also applicable to the present invention.

In the above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, the time of the carboxymethyl substitution reaction is 2-6 hours. The time of the carboxymethyl substitution reaction is not limited to this, and those skilled in the art can select the reaction time according to actual application scenarios.

In the above-mentioned preparation method of carboxymethyl chitosan with high degree of substitution and high molecular weight, after the carboxymethyl substitution reaction is completed, cleaning and drying are also performed.

The present invention provides a high degree of substitution and high molecular weight carboxymethyl chitosan prepared by using the method for preparing a high degree of substitution and high molecular weight carboxymethyl chitosan as described in any of the above. The substitution degree of carboxymethyl chitosan with high molecular weight is 1.0～1.8, and the viscosity average molecular weight is 9.0×10 ⁵ ～11.0×10 ⁵ g/mol. On the one hand, the molecular weight of the raw materials is relatively high, and on the other hand, the molecular weight of the raw materials decreases relatively small in the preparation process. Under the premise of the same raw materials, the substitution degree of the carboxymethyl chitosan prepared by the method of the present invention is 0.1~ 0.9 times (that is, 1.1-1.9 times that of the prior art), and the molecular weight is 1.5-2.1 times higher (that is, 2.5-3.1 times that of the prior art).

In the prior art, carboxymethyl chitosan is prepared by directly dispersing chitosan in a swelling agent for swelling, then adding a high-concentration strong alkali solution (generally 30-50 wt%) for alkalization treatment, and then adding chloroacetic acid to generate carboxylation. methyl substitution reaction. The reaction system is a heterogeneous system, that is, the high-concentration alkali swelling state of chitosan. Due to the existence of the crystalline region in chitosan, the substitution reaction of carboxymethyl chitosan first occurs in the amorphous region, and the crystalline region needs to be in a very high temperature. Alkali concentration and high temperature can effectively form an alkalization center for subsequent reactions. The difficulty of the reaction between the crystalline region and the amorphous region will lead to the block distribution of carboxymethyl groups, resulting in the reaction of carboxymethyl chitosan molecules. The distribution of carboxymethyl groups on the chain is not uniform, and high alkali concentration will also damage the carbon chain skeleton of chitosan, thereby breaking the molecular chain and sharply reducing the molecular weight.

In the present invention, chitosan is dissolved in a strong alkali solution. At this time, the system is a homogeneous system (solution state), the microfibrillar structure and crystal region are destroyed, the molecular chain arrangement becomes chaotic, the spacing becomes larger, and ^OH- is easier Infiltration to form an alkalization center. At this time, increasing the alkali content of the solution can more easily form an alkalization center. In addition, the addition of strong alkali solution will increase the concentration of lye, but because the control of the addition is at a lower temperature Under the conditions, gelation will not occur, and the system is still a homogeneous system. Finally, chloroacetic acid is added to carry out carboxymethyl substitution reaction to obtain carboxymethyl chitosan. Since the system is a homogeneous system at this time, no High alkali concentration, chloroacetic acid content and reaction temperature, and at the same time, no additional swelling agent is required, and the reaction conditions are milder. At this time, the carboxymethyl groups are randomly distributed along the carboxymethyl chitosan chain, and the molecular weight of carboxymethyl chitosan is relatively high. high.

beneficial effect

(1) the preparation method of a kind of high substitution degree and high molecular weight carboxymethyl chitosan of the present invention, carries out carboxymethylation reaction under homogeneous conditions, increases the probability that sodium hydroxide penetrates into chitosan molecule, and the process Simple, mild conditions, significantly improve the degree of substitution of carboxymethyl chitosan;

(2) The carboxymethyl chitosan with high substitution degree and high molecular weight of the present invention has high substitution degree and high molecular weight and has great application prospects.

Description of drawings

Figure 1 is a schematic diagram of the preparation of carboxymethyl chitosan with high degree of substitution and high molecular weight according to the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Example 1

A kind of preparation method of high degree of substitution and high molecular weight carboxymethyl chitosan, its steps are as follows:

(1) Dissolving chitosan in a strong alkali solution, the specific process is: adding chitosan powder with an average particle size of 80 meshes and a degree of deacetylation of 70% into a KOH solution with a strong alkali content of 18wt% to obtain shells After the dispersion liquid whose content of polysaccharide powder is 4wt%, freeze at -30°C for 6.5h, filter or centrifuge the undissolved part to obtain chitosan-strong alkali solution;

(2) increasing the strong alkali content in the chitosan-strong alkali solution to 41wt%, the method is as follows: under the condition that the temperature is 0 ℃, add KOH solution to the chitosan-strong alkali solution;

(3) Add chloroacetic acid whose mass is 2 times of the mass of chitosan, and carry out carboxymethyl substitution reaction in the microwave reactor for 3h under the condition of temperature of 100°C. When the microwave reactor is in the carboxymethyl substitution reaction The power is 630W; after the reaction, also carry out cleaning and drying (that is, add distilled water to the solution, adjust the pH value to 7.0 with glacial acetic acid, and then perform suction filtration, washing and drying) to obtain high degree of substitution and high Molecular weight of carboxymethyl chitosan.

The obtained high degree of substitution and high molecular weight carboxymethyl chitosan has a degree of substitution of 1.6 and a viscosity average molecular weight of 10.5×10 ⁵ g/mol. Schematic diagram of the preparation of high degree of substitution and high molecular weight carboxymethyl chitosan As shown in Figure 1, after repeated freezing and thawing stirring, the microfibrillar structure and crystal region of chitosan can be destroyed, the molecular chain arrangement becomes disordered, the spacing becomes larger, and ^OH- is more easily penetrated to form an alkalinized center.

Comparative Example 1

A preparation method of carboxymethyl chitosan, the process is as follows: adding chitosan powder with an average particle size of 80 meshes and a degree of deacetylation of 70% (the raw materials are the same as in Example 1) into isopropanol for swelling, and then After adding a KOH solution with a strong alkali content of 41 wt % to obtain a dispersion with a chitosan powder content of 4 wt %, add chloroacetic acid whose mass is 2 times that of the chitosan mass, and the added mass is the chitosan mass. 2 times the amount of chloroacetic acid, the carboxymethyl substitution reaction was carried out in a microwave reactor at a temperature of 100 °C for 3 h, and the power of the microwave reactor during the carboxymethyl substitution reaction was 630W; Cleaning and drying (that is, adding distilled water to the solution, adjusting the pH value to 7.0 with glacial acetic acid, and then performing suction filtration, washing and drying) to obtain carboxymethyl chitosan;

The substitution degree of the prepared carboxymethyl chitosan was 0.8, and the viscosity average molecular weight was 7.5×10 ⁵ g/mol.

It can be seen from the comparison between Comparative Example 1 and Example 1 that the present invention keeps chitosan in a freeze-thaw state in a concentrated alkaline solution and maintains a homogeneous distribution, so that the carboxymethyl substitution reaction can be well carried out in a homogeneous system. Take into account the degree of substitution and molecular weight.

Comparative Example 2

A preparation method of carboxymethyl chitosan is basically the same as that of Comparative Example 1, except that the content of strong alkali in the KOH solution is 60wt%.

The substitution degree of the prepared carboxymethyl chitosan was 1.0, and the viscosity average molecular weight was 3.5×10 ⁵ g/mol.

Comparing Comparative Example 2 with Example 1, it can be seen that the present invention performs the carboxymethyl substitution reaction in a homogeneous system without excessive alkali concentration, the reaction conditions are milder, and the degree of substitution and molecular weight can be well balanced.

Example 2

A kind of preparation method of high degree of substitution and high molecular weight carboxymethyl chitosan, its steps are as follows:

(1) Dissolving chitosan in a strong alkali solution, the specific process is: adding chitosan powder with an average particle size of 60 meshes and a degree of deacetylation of 75% into a KOH solution with a strong alkali content of 15wt% to obtain shells After the dispersion liquid with the content of polysaccharide powder is 3wt%, it is frozen at -33°C for 7 hours, and the undissolved part is filtered or centrifuged to obtain a chitosan-strong alkali solution;

(2) increasing the strong alkali content in the chitosan-strong alkali solution to 35wt%, the method is as follows: under the condition that the temperature is 5 ℃, add KOH solution to the chitosan-strong alkali solution;

(3) Add chloroacetic acid whose mass is 4 times the mass of chitosan, and carry out the carboxymethyl substitution reaction in the microwave reactor for 2h at a temperature of 40°C. When the microwave reactor is in the carboxymethyl substitution reaction The power is 720W; after the reaction is finished, also carry out cleaning and drying (that is, add distilled water to the solution, adjust the pH value to 7.0 with glacial acetic acid, and then perform suction filtration, washing and drying) to obtain high degree of substitution and high Molecular weight of carboxymethyl chitosan.

The obtained carboxymethyl chitosan with high degree of substitution and high molecular weight has a degree of substitution of 1.2 and a viscosity average molecular weight of 10×10 ⁵ g/mol. Under the premise of the same raw materials, the method of the present invention is more efficient than the general method. The substitution degree of carboxymethyl chitosan was 0.3 times higher and the molecular weight was 1.9 times higher.

Example 3

A kind of preparation method of high degree of substitution and high molecular weight carboxymethyl chitosan, its steps are as follows:

(1) Dissolving chitosan in a strong alkali solution, the specific process is: adding chitosan powder with an average particle size of 50 meshes and a degree of deacetylation of 80% into a KOH solution with a strong alkali content of 22wt% to obtain shells After the dispersion liquid with the content of polysaccharide powder is 6wt%, it is frozen for 7 hours at a temperature of -34°C, and the undissolved part is filtered or centrifuged to obtain a chitosan-strong alkali solution;

(2) increasing the strong alkali content in the chitosan-strong alkali solution to 45wt%, the method is as follows: adding KOH solution to the chitosan-strong alkali solution under the condition that the temperature is 10°C;

(3) Add chloroacetic acid whose mass is 6 times of the mass of chitosan, and carry out the carboxymethyl substitution reaction in the microwave reactor for 5h under the condition of temperature of 70°C. When the microwave reactor is in the carboxymethyl substitution reaction The power is 810W; after the reaction is finished, also carry out cleaning and drying (that is, add distilled water to the solution, adjust the pH value to 7.0 with glacial acetic acid, and then perform suction filtration, washing and drying) to obtain high degree of substitution and high Molecular weight of carboxymethyl chitosan.

The obtained carboxymethyl chitosan with high degree of substitution and high molecular weight has a degree of substitution of 1.8 and a viscosity average molecular weight of 11×10 ⁵ g/mol. Under the premise of the same raw materials, the method of the present invention is more efficient than the general method. The substitution degree of carboxymethyl chitosan was 0.9 times higher and the molecular weight was 2.1 times higher.

Example 4

A kind of preparation method of high degree of substitution and high molecular weight carboxymethyl chitosan, its steps are as follows:

(1) Dissolving chitosan in a strong alkali solution, the specific process is: adding chitosan powder with an average particle size of 70 meshes and a degree of deacetylation of 80% into a NaOH solution with a strong alkali content of 19wt% to obtain shells After the dispersion liquid with the content of polysaccharide powder is 5.2wt%, it is frozen at -30°C for 8 hours, and the undissolved part is filtered or centrifuged to obtain a chitosan-strong alkali solution;

(2) increasing the strong alkali content in the chitosan-strong alkali solution to 40wt%, the method is as follows: under the condition that the temperature is 8 ℃, add KOH solution to the chitosan-strong alkali solution;

(3) Add chloroacetic acid whose mass is 6 times the mass of chitosan, and carry out the carboxymethyl substitution reaction in the microwave reactor for 2h at a temperature of 85°C. When the microwave reactor is in the carboxymethyl substitution reaction The power is 450W; after the reaction is finished, also carry out cleaning and drying (that is, add distilled water to the solution, adjust the pH value to 7.0 with glacial acetic acid, and then perform suction filtration, washing and drying) to obtain high degree of substitution and high Molecular weight of carboxymethyl chitosan.

The obtained carboxymethyl chitosan with high degree of substitution and high molecular weight has a degree of substitution of 1.0 and a viscosity average molecular weight of 10.3×10 ⁵ g/mol. Under the premise of the same raw materials, the method of the present invention is more efficient than the general method. The substitution degree of carboxymethyl chitosan is 0.1 times higher and the molecular weight is 1.9 times higher.

Example 5

A kind of preparation method of high degree of substitution and high molecular weight carboxymethyl chitosan, its steps are as follows:

(1) Dissolving chitosan in a strong alkali solution, the specific process is: adding chitosan powder with an average particle size of 50 meshes and a degree of deacetylation of 85% to a NaOH solution with a strong alkali content of 25wt% to obtain shells After the dispersion liquid with the content of polysaccharide powder is 6wt%, it is frozen for 4 hours at a temperature of -33°C, and the undissolved part is filtered or centrifuged to obtain a chitosan-strong alkali solution;

(2) increasing the strong alkali content in the chitosan-strong alkali solution to 38wt%, the method is as follows: adding KOH solution to the chitosan-strong alkali solution under the condition that the temperature is 4°C;

(3) adding chloroacetic acid whose mass is 5 times of the mass of chitosan, and using oil bath heating mechanical stirring to carry out carboxymethyl substitution reaction for 4h at a temperature of 50°C (specifically, carrying out the carboxymethyl substitution reaction in an oil bath heater) ), carry out cleaning and drying (that is, add distilled water to the solution, adjust the pH value to 7.0 with glacial acetic acid, then carry out suction filtration, washing and drying), to obtain high degree of substitution and high molecular weight carboxymethyl chitosan sugar.

The obtained carboxymethyl chitosan with high degree of substitution and high molecular weight has a degree of substitution of 1.5 and a viscosity average molecular weight of 9×10 ⁵ g/mol. Under the premise of the same raw materials, the method of the present invention is more efficient than the general method. The substitution degree of carboxymethyl chitosan is 0.6 times higher and the molecular weight is 1.6 times higher.

Example 6

A kind of preparation method of high degree of substitution and high molecular weight carboxymethyl chitosan, its steps are as follows:

(1) Dissolving chitosan in a strong alkali solution, the specific process is: adding chitosan powder with an average particle size of 60 meshes and a degree of deacetylation of 90% into a NaOH solution with a strong alkali content of 17wt% to obtain shells After the dispersion liquid with the content of polysaccharide powder is 4.5wt%, it is frozen at -31°C for 7 hours, and the undissolved part is filtered or centrifuged to obtain a chitosan-strong alkali solution;

(2) increasing the strong alkali content in the chitosan-strong alkali solution to 35wt%, the method is as follows: under the condition that the temperature is 2 ℃, add NaOH solution to the chitosan-strong alkali solution;

(3) add the chloroacetic acid whose mass is 8 times of the mass of chitosan, and carry out the carboxymethyl substitution reaction for 6h by using oil bath heating mechanical stirring under the condition of temperature of 68°C (specifically, carrying out the carboxymethyl substitution reaction in the oil bath heater ), carry out cleaning and drying (that is, add distilled water to the solution, adjust the pH value to 7.0 with glacial acetic acid, then carry out suction filtration, washing and drying), to obtain high degree of substitution and high molecular weight carboxymethyl chitosan sugar. The obtained carboxymethyl chitosan with high degree of substitution and high molecular weight has a degree of substitution of 1.2 and a viscosity average molecular weight of 10×10 ⁵ g/mol. Under the premise of the same raw materials, the method of the present invention is more efficient than the general method. The substitution degree of carboxymethyl chitosan was 0.3 times higher and the molecular weight was 1.9 times higher.

Claims (10)

1. A preparation method of carboxymethyl chitosan with high substitution degree and high molecular weight is characterized in that: dissolving chitosan in a strong alkali solution to obtain a chitosan-strong alkali solution, increasing the content of strong alkali in the chitosan-strong alkali solution to 35-45 wt% by supplementing the strong alkali solution at the temperature of 0-10 ℃, adding chloroacetic acid, and performing carboxymethyl substitution reaction at the temperature of 40-100 ℃ to obtain the carboxymethyl chitosan with high substitution degree and high molecular weight.

2. The method for preparing carboxymethyl chitosan with high degree of substitution and high molecular weight as claimed in claim 1, wherein the dissolving process is: adding chitosan powder into a strong base solution a with the strong base content of 15-25 wt% to obtain a dispersion, freezing for 4-7 h at the temperature of-T ℃, wherein T is less than 35, and filtering or centrifuging to obtain an undissolved part to obtain the chitosan-strong base solution.

3. The method for preparing carboxymethyl chitosan with high degree of substitution and high molecular weight according to claim 2, wherein the average particle size of chitosan powder is 50-80 mesh, and the degree of deacetylation is 70-90%.

4. The method for preparing carboxymethyl chitosan with high degree of substitution and high molecular weight as claimed in claim 2, wherein the content of chitosan powder in the dispersion is 2-7 wt%.

5. The method for preparing carboxymethyl chitosan with high substitution degree and high molecular weight according to claim 2, wherein the method for increasing the content of strong base in the chitosan-strong base solution to 35-45 wt% is as follows: and (3) supplementing a strong alkali solution b into the chitosan-strong alkali solution, wherein the strong alkali corresponding to the strong alkali solution a and the strong alkali corresponding to the strong alkali solution b are the same or different.

6. The method of claim 5, wherein the strongly alkaline solution a or the strongly alkaline solution b is NaOH solution or KOH solution.

7. The method for preparing carboxymethyl chitosan with high substitution degree and high molecular weight according to claim 1, wherein the mass addition amount of chloroacetic acid is 2-10 times of that of chitosan; the carboxymethyl substitution reaction is carried out in a microwave reactor, the power of the microwave reactor during the carboxymethyl substitution reaction is 450-810W, or the carboxymethyl substitution reaction is carried out in an oil bath heater.

8. The method for preparing carboxymethyl chitosan with high degree of substitution and high molecular weight according to claim 1, wherein the time of carboxymethyl substitution reaction is 2-6 h.

9. The method for preparing carboxymethyl chitosan with high degree of substitution and high molecular weight as claimed in claim 1, wherein after the carboxymethyl substitution reaction is finished, washing and drying are further performed.

10. The highly substituted and high molecular weight carboxymethyl chitosan obtained by the process for preparing highly substituted and high molecular weight carboxymethyl chitosan according to any one of claims 1 to 9, wherein the highly substituted and high molecular weight carboxymethyl chitosan has a substitution degree of 1.0 to 1.8 and a viscosity average molecular weight of 9.0 × 10⁵～11.0×10⁵g/mol。

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