A process for the preparation of cationic cellulose ethers

Abstract

The application relates to the technical field of functional polymer materials, and provides a preparation method of cationic cellulose ether, wherein a sodium citrate solution is added in a reaction system, on the one hand, three carboxylic acid groups of the sodium citrate can form ion pairs with cationic monomers of a cationic etherifying agent, effectively neutralize local positive charges, weaken the charge repulsion between cationic groups of the cationic etherifying agent, and be favorable to further etherification reaction. In addition, the sodium citrate can stabilize the pH value of the reaction system and reduce the occurrence of side reactions. In addition, sodium ions of the sodium citrate can act as weak Lewis acids and cooperatively activate hydroxyl oxygen atoms on a cellulose ether main chain, further improving the reaction efficiency of the cationic etherifying agent and the cellulose ether. The preparation method can improve the cationic substitution degree of the cationic cellulose ether, can improve the reaction efficiency of the cationic etherifying agent and the cellulose ether, and the sodium citrate can be recycled, further reducing the production cost.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of functional polymer materials, in particular to a preparation method of cationic cellulose ether. BACKGROUND

[0002] Hair washing products are necessities in people's daily life, which have gradually developed from the earliest hair washing function to multifunctional cosmetics with hair washing and hair care. Among them, the hair conditioner is an important part of hair care products, and its main function is to improve the texture, luster and easy combing property of hair. Among them, the cationic cellulose ether as a hair conditioner is derived from natural cellulose, and the production process is relatively more environmentally friendly, and the irritation to the skin and hair is also smaller, so it has attracted widespread attention. Compared with natural cellulose, the cationic cellulose ether has a unique positively charged quaternary ammonium group, which can be attracted and combined with the negative charge on the surface of the hair, thereby adhering to the surface layer and providing long-lasting conditioning effect. The strength of this conditioning effect is closely related to the cationic substitution degree of the cationic cellulose ether, and the higher the cationic substitution degree, the better the conditioning effect. Therefore, it is urgent to develop a preparation method of cationic cellulose ether with high substitution degree. SUMMARY

[0003] The application aims to provide a preparation method of cationic cellulose ether to improve the cationic substitution degree of the cationic cellulose ether and reduce the production cost. The specific technical scheme is as follows:

[0004] The first aspect of the application provides a preparation method of cationic cellulose ether, which comprises the following steps:

[0005] (1) dispersing cellulose ether in a solvent to obtain a cellulose ether dispersion, then mixing the cellulose ether dispersion with an alkaline solution to perform an alkalization reaction, and obtaining a first system;

[0006] (2) adding a first part of cationic etherifying agent to the first system to perform a first stage etherification reaction, and obtaining a second system;

[0007] (3) adding a sodium citrate aqueous solution and a second part of cationic etherifying agent to the second system to perform a second stage etherification reaction, and obtaining a third system;

[0008] (4) performing solid-liquid separation on the third system to obtain a precipitate and a mother liquor, washing and drying the precipitate to obtain cationic cellulose ether;

[0009] Among them, the mass percentage content of the first part of cationic etherifying agent is 40% to 80% based on the total mass of the first part of cationic etherifying agent and the second part of cationic etherifying agent.

[0010] In some embodiments of the present application, the cellulose ether is selected from hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose or hydroxypropyl methyl cellulose; the mass percentage of the cellulose ether is 15% to 25% based on the mass of the cellulose ether dispersion.

[0011] In some embodiments of the present application, the solvent is selected from at least one of methanol aqueous solution, ethanol aqueous solution, isopropanol aqueous solution and tert-butanol aqueous solution; the mass percentage of water in the solvent is 10% to 20% based on the mass of the solvent.

[0012] In some embodiments of the present application, the alkaline solution is selected from at least one of potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, sodium carbonate aqueous solution, potassium carbonate aqueous solution; the mass fraction of the alkaline solution is 20% to 40%; the mass ratio of solute in the alkaline solution to the cellulose ether is (0.02-0.05):1.

[0013] In some embodiments of the present application, the temperature of the alkalization reaction is 30℃ to 80℃, and the alkalization reaction time is 1h to 5h.

[0014] In some embodiments of the present application, the temperature of the first stage etherification reaction is 40℃ to 90℃, and the first stage etherification reaction time is 20min to 80min.

[0015] In some embodiments of the present application, the first part cationic etherification agent and the second part cationic etherification agent are selected from 3-chloro-2-hydroxypropyl trimethyl ammonium chloride aqueous solution or 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution; the mass fraction of the first part cationic etherification agent and the second part cationic etherification agent is 40% to 60%.

[0016] In some embodiments of the present application, the first part cationic etherification agent and the second part cationic etherification agent are selected from the same substance.

[0017] In some embodiments of the present application, the total mass of solute in the first part cationic etherification agent and the second part cationic etherification agent to the mass of the cellulose ether is (0.4-0.8):1. In some embodiments of the present application, the mass fraction of the sodium citrate aqueous solution is 5% to 25%; the molar ratio of sodium citrate in the sodium citrate aqueous solution to the solute in the first part cationic etherification agent and the second part cationic etherification agent is (0.07-0.22):1.

[0018] In some embodiments of the present application, in the step (3), the specific procedure for adding the aqueous sodium citrate solution and the second part of the cationic etherification agent to the second system is mode 1: adding the first part of the aqueous sodium citrate solution to the second system at 20-80°C to obtain a charge shielding system; the mass percentage of the first part of the aqueous sodium citrate solution is 40-80% based on the total mass of the aqueous sodium citrate solution; and adding the remaining aqueous sodium citrate solution and the second part of the cationic etherification agent to the charge shielding system at 40-90°C to perform a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60-180 min, to obtain a third system.

[0019] In some embodiments of the present application, in the step (3), the specific procedure for adding the aqueous sodium citrate solution and the second part of the cationic etherification agent to the second system is mode 2: adding the aqueous sodium citrate solution to the second system at 20-80°C to obtain a charge shielding system; and adding the second part of the cationic etherification agent to the charge shielding system at 40-90°C to perform a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60-180 min, to obtain a third system.

[0020] In some embodiments of the present application, in the step (3), the specific procedure for adding the aqueous sodium citrate solution and the second part of the cationic etherification agent to the second system is mode 3: adding the aqueous sodium citrate solution and the second part of the cationic etherification agent to the second system at 40-90°C to perform a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60-180 min, to obtain a third system.

[0021] In some embodiments of the present application, in the step (4), after the third system is cooled to below 30°C, an acid solution is added to adjust the pH value of the system to 5-7, followed by solid-liquid separation to obtain a precipitate and a mother liquor.

[0022] In some embodiments of the present application, in the step (4), the mother liquor is subjected to cooling crystallization to recover sodium citrate.

[0023] The application provides a preparation method of cationic cellulose ether, which is characterized by: the etherification reaction is divided into two stages, and a sodium citrate aqueous solution is added in the second system. On the one hand, the sodium citrate acts as a charge shielding agent, and the three carboxylic acid groups of the sodium citrate can form ion pairs with the cationic groups on the cellulose ether molecular chain or the cationic groups on the cationic etherifying agent, effectively neutralizing the local positive charge, weakening the charge repulsion between the cationic groups, and being conducive to the further etherification reaction. On the other hand, the sodium citrate has strong pH buffering capacity, which can stabilize the pH value of the reaction system and reduce the occurrence of side reactions. In addition, the sodium ion of the sodium citrate acts as a weak Lewis acid, which can synergistically activate the hydroxyl oxygen atoms on the cellulose ether backbone, further improving the reaction efficiency of the cationic etherifying agent and the cellulose ether. The preparation method of the application divides the etherification reaction into two stages, and adds a sodium citrate solution in the second system. The sodium citrate plays the roles of charge shielding, pH buffering and catalyzing the etherification reaction, improves the cationic substitution degree of the cationic cellulose ether, and also improves the reaction efficiency of the cationic etherifying agent and the cellulose ether. In addition, the sodium citrate in the application can be recycled, further reducing the production cost.

[0024] Of course, implementing any of the products or methods of the application does not necessarily require achieving all the advantages described above at the same time. DETAILED DESCRIPTION

[0025] The technical solutions in the application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments. All other embodiments obtained by those skilled in the art based on the application belong to the scope of protection of the application.

[0026] The first aspect of the present application provides a method for preparing a cationic cellulose ether, comprising the following steps: (1) dispersing a cellulose ether in a solvent to obtain a cellulose ether dispersion, then mixing the cellulose ether dispersion with an alkaline solution to perform an alkalization reaction, to obtain a first system; (2) adding a first part of a cationic etherifying agent to the first system to perform a first-stage etherification reaction, to obtain a second system; (3) adding a sodium citrate aqueous solution and a second part of the cationic etherifying agent to the second system to perform a second-stage etherification reaction, to obtain a third system; (4) performing a solid-liquid separation on the third system to obtain a precipitate and a mother liquor, and performing washing and drying on the precipitate to obtain the cationic cellulose ether; wherein the mass percentage of the first part of the cationic etherifying agent is 40% to 80% based on the total mass of the first part of the cationic etherifying agent and the second part of the cationic etherifying agent. The mass percentage of the first part of the cationic etherifying agent can be 40%, 50%, 60%, 70%, 80%, or a range formed by any two of the above values, based on the total mass of the first part of the cationic etherifying agent and the second part of the cationic etherifying agent. It should be noted that when the mass percentage of the first part of the cationic etherifying agent is determined, the remaining part is the second part of the cationic etherifying agent, i.e., the mass percentage of the second part of the cationic etherifying agent is determined accordingly.

[0027] Cationization of cellulose ether refers to modification of cellulose ether to introduce cationic structures. The most common method is to use chemical modification. In the process of cationization of cellulose ether, the hydroxyl groups on the cellulose ether molecules react with some active groups (such as epoxy groups, halogenated hydrocarbon groups, etc.), to generate ether bonds while introducing cationic groups. Therefore, the reagent for cationic modification of cellulose ether is also called cationic etherifying agent.

[0028] In the cationic modification of cellulose ether, the positive charge density of the cellulose ether molecular chain increases with the introduction of each cationic group, resulting in the need to overcome increasingly greater charge repulsion for the subsequent introduction of cationic groups, ultimately leading to a decrease in reaction rate. That is, the cationic substitution degree is not linearly related to the amount of etherifying agent, but as the amount of etherifying agent increases, the degree of increase in substitution is increasingly lower, and in actual production, problems such as low product substitution degree, uneven substitution degree, and low process efficiency will occur. The inventors have found that by dividing the etherification reaction into two stages, first, a first part of the cationic etherifying agent is added to the first system to perform the first stage of etherification reaction to obtain a second system; then sodium citrate aqueous solution is introduced into the second system, and a second part of the cationic etherifying agent is used to perform the second stage of etherification reaction. By dividing the etherification reaction into two stages and introducing sodium citrate solution into the second system, on the one hand, sodium citrate acts as a charge shielding agent, and the three carboxylic acid groups of sodium citrate can form ion pairs with the cationic groups on the cellulose ether molecular chain or the cationic groups on the cationic etherifying agent, effectively neutralizing the local positive charge and weakening the charge repulsion between the cationic groups, so that the addition of sodium citrate aqueous solution in the second stage of etherification reaction is conducive to the further progress of the etherification reaction. On the other hand, sodium citrate has strong pH buffering capacity, which can stabilize the pH value of the reaction system and reduce the occurrence of side reactions. In addition, the sodium ions of sodium citrate, as weak Lewis acids, can synergistically activate the hydroxyl oxygen atoms on the cellulose ether backbone, further improving the reaction efficiency of the cationic etherifying agent and the cellulose ether. In addition, by adjusting the mass percentage content of the first part of the cationic etherifying agent to be within the above range, it is beneficial to the sufficient etherification reaction of the first part of the cationic etherifying agent with the cellulose ether, thereby improving the etherification reaction efficiency. After the etherification reaction of the first part of the cationic etherifying agent with the cellulose ether, the positive charge density of the cellulose ether molecular chain increases, resulting in the need to overcome increasingly greater charge repulsion for the subsequent introduction of cationic groups. At this time, the addition of sodium citrate aqueous solution and the second part of the cationic etherifying agent into the second system can further promote the progress of the second stage of etherification reaction and improve the cationic substitution degree of the cellulose ether. By the preparation method of the present application, the cationic substitution degree of the cationic cellulose ether can be improved, and at the same time, the reaction efficiency of the cationic etherifying agent and the cellulose ether can also be improved, and the sodium citrate of the present application can be recycled, further reducing the production cost.

[0029] When the mass percentage of the solute in the first part of the cationic etherifying agent is less than 40% based on the total mass of the solute in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent, it indicates that less cationic etherifying agent participates in the first stage of etherification reaction and more cationic etherifying agent participates in the second stage of etherification reaction. The reaction rate of the cationic etherifying agent with the cellulose ether is fast in the early stage of the etherification reaction. If most of the cationic etherifying agent participates in the second stage of etherification reaction, it is not conducive to improving the reaction efficiency of the cationic etherifying agent with the cellulose ether and the cationic degree of substitution of the cationic cellulose ether. When the mass percentage of the solute in the first part of the cationic etherifying agent is more than 80% based on the total mass of the solute in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent, it indicates that more cationic etherifying agent participates in the first stage of etherification reaction and less cationic etherifying agent participates in the second stage of etherification reaction. If most of the cationic etherifying agent participates in the first stage of etherification reaction, the effect of the slow polymerization caused by the charge repulsion is more obvious, which is not conducive to improving the reaction efficiency of the cationic etherifying agent with the cellulose ether and the cationic degree of substitution of the cationic cellulose ether. In some embodiments of the present application, the cellulose ether is selected from hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose or hydroxypropyl methyl cellulose; and the mass percentage of the cellulose ether is 15% to 25% based on the mass of the cellulose ether dispersion. For example, the mass percentage of the cellulose ether can be 15%, 18%, 20%, 23%, 25% or a range formed by any two of the above values. By adjusting the mass percentage of the cellulose ether in the cellulose ether dispersion within the range of the present application, it is conducive to the uniform dispersion of the cellulose ether in the solvent. In the present application, the cellulose ether can be prepared or purchased. The present application does not particularly limit the hydroxyl substitution degree and the weight average molecular weight of the cellulose ether, as long as the purpose of the present application can be achieved.

[0030] In some embodiments of the present application, the solvent is selected from at least one of a methanol aqueous solution, an ethanol aqueous solution, an isopropanol aqueous solution and a tert-butanol aqueous solution; and the mass percentage of water in the solvent is 10% to 20% based on the mass of the solvent. For example, the mass percentage of water can be 10%, 13%, 15%, 18%, 20% or a range formed by any two of the above values. By dispersing the cellulose ether in the solvent within the range of the present application, it is conducive to the uniform dispersion of the cellulose ether in the solvent; in addition, by adjusting the mass percentage of water in the mixed solution within the range of the present application, the cellulose ether can be swelled to a certain extent and the viscosity of the first system obtained is moderate, which is conducive to the subsequent etherification reaction.

[0031] In some embodiments of the present application, the alkaline solution is selected from at least one of a potassium hydroxide aqueous solution, a sodium hydroxide aqueous solution, a sodium carbonate aqueous solution, and a potassium carbonate aqueous solution; the mass fraction of the alkaline solution is 20% to 40%; and the mass ratio of the solute in the alkaline solution to the cellulose ether is (0.02-0.05):1. For example, the mass fraction of the alkaline solution can be 20%, 25%, 30%, 35%, 40%, or a range defined by any two of the numbers; and the mass ratio of the solute in the alkaline solution to the cellulose ether can be 0.02:1, 0.03:1, 0.04:1, 0.05:1, or a range defined by any two of the numbers. By selecting the alkaline solution within the range of the present application for the alkalization reaction with the cellulose ether dispersion, the hydroxyl groups on the cellulose ether molecules are activated, the activated hydroxyl groups have stronger attacking ability on the active groups in the cationic etherifying agent, the rate and degree of the subsequent etherification reaction are improved, and the cationic degree of substitution of the cellulose ether is improved. In addition, the alkaline condition is conducive to the better dispersion of the cellulose ether in the solvent, the molecular chain of the cellulose ether can be stretched more, the cationic etherifying agent can more uniformly react with the hydroxyl groups on the cellulose ether, and the uniformity of the cationic degree of substitution of the cellulose ether is improved.

[0032] In some embodiments of the present application, the temperature of the alkalization reaction is 30°C to 80°C, and the alkalization reaction time is 1h to 5h. For example, the temperature of the alkalization reaction can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or a range defined by any two of the numbers; and the alkalization reaction time can be 1h, 2h, 3h, 4h, 5h, or a range defined by any two of the numbers. In the present application, the alkalization reaction process can be carried out under stirring, and the stirring speed is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the stirring speed is 200rpm-800rpm. By adjusting the temperature and time of the alkalization reaction within the range of the present application, the hydroxyl groups on the cellulose ether molecules are activated by the alkaline solution, the rate and degree of the subsequent etherification reaction are improved, and the cationic degree of substitution of the cellulose ether is improved.

[0033] In some embodiments of the present application, the temperature of the first stage etherification reaction is 40°C to 90°C, and the time of the first stage etherification reaction is 20 min to 80 min. For example, the temperature of the first stage etherification reaction is 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or a range defined by any two of the above values. In the present application, the first stage etherification reaction can be carried out under stirring, and the stirring speed is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the stirring speed is 200 rpm to 800 rpm. The time of the first stage etherification reaction can be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, or a range defined by any two of the above values. By adjusting the temperature and time of the etherification reaction within the scope of the present application, it is beneficial to promote the etherification reaction of the cellulose ether with the cationic etherifying agent and improve the efficiency of the etherification reaction.

[0034] In some embodiments of the present application, the first part of the cationic etherifying agent and the second part of the cationic etherifying agent are selected from 3-chloro-2-hydroxypropyl trimethylammonium chloride aqueous solution (CHPTAC) or 2,3-epoxypropyl trimethylammonium chloride aqueous solution (EPTAC); the mass fraction of the first part of the cationic etherifying agent and the second part of the cationic etherifying agent is 40% to 60%. In some embodiments of the present application, the first part of the cationic etherifying agent and the second part of the cationic etherifying agent are selected from the same substance. For example, the mass fraction of the first part of the cationic etherifying agent and the second part of the cationic etherifying agent can be 40%, 45%, 50%, 55%, 60%, or a range defined by any two of the above values. By selecting the cationic etherifying agent within the scope of the present application, it is beneficial to promote the etherification reaction of the cellulose ether with the cationic etherifying agent, thereby introducing a positively charged quaternary ammonium group onto the cellulose ether molecular chain to achieve cationic modification of the cellulose ether.

[0035] In the present application, the first part of the cationic etherifying agent can be added to the first system by means of dropping, and the time of the first part of the cationic etherifying agent being dropped into the first system is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the time of the first part of the cationic etherifying agent being dropped into the first system is 15 min to 30 min. In the present application, the time of the first stage etherification reaction includes the dropping time of the first part of the cationic etherifying agent being dropped into the first system and the constant temperature time after the dropping is completed.

[0036] In some embodiments of the present application, the total mass of the solutes in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent to the mass of the cellulose ether is (0.4-0.8):1. For example, the mass ratio of the total mass of the solutes in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent to the mass of the cellulose ether can be 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, or a range formed by any two of the above values. By adjusting the mass ratio of the total mass of the solutes in the cationic etherifying agent to the mass of the cellulose ether within the above range, it is beneficial to allow the first part of the cationic etherifying agent to fully react with the cellulose ether, thereby improving the efficiency of the etherification reaction. After the first part of the cationic etherifying agent reacts with the cellulose ether, the positive charge density of the cellulose ether molecular chain increases, resulting in an increasingly large charge repulsion that needs to be overcome when the subsequent cationic groups are introduced. At this time, the addition of the sodium citrate solution and the second part of the cationic etherifying agent to the second system can further promote the second-stage etherification reaction and improve the cationic degree of substitution of the cellulose ether.

[0037] In some embodiments of the present application, the mass fraction of the sodium citrate aqueous solution is 5% to 25%, and the molar ratio of sodium citrate in the sodium citrate aqueous solution to the first part of the cationic etherifying agent and the second part of the cationic etherifying agent is (0.07-0.22):1. For example, the mass fraction of the sodium citrate solution can be 5%, 10%, 15%, 20%, 25%, or a range formed by any two of the above values. The molar ratio of sodium citrate in the sodium citrate aqueous solution to the first part of the cationic etherifying agent and the second part of the cationic etherifying agent can be 0.07:1, 0.08:1, 0.09, 0.1:1, 0.12:1, 0.13:1, 0.15:1, 0.18:1, 0.2:1, 0.22:1, or a range formed by any two of the above values. By introducing the sodium citrate solution into the second system, adjusting the mass fraction of the sodium citrate solution within the range of the present application, and adjusting the molar ratio of sodium citrate in the sodium citrate solution to the first part of the cationic etherifying agent and the second part of the cationic etherifying agent within the above range, it is beneficial to improve the cationic degree of substitution of the cationic cellulose ether, while also improving the reaction efficiency of the cationic etherifying agent with the cellulose ether and reducing costs.

[0038] In the present application, the second-stage etherification reaction process can be carried out under stirring. The stirring speed is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the stirring speed is 200 rpm to 800 rpm.

[0039] In some embodiments of the present application, in the step (3), the specific steps of adding the aqueous sodium citrate solution and the second part of the cationic etherifying agent into the second system are as follows: Mode 1: at 20-80°C, the first part of the aqueous sodium citrate solution is added into the second system to obtain a charge shielding system; the mass percentage of the first part of the aqueous sodium citrate solution is 40-80% based on the total mass of the aqueous sodium citrate solution; at 40-90°C, the remaining aqueous sodium citrate solution and the second part of the cationic etherifying agent are simultaneously added into the charge shielding system to perform a second-stage etherification reaction, and the second-stage etherification reaction time is 60-180 min to obtain a third system. For example, the temperature for adding the first part of the sodium citrate solution into the second system can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or a range defined by any two of them; the stirring time for adding the first part of the aqueous sodium citrate solution into the second system is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the stirring time can be 20-60 min; the mass percentage of the first part of the aqueous sodium citrate solution can be 40%, 50%, 60%, 70%, 80%, or a range defined by any two of them. The temperature of the second-stage etherification reaction can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or a range defined by any two of them, and the time of the second-stage etherification reaction can be 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 180 min, or a range defined by any two of them.

[0040] In the above Mode 1, first, the first part of the aqueous sodium citrate solution is added into the second system, which mainly shields the cationic groups on the molecular chain of the cellulose ether in the second system, thereby weakening the charge repulsion between the cationic groups on the molecular chain of the cellulose ether; then the remaining second part of the aqueous sodium citrate solution and the second part of the cationic etherifying agent are simultaneously added into the above charge shielding system, and the second part of the aqueous sodium citrate solution mainly shields the cationic groups on the cationic etherifying agent that have not participated in the reaction, which is conducive to promoting the further progress of the etherification reaction; by the above Mode 1, the aqueous sodium citrate solution and the second part of the cationic etherifying agent are added into the second system, and the sodium citrate has the effects of charge shielding, buffering pH value, and catalyzing etherification reaction, which is conducive to promoting the further progress of the etherification reaction, thereby improving the cationic degree of substitution of the cationic cellulose ether, and also improving the reaction efficiency of the cationic etherifying agent and the cellulose ether.

[0041] In the above-mentioned manner 1, the first part of the sodium citrate aqueous solution can be added into the second system by dropwise addition. The present application does not particularly limit the time for dropwise addition of the first part of the sodium citrate aqueous solution into the second system, as long as the purpose of the present application can be achieved. For example, the time for dropwise addition of the first part of the sodium citrate solution into the second system can be 15 min to 30 min.

[0042] In the above-mentioned manner 1, the second part of the sodium citrate aqueous solution and the second part of the cationic etherifying agent can be added into the charge shielding system by dropwise addition. The present application does not particularly limit the time for dropwise addition of the second part of the sodium citrate aqueous solution and the second part of the cationic etherifying agent into the charge shielding system, as long as the purpose of the present application can be achieved. For example, the time for dropwise addition of the second part of the sodium citrate solution and the second part of the cationic etherifying agent into the charge shielding system can be 15 min to 30 min. In the above-mentioned manner 1, the time for the second stage etherification reaction includes the dropwise addition time of the second part of the cationic etherifying agent and the second part of the sodium citrate aqueous solution into the charge shielding system and the constant temperature time after the dropwise addition.

[0043] In some embodiments of the present application, in the step (3), the specific steps for adding the sodium citrate aqueous solution and the second part of the cationic etherifying agent into the second system are manner 2: adding the sodium citrate aqueous solution into the second system at 20°C to 80°C to obtain a charge shielding system; and adding the second part of the cationic etherifying agent into the charge shielding system at 40°C to 90°C to perform a second stage etherification reaction, wherein the time for the second stage etherification reaction is 60 min to 180 min, to obtain a third system. For example, the temperature for adding the sodium citrate aqueous solution into the second system can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or a range defined by any two of the above-mentioned values. The present application does not particularly limit the stirring time for adding the above-mentioned sodium citrate aqueous solution into the second system, as long as the purpose of the present application can be achieved. For example, the stirring time can be 20 min to 60 min. The temperature for the second stage etherification reaction can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or a range defined by any two of the above-mentioned values. The time for the second stage etherification reaction can be 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 180 min, or a range defined by any two of the above-mentioned values.

[0044] In method 2 described above, firstly, an aqueous solution of sodium citrate is added to the second system. The sodium citrate solution shields the cationic groups on the cellulose ether molecular chains in the second system, thereby weakening the charge repulsion between the cationic groups on the cellulose ether molecular chains. Then, a second part of the cationic etherifying agent is added. Sodium citrate has the functions of charge shielding, buffering pH value, and catalyzing the etherification reaction, which is conducive to promoting the further progress of the etherification reaction, thereby increasing the cationic substitution degree of the cationic cellulose ether, and at the same time, it can also improve the reaction efficiency between the cationic etherifying agent and the cellulose ether.

[0045] In Method 2 above, the sodium citrate aqueous solution can be added to the second system dropwise. This application does not have a specific time limit for the dropwise addition of the sodium citrate aqueous solution to the second system, as long as the purpose of this application is achieved. For example, the dropwise addition time of the sodium citrate aqueous solution to the second system can be 15 to 30 minutes. In Method 2 above, the second part of the cationic etherifying agent can be added to the charge shielding system dropwise. This application does not have a specific time limit for the dropwise addition of the second part of the cationic etherifying agent to the charge shielding system, as long as the purpose of this application is achieved. For example, the dropwise addition time of the second part of the cationic etherifying agent to the charge shielding system can be 15 to 30 minutes. In Method 2 above, the time of the second-stage etherification reaction includes the dropwise addition time of the second part of the cationic etherifying agent to the charge shielding system and the isothermal time after the dropwise addition is completed.

[0046] In some embodiments of this application, the specific steps of adding the sodium citrate aqueous solution and the second part of the cationic etherifying agent to the second system in step (3) are as follows: At a temperature of 40°C to 90°C, the sodium citrate aqueous solution and the second part of the cationic etherifying agent are simultaneously added to the second system to carry out a second-stage etherification reaction. The second-stage etherification reaction time is 60 min to 180 min, resulting in a third system. For example, the temperature of the second-stage etherification reaction can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or any two of these values, and the time of the second-stage etherification reaction can be 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 180 min, or any two of these values. By using the above method 3, sodium citrate aqueous solution and a second part of cationic etherifying agent are added to the second system simultaneously. The sodium citrate aqueous solution has the functions of charge shielding, pH buffering and catalytic etherification reaction, which is conducive to promoting the further progress of etherification reaction, thereby increasing the cationic substitution degree of cationic cellulose ether, and also improving the reaction efficiency between cationic etherifying agent and cellulose ether.

[0047] In the above-mentioned manner 3, the aqueous sodium citrate solution and the second part of the cationic etherifying agent can be added into the second system by dropping. The present application does not particularly limit the time for dropping the aqueous sodium citrate solution and the second part of the cationic etherifying agent into the above-mentioned charge shielding system, as long as the purpose of the present application can be achieved. For example, the time for dropping the aqueous sodium citrate solution and the second part of the cationic etherifying agent into the above-mentioned charge shielding system can be 15 min to 30 min. In the above-mentioned manner 3, the time for the second stage etherification reaction includes the dropping time for dropping the second part of the cationic etherifying agent and the aqueous sodium citrate solution into the charge shielding system and the constant temperature time after the dropping is completed.

[0048] In some embodiments of the present application, the first stage etherification reaction and the second stage etherification reaction are carried out under an inert atmosphere, for example, can be carried out under a nitrogen atmosphere or an argon atmosphere. Carrying out the etherification reaction under an inert atmosphere is advantageous to reduce the occurrence of side reactions and improve the reaction efficiency of the cationic etherifying agent and the cellulose ether.

[0049] In some embodiments of the present application, in the step (4), the third system is cooled to below 30°C, an acid solution is added to adjust the pH of the system to 5 to 7, and then solid-liquid separation is carried out to obtain a precipitate and a mother liquor. For example, the third system can be cooled to 20°C, 22°C, 25°C, 28°C, 30°C, or a range formed by any two of the above-mentioned values, and then an acid solution is added to adjust the pH of the system. The pH of the system can be 5, 5.5, 6, 6.5, 7, or a range formed by any two of the above-mentioned values. The present application does not particularly limit the type of the acid solution, as long as the purpose of the present application can be achieved. For example, the acid solution can be sulfuric acid, hydrochloric acid, acetic acid, nitric acid, acetic acid, citric acid, etc. By adjusting the pH of the system within the above-mentioned range by adding an acid solution, the unreacted alkaline solution can be neutralized, the system is prevented from being in an over-alkaline state, and the obtained cationic cellulose ether is more suitable for use as a raw material for hair care products.

[0050] In some embodiments of the present application, in the step (4), the mother liquor is subjected to cooling crystallization to recover sodium citrate. The recovered sodium citrate can be configured as an aqueous sodium citrate solution and applied to the step (3), thereby reducing the production cost. The present application does not particularly limit the temperature and time for cooling crystallization of the mother liquor, as long as the purpose of the present application can be achieved. For example, the cooling temperature can be 0°C to 5°C, and the cooling time can be 8 h to 16 h.

[0051] Examples

[0052] Hereinafter, embodiments of the present application will be more specifically described by citing examples and comparative examples. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass. All raw materials in the examples and comparative examples of the present application can be purchased.

[0053] Test method and equipment:

[0054] Test of mass percentage of nitrogen in cationic cellulose ether and calculation of cationic substitution degree:

[0055] The mass percentage of nitrogen (N%) in the cationic cellulose ether prepared in the examples and comparative examples was measured using a Kjeldahl nitrogen analyzer, and then the substitution degree DS of the cationic cellulose ether was calculated according to the following formula:

[0056] DS = (M x N) / (14 - K x N); wherein M is the relative molecular mass of the cellulose ether structural unit, for example, when the cellulose ether is hydroxyethyl cellulose, the value of M is 206; when the cellulose ether is hydroxypropyl cellulose, the value of M is 220; when the cellulose ether is hydroxypropyl methyl cellulose, the value of M is 234; K is the relative molecular mass of the structural unit of the cationic etherifying agent grafted to the cellulose ether macromolecular backbone with a cationic group, for example, when the cationic etherifying agent is selected from 3-chloro-2-hydroxypropyl trimethyl ammonium chloride aqueous solution or 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution, K is 152.5.

[0057] Example 1-1

[0058] (1) Disperse 50 g of hydroxyethyl cellulose powder (CAS No.: 9004-62-0) in 250 g of isopropyl alcohol aqueous solution (20% mass percentage of water based on the mass of the isopropyl alcohol aqueous solution) to obtain a hydroxyethyl cellulose dispersion. Then heat the hydroxyethyl cellulose dispersion to 60°C, then add 4 g of 30% mass fraction sodium hydroxide aqueous solution, and stir at a stirring rate of 500 rpm for 1 h to obtain a first system. That is, the alkalization reaction temperature is 60°C, and the alkalization reaction time is 1 h.

[0059] (2) Under a nitrogen atmosphere, maintain the temperature of the first system at 60°C, and drop 20 g of 50% mass fraction 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution (EPTAC, first part of cationic etherifying agent) into the above first system at a dropping rate of 1 g / min, the dropping time is 20 min, after the dropping is completed, continue to react at 60°C for 30 min to obtain a second system. That is, the temperature of the first stage etherification reaction is 60°C, and the first stage etherification reaction time is 50 min.

[0060] (3) The second system is kept at 60°C, then 20 g of 15% sodium citrate aqueous solution (first part of sodium citrate aqueous solution) is added dropwise into the second system at a rate of 1 g / min, the dropping time is 20 min, after the dropping is completed, the constant temperature stirring at 60°C is continued for 30 min, to obtain a charge shielding system. Then, 20 g of 50% 2,3-epoxypropyltrimethylammonium chloride aqueous solution (second part of cationic etherification agent) is added dropwise into the charge shielding system at a rate of 1 g / min, and 10 g of 15% sodium citrate aqueous solution is added dropwise into the charge shielding system at a rate of 0.5 g / min, the temperature is controlled at 60°C during the process, after 20 min, the dropping of the 2,3-epoxypropyltrimethylammonium chloride aqueous solution and the sodium citrate aqueous solution is completed, then the constant temperature reaction at 60°C is continued for 120 min, to obtain a third system. The temperature for adding the first part of sodium citrate aqueous solution into the second system is 60°C, the temperature for the second stage etherification reaction is 60°C, and the time for the second stage etherification reaction is 140 min.

[0061] The above steps (2) to (3) are carried out under a nitrogen atmosphere.

[0062] (4) The third system obtained above is cooled to 25°C, acetic acid is added to adjust the pH of the third system to 6, then filtration is performed, to obtain a precipitate and a mother liquor, the precipitate is washed with 250 g of 85% isopropyl alcohol aqueous solution for 5 times, then the precipitate is placed in a vacuum oven at 60°C for drying for 5 h, to obtain cationic hydroxyethyl cellulose. The mother liquor is placed at 4°C for standing for 12 h, the sodium citrate in the mother liquor is cooled and crystallized, to recover the sodium citrate.

[0063] Examples 1-2 to 1-4

[0064] Except that in step (3), the total mass of the sodium citrate aqueous solution and the mass percentage of the first part of sodium citrate aqueous solution in the total sodium citrate aqueous solution are adjusted according to Table 1, and the dropping rate of the first part of sodium citrate aqueous solution is adjusted so that the dropping time remains unchanged, the rest is the same as Example 1-1.

[0065] Examples 1-5 to 1-6

[0066] The rest is the same as Example 1-1 except that in step (2) and step (3), the mass of the first part of the cationic etherifying agent and the mass of the second part of the cationic etherifying agent are adjusted according to Table 1. That is, in Example 1-5, 30 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the first system in step (2), and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate; in step (3), 30 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the charge shielding system, and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate, and the rest is the same as Example 1-1. In Example 1-6, 40 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the first system in step (2), and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate; in step (3), 40 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the charge shielding system, and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate, and the rest is the same as Example 1-1.

[0067] Examples 1-7 to 1-8

[0068] The rest is the same as Example 1-1 except that in step (2) and step (3), the mass fraction of the cationic etherifying agent and the total mass of the cationic etherifying agent are adjusted according to Table 1. That is, in Example 1-7, 25 g of a 40% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the first system in step (2), and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate; in step (3), 25 g of a 40% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the charge shielding system, and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate, and the rest is the same as Example 1-1. That is, in Example 1-8, 16.65 g of a 60% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the first system in step (2), and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate; in step (3), 16.65 g of a 60% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the charge shielding system, and the dropwise addition time is kept unchanged by adjusting the dropwise addition rate, and the rest is the same as Example 1-1.

[0069] Example 1-9

[0070] The rest is the same as Example 1-1 except that in step (2) and step (3), the type of the cationic etherifying agent is adjusted to 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (CHPTAC) according to Table 1.

[0071] Examples 1-10 to 1-11

[0072] Except that in step (2) and step (3), the mass percentage of the first part of cationic etherifying agent in the total cationic etherifying agent is adjusted according to Table 1, the rest is the same as Example 1-1. That is, in Example 1-10, 16 g of 2,3-epoxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 50% is added dropwise into the first system in step (2), and the dropwise time is kept unchanged by adjusting the dropwise rate; in step (3), 24 g of 2,3-epoxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 50% is added dropwise into the charge shielding system, and the dropwise time is kept unchanged by adjusting the dropwise rate, and the rest is the same as Example 1-1. In Example 1-11, 32 g of 2,3-epoxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 50% is added dropwise into the first system in step (2), and the dropwise time is kept unchanged by adjusting the dropwise rate; in step (3), 8 g of 2,3-epoxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 50% is added dropwise into the charge shielding system, and the dropwise time is kept unchanged by adjusting the dropwise rate, and the rest is the same as Example 1-1.

[0073] Examples 1-12 to 1-13

[0074] Except that in step (2) and step (3), the relevant temperature parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0075] Examples 1-14 to 1-15

[0076] Except that in step (2), the first stage etherification reaction time is adjusted according to Table 1, the rest is the same as Example 1-1. That is, in Example 1-14, 20 g of 2,3-epoxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 50% is added dropwise into the first system at a dropwise rate of 1 g / min in step (2), and the dropwise time is 20 min, and step (3) is carried out immediately after the dropwise addition is completed, that is, the first stage etherification reaction time is 20 min. In Example 1-15, 20 g of 2,3-epoxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 50% is added dropwise into the first system at a dropwise rate of 1 g / min in step (2), and the dropwise time is 20 min, and then the reaction is continued at a constant temperature of 60°C for 60 min, that is, the first stage etherification reaction time is 80 min.

[0077] Examples 16 to 17

[0078] The rest is the same as Example 1-1 except that in step (3), the second stage etherification reaction time is regulated according to Table 1. That is, in Example 1-16, in step (3), after the second part of the cationic etherification agent 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution and the remaining sodium citrate aqueous solution are added dropwise, the dropping time is 20 min, and then the reaction is continued at 60°C for 40 min to obtain the third system; that is, the second stage etherification reaction time is 60 min. In Example 1-17, in step (3), after the second part of the cationic etherification agent 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution and the remaining sodium citrate aqueous solution are added dropwise, the dropping time is 20 min, and then the reaction is continued at 60°C for 160 min to obtain the third system; that is, the second stage etherification reaction time is 180 min.

[0079] Example 1-18

[0080] Step (3): The second system is kept at a temperature of 60°C, and then 30 g of a 15% by mass sodium citrate aqueous solution is added dropwise to the above-mentioned second system at a rate of 1 g / min, and the dropping time is 30 min. After the dropping is completed, the stirring is continued at 60°C for another 30 min to obtain a charge shielding system. Then, 20 g of a 50% by mass 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution (second part of the cationic etherification agent) is added dropwise to the above-mentioned charge shielding system at a rate of 1 g / min, and the temperature is controlled at 60°C during the process. After 20 min, the 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution addition is completed, and then the reaction is continued at 60°C for 120 min to obtain a third system.

[0081] The rest is the same as Example 1-1 except that in step (3), the second part of the cationic etherification agent is added dropwise to the above-mentioned charge shielding system to obtain the third system according to the above method (method 2) in which all the sodium citrate aqueous solution is added dropwise to the second system at one time to obtain the charge shielding system, and then the second part of the cationic etherification agent is added dropwise to the above-mentioned charge shielding system to obtain the third system.

[0082] Example 1-19

[0083] Step (3): 20 g of a 50% by mass 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution (second part of the cationic etherification agent) is added dropwise to the second system at a rate of 1 g / min, and 30 g of a 15% by mass sodium citrate aqueous solution is added dropwise to the second system at a rate of 1.5 g / min, and the temperature is controlled at 60°C during the process. After 20 min, the 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution and the sodium citrate aqueous solution addition is completed, and then the reaction is continued at 60°C for 120 min to obtain a third system.

[0084] Example 1-1 was repeated except that in step (3), the entire sodium citrate aqueous solution and the second part of the cationic etherifying agent were simultaneously added to the second system according to the above method (Method 3) to perform the reaction, and the third system was obtained.

[0085] Examples 2-1 to 2-2

[0086] Example 1-1 was repeated except that in step (1), the kind of the basic solution was adjusted to be potassium carbonate aqueous solution according to Table 2.

[0087] Example 2-3

[0088] Example 1-1 was repeated except that in step (1), the kind of the basic solution was adjusted to be potassium carbonate aqueous solution according to Table 2.

[0089] Examples 2-4 to 2-5

[0090] Example 1-1 was repeated except that in step (1), the mass of the sodium hydroxide aqueous solution was adjusted according to Table 2.

[0091] Example 2-6

[0092] Example 1-1 was repeated except that in step (1), the mass percentage content of water in the isopropyl alcohol aqueous solution was adjusted to be 10% according to Table 2.

[0093] Example 2-7

[0094] Example 1-1 was repeated except that in step (1), the mass of the isopropyl alcohol aqueous solution was adjusted so that the mass percentage content of the cellulose ether in the cellulose ether dispersion liquid was 15%.

[0095] Example 2-8

[0096] Example 1-1 was repeated except that in step (1), the mass of the isopropyl alcohol aqueous solution was adjusted so that the mass percentage content of the cellulose ether in the cellulose ether dispersion liquid was 25%.

[0097] Examples 2-9 to 2-10

[0098] Example 1-1 was repeated except that in step (1), the kind of the cellulose ether was adjusted according to Table 2.

[0099] Comparative Example 1

[0100] The steps (2) and (3) in Example 1-1 were adjusted as follows: in a nitrogen atmosphere, the first system was kept at a temperature of 60°C, 40 g of a 50% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride was added dropwise into the first system at a dropwise addition rate of 1 g / min, the dropwise addition time was 40 min, after the dropwise addition was completed, the reaction was continued at a constant temperature of 60°C for 200 min to obtain a reaction system. The rest was the same as in Example 1-1, that is, no aqueous solution of sodium citrate was added in the etherification reaction process in Comparative Example 1.

[0101] Comparative Examples 2 to 3

[0102] Except that in steps (2) and (3), the mass percentage content of the first part of the cationic etherifying agent in the total cationic etherifying agent was adjusted according to Table 1, the rest was the same as in Example 1-1. That is, in Comparative Example 2, 12 g of a 50% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride was added dropwise into the first system in step (2), the dropwise addition time was kept unchanged by adjusting the dropwise addition rate; in step (3), 28 g of a 50% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride was added dropwise into the charge shielding system, the dropwise addition time was kept unchanged by adjusting the dropwise addition rate, and the rest was the same as in Example 1-1. In Comparative Example 2, 36 g of a 50% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride was added dropwise into the first system in step (2), the dropwise addition time was kept unchanged by adjusting the dropwise addition rate; in step (3), 4 g of a 50% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride was added dropwise into the charge shielding system, the dropwise addition time was kept unchanged by adjusting the dropwise addition rate, and the rest was the same as in Example 1-1.

[0103] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1 and Table 2.

[0104] Table 1

[0105]

[0106] Note: " / " in Table 1 indicates that the corresponding preparation parameter or substance does not exist.

[0107] Table 2

[0108]

[0109] As can be seen from Examples 1-1 to 1-19, Examples 2-1 to 2-10, and Comparative Examples 1 to 3, by dividing the etherification reaction into two stages, adding an aqueous sodium citrate solution in the second stage of the etherification reaction, and adjusting the mass percentage of the first part of the cationic etherifying agent within the range of the present application, the cationic cellulose ether prepared in the examples has a higher cationic degree of substitution. In the preparation process of Comparative Example 1, no aqueous sodium citrate solution was added, and in Comparative Examples 2 and 3, the mass percentage of the first part of the cationic etherifying agent in the total cationic etherifying agent was not within the range of the present application, and the cationic degree of substitution of the cationic cellulose ether prepared was lower.

[0110] The molar ratio of sodium citrate to the solutes in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent in the aqueous sodium citrate solution affects the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1 to 1-4, by adjusting the molar ratio of sodium citrate to the solutes in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent in the aqueous sodium citrate solution within the range of (0.07~0.22):1, the cationic cellulose ether prepared has a higher cationic degree of substitution.

[0111] The total mass of the solutes in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent to the mass of the cellulose ether affects the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1, 1-5 to 1-6, by adjusting the total mass of the solutes in the first part of the cationic etherifying agent and the second part of the cationic etherifying agent to the mass of the cellulose ether within the range of (0.4~0.8):1, the cationic cellulose ether prepared has a higher cationic degree of substitution.

[0112] The type of cationic etherifying agent and the mass fraction of the cationic etherifying agent affect the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1, 1-7 to 1-9, by selecting a cationic etherifying agent within the range of the present application, the cationic cellulose ether prepared has a higher cationic degree of substitution.

[0113] The temperature and time of the first stage of the etherification reaction and the second stage of the etherification reaction affect the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1, 1-12 to 1-17, by adjusting the temperature and time of the first stage of the etherification reaction and the second stage of the etherification reaction within the range of the present application, the cationic cellulose ether prepared has a higher cationic degree of substitution.

[0114] The way of adding the aqueous sodium citrate solution and the second part of the cationic etherifying agent into the second system can affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Example 1-1, Example 1-18 and Example 1-19, by adding the aqueous sodium citrate solution and the second part of the cationic etherifying agent into the second system in the manner 1, manner 2 and manner 3 provided by the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0115] The temperature and time of the alkalization reaction can affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Example 1-1, Example 2-1 and Example 2-2, by adjusting the temperature and time of the alkalization reaction within the scope of the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0116] The type of the alkaline solution can affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Example 1-1 and Example 2-3, by selecting the alkaline solution within the scope of the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0117] The mass ratio of the solute in the alkaline solution to the cellulose ether can affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Example 1-1, Example 2-4 and Example 2-5, by adjusting the mass ratio of the solute in the alkaline solution to the cellulose ether within the scope of the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0118] The mass percentage content of the cellulose ether in the cellulose ether dispersion and the mass percentage content of water in the solvent can affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Example 1-1 and Example 2-6 to Example 2-8, by adjusting the mass percentage content of the cellulose ether in the cellulose ether dispersion and the mass percentage content of water in the solvent within the scope of the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0119] The type of the cellulose ether can affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Example 1-1, Example 2-9 and Example 2-10, by selecting the cellulose ether within the scope of the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0120] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a cationic cellulose ether, comprising the following steps: (1) dispersing a cellulose ether in a solvent to obtain a cellulose ether dispersion, and then mixing the cellulose ether dispersion with an alkaline solution to perform an alkalization reaction, thereby obtaining a first system; (2) adding a first portion of a cationic etherifying agent to the first system to perform a first-stage etherification reaction, thereby obtaining a second system; (3) adding a sodium citrate aqueous solution and a second portion of the cationic etherifying agent to the second system to perform a second-stage etherification reaction, thereby obtaining a third system; and (4) performing a solid-liquid separation on the third system to obtain a precipitate and a mother liquor, and then performing a washing and drying on the precipitate, thereby obtaining the cationic cellulose ether; wherein, based on the total mass of the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent, the mass percentage of the first portion of the cationic etherifying agent is 40% to 80%; the molar ratio of sodium citrate in the sodium citrate aqueous solution to the solutes in the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent is (0.07-0.22): 1; and the mass ratio of the total mass of the solutes in the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent to the cellulose ether is (0.4-0.8):

1. the cellulose ether is selected from hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose or hydroxypropyl methyl cellulose; and based on the mass of the cellulose ether dispersion, the mass percentage of the cellulose ether is 15% to 25%. the solvent is selected from at least one of a methanol aqueous solution, an ethanol aqueous solution, an isopropanol aqueous solution and a tert-butanol aqueous solution; and based on the mass of the solvent, the mass percentage of water in the solvent is 10% to 20%. the alkaline solution is selected from at least one of a potassium hydroxide aqueous solution, a sodium hydroxide aqueous solution, a sodium carbonate aqueous solution and a potassium carbonate aqueous solution; the mass fraction of the alkaline solution is 20% to 40%; and the mass ratio of the solute in the alkaline solution to the cellulose ether is (0.02-0.05):

1. the temperature of the alkalization reaction is 30°C to 80°C, and the alkalization reaction time is 1h to 5h. the temperature of the first-stage etherification reaction is 40°C to 90°C, and the first-stage etherification reaction time is 20min to 80min. the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent are selected from a 3-chloro-2-hydroxypropyl trimethyl ammonium chloride aqueous solution or a 2,3-epoxypropyl trimethyl ammonium chloride aqueous solution; and the mass fraction of the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent is 40% to 60%. the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent are selected from the same substance. the mass fraction of the sodium citrate aqueous solution is 5% to 25%. in the step (3), the specific steps for adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system are mode 1: ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 1, wherein, ​ 4. The method of claim 1, wherein, ​ 5. The method of claim 1, wherein, ​ 6. The method of claim 1, wherein, ​ 7. The method of claim 1, wherein, ​ 8. The method of claim 7, wherein, ​ 9. The method of claim 1, wherein, ​ 10. The method of any one of claims 1 to 9, wherein, ​ The first part of the sodium citrate aqueous solution is added to the second system at 20-80°C to obtain a charge shielding system; the mass percentage of the first part of the sodium citrate aqueous solution is 40-80% based on the total mass of the sodium citrate aqueous solution; The remaining sodium citrate aqueous solution and the second part of the cationic etherifying agent are simultaneously added to the charge shielding system at 40-90°C to perform a second-stage etherification reaction, and the second-stage etherification reaction time is 60-180 min to obtain a third system.

11. The method of any one of claims 1 to 9, wherein, In the step (3), the specific procedure for adding the sodium citrate aqueous solution and the second part of the cationic etherifying agent to the second system is mode 2: The sodium citrate aqueous solution is added to the second system at 20-80°C to obtain a charge shielding system; The second part of the cationic etherifying agent is added to the charge shielding system at 40-90°C to perform a second-stage etherification reaction, and the second-stage etherification reaction time is 60-180 min to obtain a third system.

12. The method of any one of claims 1 to 9, wherein, In the step (3), the specific procedure for adding the sodium citrate aqueous solution and the second part of the cationic etherifying agent to the second system is mode 3: The sodium citrate aqueous solution and the second part of the cationic etherifying agent are simultaneously added to the second system at 40-90°C to perform a second-stage etherification reaction, and the second-stage etherification reaction time is 60-180 min to obtain a third system.

13. The method of any one of claims 1 to 9, wherein, In the step (4), after the third system is cooled to below 30°C, an acid solution is added to adjust the pH value of the system to 5-7, and then solid-liquid separation is performed to obtain a precipitate and a mother liquor.

14. The method of any one of claims 1 to 9, wherein, In the step (4), the mother liquor is subjected to cooling crystallization to recover sodium citrate.

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