Preparation method of cationic cellulose ether

Abstract

The invention relates to the technical field of functional polymer materials, and provides a preparation method of cationic cellulose ether.The preparation method is characterized in that a sodium citrate solution is added into a reaction system, on one hand, three carboxylic acid groups of sodium citrate and cationic monomers of a cationic etherifying agent can form ion pairs, local positive charges are effectively neutralized, and the cationic cellulose etherifying effect is improved; the charge repulsive force between cationic groups of the cationic etherifying agent is weakened, and further etherification reaction is facilitated. In addition, sodium citrate can stabilize the pH value of a reaction system and reduce side reactions. In addition, sodium ions of sodium citrate serve as weak Lewis acid and can synergistically activate hydroxyl oxygen atoms on a main chain of the cellulose ether, and the reaction efficiency of the cationic etherifying agent and the cellulose ether is further improved. According to the preparation method, the cation substitution degree of the cationic cellulose ether can be improved, the reaction efficiency of the cationic etherifying agent and the cellulose ether can be improved, the sodium citrate can be recycled, and the production cost is further reduced.

Description

Technical Field

[0001] The present application relates to the technical field of functional polymer materials, and in particular to a method for preparing cationic cellulose ether. Background Art

[0002] Hair shampoo products are a necessity in people's daily lives. They have gradually evolved from their original function of cleaning hair to multifunctional cosmetics that combine shampooing and hair care. Among them, hair conditioners, as an important component of hair care products, mainly function to improve the texture, gloss and combability of hair. Among them, cationic cellulose ether, as a hair conditioner, is derived from natural cellulose, has a relatively more environmentally friendly production process, and is less irritating to the skin and hair, and has therefore attracted widespread attention. Compared with natural cellulose, cationic cellulose ether has unique positively charged quaternary ammonium groups that can attract and bind to the negative charges on the surface of the hair, thereby adhering to the surface and providing a long-lasting conditioning effect. The strength of this conditioning effect is closely related to the cationic degree of substitution of the cationic cellulose ether. The higher the cationic degree of substitution, the better the conditioning effect. Therefore, there is an urgent need to develop a method for preparing cationic cellulose ethers with a high degree of substitution. Summary of the Invention

[0003] The purpose of this application is to provide a method for preparing cationic cellulose ether to increase the cationic substitution degree of cationic cellulose ether and reduce production costs. The specific technical solution is as follows:

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

[0005] (1) dispersing 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 to obtain a first system;

[0006] (2) adding a first portion of a cationic etherifying agent to the first system to carry out a first-stage etherification reaction to obtain a second system;

[0007] (3) adding a sodium citrate aqueous solution and a second portion of a cationic etherifying agent to the second system to carry out a second-stage etherification reaction to obtain a third system;

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

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

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

[0011] 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; based on the mass of the solvent, the mass percentage of water in the solvent is 10% to 20%.

[0012] 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 to the cellulose ether in the alkaline solution is (0.02-0.05):1.

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

[0014] 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.

[0015] In some embodiments of the present application, the first portion of cationic etherifying agent and the second portion of cationic etherifying agent are selected from 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution or 2,3-epoxypropyltrimethylammonium chloride aqueous solution; the mass fraction of the first portion of cationic etherifying agent and the second portion of cationic etherifying agent is 40% to 60%.

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

[0017] In some embodiments of the present application, 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. 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 the 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.

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

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

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

[0021] In some embodiments of the present application, in 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 to 7, and then the solid-liquid separation is performed to obtain a precipitate and a mother liquor.

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

[0023] The present application provides a method for preparing cationic cellulose ether, which divides the etherification reaction into two stages and adds a sodium citrate aqueous solution to the second system. On the one hand, sodium citrate acts as a charge shielding agent. 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, which is conducive to the further progress of the etherification reaction. On the other hand, sodium citrate has a 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 a weak Lewis acid, 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 present application divides the etherification reaction into two stages, and by adding a sodium citrate solution to the second system, the sodium citrate plays the role of charge shielding, buffering the pH value, and catalyzing the etherification reaction, thereby increasing the cationic substitution degree of the cationic cellulose ether and improving the reaction efficiency of the cationic etherifying agent and the cellulose ether. In addition, the sodium citrate of the present application can be recycled, further reducing production costs.

[0024] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

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

[0026] The first aspect of the present application provides a method for preparing a cationic cellulose ether, comprising the following steps: (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 to obtain a first system; (2) adding a first portion 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 portion of a cationic etherifying agent to the second system to perform a second-stage etherification reaction to obtain a third system; (4) performing solid-liquid separation on the third system to obtain a precipitate and a mother liquor, washing and drying the precipitate to obtain a 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%. 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 can be 40%, 50%, 60%, 70%, 80%, or a range consisting of any two of these values. It should be noted that, after the mass percentage of the first portion of the cationic etherifying agent is determined, the remaining portion is the second portion of the cationic etherifying agent, that is, the mass percentage of the second portion of the cationic etherifying agent is determined accordingly.

[0027] Cationization of cellulose ethers refers to the modification of cellulose ethers to introduce cationic structures. The most common method is chemical modification. During the cationization process of cellulose ethers, the hydroxyl groups on the cellulose ether molecules react with some active groups (such as epoxy groups, halogenated hydrocarbon groups, etc.), forming ether bonds and introducing cationic groups. Therefore, the reagents that perform cationic modification on cellulose ethers are also called cationic etherifying agents.

[0028] In the cationic modification of cellulose ethers, the positive charge density of the cellulose ether molecular chain increases with each cationic group added, resulting in the need for subsequent cationic groups to overcome increasing charge repulsion, ultimately leading to a decrease in reaction rate. In other words, the cationic degree of substitution is not linearly related to the amount of etherifying agent used. Instead, as the amount of etherifying agent used increases, the degree of substitution increases at a decreasing rate. In actual production, problems such as low and uneven product substitution and low process efficiency will arise. The inventors have discovered that by dividing the etherification reaction into two stages, first, a first portion of cationic etherifying agent is added to the first system to conduct a first-stage etherification reaction to obtain a second system; then, an aqueous sodium citrate solution is introduced into the second system, and a second-stage etherification reaction is then conducted with the second portion of cationic etherifying agent. The present application divides the etherification reaction into two stages and introduces a sodium citrate solution into the second system. On the one hand, sodium citrate acts as a charge shielding agent. 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. Therefore, the addition of a sodium citrate aqueous solution during the second stage etherification reaction is beneficial to the further progress of the etherification reaction. On the other hand, sodium citrate has a 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 a weak Lewis acid, can synergistically activate the hydroxyl oxygen atoms on the cellulose ether main chain, further improving the reaction efficiency of the cationic etherifying agent and the cellulose ether. In addition, by regulating the mass percentage of the first part of the cationic etherifying agent 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 portion of the cationic etherifying agent undergoes an etherification reaction with the cellulose ether, the positive charge density of the cellulose ether molecular chain increases, resulting in the subsequent cationic group insertion needing to overcome increasing charge repulsion. At this point, the addition of the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system can further promote the second-stage etherification reaction and increase the cationic substitution degree of the cellulose ether. The preparation method of the present application can increase the cationic substitution degree of the cationic cellulose ether, while also improving the reaction efficiency of the cationic etherifying agent and the cellulose ether. Furthermore, the sodium citrate of the present application can be recycled, further reducing production costs.

[0029] When the mass percentage of the solute in the first part of the cationic etherifying agent 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 is less than 40%, it means that less cationic etherifying agent participates in the first stage etherification reaction, more cationic etherifying agent participates in the second stage etherification reaction, and the reaction rate of the cationic etherifying agent and cellulose ether is faster in the early stage of the etherification reaction. If most of the cationic etherifying agent participates in the second stage etherification reaction, it is not conducive to improving the reaction efficiency of the cationic etherifying agent and cellulose ether, nor is it conducive to improving the cationic substitution degree of the cationic cellulose ether. When the mass percentage of the solute in the first part of the cationic etherifying agent 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 is greater than 80%, it means that more cationic etherifying agent participates in the first stage etherification reaction, and less cationic etherifying agent participates in the second stage etherification reaction. If most of the cationic etherifying agent participates in the first stage etherification reaction, the retarding effect caused by charge repulsion becomes more obvious, which is not conducive to improving the reaction efficiency of the cationic etherifying agent and cellulose ether, nor is it conducive to improving the cationic substitution degree 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; based on the mass of the cellulose ether dispersion, the mass percentage of the cellulose ether is 15% to 25%. For example, the mass percentage of the cellulose ether can be 15%, 18%, 20%, 23%, 25%, or a range consisting of any two of these values. By regulating the mass percentage of the cellulose ether in the cellulose ether dispersion within the scope of the present application, it is beneficial to uniformly disperse the cellulose ether in the solvent. In the present application, the cellulose ether can be obtained by preparation or by purchase. The present application does not particularly limit the degree of hydroxyl substitution and 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-water solution, an ethanol-water solution, an isopropanol-water solution, and a tert-butanol-water solution; the weight percentage of water in the solvent is 10% to 20% based on the mass of the solvent. For example, the weight percentage of water can be 10%, 13%, 15%, 18%, 20%, or a range consisting of any two of these values. Dispersing the cellulose ether in a solvent within the scope of the present application facilitates uniform dispersion of the cellulose ether in the solvent. Furthermore, regulating the weight percentage of water in the mixed solution within the range of the present application allows for a certain degree of swelling of the cellulose ether and a moderate viscosity of the resulting first system, facilitating the subsequent etherification reaction.

[0031] In some embodiments of the present application, the alkaline solution is selected from at least one of an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution, and an aqueous potassium carbonate solution; the mass fraction of the alkaline solution is 20% to 40%; and the mass ratio of solute to cellulose ether in the alkaline solution 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 consisting of any two of these values; and the mass ratio of solute to cellulose ether in the alkaline solution can be 0.02:1, 0.03:1, 0.04:1, 0.05:1, or a range consisting of any two of these values. Selecting an alkaline solution within the scope of the present application for the alkalization reaction with the cellulose ether dispersion facilitates activation of the hydroxyl groups on the cellulose ether molecules. The activated hydroxyl groups have a stronger ability to attack the active groups in the cationic etherifying agent, thereby increasing the rate and extent of the subsequent etherification reaction and improving the cationic degree of substitution of the cellulose ether. In addition, alkaline conditions are conducive to better dispersion of cellulose ether in the solvent, and the molecular chain of cellulose ether can stretch more open, so that the cationic etherifying agent can react more evenly with the hydroxyl groups on the cellulose ether, thereby improving the uniformity of the cationic substitution degree of cellulose ether.

[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 consisting of any two of the values therein; the time of the alkalization reaction can be 1h, 2h, 3h, 4h, 5h, or a range consisting of any two of the values therein. In the present application, the alkalization reaction process can be carried out under stirring. The present application does not particularly limit the stirring speed, as long as the purpose of the present application can be achieved. For example, the stirring speed is 200rpm~800rpm. By regulating the temperature and time of the alkalization reaction within the scope of the present application, it is beneficial for the alkaline solution to fully activate the hydroxyl groups on the cellulose ether molecules, which is beneficial to increase the rate and degree of the subsequent etherification reaction and increase the cationic substitution degree of the cellulose ether.

[0033] In some embodiments of the present application, the temperature of the first-stage etherification reaction is 40°C to 90°C, and the first-stage etherification reaction time 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 consisting of any two of these values. In the present application, the first-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. The first-stage etherification reaction time can be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, or a range consisting of any two of these values. By regulating the temperature and time of the etherification reaction within the range of the present application, it is beneficial to promote the etherification reaction between the cellulose ether and the cationic etherifying agent and improve the efficiency of the etherification reaction.

[0034] In some embodiments of the present application, the first and second cationic etherifying agents are selected from an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) or an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride (EPTAC); the mass fraction of the first and second cationic etherifying agents is 40% to 60%. In some embodiments of the present application, the first and second cationic etherifying agents are selected from the same substance. For example, the mass fraction of the first and second cationic etherifying agents can be 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of these values. Selecting a cationic etherifying agent within the scope of the present application facilitates the etherification reaction between the cellulose ether and the cationic etherifying agent, thereby introducing positively charged quaternary ammonium groups into the cellulose ether molecular chain and achieving cationic modification of the cellulose ether.

[0035] In the present application, the first portion of the cationic etherifying agent can be added dropwise to the first system. The time for adding the first portion of the cationic etherifying agent dropwise to the first system is not particularly limited, as long as the objectives of the present application can be achieved. For example, the time for adding the first portion of the cationic etherifying agent dropwise to the first system can be 15 to 30 minutes. In the present application, the time for the first-stage etherification reaction includes the time for adding the first portion of the cationic etherifying agent dropwise to the first system and the time for maintaining the temperature after the addition is completed.

[0036] In some embodiments of the present application, the ratio of the total mass of the solutes in the first and second portions of the cationic etherifying agent to the mass of the cellulose ether is (0.4-0.8):1. For example, the ratio of the total mass of the solutes in the first and second portions 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 consisting of any two of these values. By regulating the ratio of the total mass of the solutes in the cationic etherifying agent to the mass of the cellulose ether within the above range, the first portion of the cationic etherifying agent and the cellulose ether undergo a sufficient etherification reaction, thereby improving the efficiency of the etherification reaction. After the etherification reaction between the first portion of the cationic etherifying agent and the cellulose ether, the positive charge density of the cellulose ether molecular chain increases, resulting in the subsequent cationic group insertion having to overcome increasing charge repulsion. At this point, adding the sodium citrate solution and the second portion of the cationic etherifying agent to the second system can further promote the second-stage etherification reaction and increase the cationic substitution degree 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 to the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent in the sodium citrate aqueous solution 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 consisting of any two of these values. The molar ratio of sodium citrate to the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent in the sodium citrate aqueous solution 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 consisting of any two of these values. By introducing a sodium citrate solution into the second system, regulating the mass fraction of the sodium citrate solution within the range of the present application, and regulating the molar ratio of the sodium citrate to the first portion of the cationic etherifying agent and the second portion of the cationic etherifying agent in the sodium citrate solution within the above range, it is beneficial to increase the cationic substitution degree of the cationic cellulose ether, while also improving the reaction efficiency of the cationic etherifying agent and the cellulose ether and reducing costs.

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

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

[0040] In the above-mentioned method 1, first, the first portion of the sodium citrate aqueous solution is added to the second system. The first portion of the sodium citrate aqueous solution mainly 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, the remaining second portion of the sodium citrate aqueous solution and the second portion of the cationic etherifying agent are added to the above-mentioned charge shielding system at the same time. The second portion of the sodium citrate aqueous solution mainly shields the cationic groups on the cationic etherifying agent that have not yet participated in the reaction, thereby promoting the further progress of the etherification reaction. By adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system through the above-mentioned method 1, the sodium citrate has the functions of charge shielding, buffering the pH value, and catalyzing the etherification reaction, thereby promoting the further progress of the etherification reaction, thereby increasing the cationic substitution degree 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 method 1, the first part of the sodium citrate aqueous solution can be added to 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 to 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 to the second system can be 15 minutes to 30 minutes.

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

[0043] In some embodiments of the present application, in step (3), the specific steps of adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system are as follows: adding the sodium citrate aqueous solution to the second system at 20°C to 80°C to obtain a charge shielding system; adding the second portion of the cationic etherifying agent to the charge shielding system at 40°C to 90°C to carry out a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60 min to 180 min to obtain a third system. For example, the temperature for adding the sodium citrate aqueous solution to the second system can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or a range consisting of any two of these values. The present application does not particularly limit the stirring time of the sodium citrate aqueous solution when it is added to 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 of the second-stage etherification reaction can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or a range consisting of any two of these values. 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 consisting of any two of these values.

[0044] According to the above method 2, first, a sodium citrate aqueous solution is added to the second system. The sodium citrate aqueous solution shields the cationic groups on the cellulose ether molecular chain in the second system, thereby weakening the charge repulsion between the cationic groups on the cellulose ether molecular chain; and then the second portion of the cationic etherifying agent is added. Sodium citrate has the functions of charge shielding, buffering the 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 also improving the reaction efficiency of the cationic etherifying agent and the cellulose ether.

[0045] In the above-mentioned method 2, the sodium citrate aqueous solution can be added to the second system by dropwise addition. The present application does not specifically limit the time for dropwise addition of the sodium citrate aqueous solution to the second system, as long as the purpose of the present application can be achieved. For example, the time for dropwise addition of the sodium citrate aqueous solution to the second system can be 15 minutes to 30 minutes. In the above-mentioned method 2, the second portion of the cationic etherifying agent can be added to the above-mentioned charge shielding system by dropwise addition. The present application does not specifically limit the time for dropwise addition of the second portion of the cationic etherifying agent to the above-mentioned 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 portion of the cationic etherifying agent to the above-mentioned charge shielding system can be 15 minutes to 30 minutes. In the above-mentioned method 2, the time of the second-stage etherification reaction includes the dropwise addition time of the second portion of the cationic etherifying agent to the charge shielding system and the constant temperature time after the dropwise addition is completed.

[0046] In some embodiments of the present application, in step (3), the specific steps of adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system are as follows: at 40°C to 90°C, the sodium citrate aqueous solution and the second portion of the cationic etherifying agent are simultaneously added to the second system to carry out a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60 min to 180 min, to obtain 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 a range consisting of 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 a range consisting of any two of these values. By the above-mentioned method 3, the sodium citrate aqueous solution and the second portion of the cationic etherifying agent are simultaneously added to the second system. The sodium citrate aqueous solution is added to the second system. 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 also improving the reaction efficiency of the cationic etherifying agent and the cellulose ether.

[0047] In the above-mentioned method 3, the sodium citrate aqueous solution and the second portion of the cationic etherifying agent can be added dropwise to the second system. The present application does not particularly limit the time for adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the above-mentioned charge shielding system, as long as the purpose of the present application can be achieved. For example, the sodium citrate aqueous solution and the second portion of the cationic etherifying agent can be added dropwise to the above-mentioned charge shielding system for 15 to 30 minutes. In the above-mentioned method 3, the time for the second-stage etherification reaction includes the time for adding the second portion of the cationic etherifying agent and the sodium citrate solution to the charge shielding system and the time for maintaining the temperature after the addition is completed.

[0048] In some embodiments of the present application, the first-stage etherification reaction and the second-stage etherification reaction are conducted under an inert atmosphere, for example, a nitrogen atmosphere or an argon atmosphere. Conducting the etherification reaction under an inert atmosphere helps reduce the occurrence of side reactions and improves the reaction efficiency of the cationic etherifying agent and the cellulose ether.

[0049] In some embodiments of the present application, in 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 to 7, and then the 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 consisting of any two values therein, and then an acid solution is added to adjust the pH value of the system. The pH value of the system can be 5, 5.5, 6, 6.5, 7 or a range consisting of any two values therein. The present application does not particularly limit the type of acid solution, as long as it can achieve the purpose of the present application. For example, the acid solution can be sulfuric acid, hydrochloric acid, acetic acid, nitric acid, acetic acid, citric acid, etc. By adding an acid solution to adjust the pH of the system to the above range, the unreacted alkaline solution can be neutralized to prevent the pH of the system from being in an overly alkaline state, so that the obtained cationic cellulose ether is more suitable as a raw material for hair care products.

[0050] In some embodiments of the present application, in step (4), the mother liquor is cooled and crystallized to recover sodium citrate. The recovered sodium citrate can be reconstituted into a sodium citrate aqueous solution for use in step (3), thereby reducing production costs. The present application does not particularly limit the temperature and time for cooling and crystallizing 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 8h to 16h.

[0051] Example

[0052] The following examples and comparative examples are provided to further illustrate the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by weight. All raw materials in the examples and comparative examples of the present application are commercially available.

[0053] Test methods and equipment:

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

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

[0056] DS = (M × N) / (14-K × 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 with a cationic group grafted onto the main chain of the cellulose ether macromolecule by the cationic etherifying agent, for example, when the cationic etherifying agent is selected from 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution or 2,3-epoxypropyltrimethylammonium chloride aqueous solution, K is 152.5.

[0057] Example 1-1

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

[0059] (2) Under nitrogen atmosphere, the temperature of the first system was maintained at 60°C, and 20 g of a 50% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride (EPTAC, the first part of the cationic etherifying agent) was added dropwise to the first system at a drop rate of 1 g / min for 20 min. After the addition was completed, the reaction was continued at a constant temperature of 60°C for 30 min to obtain the second system. That is, the temperature of the first stage etherification reaction was 60°C, and the first stage etherification reaction time was 50 min.

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

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

[0062] (4) The third system obtained above was cooled to 25°C, and acetic acid was added to adjust the pH of the third system to 6. The solution was then filtered to obtain a precipitate and a mother liquor. The precipitate was washed five times with 250 g of an 85% by mass isopropanol aqueous solution. The precipitate was then dried in a vacuum oven at 60°C for 5 h to obtain cationic hydroxyethyl cellulose. The mother liquor was allowed to stand at 4°C for 12 h. The sodium citrate in the mother liquor was cooled and crystallized, and the sodium citrate was recovered.

[0063] Example 1-2 to Example 1-4

[0064] The process is the same as in Example 1-1 except that in step (3), the total mass of the sodium citrate aqueous solution and the mass percentage of the first part of the 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 the sodium citrate aqueous solution is adjusted so that the dropping time remains unchanged.

[0065] Example 1-5 to Example 1-6

[0066] Except that 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 in step (2) and step (3), the rest is the same as Example 1-1. That is, in Example 1-5, in step (2), 30 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the first system, and the dropping rate is adjusted so that the dropping time remains unchanged; 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 dropping rate is adjusted so that the dropping time remains unchanged. The rest is the same as Example 1-1. In Example 1-6, in step (2), 40 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution is added dropwise to the first system, and the dropping rate is adjusted so that the dropping time remains unchanged; 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 dropping rate is adjusted so that the dropping time remains unchanged. The rest is the same as in Example 1-1.

[0067] Example 1-7 to Example 1-8

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

[0069] Examples 1-9

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

[0071] Example 1-10 to Example 1-11

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

[0073] Example 1-12 to Example 1-13

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

[0075] Example 1-14 to Example 1-15

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

[0077] Example 16 to Example 17

[0078] Except that the second-stage etherification reaction time is controlled according to Table 1 in step (3), the rest is the same as Example 1-1. That is, in Example 1-16, in step (3), after the second portion of the cationic etherifying agent 2,3-epoxypropyltrimethylammonium chloride aqueous solution and the remaining sodium citrate aqueous solution are added dropwise, the addition time is 20 minutes, and then the reaction is continued at a constant temperature of 60°C for 40 minutes to obtain the third system; that is, the second-stage etherification reaction time is 60 minutes. In Example 1-17, in step (3), after the second portion of the cationic etherifying agent 2,3-epoxypropyltrimethylammonium chloride aqueous solution and the remaining sodium citrate aqueous solution are added dropwise, the addition time is 20 minutes, and then the reaction is continued at a constant temperature of 60°C for 160 minutes to obtain the third system; that is, the second-stage etherification reaction time is 180 minutes.

[0079] Examples 1-18

[0080] Step (3): The second system is maintained at a temperature of 60°C, and then 30g of a 15% sodium citrate aqueous solution is added dropwise to the second system at a rate of 1g / min for 30min. After the addition is completed, stirring is continued at a constant temperature of 60°C for 30min to obtain a charge shielding system. Then, 20g of a 50% 2,3-epoxypropyltrimethylammonium chloride aqueous solution (the second part of the cationic etherifying agent) is added dropwise to the charge shielding system at a rate of 1g / min. During the process, the temperature is controlled at 60°C. After 20min, the addition of the 2,3-epoxypropyltrimethylammonium chloride aqueous solution is completed, and then the reaction is continued at a constant temperature of 60°C for 120min to obtain a third system.

[0081] The process is the same as in Example 1-1, except that in step (3), all of the sodium citrate aqueous solution is first added dropwise to the second system at once according to the above method (method 2) to obtain a charge-shielding system, and then the second portion of the cationic etherifying agent is added dropwise to the charge-shielding system to react to obtain a third system.

[0082] Examples 1-19

[0083] Step (3): 20 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution (the second part of the cationic etherifying agent) was 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 was added dropwise to the second system at a rate of 1.5 g / min. During the process, the temperature was controlled at 60°C. After 20 minutes, the addition of the 2,3-epoxypropyltrimethylammonium chloride aqueous solution and the sodium citrate aqueous solution was completed, and then the reaction was continued at a constant temperature of 60°C for 120 minutes to obtain a third system.

[0084] Except that in step (3), all the sodium citrate aqueous solution and the second part of the cationic etherifying agent are simultaneously added dropwise to the second system according to the above method (method 3) to react to obtain the third system, the rest is the same as Example 1-1.

[0085] Example 2-1 to Example 2-2

[0086] Except that in step (1), the alkalization reaction temperature and alkalization reaction time were adjusted according to Table 2, the rest was the same as Example 1-1.

[0087] Example 2-3

[0088] Except that in step (1), the type of alkaline solution is adjusted to potassium carbonate aqueous solution according to Table 2, the rest is the same as Example 1-1.

[0089] Example 2-4 to Example 2-5

[0090] Except that the mass of the sodium hydroxide aqueous solution is adjusted according to Table 2 in step (1), the rest is the same as Example 1-1.

[0091] Examples 2-6

[0092] Except that in step (1), the mass percentage of water in the isopropyl alcohol aqueous solution is adjusted to 10% according to Table 2, the rest is the same as Example 1-1.

[0093] Examples 2-7

[0094] The same procedures as in Example 1-1 were used except that in step (1), the mass of the isopropyl alcohol aqueous solution was adjusted so that the mass percentage of cellulose ether in the cellulose ether dispersion was 15%.

[0095] Examples 2-8

[0096] The same procedures as in Example 1-1 were used except that in step (1), the mass of the isopropyl alcohol aqueous solution was adjusted so that the mass percentage of cellulose ether in the cellulose ether dispersion was 25%.

[0097] Example 2-9 to Example 2-10

[0098] Except that the type of cellulose ether was adjusted according to Table 2 in step (1), the rest was the same as Example 1-1.

[0099] Comparative Example 1

[0100] The reaction system was obtained by adjusting steps (2) and (3) of Example 1-1 to the following: under a nitrogen atmosphere, the temperature of the first system was maintained at 60°C, and 40 g of a 50% by mass 2,3-epoxypropyltrimethylammonium chloride aqueous solution was added dropwise to the first system at a dropwise rate of 1 g / min for 40 min. After the addition was completed, the reaction was continued at a constant temperature of 60°C for 200 min to obtain the reaction system. The remaining steps were the same as those of Example 1-1, that is, in Comparative Example 1, no sodium citrate aqueous solution was added during the etherification reaction.

[0101] Comparative Example 2 to Comparative Example 3

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

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

[0104] Table 1

[0105] Note: “ / ” in Table 1 indicates that there is no corresponding preparation parameter or substance.

[0106] Table 2

[0107] 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 a sodium citrate aqueous solution in the second stage, and regulating the mass percentage of the first portion of the cationic etherifying agent within the range of this application, the cationic cellulose ethers prepared in the Examples have a high degree of cationic substitution. In contrast, in Comparative Example 1, no sodium citrate aqueous solution was added during the preparation process, and the mass percentage of the first portion of the cationic etherifying agent relative to the total cationic etherifying agent in Comparative Examples 2 and 3 was outside the range of this application, resulting in a low degree of cationic substitution in the prepared cationic cellulose ethers.

[0108] 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 sodium citrate aqueous solution affects the cationic substitution degree of the cationic cellulose ether. From Examples 1-1 to 1-4, it can be seen that by regulating 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 sodium citrate aqueous solution within the range of (0.07-0.22):1, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0109] 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 cellulose ether will affect the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1, 1-5, and 1-6, by regulating 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 cellulose ether within the range of (0.4-0.8):1, the prepared cationic cellulose ether has a higher cationic degree of substitution.

[0110] The type and mass fraction of the cationic etherifying agent will affect the cationic substitution degree of the cationic cellulose ether. It can be seen from Examples 1-1, 1-7 to 1-9 that by selecting a cationic etherifying agent within the scope of this application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0111] The temperature and time of the first-stage etherification reaction and the second-stage etherification reaction will affect the cationic substitution degree of the cationic cellulose ether. It can be seen from Examples 1-1, 1-12 to 1-17 that by regulating the temperature and time of the first-stage etherification reaction and the second-stage etherification reaction within the scope of the present application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0112] The manner in which the sodium citrate aqueous solution and the second portion of the cationic etherifying agent are added to the second system affects the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1, 1-18, and 1-19, by adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system through Methods 1, 2, and 3 provided herein, the cationic cellulose ether prepared has a higher degree of cationic substitution.

[0113] The temperature and time of the alkalization reaction will affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Examples 1-1, 2-1, and 2-2, by regulating 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.

[0114] The type of alkaline solution will affect the cationic substitution degree of the cationic cellulose ether. As can be seen from Examples 1-1 and 2-3, by selecting an alkaline solution within the scope of this application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0115] The mass ratio of the solute to the cellulose ether in the alkaline solution affects the cationic substitution degree of the cationic cellulose ether. As can be seen from Examples 1-1, 2-4, and 2-5, by regulating the mass ratio of the solute to the cellulose ether in the alkaline solution within the range of the present application, the cationic cellulose ether prepared has a higher cationic substitution degree.

[0116] The mass percentage of cellulose ether in the cellulose ether dispersion and the mass percentage of water in the solvent affect the cationic degree of substitution of the cationic cellulose ether. As can be seen from Examples 1-1, 2-6, and 2-8, by regulating the mass percentage of cellulose ether in the cellulose ether dispersion and the mass percentage of water in the solvent within the range of the present application, the cationic cellulose ether prepared has a higher cationic degree of substitution.

[0117] The type of cellulose ether will affect the cationic substitution degree of the cationic cellulose ether. It can be seen from Examples 1-1, 2-9 and 2-10 that by selecting cellulose ether within the scope of this application, the prepared cationic cellulose ether has a higher cationic substitution degree.

[0118] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing cationic cellulose ether, comprising the following steps: (1) dispersing 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 to obtain a first system; (2) adding a first portion of a cationic etherifying agent to the first system to carry out a first-stage etherification reaction to obtain a second system; (3) adding a sodium citrate aqueous solution and a second portion of a cationic etherifying agent to the second system to carry out a second-stage etherification reaction to obtain a third system; (4) separating the solid and liquid of the third system to obtain a precipitate and a mother liquor, and washing and drying the precipitate to obtain a cationic cellulose ether; Wherein, based on the total mass of the first part of cationic etherifying agent and the second part of cationic etherifying agent, the mass percentage of the first part of cationic etherifying agent is 40% to 80%.

2. The method according to claim 1, wherein The cellulose ether is selected from hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose or hydroxypropyl methyl cellulose; based on the mass of the cellulose ether dispersion, the mass percentage of the cellulose ether is 15% to 25%.

3. The method according to claim 1, wherein 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; based on the mass of the solvent, the mass percentage of water in the solvent is 10% to 20%.

4. The method according to claim 1, wherein 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.

5. The method according to claim 1, wherein The temperature of the alkalization reaction is 30° C. to 80° C., and the time of the alkalization reaction is 1 hour to 5 hours.

6. The method according to claim 1, wherein 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.

7. The method according to claim 1, wherein The first part of the cationic etherifying agent and the second part of the cationic etherifying agent are selected from 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution or 2,3-epoxypropyltrimethylammonium chloride aqueous solution; 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%.

8. The method according to claim 7, wherein: The first part of the cationic etherifying agent and the second part of the cationic etherifying agent are selected from the same material.

9. The method according to claim 1, wherein 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 cellulose ether is (0.4-0.8):

1.

10. The method according to claim 1, wherein 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 of the cationic etherifying agent and the second part of the cationic etherifying agent is (0.07-0.22):

1.

11. The method according to any one of claims 1 to 10, wherein In the step (3), the specific steps of adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system are as follows: adding a first portion of the sodium citrate aqueous solution to the second system at 20° C. to 80° C. to obtain a charge shielding system; the mass percentage of the first portion of the sodium citrate aqueous solution is 40% to 80% based on the total mass of the sodium citrate aqueous solution; At 40° C. to 90° C., the remaining sodium citrate aqueous solution and the second portion of the cationic etherifying agent are simultaneously added to the charge shielding system to carry out a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60 min to 180 min to obtain a third system.

12. The method according to any one of claims 1 to 10, wherein In the step (3), the specific steps of adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system are as follows: adding a sodium citrate aqueous solution to the second system at 20° C. to 80° C. to obtain a charge shielding system; At 40° C. to 90° C., a second portion of cationic etherifying agent is added to the charge shielding system to carry out a second-stage etherification reaction, wherein the second-stage etherification reaction time is 60 min to 180 min to obtain a third system.

13. The method according to any one of claims 1 to 10, wherein In the step (3), the specific steps of adding the sodium citrate aqueous solution and the second portion of the cationic etherifying agent to the second system are as follows: At 40° C. to 90° C., sodium citrate aqueous solution and a second portion of 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 to obtain a third system.

14. The method according to any one of claims 1 to 10, 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 to 7, and then the solid-liquid separation is carried out to obtain a precipitate and a mother liquor.

15. The method according to any one of claims 1 to 10, wherein In the step (4), the mother liquor is cooled and crystallized to recover sodium citrate.

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