Ethyl hydroxyethyl cellulose and preparation method thereof

Abstract

The invention discloses ethyl hydroxyethyl cellulose and a preparation method thereof, and belongs to the technical field of cellulose production. The invention provides ethyl hydroxyethyl cellulose with low critical solution temperature and a preparation method thereof. The preparation method comprises the following steps: mixing cellulose and alkali liquor for alkalization; then adding monochloroethane into the system, and carrying out a first-stage etherification reaction; ethylene oxide is added, and a second-stage etherification reaction is carried out; and carrying out post-treatment to obtain the ethyl hydroxyethyl cellulose. Hydrophobic modification is performed on HEC by introducing an ethyoxyl group on an HEC macromolecule, so that the stability of EHEC is enhanced, and meanwhile, the water solubility is not changed; a solvent-free process is adopted for segmented etherification, generation of by-products is inhibited, the substitution uniformity of an etherifying agent is improved, purification and separation are easier, the obtained EHEC has excellent neutral enzyme stability and low critical solution temperature in water, the original water solubility and thickening property of HEC are reserved, and the EHEC can be used for preparing water-based paint.

Description

Technical Field

[0001] The invention belongs to the technical field of cellulose production, and in particular relates to ethyl hydroxyethyl cellulose and a preparation method thereof, which is a hydrophobically modified water-soluble cellulose mixed ether with a low critical solution temperature. Background Art

[0002] In order to facilitate the coating and construction of water-based paints and improve the coating performance, it is often necessary to add an appropriate amount of thickener to the paint to improve the rheological properties and water retention of the paint on the surface of the medium. Hydroxyethyl cellulose (HEC) is a water-soluble cellulose derivative. The polymer molecular chain contains a large number of hydroxyl groups, which have strong hydrogen bonding with water molecules. When added to water, it exhibits good thickening and water retention, so it is widely used as a thickener for water-based paints.

[0003] Water-based paint is a two-phase system in which color particles of various colors are dispersed in a continuous phase (water phase). The emulsion system of water-based paint contains a large number of lipophilic pigment color particles. However, HEC lacks lipophilic groups in its molecular structure, and has poor interaction with lipophilic pigment color particles, so it cannot effectively stabilize the color particles in the paint, resulting in poor construction effect. In addition, most existing cellulose ethers use solvent processes, and after the reaction is completed, the solvent often needs to be evaporated at high temperature to separate and purify the polymer or washed with an organic solvent, which leads to high production costs and is not environmentally friendly.

[0004] In order to improve the stability of HEC on the color particles in the coating, hydrophobic modification of HEC is an effective way. Ethyl hydroxyethyl cellulose (EHEC) is a hydrophobically modified macromolecule. It introduces an appropriate amount of ethoxy groups on the HEC macromolecule, which can enhance the interaction between the polymer and the lipophilic components in the coating, prevent the agglomeration of color particles, enhance the stability of water-based coatings, and will not change the water solubility of the polymer. From the perspective of thickening and stability of water-based coatings, EHEC has better performance and a wider range of applications than HEC. Since the modified EHEC has the characteristics of LCST phase transition in water, it makes the separation and purification of EHEC easier. It can be purified and separated from the solid by washing with hot water. In addition, the solvent-free production process has the advantages of high efficiency, low energy consumption, low carbon and environmental protection compared with the traditional solvent production process. The segmented etherification method can improve the uniformity of the etherification reaction. The use of this method to prepare EHEC is conducive to improving the biological stability of EHEC, reducing production costs, meeting higher environmental protection requirements, and making the product more competitive in the market. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention aims to provide a hydrophobically modified water-soluble cellulose mixed ether with a low critical solution temperature (LCST) and a preparation method thereof.

[0006] The present invention first provides a method for preparing ethyl hydroxyethyl cellulose, which comprises the following steps:

[0007] A. Mixing cellulose and alkali solution, and alkalizing under the protection of inert gas; in step A, the alkali solution is a mixture consisting of alkali, water and a dispersion medium;

[0008] B. After the alkalization is completed, ethyl chloride is added into the system, mixed evenly, and the first stage etherification reaction is carried out at 100°C to 160°C;

[0009] C. After the first stage etherification reaction is completed, the system is cooled to 10°C to 30°C, ethylene oxide is added, and after mixing evenly, the second stage etherification reaction is carried out at 70°C to 85°C;

[0010] D. After the second stage etherification reaction is completed, ethyl hydroxyethyl cellulose is obtained by post-treatment; the ethyl hydroxyethyl cellulose has a 24h neutral enzyme stability in water of ≥50%, can undergo a soluble-insoluble reversible phase transition in water, has an LCST thermal response behavior, and its LCST is 50-75°C;

[0011] The structural unit of the ethyl hydroxyethyl cellulose is shown in Formula I, wherein R comprises four groups of A, B, C and D, n is an integer ≥ 1, and the ethyl hydroxyethyl cellulose contains at least one of the A group and the B group, and contains the C group;

[0012]

[0013] The present invention introduces ethyl and hydroxyethyl groups into cellulose, so the ethyl hydroxyethyl cellulose obtained in the present invention contains at least one of the A group and the B group, and contains the C group. Of course, in general, it is difficult to achieve complete substitution of cellulose, so R in the ethyl hydroxyethyl cellulose may also be H. Therefore, the ethyl hydroxyethyl cellulose obtained in the present invention may contain four structures of A, B, C and D, or may include a combination of structures such as A, C and D or B, C and D.

[0014] Wherein, in the preparation method of the above-mentioned ethyl hydroxyethyl cellulose, in step A, the mass ratio of alkali to cellulose in the alkali solution is 0.5-1.2:1. In step A, the alkali solution used in the cellulose alkalization step is a mixture of alkali, water and a dispersion medium, and the alkali is usually present in the form of solution and solid, and the alkalization temperature is room temperature.

[0015] Preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the mass ratio of alkali to cellulose in the alkali solution is 0.6-0.8:1.

[0016] More preferably, in the method for preparing ethyl hydroxyethyl cellulose, in step A, the mass ratio of alkali to cellulose in the alkali solution is 0.7-0.75:1.

[0017] Wherein, in the preparation method of the above-mentioned ethyl hydroxyethyl cellulose, in step A, the mass ratio of water to the dispersion medium in the alkali solution is 0.35 to 0.6.

[0018] Preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the mass ratio of water to the dispersion medium in the alkali solution is 0.4 to 0.6.

[0019] More preferably, in the method for preparing ethyl hydroxyethyl cellulose, in step A, the mass ratio of water to the dispersion medium in the alkali solution is 0.5 to 0.55.

[0020] Wherein, in the preparation method of the above ethyl hydroxyethyl cellulose, in step A, the mass ratio of the cellulose to the alkali solution is 1 to 4.

[0021] Preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the mass ratio of the cellulose to the alkali solution is 1.2-2.

[0022] More preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the mass ratio of the cellulose to the alkali solution is 1.5 to 1.8.

[0023] Wherein, in the preparation method of the above ethyl hydroxyethyl cellulose, in step A, the alkalization temperature is 20° C. to 30° C. (i.e., room temperature).

[0024] Wherein, in the preparation method of the above ethyl hydroxyethyl cellulose, in step A, the alkalization time is 0.5h to 2h.

[0025] Preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the alkalization time is 0.5h to 1h.

[0026] More preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the alkalization time is 1 hour.

[0027] Wherein, in the preparation method of ethyl hydroxyethyl cellulose, in step A, the weight average molecular weight of the cellulose is 5 to 80×10 4 g / mol.

[0028] Preferably, in the preparation method of the ethyl hydroxyethyl cellulose, in step A, the weight average molecular weight of the cellulose is 10 to 60×10 4 g / mol.

[0029] More preferably, in the method for preparing ethyl hydroxyethyl cellulose, in step A, the weight average molecular weight of the cellulose is 15 to 50×10 4 g / mol.

[0030] Most preferably, in the method for preparing ethyl hydroxyethyl cellulose, in step A, the weight average molecular weight of the cellulose is 20 to 40×10 4 g / mol.

[0031] Wherein, in the preparation method of ethyl hydroxyethyl cellulose, in step A, the alkali in the alkali solution is selected from at least one of sodium hydroxide, potassium hydroxide or lithium hydroxide. Among them, lithium hydroxide has a better alkalization effect, and using it in combination with sodium hydroxide can improve the alkalization efficiency and also save costs.

[0032] Wherein, in the preparation method of the above-mentioned ethyl hydroxyethyl cellulose, in step A, the dispersion medium in the alkali solution is selected from diethyl ether or a mixed solvent with a mass ratio of diethyl ether to ethanol of 1:0.01 to 0.1.

[0033] Preferably, in the preparation method of the above ethyl hydroxyethyl cellulose, in step A, the dispersion medium in the alkali solution is selected from diethyl ether or a mixed solvent with a mass ratio of diethyl ether to ethanol of 1:0.02-0.1.

[0034] More preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the dispersion medium in the alkali solution is selected from diethyl ether or a mixed solvent with a mass ratio of diethyl ether to ethanol of 1:0.05-0.08.

[0035] Most preferably, in the method for preparing the ethyl hydroxyethyl cellulose, in step A, the dispersion medium in the alkali solution is selected from diethyl ether or a mixed solvent with a mass ratio of diethyl ether to ethanol of 1:0.06.

[0036] In the present invention, a low boiling point organic solvent is used as a reaction solvent, and the solvent becomes gaseous during the reaction process, that is, a solvent-free reaction is achieved. Compared with the solvent method, the solvent-free method used in the present invention has higher production efficiency, the solvent is also easy to recover, and the preparation process involves some side reactions (also reversible reactions). The use of the solvent-free method can change the chemical equilibrium and help inhibit the side reactions.

[0037] Wherein, in the preparation method of the above-mentioned ethyl hydroxyethyl cellulose, the ethyl substitution degree of the ethyl hydroxyethyl cellulose is 0.5 to 1.3. The properties of the ethyl hydroxyethyl cellulose obtained by the present invention, such as viscosity, LCST and stability, mainly depend on the substitution degree of the two groups. The present invention can adjust the amount of ethyl chloride according to the ethyl substitution degree. The amount of ethyl chloride added can be known according to the target ethyl substitution degree of the product. Generally, the present invention can control the mass ratio of ethyl chloride in step B and cellulose in step A to be 0.5 to 1.5:1.

[0038] Wherein, in the above-mentioned method for preparing ethyl hydroxyethyl cellulose, in step B, the time of the first stage etherification reaction is 4 to 10 hours.

[0039] Wherein, in the preparation method of the above-mentioned ethyl hydroxyethyl cellulose, the hydroxyethyl molar substitution degree of the ethyl hydroxyethyl cellulose is 1.0 to 2.5. The properties of the ethyl hydroxyethyl cellulose obtained by the present invention, such as viscosity, LCST and stability, mainly depend on the substitution degree of the two groups. The present invention can adjust the amount of ethylene oxide according to the hydroxyethyl molar substitution degree. The amount of ethylene oxide added can be known based on the target hydroxyethyl molar substitution degree of the product. Generally, the present invention can control the mass ratio of ethylene oxide in step C to cellulose in step A to be 0.3 to 1.2:1.

[0040] Wherein, in the preparation method of the above ethyl hydroxyethyl cellulose, in step C, the time of the second stage etherification reaction is 40 to 100 minutes.

[0041] In the preparation method of ethyl hydroxyethyl cellulose, in step C, after the system is cooled to 10°C to 30°C, an acid is added to the system for neutralization, the mass percentage of alkali in the system after neutralization is controlled to be 0.2% to 1%, and then ethylene oxide is added. When an acid is added to the system for neutralization in step C, the acid can be dilute hydrochloric acid or acetic acid.

[0042] Preferably, in the preparation method of the above ethyl hydroxyethyl cellulose, in step C, after the system is cooled to 10°C to 30°C, acid is added to the system for neutralization, the mass percentage of alkali in the system after neutralization is controlled to be 0.2% to 0.8%, and then ethylene oxide is added.

[0043] More preferably, in the preparation method of the above ethyl hydroxyethyl cellulose, in step C, after the system is cooled to 10°C to 30°C, acid is added to the system for neutralization, the mass percentage of alkali in the system after neutralization is controlled to be 0.4% to 0.6%, and then ethylene oxide is added.

[0044] Among them, in the preparation method of the above-mentioned ethyl hydroxyethyl cellulose, in step D, the post-treatment is specifically: distilling to remove the dispersion medium and by-products, then adjusting the system pH to 5.0-8.0, and then washing with 80-95°C hot water, after washing, solid-liquid separation, and then granulation, drying, crushing and screening.

[0045] Preferably, in the preparation method of the ethyl hydroxyethyl cellulose, in step D, hot water at 90 to 95° C. is used for washing in the post-treatment.

[0046] More preferably, in the method for preparing ethyl hydroxyethyl cellulose, in step D, hot water at 90° C. is used for washing in the post-treatment.

[0047] The present invention also provides an ethyl hydroxyethyl cellulose, which is prepared by the above-mentioned preparation method of ethyl hydroxyethyl cellulose, wherein the ethyl substitution degree of the ethyl hydroxyethyl cellulose is 0.5-1.3, and the hydroxyethyl molar substitution degree is 1.0-2.5. In addition, the 24h neutral enzyme stability in water is ≥50%, and the soluble-insoluble reversible phase transition can occur in water, and the LCST (lower critical solution temperature) thermal response behavior is provided, and the LCST range is 50-75°C.

[0048] Based on the excellent performance of the ethyl hydroxyethyl cellulose of the present invention, the present invention also provides the use of the ethyl hydroxyethyl cellulose in water-based coatings.

[0049] In the present invention, in the structural unit of formula I, the ethyl group in the cellulose ether is directly connected to the hydroxyl group of the anhydroglucose unit, rather than the end of the hydroxyethyl group, that is, the hydroxyethyl group generated after the ethylene oxide substitution is not capped, which is the key to ensure that the polymer has good water solubility. In addition, the present invention can conveniently adjust its phase transition temperature by adjusting the molecular weight of the raw material cellulose, the ethyl substitution degree and the hydroxyethyl molar substitution degree in the EHEC; and can further improve its biological stability by adjusting the amount of the etherifying agent used in the two stages (depending on the substituent), the reaction temperature and the reaction time.

[0050] In the present invention, the entire alkalization and etherification reaction process needs to be carried out under an inert atmosphere, and the distillation to remove the dispersion medium and by-products also needs to be carried out under an inert atmosphere, and subsequent washing, solid-liquid separation and other operations are not required.

[0051] Beneficial effects of the present invention:

[0052] The EHEC prepared by the invention retains the original water solubility and thickening property of hydroxyethyl cellulose (HEC).

[0053] The invention introduces a proper amount of ethoxy groups into the traditional hydroxyethyl cellulose (HEC) macromolecules through reasonable molecular structure design (such as cellulose molecular weight, ethyl substitution degree, hydroxyethyl molar substitution degree), adopts segmented etherification and solvent-free process, and performs hydrophobic modification on HEC, which can not only increase the solution viscosity through intermolecular hydrophobic association, but also enhance the interaction between the polymer and the lipophilic component in the coating, prevent the agglomeration of color particles, and enhance the stability of the water-based coating.

[0054] The EHEC prepared by the present invention also has a lower critical solution temperature (LCST) in water, that is, it dissolves at a relatively low temperature but is insoluble at a high temperature. When the temperature rises to the LCST, a reversible phase transition occurs in the EHEC aqueous solution. Through formula design, the phase transition temperature can be conveniently adjusted by adjusting the ethyl substitution degree, the hydroxyethyl molar substitution degree and the molecular weight of the raw cellulose in the EHEC molecule. The modified EHEC has the characteristics of LCST phase transition in water, which makes the separation and purification of EHEC easier, and purification and solid-liquid separation can be performed by washing with hot water.

[0055] The EHEC of the present invention is prepared by a solvent-free process, which has the advantages of suppressing the generation of by-products during the preparation of EHEC on the one hand; on the other hand, the purification and separation of the polymer is easier than the traditional solvent process, which can reduce energy consumption in industrial production and is conducive to low-carbon and environmental protection. The segmented etherification method can improve the uniformity of the substitution of the etherifying agent on the cellulose molecule, which helps to improve its biological stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is the infrared spectrum of EHEC-1 prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0057] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0058] Example 1

[0059] This embodiment provides a solvent-free process for preparing ethyl hydroxyethyl cellulose (EHEC), the steps are as follows: select a cellulose having a weight average molecular weight of 20×10 4 g / mol of cellulose was used as raw material. Under the protection of nitrogen atmosphere, sodium hydroxide, water and ether were added to 1kg of cellulose to alkalize the cellulose. Among them, the mass ratio of alkali to cotton was 0.75:1, the mass ratio of water to ether was 0.55, and the mass ratio of cellulose to alkali solution was 1.6. After alkalization at room temperature for 1 hour, a certain amount of ethyl chloride was added thereto, mixed evenly, and gradually heated to 150℃ for the first stage of etherification reaction. After 6 hours of reaction, the temperature was lowered to 15℃, and the ethoxy substitution degree was sampled and tested to be 0.7. A certain amount of ethylene oxide was added thereto, mixed evenly, and gradually heated to 85℃ for the second stage of etherification reaction. After 60 minutes of reaction, the ether and some by-products were distilled off. The pH of the mixed system was adjusted to 7.0 with dilute hydrochloric acid, and washed repeatedly with 90℃ hot water. After washing, solid-liquid separation was carried out, and then granulation, drying, crushing and sieving were carried out to obtain EHEC powder. The total substitution degree of the sample tested was 1.7, and it was numbered EHEC-1.

[0060] The obtained EHEC-1 was dissolved in water at room temperature to prepare a 1 wt % aqueous solution. The phase transition temperature was tested to be 75° C. The viscosity of the solution was tested with a Brookfield viscometer to be 2350 mPaS, and the 24 h neutral enzyme stability was 50.3%.

[0061] Figure 1 The infrared spectrum of EHEC-1 is shown in Figure 3450 cm-1. -1 The characteristic absorption peak corresponding to hydroxyl group is 2972 ​​cm -1 The stretching vibration peak corresponding to -CH2- is 2875cm -1 The stretching vibration peaks corresponding to -CH3 are 1453 and 1346 cm -1 The characteristic absorption peaks corresponding to -CH3 are 1117 and 1052 cm -1 The characteristic absorption peaks corresponding to -CO- are 918 and 882 cm -1 In summary, it can be seen from the infrared spectrum that the polymer contains hydroxyl and ethyl, which are consistent with the characteristic functional groups contained in EHEC, proving that the polymer is EHEC.

[0062] Comparative Example 1

[0063] This comparative example selected a weight average molecular weight of 21×10 4 g / mol HEC was used as a reference, and the total substitution degree of the sample was 1.7. The sample was dissolved in water at room temperature to prepare a 1wt% aqueous solution. No phase transition was observed in the solution within the range of room temperature to 100°C. The viscosity of the solution was tested by a Brookfield viscometer and was 1845mPaS.

[0064] Comparative Example 2

[0065] This comparative example selected a weight average molecular weight of 24×10 4 g / mol HEC was used as a reference, and the total substitution degree of the sample was 1.7. The sample and the EHEC in Example 1 were compared to the evaluation method for coating stability in the water-based multi-color architectural coating industry standard HG / T 4343-2012 to examine the stability of the two polymers to the color particles. After 7 days, the sample using EHEC as a thickener did not have color bleeding, and the coating color and pattern had no obvious difference. The sample using HEC in Comparative Example 2 as a thickener had slight color bleeding, and the coating color and pattern had no obvious difference. It was confirmed that the introduction of ethyl in HEC helped to stabilize the color particles in the water-based coating.

[0066] Example 2

[0067] According to the steps and methods described in Example 1, the molecular weight of the raw cellulose in Example 1 was changed to 7×10 4g / mol and 30×10 4 g / mol, and the other conditions remained unchanged to prepare EHEC-2 and EHEC-3.

[0068] EHEC-1, EHEC-2 and EHEC-3 were prepared into 1 wt% aqueous solutions, and their phase transition temperatures were tested to be 75°C, 89°C and 53°C, respectively. The viscosity of the solutions was tested using a Brookfield viscometer and was 2350 mPaS, 670 mPaS and 5350 mPaS, respectively.

[0069] Example 3

[0070] According to the steps and methods described in Example 1, the addition amounts of ethylene monochloride and ethylene oxide were adjusted to obtain EHEC with different ethyl substitution degrees and hydroxyethyl molar substitution degrees, and the other conditions remained unchanged to prepare EHEC-4, EHEC-5 and EHEC-6. The ethyl substitution degrees and hydroxyethyl molar substitution degrees were tested by sampling, and the performance comparison results of 1% solution are shown in Table 1.

[0071] Table 1 Comparison of performance of different EHEC

[0072] serial number Ethyl substitution degree Hydroxyethyl molar substitution Phase change temperature / ℃ Viscosity / mPaS EHEC-1 0.7 1.0 75 2350 EHEC-4 0.9 1.0 66 2768 EHEC-5 1.0 1.8 64 3187 EHEC-6 0.5 2.2 92 2067

[0073] Example 4

[0074] According to the steps and methods described in Example 1, before adding ethylene oxide in Example 1, a pH adjustment step is added, the acid used to adjust the pH is acetic acid, the alkali content in the system after neutralization is 0.6%, and the other conditions and steps remain unchanged to obtain EHEC-7.

[0075] It was prepared into a 1% aqueous solution and its biological stability was investigated. The results showed that the neutral enzyme stability of EHEC-7 in 24 hours was 68.5%. Therefore, adding a pH adjustment step helps to improve the etherification uniformity of the product and its stability in 24 hours of neutral enzyme.

[0076] Example 5

[0077] According to the steps and methods described in Example 1, the segmented etherification was changed to a one-time feeding etherification, specifically: after alkalization at room temperature for 1 hour, the same mass of ethylene chloride and ethylene oxide were added thereto, and after uniform mixing, the temperature was gradually increased to 150° C. for etherification reaction; after reacting for 7 hours, the ether and part of the by-products were distilled off; the pH of the mixed system was adjusted to 7.0 with dilute hydrochloric acid, and the mixture was repeatedly washed with 90° C. hot water; after washing, solid-liquid separation was performed, followed by granulation, drying, crushing and sieving to obtain EHEC powder, and the total degree of substitution of the sample tested was 1.9, and the sample was numbered EHEC-8.

[0078] The obtained EHEC-8 was dissolved in water at room temperature to prepare a 1wt% aqueous solution. The phase transition temperature was tested to be 72°C. The viscosity of the solution was tested by a Brookfield viscometer to be 2680mPaS. The 24h neutral enzyme stability was 42%. It can be seen that the etherification uniformity was poor when the material was added once, resulting in a decrease in the stability of EHEC.

Claims

1. A method for preparing ethyl hydroxyethyl cellulose, characterized in that: The following steps are involved: A. Mixing cellulose and alkali solution, and alkalizing under the protection of inert gas; in step A, the alkali solution is a mixture consisting of alkali, water and a dispersion medium; B. After the alkalization is completed, ethyl chloride is added into the system, mixed evenly, and the first stage etherification reaction is carried out at 100°C to 160°C; C. After the first stage etherification reaction is completed, the system is cooled to 10°C to 30°C, ethylene oxide is added, and after mixing evenly, the second stage etherification reaction is carried out at 70°C to 85°C; D. After the second stage etherification reaction is completed, ethyl hydroxyethyl cellulose is obtained by post-treatment; the ethyl hydroxyethyl cellulose has a 24h neutral enzyme stability in water of ≥50%, can undergo a soluble-insoluble reversible phase transition in water, has an LCST thermal response behavior, and its LCST is 50-75°C; The structural unit of the ethyl hydroxyethyl cellulose is shown in Formula I, wherein R comprises four groups of A, B, C and D, n is an integer ≥ 1, and the ethyl hydroxyethyl cellulose contains at least one of the A group and the B group, and contains the C group; 2. The method for preparing ethyl hydroxyethyl cellulose according to claim 1, characterized in that: At least one of the following is met: In step A, the mass ratio of alkali to cellulose in the alkali solution is 0.5 to 1.2:1; preferably 0.6 to 0.8:1; more preferably 0.7 to 0.75:1; In step A, the mass ratio of water to dispersion medium in the alkali solution is 0.35 to 0.6; preferably 0.4 to 0.6; more preferably 0.5 to 0.55; In step A, the mass ratio of cellulose to alkali solution is 1 to 4; preferably 1.2 to 2; more preferably 1.5 to 1.8; In step A, the alkalization temperature is 20°C to 30°C; In step A, the alkalization time is 0.5h to 2h; preferably 0.5h to 1h; more preferably 1h; In step A, the weight average molecular weight of the cellulose is 5 to 80×10 4 g / mol; preferably 10 to 60×10 4 g / mol; more preferably 15 to 50×10 4 g / mol; the most preferred is 20 to 40×10 4 g / mol; In step A, the alkali in the alkali solution is selected from at least one of sodium hydroxide, potassium hydroxide or lithium hydroxide; In step A, the dispersion medium in the alkali solution is selected from diethyl ether or a mixed solvent of diethyl ether and ethanol.

3. The method for preparing ethyl hydroxyethyl cellulose according to claim 1, characterized in that: The ethyl substitution degree of the ethyl hydroxyethyl cellulose is 0.5 to 1.

3.

4. The method for preparing ethyl hydroxyethyl cellulose according to claim 1, characterized in that: In step B, the time of the first stage etherification reaction is 4 to 10 hours.

5. The method for preparing ethyl hydroxyethyl cellulose according to claim 1, characterized in that: The molar substitution degree of hydroxyethyl of the ethyl hydroxyethyl cellulose is 1.0 to 2.

5.

6. The method for preparing ethyl hydroxyethyl cellulose according to claim 1, characterized in that: In step C, the time of the second stage etherification reaction is 40 to 100 minutes.

7. The method for preparing ethyl hydroxyethyl cellulose according to claim 1, characterized in that: In step C, after the system is cooled to 10°C to 30°C, an acid is added to the system for neutralization, and the mass percentage content of the alkali in the system after neutralization is controlled to be 0.2% to 1%, and then ethylene oxide is added; the mass percentage content of the alkali is preferably 0.2% to 0.8%; and the mass percentage content of the alkali is more preferably 0.4% to 0.6%.

8. The method for preparing ethyl hydroxyethyl cellulose according to any one of claims 1 to 7, characterized in that: In step D, the post-treatment is specifically: distilling to remove the dispersion medium and by-products, then adjusting the system pH to 5.0-8.0, then washing with 80-95° C. hot water, after washing, performing solid-liquid separation, and then granulating, drying, crushing and screening.

9. Ethyl hydroxyethyl cellulose prepared by the method for preparing ethyl hydroxyethyl cellulose according to any one of claims 1 to 8.

10. Use of the ethyl hydroxyethyl cellulose according to claim 9 in water-based coatings.

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