Nitrocellulose-based macromolecular coloring agent as well as preparation method and application thereof

Abstract

The invention discloses a nitrocellulose-based macromolecular coloring agent as well as a preparation method and application thereof, and belongs to the technical field of coloring agents and energetic materials. The preparation method of the nitrocellulose-based macromolecular coloring agent comprises the following steps: adding nitrocotton into an acetic acid solvent, and activating to obtain activated nitrocotton; adding the activated nitrocotton into a mixed solution composed of sulfuric acid, carboxyl dye and water for esterification to obtain a crude product; and sequentially washing and drying the crude product to obtain the nitrocellulose-based macromolecular coloring agent. The method is simple and convenient in process, low in cost and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of colorants and energetic materials, and relates to a nitrocellulose-based macromolecular colorant as well as a preparation method and application thereof. BACKGROUND

[0002] Nitrocellulose (nitrocellulose) is a cellulose nitrate prepared by esterification of cellulose with nitro-sulfur mixed acid, and is known as the first synthetic polymer for coating. It still plays an irreplaceable role in the fields of industrial coatings and inks. According to the nitrogen content, it can be divided into energetic and industrial grades. Nitrocellulose has excellent film-forming properties and hardness, extremely fast surface drying speed, good polishing performance, and good compatibility with other resins, and is therefore widely used as a main film-forming material for solvent-based coatings and inks. However, nitrocellulose is colorless and transparent after dissolution, and in practical applications, pigments or dyes are often added to provide color and hiding power. At present, small molecule colorants are basically used as pigments, which are uniformly distributed in the entire coating / ink system by physical mixing. Small molecule colorants can meet the coloring requirements to some extent, but long-term use will cause migration in the system, and the resistance to oxygen, ultraviolet light and moisture is poor, and long-term exposure to the outdoors can easily cause discoloration and powdering. In addition, the addition amount of small molecule pigments in the nitro-based system accounts for about 10% (mass fraction) of the formula, and the cost accounts for as high as 20-40%, which limits the formula development difficulty of nitro-based coatings / inks.

[0003] In order to solve the above problems, technicians have developed macromolecular colorants. Macromolecular colorants are color groups (pigment molecules) directly connected to high molecular chains by chemical bonds, becoming part of the polymer, thus fundamentally improving their performance, showing excellent anti-migration, heat resistance, weather resistance, solvent resistance and environmental friendliness. Through reasonable molecular design, the colorant polymer can be similar in structure or have good compatibility with the base resin, achieving molecular-level dispersion, avoiding flocculation, improving color uniformity and gloss, and simplifying the processing process and eliminating the pre-dispersion process. At present, the reported cellulose-based macromolecular colorants mostly use natural cellulose as raw material, for example: CN119081447A discloses a method for preparing a high molecular dye by dissolving cellulose in an alkali / urea solvent system and then reacting with a reactive dye; and CN119286277A prepares nanocellulose by acid hydrolysis, and then obtains a nanocolorant by compounding with an indigo dye dispersion. Although these methods achieve the functionalization of cellulose to some extent, they still have common problems such as complex process flow, use of a large amount of solvent, involvement of cellulose dissolution / regeneration or nanofiber treatment, high cost, and difficulty in large-scale application.

[0004] Therefore, in view of the complicated preparation process and high cost of the existing cellulose-based macromolecular colorant, it is urgent to develop a new type of macromolecular colorant and a preparation method thereof, which are simple in process, low in cost and suitable for industrial production, so as to meet the demand of high-end coatings and ink systems for high-performance colorants. SUMMARY

[0005] The technical problem to be solved by the present application is the complicated preparation process and high cost of the existing cellulose-based macromolecular colorant.

[0006] To achieve the above-mentioned application purposes, the technical solutions adopted by the present application are as follows: In a first aspect, the present application provides a preparation method of a nitrocellulose-based macromolecular colorant, comprising the following steps: S1. Activation: nitrocellulose is added to acetic acid solvent, and constant temperature stirring reaction is carried out at 70-90℃, then after the reaction is completed, filtration is carried out to obtain activated nitrocellulose; S2. Esterification: the activated nitrocellulose is added to a mixed solution composed of sulfuric acid, carboxyl dye and water, and esterification reaction is carried out by heating to 50-70℃, then after the reaction is completed, the system is cooled to room temperature, and after neutralization and filtration, a crude product is obtained; S3. Post-treatment: the crude product is sequentially subjected to washing and drying treatment to obtain a nitrocellulose-based macromolecular colorant.

[0007] In the step S1, the nitrogen content of the nitrocellulose is 10.7%-12.4%.

[0008] In the step S1, the mass-volume ratio of the nitrocellulose to the acetic acid solvent is 1g:20-60mL.

[0009] In the step S1, the constant temperature stirring reaction time is 2-4h.

[0010] In the step S2, the carboxyl dye includes at least one of Cy5 carboxylic acid, 2-(anthracene-9-yl)acetic acid, 2-(pyrene-1-yl)acetic acid, 2-naphthaleneacetic acid, 5-carboxyfluorescein, and carboxytetramethylrhodamine.

[0011] In the step S2, the mass-volume ratio of the activated nitrocellulose to the mixed solution is 1g:40-60mL.

[0012] In the step S2, the mass ratio of the activated nitrocellulose to the carboxyl dye is 1:5-10.

[0013] In the step S2, the mass ratio of sulfuric acid to water in the mixed solution is 70-90:10-20.

[0014] In the step S2, the heating rate of the esterification reaction is 1-3 ℃ / min.

[0015] In the step S2, the esterification reaction is performed for 6-8 hours.

[0016] In the step S2, the esterification reaction is performed under normal pressure.

[0017] In the step S2, the neutralization is performed by adjusting the pH of the system to 7-8 using any one of ammonia, sodium carbonate and potassium carbonate.

[0018] In the step S3, the washing is performed by washing three times with pure water and three times with ethanol.

[0019] In the step S3, the drying is performed by placing the product in an oven, keeping the oven in an unsealed state, slightly opening the oven door, and slowly drying the product at 50-80 ℃ under normal pressure until the solvent content is 28-32%.

[0020] In a second aspect, the present application provides a nitrocellulose-based macromolecular colorant prepared by the above method.

[0021] In a third aspect, the present application provides the use of the above nitrocellulose-based macromolecular colorant in nitro paint or ink.

[0022] The present application has the following advantages: the present application synthesizes a nitrocellulose-based macromolecular colorant through two-step chemical reactions, effectively avoids the complex pretreatment and grafting process necessary when using natural cellulose as a substrate, significantly simplifies the preparation process, and reduces production costs. By accurately controlling the nitrogen content of the nitrocellulose raw material and the reaction conditions, the nitration degree and grafting rate of the product can be effectively controlled, and the quality of the product can be accurately controlled. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as understood by those skilled in the art.

[0024] The present application provides a preparation method of a nitrocellulose-based macromolecular colorant, which is characterized in that the traditional cellulose colorant is dissolved and then regenerated / modified, and then grafted, and instead, the structural characteristics of nitrocellulose (NC) itself are utilized to prepare a macromolecular colorant with excellent performance through a two-step reaction of “activation-esterification”.

[0025] The preparation method of the nitrocellulose-based macromolecular colorant and the role thereof according to the present application specifically include the following.

[0026] Step one, activation: nitrocellulose is added to acetic acid solvent, constant temperature stirring reaction at 70~90℃, after the reaction is completed, filter to obtain activated nitrocellulose.

[0027] In an embodiment of the present application, the nitrogen content of the above nitrocellulose is 10.7%~12.4%. The nitrogen content of the nitrocellulose cannot be too low, otherwise the solubility of the nitrocellulose in the solvent will be poor, affecting the subsequent reaction and product performance; the nitrogen content cannot be too high, otherwise the degree of substitution of nitro group is too high, the number of remaining hydroxyl groups for grafting small molecules of chromophore is too small, the dye cannot be connected, affecting the color depth of the colorant.

[0028] Nitrocellulose has a complex structure of crystalline region and amorphous region, and there is a strong hydrogen bond between the molecular chains, so that the hydroxyl groups (-OH) of the polymer are wrapped inside, and the reaction accessibility is very low. The role of acetic acid solvent is not only to dissolve nitrocellulose, but also to make acetic acid molecules penetrate into the high molecular structure of nitrocellulose under heating conditions, destroy the crystalline region, weaken the hydrogen bond between the molecular chains, and make the originally wrapped hydroxyl groups fully exposed. In the present application, the purpose of the activation process is to improve the reactivity, make the physical structure of nitrocellulose "loose", and make the chemical environment of the hydroxyl group more active, so that it is easier to react with carboxylic acid in the subsequent step.

[0029] The preparation method of traditional cellulose-based macromolecular colorant usually needs to dissolve cellulose in expensive and difficult to recover solvent system (such as ionic liquid, NMMO) or strong alkali solution, so that the molecular chain is completely dispersed, and then reacted. This process has high energy consumption, complex process and high cost. The method of the present application only uses cheap and easy-to-recover acetic acid to realize "activation" through mild swelling, avoiding the complex dissolution and regeneration steps, reducing the production cost and simplifying the process.

[0030] Step two, esterification: the activated nitrocellulose is added to a mixed solution composed of sulfuric acid, carboxyl dye and water, and the temperature is raised to 50~70℃ for esterification reaction. After the reaction is completed, the system is cooled to room temperature, neutralized, filtered, and the crude product is obtained.

[0031] In an embodiment of the present application, the above carboxyl dye includes at least one of Cy5 carboxylic acid, 2-(anthracene-9-yl)acetic acid, 2-(pyrene-1-yl)acetic acid, 2-naphthaleneacetic acid, 5-carboxyfluorescein, and carboxytetramethylrhodamine.

[0032] The dyes used in the present application all contain carboxyl groups (-COOH). In the esterification reaction process, the activated hydroxyl groups (-OH) on the nitrocellulose and the carboxyl groups (-COOH) on the carboxyl dye form a firm covalent ester bond (-O-CO-) under the catalysis of sulfuric acid, so that the macromolecular colorant prepared by the present application has excellent anti-migration property, solvent resistance and high weather resistance.

[0033] In one embodiment of the present application, the mass-volume ratio of the activated nitrocellulose and the mixed solution is 1 g: 40-60 mL; the mass ratio of the activated nitrocellulose and the carboxyl dye is 1:5-10; the mass ratio of sulfuric acid and water in the mixed solution is 70-90: 10-20. The temperature rising rate of the esterification reaction is 1-3 ℃ / min; the time of the esterification reaction is 6-8 hours; the pressure of the esterification reaction is normal pressure. The mass ratio of sulfuric acid and water defined in the present application corresponds to the concentration of the sulfuric acid solution being 70-90 wt%. The purpose is to control the acidity of the reaction system and prevent excessive hydrolysis or oxidative degradation of the nitrocellulose and the dye at high temperature, such as cellulose chain rupture and dye chromophore destruction. At the same time, the water in the sulfuric acid solution helps to maintain the swelling state of the nitrocellulose, ensuring that the reaction sites are continuously accessible. The mixed solution system defined in the present application provides a mild and controllable reaction environment, which ensures the reaction efficiency while maximizing the integrity of the reactants. 50-70 ℃ is the best temperature range considering the reaction rate and material stability, and the reaction time of 6-8 hours ensures that the grafting reaction can proceed fully.

[0034] Step three, purification: the crude product is sequentially washed and dried to obtain the nitrocellulose-based macromolecular colorant.

[0035] The excess sulfuric acid in the system is neutralized with an alkali agent such as ammonia water to terminate the reaction and decompose possible by-products such as sulfuric acid esters, and at the same time the system is neutralized to facilitate subsequent processing and protect the stability of the product. Through washing and drying, unreacted dyes, salts such as ammonium sulfate, and other impurities physically adsorbed on the surface of the product are completely removed, and the final product with high purity and stable morphology is obtained. The post-processing process of the present application is simple, efficient and low in cost (only needs filtering, washing, and drying), and is suitable for industrial production.

[0036] The following specific examples will be used to explain the scheme of the present application. Those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. If the specific technology or condition is not specified in the examples, it is carried out according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0037] Example 1: Preparation of blue nitrocellulose-based macromolecular colorant, including the following steps.

[0038] (1) 1.0 g of nitrocellulose with nitrogen content of 11.2% is added to 40 mL of acetic acid solvent, and stirred at 80 ℃ for 2 hours to activate, and after the reaction is completed, it is filtered to obtain activated nitrocellulose; (2) The activated nitrocellulose obtained in step (1) is added to a mixed solution composed of a sulfuric acid solution (sulfuric acid + water) and a Cy5 carboxylic acid dye, and heated to 65℃ at a rate of 2℃ / min, and reacted for 7 hours under normal pressure; wherein the volume of the mixed solution is 40 mL, the mass ratio of the nitrocellulose to the Cy5 carboxylic acid dye is 1:8, and the concentration of the sulfuric acid solution is 74wt%; (3) After the reaction is completed, the temperature is cooled to room temperature, neutralized to pH=7 with dilute ammonia water, and the crude product is obtained by filtration; the crude product is washed with water and ethanol three times in turn, and slowly dried at 60℃ until the solvent content is about 30%, to obtain a dark blue nitrocellulose-based macromolecular colorant.

[0039] The properties of the prepared nitrocellulose-based macromolecular colorant are detected: the final nitrogen content of the product is 10.5% by elemental analysis; the dye grafting rate is 78.5mg / g by UV-visible spectrophotometry. The decrease in nitrogen content and the dye grafting rate indicate that the dye molecules have been successfully grafted onto the nitrocellulose skeleton by covalent bonds, and the grafting efficiency is high, effectively solving the core problem of small molecule dyes that are prone to migration and poor weather resistance.

[0040] Example 2: Preparation of a yellow nitrocellulose-based macromolecular colorant, including the following steps.

[0041] (1) 1.0g of nitrocellulose with a nitrogen content of 12.1% is added to 40mL of acetic acid solvent, and stirred at 80℃ for 2 hours to activate, and after the reaction is completed, the activated nitrocellulose is obtained by filtration; (2) The activated nitrocellulose obtained in step (1) is added to a mixed solution composed of a sulfuric acid solution (sulfuric acid + water) and a 5-carboxyfluorescein dye, and heated to 60℃ at a rate of 2℃ / min, and reacted for 8 hours under normal pressure; wherein the volume of the mixed solution is 40 mL, the mass ratio of the nitrocellulose to the 5-carboxyfluorescein dye is 1:6, and the concentration of the sulfuric acid solution is 76wt%; (3) After the reaction is completed, the temperature is cooled to room temperature, neutralized to pH=7 with dilute ammonia water, and the crude product is obtained by filtration; the crude product is washed with water and ethanol three times in turn, and slowly dried at 60℃ until the solvent content is about 30%, to obtain a bright yellow nitrocellulose-based macromolecular colorant.

[0042] The properties of the prepared nitrocellulose-based macromolecular colorant are detected: the final nitrogen content of the product is 11.1% by elemental analysis; the dye grafting rate is 82.1mg / g by UV-visible spectrophotometry.

[0043] Example 3: Preparation of a yellow nitrocellulose-based macromolecular colorant, including the following steps.

[0044] (1) 1.0 g of nitrocellulose with a nitrogen content of 11.4% was added to 40 mL of acetic acid solvent, and stirred at 75°C for 3 hours. After the reaction was completed, the activated nitrocellulose was obtained by filtration; (2) The activated nitrocellulose obtained in step (1) was added to a mixed solution composed of sulfuric acid solution (sulfuric acid + water) and 2-(anthracene-9-yl) acetic acid dye, and heated to 70°C at a rate of 3°C / min under normal pressure for 6 hours; wherein the volume of the mixed solution was 50 mL, the mass ratio of nitrocellulose to 2-(anthracene-9-yl) acetic acid dye was 1:5, and the concentration of sulfuric acid solution was 80 wt%; (3) After the reaction was completed, it was cooled to room temperature, neutralized to pH=7 with dilute ammonia water, and the crude product was obtained by filtration; the crude product was washed with water and ethanol three times respectively, and slowly dried at 60°C until the solvent content was about 30%, to obtain a yellow nitrocellulose-based macromolecular colorant.

[0045] The properties of the prepared nitrocellulose-based macromolecular colorant were detected: the final nitrogen content of the product was 10.8% by elemental analysis; the dye grafting rate was 68.4 mg / g by UV-visible spectrophotometry.

[0046] Comparative Example 1: The difference from Example 1 is only that in step (1), the nitrogen content of nitrocellulose is 12.8%, and the rest of the process and process parameters are the same as those in Example 1. The product prepared is lighter in color, nearly white, and its final nitrogen content is 12.6% and the dye grafting rate is <5 mg / g. The results show that the nitrocellulose used in the comparative example has too high nitrogen content, resulting in insufficient hydroxyl reaction sites.

[0047] Comparative Example 2: The difference from Example 1 is only that in step (1), the nitrogen content of nitrocellulose is 9.0%; the rest of the process and process parameters are the same as those in Example 1. The product prepared is a blocky material with uneven color, and its dye grafting rate is 25.7 mg / g. The results show that the nitrocellulose used in the comparative example has too low nitrogen content, resulting in poor solubility and accessibility of nitrocellulose in acetic acid, turbidity of the system, and difficulty in subsequent reaction, resulting in low reaction efficiency.

Claims

1. A process for the preparation of a nitrocellulose-based macromolecular colorant, characterized in that, The method comprises the following steps: S1. Activation: nitrocellulose is added to acetic acid solvent, and constant temperature stirring reaction is carried out at 70-90℃, then after the reaction is completed, filtration is carried out, and activated nitrocellulose is obtained; S2. Esterification: the activated nitrocellulose is added to a mixed solution composed of sulfuric acid, carboxyl dye and water, and esterification reaction is carried out by heating to 50-70℃, then after the reaction is completed, the system is cooled to room temperature, neutralization and filtration are carried out, and a crude product is obtained; S3. Post-treatment: the crude product is sequentially subjected to washing and drying treatment, and a nitrocellulose-based macromolecular colorant is obtained.

2. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that: In step S1, the nitrogen content of the nitrocellulose is 10.7%-12.4%.

3. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that: In step S1, at least one of the following is met: The mass-volume ratio of the nitrocellulose to the acetic acid solvent is 1g:20-60mL; The constant temperature stirring reaction time is 2-4 hours.

4. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that: In step S2, the carboxyl dye comprises at least one of Cy5 carboxylic acid, 2-(anthracene-9-yl)acetic acid, 2-(pyrene-1-yl)acetic acid, 2-naphthaleneacetic acid, 5-carboxyfluorescein, and carboxytetramethyl rhodamine.

5. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that: In step S2, at least one of the following is met: The mass-volume ratio of the activated nitrocellulose to the mixed solution is 1g:40-60mL; The mass ratio of the activated nitrocellulose to the carboxyl dye is 1:5-10; The mass ratio of sulfuric acid to water in the mixed solution is 70-90:10-20.

6. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that, In step S2, at least one of the following is met: The esterification reaction heating rate is 1-3℃ / min; The esterification reaction time is 6-8 hours; The esterification reaction pressure is normal pressure.

7. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that: In step S2, the neutralization specifically adjusts the pH of the system to 7-8 by using any one of ammonia, sodium carbonate and potassium carbonate.

8. The process for the preparation of nitrocellulose-based macromolecular colorants according to claim 1, characterized in that: In step S3, at least one of the following is met: The washing specifically comprises washing three times with pure water and three times with ethanol; The drying specifically comprises placing in an oven, keeping the oven in an unsealed state, slightly opening the oven door, and slowly drying at 50-80℃ under normal pressure until the solvent content is 28-32%.

9. The nitrocellulose-based macromolecular colorant prepared by the preparation method of any one of claims 1-8.

10. The application of the nitrocellulose-based macromolecular colorant prepared by the preparation method of any one of claims 1-8 or the nitrocellulose-based macromolecular colorant of claim 9 in nitro paint or ink.