Micromolecular sizing agent, synthetic method thereof, sizing agent solution and application

Abstract

The invention discloses a micromolecular sizing agent, a synthesis method thereof, a sizing agent solution and application, and belongs to the technical field of papermaking chemicals. The sizing agent has a double-long-chain secondary amine structure as shown in a general formula R2N (C3H6) N (CH3) 2, in which R is long-chain alkyl CnH2n + 1, and n is 14, 16 or 18. The synthesis method of the micromolecular sizing agent comprises the following steps: mixing 3-dimethylaminopropylamine and alkyl bromide in a molar ratio of 1: (2.0-2.5), and adding absolute ethyl alcohol as a solvent to prepare a mixture; and carrying out a heating reflux reaction on the mixture, and after the reaction is completed, sequentially carrying out reduced pressure distillation and recrystallization to prepare the micromolecular sizing agent. A brand new physical and chemical mechanism of electrostatic anchoring-hydrophobic shielding is utilized, and cellulose-based materials such as paper and the like are efficiently and instantly endowed with excellent hydrophobic performance under a neutral or alkaline mild condition.

Description

Technical Field

[0001] This invention belongs to the field of papermaking chemicals technology, specifically relating to a small molecule sizing agent, its synthesis method, sizing agent solution, and its application. Background Technology

[0002] Sizing is a crucial step in the papermaking process, aiming to impart resistance to liquid penetration and diffusion, thereby improving the paper's strength, durability, and performance. Currently, widely used industrial sizing agents are mainly divided into two categories: reactive sizing agents and anionic dispersible sizing agents. However, these traditional sizing agents have significant limitations in synthesis, storage, and application. The most representative reactive sizing agents are alkyl ketene dimers (AKD) and alkenyl succinic anhydride (ASA). Their mechanism of action involves esterification with the hydroxyl groups on the surface of cellulose fibers, forming stable covalent bonds, thereby permanently altering the hydrophilicity of the fiber surface.

[0003] However, AKD has a complex synthesis process, typically requiring multiple steps of reaction from fatty acid acyl chlorides, which is demanding and costly. Secondly, AKD exhibits significant hydrolytic sensitivity, readily reacting with water during storage and use to generate hydrophilic ketone byproducts, leading to a substantial decrease in sizing efficiency and the formation of harmful deposits in paper machine systems. More importantly, AKD has a "curing time" after sizing, usually requiring several hours to several days to fully achieve its water-resistant effect, severely impacting production efficiency.

[0004] ASA has higher reactivity than AKD, but it also hydrolyzes faster. It must be used immediately after emulsification on-site, which places extremely high demands on the continuity and stability of the production process. It is inconvenient to operate and carries significant risks.

[0005] Rosin and its derivatives are traditional anionic sizing agents, and their application requires a cationic medium (such as aluminum sulfate, i.e., alum) as a fixative. Rosin particles adsorb onto negatively charged fibers via positively charged aluminum hydroxyl ions generated from alum hydrolysis. This sizing system is only effective under acidic conditions (pH approximately 4.0-4.5). This not only limits the use of inexpensive alkaline fillers such as calcium carbonate, leading to decreased paper strength and brightness, but also causes significant corrosion to papermaking equipment. Acidic papermaking systems generate aluminum-rich wastewater, polluting the environment and contradicting current green and sustainable development principles. Furthermore, rosin sizing exhibits poor water resistance and durability, especially in high-temperature and alkaline environments. To adapt to neutral / alkaline papermaking, various cationic polymers have been developed as sizing agents or retention aids. However, these polymers often have large molecular weights, involve polymerization reactions in their synthesis, and their molecular structures are difficult to control precisely. Moreover, their coverage efficiency on fiber surfaces and improvement in hydrophobic properties are often less effective than those of smaller molecules. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a small molecule sizing agent, its synthesis method, sizing agent solution, and applications, thereby solving the technical bottlenecks of existing mainstream sizing agents, such as alkyl ketene dimers (AKD) and alkenyl succinic anhydride (ASA), which suffer from complex synthesis processes, easy hydrolysis, and a curing period for sizing efficiency, as well as the reliance on acidic conditions and environmental unfriendliness of rosin-based sizing agents. Based on this, the present invention provides a small molecule sizing agent with a well-defined molecular structure, an extremely simple synthesis route, convenient application, stable performance, and high environmental compatibility. Its core objective is to utilize a novel "electrostatic anchoring-hydrophobic shielding" physicochemical mechanism to efficiently and immediately impart excellent hydrophobic properties to cellulose-based materials such as paper under neutral or mild alkaline conditions.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a small molecule sizing agent, the structural formula of which is as follows:

[0008] Where n = 14, 16, 18.

[0009] This invention provides a method for synthesizing the above-mentioned small molecule sizing agent, comprising the following steps: 3-Dimethylaminopropylamine and bromoalkanes were mixed in a molar ratio of 1:(2.0~2.5), and anhydrous ethanol was added as a solvent to prepare a mixture. The mixture was heated under reflux, and after the reaction was completed, it was subjected to vacuum distillation and recrystallization in sequence to obtain a small molecule sizing agent.

[0010] In one embodiment, the molar ratio of 3-dimethylaminopropylamine to bromoalkane is 1:2.1.

[0011] In one embodiment, the bromoalkane is selected from one or more of bromotetradecane, bromohexadecane, and bromooctadecane.

[0012] In one embodiment, the temperature of the heating reflux reaction is 70~80°C and the time is 36h.

[0013] In one embodiment, the mass ratio of anhydrous ethanol to reactants is 4:1, and the reactants are 3-dimethylaminopropylamine and bromoalkane.

[0014] The present invention also provides a sizing agent solution, comprising an active component and a solvent, wherein water is used as the solvent and the small molecule sizing agent as described in claim 1 is used as the active component, and the concentration of the sizing agent solution is 0.5wt% to 2.0wt%.

[0015] In one embodiment, the concentration of the sizing agent solution is 1 wt%.

[0016] This invention also provides an application of a small molecule sizing agent or sizing agent solution in the sizing treatment of cellulose-based materials, the specific application process of which is as follows: A sizing agent solution was prepared using a small molecule sizing agent. The cellulose-based material was then immersed in the sizing agent solution for impregnation and subsequently dried to obtain a hydrophobic cellulose-based material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a small-molecule sizing agent based on a double-chain secondary amine structure, whose superior performance stems from a unique "pH-responsive intelligent adsorption and double-chain synergistic hydrophobicity" mechanism. The secondary amine group of this molecule acts as a key intelligent anchoring site, reversibly protonating under suitable weakly acidic to neutral conditions in the papermaking system to form a positively charged cation (-NH2). + The sizing agent is efficiently anchored to the negatively charged cellulose fiber surface through strong electrostatic forces, achieving a high retention rate. Simultaneously, two long-chain alkyl groups (C14-C18) connected to the central nitrogen atom play a crucial hydrophobic role: after the hydrophilic head group is fixed, the two hydrophobic chains, through strong van der Waals forces and hydrophobic interactions, are arranged side-by-side in a tight and orderly manner on the fiber surface, constructing a molecular-level hydrophobic barrier with a density far exceeding that of single-chain quaternary ammonium salts or secondary amine products. This dense outer layer, composed of low surface energy methyl groups (-CH3), effectively blocks water wetting, thus giving the treated paper a water contact angle as high as 98°. This excellent hydrophobicity is immediately apparent after drying, achieving a "zero curing period."

[0018] Compared to traditional sizing agents, the advantages of this invention are revolutionary. Compared to traditional AKD, it fundamentally solves the industry pain points of complex synthesis routes, easy hydrolysis and deactivation, and the need for a long curing period. With its simple one-step synthesis, excellent chemical stability, and immediate effectiveness, it surpasses reactive sizing agents. Compared to traditional rosin sizing agents, it completely eliminates the dependence on aluminum sulfate media and strongly acidic environments, perfectly compatible with modern environmentally friendly neutral papermaking processes, and poses no risk of equipment corrosion or aluminum pollution. Even compared to cationic quaternary ammonium salt sizing agents, the secondary amine structure used in this invention not only retains the advantages of electrostatic adsorption, but its synthetic raw materials are also cheaper and more readily available. Furthermore, the molecule itself does not contain permanent cations or halogen counterions, exhibiting better biodegradability and environmental friendliness. In summary, this dual long-chain secondary amine sizing agent, with its innovative molecular design, achieves the best balance between synthesis efficiency, sizing performance, environmental compatibility, and production cost, representing a smarter, more economical, and greener next-generation hydrophobic solution for paper. Attached Figure Description

[0019] Figure 1 The FTIR spectrum of the small molecule sizing agent prepared in Example 1 of the present invention; Figure 2 The contact angle between the paper and water after treatment with the small molecule sizing agent prepared in Example 1 of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0022] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] The first aspect of this invention provides a small molecule sizing agent having the structure shown in general formula (I): (I) Where n = 14, 16, 18.

[0026] A second aspect of this invention provides a method for synthesizing a small molecule sizing agent, comprising the following steps: a) 3-Dimethylaminopropylamine and bromoalkanes were placed in a reaction vessel at a molar ratio of 1:(2.0~2.5), and anhydrous ethanol was added as a solvent to obtain a mixture; b) The mixture from step a) is heated under reflux at 70-80°C for 36 hours; c) After the reaction is complete, the solvent anhydrous ethanol is removed by vacuum distillation to obtain the crude product; d) The crude product was recrystallized with acetone to obtain a purified small molecule sizing agent.

[0027] More preferably, the molar ratio of 3-dimethylaminopropylamine to bromoalkane in step a) is 1:2.1.

[0028] More preferably, in step a), the mass ratio of anhydrous ethanol to reactants (3-dimethylaminopropylamine and bromoalkane) is 4:1.

[0029] More preferably, the bromoalkane in step a) is selected from one or more of bromotetradecane, bromohexadecane, and bromooctadecane.

[0030] More preferably, the temperature of the heating reflux reaction in step b) is 75°C.

[0031] A third aspect of the present invention provides a sizing agent solution comprising an active component and a solvent, wherein the active component is the aforementioned small molecule sizing agent, the solvent is water, and the concentration of the sizing agent solution is an ultrapure aqueous solution of 0.5wt% to 2.0wt%, preferably 1wt%.

[0032] The fourth aspect of the present invention provides the application of the above-described small molecule sizing agent or the above-described sizing agent solution in the sizing treatment of cellulose-based materials.

[0033] A specific application process for improving the hydrophobicity of cellulose-based materials includes the following steps: i) Prepare a sizing agent solution with a concentration of 0.5wt%~2.0wt% using small molecule sizing agents; ii) Immerse the cellulose-based material in the sizing agent solution prepared in step i); iii) The impregnated cellulose-based material is dried at a temperature of 60-80°C to obtain a hydrophobic cellulose-based material.

[0034] Specifically, the present invention also provides a method for applying the synthesized small molecule sizing agent to cellulose-based materials such as paper as follows: a) Preparation of sizing solution: The purified sizing agent is prepared into a sizing agent solution with an effective concentration of 0.5wt%~2.0wt%. The solvent can be ultrapure water. The preferred sizing agent concentration is 1.0wt%, which achieves optimal economy while ensuring excellent hydrophobic effect.

[0035] b) Substrate treatment: The cellulose substrate (e.g., with a basis weight of 80 g / m³) is treated. 2 The filter paper, cardboard, or cotton fabric is in full contact with the sizing agent solution.

[0036] c) Treatment method: Immersion treatment, with an optimal immersion time of 3-10 minutes to ensure full adsorption of the sizing agent. Control the liquid absorption rate of the substrate to 60%-120% (based on the dry weight of the substrate) to obtain a uniform sizing effect.

[0037] Performance after drying: The treated substrate is placed in an oven and dried at 60-80°C for 30-60 minutes. After this drying process, the hydrophobic properties are immediately and fully manifested, without any "curing period." Figure 2 As shown, the treated paper can immediately reach a water contact angle of up to 99°, demonstrating excellent water resistance.

[0038] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0039] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0040] Example 1: This embodiment provides a method for synthesizing a dioctadecyl secondary amine sizing agent, as detailed below: In a 250 mL three-necked round-bottom flask equipped with a condenser, thermometer, and magnetic stirrer, 10.0 g of 3-dimethylaminopropylamine and 150 mL of anhydrous ethanol were added and stirred. 79.6 g of bromooctadecane was slowly added to the above solution to achieve a molar ratio of 1:2.1. The reaction mixture was placed in a constant temperature water bath at 75 °C and heated under reflux for 36 hours. After the reaction was complete, the reaction solution was transferred to a vacuum drying oven and distilled under reduced pressure at 60 °C to completely remove the solvent ethanol, yielding a pale yellow viscous crude product. 200 mL of acetone was added to the crude product, and the mixture was heated to boiling to completely dissolve it. The mixture was then allowed to cool naturally to room temperature and crystallized in an ice-water bath for 2 hours. The crystals were filtered and washed 2-3 times with a small amount of pre-cooled acetone. The resulting white crystals were dried in a vacuum drying oven at room temperature for 6 hours to obtain the final product, dioctadecylamine secondary sizing agent, whose FTIR spectrum is shown below. Figure 1 As shown.

[0041] The application and effect verification of the bis(octadecyl) secondary amine sizing agent prepared in this embodiment are as follows: Accurately weigh 1.0 g of the synthesized product and dissolve it in 99 g of ultrapure water to prepare a 1 wt% sizing agent solution, which is then solubilized by ultrasound. The solution has a quantitative concentration of 80 g / m³. 2 Qualitative filter paper was cut into appropriately sized test pieces and immersed in the sizing agent solution, ensuring complete submersion, for 5 minutes. The test pieces were then removed and suspended in a 60°C forced-air drying oven for 10 minutes. The water contact angle of the dried paper surface, cooled to room temperature, was then measured using a contact angle meter. Figure 2 As shown, the static contact angle between the paper and water was measured to be 98.5°.

[0042] Example 2: This embodiment provides a method for synthesizing and applying a dihexadecyl secondary amine sizing agent.

[0043] The synthesis steps were exactly the same as in Example 1. The difference was that the raw materials were replaced with 3-dimethylaminopropylamine (10.0 g, 0.098 mol) and hexadecane bromide (72.2 g, 0.206 mol). After reaction, concentration, recrystallization with acetone, and vacuum drying, a white powdery solid product, dihexadecyl secondary amine sizing agent, was obtained.

[0044] Application and effect verification: The application method is the same as in Example 1. A 1 wt% ultrapure water sizing solution was prepared using the product synthesized in this example. After treating and drying the paper, the static contact angle between the paper and water was measured to be 86.4°.

[0045] Example 3: This embodiment provides a method for synthesizing and applying a bis(tetradecyl)-2-amine sizing agent.

[0046] The synthesis steps were exactly the same as in Example 1. The difference was that the starting materials were replaced with 10.0 g of 3-dimethylaminopropylamine and 64.8 g of bromotetradecane. After reaction, concentration, recrystallization in acetone, and vacuum drying, a white waxy solid product, bis(tetradecyl)amine secondary sizing agent, was obtained.

[0047] Application and effect verification: The application method is the same as in Example 1. A 1 wt% ultrapure water sizing solution was prepared using the product synthesized in this example. After treating and drying the paper, the static contact angle between the paper and water was measured to be 79.8°.

[0048] Comparative Example 1: Uncoated paper The quantitative measure of the same batch is 80 g / m 2 Qualitative filter paper samples, without any sizing agent treatment, were directly used to measure their contact angle with water. The measured contact angle was 30.5°, and the water droplets were rapidly absorbed by the paper within seconds, indicating that the untreated paper has extremely strong hydrophilicity.

[0049] Comparative Example 2: Traditional single-chain quaternary ammonium salt treatment Using commercially available cetyltrimethylammonium bromide (CTAB), a 1 wt% ultrapure aqueous solution was prepared to treat paper, following the same application method as in Example 1. After drying, the contact angle between the paper and water was measured to be 58.4°. The result is significantly lower than that of the embodiments of the present invention, demonstrating that the dual long-chain secondary amine structure of the present invention has a synergistic advantage in constructing a dense hydrophobic layer that cannot be matched by single-chain quaternary ammonium salts.

[0050] Comparison of effects of different application concentrations Using the dioctadecylamine secondary sizing agent synthesized in Example 1, 0.5 wt%, 1.0 wt%, and 2.0 wt% ultrapure aqueous solutions were prepared, and paper was treated according to the method described in Example 1. The contact angle results are as follows: The contact angle of paper treated with a 0.5 wt% solution was 85.6°. The contact angle of paper treated with a 1.0 wt% solution was 98.5°. The contact angle of paper treated with a 2.0 wt% solution was 99.1°. The results indicate that this sizing agent provides excellent hydrophobic properties within a concentration range of 0.5 wt% to 2.0 wt%, with 1.0 wt% being the optimal concentration for cost-effectiveness.

[0051] This invention belongs to the field of papermaking wet end chemistry, specifically relating to a cationic small molecule sizing agent that works through an "electrostatic anchoring-hydrophobic shielding" mechanism, its synthesis method, and its application in improving the hydrophobicity of paper.

[0052] This invention belongs to the field of papermaking chemicals technology, specifically relating to a small molecule sizing agent, its synthesis method, sizing agent solution, and application. The sizing agent has a dual long-chain secondary amine structure represented by the general formula R2N(C3H6)N(CH3)2, wherein the R group is a long-chain alkyl group. n H 2n+1 The n value is 14, 16, or 18. The synthesis method involves reacting 3-dimethylaminopropylamine with corresponding bromoalkanes (such as bromotetradecane, hexadecane, or octadecane) at a molar ratio of 1:(2.0~2.5) in anhydrous ethanol under reflux at 70~80°C for 36 hours. After the reaction is complete, the product is purified by vacuum distillation and recrystallization from acetone. This invention also provides a method for preparing a 0.5wt%~2.0wt% solution of this sizing agent for application in sizing cellulose-based materials. The sizing agent of this invention, through the pH-responsive "electrostatic anchoring" effect of its secondary amine group and the synergistic "hydrophobic shielding" effect of its two long-chain alkyl groups, can immediately impart a water contact angle of up to 99° to paper without a curing period after treatment, exhibiting excellent hydrophobic properties. Compared with traditional AKD and rosin sizing agents, this invention has significant advantages such as simple synthesis route, low cost, environmental friendliness, zero curing period, and compatibility with neutral papermaking processes.

[0053] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A small molecule sizing agent, characterized in that, The structural formula of the small molecule sizing agent is as follows: Where n = 14, 16, 18.

2. A method for synthesizing the small molecule sizing agent as described in claim 1, characterized in that, Includes the following steps: 3-Dimethylaminopropylamine and bromoalkanes were mixed in a molar ratio of 1:(2.0~2.5), and anhydrous ethanol was added as a solvent to prepare a mixture. The mixture was heated under reflux, and after the reaction was completed, it was subjected to vacuum distillation and recrystallization in sequence to obtain a small molecule sizing agent.

3. The method for synthesizing the small molecule sizing agent according to claim 2, characterized in that, The molar ratio of 3-dimethylaminopropylamine to bromoalkane is 1:2.

1.

4. The method for synthesizing the small molecule sizing agent according to claim 2, characterized in that, The bromoalkane is selected from one or more of bromotetradecane, bromohexadecane, and bromooctadecane.

5. The method for synthesizing the small molecule sizing agent according to claim 2, characterized in that, The heating reflux reaction is carried out at a temperature of 70-80°C for 36 hours.

6. The method for synthesizing the small molecule sizing agent according to claim 2, characterized in that, The mass ratio of anhydrous ethanol to reactants is 4:1, and the reactants are 3-dimethylaminopropylamine and bromoalkane.

7. A sizing agent solution, characterized in that, It includes an active component and a solvent, with water as the solvent and the small molecule sizing agent as described in claim 1 as the active component, wherein the concentration of the sizing agent solution is 0.5wt% to 2.0wt%.

8. The sizing agent solution according to claim 7, characterized in that, The concentration of the sizing agent solution is 1 wt%.

9. The use of a small molecule sizing agent as described in claim 1 or a sizing agent solution as described in claim 7 in the sizing treatment of cellulose-based materials.

10. The application according to claim 9, characterized in that, The application process of small molecule sizing agents or sizing agent solutions in the sizing treatment of cellulose-based materials is as follows: A sizing agent solution was prepared using a small molecule sizing agent. The cellulose-based material was then immersed in the sizing agent solution for impregnation and subsequently dried to obtain a hydrophobic cellulose-based material.

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