Preparation process of ethanolamine modified wet strength agent

Abstract

The application discloses a preparation process of ethanolamine modified wet strength agent and relates to the technical field of wet strength agents, and comprises the following steps: carrying out an addition reaction on diethylenetriamine and ethylene oxide to obtain an ethanolamine intermediate; adding a formaldehyde solution into the ethanolamine intermediate, performing a pre-condensation reaction under an acidic condition by adopting pH gradient control to obtain a pre-condensation product; adding a catalyst and a synergist into the pre-condensation product, adding the formaldehyde solution in batches according to viscosity detection during the reaction, the added amount of the formaldehyde solution is 5-12% of the solid content of the pre-condensation product, and a crosslinking product is obtained; and adding a formaldehyde capturing agent into the crosslinking product to perform a stabilization treatment, so as to obtain the ethanolamine modified wet strength agent. By adopting the synergistic technology of pH gradient control and viscosity monitoring and batch addition of formaldehyde, the accurate control of the preparation process of the ethanolamine modified wet strength agent is realized.

Description

Technical Field

[0001] This invention relates to the field of wet strength agents, and in particular to a preparation process for an ethanolamine-modified wet strength agent. Background Technology

[0002] Wet strength agents are important chemical additives in the papermaking industry, mainly used to improve the strength retention rate of paper in a wet state. Currently, the market primarily uses traditional wet strength agents such as polyamide epichlorohydrin (PAE) and urea-formaldehyde resin. In recent years, ethanolamine-modified wet strength agents have attracted attention due to their good wet strength performance and relatively low environmental impact. Traditional ethanolamine-modified wet strength agent preparation processes typically employ a one-step synthesis, where diethylenetriamine, ethylene oxide, and formaldehyde are reacted together under specific conditions. However, this process suffers from poor reaction control; pH and reaction progress are difficult to precisely regulate, leading to uneven molecular weight distribution of the product and difficulty in controlling the degree of crosslinking, ultimately affecting the wet strength performance and stability of the product.

[0003] Another prominent problem with existing processes is the high formaldehyde residue and poor product storage stability. Traditional methods involve a large, one-time addition of formaldehyde, which can easily cause localized overheating and violent reactions. This not only increases the residue of unreacted formaldehyde but may also lead to excessive cross-linking and gel formation, resulting in product spoilage. Furthermore, the lack of effective online monitoring methods makes it difficult for operators to adjust reaction parameters in a timely manner, leading to poor product quality consistency and significant batch-to-batch variations. In addition, existing formaldehyde capture methods typically use a single component, resulting in limited capture efficiency and failing to meet increasingly stringent environmental protection requirements. Summary of the Invention

[0004] In view of the problems existing in the preparation process of ethanolamine modified wet strength agents, this invention is proposed.

[0005] Therefore, the problem to be solved by the present invention is the technical problems of crude reaction control, unstable product quality and high formaldehyde residue in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, embodiments of the present invention provide a preparation process for an ethanolamine-modified wet strength agent, comprising the following steps: reacting diethylenetriamine with ethylene oxide via an addition reaction to obtain an ethanolamine intermediate; adding formaldehyde solution to the ethanolamine intermediate and performing a pre-condensation reaction under acidic conditions using a pH gradient control to obtain a pre-condensation product; adding a catalyst and a synergist to the pre-condensation product, and replenishing formaldehyde solution in batches according to viscosity detection during the reaction, wherein the amount of formaldehyde solution replenished is 5-12% of the solid content of the pre-condensation product to obtain a crosslinked product; and adding a formaldehyde scavenger to the crosslinked product for stabilization treatment to obtain the ethanolamine-modified wet strength agent.

[0007] As a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the step of pH gradient control includes: the initial pH value of the pre-condensation reaction is 4.8-5.0; after adding formaldehyde solution to the ethanolamine intermediate and reacting for 1 hour, the pH value is adjusted to 3.8-4.2; after adjusting the pH value for 0.5 hours, the pH value is adjusted to 4.5-4.8; wherein the concentration of the formaldehyde solution is 35-42%.

[0008] The beneficial effects of this preferred technical solution are as follows: the three-stage pH gradient control technology achieves precise regulation of the pre-condensation reaction. The weakly acidic environment in the initial stage (pH 4.8-5.0) is conducive to the initial combination of formaldehyde and amine groups; the pH value is reduced to 3.8-4.2 in the middle stage, and the cross-linking reaction is promoted in depth under stronger acidic conditions; the pH value is adjusted back to 4.5-4.8 in the final stage to avoid the adverse effects of excessive acidification on product stability.

[0009] As a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the catalyst is a composite catalyst of zinc chloride and aluminum sulfate with a molar ratio of 1:0.6-1.4; the synergist is a composite of boric acid and sodium citrate with a mass ratio of 1:0.5-0.7.

[0010] As a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the step of adding formaldehyde solution in batches includes: when the viscosity of the system reaches 120-249 mPa·s, the first addition is made, and the amount added is 2-4% of the solid content of the precondensation product; when the viscosity reaches 250-349 mPa·s, the second addition is made, and the amount added is 1.5-4% of the solid content of the precondensation product; when the viscosity reaches 350-450 mPa·s, the third addition is made, and the amount added is 1.5-4% of the solid content of the precondensation product.

[0011] The beneficial effects of this preferred technical solution are: by monitoring the viscosity change of the system in real time, quantitative replenishment is carried out within a specific viscosity range, avoiding local overheating and violent reactions caused by traditional one-time feeding.

[0012] As a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the formaldehyde scavenger is a complex of urea, melamine and sodium bicarbonate in a mass ratio of 3:1:0.5.

[0013] As a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the addition reaction is carried out by programmed temperature control, specifically including: the initial temperature is 50-60℃, the reaction time is 1 hour, and the stirring speed is 150-180 rpm; the initial temperature is raised to 65-70℃, the reaction time is 2 hours, and the stirring speed is adjusted to 200-230 rpm.

[0014] In a preferred embodiment of the preparation process of the ethanolamine-modified wet strength agent of the present invention, the molar ratio of diethylenetriamine to ethylene oxide is 1:2.5-3.5.

[0015] In a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the concentration of the formaldehyde solution in the batch addition of formaldehyde solution is 25-35%.

[0016] As a preferred embodiment of the preparation process of the ethanolamine modified wet strength agent of the present invention, the total amount of the formaldehyde scavenger is 6-10% of the solid content of the crosslinking product, the stabilization treatment temperature is 40-55℃, and the treatment time is 1-2 hours.

[0017] In a preferred embodiment of the preparation process of the ethanolamine-modified wet strength agent of the present invention, the total amount of the catalyst is 0.2-0.4% of the mass of the ethanolamine-modified wet strength agent; and the amount of the synergist is 1.0-1.8% of the mass of the ethanolamine-modified wet strength agent.

[0018] The beneficial effects of this invention are: By employing a synergistic technology of pH gradient control and viscosity monitoring for batch formaldehyde replenishment, precise control of the preparation process of ethanolamine-modified wet-strength agents was achieved. The three-stage pH adjustment technology allowed the pre-condensation reaction to proceed in an orderly manner under different acidic environments, resulting in a pre-condensation product with a relatively uniform molecular weight distribution. The batch replenishment strategy based on online viscosity monitoring effectively avoided localized overheating and violent reactions caused by traditional single-stage feeding, preventing gelation due to excessive cross-linking. The synergistic effect of the composite catalyst system (zinc chloride-aluminum sulfate) and the synergist (boric acid-sodium citrate) improved reaction efficiency and shortened reaction time. These process improvements made the reaction process more stable and controllable, reducing batch-to-batch quality variations.

[0019] This invention, through process optimization and the use of a composite formaldehyde scavenging agent system (urea-melamine-sodium bicarbonate), controls the formaldehyde residue in the product to a low level, meeting increasingly stringent environmental protection requirements. The product exhibits good storage stability and flowability, facilitating transportation and use. In paper wet strength applications, this wet strength agent provides stable wet strength effects, improving the wet properties of paper. Compared to traditional preparation processes, the process of this invention has better industrial adaptability, which is beneficial for quality control and cost control in large-scale production. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The diagram shows the pH gradient control time curve of a preparation process for an ethanolamine-modified wet strength agent according to an embodiment of the present invention.

[0022] Figure 2 This is a viscosity monitoring batch replenishment timing diagram of a preparation process for an ethanolamine-modified wet strength agent provided in one embodiment of the present invention. Detailed Implementation

[0023] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0024] Reference Figures 1-2 This invention provides a preparation process for an ethanolamine-modified wet strength agent, comprising the following steps: S1. Diethylenetriamine is reacted with ethylene oxide by addition reaction to obtain an ethanol amination intermediate; S2. Add formaldehyde solution to the ethanol amination intermediate and carry out a pre-condensation reaction under acidic conditions using a pH gradient to obtain the pre-condensation product. S3. Add a catalyst and a synergist to the pre-condensation product. During the reaction, add formaldehyde solution in batches according to the viscosity test. The amount of formaldehyde solution added is 5-12% of the solid content of the pre-condensation product to obtain the cross-linked product. S4. Add a formaldehyde scavenger to the crosslinking product for stabilization treatment to obtain the ethanolamine modified wet strength agent.

[0025] In one embodiment of the present invention, in step S1, the addition reaction is controlled by programmed temperature rise, specifically including: the initial temperature is 50-60°C, the reaction time is 1 hour, and the stirring speed is 150-180 rpm; the initial temperature is raised to 65-70°C, the reaction time is 2 hours, and the stirring speed is adjusted to 200-230 rpm.

[0026] In one embodiment of the present invention, in step S1, the molar ratio of diethylenetriamine to ethylene oxide is 1:2.5-3.5.

[0027] In one embodiment of the present invention, step S2, the pH gradient control step includes: the initial pH value of the pre-condensation reaction is 4.8-5.0; after adding formaldehyde solution to the ethanol amination intermediate and reacting for 1 hour, the pH value is adjusted to 3.8-4.2; after adjusting the pH value for 0.5 hours, the pH value is adjusted to 4.5-4.8, wherein the concentration of formaldehyde solution is 35-42%.

[0028] In one embodiment of the present invention, in step S3, the catalyst is a composite catalyst of zinc chloride and aluminum sulfate, with a molar ratio of 1:0.6-1.4; the synergist is a composite of boric acid and sodium citrate, with a mass ratio of 1:0.5-0.7. The total amount of catalyst is 0.2-0.4% of the mass of the ethanolamine-modified wet-strength agent; the amount of synergist is 1.0-1.8% of the mass of the ethanolamine-modified wet-strength agent.

[0029] In one embodiment of the present invention, step S3, the step of adding formaldehyde solution in batches, includes: a first addition when the system viscosity reaches 120-249 mPa·s, the addition amount being 2-4% of the solid content of the precondensation product; a second addition when the viscosity reaches 250-349 mPa·s, the addition amount being 1.5-4% of the solid content of the precondensation product; and a third addition when the viscosity reaches 350-450 mPa·s, the addition amount being 1.5-4% of the solid content of the precondensation product.

[0030] In one embodiment of the present invention, in step S3, the concentration of formaldehyde solution in the batch replenishment of formaldehyde solution is 25-35%.

[0031] In one embodiment of the present invention, in step S4, the formaldehyde scavenger is a complex of urea, melamine and sodium bicarbonate in a mass ratio of 3:1:0.5.

[0032] In one embodiment of the present invention, in step S4, the total amount of formaldehyde scavenger is 6-10% of the solid content of the crosslinking product, the stabilization treatment temperature is 40-55°C, and the treatment time is 1-2 hours.

[0033] For clarity, the following examples will be used to provide a detailed description.

[0034] Example 1 A preparation process for an ethanolamine-modified wet strength agent includes the following steps: S1. Diethylenetriamine is reacted with ethylene oxide by addition reaction to obtain an ethanol amination intermediate; In step S1, the addition reaction is controlled by a programmed temperature increase, specifically: the initial temperature is 50°C, the reaction time is 1 hour, and the stirring speed is 180 rpm; the initial temperature is then increased to 65°C, the reaction time is 2 hours, and the stirring speed is adjusted to 230 rpm. The molar ratio of diethylenetriamine to ethylene oxide is 1:2.5.

[0035] S2. Add formaldehyde solution to the ethanol amination intermediate and carry out a pre-condensation reaction under acidic conditions using a pH gradient to obtain the pre-condensation product. In step S2, the pH gradient control step includes: the initial pH value of the pre-condensation reaction is 4.8; after adding formaldehyde solution to the ethanol amination intermediate and reacting for 1 hour, the pH value is adjusted to 3.8; after 0.5 hours of pH adjustment, the pH value is adjusted to 4.5, wherein the concentration of formaldehyde solution is 35%.

[0036] S3. Add a catalyst and a synergist to the pre-condensation product, and add formaldehyde solution in batches according to the viscosity during the reaction to obtain the cross-linked product; In step S3, the catalyst is a composite catalyst of zinc chloride and aluminum sulfate with a molar ratio of 1:0.6; the synergist is a composite of boric acid and sodium citrate with a mass ratio of 1:0.5. The total amount of catalyst used is 0.2% of the mass of the ethanolamine-modified wet strength agent; the amount of synergist used is 1.0% of the mass of the ethanolamine-modified wet strength agent.

[0037] The steps for adding formaldehyde solution in batches include: the first addition is made when the system viscosity reaches 120 mPa·s, and the addition amount is 2% of the solid content of the precondensation product; the second addition is made when the viscosity reaches 250 mPa·s, and the addition amount is 1.5% of the solid content of the precondensation product; the third addition is made when the viscosity reaches 350 mPa·s, and the addition amount is 1.5% of the solid content of the precondensation product.

[0038] In the batch addition of formaldehyde solution, the concentration of formaldehyde solution is 25%.

[0039] S4. Add a formaldehyde scavenger to the crosslinking product for stabilization treatment to obtain the ethanolamine modified wet strength agent; In step S4, the formaldehyde scavenger is a complex of urea, melamine and sodium bicarbonate in a mass ratio of 3:1:0.5.

[0040] The total amount of formaldehyde scavenger used was 6% of the solid content of the crosslinking product, the stabilization treatment temperature was 40℃, and the treatment time was 1 hour.

[0041] Example 2 A preparation process for an ethanolamine-modified wet strength agent includes the following steps: S1. Diethylenetriamine is reacted with ethylene oxide by addition reaction to obtain an ethanol amination intermediate; In step S1, the addition reaction is controlled by a programmed temperature increase, specifically including: an initial temperature of 55°C, a reaction time of 1 hour, and a stirring speed of 160 rpm; then raising the initial temperature to 65°C, a reaction time of 2 hours, and adjusting the stirring speed to 210 rpm. The molar ratio of diethylenetriamine to ethylene oxide is 1:3.

[0042] S2. Add formaldehyde solution to the ethanol amination intermediate and carry out a pre-condensation reaction under acidic conditions using a pH gradient to obtain the pre-condensation product. In step S2, the pH gradient control step includes: the initial pH value of the pre-condensation reaction is 4.9; after adding formaldehyde solution to the ethanol amination intermediate and reacting for 1 hour, the pH value is adjusted to 4.0; after 0.5 hours of pH adjustment, the pH value is adjusted to 4.6, wherein the concentration of formaldehyde solution is 40%.

[0043] S3. Add a catalyst and a synergist to the pre-condensation product, and add formaldehyde solution in batches according to the viscosity during the reaction to obtain the cross-linked product; In step S3, the catalyst is a composite catalyst of zinc chloride and aluminum sulfate with a molar ratio of 1:1; the synergist is a composite of boric acid and sodium citrate with a mass ratio of 1:0.6. The total amount of catalyst used is 0.3% of the mass of the ethanolamine-modified wet strength agent; the amount of synergist used is 1.5% of the mass of the ethanolamine-modified wet strength agent.

[0044] The steps for adding formaldehyde solution in batches include: the first addition is made when the system viscosity reaches 200 mPa·s, and the addition amount is 3% of the solid content of the precondensation product; the second addition is made when the viscosity reaches 300 mPa·s, and the addition amount is 3% of the solid content of the precondensation product; the third addition is made when the viscosity reaches 400 mPa·s, and the addition amount is 2% of the solid content of the precondensation product.

[0045] In the batch addition of formaldehyde solution, the concentration of formaldehyde solution is 30%.

[0046] S4. Add a formaldehyde scavenger to the crosslinking product for stabilization treatment to obtain the ethanolamine modified wet strength agent; In step S4, the formaldehyde scavenger is a complex of urea, melamine and sodium bicarbonate in a mass ratio of 3:1:0.5.

[0047] The total amount of formaldehyde scavenger used was 8% of the solid content of the crosslinking product, the stabilization treatment temperature was 50℃, and the treatment time was 1 hour.

[0048] Example 3 A preparation process for an ethanolamine-modified wet strength agent includes the following steps: S1. Diethylenetriamine is reacted with ethylene oxide by addition reaction to obtain an ethanol amination intermediate; In step S1, the addition reaction is controlled by a programmed temperature increase, specifically including: an initial temperature of 60°C, a reaction time of 1 hour, and a stirring speed of 150 rpm; then raising the initial temperature to 70°C, a reaction time of 2 hours, and adjusting the stirring speed to 200 rpm. The molar ratio of diethylenetriamine to ethylene oxide is 1:3.5.

[0049] S2. Add formaldehyde solution to the ethanol amination intermediate and carry out a pre-condensation reaction under acidic conditions using a pH gradient to obtain the pre-condensation product. In step S2, the pH gradient control step includes: the initial pH value of the pre-condensation reaction is 5.0; after adding formaldehyde solution to the ethanol amination intermediate and reacting for 1 hour, the pH value is adjusted to 4.2; after 0.5 hours of pH adjustment, the pH value is adjusted to 4.8, wherein the concentration of formaldehyde solution is 42%.

[0050] S3. Add a catalyst and a synergist to the pre-condensation product, and add formaldehyde solution in batches according to the viscosity during the reaction to obtain the cross-linked product; In step S3, the catalyst is a composite catalyst of zinc chloride and aluminum sulfate with a molar ratio of 1:1.4; the synergist is a composite of boric acid and sodium citrate with a mass ratio of 1:0.7. The total amount of catalyst used is 0.4% of the mass of the ethanolamine-modified wet strength agent; the amount of synergist used is 1.8% of the mass of the ethanolamine-modified wet strength agent.

[0051] The steps for adding formaldehyde solution in batches include: the first addition is made when the system viscosity reaches 249 mPa·s, and the addition amount is 4% of the solid content of the precondensation product; the second addition is made when the viscosity reaches 349 mPa·s, and the addition amount is 4% of the solid content of the precondensation product; the third addition is made when the viscosity reaches 450 mPa·s, and the addition amount is 4% of the solid content of the precondensation product.

[0052] In the batch addition of formaldehyde solution, the concentration of formaldehyde solution is 35%.

[0053] S4. Add a formaldehyde scavenger to the crosslinking product for stabilization treatment to obtain the ethanolamine modified wet strength agent; In step S4, the formaldehyde scavenger is a complex of urea, melamine and sodium bicarbonate in a mass ratio of 3:1:0.5.

[0054] The total amount of formaldehyde scavenger used was 10% of the solid content of the crosslinking product, the stabilization treatment temperature was 55℃, and the treatment time was 2 hours.

[0055] Comparative Example 1 Comparative Example 1 is a step without pH gradient control, using the same raw material ratio and reaction conditions as Example 2, but without pH gradient control in step S2, the pH value is fixed at 4.2 for the pre-condensation reaction. The other steps are exactly the same as in Example 2.

[0056] Specific procedures: Add 40% formaldehyde solution to the ethanol amination intermediate, adjust and maintain the pH of the system at 4.2, and react for 1.5 hours to obtain the pre-condensation product. Subsequent steps S3 and S4 are the same as in Example 2.

[0057] Comparative Example 2 Comparative Example 2 involved a step of batch addition without viscosity monitoring, using the same raw material ratios and reaction conditions as Example 2. However, in step S3, instead of employing the batch addition technique with viscosity monitoring, formaldehyde solution (8%, 30% concentration) was added to the pre-condensation product all at once. Other conditions remained the same as in Example 2.

[0058] Specific procedure: After adding the catalyst and synergist to the pre-condensation product, immediately add a 30% formaldehyde solution equivalent to 8% of the solid content of the pre-condensation product in one go, and stir the reaction until the viscosity reaches the predetermined range.

[0059] Comparative Example 3 Comparative Example 3 used a single catalyst and employed the same raw material ratios and reaction conditions as Example 2. However, in step S3, only zinc chloride was used as the catalyst; the aluminum sulfate composite catalyst and the boric acid-sodium citrate synergist were not used. The catalyst dosage was adjusted to 0.3% of the mass of the ethanolamine-modified wet-strength agent.

[0060] Specific procedures: Only zinc chloride catalyst was added to the pre-condensation product, and formaldehyde was added in batches according to the same viscosity monitoring method as in Example 2, while keeping other conditions the same.

[0061] Table 1: Comparison of Experimental Processes for the Preparation of Ethanolamine-Modified Wet Strength Agents

[0062] The reaction time was measured from the moment the catalyst was added to the pre-condensation product until the system viscosity reached a stable state (viscosity change less than 5% over 30 consecutive minutes). The reaction time in Example 2 was only 3.2 hours, significantly shorter than the three comparative examples. This was due to the highly efficient catalytic effect of the composite catalyst system; the synergistic effect of zinc chloride and aluminum sulfate increased the reaction rate between formaldehyde and amines, while the boric acid-sodium citrate synergist further optimized the reaction environment. In Comparative Example 1, the lack of pH gradient control resulted in uneven distribution of active sites in the pre-condensation product, affecting the efficiency of subsequent cross-linking reactions. While the initial reaction in Comparative Example 2 with a single formaldehyde addition was vigorous, it easily formed localized gels, hindering uniform cross-linking and thus prolonging the overall reaction time. Comparative Example 3, using a single catalyst, lacked a synergistic effect, resulting in relatively low catalytic efficiency and requiring a longer time to achieve the target degree of cross-linking.

[0063] The product viscosity was measured using an NDJ-8S digital viscometer at a constant temperature of 25°C, with a rotor speed of 60 rpm and a measurement time of 30 seconds. The viscosity of the product in Example 2 was 485 mPa·s, within the ideal application range. By quantitatively adding formaldehyde at specific viscosity nodes (200, 300, 400), the cross-linking reaction process was effectively controlled, avoiding a sharp increase in viscosity due to excessive cross-linking. The viscosity of Comparative Example 1 was slightly higher, mainly because improper pH control affected the uniformity of the cross-linked structure. Comparative Example 2 showed viscosity anomalies, a typical consequence of single-use formaldehyde feeding, with localized excessive cross-linking forming a high-molecular-weight gel structure. The viscosity of Comparative Example 3 was relatively low, reflecting insufficient cross-linking reaction under a single catalyst system, which may affect the final wet strength effect.

[0064] The pH value of the product was measured directly at room temperature using a PHS-3C precision pH meter, with each sample tested three times and the average value taken. The final product pH value of Example 2 was 7.1, close to neutral, which is beneficial for the application performance and storage stability of the wet strength agent. The final stage of the pH gradient control technology adjusted the reaction system to 4.6, effectively neutralizing the acidic byproducts generated during the reaction. Combined with the buffering effect of sodium bicarbonate in the formaldehyde scavenger, the ideal product pH value was finally obtained. The pH value of Comparative Example 1 was too low (6.8), which was because the acidic substances generated during the reaction under fixed acidic conditions were not effectively neutralized. The pH values ​​of Comparative Example 2 and Comparative Example 3 were 7.0 and 6.9, respectively. Although relatively reasonable, they were not as precise as the pH control in Example 2, and may affect the product stability during long-term storage.

[0065] The wet strength retention rate was determined according to the national standard GB / T 12914-2008. The filter paper treated with the wet strength agent was immersed in distilled water for 2 minutes, and its tensile strength was measured using an electronic tensile testing machine. The ratio of this tensile strength to the dry strength was the wet strength retention rate. Example 2 achieved an excellent wet strength retention rate of 38.5%, mainly due to the uniform cross-linking structure and appropriate cross-linking density. pH gradient control ensured good reactivity of the pre-condensation product, and viscosity monitoring and batch replenishment avoided over-cross-linking, forming a network structure that provided sufficient wet strength without excessive rigidity. Comparative Example 1 showed a wet strength retention rate of 32.1%, reflecting the negative impact of improper pH control on the cross-linking effect. Comparative Example 2 performed the worst; the uneven cross-linking caused by the single formaldehyde addition severely affected the wet strength performance. The results of Comparative Example 3 indicate that although a single catalyst system can achieve basic cross-linking, its effect is not as good as that of a composite catalyst system.

[0066] Storage stability was evaluated by observing changes in viscosity, precipitation, and pH drift of the product under sealed conditions at room temperature over a long period, recording the longest period the product remained stable. Example 2 exhibited excellent storage stability (12 months), which is closely related to its optimized cross-linking structure and effective formaldehyde capture. The composite formaldehyde capture system (urea-melamine-sodium bicarbonate) effectively reduced the free formaldehyde content through multiple mechanisms, reducing the possibility of further cross-linking reactions during storage. Comparative Example 1 showed stability of 8 months; product inhomogeneity caused by improper pH control was the main factor affecting long-term stability. Comparative Example 2 showed the worst stability (6 months); the gel structure formed by excessive cross-linking was prone to further structural changes during storage. Although Comparative Example 3 had a relatively low degree of cross-linking, the product stability of the single catalyst system was still inferior to that of the composite system, with a storage stability of 9 months.

[0067] The molecular weight distribution index (PDI) was determined by gel permeation chromatography (GPC), using polyethylene glycol as a standard sample for calibration. The PDI value is the ratio of weight-average molecular weight to number-average molecular weight; a smaller value indicates a more uniform molecular weight distribution. Example 2 showed a PDI value of 2.1, indicating a relatively uniform molecular weight distribution, directly reflecting the advantages of pH gradient control and viscosity monitoring in batch addition techniques. Staged pH adjustment ensured the orderly conduction of the pre-condensation reaction, avoiding excessive broadening of the molecular weight distribution, while batch formaldehyde addition further ensured the uniformity of the crosslinking reaction. Comparative Example 1 had a PDI value of 3.2; the reaction under fixed pH conditions lacked fine-tuning, resulting in a wider molecular weight distribution. Comparative Example 2 was the most severe (PDI = 4.1), where the non-uniformity caused by a single formaldehyde addition was directly reflected in the severe broadening of the molecular weight distribution. Comparative Example 3 had a PDI value of 2.8, which, while better than Comparative Examples 1 and 2, was still not as precisely controlled as the composite system in Example 2.

[0068] Gelation was assessed through visual observation and changes in stirring resistance during the reaction process, with changes in the system's fluidity recorded. In Example 2, no gelation occurred throughout the entire reaction; the system maintained good fluidity, demonstrating the controllability and reliability of the technical solution. The core advantage of the viscosity monitoring and batch addition technology lies in avoiding rapid gelation caused by excessively high local formaldehyde concentrations, ensuring the reaction proceeds within a controllable range. Comparative Examples 1 and 3 both exhibited slight gelation, which, while not severe, reflects insufficient process control. Comparative Example 2 showed significant gelation, a typical consequence of single-use formaldehyde addition. The rapid reaction of locally high-concentration formaldehyde with amine groups formed difficult-to-disperse gel particles, affecting product quality and potentially causing production accidents. This fully illustrates the necessity and importance of the batch addition technology.

[0069] In summary, by employing a synergistic technology of pH gradient control and viscosity monitoring-based batch formaldehyde addition, precise control of the preparation process of ethanolamine-modified wet-strength agents was achieved. The three-stage pH adjustment technology allowed the pre-condensation reaction to proceed in an orderly manner under different acidic environments, resulting in a pre-condensation product with a relatively uniform molecular weight distribution. The batch addition strategy based on online viscosity monitoring effectively avoided localized overheating and violent reactions caused by traditional single-stage feeding, preventing gelation due to excessive cross-linking. The synergistic effect of the composite catalyst system (zinc chloride-aluminum sulfate) and the synergist (boric acid-sodium citrate) improved reaction efficiency and shortened reaction time. These process improvements made the reaction process more stable and controllable, reducing batch-to-batch quality variations.

[0070] This invention, through process optimization and the use of a composite formaldehyde scavenging agent system (urea-melamine-sodium bicarbonate), controls the formaldehyde residue in the product to a low level, meeting increasingly stringent environmental protection requirements. The product exhibits good storage stability and flowability, facilitating transportation and use. In paper wet strength applications, this wet strength agent provides stable wet strength effects, improving the wet properties of paper. Compared to traditional preparation processes, the process of this invention has better industrial adaptability, which is beneficial for quality control and cost control in large-scale production.

[0071] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A preparation process for an ethanolamine-modified wet strength agent, characterized in that: Includes the following steps: Diethylenetriamine was reacted with ethylene oxide by an addition reaction to obtain an ethanolamine intermediate; Formaldehyde solution was added to the ethanol amination intermediate, and a pre-condensation reaction was carried out under acidic conditions with pH gradient control to obtain the pre-condensation product. A catalyst and a synergist are added to the pre-condensation product. During the reaction, formaldehyde solution is added in batches according to the viscosity test. The amount of formaldehyde solution added is 5-12% of the solid content of the pre-condensation product to obtain the cross-linked product. A formaldehyde scavenger was added to the crosslinking product for stabilization treatment to obtain the ethanolamine-modified wet strength agent; The pH gradient control steps include: The initial pH value for the pre-condensation reaction is 4.8-5.0; After adding formaldehyde solution to the ethanol amination intermediate and reacting for 1 hour, the pH value is adjusted to 3.8-4.2; 0.5 hours after pH adjustment, adjust the pH to 4.5-4.8; The concentration of the formaldehyde solution is 35-42%. The step of adding formaldehyde solution in batches includes: The first addition should be made when the viscosity of the system reaches 120-249 mPa·s, and the amount added should be 2-4% of the solid content of the precondensation product. When the viscosity reaches 250-349 mPa·s, a second addition is made, with the amount added being 1.5-4% of the solid content of the precondensation product. When the viscosity reaches 350-450 mPa·s, a third addition is made, with the amount added being 1.5-4% of the solid content of the precondensation product. The molar ratio of diethylenetriamine to ethylene oxide is 1:2.5-3.

5.

2. The preparation process of the ethanolamine-modified wet strength agent as described in claim 1, characterized in that: The catalyst is a composite catalyst of zinc chloride and aluminum sulfate, with a molar ratio of 1:0.6-1.4; The synergist is a complex of boric acid and sodium citrate, with a mass ratio of 1:0.5-0.

7.

3. The preparation process of the ethanolamine-modified wet strength agent as described in claim 2, characterized in that: The formaldehyde scavenger is a complex of urea, melamine, and sodium bicarbonate in a mass ratio of 3:1:0.

5.

4. The preparation process of the ethanolamine-modified wet strength agent as described in claim 3, characterized in that: The addition reaction is controlled by a programmed temperature rise, specifically including: The initial temperature is 50-60℃, the reaction time is 1 hour, and the stirring speed is 150-180 rpm. Raise the initial temperature to 65-70℃, react for 2 hours, and adjust the stirring speed to 200-230 rpm.

5. The preparation process of the ethanolamine-modified wet strength agent as described in claim 4, characterized in that: In the batch replenishment of formaldehyde solution, the concentration of formaldehyde solution is 25-35%.

6. The preparation process of the ethanolamine-modified wet strength agent as described in claim 5, characterized in that: The total amount of the formaldehyde scavenger is 6-10% of the solid content of the crosslinking product, the stabilization treatment temperature is 40-55℃, and the treatment time is 1-2 hours.

7. The preparation process of the ethanolamine-modified wet strength agent as described in claim 6, characterized in that: The total amount of catalyst used is 0.2-0.4% of the mass of the ethanolamine-modified wet strength agent; the amount of synergist used is 1.0-1.8% of the mass of the ethanolamine-modified wet strength agent.

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