A high charge density starch grafted phenylpropanoid surface sizing agent, its preparation method and application

Abstract

This invention discloses a high charge density starch-grafted styrene-acrylic surface sizing agent, its preparation method, and its application. The sizing agent is made from the following raw materials in parts by weight: 5-12 parts starch, 1.5-2 parts liquid alkali, 1.5-3 parts etherifying agent, 0.5-1.5 parts dispersant, 4-10 parts pH adjuster, 1.5-2.5 parts initiator, 10-20 parts vinyl monomer, and 40-60 parts deionized water. The preparation method includes: first preparing a cationic modified starch solution, then grafting and copolymerizing it with styrene and acrylate monomers, followed by dropwise polymerization and a heat-preserving reaction to obtain a brown, semi-transparent nanoemulsion. The sizing agent of this invention has a charge density as high as 300-550 μeq / g, a particle size of 50-90 nm, and a solid content of 29%-31%. When used for sizing paper surfaces, it can effectively neutralize anionic waste, enhance electrostatic adsorption with fibers, significantly improve paper surface strength and water resistance, has a fast curing speed, is environmentally friendly, and is suitable for various paper products such as packaging paper and cultural paper.

Description

Technical Field

[0001] This invention belongs to the field of papermaking chemicals technology, specifically relating to a high charge density starch-grafted styrene-acrylic surface sizing agent, its preparation method, and its application. Background Technology

[0002] The paper industry is vital to people's livelihoods and the economy, closely linked to social development, and possesses sustainable development and naturally green attributes. In recent years, due to rising costs of raw materials, energy, and labor, my country's paper industry has faced numerous challenges, with related enterprises experiencing pressures such as shrinking demand, fluctuating supply, and declining economic benefits. After multiple recycling cycles, the fibers in waste paper become shorter and more keratinized, and the residual inorganic salts in the pulp increase. These factors collectively lead to a decline in the quality of recycled paper, manifested in reduced paper strength and water resistance.

[0003] Natural starch has long been widely used in the paper industry due to its advantages such as wide availability, renewability, biodegradability, and low price. However, native starch has drawbacks such as regular molecular structure, low reactivity, high film brittleness, and poor water resistance, which limit its application in high-performance sizing fields. To overcome these problems, researchers have recently used chemical modification methods to functionalize starch, among which graft copolymerization is an effective strategy. By introducing monomers with specific functions (such as styrene and acrylates) onto the starch backbone, its film-forming properties, adhesion, and water resistance can be significantly improved.

[0004] Meanwhile, in high-speed paper machine operation and high-filler paper systems, the increased negative charge density on the fiber surface weakens the electrostatic adsorption between traditional cationic starch and fibers, affecting sizing efficiency. Therefore, developing starch-based sizing agents with high cationic charge density has become an important direction for improving sizing performance. By combining the high charge characteristics with the excellent film-forming properties of styrene-acrylate copolymers, a novel starch-grafted styrene-acrylate surface sizing agent with both strong adsorption capacity and excellent film-forming properties can be constructed. This not only effectively improves the surface strength and liquid resistance of paper but also reduces the amount of chemicals used and lowers environmental pollution, aligning with the current trend of green and low-carbon transformation in the paper industry. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high charge density starch-grafted styrene-acrylic surface sizing agent, its preparation method and application.

[0006] To solve the above-mentioned technical problems, the surface sizing agent of the present invention adopts the following technical solution: the raw materials and weight components of the surface sizing agent are: 5-12 parts starch, 1.5-2 parts liquid alkali, 1.5-3 parts etherifying agent, 0.5-1.5 parts dispersant, 4-10 parts pH adjuster, 1.5-2.5 parts initiator, 10-20 parts vinyl monomer, and 40-60 parts deionized water; the surface sizing agent has a charge density of 300-550 μeq / g, a pH of 2.0-4.0, a solid content of 29.0%-31.0%, a viscosity of 20-50 mPa·s at 25℃, and a particle size of 50-90 nm.

[0007] Furthermore, in the above-mentioned surface sizing agent technical solution, the starch is one of acetate starch, tapioca starch, or oxidized starch.

[0008] Furthermore, in the above-mentioned surface sizing agent technical solution, the vinyl monomer is a mixture of styrene, butyl acrylate, tert-butyl acrylate, methyl methacrylate, acrylonitrile, acrylic acid and methacrylic acid.

[0009] Furthermore, in the above-mentioned surface sizing agent technical solution, the etherifying agent is one or both of 2,3-epoxypropyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride.

[0010] Furthermore, in the above-mentioned surface sizing agent technical solution, the dispersant is one or more of sodium lignosulfonate, sodium dinaphthylmethane disulfonate, and sodium hexametaphosphate.

[0011] Furthermore, in the above-mentioned surface sizing agent technical solution, the pH adjuster is acetic acid or dilute sulfuric acid, and aluminum sulfate solution may be added as a crosslinking aid; the initiator is a redox system composed of hydrogen peroxide and ferrous sulfate.

[0012] The surface sizing agent preparation method of the present invention adopts the following technical solution: The surface sizing agent preparation method includes: Step (1) Preparation of modified starch solution: Dissolve starch in part of deionized water, heat to 50-55℃, add liquid alkali; continue to heat to 65-68℃, keep warm for 30-50 minutes; then heat to 75-80℃, add etherifying agent, react at 82-85℃ for 2-3 hours; add part of pH adjuster to adjust pH to 4-6; add dispersant, heat to 85-90℃, keep warm for 30-50 minutes, to obtain modified starch solution; Step (2) Monomer preparation: Mix the vinyl monomers evenly to obtain a premixed monomer solution; Step (3) Polymerization reaction: Add the remaining pH adjuster and part of the initiator to the modified starch solution in sequence; then add the premixed monomer solution and the remaining initiator dropwise at 85-90℃, the monomer dropwise addition time is 1.5-2.5 hours, and the initiator dropwise addition time is 2-3 hours; after the dropwise addition is completed, keep the reaction at 88-92℃ for 2-2.5 hours; after the reaction is completed, cool down to below 50℃, add deionized water to adjust the solid content to 29%-31%, filter and discharge the material to obtain the product. Furthermore, in the above technical solution of the surface sizing agent preparation method, the part of the modified starch solution mentioned in step (3) is 1 / 2 to 3 / 4 of the total amount of modified starch solution.

[0013] Furthermore, in the above-mentioned method for preparing surface sizing agent, step (3) further includes adding aluminum sulfate solution.

[0014] Furthermore, in the above-mentioned surface sizing agent preparation method, the initiator in step (3) is a redox system composed of hydrogen peroxide and ferrous sulfate. The first addition is 20% of the total amount of ferrous sulfate aqueous solution and hydrogen peroxide aqueous solution, and the second addition is the remaining hydrogen peroxide aqueous solution added dropwise simultaneously with the premixed monomer solution.

[0015] The surface sizing agent prepared by the above technical solution is used in paper surface sizing. The amount of the surface sizing agent is 2.5 to 3.0 kg per ton of paper. After being mixed with gelatinized starch, it is coated on the paper surface and dried to obtain sized paper.

[0016] Compared with the prior art, the present invention has the following advantages and effects:

[0017] 1. High cationic charge density (300~550μeq / g) can effectively neutralize anionic waste (such as lignin sulfonate, pectin, etc.) on the paper surface, reduce interference with sizing agents, and improve sizing effect;

[0018] 2. Good film-forming properties and high film strength: The styrene-acrylic copolymer provides excellent film-forming properties and film strength, and works synergistically with high-charge starch to enhance the water resistance and mechanical strength of paper;

[0019] 3. It has strong bonding with fibers, enhances the cationicity of the sizing solution, makes it more inclined to adhere to the paper surface, reduces penetration into the paper interior, and helps improve the surface strength of the paper.

[0020] 4. The fast curing speed can partially offset the impact of paper machine process fluctuations on water resistance and shorten the production cycle.

[0021] 5. No additional small molecule emulsifiers are needed during the polymerization process, avoiding residues that could affect film-forming performance, making it environmentally friendly.

[0022] In summary, the high charge density starch-grafted styrene-acrylic surface sizing agent of this invention has a cationic charge density of 300–550 μeq / g, exhibiting good water resistance, film-forming properties, and strong fiber bonding when used for paper sizing, thus helping to improve paper surface strength. This invention overcomes the problems of low charge density, weak fiber bonding, and poor film-forming properties of ordinary cationic starch in the prior art, achieving a synergistic improvement in paper surface strength and water resistance. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] This invention provides a high charge density starch-grafted styrene-acrylic surface sizing agent, the raw materials and their weight components being:

[0025] Starch 5-12 parts, liquid alkali 1.5-2 parts, etherifying agent 1.5-3 parts, dispersant 0.5-1.5 parts, pH adjuster 4-10 parts, initiator 1.5-2.5 parts, vinyl monomer 10-20 parts, deionized water 40-60 parts.

[0026] In the above-mentioned raw materials, the starch is one of acetate starch, cassava starch, or oxidized starch. The etherifying agent is one or a mixture of two of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) and 2,3-epoxypropyltrimethylammonium chloride (GTA). The dispersant is one or a combination of sodium lignosulfonate, sodium dinaphthylmethanedisulfonate, and sodium hexametaphosphate.

[0027] The pH adjuster is acetic acid or dilute sulfuric acid; in addition, aluminum sulfate solution (30% concentration) can be added as a crosslinking aid or to help regulate the charge environment of the system.

[0028] The initiator is a redox system composed of hydrogen peroxide and ferrous sulfate, that is, the initiator is hydrogen peroxide, and ferrous sulfate is used as a catalyst.

[0029] The vinyl monomer is a mixture of styrene, butyl acrylate, tert-butyl acrylate, methyl methacrylate, acrylonitrile, acrylic acid, and methacrylic acid.

[0030] The method for preparing the surface sizing agent of the present invention includes:

[0031] Step (1) Preparation of modified starch solution: Dissolve starch in some water, heat to 50–55℃, add liquid alkali; continue to heat to 65–68℃, keep warm for 30–50 minutes; then heat to 75–80℃, add etherifying agent, react at 82–85℃ for 2–3 hours; then add some pH adjuster to adjust pH to 4–6; add dispersant, heat to 85–90℃, keep warm for 30–50 minutes, to obtain modified starch solution.

[0032] Step (2) Monomer preparation: Add the vinyl monomers into the preparation tank in proportion, stir and mix evenly to obtain a premixed monomer solution.

[0033] Step (3) Polymerization reaction: Add the remaining pH adjuster, aluminum sulfate solution (if used), all ferrous sulfate aqueous solution, and 20% of the total hydrogen peroxide aqueous solution to the modified starch solution in sequence. After keeping it warm for 5–15 minutes, simultaneously add the premixed monomer solution and the remaining hydrogen peroxide aqueous solution dropwise. Control the reaction temperature at 85–90℃, the monomer dropwise addition time is 1.5–2.5 hours, and the hydrogen peroxide dropwise addition time is 2–3 hours. After the dropwise addition is complete, continue to keep the reaction at 88–92℃ for 2–2.5 hours. After the reaction is completed, cool down to below 50℃, and finally add an appropriate amount of deionized water to adjust the solid content. Filter the product to obtain a brown semi-transparent nanoemulsion—a high charge density starch-grafted styrene-acrylic surface sizing agent.

[0034] The surface sizing agent has a charge requirement of 300–550 μeq / g, a pH of 2.0–4.0, a solid content of 29.0–31.0%, a viscosity of 20–50 mPa·s at 25°C, and a particle size of 50–90 nm.

[0035] All raw materials used in this invention are commercially available industrial products. Charge density was determined by colloidal titration; particle size was determined by laser particle size analyzer; viscosity was determined by rotational viscometer (25℃); Cobb value was determined according to GB / T 1540-2002.

[0036] The surface sizing agent prepared by this invention can be used in the surface sizing of packaging paper. The amount of the surface sizing agent is 2.5 to 3.0 kg per ton of paper. After being mixed with gelatinized starch, it is coated on the surface of the paper and dried to obtain sized paper.

[0037] The following are specific embodiments of the present invention.

[0038] Example 1

[0039] Step (1) Preparation of modified starch solution: Dissolve 85 g of oxidized starch in 400 g of water, heat to 50°C, add 20 g of liquid alkali; heat to 65°C and keep warm for 30 minutes; continue to heat to 80°C, add 15 g of CHPTAC, and react at 85°C for 3 hours; add acetic acid to adjust pH to 4–5; dissolve 7 g of sodium lignosulfonate in 15 g of water and add it, heat to 88°C and keep warm for 30 minutes.

[0040] Step (2) Monomer preparation: Mix 60 g styrene, 40 g butyl acrylate, 25 g methyl methacrylate, 10 g tert-butyl acrylate and 5 g acrylic acid, and stir well for later use.

[0041] Step (3) Polymerization reaction: Add 110 g aluminum sulfate solution, 0.016 g ferrous sulfate (dissolved in 10 g water) and 20% of the total amount of hydrogen peroxide solution (prepared from 22 g hydrogen peroxide + 40 g water), and keep warm for 5 minutes; then add monomer (1.5 hours) and the remaining hydrogen peroxide (2 hours) dropwise at 85–90℃; after the addition is complete, keep warm at 88–92℃ for 2.5 hours; cool down to below 50℃, and finally add an appropriate amount of deionized water to adjust the solid content, and filter out the material.

[0042] Example 2

[0043] Step (1) Preparation of modified starch solution: 100 g starch acetate + 400 g water → 17 g liquid alkali at 55℃ → keep warm at 66℃ for 30 min → 20 g GTA at 78℃ → react at 80℃ for 3 h → add some aluminum sulfate to adjust pH to 4–5 → add 3 g sodium lignosulfonate + 5 g sodium dinaphthylmethane disulfonate (dissolved in 15 g water) → keep warm at 85℃ for 50 min.

[0044] Step (2) Monomer preparation: 50 g styrene + 30 g butyl acrylate + 30 g tert-butyl acrylate + 6 g methacrylic acid, stir evenly and set aside.

[0045] Step (3) Polymerization reaction: Add the remaining aluminum sulfate (total 90 g), 0.015 g ferrous sulfate (dissolved in 10 g water), and 20% of hydrogen peroxide solution (24 g hydrogen peroxide + 40 g water). After 15 min, add monomer (2 h) and hydrogen peroxide (2.5 h) dropwise. Keep warm at 88–90℃ for 2.5 h, then cool down and discharge the material.

[0046] Example 3

[0047] Step (1) Preparation of modified starch solution: 125 g oxidized starch + 450 g water → 55℃, add 20 g liquid alkali → 65℃, keep warm for 30 min → heat up to 80℃, add 10 g CHPTAC + 20 g GTA → 83℃, react for 2.3 h → add some aluminum sulfate to adjust pH to 4–5 → add 9 g sodium dinaphthylmethane disulfonate (dissolved in 20 g water) → 88℃, keep warm for 30 min.

[0048] Step (2) Monomer preparation: 40 g styrene + 40 g butyl acrylate + 10 g methyl methacrylate + 4 g methacrylic acid + 30 g tert-butyl acrylate, stir well and set aside.

[0049] Step (3) Polymerization reaction: Add acetic acid, the remaining aluminum sulfate solution, 0.018 g ferrous sulfate (dissolved in 10 g water) and 20% of hydrogen peroxide solution (22 g hydrogen peroxide + 40 g water) → keep warm for 15 min → add monomer (2 h) and hydrogen peroxide (2.5 h) dropwise at 88–90℃ → after the addition is complete, keep warm at 90–92℃ for 2 h → cool down to below 50℃, and finally add an appropriate amount of deionized water to adjust the solid content, filter and discharge.

[0050] Example 4

[0051] Step (1) Preparation of modified starch solution: 95 g cassava starch + 440 g water → 53℃, add 21 g liquid alkali → 65℃, keep warm for 30 min → heat up to 80℃, add 26 g GTA → react at 80℃ for 2.5 h → add sulfuric acid to adjust pH to 5–6 → add 8 g sodium dinaphthylmethane disulfonate + 2 g sodium hexametaphosphate (dissolved in 20 g water) → 85℃, keep warm for 50 min.

[0052] Step (2) Monomer preparation: 40 g styrene + 35 g butyl acrylate + 35 g tert-butyl acrylate + 15 g methyl methacrylate + 3 g acrylic acid, stir well and set aside.

[0053] Step (3) Polymerization reaction: Add 90 g aluminum sulfate solution, 0.02 g ferrous sulfate (dissolved in 10 g water) and 20% of the total amount of hydrogen peroxide solution (25 g hydrogen peroxide + 40 g water) → keep warm for 10 min → add monomer (2.5 h) and hydrogen peroxide solution (3 h) dropwise at 88–90℃ → keep warm at 88–90℃ for 2 h after the addition is complete → cool down to below 50℃, and finally add an appropriate amount of deionized water to adjust the solid content, filter and discharge.

[0054] Comparative Test

[0055] The products obtained in Examples 1 to 4 were compared with commercially available samples (Comparative Examples 1, 2, and 3) in terms of performance. Test method: Unsized corrugated paper was cut into A4 sizes; the surface sizing agent was mixed with gelatinized starch (12%, gelatinized at 95°C for 10 min, then cooled to 65°C), with a sizing agent dosage of 3 kg / t paper and a starch dosage of 60 kg / t paper; the sizing was applied using a K202 coating machine via a linear bar, and the paper was dried at 120°C for 5 min; the Cobb 60s value was measured. The physical properties of the products and the Cobb values ​​after sizing are shown in the table below.

[0056] Sample Solids content (%) Viscosity (mPa-s) Particle size (nm) Charge density (μeq / g) Cobb 60 (g / m²) Example 1 29.78 25 71.2 430 39.5 Example 2 30.23 30 73.6 410 40.1 Example 3 29.89 31 72.5 370 39.7 Example 4 30.07 29 73.1 350 42.3 Comparative Example 1 30.12 32 80.2 70 47.5 Comparative Example 2 29.92 31 79.6 100 46.3 Comparative Example 3 30.15 34 82.1 55 45.7

[0057] All raw materials used in the embodiments of this invention are commercially available industrial products. Charge density was determined by colloidal titration; particle size was determined by laser particle size analyzer; viscosity was determined by rotational viscometer (25℃); Cobb value was determined according to GB / T 1540-2002.

[0058] As shown in Table 1, the surface sizing agent prepared in the embodiments of the present invention has a high charge density (350–430 μeq / g), small particle size (71–74 nm), and good emulsion stability. After being used for sizing paper surfaces, the Cobb value (39.5–42.3 g / m²) is significantly lower than that of commercially available comparative examples (45.7–47.5 g / m²), indicating superior water resistance. The high charge density effectively neutralizes anionic waste, enhances the adsorption of the sizing agent to fibers, reduces penetration, and thus improves the sizing effect.

[0059] In summary, the high charge density starch-grafted styrene-acrylic surface sizing agent of the present invention can neutralize anionic waste (i.e., negatively charged dissolved / colloidal impurities in the pulp, such as lignin sulfonates and pectin) on the paper surface, reducing interference with the sizing agent and improving the sizing effect. During the sizing process, it enhances the cationicity of the sizing solution, making it more inclined to adhere to the paper surface, reducing penetration into the paper interior, and helping to improve the surface strength of the paper.

[0060] Of course, the above description is only a specific embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes or modifications made to the structure, features and principles described in the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A high charge density starch-grafted styrene-acrylic surface sizing agent, characterized in that, The raw materials and weight components of this surface sizing agent are as follows: Starch 5-12 parts, liquid alkali 1.5-2 parts, etherifying agent 1.5-3 parts, dispersant 0.5-1.5 parts, pH adjuster 4-10 parts, initiator 1.5-2.5 parts, vinyl monomer 10-20 parts, deionized water 40-60 parts; The surface sizing agent has a charge density of 300–550 μeq / g, a pH of 2.0–4.0, a solid content of 29.0%–31.0%, a viscosity of 20–50 mPa·s at 25°C, and a particle size of 50–90 nm.

2. The high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 1, characterized in that, The starch is one of acetate starch, tapioca starch, or oxidized starch.

3. The high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 1, characterized in that, The vinyl monomer is a mixture of styrene, butyl acrylate, tert-butyl acrylate, methyl methacrylate, acrylonitrile, acrylic acid, and methacrylic acid.

4. The high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 1, characterized in that, The etherifying agent is one or both of 2,3-epoxypropyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride.

5. The high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 1, characterized in that, The dispersant is one or more of sodium lignosulfonate, sodium dinaphthylmethane disulfonate, and sodium hexametaphosphate.

6. The high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 1, characterized in that, The pH adjuster is acetic acid or dilute sulfuric acid, and aluminum sulfate solution may be added as a crosslinking aid; the initiator is a redox system composed of hydrogen peroxide and ferrous sulfate.

7. A high charge density starch-grafted styrene-acrylic surface sizing agent according to any one of claims 1-6, characterized in that, The method for preparing this surface sizing agent includes: Step (1) Preparation of modified starch solution: Dissolve starch in part of deionized water, heat to 50-55℃, add liquid alkali; continue to heat to 65-68℃, keep warm for 30-50 minutes; then heat to 75-80℃, add etherifying agent, react at 82-85℃ for 2-3 hours; add part of pH adjuster to adjust pH to 4-6; add dispersant, heat to 85-90℃, keep warm for 30-50 minutes, to obtain modified starch solution; Step (2) Monomer preparation: Mix the vinyl monomers evenly to obtain a premixed monomer solution; Step (3) Polymerization reaction: Add the remaining pH adjuster and part of the initiator to the modified starch solution in sequence; then add the premixed monomer solution and the remaining initiator dropwise at 85-90℃. The monomer dropwise addition time is 1.5-2.5 hours, and the initiator dropwise addition time is 2-3 hours. After the dropwise addition is completed, keep the temperature at 88-92℃ for 2-2.5 hours. After the reaction is completed, cool down to below 50℃, add deionized water to adjust the solid content to 29%-31%, filter and discharge the material to obtain the product.

8. The high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 7, characterized in that, Step (3) also includes adding aluminum sulfate solution.

9. A high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 7, characterized in that, The initiator mentioned in step (3) is a redox system composed of hydrogen peroxide and ferrous sulfate. The first addition is 20% of the total amount of ferrous sulfate aqueous solution and hydrogen peroxide aqueous solution. The second addition is the remaining hydrogen peroxide aqueous solution added dropwise simultaneously with the premixed monomer solution.

10. A high charge density starch-grafted styrene-acrylic surface sizing agent according to claim 7, characterized in that, This surface sizing agent is used in paper surface sizing. The dosage of the surface sizing agent is 2.5 to 3.0 kg per ton of paper. After being mixed with gelatinized starch, it is coated onto the paper surface and dried to obtain sized paper.