Fiber-reinforced copolymers, methods for their preparation and use

Abstract

The application discloses a fiber synergistic copolymer and a preparation method and application thereof, and belongs to the technical field of papermaking chemicals and high polymer materials. In view of the anion garbage interference caused by the deepening of white water closed circulation in the papermaking industry and the green compliance challenge brought by 'paper instead of plastic', the copolymer is designed in structure and function by using specific polycarboxylic acid and trace cationic monomer, and has excellent anti-interference ability and permeability. In the wet end pulp strengthening, the copolymer can surpass the strengthening effect of traditional high molecular weight additives by only needing a low amount of addition, and significantly improves the drainage and retention; in the surface sizing and paper pulp molding hot pressing process, the copolymer can greatly improve the rigidity and water resistance dimensional stability of products through a unique crosslinking mechanism. The scheme effectively solves the industry pain point of low strengthening efficiency in a complex environment, and the product does not contain organic fluorine, and completely meets the environmental protection and sustainable development needs of high-performance fiber-based materials.

Description

Technical Field

[0001] This invention belongs to the technical field of papermaking chemicals and polymer materials, specifically relating to fiber-enhancing copolymers and their preparation methods and applications. Background Technology

[0002] With the rapid development of the paper industry and increasingly stringent environmental protection requirements, the recycling rate of water resources is constantly improving, and the closed-loop circulation of white water in papermaking is also deepening. However, this trend has led to a large accumulation of "anionic waste" such as dissolved and colloidal substances (DCS) in the wet end system of papermaking, resulting in a pulp system in an environment with high conductivity and high anionic interference. This interference is particularly severe in the production of packaging paper using secondary fibers such as waste cardboard (OCC).

[0003] Existing paper strengthening agents mainly include cationic polyacrylamide (CPAM), cationic starch (CS), and polyamide polyamine epichlorohydrin (PAE). In environments with high anionic interference, these traditional cationic strengthening agents readily undergo non-specific charge neutralization reactions with anionic waste in the system, leading to a significant reduction in their effective adsorption on the fiber surface and thus drastically weakening the strengthening effect. To maintain the physical strength of paper, such as ring crush strength, bursting strength, and tensile strength, paper mills often have to significantly increase the amount of strengthening agent used. This not only increases production costs but may also cause problems such as difficulty in water filtration, decreased paper uniformity, and unstable paper machine operation.

[0004] A search of existing technologies revealed, for example, Chinese patent CN111848863B discloses an amphoteric polyacrylamide paper reinforcing agent, which adapts to harsh papermaking environments by introducing acryloylmorpholine and epoxy monomers; Chinese patent CN107366182B discloses a high-ash paper reinforcing agent, focusing on improving filler retention through amphoteric polymers. However, most of the above-mentioned existing technologies have the following shortcomings: First, the molecular weight is usually set at a high level, such as greater than 1 million or even higher, aiming to utilize long chains for flocculation and bridging, but this results in poor polymer permeability in the porous fiber structure, making it difficult to enter the fiber interior to form an effective internal bonding network, and it is easy to degrade or fall off under high shear force; Second, the functional monomer design mainly focuses on charge balance and lacks highly active groups that can undergo thermosetting crosslinking, such as a high proportion of adjacent dicarboxyl groups or anhydride structures, which limits its further reinforcing potential in high-temperature processing such as pulp molding hot pressing or drying processes, and cannot meet the stringent requirements of high-performance fiber-based materials for rigidity and dimensional stability.

[0005] Furthermore, in response to the plastic ban, pulp molded products and fiber-based composites have received widespread attention as alternatives to plastics. While adding wet-strength agents such as PAE can improve water resistance, the residual organochlorine content poses environmental risks. Some existing technologies, in pursuit of water and oil resistance, add fluorinated monomers, leading to excessive levels of organofluorine, which is inconsistent with current green and environmentally friendly trends. Traditional surface sizing agents such as oxidized starch also face bottlenecks in film strength and adhesion to hydrophobic substrates.

[0006] Therefore, developing an environmentally friendly papermaking additive that can maintain high-efficiency reinforcing performance in a high-anion interference environment, and possesses medium-low molecular weight high permeability, excellent surface sizing enhancement ability and unique thermosetting crosslinking characteristics has become an urgent technical problem to be solved in the current papermaking and fiber materials field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide fiber-enhancing copolymers, their preparation methods, and applications.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a fiber-enhancing copolymer for papermaking.

[0010] The fiber-enhancing copolymer is a water-soluble or water-dispersible copolymer, and its structural units are derived from at least the following vinyl unsaturated monomers:

[0011] Acrylic acid monomers and / or methacrylic acid monomers and their salts;

[0012] Vinyl unsaturated polycarboxylic acid monomers containing adjacent dicarboxyl groups and / or anhydride structures and their salts;

[0013] Vinyl cationic monomers containing quaternary ammonium salt groups;

[0014] The dry solids mass ratio of the acrylic acid monomer and / or methacrylic acid monomer and their salts to the dry solids mass ratio of the vinyl unsaturated polycarboxylic acid monomer and its salts containing adjacent dicarboxyl groups and / or anhydride structures is 1.0:1 to 6.5:1. Specific ratios can be, for example, 1.0:1, 1.07:1, 1.2:1, 1.5:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.6:1, 2.66:1, 2.8:1, 2.85:1, 2.9:1, 3.0:1, 3.2:1, 3.5:1, 3.8:1, 4.0:1, 4.2:1, 4.5:1, 4.8:1, 5.0:1, 5.5:1, 6.0:1, 6.2:1, or 6.5:1.

[0015] The ratio of the dry solid mass of the vinyl cationic monomer containing quaternary ammonium salt groups to the total dry solid mass of the acrylic acid monomer and / or methacrylic acid monomer and its salt, as well as the vinyl unsaturated polycarboxylic acid monomer and its salt, is 0.001:1 to 0.06:1. Specific ratios can be, for example, 0.001:1, 0.0011:1, 0.002:1, 0.005:1, 0.008:1, 0.01:1, 0.015:1, 0.02:1, 0.024:1, 0.025:1, 0.026:1, 0.029:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, 0.055:1, 0.058:1, or 0.06:1, etc.

[0016] Furthermore, the viscosity-average molecular weight of the fiber-enhancing copolymer is 6.0 × 10⁻⁶. 4 ~2.8×10 5 g / mol, specifically the viscosity-average molecular weight can be, for example, 6.0 × 10⁻⁶ g / mol. 4 g / mol, 6.5×10 4 g / mol, 7.0×10 4 g / mol, 8.0×10 4 g / mol, 1.0×10 5 g / mol, 1.2×10 5 g / mol, 1.5×10 5 g / mol, 1.8×10 5 g / mol, 2.0×10 5 g / mol, 2.2×10 5 g / mol, 2.3×10 5 g / mol, 2.4×10 5 g / mol, 2.5×10 5 g / mol, 2.6×10 5 g / mol, 2.7×10 5 g / mol or 2.8 × 10 5 The acid value is 450–800 mg KOH / g, and specific acid values ​​can be, for example, 450 mg KOH / g, 460 mg KOH / g, 480 mg KOH / g, 500 mg KOH / g, 520 mg KOH / g, 550 mg KOH / g, 565 mg KOH / g, 580 mg KOH / g, 600 mg KOH / g, 620 mg KOH / g, 650 mg KOH / g, 680 mg KOH / g, 700 mg KOH / g, 720 mg KOH / g, 750 mg KOH / g, 780 mg KOH / g, or 800 mg KOH / g, etc.

[0017] Furthermore, the organic fluorine content of the fiber-enhancing copolymer is ≤5 mg / kg on a dry solids basis, for example, it can be 4 mg / kg, 3 mg / kg, 2 mg / kg, 1 mg / kg, 0.5 mg / kg or undetectable.

[0018] The vinyl unsaturated polycarboxylic acid monomer containing adjacent dicarboxyl groups and / or anhydride structures is selected from one or more of maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, citraconic acid, methylmaleic acid, methylfumaric acid, cis-aconitine, trans-aconitine, and their salts or anhydrides.

[0019] The vinyl unsaturated polycarboxylic acid monomer is selected from one or more of maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, citraconic acid, methylmaleic acid, methylfumaric acid, cis-aconitic acid, trans-aconitic acid and their salts or anhydrides.

[0020] When the vinyl unsaturated polycarboxylic acid monomer contains maleic anhydride, the ratio of the dry solid mass of maleic anhydride to the total dry solid mass of the vinyl unsaturated polycarboxylic acid monomer is 0.1:1 to 0.8:1, and specific ratios can be, for example, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.4:1, 0.42:1, 0.5:1, 0.6:1, 0.7:1, 0.75:1, or 0.8:1, etc.

[0021] The vinyl cationic monomers containing quaternary ammonium groups include quaternary ammonium diallyl monomers, quaternary ammonium acrylate monomers, quaternary ammonium methacrylate monomers, quaternary ammonium acrylamide monomers and / or quaternary ammonium methacrylamide monomers;

[0022] The vinyl cationic monomer containing a quaternary ammonium salt group is selected from one or more of dimethyl diallyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride (DMC), methacryloyloxyethyl trimethyl ammonium chloride, acrylamide propyl trimethyl ammonium chloride, methacryloamide propyl trimethyl ammonium chloride, quaternized dimethylaminoethyl acrylate, quaternized dimethylaminoethyl methacrylate, quaternized dimethylaminopropyl acrylamide, quaternized dimethylaminopropyl methacrylamide, and their halides or methyl sulfates.

[0023] The structural units of the fiber-enhancing copolymer are selected from nonionic hydrophilic monomers;

[0024] The nonionic hydrophilic monomer is one or more of the following: amide monomers, N-vinyl lactam monomers, N-vinyl amide monomers, hydroxyalkyl acrylate monomers, hydroxyalkyl methacrylate monomers, polyether acrylate monomers and / or polyether methacrylate monomers, acrylamide, methacrylamide, N,N-dimethylacrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, polyethylene glycol acrylate, and polyethylene glycol methacrylate.

[0025] And / or the structural units of the fiber-enhancing copolymer are selected from hydrophobic monomers;

[0026] The hydrophobic monomer is one or more of styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl neodecanoate, C1-C20 alkyl acrylate and / or C1-C20 alkyl methacrylate.

[0027] The ratio of the dry solid mass of the nonionic hydrophilic monomer before polymerization to the total dry solid mass of the acrylic acid monomer and / or methacrylic acid monomer and its salt, as well as the vinyl unsaturated polycarboxylic acid monomer and its salt, is 0:1 to 0.25:1. Specific ratios can be, for example, 0:1, 0.01:1, 0.033:1, 0.05:1, 0.055:1, 0.08:1, 0.086:1, 0.1:1, 0.12:1, 0.125:1, 0.15:1, 0.17:1, 0.18:1, 0.2:1, 0.22:1, or 0.25:1, etc.

[0028] Furthermore, the degree of neutralization of the fiber-enhancing copolymer is 0-60%, with specific values ​​such as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%. The gel content, based on dry solids, is ≤0.05wt%, for example, 0.04wt%, 0.03wt%, 0.02wt%, 0.01wt%, or 0wt%, etc., and the gel content is determined by filtration and weighing using a 100μm filter.

[0029] The anionic charge density of the fiber-enhancing copolymer is 1.5–10.0 meq / g, and specific density values ​​can be, for example, 1.5 meq / g, 2.0 meq / g, 2.5 meq / g, 3.0 meq / g, 3.5 meq / g, 4.0 meq / g, 4.5 meq / g, 4.6 meq / g, 4.8 meq / g, 5.0 meq / g, 5.2 meq / g, 5.5 meq / g, 6.0 meq / g, 6.5 meq / g, 7.0 meq / g, 8.0 meq / g, and 9.0 meq / g. / g or 10.0 meq / g, etc.; the cation charge density is 0.02 to 0.5 meq / g, and specific density values ​​can be, for example, 0.02 meq / g, 0.03 meq / g, 0.04 meq / g, 0.05 meq / g, 0.06 meq / g, 0.07 meq / g, 0.08 meq / g, 0.10 meq / g, 0.12 meq / g, 0.15 meq / g, 0.20 meq / g, 0.30 meq / g, 0.40 meq / g or 0.50 meq / g, etc., all on a solid basis. Furthermore, the ratio of anion charge density to cation charge density is 20:1 to 200:1, and specific ratios can be, for example, 20:1, 30:1, 40:1, 50:1, 60:1, 80:1, 100:1, 120:1, 140:1, 160:1, 166:1, 180:1, or 200:1.

[0030] The present invention also provides a method for preparing the above-mentioned fiber-enhancing copolymer, which includes the following steps:

[0031] Step 1. Using water as the reaction medium, prepare a first monomer solution by mixing acrylic acid monomers and / or methacrylic acid monomers and their salts, vinyl unsaturated polycarboxylic acid monomers and their salts, and nonionic hydrophilic and / or hydrophobic monomers. When the first monomer solution contains hydrophobic monomers, use mechanical stirring and / or high shear dispersion to disperse the hydrophobic monomers in the first monomer solution to obtain a dispersed first monomer solution. Separately, prepare a second monomer solution by mixing a vinyl cationic monomer containing a quaternary ammonium salt group with water to obtain the first monomer solution and the second monomer solution.

[0032] Step 2. Add water to the reaction vessel and heat the reactor to 50-95°C under an inert atmosphere. Specific temperatures can be, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 95°C. Add an initiator to start polymerization. Set the total polymerization dropping time and add the first monomer solution obtained in Step 1 to the reactor in stages or at a constant rate to obtain the polymerization reaction solution.

[0033] Step 3. Continue polymerization of the polymerization reaction solution obtained in Step 2. During the 45% to 90% stage of the total polymerization dripping time set in Step 2, specifically at stages such as 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%, the second monomer solution obtained in Step 1 is added dropwise in stages or at a constant rate. The ratio of the dry solid mass of the vinyl cationic monomer containing quaternary ammonium salt groups to the acrylic acid monomer and / or methacrylic acid monomer and its salts, as well as the vinyl unsaturated polycarboxylic acid monomer and its salts, is 0.001:1 to 0.06:1. The viscosity-average molecular weight of the fiber-enhancing copolymer is controlled to 6.0 × 10⁻⁶ by the combination of initiator dosage, chain transfer agent, and polymerization temperature. 4 ~2.8×10 5 g / mol, to obtain the target polymerization reaction solution;

[0034] Step 4. The target polymerization reaction solution obtained in Step 3 is subjected to heat preservation and aging, residual monomer removal or vacuum devolatilization, pH adjustment and partial neutralization control, concentration or dilution to make the solid content 8-40 wt%, filtration to remove gel, and an aqueous solution of fiber-enhancing copolymer is obtained.

[0035] The initiator is selected from one or more of persulfate, hydrogen peroxide / reducing agent redox system, and azo initiator, and the viscosity-average molecular weight and gel content of the fiber-enhancing copolymer are controlled by chain transfer agent and / or post-treatment redox system during polymerization and / or post-treatment stages.

[0036] Furthermore, the content of low molecular weight organic matter extracted from the aqueous solution is ≤0.10wt% on a dry solids basis, and the gel content, as determined by the gel content test method, is ≤0.05wt%.

[0037] The present invention also provides a method for strengthening the pulp in the wet end of papermaking.

[0038] During the papermaking process, when the pulp and / or white water circulation system is in a high anion interference environment, the fiber-enhancing copolymer is added to the pulp.

[0039] The high anion interference environment refers to a particle charge density value measured by a particle charge analyzer for pulp filtrate and / or white water samples that is in the range of -50 to -600 μeq / L. Specific charge density values ​​can be, for example, -50 μeq / L, -100 μeq / L, -200 μeq / L, -250 μeq / L, -300 μeq / L, -320 μeq / L, -350 μeq / L, -400 μeq / L, -500 μeq / L, or -600 μeq / L, etc.

[0040] The total amount of the fiber-enhancing copolymer added, based on dry solids, is 0.5–15 kg / ton of oven-dry pulp. Specific addition amounts can be, for example, 0.5 kg / ton, 1 kg / ton, 2 kg / ton, 3 kg / ton, 5 kg / ton, 6 kg / ton, 8 kg / ton, 9 kg / ton, 10 kg / ton, 12 kg / ton, or 15 kg / ton. The addition point is located in the wet end of the chemical dosing section before and / or after the pressure screen and before the headbox. The residence time from the last addition point to the headbox is 10–900 s, specifically, for example, 10 s, 30 s, 60 s, 90 s, 120 s, 150 s, 300 s, 450 s, 600 s, or 900 s.

[0041] The addition point is located after at least one cationic retention aid and / or filter aid component and before the addition of the particulate system. The cationic retention aid and / or filter aid component is selected from one or more of cationic polyacrylamide (CPAM), polydimethyldiallylammonium chloride, cationic starch, polyethyleneimine, polyaluminum chloride (PAC), aluminum sulfate, and alum.

[0042] The particulate system is selected from one or more of colloidal silica, bentonite, polymeric silicate particles, and modified silicate particles;

[0043] Alternatively, the aqueous solution of the fiber-enhancing copolymer may be added using a dual-addition-point method. The first addition point is located at any position before or after the cationic polyacrylamide and / or polyaluminum chloride, and the second addition point is located before the addition of the particulate system. The mass ratio of the addition amount of the first addition point to the second addition point is 0.2:1 to 5:1. Specific ratios may be, for example, 0.2:1, 0.33:1, 0.5:1, 0.8:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, or 5:1.

[0044] The particle charge density of the pulp system is used as the charge window control parameter. The change in particle charge density relative to the initial value (ΔPCD) is controlled to be between -10 and -110 μeq / L. Specific changes can be, for example, -10 μeq / L, -20 μeq / L, -25 μeq / L, -30 μeq / L, -35 μeq / L, -40 μeq / L, -50 μeq / L, -60 μeq / L, -70 μeq / L, -80 μeq / L, -90 μeq / L, -100 μeq / L, or -110 μeq / L. Here, ΔPCD is the particle charge density after adding the fiber-enhancing copolymer minus the particle charge density before addition.

[0045] Alternatively, when adding the fiber-enhancing copolymer, it can be prepared as a working solution with a solid content controlled at 0.1–10 wt%.

[0046] The present invention also provides a method for surface synergistic application.

[0047] The fiber-enhancing copolymer is added to the gelatinized surface sizing solution and applied to the paper surface, wherein the amount of fiber-enhancing copolymer added relative to the dry starch is 0.05-20 wt%, or the amount of fiber-enhancing copolymer applied is 0.5-20 kg / ton of paper.

[0048] The present invention also provides a method for enhancing the effect of sprayed starch. The fiber-enhancing copolymer is added to a gelatinized starch spray solution and applied to the surface of a paper sheet, wherein the amount of fiber-enhancing copolymer added relative to the dry starch is 0.05-20 wt%, or the amount of fiber-enhancing copolymer applied is 0.5-20 kg / ton of paper.

[0049] The present invention also provides a method for pulp molding reinforcement.

[0050] The fiber-enhancing copolymer is added to the fiber suspension during the molding slurry preparation stage, such that the amount of fiber-enhancing copolymer added is 0.1–5 wt% based on oven-dry fiber or granule dry basis;

[0051] After molding or pressing, dehydration, drying, and heat treatment at 80–200℃ for 0.5–30 min, the specific heat treatment temperature can be, for example, 80℃, 100℃, 120℃, 140℃, 150℃, 160℃, 180℃, or 200℃, and the specific heat treatment time can be, for example, 0.5 min, 1 min, 2 min, 5 min, 10 min, 15 min, 20 min, or 30 min, to improve the strength and dimensional stability of the product.

[0052] This invention also provides a method for bonding fiber / particle composite materials. The fiber-enhancing copolymer is applied to at least one of wood fibers, bamboo fibers, wood chips, cork particles, or synthetic fibers, such that the amount of the fiber-enhancing copolymer added, on a dry basis of particles, is 0.1–5 wt%.

[0053] After molding or pressing, dehydration, drying, and heat treatment at 80–200℃ for 0.5–30 min, the specific heat treatment temperature can be, for example, 80℃, 100℃, 120℃, 140℃, 150℃, 160℃, 180℃, or 200℃, and the specific heat treatment time can be, for example, 0.5 min, 1 min, 2 min, 5 min, 10 min, 15 min, 20 min, or 30 min, to improve the strength and dimensional stability of the product.

[0054] The present invention also provides a fiber-based article. The fiber-based article is paper, paperboard, pulp molded article or fiber / particle composite material, and the fiber-based article contains the fiber-enhancing copolymer, wherein the fiber-enhancing copolymer accounts for 0.01 to 5 wt% of the oven-dry weight of the fiber-based article on a solid basis.

[0055] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0056] Strong resistance to anionic interference: The fiber-enhancing copolymer described in this invention, through its unique monomer component design, particularly the introduction of a high proportion of adjacent dicarboxyl / anhydride monomers and trace amounts of cationic monomers, combined with specific control of medium and low molecular weight, exhibits strong adaptability to high anionic interference environments in papermaking wet-end applications. It can effectively shield against the interference of anionic waste, and through the synergistic effect with cationic retention aids and microparticle systems, it significantly improves the retention rate of fine fibers and fillers, as well as water filtration performance, thereby greatly improving the physical strength of paper.

[0057] Significant surface synergistic effect: In surface sizing and spraying systems, this copolymer can form a strong hydrogen bond network with starch, improving surface strength and interlayer bonding.

[0058] Excellent thermosetting and reinforcing effect: In the field of pulp molding and fiber composite materials, this copolymer can undergo thermosetting crosslinking reaction under high temperature heat treatment, which significantly improves the rigidity, strength and water resistance dimensional stability of the product.

[0059] Green and environmentally friendly: The product of this invention has extremely low organic fluorine content, which meets the requirements of green and environmentally friendly products. Attached Figure Description

[0060] Figure 1 This is a schematic diagram illustrating the reinforcement mechanism of the fiber-enhancing copolymer described in this invention in the wet end of papermaking, which includes a microparticle system.

[0061] In the figure, 1-wood fiber; 2-fiber synergist copolymer; 3-cationic retention and / or filtration aid component; 4-microparticle system. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0063] To avoid ambiguity in terminology, the term "aqueous solution of fiber-enhancing copolymer" in this specification refers to an aqueous system composed of fiber-enhancing copolymer and water; "on a dry solids basis" refers to the dry solids mass of the fiber-enhancing copolymer as the measurement standard; and "working solution" refers to the dosage solution obtained by diluting the aqueous solution of fiber-enhancing copolymer with water as needed for use.

[0064] Figure 1 This is a schematic diagram illustrating the reinforcing mechanism of the fiber-enhancing copolymer of the present invention in the wet end of papermaking containing a particulate system. As shown in the figure, 1 represents wood fibers in the pulp, whose surfaces are adsorbed with positively charged particulate matter, namely the cationic retention aid and / or filter aid component shown as 3. 2 represents the fiber-enhancing copolymer of the present invention, whose molecular chains carry a negative charge (indicated by "-" in the figure). This fiber-enhancing copolymer 2 not only forms a bridge by combining with the cationic retention aid and / or filter aid component 3 adsorbed on the surface of the wood fibers 1 through electrostatic interactions, but also interacts with the particulate system 4 (e.g., colloidal silica or bentonite particles) dispersed in the system. The polymer chains encapsulate or connect the particulate system 4, forming a more compact and complex micro-floc structure. This multiple interaction further enhances the bonding network between fibers, improves the retention rate of fine fibers and fillers, thereby significantly improving the physical strength and uniformity of the paper sheet.

[0065] The main reagents and raw materials used in the embodiments and comparative examples of this invention are shown in the table below:

[0066] Table 1. Main reagent and raw material names, product models / specifications, and manufacturers:

[0067]

[0068] The main analytical and testing instruments used in the embodiments of this invention are shown in the table below:

[0069] Table 2 mainly analyzes the names, product models / specifications, and manufacturers of the testing instruments:

[0070]

[0071] Main testing standards:

[0072] Sample temperature and humidity treatment: GB / T 10739-2023.

[0073] Tensile strength index: GB / T 12914-2018.

[0074] Bursting strength index: GB / T 454-2020.

[0075] Ring pressure index: GB / T 2679.8-2016.

[0076] Canadian Standard Filterability (CSF): ISO 5267-2:2025.

[0077] Internal bond strength (Scott Bond): ISO 16260:2025.

[0078] Bending stiffness: GB / T 22364-2018 (Use the Taber stiffness tester method or constant speed bending method, and perform according to the instrument conditions and data expression methods specified in the standard).

[0079] Printed surface strength (IGT): GB / T 22365-2008.

[0080] Cobb absorbency: GB / T 1540-2002.

[0081] Total organic carbon (TOC): HJ 501-2009.

[0082] Compressive strength of molded pulp products (flat compression): Refer to GB / T 4857.4-2008.

[0083] Static bending strength (MOR) and 24h thickness swelling rate of fiber / particle composite boards: GB / T 17657-2022.

[0084] The physicochemical properties, including viscosity-average molecular weight (Mv), acid value, anionic charge density, cationic charge density, content of extracted low-molecular-weight organic matter, gel content, organic fluorine content, TOC removal rate, and particle charge density, were all determined using the following methods:

[0085] Viscosity-average molecular weight Mv: In a 1.0 mol / L sodium chloride solution system at 25℃ and pH 9.0, the viscosity of solutions of different concentrations was measured using an Ubbelohde viscometer, and the intrinsic viscosity [η] was extrapolated. Then, the Mark-Houwink equation ([η] = K × Mv) was used. α Calculate the molecular weight, where parameter K is taken as 1.307 × 10⁻⁶. -4 dL / g, α is 0.759.

[0086] Acid value: After drying the sample to constant weight at 105℃, pulverize it and weigh 0.5000g of the dry sample into a 250mL Erlenmeyer flask. Add 100.0mL of deionized water and stir magnetically for 30min to dissolve or fully disperse the sample. Add 2 drops of phenolphthalein indicator and titrate with 0.1000mol / L potassium hydroxide standard solution until the solution turns a persistent faint red color and remains so for 30s, or titrate with a pH meter until pH=8.30 as the endpoint. Calculate the acid value as (V-V0)×c×56.1 / m, with units of mg KOH / g, where V is the sample titration volume (mL), V0 is the blank titration volume (mL), c is the equivalent concentration of potassium hydroxide standard solution (mol / L), and m is the dry solid mass of the sample (g).

[0087] Charge density determination: Titration was performed using a particle charge analyzer (PCD). PVSK was used as the titrant for cation charge density determination, and polydimethyldiallylammonium chloride (PolyDADMAC) was used as the titrant for anion charge density determination. The equivalent concentration of the titrants was 0.0020N, ​​and they were calibrated with standard solutions before use. The sample was diluted to a 0.20wt% solution, and the pH of the sample was adjusted to 5.0 with dilute hydrochloric acid / dilute sodium hydroxide. Titration was performed at 25℃, with the zero-crossing point of the PCD signal as the endpoint, and the titration volume V was recorded. Charge density (meq / g) = V × c / m, where V is the titration volume (mL), c is the equivalent concentration of the titrant (eq / L), and m is the dry basis mass of the sample (g).

[0088] Gel content: Weigh the sample and prepare a 0.50 wt% solution based on dry solids. After standing at room temperature for 12 hours to fully hydrate, filter through a 100 μm filter. Wash the residue on the filter with deionized water until the filtrate is clear. Dry the residue at 105℃ to constant weight and weigh the residue to obtain the mass m. 凝胶 According to gel content = m 凝胶 / m 固体 Calculate by multiplying by 100%, where m 固体 This represents the mass of dry solids contained in the sample before filtration.

[0089] Determination of low molecular weight organic matter content by extraction: Dialysis was used, with a dialysis bag having a molecular weight cutoff (MWCO) of 1000 Da. The sample was prepared as a 1.0 wt% solution on a dry solids basis, and 100.0 mL was accurately measured and placed into the dialysis bag, which was then sealed tightly. The dialysis bag was placed in 2.0 L of deionized water and dialyzed at 25 °C with magnetic stirring (300 r / min) for 24 h. The external phase deionized water was replaced at 2 h, 4 h, 8 h, and 16 h, and the previous stage of external phase dialysate was collected and retained each time. After dialysis, the external phase dialysates from each stage were combined, and the total combined volume V was recorded. total(L), after mixing, the total organic carbon (TOC) of the combined dialysate was determined using a TOC analyzer (mg / L, as carbon); the mass of low molecular weight organic carbon (m) was also determined. C (mg) = TOC (mg / L) × V total (L); then, based on 50% of the average carbon mass fraction of low molecular weight organic matter, the mass of low molecular weight organic matter m LMW (mg)=m C ×2.0; Extraction of low molecular weight organic matter content (wt%) = m LMW / Mass of dry solids in the sample × 100%.

[0090] Determination of organic fluorine content: The sample was dried to constant weight at 105℃ and pulverized. 0.50 g of the dry sample was placed in an oxygen bomb. 10.0 mL of 0.10 mol / L sodium hydroxide solution was added as the absorbent. Oxygen was introduced to 3.0 MPa and then ignited. After combustion, the inner wall of the oxygen bomb was washed with deionized water and the absorbent was added back in. The volume was adjusted to 50.0 mL. An equal volume of TISAB buffer (TISAB-II, commercial) was added to the test solution. The total fluorine was determined using a fluoride ion-selective electrode (calibrated with sodium fluoride standard solution). The determination of inorganic fluorine was performed by water extraction: 0.50 g of the dry sample was added to 50.0 mL of deionized water, shaken at 25℃ for 30 min, and then filtered. The fluoride ion content of the filtrate was determined by the electrode method described above. Organic fluorine content = total fluorine - inorganic fluorine. Results are expressed as dry sample (mg / kg); when the organic fluorine content "based on the aqueous solution of fiber-enhancing copolymer" is required, it is converted by multiplying the dry sample organic fluorine content by the sample solid content (mass fraction).

[0091] TOC removal rate: The total organic carbon concentration (TOC0) of pulp filtrate or white water before dosing and the total organic carbon concentration (TOC1) after dosing are measured respectively, and the TOC removal rate is calculated as (TOC0-TOC1) / TOC0×100%.

[0092] Particle charge density value: After sampling the pulp, filter the filtrate or take a white water sample, and use a particle charge meter to measure and read the particle charge density value under uniform conditions. The unit is μeq / L.

[0093] Apparent viscosity was determined using a rotational viscometer (Brookfield DV2T). The sample was kept at a constant temperature of 25±0.5℃ before measurement. An LV series rotor was selected according to the viscosity range of the sample and the rotor number was recorded. The rotational speed was fixed at 30 rpm. The test conditions were adjusted so that the torque reading was within the range of 20% to 80%. The apparent viscosity (mPa·s) was recorded after the reading stabilized for 60 seconds.

[0094] Determination of solid content: Weigh sample m0 and dry it at 105℃ to constant weight to obtain dry sample mass m1; solid content (wt%) = m1 / m0 × 100%.

[0095] pH determination: The pH of the sample was directly measured at 25℃ using a pH meter (two-point calibration).

[0096] Ash content determination: Ash content of the sheet was determined by weighing method. The sheet was dried at 105℃ and weighed m2. After being ignited in a muffle furnace at 525℃ for 2 hours, it was cooled and weighed m3. Ash content (wt%) = m3 / m2 × 100%.

[0097] Waste paper pulp preparation process:

[0098] Waste cardboard raw material was soaked in deionized water for 12 hours to adjust the pulp concentration to 3.0 wt%. Pulp dispersion (3000 r / min, 10 min) was used to fully dissociate the fibers. The pulp was then screened through a 0.20 mm slotted sieve to remove impurities such as plastic and sand, and then washed and deinked with deionized water. The pH of the pulp was adjusted to 7.0 with a 30 wt% sodium hydroxide aqueous solution. The resulting pulp was centrifuged at 3000 r / min for 10 min to remove coarse particles, yielding waste paper pulp. This waste paper pulp was used in the preparation of fiber raw materials for Application Examples 1, 2, and 5 of this specification.

[0099] General preparation process for the examples:

[0100] Step 1. Preparation of the first monomer solution: Add the acrylic acid monomer and / or methacrylic acid monomer, vinyl unsaturated polycarboxylic acid monomer and / or anhydride monomer, and nonionic hydrophilic monomer and / or hydrophobic monomer in the amounts specified in each embodiment to deionized water to prepare a first monomer solution with a dry basis mass fraction of 30.0 wt%. The acrylic acid monomer and / or methacrylic acid monomer and their salts can be in acid form or partially neutralized salt form. When it is necessary to participate in polymerization in salt form, the corresponding acid monomer can be pre-neutralized with sodium hydroxide aqueous solution before preparing the first monomer solution to form its salt. When the formulation contains hydrophobic monomers, add sodium dodecyl sulfate (SDS) as a dispersant to the first monomer solution at an amount of 0.05 wt% of the total dry basis mass of the monomers. Then disperse using a shear disperser at 10000 r / min for 3 min, and let stand at room temperature for 30 min to obtain a stable first monomer solution.

[0101] Step 2. Preparation of the second monomer solution: Dilute the vinyl cationic monomer containing quaternary ammonium salt groups with deionized water based on an 80wt% aqueous solution of acryloyloxyethyltrimethylammonium chloride to prepare a second monomer solution with an effective component mass fraction of 20.0wt%.

[0102] Step 3. Polymerization start-up: Add deionized water to the aqueous free radical polymerization reactor, turn on the mechanical stirrer at a speed of 300 r / min; introduce nitrogen gas at 0.2 L / min for 30 min to deoxygenate; after heating to 80℃, add ammonium persulfate initiator in one go. The initiator is prepared as a 10 wt% aqueous solution and added in one go. The amount is 0.06 wt% based on all dry monomers.

[0103] Step 4. Dropping and copolymerization: The first monomer solution is added dropwise at a constant rate at 80°C for 120 min; when the first monomer solution has been added for a cumulative total of 72 min, the second monomer solution is added dropwise within 10 min; the chain transfer agent sodium hypophosphite is added to the first monomer solution in the amount described in the formulation of each embodiment.

[0104] Step 5. Post-processing: After the first monomer solution is added dropwise, continue the reaction at 80℃ for 60 min; then cool down to 60℃, add hydrogen peroxide / sodium bisulfite redox system to remove residual monomers, with 0.05 wt% hydrogen peroxide and 0.05 wt% sodium bisulfite on a dry basis of all monomers, and keep warm for 30 min; after cooling to 25℃, achieve the required partial neutralization by adding 30 wt% sodium hydroxide aqueous solution, and adjust the pH of the system to the measured pH listed in Table 11 with 37 wt% hydrochloric acid; finally, filter through a 100 μm stainless steel filter to remove gel, and obtain an aqueous solution of fiber-enhanced copolymer.

[0105] The degree of partial neutralization (%) is calculated based on the carboxyl equivalent: degree of partial neutralization (%) = n(NaOH) / n(total equivalent of neutralizable acid groups) × 100%; n(NaOH) is the amount of NaOH actually added, and n(total equivalent of neutralizable acid groups) is the sum of the equivalents of neutralizable acid groups in the system. Carboxyl groups in acrylic acid, methacrylic acid, polycarboxylic acid monomers, and carboxyl groups formed after hydrolysis of acid anhydride monomers are all included.

[0106] Example:

[0107] The formulation and process parameters for the examples are as follows (all parts by weight are on a dry basis):

[0108] Example 1: Acrylic acid 180 parts; itaconic acid 45 parts; maleic anhydride 15 parts; DMC 7 parts; acrylamide 30 parts. Sodium hypophosphite, the chain transfer agent, was used at 0.05 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 30%, and the Mv to 2.5 × 10⁻⁶. 5 g / mol, gel content is 0.02wt%.

[0109] Example 2: Acrylic acid 175 parts; itaconic acid 45 parts; maleic anhydride 15 parts; DMC 7 parts; acrylamide 30 parts; butyl acrylate 10 parts. The chain transfer agent, sodium hypophosphite, was used at 0.05 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 30%, and the Mv to 2.4 × 10⁻⁶. 5 g / mol, gel content is 0.02wt%.

[0110] Example 3: 200 parts acrylic acid; 70 parts itaconic acid; 0.3 parts DMC; 15 parts acrylamide. The chain transfer agent, sodium hypophosphite, was used at 0.04 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 25%, and the Mv to 2.6 × 10⁻⁶. 5 g / mol, gel content is 0.01wt%.

[0111] Example 4: 150 parts acrylic acid; 80 parts itaconic acid; 60 parts maleic anhydride; 7 parts DMC; 25 parts acrylamide. The chain transfer agent, sodium hypophosphite, was used at 0.06 wt% of the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 60%, and the Mv to 2.3 × 10⁻⁶. 5 g / mol, gel content is 0.03wt%.

[0112] Example 5: Acrylic acid 210 parts; itaconic acid 15 parts; maleic anhydride 45 parts; DMC 15 parts; acrylamide 0 parts. Sodium hypophosphite, the chain transfer agent, was used at 0.03 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 10%, and the Mv to 2.7 × 10⁻⁶. 5 g / mol, gel content is 0.04wt%.

[0113] Example 6: 160 parts methacrylic acid; 60 parts fumaric acid; 7 parts DMC; 20 parts 2-hydroxyethyl acrylate; 20 parts acrylamide. The chain transfer agent, sodium hypophosphite, was used at 0.10 wt% of the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 30%, and the Mv to 1.8 × 10⁻⁶. 5 g / mol, gel content is 0.02wt%.

[0114] Example 7: Acrylic acid 260 parts; itaconic acid 40 parts; DMC 8 parts; styrene 10 parts; acrylamide 0 parts. Sodium hypophosphite, the chain transfer agent, was used at 0.07 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 20 wt%, the degree of partial neutralization to 30%, and the Mv to 2.2 × 10⁻⁶. 5 g / mol, gel content is 0.03wt%.

[0115] Example 8: 180 parts acrylic acid; 45 parts itaconic acid; 15 parts maleic anhydride; 7 parts DMC; 30 parts acrylamide. The chain transfer agent, sodium hypophosphite, was used at 0.02 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 40 wt%, the degree of partial neutralization to 30%, and the Mv to 2.8 × 10⁻⁶. 5 g / mol, gel content is 0.04wt%.

[0116] Example 9: 180 parts acrylic acid; 45 parts itaconic acid; 15 parts maleic anhydride; 7 parts DMC; 30 parts acrylamide. The chain transfer agent, sodium hypophosphite, was used at 0.20 wt% based on the total dry solids of the monomers. Post-treatment adjusted the solids content to 8 wt%, the degree of partial neutralization to 30%, and the Mv to 6.5 × 10⁻⁶. 4 g / mol, gel content is 0.01wt%.

[0117] Table 3: Formulations and Key Results of Examples 1-9 (parts by weight):

[0118]

[0119] Note:

[0120] 1. (A) Acrylic monomers: including acrylic acid and methacrylic acid;

[0121] 2. Polycarboxylic acid / anhydride monomers: including itaconic acid, maleic anhydride, and fumaric acid;

[0122] 3. Cationic monomer: Acryloyloxyethyltrimethylammonium chloride (DMC);

[0123] 4. Functional comonomers: including acrylamide, 2-hydroxyethyl acrylate, butyl acrylate, and styrene; wherein in Examples 2 and 7, 0.05 wt% sodium dodecyl sulfate (SDS) was additionally added as a dispersant.

[0124] 5. Chain transfer agent: Sodium hypophosphite (mass percentage relative to the total amount of monomers).

[0125] Comparative example:

[0126] Comparative Example 1: Blank Control. In the subsequent application performance tests, except for the absence of any fiber-enhancing copolymers or reinforcing agents (replaced with an equal amount of deionized water), the pulp raw material formulation, basic auxiliary agent system, and papermaking process conditions were kept completely consistent with the experimental group of Example 1, serving as a comparative benchmark.

[0127] Comparative Example 2: High molecular weight polyacrylamide (PAM), with a molecular weight (Mv) of 1.2 × 10⁻⁶. 6g / mol. Preparation process: Aqueous solution polymerization was used. Acrylamide monomer was dissolved in deionized water under nitrogen protection to prepare a 25wt% monomer solution. The reactor was stirred at 300 r / min, and nitrogen gas was introduced at 0.2 L / min for 30 min for deoxygenation. The temperature was then raised to 65℃. 10wt% ammonium persulfate aqueous solution was added as an initiator, with a concentration of 0.05wt% based on the dry basis of acrylamide. The reaction was carried out at 65℃ for 3.5 h. After the reaction was completed, the mixture was cooled to room temperature to obtain a high molecular weight PAM aqueous solution. The gel content was measured to be 0.12wt%.

[0128] Comparative Example 3: Conventional amphoteric polyacrylamide (PAM), with a cationicity of 15%. Preparation process: Acrylamide was used as the main monomer. A monomer mixture was prepared using 70 parts acrylamide, 15 parts acrylic acid, and 15 parts DMC (by dry basis weight). Acrylic acid was pre-neutralized to 50% neutralization with a 30wt% sodium hydroxide aqueous solution. Deionized water was added to the reactor to bring the total monomer concentration to 25wt%. The stirring speed was 300 r / min, and nitrogen gas was introduced at 0.2 L / min for 30 min for deoxygenation. The temperature was then raised to 65℃. A 10wt% ammonium persulfate aqueous solution was added as an initiator (0.06wt% by dry basis of monomer). The reaction was carried out at 65℃ for 3.5 h to obtain a conventional amphoteric PAM aqueous solution with a cationicity of 15%, and the measured Mv was 5.0 × 10⁻⁶. 5 g / mol, gel content is 0.08wt%.

[0129] Comparative Example 4: Hydroxymethyl self-crosslinking polyacrylamide containing NMA. Preparation process: Based on Comparative Example 2, N-hydroxymethylacrylamide (NMA) was introduced as a self-crosslinking monomer, with the amount of NMA being 5.0 wt% of the acrylamide dry basis; the remaining polymerization conditions were as described in Comparative Example 2: total monomer concentration 25 wt%, nitrogen deoxygenation for 30 min, reaction at 65℃ for 3.5 h, and ammonium persulfate as the initiator, amounting to 0.05 wt% based on the acrylamide dry basis. An aqueous solution of hydroxymethyl self-crosslinking polyacrylamide was obtained, and the gel content was measured to be 0.20 wt%.

[0130] Comparative Example 5: Crosslinked branched polyacrylamide containing MBA. Preparation process: Based on Comparative Example 2, N,N'-methylenebisacrylamide (MBA) was introduced as a crosslinking agent, with the amount of MBA being 0.03 wt% of the acrylamide dry basis; the remaining polymerization conditions were as described in Comparative Example 2: total monomer concentration 25 wt%, nitrogen deoxygenation for 30 min, reaction at 65℃ for 3.5 h, and ammonium persulfate as the initiator, at 0.05 wt% of the acrylamide dry basis, to obtain an aqueous solution of crosslinked branched polyacrylamide, with a gel content of 0.15 wt%.

[0131] Preparation process of Comparative Example 6: 88 parts acrylamide, 10 parts cationic monomer DMC, and 2 parts hydrophobic monomer butyl acrylate were prepared by weight of monomers (dry basis). The monomers were dissolved in deionized water to prepare a 30wt% aqueous phase. White oil was used as the oil phase, and Span 80 was added as an emulsifier (6.0wt% of the oil phase). The mixture was stirred at 1000 r / min for 10 min at 25°C. The aqueous phase was slowly added to the oil phase to form an oil-in-water (W / O) emulsion. A photoinitiator (0.20wt% of the monomers) was added, and in-situ photopolymerization was performed under a 365 nm UV lamp with a light intensity of 5000 μW / cm², an irradiation distance of 10 cm, and an irradiation time of 30 min. A photoinitiated polyacrylamide microsphere emulsion was obtained, with a gel content of 0.25wt%.

[0132] Comparative Example 7: Glyoxal-modified polyacrylamide. Preparation process: The polymer from Comparative Example 2 was prepared into a 10 wt% aqueous solution and stirred at 300 r / min; the pH of the solution was adjusted to 4.5 with 37 wt% hydrochloric acid; glyoxal was added, with an effective component of 1.0 wt% of the polymer dry basis, and aluminum chloride, with anhydrous aluminum chloride, was added, with an effective component of 0.20 wt% of the polymer dry basis; the temperature was raised to 55℃ and maintained for 2 h; after the reaction was completed, the mixture was cooled to room temperature to obtain glyoxal-modified polyacrylamide, and the gel content was measured to be 0.30 wt%.

[0133] The proportion of polycarboxylic acid monomers in Comparative Example 8 was too low. The formulation was as follows: 270 parts acrylic acid; 30 parts itaconic acid, with an acidic monomer to polycarboxylic acid monomer ratio of 9.0:1, exceeding the range of 6.5:1; 7 parts DMC; and 30 parts acrylamide. The preparation process followed the general process of the examples, with post-treatment adjusting the solid content to 20 wt% and the Mv to 2.5 × 10⁻⁶. 5 g / mol, gel content is 0.02wt%.

[0134] Comparative Example 9 had an excessively high proportion of cationic monomers. The formulation consisted of: 180 parts acrylic acid; 45 parts itaconic acid; 15 parts maleic anhydride; 30 parts DMC (based on the dry solids mass of DMC, the ratio of its dry solids mass to the total dry solids mass of acrylic acid monomers and vinyl unsaturated polycarboxylic acid monomers was 0.125:1, exceeding the range of 0.06:1); and 30 parts acrylamide. The preparation process followed the general process of the examples, with post-treatment adjusting the solids content to 20 wt% and the Mv to 2.5 × 10⁻⁶. 5 g / mol, gel content is 0.05wt%.

[0135] Table 4 Comparative Examples 1-9 Formulations and Key Results (parts by weight):

[0136]

[0137] Note:

[0138] 1. Basic monomer system: Total monomer amount by mass parts. Comparative Examples 2-7 are systems mainly composed of acrylamide; Comparative Examples 8-9 are multi-component copolymer systems similar to those in the examples;

[0139] 2. Special Modifiers / Additives: NMA = N-hydroxymethylacrylamide; MBA = N,N'-methylenebisacrylamide; Glyoxal / AlCl3 is a post-reaction crosslinking agent; Oil phase / Span 80 is used for reverse emulsion polymerization.

[0140] Application example:

[0141] Application Example 1: Comparison of single-point addition performance under high anion interference environment.

[0142] This application example compares the application performance of Examples 1-9 and Comparative Examples 1-9 in a single-point addition method under a high anion interference environment.

[0143] Experimental conditions: Bleached softwood pulp and recycled fiber pulp from waste corrugated cardboard (OCC) were mixed at an oven-dry weight ratio of 40 / 60, and the pulp concentration was adjusted to 0.50 wt%. Heavy calcium carbonate (GCC) was added to achieve a target ash content of 15 wt%. Sodium lignosulfonate and sodium polyacrylate were each prepared as 1.0 wt% aqueous solutions. The sodium lignosulfonate aqueous solution was added first and stirred at 300 r / min for 60 s. After stirring, a sample was taken and filtered to determine the PCD of the filtrate. Then, sodium polyacrylate aqueous solution was added gradually, and after each addition, the mixture was stirred at 300 r / min for 60 s and a sample was taken and filtered to determine the PCD. The PCD of the pulp was adjusted to -320 μeq / L before adding the chemicals. The sheet yield was 120 g / m².

[0144] Feeding process: The aqueous solution of the fiber-reinforcing copolymer is diluted to a working solution with a solid content of 1.0 wt% and added. The sample with a solid content of 20 wt% is diluted at a water-to-fiber-reinforcing copolymer aqueous solution mass ratio of 19:1, the sample with a solid content of 40 wt% is diluted at a water-to-fiber-reinforcing copolymer aqueous solution mass ratio of 39:1, and the sample with a solid content of 8 wt% is diluted at a water-to-fiber-reinforcing copolymer aqueous solution mass ratio of 7:1. The working solution is added to the slurry at a dosage of 9 kg / ton of oven-dry slurry based on the dry solids of the fiber-reinforcing copolymer. After addition, the mixture is stirred at 300 r / min for 30 s and then allowed to stand for another 90 s, so that the equivalent residence time from the addition point to the headbox is 120 s. Subsequently, a hand-made sheet is prepared using a laboratory hand-made sheet forming device. After sheet forming, it is subjected to temperature and humidity treatment according to GB / T 10739-2023.

[0145] Test indicators: Tensile index was determined according to GB / T 12914-2018, burst index according to GB / T 454-2020, ring crush index according to GB / T 2679.8-2016, and Canadian standard filterability according to ISO 5267-2:2025. Ash retention rate was calculated based on the ash content of the sheet and the theoretical ash content added. In the TOC removal rate test, TOC0 was taken from the slurry filtrate or white water sample before dosing, and TOC1 was taken from the filtrate or white water sample after dosing and the residence time reached 120s. The TOC removal rate was calculated as (TOC0-TOC1) / TOC0×100%.

[0146] Table 5 Performance Comparison Data for Application Example 1:

[0147]

[0148] Note: Comparative Example 1 is a blank control, no polymer was added, and the TOC removal rate index is not applicable.

[0149] Table 6 Application Example 1 Particle Charge Density Window Control Data:

[0150]

[0151] Note: ΔPCD is the PCD after drug administration minus the PCD before drug administration.

[0152] Analysis: Experimental data show that under high anion interference environment, the strengthening effect of samples 1-9 is significantly better than that of the comparative examples. Taking the tensile index as an example, the tensile index of Example 4 is 54.0 N·m / g, and that of Example 9 is 49.5 N·m / g, both higher than that of the blank group comparative example 1 (46.0 N·m / g) and also higher than that of the high molecular weight PAM comparative example 2 (47.5 N·m / g). In terms of charge control, the ΔPCD of Example 1 is -40 μeq / L, and that of Example 8 is -80 μeq / L, with no charge reversal. In contrast, comparative example 9 has a positive PCD shift (ΔPCD of +40 μeq / L) due to the excess of cationic monomer, resulting in a tensile index of 46.5 N·m / g; comparative example 8, with a low polycarboxylic acid ratio, has a tensile index of 48.0 N·m / g, weaker than that of Example 1 (52.0 N·m / g), indicating that a specific carboxyl / anhydride ratio has a key contribution to fiber binding force.

[0153] Application Example 2: Performance Synergy under Two-Point Addition Process.

[0154] This experiment investigated the synergistic effect of polymers in a dual-addition-point process. The basic slurry conditions were consistent with those in Application Example 1, and the slurry PCD was adjusted to -250 μeq / L by gradually adding sodium lignosulfonate and sodium polyacrylate (each prepared as a 1.0 wt% aqueous solution, stirred at 300 rpm for 60 s after each addition and with PCD measured). The dual-addition process and microparticle system were set up as follows: First, cationic polyacrylamide (CPAM, 0.5 kg / ton oven-dry slurry based on active ingredient) and polyaluminum chloride (PAC, 1.0 kg / ton oven-dry slurry based on active ingredient) were added before the pressure sieve, and stirred at 300 rpm for 30 s. The fiber-enhancing copolymer was added using a two-point addition method: the first polymer addition point was located before the pressure screen and after CPAM / PAC, with an addition amount of 6 kg / ton of oven-dry slurry (dry solids), followed by stirring at 300 rpm for 30 s; the second polymer addition point was located before the headbox and before the addition of the microparticle system, with an addition amount of 3 kg / ton of oven-dry slurry (dry solids), followed by stirring at 300 rpm for 30 s. Subsequently, the colloidal silica microparticle system was added before the headbox at 1.0 kg / ton of oven-dry slurry (SiO2 dry solids) (corresponding to 3.33 kg / ton of oven-dry slurry when using LUDOXsM-30 (30%)), followed by stirring at 300 rpm for 30 s. After the final addition, the mixture was allowed to stand for 90 s, ensuring an equivalent residence time of 120 s from the last addition point to sheet formation, followed by hand sheet formation and testing. The total amount of fiber-enhancing copolymer added was maintained at 9 kg / ton of oven-dry slurry (dry solids). The testing process strictly monitors the filtration speed and retention rate. After the sample is taken, various physical strength indicators and TOC removal rate are tested according to standard procedures.

[0155] Table 7 Performance Comparison Data for Application Example 2:

[0156]

[0157] Note: Comparative Example 1 is a blank control, and the TOC removal rate indicator is not applicable.

[0158] Analysis: Under the two-point addition process, the performance advantages of the products in the examples are further amplified. Compared with the single-point addition data of Application Example 1, the tensile index of Example 1 under the two-point process increased from 52.0 to 56.5 N·m / g, and the burst index increased from 3.20 to 3.70 kPa·m² / g, indicating that the segmented addition helps the polymer to achieve multilayer adsorption and conformation optimization on the fiber surface. Compared with the comparative examples, Examples 1-9 maintained a high TOC removal rate, for example, the TOC removal rate of Example 9 was 45.0%, and the TOC removal rate of Example 4 was 55.6%, without sacrificing the water filtration performance as severely as Comparative Example 9 (CSF decreased to 390 mL). This is due to its specific molecular weight and charge distribution design, which allows it to form a good floc structure with the CPAM / microparticle system rather than dense clogging. Although the conventional modified PAM (Comparative Examples 4-7) showed a slight improvement in strength, its overall efficiency was still lower than that of the example group, indicating that the specific polycarboxylic acid / quaternary ammonium salt monomer ratio of the present invention has better adaptability and anti-interference ability in complex microparticle retention systems.

[0159] Application Example 3: Compatibility of different formulations under different two-point ratios.

[0160] This application example uses the fiber-enhancing copolymer prepared in Example 1 to investigate the effects of different addition ratios in a dual-addition-point process on the physical properties and internal bond strength of paper. The experiment was conducted under constant pulp ratios and charge interference conditions (PCD adjusted to -250 μeq / L). The basic retention aid system was fixed at CPAM (0.5 kg / ton oven-dry pulp based on active ingredient) and PAC (1.0 kg / ton oven-dry pulp based on active ingredient); the particulate system was fixed at 1.0 kg / ton oven-dry pulp based on colloidal silica (SiO2 dry solids) (corresponding to a LUDOXsM-30 (30%) addition of 3.33 kg / ton oven-dry pulp). Two polymer addition points were set: the first polymer addition point was located before the pressure screen and after the retention aid addition; the second polymer addition point was located before the headbox and before the particulate system addition.

[0161] The experiment was designed with 11 experimental groups, each with an independently adjusted copolymer addition amount (range 0-12 kg / ton of oven-dry pulp) at two addition points, covering various working conditions such as single-point addition, equal-ratio two-point addition, and asymmetric two-point addition.

[0162] In each experiment, CPAM and PAC were added sequentially and stirred at 300 rpm for 30 s; the copolymer at the first addition point was added and stirred at 300 rpm for 30 s; the copolymer at the second addition point was added and stirred at 300 rpm for 30 s; then the colloidal silica microparticle system was added and stirred at 300 rpm for 30 s; finally, after the addition of the chemicals, the mixture was allowed to stand for 90 s, so that the equivalent residence time from the last addition point to the sheet forming was 120 s, after which the sheet was formed by hand. After the samples were subjected to temperature and humidity treatment according to GB / T 10739-2023 standard for 24 h, the tensile index, Scott internal bond strength, and flexural stiffness were tested.

[0163] Table 8 Performance data of Example 1 under different two-point ratios:

[0164]

[0165] Note: Experimental group 1 was a blank control, without the addition of fiber-enhancing copolymer; all other groups used the sample from Example 1.

[0166] Analysis: Experimental data show that the mass distribution of fiber-enhancing copolymers at different addition points has a significant regulatory effect on the final properties of paper. Comparing experimental groups with a total dosage of 9 kg / t, it was found that as the proportion of the second addition point (closer to the headbox) increases, the tensile index and internal bond strength of the paper show a significant upward trend. For example, experimental group 6, with 9 kg / t added solely at the second addition point, achieved an internal bond strength of 220 J / m², significantly better than the 200 J / m² achieved with 9 kg / t added solely at the first addition point (experimental group 5). When the total dosage increased to 12 kg / t, experimental group 8, using an asymmetric ratio of "less at the beginning and more at the end" (3 kg / t and 9 kg / t), obtained the highest internal bond strength (230 J / m²) and excellent ash retention. This indicates that in complex wet-end environments, adding the main dose of copolymer to the post-particulate system can more effectively reduce the consumption of polymers by interfering substances and optimize the construction of the bonding network between fibers, while adding an appropriate amount at the front end helps with pre-flocculation and retention of fine fibers, with the two having the best synergistic effect.

[0167] Application Example 4: Enhanced performance of surface sizing and sprayed starch.

[0168] This application example evaluates the dual synergistic effect of fiber-enhanced copolymers in both surface sizing and interlayer spraying systems, verifying their improvement on film-forming properties and interlayer bonding strength.

[0169] Surface application test:

[0170] An oxidized starch solution with a mass fraction of 8.0% was prepared and gelatinized at 95°C for 30 min, followed by cooling to 60°C. At this temperature, 1.0% of the dry starch mass of each example and comparative sample was added to the starch solution, and the mixture was stirred at low speed for 10 min to prepare a sizing solution. The sizing solution was uniformly coated onto the surface of the base paper using a laboratory coater (LABCOATER), with the sizing amount on one side controlled at 2.0 ± 0.1 g / m². The paper samples were dried in hot air at 105°C for 2 min, and after 24 hours of standard temperature and humidity treatment, the IGT surface strength and Cobb strength were tested. 60 Water absorption and water droplet contact angle.

[0171] Starch spray interlayer reinforcement experiment:

[0172] This study simulates the interlayer spraying process in multi-layer paperboard fabrication. A 3.0% (w / w) virgin corn starch slurry was prepared, gelatinized at 95°C for 30 min, and then cooled to 60°C. Samples from each example and comparative example were added to the sprayed starch slurry at 5.0% (dry basis) of the starch, and stirred at low speed for 10 min to ensure homogeneity. Two undried wet paper webs with a basis weight of 80 g / m² were used. These wet paper webs were formed using a laboratory hand-made sheet forming device, and the forming slurry was kept consistent with the other conditions of this application example. After forming, the wet paper webs were only dehydrated under vacuum, without hot air or oven drying. The dryness of the wet paper webs was adjusted to 15.0%, and the dryness was determined by weighing and drying at -105°C to constant weight. The spray solution was uniformly sprayed between the two wet paper webs, with the spraying amount controlled at a starch dry basis of 1.5 g / m². Under the condition of a starch mass fraction of 3.0%, the wet addition amount of the spray solution was 50.0 g / m². Immediately after spraying, the two wet paper webs were laminated and dewatered by pressing (pressing pressure 0.40 MPa, pressing time 120 s), and then dried at 105℃ to constant weight. After the paper samples were subjected to temperature and humidity treatment according to GB / T 10739-2023 standard for 24 h, the Scott internal bond strength was tested according to ISO 16260:2025 to characterize the interlayer bonding performance.

[0173] Table 9. Comparison of Synergistic Effects between Surface Sizing and Sprayed Starch:

[0174]

[0175] Note: Comparative Example 1 is a blank control, using only pure starch solution without polymer additives.

[0176] Analysis: Experimental data show that the fiber-enhancing copolymer exhibits significant synergistic effects in both surface sizing and spraying systems. Regarding surface sizing, the IGT surface strength of the paper samples with added Examples 1-9 reached 1.42 to 1.52 m / s, significantly better than the 1.20 m / s of pure starch sizing and the 1.25 m / s of conventional high molecular weight PAM. This is attributed to the abundant carboxyl groups in the copolymer forming a hydrogen-bonded complex network with the starch hydroxyl groups, enhancing the toughness and surface adhesion of the starch film. In particular, Examples 2 and 7, which introduced hydrophobic monomers, showed significant improvements in Cobb... 60 The value is reduced to 26.0 to 26.5 g / m², and the contact angle is increased to 88°, giving the paper excellent water barrier properties.

[0177] Regarding interlayer reinforcement during spraying, the interlayer bonding strength of the example groups generally reached 365 to 395 J / m², an improvement of more than 30% compared to the blank group, and significantly better than glyoxal-modified PAM (Comparative Example 7, 345 J / m²). This is because the copolymer of the present invention not only promotes starch retention on the fiber surface through high anionic charge density, but its specific molecular weight distribution and polycarboxylic acid structure also promote cross-linking and entanglement between interlayer fibers and starch macromolecules during the drying process. Comparative Example 8, due to its low proportion of carboxylic acid monomers, had weak interaction with starch, resulting in limited improvement in interlayer bonding strength; Comparative Example 9, due to its excessively high cationic charge, easily reacted prematurely with anionic impurities in the slurry, which interfered with the uniform film formation of starch between layers, resulting in poor performance.

[0178] Application Example 5: Pulp molding and fiber / particle composite reinforcement.

[0179] This application example verifies the reinforcing and dimensional stabilizing effects of fiber-enhancing copolymers in pulp molded products and high-density fiber / particle composites, particularly examining their thermosetting and crosslinking properties under high-temperature heat treatment conditions.

[0180] Pulp molding reinforcement experiment:

[0181] This experiment simulates the production process of molded pulp products to verify the reinforcing and dimensional stabilizing effects of the polymer. Waste paper pulp was loosened and diluted to a concentration of 3.0 wt%. The aqueous solution of the fiber-enhancing copolymer was pre-diluted with deionized water to a polymer working solution with a solid content of 1.0 wt%. The polymer working solution was added at 0.50% of the dry solids of the fiber-enhancing copolymer (based on the dry fiber mass), stirred at 300 rpm for 2 minutes, and then allowed to stand for 2 minutes for adsorption. The pulp was then formed on a vacuum filtration molding device (vacuum degree -60 kPa, filtration for 60 s) to obtain a wet preform. The wet preform was then wet-pressed on a pressing device (pressing pressure 0.40 MPa, pressing time 120 s). After drying to constant weight in an oven at 105℃, the wet preform was immediately subjected to heat treatment at 160℃ for 10 minutes for thermosetting. After cooling to room temperature, the product properties were tested: compressive strength was tested using a universal testing machine with a flat plate compression test (sample size 100mm × 100mm, loading speed 10mm / min, and the maximum compressive force was recorded as the compressive strength); Cobb 60 Water absorption was determined according to GB / T 1540-2002; the dimensional change rate under damp heat was measured after 24 hours of placement at 90% RH and 40℃, and calculated as (L1-L0) / L0×100%, where L0 is the length before treatment and L1 is the length after treatment.

[0182] Fiber / particle composite bonding experiment:

[0183] Wood chips (passed through a 40-mesh sieve) and unbleached sulfate softwood pulp were mixed at a dry weight ratio of 80:20 as the composite material matrix. Polymer solutions / dispersions with a solid content of 10.0 wt% were prepared for each example and comparative sample. 2.0% of the polymer dry solids were added based on the total amount of the oven-dry matrix matrix, i.e., 20.0 g of polymer dry solids were added per 1000 g of oven-dry matrix matrix. The polymer solution was sprayed onto the matrix matrix in batches using a spray method and stirred for 5 minutes to ensure uniform dispersion, resulting in a mixture. The mixture was loaded into a mold and pre-pressed (pre-pressing pressure 0.50 MPa, pre-pressing time 30 s), followed by hot pressing at 180℃ and 5 MPa pressure for 5 minutes to obtain a fiber / particle composite board with a thickness of 3.0 mm. After hot pressing, the board was cooled at room temperature for 30 minutes and samples were taken. After the board is subjected to temperature and humidity treatment for 24 hours according to GB / T 10739-2023, the static bending strength (MOR) and the thickness expansion rate after 24 hours of water absorption are tested according to GB / T 17657-2022 (immersion temperature 20℃, immersion time 24 hours).

[0184] Table 10 Comparison of Performance Data between Pulp Molding and Fiber / Particle Composite Materials:

[0185]

[0186] Note: Comparative Example 1 is a blank control, with only water added as the dispersion medium and no polymer added.

[0187] Analysis: Experimental results show that after high-temperature heat treatment at 160 to 180°C, the fiber-enhancing copolymer prepared by this invention can significantly improve the mechanical properties and dimensional stability of fiber-based materials.

[0188] In pulp molding experiments, Example 4 (high acid content, high partial neutralization) exhibited a compressive strength as high as 325 N, a 30% improvement over the control group and superior to glyoxal-modified PAM (Comparative Example 7, 315 N). This indicates that the ortho-dicarboxyl / anhydride structure in the polymer can undergo dehydration condensation or curing crosslinking at high temperatures, thereby forming a more rigid crosslinked network. Examples 2 and 7, which introduced hydrophobic monomers, showed the best performance in reducing Cobb value and hygrothermal dimensional change rate, indicating a synergistic effect between hydrophobic modification and thermal crosslinking mechanism.

[0189] In the fiber / particle composite material experiments, this thermosetting crosslinking effect was even more significant. The static bending strength of the boards in the example groups was generally above 40 MPa, with Example 4 reaching 46.5 MPa, far exceeding the 28.0 MPa of the control group. More importantly, the 24-hour water absorption thickness swelling rates of Examples 2 and 7 were as low as 10.8% and 11.0%, respectively, demonstrating excellent water-resistant bonding performance. In contrast, although conventional PAM (Comparative Example 2) has a high molecular weight, it lacks thermosetting groups, resulting in poor static bending strength and water resistance; while Comparative Example 8, due to the lack of sufficient crosslinking active sites (insufficient polycarboxylic acid monomers), showed a significantly weaker reinforcing effect in the composite material compared to the example groups, failing to meet the bonding requirements of high-strength boards. This further demonstrates that the specific monomer ratio in this invention is crucial for achieving reinforcement and dimensional stabilization under high-temperature heat treatment.

[0190] Application Example 6: Verification of physicochemical properties.

[0191] This application example demonstrates comprehensive physicochemical testing of all synthesized examples and comparative samples to verify the precise control of the synthesis process. The tests strictly adhered to the aforementioned standards: solid content was determined using the drying and weighing method; pH was measured using a precision pH meter; viscosity-average molecular weight (Mv) was determined using an Ubbelohde viscometer and calculated using the Mark-Houwink equation; charge density was determined using PCD titration to distinguish between anions and cations; and organic fluorine content was detected using the oxygen bomb combustion-ion selective electrode method. All tests were conducted at a constant temperature of 25°C, with each sample measured in triplicate and the average value taken to ensure data accuracy and reproducibility.

[0192] Table 11 Comparison of Physicochemical Properties:

[0193]

[0194] Note: The content of low molecular weight organic matter extracted in all examples is ≤0.10wt%.

[0195] Analysis: Physicochemical analysis results confirmed that the sample examples accurately achieved the design objectives. The viscosity-average molecular weight (Mv) of all examples was controlled at 6.0 × 10⁻⁶. 4 Up to 2.8×10 5 The concentrations were between g / mol, indicating that the chain transfer agent and polymerization process effectively suppressed excessive crosslinking. The acid values ​​(450-680 mg KOH / g) and charge density data (anionic 2.5-6.0 meq / g, cationic 0.03-0.12 meq / g) matched the preset monomer ratios, ensuring high anionicity and trace amphoteric charge characteristics. In contrast, Comparative Example 2 had a molecular weight as high as 1.2 × 10⁻⁶. 6 The concentration of fluorine in the sample was g / mol, exceeding the high-permeability design range of this invention; the cation charge density of Comparative Example 9 reached 1.05 meq / g, making it prone to excessive flocculation in application. The organic fluorine content of all samples was less than 5 mg / kg, meeting environmental protection requirements. The consistency of the physicochemical data provides a solid material basis for explaining the differences in application performance.

[0196] Experimental Results and Analysis:

[0197] Based on the experimental data from Examples 1-9, Comparative Examples 1-9, and Application Examples 1-6, the performance and structure-property relationship of the fiber-enhancing copolymer for papermaking described in this invention are analyzed as follows:

[0198] The influence of monomer components on environmental adaptability to high anion interference:

[0199] Experimental data clearly show that the specific monomer composition design of this invention is key to dealing with high anion interference environments.

[0200] Comparing Examples 1-9 with Comparative Example 1 (as a blank control) and Comparative Examples 2-7 (as conventional PAM additives), in Application Example 1 simulating a high conductivity and high DCS environment, the copolymers of the present invention exhibit significant advantages in strength indicators such as tensile index and burst index. This is attributed to the specific ratio of acrylic monomers to polycarboxylic acid monomers containing adjacent dicarboxyl groups or anhydride structures in the copolymer structure.

[0201] In particular, comparing Example 1, with an acrylic acid to polycarboxylic acid mass ratio of approximately 3:1, with Comparative Example 8, which has a ratio of 9:1 exceeding the range of 1.0:1 to 6.5:1, the former has a tensile index of 52.0 N·m / g, significantly better than the latter's 48.0 N·m / g. This confirms that when the proportion of polycarboxylic acid monomers is too low, the high-density coordination sites on the polymer chain decrease, weakening its ability to shield anionic waste and form multi-point hydrogen bonds with fibers.

[0202] Meanwhile, the introduction of trace cationic monomers is crucial. Examples 1-9 strictly control the cationic monomer ratio between 0.001:1 and 0.06:1. For example, Example 3 has extremely low cationicity, while Example 5 has relatively high cationicity, both achieving good charge control, with ΔPCD controlled within the ideal window of -20 to -80 μeq / L. In contrast, Comparative Example 9, due to an excess of cationic monomer at a ratio of approximately 0.125:1, resulted in a positive ΔPCD of +40 μeq / L, leading to charge reversal and excessive flocculation, which reduced uniformity and strength, causing its tensile index to drop to 46.5 N·m / g. This indicates that the trace cationic range defined in this invention is precisely at the balance point between anti-interference and anti-flocculation.

[0203] The effect of molecular weight on internal binding strength and permeability:

[0204] This invention controls the viscosity-average molecular weight (Mv) to be 6.0 × 10⁻⁶. 4 Up to 2.8×10 5 In the low to medium range of g / mol, this design was validated in the internal binding strength test of Application Example 3.

[0205] The viscosity-average molecular weight (Mv) is 6.5 × 10⁻⁶. 4 Example 9: g / mol and Mv: 2.8 × 10⁻⁶ 5 Example 8, with a concentration of g / mol, all exhibited excellent performance. In contrast, the high molecular weight PAM with an Mv of 1.2 × 10⁻⁶ showed superior performance. 6 Although Comparative Example 2 has a much larger molecular weight (g / mol), its internal bond strength and tensile index are inferior to those of the Example group. This indicates that excessively high molecular weight causes the polymer to mainly adsorb onto the fiber surface, resulting in flocculation, and it cannot penetrate into the micropores or interlayer regions of the fiber cell wall. The low to medium molecular weight distribution of the present invention ensures that the copolymer has excellent permeability, enabling it to enter the fiber interior and form internal reinforcement, thereby significantly improving the Scott internal bond strength. For example, in Application Example 4, the Example group generally reaches above 365 J / m², while Comparative Example 2 is only 310 J / m².

[0206] Synergistic effect of surface sizing and hydrophobic modification:

[0207] In the surface sizing experiment of Application Example 4, the synergistic effect between the copolymer and starch was significant. The surface strength of IGT in Examples 1-9 was superior to that of pure starch and conventional additives. In particular, Example 2, containing butyl acrylate, and Example 7, containing styrene, showed superior Cobb surface strength. 60 The water absorption decreased to 26.0 g / m² and 26.5 g / m², respectively, and the water droplet contact angle increased to 88°. This indicates that the hydrophobic monomers effectively migrated and oriented to the surface during the paper drying and film formation process, giving the paper excellent water resistance and verifying the effectiveness of the selection of hydrophobic monomers such as aromatic vinyl groups, vinyl esters, alkyl acrylates, or alkyl methacrylates in the claims.

[0208] The manifestation of thermosetting crosslinking mechanism in molding and composite materials:

[0209] The data from Example 5 strongly demonstrate the unique thermosetting strengthening mechanism of this invention. Under high-temperature treatment at 160°C to 180°C, the pulp molding compressive strength of Example 4, containing a higher proportion of itaconic acid and maleic anhydride, reached 325 N, and the static bending strength of the fiber composite board reached 46.5 MPa, significantly better than the unmodified or conventionally PAM-modified comparative examples.

[0210] Analysis suggests this may be related to the dehydration and condensation of adjacent dicarboxyl or anhydride groups derived from maleic acid or itaconic acid on the copolymer chain at high temperatures, leading to curing and crosslinking, thus forming a rigid crosslinked network. Comparative Example 8, due to insufficient polycarboxylic acid content, could not form enough crosslinking points, resulting in a weak high-temperature reinforcing effect. This result strongly supports the key contribution of the types and ratios of polycarboxylic acid monomers, such as maleic anhydride ratios of 0.1:1 to 0.8:1, to the thermosetting properties as described in the invention.

[0211] The effect of changes in component content on experimental results:

[0212] Based on the data trend analysis of various application examples, the changes in component content have a regular impact on the application performance of the copolymer.

[0213] Regarding the monomer ratio, experimental data show that the copolymer exhibits distinct peak characteristics in performance as the mass ratio of acrylic acid to polycarboxylic acid monomers changes. When this ratio is in the intermediate region, such as 2.0:1 to 4.0:1, the copolymer exhibits optimal overall strength properties, corresponding to the best balance between carboxyl group density and polymer chain conformation. As the relative content of the polycarboxylic acid component decreases, i.e., the ratio extends towards 6.5:1, although the performance center of gravity shifts slightly, a highly efficient reinforcing effect is still maintained; however, when the content of the polycarboxylic acid component is too low, exceeding the scope of this invention, such as Comparative Example 8, its reinforcing effect decreases significantly.

[0214] Regarding molecular weight distribution, the application properties of the copolymer change as the molecular weight increases or decreases: the mid-range molecular weight is approximately 1.5 × 10⁻⁶. 5 Up to 2.5×10 5 g / mol achieved an ideal balance between wet end retention and fiber bonding strength; as the molecular weight decreased to the lower end, it tended towards 6.0 × 10⁻⁶. 4 g / mol, the copolymer's penetration ability is enhanced, which is more conducive to improving the interlayer bonding force of high-density paper types; while as the molecular weight increases to the high end, it tends to be 2.8×10. 5 At a concentration of g / mol, it has a slight advantage in retention performance. The above experimental results demonstrate that by adjusting the component content and molecular weight parameters, specific papermaking process requirements can be precisely met, demonstrating sufficient technical rationale.

[0215] In summary, the fiber-enhancing copolymer of the present invention successfully solves the reinforcement problem under high anion interference environment by precisely controlling monomer components, charge density and molecular weight distribution, and has excellent surface enhancement and thermosetting properties, and has extremely low organic fluorine content. It is a highly efficient, multifunctional and environmentally friendly papermaking chemical.

[0216] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A papermaking fiber-boosting copolymer characterized by: The fiber-enhancing copolymer is a water-soluble or water-dispersible copolymer, and its structural units are derived from at least the following vinyl unsaturated monomers: Acrylic acid monomers and / or methacrylic acid monomers and their salts; Vinyl unsaturated polycarboxylic acid monomers containing adjacent dicarboxyl groups and / or anhydride structures and their salts; Vinyl cationic monomers containing quaternary ammonium salt groups; The dry solids mass ratio of the acrylic acid monomer and / or methacrylic acid monomer and its salt to the dry solids mass ratio of the vinyl unsaturated polycarboxylic acid monomer containing adjacent dicarboxyl groups and / or anhydride structures and its salt is 1.0:1 to 6.5:

1. The ratio of the dry solid mass of the vinyl cationic monomer containing quaternary ammonium salt groups to the total dry solid mass of the acrylic acid monomer and / or methacrylic acid monomer and its salt, as well as the vinyl unsaturated polycarboxylic acid monomer and its salt, is 0.001:1 to 0.06:

1. Furthermore, the viscosity-average molecular weight of the fiber-enhancing copolymer is 6.0 × 10⁻⁶. 4 ~2.8×10 5 g / mol, acid value 450~800mg KOH / g; Furthermore, the organic fluorine content of the fiber-enhancing copolymer is ≤5 mg / kg on a dry solids basis.

2. The fiber-enhancing copolymer according to claim 1, characterized in that: The vinyl unsaturated polycarboxylic acid monomer containing adjacent dicarboxyl groups and / or anhydride structures is selected from one or more of maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, citraconic acid, methylmaleic acid, methylfumaric acid, cis-aconitine, or trans-aconitine. When the vinyl unsaturated polycarboxylic acid monomer contains maleic anhydride, the ratio of the dry solid mass of maleic anhydride to the total dry solid mass of the vinyl unsaturated polycarboxylic acid monomer is 0.1:1 to 0.8:

1. The vinyl cationic monomer containing a quaternary ammonium salt group is selected from one or more of dimethyl diallyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, acrylamide propyl trimethyl ammonium chloride, methacryloamide propyl trimethyl ammonium chloride, quaternized dimethylaminoethyl acrylate, quaternized dimethylaminoethyl methacrylate, quaternized dimethylaminopropyl acrylamide, or quaternized dimethylaminopropyl methacrylamide.

3. The fiber-enhancing copolymer according to claim 1, characterized in that: The structural units of the fiber-enhancing copolymer are selected from nonionic hydrophilic monomers; The nonionic hydrophilic monomer is one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, polyethylene glycol acrylate, and polyethylene glycol methacrylate. And / or the structural units of the fiber-enhancing copolymer are selected from hydrophobic monomers; The hydrophobic monomer is one or more of styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl neodecanoate, C1-C20 alkyl acrylate and / or C1-C20 alkyl methacrylate.

4. The fiber-enhancing copolymer according to claim 3, characterized in that, The ratio of the dry solid mass of the nonionic hydrophilic monomer to the total dry solid mass of the acrylic acid monomer and / or methacrylic acid monomer and its salt, as well as the vinyl unsaturated polycarboxylic acid monomer and its salt, is 0:1 to 0.25:

1. Furthermore, the degree of partial neutralization of the fiber-enhancing copolymer is 0-60%, and the gel content, calculated on a dry solids basis, is ≤0.05wt%. The gel content is determined by filtration and weighing using a 100μm filter screen. The fiber-enhancing copolymer has an anionic charge density of 1.5–10.0 meq / g and a cationic charge density of 0.02–0.5 meq / g, both on a solid basis, and the ratio of anionic charge density to cationic charge density is 20:1–200:

1.

5. A process for the preparation of the fiber-reinforced copolymer according to claim 3 or 4, characterized in that The preparation method includes the following steps: Step 1. Using water as the reaction medium, prepare a first monomer solution by mixing acrylic acid monomers and / or methacrylic acid monomers and their salts, vinyl unsaturated polycarboxylic acid monomers and their salts, and nonionic hydrophilic and / or hydrophobic monomers. When the first monomer solution contains hydrophobic monomers, use mechanical stirring and / or high shear dispersion to disperse the hydrophobic monomers in the first monomer solution to obtain a dispersed first monomer solution. Separately, prepare a second monomer solution by mixing a vinyl cationic monomer containing a quaternary ammonium salt group with water to obtain the first monomer solution and the second monomer solution. Step 2. Add water to the reaction vessel, heat the reactor to 50-95°C under an inert atmosphere, add an initiator to start the polymerization, set the total polymerization dropping time, and add the first monomer liquid obtained in Step 1 to the reactor in stages or at a constant rate to obtain the polymerization reaction liquid; Step 3. Continue polymerization of the polymerization reaction solution obtained in Step 2. Add the second monomer solution obtained in Step 1 in stages or at a constant rate during 45%–90% of the total polymerization dropping time set in Step 2, so that the ratio of the dry solid mass of the vinyl cationic monomer containing quaternary ammonium salt groups to the acrylic acid monomer and / or methacrylic acid monomer and its salts, and the vinyl unsaturated polycarboxylic acid monomer and its salts is 0.001:1–0.06:

1. The viscosity-average molecular weight of the fiber-enhancing copolymer is controlled to 6.0 × 10⁻⁶ by combining the initiator dosage, chain transfer agent, and polymerization temperature. 4 ~2.8×10 5 g / mol, to obtain the target polymerization reaction solution; Step 4. The target polymerization reaction solution obtained in Step 3 is subjected to heat preservation and aging, residual monomer removal or vacuum devolatilization, pH adjustment and partial neutralization control, concentration or dilution to make the solid content 8-40 wt%, filtration to remove gel, and an aqueous solution of fiber-enhancing copolymer is obtained. The initiator is selected from one or more of persulfate, hydrogen peroxide / reducing agent redox system, and azo initiator, and the viscosity-average molecular weight and gel content of the fiber-enhancing copolymer are controlled by chain transfer agent and / or post-treatment redox system during polymerization and / or post-treatment stages; and the content of low molecular weight organic matter extracted from the obtained aqueous solution is ≤0.10wt% on a dry solids basis.

6. A papermaking wet-end pulp internal strengthening method characterized by, The method includes adding the fiber-enhancing copolymer of any one of claims 1 to 4 to the pulp during the papermaking process when the pulp and / or white water recycling system is in a high anion interference environment; The high anion interference environment refers to the particle charge density values ​​measured by a particle charge analyzer for pulp filtrate and / or white water samples being in the range of -50 to -600 μeq / L. The total amount of the fiber-enhancing copolymer added, based on dry solids, is 0.5–15 kg / ton of oven-dry pulp. The addition point is located in the wet section before and / or after the pressure screen and before the headbox, and the residence time from the last addition point to the headbox is 10–900 s.

7. The method of claim 6, wherein, The addition point is located after at least one cationic retention aid and / or filter aid component and before the addition of the particulate system, wherein the cationic retention aid and / or filter aid component is selected from one or more of cationic polyacrylamide, polydimethyldiallylammonium chloride, cationic starch, polyethyleneimine, polyaluminum chloride, aluminum sulfate, and alum; The particulate system is selected from one or more of colloidal silica, bentonite, polymeric silicate particles, and modified silicate particles; Alternatively, the aqueous solution of the fiber-enhancing copolymer may be added using a dual-addition-point method, with the first addition point located at any position before or after the cationic polyacrylamide and / or polyaluminum chloride, and the second addition point located before the addition of the particulate system, and the mass ratio of the addition amount of the first addition point to the second addition point being 0.2:1 to 5:

1.

8. The method of claim 6, wherein, The method uses the particle charge density value of the pulp system as the charge window control parameter, and controls the change in particle charge density relative to the value before addition, ΔPCD, to be -10 to -110 μeq / L, where ΔPCD is the particle charge density value after addition of the fiber-enhancing copolymer minus the particle charge density value before addition. Alternatively, when adding the fiber-enhancing copolymer, it can be prepared as a working solution with a solid content controlled at 0.1–10 wt%.

9. A surface sizing boost method, characterized by, The method includes adding the fiber-enhancing copolymer of any one of claims 1 to 4 to a gelatinized surface sizing solution and applying it to the surface of a paper sheet, wherein the amount of fiber-enhancing copolymer added relative to the dry starch base is 0.05 to 20 wt%, or the amount of fiber-enhancing copolymer applied is 0.5 to 20 kg / ton of paper.

10. A method of spray starch potentiation, characterized by, The method includes adding the fiber-enhancing copolymer of any one of claims 1 to 4 to a gelatinized starch spray solution and applying it to the surface of a paper sheet, wherein the amount of fiber-enhancing copolymer added relative to the dry starch is 0.05 to 20 wt%, or the amount of fiber-enhancing copolymer applied is 0.5 to 20 kg / ton of paper.

11. A method for reinforcing pulp through molding, characterized in that, The method includes adding the fiber-enhancing copolymer of any one of claims 1 to 4 to the fiber suspension during the molding slurry preparation stage, such that the amount of the fiber-enhancing copolymer added is 0.1 to 5 wt% based on oven-dry fiber or particulate dry basis; The product is formed or pressed, dehydrated, dried, and then heat-treated at 80–200°C for 0.5–30 min to improve its strength and dimensional stability.

12. A method of bonding a fiber / particle composite material, characterized by, The method comprises applying the fiber-enhancing copolymer according to any one of claims 1 to 4 to at least one of wood fiber, bamboo fiber, wood chips, cork particles, or synthetic fiber, such that the amount of fiber-enhancing copolymer added, based on the dry basis of oven-dry fiber or particles, is 0.1 to 5 wt%. The product is formed or pressed, dehydrated, dried, and then heat-treated at 80–200°C for 0.5–30 min to improve its strength and dimensional stability.

13. A fibrous base article characterized by, The fiber-based product is paper, paperboard, pulp molded product or fiber / particle composite material, and the fiber-based product contains the fiber-enhancing copolymer according to any one of claims 1 to 4, and the fiber-enhancing copolymer accounts for 0.01 to 5 wt% of the oven-dry weight of the fiber-based product in solids.

Images