A nanocellulose modified polyacrylate papermaking pulp internal sizing agent

Abstract

This application relates to the field of papermaking additives technology, and discloses a nanocellulose-modified polyacrylate papermaking pulp internal sizing agent. This sizing agent combines high hydrophobicity, water pressure resistance, and mechanical reinforcement, and is prepared by mixing a positively charged polyacrylate emulsion with a modified nanocellulose dispersion. The positively charged polyacrylate emulsion is polymerized from deionized water, polyoxyethylene octylphenyl ether, hexadecyltrimethylammonium bromide, potassium persulfate, methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, methacryloxyethyltrimethylammonium chloride, and ethylene glycol dimethacrylate. The modified nanocellulose dispersion is prepared by mixing hydrophobic modified nanocellulose with deionized water; the hydrophobic modified nanocellulose is prepared by reacting oven-dried nanocellulose, deionized water, potassium persulfate, and methyl methacrylate. Methacryloxyethyltrimethylammonium chloride introduces cationic groups, improving the retention rate of the nanocellulose-modified polyacrylate papermaking pulp internal sizing agent.

Description

Technical Field

[0001] This invention relates to the field of papermaking additives technology, specifically to a nanocellulose-modified polyacrylate papermaking pulp internal sizing agent. Background Technology

[0002] In the papermaking industry, internal sizing agents are widely used to improve the water resistance of paper. Polyacrylate emulsion, as a common internal sizing agent, can form a film that covers the surface of pulp fibers, thereby preventing water from penetrating into the paper. Conventional anionic or nonionic polyacrylate emulsions lack positive charge and cannot form effective electrostatic adsorption on the negatively charged surface of pulp fibers. This results in a low retention rate of polyacrylate emulsion during the papermaking process, with a large amount of polyacrylate emulsion being lost with white water. This leads to poor sizing effect of the internal sizing agent and increased production costs. At the same time, the mechanical strength of the film formed by conventional polyacrylate emulsion is limited. The waterproof film formed by polyacrylate emulsion is easily damaged when the paper is subjected to external forces, which limits the improvement of the final water resistance of the paper.

[0003] Nanocellulose possesses physical characteristics such as large specific surface area and high mechanical strength, making it suitable for inclusion as a reinforcing material in polymer systems. However, unmodified nanocellulose contains a large number of polar hydroxyl groups on its surface, exhibiting hydrophilic properties. When unmodified nanocellulose is directly added to hydrophobic polyacrylate emulsions, hydrogen bonding easily occurs between the unmodified nanocellulose particles, leading to localized aggregation. This aggregation prevents the unmodified nanocellulose from being evenly distributed within the polyacrylate emulsion matrix. Consequently, it not only fails to exert the structural reinforcing effect of nanocellulose but also damages the physical stability of the polyacrylate emulsion, causing demulsification or gelation of the polyacrylate paper pulp internal sizing agent during long-term storage and actual use.

[0004] Therefore, this invention proposes a nanocellulose-modified polyacrylate paper pulp internal sizing agent to overcome the shortcomings of the prior art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a nanocellulose-modified polyacrylate paper pulp internal sizing agent. This sizing agent combines high hydrophobicity, water pressure resistance, and mechanical enhancement, solving the problems of poor sizing effect due to low retention rate on pulp fiber surface and insufficient film strength of polyacrylate emulsion limiting the improvement of water resistance performance of the sizing agent.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a nanocellulose-modified polyacrylate paper pulp internal sizing agent, which is prepared by mixing a positively charged polyacrylate emulsion with a modified nanocellulose dispersion; By weight, the positively charged polyacrylate emulsion is polymerized from emulsion preparation raw materials, which include: 250-350 parts by weight of deionized water, 2.0-3.0 parts by weight of polyoxyethylene octylphenyl ether, 2.0-3.0 parts by weight of hexadecyltrimethylammonium bromide, 0.5-1.5 parts by weight of potassium persulfate, 70-76 parts by weight of methyl methacrylate, 14-21 parts by weight of butyl acrylate, 4-8 parts by weight of hydroxyethyl acrylate, 2-6 parts by weight of methacryloyloxyethyltrimethylammonium chloride, and 1-3 parts by weight of ethylene glycol dimethacrylate. After polymerization, the emulsion preparation raw materials form 90-110 parts by weight of oven-dry solids in the positively charged polyacrylate emulsion. The modified nanocellulose dispersion contains 20-34 parts by weight of hydrophobic modified nanocellulose and 400-670 parts by weight of deionized water; Hydrophobically modified nanocellulose is made from cellulose-modified raw materials, which include: 8-12 parts by weight of oven-dried nanocellulose, 700-900 parts by weight of deionized water, 0.6-1.3 parts by weight of potassium persulfate, and 50-75 parts by weight of methyl methacrylate.

[0007] By adopting the above technical solution, the emulsion system is constructed by mixing polyoxyethylene octylphenyl ether and hexadecyltrimethylammonium bromide. Combined with potassium persulfate initiating the free radical polymerization reaction of methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, methacryloxyethyltrimethylammonium chloride, and ethylene glycol dimethacrylate, the methacryloxyethyltrimethylammonium chloride introduces quaternary ammonium salt cationic groups into the polymer chain segments during the reaction. This gives the positively charged polyacrylate emulsion a positive charge, while the pulp fiber surface becomes negatively charged. The positively charged polyacrylate emulsion can be adsorbed onto the pulp fiber surface using the attraction between positive and negative charges, improving the retention rate of sizing agents in papermaking pulp. Ethyl glycol dimethacrylate participates in the copolymerization reaction to generate crosslinking nodes, constructing a three-dimensional network crosslinked structure, thus enhancing the structural stability of the positively charged polyacrylate emulsion. Meanwhile, potassium persulfate was used to initiate a graft copolymerization reaction of methyl methacrylate on the surface of oven-dried nanocellulose. The specific reaction mechanism included: First, potassium persulfate decomposed under heating conditions to generate sulfate radicals. The sulfate radicals extracted hydrogen atoms from the hydroxyl groups on the surface of oven-dried nanocellulose, generating cellulose macromolecular radicals. The cellulose macromolecular radicals initiated chain initiation and chain growth reactions of methyl methacrylate monomers, forming polymethyl methacrylate branches on the surface of oven-dried nanocellulose, thus completing the hydrophobic modification of oven-dried nanocellulose. After hydrophobic modification, the surface polarity of the hydrophobic modified nanocellulose was reduced, allowing it to be uniformly dispersed in positively charged polyacrylate emulsions. The hydrophobic modified nanocellulose was distributed inside the polyacrylate matrix. Relying on the physical entanglement between the surface grafted segments and the positively charged polyacrylate emulsion molecular chains, the mechanical strength and water resistance of the positively charged polyacrylate emulsion film were enhanced. Therefore, the retention rate of the internal sizing agent in paper pulp and the water resistance of the paper were improved.

[0008] Preferably, the preparation process of the positively charged polyacrylate emulsion includes: dissolving deionized water, polyoxyethylene octylphenyl ether, and hexadecyltrimethylammonium bromide in the emulsion preparation raw materials; then adding methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, methacryloyloxyethyltrimethylammonium chloride, and ethylene glycol dimethacrylate in the emulsion preparation raw materials; mechanically stirring at 700 r / min to 900 r / min at room temperature for 30 min to 50 min to obtain a pre-emulsion; dissolving potassium persulfate in 15 to 25 parts by weight of deionized water in the emulsion preparation raw materials to obtain a potassium persulfate aqueous solution; adding 30% to 35% of the pre-emulsion by weight into a reaction vessel and heating to 70°C. At 80℃, add 45%–55% potassium persulfate aqueous solution (by mass) and mechanically stir for 20–40 minutes at a constant temperature to form a seed emulsion. Add the remaining unmixed pre-emulsion and the remaining unmixed potassium persulfate aqueous solution dropwise to the reaction vessel containing the seed emulsion at a uniform rate, setting the dropwise addition time to 2.5–3.5 hours, and controlling the reaction temperature within the reaction vessel to be constant at 76℃–79℃. After the dropwise addition is complete, maintain the reaction temperature at 76℃–79℃ for 1.0–2.0 hours. After the reaction is complete, cool the temperature to 15℃–30℃ and add 4%–6% sodium bicarbonate aqueous solution as an alkaline regulator to adjust the pH value of the substances in the reaction vessel to 6.2–6.8. Filter through an 80–120 mesh filter to obtain a positively charged polyacrylate emulsion.

[0009] By adopting the above technical solution, a seed emulsion is pre-formed as the reaction center for the polymerization reaction. Subsequently, a pre-emulsion and potassium persulfate aqueous solution are added dropwise at a uniform rate to control the monomer concentration and free radical concentration. This allows for control of the particle size and distribution of the positively charged polyacrylate emulsion, preventing burst polymerization. The isothermal reaction and heat preservation reaction improve the monomer conversion rate. After cooling, sodium bicarbonate aqueous solution is added to adjust the pH of the reaction system, preventing the positively charged polyacrylate emulsion from demulsifying and gelling under acidic conditions, and maintaining the long-term storage stability of the positively charged polyacrylate emulsion.

[0010] Preferably, the preparation process of hydrophobically modified nanocellulose includes: dispersing oven-dried nanocellulose in deionized water in cellulose-modified raw materials, adding potassium persulfate from the cellulose-modified raw materials, and mechanically stirring for 1.5h to 2.5h under constant temperature water bath heating at 60℃ to 65℃ for the first stage of mechanical stirring; then adding methyl methacrylate from the cellulose-modified raw materials, and continuing mechanical stirring for 7h to 9h under constant temperature water bath heating at 60℃ to 65℃ for the second stage of mechanical stirring to obtain a mixed reaction product; centrifuging the mixed reaction product to collect the lower colloidal product, and centrifuging and washing the lower colloidal product 2 to 4 times with deionized water, ethyl acetate, and acetone respectively, with each centrifugation and washing time set to 8min to 12min; and drying to obtain hydrophobically modified nanocellulose.

[0011] By adopting the above technical solution, the first stage of mechanical stirring allows potassium persulfate to penetrate into the oven-dry nanocellulose dispersion system to generate initial active free radicals. The second stage of mechanical stirring adds methyl methacrylate monomer, allowing the graft polymerization reaction to fully proceed on the surface of the oven-dry nanocellulose. Centrifugation and subsequent washing with deionized water, ethyl acetate, and acetone can remove unreacted methyl methacrylate monomers and polymethyl methacrylate homopolymers generated in the mixed reaction product, thereby improving the purity of the hydrophobically modified nanocellulose and preventing impurities from interfering with the subsequent mixing of the hydrophobically modified nanocellulose and the positively charged polyacrylate emulsion.

[0012] Preferably, the preparation process of the nanocellulose-modified polyacrylate paper pulp internal sizing agent is as follows: hydrophobic modified nanocellulose is dispersed in 400-670 parts by weight of deionized water contained in the modified nanocellulose dispersion to obtain a modified nanocellulose dispersion. The modified nanocellulose dispersion is added to a positively charged polyacrylate emulsion and mechanically stirred in a constant temperature water bath at 55℃-65℃ for 1.5h-2.5h. After cooling to room temperature, the nanocellulose-modified polyacrylate paper pulp internal sizing agent is obtained.

[0013] By adopting the above technical solution, the hydrophobic modified nanocellulose is pre-dispersed in deionized water to form a uniform state, which can avoid the local agglomeration caused by the direct addition of hydrophobic modified nanocellulose to the positively charged polyacrylate emulsion. Mechanical stirring is carried out under constant temperature water bath conditions of 55℃~65℃ to promote the mixing between the modified nanocellulose dispersion and the positively charged polyacrylate emulsion, so that the hydrophobic modified nanocellulose is uniformly distributed inside the positively charged polyacrylate emulsion, and a nanocellulose modified polyacrylate paper pulp internal sizing agent with uniform component distribution is obtained.

[0014] This invention provides a nano-cellulose-modified polyacrylate paper pulp internal sizing agent. It has the following beneficial effects: 1. This invention involves adding methacryloyloxyethyltrimethylammonium chloride to the raw materials for emulsion preparation to participate in the free radical polymerization reaction. Methacryloxyethyltrimethylammonium chloride introduces quaternary ammonium salt cationic groups into the polymer chain segments, making the positively charged polyacrylate emulsion have positive charge properties and the pulp fiber surface have negative charge. The positively charged polyacrylate emulsion can be adsorbed onto the pulp fiber surface by the attraction between positive and negative charges, thereby improving the retention rate of nanocellulose modified polyacrylate paper pulp internal sizing agent on the pulp fiber surface.

[0015] 2. This invention utilizes potassium persulfate to initiate a graft copolymerization reaction of methyl methacrylate on the surface of oven-dry nanocellulose, generating hydrophobically modified nanocellulose with polymethyl methacrylate side chains on its surface. After hydrophobic modification, the surface polarity of the hydrophobically modified nanocellulose is reduced, allowing it to be uniformly distributed within the positively charged polyacrylate emulsion. The grafted segments on the surface of the hydrophobically modified nanocellulose become physically entangled with the molecular chains of the positively charged polyacrylate emulsion, enhancing the mechanical strength and water resistance of the positively charged polyacrylate emulsion film and improving the water resistance of paper sizing.

[0016] 3. In this invention, ethylene glycol dimethacrylate is added to the raw materials for emulsion preparation. Ethylene glycol dimethacrylate participates in the free radical copolymerization reaction to generate cross-linking nodes, which promotes the construction of a three-dimensional network cross-linked structure in the positively charged polyacrylate emulsion. After the reaction is completed, the temperature is lowered and sodium bicarbonate aqueous solution is added dropwise to adjust the pH value, preventing the positively charged polyacrylate emulsion from demulsifying and gelling under acidic conditions, and maintaining the structural stability and long-term storage stability of the positively charged polyacrylate emulsion and the nanocellulose-modified polyacrylate paper pulp internal sizing agent.

[0017] 4. When the nanocellulose-modified polyacrylate pulp sizing agent prepared in this invention is applied to the papermaking of high-end specialty papers such as car speaker cones, the natural polysaccharide skeleton structure retained inside the hydrophobic modified nanocellulose remains intact. The residual hydroxyl groups carried by the natural polysaccharide skeleton form a dense hydrogen bond network with the pulp fibers. The dense hydrogen bond network, together with the polymer hydrophobic membrane, improves the overall density, macroscopic bending stiffness, and elastic modulus of the car speaker cone. The increase in elastic modulus increases the propagation speed of ultrasonic pulses inside the car speaker cone, thereby improving the acoustic response efficiency of the car speaker cone in the high-frequency electroacoustic signal conversion process. Attached Figure Description

[0018] Figure 1 This is a magnified comparison diagram of the infrared spectrum of the present invention. Figure 2 This is a schematic diagram of the Zeta potential comparison of the present invention; Figure 3 This is a schematic diagram comparing the centrifugal sedimentation rates of the present invention; Figure 4 This is a comparative schematic diagram showing the retention effect of the sizing agent in the slurry according to the present invention; Figure 5 This is a schematic diagram comparing the conventional hydrophobic properties of the paper surface according to the present invention; Figure 6 This is a schematic diagram comparing the paper's depth impermeability and water pressure resistance according to the present invention; Figure 7 This is a comparative schematic diagram of the paper mechanical strengthening properties of the present invention; Figure 8 This is a schematic diagram comparing the hydrophobic properties of the present invention; Figure 9 This is a comparative schematic diagram of the water pressure resistance performance of the present invention; Figure 10 This is a schematic diagram comparing the mechanical and acoustic properties of the present invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing hydrophobically modified nanocellulose, including the following steps: Disperse 10g of oven-dried nanocellulose in 800mL of deionized water into a three-necked flask, add 0.9g of potassium persulfate, and mechanically stir for 2h under constant temperature water bath heating at 62℃. Add 60g of methyl methacrylate to a three-necked flask and continue mechanical stirring for 7.5h under constant temperature water bath conditions of 62℃; After the reaction was completed, the suspension was centrifuged at high speed for 10 minutes and the lower colloidal product was collected. The lower colloidal product was washed three times each with deionized water, ethyl acetate, and acetone, with each washing time being 10 min, to remove unreacted methyl methacrylate monomers and polymethyl methacrylate homopolymers. After drying, hydrophobic modified nanocellulose was obtained.

[0021] Preparation Example 2: This preparation example provides a method for preparing hydrophobically modified nanocellulose, including the following steps: Disperse 8g of oven-dried nanocellulose in 700mL of deionized water into a three-necked flask, add 0.6g of potassium persulfate, and mechanically stir for 1.5h under constant temperature water bath heating at 60℃. Add 50g of methyl methacrylate to a three-necked flask and continue mechanical stirring for 7h under constant temperature water bath conditions of 60℃; After the reaction was completed, the suspension was centrifuged at high speed for 10 minutes and the lower colloidal product was collected. The lower colloidal product was washed twice by centrifugation with deionized water, ethyl acetate, and acetone, respectively, for 8 minutes each time, to remove unreacted methyl methacrylate monomers and polymethyl methacrylate homopolymers. After drying, hydrophobic modified nanocellulose was obtained.

[0022] Preparation Example 3: This preparation example provides a method for preparing hydrophobically modified nanocellulose, including the following steps: Disperse 12g of oven-dried nanocellulose in 900mL of deionized water into a three-necked flask, add 1.3g of potassium persulfate, and mechanically stir for 2.5h under constant temperature water bath heating at 65℃. Add 75g of methyl methacrylate to a three-necked flask and continue mechanical stirring for 9 hours under constant temperature water bath conditions of 65℃; After the reaction was completed, the suspension was centrifuged at high speed for 10 minutes and the lower colloidal product was collected. The lower colloidal product was washed four times each with deionized water, ethyl acetate, and acetone, with each washing time being 12 min, to remove unreacted methyl methacrylate monomers and polymethyl methacrylate homopolymers. After drying, hydrophobic modified nanocellulose was obtained.

[0023] Examples 1-3: Example 1: This example provides a nanocellulose-modified polyacrylate paper pulp internal sizing agent, comprising: Add 300 parts by weight of deionized water, 2.5 parts by weight of polyoxyethylene octylphenyl ether, and 2.5 parts by weight of hexadecyltrimethylammonium bromide to a beaker, and stir until the polyoxyethylene octylphenyl ether and hexadecyltrimethylammonium bromide are completely dissolved. 76 parts by weight of methyl methacrylate, 15 parts by weight of butyl acrylate, 8 parts by weight of hydroxyethyl acrylate, 3 parts by weight of methacryloyloxyethyltrimethylammonium chloride, and 3 parts by weight of ethylene glycol dimethacrylate were added to a beaker in sequence. The mixture was mechanically stirred at 800 r / min for 40 min at room temperature to obtain a pre-emulsion. Dissolve 1.0 part by weight of potassium persulfate in 20 parts by weight of deionized water to prepare an aqueous solution of potassium persulfate; add one-third of the pre-emulsion to a three-necked flask equipped with a condenser and a mechanical stirrer, heat to 75°C, add half of the potassium persulfate aqueous solution, and stir mechanically at a constant temperature for 30 minutes to form a seed emulsion. Over the next 3 hours, the remaining two-thirds of the pre-emulsion and the remaining half of the potassium persulfate aqueous solution were added dropwise to the three-necked flask at a constant rate, while maintaining the reaction temperature in the three-necked flask at 78°C. After the addition was completed, the reaction was continued at 78°C for 1.5 hours. After the reaction is complete, the temperature is lowered to below 30°C, and a 5% sodium bicarbonate aqueous solution is slowly added dropwise to adjust the pH of the reaction product to 6.5. The product is then filtered through a 100-mesh filter to obtain a positively charged polyacrylate emulsion. Weigh 25 parts by weight of the hydrophobic modified nanocellulose prepared in Example 1, disperse the hydrophobic modified nanocellulose in 500 parts by weight of deionized water, and ultrasonically disperse it for 30 minutes using an ultrasonic cell disruptor to obtain a modified nanocellulose dispersion. Measure 100 parts by weight of positively charged polyacrylate emulsion based on oven-dry solids content, slowly add modified nanocellulose dispersion to positively charged polyacrylate emulsion, and place the mixture of positively charged polyacrylate emulsion and modified nanocellulose dispersion in a constant temperature water bath at 60℃ and mechanically stir for 2 hours; after cooling to room temperature, nanocellulose modified polyacrylate paper pulp internal sizing agent is obtained.

[0024] Example 2: This example provides a nanocellulose-modified polyacrylate paper pulp internal sizing agent, comprising: Add 250 parts by weight of deionized water, 2.0 parts by weight of polyoxyethylene octylphenyl ether, and 2.0 parts by weight of hexadecyltrimethylammonium bromide to a beaker, and stir until the polyoxyethylene octylphenyl ether and hexadecyltrimethylammonium bromide are completely dissolved. Add 70 parts by weight of methyl methacrylate, 14 parts by weight of butyl acrylate, 4 parts by weight of hydroxyethyl acrylate, 2 parts by weight of methacryloyloxyethyltrimethylammonium chloride, and 1 part by weight of ethylene glycol dimethacrylate to a beaker in sequence. Stir mechanically at 700 r / min for 30 min at room temperature to obtain a pre-emulsion. Dissolve 0.5 parts by weight of potassium persulfate in 15 parts by weight of deionized water to prepare an aqueous solution of potassium persulfate; add 30% of the total mass of the pre-emulsion to a three-necked flask equipped with a condenser and a mechanical stirrer, heat to 70°C, add 45% of the total mass of the potassium persulfate aqueous solution, and stir mechanically at a constant temperature for 20 minutes to form a seed emulsion. Over the next 2.5 hours, the remaining 70% by mass of the pre-emulsion and the remaining 55% by mass of the potassium persulfate aqueous solution were added dropwise to the three-necked flask at a constant rate, while maintaining the reaction temperature in the three-necked flask at 76°C. After the addition was completed, the reaction was continued at 76°C for 1.0 hour. After the reaction was completed, the temperature was lowered to 15°C, and a 4% sodium bicarbonate aqueous solution was slowly added dropwise to adjust the pH of the reaction product to 6.2. The product was then filtered through an 80-mesh filter to obtain a positively charged polyacrylate emulsion. Weigh 20 parts by weight of the hydrophobic modified nanocellulose prepared in Example 2, disperse the hydrophobic modified nanocellulose in 400 parts by weight of deionized water, and ultrasonically disperse it for 30 minutes using an ultrasonic cell disruptor to obtain a modified nanocellulose dispersion. Measure 100 parts by weight of positively charged polyacrylate emulsion based on oven-dry solids content, slowly add modified nanocellulose dispersion to positively charged polyacrylate emulsion, and place the mixture of positively charged polyacrylate emulsion and modified nanocellulose dispersion in a constant temperature water bath at 55℃ and mechanically stir for 1.5h; after cooling to room temperature, nanocellulose modified polyacrylate paper pulp internal sizing agent is obtained.

[0025] Example 3: This example provides a nanocellulose-modified polyacrylate paper pulp internal sizing agent, comprising: Add 350 parts by weight of deionized water, 3.0 parts by weight of polyoxyethylene octylphenyl ether, and 3.0 parts by weight of hexadecyltrimethylammonium bromide to a beaker, and stir until the polyoxyethylene octylphenyl ether and hexadecyltrimethylammonium bromide are completely dissolved; 70 parts by weight of methyl methacrylate, 21 parts by weight of butyl acrylate, 4 parts by weight of hydroxyethyl acrylate, 6 parts by weight of methacryloyloxyethyltrimethylammonium chloride, and 1 part by weight of ethylene glycol dimethacrylate were added to a beaker in sequence. The mixture was mechanically stirred at 900 r / min for 50 min at room temperature to obtain a pre-emulsion. Dissolve 1.5 parts by weight of potassium persulfate in 25 parts by weight of deionized water to prepare an aqueous solution of potassium persulfate; add 35% of the total mass of the pre-emulsion to a three-necked flask equipped with a condenser and a mechanical stirrer, heat to 80°C, add 55% of the total mass of the potassium persulfate aqueous solution, and stir mechanically at a constant temperature for 40 minutes to form a seed emulsion. Over the next 3.5 hours, the remaining 65% by mass of the pre-emulsion and the remaining 45% by mass of the potassium persulfate aqueous solution were added dropwise to the three-necked flask at a constant rate, while maintaining the reaction temperature in the three-necked flask at 79°C. After the addition was completed, the reaction was continued at 79°C for 2.0 hours. After the reaction was completed, the temperature was lowered to 30°C, and a 6% sodium bicarbonate aqueous solution was slowly added dropwise to adjust the pH of the reaction product to 6.8. The product was then filtered through a 120-mesh filter to obtain a positively charged polyacrylate emulsion. Weigh 34 parts by weight of the hydrophobic modified nanocellulose prepared in Example 3, disperse the hydrophobic modified nanocellulose in 670 parts by weight of deionized water, and ultrasonically disperse it for 30 min using an ultrasonic cell disruptor to obtain a modified nanocellulose dispersion. Measure 100 parts by weight of positively charged polyacrylate emulsion based on oven-dry solids content, slowly add modified nanocellulose dispersion to positively charged polyacrylate emulsion, and place the mixture of positively charged polyacrylate emulsion and modified nanocellulose dispersion in a constant temperature water bath at 65℃ and mechanically stir for 2.5h; after cooling to room temperature, nanocellulose modified polyacrylate paper pulp internal sizing agent is obtained.

[0026] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that: no modified nanocellulose dispersion is added in this comparative example, and the steps of mixing the positively charged polyacrylate emulsion with the modified nanocellulose dispersion and water bath heating and stirring are not performed; all other steps are the same.

[0027] Comparative Example 2: Compared with Example 1, the difference is that the hydrophobic modified nanocellulose in this comparative example is replaced with an equal amount of unmodified nanocellulose at oven-dry weight, while all other aspects are the same.

[0028] Comparative Example 3: The difference from Example 1 is that: in this comparative example, methacryloyloxyethyltrimethylammonium chloride was not added when preparing the preemulsion, but all other aspects were the same.

[0029] Comparative Example 4: Compared with Example 1, the difference is that in this comparative example, when preparing the preemulsion, 2.5 parts by weight of polyoxyethylene octylphenyl ether and 2.5 parts by weight of hexadecyltrimethylammonium bromide were replaced with 5.0 parts by weight of sodium dodecylbenzenesulfonate, an anionic emulsifier, while the rest were the same.

[0030] Test Examples 1-5: Test Example 1: Verification of the Chemical Structure and Surface Charge of Sizing Agent Components Unmodified nanocellulose and hydrophobic modified nanocellulose prepared in Preparation Example 1 were placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain completely dried powder samples.

[0031] Weigh 2 mg of dried unmodified nanocellulose powder and mix it with 200 mg of potassium bromide powder. Grind the mixture evenly in an agate mortar and press it into transparent sheets using a tablet press at a pressure of 10 MPa. The same steps were used to press the dried hydrophobic modified nanocellulose powder obtained in Preparation Example 1 into transparent sheets.

[0032] The transparent thin film was placed in the sample chamber of the Fourier transform infrared spectrometer at 4000 cm⁻¹. -1 Up to 400cm -1 The infrared spectrum was recorded by scanning within the wavenumber range, and the data was extracted at 1720 cm⁻¹. -1 The transmittance values ​​of the characteristic absorption peaks representing the carbonyl group of the ester.

[0033] Take 1g of each of the positively charged polyacrylate emulsions prepared in Example 1, Example 2, and Example 3, and add them to 1000g of deionized water, stirring until homogeneous to prepare diluted test solutions. Prepare a 0.1% (w / w) suspension by adding unmodified nanocellulose to deionized water.

[0034] The diluted test solution and suspension were injected separately into the sample cell of the Zeta potential analyzer and measured under constant temperature conditions of 25°C. The Zeta potential values ​​were recorded.

[0035] Table 1. Test data of chemical structural characteristic peaks and surface charge of sizing agent components Conclusions and Analysis: According to Table 1, Figure 1 and Figure 2 Data shows that unmodified nanocellulose at 1720 cm⁻¹ -1 The transmittance of the nearby ester carbonyl absorption peak was 98.4%, and it did not exhibit characteristic absorption; the hydrophobic modified nanocellulose prepared in Example 1 showed a transmittance of 1720 cm⁻¹. -1The transmittance of the nearby ester carbonyl absorption peak decreased to 62.7%, and a characteristic absorption peak appeared. This indicates that, under the action of the initiator, methyl methacrylate monomers underwent a graft copolymerization reaction on the surface of nanocellulose. The grafting of methyl methacrylate onto the nanocellulose surface forms hydrophobic side chains, reducing the density of hydrophilic hydroxyl groups on the nanocellulose surface. This solves the problem of untreated nanocellulose agglomerating in a hydrophobic polyacrylate matrix, ensuring the interfacial compatibility when the hydrophobically modified nanocellulose is mixed with the polyacrylate emulsion.

[0036] According to Table 1, Figure 1 and Figure 2 According to the data, the Zeta potentials of the positively charged polyacrylate emulsions prepared in Example 1, Example 2, and Example 3 were +35.4 mV, +31.7 mV, and +47.2 mV, respectively, all of which were positively charged. The Zeta potential of the unmodified nanocellulose was -16.8 mV, indicating a negative charge. The pulp fibers in the papermaking system also carried a negative charge. The introduction of the cationic monomer methacryloyloxyethyltrimethylammonium chloride during the polyacrylate emulsion synthesis stage resulted in a positive charge on the surface of the polyacrylate emulsion particles. These positively charged polyacrylate emulsion particles could be adsorbed and precipitated onto the negatively charged pulp fibers and nanocellulose surface through electrostatic attraction. The electrostatic adsorption of the positively charged polyacrylate emulsion reduced the loss of waterproofing components in the papermaking white water, solving the problem of low retention rate of non-ionic waterproofing emulsions when added to papermaking pulp.

[0037] Test Example 2: Evaluation of Emulsion Stability and In-Plasma Retention Rate 50 mL of the nanocellulose-modified polyacrylate paper pulp internal sizing agent prepared in Examples 1 to 3 and the reaction mixture prepared in Comparative Examples 2 to 4 were respectively placed into centrifuge tubes with a volume of 100 mL.

[0038] Centrifuge tubes containing the test samples were placed in a benchtop high-speed centrifuge and centrifuged continuously at 3000 rpm for 15 min. After centrifugation, the centrifuge tubes were removed, the supernatant was poured off, and the precipitate at the bottom of the tubes was transferred to a pre-weighed petri dish. The petri dish was then placed in a 105℃ constant-temperature drying oven and dried to constant weight. The mass of the dried precipitate was weighed, and the centrifugal sedimentation rate was calculated.

[0039] Weigh out a fixed amount of oven-dried bleached coniferous sulfate pulp board, soak and tear the board, then place it in a Walley beater for beating until the pulp freeness reaches 40°SR. Dilute the beated pulp with deionized water to obtain a pulp suspension with a mass fraction of 1.0%.

[0040] Weigh 1000g of pulp suspension into a beaker, and add the nanocellulose-modified polyacrylate paper pulp internal sizing agent prepared in Examples 1 to 3 (based on 3.0% of the oven-dry pulp weight), and the reaction mixture prepared in Comparative Examples 2 to 4. Mechanically stir the mixture in the beaker at 500 rpm for 5 minutes.

[0041] The well-stirred pulp suspension is poured into a sheet forming machine for sheet forming and dewatering. All white water that leaks through the filter during dewatering is collected. The chemical oxygen demand (COD) of the white water is measured using a rapid COD analyzer. The retention rate is calculated based on the difference between the total organic matter content in the added sizing agent and the residual organic matter content in the white water.

[0042] Table 2. Test data on centrifugal stability and retention rate of sizing agent emulsions in slurry. Conclusions and Analysis: According to Table 2, Figure 3 and Figure 4 According to the data, the centrifugal sedimentation rate of the nanocellulose-modified polyacrylate paper pulp internal sizing agent prepared in Example 1 was 1.2%, while the centrifugal sedimentation rate of the reaction mixture prepared in Comparative Example 2 reached 18.4%. In Comparative Example 2, the unmodified nanocellulose surface had a large number of hydrophilic hydroxyl groups, exhibiting poor compatibility in the hydrophobic positively charged polyacrylate emulsion matrix, easily leading to particle agglomeration and sedimentation. In Example 1, the hydrophobically modified nanocellulose surface was grafted with hydrophobic polymethyl methacrylate side chains, significantly improving the interfacial compatibility between the nano-reinforcing phase and the polyacrylate continuous phase, maintaining the uniform dispersion of nanocellulose in the composite emulsion. The centrifugal sedimentation rate of the reaction mixture prepared in Comparative Example 4 reached... 45.7% of sodium dodecylbenzenesulfonate, as an anionic emulsifier, underwent a strong charge neutralization reaction with the cationic monomer methacryloyloxyethyltrimethylammonium chloride introduced in the synthesis of polyacrylate, leading to demulsification and flocculation. The polyoxyethylene octylphenyl ether and hexadecyltrimethylammonium bromide composite emulsification system established in this invention avoids the problem of positive and negative charge conflict and ensures the physical stability of the polymerization system and the final product. In Comparative Example 4, a large number of coarse polymer particles were generated due to demulsification and flocculation. Although these coarse particles were physically intercepted by the fiber network during papermaking, resulting in acceptable retention data, they completely lost the ability to uniformly form a film on the surface of micron-sized fibers, thus seriously affecting the actual sizing effect.

[0043] According to Table 2, Figure 3 and Figure 4According to the data, the pulp retention rate of Example 1 reached 92.4%, and the corresponding white water chemical oxygen demand was as low as 124.5 mg / L. The pulp retention rate of the reaction mixture prepared in Comparative Example 3 was only 42.3%, and the corresponding white water chemical oxygen demand soared to 895.6 mg / L. In Comparative Example 3, no methacryloyloxyethyltrimethylammonium chloride was added during the reaction process. The synthesized polyacrylate emulsion lacked the permanent structural positive charge provided by the cationic monomer copolymerization. Although cationic surfactants were present in the system, under the extremely diluted conditions of the papermaking process, small molecule surfactants were easily desorbed from the surface of polymer particles. Polymer microparticles themselves cannot generate stable and strong electrostatic attraction with naturally negatively charged pulp fibers. In the papermaking and dewatering process, a large number of polymer microparticles lacking electrostatic adsorption capacity fail to adhere to the fiber surface and instead enter the white water system in large quantities through the filter screen with the water flow, resulting in the loss of active ingredients and a sharp increase in the wastewater treatment load of papermaking. In Example 1, the cationic monomer methacryloyloxyethyltrimethylammonium chloride provides a permanent positive charge to the polyacrylate emulsion particles. The positively charged polyacrylate emulsion particles can quickly deposit and coat the negatively charged pulp fiber surface by relying on strong opposite electrostatic attraction, trapping most of the waterproof effective ingredients inside the paper. This effectively verifies the necessity and feasibility of cationization modification for the internal sizing process of papermaking pulp.

[0044] Test Example 3: Comparative Test of Conventional Hydrophobic Properties of Paper Surfaces The papermaking batch containing the nanocellulose-modified polyacrylate papermaking pulp internal sizing agent prepared in Examples 1 to 3 and the reaction mixture prepared in Comparative Examples 1 to 4, respectively, had a basis weight of 80 g / m³. 2 The paper sample was placed in a constant temperature and humidity chamber at 23℃ and 50% relative humidity for 24 hours for equilibration.

[0045] After balancing, the paper sample was laid flat and fixed on the stage of the contact angle measuring instrument. A 5 μL drop of deionized water was dropped onto the surface of the paper sample using a microsyringe. After standing for 10 seconds, an image was captured, and the static water contact angle between the deionized water droplet and the paper sample surface was measured. The test was repeated 5 times at different locations on the same paper sample, and the average static water contact angle was calculated.

[0046] After balancing, the paper sample was cut into circular specimens with a diameter of 125 mm, and the initial mass of the circular specimens was measured using an electronic balance. The circular specimens were then fixed in the bottom clamp of the metal cylinder of the Cobb water absorption tester, and 100 mL of deionized water was poured into the metal cylinder, maintaining contact between the deionized water and the surface of the circular specimens for 60 seconds.

[0047] After the specified time has elapsed, pour out the deionized water from the metal cylinder, loosen the clamp, and remove the circular sample. Place the water-absorbed circular sample flat on quantitative filter paper, and use a standard pressure roller to repeatedly roll the surface of the circular sample to absorb excess free deionized water. Immediately weigh the circular sample after the surface deionized water has been absorbed. Based on the difference in mass of the circular sample before and after water absorption and the test area, calculate the mass of water absorbed per square meter of paper sample within 60 seconds, and obtain the Cobb60 water absorption value.

[0048] Table 3. Test data on conventional hydrophobic properties of sizing agents on paper surface Conclusions and Analysis: According to Table 3 and Figure 5 According to the data, the static water contact angle of the paper samples corresponding to the nanocellulose-modified polyacrylate paper pulp internal sizing agents prepared in Examples 1 to 3 was greater than 114°, and the Cobb60 water absorption value was less than 24 g / m³. 2 Example 1 exhibits exceptionally good hydrophobic and impermeable properties, with a static water contact angle reaching 138.0° and a Cobb 60 water absorption value of 13.0 g / m³. 2 In Comparative Example 1, the reaction mixture without the addition of hydrophobically modified nanocellulose dispersion resulted in a decrease in the static water contact angle of the corresponding paper sample to 98.6° and an increase in the Cobb60 water absorption value to 39.2 g / m³. 2 Although polyacrylate emulsions can demulsify and form a polymer film during hot-press drying, coating the surface of micron-sized pulp fibers to provide basic hydrophobic properties, the polyacrylate polymer film alone cannot completely seal the huge pore network formed by the interwoven micron-sized pulp fibers, and free water can still permeate through the pore channels.

[0049] In Examples 1 to 3, hydrophobically modified nanocellulose, as a nanoscale filler, fully fills the pores formed by the interwoven micron-sized pulp fibers and crosslinks with the surface-forming polyacrylate film. This constructs a hierarchical structure consisting of a micron-fiber framework, nanofiller, and crosslinked polymer film. This hierarchical structure seals the capillary channels inside the paper, reduces the overall surface energy of the paper, and increases the contact angle between deionized water droplets and the paper surface to 138.0°. From a physical fluid dynamics perspective, this blocks the downward penetration path of water, greatly limiting the paper's water absorption value to 13.0 g / m³. 2 about.

[0050] According to Table 3 and Figure 5 According to the data from Comparative Example 2, when the hydrophobically modified nanocellulose was replaced with an equal amount of unmodified nanocellulose at oven-dry weight in the reaction mixture, the static water contact angle of the corresponding paper sample decreased to 79.2°, and the water absorption value of Cobb60 reached as high as 61.5 g / m³.2 Unmodified nanocellulose has a large number of hydrophilic hydroxyl groups on its surface, which makes it prone to agglomeration and sedimentation in a positively charged hydrophobic polyacrylate emulsion matrix, failing to disperse evenly and fill the pores of the paper. The introduction of a large number of hydroxyl groups creates new hydrophilic absorption points inside the paper structure, accelerating the diffusion of moisture and leading to a decline in waterproof performance.

[0051] The reaction mixture prepared in Comparative Example 3, without the addition of methacryloyloxyethyltrimethylammonium chloride, showed a static water contact angle of only 45.3° on the paper sample, and a Cobb 60 water absorption value as high as 124.8 g / m³. 2 The absence of cationic monomers causes polyacrylate microparticles to lose their structural permanent positive charge, making them unable to generate electrostatic attraction with negatively charged pulp fibers. As a result, most of the effective sizing components are lost with the white water during papermaking, leading to a lack of hydrophobic barriers inside the paper. The nanocellulose-modified polyacrylate papermaking pulp sizing agent prepared in this invention achieves high retention rate by relying on permanent positive charge. Combined with grafted modified nanocellulose fillers, it endows the final paper with excellent conventional hydrophobic and water-resistant properties.

[0052] Test Example 4: Comparative Test of Paper Depth Water Permeability and Water Pressure Resistance The papermaking batch containing the nanocellulose-modified polyacrylate papermaking pulp internal sizing agent prepared in Examples 1 to 3 and the reaction mixture prepared in Comparative Examples 1 to 4, respectively, had a basis weight of 80 g / m³. 2 The paper sample was placed in a constant temperature and humidity environment of 23℃ and 50% for 24 hours to equilibrate.

[0053] After balancing, the paper sample is cut into square test samples of 100mm×100mm using a special paper cutter. Check the surface of the square test samples for creases or visible holes and reject any square test samples with defects.

[0054] Lay the square test paper flat and clamp it between the lower and upper clamps of the hydrostatic pressure tester, then tighten the fastening bolts to seal the edges of the clamps. Open the water injection valve of the hydrostatic pressure tester and inject deionized water evenly into the bottom of the square test paper.

[0055] Adjust the pressure control system of the hydrostatic pressure tester to establish and maintain a constant hydrostatic pressure of 10 kPa on the bottom surface of the square test paper sample, equivalent to the pressure of a water column at a height of 1.0 m. Start the timer and observe the changes on the upper surface of the square test paper sample under strong light illumination. Stop the timer when the third drop of deionized water seeps out from the upper surface of the square test paper sample, and record the time consumed as the hydrostatic pressure seepage resistance time.

[0056] Table 4. Test data on the depth impermeability and water pressure resistance of sizing paper Conclusions and Analysis: According to Table 4 and Figure 6 According to the data, the hydrostatic pressure impermeability time of the paper samples corresponding to the nanocellulose-modified polyacrylate paper pulp internal sizing agents prepared in Examples 1 to 3 was all greater than 22h. The hydrostatic pressure impermeability time of the paper sample corresponding to the reaction mixture prepared in Comparative Example 1 was shortened to 3.2h. In Comparative Example 1, no hydrophobic modified nanocellulose dispersion was added, and the polyacrylate emulsion was used to coat the pulp fiber surface to form a film. The pore network formed by the interweaving of micron-sized pulp fibers was much larger than the coverage capacity of the polymer film alone. A large number of unclosed capillary channels remained inside the paper structure. Under the action of 10kPa hydrostatic pressure, deionized water quickly penetrated deeply along the unclosed capillary channels.

[0057] In Examples 1 to 3, hydrophobically modified nanocellulose served as a nanoscale filler, fully filling the pores formed by the interweaving of micron-sized pulp fibers. The nanoscale filler, together with the polymer film formed by the cross-linking of polyacrylate emulsion after demulsification, constructed a dense hierarchical structure of micron-sized fiber skeleton combined with nanoscale filler and cross-linked polymer film. The dense hierarchical structure sealed the capillary channels inside the paper, blocking the water penetration path from a physical fluid dynamics perspective, and endowing the final paper with excellent water pressure resistance and deep waterproofing ability.

[0058] According to Table 4 and Figure 6 According to the data, the hydrostatic pressure impermeability time of the paper sample corresponding to the reaction mixture prepared in Comparative Example 2 dropped sharply to 1.5h. Comparative Example 2 used unmodified nanocellulose for compounding. The unmodified nanocellulose agglomerated in the positively charged hydrophobic polyacrylate emulsion matrix, lost the uniform dispersion of nano-fillers, and could not fill the pores of the paper. The hydrophilic hydroxyl groups on the surface of the unmodified nanocellulose constructed interconnected water-conducting channels inside the paper, which accelerated the penetration process of deionized water under high pressure.

[0059] The hydrostatic pressure resistance time of the paper sample corresponding to the reaction mixture prepared in Comparative Example 3 was only 0.4 h. Comparative Example 3 did not introduce methacryloyloxyethyltrimethylammonium chloride, and the nonionic polyacrylate particles were not adsorbed on the negatively charged pulp fiber surface. The waterproof components were lost in large quantities with the white water of papermaking, resulting in the paper having almost no ability to resist water pressure penetration. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent prepared in Example 1 ensured a high retention rate by utilizing the electrostatic adsorption effect of positively charged polymers. At the same time, it perfectly solved the defect of traditional sizing agents being prone to capillary penetration under hydrostatic pressure by utilizing the hierarchical physical filling effect of hydrophobic modified nanocellulose.

[0060] Test Example 5: Comparative Test of Paper Mechanical Strengthening Properties The papermaking batch containing the nanocellulose-modified polyacrylate papermaking pulp internal sizing agent prepared in Examples 1 to 3 and the reaction mixture prepared in Comparative Examples 1 to 4, respectively, had a basis weight of 80 g / m³. 2 The paper sample was placed in a constant temperature and humidity environment of 23℃ and 50% for 24 hours for equilibration. The equilibrated paper sample was then cut into strips with a width of 15mm and a length of 250mm using a paper cutter.

[0061] A long strip specimen is vertically clamped between the upper and lower clamps of a computer-controlled electronic universal testing machine. The initial distance between the upper and lower clamps is set to 180 mm, and the tensile speed is set to 20 mm / min. The computer-controlled electronic universal testing machine is started to apply uniform tension to the long strip specimen until it breaks. The maximum tensile force at break is recorded. The dry tensile index is calculated based on the basis weight and width of the long strip specimen. The same paper sample is tested five times, and the average dry tensile index is taken.

[0062] Cut a number of spare long strip samples of the same size, immerse the spare long strip samples completely in deionized water at 23°C for 1 hour, take out the soaked long strip samples, place them flat on quantitative filter paper to absorb the free deionized water adhering to the surface of the long strip samples.

[0063] After the surface moisture is absorbed, the long strip specimen is clamped in the upper and lower clamps of the microcomputer-controlled electronic universal testing machine. Tensile tests are performed according to the same test parameters as described above. The maximum tensile force value when the long strip specimen breaks under wet conditions is recorded, and the wet tensile index is calculated.

[0064] Table 5. Test data on the mechanical strengthening properties of sizing agents in paper. Conclusions and Analysis: According to Table 5 and Figure 7 According to the data, the dry tensile index of the paper samples corresponding to the nanocellulose-modified polyacrylate paper pulp internal sizing agents prepared in Examples 1 to 3 was greater than 68 N·m / g, and the wet tensile index was greater than 15 N·m / g. In contrast, the dry tensile index of the paper sample corresponding to the reaction mixture prepared in Comparative Example 1 was 43.6 N·m / g, and the wet tensile index was only 5.2 N·m / g. Comparative Example 1 did not add hydrophobic modified nanocellulose dispersion; its paper structure relied solely on the interweaving of micron-sized pulp fibers and the physical bonding generated by a small portion of polyacrylate emulsion film formation. The micron-sized pulp fibers are relatively large, and the number of bonding points between the fibers is limited, resulting in weak macroscopic physical strength of the paper.

[0065] In Examples 1 to 3, the hydrophobically modified nanocellulose retains the high specific surface area and high mechanical strength of nanocellulose itself. The hydrophobically modified nanocellulose is interwoven and filled in the porous network formed by the interlacing of micron-sized pulp fibers. After the positively charged polyacrylate emulsion breaks down and forms a film, the hydrophobically modified nanocellulose is firmly bonded to the micron-sized pulp fibers. The multi-scale hierarchical structure formed by the micron-sized fiber skeleton, nano-sized filler, and cross-linked polymer film increases the bonding area between fiber materials, effectively transfers and disperses the mechanical stress applied externally, and significantly improves the dry tensile index and wet tensile index of the paper.

[0066] According to Table 5 and Figure 7 According to the data, the dry tensile index of the paper sample corresponding to the reaction mixture prepared in Comparative Example 2 decreased to 38.5 N·m / g, and the wet tensile index decreased to 3.8 N·m / g. Comparative Example 2 replaced the hydrophobically modified nanocellulose with unmodified nanocellulose. Unmodified nanocellulose exhibited severe agglomeration and sedimentation in the hydrophobic polyacrylate emulsion, forming large stress concentration points within the paper matrix. When the paper sample was subjected to external tension, these agglomeration points were the first to rupture and shrink, failing to provide the reinforcing effect of the nanofiller and instead disrupting the original structural uniformity of the paper. The polymethyl methacrylate side chains grafted onto the surface of nanocellulose by methyl methacrylate effectively solved the agglomeration problem and ensured the uniform dispersion of the nano-scale filler in the polymer matrix.

[0067] The dry tensile index of the paper sample corresponding to the reaction mixture prepared in Comparative Example 3 decreased to 35.2 N·m / g, and the wet tensile index plummeted to 1.4 N·m / g. In Comparative Example 3, methacryloyloxyethyltrimethylammonium chloride was not introduced during the polymerization stage. The synthesized polymer particles did not have a positive charge on their surface and could not be adsorbed onto the negatively charged pulp fiber surface by electrostatic attraction. A large number of polymer particles were lost with the white water, resulting in a lack of cross-linked polymer film encapsulation and water-resistant protection inside the paper. Under the condition of deionized water soaking, the deionized water rapidly penetrated into the micron-sized pulp fiber, completely destroying the weak bonds between fibers that depend on hydrogen bonds, resulting in a basic loss of wet mechanical strength. The nanocellulose modified polyacrylate paper pulp internal sizing agent of the present invention utilizes surface charge and hydrophobic modification technology to achieve uniform dispersion and high retention of nanocellulose in the polymer matrix.

[0068] Test Example 6: Specialty Paper Application and Addition Gradient Test Weigh out a certain amount of oven-dry unbleached softwood sulfate pulp board and unbleached hardwood sulfate pulp board and mix them at a mass ratio of 7:3. Put the mixed pulp board into a Walley beater and add water to beat it until the beatness of the mixed pulp board reaches 45°SR. Add deionized water to the beaten pulp for dilution to obtain a pulp suspension with a mass fraction of 1.0% for vehicle speaker cones.

[0069] Prepare 7 beakers of the same size, and add equal volumes of the pulp suspension for car speaker paper cones into the 7 beakers. Add the nanocellulose modified polyacrylate paper pulp sizing agent prepared in Example 1, calculated according to 0%, 5%, 10%, 15%, 20%, 25%, and 30% of the oven-dry pulp mass, respectively. Turn on the mechanical stirrer and stir and disperse at 500 r / min for 10 min.

[0070] The uniformly dispersed pulp suspensions containing different amounts of nanocellulose-modified polyacrylate sizing agent prepared in Example 1 were poured into paper forming machines. After being dehydrated by a filter screen, pressed and formed, and dried on the surface of a cylindrical dryer at 105°C, test samples of car speaker paper cone base paper with different sizing agent addition amounts were prepared.

[0071] All car speaker cone raw paper test samples were placed in a constant temperature and humidity chamber at 23℃ and 50% relative humidity for 24 hours for equilibration.

[0072] Test strips were cut from the balanced car speaker cone paper sample and placed on the contact angle measuring instrument platform. A 5μL drop of deionized water was added, and the static shape of the deionized water drop was captured by a high-speed camera and the surface water contact angle value was recorded. Then, the contact angle measuring instrument platform was slowly tilted, and the angle formed between the platform and the horizontal plane at the moment when the deionized water drop began to slide off the surface of the car speaker cone paper sample was recorded as the roll-off angle.

[0073] The mass of deionized water absorbed by the surface of the car speaker cone base paper sample after equilibrium treatment within 60 seconds was measured using a Cobb absorbency tester and recorded as the Cobb60 absorbency value.

[0074] The balanced car speaker cone paper sample was cut into circular specimens and installed inside the fixtures of two independent hydrostatic pressure testers and tightened and sealed. The water injection valves at the bottom of the two hydrostatic pressure testers were adjusted to keep the height of the deionized water column above the test surface constant at 1.2m and 1.5m respectively. The timing device was turned on, and the time span during which the third drop of water seeped out from the bottom of the circular specimen was observed and recorded as the hydrostatic pressure resistance time.

[0075] The tensile strength of the car speaker cone paper sample after balancing was determined using a microcomputer-controlled electronic universal testing machine; the bending stiffness of the car speaker cone paper sample was determined using a computer-controlled stiffness meter; the elastic modulus of the car speaker cone paper sample was determined using a dynamic thermomechanical analyzer; the density of the car speaker cone paper sample was calculated using a precision thickness gauge and an electronic balance; and the velocity of ultrasonic pulses propagating inside the car speaker cone paper sample was measured using an ultrasonic wave velocity meter.

[0076] Table 7. Hydrophobicity test data of the paper base material for vehicle speaker cones Table 8. Hydrostatic water resistance test data of car speaker cone base paper samples Table 9. Test data on the mechanical and acoustic properties of the paper sample for vehicle speaker cones Conclusions and Analysis: According to Table 7 and Figure 8 According to the data, the surface water contact angle of the blank group of car speaker cone paper samples without sizing agent was only 56.4°, indicating a hydrophilic state. When the proportion of sizing agent added to the nanocellulose-modified polyacrylate pulp prepared in Example 1 reached 20%, the surface water contact angle of the car speaker cone paper samples climbed to a peak of 138.2°, the surface water roll-off angle decreased to 8.2°, and the Cobb60 water absorption value decreased to 13.1 g / m³. 2 The data showing a surface water contact angle greater than 120° and a surface water roll-off angle less than 10° confirms that the surface of the car speaker cone paper sample has reached a highly hydrophobic state. The formation of the highly hydrophobic state is attributed to the deposition and cross-linking of hydrophobically modified nanocellulose and positively charged polyacrylate particles on the pulp fiber surface, which constructs a micron- and nano-scale rough composite topology similar to the surface of a lotus leaf. The micron- and nano-scale rough composite topology, together with the low surface energy alkyl side chains provided by polyacrylate, changes the wetting mode of deionized water droplets on the paper surface from a wetting state in which the water droplets completely penetrate the rough grooves to a wetting state in which the water droplets are suspended at the top of the rough structure and trap air at the bottom of the water droplets, thereby reducing the adhesion of deionized water droplets.

[0077] According to Table 8 and Figure 9According to the data, when the proportion of the sizing agent in the nanocellulose-modified polyacrylate pulp prepared in Example 1 increased from 5% to 20%, the water resistance time of the car speaker cone base paper sample under a 1.2m water column increased from 15.2h to 72.3h, and the water resistance time under a 1.5m water column increased from 10.3h to 50.1h. The impermeability performance met the conventional IPX7 waterproof technical requirements. When the proportion of the sizing agent in the nanocellulose-modified polyacrylate pulp prepared in Example 1 exceeded 20% and reached 25% and 30%, the water resistance time under a 1.2m water column showed a slight decreasing trend. The resistance remained around 71.4 hours, and the water resistance time under a 1.5m water column stopped increasing. The data on the addition ratio showed that a 20% mass ratio enabled the hydrophobic modified nanocellulose to fill the internal pore network formed by the interwoven micron-sized pulp fibers and form a continuous, defect-free polymeric hydrophobic membrane. Excessive sizing agent accumulation inside the pulp fibers would cause local physical agglomeration of nanoparticles. The volume expansion of the physical agglomeration would lead to the generation of microscopic physical cracks inside the polymeric hydrophobic membrane. Under continuous impact of high hydrostatic pressure, these microscopic physical cracks would become weak points where water molecules preferentially penetrate and seep out, limiting the further improvement of the water pressure resistance time.

[0078] According to Table 9 and Figure 10 The data shows that as the proportion of the nanocellulose-modified polyacrylate pulp sizing agent added in Example 1 increased from 0% to 20%, the stiffness of the car speaker cone paper sample increased from 5068.4 mN·m to 9879.3 mN·m, the elastic modulus E increased from 2.08 GPa to 4.11 GPa, and the sound velocity increased from 1.76 m / s to 2.19 m / s. The mechanical enhancement and sound velocity increase data confirm that the natural polysaccharide skeleton retained inside the composite sizing agent did not break or degrade. The residual hydroxyl groups carried by the natural polysaccharide skeleton formed a dense hydrogen bond network with the pulp fibers. The dense hydrogen bond network eliminated the free interface of the pulp fibers, improved the overall density and rigidity of the car speaker cone paper sample, and the enhanced rigidity directly led to an increase in the elastic modulus. When sound waves propagate in a solid dense medium with a higher elastic modulus, the energy loss is lower and the propagation speed is faster, thus improving the acoustic response efficiency of the car speaker cone paper sample in the high-frequency electroacoustic signal conversion process.

Claims

1. A nanocellulose modified polyacrylate papermaking pulp internal sizing agent, characterized in that, It is prepared by mixing a positively charged polyacrylate emulsion with a modified nanocellulose dispersion; The positively charged polyacrylate emulsion is polymerized from emulsion preparation raw materials, which include: The emulsion preparation raw materials consist of 265-375 parts by weight of deionized water, 2.0-3.0 parts by weight of polyoxyethylene octylphenyl ether, 2.0-3.0 parts by weight of hexadecyltrimethylammonium bromide, 0.5-1.5 parts by weight of potassium persulfate, 70-76 parts by weight of methyl methacrylate, 14-21 parts by weight of butyl acrylate, 4-8 parts by weight of hydroxyethyl acrylate, 2-6 parts by weight of methacryloyloxyethyltrimethylammonium chloride, and 1-3 parts by weight of ethylene glycol dimethacrylate. After polymerization, the raw materials form 90-110 parts by weight of oven-dry solids in a positively charged polyacrylate emulsion. The modified nanocellulose dispersion contains 20-34 parts by weight of hydrophobic modified nanocellulose and 400-670 parts by weight of deionized water; The hydrophobically modified nanocellulose is made from cellulose-modified raw materials, which include: 8-12 parts by weight of oven-dried nanocellulose, 700-900 parts by weight of deionized water, 0.6-1.3 parts by weight of potassium persulfate, and 50-75 parts by weight of methyl methacrylate.

2. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 1, characterized in that, The preparation process of the positively charged polyacrylate emulsion includes: mixing and dissolving deionized water, polyoxyethylene octylphenyl ether, and hexadecyltrimethylammonium bromide in the emulsion preparation raw materials, and then adding methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, methacryloyloxyethyltrimethylammonium chloride, and ethylene glycol dimethacrylate in the emulsion preparation raw materials, and mechanically stirring to obtain a pre-emulsion. A portion of the pre-emulsion was mixed with an aqueous solution of potassium persulfate and heated to obtain a seed emulsion; The remaining unmixed pre-emulsion and the remaining unmixed potassium persulfate aqueous solution were added dropwise to the seed emulsion to carry out the polymerization reaction. After the polymerization reaction was completed, an alkaline regulator was added and the mixture was filtered to obtain a positively charged polyacrylate emulsion.

3. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 2, characterized in that, The process of preparing the preemulsion by mechanical stirring specifically includes: Mechanical stirring was performed at a speed of 700 r / min to 900 r / min at room temperature for a stirring time of 30 min to 50 min.

4. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 2, characterized in that, The process of mixing a portion of the pre-emulsion with a potassium persulfate aqueous solution and heating it to obtain the seed emulsion specifically includes: The potassium persulfate aqueous solution is prepared by dissolving potassium persulfate in 15-25 parts by weight of deionized water in the emulsion preparation raw materials. Add 30%–35% of the pre-emulsion (by mass) to a reaction vessel, heat to 70°C–80°C, add 45%–55% of the potassium persulfate aqueous solution (by mass), and mechanically stir at a constant temperature for 20–40 minutes to form a seed emulsion.

5. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 4, characterized in that, The process of adding the remaining unmixed pre-emulsion and the remaining unmixed potassium persulfate aqueous solution dropwise to the seed emulsion for polymerization, followed by adding an alkaline regulator and filtering after polymerization to obtain a positively charged polyacrylate emulsion specifically includes: The remaining unmixed pre-emulsion and the remaining unmixed potassium persulfate aqueous solution are added dropwise at a uniform rate to the reaction vessel that forms the seed emulsion. The dropwise addition time is set to 2.5 h to 3.5 h, and the reaction temperature in the reaction vessel is controlled to be constant at 76 ° C to 79 ° C. After the addition is complete, maintain the temperature at 76℃~79℃ for 1.0h~2.0h. After the heat preservation reaction is completed, the temperature is lowered to 15℃~30℃, and a sodium bicarbonate aqueous solution with a mass fraction of 4%~6% is added dropwise as an alkaline regulator to adjust the pH value of the substances in the reaction vessel to 6.2~6.

8. The mixture is then filtered through an 80~120 mesh filter.

6. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 1, characterized in that, The preparation process of the hydrophobically modified nanocellulose includes: The absolutely dry nanocellulose is dispersed in deionized water in the cellulose modified raw material, potassium persulfate in the cellulose modified raw material is added, and the first stage of mechanical stirring is carried out under heating conditions. Then, methyl methacrylate from the cellulose-modified raw material was added, and a second stage of mechanical stirring was carried out under heating conditions to obtain a mixed reaction product. The mixed reaction product was centrifuged to collect the lower colloidal product. The lower colloidal product was then washed with a washing solvent by centrifugation and dried to obtain the hydrophobic modified nanocellulose.

7. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 6, characterized in that, The specific conditions for the first stage of mechanical stirring and the second stage of mechanical stirring include: The first stage of mechanical stirring is carried out under constant temperature water bath heating conditions of 60℃~65℃ for 1.5h~2.5h; The second stage of mechanical stirring involves mechanical stirring for 7 to 9 hours under a constant temperature water bath heating condition of 60℃ to 65℃.

8. The nanocellulose modified polyacrylate papermaking pulp internal sizing agent according to claim 6, characterized in that, The process of centrifuging and washing the lower colloidal product with a washing solvent specifically includes: The lower colloidal product was centrifuged and washed 2 to 4 times with deionized water, ethyl acetate, and acetone, respectively, with each centrifugation and washing time set to 8 to 12 minutes.

9. The nanocellulose-modified polyacrylate paper pulp internal sizing agent according to claim 1, characterized in that, The preparation process of the modified nanocellulose dispersion is as follows: The hydrophobic modified nanocellulose is dispersed in 400-670 parts by weight of deionized water contained in the modified nanocellulose dispersion to obtain a modified nanocellulose dispersion.

10. The nanocellulose-modified polyacrylate paper pulp internal sizing agent according to claim 1, characterized in that, The process of preparing the mixture by mixing a positively charged polyacrylate emulsion with a modified nanocellulose dispersion includes: The modified nanocellulose dispersion was added to the positively charged polyacrylate emulsion and mechanically stirred in a constant temperature water bath at 55℃~65℃ for 1.5h~2.5h. After cooling to room temperature, nanocellulose modified polyacrylate paper pulp internal sizing agent was obtained.

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