Modified nanochitin paper reinforcing agent and preparation method and application thereof

Abstract

The application belongs to the field of natural polymer modification and the application of paper mechanical property enhancement, and particularly relates to a modified nano-chitin paper reinforcing agent and a preparation method and application thereof. The application uses chitin as raw material, and modifies the chitin by using NaOH and a modifier, wherein the modifier is at least one of allyl glycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether and 1,4-butanediol diglycidyl ether. The nano-chitin prepared by the application has uniform size, and when added in paper, can greatly improve the mechanical property (tensile index can be increased by 40%) of the paper, greatly improve the wet strength (wet tensile index can be increased by 175%) of the paper, and endow the paper with antibacterial function, thereby meeting the demand of high-end medical packaging materials (such as dialysis paper).

Description

Technical Field

[0001] This invention pertains to the field of natural polymer modification and its application in enhancing the mechanical properties of paper. Specifically, it relates to a modified nano-chitosan paper reinforcing agent, its preparation method, and its application. Background Technology

[0002] As a core material for sterilization packaging, the performance of medical dialysis paper directly impacts medical safety. While traditional plastic composite packaging such as PE or PP films can inhibit bacterial growth, they suffer from poor air permeability, non-degradability, and weak antibacterial properties, making them unsuitable for the high standards of modern medicine. Medical dialysis paper, on the other hand, requires high-pressure steam sterilization or ethylene oxide (EO) sterilization, demanding high paper strength, especially wet strength. This places high demands on functional additives, particularly reinforcing agents, used in the base paper. Traditional reinforcing agents such as petroleum-based synthetic polymers like polyacrylamide (PAM) and polyvinyl alcohol (PVA) are widely used due to their low cost and certain reinforcing efficiency, but their shortcomings are becoming increasingly apparent. First, production relies on non-renewable fossil resources and has extremely poor degradability (PAM has a half-life of over 100 years), leading to microplastic pollution, which is inconsistent with the concept of sustainable development. Second, synthetic reinforcing agents usually need to be used under acidic conditions (pH 4-6), while modern papermaking processes mostly use a medium-alkaline system (pH 7-8.5) to extend equipment life and avoid fiber degradation, resulting in a 30%-50% decrease in actual reinforcing efficiency. In addition, residual monomers such as acrylamide in the process of using synthetic reinforcing agents may migrate to food packaging paper, posing a carcinogenic risk and failing to meet the requirements of the EU REACH regulation (strictly limiting residue levels to <0.1 ppm).

[0003] To replace synthetic polymer reinforcing agents, natural derivatives such as starch and carboxymethyl cellulose (CMC) have been extensively studied, but they have inherent drawbacks: (1) Poor moisture resistance: Starch is prone to moisture regain in humid environments, resulting in a 40%-60% loss in paper strength; (2) High cost of cationic modification: Natural polysaccharides need to be introduced into cationic groups through complex processes such as etherification and graft copolymerization to achieve fiber adsorption, which increases the energy consumption of the process by 15%-20%; (3) Lack of antibacterial properties: It cannot inhibit the microbial degradation of paper during use, thus shortening the product life.

[0004] Chitosan is the only cationic natural polysaccharide in nature, and it is also the most abundant polysaccharide in nature besides cellulose. It has the following characteristics: (1) Green and sustainable: The raw materials come from biological waste such as shrimp and crab shells, with an annual output of over 1 million tons, which is in line with the concept of circular economy; (2) High reactivity: The molecular chain is rich in amino (-NH2) and hydroxyl (-OH), which can bind to cellulose fibers through hydrogen bonding and electrostatic interaction (binding energy reaches 5-8 kJ / mol); (3) Multifunctionality: Chitosan’s natural antibacterial and biodegradable properties (degradation rate of over 80% in soil within 6 months) meet the needs of high-value-added application fields such as food packaging and medical paper.

[0005] In recent years, chitosan modification technology has made several advances: some reports mention that chitosan can fill the gaps and spaces between fibers, and even penetrate into the fiber pores, enhancing the load-bearing capacity of cellulose fibers (Bhardwaj et al., 2017; Htwe, Lwin, & Oo, 2008). Furthermore, other studies have mentioned that the linear structure of chitosan and its highly charged cationic properties can adsorb negatively charged cellulose in pulp suspensions, thereby improving the mechanical properties of paper (Amiri, Rahmaninia, & Khosravani, 2019; Rohi et al., 2016). These studies indicate that the cationic charge of chitosan—NH3… + This facilitates its adsorption onto the cellulose surface. Furthermore, the polar groups —OH and —NH2 on the chitosan molecule can participate in hydrogen bonding, making it easier for it to connect with cellulose to form a higher density of hydrogen bonds.

[0006] Despite the enormous potential of chitosan, its industrial application is still constrained by the following key issues: (1) Most modified chitosans need to be dissolved in acidic or organic solvents (such as acetic acid solution), which is incompatible with the commonly used medium-alkaline papermaking wet end system (pH 7-8.5), resulting in flocculation failure and the inability to exert the effect of chitosans. (2) Imbalance between cost and stability: High-purity chitosan (degree of deacetylation >90%) is expensive (about US$50 / kg), while low-purity products are prone to agglomeration in pulp, resulting in a decrease in paper uniformity (uniformity index decreases by 15%-20%).

[0007] Therefore, chitin or chitosan must be chemically modified to improve its dispersion properties, making it easier to adsorb and adhere to cellulose, thereby facilitating the formation of richer hydrogen bonds and improving the physical properties of paper. Summary of the Invention

[0008] To address the current technical challenges of using chitosan as a paper reinforcing agent, we are considering a safe and environmentally friendly process to etherify and modify chitin, followed by mechanical treatment, to obtain a nano-chitosan derivative. We will then investigate its application in enhancing the mechanical properties of medical dialysis paper.

[0009] The primary objective of this invention is to provide a modified nano-chitosan derivative and its preparation method. The method uses chitosan as the raw material, which, due to its wide availability, biodegradability, antibacterial properties, and environmental friendliness, shows great potential in enhancing the mechanical properties of composite materials. This preparation method is safe, chlorine-free, environmentally friendly, and uses readily available raw materials with a simple preparation process.

[0010] Another objective of this invention is to provide the application of this modified nano-chitosan derivative in paper reinforcement. This nano-chitosan derivative has a rod-like structure with a high aspect ratio. First, its micro-nano size allows it to fill the pores in paper cellulose fibers, improving fiber strength. Second, the surface of this micro-nano chitosan carries a high charge (Zeta potential of approximately 40-60 mV at pH 4-7), enabling strong electrostatic adsorption with negatively charged cellulose (Zeta potential of approximately -20 to -30 mV), thus enhancing the reinforcing effect of this reinforcing agent. Third, this chitosan derivative contains a large number of hydroxyl groups, which can form numerous hydrogen bonds with cellulose, significantly improving the wet strength of the fiber to withstand high humidity environments, such as the high-temperature, high-pressure steam sterilization environment required for medical dialysis paper.

[0011] The technical solution of this invention is implemented as follows: A method for preparing a modified nano-chitosan paper reinforcing agent, characterized by comprising the following steps: (1) Chitosan powder was soaked in sodium hydroxide solution and ethanol to carry out deacetylation reaction; (2) Adjust the pH of the reaction system to weak alkalinity, add an appropriate amount of ethanol, and add a modifier to react; (3) Adjust the pH of the reaction system to neutral, collect the solid and wash it with alcohol until the conductivity of the supernatant after centrifugation is less than 50 μS / cm; (4) Add the solid collected in step (3) to water, then add acetic acid, let stand, and then process with a colloid mill to obtain the modified nano-chitosan paper reinforcing agent.

[0012] Preferably, in step (1), the chitin powder has a size of 40-200 mesh; and the sodium hydroxide solution has a concentration of 40-60 wt%. The ratio of chitin powder, sodium hydroxide solution, and ethanol is 8g:(20~30)g:(40~60)mL.

[0013] Preferably, in step (1), the deacetylation reaction is performed as follows: mechanical stirring at 80~90 ℃ for 0.5~3h, cooling and refrigerating for 12h, then connecting a condenser and refluxing at 60~80 ℃ for 3h, while simultaneously mechanical stirring at 200 rpm.

[0014] Preferably, in step (2), the modifier is at least one of allyl glycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether, and 1,4-butanediol diglycidyl ether, and the amount used is 0.8 to 5 times the weight of chitin.

[0015] Preferably, in step (2), the volume of the added ethanol is 10-20 mL; the reaction time is 12-24 h; and the reaction temperature is 30-60 °C.

[0016] Preferably, the pH in step (2) is 7~9, and the pH in step (3) is 7±0.2.

[0017] Preferably, in step (4), the volume of water is 300~500 mL; the amount of acetic acid added is such that the concentration of acetic acid in the system is 0.5~1.0 wt%; the standing time is 1~3 h, and the colloid milling time is 20~40 min.

[0018] The paper strengthening agent prepared by any of the methods described in this invention.

[0019] The application of the paper strengthening agent described in this invention in papermaking.

[0020] Preferably, it is used to prepare medical dialysis paper; The paper strengthening agent is added to the dissolved pulp at 1-5% of the oven-dry weight of the pulp. After dissolving for 1000-2000 revolutions and mixing evenly, water is added to dilute and adjust the pulp concentration to 0.3 wt%, and then the pulp is formed into paper.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The raw material of this invention is chitin, a natural polysaccharide with the advantages of wide availability, safety, non-toxicity, and good biodegradability. Furthermore, chitosan, a derivative of chitin after deacetylation, is rich in amino and hydroxyl groups and exhibits good chemical activity.

[0022] 2. This invention utilizes a rationally optimized process, resulting in an easy-to-operate reaction process and a low-cost, non-toxic modifier. The obtained nano-chitosan has a uniform size (between 100 nm and 2000 nm) and can remain stable for 3 to 6 months.

[0023] 3. When the nano-chitosan derivatives prepared by this invention are added to paper, they can significantly improve the mechanical properties of paper (tensile index can be increased by up to 40%) and greatly improve the wet strength of paper (wet tensile index can be increased by up to 175%). Attached Figure Description

[0024] Figure 1 The image shows an infrared comparison of the modified nano-chitoxin derivative and the original chitoxin powder in Example 7 of this invention.

[0025] Figure 2 This is an atomic force microscope (AFM) image of the modified nano-chitosan derivative of Example 7 of the present invention.

[0026] Figure 3 This is a comparison image of the sample from Example 7 after it has been left to stand at room temperature for 4 months.

[0027] Figure 4 The zeta potential values ​​are for the sample in Example 7 under different pH conditions.

[0028] Figure 5 These are infrared comparison images of embodiments 7, 8, and 9 of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. Example 1

[0030] A method for preparing a modified nano-chitosan derivative, the method comprising the following steps: (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 40% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 80℃ for 0.5 h, cool and refrigerate for 12 h, then connect a condenser and heat to 75℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 10.0 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 20 mL of ethanol, and add 11.95 g of 1,4-butanediol diglycidyl ether at 30°C and stir for 12 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 2.5 mL of acetic acid (to make the acetic acid concentration 0.5 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and the soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative. Example 2

[0031] A method for preparing a modified nano-chitosan derivative, the method comprising the following steps: (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 50% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 80℃ for 1 h, cool and refrigerate for 12 h, then connect a condenser and heat to 75℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 16.32 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 20 mL of ethanol, and add 23.89 g of 1,4-butanediol diglycidyl ether at 30 °C and stir for 24 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 5 mL of acetic acid (to make the acetic acid concentration 1.0 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative. Example 3

[0032] A method for preparing a modified nano-chitosan derivative, the method comprising the following steps: (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 60% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 90℃ for 0.5 h, cool and refrigerate for 12 h, then connect a condenser and heat to 70℃ and reflux for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 19.58 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 20 mL of ethanol, and add 8.0 g of polyethylene glycol glycidyl ether at 40 °C and stir for 12 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 2.5 mL of acetic acid (to make the acetic acid concentration 0.5 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and the soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative. Example 4

[0033] A method for preparing a modified nano-chitosan derivative, the method comprising the following steps: (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 60% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 90 ℃ for 1 h, cool and refrigerate for 12 h, then connect a condenser and heat to 70 ℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 19.58 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 20 mL of ethanol, and add 16.0 g of polyethylene glycol glycidyl ether at 40°C and stir for 24 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 5 mL of acetic acid (to make the acetic acid concentration 1.0 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative. Example 5

[0034] A method for preparing a modified nano-chitosan derivative, the method comprising the following steps: (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 40% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 80 ℃ for 0.5 h, cool and refrigerate for 12 h, then connect a condenser and heat to 65 ℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 10.0 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 10 mL of ethanol, and add 7.69 g of allyl glycidyl ether at 50 °C and stir for 12 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 0.5 wt% acetic acid, stir at low speed and let stand for 2 h, add the acetic acid solution and soaked material to a colloid mill and process for 30 min to obtain a modified nano-chitosan derivative. Example 6

[0035] The preparation reaction formula of the modified nano-chitosan paper reinforcing agent described in this embodiment is as follows:

[0036] (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 50% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 80 ℃ for 1 h, cool and refrigerate for 12 h, then connect a condenser and heat to 65 ℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 16.32 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 10 mL of ethanol, and add 15.38 g of butyl glycidyl ether at 50 °C and stir for 24 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 2.5 mL of acetic acid (to make the acetic acid concentration 0.5 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and the soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative. Example 7

[0037] The preparation reaction formula of the modified nano-chitosan paper reinforcing agent described in this embodiment is as follows:

[0038] (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 50% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 90 ℃ for 1 h, cool and refrigerate for 12 h, then connect a condenser and heat to 65 ℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 16.32 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 10 mL of ethanol, and add 23.07 g of butyl glycidyl ether at 60°C and stir for 24 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 5.0 mL of acetic acid (to make the acetic acid concentration 1.0 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative.

[0039] Figure 1 This is a comparison of infrared images of the modified nano-chitosan derivative and the original chitosan powder in this embodiment. The important characteristic peak is at 1658 cm⁻¹. -1 and 1560 cm -1 The peak at 3450 cm⁻¹ is attributed to the C=O stretching vibration and the N-H bending vibration, and is a typical characteristic peak of chitin. The modified nano-chitin derivative shows reduced transmission at these two peaks, indicating an increase in N-H groups, which is due to deacetylation. Compared to chitin, the modified nano-chitin derivative shows higher transmission at 3450 cm⁻¹. -1 A stronger and wider characteristic absorption band exists, which is caused by the stretching vibration of hydroxyl (-OH) or hydrogen-bonded groups of the modified nano-chitosan derivative, proving that this reinforcing agent has more hydroxyl groups that can form hydrogen bonds with cellulose fibers, thereby improving the tensile strength of the paper.

[0040] Figure 2 The image shown is an atomic force microscope (AFM) image of the modified nano-chitosan derivative of this embodiment, illustrating rod-shaped crystals with micro / nano dimensions.

[0041] Example 7: Zeta potential values ​​of samples under different pH conditions are as follows Figure 4 As shown. Example 8

[0042] The preparation reaction formula of the modified nano-chitosan paper reinforcing agent described in this embodiment is as follows:

[0043] (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 50% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 90 ℃ for 1 h, cool and refrigerate for 12 h, then connect a condenser and heat to 65 ℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 16.32 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 10 mL of ethanol, and add 7.69 g of butyl glycidyl ether at 60°C and stir for 24 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 5.0 mL of acetic acid (to make the acetic acid concentration 1.0 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative. Example 9

[0044] The preparation reaction formula of the modified nano-chitosan paper reinforcing agent described in this embodiment is as follows:

[0045] (1) Soak 8.0 g of chitin powder (40~200 mesh) in 25 g of 50% sodium hydroxide solution, add 50 mL of ethanol, stir mechanically at 90 ℃ for 1 h, cool and refrigerate for 12 h, then connect a condenser and heat to 65 ℃ for 3 h while stirring mechanically (speed 200 rpm). (2) After condensation, slowly add 16.32 g of acetic acid (stirring is required at 400 rpm) to make the pH of the reaction system weakly alkaline, add 10 mL of ethanol, and add 15.38 g of butyl glycidyl ether at 60°C and stir for 24 h. (3) After the reaction is complete, add 3~6 g of acetic acid and stir to adjust the system to neutral (pH=7). Collect the obtained solid, add alcohol to wash several times until the conductivity of the supernatant after centrifugation is less than 50 μS / cm, centrifuge and collect the solid. (4) Add the solid collected in (3) to 500 mL of deionized water, add 5.0 mL of acetic acid (to make the acetic acid concentration 1.0 wt%), stir at low speed and let stand for 2 h, add the acetic acid solution and soaked material to a colloid mill and treat for 30 min to obtain a modified nano-chitosan derivative.

[0046] Figure 5 These are infrared comparison images of the modified nano-chitosan derivatives from Examples 7, 8, and 9. When the amount of modifier is increased, the product at 3400 cm⁻¹... -1 The absorption peak at the cellulose ether tends to gradually become stronger, which is attributed to the fact that more butyl glycidyl ether is grafted onto the -OH position of the C6 position of chitin after modification, thus having more opportunities to form intermolecular hydrogen bonds with cellulose. Implementation effect

[0047] Weigh 1.26 g of oven-dry pulp (hemp pulp) and place it in a fiber de-fiber machine for 8000 revolutions. Add the obtained modified nano-chitosan derivative (equivalent to 1% of the effective component of the oven-dry pulp) to the de-fiberized pulp and de-fiberize for another 1000 revolutions to ensure uniform mixing. Dilute with water to adjust the pulp consistency to 0.3 wt%, and perform manual papermaking according to GB / T 4688-2023. Place the paper sheets in a standard constant temperature and humidity chamber at 23℃ and 50%RH to equilibrate the moisture for 24 h to obtain paper reinforced with the nano-chitosan derivative. Another 1.26 g of oven-dry hemp pulp was thoroughly loosened in a fiber loosening machine for 8000 revolutions. The pulp was then manually formed according to GB / T4688-2023, but without the added synthetic nano-chitosan derivative reinforcing agent. The formed paper was then placed in a standard constant temperature and humidity chamber at 23 ℃ and 50%RH for 24 h to equilibrate the moisture, obtaining a blank control paper sample. The tensile strength of the obtained paper was determined according to GB / T12914-2023. After the modified nano-chitosan paper was equilibrated in a constant temperature and humidity chamber, its tensile index was compared with that of the blank control paper sample. The results are shown in Table 2.

[0048] Table 1. Degree of deacetylation of derivatives from different embodiments

[0049] Table 2 Implementation Effects of Different Embodiments

[0050] Table 2 shows that, compared to the blank control paper sample, the tensile index of the paper samples with additives 3, 4, 5, 6, and 7 were all improved. Example 7 showed the most significant strengthening effect, with a 40.00% increase in tensile index and a 175.72% increase in wet tensile index, indicating that the reaction conditions in this example were optimal. After being left to stand at room temperature for 4 months, the system of Example 7 remained stable. Figure 3 .

[0051] As shown in Table 1, the reinforcing effect begins to decline when the degree of deacetylation reaches 75% or more. This may be due to two reasons: firstly, the high zeta charge of the suspension causes uneven fiber distribution; and secondly, the reduction of the hydrophobic acetamino group (-NHCOCH3) leads to a decrease in wet strength.

[0052] According to standards such as ASTM F1608 and ISO 20743, the antibacterial properties (E. coli) of the paper reinforced with nano-chitosan derivatives obtained in Example 7 were tested, and the results are shown in Table 3.

[0053] Table 3. Antibacterial rate of medical dialysis paper with the reinforcing agent in Example 7

[0054] As shown in Table 3, when the addition amount is 3%, the antibacterial rate of the paper reinforced by this nano-chitosan derivative is 70.06%. In addition, this paper has excellent wet strength, which can meet the strength requirements of dialysis paper, indicating its great potential in the field of medical dialysis paper.

[0055] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a modified nano-chitosan paper reinforcing agent, characterized in that, Includes the following steps: (1) Chitosan powder was soaked in sodium hydroxide solution and ethanol to carry out deacetylation reaction; (2) Adjust the pH of the reaction system to weak alkalinity, add an appropriate amount of ethanol, and add a modifier to react; (3) Adjust the pH of the reaction system to neutral, collect the solid and wash it with alcohol until the conductivity of the supernatant after centrifugation is less than 50 μS / cm; (4) Add the solid collected in step (3) to water, then add acetic acid, let stand, and then process with a colloid mill to obtain the modified nano-chitosan paper reinforcing agent.

2. The method for preparing a modified nano-chitosan paper reinforcing agent according to claim 1, characterized in that, In step (1), the chitin powder has a size of 40-200 mesh; the sodium hydroxide solution has a concentration of 40-60 wt%. The ratio of chitin powder, sodium hydroxide solution, and ethanol is 8g:(20~30)g:(40~60)mL.

3. The method for preparing a modified nano-chitosan paper reinforcing agent according to claim 2, characterized in that, In step (1), the deacetylation reaction is performed as follows: mechanical stirring at 80~90 ℃ for 0.5~3h, cooling and refrigerating for 12h, then connecting a condenser and refluxing at 60~80 ℃ for 3h, while simultaneously mechanical stirring at 200 rpm.

4. The method for preparing a modified nano-chitosan paper reinforcing agent according to claim 1, characterized in that, In step (2), the modifier is at least one of allyl glycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether, and 1,4-butanediol diglycidyl ether, and the amount used is 0.8 to 5 times the amount of chitosan.

5. The method for preparing a modified nano-chitosan paper reinforcing agent according to claim 4, characterized in that, In step (2), the volume of the added ethanol is 10-20 mL; the reaction time is 12-24 h; and the reaction temperature is 30-60 °C.

6. The method for preparing a modified nano-chitosan paper reinforcing agent according to claim 1, characterized in that, The pH in step (2) is 7~9, and the pH in step (3) is 7±0.

2.

7. The method for preparing a modified nano-chitosan paper reinforcing agent according to claim 1, characterized in that, In step (4), the volume of water is 300-500 mL; the amount of acetic acid added is such that the concentration of acetic acid in the system is 0.5-1.0 wt%; the standing time is 1-3 h, and the colloid milling time is 20-40 min.

8. The paper strengthening agent prepared by the method according to any one of claims 1 to 7.

9. The use of the paper strengthening agent according to claim 8 in papermaking.

10. The application according to claim 9, characterized in that, Used in the preparation of medical dialysis paper; The paper strengthening agent is added to the dissolved pulp at 1-5% of the oven-dry weight of the pulp. After dissolving for 1000-2000 revolutions and mixing evenly, water is added to dilute and adjust the pulp concentration to 0.3 wt%, and then the pulp is formed into paper.

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