Food-grade high-strength and high-toughness pulp, paper product and preparation method thereof

Abstract

The application discloses a food-grade high-strength and high-toughness paper pulp, paper products and a preparation method thereof, and belongs to the technical field of papermaking. The food-grade high-strength and high-toughness paper pulp comprises 100 parts of virgin wood pulp, 1-3 parts of alginic fiber, and 0.3-1.5 parts of a wet strength agent, and the wet strength agent is a random copolymer of methyl acrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydro-jasmine acid methyl acryloyl oxy hydroxypropyl ester and acrylamide propyl trimethyl ammonium chloride. The alginic fiber and the wet strength agent are added into the virgin wood pulp, so that the strength and toughness of the paper products are improved.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a food-grade high-strength and high-toughness pulp, paper products, and their preparation methods. Background Technology

[0002] Paper and paper products are widely used in daily life. A crucial property of paper products is wet strength, which refers to the paper's ability to maintain its strength and integrity in a humid environment. However, due to the humidity sensitivity of cellulose hydrogen bonds, paper typically has low wet strength. Moisture disrupts hydrogen bonds and breaks down molecular packing within the fibers, causing severe swelling and weakening, and affecting the transmission of mechanical stress within the fiber network. At the paper level, due to the dissipation of intermolecular interactions at fiber-to-fiber connections, water molecules disrupt the hydrogen bond network between cellulose fibers, leading to dimensional instability. This low wet strength characteristic of paper limits its widespread use, especially in food packaging where it comes into direct contact with liquids. Improving the hydrogen bonds in the pulp fiber network alone is insufficient to withstand the high tensile forces under wet conditions, as most hydrogen bonds are broken in high humidity environments or water. Effective wet strengthening requires covalent bonds to improve the adhesion at fiber-to-fiber bonds.

[0003] Wet strength agents are resin additives introduced into the pulp fiber suspension before the fiber network forms. They are effectively adsorbed onto the fiber surface through electrostatic interactions between the positively charged groups of the resin and the negatively charged groups of the cellulose fibers. When the paper dries, the resin cross-links under heating conditions, forming a reinforced paper network, resulting in wet-strengthened paper. The most commonly used synthetic wet strength agents include urea-formaldehyde resin (UF), melamine-formaldehyde resin (MF), acetaldehyde-modified polyacrylamide (GPAM), and polyamide-epoxychloropropane (PAE). These synthetic wet strength agents can be used alone or in combination with other substances to achieve the desired wet strength properties and a certain degree of moisture resistance. However, the byproducts of these wet strength resins pose a risk of migration into the environment and human body. Furthermore, how to improve paper strength while maintaining its softness and toughness remains a challenge. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention provides a food-grade high-strength and high-toughness pulp, which is a wet strength agent prepared by adding a random copolymer of methacrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydrojasmonic acid methacryloyloxyhydroxypropyl ester and acrylamide propyltrimethylammonium chloride, and achieves the effects of safety, strengthening, toughening and antibacterial properties.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A food-grade high-strength and high-toughness pulp, by weight, comprises 100 parts of virgin wood pulp, 1-3 parts of alginate fiber, and 0.3-1.5 parts of wet strength agent, wherein the wet strength agent is a random copolymer of methacrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydrojasmonic acid methacryloyloxyhydroxypropyl ester, and acrylamide propyltrimethylammonium chloride.

[0007] In one specific embodiment, the glycidyl ether-based polyethylene glycol monoallyl ether is prepared by reacting polyethylene glycol monoallyl ether with epichlorohydrin under alkaline and dehydrating agent conditions through a ring-opening-etherification-ring-closing reaction. The alkaline is one or more of sodium hydroxide, potassium hydroxide, and potassium carbonate, and the dehydrating agent is one or more of toluene or xylene. The molar ratio of polyethylene glycol monoallyl ether to epichlorohydrin is 1:(1~1.5), and the molecular weight of the polyethylene glycol monoallyl ether is 300~2500, preferably 400~1000.

[0008] In one specific embodiment, the methacrylate is selected from one or more of methyl methacrylate, ethyl methacrylate, and butyl methacrylate.

[0009] In one specific embodiment, the structure of the dihydrojasmonic acid methacryloyloxyhydroxypropyl ester is shown in Formula 1:

[0010] Formula 1.

[0011] In one specific embodiment, the dihydrojasmonic acid methacryloyloxyhydroxypropyl ester is the reaction product of dihydrojasmonic acid and glycidyl methacrylate, wherein the molar ratio of dihydrojasmonic acid to glycidyl methacrylate is 1:(1~1.5), the catalyst is triethylamine or N,N-dimethylbenzylamine, and a polymerization inhibitor may also be added during the reaction, wherein the polymerization inhibitor is one or more of p-methoxyphenol, 2,6-di-tert-butyl-p-cresol, and hydroquinone.

[0012] In one specific embodiment, the molar ratio of the methacrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydrojasmonic acid methacryloyloxyhydroxypropyl ester, and acrylamide propyltrimethylammonium chloride is (2~4):1:(0.5~1):(0.5~2).

[0013] In one specific embodiment, the alginate fiber is obtained by wet spinning of sodium alginate solution.

[0014] In one specific embodiment, the wet spinning includes the following steps: dissolving, filtering, defoaming, spinning, coagulation, washing, drawing, setting, and drying; the dissolving step involves preparing a sodium alginate solution with a concentration of 4-6 wt% and a temperature of 50-55°C; the coagulation step involves the sodium alginate solution being sprayed through a spinneret and solidified by a coagulation solution with a temperature controlled at 40-50°C; the coagulation solution is a calcium chloride solution with a concentration of 3-5 wt%; and the spinneret has a spinneret orifice diameter of less than 100 μm.

[0015] This invention also protects the method for preparing the food-grade high-strength and high-toughness pulp, comprising the following steps:

[0016] S1. Wood chips are cooked, oxygen bleached, bleached, and refined to obtain virgin wood pulp;

[0017] S2. The virgin wood pulp is thoroughly mixed with alginate fiber and wet strength agent in a certain proportion to obtain the pulp, which is food-grade high-strength and high-toughness pulp, with the concentration controlled at 4.0~5.0w / w.

[0018] This invention also protects a food-grade high-strength and high-toughness paper product made from the aforementioned food-grade high-strength and high-toughness pulp.

[0019] This invention also protects a method for preparing food-grade high-strength and high-toughness paper products. Specifically, the method involves preparing food-grade high-strength and high-toughness pulp with a concentration of 0.1~2.0 w / w%, adding Na2CO3 or NaHCO3 solution to adjust the pH value to 7.5~8.5, sizing, passing the pulp through a pressure headbox, and then dewatering it to 40 w / w through a wet end vacuum and press mixing machine. Finally, the pulp is dewatered by steam and high-temperature hood drying to obtain the initial roll of base paper, which is then folded or rewound to obtain food-grade high-strength and high-toughness paper products.

[0020] Beneficial effects

[0021] This invention provides a food-grade high-strength and high-toughness pulp, paper products, and their preparation method. It involves adding alginate fiber and a wet-strength agent to virgin wood pulp. The wet-strength agent is a random copolymer of methacrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydrojasmonic acid methacryloyloxyhydroxypropyl ester, and acrylamide propyltrimethylammonium chloride. Acrylamide propyltrimethylammonium chloride, as a cationic monomer, can adsorb onto the negatively charged cellulose fiber surface during the pulping stage, firmly anchoring the polymer to the fiber. Furthermore, the quaternary ammonium salt cationic monomer also provides a certain antibacterial function to the paper towel. During paper drying and curing, the epoxy groups on the glycidyl ether-based polyethylene glycol monoallyl ether segments can undergo ring-opening reactions with the hydroxyl and carboxyl groups on the cellulose fibers, forming strong covalent bonds. Simultaneously, the epoxy groups may also react with each other, undergoing self-crosslinking on the fiber surface, or the resin may penetrate into the cell wall, forming an interpenetrating network with the fiber cell wall, thereby significantly improving the dry and wet strength of paper products such as paper towels. Dihydrojasmonic acid methacryloyloxyhydroxypropyl ester contains a derivative structure from plant jasmonic acid, which can provide paper towels with a long-lasting fragrance and a certain antibacterial effect. Simultaneously, its structure features long, flexible hydrophobic chains and a five-membered ring structure, which can lower the glass transition temperature of the polymer. This allows the cross-linked network to undergo a certain degree of deformation under stress, rather than brittle fracture, thereby improving the paper towel's toughness, making it more resistant to rubbing and folding, and less prone to tearing during use. This overcomes the stiffness of paper caused by traditional strong cross-linking wet-strength agents. The hydrophilic polyethylene glycol segments and alginate fibers help water quickly penetrate and diffuse within the paper towel, increasing absorption speed and rate. The flexibility of the polyethylene glycol segments also improves the paper towel's toughness and softness, allowing it to retain a certain amount of moisture and a gel-like feel when wet, preventing it from drying out completely and enhancing the sense of fullness and satisfaction during use. Attached Figure Description

[0022] Figure 1 A schematic diagram of the synthetic route for glycidyl ether-based polyethylene glycol monoallyl ether and dihydrojasmonic acid methacryloyloxyhydroxypropyl ester;

[0023] Figure 2 The image shows the 1H NMR spectrum of dihydrojasmonomethyl methacryloyloxyhydroxypropyl ester. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0026] The raw materials used in the examples and comparative examples are described below:

[0027] Alginate fiber: prepared by wet spinning of sodium alginate solution, wherein the concentration of sodium alginate solution is 4-6% and the temperature is 50-55℃. The wet spinning includes the following steps: dissolving, filtering, degassing, metering spinning, coagulation, washing, drawing, setting and drying; the temperature of the coagulation solution is controlled at 43℃ and the liquid of the coagulation solution is a 4% calcium chloride solution; the diameter of the spinneret orifice is 75μm.

[0028] Acrylamidopropyltrimethylammonium chloride: 75% aqueous solution, Shanghai Maclean Biochemical Technology Co., Ltd.

[0029] Polyethylene glycol monoallyl ether: molecular weight 1000, polyether APEG-400, Nantong Yuanlai New Materials Co., Ltd.

[0030] Glycidyl ether-based polyethylene glycol monoallyl ether: Add 1 mol of polyethylene glycol monoallyl ether and 0.3 mol of toluene to a three-necked flask equipped with a stirrer, thermometer, constant-pressure dropping funnel, water separator, and reflux condenser. The upper end of the condenser is connected to a drying tube filled with anhydrous calcium chloride. Start stirring and add 1.1 mol of solid sodium hydroxide to the reaction system in batches. Heat the reaction system to 110-120°C and continue reflux until no more water separates from the water separator. Cool the reaction system to 0-5°C. Under nitrogen protection, slowly add 1.2 mol of epichlorohydrin dropwise through the constant-pressure dropping funnel, controlling the dropping rate to keep the reaction temperature below 10°C. Complete the addition over 1-2 hours. After the addition is complete, remove the ice bath and allow the reaction solution to slowly warm to room temperature. Then, continue stirring the reaction at 40°C for 4-6 hours to ensure the reaction is complete. Add 0.4 mol of solid sodium hydroxide, heat the reaction system to 60°C, and stir the reaction at this temperature for 4-6 hours. After the reaction is complete, cool the system, filter to remove the generated sodium chloride solid, and use a rotary evaporator to distill under reduced pressure to remove the solvent, excess epichlorohydrin and small molecule byproducts. The crude product is further filtered through a neutral alumina (ethyl acetate / petroleum ether = 2:1) short column and concentrated again under reduced pressure to obtain glycidyl ether-based polyethylene glycol monoallyl ether with a yield of 93.5%.

[0031] Dihydrojasmonic acid methacryloyloxyhydroxypropyl ester: 0.1 mol dihydrojasmonic acid, 200 ppm polymerization inhibitor p-methoxyphenol, and 100 mL tetrahydrofuran were added to a three-necked flask. The mixture was refluxed at -0.09 MPa for 30 min at 60 °C. After cooling to 40 °C, 0.12 mol glycidyl methacrylate and 0.03 mol triethylamine were slowly added dropwise using a syringe under nitrogen protection. The mixture was stirred at 40 °C for 6 hours. After the reaction was complete, the system was cooled to room temperature, and 0.05% p-methoxyphenol was added to inhibit polymerization. THF was recovered by vacuum distillation at -0.095 MPa at 45 °C. The reaction solution was washed twice with 0.5 mol / L H3PO4 and once with saturated NaCl, and dried over anhydrous MgSO4. Low-boiling components were removed by short-path distillation at 0.3 mmHg at 150 °C. The product was filtered through a 0.22 μm PTFE membrane to obtain dihydrojasmonic acid methacryloyloxyhydroxypropyl ester, with a yield of 75.6%.

[0032] Wet strength agent: Dissolve methacrylate and dihydrojasmonic acid methacryloyloxyhydroxypropyl ester in isopropanol. Dissolve a 25% / 75% isopropanol and water mixture of glycidyl ether-based polyethylene glycol monoallyl ether. Dilute an aqueous solution of acrylamide propyltrimethylammonium chloride to a concentration of 50%. The total proportions of isopropanol and water are shown in Table 1. Add half of the monomers to the reaction flask according to the proportions in Table 1. Start stirring until a homogeneous, slightly viscous, transparent solution is formed. Purge with nitrogen for 30 minutes and heat to 70°C. When the reaction system temperature stabilizes at 70°C, slowly add the mixture of the remaining monomers and the initiator 2,2'-azobisisobutylamidine dihydrochloride (dissolved in a small amount of water) dropwise. After all monomers have been added, continue the reaction at 70°C for 4 hours. After the reaction was completed, the system was cooled to below 40°C, filtered using a 0.22 μm filter membrane, and distilled under reduced pressure at 50°C and -0.09 MPa to remove most of the isopropanol. Deionized water was added, and the polymer solid content was adjusted to 20 ± 2% to obtain the wet strength agent. The molecular weight was tested by GPC, and the results are shown in Table 1.

[0033] Table 1. Components and proportions of wet strength agent

[0034]

[0035] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0036] Examples and Comparative Examples

[0037] A food-grade high-strength and high-toughness pulp and paper products, with the composition and formulation as shown in Table 2, are prepared by the following method:

[0038] S1. Soak wood chips in white liquor and cook at 160-170℃ and 0.6-0.8 MPa for 90 min. Wash, add 1wt% NaOH to the wood chips and mix for 5-8 s. Introduce 0.5wt% oxygen and hold at 100℃ and 0.6 MPa for 60 min for oxygen bleaching and deligation. Wash, and perform ECF bleaching: treat with 0.8% ClO2 at 60℃ for 30 min, 0.3% H2O2 and 1% NaOH at 75℃ for 60 min, and 0.3% ClO2 at 75℃ for 120 min respectively. Wash, and use a high-efficiency double-disc mill to pulp the wood chips to a pulp concentration of 4.5-5.0 w / w% to obtain virgin wood pulp.

[0039] S2. The virgin wood pulp is thoroughly mixed with alginate fiber and wet strength agent in a certain proportion to obtain food-grade high-strength and high-toughness pulp with a concentration controlled at 4.0~5.0 w / w%.

[0040] S3. Prepare food-grade high-strength and high-toughness pulp with a concentration of 0.1~2.0 w / w%, add 1 mol / L Na2CO3 solution to adjust the pH value to 7.5~8.5, sizing, and then pass the pulp through a pressure headbox, followed by wet end vacuum and press mixing mechanical dewatering to 40 w / w%, and finally dewatering by steam and high-temperature hood drying to obtain primary roll base paper, which is then rewound to obtain food-grade high-strength and high-toughness paper products.

[0041] Table 2. Composition and proportions (parts by weight) of pulp in the examples and comparative examples.

[0042]

[0043] The paper products prepared in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 3.

[0044] (1) Strength and toughness: Before testing, single-layer paper towel samples were placed under constant temperature and humidity (23℃ and 50% humidity) for at least 24 hours to equilibrate. The longitudinal tensile strength of the paper towel was tested 5 times according to standard GB / T 12914-2018, and the average value was calculated to determine the dry tensile strength and elongation to characterize the strength and toughness of the paper towel.

[0045] (2) Wet strength: Before testing, place the single-layer paper towel sample under constant temperature and humidity (23℃ and 50% humidity) for at least 24 hours to equilibrate. Immerse the paper towel sample in distilled water at 23±1℃ for 30 seconds. After taking it out, gently absorb the water on the surface of the sample with filter paper or absorbent paper. Then test the wet tensile strength of the paper towel according to standard GB / T 465.2-2008.

[0046] (3) Water absorption rate: The water absorption performance of a single-layer paper towel is tested according to the standard ISO 12625-8:2006.

[0047] (4) Aroma evaluation: A group of 10 people conducted a blind olfaction evaluation of the tissue paper samples in a constant temperature and humidity environment; the odor label is as follows: jasmine, grass, sweet, sour, chemical, odorless; aroma intensity score (0-5): 0=odorless, 1=very weak, 2=weak, 3=moderate (obvious but not pungent), 4=strong (distinguished from a distance), 5=very strong (pungent, unpleasant), and the mode is taken as the final evaluation.

[0048] (5) Antibacterial performance test: The test was conducted in accordance with GB 15979-2002 "Hygienic Standard for Disposable Sanitary Products" to test the antibacterial performance of the paper towel against Escherichia coli, Candida albicans and Staphylococcus aureus.

[0049] Table 3 Test results of the examples and comparative examples

[0050]

[0051] As can be seen from the examples and comparative examples, the addition of wet strength agent and alginate fiber significantly improves the dry tensile strength, wet strength, and toughness of the wet wipes. Furthermore, the absorbency is higher than that of conventional wet strength agent-modified paper towels. They also possess a jasmine fragrance and certain antibacterial properties, making them particularly suitable for use as high-end or food-grade paper towels. As can be seen from Examples 1-3 and Comparative Example 5, the amount of wet strength agent added should not be too high; otherwise, excessively high cross-linking strength will lead to overly stiff paper towels.

[0052] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A food-grade high-strength and high-toughness pulp, characterized in that, The product comprises, by weight, 100 parts virgin wood pulp, 1-3 parts alginate fiber, and 0.3-1.5 parts wet strength agent, wherein the wet strength agent is a random copolymer of methacrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydrojasmonic acid methacryloyloxyhydroxypropyl ester, and acrylamide propyltrimethylammonium chloride; the structure of the dihydrojasmonic acid methacryloyloxyhydroxypropyl ester is shown in Formula 1. Formula 1; The molar ratio of the methacrylate, glycidyl ether-based polyethylene glycol monoallyl ether, dihydrojasmonic acid methacryloyloxyhydroxypropyl ester, and acrylamide propyltrimethylammonium chloride is (2~4):1:(0.5~1):(0.5~2).

2. The food-grade high-strength and high-toughness pulp as described in claim 1, characterized in that, The glycidyl ether-based polyethylene glycol monoallyl ether is prepared by reacting polyethylene glycol monoallyl ether with epichlorohydrin under alkaline and dehydrating conditions through a ring-opening-etherification-ring-closing reaction. The methacrylate is selected from one or more of methyl methacrylate, ethyl methacrylate, and butyl methacrylate.

3. The food-grade high-strength and high-toughness pulp as described in claim 1, characterized in that, The dihydrojasmonic acid methacryloyloxyhydroxypropyl ester is the reaction product of dihydrojasmonic acid and glycidyl methacrylate.

4. The food-grade high-strength and high-toughness pulp as described in claim 1, characterized in that, The alginate fiber is obtained by wet spinning of sodium alginate solution.

5. The food-grade high-strength and high-toughness pulp as described in claim 4, characterized in that, The wet spinning process includes the following steps: dissolving, filtering, defoaming, spinning, coagulation, washing, drawing, setting, and drying. The dissolving step involves preparing a sodium alginate solution with a concentration of 4-6 wt% and a temperature of 50-55°C. The coagulation step involves the sodium alginate solution being sprayed through a spinneret and solidified in a coagulation solution with a temperature controlled at 40-50°C. The coagulation solution is a calcium chloride solution with a concentration of 3-5 wt%. The spinneret has a spinneret orifice diameter of less than 100 μm.

6. The method for preparing food-grade high-strength and high-toughness pulp according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Wood chips are cooked, oxygen bleached, bleached, and refined to obtain virgin wood pulp; S2. The virgin wood pulp is thoroughly mixed with alginate fiber and wet strength agent in a certain proportion to obtain the pulp, which is food-grade high-strength and high-toughness pulp, with the concentration controlled at 4.0~5.0w / w.

7. A food-grade high-strength and high-toughness paper product, characterized in that, It is made from the food-grade high-strength and high-toughness pulp as described in any one of claims 1 to 6.

8. The method for preparing food-grade high-strength and high-toughness paper products as described in claim 7, characterized in that, Food-grade high-strength and high-toughness pulp is prepared with a concentration of 0.1~2.0w / w%, and then sized. After sizing, the pulp is passed through a pressure headbox, and then dewatered to 40w / w through a wet end vacuum and press mixing machine. Finally, it is dewatered by steam and high-temperature hood to obtain the initial roll base paper. After folding or rewinding, food-grade high-strength and high-toughness paper products are obtained.

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