A method for producing a breathable paper

Abstract

This invention relates to a method for preparing paper, specifically a method for preparing breathable paper for use in packaging materials. The invention involves a Schiff base reaction between chitosan and sodium alginate oxide, resulting in a more open and porous coating layer on the fiber surface, which facilitates gas flow and thus improves the paper's permeability to a certain extent. The covalent bonds formed by the Schiff base reaction enhance the bonding force between chitosan and sodium alginate oxide, making the coating layer more firmly attached to the wood pulp fiber surface. This enhanced bonding force helps improve the paper's tensile strength, burst strength, and other mechanical properties. The imine bonds generated by the Schiff base reaction have high chemical stability, resisting the effects of external environmental changes such as humidity and temperature on the coating layer, thereby maintaining the long-term stability of the paper's performance.

Description

Technical Field

[0001] This invention relates to a method for preparing paper, specifically a method for preparing breathable paper for use in packaging materials. Background Technology

[0002] Packaging paper, as an indispensable material in the modern packaging industry, is widely used for packaging, securing, protecting, and beautifying various commodities. It not only carries basic product information but also represents the first visual contact between the product and the consumer; therefore, its quality and performance are crucial. Among the performance indicators of packaging paper, paper strength and air permeability are two particularly critical factors. Paper strength directly determines the packaging paper's resistance to damage during transportation and storage, forming the basis for ensuring the safe delivery of goods to consumers. Air permeability affects air circulation and humidity regulation within the packaging, playing an indispensable role in maintaining the freshness of goods and extending shelf life. Especially in the packaging of sensitive goods such as food and pharmaceuticals, proper control of air permeability is key to both product quality and consumer health.

[0003] Wood pulp fiber, as one of the main raw materials in the papermaking industry, is highly favored for its abundant sources, good processability, and environmental friendliness. In the manufacturing process of packaging paper, adding wood pulp fiber can significantly improve the paper's strength. The long-chain structure and natural toughness of wood pulp fiber allow the paper to better disperse and absorb stress when subjected to external forces, thereby enhancing the paper's tensile strength, bursting strength, and other mechanical properties. To further improve paper strength, the inventors attempted to replace ordinary wood pulp fiber with chitosan-coated wood pulp fiber. While this improved strength, the film filled or covered the gaps between the fibers, reducing the paper's internal porosity and decreasing its air permeability.

[0004] Therefore, it is an urgent problem to solve the issue of how to improve paper strength while avoiding a decrease in paper breathability. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method of coating wood fibers with modified chitosan and adding it to wood pulp, thereby improving the air permeability and strength of paper and exhibiting good stability.

[0006] This invention provides a method for preparing breathable paper, which includes the following steps:

[0007] (a) Heat the chitosan solution, add wood pulp fibers to the chitosan solution, and stir for 30-100 min;

[0008] (b) Add sodium alginate oxidase solution dropwise to the solution obtained in step (a) and stir for 30-100 min;

[0009] (c) Let stand for 8-24 hours, adjust the pH of the solution to 8-9 with a sodium hydroxide solution with a mass percentage concentration of 2-6%, centrifuge to remove the supernatant and wash with water, and then dry at 45-65℃ for 3-5 hours;

[0010] (d) The wood pulp fibers obtained in step (c) are subjected to surface roughening treatment to obtain wood pulp fibers with rough surfaces;

[0011] (e) The surface roughened wood pulp fibers are subjected to ultrasonic treatment, and then the pH of the solution is adjusted to 4-6 with a sodium hydroxide solution with a mass percentage concentration of 2-6%.

[0012] (f) Centrifuge to remove the supernatant and wash with water, then dry at 45-65℃ for 1-2 hours;

[0013] (g) The wood pulp fibers obtained in step (f) are added to the wood pulp for papermaking, and then a wet strength agent and a lubricant are added. After pressing, a breathable packaging paper is obtained.

[0014] Preferably, the chitosan solution in step (a) is prepared by dissolving chitosan in an acetic acid solution with a concentration of 40-70 wt%, and then adding a sodium hydroxide solution with a concentration of 20-50 wt% to adjust the pH of the chitosan solution to 7-8.5, wherein the concentration of the chitosan solution is 1-3 wt%, and the molecular weight of the chitosan is 1.18 × 10⁻⁶. 5 -1.51×10 5 .

[0015] Preferably, the mass ratio of wood pulp fiber to chitosan in step (a) is (5-20):1.

[0016] Preferably, the concentration of the sodium alginate solution in step (b) is 2-6 wt%, the oxidation degree of sodium alginate is 24-35%, and the mass ratio of sodium alginate to chitosan is (0.5-2):1.

[0017] Preferably, the surface roughening treatment in step (d) is to mechanically treat the wood pulp fibers, and the mechanical treatment methods include ball milling or high-pressure microjet treatment.

[0018] Preferably, the pressing pressure in step (g) is 300-800 kPa and the pressing temperature is 80-120℃.

[0019] Preferably, the breathable packaging paper in step (g) comprises the following raw materials by weight: 50-83 parts wood pulp, 15-48 parts chitosan-modified wood pulp fiber, 1-3 parts wet strength agent, and 1-5 parts lubricant.

[0020] Preferably, the wet strength agent in step (g) is at least one of polyamide epichlorohydrin resin, melamine formaldehyde resin, and polyethyleneimine.

[0021] Preferably, the lubricant in step (g) is at least one of stearic acid, sodium stearate, calcium stearate, and zinc stearate.

[0022] The present invention also provides a breathable paper prepared according to the above-described method for preparing breathable paper, comprising 50-83 parts of wood pulp, 15-48 parts of chitosan-modified wood pulp fiber, 1-3 parts of wet strength agent, and 1-5 parts of lubricant.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] First, this invention involves a Schiff base reaction between chitosan and sodium alginate oxide, forming a more open and porous coating layer on the fiber surface. This facilitates gas flow and improves the paper's permeability to some extent. Furthermore, the covalent bonds formed by the Schiff base reaction enhance the bonding force between chitosan and sodium alginate oxide, resulting in a more firmly attached coating layer to the wood pulp fiber surface. This enhanced bonding helps improve the paper's tensile strength, burst strength, and other mechanical properties. The imine bonds generated by the Schiff base reaction possess high chemical stability, resisting the effects of external environmental changes such as humidity and temperature on the coating layer, thus maintaining long-term stability of the paper's performance.

[0025] Secondly, this invention roughens the surface of the treated wood pulp fibers, creating burrs on the fiber surface and increasing the gaps between the fibers, making it easier for small gas molecules to pass through. Ultrasonic treatment promotes the physical and chemical bonding between the fibers, increasing the friction and interlocking forces, which helps improve the overall strength of the paper, enabling it to withstand greater external forces and pressures. Detailed Implementation

[0026] 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.

[0027] Example 1: A breathable paper, comprising the following raw materials by weight: 60 parts wood pulp, 45 parts chitosan-modified wood pulp fiber, 2.5 parts wet strength agent polyamide epichlorohydrin resin, and 3.2 parts lubricant sodium stearate. The specific preparation method is as follows:

[0028] (a) The average molecular weight is 1.25 × 10 5Chitosan was dissolved in a 50 wt% acetic acid solution, and then a 20 wt% sodium hydroxide solution was added to adjust the pH of the chitosan solution to 7.2, wherein the concentration of chitosan in the solution was 3 wt%. The chitosan solution was heated, and wood pulp fiber was added to the chitosan solution (the mass ratio of wood pulp fiber to chitosan was 8:1), and stirred for 60 min.

[0029] (b) Add a 5 wt% sodium alginate oxidized solution (oxidation degree of 30%) to the solution obtained in step (a) and stir for 60 min;

[0030] (c) Let stand for 12 hours, adjust the pH of the solution to 8.5 with a 4 wt.% sodium hydroxide solution, centrifuge to remove the supernatant and wash with water, and then dry at 60°C for 3 hours;

[0031] (d) The wood pulp fibers obtained in step (c) are subjected to ball milling (ball milling speed 100 rpm, ball milling time 0.5 h) to obtain wood pulp fibers with rough surface;

[0032] (e) The surface roughened wood pulp fibers were subjected to ultrasonic treatment for 10 min, and then the pH of the solution was adjusted to 5 with a sodium hydroxide solution with a mass concentration of 4 wt.%.

[0033] (f) Centrifuge to remove the supernatant and wash with water, then dry at 60°C for 1 hour;

[0034] (g) The wood pulp fibers obtained in step (f) are added to the wood pulp for papermaking, and then wet strength agent and lubricant are added. After pressing (pressing pressure is 600 kPa and pressing temperature is 100℃), breathable packaging paper is obtained.

[0035] Example 2: A breathable paper, comprising the following raw materials by weight: 80 parts wood pulp, 30 parts chitosan-modified wood pulp fiber, 2.5 parts wet strength agent polyamide epichlorohydrin resin, and 3.2 parts lubricant sodium stearate. The specific preparation method is as follows:

[0036] (a) The average molecular weight is 1.25 × 10 5 Chitosan was dissolved in a 50 wt% acetic acid solution, and then a 20 wt% sodium hydroxide solution was added to adjust the pH of the chitosan solution to 7.2, wherein the concentration of chitosan in the solution was 3 wt%. The chitosan solution was heated, and wood pulp fiber was added to the chitosan solution (the mass ratio of wood pulp fiber to chitosan was 8:1), and stirred for 60 min.

[0037] (b) Add a 5 wt% sodium alginate oxidized solution (oxidation degree of 30%) to the solution obtained in step (a) and stir for 60 min;

[0038] (c) Let stand for 12 hours, adjust the pH of the solution to 8.5 with a 4 wt.% sodium hydroxide solution, centrifuge to remove the supernatant and wash with water, and then dry at 60°C for 3 hours;

[0039] (d) The wood pulp fibers obtained in step (c) are subjected to ball milling (ball milling speed 100 rpm, ball milling time 0.5 h) to obtain wood pulp fibers with rough surface;

[0040] (e) The surface roughened wood pulp fibers were subjected to ultrasonic treatment for 10 min, and then the pH of the solution was adjusted to 5 with a sodium hydroxide solution with a mass concentration of 4 wt.%.

[0041] (f) Centrifuge to remove the supernatant and wash with water, then dry at 60°C for 1 hour;

[0042] (g) The wood pulp fibers obtained in step (f) are added to the wood pulp for papermaking, and then wet strength agent and lubricant are added. After pressing (pressing pressure is 600 kPa and pressing temperature is 100℃), breathable packaging paper is obtained.

[0043] Comparative Example 1: Comparative Example 1 is basically the same as Example 1, except that sodium oxidized alginate is not added during the preparation of chitosan modified wood pulp fiber.

[0044] Comparative Example 2: Comparative Example 1 is basically the same as Example 1, except that the wood pulp fibers were not ball-milled.

[0045] Comparative Example 3: Comparative Example 1 is basically the same as Example 1, except that the wood pulp fibers after ball milling were not subjected to ultrasonic treatment.

[0046] To comprehensively evaluate the performance of the breathable paper of the present invention, the embodiments and comparative examples will be characterized, mainly involving the paper's strength, air permeability, and stability. The specific characterization methods, standards, and conditions, as well as the specific characterization results, are described below.

[0047] Characterization methods and standards

[0048] Paper strength test

[0049] Characterization method: The tensile strength tester was used to test the tensile strength according to the ISO 1924-2 standard.

[0050] Characterization standards: record the tensile strength (unit: N / m²) and bursting strength (unit: kPa) of the paper.

[0051] Breathability test

[0052] Characterization method: The air permeability tester was used to conduct the test according to ASTM D737 standard.

[0053] Characterization standards: measure the air permeability (unit: mL / s·cm²) and air resistance (unit: s / 100mL) of the paper.

[0054] Stability test

[0055] Characterization method: The paper was placed in different humidity (e.g., 30%, 50%, 70%RH) and temperature (e.g., 20℃, 40℃, 60℃) environments, and the changes in paper strength were observed.

[0056] Characterization standard: Record the tensile strength retention rate (%) of paper under different conditions.

[0057] Table 1 Characterization results of the examples and comparative examples

[0058]

[0059] Through the above characterization data and comparative analysis, it is evident that the breathable paper of this invention exhibits excellent performance in terms of strength, air permeability, and stability. In particular, the addition of oxidized sodium alginate, ball milling, and ultrasonic treatment significantly improve the paper's performance. The comparative examples, however, show varying degrees of performance deficiencies, further validating the effectiveness and innovation of the technical solution of this invention.

Claims

1. A method for preparing breathable paper, characterized in that... Includes the following steps: (a) Heat the chitosan solution, add wood pulp fibers to the chitosan solution, and stir for 30-100 min; (b) Add sodium alginate oxidase solution dropwise to the solution obtained in step (a) and stir for 30-100 min; (c) Let stand for 8-24 hours, adjust the pH of the solution to 8-9 with a sodium hydroxide solution with a mass percentage concentration of 2-6%, centrifuge to remove the supernatant and wash with water, and then dry at 45-65℃ for 3-5 hours; (d) The wood pulp fibers obtained in step (c) are mechanically treated to obtain wood pulp fibers with rough surfaces. The mechanical treatment methods include ball milling or high-pressure microjet treatment. (e) The mechanically treated wood pulp fibers are subjected to ultrasonic treatment, and then the pH of the solution is adjusted to 4-6 with a sodium hydroxide solution with a mass percentage concentration of 2-6%. (f) Centrifuge to remove the supernatant and wash with water, then dry at 45-65℃ for 1-2 hours; (g) The wood pulp fibers obtained in step (f) are added to the wood pulp for papermaking, followed by the addition of a wet strength agent and a lubricant. After pressing, a breathable packaging paper is obtained. The preparation method of the chitosan solution in step (a) is as follows: chitosan is dissolved in an acetic acid solution with a concentration of 40-70 wt%, and then a sodium hydroxide solution with a concentration of 20-50 wt% is added to adjust the pH of the chitosan solution to 7-8.5, wherein the concentration of the chitosan solution is 1-3 wt%, and the molecular weight of the chitosan is 1.18 × 10⁻⁶. 5 -1.51×10 5 The mass ratio of wood pulp fiber to chitosan is (5-20):1; the concentration of sodium alginate solution in step (b) is 2-6 wt%, the oxidation degree of sodium alginate is 24-35%, and the mass ratio of sodium alginate to chitosan is (0.5-2):

1.

2. The method according to claim 1, characterized in that... In step (g), the pressing pressure is 300-800 kPa and the pressing temperature is 80-120℃.

3. The method according to claim 1, characterized in that... The breathable packaging paper in step (g) comprises the following raw materials by weight: 50-83 parts wood pulp, 15-48 parts chitosan-modified wood pulp fiber, 1-3 parts wet strength agent, and 1-5 parts lubricant.

4. The method according to claim 1, characterized in that... The wet strength agent mentioned in step (g) is at least one of polyamide epichlorohydrin resin, melamine formaldehyde resin, and polyethyleneimine.

5. The method according to claim 1, characterized in that... The lubricant mentioned in step (g) is at least one of stearic acid, sodium stearate, calcium stearate, and zinc stearate.

6. The breathable paper prepared by the method for preparing breathable paper according to claim 1, characterized in that... It comprises 50-83 parts wood pulp, 15-48 parts chitosan-modified wood pulp fiber, 1-3 parts wet strength agent, and 1-5 parts lubricant.

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