Preparation method of breathable paper

Abstract

The invention relates to a preparation method of paper, in particular to a preparation method of breathable paper applied to a packaging material. Chitosan and oxidized sodium alginate are subjected to a Schiff base reaction, so that a more open and loose coating layer is formed on the fiber surface, gas circulation is facilitated, and the air permeability of the paper is improved to a certain extent. And a covalent bond formed by Schiff base reaction enhances the binding force between chitosan and oxidized sodium alginate, so that the coating layer is more firmly attached to the surface of wood pulp fiber. The enhanced binding force is favorable for improving the mechanical properties such as tensile strength and breakage resistance of the paper, and an imine bond generated by the Schiff base reaction has higher chemical stability and can resist the influence of changes of external environments such as humidity, temperature and the like on the coating layer, so that the long-term stability of the performance of the paper is kept.

Description

Technical Field

[0001] The invention relates to a method for preparing paper, and in particular to a method for preparing breathable paper used for packaging materials. Background Art

[0002] As one of the indispensable materials in the modern packaging industry, packaging paper is widely used in packaging, fixing, protecting and beautifying various commodities. It not only carries the basic information of the commodity, but also is the first visual contact between the commodity and the consumer, so 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 ability of packaging paper to resist damage during transportation and storage, and is the basis for ensuring that the commodity reaches the hands of consumers safely. Air permeability affects the air circulation and humidity regulation inside the package, and plays an important role in maintaining the freshness of the commodity and extending the shelf life. Especially in the packaging of sensitive commodities such as food and medicine, the reasonable control of air permeability is the key to commodity quality and consumer health.

[0003] Wood pulp fiber, as one of the main raw materials in the papermaking industry, is 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 strength of paper. The long chain structure and natural toughness of wood pulp fiber enable the paper to better disperse and absorb stress when subjected to external forces, thereby enhancing the paper's mechanical properties such as tensile strength and tear resistance. In order to further improve the strength of the paper, the inventor tried to use chitosan-coated wood pulp fibers to replace ordinary wood pulp fibers. The strength of the invention was improved, but the film would fill or cover the gaps between the fibers, thereby reducing the porosity inside the paper and reducing the air permeability of the paper.

[0004] Therefore, how to improve the strength of paper while avoiding the reduction of the air permeability of paper is an urgent problem to be solved. Summary of the invention

[0005] In view of the above problems, the present invention provides a method of coating wood fibers with modified chitosan and adding the modified chitosan to wood pulp, thereby improving the air permeability and strength of paper and providing good stability.

[0006] The present invention provides a method for preparing breathable paper, which comprises the following steps: (a) heating a chitosan solution, adding wood pulp fibers into the chitosan solution, and stirring for 30-100 minutes; (b) adding the oxidized sodium alginate solution dropwise to the solution obtained in step (a) and stirring for 30-100 minutes; (c) standing for 8-24 hours, adjusting the pH value of the solution to 8-9 with a sodium hydroxide solution having a mass percentage concentration of 2-6%, centrifuging to remove the supernatant and washing with water, and then drying at 45-65° C. for 3-5 hours; (d) performing a surface roughening treatment on the wood pulp fibers obtained in step (c) to obtain wood pulp fibers with rough surfaces; (e) subjecting the surface roughened wood pulp fibers to ultrasonic treatment, and then adjusting the pH value of the solution to 4-6 using a sodium hydroxide solution having a mass percentage concentration of 2-6%; (f) removing the supernatant by centrifugation and washing with water, and then drying at 45-65° C. for 1-2 h; (g) adding the wood pulp fiber obtained in step (f) into wood pulp to make paper, adding a wet strength agent and a lubricant, and pressing to obtain a breathable packaging paper.

[0007] Preferably, the preparation method of the chitosan solution in step (a) is: dissolving chitosan in an acetic acid solution with a concentration of 40-70wt%, and then adding a sodium hydroxide solution with a concentration of 20-50wt% to adjust the pH of the chitosan solution to 7-8.5, wherein the concentration of the chitosan solution is 1-3wt%, and the molecular weight of chitosan is 1.18×10 5 -1.51×10 5 .

[0008] Preferably, in step (a), the mass ratio of wood pulp fiber to chitosan is (5-20):1.

[0009] Preferably, the concentration of the oxidized sodium alginate solution in step (b) is 2-6wt%, the degree of oxidation of the oxidized sodium alginate is 24-35%, and the mass ratio of the oxidized sodium alginate to chitosan is (0.5-2):1.

[0010] Preferably, the surface roughening treatment in step (d) is performed by mechanically treating the wood pulp fibers, and the mechanical treatment includes ball milling or high-pressure microfluidization treatment.

[0011] Preferably, in step (g), the pressing pressure is 300-800 kPa and the pressing temperature is 80-120°C.

[0012] Preferably, the breathable packaging paper in step (g) comprises the following raw materials by weight: 50-83 parts of wood pulp, 15-48 parts of chitosan-modified wood pulp fibers, 1-3 parts of wet strength agent, and 1-5 parts of lubricant.

[0013] Preferably, the wet strength agent in step (g) is at least one of polyamide epichlorohydrin resin, melamine formaldehyde resin and polyethyleneimine.

[0014] Preferably, the lubricant in step (g) is at least one of stearic acid, sodium stearate, calcium stearate and zinc stearate.

[0015] The present invention also provides breathable paper prepared according to the method for preparing breathable paper, which comprises 50-83 parts of wood pulp, 15-48 parts of chitosan modified wood pulp fibers, 1-3 parts of wet strength agent, and 1-5 parts of lubricant.

[0016] Compared with the prior art, the present invention has the following advantages: First, the present invention conducts a Schiff base reaction between chitosan and oxidized sodium alginate, thereby forming a more open and loose coating layer on the fiber surface, which is conducive to the circulation of gas, thereby improving the air permeability of the paper to a certain extent. The covalent bond formed by the Schiff base reaction enhances the binding force between chitosan and oxidized sodium alginate, so that the coating layer is more firmly attached to the surface of the wood pulp fiber. This enhanced binding force helps to improve the mechanical properties of the paper, such as tensile strength and tear resistance. The imine bond generated by the Schiff base reaction has high chemical stability and can resist the influence of changes in the external environment such as humidity and temperature on the coating layer, thereby maintaining the long-term stability of the paper performance.

[0017] Secondly, the present invention roughens the surface of the treated wood pulp fibers to form burrs on the surface of the wood pulp fibers, increasing the gaps between the fibers and making it easier for small gas molecules to pass through. Ultrasonic treatment can promote physical and chemical bonding between fibers, increase friction and meshing force between fibers, which helps to improve the overall strength of paper and enable it to withstand greater external forces and pressures. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1: A breathable paper comprises the following raw materials by weight: 60 parts of wood pulp, 45 parts of chitosan-modified wood pulp fiber, 2.5 parts of wet strength agent polyamide epichlorohydrin resin, and 3.2 parts of lubricant sodium stearate. The specific preparation method is as follows: (a) The average molecular weight is 1.25×10 5Chitosan was dissolved in a 50wt% acetic acid solution, and then a 20wt% 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 3wt%; 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 minutes; (b) adding a 5 wt % oxidized sodium alginate solution (oxidation degree 30%) to the solution obtained in step (a) and stirring for 60 min; (c) standing for 12 h, adjusting the pH value of the solution to 8.5 with a sodium hydroxide solution having a mass concentration of 4 wt.%, centrifuging to remove the supernatant and washing with water, and then drying at 60 ° C for 3 h; (d) ball milling the wood pulp fiber obtained in step (c) (ball milling speed of 100 rpm, ball milling time of 0.5 h) to obtain wood pulp fiber with a rough surface; (e) subjecting the surface roughened wood pulp fibers to ultrasonic treatment for 10 minutes, and then adjusting the pH value of the solution to 5 using a sodium hydroxide solution having a mass concentration of 4 wt.%; (f) removing the supernatant by centrifugation and washing with water, and then drying at 60°C for 1 h; (g) adding the wood pulp fiber obtained in step (f) into wood pulp to make paper, adding a wet strength agent and a lubricant, and pressing (pressing pressure of 600 kPa, pressing temperature of 100° C.) to obtain breathable packaging paper.

[0020] Example 2: A breathable paper comprises the following raw materials by weight: 80 parts of wood pulp, 30 parts of chitosan-modified wood pulp fiber, 2.5 parts of wet strength agent polyamide epichlorohydrin resin, and 3.2 parts of lubricant sodium stearate. The specific preparation method is as follows: (a) The average molecular weight is 1.25×10 5 Chitosan was dissolved in a 50wt% acetic acid solution, and then a 20wt% 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 3wt%; 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 minutes; (b) adding a 5 wt % oxidized sodium alginate solution (oxidation degree 30%) to the solution obtained in step (a) and stirring for 60 min; (c) standing for 12 h, adjusting the pH value of the solution to 8.5 with a sodium hydroxide solution having a mass concentration of 4 wt.%, centrifuging to remove the supernatant and washing with water, and then drying at 60 ° C for 3 h; (d) ball milling the wood pulp fiber obtained in step (c) (ball milling speed of 100 rpm, ball milling time of 0.5 h) to obtain wood pulp fiber with a rough surface; (e) subjecting the surface roughened wood pulp fibers to ultrasonic treatment for 10 minutes, and then adjusting the pH value of the solution to 5 using a sodium hydroxide solution having a mass concentration of 4 wt.%; (f) removing the supernatant by centrifugation and washing with water, and then drying at 60°C for 1 h; (g) adding the wood pulp fiber obtained in step (f) into wood pulp to make paper, adding a wet strength agent and a lubricant, and pressing (pressing pressure of 600 kPa, pressing temperature of 100° C.) to obtain breathable packaging paper.

[0021] Comparative Example 1: Comparative Example 1 is substantially the same as Example 1, except that oxidized sodium alginate is not added during the preparation of the chitosan-modified wood pulp fiber.

[0022] Comparative Example 2: Comparative Example 1 is substantially the same as Example 1, except that the wood pulp fibers are not ball-milled.

[0023] Comparative Example 3: Comparative Example 1 is substantially the same as Example 1, except that the ball-milled wood pulp fibers are not subjected to ultrasonic treatment.

[0024] In order to comprehensively evaluate the performance of the breathable paper of the present invention, the embodiments and comparative examples are characterized, mainly involving the strength, air permeability and stability of the paper. The following are specific characterization methods, characterization standards and conditions, and specific characterization results.

[0025] Characterization methods and standards Paper strength test Characterization method: The tensile strength tester was used to test according to ISO 1924-2 standard.

[0026] Characterization standard: Record the tensile strength (unit: N / m²) and bursting strength (unit: kPa) of the paper.

[0027] Air permeability test Characterization method: Use an air permeability tester to test according to ASTM D737 standard.

[0028] Characterization standard: measure the air permeability (unit: mL / s·cm²) and air permeability resistance (unit: s / 100mL) of paper.

[0029] Stability test Characterization method: Place the paper in different humidity (such as 30%, 50%, 70%RH) and temperature (such as 20℃, 40℃, 60℃) environments, and observe the changes in paper strength.

[0030] Characterization standard: record the tensile strength retention rate (%) of paper under different conditions.

[0031] Table 1 Characterization results of examples and comparative examples

[0032] Through the above characterization data and comparative analysis, it can be clearly seen that the breathable paper of the present invention performs well in strength, air permeability and stability. In particular, the performance of the paper is significantly improved by adding oxidized sodium alginate, ball milling and ultrasonic treatment. The comparative examples show performance deficiencies to varying degrees, further verifying the effectiveness and innovation of the technical solution of the present invention.

Claims

1. A method for preparing breathable paper, characterized in that The steps include: (a) heating a chitosan solution, adding wood pulp fibers into the chitosan solution, and stirring for 30-100 minutes; (b) adding the oxidized sodium alginate solution dropwise to the solution obtained in step (a) and stirring for 30-100 minutes; (c) standing for 8-24 hours, adjusting the pH value of the solution to 8-9 with a sodium hydroxide solution having a mass percentage concentration of 2-6%, centrifuging to remove the supernatant and washing with water, and then drying at 45-65° C. for 3-5 hours; (d) performing a surface roughening treatment on the wood pulp fibers obtained in step (c) to obtain wood pulp fibers with rough surfaces; (e) subjecting the surface roughened wood pulp fibers to ultrasonic treatment, and then adjusting the pH value of the solution to 4-6 using a sodium hydroxide solution having a mass percentage concentration of 2-6%; (f) removing the supernatant by centrifugation and washing with water, and then drying at 45-65° C. for 1-2 h; (g) adding the wood pulp fiber obtained in step (f) into wood pulp to make paper, adding a wet strength agent and a lubricant, and pressing to obtain a breathable packaging paper.

2. The method according to claim 1, characterized in that 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 40-70wt%, and then a sodium hydroxide solution with a concentration of 20-50wt% is added to adjust the pH of the chitosan solution to 7-8.5, wherein the concentration of the chitosan solution is 1-3wt%, and the molecular weight of chitosan is 1.18×10 5 -1.51×10 5 .

3. The method according to claim 1, characterized in that In step (a), the mass ratio of wood pulp fiber to chitosan is (5-20):

1.

4. The method according to claim 1, characterized in that The concentration of the oxidized sodium alginate solution in step (b) is 2-6wt%, the degree of oxidation of the oxidized sodium alginate is 24-35%, and the mass ratio of sodium alginate to chitosan is (0.5-2):

1.

5. The method according to claim 1, characterized in that The surface roughening treatment in step (d) is performed by mechanically treating the wood pulp fibers, and the mechanical treatment includes ball milling or high-pressure microfluidization treatment.

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

7. 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 of wood pulp, 15-48 parts of chitosan modified wood pulp fibers, 1-3 parts of wet strength agent, and 1-5 parts of lubricant.

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

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

10. The breathable paper prepared by the method for preparing breathable paper according to claim 1, characterized in that The invention comprises 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.

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