High-strength cross-linked regenerated cellulose membrane, its preparation method and application

Abstract

This invention relates to a high-strength cross-linked regenerated cellulose membrane, its preparation method, and its applications. The preparation method includes the following steps: (1) adding cotton fibers to a maleic acid solution and mixing and stirring to obtain fully swollen cotton fibers; (2) adding pre-cooled concentrated sulfuric acid at low temperature to the maleic acid solution in step (1) and stirring for 10-20 minutes to obtain a regenerated cellulose solution; (3) uniformly coating the regenerated cellulose solution using a casting coating method and placing it in a sodium hydroxide regeneration bath, replacing the sodium hydroxide regeneration bath several times at regular intervals to obtain the regenerated cellulose membrane, and air-drying it naturally to obtain a high-strength cross-linked regenerated cellulose membrane. The high-strength cross-linked regenerated cellulose membrane of this invention has good biocompatibility, green and completely degradable properties, excellent light transmittance, and high mechanical tensile properties. It can be applied to food packaging, mulch film, bioimaging, and biomaterials, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of cellulose membrane technology, specifically relating to high-strength cross-linked regenerated cellulose membranes, their preparation methods, and applications. Background Technology

[0002] Packaging materials are an integral part of human life, and are widely popular across various industries due to their low cost and ease of processing. However, traditional packaging materials are mostly synthetic plastics, which cause serious environmental problems due to their slow degradation, the production of toxic gases when burned, and the resulting white pollution from large-scale disposal. Therefore, it is imperative to develop a method for preparing packaging materials that are biocompatible, green, biodegradable, simple, and high-strength.

[0003] Cellulose, due to its advantages such as wide availability, low price, and environmental friendliness, has already seen initial commercial applications in food packaging, mulch films, bioimaging, and biomaterials. However, because cellulose itself has a strong three-dimensional hydrogen bond network structure, how to efficiently and rapidly dissolve cellulose while minimizing cellulose hydrolysis is a pressing issue that needs to be addressed when preparing various multifunctional and multi-application materials using cellulose as a raw material.

[0004] Currently, methods for preparing regenerated cellulose membranes by dissolving cellulose in the market are divided into aqueous solvents and non-aqueous solvents. Aqueous solvents include inorganic salt solvents, alkaline solvents, NMMO (N-methylmorpholine-N-oxide), TBAH (tetrabutylammonium hydroxide), and TBPH (tetrabutylphosphine hydroxide). Among them, inorganic salt solvents, due to the high-temperature conditions (60-300℃), lead to decreased solution stability and severe hydrolysis. Alkaline solutions can hardly dissolve high-polymerization cellulose and have limited solubility, which is also unfavorable for industrial production. NMMO, TBAH, and TBPH solutions face the problems of solution instability and the tendency of cellulose to fibrillate. Non-aqueous solvents include ionic liquids and LiCl / DMAC (lithium chloride / dimethylacetamide). Non-aqueous solvents are also unfavorable for industrial production due to their high cost and complex processes. For example, patent document CN1252163C discloses a new solvent for dissolving cellulose by a freeze-thaw method or a direct dissolution method, and a method for preparing regenerated cellulose filaments and membranes using this solvent. However, this solvent cannot dissolve high molecular weight cellulose, and a concentrated solution of high molecular weight cellulose cannot be obtained. For example, patent document CN109337097A discloses an ionic liquid and N-hydroxyalkyl caprolactam for dissolving cellulose, which greatly improves dissolution efficiency and makes cellulose less prone to degradation. However, this solvent is too expensive, resulting in low economic benefits and hindering mass production. In summary, the existing dissolution systems for preparing regenerated cellulose membranes still have significant shortcomings, and there is an urgent need to develop a stable and low-cost solvent.

[0005] Therefore, this invention addresses these issues by proposing a method for preparing a high-strength cross-linked regenerated cellulose membrane based on a mixed acid dissolution system. This method can fully dissolve cotton fibers in a shorter time and under lower acidity, significantly reducing the degree of hydrolysis during the dissolution process. Furthermore, by altering the regeneration bath conditions, the mechanical tensile strength of the regenerated cellulose membrane is further improved. The mechanical tensile strength of the regenerated cellulose membrane prepared by this invention is significantly improved compared to existing commercially available methods for preparing regenerated cellulose membranes by dissolving cotton fibers. Additionally, the dissolution temperature used in this invention is limited to 0-30°C, greatly reducing energy loss compared to other dissolution systems, which is more conducive to large-scale industrial production and can generate greater economic benefits. Summary of the Invention

[0006] The purpose of this invention is to provide a high-strength cross-linked regenerated cellulose membrane based on a mixed acid dissolution system, its preparation method, and its applications. This method features a simple preparation path, convenient operation, inexpensive and environmentally friendly raw materials, a stable, rapid, and efficient dissolution system, and a product exhibiting biocompatibility, excellent light transmittance, thermal stability, and high tensile strength. It is easy to industrially produce, can generate significant economic benefits, and has broad application prospects in food packaging, agricultural films, bioimaging, and biomaterials.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a high-strength cross-linked regenerated cellulose membrane includes the following steps:

[0009] (1) Add cotton fibers to maleic acid solution and mix and stir to obtain fully swollen cotton fibers;

[0010] (2) Add concentrated sulfuric acid pre-cooled under low temperature conditions to the maleic acid solution in step (1) and stir for 10-20 min to obtain a regenerated cellulose solution;

[0011] (3) The regenerated cellulose solution is uniformly coated by casting and placed in a sodium hydroxide regeneration bath. The sodium hydroxide regeneration bath is replaced several times at regular intervals to obtain the regenerated cellulose membrane, which is then air-dried to obtain a high-strength cross-linked regenerated cellulose membrane.

[0012] As a preferred embodiment, in step (1), the solid-liquid ratio of maleic acid to water in the maleic acid solution is 1g:3-5mL.

[0013] As a preferred embodiment, steps (1) and (2) are both carried out under environmental conditions with a temperature of 0-30℃.

[0014] As a preferred embodiment, in step (2), the pre-cooling under low temperature conditions is 0-10℃.

[0015] As a preferred embodiment, in step (2), the degree of polymerization of the cotton fiber is 1400-1800.

[0016] As a preferred embodiment, the cotton fiber accounts for 2.5-10% of the mass fraction of the mixed acid dissolution system composed of concentrated sulfuric acid and maleic acid solution.

[0017] As a preferred embodiment, the concentrated sulfuric acid accounts for 50-60% of the mass fraction of the mixed acid dissolution system.

[0018] As a preferred embodiment, in step (3), a new regeneration bath is replaced every 30-40 minutes, for a total of 3-4 replacements.

[0019] The present invention also provides a high-strength cross-linked regenerated cellulose membrane prepared by the preparation method described in any of the preceding embodiments.

[0020] The present invention also provides applications of the high-strength cross-linked regenerated cellulose membrane described above, for use in food packaging, mulch film, or bioimaging.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) This invention uses cotton fiber, which is widely available and inexpensive, as raw material, and has the advantages of being green, environmentally friendly, and completely biodegradable.

[0023] (2) The preparation method used in this invention is simple and convenient, easy to mass-produce, and has a large market demand, thus having considerable social and economic benefits.

[0024] (3) The high-strength cross-linked regenerated cellulose membrane of the present invention has good biocompatibility, green and completely degradable properties, excellent light transmittance, and high mechanical tensile properties of cellulose materials. It can be applied to food packaging, mulch film, bioimaging and biomaterials, and has broad application prospects. Attached Figure Description

[0025] Figure 1 This is a field emission scanning electron microscope (FE-SEM) image of the surface of the high-strength cross-linked regenerated cellulose membrane in Example 1 of the present invention;

[0026] Figure 2 This is a field emission scanning electron microscope (FE-SEM) image of the cross-section of the high-strength cross-linked regenerated cellulose membrane in Example 1 of the present invention;

[0027] Figure 3 These are the universal tensile test diagrams of the cellulose membranes of Examples 1-4 and Comparative Example 5 of the present invention.

[0028] Figure 4The thermogravimetric analysis results are for the cellulose membrane and raw material cotton of Examples 1-4 and Comparative Example 5 of this invention. Detailed Implementation

[0029] The technical solution of the present invention will be explained in detail below through specific embodiments.

[0030] Example 1:

[0031] The method for preparing the high-strength cross-linked regenerated cellulose membrane in this embodiment includes:

[0032] Prepare a maleic acid aqueous solution with a ratio of 1g:3mL, wherein the maleic acid was purchased from Aladdin Company, and stir for 5min;

[0033] Weigh 1g of cotton fiber, wherein the degree of polymerization of the cotton fiber is 1400; the mass fraction of the cotton fiber in the mixed acid dissolution system consisting of concentrated sulfuric acid, maleic acid solution and cotton fiber is 2.63%;

[0034] Weigh out a certain amount of concentrated sulfuric acid. The mass ratio of concentrated sulfuric acid to mixed acid in the dissolution system is 1:1.73. The concentrated sulfuric acid was purchased from Aladdin Company, AR grade, with a purity of ≥99.5%. It was pre-cooled at low temperature (5℃).

[0035] Prepare a sodium hydroxide aqueous solution with a ratio of 1g:80mL, wherein the sodium hydroxide was purchased from Aladdin Company, AR grade, purity ≥98%, and stirred for 5min;

[0036] Under low temperature (0℃) conditions, the above cotton fibers were placed in the prepared maleic acid solution and stirred for 4 min; under low temperature (0℃ ice bath) stirring (speed 100 rpm / min) conditions, the treated concentrated sulfuric acid was added dropwise to the above cotton fiber solution swollen by maleic acid and stirred thoroughly for 20 min to obtain a regenerated cellulose solution.

[0037] The regenerated cellulose solution was uniformly coated using a film-coating method, and then placed in the prepared sodium hydroxide solution. The regeneration bath was changed every 30 minutes, and the bath was changed 3 times. Finally, the solution was removed and allowed to air dry at room temperature to obtain a high-strength cross-linked regenerated cellulose membrane.

[0038] Example 2:

[0039] The method for preparing the high-strength cross-linked regenerated cellulose membrane in this embodiment includes:

[0040] Prepare a maleic acid aqueous solution with a ratio of 1g:3mL, wherein the maleic acid was purchased from Aladdin Company, and stir for 5min;

[0041] Weigh out 1g of cotton fiber, wherein the degree of polymerization of the cotton fiber is 1400;

[0042] Weigh out a certain amount of concentrated sulfuric acid. The mass ratio of concentrated sulfuric acid to the mixed acid dissolution system composed of concentrated sulfuric acid, maleic acid solution and cotton fiber is 1:2. The concentrated sulfuric acid is purchased from Aladdin Company, AR grade, with a purity of ≥99.5%. It is pre-cooled at low temperature (5℃).

[0043] Prepare a sodium hydroxide solution with a ratio of 1g:80mL, wherein the sodium hydroxide was purchased from Aladdin Company, AR grade, purity ≥98%, and stirred for 5min;

[0044] Under low temperature (0℃) conditions, the above cotton fibers were placed in the prepared maleic acid solution and stirred for 4 min; under low temperature (0℃ ice bath) stirring (speed 100 rpm / min) conditions, the treated concentrated sulfuric acid was added dropwise to the above cotton fiber solution swollen by maleic acid and stirred thoroughly for 20 min to obtain a regenerated cellulose solution.

[0045] The regenerated cellulose solution was uniformly coated using a film-coating method, and then placed in the prepared sodium hydroxide solution. The regeneration bath was changed every 30 minutes, and the bath was changed 3 times. Finally, the solution was removed and allowed to air dry at room temperature to obtain a high-strength cross-linked regenerated cellulose membrane.

[0046] Example 3:

[0047] The method for preparing the high-strength cross-linked regenerated cellulose membrane in this embodiment includes:

[0048] Prepare a maleic acid aqueous solution with a ratio of 1g:3mL, wherein the maleic acid was purchased from Aladdin Company, and stir for 5min;

[0049] Weigh out 1g of cotton fiber, wherein the degree of polymerization of the cotton fiber is 1400;

[0050] Weigh out a certain amount of concentrated sulfuric acid. The mass ratio of concentrated sulfuric acid to mixed acid in the dissolution system is 1:1.73. The concentrated sulfuric acid was purchased from Aladdin Company, AR grade, with a purity of ≥99.5%. It was pre-cooled at low temperature (5℃).

[0051] Prepare a sodium hydroxide solution with a ratio of 1g:80mL, wherein the sodium hydroxide was purchased from Aladdin Company, AR grade, purity ≥98%, and stirred for 5min;

[0052] Under low temperature (0℃) conditions, the above cotton fibers were placed in the prepared maleic acid solution and stirred for 4 min; under low temperature (0℃ ice bath) stirring (speed 100 rpm / min) conditions, the treated concentrated sulfuric acid was added dropwise to the above cotton fiber solution swollen by maleic acid and stirred thoroughly for 15 min to obtain a regenerated cellulose solution.

[0053] The regenerated cellulose solution was uniformly coated using a film-coating method, and then placed in the prepared sodium hydroxide solution. The regeneration bath was changed every 30 minutes, and the bath was changed 3 times. Finally, the solution was removed and allowed to air dry at room temperature to obtain a high-strength cross-linked regenerated cellulose membrane.

[0054] Example 4:

[0055] The method for preparing the high-strength cross-linked regenerated cellulose membrane in this embodiment includes:

[0056] Prepare a maleic acid aqueous solution with a ratio of 1g:3mL, wherein the maleic acid was purchased from Aladdin Company, and stir for 5min;

[0057] Weigh out 1g of cotton fiber, wherein the degree of polymerization of the cotton fiber is 1400;

[0058] Weigh out a certain amount of concentrated sulfuric acid. The mass ratio of concentrated sulfuric acid to mixed acid in the dissolution system is 1:1.73. The concentrated sulfuric acid was purchased from Aladdin Company, AR grade, with a purity of ≥99.5%. It was pre-cooled at low temperature (5°C).

[0059] Prepare a sodium hydroxide solution with a ratio of 1g:80mL, wherein the sodium hydroxide was purchased from Aladdin Company, AR grade, purity ≥98%, and stirred for 5min;

[0060] Under low temperature (0℃) conditions, the above cotton fibers were placed in the prepared maleic acid solution and stirred for 4 min; under low temperature (0℃ ice bath) stirring (speed 100 rpm / min) conditions, the treated concentrated sulfuric acid was added dropwise to the above cotton fiber solution swollen by maleic acid and stirred thoroughly for 10 min to obtain a regenerated cellulose solution.

[0061] The regenerated cellulose solution was uniformly coated using a film-coating method, and then placed in the prepared sodium hydroxide solution. The regeneration bath was changed every 30 minutes, and the bath was changed 3 times. Finally, the solution was removed and allowed to air dry at room temperature to obtain a high-strength cross-linked regenerated cellulose membrane.

[0062] Comparative Example 1:

[0063] The preparation method of this comparative example differs from that of Example 1 in that:

[0064] The maleic acid solution in Example 1 was replaced with a concentrated sulfuric acid solution with a mass fraction of 45%, while other process steps remained unchanged.

[0065] The preparation process of Comparative Example 1 failed to form a complete cellulose membrane. This is because the strong acid environment of the concentrated sulfuric acid dissolution system used in Comparative Example 1 causes excessive loss of free water in the final film-forming stage, resulting in low toughness of the cellulose membrane prepared by this system, which ultimately fails to form a complete cellulose membrane.

[0066] The mixed acid dissolution system used in this invention has a lower acidity environment compared to the concentrated sulfuric acid dissolution system, which can effectively alleviate the hydrolysis of cotton fibers during the dissolution process. In addition, the maleic acid used in this invention is an organic acid. Compared with concentrated sulfuric acid (inorganic acid), this solvent itself has a carboxyl functional group, which can accelerate the dissolution rate during the dissolution process, break the hydrogen bonds between protocellulose chains, and form stronger cross-linked hydrogen bonds. Ultimately, it can enable the prepared regenerated cellulose membrane to maintain a good mechanical tensile strength.

[0067] Comparative Example 2:

[0068] The preparation method of this comparative example differs from that of Example 1 in that:

[0069] The solid-liquid ratio of the maleic acid solution in Example 1 was changed to 1g:6mL, while other process steps remained unchanged.

[0070] In Comparative Example 2, it was found that cotton fibers could not swell sufficiently in maleic acid solution, nor could they be made into regenerated cellulose membranes.

[0071] Comparative Example 3:

[0072] The preparation method of this comparative example differs from that of Example 1 in that:

[0073] Following the process described in Example 1, after adding concentrated sulfuric acid with a mass fraction of 98% dropwise, the stirring time was less than 10 minutes, while other process steps remained unchanged; it was found that the cotton fiber could not be fully dissolved, and ultimately, a regenerated cellulose membrane could not be prepared.

[0074] Comparative Example 4:

[0075] The preparation method of this comparative example differs from that of Example 1 in that:

[0076] In Example 1, after adding concentrated sulfuric acid with a mass fraction of 98% dropwise and stirring for more than 20 minutes, while keeping other process steps unchanged, it was found that the regenerated cellulose solution was severely hydrolyzed and ultimately could not be used to prepare a regenerated cellulose membrane.

[0077] Comparative Example 5:

[0078] The preparation method of this comparative example differs from that of Example 1 in that:

[0079] The regeneration bath described in Example 1 was replaced with deionized water, while other process steps remained unchanged. A regenerated cellulose membrane with a strength of 43 MPa was successfully prepared.

[0080] like Figure 1 The field emission scanning electron microscope image of the high-strength cross-linked regenerated cellulose membrane prepared in Example 1 of this invention shows that the surface of the regenerated cellulose membrane is flat and smooth, indicating that the cotton fibers are completely dissolved; as shown in the image. Figure 2 As shown, the regenerated cellulose membrane has a dense and compact cross-section with regular corrugations, indicating that the regenerated cellulose membrane forms a denser structure during the regeneration process, thus exhibiting excellent tensile properties.

[0081] like Figure 3 As shown, cotton fibers were dissolved in this mixed acid system. Different process conditions resulted in regenerated cellulose fibers with varying tensile strengths. The regenerated cellulose membrane obtained by dissolving cotton fibers in the mixed acid system with sodium hydroxide as the regeneration bath exhibited the highest strength, reaching 122 MPa. This is attributed to the lower acidity during dissolution, which effectively slowed down the hydrolysis of the cotton fibers. Furthermore, the introduction of functional groups during dissolution led to physical cross-linking between these functional groups and the cellulose chains, accelerating the dissolution of cellulose. Additionally, sodium hydroxide neutralized the acidity of the regeneration solution at a faster rate during regeneration, slowing down the degradation rate of the regeneration solution. This resulted in a regenerated cellulose membrane with a larger molecular weight and stronger tensile strength. Figure 4 As shown, the regenerated cellulose membrane prepared in Example 1, as determined by thermogravimetric analysis, exhibits a larger Tg compared to other systems. o and T max This indicates that the regenerated cellulose membrane prepared by this invention has better thermal stability. This also verifies that the regenerated cellulose membrane prepared by this invention has a larger molecular weight and a more compact molecular structure. Similarly, the regenerated cellulose membrane has superior tensile strength. Therefore, the regenerated fiber membrane of this invention can be applied to food packaging, mulch films, bioimaging, and biomaterials, and has broad application prospects.

[0082] In the above embodiments and their alternatives, the solid-liquid ratio of maleic acid to water in the maleic acid solution is 1g:3.5mL, 1g:4mL, 1g:4.5mL, 1g:5mL, etc.

[0083] In the above embodiments and their alternatives, the temperature of the preparation process environment can also be 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, etc.

[0084] In the above embodiments and their alternatives, the temperature for precooling concentrated sulfuric acid can also be 0°C, 2°C, 4°C, 6°C, 7°C, 8°C, 9°C, 10°C, etc.

[0085] In the above embodiments and their alternatives, the degree of polymerization of cotton fibers can also be 1500, 1600, 1700, 1800, etc.

[0086] In the above embodiments and their alternatives, the mass fraction of cotton fibers in the mixed acid dissolution system composed of concentrated sulfuric acid, maleic acid solution and cotton fibers is 2.5%, 3.5%, 4%, 5.5%, 6%, 8%, 9%, 10%, etc.

[0087] In the above embodiments and their alternatives, the mass fraction of concentrated sulfuric acid in the mixed acid dissolution system is 52%, 55%, 57%, 59%, 60%, etc.

[0088] In the above embodiments and their alternatives, the regeneration bath is replaced every 30-40 minutes, for a total of 3-4 times, the specific number of times to be replaced can be determined according to the actual application requirements.

[0089] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength cross-linked regenerated cellulose membrane, characterized in that, The following steps are involved: (1) Add cotton fibers to maleic acid solution and mix and stir to obtain fully swollen cotton fibers; (2) Add concentrated sulfuric acid pre-cooled under low temperature conditions to the maleic acid solution in step (1) and stir for 10-20 min to obtain a regenerated cellulose solution; (3) The regenerated cellulose solution is uniformly coated by casting and placed in a sodium hydroxide regeneration bath. The sodium hydroxide regeneration bath is replaced several times at regular intervals to obtain the regenerated cellulose membrane, which is then air-dried to obtain a high-strength cross-linked regenerated cellulose membrane. Both steps (1) and (2) are carried out under environmental conditions with a temperature of 0-30℃; Pre-cooling at low temperatures is 0-10℃.

2. The preparation method according to claim 1, characterized in that, In step (1), the solid-liquid ratio of maleic acid to water in the maleic acid solution is 1g:3-5mL.

3. The preparation method according to claim 1, characterized in that, In step (2), the degree of polymerization of cotton fibers is 1400-1800.

4. The preparation method according to claim 1, characterized in that, The cotton fiber accounts for 2.5-10% of the mass fraction of the mixed acid dissolution system consisting of concentrated sulfuric acid, maleic acid solution, and cotton fiber.

5. The preparation method according to claim 1, characterized in that, The concentrated sulfuric acid accounts for 50-60% of the mass fraction of the mixed acid dissolution system.

6. The preparation method according to claim 1, characterized in that, In step (3), a new regeneration bath is replaced every 30-40 minutes, for a total of 3-4 times.

7. The high-strength cross-linked regenerated cellulose membrane prepared by the preparation method according to any one of claims 1-6.

8. The application of the high-strength cross-linked regenerated cellulose membrane as described in claim 7, characterized in that, Used in food packaging, mulch film, or bioimaging.

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