Preparation method of cellulose membrane based on wheat straw

Abstract

The invention discloses a preparation method of a cellulose membrane based on wheat straw, and belongs to the technical field of biomass materials and environment-friendly materials. The method comprises the following steps: carrying out delignification treatment on wheat straws to obtain cellulosic fibers; and carrying out hot pressing treatment on the cellulose fibers to obtain a cellulose membrane, dipping the cellulose membrane in a gelatin solution, taking out and drying to obtain the cellulose membrane based on the wheat straws. The material obtained by the method not only has excellent mechanical properties and water resistance, but also has good biocompatibility and sustainability, is suitable for multiple fields of packaging, biomedicine and the like, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical fields of biomass materials and environmental protection materials, and particularly relates to a preparation method of a cellulose film based on wheat straw. Background Art

[0002] With the vigorous development of ecological agriculture and the continuous improvement of the degree of agricultural production mechanization, the comprehensive utilization rate of crop straw has been significantly improved. This not only helps to enhance soil fertility, provide raw materials for sustainable energy, but also promotes farmers' income increase through new utilization methods. Therefore, continuously strengthening the comprehensive utilization and development of crop straw and developing agricultural circular economy are of great significance for accelerating the construction of the ecological environment.

[0003] As a rich agricultural waste, wheat straw has the advantages of high cellulose content, wide source, and low price. However, the presence of lignin limits its application in high-performance materials. Through delignification treatment and subsequent modification processes, the performance of wheat straw cellulose can be significantly improved, and a cellulose film with excellent mechanical properties and functionality can be developed. This cellulose film is not only a natural, renewable, and biodegradable polymer material, but also of great significance in the development of film-making technology for reducing environmental pollution and replacing hard-to-degrade petroleum-based plastic films. A large amount of petroleum-based plastic films are consumed globally every year, and these materials are difficult to degrade in the natural environment, causing serious white pollution. As an environmentally friendly material, cellulose film can effectively reduce this kind of pollution.

[0004] Cellulose is one of the most abundant natural polymer materials in nature, and the amount of cellulose produced in nature every year exceeds hundreds of billions of tons. Developing cellulose film-making technology helps to achieve the efficient and sustainable utilization of this rich resource. Cellulose film has a wide range of applications in fields such as daily necessities, printing and compounding, medicine and food packaging, tapes, cables, and insulating substrates due to its unique excellent properties such as non-toxic, odorless, fully biodegradable, antistatic, easy to dye, good extensibility, and high temperature resistance. These applications provide a broad market for the commercialization of cellulose film and also provide strong support for promoting the green transformation of related industries.

[0005] Traditional cellulose film production processes have problems such as complexity, high energy consumption, and serious pollution. Therefore, developing new efficient and green preparation technologies for cellulose films has important economic and social significance. Summary of the Invention

[0006] In view of the above technical problems, the present invention proposes a preparation method of a cellulose film based on wheat straw.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the objectives of the present invention is to provide a method for preparing a cellulose film based on wheat straw, which comprises the following steps: subjecting wheat straw to delignification treatment to obtain cellulose fibers; subjecting the cellulose fibers to hot pressing treatment, impregnating the obtained cellulose film in a gelatin solution, taking it out and drying it to obtain a cellulose film based on wheat straw.

[0009] The present invention performs delignification treatment on wheat straw by a chemical method to remove lignin and part of hemicellulose, and retains the porous structure of cellulose fibers, providing a basis for subsequent treatment. The delignified cellulose fibers are subjected to hot pressing treatment at a high temperature, so that the cellulose molecular chain segments obtain energy and undergo plastic deformation. During the hot pressing process, the cellulose molecular chains are rearranged to form a dense film structure, improving the crystallinity and mechanical properties of the cellulose film. The hot-pressed cellulose film is immersed in a gelatin solution, and the gelatin penetrates into the pores of the cellulose film through capillary action. The amino groups (-NH2) and hydroxyl groups (-OH) in the gelatin form hydrogen bonds or covalent bonds with the hydroxyl groups on the surface of the cellulose fibers, enhancing the mechanical properties and water resistance of the cellulose film. After drying, the gelatin solidifies to form a stable network structure.

[0010] Gelatin has the advantages of excellent biocompatibility, good film-forming property, wide sources, etc., but its disadvantages such as low mechanical strength, poor water resistance (easy to dissolve in water), and insufficient thermal stability (melting point is about 60 °C) limit its independent application. Cellulose has the advantages of renewable resources, high mechanical strength (especially after nanometerization), good chemical stability, etc., but its disadvantages such as poor solubility (requiring strong alkali treatment), weak film-forming property, and difficult processing also restrict its wide application. The present invention combines gelatin with cellulose and utilizes the synergistic effect of the two. Gelatin enhances the film-forming property and flexibility of the material, while cellulose improves the mechanical strength and thermal stability, thereby developing a functional film material with excellent comprehensive performance. This modification method significantly improves the mechanical properties, water resistance and biocompatibility of cellulose, providing a new approach for the development of high-performance environmental protection materials.

[0011] Further, the specific operation steps of the delignification treatment include: first cutting the wheat straw into sections and soaking it in an NaOH solution, taking it out and rinsing it with deionized water until neutral; then soaking it in an NaClO2 solution, adjusting the pH to acidic, heating and reacting, taking it out and rinsing it with deionized water until neutral; finally soaking it in an H2O2 solution for bleaching to obtain cellulose fibers.

[0012] After removing lignin, the pore structure of the cellulose fibers becomes more obvious, which is beneficial to subsequent gelatin impregnation, and at the same time improves the purity and transparency of the cellulose fibers, providing a basis for preparing a high-performance cellulose film.

[0013] Furthermore, the soaking time of the cut wheat straw in the NaOH solution is 6 - 24 hours; the concentration of the NaOH solution is 4 wt%. The length of the cut wheat straw is 10 cm.

[0014] Furthermore, the conditions for the heating reaction are: reacting at 80°C for 1 - 5 hours; the concentration of the NaClO2 solution is 5 wt%.

[0015] Furthermore, the acid used to adjust the pH to acidic (3 - 5) is acetic acid.

[0016] Furthermore, the bleaching time is 15 minutes.

[0017] Further, the conditions for the hot pressing treatment are: hot pressing at 120°C for 60 minutes.

[0018] Hot pressing for film formation is a process of pressing materials under high temperature and high pressure conditions to form a film. At high temperature, the molecular chain segments of the materials obtain sufficient energy, becoming more active and prone to plastic deformation. During the hot pressing process, the molecular chains of the materials are rearranged under the action of pressure to form a dense film structure. During the hot pressing process, the crystallinity of the materials may change, thus affecting the physical properties of the film. In the present invention, through high temperature and high pressure, the cellulose fibers are rearranged to form a dense film structure, improving the crystallinity and mechanical properties of the cellulose film. At the same time, the defects and pores inside the cellulose film are reduced, enhancing its mechanical properties and optical properties.

[0019] Further, the concentration of the gelatin solution is 2.5 - 6.5 wt%.

[0020] Further, the soaking conditions of the cellulose film in the gelatin solution are: temperature 40 - 60°C, time 30 minutes.

[0021] When the cellulose film is impregnated in gelatin, the gelatin will fill the pores of the cellulose film, reducing light scattering and increasing transparency. At the same time, the chemical bonding (hydrogen bonds and covalent bonds) between the gelatin and the cellulose fibers will significantly enhance the mechanical properties and water resistance of the cellulose film.

[0022] The second object of the present invention is to provide a wheat straw-based cellulose film prepared by using the above preparation method.

[0023] The third object of the present invention is to provide an application of the wheat straw-based cellulose film in the field of packaging materials.

[0024] The fourth object of the present invention is to provide an application of the wheat straw-based cellulose film in the preparation of drug sustained-release carrier materials.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] Through delignification treatment, hot pressing and gelatin impregnation modification, the present invention converts wheat straw into a high-performance, transparent and environmentally friendly cellulose membrane material. This material not only has excellent mechanical properties and water resistance, but also has good biocompatibility and sustainability, and is applicable to multiple fields such as packaging and biomedicine, with broad application prospects.

[0027] The cellulose membrane prepared by the present invention has excellent mechanical properties (tensile strength can reach more than 399 MPa), water resistance (strength retention rate is more than 80% after soaking in water for 24 hours) and biocompatibility, and is applicable to fields such as packaging. The present invention realizes the high-value utilization of wheat straw, which is in line with the concept of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 is the infrared characteristic diagram of the raw wheat straw raw material in Example 1;

[0030] Figure 2 is the infrared characteristic diagram of the cellulose membrane after delignification treatment in Example 1;

[0031] Figure 3 is the infrared characteristic diagram of the wheat straw-based cellulose membrane prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0032] The various exemplary embodiments of the present invention will be described in detail below. This detailed description should not be considered as a limitation to the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0033] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range and each smaller range between any other stated value or intermediate value within the stated range are also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0035] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of this invention's specification, which are obvious to those skilled in the art. Other embodiments obtained from this invention's specification are obvious to those skilled in the art. This invention's specification and examples are merely exemplary.

[0036] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0037] An embodiment of this invention provides a method for preparing a cellulose film based on wheat straw, comprising the following steps:

[0038] (1) Delignification treatment:

[0039] 1) After cutting the wheat straw into small sections of 10 cm, place it in a 4 wt% NaOH solution, soak for 6 - 24 hours (such as 6 hours, 18 hours or 24 hours), take it out after soaking, and rinse with deionized water;

[0040] 2) Place the wheat straw treated in step 1) in a 5 wt% NaClO2 solution, add an appropriate amount of acetic acid to adjust the pH value to acidic, control the temperature at 80 °C and react for 1 - 5 hours (such as 1 hour, 3 hours or 5 hours), take it out after soaking, and rinse with deionized water;

[0041] 3) Place the wheat straw treated in step 2) in an H2O2 solution for bleaching to obtain delignified cellulose fibers;

[0042] (2) Hot pressing treatment: Place the cellulose fibers in a mold and hot press at 120 °C for 60 min to form a cellulose film;

[0043] (3) Immerse the cellulose film in a gelatin solution with a concentration of 2.5 - 6.5 wt% (such as 2.5 wt%, 3.5 wt%, 4.5 wt%, 5.5 wt% or 6.5 wt%), soak for 30 min, the soaking temperature is 40 - 60 °C. After soaking, take out the cellulose film and dry it to obtain a cellulose film based on wheat straw.

[0044] All raw materials used in the present invention are obtained by purchasing on the market.

[0045] The technical solution of the present invention will be further described below through examples.

[0046] Example 1

[0047] A preparation method of a cellulose film based on wheat straw, comprising the following steps:

[0048] (1) Delignification treatment:

[0049] 1) After cutting the wheat straw into small sections of 10 cm, it is placed in a 4 wt% NaOH solution, soaked for 24 hours, taken out after soaking, and rinsed with deionized water until neutral.

[0050] 2) The wheat straw treated in step 1) is placed in a 5 wt% NaClO2 solution, and an appropriate amount of acetic acid is added to adjust the pH value to between 3 and 5, and the temperature is controlled at 80 °C for reaction for 3 hours. After soaking, it is taken out and rinsed with deionized water until neutral.

[0051] 3) The wheat straw treated in step 2) is bleached in a H2O2 solution for 15 minutes to obtain delignified cellulose fibers.

[0052] (2) Hot pressing treatment: The cellulose fibers are placed in a mold and hot pressed at 120 °C for 60 min to form a cellulose film.

[0053] (3) The cellulose film is immersed in a gelatin solution with a concentration of 5.5 wt%, the soaking time is 30 min, the soaking temperature is 60 °C. After soaking, the cellulose film is taken out and dried to obtain a cellulose film based on wheat straw.

[0054] Example 2

[0055] Same as Example 1, except that the concentration of the gelatin solution is adjusted to 2.5 wt%.

[0056] Example 3

[0057] Same as Example 1, except that the concentration of the gelatin solution is adjusted to 3.5 wt%.

[0058] Example 4

[0059] Same as Example 1, except that the concentration of the gelatin solution is adjusted to 4.5 wt%.

[0060] Example 5

[0061] Same as Example 1, except that the concentration of the gelatin solution is adjusted to 6.5 wt%.

[0062] Example 6

[0063] A method for preparing a cellulose membrane based on wheat straw (adjusting the soaking time in sodium hydroxide), comprising the following steps:

[0064] (1) Delignification treatment:

[0065] 1) After cutting the wheat straw into 10-cm segments, place it in a 4 wt% NaOH solution, soak for 6 hours, take it out after soaking, and rinse with deionized water;

[0066] 2) Place the wheat straw treated in step 1) in a 5 wt% NaClO2 solution, add an appropriate amount of acetic acid to adjust the pH value to between 3 and 5, control the temperature at 80 °C and react for 3 hours, take it out after soaking, and rinse with deionized water;

[0067] 3) Place the wheat straw treated in step 2) in an H2O2 solution for bleaching for 15 minutes to obtain delignified cellulose fibers;

[0068] (2) Hot pressing treatment: Place the cellulose fibers in a mold and hot press at 120 °C for 60 min to form a cellulose membrane;

[0069] (3) Immerse the cellulose membrane in a 5.5 wt% gelatin solution, soak for 30 min at a soaking temperature of 60 °C. After soaking, take out the cellulose membrane and dry it to obtain a cellulose membrane based on wheat straw.

[0070] Example 7

[0071] A method for preparing a cellulose membrane based on wheat straw (adjusting the soaking time in sodium hydroxide), comprising the following steps:

[0072] (1) Delignification treatment:

[0073] 1) After cutting the wheat straw into 10-cm segments, place it in a 4 wt% NaOH solution, soak for 18 hours, take it out after soaking, and rinse with deionized water;

[0074] 2) Place the wheat straw treated in step 1) in a 5 wt% NaClO2 solution, add an appropriate amount of acetic acid to adjust the pH value to between 3 and 5, control the temperature at 80 °C and react for 3 hours, take it out after soaking, and rinse with deionized water;

[0075] 3) Place the wheat straw treated in step 2) in an H2O2 solution for bleaching for 15 minutes to obtain delignified cellulose fibers;

[0076] (2) Hot pressing treatment: Place the cellulose fiber in a mold and hot press it at 120 °C for 60 min to form a cellulose film;

[0077] (3) Immerse the cellulose film in a gelatin solution with a concentration of 5.5 wt%, soak for 30 min at a soaking temperature of 60 °C. After soaking, take out the cellulose film and dry it to obtain a cellulose film based on wheat straw.

[0078] Example 8

[0079] A preparation method of a cellulose film based on wheat straw (adjusting the soaking time in NaClO2) includes the following steps:

[0080] (1) Delignification treatment:

[0081] 1) Cut the wheat straw into small sections of 10 cm, place them in a 4 wt% NaOH solution, soak for 24 hours, take them out after soaking, and rinse with deionized water;

[0082] 2) Place the wheat straw treated in step 1) in a 5 wt% NaClO2 solution, add an appropriate amount of acetic acid to adjust the pH value to between 3 and 5, control the temperature at 80 °C and react for 1 hour. Take it out after soaking and rinse with deionized water;

[0083] 3) Place the wheat straw treated in step 2) in an H2O2 solution for bleaching for 15 minutes to obtain delignified cellulose fiber;

[0084] (2) Hot pressing treatment: Place the cellulose fiber in a mold and hot press it at 120 °C for 60 min to form a cellulose film;

[0085] (3) Immerse the cellulose film in a gelatin solution with a concentration of 5.5 wt%, soak for 30 min at a soaking temperature of 60 °C. After soaking, take out the cellulose film and dry it to obtain a cellulose film based on wheat straw.

[0086] Example 9

[0087] A preparation method of a cellulose film based on wheat straw (adjusting the soaking time in NaClO2) includes the following steps:

[0088] (1) Delignification treatment:

[0089] 1) Cut the wheat straw into small sections of 10 cm, place them in a 4 wt% NaOH solution, soak for 24 hours, take them out after soaking, and rinse with deionized water;

[0090] (2) The wheat straw treated in step (1) is placed in an NaClO₂ solution containing 5 wt%, and an appropriate amount of acetic acid is added to adjust the pH value to between 3 and 5. The temperature is controlled at 80 °C for reaction for 5 hours. After soaking, it is taken out and rinsed with deionized water;

[0091] (3) The wheat straw treated in step (2) is bleached in an H₂O₂ solution for 15 minutes to obtain cellulose fibers after delignification treatment;

[0092] (2) Hot pressing treatment: The cellulose fibers are placed in a mold and hot pressed at 120 °C for 60 min to form a cellulose film;

[0093] (3) The cellulose film is immersed in a gelatin solution with a concentration of 5.5 wt% for 30 min at a soaking temperature of 60 °C. After soaking, the cellulose film is taken out and dried to obtain a wheat straw-based cellulose film.

[0094] Figure 1 is the infrared characteristic diagram of the original wheat straw raw material in Example 1. Figure 2 is the infrared characteristic diagram of the cellulose film after delignification treatment in Example 1. Figure 3 is the infrared characteristic diagram of the wheat straw-based cellulose film prepared in Example 1.

[0095] Comparison Figure 1 and Figure 3 It can be seen that compared with the cellulose film, the lignin-containing straw shows strong absorbance at 1315, 1370, 1421, 1507, and 1595 cm -1 . These are all characteristic peaks of the aromatic ring vibration of lignin molecules. In addition, compared with delignification, the original straw also has a strong absorption peak at 1639 cm -1 , corresponding to the C=O bond in lignin molecules.

[0096] From Figure 2 it can be seen that the peaks at 1595 cm -1 and 1507 cm -1 are the vibration characteristics of aromatic compounds. The flattening of these bands in the sample provides evidence of lignin extraction. In the sample, it can also be noted that there is a significant decrease at 1731 cm -1 , which is related to the C-O stretching vibration associated with the carboxyl and ester bonds present in the hemicellulose in the straw. A similar decrease in peak intensity is observed in the band near 1239 cm -1 , which is attributed to C-O single bonds and ether bonds. Although present in all straw components, these bands are generally associated with the presence of hemicellulose.

[0097] From Figure 3It can be seen that at around 3300 cm -1 , there is an N-H stretching vibration near it. The N-H stretching vibration of the amino group shows a broad and strong absorption peak. This is because of the hydrogen bond interaction between cellulose and gelatin, which leads to the broadening of the absorption peak. This peak is direct evidence of the existence of the amino group. The existence of this peak indicates that the gelatin molecule contains free amino groups or amino groups participating in hydrogen bonds. The absorption band at 1636 cm -1 is attributed to the stretching vibration of the amide carbonyl group of gelatin. In addition, the absorption peak at 1624 cm -1 shows a slight shift, which is mainly attributed to the interaction between the carbonyl group and the amino group of gelatin to form an amide bond.

[0098] Performance test:

[0099] The cellulose films based on wheat straw prepared in Examples 1-9 were subjected to a tensile strength test, and the delignified cellulose film (i.e., the cellulose film obtained in step (2) of Example 1) was used as a control group. The test results are shown in Table 1.

[0100] Table 1 Tensile strength of different samples

[0101]

[0102]

[0103] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of a cellulose membrane based on wheat straw, characterized in that, It includes the following steps: Perform delignification treatment on wheat straw to obtain cellulose fibers; Perform hot pressing treatment on the cellulose fibers, immerse the obtained cellulose film in a gelatin solution, take it out and dry it to obtain a cellulose film based on wheat straw.

2. The preparation method of the cellulose membrane based on wheat straw according to claim 1, characterized in that, The specific operation steps of the delignification treatment include: First, cut the wheat straw into sections and soak it in a NaOH solution, take it out and wash it until neutral; then soak it in a NaClO2 solution, adjust the pH to acidic, heat and react, take it out and wash it until neutral; finally, soak it in an H2O2 solution for bleaching to obtain cellulose fibers.

3. The preparation method of the cellulose film based on wheat straw according to claim 2, characterized in that The soaking time of the cut wheat straw in the NaOH solution is 6-24 hours; the concentration of the NaOH solution is 4 wt%; and / or The conditions for the heating reaction are: react at 80°C for 1-5 hours; the concentration of the NaClO2 solution is 5 wt%.

4. The preparation method of the cellulose film based on wheat straw according to claim 2, characterized in that The bleaching time is 15 minutes.

5. The preparation method of the cellulose membrane based on wheat straw according to claim 1, wherein The conditions for the hot pressing treatment are: hot press at 120°C for 60 minutes.

6. The preparation method of the cellulose film based on wheat straw according to claim 1, characterized in that The concentration of the gelatin solution is 2.5-6.5 wt%.

7. The preparation method of the cellulose film based on wheat straw according to claim 1, wherein The soaking conditions of the cellulose film in the gelatin solution are: temperature 40-60°C, time 30 minutes.

8. A cellulose film based on wheat straw prepared by using the preparation method according to any one of claims 1-7.

9. An application of the cellulose film based on wheat straw according to claim 8 in the field of packaging materials.

10. An application of the cellulose film based on wheat straw according to claim 8 in the preparation of a drug sustained-release carrier material.

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