Cellulose film and preparation method thereof
By pretreating and activating cellulose, hydrogel is formed and thermal acetal reaction is carried out, the problem of poor mechanical properties of cellulose films is solved, the tensile strength and mechanical properties are improved, environmental pollution is avoided, and application is broadened scope.
Patent Information
- Application Number
- CN202411438759.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-15
- Publication Date
- 2024-12-10
AI Technical Summary
The existing cellulose films have shortcomings in the problems of poor mechanical properties, poor biodegradability and wrinkles, and environmental pollution may occur during the preparation of chemical crosslinks.
By pretreating cellulose raw materials, cellulose aldehyde is prepared and activated, and then a hydrogel is formed in a mixed solution of lithium chloride and organic solvents. The acetal reaction between cellulose aldehydes is caused by hot pressing technology to form a more Strong cellulose chain link.
It significantly improves the tensile strength and mechanical properties of the cellulose film, overcomes the problems of wrinkles, poor biodegradability and poor mechanical properties, and avoids environmental pollution and broadens the application range of cellulose-based films.
Smart Images
Figure CN119101268A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of film preparation, and in particular relates to a cellulose film and a preparation method thereof. Background Art
[0002] As a natural biomaterial, cellulose has excellent renewability, non-toxicity, biodegradability and excellent film-forming properties. The solvent regeneration method for preparing physically cross-linked cellulose has been widely developed, but in this process, the common crystallization behavior of polysaccharides can cause various problems such as wrinkles, poor biodegradability and poor mechanical properties in cellulose-based films, limiting its application. At present, chemical cross-linking has been recognized as a method to improve the mechanical properties of materials, but the free radical-induced cross-linking in chemical cross-linking to prepare cellulose films will cause environmental problems. Taking into account the performance and greenness of cellulose-based films is of practical significance for cellulose films. In order to improve the performance and greenness of cellulose films and better expand the application of cellulose-based films, it is urgent to study a method to prepare cellulose films with better performance. Summary of the invention
[0003] In view of the deficiencies in the prior art, the object of the present invention is to provide a cellulose film and a preparation method thereof, so as to solve the problem of poor mechanical properties of the existing cellulose film.
[0004] The technical solution of the present invention to solve the above technical problem is as follows: a method for preparing a cellulose film is provided, comprising:
[0005] S1. Pretreatment: treating the cellulose raw material with an alkaline solution, then washing with deionized water until neutral, and drying to obtain a pretreated cellulose raw material;
[0006] S2. Preparation of cellulose aldehyde: Weigh the pretreated cellulose raw material and add the periodate solution in an amount of 1 to 1.5 g / 100 ml, react in a dark environment for 1 to 3 hours, then wash with deionized water and dry to obtain cellulose aldehyde; the structural formula of cellulose aldehyde is shown in formula (I), wherein n is an integer:
[0007]
[0008] S3. Activation treatment: cellulose aldehyde was activated with water, methanol and an organic solvent in sequence, and dried in vacuo to obtain activated cellulose aldehyde;
[0009] S4. Preparation of hydrogel: adding activated cellulose aldehyde to a mixed solution of lithium chloride and an organic solvent to obtain a cellulose aldehyde solution having a mass fraction of 0.5 to 5 wt%, centrifuging, taking the supernatant to form a film, and regenerating in deionized water to form a hydrogel;
[0010] S5. Film preparation: hot-pressing the hydrogel to obtain a cellulose film.
[0011] The beneficial effects of the present invention are as follows: based on the active hydroxyl groups on the cellulose chains, the present invention uses a chemical method to modify cellulose to obtain cellulose aldehyde, and then uses a hot pressing technology to cause an acetal reaction between the cellulose aldehydes to form a stronger connection between the cellulose chains. This chemical cross-linking effect can greatly increase the rigidity and tensile strength of the cellulose film and improve its mechanical properties.
[0012] On the basis of the above technical solution, the present invention can also be improved as follows:
[0013] Furthermore, the cellulose raw material is cotton.
[0014] Furthermore, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.
[0015] Furthermore, the mass fraction of the alkaline solution is 25-40wt%.
[0016] Furthermore, the periodate solution is a potassium periodate solution or a sodium periodate solution.
[0017] Furthermore, in steps S3 and S4, the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.
[0018] Furthermore, in step S3, the activation treatment method of cellulose aldehyde is to soak in water for 1 hour, methanol for 1 hour and N,N-dimethylacetamide for 2 hours in sequence.
[0019] Furthermore, the mass fraction of the cellulose aldehyde solution is 0.5 to 2 wt %.
[0020] Furthermore, in step S5, the hot pressing temperature is 40-50° C., the pressure is 0.1-1 MPa, and the hot pressing time is 0.5-10 h.
[0021] The present invention also provides a cellulose film prepared by the above preparation method.
[0022] The present invention has the following beneficial effects:
[0023] 1. The cellulose raw material selected in the present invention is cotton, which is green, biodegradable and biocompatible, and is not only low in cost but also environmentally friendly and safe.
[0024] 2. The cellulose film (ORC) prepared by the present invention through simple periodate oxidation and hot pressing synergistic technology has high tensile strength and excellent mechanical properties, which overcomes the environmental problems caused by its preparation process and the problems of wrinkles, poor biodegradability and poor mechanical properties of the film itself, and broadens the application of cellulose-based films. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 is the reaction formula for preparing cellulose aldehyde by oxidizing cellulose with periodate in an embodiment of the present invention;
[0026] Figure 2 The infrared deconvolution spectra of the cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1;
[0027] Figure 3 XRD patterns of the cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1;
[0028] Figure 4 SEM images of the cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1, wherein a is a surface image of RC, a1 is a cross-sectional image of RC, b is a surface image of ORC, and b1 is a cross-sectional image of ORC;
[0029] Figure 5 This is a weight diagram of the cotton-based cellulose film (ORC) prepared in Example 3 bearing 500g;
[0030] Figure 6 The stress-strain curves of the cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1 are shown. DETAILED DESCRIPTION
[0031] The principles and features of the present invention are described below in conjunction with the examples, which are only used to explain the present invention and are not intended to limit the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.
[0032] Embodiment 1:
[0033] A method for preparing a cellulose film comprises the following steps (reaction equation as shown in Figure 1 As shown, where n is an integer from 3000 to 5000):
[0034] S1. Pretreatment: The cotton was treated with a 30wt% sodium hydroxide solution, immersed in the sodium hydroxide solution for 48h to remove impurities and grease on the surface of the cotton fiber, washed with deionized water until neutral, and dried with air for 48h to obtain cotton-based cellulose;
[0035] S2. Preparation of cellulose aldehyde: 3 g of cotton-based cellulose was weighed and dispersed in 200 mL of a 0.015 mol / L sodium periodate solution, oxidized in a dark environment, reacted at 40° C. for 2 h, then washed repeatedly with deionized water 10 times to ensure that impurities such as sodium periodate were completely removed, and dried at 50° C. for 48 h to obtain cellulose aldehyde;
[0036] S3. Activation treatment: cellulose aldehyde was sequentially immersed in water for 1 hour, methanol for 1 hour and N, N-dimethylacetamide (DMAc) for 2 hours for activation treatment, and vacuum dried at 55 ° C for 48 hours, and dried to obtain activated cellulose aldehyde;
[0037] S4. Preparation of hydrogel: 92 g DMAc and 8 g LiCl were weighed and mixed, and stirred at 600 rpm to dissolve, and then 0.75 g activated cellulose aldehyde was added, and stirred at 900 rpm for 4 h to obtain a clear and transparent cellulose aldehyde solution. The cellulose aldehyde solution was centrifuged at 10,000 r / min for 10 min, and 40 g of the supernatant was cast into a 15 cm × 15 cm polytetrafluoroethylene mold to lay a film. The solvent was evaporated at room temperature until a film was formed, and the film was placed in deionized water to regenerate to form a hydrogel;
[0038] S5. Film preparation: The hydrogel was hot-pressed at 40°C and 0.1 MPa for 2 h to obtain a cotton-based cellulose film (ORC).
[0039] Embodiment 2:
[0040] A method for preparing a cellulose film comprises the following steps (reaction equation as shown in Figure 1 As shown, where n is an integer from 3000 to 5000):
[0041] S1. Pretreatment: The cotton was treated with a 30wt% sodium hydroxide solution, immersed in the sodium hydroxide solution for 48h to remove impurities and grease on the surface of the cotton fiber, washed with deionized water until neutral, and dried with air for 48h to obtain cotton-based cellulose;
[0042] S2. Preparation of cellulose aldehyde: 3 g of cotton-based cellulose was weighed and dispersed in 200 mL of a 0.015 mol / L potassium periodate solution, oxidized in a dark environment, reacted at 40° C. for 2 h, then washed repeatedly with deionized water 6 times to ensure that impurities such as potassium periodate were completely removed, and dried at 50° C. for 48 h to obtain cellulose aldehyde;
[0043] S3. Activation treatment: cellulose aldehyde was sequentially immersed in water for 1 hour, methanol for 1 hour and N, N-dimethylacetamide (DMAc) for 2 hours for activation treatment, and vacuum dried at 55 ° C for 48 hours, and dried to obtain activated cellulose aldehyde;
[0044] S4. Preparation of hydrogel: 92 g DMAc and 8 g LiCl were weighed and mixed, and stirred at 600 rpm to dissolve, and then 1 g activated cellulose aldehyde was added, and stirred at 900 rpm for 4 h to obtain a clear and transparent cellulose aldehyde solution. The cellulose aldehyde solution was centrifuged at 10,000 r / min for 10 min, and 40 g of the supernatant was cast into a 15 cm × 15 cm polytetrafluoroethylene mold to lay a film. The solvent was evaporated at room temperature until a film was formed, and the film was placed in deionized water to regenerate to form a hydrogel;
[0045] S5. Film preparation: The hydrogel was hot-pressed at 50°C and 0.2 MPa for 2 h to obtain a cotton-based cellulose film (ORC).
[0046] Embodiment 3:
[0047] A method for preparing a cellulose film comprises the following steps (reaction equation as shown in Figure 1 As shown, where n is an integer from 3000 to 5000):
[0048] S1. Pretreatment: The cotton was treated with a 30wt% sodium hydroxide solution, immersed in the sodium hydroxide solution for 48h to remove impurities and grease on the surface of the cotton fiber, washed with deionized water until neutral, and dried with air for 48h to obtain cotton-based cellulose;
[0049] S2. Preparation of cellulose aldehyde: 3 g of cotton-based cellulose was weighed and dispersed in 200 mL of a 0.015 mol / L sodium periodate solution, oxidized in a dark environment, reacted at 40° C. for 2 h, then washed repeatedly with deionized water 10 times to ensure that impurities such as sodium periodate were completely removed, and dried at 50° C. for 48 h to obtain cellulose aldehyde;
[0050] S3. Activation treatment: cellulose aldehyde was sequentially immersed in water for 1 hour, methanol for 1 hour and N, N-dimethylacetamide (DMAc) for 2 hours for activation treatment, and vacuum dried at 55 ° C for 48 hours, and dried to obtain activated cellulose aldehyde;
[0051] S4. Preparation of hydrogel: 92 g DMAc and 8 g LiCl were weighed and mixed, and the mixture was stirred at 600 rpm to dissolve, and then 2 g activated cellulose aldehyde was added, and the mixture was stirred at 900 rpm for 4 h to obtain a clear and transparent cellulose aldehyde solution. The cellulose aldehyde solution was centrifuged at 10,000 r / min for 10 min, and 40 g of the supernatant was cast into a 15 cm × 15 cm polytetrafluoroethylene mold to form a film. The solvent was evaporated at room temperature until a film was formed, and the film was placed in deionized water to regenerate to form a hydrogel;
[0052] S5. Film preparation: The hydrogel was hot-pressed at 40°C and 0.1 MPa for 0.5 h, and then hot-pressed at 50°C and 0.2 MPa for 1.5 h to obtain a cotton-based cellulose film (ORC).
[0053] Embodiment 4:
[0054] A method for preparing a cellulose film comprises the following steps (reaction equation as shown in Figure 1 As shown, where n is an integer from 3000 to 5000):
[0055] S1. Pretreatment: The cotton was treated with a 30wt% sodium hydroxide solution, immersed in the sodium hydroxide solution for 48h to remove impurities and grease on the surface of the cotton fiber, washed with deionized water until neutral, and dried with air for 48h to obtain cotton-based cellulose;
[0056] S2. Preparation of cellulose aldehyde: 3 g of cotton-based cellulose was weighed and dispersed in 200 mL of a 0.015 mol / L potassium periodate solution, oxidized in a dark environment, reacted at 40° C. for 2 h, then washed repeatedly with deionized water 8 times to ensure that impurities such as potassium periodate were completely removed, and dried at 50° C. for 48 h to obtain cellulose aldehyde;
[0057] S3. Activation treatment: cellulose aldehyde was sequentially immersed in water for 1 hour, methanol for 1 hour and N, N-dimethylacetamide (DMAc) for 2 hours for activation treatment, and vacuum dried at 55 ° C for 48 hours, and dried to obtain activated cellulose aldehyde;
[0058] S4. Preparation of hydrogel: 92 g DMAc and 8 g LiCl were weighed and mixed, and stirred at 600 rpm to dissolve, and then 1 g activated cellulose aldehyde was added, and stirred at 900 rpm for 4 h to obtain a clear and transparent cellulose aldehyde solution. The cellulose aldehyde solution was centrifuged at 10,000 r / min for 10 min, and 40 g of the supernatant was cast into a 15 cm × 15 cm polytetrafluoroethylene mold to lay a film. The solvent was evaporated at room temperature until a film was formed, and the film was placed in deionized water to regenerate to form a hydrogel;
[0059] S5. Film preparation: The hydrogel was hot-pressed at 40°C and 0.1 MPa for 0.5 h, and then hot-pressed at 50°C and 0.2 MPa for 1.5 h to obtain a cotton-based cellulose film (ORC).
[0060] Comparative Example 1:
[0061] Preparation steps of cellulose membrane (RC)
[0062] S1. Pretreatment: The cotton was treated with a 30wt% sodium hydroxide solution, immersed in the sodium hydroxide solution for 48h to remove impurities and grease on the surface of the cotton fiber, washed with deionized water until neutral, and dried with air for 48h to obtain cotton-based cellulose;
[0063] S2. Activation treatment: The cotton-based cellulose was sequentially immersed in water for 1 hour, methanol for 1 hour, and N,N-dimethylacetamide (DMAc) for 2 hours for activation treatment, and then vacuum dried at 55°C for 48 hours, and dried to obtain activated cellulose;
[0064] S3. Preparation of hydrogel: 92 g DMAc and 8 g LiCl were weighed and mixed, and stirred at 600 rpm to dissolve, and then 2 g activated cellulose was added and stirred at 900 rpm for 4 h to obtain a clear and transparent cellulose solution. The cellulose solution was centrifuged at 10,000 r / min for 10 min, and 40 g of the supernatant was cast into a 15 cm × 15 cm polytetrafluoroethylene mold to form a film. The solvent was evaporated at room temperature until a film was formed, and the film was placed in deionized water to regenerate to form a hydrogel;
[0065] S4. Film formation: The hydrogel was hot-pressed at 40°C and 0.1 MPa for 0.5 h, and then at 50°C and 0.2 MPa for 1.5 h to obtain a cellulose film (RC).
[0066] Experimental example:
[0067] The properties of the cellulose films (ORC) prepared in Examples 1-4 of the present invention are similar. The cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1 were tested to verify their effects.
[0068] 1. Structural Characterization
[0069] (1) Infrared deconvolution spectrum detection
[0070] The cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1 were subjected to infrared deconvolution spectroscopy detection, and the deconvolution range was 1136-921 cm -1 , the results are as follows Figure 2 shown.
[0071] from Figure 2 It can be seen that ORC is at 1066cm -1 and 1019cm -1The characteristic peak at belongs to the acetal structure, indicating that there is acetal cross-linking in the ORC film. The acetal cross-linking structure can effectively enhance the interaction force between cellulose chains, thereby improving the tensile strength and toughness of the film; this cross-linking structure enables the film to better disperse stress when subjected to force, reduce the generation and expansion of cracks, and plays a vital role in improving the mechanical properties of the ORC film.
[0072] (2) X-ray diffractometer (XRD) detection
[0073] The cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1 were tested by X-ray diffractometer (XRD). The results are as follows: Figure 3 shown.
[0074] from Figure 3 It can be seen that the cotton-based cellulose film (ORC) obtained by the present invention has a high crystallinity of 73.92%, and the crystalline part forms a tight network structure with strong interaction between molecules, thereby improving the tensile strength and stiffness of the film. Therefore, the improvement of crystallinity can also improve the mechanical properties of the film.
[0075] (3) Scanning electron microscope (SEM) inspection
[0076] The cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1 were examined using a scanning electron microscope (SEM). The results are as follows: Figure 4 As shown (a-surface image of RC, a1-cross-sectional image of RC, b-surface image of ORC, b1-cross-sectional image of ORC).
[0077] from Figure 4 It can be seen that compared with the cellulose film (RC), the surface of the cotton-based cellulose film (ORC) prepared by the present invention is relatively flat. Due to the excellent film-forming properties of cellulose, the ORC film has a denser layered structure in cross-sectional morphology, which can improve the tensile strength, elastic modulus and overall mechanical properties of the film by enhancing hydrogen bonding, optimizing fiber orientation, reducing micropores and retaining crystalline regions, etc.
[0078] 2. Mechanical properties
[0079] In order to evaluate the potential of the film as a packaging material, the mechanical properties of the cotton-based cellulose film (ORC) prepared in Example 3 and the cellulose film (RC) prepared in Comparative Example 1 were tested. Figure 5 This is the ORC weight diagram of 500g. Figure 6 Figure 2 is the stress-strain curve of ORC and RC.
[0080] from Figure 6It can be seen that the maximum stress of the cotton-based cellulose film (ORC) prepared by the present invention is greatly improved compared with the cellulose film (RC), which is 154.27 MPa, which meets the requirements of the Chinese national standard GB / T 16606.3-2018 for plastic packaging with a tensile strength greater than 20 MPa and can support a weight of 500 grams.
[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for preparing a cellulose film, characterized in that: The following steps are involved: S1. Pretreatment: treating the cellulose raw material with an alkaline solution, then washing with deionized water until neutral, and drying to obtain a pretreated cellulose raw material; S2. Preparation of cellulose aldehyde: Weigh the pretreated cellulose raw material and add the periodate solution in an amount of 1 to 1.5 g / 100 ml, react in a dark environment for 1 to 3 hours, then wash with deionized water and dry to obtain cellulose aldehyde; the structural formula of the cellulose aldehyde is shown in formula (I), wherein n is an integer: S3. Activation treatment: cellulose aldehyde was activated with water, methanol and an organic solvent in sequence, and dried in vacuo to obtain activated cellulose aldehyde; S4. Preparation of hydrogel: adding activated cellulose aldehyde to a mixed solution of lithium chloride and an organic solvent to obtain a cellulose aldehyde solution having a mass fraction of 0.5 to 5 wt%, centrifuging, taking the supernatant to form a film, and regenerating in deionized water to form a hydrogel; S5. Film preparation: hot-pressing the hydrogel to obtain a cellulose film.
2. The method for preparing a cellulose film according to claim 1, characterized in that: The cellulose raw material is cotton.
3. The method for preparing a cellulose film according to claim 1, characterized in that: The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.
4. The method for preparing a cellulose film according to claim 3, characterized in that: The mass fraction of the alkaline solution is 25-40wt%.
5. The method for preparing a cellulose film according to claim 1, characterized in that: The periodate solution is a potassium periodate solution or a sodium periodate solution.
6. The method for preparing a cellulose film according to claim 1, characterized in that: The organic solvent in steps S3 and S4 is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.
7. The method for preparing a cellulose film according to claim 6, characterized in that: The activation treatment method of cellulose aldehyde in step S3 is to soak it in water for 1 hour, methanol for 1 hour and N,N-dimethylacetamide for 2 hours in sequence.
8. The method for preparing a cellulose film according to claim 1, characterized in that: The mass fraction of the cellulose aldehyde solution is 0.5-2wt%.
9. The method for preparing a cellulose film according to claim 1, characterized in that: In step S5, the hot pressing temperature is 40-50° C., the pressure is 0.1-1 MPa, and the hot pressing time is 0.5-10 h.
10. A cellulose film prepared by the method for preparing a cellulose film according to any one of claims 1 to 9.