Hydrophobic deep-eutectic solvent modified chitosan degradable film and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer material preparation, and particularly relates to a hydrophobic deep-eutectic solvent modified chitosan degradable film and a preparation method thereof. The performance of the hydrophobic deep-eutectic solvent modified chitosan degradable film is remarkably improved, and the process is green, simple and convenient. The introduced thymol-camphor eutectic solvent effectively improves the mechanical strength, water stability and light transmission performance of the chitosan film on the premise of not using a toxic cross-linking agent or an organic solvent, and meanwhile, the preparation process is simple, the operation condition is mild, and the preparation method is suitable for large-scale production. Thymol and camphor have good antioxidant and antibacterial properties, and DES is introduced to endow the film with functional activity, so that the film has certain free radical scavenging ability, and is suitable for the fields of food packaging, preservative films, medical functional films and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, and particularly relates to a hydrophobic deep eutectic solvent-modified chitosan degradable film and a preparation method thereof. Background Art

[0002] With the growing problem of plastic pollution, the development of new green, biodegradable packaging materials has become a key research topic in materials science and environmental science. Chitosan, a widely available, non-toxic, biodegradable natural polysaccharide, exhibits broad application prospects in food packaging, biomedical dressings, agricultural films, and other fields due to its excellent film-forming properties, biocompatibility, and antibacterial properties. However, pure chitosan films still face numerous performance bottlenecks during use, such as poor mechanical properties and high water solubility, which severely limit their practical application in functional films.

[0003] To enhance the overall performance of chitosan membranes, researchers typically employ physical or chemical modifications such as plasticizer doping, crosslinking, compounding, and the introduction of nanofillers. The use of natural functional small molecules as modifiers not only improves material properties but also offers the potential to impart more active functions, making this a hot topic in green packaging material research.

[0004] In recent years, deep eutectic solvents (DES) have garnered widespread attention due to their ease of preparation, tunability, environmental friendliness, low toxicity, and excellent biocompatibility. DES are typically formed through non-covalent interactions between hydrogen bond donors and hydrogen bond acceptors, and their physical and functional properties undergo significant changes after formation. Studies have shown that DES based on natural ingredients (such as organic acids, phenols, and terpenes) can be used not only as pharmaceutical solvents and for the extraction of active substances, but also in polymer modification systems.

[0005] Therefore, there is an urgent need to develop a biodegradable membrane material system with green origin, good film-forming properties, and hydrophobicity, antioxidant properties and physical strength, so as to expand its application value in green material fields such as functional packaging and biomedicine. Summary of the Invention

[0006] The purpose of the present invention is to address the existing problems and provide a hydrophobic low eutectic solvent modified chitosan degradable film and a preparation method thereof, which significantly improves its mechanical strength, water stability, water barrier properties, oxidation resistance and degradability.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for preparing a hydrophobic deep eutectic solvent-modified chitosan degradable film comprises the following steps:

[0009] S1. Place thymol and camphor in a container, heat, mix and stir to form a transparent liquid to obtain a deep eutectic solvent;

[0010] S2, dissolving chitosan in an acetic acid aqueous solution, mixing and stirring to form a uniform chitosan solution;

[0011] S3, adding a deep eutectic solvent to the chitosan solution, and continuing to stir to obtain a film-forming solution;

[0012] S4. The membrane-forming liquid is centrifuged to remove bubbles in the solution, and then cast on a mold, dried at a constant temperature to form a membrane, cooled naturally to room temperature, and peeled off to obtain a chitosan composite membrane.

[0013] Furthermore, the molar ratio of thymol to camphor in step S1 is 1:1.

[0014] Furthermore, the chitosan solution in step S2 is prepared by dissolving 2 g of chitosan in a 1% acetic acid aqueous solution.

[0015] Furthermore, the mixing and stirring in step S2 is magnetic stirring at room temperature for 4 to 6 hours.

[0016] Furthermore, the ratio of the deep eutectic solvent added to the chitosan solution in step S3 is 5-15%.

[0017] Furthermore, the rotation speed of the membrane-forming liquid during centrifugation in step S4 is 6000 rpm, and the centrifugation time is 5 minutes.

[0018] Furthermore, the constant temperature drying film forming in step S4 has a drying temperature of 40 to 60° C. and a drying time of 6 to 8 hours.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The hydrophobic low eutectic solvent modified chitosan degradable film of the present invention has significantly improved performance, and the process is green and simple. Thymol and camphor are both natural monoterpenoid small molecules, each with good antioxidant and antibacterial activity. The two can form a stable hydrophobic low eutectic solvent through hydrogen bonding. In the field of functional membrane materials, this type of natural DES can not only be used as a green plasticizer to improve the inter-polymer chain force and dispersibility, but also give the membrane material certain active functions. The introduced thymol-camphor low eutectic solvent effectively improves the mechanical strength, water stability and light transmittance of the chitosan film without using toxic cross-linking agents or organic solvents. At the same time, the preparation process is simple, the operating conditions are mild, and it is suitable for large-scale production.

[0021] 2. The hydrophobic deep eutectic solvent-modified chitosan biodegradable film of the present invention imparts functional activity, expanding its application areas. Thymol and camphor inherently possess excellent antioxidant and antibacterial properties. The introduction of this DES imparts functional activity to the film, imparting a certain degree of free radical scavenging ability, making it suitable for use in food packaging, cling film, and medical functional films.

[0022] 3. The hydrophobic deep eutectic solvent-modified chitosan biodegradable film material of the present invention is environmentally friendly and sustainable. Composed primarily of natural chitosan and a natural small molecule eutectic solvent, the film exhibits excellent biocompatibility and biodegradability, meeting the requirements of green packaging and environmentally friendly materials, and possessing excellent ecological safety and market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM image of the material in Example 3;

[0024] Figure 2 This is the SEM image of the material of Comparative Example 1;

[0025] Figure 3 The degradation status diagram in soil at different time points. DETAILED DESCRIPTION

[0026] In order to further explain the present invention, it is described below with reference to the following specific embodiments.

[0027] Example 1

[0028] A method for preparing a hydrophobic deep eutectic solvent-modified chitosan degradable film comprises the following steps:

[0029] (1) Thymol and camphor were mixed in a container at a mass ratio of 1:1 and stirred at 50°C for 30 minutes to prepare a hydrophobic DES;

[0030] (2) 2 g of chitosan and 100 g of deionized water were placed in a container, and the chitosan was fully dispersed in the deionized water by magnetic stirring. 1 g of acetic acid was added thereto, and the mixture was stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved to obtain a chitosan solution;

[0031] (3) adding 0.12 g of hydrophobic DES to the obtained chitosan solution and stirring at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution;

[0032] (4) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0033] Example 2

[0034] A method for preparing a hydrophobic deep eutectic solvent-modified chitosan degradable film comprises the following steps:

[0035] (1) Thymol and camphor were mixed in a container at a mass ratio of 1:1 and stirred at 50°C for 30 minutes to prepare a hydrophobic DES;

[0036] (2) 2 g of chitosan and 100 g of deionized water were placed in a container, and the chitosan was fully dispersed in the deionized water by magnetic stirring. 1 g of acetic acid was added thereto, and the mixture was stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved to obtain a chitosan solution;

[0037] (3) adding 0.16 g of hydrophobic DES to the obtained chitosan solution and stirring at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution;

[0038] (4) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0039] Example 3

[0040] A method for preparing a hydrophobic deep eutectic solvent-modified chitosan degradable film comprises the following steps:

[0041] (1) Thymol and camphor were mixed in a container at a mass ratio of 1:1 and stirred at 50°C for 30 minutes to prepare a hydrophobic DES;

[0042] (2) 2 g of chitosan and 100 g of deionized water were placed in a container, and the chitosan was fully dispersed in the deionized water by magnetic stirring. 1 g of acetic acid was added thereto, and the mixture was stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved to obtain a chitosan solution;

[0043] (3) adding 0.2 g of hydrophobic DES to the obtained chitosan solution and stirring at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution;

[0044] (4) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0045] Example 4

[0046] A method for preparing a hydrophobic deep eutectic solvent-modified chitosan degradable film comprises the following steps:

[0047] (1) Thymol and camphor were mixed in a container at a mass ratio of 1:1 and stirred at 50°C for 30 minutes to prepare a hydrophobic DES;

[0048] (2) 2 g of chitosan and 100 g of deionized water were placed in a container, and the chitosan was fully dispersed in the deionized water by magnetic stirring. 1 g of acetic acid was added thereto, and the mixture was stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved to obtain a chitosan solution;

[0049] (3) adding 0.24 g of hydrophobic DES to the obtained chitosan solution and stirring at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution;

[0050] (4) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0051] Comparative Example 1

[0052] A preparation method of a chitosan composite film comprises the following steps:

[0053] (1) 2 g of chitosan and 100 g of deionized water were placed in a container and magnetically stirred to fully disperse the chitosan in the deionized water. 1 g of acetic acid was added thereto and stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved. The mixture was then stirred at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution.

[0054] (2) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0055] Comparative Example 2

[0056] A preparation method of a chitosan composite film comprises the following steps:

[0057] (1) 2 g of chitosan and 100 g of deionized water were placed in a container and magnetically stirred to fully disperse the chitosan in the deionized water. 1 g of acetic acid was added thereto and stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved to obtain a chitosan solution.

[0058] (2) adding 0.2 g of glycerol to the obtained chitosan solution and stirring at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution;

[0059] (3) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0060] Comparative Example 3

[0061] A preparation method of a chitosan composite film comprises the following steps:

[0062] (1) Menthol and cinnamon essential oil were mixed in a container at a mass ratio of 1:1 and stirred at 50°C for 30 minutes to prepare DES;

[0063] (2) 2 g of chitosan and 100 g of deionized water were placed in a container, and the chitosan was fully dispersed in the deionized water by magnetic stirring. 1 g of acetic acid was added thereto, and the mixture was stirred at 500 rpm and 25°C for 5 h until the chitosan was completely dissolved to obtain a chitosan solution;

[0064] (3) Add 0.2 g of DES to the obtained chitosan solution and stir at 800 rpm and 50°C for 2 h to obtain a membrane-forming solution;

[0065] (4) The film-forming solution was centrifuged at 6000 rpm for 5 min to remove bubbles in the solution, and the supernatant was cast on a mold. The film was dried at a constant temperature of 50°C for 6 h, cooled naturally to room temperature, and peeled off to obtain a chitosan composite film.

[0066] Performance Testing

[0067] 1. Mechanical properties test

[0068] The tensile strength and elongation at break of film samples were tested according to GB / T 1040.3-2006. The film materials from the examples and comparative examples were cut into rectangular specimens measuring 50 mm x 10 mm. The specimens were tested on a tensile testing machine at a rate of 50 mm / min. Each sample was tested five times, and the average result was taken as the final result. The tensile strength obtained was expressed in MPa, and the elongation at break was expressed as the percentage of the specimen's original length at break. The test results are shown in Table 1 below.

[0069] Table 1

[0070]

[0071]

[0072] As shown in Table 1 above, Examples 1-3 show that increasing the amount of thymol-camphor DES added significantly increases the elongation at break of the films, while slightly decreasing the tensile strength. Compared to Comparative Examples 1-3, the films obtained in Examples exhibit superior performance in both tensile strength and elongation at break.

[0073] 2. Water vapor transmission rate test method

[0074] Testing was performed using the modified water cup method in accordance with ASTM E96 / E96M-16. The membrane sample was sealed over the opening of a centrifuge tube filled with ultrapure water, ensuring a tight fit between the membrane and the tube opening and secured with sealing tape. The device was placed in a desiccator at room temperature and 20% relative humidity to establish a stable water vapor partial pressure gradient across the membrane. The centrifuge tube was weighed every 24 hours, and the water loss was recorded. Each sample was tested three times, and the average value was used as the water vapor transmission rate result. The test results are shown in Table 2 below.

[0075] Table 2

[0076]

[0077]

[0078] As shown in Table 2 above, as the amount of DES composed of thymol-camphor increases, the water vapor permeability of the membrane material decreases overall, indicating that its water vapor barrier capability is effectively enhanced. Among them, the membrane material with a DES addition of 10% (Example 3) has the lowest water vapor permeability, which is only 7.37×10 -11 g·m -1 ·s -1 ·Pa -1 , compared with the unmodified comparative example 1 (24.38×10 -11 ) was significantly reduced. In contrast, while Comparative Example 3 also showed some improvement, its barrier performance was still significantly lower than that of the thymol-camphor DES-modified film. These results demonstrate that the deep eutectic solvent composed of thymol and camphor can significantly improve the water barrier properties of chitosan films, making it suitable for packaging applications requiring high water vapor barrier properties in high-humidity environments.

[0079] 3. Moisture content and water solubility test methods

[0080] The film sample cut into 2×2 cm was initially weighed, and its original mass W0 was recorded. Subsequently, the sample was placed in an oven at 105°C and dried until the mass was constant, and the dry mass W1 was obtained. To determine its water absorption and swelling properties, the dried film was completely immersed in 20 mL of deionized water and allowed to stand at room temperature for 24 hours. After taking it out, use filter paper to gently remove excess water on the surface, weigh it again, and record the mass W2 in the wet state. Then, the sample was placed in an oven again and dried at 105°C to constant weight, and the mass W3 of the undissolved residue after drying was recorded. The calculation formulas for moisture content and water solubility are as follows.

[0081]

[0082]

[0083] The test results are shown in Table 3 below.

[0084] Table 3

[0085] Moisture content / % Water solubility / % Example 1 9.73 10.83 Example 2 9.38 10.56 Example 3 8.37 9.32 Example 4 8.22 9.21 Comparative Example 1 19.52 20.46 Comparative Example 2 25.84 26.74 Comparative Example 3 14.13 15.38

[0086] As shown in Table 3, as the thymol-camphor deep eutectic solvent (DES) content increases, the moisture content and water solubility of the film material both show a downward trend. Among them, Example 3 has the lowest moisture content, 8.37%, and a water solubility of 9.32%, which is significantly better than Comparative Example 1 without DES (moisture content of 19.52% and water solubility of 20.46%), Comparative Example 2 with glycerol addition, and Comparative Example 3 modified with DES composed of menthol and cinnamon essential oil. The results show that the natural DES can effectively enhance the density of the film structure, inhibit water penetration and swelling behavior, and thus significantly improve the water stability of the film material. It is particularly suitable for degradable packaging film products that require moisture resistance.

[0087] 4. Antioxidant test method

[0088] The antioxidant activity of membrane samples was assessed using a DPPH free radical scavenging assay. A certain amount of membrane sample was placed in a brown centrifuge tube and a 0.1 mmol / L DPPH ethanol solution was added. After incubation in the dark for 30 minutes, the absorbance of the solution at 517 nm was measured. Using a blank control solution as a reference, the DPPH free radical scavenging rate of the membrane sample was calculated, reflecting its antioxidant capacity. Each sample was tested three times, and the average value was taken as the final result. The test results are shown in Table 4 below.

[0089] Table 4

[0090] DPPH clearance rate / % Example 1 84.72 Example 2 86.82 Example 3 87.81 Example 4 89.54 Comparative Example 1 60.27 Comparative Example 2 60.72 Comparative Example 3 80.12

[0091] As shown in Table 4, the film samples from each example exhibited excellent DPPH free radical scavenging ability, significantly exceeding that of Comparative Example 1 (60.27%) and Comparative Example 2 (60.72%). The DPPH scavenging rate of Comparative Example 3 was 80.12%, slightly higher than that of the unmodified film, but still lower than that of the thymol-camphor DES-modified film. These results demonstrate that this natural deep eutectic solvent not only imparts excellent antioxidant properties to the film material but also exhibits significant synergistic enhancement, potentially enhancing the film's potential for applications in food packaging and active functional membranes.

[0092] 5. Soil degradation test method

[0093] Evaluation was conducted using an outdoor soil burial method under natural conditions. Film samples from Example 3, Comparative Examples 1, and Comparative Examples 3 were cut into approximately 2 cm x 2 cm sections and buried approximately 10 cm below the soil surface at 23°04′N, 113°41′E. Throughout the testing period, film samples were removed and observed every two weeks, and photographs were taken to record changes in their appearance to monitor degradation. The degradation process was conducted without human intervention, simulating natural degradation behavior under actual soil conditions.

[0094] Degradation test results such as Figure 3 As shown, the modified membrane sample in Example 3 began to show significant cracking after the fourth week in the soil environment and was essentially completely degraded by the tenth week, with no visible membrane residue. In contrast, the degradation rate of the comparative example was significantly slower than that of Example 3. These results demonstrate that chitosan membranes modified with the thymol-camphor deep eutectic solvent exhibit superior degradability in natural soil environments, better meeting the practical application requirements of green and environmentally friendly materials.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by persons skilled in the art without departing from the spirit and technical concepts disclosed herein shall be encompassed by the claims of the present invention.

Claims

1. A method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film, characterized in that: The steps include: S1. Place thymol and camphor in a container, heat, mix and stir to form a transparent liquid to obtain a deep eutectic solvent; S2, dissolving chitosan in an acetic acid aqueous solution, mixing and stirring to form a uniform chitosan solution; S3, adding a deep eutectic solvent to the chitosan solution, and continuing to stir to obtain a film-forming solution; S4. The membrane-forming liquid is centrifuged to remove bubbles in the solution, and then cast on a mold, dried at a constant temperature to form a membrane, cooled naturally to room temperature, and peeled off to obtain a chitosan composite membrane.

2. The method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film according to claim 1, characterized in that: The molar ratio of thymol to camphor in step S1 is 1:

1.

3. The method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film according to claim 1, characterized in that: The chitosan solution described in step S2 is prepared by dissolving 2 g of chitosan in a 1% acetic acid aqueous solution.

4. The method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film according to claim 1, characterized in that: The mixing and stirring in step S2 is magnetic stirring at room temperature for 4 to 6 hours.

5. The method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film according to claim 1, characterized in that: The ratio of the deep eutectic solvent added to the chitosan solution in step S3 is 5-15%.

6. The method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film according to claim 1, characterized in that: The membrane-forming liquid in step S4 is centrifuged at a speed of 6000 rpm for 5 minutes.

7. The method for preparing a hydrophobic deep eutectic solvent modified chitosan degradable film according to claim 1, characterized in that: The constant temperature drying film forming in step S4 is carried out at a drying temperature of 40 to 60° C. and a drying time of 6 to 8 hours.

8. A hydrophobic deep eutectic solvent modified chitosan degradable film, characterized in that: The method is prepared by any one of claims 1 to 7.

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