A fatty acid grafted chitosan polymer film, its preparation method and application

Abstract

The application discloses a kind of fatty acid grafting chitosan polymer film and its preparation method and application;The method comprises the following steps: S1, fatty acid grafting chitosan powder and glacial acetic acid are mixed and dissolved, and after centrifugal defoaming, film is prepared by flow casting method;S2, the film is soaked in alkaline solution, and wet film is obtained by washing;S3, the wet film is uniaxially stretched, and fatty acid grafting chitosan polymer film is obtained by drying.The fatty acid grafting chitosan powder is used as raw material in the application, film is prepared by flow casting method, and finally treated by alkali and uniaxial stretching treatment, which greatly improves the piezoelectric property of fatty acid grafting chitosan polymer film of the application.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a fatty acid-grafted chitosan polymer film, its preparation method, and its application. Background Technology

[0002] Piezoelectric materials are functional materials that enable the conversion between mechanical and electrical energy, and are widely used in sensors, transducers, and energy harvesting. While traditional piezoelectric ceramics (such as lead zirconate titanate, PZT) exhibit excellent performance, their brittleness and lead toxicity limit their application in flexible electronics and biomedicine. Organic piezoelectric materials (such as polyvinylidene fluoride, PVDF), although flexible, suffer from poor biocompatibility and biodegradability, making them unsuitable for implantable devices.

[0003] Chitosan, an abundant natural alkaline polysaccharide, is a product of chitin deacetylation and is widely found in the shells of marine organisms such as shrimp and crab, as well as in the cell walls of some fungi. Its molecular chain consists of D-glucosamine and N-acetyl-D-glucosamine units linked by β-(1,4) glycosidic bonds, and is rich in active functional groups such as amino (-NH2) and hydroxyl (-OH). These functional groups endow chitosan with good chemical reactivity, and its solubility and mechanical properties can be controlled by introducing functional side chains through chemical modification. However, chitosan materials have a very low piezoelectric effect.

[0004] Therefore, it is necessary to develop a preparation process for fatty acid-grafted chitosan polymers so that the prepared products have excellent piezoelectric properties. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a method for preparing a fatty acid-grafted chitosan polymer film, the product prepared by this method having excellent piezoelectric properties.

[0006] A second aspect of the present invention also provides a fatty acid-grafted chitosan polymer film.

[0007] A third aspect of the present invention also provides a piezoelectric thin film.

[0008] A fourth aspect of the present invention also provides the application of a fatty acid-grafted chitosan polymer film as a piezoelectric material.

[0009] A method for preparing a fatty acid-grafted chitosan polymer according to a first aspect of the present invention includes the following steps: S1. Mix and dissolve fatty acid-grafted chitosan powder with glacial acetic acid, centrifuge to defoam, and then prepare a film by casting. S2. The film is soaked and washed in an alkaline solution to obtain a wet film; S3. The wet film is uniaxially stretched and dried to obtain a fatty acid-grafted chitosan polymer film.

[0010] According to a preferred embodiment of the present invention, in step S2, the concentration of the alkaline solution is 0.8-1.2M.

[0011] According to a preferred embodiment of the present invention, in step S2, the alkali in the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0012] According to a preferred embodiment of the present invention, in step S2, the washing refers to washing until the film is neutral.

[0013] According to a preferred embodiment of the present invention, the uniaxial stretching amount is 15% to 25%.

[0014] According to a preferred embodiment of the present invention, in step S3, the drying temperature is 25~45°C.

[0015] According to a preferred embodiment of the present invention, the mass-to-volume ratio of the fatty acid-grafted chitosan powder to glacial acetic acid is 1g:95~105mL.

[0016] According to a preferred embodiment of the present invention, the fatty acid-grafted chitosan powder is prepared by the following method: (1) Mix chitosan and glacial acetic acid and let stand at 0~5℃; then add alcohol solution and adjust the pH to 3.5~4.5, and sonicate to obtain chitosan solution; (2) Add fatty acids and carboxyl activators to the chitosan solution to carry out a coupling reaction; (3) After the reaction is completed, the reaction solution is sonicated to adjust the pH to 5.5~6.5, and then allowed to stand at 0~5℃. The precipitate is obtained after post-treatment. (4) The precipitate is resuspended in water, the pH is adjusted to 8.5~9.5, and it is allowed to stand at 0~5℃. The precipitate is then obtained by post-treatment. The precipitate is filtered, washed and ground to obtain fatty acid grafted chitosan powder.

[0017] According to a preferred embodiment of the present invention, the fatty acid has ≥10 carbon atoms.

[0018] According to a preferred embodiment of the present invention, in step (1), the mass-to-volume ratio of chitosan to glacial acetic acid is 1g:95~105mL.

[0019] According to a preferred embodiment of the present invention, the carboxyl activator includes an EDAC / NHS system and an EDAC / DCC system. According to a preferred embodiment of the present invention, the molar ratio of chitosan, fatty acid, EDAC and NHS is 1:(0.9~1.1):(0.9~1.1):(0.9~1.1).

[0020] According to a preferred embodiment of the present invention, in steps (3) and (4), the settling time is 12 to 24 hours.

[0021] The alcohol solutions include methanol and ethanol solutions.

[0022] The preparation method according to embodiments of the present invention has at least the following beneficial effects: This invention uses fatty acid-grafted chitosan powder as raw material, prepares it into a film by casting, and then performs alkali treatment and uniaxial stretching treatment, which greatly improves the piezoelectric properties of the fatty acid-grafted chitosan polymer film of this invention and solves the technical problem of poor piezoelectric properties of chitosan itself in the prior art.

[0023] Furthermore, the fatty acid grafting-induced ordered arrangement of molecular chains in this invention achieves a significant enhancement in piezoelectric properties.

[0024] A fatty acid-grafted chitosan polymer film according to a second aspect of the present invention is prepared by the preparation method described in the first aspect of the present invention.

[0025] A third aspect of the present invention provides a piezoelectric film comprising the fatty acid-grafted chitosan polymer film described in the second aspect of the present invention.

[0026] The fourth aspect of the present invention provides the application of the fatty acid-grafted chitosan polymer film described in the second aspect of the present invention in the preparation of piezoelectric materials.

[0027] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 These are the infrared spectra of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1 of the present invention. Figure 2 These are the XRD patterns of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1 of the present invention. Figure 3 These are cleanliness diagrams of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1. Figure 4 These are cross-sectional SEM images of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1. Figure 5 These are SEM images of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1 at different magnifications. Figure 6 This is a frequency capacitance variation diagram of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1. Figure 7 This is a bar chart comparing the relative permittivity of the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1. Figure 8 This is a voltage output diagram of the fatty acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1 under a constant 1N force impact. Figure 9 This is a response time diagram of a single voltage signal for the lauric acid-grafted chitosan polymer film of Example 1 and the chitosan film of Comparative Example 1. Detailed Implementation

[0029] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0030] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0031] In some embodiments of the present invention, a method for preparing a fatty acid-grafted chitosan polymer is provided, comprising the following steps: S1. Mix and dissolve fatty acid-grafted chitosan powder with glacial acetic acid, centrifuge to defoam, and then prepare a film by casting. S2. The film is soaked and washed in an alkaline solution to obtain a wet film; S3. The wet film is uniaxially stretched and dried to obtain a fatty acid-grafted chitosan polymer film.

[0032] It is understood that the present invention uses fatty acid-grafted chitosan powder as raw material, prepares a film by casting, and then performs alkali treatment and uniaxial stretching treatment, which greatly improves the piezoelectric properties of the fatty acid-grafted chitosan polymer film of the present invention and solves the technical problem of poor piezoelectric properties of chitosan itself in the prior art.

[0033] Furthermore, the fatty acid side chains of the present invention can be grafted and induced to arrange the molecular chains in an orderly manner during the film formation process, thereby achieving a significant enhancement of piezoelectric properties.

[0034] Furthermore, the present invention utilizes alkaline solution treatment to make chitosan ammonium salt (-NH3) + The deprotonation process converts the polymer film into free amino groups (-NH2), removes residual acid, and restores the hydrogen bond network between molecular chains, thereby increasing crystallinity and improving the piezoelectric properties of the polymer film.

[0035] Furthermore, the uniaxial stretching treatment of the present invention can induce chitosan molecular chains to align along the stretching direction. Oriented molecular chains are more likely to pack tightly, forming a more ordered crystalline structure, further improving crystallinity; this is more beneficial for enhancing the piezoelectric properties of the polymer film.

[0036] In some embodiments of the present invention, in step S2, the concentration of the alkaline solution is 0.8~1.2M.

[0037] In some embodiments of the present invention, in step S2, the alkali in the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0038] In some embodiments of the present invention, in step S2, the washing refers to washing until the film is neutral.

[0039] In some embodiments of the present invention, the amount of stretching in the uniaxial stretching is 15% to 25%.

[0040] In some embodiments of the present invention, in step S3, the drying temperature is 25~45°C.

[0041] In some embodiments of the present invention, the mass-to-volume ratio of the fatty acid-grafted chitosan powder to glacial acetic acid is 1 g: 95-105 mL.

[0042] In some embodiments of the present invention, the fatty acid-grafted chitosan powder is prepared by the following method: (1) Mix chitosan and glacial acetic acid and let stand at 0~5℃; then add alcohol solution and adjust the pH to 3.5~4.5, and sonicate to obtain chitosan solution; (2) Add fatty acids and carboxyl activators to the chitosan solution to carry out a coupling reaction; (3) After the reaction is completed, the reaction solution is sonicated to adjust the pH to 5.5~6.5, and then allowed to stand at 0~5℃. The precipitate is obtained after post-treatment. (4) The precipitate is resuspended in water, the pH is adjusted to 8.5~9.5, and it is allowed to stand at 0~5℃. The precipitate is then obtained by post-treatment. The precipitate is filtered, washed and ground to obtain fatty acid grafted chitosan powder.

[0043] Understandably, the addition of methanol adjusts the solvent polarity, which both dissolves chitosan and accommodates subsequent hydrophobic fatty acids.

[0044] It is understood that steps (3) and (4) of this invention form a pH gradient precipitation. The pH of the reaction solution is adjusted to 6.0. Under this pH condition, the amino groups on the chitosan molecular chain are deprotonated, and the intermolecular hydrogen bonding is weakened. At this time, fatty acid-grafted chitosan preferentially aggregates and precipitates due to the hydrophobic interaction of its side chain fatty acid groups; while ungrafted chitosan, lacking hydrophobic side chains, still maintains good water solubility and remains in the solution. By centrifugation, ungrafted chitosan can be effectively removed; further, by increasing the pH, the chitosan amino groups are completely deprotonated, and all chitosan derivatives lose their solubility and precipitate completely. This step has a dual function: on the one hand, it enriches the grafted product, facilitating subsequent purification operations; on the other hand, it neutralizes the residual acetic acid in the system, eliminating the interference of the acidic environment on subsequent dialysis or washing steps.

[0045] In some embodiments of the present invention, the fatty acid has ≥10 carbon atoms. Further, the fatty acid has ≤20 carbon atoms. Examples include caprylic acid, lauric acid, myristic acid, palmitic acid, and stearic acid.

[0046] In some embodiments of the present invention, in step (1), the mass-to-volume ratio of chitosan to glacial acetic acid is 1g:95~105mL.

[0047] In some embodiments of the present invention, the carboxyl activator includes the EDAC / NHS system and the EDAC / DCC system.

[0048] In some embodiments of the present invention, the molar ratio of chitosan, fatty acid, EDAC and NHS is 1:(0.9~1.1):(0.9~1.1):(0.9~1.1).

[0049] In some embodiments of the present invention, in steps (3) and (4), the settling time is 12 to 24 hours.

[0050] In some embodiments of the present invention, a fatty acid-grafted chitosan polymer film is provided, which is prepared by the preparation method described in the first aspect of the present invention.

[0051] In some embodiments of the present invention, a piezoelectric film is provided, comprising the fatty acid-grafted chitosan polymer film described in the second aspect of the present invention.

[0052] In some embodiments of the present invention, an application of the fatty acid-grafted chitosan polymer film described in the second aspect of the present invention is provided in the preparation of piezoelectric materials.

[0053] Example 1 This example provides a lauric acid-grafted chitosan polymer film, the preparation method of which is as follows: 1. The reaction formula and preparation method for synthesizing lauric acid-grafted chitosan are as follows: ; (1) Dissolve 1g of chitosan (CS) in 100ml of 1% (V / V) glacial acetic acid solution and stir until completely dissolved. Place the dissolved CS solution at 4℃ for 24h.

[0054] Add 40 ml of methanol solution to the CS solution after it has been placed, stir for 10 min, adjust the pH of the solution to 4 with 1% (V / V) glacial acetic acid solution, and then place the solution under sonication for 10 min.

[0055] (2) Control the molar ratio of CS:lauric acid (LA):EDC:NHS = 1:1:1:1. Weigh a certain amount of LA, EDC and NHS according to the ratio, add 20ml of anhydrous ethanol and stir for 4h under the dark until the fatty acids are activated.

[0056] (3) Under the condition of stirring, the activated fatty acid solution was added dropwise to the CS solution and the coupling reaction was carried out at room temperature under continuous magnetic stirring for 24 hours.

[0057] (4) After the reaction, the solution was sonicated for 10 min, the pH of the reaction solution was adjusted to 6.0, and the solution was allowed to stand at 4℃ for 24 hours. The solution was then centrifuged at 5000×g for 10 minutes to collect the precipitate and discard the supernatant.

[0058] (5) Resuspend the precipitate in deionized water, adjust the pH to 9.0 with 2 mol / L NaOH solution, and let it stand at 4°C for 24 hours. Centrifuge at 5000×g for 10 minutes and collect the precipitate.

[0059] (6) Take out the preserved solution and centrifuge it at a speed of 5000×g. Wash the precipitate thoroughly with deionized water three times to remove residual sodium hydroxide.

[0060] (7) Repeat the above operation, and then wash three times with an ethanol-acetone mixture (ethanol:acetone = 3:1) to remove unreacted alkyl acids, EDAC and NHS.

[0061] (8) Dry the precipitate in a vacuum drying oven. Then use a ball mill to grind the dried sample for later use.

[0062] Synthesis of lauric acid-grafted chitosan polymer films: S1. Dissolve 1g of fatty acid-grafted chitosan powder in 100ml of 1% (V / V) glacial acetic acid solution and stir until completely dissolved. Pour the solution into a centrifuge tube and centrifuge at 5000×g for ten minutes to eliminate air bubbles. Use a pipette to take a certain amount of solution and place it on a petri dish. Prepare a film using the solution casting method and dry it under vacuum at 40℃ and 200 mbar overnight. After drying, remove the film.

[0063] S2. Immerse the membrane in 1 M NaOH solution for 55 minutes, then rinse several times with deionized water until the pH returns to 7.

[0064] S3. In the wet film state after neutralization treatment, perform 20% uniaxial stretching, and then dry and fix the film in a 40℃ drying oven.

[0065] Example 2 This example provides a butyric acid-grafted chitosan polymer film, which is prepared in the same way as in Example 1, except that lauric acid is replaced with an equimolar amount of butyric acid.

[0066] The relative permittivity of the butyric acid-grafted chitosan polymer film at 100 Hz (defined as the ratio of the capacitance of the film as a medium to the capacitance of vacuum as a medium under the same electrode conditions) is 16.7.

[0067] Example 3 This example provides an octanoic acid-grafted chitosan polymer film, which is prepared in the same way as in Example 1, except that octanoic acid is used in place of lauric acid in equal molar amounts.

[0068] Calculations show that the relative permittivity of the octanoic acid-grafted chitosan polymer film is 23.4 at 100 Hz.

[0069] Comparative Example 1 This example provides a pure chitosan film. 1.0 g of chitosan with a degree of deacetylation of 95% was weighed and dissolved in 100 mL of 0.5% (v / v) acetic acid aqueous solution, and stirred overnight at room temperature. The solution was then allowed to stand at 4°C for 24 hours. The solution was then poured into a centrifuge tube and centrifuged at 5000×g for ten minutes to remove air bubbles, and then set aside. A certain amount of the solution was pipetted onto a petri dish, and a film was prepared using the solution casting method. The film was then dried under vacuum at 40°C and 200 mbar overnight. After drying, the film was removed.

[0070] Comparative Example 2 This example provides a chitosan derivative film, prepared by the following method: Steps: ① Dissolve 1 g of chitosan in 100 mL of 0.5% (v / v) acetic acid aqueous solution and stir overnight at room temperature to obtain a 1% (w / v) chitosan solution.

[0071] ② To observe the initial signs of precipitation, the prepared chitosan solution was alkalized with 0.5, 0.01, and 0.2 M NaOH solutions to determine the optimal NaOH concentration.

[0072] ③ Dissolve 1 mM lauric acid (LA) in 50 mL of methanol, then add 2 mM EDAC and 1.8 mM NHS, and stir for 4 hours to activate the saturated fatty acid.

[0073] ④ Add the activated lauric acid solution dropwise to the previously prepared chitosan solution and continue to react with magnetic stirring at room temperature for 24 hours.

[0074] ⑤ To remove unbound lauric acid, residual reagents, and byproducts, the reaction mixture was dialyzed in deionized water for three days using a dialysis bag.

[0075] ⑥ The synthesized chitosan-lauric acid derivative (Chi-LA) was freeze-dried using a freeze dryer (Christ Beta 18K, Germany) and stored at 4°C.

[0076] Preparation of thin film: Take 1.0 g of chitosan-lauric acid derivative and dissolve it in 100 mL of 0.5% (v / v) acetic acid aqueous solution and stir overnight at room temperature; let the resulting solution stand at 4℃ for 24 h, and then centrifuge at 5000×g for 10 min to remove air bubbles; then take a quantitative amount of solution and place it in a petri dish, form a film by solution casting, and vacuum dry overnight at 40℃ and 200 mbar to obtain the target thin film.

[0077] This chitosan-lauric acid derivative was prepared into a thin film, and the relative permittivity of the film at 100 Hz was only 25.3. Moreover, the preparation time and process of this method are longer and more complicated.

[0078] Performance testing First, the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example were subjected to infrared spectroscopy, and the results are as follows. Figure 1 As shown, compared with the pure chitosan spectrum, the derivative spectrum is at 1645 cm⁻¹. - A new absorption peak appears at ¹, attributed to the amide I band (C=O stretching vibration); at 1550 cm⁻¹ - A new absorption peak appears at ¹, attributed to the amide II band (NH bending vibration and CN stretching vibration). Simultaneously, at 2920 cm⁻¹... - ¹ and 2850 cm - The intensity of the methylene (-CH2-) stretching vibration peak at position ¹ is significantly enhanced. This indicates that lauric acid has been successfully grafted onto the chitosan molecular chain via amide bonds.

[0079] Furthermore, the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example were subjected to XRD tests, and the results are as follows: Figure 2 As shown, pure chitosan exhibits a broad, diffuse peak at 2θ≈20°, indicating its low crystallinity. In contrast, the lauric acid-grafted chitosan polymer shows new, sharp diffraction peaks at 2θ≈21.5° and 23.8°. This suggests that the introduction of long-chain fatty acids induces the ordered arrangement of molecular chains, forming a new crystalline structure, which is beneficial for improving piezoelectric properties.

[0080] Furthermore, the crystallinity of the lauric acid-grafted chitosan polymer prepared in Example 1 of the present invention and the chitosan film prepared in the comparative example were calculated, and the results are as follows: Figure 3 As shown, the crystallinity of both the F(110) peak and the overall crystallinity of the chitosan-lauric acid grafted chitosan polymer film were improved. The crystallinity of the F(110) peak increased from 40.3% to 46.7%, and the overall crystallinity increased from 50.06% to 66.71%.

[0081] Furthermore, the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example were subjected to SEM testing. The SEM images of the cross-sections of the films are shown below. Figure 4 As shown, the cross-section of the thin film exhibits a dense and uniform structure, with obvious brittle fracture texture. This dense microstructure is beneficial to the stable output of the piezoelectric response.

[0082] Furthermore, the surface microstructures of the lauric acid-grafted chitosan polymer prepared in Example 1 and the chitosan film prepared in the comparative example were investigated at different magnifications. The results are as follows: Figure 5 As shown, Figure 5 (a) SEM image of CS film at 1500x magnification; (b) SEM image of CS-LA film at 1500x magnification; (c) SEM image of CS film at 5000x magnification; (d) SEM image of CS-LA film at 5000x magnification; (e) SEM image of CS film at 10000x magnification; (f) SEM image of CS-LA film at 10000x magnification. At low magnification (1500x), the surface of the pure CS film is smooth and flat, while the CS-LA film has begun to show roughening texture. As the magnification increases to 5000x and 10000x, the surface of the pure CS film remains relatively dense and uniform, with only a fine granular texture. However, the surface of the CS-LA film shows a large number of dense nanoscale protrusions or island structures, exhibiting obvious roughening and microphase separation characteristics. This morphological change directly confirms the successful grafting of lauric acid. Its hydrophobic alkyl chains self-assemble and aggregate on the hydrophilic chitosan substrate, which not only changes the aggregated structure of the film but also significantly increases the specific surface area, indicating that the hydrophobicity and functionality of the modified film may be enhanced.

[0083] Furthermore, the capacitance of the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example were tested at different frequencies, and the results are as follows. Figure 6 As shown, with the test frequency increasing from 10 Hz to 1 MHz, the capacitance values ​​of both pure chitosan (CS) and lauric acid-grafted chitosan polymer (CS-LA) films exhibit typical dielectric relaxation behavior, i.e., a continuous decrease. However, it is noteworthy that the capacitance of the CS-LA film is significantly higher than that of pure CS at all frequencies, increasing from 0.21 nF to 0.35 nF (an increase of approximately 67%) in the low-frequency region (10 Hz) and from 0.06 nF to 0.15 nF (an increase of 150%) in the high-frequency region (1 kHz). Combined with the enhanced crystallinity revealed by previous XRD and the nanoscale rough surface morphology observed by SEM, it can be inferred that the grafting of lauric acid successfully introduced more interfacial polarization and microphase separation structures, while increasing the specific surface area, thereby significantly improving the charge storage capacity and dielectric properties of the material. This indicates that chemical modification not only alters the microstructure of chitosan but also effectively optimizes its electrical properties.

[0084] Furthermore, the relative permittivity of the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example were tested, and the results are as follows: Figure 7 The figure shows a comparison of the relative permittivity of lauric acid-grafted chitosan polymer films and pure chitosan films at various frequencies. The lauric acid-grafted chitosan polymer film exhibits higher permittivity at 10⁻¹⁰ ppm. 6 Significant improvements were observed in all frequencies, particularly in the 1 kHz mid-frequency range, where the oscillation intensity increased from 3.86 to 15.96 (an increase of over four times), indicating a substantial enhancement in ion transport capability and electrochemically active surface area. Lauric acid grafting, by introducing more interfacial structures, optimizing pore characteristics, and improving ion diffusion kinetics, resulted in superior charge storage capacity in the material under wet electrochemical conditions. This modification strategy effectively enhances the application potential of chitosan in supercapacitors or bioelectrochemical devices.

[0085] Furthermore, the voltage output of the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example were tested under a constant 1N force impact, and the results are as follows: Figure 8 As shown. In terms of piezoelectric properties, the output voltage of the butyric acid-grafted chitosan polymer film is 0.192V, and that of the octanoic acid-grafted chitosan polymer film is 0.251V, both lower than that of the lauric acid-grafted chitosan polymer film in Example 1. The output voltage of the lauric acid-grafted chitosan polymer film is significantly higher than that of the pure chitosan film, reaching approximately twice that of the pure chitosan film overall.

[0086] Furthermore, the response time diagrams of a single voltage signal were tested for the lauric acid-grafted chitosan polymer prepared in Example 1 of this invention and the chitosan film prepared in the comparative example. The results are as follows. Figure 9 As shown, in the millisecond-level transient response test of a single voltage step signal, the lauric acid-grafted chitosan polymer film (CS-LA) exhibits electrochemical response characteristics far superior to pure chitosan (CS): CS-LA generates a transient response of 0.42 at 0 seconds and reaches a peak of 0.80 at 112 milliseconds; while CS only starts to respond after a delay of 40 milliseconds, with a peak value of only 0.14 and rapid decay. This difference indicates that the nano-roughened surface formed by grafting lauric acid in CS-LA (confirmed by SEM) provides more electrochemical active sites, enabling it to rapidly adsorb ions and form an electric double layer at the moment of voltage step. At the same time, the optimized bulk structure also supports subsequent ion diffusion, thus achieving faster response, higher peak value, and better steady-state maintenance electrochemical performance, further confirming its great potential in supercapacitors or electrochemical biosensors.

[0087] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing a fatty acid-grafted chitosan polymer film, characterized in that, Includes the following steps: S1. Mix and dissolve fatty acid-grafted chitosan powder with glacial acetic acid, centrifuge to defoam, and then prepare a film by casting. S2. The film is soaked and washed in an alkaline solution to obtain a wet film; S3. The wet film is uniaxially stretched and dried to obtain a fatty acid-grafted chitosan polymer film.

2. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the alkaline solution is 0.8~1.2M.

3. The preparation method according to claim 1, characterized in that, In step S2, the alkali in the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, or sodium bicarbonate.

4. The preparation method according to claim 1, characterized in that, The uniaxial stretching amount is 15%~25%.

5. The preparation method according to claim 1, characterized in that, The fatty acid-grafted chitosan powder is prepared by the following method: (1) Mix chitosan and glacial acetic acid and let stand at 0~5℃; then add alcohol solution and adjust the pH to 3.5~4.5, and sonicate to obtain chitosan solution; (2) Add fatty acids and carboxyl activators to the chitosan solution to carry out a coupling reaction; (3) After the reaction is completed, the reaction solution is sonicated to adjust the pH to 5.5~6.5, and then allowed to stand at 0~5℃. The precipitate is obtained after post-treatment. (4) Resuspend the precipitate in water, adjust the pH to 8.5~9.5, let it stand at 0~5℃, and then process it to obtain the precipitate. The fatty acid-grafted chitosan powder was obtained by filtration, washing, and grinding.

6. The preparation method according to claim 1, characterized in that, The fatty acid has ≥10 carbon atoms.

7. The preparation method according to claim 5, characterized in that, The carboxyl activator includes the EDAC / NHS system and the EDAC / DCC system; Preferably, the molar ratio of chitosan, fatty acid, EDAC and NHS is 1:(0.9~1.1):(0.9~1.1):(0.9~1.1).

8. A fatty acid-grafted chitosan polymer film, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. A piezoelectric thin film, characterized in that, Includes the fatty acid-grafted chitosan polymer film as described in claim 8.

10. The application of the fatty acid-grafted chitosan polymer film according to claim 8 in the preparation of piezoelectric materials.

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