Preparation method of a high-strength biaxially oriented chitin sheet and product thereof

Abstract

The present invention discloses a preparation method of a high-strength biaxially oriented chitin sheet and its product, belonging to the technical field of materials for surgical supplies. The preparation method includes the following steps: (1) adding a cross-linking agent to a chitin solution to prepare a chitin hydrogel; (2) performing pre-stretching along the longitudinal direction of the chitin hydrogel and fixing the pre-stretched orientation to obtain a uniaxially oriented chitin hydrogel; (3) performing stretching along the transverse direction of the uniaxially oriented chitin hydrogel and fixing the biaxial orientation to obtain a biaxially oriented chitin hydrogel; (4) subjecting the biaxially oriented chitin hydrogel to replacement treatment and drying to obtain a high-strength biaxially oriented chitin sheet. The raw materials of the present invention are widely sourced, the operation is simple, it is environmentally friendly, and it is easy to industrialize. The obtained chitin sheet has high strength and toughness, and has excellent biocompatibility and degradability.

Description

Technical Field

[0001] The present invention relates to the technical field of materials for surgical supplies, and particularly to a preparation method and product of a high-strength biaxially oriented chitin sheet. Background Art

[0002] A fracture is defined in medicine as an interruption of the integrity or continuity of a bone. The clinical treatment of fractures mainly includes three stages: reduction, fixation, and postoperative rehabilitation. The fixation materials used clinically include external fixation and internal fixation materials. External fixation can avoid damaging the soft tissues at the fracture site, but it is prone to cause infections at the fracture site and the recovery is relatively slow. Currently, internal fixation materials are mainly used for fracture repair in China.

[0003] The fracture internal fixation materials used clinically are mainly divided into metal internal fixation materials and polymer internal fixation materials. Metal internal fixation materials are inexpensive, but due to their poor biocompatibility and large rigidity, they are prone to cause infections and inflammation at the fracture fixation site, and at the same time, a second operation is required to remove them. The biodegradable polymers that can be absorbed by the human body mainly include polyesters, polyanhydrides, polyether esters, polyamino acids, and polyorthoesters. Currently, the main absorbable fracture internal fixation material used in orthopedic surgery clinically is polylactic acid (PLA), but the strength of PLA is still lower than that of metals, and local lactic acid may be too high after degradation, leading to inflammation. Therefore, the development of new absorbable fracture internal fixation materials will provide new ideas and treatment methods for solving the above problems in clinical practice.

[0004] Chitin is a natural polymer that ranks second only to cellulose in nature and mainly exists in the exoskeletons of shrimps and crabs. Due to its high chain rigidity, high crystallinity, and strong intermolecular hydrogen bonds, chitin-based materials have excellent strength. At the same time, due to their excellent biocompatibility and biodegradability, they have received extensive attention in the fields of tissue engineering, wearable devices, sustainable applications, etc. Preparing a chitin sheet can provide a new material for fracture internal fixation medical devices. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, a preparation method of a high-strength biaxially oriented chitin sheet with simple operation, environmental friendliness, and easy industrialization is provided, including the following steps:

[0006] (1) Adding a crosslinking agent to a chitin solution to prepare a chitin hydrogel;

[0007] (2) Pre-stretching along the longitudinal direction of the chitin hydrogel and fixing the pre-stretched orientation to obtain a uniaxially oriented chitin hydrogel;

[0008] (3) Stretching along the transverse direction of the uniaxially oriented chitin hydrogel and fixing the biaxial orientation to obtain a biaxially oriented chitin hydrogel;

[0009] (4) The biaxially oriented chitin hydrogel is subjected to replacement treatment and drying to obtain a high-strength biaxially oriented chitin sheet.

[0010] Preferably, the specific operation of step (1) is as follows: Dissolve the purified chitin in a sodium hydroxide / urea solution system to obtain a chitin solution; Add a cross-linking agent to the chitin solution and mix evenly, centrifuge to remove excess bubbles and impurities, and obtain a chitin hydrogel through curing.

[0011] More preferably, the sodium hydroxide / urea solution system is a solution formed by sodium hydroxide, urea, and water in a mass ratio of 11:4:79 - 81.

[0012] More preferably, the temperature of the mixing is -10 to 10°C; the temperature of the centrifugation is -10 to 10°C.

[0013] Low temperature is beneficial to preventing the premature gelation of the chitin solution and removing bubbles and impurities before gelation.

[0014] More preferably, the temperature of the curing is 0 to 5°C, and the curing time is 8 to 18 h.

[0015] Preferably, in step (1), the mass percentage concentration of the chitin solution is 4% - 6%.

[0016] Preferably, in step (1), the cross-linking agent is epichlorohydrin or 1,4-butanediol diglycidyl ether.

[0017] More preferably, when the cross-linking agent is epichlorohydrin, the mass ratio of chitin to epichlorohydrin in the chitin solution is 2.54 - 5.08:1; when the cross-linking agent is 1,4-butanediol diglycidyl ether, the mass ratio of chitin to 1,4-butanediol diglycidyl ether in the chitin solution is 3.41 - 4.54:1.

[0018] Preferably, in step (2), the longitudinal stretching ratio of the pre-stretching is 30% - 150%.

[0019] Preferably, in step (2), the method for fixing the pre-stretched orientation is: Immerse the hydrogel stretched in the longitudinal direction in an ethanol aqueous solution with an excessive volume percentage concentration of 50% - 70% for 8 - 24 h.

[0020] Preferably, in step (3), the transverse stretching ratio of the stretching is 30% - 150%.

[0021] Preferably, in the step (3), the method for fixing the biaxial orientation is as follows: soaking the hydrogel stretched in the transverse direction in an excessive amount of ethanol aqueous solution with a volume percentage concentration ≥ 70% or absolute ethanol for 12 - 24 h.

[0022] After the pre - stretching and orientation are fixed, the hydrogel network is fixed. Therefore, after transverse stretching, it is more difficult to fix the hydrogel network structure during the fixation of biaxial orientation. In the process of fixing biaxial orientation, the present invention uses a higher - concentration ethanol aqueous solution, which is beneficial to the smooth progress of fixation.

[0023] Preferably, in the step (4), the replacement treatment is carried out in two steps. First, replace with an excessive amount of ethanol aqueous solution with a volume percentage concentration ≥ 20% or absolute ethanol having a gradient concentration, and the total replacement time for this step is 24 h. Subsequently, replace with an excessive amount of acetone for 3 - 5 times.

[0024] The replacement with ethanol solution of gradient concentration can facilitate the formation of more hydrogen bonds between chitin molecular chains, thereby further improving the strength and toughness of the hydrogel.

[0025] More preferably, the method for the replacement treatment is as follows: replace with ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, and 75% and absolute ethanol for 6 h respectively, and then replace with an excessive amount of acetone for 3 - 5 times.

[0026] In the second aspect of the present invention, there is provided a high - strength biaxially oriented chitin sheet with good biocompatibility, high strength and toughness, and low swelling ratio. This high - strength biaxially oriented chitin sheet is prepared by using the preparation method of the first aspect of the present invention.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] The present invention provides a preparation method for a high - strength biaxially oriented chitin sheet. This method has wide raw material sources, is simple to operate, environmentally friendly, and easy to industrialize. This process enables the chitin hydrogel to have excellent strength and toughness by biaxially stretching and fixing the biaxial orientation network of the chitin hydrogel.

[0029] The present invention also provides a high - strength biaxially oriented chitin sheet, which has excellent biocompatibility and degradability, and high strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a partial process schematic diagram of the preparation method for a high - strength biaxially oriented chitin sheet;

[0031] Figure 2 It is the flexural stress - strain curves of the uniaxially oriented chitin sheets obtained under different pre - stretching ratios in Comparative Examples 1 - 3;

[0032] Figure 3 For Examples 3 to 5 and Comparative Example 4, when the pre-stretching draw ratio is 90%, the flexural stress-strain curves of the chitin sheets obtained at different transverse draw ratios. Detailed implementation manners

[0033] The present invention will be further illustrated below by way of examples, but the present invention is not limited to the scope of the examples described herein. For the experimental methods without specific conditions indicated in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0034] Example 1

[0035] A high-strength biaxially oriented chitin sheet is prepared by the following method:

[0036] (1) Dissolve 11 g of sodium hydroxide and 4 g of urea in 79 g of deionized water, then add 6 g of purified chitin powder. After mixing evenly, place it in an environment at -40°C and freeze for 2.5 h, then stir and thaw at room temperature. Place the thawed mixture in an environment at -40°C again and freeze for 24 h, and stir and thaw at room temperature to obtain a transparent chitin solution; add 2 mL of epichlorohydrin to the chitin solution, mix and stir in an ice-water bath for 10 min, transfer the stirred solution to a centrifuge tube, and centrifuge at 8000 rpm and -10°C for 5 min to remove air bubbles and impurities in the solution; pour the centrifuged solution into a rectangular mold and place it in a 4°C refrigerator for curing for 18 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network;

[0037] (2) Take out the chitin hydrogel from the rectangular mold, soak it in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 1 h and then take it out; place the taken-out chitin hydrogel on a fixture and pre-stretch it longitudinally to 140% of the initial length. At this time, the pre-stretching draw ratio of the chitin hydrogel is 40%. Soak the pre-stretched chitin hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 70% for 12 h to fix the pre-stretched orientation, and obtain a uniaxially oriented chitin hydrogel;

[0038] (3) Stretch the uniaxially oriented chitin hydrogel transversely to 140% of the transverse length. At this time, the transverse draw ratio of the hydrogel is 40%; soak the stretched hydrogel in an excessive amount of absolute ethanol for 24 h to fix the biaxial orientation, and obtain a biaxially oriented chitin hydrogel;

[0039] (4) After washing the biaxially oriented chitin hydrogel with deionized water, it was successively replaced with excessive ethanol aqueous solutions with volume percentages of 25%, 50%, 75%, and absolute ethanol for 6 hours each, and then replaced with excessive acetone three times. Finally, it was naturally dried in the air to obtain a high-strength biaxially oriented chitin sheet.

[0040] Example 2

[0041] A high-strength biaxially oriented chitin sheet was prepared by the following method:

[0042] (1) Dissolve 22 g of sodium hydroxide and 8 g of urea in 158 g of deionized water, then add 12 g of purified chitin powder. After mixing evenly, place it in a -40°C environment and freeze for 3.5 hours. Then stir and thaw it at room temperature. Place the thawed mixture in a -40°C environment again and freeze for 24 hours. Stir and thaw it at room temperature to obtain a transparent chitin solution. Add 4 mL of epichlorohydrin to the chitin solution, mix and stir in an ice-water bath for 10 minutes. Transfer the stirred solution to a centrifuge tube and centrifuge at 8000 rpm and -10°C for 5 minutes to remove air bubbles and impurities in the solution. Pour the centrifuged solution into a rectangular mold and place it in a 4°C refrigerator to cure for 18 hours. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network.

[0043] (2) Take out the chitin hydrogel from the rectangular mold, soak it in an excessive ethanol aqueous solution with a volume percentage of 50% for 1 hour and then take it out. Place the taken-out chitin hydrogel on a fixture and pre-stretch it along the longitudinal direction to 180% of its initial length. At this time, the pre-stretch ratio of the chitin hydrogel is 80%. Soak the pre-stretched chitin hydrogel in an excessive ethanol aqueous solution with a volume percentage of 70% for 12 hours to fix the pre-stretched orientation, and obtain a uniaxially oriented chitin hydrogel.

[0044] (3) Stretch the uniaxially oriented chitin hydrogel along the transverse direction to 180% of its transverse length. At this time, the transverse stretch ratio of the hydrogel is 80%. Soak the stretched hydrogel in excessive absolute ethanol for 24 hours to fix the biaxial orientation, and obtain a biaxially oriented chitin hydrogel.

[0045] (4) After washing the biaxially oriented chitin hydrogel with deionized water, it was successively replaced with excessive ethanol aqueous solutions with volume percentages of 25%, 50%, 75%, and absolute ethanol for 6 hours each, and then replaced with excessive acetone three times. Finally, it was naturally dried in the air to obtain a high-strength biaxially oriented chitin sheet.

[0046] Example 3

[0047] A high-strength biaxially oriented chitin sheet was prepared by the following method:

[0048] (1) Dissolve 11 g of sodium hydroxide and 4 g of urea in 80 g of deionized water. Subsequently, add 5 g of purified chitin powder. After mixing evenly, place it in an environment at -40 °C and freeze for 2.5 h. Then, stir and thaw it at room temperature. Place the thawed mixture in an environment at -40 °C again and freeze for 24 h. Stir and thaw it at room temperature to obtain a transparent chitin solution; add 1.3 mL of 1,4-butanediol diglycidyl ether dropwise to the chitin solution, mix and stir in an ice-water bath for 10 min. Transfer the stirred solution to a centrifuge tube, centrifuge at 8000 rpm and -10 °C for 5 min to remove air bubbles and impurities in the solution; pour the centrifuged solution into a rectangular mold and place it in a 4 °C refrigerator to solidify for 18 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network;

[0049] (2) Take out the chitin hydrogel from the rectangular mold, soak it in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 1 h and then take it out; place the taken-out chitin hydrogel on a fixture, pre-stretch it longitudinally to 190% of the initial length. At this time, the pre-stretch ratio of the chitin hydrogel is 90%. Soak the pre-stretched chitin hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 70% for 12 h to fix the pre-stretch orientation, and obtain a uniaxially oriented chitin hydrogel;

[0050] (3) Stretch the uniaxially oriented chitin hydrogel transversely to 130% of the transverse length. At this time, the transverse stretch ratio of the hydrogel is 30%; soak the stretched hydrogel in an excessive amount of absolute ethanol for 12 h to fix the biaxial orientation, and obtain a biaxially oriented chitin hydrogel;

[0051] (4) After washing the biaxially oriented chitin hydrogel with deionized water, replace it successively with excessive ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, 75% and absolute ethanol for 6 h each, then replace it with excessive acetone three times, and finally let it dry naturally in the air to obtain a high-strength biaxially oriented chitin sheet, denoted as 90%-30% according to the process stretch ratio.

[0052] Example 4

[0053] This example is basically the same as Example 3, except that in this example, the transverse stretch ratio during stretching is 60%, and according to the process stretch ratio, this example is denoted as 90%-60%.

[0054] Example 5

[0055] This example is basically the same as Example 3, except that in this example, the transverse stretch ratio during stretching is 100%, and according to the process stretch ratio, this example is denoted as 90%-100%.

[0056] Example 6

[0057] A high-strength biaxially oriented chitin sheet is prepared by the following method:

[0058] (1) Dissolve 11 g of sodium hydroxide and 4 g of urea in 81 g of deionized water, then add 4 g of purified chitin powder. After mixing evenly, place it in a -40 °C environment and freeze for 2.5 h, then stir and thaw at room temperature. Place the thawed mixture in a -40 °C environment again and freeze for 24 h, then stir and thaw at room temperature to obtain a transparent chitin solution; Drop 2 mL of epichlorohydrin into the chitin solution, mix and stir at -10 °C for 10 min, transfer the stirred solution to a centrifuge tube, and centrifuge at 8000 rpm and -10 °C for 5 min to remove air bubbles and impurities in the solution; Pour the centrifuged solution into a rectangular mold and place it in a 5 °C refrigerator to solidify for 8 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network;

[0059] (2) Take out the chitin hydrogel from the rectangular mold, soak it in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 1 h and then take it out; Place the taken-out chitin hydrogel on a fixture and pre-stretch it longitudinally to 130% of its initial length. At this time, the pre-stretch ratio of the chitin hydrogel is 30%. Soak the pre-stretched chitin hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 24 h to fix the pre-stretched orientation, and obtain a uniaxially oriented chitin hydrogel;

[0060] (3) Stretch the uniaxially oriented chitin hydrogel transversely to 130% of its transverse length. At this time, the transverse stretch ratio of the hydrogel is 30%; Soak the stretched hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 70% for 24 h to fix the biaxial orientation, and obtain a biaxially oriented chitin hydrogel;

[0061] (4) After washing the biaxially oriented chitin hydrogel with deionized water, replace it successively with excessive ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, 75% and absolute ethanol for 6 h each, then replace it with excessive acetone 3 times, and finally let it dry naturally in the air to obtain a high-strength biaxially oriented chitin sheet.

[0062] Example 7

[0063] A high-strength biaxially oriented chitin sheet is prepared by the following method:

[0064] (1) Dissolve 11 g of sodium hydroxide and 4 g of urea in 81 g of deionized water. Subsequently, add 4 g of purified chitin powder. After mixing evenly, place it in an environment at -40 °C and freeze for 2.5 h. Then, stir and thaw it at room temperature. Place the thawed mixture in an environment at -40 °C again and freeze for 24 h. Stir and thaw it at room temperature to obtain a transparent chitin solution. Add 1 mL of epichlorohydrin to the chitin solution, mix and stir at 10 °C for 10 min. Transfer the stirred solution to a centrifuge tube and centrifuge at 8000 rpm and 10 °C for 5 min to remove air bubbles and impurities in the solution. Pour the centrifuged solution into a rectangular mold and place it in a 0 °C refrigerator to solidify for 18 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network.

[0065] (2) Take out the chitin hydrogel from the rectangular mold, soak it in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 1 h and then take it out. Place the taken-out chitin hydrogel on a fixture and pre-stretch it longitudinally to 250% of its initial length. At this time, the pre-stretch ratio of the chitin hydrogel is 150%. Soak the pre-stretched chitin hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 8 h to fix the pre-stretched orientation, and obtain a uniaxially oriented chitin hydrogel.

[0066] (3) Stretch the uniaxially oriented chitin gel transversely to 250% of its transverse length. At this time, the transverse stretch ratio of the hydrogel is 150%. Soak the stretched hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 70% for 24 h to fix the biaxial orientation, and obtain a biaxially oriented chitin hydrogel.

[0067] (4) After washing the biaxially oriented chitin hydrogel with deionized water, replace it successively with excessive ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, 75% and absolute ethanol for 6 h each, then replace it with excessive acetone three times, and finally air-dry it naturally in the air to obtain a high-strength biaxially oriented chitin sheet.

[0068] Comparative Example 1

[0069] A high-strength chitin sheet is prepared by the following method:

[0070] (1) Dissolve 22 g of sodium hydroxide and 8 g of urea in 158 g of deionized water. Then add 12 g of purified chitin powder. After mixing evenly, place it in an environment of -40 °C and freeze for 3.5 h. Then stir and thaw at room temperature. Place the thawed mixture in an environment of -40 °C again and freeze for 24 h. Stir and thaw at room temperature to obtain a transparent chitin solution. Drop 4 mL of epichlorohydrin into the chitin solution, mix and stir in an ice-water bath for 10 min. Transfer the stirred solution to a centrifuge tube, centrifuge at 8000 rpm and -10 °C for 5 min to remove air bubbles and impurities in the solution. Pour the centrifuged solution into a rectangular mold and place it in a 4 °C refrigerator to solidify for 18 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network.

[0071] (2) Take out the chitin hydrogel from the rectangular mold and soak it in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 50% for 1 h and then take it out. Place the taken-out chitin hydrogel on a fixture and pre-stretch it to 180% of the initial length in the longitudinal direction. At this time, the pre-stretch ratio of the chitin hydrogel is 80%. Immerse the pre-stretched chitin hydrogel in an excessive amount of ethanol aqueous solution with a volume percentage concentration of 70% for 12 h to fix the pre-stretch orientation, and obtain a uniaxially oriented chitin gel. After washing the uniaxially oriented chitin hydrogel with deionized water, replace it successively with excessive ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, 75% and absolute ethanol for 6 h each, then replace it with excessive acetone three times, and finally let it dry naturally in the air to obtain a high-strength chitin sheet, denoted as 80% according to the process stretch ratio.

[0072] Comparative Example 2

[0073] This comparative example is basically the same as Comparative Example 1, except that in this example, the pre-stretch ratio is 40%, and this comparative example is denoted as 40%.

[0074] Comparative Example 3

[0075] The chitin sheet is prepared by the following method:

[0076] Dissolve 22 g of sodium hydroxide and 8 g of urea in 158 g of deionized water. Subsequently, add 12 g of purified chitin powder. After mixing evenly, place it in an environment at -40 °C and freeze for 3.5 h. Then, stir and thaw it at room temperature. Place the thawed mixture in an environment at -40 °C again and freeze for 24 h. Stir and thaw it at room temperature to obtain a transparent chitin solution. Add 4 mL of epichlorohydrin dropwise to the chitin solution, mix and stir in an ice-water bath for 10 min. Transfer the stirred solution to a centrifuge tube and centrifuge at 8000 rpm and -10 °C for 5 min to remove air bubbles and impurities in the solution. Pour the centrifuged solution into a rectangular mold and place it in a 4 °C refrigerator to solidify for 18 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network. After washing the chitin hydrogel with deionized water, displace it successively with an excessive amount of ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, 75%, and absolute ethanol for 6 h each, then displace it with excessive acetone three times, and finally air-dry it naturally in the air to obtain a chitin sheet. In this comparative example, no pre-stretching was performed, the stretching ratio was 0%, denoted as 0%.

[0077] To explore the influence of only pre-stretching on the mechanical properties and swelling ratio of the finished chitin sheet, the bending properties and swelling ratio of Comparative Examples 1 - 3 were measured respectively. The bending properties were measured by a universal mechanical testing machine, and the swelling ratio test adopted a general test method. To simulate the application environment of the sheet, the test solution for the swelling ratio test was selected as SBF simulated body fluid. As Figure 2 shown, the bending strength of the uniaxially oriented chitin sheet increases with the increase of the pre-stretching ratio. When the pre-stretching ratio in Comparative Example 1 is 80%, the bending strength is better than that in Comparative Example 2 and is 55.7% higher than that of the non-stretched chitin sheet in Comparative Example 3. In the swelling ratio test, the swelling ratio of Comparative Example 1 is 67.8% lower than that of the non-stretched chitin sheet.

[0078] Comparative Example 4

[0079] The chitin sheet was prepared by the following method:

[0080] (1) Dissolve 11 g of sodium hydroxide and 4 g of urea in 80 g of deionized water. Then add 5 g of purified chitin powder. After mixing evenly, place it in an environment at -40 °C and freeze for 2.5 h. Then stir and thaw it at room temperature. Place the thawed mixture in an environment at -40 °C again and freeze for 24 h. Stir and thaw it at room temperature to obtain a transparent chitin solution. Drop 1.3 mL of 1,4-butanediol diglycidyl ether into the chitin solution, mix and stir in an ice-water bath for 10 min. Transfer the stirred solution to a centrifuge tube, centrifuge at 8000 rpm and -10 °C for 5 min to remove the bubbles and impurities in the solution. Pour the centrifuged solution into a rectangular mold and place it in a 4 °C refrigerator to solidify for 18 h. During this process, the chitin solution gradually gels to form a chitin hydrogel with a loose cross-linked network. After washing the chitin hydrogel with deionized water, successively displace it with excessive ethanol aqueous solutions with volume percentage concentrations of 25%, 50%, 75% and absolute ethanol for 6 h each, then displace it with excessive acetone three times, and finally let it dry naturally in the air to obtain a chitin plate. In this comparative example, no pre-stretching was carried out, the stretching ratio was 0%, denoted as 0%.

[0081] Respectively test the bending properties of the chitin plates obtained at different transverse stretching ratios when the pre-stretching ratio is 90%. The test objects are Examples 3 - 5 and Comparative Example 4. The chitin plates obtained in Examples 3 - 5 are biaxially oriented, and Comparative Example 4 is an isotropic chitin plate. From Figure 3 It can be seen that when the pre-stretching ratio of the biaxially oriented chitin plate is fixed, the larger the transverse stretching ratio, the higher its bending strength, and all are higher than the non-stretched chitin plate. Among them, Example 3 has the optimal bending properties relative to other groups.

[0082] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art shall fall within the protection scope determined by the claims.

Claims

1. A method for preparing a high-strength biaxially oriented chitosan sheet, characterized in that: The steps include: (1) Dissolving the purified chitosan in a sodium hydroxide / urea solution system to obtain a chitosan solution; adding a crosslinking agent to the chitosan solution and mixing it evenly; centrifuging to remove excess bubbles and impurities; and curing to obtain a chitosan hydrogel; The mass percentage concentration of the chitin solution is 4% to 6%; the crosslinking agent is epichlorohydrin or 1,4-butanediol diglycidyl ether; when the crosslinking agent is epichlorohydrin, the mass ratio of chitin to epichlorohydrin in the chitin solution is 2.54 to 5.08:1; when the crosslinking agent is 1,4-butanediol diglycidyl ether, the mass ratio of chitin to 1,4-butanediol diglycidyl ether in the chitin solution is 3.41 to 4.54:1 (2) pre-stretching the chitin hydrogel along the longitudinal direction, and immersing the hydrogel stretched along the longitudinal direction in an excess of 50% to 70% ethanol aqueous solution for 8 to 24 hours to obtain a uniaxially oriented chitin hydrogel; The longitudinal stretching ratio of pre-stretching is 30%~150%; (3) stretching the uniaxially oriented chitin hydrogel in a transverse direction, and immersing the hydrogel stretched in an excess of an ethanol aqueous solution or anhydrous ethanol with a volume percentage concentration of ≥70% for 12 to 24 hours to obtain a biaxially oriented chitin hydrogel; The transverse stretching ratio of stretching is 30%~150%; (4) The biaxially oriented chitin hydrogel is subjected to replacement treatment and drying to obtain a high-strength biaxially oriented chitin sheet; The replacement treatment was carried out in two steps. First, the solution was replaced with an excess of ethanol aqueous solution or anhydrous ethanol at a concentration of 25%, 50%, or 75% by volume for 6 hours, respectively. Then, the solution was replaced with excess acetone for 3 to 5 times.

2. The method according to claim 1, wherein: The sodium hydroxide / urea solution system is a solution formed by sodium hydroxide, urea, and water in a mass ratio of 11:4:79-81; the mixing temperature is -10-10°C; the centrifugation temperature is -10-10°C; the solidification temperature is 0-5°C, and the solidification time is 8-18 hours.

3. A high-strength biaxially oriented chitosan sheet, characterized by: The method according to claim 1 or 2 is used for preparation.

Images