Critical-concentration-adjustable extremely-low-concentration chitin fiber liquid crystal material and preparation method thereof
Through high-pressure homogenization technology and deacetylation degree gradient control, the problem of low fiber aspect ratio in traditional chitin fiber preparation was solved, low-concentration ordered arrangement and morphology control of high-performance chitin fibers were achieved, and the fiber aspect ratio and stability were improved.
Patent Information
- Application Number
- CN202511009342.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-22
- Publication Date
- 2025-10-10
AI Technical Summary
In the traditional chitin fiber preparation process, high-concentration solutions lead to discrete fiber diameter distribution and low aspect ratio, and chemical modification causes chain breakage and solvent residue, making it difficult to achieve large-scale preparation of high-performance fibers.
By adopting high-pressure homogenization technology combined with gradient control of deacetylation degree, and through the synergistic effect of multi-stage shear field and dynamic temperature control module, the orderly arrangement of chitin molecules at low concentration is achieved, the fiber aspect ratio is controlled to be adjustable between 100-500, and the fiber refinement is regulated by the gradient of acetyl content.
It achieves a significant improvement in the fiber aspect ratio, reduces the concentration of liquid crystal formation, reduces the environmental load, and provides a preparation solution for high-performance chitin materials. The fiber maintains high elastic storage modulus and low viscosity at low concentrations and has good stability.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the field of bio-based functional materials, specifically a method for preparing high aspect ratio and low concentration chitin fiber liquid crystal materials through mechanical high-pressure homogenization combined with deacetylation degree regulation, and achieving critical concentration breakthrough by matching deacetylation degree and homogenization process parameters. Background Art
[0002] The traditional chitin fiber preparation process is limited by the disordered arrangement of molecular chains and the solvation effect, making it difficult to balance the control of fiber morphology and performance optimization. Conventional wet spinning relies on high-concentration solutions (>5wt%) to induce the formation of a liquid crystal phase through shear force, but the excessive accumulation of molecular chains leads to a discrete fiber diameter distribution, and the aspect ratio is generally less than 100. Although existing technologies have attempted to improve the degree of orientation through chemical modification or external field assistance, the fiber aspect ratio is still limited to a narrow range due to chain breakage and solvent residue caused by strong acid and alkali treatment. The essence of this high concentration dependence is that traditional processes cannot effectively weaken intermolecular hydrogen bonds and van der Waals forces. It is necessary to force the molecular chains into an oriented state by increasing the solution concentration, and the sharp increase in viscosity in turn limits the shear efficiency, forming a vicious cycle.
[0003] The degree of deacetylation shows a significant correlation with the regulation of fiber morphology, and its inherent mechanism stems from the competitive effect between acetyl groups and amino groups. As the degree of deacetylation increases, the flexibility of the rigid molecular chain increases, and the reconstruction of the intermolecular hydrogen bond network causes the fiber diameter to be refined to the submicron level. However, in traditional processes, high-deacetylation raw materials cause excessive swelling, which in turn leads to a decrease in aspect ratio. The existing system fails to effectively utilize this property. The root cause is that the solvation effect during the dissolution process masks the differentiated response of the deacetylation degree, and the uncontrollable interference of the protonation state of the amino group by acid and base treatment further aggravates the artificially high concentration of liquid crystal phase formation. This process-structure decoupling phenomenon is essentially due to the lack of adaptive design of the deacetylation gradient and shear field parameters.
[0004] Therefore, it is of great significance to develop a new method for preparing high aspect ratio and low concentration chitin fiber liquid crystal materials. Summary of the Invention
[0005] In view of the defects of the prior art, the present application aims to break through the path dependence of traditional chitin fiber preparation on high concentration solution and chemical modification, and to establish a new low concentration liquid crystal system based on deacetylation degree gradient regulation. In view of the defects of the existing process, such as low fiber aspect ratio (<100) due to disordered entanglement of molecular chains, high liquid crystal formation concentration (>5wt%), and heavy environmental load, through the synergistic mechanism of multi-stage shear field and dynamic temperature control module constructed by high pressure homogenization technology, the ordered arrangement of chitin molecules is realized in the 0.3-1.2wt% ultra-low concentration range. Based on the difference in deacetylation degree, the pressure-circulation time parameters are matched accurately, so that the fiber aspect ratio is expanded to 100-500 adjustable range, and the fiber refinement process is regulated by the gradient of acetyl content (the fiber diameter is reduced by 15% on average for every 9% increase in deacetylation degree), which provides a scientific and economic technical solution for the large-scale preparation of high-performance chitin materials.
[0006] The technical scheme adopted by the present application to solve the above technical problems is as follows: A preparation method of a critical concentration adjustable ultra-low concentration chitin fiber liquid crystal material, comprising the following steps: Step S1: removing protein and calcium carbonate from chitin raw materials by alternating acid and alkali treatment, and then performing decolorization treatment to obtain clean chitin; Step S2: crushing the clean chitin and mixing with sodium hydroxide solution to perform deacetylation reaction, to obtain deacetylated chitin with a deacetylation degree of 20.8%-38.1%; Step S3: mixing the deacetylated chitin with water, adjusting the pH value to 4.0±0.1, first using a high-speed homogenizer for the first homogenization, and then using a high-pressure homogenizer for the second homogenization, to obtain a critical concentration adjustable ultra-low concentration chitin fiber liquid crystal material.
[0007] As a preferred technical scheme of the present application, in step S1, the chitin raw material can be fresh crab shell, and further, the fresh crab shell is kitchen waste.
[0008] As a preferred technical scheme of the present application, in step S1, the alkali can be sodium hydroxide, specifically 1mol / L sodium hydroxide solution.
[0009] According to the embodiment of the present application, the method for removing protein is specifically: adding chitin raw material (fresh crab shell) into sufficient 1mol / L sodium hydroxide solution, waiting for 12h, and removing residual protein.
[0010] As a preferred technical scheme of the present application, in step S1, the acid can be hydrochloric acid, specifically 1mol / L hydrochloric acid solution.
[0011] According to an embodiment of the present invention, the method for removing calcium carbonate is specifically as follows: adding the chitin raw material from which protein has been removed into a sufficient amount of 1 mol / L hydrochloric acid solution, and waiting for 12 hours to remove the calcium carbonate.
[0012] As a preferred technical solution of the present invention, in step S1, the acid-base alternating treatment can be performed three times to obtain unbleached chitosan.
[0013] As a preferred technical solution of the present invention, in step S1, the decolorization treatment can be performed using sodium hypochlorite, and the sodium hypochlorite can be a 0.1%wt sodium hypochlorite solution.
[0014] According to an embodiment of the present invention, the decolorization treatment is specifically as follows: adding a sufficient amount of 0.1%wt sodium hypochlorite solution to the undecolorized chitosan, reacting at 90 degrees Celsius for 2 hours to remove the pigment.
[0015] The clean chitin obtained in step S1 can be stored sealed in a refrigerator at 4°C for up to two years. Maintaining moisture during storage allows for subsequent homogenization, which reduces energy consumption for fiber extraction and facilitates breaking hydrogen bonds between fibers. The extracted chitin fiber liquid crystal can be stored sealed in a refrigerator at 4°C for up to six months without changing its aspect ratio.
[0016] As a preferred technical solution of the present invention, in step S2, the concentration of the sodium hydroxide solution is 8 mol / L-12 mol / L, and the deacetylation reaction time is 3-5 hours.
[0017] According to an embodiment of the present invention, in step S2, a sufficient amount of 10 mol / L sodium hydroxide solution is used for deacetylation, and the reaction time is controlled by a single variable to be 3 h, 4 h, and 5 h, respectively, to obtain deacetylated chitin with a gradient deacetylation degree of 20.8%, 29%, and 38.1%.
[0018] In the present invention, the deacetylation of different chitins is performed by dissolving them in deuterated trifluoroacetic acid, and the different degrees of deacetylation are calculated by H1 nuclear magnetic resonance. The error range of the nuclear magnetic resonance measurement is ±0.5%.
[0019] As a preferred technical solution of the present invention, in step S3, the conditions for the first homogenization are: treatment by a high-speed homogenizer at 8000 r / min for 3 minutes to obtain coarse chitin fibers; the conditions for the second homogenization are: treatment by a high-pressure homogenizer at 600-800 bar for 5 minutes, and at the same time, condensed water circulation operation is performed during the high-pressure homogenization operation to control the overall homogenization temperature (specifically, the temperature can be maintained at 4°C).
[0020] According to an embodiment of the present invention, the second homogenization was repeated for 5 minutes for three chitosans with deacetylation degrees of 20.8%, 29%, and 38.1% under a high-pressure homogenizer at 700 bar. The diameter of the liquid crystal material decreased as the deacetylation degree increased.
[0021] As a preferred technical solution of the present invention, to obtain fibers of varying degrees of deacetylation with uniform thickness, the homogenization conditions include: first homogenizing the chitin fibers in a high-speed homogenizer at 8000 rpm for 3 minutes to obtain coarse chitin fibers, then repeatedly homogenizing the chitin fibers in a high-pressure homogenizer at 800 bar, 700 bar, and 600 bar for 5 minutes each for three different degrees of deacetylation: 20.8%, 29%, and 38.1%. The diameters of the resulting liquid crystal materials remained similar when the pressure of the second homogenization was varied within a range of 550 bar to 850 bar.
[0022] As a preferred technical solution of the present invention, in step S3, the matching relationship between the high-pressure homogenization pressure and the deacetylation degree is: a deacetylation degree of 20.8% corresponds to 800 bar, 29% corresponds to 700 bar, and 38.1% corresponds to 600 bar, and the pressure deviation is allowed to be ±50 bar.
[0023] As a preferred technical solution of the present invention, in step S3, in order to avoid introducing other ions, acetic acid is selected as the reagent used to adjust the pH value.
[0024] As a preferred technical solution of the present invention, in step S3, acetic acid is used to adjust the step-by-step addition, and a pH detector is used to monitor the pH condition in real time.
[0025] The extremely low concentration chitin fiber liquid crystal material of the present invention can be obtained by diluting a high concentration chitin fiber liquid crystal material (deionized water); the extremely low concentration chitin fiber liquid crystal material can also be obtained by adjusting the feed ratio during the preparation process.
[0026] According to the method of the present invention, a chitin fiber liquid crystal material with an aspect ratio of 100-500 can be obtained, and the critical concentration thereof can be adjusted in the range of 0.3-1.2 wt %.
[0027] The aspect ratios of the three fibers prepared from the three chitosans with different deacetylation degrees are similar, and the ratios are all within the range of 100-500.
[0028] Comparing the three chitin liquid crystal solutions, the critical concentration decreases with the increase of deacetylation degree, and then the critical concentration increases.
[0029] The three chitin liquid crystal solutions are nematic liquid crystals with a typical cross-striped texture. The three liquid crystal materials with the same thickness, similar aspect ratio and different deacetylation degrees are all accompanied by black brush intersection points (defect points) at 1.2%wt.
[0030] Decreasing the concentration of the three chitin fiber liquid crystal solutions triggers a significant phase behavior transition. At high concentrations, the molecules form a nematic phase with long-range orientational order through hydrophobic or electrostatic interactions, exhibiting a typical liquid crystal texture. When the concentration drops below a critical value, the driving force for the ordered arrangement of molecules weakens, and the nematic phase gradually disintegrates, transforming into an isotropic liquid phase with disordered molecules.
[0031] In the nematic phase, chitin liquid crystal solutions exhibit a high elastic storage modulus (G') significantly higher than the loss modulus (G'') due to the ordered molecular orientation, and the viscosity decreases significantly with increasing shear rate (shear thinning effect). As the concentration of the chitin liquid crystal solution decreases, the elastic modulus (G') gradually decays, and the viscosity decreases simultaneously. Once in the isotropic phase, (G'') dominates the rheological behavior (viscosity characteristics), the viscosity approaches that of the solvent, and the shear thinning effect weakens.
[0032] The chitin fiber liquid crystal material has an elastic modulus G'> loss modulus G'' at a concentration of 0.6 wt%, and a shear rate of 0.1 s - ¹Increased to 100s - ¹The viscosity decreases by more than 80%.
[0033] The chitosan fiber liquid crystal material prepared by the present invention exhibits a nematic liquid crystal phase at a concentration of 1.2 wt%, displays a cross-stripe texture accompanied by black brush defects under a polarizing microscope, and decreases the critical concentration by 50% with every 9% increase in the deacetylation degree. The chitosan fiber liquid crystal material prepared by the present invention can be stably stored for 6 months under humid and sealed storage conditions at 4°C, with a fiber aspect ratio attenuation rate of less than 5% within 6 months and a critical concentration offset of less than 0.1wt%.
[0034] The present invention adopts the method of high-pressure homogenization mechanical treatment to break the inherent shackles of concentration-morphology through multi-scale physical field collaboration, directly obtaining a fiber material with an aspect ratio of up to 500, so that the concentration of liquid crystal phase formation is reduced to less than 1 / 5 of the traditional process. At the same time, by controlling the treatment of the deacetylation degree of different fibers, long fibers of different thicknesses can be obtained, but their aspect ratios do not differ too much. As the deacetylation degree changes, we will find that the critical concentration for forming the liquid crystal phase is also changing. When the fibers are dried, the ones with high deacetylation degree are more likely to aggregate. Compared to the existing technology that relies on chemical modification, this physical regulation strategy achieves precise customization of fiber morphology while maintaining the integrity of the molecular chain, providing a new paradigm for the performance breakthrough of chitin materials. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Figure 1 The chitosan liquid crystal material solutions with different concentrations of deacetylation degree of 29.0% according to the embodiment of the present invention are as follows: 1.2wt%, 0.6wt%, and 0.3wt% from left to right; Figure 2 TEM images of chitin fibers under the same homogeneous conditions with different deacetylation degrees according to the embodiment of the present invention; Figure 3 is the average diameter of chitin fibers under the same homogeneous conditions with different deacetylation degrees in the embodiments of the present invention; Figure 4 TEM images of chitin fibers under different deacetylation degrees and different homogeneity conditions according to the present invention; Figure 5 The aspect ratio data of the chitin fiber with a degree of deacetylation of 29.0% in the embodiment of the present invention; Figure 6 Polarization data of chitin fibers with different deacetylation degrees according to the embodiment of the present invention; Figure 7 The figure shows the rheological data comparison of different deacetylation degrees (DD) of 0.6% in the examples of the present invention. DETAILED DESCRIPTION
[0036] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.
[0037] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.
[0038] Example 1. Preparation of chitin with different degrees of deacetylation Step S1: Add cleaned fresh crab shells to a sufficient amount of sodium hydroxide solution with a molar concentration of 1 mol / L, wait for 12 hours to remove residual protein, then add the fresh crab shells treated with sodium hydroxide to a sufficient amount of hydrochloric acid solution with a molar concentration of 1 mol / L, and wait for 12 hours to remove the calcium carbonate on the crab shell skeleton. Repeat the above steps three times to obtain unbleached chitosan. Then, add a sufficient amount of 0.1%wt sodium hypochlorite solution to the unbleached chitosan and react at 90 degrees Celsius for 2 hours to remove the pigment. The depigmented chitosan is filtered, washed with water, and dried to obtain pure white chitosan. The chitosan can be stored at 4 degrees Celsius.
[0039] Step S2: Chitosan was crushed using a household blender to obtain chitosan particles. The chitosan particles were then added to a sufficient amount of 10 mol / L sodium hydroxide solution for deacetylation. The reaction times were 3 h, 4 h, and 5 h, resulting in deacetylated chitosan with deacetylation degrees of 20.8%, 29%, and 38.1%, respectively.
[0040] Example 2: Preparation of Chitosan Fiber Liquid Crystal Material 1.2 g of each of the three deacetylated chitins were mixed with 100 ml of deionized water, and the pH value was adjusted to 4. The first homogenization was performed using a high-speed homogenizer at 8000 r / min for 3 min. A high-pressure homogenizer was then used for a second homogenization. During the homogenization process, a condensation circulation device was used to maintain the overall temperature, specifically at 4° C., to obtain a chitosan liquid crystal material.
[0041] Chitosan liquid crystal material solutions of different concentrations prepared from chitosan with a deacetylation degree of 29.0% (700 bar circulating homogenization treatment for 5 minutes) are shown in the following pictures. Figure 1 As shown, the concentrations from left to right are: 1.2wt%, 0.6wt%, 0.3wt% (wherein, 0.6wt% and 0.3wt% are obtained by diluting 1.2wt% chitin liquid crystal material with deionized water). In order to obtain chitin fibers of different morphologies, three chitins with deacetylation degrees of 20.8%, 29%, and 38.1% were cyclically homogenized for 5 minutes at 700 bar to obtain low-concentration liquid crystal materials. Transmission electron microscope (TEM) images of chitin fibers obtained under the same homogenization conditions (700 bar cyclic homogenization for 5 minutes) with different deacetylation degrees are shown in the figure below. Figure 2 As shown. Figure 2 TEM transmission electron microscope images show that the morphology of chitin fibers under the same homogeneous conditions with different deacetylation degrees still maintains the fiber morphology. Figure 2 The average diameter of chitin fibers obtained under the same homogenization conditions (700 bar circulation homogenization treatment for 5 minutes) with different deacetylation degrees is shown in the following table. Figure 3 As shown. Figure 3 It can be seen that the diameters of the three liquid crystal materials decrease as the deacetylation degree increases.
[0042] Under the conditions of 800bar, 700bar and 600bar respectively, the chitin with three deacetylation degrees of 20.8%, 29% and 38.1% was cyclically homogenized for 5 minutes, and the diameters were not much different. The transmission electron microscope images of chitin fibers under different deacetylation degrees and different homogenization conditions are shown in Figure 1. Figure 4As shown. According to statistics, the aspect ratio of chitin fiber is in the range of 100-500. The aspect ratio of 29% deacetylated chitin fiber is shown as follows Figure 5 As shown. Figure 5 It can be seen that after being treated at 700 bar for five minutes, the aspect ratio of 29.0% deacetylated chitin fibers is concentrated between 100 and 500.
[0043] Example 3: Observation of Chitosan Fiber Liquid Crystal Material Under the conditions of 800bar, 700bar and 600bar, three chitin fiber liquid crystal materials with deacetylation degrees of 20.8%, 29% and 38.1% were circulated and homogenized for 5 minutes. The chitin fiber liquid crystal materials with similar diameters were observed under polarization, and the single variable was the deacetylation degree. The high-concentration chitin fiber liquid crystal material was diluted with deionized water to obtain chitin fiber liquid crystals with different mass fractions of 1.2%wt, 0.9%wt, 0.6%wt, 0.3%wt and 0.15%wt. Figure 6 Polarization data of chitin fibers with different deacetylation degrees show that their critical concentration first decreases and then increases. Figure 7 Comparison of rheological data at different deacetylation degrees (DD) concentrations (0.6%) confirmed that DD significantly influences the strong hydrogen bond network at the intersections by altering the flexibility and interaction strength of the chitin liquid crystal chains. Low DD leads to slow chain relaxation, resulting in intersections at low frequencies. Increasing DD enhances electrostatic repulsion, accelerating relaxation, and shifting the intersections toward higher frequencies. Rheological data for chitin fibers with three DD concentrations were measured above the critical concentration, where the molecular chains form a long-range oriented, ordered structure through a balance between hydrophobic interactions and electrostatic repulsion. The elastic modulus (G') is significantly higher than the loss modulus (G'') in the low-frequency region (typically G' / G'' > 2), demonstrating solid-like elastic behavior.
[0044] The present invention has been described in detail above. It will be apparent to those skilled in the art that the present invention may be practiced over a wide range of parameters, concentrations, and conditions without departing from the spirit and scope of the present invention and without unnecessary experimentation. Although specific embodiments have been given herein, it should be understood that further modifications may be made to the present invention. In summary, this application is intended to encompass any variations, uses, or improvements to the present invention, including those made by conventional techniques known in the art that depart from the scope of the present invention. Applications of the essential features may be made within the scope of the following claims.
Claims
1. A method for preparing an extremely low concentration chitin fiber liquid crystal material with adjustable critical concentration, comprising the following steps: Step S1: The chitosan raw material is subjected to alternating acid and alkali treatment to remove protein and calcium carbonate, and then subjected to decolorization treatment to obtain clean chitosan; Step S2: crushing the clean chitosan and mixing it with a sodium hydroxide solution to perform a deacetylation reaction to obtain deacetylated chitosan with a deacetylation degree of 20.8%-38.1%; Step S3: mixing the deacetylated chitosan with water, adjusting the pH value to 4.0±0.1, first homogenizing the mixture using a high-speed homogenizer, and then homogenizing the mixture a second time using a high-pressure homogenizer to obtain an extremely low concentration chitosan fiber liquid crystal material with an adjustable critical concentration.
2. The preparation method according to claim 1, wherein: In step S1, the chitosan raw material is fresh crab shells, and further, the fresh crab shells are kitchen waste.
3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the base is sodium hydroxide, specifically 1 mol / L sodium hydroxide solution; And / or, in step S1, the acid is hydrochloric acid, specifically a 1 mol / L hydrochloric acid solution; And / or, in step S1, the decolorization treatment is performed using sodium hypochlorite, and the sodium hypochlorite is a 0.1%wt sodium hypochlorite solution.
4. The preparation method according to any one of claims 1 to 3, characterized in that: In step S2, the concentration of the sodium hydroxide solution is 8 mol / L-12 mol / L, and the deacetylation reaction time is 3-5 hours.
5. The preparation method according to claim 4, characterized in that: In step S2, a sufficient amount of 10 mol / L sodium hydroxide solution is used for deacetylation. The deacetylation reaction time is 3 hours, 4 hours, and 5 hours, respectively, corresponding to a deacetylation degree gradient of 20.8%, 29%, and 38.1%. The error range of the deacetylation degree measured by nuclear magnetic resonance is ±0.5%.
6. The preparation method according to any one of claims 1 to 5, characterized in that: In step S3, the first homogenization condition is: processing by a high-speed homogenizer at 8000 r / min for 3 minutes to obtain coarse chitin fibers; the second homogenization condition is: processing by a high-pressure homogenizer at 550-850 bar for 5 minutes; Furthermore, in step S3, the matching relationship between the pressure of the second homogenization and the deacetylation degree is: chitosan with a deacetylation degree of 20.8% corresponds to 800 bar, chitosan with a deacetylation degree of 29% corresponds to 700 bar, and chitosan with a deacetylation degree of 38.1% corresponds to 600 bar, and the pressure deviation is allowed to be ±50 bar.
7. The preparation method according to any one of claims 1 to 6, characterized in that: In step S3, in order to avoid introducing other ions, acetic acid is selected as the reagent used to adjust the pH value; Preferably, in step S3, acetic acid is used to adjust the stepwise addition, and a pH detector is used to monitor the pH condition in real time.
8. The preparation method according to any one of claims 1 to 7, characterized in that: The extremely low concentration chitin fiber liquid crystal material with adjustable critical concentration has an aspect ratio of 100-500 and an adjustable critical concentration range of 0.3-1.2 wt %.
9. The chitin fiber liquid crystal material prepared by the method according to any one of claims 1 to 8.
10. The chitin fiber liquid crystal material according to claim 9, characterized in that: The chitin fiber liquid crystal material exhibits a nematic liquid crystal phase at a concentration of 1.2 wt%, and exhibits a cross-stripe texture accompanied by black brush defects under a polarizing microscope. Furthermore, the critical concentration decreases by 50% with every 9% increase in the degree of deacetylation. And / or, the chitin fiber liquid crystal material has an elastic modulus G'> loss modulus G'' at a concentration of 0.6 wt%, and the shear rate is from 0.1 s - ¹Increased to 100s - ¹The viscosity decrease is >80%; And / or, the chitosan fiber liquid crystal material can be stably stored for 6 months under humidified sealed storage conditions at 4° C., the fiber aspect ratio attenuation rate within 6 months is less than 5%, and the critical concentration offset is less than 0.1 wt%.