A method for producing microfibrillated cellulose fibers, a method for producing a cellulose film

Abstract

The application belongs to the technical field of biomass pretreatment, and particularly relates to a preparation method of microfibrillated cotton fiber and a preparation method of cellulose film. The microfibrillated product is obtained by subjecting cotton fiber to a microfibrillating reaction with a eutectic solvent. After introducing Lewis acid into the choline chloride / organic acid-based eutectic solvent, the viscosity of the ternary eutectic solvent is low, and the microfibrillating effect on the cotton fiber is enhanced, so that the microfibrillating effect can be quickly achieved within more than ten minutes. This greatly reduces the high energy consumption of the traditional mechanical method, and the yield of the microfibrillated cotton fiber is high. In addition, the ternary eutectic solvent can be repeatedly used, thereby reducing the production cost. The microfibrillated cotton fiber can be used to prepare cellulose film with large size and high strength, and is a potential substitute for traditional polylactic acid.

Description

Technical Field

[0001] This invention belongs to the field of biomass pretreatment technology, specifically relating to a method for preparing microfibrillated cotton fibers and a method for preparing cellulose membranes. Background Technology

[0002] Fiber and lignocellulosic feedstocks, as well as waste such as agricultural residues, timber, forestry waste, sludge from the paper industry, and municipal and industrial solid waste, provide potentially valuable renewable feedstocks for the production of valuable products such as fuels and other chemicals. The process of treating biomass feedstocks to prepare carbohydrate polymers from fibrous and lignocellulosic materials that are more readily utilized by saccharifying enzymes is commonly referred to as pretreatment. Eutectic solvent methods are frequently used for biomass pretreatment; however, they are primarily used to separate lignin from biomass, and the microfibrilation of biomass feedstocks generally employs energy-intensive mechanical pretreatment methods such as ball milling, pulverization, and extrusion. Reports exploring the use of eutectic solvents for biomass microfibrilation are limited. Furthermore, commonly used eutectic solvents, such as choline chloride / oxalic acid, have high viscosity, which restricts their application in biomass pretreatment. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing microfibrillated cotton fibers and a method for preparing cellulose membranes. The eutectic solvent provided by this invention has low viscosity, which can quickly microfibrillate cotton fibers, resulting in a high yield of microfibrillated cotton fibers. The fiber membrane prepared from microfibrillated cotton fibers has high mechanical properties.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing microfibrillated cotton fibers, comprising the following steps:

[0006] Cotton fibers and a eutectic solvent are mixed to carry out a microfibrillation reaction to obtain microfibrillated products;

[0007] The microfibrilation product was subjected to solid-liquid separation to obtain a solid and a recovered eutectic solvent.

[0008] The solid was sequentially washed with water and dried to obtain microfibrillated cotton fibers.

[0009] The eutectic solvent includes choline chloride, organic acids, and Lewis acids;

[0010] The Lewis acids include one or more of aluminum chloride, ferric chloride, calcium chloride, and magnesium chloride.

[0011] Preferably, the organic acid includes one or more of lactic acid, malic acid, formic acid, acetic acid, propionic acid, oxalic acid, and maleic acid.

[0012] Preferably, the molar ratio of choline chloride to organic acid is 1:1 to 15.

[0013] Preferably, the molar ratio of choline chloride to Lewis acid is 1:0.01 to 1.

[0014] Preferably, the method for preparing the eutectic flux includes the following steps:

[0015] Choline chloride, organic acid, and Lewis acid are mixed and heated until clear and transparent to obtain the eutectic flux.

[0016] Preferably, the heating temperature is 60–100°C.

[0017] This invention also provides a method for preparing a cellulose membrane, comprising the following steps:

[0018] The microfibrillated cotton fibers prepared by the preparation method described above are dispersed in a mixed solution of metal hydroxide and urea. After freezing and thawing, the resulting dispersion is separated into solid and liquid phase components.

[0019] The mixture of the liquid phase component and the crosslinking agent is placed in a mold and gelled to form a cellulose hydrogel. The mixture is then washed and dried to obtain a cellulose membrane.

[0020] Preferably, the solid content of the dispersion is 3-6%.

[0021] Preferably, the freezing temperature is -12 to -20°C; and the freezing time is preferably 3 to 12 hours.

[0022] Preferably, the thawing temperature is 40–70°C.

[0023] This invention provides a method for preparing microfibrillated cotton fibers, comprising the following steps: mixing cotton fibers and a eutectic solvent to carry out a microfibrillation reaction to obtain a microfibrillated product; separating the microfibrillated product into a solid and recovering the eutectic solvent; sequentially washing and drying the solid to obtain microfibrillated cotton fibers; wherein the eutectic solvent includes choline chloride, organic acids, and Lewis acids; and wherein the Lewis acids include one or more of aluminum chloride, ferric chloride, calcium chloride, and magnesium chloride.

[0024] This invention introduces a Lewis acid into a choline chloride / organic acid-based eutectic solvent, resulting in a ternary eutectic solvent with low viscosity and reduced hydrated H+ in the acidic system. +The swelling effect on cotton fibers increases the inter-fiber gaps, allowing metal cations in the Lewis acid to diffuse more easily to the β-1,4 glycosidic bond sites, leading to bond breakage and enhanced microfibrillation. This microfibrillation effect can be achieved rapidly within ten minutes, significantly reducing the high energy consumption of traditional mechanical methods and resulting in a high yield of microfibrillated cotton fibers. Furthermore, this ternary eutectic solvent can be reused multiple times, reducing production costs. The microfibrillated cotton fibers can be used to prepare large-size, high-strength cellulose membranes, representing a potential alternative to traditional polylactic acid. Attached Figure Description

[0025] Figure 1 Time diagram of microfibrilation of cotton fibers in eutectic solvent formed by choline chloride and different types of organic acids in different proportions;

[0026] Figure 2 Timeline of microfibrilation of cotton fibers by eutectic solvents formed from choline chloride, lactic acid, and Lewis acids;

[0027] Figure 3 This is a scanning electron microscope image of the surface of raw cotton fibers;

[0028] Figure 4 Scanning electron microscope image of microfibrillated cotton fibers obtained by microfibrillation under the action of choline chloride / lactic acid / hydrated aluminum chloride;

[0029] Figure 5 Scanning electron microscope image of microfibrillated cotton fibers obtained by microfibrillation under the action of choline chloride / lactic acid / hydrated aluminum chloride;

[0030] Figure 6 The graph shows the time required for microfibrilation, the recovery rate of the eutectic solvent, and the yield of microfibrilated cotton fibers during 7 cycles of choline chloride / lactic acid / hydrated aluminum chloride.

[0031] Figure 7 The mechanical properties of cellulose membranes prepared at different microfibrillation times are shown in the figure.

[0032] Figure 8 Image of an 85×30cm cellulose membrane prepared from microfibrilated cotton fibers;

[0033] Figure 9 The graph shows the biodegradability test results of the fiber membrane prepared in Application Example 1. Detailed Implementation

[0034] This invention provides a method for preparing microfibrillated cotton fibers, comprising the following steps:

[0035] Cotton fibers and a eutectic solvent are mixed to carry out a microfibrillation reaction to obtain microfibrillated products;

[0036] The microfibrilation product was subjected to solid-liquid separation to obtain a solid and a recovered eutectic solvent.

[0037] The solid was sequentially washed with water and dried to obtain microfibrillated cotton fibers.

[0038] The eutectic solvent includes choline chloride, organic acids, and Lewis acids;

[0039] The Lewis acids include one or more of aluminum chloride, ferric chloride, calcium chloride, and magnesium chloride.

[0040] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0041] This invention involves mixing cotton fibers with a eutectic solvent to carry out a microfibrillation reaction, thereby obtaining a microfibrillated product.

[0042] In this invention, the eutectic solvent includes choline chloride, organic acids, and Lewis acids; the Lewis acids include one or more of aluminum chloride, ferric chloride, calcium chloride, and magnesium chloride, preferably aluminum chloride; the organic acids include one or more of lactic acid, malic acid, formic acid, acetic acid, propionic acid, oxalic acid, and maleic acid, preferably lactic acid.

[0043] In this invention, the molar ratio of choline chloride to organic acid is preferably 1:1 to 15, more preferably 1:5 to 10; the molar ratio of choline chloride to Lewis acid is preferably 1:0.01 to 1, more preferably 1:0.05 to 0.075.

[0044] In this invention, the method for preparing the eutectic solvent includes the following steps:

[0045] Mix choline chloride, organic acid, and Lewis acid, heat to a clear and transparent solution, seal and dry for storage.

[0046] In this invention, the heating temperature is preferably 60-100°C, more preferably 70-80°C.

[0047] In this invention, the preferred mass ratio of the cotton fiber to the volume ratio of the eutectic solvent is 1 g:(5-100) mL, more preferably 1 g:(10-25) mL.

[0048] In this invention, the temperature of the microfibrillation reaction is preferably 60-120°C, more preferably 70-90°C; the holding time of the microfibrillation reaction is preferably 3-180 min, more preferably 15-120 min; the microfibrillation reaction is preferably carried out under stirring conditions; the stirring rate is preferably 200-1000 rpm, more preferably 300-500 rpm.

[0049] In this invention, the microfibrillation reaction is carried out under heating and stirring conditions. The reaction involves both physical and chemical reactions. The physical reaction manifests as the disruption of van der Waals forces and hydrogen bonds in the cellulose chains by the eutectic solvent system; the chemical reaction may involve Al... 3+ The disruption of the β-1,4 glycosidic bonds between cellulose units is also manifested in the esterification reaction of the carboxyl group in lactic acid and the C6 hydroxyl group in cellulose.

[0050] This invention introduces a Lewis acid into a choline chloride / organic acid-based eutectic solvent, resulting in a ternary eutectic solvent with low viscosity and reduced hydrated H+ in the acidic system. + The swelling effect on cotton fibers increases the inter-fiber gaps, allowing metal cations in Lewis acids to diffuse more easily to the β-1,4 glycosidic bond positions, causing the β-1,4 glycosidic bonds to break. This enhances the microfibrillation effect on cotton fibers, achieving a rapid microfibrillation effect within ten minutes. This significantly reduces the high energy consumption of traditional mechanical methods, and the yield of microfibrillated cotton fibers is high.

[0051] After the microfibrillation reaction is completed, the product obtained from the microfibrillation reaction is preferably cooled naturally to room temperature.

[0052] After obtaining the microfibrillated product, the present invention performs solid-liquid separation to obtain a solid and recover the eutectic solvent.

[0053] In this invention, the solid-liquid separation is preferably vacuum filtration; the vacuum degree of the vacuum filtration is preferably 1 bar; the vacuum filtration time is preferably 1 to 8 hours, more preferably 2 to 5 hours; and the equipment used for the vacuum filtration is preferably a circulating water vacuum pump.

[0054] After obtaining the recovered eutectic solvent, the present invention preferably reuses the recovered eutectic solvent for the microfibrillation of cotton fibers; the number of repetitions is preferably ≥7 times, more preferably 7 times.

[0055] This invention separates microfibrillated cotton fibers and eutectic solvent through solid-liquid separation. The recovered eutectic solvent can be reused multiple times for the microfibrillation of cotton fibers.

[0056] After obtaining the solid, the present invention washes and dries the solid sequentially to obtain microfibrillated cotton fibers.

[0057] In this invention, the washing is preferably performed until the washing solution is neutral; the drying temperature is preferably 50-105°C, more preferably 60°C; and the drying is preferably performed until constant weight.

[0058] In this invention, the diameter of the microfibrillated cotton fiber is preferably 5-30 μm, more preferably 10-20 μm, and the length is preferably 50-450 μm, more preferably 150-450 μm.

[0059] This invention employs a eutectic solvent method, which can rapidly and efficiently achieve microfibrillation of cotton fibers, resulting in a high yield of microfibrillated cotton fibers. While maintaining efficient and high-yield microfibrillation, the eutectic solvent can be recycled multiple times.

[0060] This invention provides a method for preparing a cellulose membrane, comprising the following steps:

[0061] The microfibrillated cotton fibers prepared by the preparation method described above are dispersed in a mixed solution of metal hydroxide and urea. After freezing and thawing, the resulting dispersion is separated into solid and liquid phase components.

[0062] The mixture of the liquid phase component and the crosslinking agent is placed in a mold and gelled to form a cellulose hydrogel. The mixture is then washed and dried to obtain a cellulose membrane.

[0063] The present invention disperses the microfibrillated cotton fibers prepared by the preparation method described above in a mixed solution of metal hydroxide and urea. After freezing and thawing, the resulting dispersion is separated into solid and liquid phase components.

[0064] In this invention, the metal hydroxide includes one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide, more preferably sodium hydroxide; the mass ratio of the metal hydroxide to urea is preferably (1-3):(1-2), more preferably 3:2.

[0065] In this invention, the solid content of the dispersion is preferably 3-6%, more preferably 4-5%; the dispersion is preferably carried out at room temperature; the dispersion is preferably carried out by stirring; the stirring rate is preferably 200-1000 rpm, more preferably 300-550 rpm; the stirring time is preferably 1-30 min, more preferably 5-30 min.

[0066] In this invention, the freezing temperature is preferably -12 to -20°C, more preferably -10 to -18°C; the freezing time is preferably 3 to 12 hours, more preferably 4 to 8 hours.

[0067] In this invention, the thawing temperature is preferably 40-70°C, more preferably 50-60°C.

[0068] After thawing, the present invention preferably stirs the thawed mixture at room temperature; the stirring rate is preferably 200-1000 rpm, more preferably 300-900 rpm; the stirring time is preferably 0.5-2 h, more preferably 1-2 h.

[0069] In this invention, the solid-liquid separation is preferably vacuum filtration; the vacuum degree of the vacuum filtration is preferably 1 bar; the vacuum filtration time is preferably 1 to 8 hours, more preferably 3 to 8 hours; and the equipment used for the vacuum filtration is preferably a circulating water vacuum pump.

[0070] After obtaining the liquid component, the present invention places the mixture of the liquid component and the crosslinking agent in a mold, performs gelation to form a cellulose hydrogel, and then washes and dries it to obtain a cellulose membrane.

[0071] In this invention, the crosslinking agent preferably includes epichlorohydrin and / or citric acid, more preferably epichlorohydrin; the mass of the crosslinking agent is preferably 50-100% of the mass of the microfibrillated cotton fiber, more preferably 60-100%; the method for preparing the mixture of filtrate and crosslinking agent is preferably: mixing the filtrate and crosslinking agent and stirring at room temperature; the stirring rate is preferably 1000-1500 rpm, more preferably 1000-1200 rpm; the stirring time is preferably 1-3 h, more preferably 2 h.

[0072] Before preparing the mixture of the filtrate and the crosslinking agent, the present invention preferably degassing the filtrate by ultrasonication; the ultrasonication is preferably performed at room temperature; the power of the ultrasonication is preferably 40-400W, more preferably 200-400W; the duration of the ultrasonication is preferably 1-20min, more preferably 10-20min.

[0073] In this invention, the gelation temperature is preferably 60-80°C, more preferably 70-80°C; the washing is preferably performed with water; the washing is preferably performed until the washing liquid is neutral; the drying temperature is preferably 60-80°C, more preferably 70-80°C; and the drying time is preferably 1-12 hours, more preferably 5-10 hours.

[0074] The eutectic solvent used in this invention has a low viscosity, resulting in a high yield of microfibrillated cotton fibers. The eutectic solvent method can quickly and efficiently achieve the microfibrillation of cotton fibers. While maintaining efficient and high-yield microfibrillation, the eutectic solvent can be recycled ≥7 times. The prepared cellulose membrane has high mechanical properties and is a potential substitute for polylactic acid.

[0075] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0076] Example 1

[0077] (1) Preparation of eutectic solvent: choline chloride, lactic acid and hydrated aluminum chloride are mixed in a mass ratio of 1:5:0.075, heated at 80°C until a clear and transparent solution is formed, and then sealed and dried for storage.

[0078] (2) Eutectic solvent microfibrillated cotton fiber: 1.0 g of cotton fiber was mixed with 25 mL of the above eutectic solvent and reacted at 300 rpm for 15 min at 90 °C. After the reaction was completed, the mixture was naturally cooled to room temperature and vacuum filtered for 8 h using a circulating water vacuum pump (vacuum degree 1 bar) to separate the microfibrillated cotton fiber and eutectic solvent. The microfibrillated cotton fiber was washed with water until the washing liquid was neutral and then dried in an oven at 60 °C to constant weight for later use.

[0079] (3) Preparation of cellulose membrane: 8.0 g of microfibrillated cotton fibers were dispersed in a mixed solution of 200 g of sodium hydroxide and urea (mass ratio of sodium hydroxide to urea: 3:2). The solution was stirred at 550 rpm for 5 min at room temperature, then frozen at -18℃ for 8 h. The frozen cotton fiber / sodium hydroxide / urea system was thawed at 40℃ and stirred at 900 rpm for 2 h at room temperature. Vacuum filtration was then performed using a circulating water vacuum pump (vacuum degree 1 bar) for 8 h to separate insoluble impurities. The resulting filtrate was ultrasonicated at 400 W for 20 min at room temperature to remove bubbles. Then, 8.0 g of epichlorohydrin was added, and the solution was stirred at 1000 rpm for 2 h at room temperature. The mixture was then transferred to a mold and gelled at 60℃ to form a cellulose hydrogel. After washing with water until the washing solution was neutral, the membrane was dried at 80℃ for 5 h to obtain the cellulose membrane.

[0080] Example 2

[0081] (1) Eutectic solvent microfibrillated cotton fibers: 1.0 g of cotton fibers were mixed with 25 mL of the eutectic solvent prepared in Example 1 and reacted at 90 °C at 300 rpm for 15 min, 30 min, 45 min, 60 min, 120 min and 180 min respectively. After the reaction was completed, the mixture was naturally cooled to room temperature and vacuum filtered for 8 h using a circulating water vacuum pump (vacuum degree 1 bar) to separate the microfibrillated cotton fibers and the eutectic solvent. The microfibrillated cotton fibers were washed with water until the washing liquid was neutral and then dried in an oven at 60 °C to constant weight for later use.

[0082] (2) Preparation of cellulose membrane: 8.0 g of microfibrillated cotton fibers were dispersed in a mixed solution of 200 g of sodium hydroxide and urea (mass ratio of sodium hydroxide to urea: 3:2). The solution was stirred at 550 rpm for 5 min at room temperature, then frozen at -18℃ for 8 h. The frozen cotton fiber / sodium hydroxide / urea system was thawed at 40℃ and stirred at 900 rpm for 2 h at room temperature. Vacuum filtration was then performed using a circulating water vacuum pump (vacuum degree 1 bar) for 8 h to separate insoluble impurities. The resulting filtrate was ultrasonicated at 400 W for 20 min at room temperature to remove bubbles. Then, 8.0 g of epichlorohydrin was added, and the solution was stirred at 1000 rpm for 2 h at room temperature. The mixture was then transferred to a mold and gelled at 60℃ to form a cellulose hydrogel. After washing with water until the washing solution was neutral, the membrane was dried at 80℃ for 5 h to obtain the cellulose membrane.

[0083] Comparative Example 1

[0084] Qi et al.'s research team prepared cellulose nanofibers from raw cotton using the following steps: The raw cotton fibers were treated with an acidified sodium chlorite solution at 75°C for 1 hour, repeated three times to remove impurities. Then, the sample was dispersed in an 8 wt% sodium hydroxide solution at room temperature, allowed to stand overnight, and then heated at 80°C for 2 hours. After filtration, the sample was dispersed in a 1 wt% hydrochloric acid solution and heated at 80°C for 2 hours to further remove alkali-insoluble substances. The resulting cotton pulp was treated with a high-speed mixer for 4 minutes and then passed through a 300 μm sieve. This process was repeated multiple times until all the cotton pulp passed through the sieve. The supernatant was left to stand overnight, and then centrifuged, mechanically stirred for 8 hours, and ultrasonically treated for 30 minutes before cotton cellulose nanofibers could be prepared. For details, please refer to the existing technology (Qi J, Xie Y, Liang H, et al. Lightweight, Flexible, Thermally-Stable, and Thermally-Insulating Aerogels Derived from Cotton Nanofibrillated Cellulose[J].ACS Sustainable Chemistry & Engineering, 2019, 7(10): 9202-9210).

[0085] Comparative Example 2

[0086] Shao et al.'s research team prepared corn cob microcrystalline cellulose using corn cob. The specific steps were as follows: Corn cob powder was dispersed in 1M hydrochloric acid solution at a solid-liquid ratio of 1:10 and refluxed at 90℃ for 1 hour. After the reaction, the mixture was vacuum filtered, and the filter cake was washed with deionized water and ethanol until the filtrate was neutral, yielding acid-treated corn cobs. The acid-treated corn cobs were then subjected to bleaching and delignin treatment, i.e., a mixture of 10g corn cob / 2.5mL acetic acid / 1.5g sodium chlorite / 325mL deionized water was reacted at 75℃ for 1 hour, and this process was repeated three times. After cooling to room temperature, the mixture was vacuum filtered and washed with deionized water, ethanol, and acetone until the pH reached 7. The bleached corn cob residue can be freeze-dried to obtain corn cob microcrystalline cellulose, as detailed in the existing technology (Shao X, Wang J, Liu Z, et al. Preparation and Characterization of Porous Microcrystalline Cellulose from Corncob[J]. Industrial Crops and Products, 2020, 151:112457).

[0087] Performance testing

[0088] (1) The viscosity of the eutectic solvent formed by choline chloride and different types of organic acids in different ratios is shown in Table 1.

[0089] Table 1. Viscosities of eutectic solvents formed from choline chloride and different types of organic acids in different proportions.

[0090]

[0091] As shown in Table 1, the viscosity of the eutectic solvent of choline chloride / lactic acid is relatively lower than that of eutectic solvents such as oxalic acid group and citrate group, and the higher the lactic acid content, the lower the viscosity.

[0092] (2) The time required for microfibrilation of cotton fibers using eutectic solvents formed from choline chloride and different types of organic acids in varying proportions was tested, and the results are as follows: Figure 1 As shown.

[0093] Depend on Figure 1 It can be seen that the eutectic solvent formed by choline chloride / lactic acid requires a shorter microfibrillation time, and the yield of microfibrillated cotton fibers is close to 100%.

[0094] (3) The time required for the formation of microfibrillated cotton fibers by a eutectic solvent of choline chloride, lactic acid, and Lewis acid was tested, and the results are as follows: Figure 2 As shown.

[0095] Depend on Figure 2It is evident that introducing Lewis acids into choline chloride / lactic acid drastically shortens the microfibrillation time under the same reaction conditions (90℃, 1 / 25 g / mL). When the molar ratio of choline chloride:lactic acid:hydrated aluminum chloride is 1:5:0.075, the microfibrillation time is shortened, and the yield of microfibrillated cotton fibers approaches 100%.

[0096] (4) Figure 3 This is a scanning electron microscope image of the surface of raw cotton fibers. Figure 4 The image shows a scanning electron microscope (SEM) image of microfibrillated cotton fibers obtained by microfibrillation under the action of choline chloride / lactic acid / hydrated aluminum chloride. The microfibrillation reaction conditions were 90℃, 1 / 25 g / mL, and 15 min. Figure 5 The image shows a scanning electron microscope (SEM) image of microfibrillated cotton fibers obtained by microfibrillation under the action of choline chloride / lactic acid / hydrated aluminum chloride. The microfibrillation reaction conditions were 90℃, 1 / 25 g / mL, and 3.5 h.

[0097] Depend on Figures 3-5 It can be seen that the surface of raw cotton fibers is smooth and the fibers are relatively long. However, in microfibrillated cotton fibers, clear fracture cross-sections of the cotton fibers can be observed. Extending the reaction time of cotton fibers with choline chloride / lactic acid / hydrated aluminum chloride to 3.5 hours resulted in severe damage to the cotton fibers.

[0098] (5) The time required for microfibrillation, the recovery rate of the eutectic solvent, and the yield of microfibrillated cotton fibers during 7 cycles of choline chloride / lactic acid / hydrated aluminum chloride were tested. The results are as follows: Figure 6 As shown.

[0099] Depend on Figure 6 It can be seen that during 7 cycles of choline chloride / lactic acid / hydrated aluminum chloride, cotton fibers can be microfibrilized within 15 minutes, and the low eutectic solvent recovery rate is about 90%, with a yield of microfibrilized cotton fibers >95wt%.

[0100] (6) The mechanical properties of cellulose membranes prepared at different microfibrillation times were tested, and the results are shown in 7 and Table 2.

[0101] Table 2 Mechanical properties of cellulose membranes prepared at different microfibrillation times

[0102]

[0103] Depend on Figure 7 As shown in Table 2, the cellulose membrane prepared from cotton fibers microfibrilated for 30 min exhibits the best mechanical properties, with a tensile strength of 59.5 MPa, a Young's modulus of 3.6 GPa, an elongation at break of 5.3%, and a toughness of 2.3 MJ·m. -3 It is a potential alternative to polylactic acid.

[0104] (7) An 85×30cm cellulose membrane was prepared using microfibrillated cotton fibers, such as... Figure 8 As shown.

[0105] Depend on Figure 8 It is known that cotton microfibers obtained from eutectic solvents can be used to prepare large-sheet cellulose membrane materials, and have certain potential for large-scale production.

[0106] (8) The biodegradability of the fiber membrane prepared in Case 1 was tested, and the results are as follows: Figure 9 As shown.

[0107] Depend on Figure 9 It is known that the cellulose membrane prepared by this invention can be rapidly degraded.

[0108] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a cellulose membrane, characterized in that, Includes the following steps: Microfibrillated cotton fibers are dispersed in a mixed solution of metal hydroxide and urea. The resulting dispersion is then frozen and thawed, and the solid-liquid phase is separated to obtain the liquid phase component. The solid content of the dispersion is 3-6%. The metal hydroxide includes one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide. The mass ratio of the metal hydroxide to urea is (1-3):(1-2). The mixture of the liquid phase component and the crosslinking agent is placed in a mold and gelled to form a cellulose hydrogel. The mixture is then washed and dried to obtain a cellulose membrane. Before preparing the mixture of the liquid phase component and the crosslinking agent, the liquid phase component is ultrasonically degassed. The mass of the crosslinking agent is 50-100% of the mass of the microfibrillated cotton fiber. The method for preparing the microfibrillated cotton fiber includes the following steps: Cotton fibers and a eutectic solvent are mixed to carry out a microfibrillation reaction to obtain microfibrillated products; The microfibrilation product was subjected to solid-liquid separation to obtain a solid and a recovered eutectic solvent. The solid is sequentially washed with water and dried to obtain microfibrillated cotton fibers; the diameter of the microfibrillated cotton fibers is 5~30μm and the length is 50~450μm; The eutectic solvent includes choline chloride, organic acids, and Lewis acids; the mass ratio of the cotton fiber to the volume ratio of the eutectic solvent is 1 g:(5~100) mL. The Lewis acid includes one or more of aluminum chloride, ferric chloride, calcium chloride, and magnesium chloride; The organic acids include one or more of lactic acid, malic acid, formic acid, acetic acid, propionic acid, oxalic acid, and maleic acid; The molar ratio of choline chloride to organic acid is 1:1 to 15; the molar ratio of choline chloride to Lewis acid is 1:0.01 to 1. The holding time for the microfibrillation reaction is 15-60 min; the temperature for the microfibrillation reaction is 60-120℃; the microfibrillation reaction is carried out under stirring conditions; the stirring rate is 200-1000 rpm. The crosslinking agent includes epichlorohydrin and / or citric acid; The gelation temperature is 60~80℃.

2. The preparation method according to claim 1, characterized in that, The method for preparing the eutectic solvent includes the following steps: Choline chloride, organic acid, and Lewis acid are mixed and heated until clear and transparent to obtain the eutectic solvent.

3. The preparation method according to claim 2, characterized in that, The heating temperature is 60~100℃.

4. The preparation method according to claim 1, characterized in that, The freezing temperature is -12 to -20°C; the freezing time is 3 to 12 hours.

5. The preparation method according to claim 1, characterized in that, The thawing temperature is 40~70℃.

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