A method for preparing nanocellulose based on guanidinium sulfamate deep eutectic solvent

Abstract

The application discloses a method for preparing nanocellulose based on guanidinium sulfamate low eutectic solvent, and belongs to the field of modified nanocellulose materials. Firstly, in a certain temperature, water is used as a reaction medium, sodium periodate is used as an oxidant, and lithium chloride is used as a catalyst to oxidize cellulose into dialdehyde cellulose DAC. Secondly, a guanidinium sulfamate-choline chloride binary eutectic solvent or a guanidinium sulfamate-glycerol binary eutectic solvent is configured, and then DAC is added into the two kinds of eutectic solvents respectively. DAC is swollen in the two kinds of eutectic solvents and reacts with guanidinium sulfonic acid groups to graft guanidinium sulfonic acid groups. In the process, the cellulose is swollen in the solvent and the surface charge density is increased, which promotes the subsequent ultrasonic nanocrystallization process, and the guanidinium sulfonic acid group nanocellulose with high transparency and good flame retardant effect is successfully prepared. The application has the advantages of simple operation, low cost, effective reduction of energy loss in the nanocrystallization process of fibers, good flame-retardant modification effect on nanocellulose, environmental friendliness of the used eutectic solvent, and facilitation of industrial production and application of the guanidinium sulfonic acid group nanocellulose and guanidinium sulfonic acid group nanocellulose membrane.

Description

Technical Field

[0001] This invention belongs to the field of modified nanocellulose materials technology, specifically relating to a method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvents. Background Technology

[0002] With increasing environmental awareness, the replacement of traditional fossil fuels with biomass energy has become an inevitable trend. Cellulose is the most abundant biomass resource on Earth, with rich sources and wide distribution, found in plants such as wood, bamboo, cotton, and hemp, as well as some marine organisms (such as algae). Cellulose not only possesses advantages such as renewability, biocompatibility, biodegradability, and non-toxicity, but also has good mechanical properties, making it an important raw material for traditional industries such as papermaking, textiles, and pharmaceuticals. Therefore, the efficient development and utilization of renewable resources such as cellulose is of great significance for achieving sustainable development of a green economy.

[0003] Nanocellulose (NC) is a nanoscale material extracted from cellulose. It has many advantages such as being renewable, biodegradable, non-toxic, having high mechanical strength, good biocompatibility, and easy chemical modification. It has great development prospects in food packaging, electronic devices, composite materials and other fields, and has received widespread attention in recent years.

[0004] Nanocellulose is generally prepared through mechanical processing. However, due to the ordered hydrogen bond structure of cellulose, the preparation of nanocellulose through simple mechanical processing requires a large amount of energy. To further reduce energy consumption, appropriate pretreatment methods (such as chemical modification) are usually combined with mechanical processing. For example, patent CN107815908A discloses a method for preparing sisal nanocellulose. First, sisal leaves are crushed, then esterified and allowed to stand to obtain sisal leaf pulp. Then, the pulp is cooked to obtain a suspension, which is then centrifuged, sonicated, centrifuged again, and dried to obtain solid sisal nanocellulose.

[0005] Eutectic solvents (DES) are colorless and transparent liquid mixtures formed by heating hydrogen bond acceptors and donors in a certain molar ratio through hydrogen bonding. They are analogs of ionic liquids and are considered potential alternatives to traditional molecular solvents. DES not only possesses low vapor pressure, good solubility and biocompatibility, but is also inexpensive, easy to prepare, non-toxic, and environmentally friendly. DES can swell and even dissolve cellulose, making DES treatment an effective pretreatment method for preparing nanocellulose. It can both swell and dissolve cellulose, reducing the energy consumption of subsequent mechanical processing, and introduce surface functional groups to modify cellulose. The operation is simple and highly reproducible, thus showing broad application prospects. For example, patent CN115418876A discloses a method for preparing elephant grass nanocellulose using a eutectic solvent combined with ultrasound, comprising the following steps: S1: preparing a eutectic solvent by mixing choline chloride as a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond donor is selected from citric acid monohydrate and / or aluminum trichloride hexahydrate; S2: mixing elephant grass straw powder and the eutectic solvent evenly, and then obtaining cellulose residue by heat treatment, washing, and filtration; S3: bleaching, filtration, and drying the cellulose residue to obtain cellulose; S4: dispersing the cellulose in deionized water, and then obtaining elephant grass nanocellulose fibers by ultrasound, centrifugation, and freeze-drying. Summary of the Invention

[0006] To address the shortcomings of current nanocellulose methods, such as flammability and poor thermal stability, this invention provides a method for preparing thermally stable nanocellulose using guanidine aminosulfonate eutectic solvents. The method combines eutectic solvent swelling, modification pretreatment, and ultrasonic treatment with a cell disruptor to prepare nanocellulose. Compared to traditional methods, this method is simpler to operate, has lower energy consumption, less environmental pollution, and produces modified nanocellulose with excellent flame retardant properties and transparency.

[0007] To achieve the above-mentioned technical objectives, the present invention relates to a method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvents, comprising the following steps:

[0008] (1) Synthesis of dialdehyde cellulose: Cellulose was added to water and stirred, sodium periodate and lithium chloride were added, and the reaction was carried out in the dark to obtain oxidized dialdehyde cellulose;

[0009] (2) Synthesis of binary eutectic solvent: Guanidine aminosulfonate is stirred with choline chloride and glycerol respectively until a uniform and transparent liquid is formed to obtain guanidine aminosulfonate-choline chloride binary eutectic solvent or guanidine aminosulfonate-glycerol binary eutectic solvent.

[0010] (3) Modification pretreatment: Add dialdehyde cellulose to a guanidine aminosulfonate-choline chloride binary eutectic solvent or a guanidine aminosulfonate-glycerol binary eutectic solvent and react at 25-95℃ for a certain time. After the reaction is completed, wash with deionized water to obtain modified cellulose.

[0011] (4) Nanoforming treatment: The modified cellulose is diluted, then ultrasonically nanoformed, and finally the ultrasonically treated liquid is centrifuged to obtain a guanidine sulfonate nanocellulose solution.

[0012] The temperature when sodium periodate and lithium chloride are added in step (1) is 75°C and the reaction time is 3h.

[0013] The preparation method of the binary eutectic solvent in step (2) is as follows: glycerol and guanidine aminosulfonate in a molar ratio of 5 to 20:1 are stirred at 35 to 95°C until a uniform and transparent liquid is formed; choline chloride and guanidine aminosulfonate in a molar ratio of 1:0.5 to 5 are stirred at 35 to 90°C until a uniform and transparent liquid is formed. Preferably, the molar ratio of glycerol to guanidine aminosulfonate is 10:1, and the molar ratio of choline chloride to guanidine aminosulfonate is 1:2.

[0014] In step (2), the preferred temperature for forming the binary eutectic solvent is 80–90°C, more preferably 90°C, and the stirring time is 30–60 min.

[0015] Preferably, in step (3), the mass ratio of dialdehyde cellulose to binary eutectic solvent is 1% to 20%; the reaction time of dialdehyde cellulose with DES is 0.5-24h, preferably 5-60min.

[0016] Step (4) is as follows: the modified cellulose is diluted with deionized water to a concentration of 0.1-0.75 wt%, preferably 0.5 wt%, and ultrasonically treated with an ultrasonic cell disruptor equipped with a cylindrical probe. Finally, the ultrasonically treated liquid is centrifuged at 8000 rpm for 10 min to obtain a nanocellulose solution. The cylindrical probe used has a diameter of 20 mm, an amplitude of 80%, an on / off pulse of 2 / 3 s, and an ultrasonic duration of 120 min.

[0017] The guanidine sulfonate nanocellulose has flame retardancy and high transparency, and can be applied in packaging films (such as highly transparent flame retardant food packaging films), papermaking (such as flame retardant paper), and batteries (such as flame retardant films for batteries).

[0018] The beneficial effects of this invention are as follows:

[0019] (1) In this invention, cellulose is first oxidized to dialdehyde cellulose, and then the dialdehyde cellulose is added to a binary eutectic solvent containing guanidine aminosulfonate. The binary eutectic solvent not only swells the dialdehyde cellulose, but also allows the guanidine aminosulfonate in it to react with the dialdehyde cellulose and graft onto it. The binary eutectic solvent achieves aminosulfonation modification of the dialdehyde cellulose (increasing the charge density) while swelling it. The swelling effect of the two guanidine aminosulfonate binary eutectic solvents on the fiber and the increased charge density in the cellulose structure greatly reduce the energy loss of subsequent ultrasonic treatment, and successfully prepare guanidine sulfonate-based nanocellulose with good transparency and flame retardant effect.

[0020] (2) This invention is simple to operate and low in cost. The binary eutectic solvent can both swell dialdehyde cellulose and react with it. It effectively reduces the energy loss of mechanical processing during fiber nanoforming while also providing good flame retardant modification of cellulose nanofibers and exhibiting high transparency. The used binary eutectic solvent is green and environmentally friendly, recyclable, and conducive to the further industrial production and application of guanidine sulfonate nanofibers. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the reaction principle of the method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvents according to the present invention.

[0022] Figure 2 The images show the binary eutectic solvents prepared in Examples 1 and 2, where a is before mixing and b is after mixing.

[0023] Figure 3 Infrared images of bleached softwood pulp, dialdehyde cellulose, and two types of guanidine sulfonate nanocellulose prepared in Examples 1 and 2.

[0024] Figure 4 Thermogravimetric analysis of two types of guanidine sulfonate nanocellulose prepared for bleaching softwood pulp, Examples 1 and 2.

[0025] Figure 5 Transmission electron microscopy (TEM) images of the two guanidine sulfonate-based nanocelluloses prepared in Examples 1 and 2, wherein a) and b) are glycerol-guanidine aminosulfonate modified nanocellulose; and c) and d) are choline chloride-guanidine aminosulfonate modified nanocellulose.

[0026] Figure 6 The images show the optical properties of two types of guanidine sulfonate-based cellulose nanofilms. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0028] Example 1

[0029] This embodiment relates to a method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvents, comprising the following steps:

[0030] (1) Add 15g of bleached softwood pulp to 1500ml of water and stir until evenly dispersed. Then heat to 75℃, add 27g of sodium periodate and 12.3g of lithium chloride, and react in the dark for 3h. After the reaction, wash with deionized water until the conductivity drops below 50μs / cm. The resulting oxidized dialdehyde cellulose is then stored under cold storage.

[0031] (2) Mix 0.2 mol of glycerol and 0.02 mol of guanidine aminosulfonate and heat to 65°C. Stir magnetically for 30 min at a speed of 500 r / min to form a transparent eutectic solvent.

[0032] (3) Add dialdehyde cellulose to the eutectic solvent. The mass ratio of dialdehyde cellulose to the eutectic solvent is 5%. The reaction is carried out at 80°C for 10 min. After the reaction is completed, the modified cellulose is repeatedly filtered and washed with deionized water until the conductivity of the filtrate drops below 50 μs / cm. The washed modified cellulose is then stored in a refrigerator.

[0033] (4) Add the modified cellulose to deionized water and disperse it into a suspension with a concentration of 0.5wt%. Then, use an ultrasonic cell disruptor with a cylindrical probe with a diameter of 20mm to sonicate for 120min at an amplitude of 80% and an on / off pulse of 2 / 3s. Finally, centrifuge the sonicated suspension at 8000rpm for 10min to remove the super-large fibers and other impurities. The clear and transparent supernatant is the glycerol-guanidine aminosulfonate modified nanocellulose solution.

[0034] Furthermore, the dissolution temperature in step (2) can also be 35℃, 55℃, 70℃, 80℃, or 90℃. The mass ratio of dialdehyde cellulose to the ternary eutectic solvent in step (3) can also be 1%, 2%, 3%, 4%, 6%, 7%, 8%, 9%, or 10%. The concentration of the modified cellulose suspension in step (4) can also be 0.1wt%, 0.25wt%, or 0.75wt%.

[0035] Example 2

[0036] In this embodiment, choline chloride-guanidine aminosulfonate modified nanocellulose was prepared. Except for step (2), all other steps were the same as in Example 1.

[0037] (2) Mix 0.025 mol of choline chloride and 0.05 mol of guanidine aminosulfonate and heat to 65°C. Stir magnetically for 30 min at a speed of 500 r / min to form a transparent eutectic solvent.

[0038] Figure 3 The images show the infrared spectra of cellulose (bleached softwood pulp), dialdehyde cellulose, glycerol-guanidine aminosulfonate modified cellulose, and choline chloride-guanidine aminosulfonate modified cellulose in Examples 1 and 2. The images show that dialdehyde cellulose exhibits a C=O peak at 1730 nm, indicating successful preparation. Both glycerol-guanidine aminosulfonate modified cellulose and choline chloride-guanidine aminosulfonate modified cellulose show a C=N absorption peak at 1650 nm, indicating successful reaction between dialdehyde cellulose and guanidine aminosulfonate.

[0039] Figure 4 Thermogravimetric analyses (TGAs) are for cellulose (bleached softwood pulp), glycerol-guanidine aminosulfonate modified cellulose, and choline chloride-guanidine aminosulfonate modified cellulose. The TGAs show that the modified cellulose exhibits increased residual carbon after combustion, indicating a certain flame-retardant effect.

[0040] Figure 5 The images show transmission electron microscopy (TEM) images of the two types of guanidine sulfonate nanocellulose prepared in Examples 1 and 2 of this invention. As can be seen from the images, nanocellulose nanocellulose of nanoscale size was successfully prepared.

[0041] Examples 3-4

[0042] Except for the reaction temperatures in step (3), which are 65°C and 90°C respectively, Examples 3 and 4 are the same as Example 1.

[0043] Examples 5-7

[0044] Examples 5-7 are the same as Example 1 except that the reaction time in step (3) is 5 min, 30 min and 60 min respectively.

[0045] Application examples

[0046] Two modified nanocellulose solutions prepared in Examples 1 and 2 with a concentration of 1 wt% were poured into a petri dish with a diameter of 10 cm and naturally dried in a fume hood for 7 days to form a transparent nanocellulose film, which can be used as a highly transparent flame-retardant food packaging film.

[0047] Figure 6 The figures show the optical properties of nanocellulose films prepared from the two modified nanocellulose solutions used in Examples 1 and 2. As shown, both types of modified nanocellulose films exhibit excellent transmittance (above 90%) in the visible light wavelength range of 380-700 nm. Compared to films prepared using the TEMPO oxidation method with bleached softwood pulp, the films prepared by this method have a transmittance of approximately 90% at 600 nm.

Claims

1. A method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvents, characterized in that, Includes the following steps: (1) Synthesis of dialdehyde cellulose: Cellulose was added to water and stirred, sodium periodate and lithium chloride were added, and the reaction was carried out in the dark to obtain oxidized dialdehyde cellulose; (2) Synthesis of binary eutectic solvent: Guanidine aminosulfonate is stirred with choline chloride and glycerol respectively until a uniform and transparent liquid is formed to obtain guanidine aminosulfonate-choline chloride binary eutectic solvent or guanidine aminosulfonate-glycerol binary eutectic solvent. (3) Modification pretreatment: Add dialdehyde cellulose to a guanidine aminosulfonate-choline chloride binary eutectic solvent or a guanidine aminosulfonate-glycerol binary eutectic solvent and react at 25-95℃ for a certain time. After the reaction is completed, wash with deionized water to obtain modified cellulose. (4) Nanoforming treatment: The modified cellulose is diluted, then ultrasonically nanoformed, and finally the ultrasonically treated liquid is centrifuged to obtain a guanidine sulfonate nanocellulose solution.

2. The method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvent according to claim 1, characterized in that, The temperature when sodium periodate and lithium chloride are added in step (1) is 75°C and the reaction time is 3h.

3. The method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvent according to claim 1, characterized in that, The preparation method of the binary eutectic solvent in step (2) is as follows: stir glycerol and guanidine aminosulfonate in a molar ratio of 5 to 20:1 at 35 to 95°C until a uniform and transparent liquid is formed; stir choline chloride and guanidine aminosulfonate in a molar ratio of 1:0.5 to 5 at 35 to 90°C until a uniform and transparent liquid is formed.

4. The method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvent according to claim 1, characterized in that, In step (2), the temperature conditions for the formation of the binary eutectic solvent are 80-90℃ and the stirring time is 30-60min.

5. The method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvent according to claim 1, characterized in that, In step (3), the mass ratio of dialdehyde cellulose to binary eutectic solvent is 1% to 20%.

6. The method for preparing nanocellulose based on guanidine aminosulfonate eutectic solvent according to claim 1, characterized in that, Step (4): The modified cellulose was diluted with deionized water to a concentration of 0.1-0.75 wt%, and ultrasonically treated with an ultrasonic cell disruptor equipped with a cylindrical probe. Finally, the ultrasonically treated liquid was centrifuged at 8000 rpm for 10 min to obtain a nanocellulose solution. The cylindrical probe used had a diameter of 20 mm, an amplitude of 80%, an on / off pulse of 2 / 3 s, and an ultrasonic duration of 120 min.

7. The guanidine sulfonate nanocellulose prepared by any one of claims 1-6.

8. The application of the guanidine sulfonate nanocellulose of claim 7 in packaging films, flame-retardant paper and flame-retardant films for batteries.

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