Cellulose nanofibril and green preparation method and application thereof

Abstract

This invention discloses a plant-based cellulose nanofiber, its green preparation method, and its application, belonging to the field of biomass cellulose nanofiber preparation technology. The cellulose nanofiber is obtained by pretreating plant raw materials with a eutectic solvent and Fenton's reagent, followed by high-intensity ultrasonic treatment. The plant-based cellulose nanofiber has a surface carboxyl group content >0.4 mmol / g and a crystallinity >50%. The zeta potential of the plant-based cellulose nanofiber suspension is <-35 mV. The cellulose nanofiber prepared by this invention has a high surface carboxyl group content and can increase crystallinity by more than 3 times. When applied to nanofiber films, it can significantly increase the mechanical properties of the films and impart good water stability and biodegradability. The preparation method is simple, easy to implement, and uses mild reaction conditions. The eutectic solvent used is environmentally friendly and can be reused more than 7 times after simple recycling, enabling continuous industrial production with low production input.

Description

Technical Field

[0001] This invention belongs to the field of biopolymer materials technology, specifically relating to a cellulose nanofiber and its green preparation method and application. Background Technology

[0002] With the continuous and rapid development of society and the economy, the problem of increasingly scarce fossil energy has become increasingly prominent. Therefore, there is an urgent need to develop renewable and biodegradable sustainable materials to alleviate the current environmental and energy crisis. Wheat bran, a byproduct of wheat processing, is rich in cellulose. However, it is currently mainly used as animal feed or rural fuel, resulting in low added value and significant resource waste. Therefore, realizing the effective utilization of wheat bran and increasing its added value is of great significance for alleviating environmental problems and improving economic efficiency. Cellulose is the most abundant natural polymer in nature, widely found in plant cell walls. Due to its abundant source, low price, renewable nature, and biodegradability and biocompatibility, cellulose is widely used in materials, chemicals, food, medicine, and environmental fields.

[0003] Cellulose nanofibers (CNF), obtained through physical or chemical treatment of cellulose, are filamentous nanocellulose fibers typically prepared from wood or other plant fibers via mechanical or combined chemical and mechanical processes. These fibers have diameters in the nanometer range and lengths in the micrometer range. Nanocellulose has a wide range of raw material sources, including wood, agricultural byproducts, and waste paper, all rich in cellulose. It possesses advantages such as high surface area, high aspect ratio, high Young's modulus, high strength, and biodegradability. These properties enable it to impart novel properties to materials, leading to its wide application in food packaging, coatings, papermaking, 3D printing, cosmetics, polymer reinforcement, and other emerging functional materials.

[0004] There are many methods for preparing CNFs, with physical methods being the most common, involving the mechanical treatment of cellulose into fibrils. However, mechanical methods are energy-intensive, and the resulting CNFs exhibit uneven particle size and poor dispersibility. To address this, scholars both domestically and internationally have developed a series of chemical or biological pretreatment methods, including TEMPO catalytic oxidation, carboxymethylation, and enzymatic hydrolysis. However, these methods still present several problems: enzymatic hydrolysis requires a long time and involves expensive enzymes; the catalysts used in TEMPO catalysis are expensive and difficult to recycle; and the carboxymethylation method requires large amounts of organic reagents, which can easily pollute the environment.

[0005] Therefore, developing a plant-based nanocellulose filament and its green preparation method is of great significance for alleviating environmental pollution and the energy crisis. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a cellulose nanofiber.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: the nanocellulose filaments are obtained by pretreating plant raw materials with a eutectic solvent and Fenton's reagent, followed by high-intensity ultrasonic treatment, wherein:

[0010] (i) The carboxyl group content on the surface of the plant-based nanocellulose filaments is >0.4 mmol / g;

[0011] (ii) The crystallinity of the plant-based nanocellulose filaments is >50%;

[0012] (iii) The zeta potential of the plant-based nanocellulose filament suspension is < -35mV.

[0013] Another objective of this invention is to overcome the shortcomings of the prior art and provide a green method for preparing cellulose nanofibers.

[0014] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0015] Plant-based raw materials, after removing lipids and starch, were added to a eutectic solvent and Fenton's reagent, stirred at 80°C, and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then sonicated in an ice bath at 0°C to obtain plant-based cellulose nanofibers.

[0016] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the eutectic solvent is a mixture of oxalic acid and choline chloride, wherein the molar ratio of oxalic acid to choline chloride is 1:1 to 3.

[0017] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the ratio of the plant raw material to the eutectic solvent is 1:10 to 100.

[0018] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the Fenton reagent is composed of H2O2 and FeSO4·7H2O, and 0.25–1 mmol of H2O2 and 0.45–1.8 μmol of FeSO4·7H2O are added per 1 g of eutectic solvent.

[0019] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the heating is performed in an oil bath at 80–90°C.

[0020] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the stirring time is 2-3 hours.

[0021] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the ultrasonic power is 300W, the frequency is 20kHz, and the ultrasonic intensity is 10W / mL.

[0022] In a preferred embodiment of the green preparation method of plant-based nanocellulose filaments described in this invention, the ultrasonic time lasts for 10 to 30 minutes, with a 1-second interval between every 2 seconds of ultrasonication.

[0023] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of cellulose nanofibers in the preparation of biodegradable nanocellulose films.

[0024] Beneficial effects of this invention:

[0025] (1) The nanocellulose filaments prepared by this invention have a surface carboxyl content >0.4mmol / g and a crystallinity more than 3 times that of the raw material. They have good thermal stability and dispersibility, and the suspension has a zeta potential <-35mV, indicating extremely high stability.

[0026] (2) The nanocellulose filaments prepared by this invention, when applied to nanocellulose films, can significantly improve the mechanical properties of the films, such as elongation at break, and can also impart good water stability and biodegradability to the films, enabling them to degrade naturally in soil, thus serving as an environmentally friendly material. This provides a theoretical basis for the high-value-added development and utilization of wheat bran.

[0027] (3) Compared with traditional enzyme hydrolysis pretreatment, inorganic acid hydrolysis pretreatment, carboxymethylation pretreatment and TEMPO catalytic oxidation pretreatment, this invention has a shorter time consumption, no large amount of waste liquid production, low eutectic solvent is green and environmentally friendly and can be recovered by rotary evaporation and other methods. While ensuring the effect, it can be recycled more than 7 times, which is environmentally friendly, meets the production standards of green chemistry, and has good practical application value. Compared with mechanical pretreatment, it saves energy and reduces consumption and the obtained CNFs products have excellent properties. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0029] Figure 1 These are WB and CNF scanning electron microscope images from an embodiment of the present invention.

[0030] Figure 2 These are WB and CNF thermogravimetric spectra used in this invention.

[0031] Figure 3 These are WB and CNF nuclear magnetic resonance spectra in an embodiment of the present invention.

[0032] Figure 4 This is a graph showing the reuse rate of the eutectic solvent in the implementation of this invention.

[0033] Figure 5 This is a diagram showing the tensile properties of films with different CNF contents in this invention.

[0034] Figure 6 This is a diagram showing the water stability of different CNF films in the embodiments of the present invention.

[0035] Figure 7 This is a diagram showing the biodegradability of different CNF films in this invention. Detailed Implementation

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0037] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0038] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0039] The plant-based raw material wheat bran used in this invention was purchased from Shangqiu Fuxinkang Flour Industry Co., Ltd.

[0040] The steps of removing lipids and starch from plant materials in this invention are as follows:

[0041] 1) After washing and removing dust and impurities, the wheat bran is passed through a 40-mesh sieve and then magnetically stirred with anhydrous ethanol for 12 hours. It is then air-dried to remove grease.

[0042] 2) Remove starch from dried wheat bran by mechanically stirring at 70°C for 1 hour with 0.6% (w / v) α-amylase.

[0043] The Malvern Zeta potentiometer used in this invention is model ZetasizerAdvance, manufactured by Malvern Panaco Ltd. in the United Kingdom.

[0044] The automatic potentiometric titrator used in this invention is model AT510, manufactured by Kyoto Electronics Co., Ltd. of Japan.

[0045] Unless otherwise specified, all raw materials used in this invention are commercially available in the field.

[0046] Example 1

[0047] This embodiment provides a method for preparing plant-based cellulose nanofibers, specifically as follows:

[0048] 1) Mix oxalic acid and choline chloride in a molar ratio of 1:1 and heat in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0049] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. 0.25 mmol of H2O2 and 0.45 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath with an ultrasonic power of 300 W, a frequency of 20 kHz, an ultrasonic intensity of 10 W / mL, an ultrasonic treatment time of 2 s followed by a 1 s interval, and an ultrasonic treatment time of 20 min. Cellulose nanofibers that can be stably dispersed in aqueous solution were obtained and named CNF-0.45 after freeze-drying.

[0050] Example 2

[0051] The difference between this embodiment and Embodiment 1 is that the amount of Fenton's reagent is adjusted, specifically:

[0052] 1) Mix oxalic acid and choline chloride in a molar ratio of 1:1 and heat in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0053] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. 1 mmol of H2O2 and 1.8 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment time lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-1.8 after freeze-drying.

[0054] Example 3

[0055] The difference between this embodiment and Embodiment 1 is that the amount of Fenton's reagent is adjusted, specifically:

[0056] 1) Mix oxalic acid and choline chloride in a molar ratio of 1:1 and heat in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0057] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. 0.5 mmol of H2O2 and 0.9 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-1:1 after freeze-drying.

[0058] Example 4

[0059] The difference between this embodiment and Embodiment 1 is that the amount of Fenton's reagent is adjusted, specifically:

[0060] 1) Mix oxalic acid and choline chloride in a molar ratio of 1:1 and heat in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0061] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. 0.75 mmol of H2O2 and 1.35 μmol of FeSO4·7H2O were added per 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath with an ultrasonic power of 300 W, a frequency of 20 kHz, an ultrasonic intensity of 10 W / mL, an ultrasonic treatment time of 2 s followed by a 1 s interval, and an ultrasonic treatment time of 20 min. Cellulose nanofibers that can be stably dispersed in aqueous solution were obtained and named CNF-1.35 after freeze-drying.

[0062] Comparative Example 1

[0063] Comparative Example 1 is based on Example 1, but differs from Example 1 in that oxalic acid and choline chloride are not added. Specifically:

[0064] Wheat bran, after removing lipids and starch, was added to deionized water at a material-to-liquid ratio of 1:50. 0.5 mmol of H₂O₂ and 0.9 μmol of FeSO₄·7H₂O were added to every 1 g of deionized water. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath at a power of 300 W, a frequency of 20 kHz, an intensity of 10 W / mL, a duration of 2 s with a 1 s interval, and a duration of 20 min. This yielded cellulose nanofibers that could be stably dispersed in aqueous solution, which were then freeze-dried and named CNF-Fenton.

[0065] Comparative Example 2

[0066] Comparative Example 2 is based on Example 1. The difference between Comparative Example 2 and Example 1 is that Fenton's reagent is not added. Specifically:

[0067] 1) Mix oxalic acid and choline chloride in a molar ratio of 1:1 and heat in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0068] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. After stirring at 100℃ for 2.5h, the mixture was centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath with an ultrasonic power of 300W, a frequency of 20kHz, an ultrasonic intensity of 10W / mL, an ultrasonic treatment time of 2s followed by a 1s interval, and an ultrasonic treatment time of 20min. Cellulose nanofibers that can be stably dispersed in aqueous solution were obtained and freeze-dried and named CNF-DES.

[0069] Comparative Example 3

[0070] Comparative Example 3 is based on Example 1. The difference between Comparative Example 3 and Example 1 is that the molar ratio of oxalic acid and choline chloride is adjusted, specifically:

[0071] 1) Oxalic acid and choline chloride are mixed in a molar ratio of 2:1 and heated in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0072] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. 0.5 mmol of H2O2 and 0.9 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-2:1 after freeze-drying.

[0073] Comparative Example 4

[0074] Comparative Example 4 is based on Example 1. The difference between Comparative Example 4 and Example 1 is that the molar ratio of oxalic acid and choline chloride and the solid-liquid ratio are adjusted, specifically:

[0075] 1) Oxalic acid and choline chloride are mixed in a molar ratio of 2:1 and heated in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0076] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:25. 0.5 mmol of H2O2 and 0.9 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-1:25 after freeze-drying.

[0077] Comparative Example 5

[0078] Comparative Example 5 is based on Example 1. The difference between Comparative Example 5 and Example 1 is that the molar ratio of oxalic acid and choline chloride and the solid-liquid ratio are adjusted, specifically:

[0079] 1) Oxalic acid and choline chloride are mixed in a molar ratio of 2:1 and heated in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0080] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:10. 0.5 mmol of H2O2 and 0.9 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-1:10 after freeze-drying.

[0081] Comparative Example 6

[0082] Comparative Example 6 is based on Example 1. The difference between Comparative Example 6 and Example 1 is that the molar ratio of oxalic acid and choline chloride is adjusted, specifically:

[0083] 1) Oxalic acid and choline chloride are mixed in a molar ratio of 3:1 and heated in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0084] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:50. 0.5 mmol of H2O2 and 0.9 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-3:1 after freeze-drying.

[0085] Comparative Example 7

[0086] Comparative Example 7 is based on Example 1. The difference between Comparative Example 7 and Example 1 is that the molar ratio of oxalic acid and choline chloride and the solid-liquid ratio are adjusted, specifically:

[0087] 1) Oxalic acid and choline chloride are mixed in a molar ratio of 2:1 and heated in an oil bath at 80°C to form a colorless and transparent liquid, thus obtaining a eutectic solvent;

[0088] 2) Wheat bran, after removing lipids and starch, was added to a eutectic solvent at a material-to-liquid ratio of 1:100. 0.5 mmol of H2O2 and 0.9 μmol of FeSO4·7H2O were added to each 1 g of eutectic solvent. The mixture was stirred at 100 °C for 2.5 h and then centrifuged. The precipitate was then washed with deionized water to bring the pH to 7. The precipitate was then subjected to ultrasonic treatment in an ice bath. The ultrasonic power was 300 W, the frequency was 20 kHz, the ultrasonic intensity was 10 W / mL, the ultrasonic treatment lasted for 2 s with a 1 s interval, and the ultrasonic treatment lasted for 20 min. Cellulose nanofibers that could be stably dispersed in aqueous solution were obtained and named CNF-1:100 after freeze-drying.

[0089] Performance testing

[0090] The freeze-dried raw material wheat bran (WB) and the plant-based nanocellulose filaments obtained in Examples 1-4 and Comparative Examples 1-7 were analyzed as follows:

[0091] Dynamic light scattering of CNF suspensions prepared under different treatment conditions was performed using a laser light scattering instrument. The scattering angle was measured at 90° and the working wavelength was 532 nm. The average particle size of the samples was obtained by multiple measurements.

[0092] The zeta potential of CNF prepared under different treatment conditions was measured using a Malvern zeta potential meter with water as the dispersant. The measurements were repeated three times and the average value was taken.

[0093] The carboxyl content of CNF was quantitatively determined by conductive titration using an automated potentiometric titrator. 0.1 mol / L hydrochloric acid and 1 mmol / L sodium chloride solution were added to the 1% concentration sample, and the solution was fully protonated.

[0094]

[0095] Surface functional groups. Then, the sample was titrated with 0.1 mol / L sodium hydroxide and the change in conductivity was recorded. The calculation formula is as follows:

[0096] In the formula:

[0097] (V2–V1) — Volume of sodium hydroxide solution consumed to neutralize the carboxyl group, mL

[0098] Dry weight of M-CNF sample, g

[0099] C—Sodium hydroxide solution concentration, mol / L

[0100] The changes in WB and CNF particle size, zeta potential, and carboxyl content are shown in Table 1.

[0101] Table 1. Changes in WB and CNF particle size, zeta potential, and carboxyl content.

[0102]

[0103] Note: Data are expressed as mean ± standard deviation. Different lowercase letters indicate significant differences between numbers in the same column, p < 0.05.

[0104] Appearance and morphology:

[0105] The morphology of cellulose nanofibers was observed using scanning electron microscopy. The cross-section of the freeze-dried hydrogel sample was rapidly cut with a knife, then adhered to the conductive adhesive on the stage, and platinum was sprayed three times at 30 Pa pressure for 60 s each time to avoid charging effects. The diameter distribution of more than 150 CNFs was analyzed using ImageJ software.

[0106] Figure 1 These are scanning electron microscope images of WB and CNF.

[0107] Depend on Figure 1 It can be seen that the surface of raw material WB is a rough sheet-like structure, while CNF obtained after treatment with eutectic solvent and Fenton reagent is a long fibrous structure. CNF treated with eutectic solvent alone has a smooth surface but uneven thickness, while CNF treated with Fenton reagent alone has a rough surface and a larger diameter. This is because the single reagent has a low degree of cellulose stripping and a weak ability to further cellulose fibrillation.

[0108] Thermal stability analysis:

[0109] Thermogravimetric analysis (TGA) was used to characterize the thermal stability of freeze-dried WB and CNF samples. 3-5 mg of sample was placed in an Al2O3 crucible and subjected to thermal degradation weight loss analysis under a nitrogen atmosphere of 0.1 MPa. The heating rate was 10 °C / min, and the degradation temperature range was 25 °C to 600 °C. The thermogravimetric parameters are shown in Table 2.

[0110] Table 2

[0111]

[0112] Figure 2 Thermogravimetric spectra of WB and CNF are TGA(a) and DTG(b).

[0113] From Table 1 and Figure 2 It can be seen that, except for the CNF prepared by the Fenton treatment alone, the Tmax of CNF obtained after different treatments is above 300℃ and the thermal stability of the obtained CNF is better than that of the raw material WB, indicating that the prepared CNF has good thermal stability.

[0114] Crystallinity analysis:

[0115] Weigh 7% sodium hydroxide and 12% urea into 0.5 mL of deuterium water. Cool the mixture to -20°C and add 10 mg of CNF sample. Shake vigorously until the solution becomes transparent and the sample is completely dissolved. Then add the solution into an NMR tube with a diameter of 5 mm and a length of 18 cm. Measure and analyze the sample using an AVANCE III NMR spectrometer.

[0116] Figure 3 X-ray diffraction patterns (a) and corresponding crystallographic patterns (b) of WB and CNF.

[0117] Depend on Figure 3 As shown in Figure (a), both WB and CNF exhibited typical X-ray diffraction characteristic peaks of cellulose Iβ on the 110 (14.7°) and 200 (22.1°) crystal planes, indicating that CNF treated with DES-Fenton did not destroy the cellulose Iβ structure. As shown in Figure (b), the crystallinity of the samples treated with DES-Fenton increased, more than three times that of the raw material (15.39%).

[0118] Analysis of the reusability of eutectic solvents

[0119] The eutectic solvent was obtained by centrifugation (3500 rpm, 10 min), and the supernatant was thoroughly dried using a vacuum rotary evaporator at 60 °C. The resulting solution was used to prepare CNF again, and the particle size and yield were determined, and the reusability of the solvent was analyzed.

[0120] Table 3 Preparation of CNF by Reusing Eutectic Solvents

[0121]

[0122] Note: Data are expressed as mean ± standard deviation. Different lowercase letters indicate significant differences between numbers in the same column, p < 0.05.

[0123] Figure 4 This is a graph showing the overlap utilization rate of eutectic solvents.

[0124] From Table 3 and Figure 4It was found that the yield of CNF obtained by repeated WB treatment with the eutectic solvent after recycling remained largely unchanged after 8 cycles, while the particle size significantly increased from 457.1±20.62 nm to 686.4±83.16 nm. The CNF prepared by solvent reuse in the 9th and 10th cycles showed smaller particle sizes, which may be related to lignin's ability to promote fibrillation. Repeated use of the eutectic solvent system reduced the effectiveness of subsequent treatments, leading to increased residual lignin and hemicellulose. Lignin, as a known antioxidant, can stabilize cellulose free radicals formed during mechanical processing. Cellulose free radicals exhibit strong reactivity in recombination reactions; at higher lignin contents, lignin's free radical scavenging ability leads to less pronounced cellulose cross-linking, making cellulose more prone to decomposition and resulting in a smaller particle size. Therefore, DES can be reused at least 7 times to prepare CNF after recycling.

[0125] Example 5

[0126] This embodiment provides an application of plant-based nanocellulose filaments in the preparation of biodegradable nanocellulose films, specifically:

[0127] Different volumes of the prepared CNF suspension were taken and filtered through a 0.22 μm pore size filter membrane using a vacuum filtration method. When the water in the dispersion was basically filtered out, the filter membrane was removed and dried at room temperature to obtain nanocellulose films with different CNF contents.

[0128] Application characteristics in biodegradable cellulose nanofilms

[0129] Tensile strength and elongation at break of nanocellulose films

[0130] The tensile properties of the film were determined at room temperature using an electronic testing machine. The samples were cut into uniform, regular sizes (30 mm × 5 mm), and stretched at a constant speed of 5 mm / min until fracture. The tensile strength and elongation at break of the film were then measured.

[0131] Figure 5 The tensile properties of films with different CNF contents are shown in the figure.

[0132] Depend on Figure 5 It can be seen that the tensile stress and tensile strain of the film change with increasing CNF content. The ordered arrangement of CNF and the network structure of the film enhance the interaction between filaments, thus improving the mechanical properties of the film with increasing CNF content for the same surface area. Under external force, the film converts the work done by the external force into elastic potential energy. With increasing CNF content, the elastic potential energy increases, thereby increasing the elongation at break of the nanocellulose film.

[0133] Water stability of nanocellulose films

[0134] In the water stability test, ordinary filter paper was used as a control. The nanocellulose film was immersed in water at room temperature and its changes were observed periodically.

[0135] Figure 6 The water stability diagrams for different CNF films are shown.

[0136] Figure 6 The stability of ordinary filter paper and cellulose nanofilms with different CNF contents in water was compared. As shown in the figure, after immersion in water for 90 days, the filter paper exhibited delamination and degradation. In contrast, the cellulose nanofilms maintained good stability in the humid environment, retaining their original shape without delamination or breakage.

[0137] Biodegradability of cellulose nanofilms

[0138] In the soil degradation experiment, natural soil was randomly selected from the campus, and the nanocellulose film was buried 5 cm deep in the soil to test its degradation in the soil. Polyvinyl chloride (PVC) film was used as a control. The samples were taken out periodically under room temperature and humidity conditions to observe the changes.

[0139] Figure 7 The biodegradability of different CNF films.

[0140] Depend on Figure 7 It is evident that the degradation time increases with increasing CNF content. After 105 days of natural degradation in soil, all films were completely degraded. In contrast, PVC films maintained their original shape without any change within the same timeframe, indicating that PVC products are difficult to degrade under natural conditions and easily impose a long-term burden on the environment. The combined water stability results of the films demonstrate that CNF films possess good biodegradability, providing a theoretical reference for the development of next-generation sustainable biodegradable products.

[0141] In summary, the surface carboxyl content of the nanocellulose filaments prepared by this invention can be increased by 40%, the crystallinity is more than 3 times that of the raw material, and it has good thermal stability and dispersibility. The zeta potential of the suspension is <-35mV, indicating extremely high stability.

[0142] The nanocellulose filaments prepared by this invention, when applied to nanocellulose films, can significantly improve the mechanical properties of the films, such as elongation at break. Furthermore, they impart good water stability and biodegradability, enabling the films to degrade naturally in soil, thus serving as an environmentally friendly material. This provides a theoretical basis for the high-value-added development and utilization of wheat bran.

[0143] Compared with traditional enzymatic hydrolysis pretreatment, inorganic acid hydrolysis pretreatment, carboxymethylation pretreatment, and TEMPO catalytic oxidation pretreatment, this invention is less time-consuming, produces no large amount of waste liquid, uses low eutectic solvents that are environmentally friendly and can be recovered by methods such as rotary evaporation, and can be recycled more than 7 times while ensuring effectiveness. It is environmentally friendly, meets the production standards of green chemistry, and has good practical application value. Compared with mechanical pretreatment, it saves energy and reduces consumption, and the obtained CNFs products have excellent properties.

[0144] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A plant-based nanocellulose filament, characterized in that: The plant-based nanocellulose filaments are obtained by pretreating wheat bran with a eutectic solvent and Fenton's reagent, followed by high-intensity ultrasonic treatment, wherein: (i) The carboxyl group content on the surface of the plant-based nanocellulose filaments is >0.4 mmol / g; (ii) The crystallinity of the plant-based nanocellulose filaments is >50%; (iii) The zeta potential of the plant-based nanocellulose filament suspension is < -35mV; The green preparation method of the plant-based nanocellulose filaments is characterized by comprising: Wheat bran, after removing lipids and starch, was added to a eutectic solvent and Fenton's reagent. After stirring at 80°C, it was centrifuged. The precipitate was then washed with deionized water to make the pH 7. The precipitate was then sonicated in an ice bath at 0°C to obtain plant-based nanocellulose filaments. The ratio of wheat bran to eutectic solvent is 1:10~50; The Fenton reagent is composed of H2O2 and FeSO4·7H2O. For every 1g of eutectic solvent, 0.25-1mmol of H2O2 and 0.9-1.8μmol of FeSO4·7H2O need to be added. The ultrasonic power is 300W, the frequency is 20kHz, and the ultrasonic intensity is 10W / mL. The ultrasound duration is 10-30 minutes, with a 1-second pause between every 2 seconds of ultrasound. The eutectic solvent is a mixture of oxalic acid and choline chloride, wherein the molar ratio of oxalic acid to choline chloride is 1:

1.

2. The plant-based nanocellulose filament according to claim 1, characterized in that: The stirring time is 2-3 hours.

3. The application of plant-based nanocellulose filaments as described in any one of claims 1 or 2 in the preparation of biodegradable nanocellulose films.

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