Green and Low-Energy Preparation Method for Cellulose Nanofibers Based on Cold Plasma
The cold plasma and FeSO4 catalyst method effectively addresses the inefficiencies of existing CNF production by providing a green and low-energy process for producing CNFs with high yield and tunable properties, overcoming energy and environmental challenges.
Patent Information
- Application Number
- US18/703478
- Authority / Receiving Office
- US · United States
- Patent Type
- Applications(United States)
- Current Assignee / Owner
- Priority Date
- 2021-12-02
- Filing Date
- 2022-09-30
- Publication Date
- 2026-02-26
AI Technical Summary
Existing methods for preparing cellulose nanofibers (CNFs) face high energy consumption, chemical toxicity, and environmental pollution, limiting their widespread application due to high costs and inefficiencies.
A green and low-energy method using cold plasma and a FeSO4 catalyst to oxidize cellulose, followed by mechanical fibrillation, which forms a high-oxidizing environment to weaken the cellulose structure and produce CNFs without harmful chemicals.
The method achieves efficient, low-energy, and environmentally friendly production of CNFs with high yield and tunable properties, reducing energy consumption and chemical use while maintaining high oxidation rates.
Smart Images
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Abstract
Description
TECHNICAL FIELD
[0001] The present disclosure relates to the field of cellulose nanofibers (CNFs), and particularly to a green and low-energy preparation method for CNFs based on cold plasma.BACKGROUND
[0002] CNFs are a kind of nano-scale cellulose fiber isolated from cellulose, with a diameter of approximately 5-50 nm and a length reaching the micron scale, which represent an emerging star material in the cellulose family. Due to their unique properties such as a large surface area and good mechanical performance, biocompatibility, and biodegradability, CNFs have received extensive attention from academia and industry, and are widely used as nano-fillers, coatings, or membrane materials in food packaging, nanocomposite reinforcement, biomimetic materials, and flexible electronic devices. Nowadays, the energy crisis has become increasingly severe, and the demand for sustainable green development is rising. As a renewable and high value-added natural resource, the application research of CNFs holds great significance in promoting the development of green chemistry and the innovation and research of new materials.SUMMARYTechnical Problems
[0003] Currently, CNFs are mainly prepared by methods such as mechanical shearing treatment (high-pressure homogenization, micro-fluidization, grinding, and ultrasonic treatment), chemical pretreatment in combination with mechanical treatment, etc. However, the problems such as high energy consumption, high costs, high consumption of chemical reagents, and wastewater pollution existing in these preparation methods have become bottlenecks for the further development of CNFs. For example, the energy demand in the mechanical method is 30,000-70,000 kWh / t. In chemical modification, the demand for chemicals per ton of raw material can reach several hundred kilograms, and most of them are non-environment-friendly chemicals. For example, the classic TEMPO oxidation method may involve the use of significant amount of environmentally harmful halogen-containing compounds such as sodium bromide and sodium hypochlorite, and the TEMPO compounds are expensive. Although the “Manufacturing Method for CNFs” disclosed in the Chinese patent application 201880025169.9 has made improvements based on the classic TEMPO oxidation method to ensure that N-oxy compounds such as TEMPO do not remain in the CNFs, environmentally harmful compounds such as hypochlorous acid or sodium hypochlorite are still extensively used during the preparation of the CNFs. In addition, the “Preparation Method for CNFs with Low Energy Consumption” disclosed in Chinese patent ZL201710534501.1 can obtain CNFs in one step without any form of mechanical dispersion. However, during this method, in the early stage, the raw materials for cellulose need to be subjected to mechanical defibration; and in the later stage, maleic anhydride with acute toxicity and pollution, expensive ionic liquids, and various organic solvents such as dimethyl sulfoxide, N,N-dimethyl formamide, and N,N-dimethyl acetamide are needed for preparation. Moreover, the Chinese patent application with application number 202011083783.6 discloses “Plant CNFs and Green Preparation Method therefor”, which does not involve the use of toxic or harmful reagents, making it environmentally friendly, safe, and energy-efficient. However, the method requires a ball-milling treatment lasting for 0.5-3 hours in the early stage, followed by enzymatic hydrolysis in a reaction kettle at 45-55° C. for 2-3 hours, enzyme inactivation at a high temperature of 121° C. for 10-20 minutes, and finally, nanocrystallization through mechanical treatment. The whole process is time consuming and requires high temperatures, and the enzyme is expensive. Therefore, it is urgent to develop a more green, efficient, and low-cost CNF separation technology to solve the existing bottlenecks and realize the further wide application of CNFs.
[0004] Low-temperature plasma technology is low-temperature, non-toxic, low-cost, easy-to-handle, flexible, and effective technology that may use air as the working gas. Plasma is a collection consisting of active particles such as electrons, photons, atoms, radicals, positive and negative ions, and excited or non-excited molecules, which is called the fourth state of matter. There exist a variety of elementary processes and interactions between the plasma and solid or liquid surfaces in the plasma system, with unique physical properties such as light, heat, and electricity, which may generate a variety of physical and chemical processes to form active oxidation systems, such as hydroxyl radicals (·OH), singlet oxygen (·1O2), superoxide anion (·O2−), and hydrogen peroxide (H2O2). In addition, etching phenomena caused by bombarding the surface of the material with plasma-generated energetic particles may increase the accessibility of the material. However, the green and low-energy method for preparing CNFs by using a cold plasma composite catalyst to construct a high-oxidation environment has not been reported.Technical Solution
[0005] In view of the above shortcomings and deficiencies existing in prior art, an object of the present disclosure is to provide a green and low-energy preparation method for CNFs based on cold plasma, which is a breakthrough to the existing CNF preparation technology and solves the bottlenecks existing in prior art.
[0006] The object of the present disclosure is achieved by the following technical solution.
[0007] A green and low-energy preparation method for CNFs based on cold plasma is provided, including the following steps:
[0008] (1) uniformly mixing cellulose with a FeSO4 solution, so that FeSO4 is immersed to the cellulose into the cellulose, and then performing cold plasma treatment under atmospheric-pressure air to obtain oxidized cellulose; and
[0009] (2) washing the oxidized cellulose obtained in step (1), and carrying out suction filtration and mechanical fibrillation treatment to obtain the CNFs.
[0010] Preferably, water in the FeSO4 solution in step (1) is subjected to cold plasma treatment.
[0011] Preferably, the preparation of the FeSO4 solution in step (1) includes the following steps:
[0012] treating deionized water with the cold plasma under the atmospheric-pressure air, and then dissolving a FeSO4 catalyst into the deionized water to obtain the FeSO4 solution.
[0013] Preferably, the cold plasma treats the deionized water at an operating voltage of 120-160 kV for 1-5 min.
[0014] Preferably, in step (1), the cold plasma treats the cellulose at an operating voltage of 120-160 kV for 45-90 min.
[0015] Preferably, a mass ratio of FeSO4 to the cellulose in step (1) is 1-4:100.
[0016] Preferably, in step (1), the cold plasma treats the cellulose at an operating voltage of 120-140 kV for 60-90 min; and a mass ratio of FeSO4 to the cellulose is 3-4:100.
[0017] Preferably, a concentration of FeSO4 in the FeSO4 solution in step (1) is 0.1 wt %-0.4 wt %.
[0018] Preferably, a solid-to-liquid ratio of the cellulose to the FeSO4 solution in step (1) is 1 g: 10 mL.
[0019] Preferably, a mixing time in step (1) is 10-20 min.
[0020] Preferably, in step (2), the oxidized cellulose is treated under an ultrasonic condition of 600 W at a concentration of 0.5 wt %-2 wt % for 90 min to obtain the CNFs.
[0021] The mechanism of the present disclosure is as follows.
[0022] The cold plasma may form active oxidation systems, such as hydroxyl radicals (·OH), singlet oxygen (1O2), superoxide anion (·O2-), and hydrogen peroxide (H2O2). The added FeSO4 catalyst may undergo a Fenton reaction (see the following formula) with H2O2 produced by the cold plasma, compounding to build a higher oxidizing environment and produce more highly oxidizing active OH. OH oxidizes hydroxyl on cellulose C2, C3, and C6 to form carboxyl, and the electrostatic repulsion generated by the electronegative carboxyl may weaken the structure of cellulose. Meanwhile, β-1,4 glycosidic bonds of cellulose chains are oxidatively degraded, thereby reducing the polymerization degree of cellulose. The above action destroys the network structure of microfibrils that form the cell wall of the fiber, resulting in the weakening of the fiber structure, which may be dissociated under weak mechanical action to obtain the CNFs.Beneficial Effects
[0023] Compared with prior art, the present disclosure has the following advantages and beneficial effects.
[0024] (1) According to the present disclosure, cellulose may be oxidized to a high degree by using a highly oxidizing environment constructed by compounding the cold plasma and the FeSO4 catalyst, and meanwhile, etching phenomena caused by bombarding the surface of cellulose with energetic particles generated by the cold plasma may increase the accessibility of cellulose, thereby improving the oxidation rate and oxidation effect of cellulose.
[0025] (2) The whole process for preparing the CNFs according to the present disclosure is carried out at normal temperature. The method is simple and mild, does not require other non-environment-friendly chemicals, and is efficient, green, and non-polluting. The final nanocrystallization process requires only weak mechanical treatment, and the energy consumption is greatly reduced.
[0026] (3) The CNFs obtained according to the present disclosure are uniformly dispersed and have a high yield.
[0027] (4) By adjusting the processing time and operating voltage of the cold plasma, the present disclosure may obtain CNFs with different carboxyl contents, sizes, structures, and performances of the surface, which may be applied to different scenarios.BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a flowchart for preparing CNFs according to the present disclosure;
[0029] FIG. 2 is a scanning electron microscope graph of CNFs prepared according to example 1 of the present disclosure;
[0030] FIG. 3 is a scanning electron microscope graph of CNFs prepared according to example 2 of the present disclosure;
[0031] FIG. 4 is a scanning electron microscope graph of CNFs prepared according to example 3 of the present disclosure;
[0032] FIG. 5 is a graph showing carboxyl contents of oxidized cellulose prepared according to examples 1-3 of the present disclosure; and
[0033] FIG. 6 is a graph showing a polymerization degree of oxidized cellulose prepared according to examples 1-3 of the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTS
[0034] Specific embodiments of the present disclosure are further described below in conjunction with examples and accompanying drawings, but the embodiments of the present disclosure are not limited thereto.
[0035] A flowchart for preparing CNFs according to the present disclosure is shown in FIG. 1.Example 1
[0036] 1000 mL of deionized water was treated with cold plasma under atmospheric-pressure air (with treatment time of 3 min, and operating voltage of 150 kV), and then 1 g of FeSO4 catalyst was added to obtain a FeSO4 solution. 100 g of cellulose and the FeSO4 solution were magnetically stirred and mixed for 20 min, so that FeSO4 was immersed into the cellulose, and then cold plasma treatment was continued under atmospheric-pressure air (with treatment time of 45 min, and operating voltage of 160 kV). Obtained oxidized cellulose was washed with deionized water, and suction filtration was carried out (with a carboxyl content and a polymerization degree of the oxidized cellulose shown in FIG. 5 and FIG. 6). Finally, mechanical fibrillation treatment was performed on the oxidized cellulose at a mass fraction of 1% (w / w) by an ultrasonic biomixer (600 W, 90 min) to obtain CNFs (FIG. 2) with a yield of 70.7%. The whole process did not involve use of any non-environment-friendly chemicals, and was simple, efficient, green, and non-polluting.Example 2
[0037] 1000 mL of deionized water was treated with cold plasma under atmospheric-pressure air (with treatment time of 5 min, and operating voltage of 120 kV), and then 3 g of FeSO4 catalyst was added to obtain a FeSO4 solution. 100 g of cellulose and the FeSO4 solution were magnetically stirred and mixed for 15 min, so that FeSO4 was immersed into the cellulose, and then cold plasma treatment was continued under atmospheric-pressure air (with treatment time of 60 min, and operating voltage of 140 kV). Obtained oxidized cellulose was washed with deionized water, and suction filtration was carried out (with a carboxyl content and a polymerization degree of the oxidized cellulose shown in FIG. 5 and FIG. 6). Finally, mechanical fibrillation treatment was performed on the oxidized cellulose at a mass fraction of 1% (w / w) by an ultrasonic biomixer (600 W, 90 min) to obtain CNFs (FIG. 3) with a yield of 90.1%. The whole process did not involve use of any non-environment-friendly chemicals, and was simple, efficient, green, and non-polluting.Example 3
[0038] 1000 mL of deionized water was treated with cold plasma under atmospheric-pressure air (with treatment time of 1 min, and operating voltage of 160 kV), and then 4 g of FeSO4 catalyst was added to obtain a FeSO4 solution. 100 g of cellulose was mixed with the FeSO4 solution for 10 min, so that FeSO4 was immersed into the cellulose, and then cold plasma treatment was continued under atmospheric-pressure air (with treatment time of 90 min, and operating voltage of 120 kV). Obtained oxidized cellulose was washed with deionized water, and suction filtration was carried out (with a carboxyl content and a polymerization degree of the oxidized cellulose shown in FIG. 5 and FIG. 6). Finally, mechanical fibrillation treatment was performed on the oxidized cellulose at a mass fraction of 1% (w / w) by an ultrasonic biomixer (600 W, 90 min) to obtain CNFs (FIG. 4) with a yield of 95.2%. The whole process did not involve use of any non-environment-friendly chemicals, and was simple, efficient, green, and non-polluting.Comparative Example 1
[0039] 100 g of cellulose was mixed with 1000 mL of deionized water, and then cold plasma treatment was performed under atmospheric-pressure air (with treatment time of 60 min, and operating voltage of 140 kV). Obtained oxidized cellulose was washed with deionized water, and suction filtration was carried out. Finally, mechanical fibrillation treatment was performed on the oxidized cellulose at a mass fraction of 1% (w / w) by an ultrasonic biomixer (600 W, 90 min) to obtain CNFs with a yield of 55.9%.Comparative Example 2
[0040] 3 g of FeSO4 catalyst was dissolved in 1000 mL of deionized water to obtain a FeSO4 solution, and 100 g of cellulose was mixed with the FeSO4 solution for 15 min, so that FeSO4 was immersed into the cellulose, and then cold plasma treatment was performed under atmospheric-pressure air (with treatment time of 60 min, and operating voltage of 140 kV). Obtained oxidized cellulose was washed with deionized water, and suction filtration was carried out. Finally, mechanical fibrillation treatment was performed on the oxidized cellulose at a mass fraction of 1% (w / w) by an ultrasonic biomixer (600 W, 90 min) to obtain CNFs with a yield of 62.1%.
[0041] The above-mentioned examples are preferred embodiments of the present disclosure, but the embodiments of the present disclosure are not limited to the above-mentioned examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present disclosure are intended to be equivalent substitution modes and are intended to be within the scope of protection of the present disclosure.
Claims
1: A green and low-energy preparation method for cellulose nanofibers (CNFs) based on cold plasma, comprising the following steps:(1) uniformly mixing cellulose with a FeSO4 solution, so that FeSO4 is immersed into the cellulose, and then performing cold plasma treatment under atmospheric-pressure air to obtain oxidized cellulose; and(2) washing the oxidized cellulose obtained in step (1), and carrying out suction filtration and mechanical fibrillation treatment to obtain the CNFs.2: The method according to claim 1, wherein water in the FeSO4 solution in step (1) is subjected to cold plasma treatment.3: The method according to claim 2, wherein the preparation of the FeSO4 solution in step (1) comprises the following steps:treating deionized water with the cold plasma under the atmospheric-pressure air, and then dissolving a FeSO4 catalyst into the deionized water to obtain the FeSO4 solution.4: The preparation method according to claim 3, wherein the cold plasma treats the deionized water at an operating voltage of 120-160 kV for 1-5 min.5: The preparation method according to claim 1, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-160 kV for 45-90 min.6: The preparation method according to claim 1, wherein a mass ratio of FeSO4 to the cellulose in step (1) is 1-4:100.7: The preparation method according to claim 1, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-140 kV for 60-90 min; and a mass ratio of FeSO4 to the cellulose is 3-4:100.8: The preparation method according to claim 1, wherein a concentration of FeSO4 in the FeSO4 solution in step (1) is 0.1 wt %-0.4 wt %.9: The preparation method according to claim 1, wherein a mixing time in step (1) is 10-20 min.10: The preparation method according to claim 1, wherein in step (2), the oxidized cellulose is treated under an ultrasonic condition of 600 W at a concentration of 0.5 wt %-2 wt % for 90 min to obtain the CNFs.11: The preparation method according to claim 2, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-160 kV for 45-90 min.12: The preparation method according to claim 3, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-160 kV for 45-90 min.13: The preparation method according to claim 4, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-160 kV for 45-90 min.14: The preparation method according to claim 2, wherein a mass ratio of FeSO4 to the cellulose in step (1) is 1-4:100.15: The preparation method according to claim 3, wherein a mass ratio of FeSO4 to the cellulose in step (1) is 1-4:100.16: The preparation method according to claim 4, wherein a mass ratio of FeSO4 to the cellulose in step (1) is 1-4:100.17: The preparation method according to claim 2, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-140 kV for 60-90 min; and a mass ratio of FeSO4 to the cellulose is 3-4:100.18: The preparation method according to claim 3, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-140 kV for 60-90 min; and a mass ratio of FeSO4 to the cellulose is 3-4:100.19: The preparation method according to claim 4, wherein in step (1), the cold plasma treats the cellulose at an operating voltage of 120-140 kV for 60-90 min; and a mass ratio of FeSO4 to the cellulose is 3-4:100.20: The preparation method according to claim 4, wherein in step (2), the oxidized cellulose is treated under an ultrasonic condition of 600 W at a concentration of 0.5 wt %-2 wt % for 90 min to obtain the CNFs.