CN116377609A

CN116377609A - Cellulose nanofibrils and preparation method and application thereof

Info

Publication number: CN116377609A
Application number: CN202310255430.7A
Authority: CN
Inventors: 姜言; 王欣宜; 刘秀宇; 孟志谦; 张梦阳; 黄钦; 王双飞
Original assignee: Guangxi University
Current assignee: Guangxi University
Priority date: 2023-03-16
Filing date: 2023-03-16
Publication date: 2023-07-04

Abstract

The invention discloses a cellulose nanofibril, a preparation method and application thereof, and belongs to the technical field of nanocellulose. The preparation method of the cellulose nanofibrils comprises the following steps: (1) pretreatment: pretreating fir strips at high temperature by using a peroxyacetic acid solution, and washing by using a sodium hydroxide solution to obtain fir fibers; (2) mechanical microfibrillation: adding fir fiber into the ionic liquid-water mixture, and placing the mixture into a stirrer for mechanical stirring to obtain a suspension; (3) dialysis: and (3) placing the suspension in a dialysis bag for dialysis to obtain the cellulose nanofibrils. The prepared cellulose nanofibrils have the advantages of narrow diameter distribution range, uniform size, ultrahigh length-diameter ratio, good dispersibility, greenness, no toxicity and degradability. The preparation method has the advantages of simple process, environment friendliness, mild reaction condition, low energy consumption, low cost and recoverable reaction solvent. The prepared cellulose nanofibrils can be used as a lithium battery diaphragm and have good application prospects.

Description

Cellulose nanofibrils and preparation method and application thereof

Technical Field

The invention belongs to the technical field of nanocellulose, and particularly relates to a cellulose nanofibril, a preparation method and application thereof.

Background

With the implementation of the plastic-limiting cement in the background of double carbon, the times of 'rear plastic' and 'wood plastic' are of course, namely, cellulose Nanofibrils (CNF) are used as raw materials to replace the artificially synthesized high polymers which are difficult to degrade and have high pollution in plastic products. Cellulose is the most abundant renewable biopolymer, can be obtained from industrial and agricultural wastes with abundant resources, and has the characteristics of low cost, reproducibility and the like.

The fir as the local characteristic biomass resource of Guangxi province has stable and uniform components, the lignocellulose content is up to more than 90%, wherein the cellulose content is 40-50%, the hemicellulose content is 15-25%, and the lignin content is 30-40%. However, most of fir is used as biomass fuel or directly abandoned, and the small part of fir is used for furniture and pulping and papermaking, so that the problems of low utilization rate, low utilization value and the like exist. Therefore, the fir is converted into a high added value product, and the method has great significance on the local economic development.

Nanocellulose is a high added value product obtained by nanocrystallization of cellulose fibers by mechanical, biological, chemical and other methods, wherein the fiber diameter is 5-100 nm, and the length-diameter ratio is more than 10. At present, the method for preparing the nanocellulose from the natural lignocellulose has the problems of using toxic and harmful chemicals, high energy consumption and high water consumption. The nanocellulose prepared by the mechanical method has the defects of wide diameter distribution range and nonuniform size, and natural fibers with compact structure and firm texture are extremely easy to be entangled together to cause the blockage and abrasion of a high-pressure homogenizer.

The preparation of lignocellulosic nanofibers involves the breakdown/defibrillation of plant fiber cells into individual cellulose nanofibers. The first step is to process into cellulose fibers by removing lignin and hemicellulose, and then pre-treating (chemical or enzymatic) fibers about 3mm long and about 30 μm in diameter, which can break down their dense hierarchical structure, improving fiber accessibility, to reduce energy dissipation during subsequent mechanical defibrillation. There are many pretreatment methods reported in the literature, 2, 6-tetramethylpiperidine oxide (TEMPO) mediated oxidation is most widely used, and the fibrils obtained by this method have a uniform diameter of less than 4nm and a length of about 800nm. TEMPO catalysts are however toxic, which prevents TEMPO-CNF from being used in certain applications. Also, the preparation of CNF by enzymatic (Enz) pretreatment, such as pretreatment of pulp by endoglucanase, can result in selective cellulose hydrolysis and is an environmentally friendly and low cost process, but Enz-CNF shows large differences in diameter and length distribution and contains incompletely fibrillated branched fibrils, and hemicellulose content in industrial lignocellulose fibers is low, surface charge is low, resulting in aggregation problems of the suspension. CNF prepared by TEMPO or enzymatic pretreatment is not in a natural state in terms of fibril length, crystallinity, and mechanical damage.

Therefore, a preparation method of the cellulose nanofibrils with good product dispersibility, simple preparation process, environment friendliness, mild reaction conditions, low energy consumption and low cost needs to be sought.

Disclosure of Invention

Aiming at the problems, the invention provides a preparation method of cellulose nanofibrils, which comprises the steps of pretreating fir strips by using a peroxyacetic acid solution, removing most lignin, promoting fiber microfibrillation by using an ionic liquid-water system, and dissociating the cellulose nanofibrils by combining a mechanical method. The preparation process is simple, environment-friendly, mild in reaction condition, low in energy consumption and low in cost, and the obtained cellulose nanofibrils are narrow in diameter distribution range, uniform in size and good in dispersibility.

The invention is realized by the following technical scheme:

a method for preparing cellulose nanofibrils, comprising the steps of:

(1) Pretreatment: pretreating fir strips at high temperature by using a peroxyacetic acid solution, and washing by using a sodium hydroxide solution to obtain fir fibers;

(2) Mechanical microfibrillation: adding fir fiber into the ionic liquid-water mixture, and placing the mixture into a stirrer for mechanical stirring to obtain a suspension;

(3) And (3) dialysis: and (3) placing the suspension in a dialysis bag for dialysis to obtain the cellulose nanofibrils which are uniformly dispersed.

In the step (2), the ionic liquid in the ionic liquid-water mixture is 1-ethyl-3-methylimidazole acetate, and the concentration ratio of the ionic liquid to water is 0-50%.

As the optimization of the technical scheme, in the step (2), the mass ratio of the fir fiber to the ionic liquid-water mixture is 1:150-200.

Preferably, in the step (2), the mechanical stirring time is 0.5-2.5 h.

As the optimization of the technical scheme, in the step (1), the mass ratio of the fir wood strips to the peracetic acid solution is 1:5-6.

Preferably, in the step (1), the concentration of the peroxyacetic acid is 4 to 10wt% and the concentration of the sodium hydroxide solution is 0.01 to 0.02mol/L.

As the optimization of the technical scheme, in the step (1), the fir wood strips are treated for 3-4 times at the temperature of 80-85 ℃ by using the peracetic acid solution, and the treatment time is 35-45 min each time.

Preferably, in the step (3), the dialysis time is 6 to 7 days.

A cellulose nanofibril produced by the method of producing a cellulose nanofibril as described above.

The cellulose nanofibrils of the invention have the diameter distribution of 3-12 nm, the length distribution of 3-40 mu m and the length-diameter ratio of 950-1000.

Use of a cellulose nanofibril as described above in a lithium battery separator.

The reaction principle of the invention for preparing cellulose nanofibrils:

the preparation method comprises the steps of firstly pretreating fir strips by using a peroxyacetic acid solution, removing most lignin, simultaneously well retaining hemicellulose, then taking a non-dissolving/degradable ionic liquid-water solvent which weakens a hemicellulose molecular hydrogen bond network as a guide as a medium system, taking 1-ethyl-3-methylimidazole acetate as an ionic liquid, weakening intermolecular hydrogen bond action of cellulose and hemicellulose under the action of the ionic liquid, increasing the microfibrillation degree of the fiber, and then combining a mechanical method to gently and efficiently dissociate cellulose nanofibrils with super length-diameter ratio from hemicellulose and cellulose fibers with high content.

Compared with the prior art, the invention has the advantages that:

1. the preparation method comprises the steps of firstly, preprocessing fir strips by using a peroxyacetic acid solution to obtain fir fibers, adding the obtained fir fibers into an ionic liquid-water mixture, mechanically stirring, and preparing cellulose nanofibrils with uniform dispersion after simple dialysis. The cellulose nanofibrils prepared by the method have the advantages of 3-12 nm of diameter distribution, 3-40 mu m of length distribution, 950-1000 of length-diameter ratio, narrow diameter distribution range, uniform size, ultrahigh length-diameter ratio, good dispersibility, greenness, no toxicity and degradability.

2. The ionic liquid-water system used in the invention is composed of 1-ethyl-3-methylimidazole acetate and water, the ionic liquid has the characteristics of no toxicity, biodegradability and recoverability, and the ionic liquid-water system is used for regulating the hydrogen bond distribution of hemicellulose macromolecular structure, so that the swelling of hemicellulose is effectively promoted, the swelling of cellulose is promoted, the hydrogen bond action and Van der Waals force are weakened, the microfibrillation process of fiber is promoted, and the mechanical energy consumption is obviously reduced.

3. According to the invention, the fiber microfibrillation is promoted by the ionic liquid-water system, and then the cellulose nanofibrils are dissociated by a combined mechanical method, so that the high-energy consumption and high-pollution delignification and hemicellulose removal processes are avoided, the hemicellulose reserved in the process of preparing the cellulose nanofibrils can reduce the energy consumption required by machinery, the aggregation of the fibers can be prevented, and the dispersibility of the cellulose nanofibrils is improved.

4. The preparation method disclosed by the invention is simple in process, environment-friendly, mild in reaction condition, low in energy consumption and cost, and the reaction solvent can be recycled for high-value utilization. Meanwhile, the cellulose nanofibrils are prepared from the fir raw materials, so that the utilization rate and the utilization value of the fir can be improved, the fir is converted into a high-added-value product, and the method has a good promotion effect on economic development.

5. Compared with the traditional methods TEMPO-CNF and Enz-CNF, the preparation method provided by the invention has the advantages that 1.6074 yuan/g and 2.457 yuan/g can be respectively reduced in the whole process of preparing the cellulose nanofibrils, so that the preparation method provided by the invention has great advantages in the aspects of low energy consumption, low cost and high-value utilization.

6. The preparation method of the invention can also prepare the nanometer paper, and the prepared nanometer paper has high strength, thermal stability and high transparency. The cellulose nanofibrils prepared by the method can be used as a lithium battery diaphragm, can effectively solve the problems of poor electrolyte wettability and thermal stability of polyolefin diaphragms, and has good application prospects.

Drawings

Fig. 1 is a scanning electron microscope image and an atomic force microscope image of cellulose nanofibrils produced in comparative example 1, example 1 and example 2.

FIG. 2 is a graph showing intermolecular interactions of cellulose nanofibrils produced in comparative example 1 and example 1.

Fig. 3 is a graph of rheometer data for cellulose nanofluids prepared in comparative example 1 and example 1.

Fig. 4 is a fourier transform infrared spectrum of the nanopaper prepared in comparative example 2, example 5, and example 6.

FIG. 5 is an XPS chart of the nanopaper prepared in comparative example 2 and examples 5 to 7.

Fig. 6 is a graph showing transmittance and haze of the nanopaper sheets prepared in comparative example 2, example 5, and example 6.

Fig. 7 is a schematic view of thermal stability of the nanopaper prepared in comparative example 2, example 5, and example 6.

FIG. 8 is a graph showing the mechanical strength of the nanopaper prepared in comparative example 2 and examples 5 to 8.

FIG. 9 is a scanning electron microscope image of the tensile fracture surface of the nano paper prepared in example 5.

Detailed Description

The present invention is further illustrated by the following examples, which are only intended to illustrate the present invention and not to limit the scope of the present invention.

Example 1

Preparation of cellulose nanofibrils:

(1) Pretreatment: repeatedly soaking and washing 200g of fir wood strips with deionized water and ethanol until the washing solution is clear, then completely drying in an oven at 60 ℃, cutting the cleaned and dried fir wood strips into fine wood strips with the width of 2mm, then treating with 1200g of peroxyacetic acid solution (4 wt% aqueous solution, pH=4.8 before reaction) at 85 ℃ for 4 times, treating for 45 minutes each time, washing with 0.01mol/L sodium hydroxide solution, and finally washing with deionized water to remove residual chemical substances to obtain fir wood fibers;

(2) Mechanical microfibrillation: adding 2g of fir fiber into 300g of ionic liquid-water mixture with ionic liquid concentration of 24%, wherein the ionic liquid is 1-ethyl-3-methylimidazole acetate, and placing the mixture in a kitchen stirrer for mechanical stirring for 2.5h to obtain a suspension;

(3) And (3) dialysis: and (3) placing the suspension in a dialysis bag for dialysis for 7 days to obtain cellulose nanofibrils which are uniformly dispersed, and recovering the ionic liquid.

The cellulose nanofibrils prepared by detection and analysis have the diameter distribution of 3-12 nm, the length distribution of 3-40 mu m and the length-diameter ratio of 950-1000.

Comparative example 1

Comparative example 1 was different from example 1 in that in comparative example 1, an ionic liquid was not used at the time of mechanical microfibrillation, fir fiber was always in an aqueous solution, and the other preparation conditions were the same as in example 1, to prepare cellulose nanofibrils.

Example 2

Preparation of cellulose nanofibrils:

(1) Pretreatment: repeatedly soaking and washing 200g of fir wood strips with deionized water and ethanol until the washing solution is clear, then completely drying in an oven at 60 ℃, cutting the cleaned and dried fir wood strips into fine wood strips with the width of 2mm, then treating the fine wood strips with 1200g of peroxyacetic acid solution (5 wt% aqueous solution, pH=4.8 before reaction) for 4 times at 80 ℃ for 40min each time, washing with 0.01mol/L sodium hydroxide solution, and finally washing with deionized water to remove residual chemical substances to obtain fir wood fibers;

(2) Mechanical microfibrillation: adding 2g of fir fiber into 300g of ionic liquid-water mixture with the ionic liquid concentration of 50%, wherein the ionic liquid is 1-ethyl-3-methylimidazole acetate, and placing the mixture in a kitchen stirrer for mechanical stirring for 0.5h to obtain a suspension;

Example 3

Preparation of cellulose nanofibrils:

(2) Mechanical microfibrillation: adding 2g of fir fiber into 300g of an ionic liquid-water mixture with the ionic liquid concentration of 15%, wherein the ionic liquid is 1-ethyl-3-methylimidazole acetate, and placing the mixture in a kitchen stirrer for mechanical stirring for 2.5h to obtain a suspension;

Example 4

Preparation of cellulose nanofibrils:

(2) Mechanical microfibrillation: adding 2g of fir fiber into 300g of an ionic liquid-water mixture with the ionic liquid concentration of 12%, wherein the ionic liquid is 1-ethyl-3-methylimidazole acetate, and placing the mixture in a kitchen stirrer for mechanical stirring for 2.5h to obtain a suspension;

Example 5

Preparation of the nano paper:

the suspension prepared in example 1 was placed on a hydrophilic polyvinylidene fluoride filter membrane for vacuum filtration for 1min, after the completion of the vacuum filtration, a second filter membrane was placed on top, and the whole assembly was dried at 25 ℃ with a relative humidity of 50% and a weight of 500g for 5h, during which the bottom and top filter membranes were continuously replaced, and finally placed in an oven at 60 ℃ for 6h to obtain the nanopaper.

Comparative example 2

Comparative example 2 was different from example 5 in that the suspension in comparative example 2 was the suspension prepared in comparative example 1, and the remaining preparation conditions were the same as in example 5, to prepare a nanopaper.

Example 6

Example 6 is different from example 5 in that the suspension in example 6 is the suspension prepared in example 2, and the other preparation conditions are the same as those of example 5, so that the nanopaper is prepared.

Example 7

Example 7 is different from example 5 in that the suspension in example 7 is the suspension prepared in example 3, and the other preparation conditions are the same as those of example 5, so that the nanopaper is prepared.

Example 8

Example 8 is different from example 5 in that the suspension in example 8 is the suspension prepared in example 4, and the other preparation conditions are the same as those of example 5, so that the nanopaper is prepared.

Characterization analysis of cellulose nanofibrillar material

Microscopic test analysis of cellulose nanofibrils

The cellulose nanofibrils produced in comparative example 1, example 1 and example 2 were subjected to microscopic test analysis, and the test results are shown in fig. 1, and fig. 1 is a Transmission Electron Microscope (TEM) and Atomic Force Microscope (AFM) image of the cellulose nanofibrils produced in comparative example 1, example 1 and example 2. In fig. 1, (a) and (d), (b) and (e), (c) and (f) are respectively represented by transmission electron microscopy and atomic force microscopy images of cellulose nanofibrils produced in comparative example 1, example 2.

As can be seen from fig. 1 (a) and (d), the fibers not treated with the ionic liquid in comparative example 1, i.e., the fibers were only in aqueous solution, the fiber bundles were in a dispersed state, and the mild kitchen stirrer defibrillation process was small in mechanical damage and small in length shortening, and the diameter of the fibers dispersed in water was hundreds of nanometers. As can be seen from fig. 1 (b) and (e), the fibers were treated with an appropriate amount of ionic liquid concentration (24%) in example 1, the cellulose was separated into thinner bundles, and even individual nanofibers were observed. From FIGS. 1 (c) and (f), it can be seen that the fibers were treated with a high concentration of ionic liquid (50%) in example 2, with fiber length and diameter dips, shown as individual staple fibers. From the comparison of example 1, example 2 and comparative example 1 above, in the presence of a low concentration of ionic liquid (24%), hemicellulose located between nanofibrils is swelling "pushing them apart", which facilitates the separation of the fibre bundles.

Analysis of the Effect of holocellulose on colloidal Probe adhesion

The effect of the holocellulose on the adhesion of the colloidal probe in comparative example 1 and example 1 was analyzed, and the analysis results are shown in fig. 2, and fig. 2 is a graph showing intermolecular interactions of cellulose nanofibrils produced in comparative example 1 and example 1.

From FIG. 2, it can be seen that in example 1, the unique core-shell structure, i.e., hemicellulose-coated cellulose, can still retain a very good aspect ratio (> 1000) under mechanical action in the presence of ionic liquid. The AFM probe and the surface are contacted under the action of external force, so that Van der Waals force dominates the interaction, and the force is continuously measured in the process of contact and separation of the probe and the surface. The treated fibers with the appropriate amount (24%) of ion concentration possess high adhesion, both maximum force and maximum distance being highest, which means that the adhesion energy is also highest. The low adhesion and adhesion energy reflected by both sets of data is due to the natural biosynthetic core-shell structure. The swelled hemicellulose maintains fibril separation through steric hindrance and charge repulsion, reflects that the potential difference is small, the microfibrillation degree is increased after the ionic liquid is treated, the length-diameter ratio is increased, the intermolecular hydrogen bonding effect is enhanced, and therefore the adhesion force and the adhesion energy are increased.

Viscoelastic analysis of suspensions (III)

The viscoelasticity of the suspensions of comparative example 1 and example 1 was analyzed, and the analysis results are shown in fig. 3, and fig. 3 is a rheometer data graph of cellulose nanofilm filaments prepared in comparative example 1 and example 1.

As can be seen from FIG. 3 (a), the frequency dependence of the elastic (G ') and viscous (G') moduli of the 0.18 wt.% cellulose of comparative example 1 dispersed in the non-ionic liquid, all suspensions showed a gel behaviour, G 'being higher than G', which is typical of CNF suspensions, between CNFs and CNF and H after dialysis ₂ The hydrogen bonding between O is very weak and therefore the suspension is dominated by physical entanglement. The suspension obtained after the treatment with the ionic liquid (24%) in example 1 shows high aspect ratio and flexibility of the fibers, and even at low concentrations, the physical entanglement is strong, becoming a solid-like viscoelastic property, which is higher than the fibers in pure water.

There was a significant difference between the ionic liquid-water suspension of example 1 and the pure water suspension of comparative example 1: the modulus of the 0.18wt% to 24% ionic liquid-water suspension in example 1 is about 1 order of magnitude higher than the response value of comparative example 1 without ionic liquid. The frequency independent areas of G 'and G "of 0.18wt% to 24% ionic liquid-water suspension were wider than those of G' and G" of 0.18wt% to water suspension, which also indicated a stronger gel behavior. With ionic liquids, there is not only physical entanglement but also hydrogen-bond interactions between the fibers, increasing the modulus by about 1 order of magnitude.

It can be seen from FIG. 3 (b) that the complex viscosity of the 0.18wt% to 24% ionic liquid-water suspension in example 1 is also much higher than that of the pure water suspension of comparative example 1.

It can be seen from fig. 3 (c) that the viscosity of the suspension decreases with increasing shear rate, a typical shear thinning behaviour of nanocellulose suspensions, which indicates that this suspension is a pseudoplastic fluid, the dispersion of which in water is not hindered. The thinner the fiber bundles, the more easily a highly entangled elastic network is formed, resulting in an increase in both the viscoelastic modulus and viscosity.

Characterization analysis of nanopaper materials

Analysis of chemical bond changes in nanopaper

The chemical bond changes of the nanopaper prepared in comparative example 2 and examples 5 to 7 were analyzed, and the analysis results are shown in fig. 4 and 5, and fig. 4 is fourier transform infrared spectrograms of the nanopaper prepared in comparative example 2, example 5 and example 6. FIG. 5 is an XPS chart of the nanopaper prepared in comparative example 2 and examples 5 to 7.

As can be seen from fig. 4 and 5, in the fiber treated with an appropriate amount of ionic liquid (24%) in example 5, the C2 peak area was increased, the exposed-0H peak was increased, and the stretching vibration of c=o bond was hardly changed, i.e., the degree of microfibrillation was increased, corresponding to the decrease in the fiber diameter as described above, and the fiber was not degraded. With increasing ion concentration (50%) in example 6, the area of the C1 peak suddenly decreased, the exposed-0H peak increased sharply, and the c=o bond stretching vibration became smaller, corresponding to the fiber diameter being smaller and the length being shorter as described above, the fiber was degraded, and the c—c bond was broken.

Transmittance and haze analysis of (two) nanopaper

The transmittance and haze of the nanopaper prepared in comparative example 2, example 5 and example 6 were analyzed, and the analysis results are shown in fig. 6, and fig. 6 is a schematic diagram of the transmittance and haze of the nanopaper prepared in comparative example 2, example 5 and example 6.

As can be seen from fig. 6, the optical transmittance at 550nm is higher than 85%, the optical haze varies from 65% to 40% with increasing wavelength, and a coarser surface causes an increase in haze, which is also confirmed by roughness values Ra and Rq.

Thermal stability analysis of (III) nanopaper

The thermal stability of the nanopaper prepared in comparative example 2, example 5 and example 6 was analyzed, and the analysis results are shown in fig. 7, and fig. 7 is a schematic view of the thermal stability of the nanopaper prepared in comparative example 2, example 5 and example 6.

As can be seen from fig. 7, the thermal stability of the nano paper obtained after the treatment of the ionic liquid is improved. TGA _5％ Up to approximately 300 c. Therefore, the lithium battery diaphragm membrane prepared from the cellulose nanofibrils can be kept stable in size within a certain temperature range, and the lithium battery can be ensured to work normally at a higher temperature.

Analysis of tensile Property of nanopaper

The nanopaper prepared in comparative example 2 and examples 5 to 8 was analyzed for tensile properties, and the analysis results are shown in fig. 8, and fig. 8 is a graph of mechanical strength of the nanopaper prepared in comparative example 2 and examples 5 to 8.

As can be seen from fig. 8, the tensile strength of the nano paper obtained after the treatment of the ionic liquid can reach 400MPa, and the extension is also increased.

Analysis of tensile Property of nanopaper

The tensile properties of the nano paper prepared in example 5 were analyzed, and the analysis results are shown in fig. 9, and fig. 9 is a scanning electron microscope image of the tensile fracture surface of the nano paper prepared in example 5.

As can be seen from fig. 9, the nano paper prepared in example 5 has obvious fiber extraction when broken, and can also verify that the hydrogen bond plays a good role in blocking during stretching and sliding.

Cost comparison required for the preparation of cellulose nanofibrils

The cost required for preparing cellulose nanofibrils according to example 1 of the present invention was compared with that of TEMPO-CNF, enz-CNF, respectively, according to the conventional method, and the comparison results are shown in table 1 below:

TABLE 1 cost Table for preparation of cellulose nanofibrils, TEMPO-CNF, enz-CNF example 1

As shown in Table 1 above, compared with the conventional methods TEMPO-CNF and Enz-CNF, 0.8186 yuan/g and 0.581 yuan/g can be reduced in the delignification process of the invention, 0.1912 yuan/g and 0.3928 yuan/g can be reduced in the defibrillation process, and 0.5976 yuan/g and 1.4832 yuan/g can be reduced in the centrifugation process. In summary, the present invention can reduce 1.6074 yuan/g and 2.457 yuan/g, respectively, in the whole process of preparing cellulose nanofibrils.

The comparison of the cost shows that compared with the traditional methods TEMPO-CNF and Enz-CNF, the preparation method of the cellulose nanofibrils has great advantages in the aspects of low energy consumption, low cost and high-value utilization.

Application example 1

Preparation of a lithium battery separator:

the cellulose nanofibrils prepared in the example 1 are subjected to reduced pressure suction filtration by utilizing a sand core funnel and a hydrophilic polytetrafluoroethylene filter membrane, and the suction filtration is stopped when the water liquid in the funnel is pumped out; removing the filter membrane along with the wet cellulose membrane, and transferring the filter membrane into absolute ethyl alcohol for solvent replacement for 2 hours; the replaced wet film is clamped by a layer of filter film, placed in a glass plate to be kept flat, and dried for 24 hours at 60 ℃ in a constant-temperature blast drying box to obtain the dried nanocellulose film. The thickness of the final fibrous membrane is controlled by controlling the volume of suspension used for suction filtration, and the lithium battery diaphragm with the thickness of 15 mu m, 25 mu m and 35 mu m is prepared, so that the prepared lithium battery diaphragm can effectively solve the problems of poor electrolyte wettability and thermal stability of polyolefin diaphragms.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims

1. A method for preparing cellulose nanofibrils, comprising the steps of:

2. The method for preparing cellulose nanofibrils according to claim 1, wherein in step (2), the ionic liquid in the ionic liquid-water mixture is 1-ethyl-3-methylimidazole acetate, and the concentration ratio of the ionic liquid to water is 0-50%.

3. The method of claim 1, wherein in step (2), the mass ratio of fir fiber to ionic liquid-water mixture is 1:150-200.

4. The method of producing cellulose nanofibrils according to claim 1, wherein in step (2), the mechanical stirring time is 0.5 to 2.5 hours.

5. The method of claim 1, wherein in step (1), the mass ratio of fir wood chips to the peroxyacetic acid solution is 1:5-6.

6. The method of preparing cellulose nanofibrils according to claim 1, wherein in step (1), the fir wood chips are treated 3 to 4 times with a peroxyacetic acid solution at a temperature of 80 to 85 ℃ for 35 to 45 minutes each time.

7. The method for producing cellulose nanofibrils according to claim 1, wherein in step (3), the dialysis time is 6 to 7 days.

8. A cellulose nanofibril produced by the method of producing a cellulose nanofibril according to any of claims 1 to 7.

9. The cellulose nanofibril according to claim 8, characterized in that the cellulose nanofibril has a diameter distribution of 3 to 12nm, a length distribution of 3 to 40 μm and an aspect ratio of 950 to 1000.

10. Use of the cellulose nanofibrils according to claim 8 in a lithium battery separator.