Sulfonated nanocellulose film having high proton conductivity and method for producing the same

Abstract

The application relates to the field of nanocellulose films, and relates to a sulfonated nanocellulose film with high proton conductivity and a preparation method thereof. In the method, deionized water is used as a medium, and cellulose is subjected to a light-avoiding oxidation reaction by using sodium periodate under the condition that the pH is 2-3, so as to obtain dialdehyde cellulose; the dialdehyde cellulose, 2-aminoethanesulfonic acid and 2-methylpyridine borane are subjected to a Schiff base reduction amination reaction in deionized water at 59-65 DEG C, and then impurities are removed, so as to obtain a sulfonated nanocellulose suspension; the sulfonated nanocellulose suspension is formed by using a vacuum filtration method, and then is dried, so as to obtain the sulfonated nanocellulose film with high proton conductivity. The application solves the problems of low cellulose proton conductivity, non-degradability and indirect environmental pollution caused by the preparation process, and has high proton conductivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nanocellulose films, in particular to a sulfonated nanocellulose film with high proton conductivity and a preparation method thereof. BACKGROUND

[0002] In recent years, the harsh requirements of high performance and environmental friendliness of proton exchange membrane fuel cells have led to intensive improvement of their proton exchange membrane materials. Currently, the commonly used perfluorosulfonic acid resin membrane (Nafion, Dupont) is limited in further development due to its poor proton conduction performance under low humidity conditions (≤15 mS / cm, 33% RH, basic requirement ≥100 mS / cm), high cost, and non-green and environmentally friendly material components. Therefore, it is urgent to develop a new type of proton exchange membrane material to solve this problem.

[0003] Biomass materials are the best choice for new proton exchange membrane materials, and cellulose, as one of the raw materials of biomass materials, has the advantages of abundant raw materials, rapid regeneration, good environmental and biological compatibility, and biodegradability. However, the deprotonation ability of its surface hydroxyl groups is weak, which limits its rapid development in this field.

[0004] Based on the polyhydroxy structure of cellulose, methods such as introducing high proton conductivity polymers, strong deprotonation sulfonic acid groups, and phosphoric acid groups have been reported to improve the proton conduction carrier in cellulose membranes. Among them, the introduction of sulfonic acid groups is the most outstanding in improving proton conduction performance, but there are still many problems in the process of introduction: first, the source of the sulfonic acid groups used, such as acrylic acid and sulfosuccinic acid, has complex synthesis process, certain toxicity and makes the synthesized cellulose membrane non-degradable; second, the way of introducing sulfonic acid groups through hydrogen bonds or dynamic covalent bonds is easy to cause the loss of acid groups in long-term use, resulting in poor proton conduction performance. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a sulfonated nanocellulose film with high proton conductivity and a preparation method thereof, to solve the problems of low cellulose proton conductivity, non-degradability and indirect environmental pollution in the preparation process, and high proton conduction performance.

[0006] The present application is implemented by adopting the following technical solutions:

[0007] A preparation method of a sulfonated nanocellulose film with high proton conductivity, comprising the following steps:

[0008] S1, in deionized water as medium, under the condition of pH 2~3, using sodium periodate to carry out light-avoiding oxidation reaction on cellulose, the mass ratio of sodium periodate and cellulose is (1.2~1.4):(0.9~1.1), to obtain dialdehyde cellulose;

[0009] S2, in deionized water at 59~65 ℃, according to the mass ratio of (0.9~1.1):(2.0~6.0):(0.3~0.33), Schiff base reduction amination reaction is carried out on dialdehyde cellulose, 2-aminoethanesulfonic acid and 2-methylpyridine borane, and then impurities are removed, to obtain sulfonated nanocellulose suspension;

[0010] S3, the sulfonated nanocellulose suspension is formed by vacuum filtration, and then dried, to obtain sulfonated nanocellulose film with high proton conductivity.

[0011] Further improvement of the application is:

[0012] The light-avoiding oxidation reaction in S1 is carried out at 48~52 ℃ for 3.0~3.8 h.

[0013] The cellulose in S1 is bleached conifer cellulose.

[0014] In S1, the bleached conifer cellulose is uniformly dispersed in deionized water, the mass ratio of deionized water and bleached conifer cellulose is (99~101):(0.9~1.1), then sodium periodate is added to obtain a mixed solution, 0.1 M HCl solution is used to adjust the pH of the mixed solution to 2~3, and finally the oxidation reaction is carried out under light-avoiding condition to obtain a first reaction liquid, and the product in the first reaction liquid is washed to obtain dialdehyde cellulose.

[0015] In S1, deionized water and ethanol are used to wash the product by vacuum filtration until the washing liquid is neutral, to obtain dialdehyde cellulose, and then deionized water is added, the mass ratio of deionized water and bleached conifer cellulose is (0.9~1.1):(9.9~11.1), to obtain dialdehyde cellulose suspension.

[0016] In S2, 2-aminoethanesulfonic acid and 2-methylpyridine borane are added to the dialdehyde cellulose suspension, and Schiff base reduction amination reaction is carried out at 59~65 ℃, the reaction time is 10~13 h, to obtain a second reaction liquid, and then impurities are removed, to obtain sulfonated nanocellulose suspension.

[0017] In S2, the second reaction liquid is dialyzed in deionized water for 69~75 h, to obtain sulfonated nanocellulose suspension.

[0018] S3 forms the sulfonated nanocellulose suspension on the PVDF film by means of vacuum filtration, and then dries at 40-50 DEG C for 5.5-6.5 h to form the sulfonated nanocellulose film with high proton conductivity on the PVDF film.

[0019] S3 peels off the sulfonated nanocellulose film with high proton conductivity on the PVDF film to obtain the sulfonated nanocellulose film with high proton conductivity.

[0020] A sulfonated nanocellulose film with high proton conductivity obtained by the preparation method of the sulfonated nanocellulose film with high proton conductivity according to any one of the preceding claims, wherein the sulfonated nanocellulose film has a proton conductivity of 44.23-128.0 mS / cm. -1 .

[0021] Compared with the prior art, the present application has the following beneficial technical effects:

[0022] The present application is a preparation method of a sulfonated nanocellulose film with high proton conductivity, which first performs a light-avoiding oxidation reaction on cellulose in deionized water at a pH of 2-3 by using sodium periodate, and by adjusting the mass ratio of sodium periodate to cellulose, a pair of adjacent hydroxyl groups in the cellulose molecule is oxidized into an aldehyde group to obtain a dialdehyde cellulose, then a Schiff base reduction amination reaction is performed on the dialdehyde cellulose by using taurine (2-aminoethanesulfonic acid) containing an amino group and a sulfonic acid group and 2-methylpyridine borane as a reducing agent, the sulfonic acid group is successfully grafted on the aldehyde group of the molecular structure of the dialdehyde cellulose through a C-N bond, and then impurities are removed to obtain a sulfonated nanocellulose material, the sulfonic acid modification of cellulose does not change the crystal form of cellulose, the nanomorphology of the sulfonated nanocellulose is calculated to have a fiber length of 179.37 ± 28.86 nm and a fiber width of 8.11 ± 3.21 nm, and finally the sulfonated nanocellulose suspension is formed by means of vacuum filtration, and then dried to obtain a sulfonated nanocellulose film with high proton conductivity. -1 . BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FTIR diagrams of the dialdehyde cellulose, sulfonated nanocellulose and pulp obtained in Examples 1-3 of the present application.

[0024] Figure 2XRD patterns of the sulfonated nanocellulose obtained in Examples 1-3 of the present application and the original pulp.

[0025] Figure 3 XPS patterns of the sulfonated nanocellulose obtained in Examples 1-3 of the present application and the original pulp.

[0026] Figure 4 TEM pattern of the sulfonated nanocellulose obtained in Example 3 of the present application.

[0027] Figure 5a Plots of the change in proton conductivity of the sulfonated nanocellulose obtained in Examples 1-3 of the present application and the perfluorosulfonic acid type resin membrane with temperature and humidity.

[0028] Figure 5b Plots of the change in proton conductivity of the sulfonated nanocellulose obtained in Examples 1-3 of the present application and the perfluorosulfonic acid type resin membrane with temperature and humidity.

[0029] Figure 6 Equations and specific structural formulas for the preparation of the sulfonated nanocellulose in the present application. DETAILED DESCRIPTION

[0030] The present application will be further described in conjunction with specific examples, which are intended to explain but not limit the present application.

[0031] The present application is a method for preparing a sulfonated micro-nano cellulose film with high proton conductivity, by mass fraction, specifically comprising the following steps:

[0032] Step 1, take 0.9-1.1 parts of bleached coniferous wood cellulose, measure 99-101 parts of deionized water, after the cellulose is fully dispersed, add 1.2-1.4 parts of sodium periodate, use 0.1 M HCl solution to adjust the pH to 2-3, and carry out the oxidation reaction as shown in Figure 6 at 48-52 ℃ in the dark for 3.0-3.8 h, then wash to neutral by water and ethanol combined with vacuum filtration, to obtain a dialdehyde cellulose solid with low water content, the dialdehyde cellulose is denoted as DAC, add 9.9-11.1 parts of deionized water to obtain a dialdehyde cellulose suspension, i.e. a dialdehyde cellulose suspension containing absolutely dry dialdehyde cellulose.

[0033] Step 2, take 0.9-1.1 parts of absolutely dry dialdehyde cellulose-containing dialdehyde cellulose suspension, 2.0-6.0 parts of 2-aminoethanesulfonic acid, and 0.3-0.33 parts of 2-methylpyridine borane, carry out the reaction as shown in Figure 6The Schiff base reduction amination reaction is shown for 10-13 h, and the sulfonated nanocellulose suspension is obtained after dialysis in deionized water for 69-75 h. The sulfonated nanocellulose film is constructed on a PVDF membrane (polyvinylidene fluoride membrane) by vacuum filtration, dried at 40-50 DEG C for 5.5-6.5 h, and recorded as a sulfonated nanocellulose (SNC) film.

[0034] The internal impedance of the sulfonated nanocellulose film is characterized by electrochemical impedance method under certain temperature and humidity, and the proton conductivity value can be obtained by impedance calculation. The proton conductivity of the sulfonated nanocellulose film is 44.23-128.0 mS / cm. -1 .

[0035] Example 1

[0036] The preparation method of the sulfonated nanocellulose film with high proton conductivity specifically comprises the following steps:

[0037] Step 1) 1 part of bleached coniferous wood cellulose is weighed, 100 parts of deionized water is measured, and after the cellulose is fully dispersed, 1.3 parts of sodium periodate is added. A 0.1 M HCl solution is used to adjust the pH to 2, and the reaction is carried out at 48 DEG C in the dark for 3.5 h. Then, water and ethanol are used for washing to neutral, and 10 parts of deionized water is added to obtain a dialdehyde cellulose suspension.

[0038] Step 2) 1 part of absolutely dry dialdehyde cellulose in the dialdehyde cellulose suspension, 2 parts of 2-aminoethanesulfonic acid, and 0.3 parts of 2-methylpyridine borane are weighed, and the reaction is carried out at 60 DEG C for 12 h. The dialdehyde cellulose suspension is dialyzed in deionized water for 72 h to obtain a sulfonated nanocellulose suspension. The sulfonated nanocellulose film (recorded as SNC-2) is obtained by vacuum filtration on a PVDF membrane and dried at 45 DEG C for 6 h.

[0039] The proton conductivity of the obtained sulfonated nanocellulose film is 61.10 mS / cm at 80 DEG C and 98% RH. -1 .

[0040] Example 2

[0041] The preparation method of the sulfonated nanocellulose film with high proton conductivity specifically comprises the following steps:

[0042] Step 1) 1 part of bleached coniferous wood cellulose is weighed, 100 parts of deionized water is measured, and after the cellulose is fully dispersed, 1.3 parts of sodium periodate is added. A 0.1 M HCl solution is used to adjust the pH to 2, and the reaction is carried out at 48 DEG C in the dark for 3.5 h. Then, water and ethanol are used for washing to neutral, and 10 parts of deionized water is added to obtain a dialdehyde cellulose suspension.

[0043] Step 2) Take 1 part of the dialdehyde cellulose suspension containing absolutely dry dialdehyde cellulose, 4 parts of 2-aminoethanesulfonic acid, 0.3 parts of 2-methylpyridine borane, and react at 60 ℃ for 12 h. Dialysis in deionized water for 72 h obtains a sulfonated nanocellulose suspension. Vacuum suction filtration on a PVDF membrane, and then drying at 40 ℃ for 6.5 h, to obtain a sulfonated nanocellulose film (denoted as SNC-4).

[0044] The proton conductivity of the obtained sulfonated nanocellulose film is 96.77 mS·cm -1 at 80 ℃, 98% RH.

[0045] Example 3

[0046] The application discloses a preparation method of a sulfonated nanocellulose film with high proton conductivity, which specifically comprises the following steps:

[0047] Step 1) Take 1 part of bleached coniferous wood cellulose, and measure 100 parts of deionized water. After the cellulose is fully dispersed, 1.3 parts of sodium periodate is added, a 0.1 M HCl solution is used to adjust the pH to 2, and then the mixture is reacted at 52 ℃ for 3.5 h in the dark. Then the mixture is washed to neutral by water and ethanol in combination with vacuum suction filtration, and 10 parts of deionized water is added to obtain a dialdehyde cellulose suspension.

[0048] Step 2) Take 1 part of the dialdehyde cellulose suspension containing absolutely dry dialdehyde cellulose, 6 parts of 2-aminoethanesulfonic acid, and 0.3 parts of 2-methylpyridine borane, and react at 60 ℃ for 12 h. Dialysis in deionized water for 72 h obtains a sulfonated nanocellulose suspension. Vacuum suction filtration on a PVDF membrane, and then drying at 50 ℃ for 5.5 h, to obtain a sulfonated nanocellulose film (denoted as SNC-6).

[0049] The proton conductivity of the obtained sulfonated nanocellulose film is 128.0 mS·cm -1 at 80 ℃, 98% RH, and 44.23 mS·cm -1 at 80 ℃, 33% RH.

[0050] From the FTIR of Figure 1 , the chemical structure characteristic changes of the sulfonated nanocellulose and the pulp can be analyzed. As shown in the figure, the C=N, S=O and S-O characteristic absorption peaks of the cellulose after sulfonation modification appear at 1515, 1220 and 737 cm -1 , which proves that the sulfonic acid groups are successfully grafted on the molecular structure of the cellulose.

[0051] From the FTIR of Figure 2XRD analysis reveals changes in the crystal structure of sulfonated nanocellulose and native cellulose. The figure shows that both the modified and unmodified cellulose exhibit three primary diffraction peaks near 2θ = 15°, 17°, and 23°, representing type I cellulose. This indicates that the sulfonation modification of cellulose does not alter its crystal form.

[0052] Figure 3 The XPS spectra of sulfonated nanocellulose and original cellulose are shown. It can be seen from the figure that the modified cellulose structure contains nitrogen and sulfur elements, which confirms the successful preparation of sulfonated nanocellulose.

[0053] from Figure 4 TEM analysis showed that the sulfonated nanofibers exhibited a nanomorphology. The fiber length was 179.37 ± 28.86 nm and the fiber width was 8.11 ± 3.21 nm after particle size calculation.

[0054] from Figure 5a and Figure 5b The changes in proton conductivity of the sulfonated nanocellulose films and perfluorosulfonic acid resin membranes obtained in Examples 1-3 of the present invention at 33% RH and 98% RH, respectively, are shown. At 33% RH, all sulfonated nanocellulose films exhibited greater proton conductivity than the perfluorosulfonic acid resin membrane. The proton conductivity of the sulfonated nanocellulose films and perfluorosulfonic acid resin membranes obtained in Examples 1-3 increased with increasing humidity. The sulfonated nanocellulose films exhibited a proton conductivity of 128.0 mS / cm at 98% RH and 80°C, demonstrating high proton conductivity.

Claims

1. A method for preparing a sulfonated nanocellulose film with high proton conductivity, characterized in that: The following steps are involved: S1, using deionized water as the medium, at a pH of 2-3, cellulose is subjected to a light-protected oxidation reaction using sodium periodate, with a mass ratio of sodium periodate to cellulose of (1.2-1.4): (0.9-1.1) to obtain dialdehyded cellulose; S2, dialdehyded cellulose, 2-aminoethanesulfonic acid, and 2-methylpyridine borane were subjected to Schiff base reductive amination reaction in deionized water at 59-65 °C at a mass ratio of (0.9-1.1): (2.0-6.0): (0.3-0.33), and then impurities were removed to obtain a sulfonated nanocellulose suspension; S3, forming the sulfonated nanocellulose suspension by vacuum filtration, and then drying it to obtain a sulfonated nanocellulose film with high proton conductivity.

2. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 1, characterized in that: The light-protected oxidation reaction described in S1 was carried out at 48-52 °C for 3.0-3.8 h.

3. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 1, characterized in that: The cellulose described in S1 is bleached coniferous wood cellulose.

4. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 1, characterized in that: S1 first disperses the bleached coniferous cellulose uniformly in deionized water, and the mass ratio of deionized water to bleached coniferous cellulose is (99~101): (0.9~1.1). Then, sodium periodate is added to obtain a mixed solution. The pH of the mixed solution is adjusted to 2~3 using 0.1 M HCl solution. Finally, an oxidation reaction is carried out under light-proof conditions to obtain a first reaction solution. The product in the first reaction solution is washed to obtain dialdehyded cellulose.

5. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 4, characterized in that: S1 uses deionized water and ethanol, combined with vacuum filtration to wash the product until the washing liquid is neutral to obtain dialdehyded cellulose, and then deionized water is added. The mass ratio of deionized water to bleached coniferous cellulose is (0.9~1.1): (9.9~11.1) to obtain a dialdehyded cellulose suspension.

6. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 5, characterized in that: S2 adds 2-aminoethanesulfonic acid and 2-methylpyridine borane to the dialdehyded cellulose suspension, and carries out Schiff base reductive amination reaction at 59~65℃ for 10~13 hours to obtain a second reaction solution. Then, impurities are removed to obtain a sulfonated nanocellulose suspension.

7. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 6, characterized in that: S2: dialyzing the second reaction solution in deionized water for 69-75 hours to obtain a sulfonated nanocellulose suspension.

8. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 1, characterized in that: S3 forms the sulfonated nanocellulose suspension on a PVDF membrane by vacuum filtration, and then dries it at 40-50° C. for 5.5-6.5 hours to form a sulfonated nanocellulose film with high proton conductivity on the PVDF membrane.

9. The method for preparing a sulfonated nanocellulose film with high proton conductivity according to claim 8, characterized in that: S3 peels off the sulfonated nanocellulose film with high proton conductivity on the PVDF membrane to obtain the sulfonated nanocellulose film with high proton conductivity.

10. A sulfonated nanocellulose film with high proton conductivity obtained by the method for preparing a sulfonated nanocellulose film with high proton conductivity according to any one of claims 1 to 9.

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