Modified nanocellulose, and methods of making and using the same

Abstract

The application discloses modified nanocellulose as well as a preparation method and application thereof. The modified nanocellulose is esterification modified on the surface of nanocellulose, and the structural formula of the surface after modification is shown as formula I: wherein n is 150-1300, R1 is selected from C 3～12 alkyl, and R2 is -CH2OH or -CHO. The modified nanocellulose provided by the application retains the original microstructure and morphology of nanocellulose, hybridizes the boron element with green friction activity, and simultaneously enhances the surface hydrophobic property of nanocellulose.

Description

Technical Field

[0001] This invention relates to the field of nanocellulose technology, and in particular to a modified nanocellulose, its preparation method, and its applications. Background Technology

[0002] Nanocellulose is a novel type of nanomaterial with superior mechanical and physical properties, and has been widely used in food packaging, biomedicine, and biomimetic materials. The surface of nanocellulose is rich in hydroxyl groups, possessing abundant active sites and strong hydrophilicity, providing a natural advantage for its application in hydrophilic environments. However, this also significantly limits its application in hydrophobic environments. Therefore, to adjust the surface hydrophilicity and hydrophobicity properties of nanocellulose to expand its application value, researchers have conducted in-depth studies on nanocellulose modification techniques.

[0003] However, a method for modifying the surface of cellulose nanocrystals by esterification disclosed in related technologies involves reacting nanocellulose with a mixture of propionic acid and nitric acid to obtain surface-esterified nanocellulose. However, current methods for modifying nanocellulose by esterification often use aqueous solvents, and the esterification products are partially hydrolyzed, resulting in low yields. In addition, the preparation process requires strong acids / bases as catalysts, which makes subsequent waste liquid treatment very difficult and raises significant environmental issues.

[0004] Therefore, it is necessary to provide a new esterified modified nanocellulose. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention provides a modified nanocellulose.

[0006] A second aspect of the present invention also provides a method for preparing modified nanocellulose.

[0007] A third aspect of the present invention also provides an application of modified nanocellulose.

[0008] According to a first aspect of the present invention, a modified nanocellulose is provided, wherein the modified nanocellulose is esterified on the surface of the nanocellulose, and the modified surface has a structural formula as shown in Formula I:

[0009]

[0010] Where n is 150 to 1300, and R1 is selected from C 3～12 The alkyl group, R2 is -CH2OH or -CHO.

[0011] The modified nanocellulose according to embodiments of the present invention has at least the following beneficial effects:

[0012] The modified nanocellulose provided by this invention retains the original microstructure and morphology of nanocellulose and possesses the excellent physical and mechanical properties of the original nanocellulose. In addition, it significantly improves the surface hydrophobic properties of the original nanocellulose and incorporates boron, which has green tribological activity. Therefore, it can achieve good and stable dispersion in non-polar media and is suitable for reinforcing composite materials, film materials, and lubricating materials to effectively enhance mechanical and tribological properties. In particular, as a lubricating additive, it can reduce the coefficient of friction and wear rate.

[0013] The method for preparing the modified nanocellulose described above, according to a second aspect embodiment of the present invention, includes the following steps:

[0014] S1. Mix nanocellulose and the first organic solvent to obtain a suspension;

[0015] S2. The compound of formula 2, the ionic liquid catalyst and the suspension are mixed and reacted, and the modified nanocellulose is obtained by solid-liquid separation.

[0016] The structural formula of compound 2 is as follows:

[0017] The definition of R1 is the same as the definition of R1 above.

[0018] The method for preparing modified nanocellulose according to embodiments of the present invention has at least the following beneficial effects:

[0019] This invention avoids the use of strong acids, employing acidic ionic liquids as catalysts to react the raw materials in an aprotic polar organic solvent, thus achieving a successful green wet chemical method for preparing modified nanocellulose. The method of this application significantly improves the yield of easily hydrolyzed borate-esterified nanocellulose.

[0020] According to some embodiments of the present invention, the acidic ionic liquid catalyst is selected from at least one of imidazole acidic ionic liquids, pyridine acidic ionic liquids, and pyrrolidone acidic ionic liquids.

[0021] According to some embodiments of the present invention, the imidazole acidic ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium hydrogen sulfate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-ethyl-3-methylimidazolium dihydrogen phosphate.

[0022] According to some embodiments of the present invention, in step S1, the concentration of nanocellulose in the suspension is 3 to 12 mg / mL.

[0023] According to some embodiments of the present invention, in step S2, the concentration of the compound of formula 2 is 12 to 48 mg / mL.

[0024] According to some embodiments of the present invention, the aprotic polar organic solvent is selected from at least one of DMSO and DMF.

[0025] According to some embodiments of the present invention, in step S2, the temperature of the reaction is 60–100°C.

[0026] According to some embodiments of the present invention, in step S2, the reaction time is 2.5 to 10 hours.

[0027] According to some embodiments of the present invention, in step S2, the concentration of the ionic liquid catalyst is 9–36 mg / mL.

[0028] According to some embodiments of the present invention, the nanocellulose is selected from cellulose nanocrystals (CNC) and cellulose nanofibers (CNF).

[0029] According to some embodiments of the present invention, the solid-liquid separation is performed by centrifugation.

[0030] A third aspect of the present invention provides the application of the modified nanocellulose described above or the modified nanocellulose prepared by the method described above in reinforced composite materials, film materials or lubricating materials.

[0031] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0033] Figure 1 These are digital photographs of the appearance of nanocellulose and the organoboronized nanocellulose powders prepared in Examples 1-4.

[0034] Figure 2 These are the FT-IR spectra of nanocellulose and the organoboronized nanocellulose prepared in Examples 1-3.

[0035] Figure 3 This is the XPS spectrum of the organoboroesterified cellulose nanoparticles prepared in Example 2.

[0036] Figure 4 These are TEM images of nanocellulose and the organoboronized nanocellulose prepared in Example 2.

[0037] Figure 5 The friction coefficient curves and average wear rate diagrams are for nanocellulose and the organoboron esterified nanocellulose prepared in Example 2, respectively, when used as castor oil lubricating additives. Detailed Implementation

[0038] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0039] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0040] Example 1

[0041] Example 1 provides a modified nanocellulose, which is prepared by esterification modification of the surface of nanocellulose. The general structural formula of the surface modification is shown in Formula I. The preparation method is as follows:

[0042]

[0043] S1. Take 0.15g of CNC (Tianjin Wood Elf Biotechnology Co., Ltd. (PS200 type: l=150-200nm, d=3-20nm),) and add it to DMSO (25mL). Incubate in a constant temperature water bath (85℃) and simultaneously disperse using ultrasonic vibration (40kHZ, 5h) to obtain a stable and uniform suspension.

[0044] S2. Separately, add 1-ethyl-3-methylimidazolium hydrogen sulfate and n-butylboronic acid to the cooled suspension. Under an inert atmosphere, stir and heat the suspension and maintain the temperature (360 rpm, 60°C, 3 h) to induce esterification on the CNC surface. After the reaction, cool and centrifuge to separate the product. Wash the product three times with DMSO, allow it to dry naturally, grind it, and vacuum dry it at 60°C for 1 hour to obtain borate-esterified cellulose nanoparticles.

[0045] Example 2

[0046] Example 2 provides a modified nanocellulose, which is prepared by esterification modification of the surface of nanocellulose. The general structural formula of the surface modification is shown in Formula I. The preparation method is as follows:

[0047]

[0048] S1. Take CNC (0.15g) and add it to DMSO (25mL). Incubate in a constant temperature water bath (85℃) and simultaneously disperse using ultrasonic vibration (40kHZ, 5h) to obtain a stable and uniform suspension.

[0049] S2. Separately, add 1-ethyl-3-methylimidazolium hydrogen sulfate and n-butylboronic acid to the cooled suspension. Under an inert atmosphere, stir and heat the suspension and keep it at 360 rpm, 80°C, for 5 hours to induce esterification on the CNC surface. After cooling, centrifuge to separate the product. Then, wash the product three times with a mixture of DMSO and DMF by centrifugation, allow it to dry naturally, grind it, and vacuum dry it at 60°C for 1 hour to obtain borate-esterified cellulose nanoparticles.

[0050] Example 3

[0051] Example 3 provides a modified nanocellulose, which is prepared by esterification modification of the surface of nanocellulose. The general structural formula of the surface modification is shown in Formula I. The preparation method is as follows:

[0052]

[0053] S1. Take CNC (0.15g) and add it to DMSO (25mL). Incubate in a constant temperature water bath (85℃) and simultaneously disperse using ultrasonic vibration (40kHZ, 5h) to obtain a stable and uniform suspension.

[0054] S2. Separately, add 1-ethyl-3-methylimidazolium hydrogen sulfate and n-butylboronic acid to the cooled suspension. Under an inert atmosphere, stir and heat the suspension and maintain the temperature (360 rpm, 100°C, 10 h) to induce esterification on the CNC surface. After the reaction, cool and centrifuge to separate the product. Wash the product three times with DMF, allow it to dry naturally, grind it, and vacuum dry it at 60°C for 1 hour to obtain borate-esterified cellulose nanoparticles.

[0055] Example 4

[0056] Example 4 provides a modified nanocellulose, which is prepared by esterification modification of the nanocellulose surface. The general structural formula of the surface modification is shown in Formula I. The preparation method is as follows:

[0057]

[0058] S1. Take CNF (Tianjin Wood Elf Biotechnology Co., Ltd. (PL2 type: l=400-1000nm, d=5-10nm), 0.30g) and add it to DMSO (25mL). Incubate in a constant temperature water bath (85℃) and simultaneously disperse using ultrasonic vibration (40kHZ, 5h) to obtain a stable and uniform suspension.

[0059] S2. Separately, add 1-ethyl-3-methylimidazolium tetrafluoroborate and n-butylboronic acid to the cooled suspension. Under an inert atmosphere, stir and heat the suspension and maintain the temperature (360 rpm, 80°C, 5 h) to induce esterification on the CNF surface. After the reaction, cool and centrifuge to separate the product. Wash the product three times with a mixture of DMSO and DMF by centrifugation, allow it to dry naturally, grind it, and vacuum dry it at 60°C for 1 hour to obtain borate-esterified nanocellulose powder.

[0060] Physical samples of nanocellulose and the modified nanocellulose prepared in Examples 1-4 are shown below. Figure 1 .

[0061] Example 5

[0062] Example 5 provides a modified nanocellulose, which is prepared by esterification modification of the nanocellulose surface. The general structural formula of the surface modification is shown in Formula I. The preparation method is as follows:

[0063]

[0064] S1. Add CNF (0.08g) to DMF (25mL), incubate in a constant temperature water bath (85℃) and simultaneously disperse using ultrasonic vibration (40kHZ, 5h) to obtain a stable and uniform suspension.

[0065] S2. Separately, add 1-ethyl-3-methylimidazolium phosphate and n-octylboronic acid to the cooled suspension. Under an inert atmosphere, stir and heat the suspension and maintain the temperature (360 rpm, 60°C, 3 h) to induce esterification on the CNF surface. After the reaction, cool and centrifuge to separate the product. Wash the product three times with DMF by centrifugation, allow it to dry naturally, grind it, and vacuum dry it at 60°C for 1 hour to obtain borate-esterified cellulose nanoparticles.

[0066] Characterization analysis

[0067] Figure 1 The images shown are digital photographs of the appearance of nanocellulose and the organoboronized nanocellulose powders prepared in Examples 1-4. Observation reveals that the dry nanocellulose powder is slightly yellow and glossy, exhibiting an aggregated state, which is due to the strong hydrogen bonding between the nanocellulose particles after drying. In contrast, the powders of Examples 1-4 are white, lack luster, and show significantly reduced agglomeration, indicating that the modified nanocellulose likely underwent some chemical changes.

[0068] Figure 2 The images show the FT-IR spectra of cellulose nanoparticles and the organoboroesterified cellulose nanoparticles prepared in Examples 1-3. Comparative analysis shows that the spectra of Examples 1-3 all retain the characteristic infrared absorption peak of CNC, with a peak at 1730 cm⁻¹.-1 1570cm -1 950cm -1 New absorption peaks appeared at the wavenumber positions, which were attributed, in turn, to the stretching vibration of the aldehyde group (-CHO), the asymmetric stretching vibration of the BO bond, and the symmetric contraction vibration of the BO bond. Furthermore, compared to CNC, the hydroxyl (-OH) stretching vibration peak (i.e., 3350 cm⁻¹) appeared in the spectra of Examples 1-3. -1 A significant blue shift occurred in the surrounding area, indicating that the modification site is the hydroxyl group: after modification, a large number of hydroxyl groups on the surface of nanocellulose are converted into -CHO or BO bonds, which significantly weakens the hydrogen bonding between nanocellulose and causes the blue shift.

[0069] Figure 3 The XPS spectrum of the organoborocyanate-esterified cellulose nanoparticles prepared in Example 2 is shown. Analysis reveals that the C / O atomic ratio of the product in Example 2 is approximately 1:2, significantly higher than the original cellulose nanoparticles (approximately 1:3), indicating the introduction of other external carbon elements onto the surface of the modified cellulose nanoparticles. Furthermore, the C1s spectrum shows that the proportion of C-C bonds increased from 9.29% to 16.38% after modification, further supporting this conclusion. Additionally, the B1s spectrum shows a distinct characteristic peak at the 192.5 eV binding energy position, attributed to the BO bond, indicating that the modification introduced B elements onto the surface of the cellulose nanoparticles. Therefore, combining the original surface chemical structure of the cellulose nanoparticles with the FT-IR spectral analysis results, it can be determined that the active sites (-OH) on the surface of the cellulose nanoparticles underwent an esterification reaction with organoboronic acid, thereby introducing B elements and their alkyl chains, thus proving the successful preparation of organoborocyanate-esterified cellulose nanoparticles.

[0070] Figure 4 The images shown are TEM images of cellulose nanocrystals and the organoboronized cellulose nanofibers prepared in Example 2. Comparative observation reveals that the microstructure and size of the organoboronized cellulose nanofibers are not significantly different from those of the cellulose nanocrystals; they still exhibit a nanorod-like shape, with a length of approximately several hundred nanometers and a diameter of approximately several tens of nanometers. The above analysis indicates that organoboronization modification only alters the surface chemical structure of the nanofibers without damaging their original microstructure.

[0071] Performance testing

[0072] Using castor oil as the base lubricant, cellulose nanocrystals and the organoboron esterified nanocellulose prepared in Example 2 were used as lubricating additives, respectively. Reciprocating tribological performance was tested using the ball-disc method (test conditions: ambient temperature; concentration 2 wt.%; test duration 30 min; load 6 N; frequency 8 Hz; stroke 10 mm; Si3N4 ball (G5 precision, d = 6 mm); GCr15 steel disk (R... a ≈0.16μm), the result is as follows Figure 5 As shown.

[0073] observe Figure 5 (a) It can be seen that the friction coefficient curves of castor oil, castor oil + CNC, and castor oil + Example 2 all first experience a very brief upward phase (nearly 20 seconds) and then remain in a very stable state, indicating that the required running-in time for this friction pair is very short, and it can quickly reach the stable wear stage of smooth operation. Further analysis Figure 5 (b) It can be seen that the average coefficient of friction of castor oil is about 0.075, castor oil + CNC is about 0.062, and castor oil + Example 2 is 0.058. This indicates that both nanocellulose and the product of Example 2 have friction-reducing effects, but the latter is slightly more effective. In addition, the wear rate corresponding to castor oil + Example 2 is only 2.25 × 10⁻⁶. -7 mm 3 / (N·m), compared to pure castor oil (approximately 5.38 × 10⁻⁶ N·m), -7 mm 3 / (N·m)) decreased by approximately 58.2%, compared to castor oil + CNC (approximately 3.85×10). -7 mm 3 / (N·m)) decreased by approximately 41.6%.

[0074] Performance test results show that when the esterified nanocellulose prepared in Example 2 is used as a lubricating additive, it can effectively reduce the coefficient of friction and the wear rate. Compared with nanocellulose, it has more efficient friction-reducing and anti-wear properties, thus demonstrating its potential as a lubricating material. The esterified nanocellulose prepared in other embodiments of the present invention has similar effects, and will not be repeated to avoid redundancy.

[0075] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A modified nanocellulose, characterized in that, The modified nanocellulose is obtained by esterification modification of the surface of nanocellulose, and the modified surface structure is shown in Formula I: Where n is 150 to 1300, and R1 is selected from C 3～12 The alkyl group, R2 is -CH2OH and / or -CHO.

2. The method for preparing modified nanocellulose according to claim 1, characterized in that, Includes the following steps: S1. Mix nanocellulose and aprotic polar organic solvent to obtain a suspension; S2. The compound of formula 2, the acidic ionic liquid catalyst and the suspension are mixed and reacted, and the modified nanocellulose is obtained by solid-liquid separation. The structural formula of compound 2 is as follows: The definition of R1 is the same as that of claim 1.

3. The preparation method according to claim 2, characterized in that, The acidic ionic liquid catalyst is selected from at least one of imidazole acidic ionic liquids, pyridine acidic ionic liquids, and pyrrolidone acidic ionic liquids.

4. The preparation method according to claim 2, characterized in that, In step S1, the concentration of nanocellulose in the suspension is 3-12 mg / mL.

5. The preparation method according to claim 2, characterized in that, In step S2, the concentration of the compound of formula 2 is 12–48 mg / mL.

6. The preparation method according to claim 2, characterized in that, The aprotic polar organic solvent is selected from at least one of DMSO and DMF.

7. The preparation method according to claim 2, characterized in that, In step S2, the reaction temperature is 60–100°C.

8. The preparation method according to claim 2, characterized in that, In step S2, the reaction time is 2.5 to 10 hours.

9. The preparation method according to claim 2, characterized in that, In step S2, the concentration of the ionic liquid catalyst is 9–36 mg / mL.

10. The application of the modified nanocellulose according to claim 1 or the modified nanocellulose prepared by the method according to any one of claims 2 to 9 in reinforced composite materials, film materials or lubricating materials.

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