Method for reducing viscosity of ionic liquid cellulose solution

Abstract

The invention relates to the technical field of cellulose materials, in particular to a method for reducing viscosity of an ionic liquid cellulose solution. The method comprises the following steps: mixing an ionic liquid cellulose solution with transition metal salt; the transition metal salt is at least one of copper chloride, manganese chloride, anhydrous zinc acetate, zinc acrylate, anhydrous copper acetate and zinc iodide. The non-covalent interaction between anion and cation pairs in the ionic liquid is adjusted based on the complexing action of transition metal ions, a simple and effective method for reducing the viscosity of an ionic liquid cellulose solution system is provided, and meanwhile, the loss of the performance of a cellulose material caused by the use of a cosolvent is avoided; the method provided by the invention is beneficial to solving the problem that the high-viscosity cellulose solution hinders the development and utilization of cellulose resources, is simple and practicable, is relatively low in cost, and has a very wide industrial application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of cellulose materials, and in particular to a method for reducing the viscosity of an ionic liquid cellulose solution. Background Art

[0002] Cellulose is a linear polymer formed by β-glucose linked end to end by glycosidic bonds. It is widely present in the cell walls of plants, bacteria and other organisms. The average content of cellulose in plant cells is about 33%, making it one of the most abundant biomass materials on earth. The efficient development and utilization of cellulose resources is of great significance to the sustainable development of human civilization. Research on the dissolution of cellulose in ionic liquids has always been a hot topic.

[0003] However, ionic liquids usually have very high viscosities, usually two orders of magnitude higher than conventional organic solvents. On the one hand, the dissolution rate of cellulose is limited by the high viscosity of ionic liquids. On the other hand, dissolved cellulose with a high molecular weight can still further increase the viscosity, leading to difficulties in subsequent processes. Studies have pointed out that the high viscosity of ionic bodies is due to the strong non-covalent interactions between cations and anions in ionic liquid molecules, including electrostatic forces and hydrogen bonding interactions. For ionic liquids with cellulose solubility, the hydrogen bond alkalinity of their anions must reach a certain threshold, otherwise they will lose their solubility for cellulose. Therefore, it is difficult to adjust the interaction between anions and cations to reduce viscosity by adjusting the anion-cation pairs.

[0004] So far, the viscosity of cellulose solution can only be reduced by using co-solvents. However, the addition of co-solvents will inevitably lead to a decrease in cellulose concentration and a loss of its regeneration material properties. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention proposes a method for reducing the viscosity of an ionic liquid cellulose solution, wherein the ionic liquid cellulose solution is mixed with a transition metal salt; the transition metal salt is at least one of cupric chloride, manganese chloride, anhydrous zinc acetate, zinc acrylate, anhydrous copper acetate, and zinc iodide.

[0006] The present invention finds that the addition of transition metal salts will form coordinated ions with ionic liquid anions, change the original hydrogen bond network in the ionic liquid and achieve the regulation of non-covalent interactions between anions and cations. Therefore, adding transition metal salts to ionic liquid cellulose solutions is expected to reduce the viscosity of the system. However, after a large number of screenings of transition metal salts, the present invention finds that not all transition metal salts can effectively reduce the viscosity of the system, only specific types of transition metal salts can effectively reduce the viscosity of the ionic liquid cellulose solution, and different types of transition metal salts have different viscosity reducing effects. When the above transition metal salts are selected, not only can the viscosity of the ionic liquid cellulose solution system be effectively reduced, but also the physical and chemical properties of the regenerated cellulose will not be changed.

[0007] Preferably, the ionic liquid is 1-butyl-3-methylimidazolium chloride.

[0008] Preferably, the method for preparing the ionic liquid cellulose solution comprises: mixing the ionic liquid with microcrystalline cellulose, and heating and stirring to obtain the ionic liquid cellulose solution.

[0009] Preferably, the heating temperature is above 110°C.

[0010] Preferably, the stirring speed is above 300 rpm.

[0011] Preferably, the mass ratio of the ionic liquid to the microcrystalline cellulose is 100:(1-10).

[0012] Preferably, the mass ratio of the ionic liquid to the microcrystalline cellulose is 100:(2-8).

[0013] Preferably, the mass ratio of the ionic liquid to the microcrystalline cellulose is 100:(4-6).

[0014] Preferably, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1:2 to 1:5 (eg, 1:2, 1:3, 1:4, 1:5).

[0015] Preferably, when the transition metal salt contains cupric chloride, anhydrous zinc acetate or zinc acrylate, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1:(2-5); when the transition metal salt contains manganese chloride or anhydrous copper acetate, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1:(4-5); when the transition metal salt contains zinc iodide, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1:(3-5).

[0016] Furthermore, the present invention provides application of the method in any of the above embodiments in the preparation of cellulose materials.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention regulates the non-covalent interaction between anion and cation pairs in ionic liquids based on the complexation of transition metal ions, provides a simple and effective method for reducing the viscosity of ionic liquid cellulose solution systems, and avoids the loss of performance of cellulose materials caused by the use of co-solvents, which is conducive to solving the problem that high-viscosity cellulose solutions hinder the development and utilization of cellulose resources. The method of the present invention is simple, easy to operate, low in cost, and has a very broad prospect for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a comparison of cellulose solution before and after adding copper chloride.

[0019] Figure 2 These are the infrared and Raman spectra of the cellulose solution and the cellulose solution with copper chloride added.

[0020] Figure 3 The characterization results of the regenerated cellulose line are infrared spectrum (a), solid nuclear magnetic carbon spectrum (b), and X-ray diffraction spectrum (c).

[0021] Figure 4 The infrared spectral imaging results of the cross section of the regenerated cellulose thread obtained before and after the addition of copper chloride, wherein (a) and (c) are the infrared spectral imaging results of the cross section of the regenerated cellulose thread obtained before the addition of copper chloride, (b) and (d) are the infrared spectral imaging results of the cross section of the regenerated cellulose thread obtained after the addition of copper chloride. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] In the following examples, the Raman spectra were measured using a LabRAM HR Everlution laser confocal Raman spectrometer from Horiba, Japan. The samples were placed in glass capillaries for testing, with a laser wavelength of 632 nm. The infrared spectra were measured using a Frontier Fourier transform infrared spectrometer from PerkinElmer, USA, with a wavelength range of 4000-650 cm -1 , attenuated total reflection mode test, cumulative scan 16 times, spectral resolution 4 cm-1 The XRD test was carried out using a D8 Advances X-ray diffractometer from Bruker, Germany, with Cu Kα rays as the excitation source at 40 kV and 2 θ The range is 5~60°, and the scanning rate is 5° / min. The solid-state NMR carbon spectrum was measured using a JNM-ECZ600R / M1 cross-polarization magic angle spinning NMR spectrometer from JEOL Ltd. The magic angle spinning frequency was 12 kHz, the cross-polarization contact time was 2 milliseconds, and the relaxation time before each signal acquisition was 2 seconds.

[0024] The infrared spectral imaging characterization method of regenerated cellulose thread is as follows: the regenerated cellulose thread is embedded in resin and then sliced ​​into calcium fluoride salt slices. The imaging characterization is performed using a Spotlight 400 spectral microscope from PerkinElmer, USA. The spectral range is 4000~3000 cm -1 (The resin has no characteristic infrared absorption in this spectral range), spatial resolution 6.25×6.25 μm, spectral resolution 8 cm -1 , 8 cumulative scans. The instrument's own software SpectrumIMAGE was used to perform principal component analysis on the test data to obtain a chemical image of the principal component score distribution.

[0025] The test method for the viscosity of the ionic liquid cellulose solution system is as follows: the viscosity is tested using a Shanghai Jingtian SNB-AI digital viscometer, the test mode is selected as manual mode, 27# rotor, test temperature is 80°C, and the rotor speed is 80 r / min.

[0026] Example 1 Preparation of ionic liquid cellulose solution

[0027] Weigh the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 0.2 g of microcrystalline cellulose at a 5wt% addition ratio. Add the two into a stoppered transparent glass bottle in turn and shake them thoroughly to mix them completely. Heat the glass bottle in a 110 ℃ oil bath for 30 min while magnetically stirring at 300 rpm to dissolve, and obtain a clear and transparent ionic liquid cellulose solution.

[0028] Example 2

[0029] Weigh 0.75 g of copper chloride (the molar ratio of copper chloride to ionic liquid is 1:4) and add it to the ionic liquid cellulose solution prepared in Example 1, and stir until the copper chloride is completely dissolved to obtain an orange-yellow solution. Figure 1 The infrared and Raman spectra of cellulose solution and cellulose solution after adding copper chloride are shown in Figure 2 After adding copper chloride, the Raman spectrum is at ~270 cm -1The appearance of characteristic bands indicates that chloride ions and copper ions form coordinated ions; the infrared spectrum belongs to the CH stretching vibration absorption band of the 2# carbon position on the imidazole ring of the ionic liquid, which has obvious displacement and deformation, indicating that the addition of copper ions has significantly changed the non-covalent interaction between the anion and cation pairs in the ionic liquid. Viscosity testing found that the viscosity of the system decreased by about 39% after the addition of copper chloride.

[0030] The cellulose solution obtained before and after the addition of copper chloride was squeezed into pure water through a syringe to obtain a regenerated cellulose gel line. After washing several times to remove the ionic liquid and copper chloride, the regenerated cellulose line was dried in an oven at 90°C.

[0031] Figure 3 The infrared spectrum, solid nuclear magnetic carbon spectrum and X-ray diffraction spectrum characterization results of the regenerated cellulose line. By comparing the spectra, it was found that the addition of copper chloride does not change the molecular structure of regenerated cellulose, the conformation of cellulose molecules, the crystal structure and crystallinity.

[0032] Figure 4 The infrared spectroscopy imaging results of the cross-section of the regenerated cellulose thread before and after the addition of copper chloride. It can be seen that the addition of copper chloride does not change the microstructure of the regenerated cellulose thread, and the cellulose thread still has a high crystallinity in the outer layer and a low crystallinity in the inner layer.

[0033] Example 3

[0034] Different proportions (the molar ratio of transition metal salt to ionic liquid was set to 1:2, 1:3, 1:4, 1:5, respectively) and different types of transition metal salts were added to the ionic liquid cellulose solution prepared in Example 1, and the viscosity of the cellulose solutions before and after treatment in different treatment groups was tested. The viscosity change of the system was statistically calculated (change (%) = (viscosity after treatment-viscosity before treatment) / viscosity before treatment × 100%). The results are shown in Table 1.

[0035] Table 1

[0036] Note: — indicates that the viscosity of the system increases.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing the viscosity of an ionic liquid cellulose solution, characterized in that: The ionic liquid cellulose solution is mixed with a transition metal salt; the transition metal salt is at least one of cupric chloride, manganese chloride, anhydrous zinc acetate, zinc acrylate, anhydrous copper acetate, and zinc iodide.

2. The method according to claim 1, characterized in that The ionic liquid is 1-butyl-3-methylimidazolium chloride.

3. The method according to claim 1, characterized in that The preparation method of the ionic liquid cellulose solution comprises: mixing the ionic liquid with microcrystalline cellulose, and heating and stirring to obtain the ionic liquid cellulose solution.

4. The method according to claim 3, characterized in that: The heating temperature is above 110°C.

5. The method according to claim 3, characterized in that: The stirring speed is above 300 rpm.

6. The method according to claim 3, characterized in that The mass ratio of ionic liquid to microcrystalline cellulose is 100:(1~10).

7. The method according to claim 1, characterized in that The ionic liquid cellulose solution is mixed with the transition metal salt according to a molar ratio of the transition metal salt to the ionic liquid of 1:2 to 1:

5.

8. The method according to claim 7, characterized in that When the transition metal salt contains copper chloride, anhydrous zinc acetate or zinc acrylate, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1: (2-5); when the transition metal salt contains manganese chloride or anhydrous copper acetate, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1: (4-5); when the transition metal salt contains zinc iodide, the ionic liquid cellulose solution is mixed with the transition metal salt in a molar ratio of the transition metal salt to the ionic liquid of 1: (3-5).

9. Use of the method according to any one of claims 1 to 8 in the preparation of cellulose materials.

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