CN107245766A - A kind of cellulose nano-fibrous preparation method of low energy consumption - Google Patents

Abstract

The invention discloses a method for preparing cellulose nanofibers with low energy consumption. The dried cellulose raw materials are fully stirred and swollen in a mixed solution of tetrabutylammonium acetate and dimethyl sulfoxide, and then maleic anhydride is added. After reacting under mild conditions, the prepared cellulose nanofibers are replaced with water by centrifugation and washing to obtain a stable aqueous dispersion of cellulose nanofibers. The method can obtain evenly dispersed and uniformly sized cellulose nanofibers in one step without any form of mechanical treatment. The diameter of the fibers is uniformly distributed, about 5‑10 nm, and the length is >500 nm. The method provided by the invention can effectively prepare cellulose nanofibers from bamboo dissolving pulp in one step, the process is simple and easy to operate, the energy consumption is low, and the surface modification of cellulose can be completed simultaneously in the preparation process, so it has broad applications Prospects.

Description

A kind of preparation method of cellulose nanofiber with low energy consumption

technical field

The invention belongs to the field of natural polymer materials, and in particular relates to a preparation method of cellulose nanofibers with low energy consumption.

Background technique

In recent years, with people's in-depth understanding of green life and environmental protection, people's demand for green biodegradable products is increasing day by day. As a biodegradable material, cellulose has also received more and more attention. As the most abundant natural polymer in the world, nature can synthesize about 100 billion tons of cellulose every year, and it can be recycled. Due to the hydrogen bond between natural cellulose molecules, the cellulose has a strong hydrogen bond network structure, high molecular weight and crystallinity, but due to its supramolecular structure, it is difficult to dissolve cellulose in general solvents. The melting temperature is close to its decomposition temperature, which greatly limits its application range. Controlling cellulose molecules and their supramolecular aggregates in the nanoscale range, and thus creating new nanofine chemicals and new nanomaterials with excellent functions, has become the frontier of cellulose science. Compared with powdered cellulose and microcrystalline cellulose, cellulose nanofibers (CNF) have many excellent properties, such as high transparency, high crystallinity, high purity, high Young's modulus, ultrafine structure, High degree of polymerization, high hydrophilicity and high strength, etc. Therefore, the research on the preparation and application of cellulose nanofibers is the focus and hotspot of cellulose chemistry research at home and abroad.

Although many methods for preparing cellulose nanofiber materials have been developed at present, such as physical mechanical methods (CN102220718A, CN103492637A), TEMPO oxidation (CN103827146A, Biomacromolecules, 2006,7, 1687) and other methods, but because these methods either have high energy consumption or There is a problem of polluting the environment, which prevents the production and application of cellulose nanofibers in large quantities.

Room temperature ionic liquids can dissolve various organic and inorganic substances and can be recycled. As an environmentally friendly green solvent, it is gradually being applied to the preparation of cellulose nanofibers. Since 1970, some organic solvent systems have been developed for directly dissolving cellulose, such as dimethylacetamide-lithium chloride mixed system (DMAc-LiCl) (US, 1980; Cellulose, 2003, 10, 283) N- Methylmorpholine oxide-water mixed system (NMMO-H ₂ O) (Progressin Polymer Science, 2001, 26, 1473; ActaPolytechnicaHungarica, 2008, 5; Cellulose, 2002, 9, 283), and other solvent systems. The solubility of cellulose in DMAc-LiCl is very low, so its commercial application is limited. Cellulose has a high solubility in NMMO-H ₂ O and has been applied in the industrial production of cellulose fibers. This process is a closed-loop system and NMMO can be recycled, so it is recognized as an environmentally friendly method for preparing cellulose fibers. However, both NMMO and cellulose tend to decompose under harsh dissolution conditions (Cellulose, 2002, 9, 283; Holzforschung, 2001, 55, 661).

In recent years, quaternary ammonium salt ionic liquids, such as tetrabutylammonium fluoride (TBAF) (Macromolecular Chemistry & Physics, 2000, 201, 627), tetraethylammonium chloride (TEAC), 40% tetrabutylammonium hydroxide ( TBAH) and co-solvents were found to dissolve cellulose and have high solvency (Chemical Communications, 2012, 48, 1808). For TBAF and TEAC, DMSO is an excellent co-solvent (Journal of Polymer Science Polymer Symposia, 1973, 42, 1531); and DMSO is an excellent polymer swelling agent (Biomacromolecules, 2009, 10, 2401) .

Using the synergistic effect of quaternary ammonium salt ionic liquids and co-solvents to dissolve cellulose raw materials in an adjustable manner, on this basis, a method for preparing cellulose nanofibers can be developed, which can effectively reduce the energy consumption in the preparation process and prepare Produce uniform and stable cellulose nanofibers.

Contents of the invention

Purpose of the invention: The purpose of the present invention is to provide a method for preparing cellulose nanofibers with low energy consumption, which can effectively prepare single cellulose nanofibers with uniform dispersion and uniform and controllable size.

Technical solution: In order to realize the above-mentioned purpose of the invention, the technical solution adopted in the present invention is:

A method for preparing cellulose nanofibers with low energy consumption, comprising the steps of:

1) Fleece and disperse the cellulose raw material;

2) Swell the dispersed cellulose raw material in the ionic liquid, and then add the acid anhydride directly into the ionic liquid for reaction;

3) Wash the fibers in step 2) with dimethyl sulfoxide, centrifuge, remove the ionic liquid and unreacted anhydride, and obtain a stable cellulose nanofiber suspension;

4) Disperse the cellulose nanocellulose obtained in step 3) in an organic solvent, or disperse it in water after replacing with an ethanol solvent, to obtain a stable aqueous suspension.

In the low-energy-consumption cellulose nanofiber preparation method, the swelling temperature is 30°C, and the swelling time is 30min-2h.

In the method for preparing cellulose nanofibers with low energy consumption, the acid anhydride used is maleic anhydride or succinic anhydride.

In the method for preparing cellulose nanofibers with low energy consumption, in the reaction between cellulose and acid anhydride, the molar ratio of acid anhydride to anhydroglucose is 2-25:1.

In the method for preparing cellulose nanofibers with low energy consumption, in the reaction of cellulose and acid anhydride, the reaction temperature is 30°C, and the reaction time is 30min-1h.

In the method for preparing cellulose nanofibers with low energy consumption, the organic solvent includes dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

In step 1), the specific process is: use PTI and PFI mills to decompose the cellulose raw materials, dry the decomposed raw materials, and then disperse them with an IKA grinder for 5 minutes to obtain a fluffy cellulose raw material; specific operating conditions: use a PTI mill Decompose at 15000rpm for 10min, then use PFI mill to decompose for 10min at 1000rpm-3000rpm.

In step 2), specifically: use TBAA/DMSO ionic liquid system with TBAA concentration of 1%-5% to swell the cellulose raw material at 30°C for 1 hour, and then add different proportions of acid anhydride to react at a suitable temperature.

In step 3), specifically: centrifugation treatment: the above-mentioned cellulose ionic liquid mixture after the acid anhydride reaction is washed with dimethyl sulfoxide, centrifuged at 12500 rpm for 10 minutes, the supernatant is removed, and the cellulose is precipitated to obtain a stable dispersion. cellulose nanofiber solution.

Beneficial effect: compared with the prior art, the advantages of the present invention include:

1) The overall energy consumption required for the preparation process of the present invention is low, and the cellulose nanofibers with uniform size can be obtained without any mechanical treatment after the cellulose raw materials are swelled and reacted with acid anhydride. What is not in the technology is a breakthrough to the existing technology.

2) The reactions in the present invention are all around room temperature, and the conditions are mild and easy to control.

3) Cellulose nanofibers with different degrees of surface substitution can be obtained by adjusting the proportion of acid anhydride added; the obtained cellulose nanofibers with higher degrees of surface substitution are easy to form gels in water, and have good application prospects.

4) The cellulose nanofibers prepared by the present invention are uniform in size, relatively large in length and diameter, with a fiber diameter of about 5-10 nm and a length greater than 500 nm.

5) The present invention solves the problems of the existing chemical and physical methods, strong acid corrosion, high equipment requirements, high energy consumption, uneven size of the prepared cellulose nanofibers, and easy aggregation between fibers. The invention is simple and efficient in operation and can directly obtain surface-modified cellulose nanofibers.

Description of drawings

Fig. 1 is the transmission electron micrograph of the cellulose nanofiber that embodiment 1 makes;

Fig. 2 is the transmission electron micrograph of the cellulose nanofiber that embodiment 2 makes;

Fig. 3 is the transmission electron micrograph of the cellulose nanofiber that embodiment 3 makes;

Fig. 4 is the X-ray diffraction pattern of the used raw material bamboo dissolving pulp and the prepared cellulose nanofibers.

detailed description

The content of the present invention will be described below in conjunction with specific examples. It should be understood that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Example 1

Dissolve the bamboo dissolving pulp board with PTI mill at 15000rpm for 10min, then use PFI mill at 1000rpm-3000rpm for 10min; after drying the pulp board after deflaking, disperse with IKA mill for 5min to obtain fluffy cellulose raw material. Take 0.1 g of the dispersed bamboo dissolving pulp and add it into 10 g of TBAA/DMSO ionic liquid system with TBAA concentration of 3%, and swell at 30°C for 1 h. Subsequently, maleic anhydride with a molar ratio of 25:1 was added immediately, and reacted at 65° C. for 60 minutes. Finally add DMSO to wash, centrifuge at 12500rpm for 10min, remove the supernatant, repeat several times until white cellulose nanofibers are obtained; add ethanol and centrifuge to remove the supernatant, wash twice; finally add water and centrifuge once to obtain cellulose nanofibers Hydrogels.

Example 2

Dissolve the bamboo dissolving pulp board with PTI mill at 15000rpm for 10min, then use PFI mill at 1000rpm-3000rpm for 10min; after drying the pulp board after deflaking, disperse with IKA mill for 5min to obtain fluffy cellulose raw material. Take 0.1 g of the dispersed bamboo dissolving pulp and add it to 10 g of TBAA/DMSO ionic liquid system with TBAA concentration of 3%, and swell at 30°C for 1 hour. Subsequently, maleic anhydride with a molar ratio of 8:1 was added immediately, and reacted at 60° C. for 30 minutes. Finally add DMSO to wash, centrifuge at 12500 rpm for 10 min, remove the supernatant, and repeat several times until white cellulose nanofibers are obtained; add ethanol and centrifuge to remove the supernatant, wash twice; finally add water and centrifuge once to obtain cellulose nanofibrous hydrogels.

Example 3

Dissolve the bamboo dissolving pulp board with PTI mill at 15000rpm for 10min, then use PFI mill at 1000rpm-3000rpm for 10min; after drying the pulp board after deflaking, disperse with IKA mill for 5min to obtain fluffy cellulose raw material. Take 0.1 g of the dispersed bamboo dissolving pulp and add it to 10 g of TBAA/DMSO ionic liquid system with TBAA concentration of 3%, and swell at 30°C for 1 hour. Subsequently, maleic anhydride with a molar ratio of 8:1 was added immediately, and reacted at 30 °C for 30 min. Finally, add DMSO, centrifuge at 12500rpm for 10 min, remove the supernatant, repeat several times until white cellulose nanofibers are obtained; add ethanol and centrifuge to remove the supernatant, wash twice; finally add water and centrifuge once to obtain cellulose nanofibers Hydrogels.

Example 4

Dissolve the bamboo dissolving pulp board with PTI mill at 15000rpm for 10min, then use PFI mill at 1000rpm-3000rpm for 10min; after drying the pulp board after deflaking, disperse with IKA mill for 5min to obtain fluffy cellulose raw material. Take 0.1 g of the dispersed bamboo dissolving pulp and add it to 10 g of TBAA/DMSO ionic liquid system with TBAA concentration of 3%, and swell at 30°C for 1 hour. Subsequently, maleic anhydride with a molar ratio of 6:1 was added immediately, and reacted at 30° C. for 30 minutes. Finally, add DMSO, centrifuge at 12500rpm for 10 min, remove the supernatant, repeat several times until white cellulose nanofibers are obtained; add ethanol and centrifuge to remove the supernatant, wash twice; finally add water and centrifuge once to obtain cellulose nanofibers Hydrogels.

Example 5

Dissolve the bamboo dissolving pulp board with PTI mill at 15000rpm for 10min, then use PFI mill at 1000rpm-3000rpm for 10min; after drying the pulp board after deflaking, disperse with IKA mill for 5min to obtain fluffy cellulose raw material. Take 0.1 g of the dispersed bamboo dissolving pulp and add it to 10 g of TBAA/DMSO ionic liquid system with TBAA concentration of 2%, and swell at 30°C for 1 h. Subsequently, maleic anhydride with a molar ratio of 6:1 was added immediately, and reacted at 60° C. for 30 minutes. Finally, add DMSO, centrifuge at 12500rpm for 10 min, remove the supernatant, repeat several times until white cellulose nanofibers are obtained; add ethanol and centrifuge to remove the supernatant, wash twice; finally add water and centrifuge once to obtain cellulose nanofibers Hydrogels.

Example 6

Dissolve the bamboo dissolving pulp board with PTI mill at 15000rpm for 10min, then use PFI mill at 1000rpm-3000rpm for 10min; after drying the pulp board after deflaking, disperse with IKA mill for 5min to obtain fluffy cellulose raw material. Take 0.1 g of the dispersed bamboo dissolving pulp and add it to 10 g of TBAA/DMSO ionic liquid system with TBAA concentration of 3%, and swell at 30°C for 1 hour. Subsequently, succinic anhydride with a molar ratio of 4:1 was added immediately, and reacted at 30° C. for 30 minutes. Finally, add DMSO, centrifuge at 12500rpm for 10 min, remove the supernatant, repeat several times until white cellulose nanofibers are obtained; add ethanol and centrifuge to remove the supernatant, wash twice; finally add water and centrifuge once to obtain cellulose nanofibers Hydrogels.

Referring to the accompanying drawings, the cellulose nanofibers prepared in Examples 1, 2, and 3 were tested by TEM, and the results showed that the prepared cellulose nanofibers were single fibers with uniform dispersion and uniform size. The diameter is between 5-10nm.

Claims (10)

1. A method for preparing cellulose nanofibers with low energy consumption, comprising the steps of: 1) Fleece and disperse the dried cellulose raw materials; 2) Swell the dispersed cellulose raw material in the ionic liquid, and then add the acid anhydride directly into the ionic liquid for reaction; 3) Wash the fibers in step 2) with dimethyl sulfoxide, centrifuge, remove the ionic liquid and unreacted anhydride, and obtain a stable cellulose nanofiber suspension; 4) Disperse the cellulose nanocellulose obtained in step 3) in an organic solvent, or disperse it in water after replacing with an ethanol solvent, to obtain a stable aqueous suspension. 2. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: the adopted ionic liquid is tetrabutylammonium acetate, and the co-solvent is dimethyl sulfoxide. 3. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: the swelling temperature is 30-65°C, and the swelling time is 30min-2h. 4. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: the acid anhydride used is maleic anhydride or succinic anhydride. 5. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: in the reaction between cellulose and acid anhydride, the molar ratio of acid anhydride to anhydroglucose is 2-25:1. 6. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: in the reaction of cellulose and acid anhydride, the reaction temperature is 30-65°C, and the reaction time is 30min-1h. 7. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: organic solvents include dimethylsulfoxide, N,N-dimethylformamide, N,N-dimethylethane amides. 8. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that: in step 1), the specific process is: use PTI and PFI mills to decompose the cellulose raw materials, and the decomposed raw materials are dried , and then disperse for 5 minutes with an IKA grinder (A10 basic) to obtain a fluffy cellulose raw material. 9. The low-energy-consumption cellulose nanofiber preparation method according to claim 1, characterized in that: in step 2), specifically: using a TBAA/DMSO ionic liquid system with a TBAA concentration of 1%-5% to disperse The cellulose raw material was swelled at 30°C for 1 h, and then reacted at an appropriate temperature by adding different proportions of acid anhydride. 10. The method for preparing cellulose nanofibers with low energy consumption according to claim 1, characterized in that in step 3), specifically: centrifugation treatment: the cellulose ionic liquid mixture is washed with dimethyl sulfoxide after the acid anhydride reaction Afterwards, centrifuge at 12500 rpm for 10 min, remove the supernatant, take the cellulose precipitate, and finally obtain a stable dispersed cellulose nanofiber solution.