CN112010985A - Method for preparing cellulose nanocrystals by hydrolyzing cellulose with eutectic solvent - Google Patents
Method for preparing cellulose nanocrystals by hydrolyzing cellulose with eutectic solvent Download PDFInfo
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Abstract
The invention relates to a method for preparing cellulose nanocrystals by hydrolyzing cellulose with a eutectic solvent, belonging to the field of preparation of natural high polymer materials. The cellulose nanocrystal is prepared by catalyzing and hydrolyzing 1-10 parts by mass of cellulose pulp by an acidic eutectic system consisting of 40-50 parts by mass of citric acid, 40-50 parts by mass of betaine, 5-10 parts by mass of distilled water and 5-10 parts by mass of sulfuric acid, wherein the reaction time is 2-6 h, and the reaction temperature is 50-65 ℃. The reaction condition is mild, and the operation is simple. The cellulose nanocrystals are prepared by using the acidic eutectic solvent in one step, the reaction efficiency of preparing the cellulose nanocrystals by using the eutectic system is effectively improved, and the product properties of the cellulose nanocrystals are improved. The prepared cellulose nanocrystal has good thermal stability and high crystallinity, and is stable in dispersion in water.
Description
Technical Field
The invention relates to the field of preparation of natural high polymer materials, in particular to a method for preparing cellulose nanocrystals by hydrolyzing cellulose with a eutectic solvent.
Background
Cellulose, a natural polymer material widely existing in nature, has the characteristics of biodegradability, chemical modification, renewability and the like. In recent years, research on nanocellulose has led to more widespread and abundant utilization of cellulose. Due to the existence of the special structures of crystalline regions and amorphous regions of the cellulose, the preparation and application of the nano-cellulose have diversified development.
Cellulose Nanocrystals (CNCs) have biodegradability, high strength, low density, high crystallinity, high aspect ratio, and unique optical properties. In addition, the polyhydroxy structure on the surface of the CNCs is easier to further modify, and other special properties can be provided. Meanwhile, the CNCs are simple in preparation mode, can be separated from biological resources such as wood, cotton, hemp, flax, tunica (aquatic invertebrates) and the like, and can also be obtained in a bottom-up biomolecular synthesis mode. Therefore, the CNCs show good application prospects in the fields of biomedical application, sensors, papermaking, sewage treatment, packaging printing and the like.
The eutectic solvent (DES) was first a mixture with a low melting point prepared in 2001 by Abott et al, mixed with a hydrogen bond donor and a hydrogen bond acceptor. The DES comprises a hydrogen bond donor and a hydrogen bond acceptor, two or three components are simply heated according to a certain proportion to obtain a clear solvent (DES), and the DES has strong dissolving capacity, difficult volatilization, high boiling point, low melting point, low toxicity and environmental protection, and is called as a green solvent. Nowadays, DES has been applied in the fields of pretreatment for bioethanol production, electrolytes, synthesis media, electrochemistry, DNA and RNA technology mediators, biocatalysis, nanoparticle synthesis, bioactive substance extraction, etc.
The sulfuric acid hydrolysis method is the most commonly used method in the inorganic acid hydrolysis method. CNCs prepared by sulfuric acid hydrolysis have the same cellulose-I type crystal structure as natural cellulose, and the structural size distribution is uniform. The resulting CNCs are usually present as a stable suspension, but are highly susceptible to aggregation upon drying. In addition, sulfonic acid esters can be introduced during the sulfuric acid hydrolysis process, thereby resulting in poor thermal stability of the CNCs and affecting subsequent processing applications thereof. And the preparation process of the sulfuric acid has the defects of strong corrosivity, difficult waste acid treatment, serious pollution and the like. Compared with the prior art, the organic acid hydrolysis reaction condition is mild, the corrosivity is low, the surface modification of the nano-cellulose can be synchronously realized, functional groups are introduced, the environmental protection pressure is low, and the cyclic utilization can be realized. But still has the defects of slow reaction speed, higher acid dosage, water dosage, higher treatment temperature and the like.
Eutectic systems have strong capability of breaking hydrogen bonds of cellulose, and are commonly used for pretreatment of cellulose, such as the method for preparing cellulose nanocrystals, and usually need mechanical means. Although the method solves the problems of low yield and low product thermal stability caused by using inorganic acid to prepare the cellulose nanocrystals, the whole steps are complicated. If the eutectic system is not assisted by mechanical means at a lower temperature, the preparation of the CNCs can be realized efficiently in one step, the product properties can be effectively improved, and the method has important significance for industrial production and utilization of the CNCs.
Disclosure of Invention
The invention mainly aims to further improve the hydrolysis reaction efficiency of preparing the cellulose nanocrystals by the hydrolysis of the eutectic solvent and effectively improve the product properties.
In order to achieve the above purpose, the present invention improves the hydrolysis reaction activity by changing the composition of the eutectic system and introducing a catalyst into the eutectic system, and specifically comprises the following steps:
(1) adding 40 parts by mass of citric acid, 40-50 parts by mass of betaine and 5-10 parts by mass of distilled water into a reactor at the temperature of 0-30 ℃, heating to 50-65 ℃, stirring for 5-10 min to form a eutectic solvent, adding 5-10 parts by mass of concentrated sulfuric acid into the reactor, stirring for 5-10 min, adding 1-10 parts by mass of cellulose pulp, and continuously stirring for 2-6 h at the temperature of 50-65 ℃;
(2) adding 300-700 parts by mass of 60-90 ℃ distilled water into the reaction system in the step (1), centrifuging for 5-10 min at the rotating speed of 6000 r/min-10000 r/min while the solution is hot, pouring out the supernatant to keep a precipitate part, dispersing the obtained precipitate by 100-800 parts by mass of distilled water, centrifuging for 5-10 min at the rotating speed of 6000 r/min-10000 r/min, repeating the centrifugal washing process by using the distilled water for 3-6 times, and freeze-drying or spray-drying the solid obtained after washing to prepare the cellulose nanocrystals;
the cellulose pulp is one of bleached wood pulp, cotton pulp and dissolving pulp.
The stirring is preferably mechanical stirring, and the stirring speed is 100 r/min-300 r/min.
The mass fraction of the concentrated sulfuric acid is 98%.
And (3) concentrating the supernatant in the step (2) in a reduced pressure distillation mode, and taking a mixture obtained after concentration as a eutectic reaction solution to be reused for preparing the cellulose nanocrystals, wherein the repetition time is 3-4 times.
Has the advantages that:
the method for preparing the cellulose nanocrystals has mild reaction conditions, does not need subsequent mechanical treatment, and simplifies the preparation process; compared with the method (CN201810119925.6) which simultaneously uses sulfuric acid and organic acid (anhydrous oxalic acid and maleic acid) aqueous solution as reaction reagents, the reaction speed is improved, and the reaction temperature is obviously reduced. Compared with the oxalic acid dihydrate/choline chloride eutectic system as a hydrolysis medium (CN202010471311.1), the thermal stability, the crystallinity and the yield of the obtained product are improved.
Drawings
Figure 1 of the accompanying drawings is a transmission electron micrograph of cellulose nanocrystals prepared according to example 1.
Detailed Description
The following examples are given by way of illustration of embodiments of the invention and are not to be construed as limiting the invention, and it will be understood by those skilled in the art that modifications may be made without departing from the spirit and scope of the invention.
Example 1
40g of citric acid and 45g of betaine were charged into a 250mL three-necked flask at 25 ℃ and 5g of distilled water was added thereto, then heating by using an oil bath, raising the temperature to 50 ℃, mechanically stirring for 10min at the stirring speed of 100r/min to form a eutectic solvent, adding 5g of 98% sulfuric acid into a three-neck flask, stirring for 5min, adding 1g of bleached eucalyptus pulp, stirring at 55 deg.C for 5 hr, diluting the reaction mixture with 300g of 90 deg.C distilled water, centrifuging at 10000r/min for 5min, pouring out supernatant and retaining precipitate, dispersing the obtained precipitate with 100g of distilled water, centrifuging at 10000r/min for 5min, repeating the centrifuging and washing process with distilled water for 3 times, the solid obtained after washing was freeze-dried, and the yield of cellulose nanocrystals was 74.5%. The temperature of the obtained product with 5 percent of thermal decomposition weight loss is 330 ℃. The crystallinity of the product obtained was 86.3%. The product was dispersed in water at a concentration of 1 wt% and left to stand for 30 days without settling.
Example 2
40g of citric acid and 50g of betaine were charged into a 250mL three-necked flask at 25 ℃, 5g of distilled water was added thereto, then heating to 55 ℃ by using an oil bath, mechanically stirring for 10min at the stirring speed of 300r/min to form a eutectic solvent, then adding 10g of sulfuric acid with the mass concentration of 98% into a three-necked flask, stirring for 5min, adding 10g of dissolving pulp, continuously stirring for 4h at 55 ℃, diluting the reaction mixture with 700g of 60 ℃ distilled water, centrifuging at 10000r/min for 8min, pouring out supernatant and retaining precipitate, dispersing the obtained precipitate with 800g of distilled water, centrifuging at 10000r/min for 8min, repeating the centrifuging and washing process with distilled water for 5 times, the solid obtained after washing was freeze-dried, and the yield of the obtained nanocellulose crystal was 78.0%. The temperature of the obtained product with 5 percent of thermal decomposition weight loss is 332 ℃. The crystallinity of the product obtained was 80.5%. The product was dispersed in water at a concentration of 1 wt% and left to stand for 30 days without settling.
Example 3
40g of citric acid and 40g of betaine were charged into a 250mL three-necked flask at 30 ℃, 10g of distilled water was added thereto, then heating by using an oil bath, raising the temperature to 60 ℃, mechanically stirring for 10min at the stirring speed of 200r/min to form a eutectic solvent, then adding 10g of 98% sulfuric acid into a three-necked flask, stirring for 5min, adding 3g of cotton pulp, stirring at 60 deg.C for 2.5h, diluting the reaction mixture with 300g of 65 deg.C distilled water, centrifuging at 8000r/min for 5min, pouring out supernatant and retaining precipitate, dispersing the obtained precipitate with 600g of distilled water, centrifuging at 8000r/min for 5min, repeating the centrifuging and washing process with distilled water for 5 times, the solid obtained after washing was spray-dried, and the yield of the obtained nanocellulose crystals was 81.5%. The temperature of the obtained product with 5 percent of thermal decomposition weight loss is 333 ℃. The crystallinity of the product obtained was 82.7%. The product was dispersed in water at a concentration of 1 wt% and left to stand for 30 days without settling.
Example 4
40g of citric acid and 45g of betaine were charged into a 250mL three-necked flask at 25 ℃, 10g of distilled water was added thereto, then heating by using an oil bath, raising the temperature to 65 ℃, mechanically stirring for 10min at the stirring speed of 300r/min to form a eutectic solvent, adding 5g of 98% sulfuric acid into a three-necked flask, stirring for 5min, adding 10g of bleached softwood pulp, stirring at 65 deg.C for 2h, diluting the reaction mixture with 700g of 80 deg.C distilled water, centrifuging at 10000r/min for 8min, pouring out supernatant and retaining precipitate, dispersing the obtained precipitate with 800g of distilled water, centrifuging at 10000r/min for 8min, repeating the centrifuging and washing process with distilled water for 5 times, the solid obtained after washing was freeze-dried, and the yield of the obtained nanocellulose crystals was 75.2%. The temperature of the obtained product with 5 percent of thermal decomposition weight loss is 331 ℃. The crystallinity of the obtained product is 83.6 percent. The product was dispersed in water at a concentration of 1 wt% and left to stand for 30 days without settling.
Claims (3)
1. A method for preparing cellulose nanocrystals by hydrolyzing cellulose with a eutectic solvent, the method comprising the steps of:
(1) adding 40 parts by mass of citric acid, 40-50 parts by mass of betaine and 5-10 parts by mass of distilled water into a reactor at the temperature of 0-30 ℃, heating to 50-65 ℃, stirring for 5-10 min to form a eutectic solvent, adding 5-10 parts by mass of concentrated sulfuric acid into the reactor, stirring for 5-10 min, adding 1-10 parts by mass of cellulose pulp, and continuously stirring for 2-6 h at the temperature of 50-65 ℃;
(2) adding 300-700 parts by mass of 60-90 ℃ distilled water into the reaction system in the step (1), centrifuging for 5-10 min at the rotating speed of 6000 r/min-10000 r/min while the solution is hot, pouring out the supernatant to keep a precipitate part, dispersing the obtained precipitate by 100-800 parts by mass of distilled water, centrifuging for 5-10 min at the rotating speed of 6000 r/min-10000 r/min, repeating the centrifugal washing process by using the distilled water for 3-6 times, and freeze-drying or spray-drying the solid obtained after washing to prepare the cellulose nanocrystals;
the mass fraction of the concentrated sulfuric acid is 98%.
2. The method for preparing cellulose nanocrystals by hydrolyzing cellulose with the eutectic solvent according to claim 1, wherein the cellulose pulp is one of bleached wood pulp, cotton pulp and dissolving pulp.
3. The method for preparing cellulose nanocrystals by hydrolyzing cellulose with the eutectic solvent according to claim 1, wherein the stirring is mechanical stirring at a speed of 100r/min to 300 r/min.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113862318A (en) * | 2021-09-28 | 2021-12-31 | 北京化工大学 | Green and efficient refining system and method for lignocellulose |
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| RU2708307C1 (en) * | 2019-06-13 | 2019-12-05 | Федеральное государственное бюджетное учреждение науки Институт высокомолекулярных соединений Российской академии наук | Method of producing bacterial cellulose nanofibers |
| CN111187356A (en) * | 2020-03-25 | 2020-05-22 | 齐鲁工业大学 | Method for preparing microcrystalline cellulose by treating poplar wood powder with eutectic solvent and acid |
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Patent Citations (4)
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| CN108299563A (en) * | 2018-02-06 | 2018-07-20 | 天津科技大学 | A kind of sulfuric acid catalysis organic acid hydrolysis prepares the nanocrystalline method of ball shaped cellulose |
| RU2708307C1 (en) * | 2019-06-13 | 2019-12-05 | Федеральное государственное бюджетное учреждение науки Институт высокомолекулярных соединений Российской академии наук | Method of producing bacterial cellulose nanofibers |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113862318A (en) * | 2021-09-28 | 2021-12-31 | 北京化工大学 | Green and efficient refining system and method for lignocellulose |
| CN113862318B (en) * | 2021-09-28 | 2023-12-15 | 北京化工大学 | Lignocellulose refining system and method |
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