CN108178802B - Preparation method of oxidized cellulose nanofibrils based on nitric acid and hydrogen peroxide - Google Patents
Preparation method of oxidized cellulose nanofibrils based on nitric acid and hydrogen peroxide Download PDFInfo
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- CN108178802B CN108178802B CN201810173515.XA CN201810173515A CN108178802B CN 108178802 B CN108178802 B CN 108178802B CN 201810173515 A CN201810173515 A CN 201810173515A CN 108178802 B CN108178802 B CN 108178802B
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- hydrogen peroxide
- nitric acid
- oxidized cellulose
- ethyl alcohol
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
- C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
- D01F2/24—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from cellulose derivatives
Abstract
The invention discloses a preparation method of oxidized cellulose nanofibrils based on nitric acid and hydrogen peroxide, which is based on a nitric acid hydrolysis system and introduces a hydrogen peroxide oxidizing reagent, and specifically comprises the following operation steps: mixing a biomass raw material, 1-8 mol/L nitric acid and 30% hydrogen peroxide, stirring and reacting for 6-96 hours at 20-80 ℃, adding absolute ethyl alcohol to terminate the reaction, standing and layering the solution, pouring out the supernatant, retaining the lower-layer precipitate, sequentially washing the lower-layer precipitate with the absolute ethyl alcohol, 50% ethanol and water, and treating by a high-pressure homogenizer to obtain the oxidized cellulose nanofibril. The method has simple and convenient process, less chemical varieties and low price, and the prepared oxidized cellulose nano-fibril has wide application prospect in the fields of water treatment, oil-water separation, nano composite materials and the like.
Description
Technical Field
The invention belongs to the technical field of nanocellulose manufacturing, and particularly relates to a method for directly preparing oxidized cellulose nanofibrils from biomass.
Background
The nano-cellulose not only has the characteristics of renewable and biodegradable natural cellulose, but also has the advantages of large specific surface area, high hydrophilicity, high transparency, high strength, high Young modulus, low thermal expansion coefficient and the like, provides possibility for forming various functional composite materials, and has wide application prospect. The biomass has the advantages of wide source, abundant reserves, reproducibility and environmental friendliness. Starting from biomass, the acquisition of biomass resources in various morphologies, in particular the manipulation, design and assembly of natural cellulose in the nanometer size range, has become a hot topic of current research in the field.
The preparation of the nano-cellulose comprises the following steps: preparation of nano microcrystalline cellulose (NCC). The NCC is obtained by hydrolyzing strong acid or cellulase to remove an amorphous area of cellulose and reserving a compact crystalline area, has a needle-shaped whisker structure (the diameter is 5-70 nm, the length is 100-400 nm), and has high crystallinity (60-90%). However, the high-intensity hydrolysis can cause a great amount of cellulose degradation, the product yield is low, and the requirement on equipment is high. And (II) preparing hairy cellulose nano crystal (HC-NC), wherein amorphous regions are obtained by cutting by chemical agents, crystalline regions are similar to NCC (the diameter is 5-10 nm, the length is 100-200 nm), and amorphous regions at two ends have a plurality of polymer high molecular chains (the length is about 100 nm). (III) preparation of microfibrillated cellulose (MFC). MFC is also called nanofibril cellulose and cellulose nanofiber, is in a fibrillar shape, has the diameter of 5-60 nm and the length of 1000-10000 nm, has flexibility, and has a molecular structure consisting of a crystalline region and an amorphous region alternately. The method has the following defects: (1) MFC is typically prepared by mechanical processes (e.g., high pressure homogenization), where cellulose is extracted from the feedstock by chemical pretreatment, followed by high-intensity mechanical forces (e.g., high pressure homogenization, high shear, microfluidization, milling, etc.) to break and fibrillate the cellulose. The preparation process of the high-pressure homogenization method generally has less pollution to the environment, but has high requirements on equipment and huge energy consumption. (2) MFC is prepared by a TEMPO oxidation method, TEMPO (piperidine nitroxide radical) -NaBr-NaClO is used for selectively oxidizing hydroxyl at the C6 position on a glucose unit into carboxyl, and electrostatic repulsion force of ionization of the carboxyl on the surface of the fiber is used for promoting the separation of the fiber. Other methods for preparing nanocellulose, such as etherification, oxidation, esterification, carboxymethylation, etc., have a similar principle to the TEMPO oxidation method. The method has mild reaction conditions and simple operation, and is the most commonly adopted method at present. The disadvantages of these methods are that raw materials need to be pretreated (including cooking, multi-stage bleaching, etc.), and the whole process consumes a lot of resources such as electricity, heat, chemical reagents and water. (3) The MFC is prepared by an electrostatic spinning method, and the concentrated cellulose solution passes through a metal needle-shaped injector and is stably extruded under the induction action of a high-voltage electrostatic field to prepare the nano-cellulose. The nano-fiber obtained by electrostatic spinning has smooth surface, uniform diameter distribution and indefinite length. Electrospinning nanocellulose is an energy intensive process and dissolution of cellulose is difficult. (IV) preparation of Bacterial Nanocellulose (BNC). BNC is produced by biological polymerization of glucose by bacteria under the action of biological enzyme, has crystallinity higher than that of plant cellulose, indefinite length, diameter of 20-100 nm, high tensile strength and good shape maintaining capability. The bacterial method can regulate and control the structure, crystal form, particle size distribution and the like of the prepared cellulose, and in addition, the method has low energy consumption and no pollution. However, domestic research is still in the primary stage, and the problems of low yield, high cost, long production period, difficult regulation and control of processing technology and the like exist, so that large-scale industrialization is difficult to realize.
The oxidized cellulose nano-fibril has large length-diameter ratio, good dispersibility and functional groups such as carboxyl and the like, and is an important natural cellulose derivative. Oxidized cellulose nanofibrils are currently the most commonly used method for preparation by means of TEMPO oxidation, which uses TEMPO (piperidine nitroxide radical) -NaBr-NaClO to selectively oxidize the hydroxyl group at the C6 position on the glucose unit to a carboxyl group, and uses electrostatic repulsion of the ionization of the carboxyl group on the surface of the filaments to facilitate the separation of the filaments. Other methods for preparing nanocellulose, such as etherification, oxidation, esterification, carboxymethylation, etc., have a similar principle to the TEMPO oxidation method. The disadvantages of these methods are that raw materials need to be pretreated (including cooking, multi-stage bleaching, etc.), the whole process consumes a lot of electricity, heat, chemical reagents, water, etc., and the high-strength pretreatment process results in that the natural microfibril structure is broken to different degrees, and the polymerization degree of cellulose is greatly reduced.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a preparation method of oxidized cellulose nanofibrils based on nitric acid and hydrogen peroxide.
The invention solves the technical problems by the following technical scheme:
the invention relates to a preparation method of oxidized cellulose nanofibrils based on nitric acid and hydrogen peroxide, which comprises the following operation steps: mixing a biomass raw material, 1-8 mol/L nitric acid and 30% hydrogen peroxide, stirring and reacting for 6-96 hours at 20-80 ℃, adding absolute ethyl alcohol to terminate the reaction, standing and layering the solution, pouring out the supernatant, retaining the lower-layer precipitate, sequentially washing the lower-layer precipitate with the absolute ethyl alcohol, 50% ethanol and water, and treating by a high-pressure homogenizer to obtain the oxidized cellulose nanofibril.
The biomass raw material, the nitric acid and the hydrogen peroxide are in the following ratio: 10g biomass feedstock 150ml nitric acid: 15-50 ml of hydrogen peroxide.
The biomass raw materials comprise bagasse, bamboo chips and eucalyptus bark chips.
Compared with the prior art, the method has the following beneficial effects:
(1) the preparation method is simple in preparation process, does not need high-strength pretreatment, and is suitable for large-scale industrial production;
(2) the raw materials used in the invention comprise all available biomass, such as bagasse, bark, bamboo and the like, and also comprise biomass such as unutilized weeds, shrubs and the like;
(3) the invention has the advantages that the adopted chemicals are few in types and easy to obtain and low in price;
(4) the oxidized cellulose nano-fibril prepared by the invention has wide application prospect in the fields of water treatment, oil-water separation, nano composite materials and the like.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
Adding 10g of bagasse, 150ml of nitric acid with the concentration of 4mol/L and 45ml of hydrogen peroxide with the mass concentration of 30% into a 500ml three-neck flask, stirring and reacting for 48 hours at 50 ℃, adding absolute ethyl alcohol to stop the reaction, transferring the solution into a 500ml measuring cylinder, standing and layering, pouring out the supernatant, retaining the precipitate at the lower layer, sequentially washing the precipitate at the lower layer with the absolute ethyl alcohol, the ethyl alcohol with the volume concentration of 50% and the water, and treating by a high-pressure homogenizer to obtain the oxidized cellulose nanofibrils.
The diameter of the obtained oxidized cellulose nano-fibril is within the range of 5-50 nm, and the carboxyl content is 1.036 mmol/g.
Example 2
Adding 10g of arundo donax linn, 150ml of nitric acid with the concentration of 8mol/L and 15ml of hydrogen peroxide with the mass concentration of 30% into a 500ml three-neck flask, stirring and reacting for 6 hours at 80 ℃, adding absolute ethyl alcohol to stop the reaction, transferring the solution into a 500ml measuring cylinder, standing and layering, pouring out the supernatant, retaining the precipitate at the lower layer, sequentially washing the precipitate at the lower layer with the absolute ethyl alcohol, the ethyl alcohol with the volume concentration of 50% and the water, and treating by a high-pressure homogenizer to obtain the oxidized cellulose nanofibrils.
The diameter of the obtained oxidized cellulose nano-fibril is within the range of 20-80 nm, and the carboxyl content is 0.791 mmol/g.
Example 3
Adding 10g of eucalyptus bark slices, 150ml of nitric acid with the concentration of 1mol/L and 50ml of hydrogen peroxide with the mass concentration of 30% into a 500ml three-neck flask, stirring and reacting for 96 hours at the temperature of 20 ℃, adding absolute ethyl alcohol to stop the reaction, transferring the solution into a 500ml measuring cylinder, standing and layering, pouring out the supernatant, retaining the precipitate at the lower layer, sequentially washing the precipitate at the lower layer with the absolute ethyl alcohol, the ethyl alcohol with the volume concentration of 50% and the water, and treating by a high-pressure homogenizer to obtain the oxidized cellulose nanofibrils.
The diameter of the obtained oxidized cellulose nano-fibril is within the range of 10-50 nm, and the carboxyl content is 1.275 mmol/g.
Claims (1)
1. A preparation method of oxidized cellulose nanofibrils based on nitric acid and hydrogen peroxide is characterized by comprising the following operation steps: mixing a biomass raw material, 1-8 mol/L nitric acid and 30% hydrogen peroxide, stirring and reacting for 6-96 hours at 20-80 ℃, adding absolute ethyl alcohol to stop the reaction, standing and layering the solution, pouring out the supernatant, retaining the lower-layer precipitate, sequentially washing the lower-layer precipitate with the absolute ethyl alcohol, 50% ethanol and water, and treating by a high-pressure homogenizer to obtain oxidized cellulose nanofibrils;
the biomass raw materials comprise bagasse, arundo donax linn, eucalyptus bark slices, weeds and shrubs;
the ratio of the biomass raw material to the nitric acid to the hydrogen peroxide is as follows: 10g biomass feedstock 150ml nitric acid: 15-50 ml of hydrogen peroxide.
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