CN113105563A - Method for preparing Cellulose Nanofibrils (CNF) through metal salt/organic acid synergistic treatment - Google Patents

Method for preparing Cellulose Nanofibrils (CNF) through metal salt/organic acid synergistic treatment Download PDF

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CN113105563A
CN113105563A CN202110352978.4A CN202110352978A CN113105563A CN 113105563 A CN113105563 A CN 113105563A CN 202110352978 A CN202110352978 A CN 202110352978A CN 113105563 A CN113105563 A CN 113105563A
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slurry
acid
metal salt
reactor
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杨秋林
徐双
侯庆喜
王凯晴
霍丹
张凤山
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Tianjin University of Science and Technology
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Tianjin University of Science and Technology
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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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Abstract

The invention discloses a method for preparing Cellulose Nanofibrils (CNF) by adopting metal salt/organic acid synergistic treatment, belonging to the field of natural high polymer materials. The metal salt can effectively improve the activity of the organic acid and reduce the activation energy of the cellulose hydrolysis reaction, thereby reducing the energy consumption for preparing the CNF. Chemical pulp is used as a raw material, cellulose is depolymerized through metal salt/organic acid synergistic treatment, then oxidation treatment is carried out to improve the dispersibility of CNF, and finally the oxidized pulp is homogenized under high pressure to obtain CNF colloid. The CNF prepared by the method has the characteristics of high yield (more than 90%), good dispersibility (Zeta potential less than-35 mV), uniform size distribution (diameter of 5-50nm) and the like, and has good application prospect.

Description

Method for preparing Cellulose Nanofibrils (CNF) through metal salt/organic acid synergistic treatment
Technical Field
The invention provides a method for preparing Cellulose Nanofibrils (CNF) by metal salt/organic acid synergistic treatment, which has the properties of high yield, good dispersibility, low preparation energy consumption and the like.
Background
CNF is a nanofiber material that retains crystalline and amorphous regions in cellulose and has a high aspect ratio, and has a diameter of 5 to 60nm and a length of several micrometers. The CNF has many excellent characteristics, such as high length-diameter ratio, high strength, high crystallinity, high hydrophilicity, hyperfine structure, large specific surface area, good biocompatibility, good biodegradability and the like, and the nano cellulose film and the aerogel prepared by taking the CNF as the raw material have wide application prospects in the fields of chemical industry, materials, food, medicine and the like. The energy consumption required for preparing CNF by using a mechanical method is large, and chemical pretreatment is combined with the mechanical method for preparation at the present stage.
At present, the high-pressure homogenization method is the most common method for preparing the CNF, and chemical treatment is carried out before the high-pressure homogenization, so that the energy consumption for preparing the CNF can be effectively reduced. Among them, acid hydrolysis belongs to a relatively common chemical treatment method. The acid hydrolysis of cellulose may be carried out using inorganic or organic acids. The acid acts as a catalyst, providing hydrogen ions which first enter the amorphous regions of the cellulose and break the hydrogen bonds, and some of the crystalline irregularities of the crystalline regions are also hydrolyzed, increasing the crystallinity of the cellulose. In addition, the glycosidic bond of the glucose unit ring is cleaved to some extent at an appropriate hydrogen ion concentration, resulting in a decrease in the degree of polymerization of the cellulose. The activation energy of the cellulose hydrolysis reaction can be obviously reduced by the combined action of the metal ions and the hydrogen ions. The metal ions form a complex with the hydroxyl groups in the cellulose molecule, facilitating the hydrolysis reaction. In addition, the charges of the metal ions can destroy the charge balance among cellulose macromolecular chains, which is beneficial to the breakage of the molecular chains and promotes the partial decomposition body of the cellulose supermolecular structure. Based on the theory, the invention provides a method for preparing CNF by metal salt/organic acid synergistic treatment.
The invention provides a method for preparing CNF by metal salt/organic acid synergistic treatment, which has the characteristics of low pollution, low energy consumption, short preparation time, low cost and the like. The prepared CNF has the advantages of high yield, uniform size distribution, good dispersibility, large length-diameter ratio and the like. Therefore, the preparation method has better commercial application prospect.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a method for preparing CNF with high yield and high dispersibility, reduces the preparation energy consumption and cost, and lays a foundation for commercial application.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for preparing CNF by metal salt/organic acid synergistic treatment comprises the steps of metal salt/organic acid synergistic treatment of raw materials, oxidation treatment, high-pressure homogenization and the like, and specifically comprises the following steps:
(1) pretreatment of the pulp raw material: shredding chemical pulp raw material into small pieces, soaking in water for use, or defibering with defibering machine for 1-2min, and dewatering for use;
(2) metal salt/organic acid co-processing: and (2) placing the pulp raw material obtained in the step (1) into a reactor, adding water, metal salt and organic acid, mixing with the raw material, and performing high-temperature short-time treatment. The solid-liquid ratio (the mass ratio of the raw materials to the liquid medicine) adopted in the reactor is 1: 5-1: 15, the adding amount of the metal salt is 0.01-0.3mol/L, the adding amount of the organic acid is 0.05-0.5mol/L, and the mixture in the reactor is treated at the temperature of 100 ℃ and 180 ℃ for 5min-2 h. After the reaction is finished, stopping heating, stirring and other operations, immediately carrying out pressure relief and temperature reduction on the reactor, and stopping the reaction;
(3) washing the slurry: washing the slurry obtained in the step (2) until the washing liquid is neutral to obtain hydrolyzed slurry;
(4) and (3) oxidizing the slurry: and (4) placing the hydrolysis slurry obtained in the step (3) into a reactor, mixing the hydrolysis slurry with water and an oxidizing agent, and carrying out oxidation treatment. The concentration of the slurry adopted in the reactor is 5-20%, the dosage of the oxidant is 3-20% (relative to the absolute dry raw material), the initial pH of the reaction is 7-12, and the mixture in the reactor is oxidized for 0.5-3h at the temperature of 70-120 ℃.
(5) Washing the slurry: and (4) washing the slurry obtained in the step (4) to remove residual oxidant to obtain oxidized slurry.
(6) High-pressure homogenization: and (5) carrying out high-pressure homogenization treatment on the slurry obtained in the step (5). The high-pressure homogenization conditions adopted are as follows: the concentration of the slurry is 1.0-2.0%, the homogenizing pressure is 600-1000bar, the homogenizing times are 5-30 times, and finally the colloidal CNF product with qualified size is obtained.
Preferably, in the CNF production method, the chemical pulp raw material used in step (1) is one or more of softwood chemical pulp, hardwood chemical pulp, and non-wood chemical pulp. Wherein the raw material of the non-wood chemical pulp comprises bamboo, cotton and hemp, gramineae and the like.
Preferably, in the above CNF preparation method, the molecular formula of the metal salt used in step (2) is XY, XY2、XY3Or X2Y3One or more of them. Wherein X is one of Ca, Mg, Al, Fe, Zn, K and Na, and Y is Cl or NO3、SO4COOH and CH2One kind of COOH.
Preferably, in the above CNF production method, the organic acid used in step (2) may be one or more of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and citric acid.
Preferably, in the CNF production method, the oxidizing agent used in step (4) is one or more of hydrogen peroxide, sodium hypochlorite, sodium chlorite, potassium hypochlorite, chlorine dioxide, and sodium hydrosulfite.
The invention has the beneficial effects that:
according to the method for preparing the CNF by metal salt/organic acid synergistic treatment, the metal salt is adopted to catalyze and improve the activity of the organic acid, the temperature and time for cellulose acidolysis are reduced, the CNF is ensured to have the characteristics of high yield, high dispersibility and the like, and the energy consumption and the cost for preparing the CNF are reduced. The adopted processes of metal salt/organic acid synergistic treatment, oxidation treatment, high-pressure homogenization and the like have commercial application foundation and are suitable for the requirement of large-scale industrial production.
Detailed Description
The technical solutions of the present invention are further described below with reference to specific examples, which should be noted that the examples are not intended to limit the scope of the present invention.
Example 1
In this example 1, hardwood kraft pulp is used as a research object, and CNF is prepared by using zinc chloride/citric acid co-treatment and chlorine dioxide oxidation, and the specific steps are as follows:
(1) pretreatment of the pulp raw material: shredding the chemical pulp raw material into small pieces, and soaking the small pieces in water for later use;
(2) zinc chloride/organic acid co-treatment: and (2) putting the pretreated raw material obtained in the step (1) into a reactor, adding water, zinc chloride and citric acid, mixing with the raw material, and carrying out high-temperature short-time treatment. The solid-liquid ratio adopted in the reactor is 1: 10, the adding amount of zinc chloride is 0.05mol/L, the adding amount of citric acid is 0.1mol/L, and the mixture in the reactor is subjected to acidolysis treatment at the temperature of 170 ℃ for 15 min. After the reaction is finished, stopping heating, stirring and other operations, immediately carrying out pressure relief and temperature reduction on the reactor, and stopping the reaction;
(3) washing the slurry: and (3) washing the slurry obtained in the step (2) until the washing liquid is neutral to obtain hydrolyzed slurry.
(4) And (3) oxidizing the slurry: and (4) placing the hydrolysis slurry obtained in the step (3) into a reactor, mixing the hydrolysis slurry with water and a chlorine dioxide solution, and carrying out oxidation treatment. The concentration of the slurry adopted in the reactor is 10 percent, the adding amount of chlorine dioxide is 5.0 percent (relative to the absolute dry raw material), the initial pH of the reaction is 11.0, and the mixture in the reactor is oxidized for 2 hours at the temperature of 80 ℃.
(5) Washing the slurry: and (4) washing the slurry obtained in the step (4) to remove residual oxidant to obtain oxidized slurry.
(6) High-pressure homogenization: and (5) carrying out high-pressure homogenization treatment on the slurry obtained in the step (5). The high-pressure homogenization conditions adopted are as follows: the concentration of the slurry is 1.5 percent, the homogenizing pressure is 700bar, and the homogenizing times are 15 times.
The CNF obtained by the preparation method in example 1 has the yield of 92.1 percent, the Zeta potential of-35.2 mV, the diameter of 5-50nm and the length-diameter ratio of more than 100.
Example 2
In this example 2, broadleaf wood sulfate dissolving pulp is used as a research object, and the CNF is prepared by synergistic treatment of magnesium chloride/adipic acid and oxidation of sodium chlorite, which includes the following steps:
(1) pretreatment of raw materials: diluting the broadleaf wood sulfate dissolving pulp with water until the pulp concentration is 1.5%, then scattering for 2min by using a fluffer, and dehydrating for later use;
(2) magnesium chloride/adipic acid co-treatment: and (2) putting the pretreated raw material obtained in the step (1) into a reactor, adding water, magnesium chloride and adipic acid, mixing with the raw material, and carrying out high-temperature short-time treatment. The solid-liquid ratio adopted in the reactor is 1: 12, the adding amount of magnesium chloride is 0.1mol/L, the adding amount of adipic acid is 0.2mol/L, and the mixture in the reactor is subjected to acidolysis treatment for 30min at the temperature of 160 ℃. After the reaction is finished, stopping heating, stirring and other operations, immediately carrying out pressure relief and temperature reduction on the reactor, and stopping the reaction;
(3) washing the slurry: and (3) washing the slurry obtained in the step (2) until the washing liquid is neutral to obtain hydrolyzed slurry.
(4) And (3) oxidizing the slurry: and (4) placing the hydrolysis slurry obtained in the step (3) into a reactor, mixing the hydrolysis slurry with water and sodium chlorite, and carrying out oxidation treatment. The slurry concentration used in the reactor was 10%, the sodium chlorite addition was 10.0% (to absolutely dry raw material), the initial reaction pH was 8.5, and the mixture in the reactor was oxidized at 80 ℃ for 1.5 h.
(5) Washing the slurry: and (4) washing the slurry obtained in the step (4) to remove residual oxidant to obtain oxidized slurry.
(6) High-pressure homogenization: and (5) carrying out high-pressure homogenization treatment on the slurry obtained in the step (5). The high-pressure homogenization conditions adopted are as follows: the concentration of the slurry is 2.0 percent, the homogenizing pressure is 800bar, and the homogenizing times are 10 times.
The CNF obtained by the preparation method in example 2 has the yield of 94.5 percent, the Zeta potential of-40.1 mV, the diameter of 5-40 nm and the length-diameter ratio of more than 100.
Example 3
In this example 3, coniferous wood sulfite pulp is used as a research object, and the CNF is prepared by using magnesium acetate/acetic acid co-treatment and hydrogen peroxide oxidation, and the specific steps are as follows:
(1) loosening or scattering raw materials: diluting the sulfite pulp of coniferous wood with water until the pulp concentration is 1.0%, then scattering for 1min by a fluffer, and dehydrating for later use;
(2) magnesium acetate/acetic acid co-treatment: and (2) putting the pretreated raw material obtained in the step (1) into a reactor, adding water, magnesium acetate and acetic acid to mix with the raw material, and carrying out high-temperature short-time treatment. The solid-liquid ratio adopted in the reactor is 1: 10, the adding amount of magnesium acetate is 0.15mol/L, the adding amount of acetic acid is 0.3mol/L, and the mixture in the reactor is subjected to acidolysis treatment at the temperature of 170 ℃ for 30 min. After the reaction is finished, stopping heating, stirring and other operations, immediately carrying out pressure relief and temperature reduction on the reactor, and stopping the reaction;
(3) washing the slurry: and (3) washing the slurry obtained in the step (2) until the washing liquid is neutral to obtain hydrolyzed slurry.
(4) And (3) oxidizing the slurry: and (4) placing the hydrolysis slurry obtained in the step (3) into a reactor, mixing with water and hydrogen peroxide, and carrying out oxidation treatment. The slurry concentration adopted in the reactor is 10%, the addition amount of hydrogen peroxide is 12.0% (relative to the absolute dry raw material), the initial pH of the reaction is 10.0, and the mixture in the reactor is oxidized for 1.5h at the temperature of 90 ℃.
(5) Washing the slurry: and (4) washing the slurry obtained in the step (4) to remove residual oxidant to obtain oxidized slurry.
(6) High-pressure homogenization: and (5) carrying out high-pressure homogenization treatment on the slurry obtained in the step (5). The high-pressure homogenization conditions adopted are as follows: the concentration of the slurry is 2.5 percent, the homogenizing pressure is 900bar, and the homogenizing times are 10 times.
The CNF obtained by the preparation method in the example 3 has the yield of 93.2 percent, the Zeta potential of-39.1 mv, the diameter of 20-50 nm and the length-diameter ratio of more than 100.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (6)

1. A method for preparing Cellulose Nanofibrils (CNF) by means of metal salt/organic acid co-treatment, characterized in that: the preparation method of the CNF comprises the main steps of metal salt/organic acid treatment, oxidation treatment, high-pressure homogenization and the like of chemical pulp, and specifically comprises the following steps in sequence:
(1) pretreatment of the pulp raw material: shredding chemical pulp raw material into small pieces, soaking in water for use, or defibering with defibering machine for 1-2min, and dewatering for use;
(2) metal salt/organic acid co-processing: and (2) placing the pulp raw material obtained in the step (1) into a reactor, adding water, metal salt and organic acid, mixing with the raw material, and performing high-temperature short-time treatment. The solid-liquid ratio (the mass ratio of the raw materials to the liquid medicine) adopted in the reactor is 1: 5-1: 15, the adding amount of the metal salt is 0.01-0.3mol/L, the adding amount of the organic acid is 0.05-0.5mol/L, and the mixture in the reactor is treated at the temperature of 100 ℃ and 180 ℃ for 5min-2 h. After the reaction is finished, stopping heating, stirring and other operations, immediately carrying out pressure relief and temperature reduction on the reactor, and stopping the reaction;
(3) washing the slurry: washing the slurry obtained in the step (2) until the washing liquid is neutral to obtain hydrolyzed slurry;
(4) and (3) oxidizing the slurry: and (4) placing the hydrolysis slurry obtained in the step (3) into a reactor, mixing the hydrolysis slurry with water and an oxidizing agent, and carrying out oxidation treatment. The concentration of the slurry adopted in the reactor is 5-20%, the dosage of the oxidant is 3-20% (relative to the absolute dry raw material), the initial pH of the reaction is 7-12, and the mixture in the reactor is oxidized for 0.5-3h at the temperature of 70-120 ℃.
(5) Washing the slurry: and (4) washing the slurry obtained in the step (4) to remove residual oxidant to obtain oxidized slurry.
(6) High-pressure homogenization: and (5) carrying out high-pressure homogenization treatment on the slurry obtained in the step (5). The high-pressure homogenization conditions adopted are as follows: the concentration of the slurry is 1.0-2.0%, the homogenizing pressure is 600-1000bar, the homogenizing times are 5-30 times, and finally the colloidal CNF product with qualified size is obtained.
2. The method for preparing Cellulose Nanofibrils (CNF) according to claim 1, comprising: the chemical pulp adopted in the step (1) is one or more of softwood chemical pulp, hardwood chemical pulp and non-wood chemical pulp. The raw materials of the non-wood chemical pulp comprise bamboo, cotton and hemp, gramineae plants and the like.
3. The method for preparing Cellulose Nanofibrils (CNF) according to claim 1, comprising: the molecular formulas of the metal salt adopted in the step (2) are XY and XY2、XY3Or X2Y3. Wherein X is one of Ca, Mg, Al, Fe, Zn, K and Na, and Y is Cl or NO3、SO4COOH and CH2One kind of COOH.
4. The method for preparing Cellulose Nanofibrils (CNF) according to claim 1, comprising: the organic acid used in the step (2) may be one or more of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid and citric acid.
5. The method for preparing Cellulose Nanofibrils (CNF) according to claim 1, comprising: the oxidant adopted in the step (4) is one or more of hydrogen peroxide, sodium hypochlorite, sodium chlorite, potassium hypochlorite, chlorine dioxide and sodium hydrosulfite.
6. The process for the preparation of Cellulose Nanofibrils (CNF) according to any of claims 1 to 5, characterised in that: the diameter of the CNF is 5-50nm, and the length-diameter ratio is more than 100.
CN202110352978.4A 2021-03-22 2021-03-22 Method for preparing Cellulose Nanofibrils (CNF) through metal salt/organic acid synergistic treatment Pending CN113105563A (en)

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