CN117624387A - Preparation method of carboxylated cellulose nanofiber and nanocrystalline - Google Patents
Preparation method of carboxylated cellulose nanofiber and nanocrystalline Download PDFInfo
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- CN117624387A CN117624387A CN202311581718.XA CN202311581718A CN117624387A CN 117624387 A CN117624387 A CN 117624387A CN 202311581718 A CN202311581718 A CN 202311581718A CN 117624387 A CN117624387 A CN 117624387A
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- 229920002678 cellulose Polymers 0.000 title claims abstract description 119
- 239000001913 cellulose Substances 0.000 title claims abstract description 119
- 239000002121 nanofiber Substances 0.000 title claims abstract description 63
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
- 238000000034 method Methods 0.000 claims abstract description 39
- 239000002159 nanocrystal Substances 0.000 claims abstract description 39
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 33
- 239000012065 filter cake Substances 0.000 claims abstract description 15
- 230000001105 regulatory effect Effects 0.000 claims abstract description 15
- 239000012043 crude product Substances 0.000 claims abstract description 14
- 238000000967 suction filtration Methods 0.000 claims abstract description 13
- 239000002994 raw material Substances 0.000 claims abstract description 12
- 230000003113 alkalizing effect Effects 0.000 claims abstract description 8
- 238000006473 carboxylation reaction Methods 0.000 claims abstract description 8
- 238000011010 flushing procedure Methods 0.000 claims abstract description 8
- 230000002378 acidificating effect Effects 0.000 claims abstract description 7
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 66
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical group CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 22
- 229920000742 Cotton Polymers 0.000 claims description 19
- 238000003756 stirring Methods 0.000 claims description 15
- FOCAUTSVDIKZOP-UHFFFAOYSA-N chloroacetic acid Chemical compound OC(=O)CCl FOCAUTSVDIKZOP-UHFFFAOYSA-N 0.000 claims description 14
- 229940106681 chloroacetic acid Drugs 0.000 claims description 14
- VODRWDBLLGYRJT-UHFFFAOYSA-N propan-2-yl 2-chloroacetate Chemical compound CC(C)OC(=O)CCl VODRWDBLLGYRJT-UHFFFAOYSA-N 0.000 claims description 13
- 239000003054 catalyst Substances 0.000 claims description 12
- 239000011259 mixed solution Substances 0.000 claims description 12
- NLKNQRATVPKPDG-UHFFFAOYSA-M potassium iodide Chemical compound [K+].[I-] NLKNQRATVPKPDG-UHFFFAOYSA-M 0.000 claims description 12
- 238000006243 chemical reaction Methods 0.000 claims description 10
- 238000002791 soaking Methods 0.000 claims description 10
- 239000003960 organic solvent Substances 0.000 claims description 9
- 239000000243 solution Substances 0.000 claims description 7
- 238000011282 treatment Methods 0.000 claims description 7
- 230000008569 process Effects 0.000 claims description 6
- 229920001131 Pulp (paper) Polymers 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 238000005406 washing Methods 0.000 claims description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 4
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 claims description 4
- 238000001914 filtration Methods 0.000 claims description 4
- 239000001632 sodium acetate Substances 0.000 claims description 4
- 235000017281 sodium acetate Nutrition 0.000 claims description 4
- 238000010979 pH adjustment Methods 0.000 claims description 3
- 239000002904 solvent Substances 0.000 claims description 2
- 239000002086 nanomaterial Substances 0.000 abstract description 4
- 239000006185 dispersion Substances 0.000 description 16
- 239000000047 product Substances 0.000 description 11
- 229920001046 Nanocellulose Polymers 0.000 description 10
- 239000006227 byproduct Substances 0.000 description 10
- 239000007788 liquid Substances 0.000 description 10
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- 239000008367 deionised water Substances 0.000 description 7
- 229910021641 deionized water Inorganic materials 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 229920003123 carboxymethyl cellulose sodium Polymers 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 6
- 238000006266 etherification reaction Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000006467 substitution reaction Methods 0.000 description 6
- 238000002441 X-ray diffraction Methods 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 3
- 239000001768 carboxy methyl cellulose Substances 0.000 description 3
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 3
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 3
- 239000003153 chemical reaction reagent Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000009776 industrial production Methods 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 244000166124 Eucalyptus globulus Species 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 238000003917 TEM image Methods 0.000 description 2
- 239000007900 aqueous suspension Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 2
- 230000021523 carboxylation Effects 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000009775 high-speed stirring Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- GDOPTJXRTPNYNR-UHFFFAOYSA-N methyl-cyclopentane Natural products CC1CCCC1 GDOPTJXRTPNYNR-UHFFFAOYSA-N 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000004904 shortening Methods 0.000 description 2
- 159000000000 sodium salts Chemical class 0.000 description 2
- 230000001360 synchronised effect Effects 0.000 description 2
- 241000195493 Cryptophyta Species 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 241001465754 Metazoa Species 0.000 description 1
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 1
- 230000001580 bacterial effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000002537 cosmetic Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 239000002657 fibrous material Substances 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- JDNTWHVOXJZDSN-UHFFFAOYSA-N iodoacetic acid Chemical compound OC(=O)CI JDNTWHVOXJZDSN-UHFFFAOYSA-N 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000000825 pharmaceutical preparation Substances 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000036632 reaction speed Effects 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- FDRCDNZGSXJAFP-UHFFFAOYSA-M sodium chloroacetate Chemical compound [Na+].[O-]C(=O)CCl FDRCDNZGSXJAFP-UHFFFAOYSA-M 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 125000001273 sulfonato group Chemical group [O-]S(*)(=O)=O 0.000 description 1
- 230000008961 swelling Effects 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
Abstract
The invention relates to the technical field of cellulose nano material preparation, in particular to a preparation method of carboxylated cellulose nano fibers and nano crystals. The method comprises the following steps: alkalizing a cellulose raw material, performing carboxylation reaction, performing suction filtration to obtain a crude product, and performing back flushing and suction filtration on the crude product by using water to obtain a carboxylated cellulose pulp filter cake; adding the carboxylated cellulose pulp filter cake into water, and regulating the pH value to obtain carboxylated cellulose nano fibers or nano crystals; when the pH is regulated to be acidic, carboxylated cellulose nanocrystalline is obtained; and when the pH value is regulated to be alkaline, the carboxylated cellulose nanofiber is obtained. The crystallinity of the carboxylated cellulose nano-fibers and the nano-crystals obtained by the method is up to more than 74%, and the carboxylated cellulose nano-fibers with the ultra-high length-diameter ratio still have the viscosity of up to 26760 mPa.s even at the low mass concentration content (less than 1%).
Description
Technical Field
The invention relates to the technical field of cellulose nano material preparation, in particular to a preparation method of carboxylated cellulose nano fibers and nano crystals.
Background
Cellulose is one of the most abundant renewable resources in nature today, and is widely found in plants, animals, algae, and some bacterial organisms. While nanocellulose refers to a cellulosic material with at least one dimension in the nanometer range, which attracts wide attention by virtue of excellent mechanical properties, nanosize, low density, low coefficient of thermal expansion, reproducibility, biodegradability, non-toxicity and biocompatibility. As a new generation of environment-friendly nano material, the nano material has huge application potential in the fields of high-performance composite materials, special paper, food packaging, pharmaceutical preparations, medical engineering, lithium/sodium ion batteries, super capacitors, cosmetics and the like.
Carboxylated nanocellulose is a nanocellulose material with carboxyl groups on the surface. At present, TEMPO reagent and etherification method are mainly used for preparing carboxylated cellulose nanofibers with high length-diameter ratio, but TEMPO reagent is more expensive, the preparation process is more severe, and the industrial production cost is high. Although the etherification method can reduce the cost for preparing the carboxylated cellulose nanofibers, the related large-scale process still has more complicated production period and higher content of byproduct carboxymethyl cellulose (sodium), so that the obtained cellulose nanofiber product has uneven quality and low crystallinity, and particularly the use performance of the cellulose nanofibers is affected by the existence of the byproduct. In addition, compared with the cellulose nanocrystals obtained by the traditional acidolysis method, the surface of the cellulose nanocrystals has sulfonate groups or no charge, and the preparation method of the cellulose nanocrystals with carboxyl groups on the surface is few at present. Therefore, the synchronous large-scale preparation technology of the carboxylated cellulose nano-fiber and the cellulose nano-crystal, which is simple, convenient, quick, low in cost and high in purity, is a new breakthrough of the nano-cellulose production technology and has very high international competitiveness.
Disclosure of Invention
Aiming at the problems of long production period, high byproduct content, uneven product quality and the like in the production process of carboxylated nanocellulose in the prior art, the invention provides a preparation method of carboxylated cellulose nanofibers and nanocrystals, which can synchronously produce cellulose nanofibers (with ultrahigh length-diameter ratio) and nanocrystals (with certain length-diameter ratio) in a large scale.
In order to achieve the above object, the present invention provides the following solutions:
according to one of the technical schemes, the preparation method of the carboxylated cellulose nanofiber and the nanocrystalline comprises the following steps:
alkalizing a cellulose raw material, performing carboxylation reaction, performing suction filtration to obtain a crude product, and performing back flushing and suction filtration on the crude product by using water to obtain a carboxylated cellulose pulp filter cake;
adding the carboxylated cellulose pulp filter cake into water, and regulating the pH value to obtain carboxylated cellulose nano fibers or nano crystals;
when the pH is regulated to be acidic, carboxylated cellulose nanocrystalline is obtained; and when the pH value is regulated to be alkaline, the carboxylated cellulose nanofiber is obtained.
According to the second technical scheme, the carboxylated cellulose nanofiber or nanocrystal prepared by the preparation method is prepared.
According to the third technical scheme, the method for improving the purity of the carboxylated cellulose nanofiber or nanocrystal is adopted.
The invention discloses the following technical effects:
(1) The invention optimizes the process by using water for back flushing, improves the removal efficiency of byproducts and improves the purity of carboxylated cellulose nanofibers or nanocrystals.
(2) The method expands the preparation technology of the carboxylated cellulose nanocrystals on the basis of the carboxylated cellulose nanofibers, and is suitable for popularization of synchronous industrial production technology of carboxylated nanocellulose products with two different morphologies.
(3) The crystallinity of the carboxylated cellulose nano-fibers and the nano-crystals obtained by the method is up to more than 74%, and the carboxylated cellulose nano-fibers with the ultra-high length-diameter ratio still have the viscosity of up to 26760 mPa.s even at the low mass concentration content (less than 1%).
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an X-ray diffraction pattern a and a transmission electron micrograph b of carboxylated cellulose nanocrystals prepared in example 1 of the present invention.
FIG. 2 is an X-ray diffraction pattern a and a transmission electron micrograph b of the carboxylated cellulose nanofibers prepared in example 2 of the present invention.
Detailed Description
Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.
The "parts" in the present invention, unless otherwise specified, refer to parts by mass.
The first aspect of the invention provides a method for preparing carboxylated cellulose nanofibers and nanocrystals, comprising the steps of:
alkalizing a cellulose raw material, performing carboxylation reaction, performing suction filtration to obtain a crude product, and performing back flushing and suction filtration on the crude product by using water to obtain a carboxylated cellulose pulp filter cake;
adding the carboxylated cellulose pulp filter cake into water, and regulating the pH value to obtain carboxylated cellulose nano fibers or nano crystals;
when the pH is regulated to be acidic, carboxylated cellulose nanocrystalline is obtained; and when the pH value is regulated to be alkaline, the carboxylated cellulose nanofiber is obtained. Carboxylated cellulose nanofibers can also be obtained when the pH is adjusted to neutral (i.e. pH 7), but in a lower yield than when the pH is alkaline.
In a preferred embodiment of the invention, the cellulosic feedstock is purified cotton or dry bleached wood pulp. The cellulose raw material is subjected to alkalization treatment and then comprises a step of grinding into powder.
The refined cotton is a commercially available refined cotton product treated by natural cotton, and the dry bleached wood pulp can be bleached eucalyptus pulp (but is not limited to the bleached eucalyptus pulp, and can also comprise bleached wood pulp obtained by other wood treatments), and the main component of the refined cotton is cellulose, has higher crystallinity and is a fibrous material with the diameter of 10-20 micrometers and the length of millimeter.
In a preferred embodiment of the present invention, the cellulose raw material is subjected to an alkalization treatment using a mixed solution containing potassium hydroxide; the solvent of the mixed solution containing potassium hydroxide is water and an organic solvent; the organic solvent is isopropanol and/or absolute ethanol; when the organic solvent is isopropanol and absolute ethyl alcohol, the volume ratio of the isopropanol to the absolute ethyl alcohol is 1-3:1; in the mixed solution containing potassium hydroxide, the volume of the organic solvent is 10-15 times of the volume of water, and the mass ratio of the potassium hydroxide to the water is 1:10.
The volume ratio of the organic solvent to the water is lower than the parameters described above, which is not beneficial to the swelling of cellulose and the damage and conversion of a crystallization area thereof, thereby reducing the uniformity and purity of the product; the ratio of the organic solvent to the water is higher than the parameters described above, so that the degree of damage of the crystalline structure of the cellulose in the reaction process is reduced, the substitution degree of the obtained carboxylated cellulose pulp filter cake is low, and the yield of the final nanocellulose is reduced.
The mass ratio of potassium hydroxide to water is higher than the parameters described above, which can lead to too high substitution degree of the obtained carboxylated cellulose pulp filter cake, on the one hand, to high content of byproduct carboxymethyl cellulose, and increase the purification difficulty, and on the other hand, also affects the yield of final nanocellulose; the mass ratio of potassium hydroxide to water is lower than the parameters described above, which can lead to too low substitution degree of the obtained carboxylated cellulose pulp filter cake, cause certain difficulty to the subsequent homogenizing or high-speed stirring process, and reduce the yield and product quality (uneven particle size) of the final nanocellulose.
In a preferred embodiment of the present invention, the mass ratio of the cellulose raw material to the potassium hydroxide is (1-3): 1.
The mass ratio of cellulose raw material to potassium hydroxide is higher or lower than the above-described parameters, which results in a significant reduction in the final nanocellulose yield.
In a preferred embodiment of the present invention, the alkalizing treatment is performed at a temperature of 30 to 35 ℃ for 40 minutes.
In a preferred embodiment of the present invention, the carboxylation reaction is specifically: chloroacetic acid, isopropyl chloroacetate and a catalyst were added to the reaction solution after the alkalization treatment, and the mixture was reacted at 70℃for 1 hour.
In a preferred embodiment of the invention, the mass ratio of the potassium hydroxide to the chloroacetic acid and the isopropyl chloroacetate is (3.3.5): (1.8-2.1): (2.5-3.0); the catalyst is a mixture of potassium iodide and sodium acetate in a molar ratio of 1:1; the catalyst is used in an amount of 0.5-1.5% of the total molar amount of the chloroacetic acid and the isopropyl chloroacetate.
The mass ratio of potassium hydroxide to chloroacetic acid and isopropyl chloroacetate, both above and below the parameters described above, results in a significant reduction in the final nanocellulose yield or a reduction in the product purity.
The catalyst has the functions of improving the etherification reaction speed, shortening the etherification reaction time and improving the substitution uniformity. This is due to I in the catalyst - Is a better leaving group with Cl in chloroacetic acid - Exchange occurs to generate iodoacetic acid, so that the etherifying agent is more active, and the improvement of the reaction rate and the substitution degree is promoted. The catalytic reaction effect is not obvious when the dosage of the catalyst is lower than 0.5-1.5% of the total molar quantity of the chloroacetic acid and the isopropyl chloroacetate, and the catalytic effect is not improved obviously when the dosage of the catalyst is higher than 0.5-1.5% of the total molar quantity of the chloroacetic acid and the isopropyl chloroacetate, so that the dosage of the catalyst is preferably limited to 0.5-1.5% of the total molar quantity of the chloroacetic acid and the isopropyl chloroacetate in consideration of the comprehensive catalytic effect and cost.
The etherifying agent (chloroacetic acid and isopropyl chloroacetate) and the catalyst are used for further optimizing the process, greatly shortening the production period, improving the large-scale production efficiency and the quality of the final product, solving the problems of long production period, unstable product quality, higher content of byproduct carboxymethyl cellulose (sodium) and the like in the existing preparation process of the carboxylated cellulose nano-fiber, and particularly further expanding the preparation technology of carboxylated cellulose nano-crystals, and synchronously carrying out large-scale industrial production on carboxylated nano-cellulose products with two different morphologies.
In a preferred embodiment of the invention, the pH adjustment is acidic, in particular pH adjustment of 3-5; the pH value is adjusted to be alkaline, specifically, the pH value is adjusted to be 10-11; the method further comprises the steps of soaking, stirring, homogenizing, centrifuging, washing, or soaking, stirring at a high speed and filtering after the pH is regulated.
The method comprises the following steps of soaking, stirring, homogenizing, centrifuging, washing or soaking, high-speed stirring and suction filtration: regulating the pH value to 3-5, soaking and continuously stirring for 12 hours, homogenizing for 5-10 times by a homogenizer, repeatedly centrifuging/washing the obtained dispersion liquid for 3 times, and then re-dispersing to obtain carboxylated cellulose nanocrystalline aqueous dispersion liquid; or, adjusting the pH value to 10-11, soaking for 5-6 hours, stirring at a high speed of 20000 rpm for 5-10 minutes, then diluting the obtained viscous liquid with deionized water, and filtering by suction to obtain a carboxylated cellulose nanofiber aqueous dispersion system.
The second aspect of the invention provides carboxylated cellulose nanofibers or nanocrystals prepared according to the preparation method described above.
The third aspect of the invention provides a method for improving the purity of carboxylated cellulose nanofibers or nanocrystals, which adopts the preparation method of carboxylated cellulose nanofibers and nanocrystals.
The raw materials used in the examples of the present invention, unless otherwise specified, were all available commercially.
The chemical reagents used in the following examples and comparative examples of the present invention were all analytically pure.
The refined cotton used in the following examples and comparative examples of the present invention was model M650.
Example 1
(1) 9 g of purified cotton was further ground by a grinder to a cotton powder having a diameter of about 10-20um and a length of about 500-1000 mm.
(2) 3 g of potassium hydroxide and 30 g of deionized water are added into a three-neck flask, after the potassium hydroxide is completely dissolved, 300 ml of isopropanol is added and stirred uniformly, so as to obtain a water/isopropanol mixed solution of potassium hydroxide.
(3) Adding the cotton powder obtained in the step (1) into the mixed solution obtained in the step (2), alkalizing for 40 minutes at 30 ℃ after stirring uniformly, then adding 1.8 g of chloroacetic acid, 2.5g of isopropyl chloroacetate, 0.03 g of potassium iodide and 0.015 g of sodium acetate, reacting for 1 hour at 70 ℃ after stirring uniformly, carrying out suction filtration on the reaction solution to obtain a crude product, carrying out back flushing on the crude product by using deionized water, and finally carrying out suction filtration to obtain a carboxylated cellulose pulp filter cake.
(4) Adding water into the carboxylated cellulose pulp filter cake obtained in the step (3) to prepare cellulose dispersion liquid with the mass percent concentration of 1%, adjusting the pH value to 4 by using hydrochloric acid, soaking and continuously stirring for 12 hours at 100rpm, homogenizing for 8 times by using a homogenizer of 60MPa, repeatedly centrifuging/washing the obtained dispersion liquid for 3 times, and redispersing to obtain carboxylated cellulose nanocrystalline aqueous dispersion liquid.
The X-ray diffraction analysis shows that the carboxylated cellulose nanocrystals prepared in this example still maintain the crystalline structure of cellulose i (see fig. 1 a), wherein the crystallinity CI is 75.9% as calculated by the method of Segal, etc., indicating that the purity of the carboxylated cellulose nanocrystals obtained is higher (the crystallinity of the purified cotton used in this example is 78.8% as measured by the same method); the transmission electron microscope test result shows that the carboxylated cellulose nanocrystals prepared in this example have a diameter of about 10 nm to 20 nm and a length of about 100-500 nm, and are a nanofiber material with a certain length-diameter ratio (see b in fig. 1).
Example 2
(1) 7 g of purified cotton is further ground by a grinder into cotton powder with the diameter of about 10-20um and the length of about 500-1000 mm.
(2) 3.5 g of potassium hydroxide and 35 g of deionized water are added into a three-neck flask, after the potassium hydroxide is completely dissolved, 350 ml of isopropanol is added and stirred uniformly, so as to obtain a water/isopropanol mixed solution of potassium hydroxide.
(3) Adding the cotton powder obtained in the step (1) into the mixed solution obtained in the step (2), alkalizing for 40 minutes at 30 ℃ after stirring uniformly, then adding 2.1 g of chloroacetic acid, 3.0g of isopropyl chloroacetate, 0.036 g of potassium iodide and 0.018 g of sodium acetate, reacting for 1 hour at 70 ℃ after stirring uniformly, carrying out suction filtration on the reaction solution to obtain a crude product, carrying out back flushing on the crude product by using deionized water, and finally carrying out suction filtration to obtain the carboxylated cellulose pulp filter cake.
(4) Adding water into the carboxylated cellulose pulp filter cake obtained in the step (3) to prepare cellulose dispersion liquid with the mass percent concentration of 0.7%, adjusting the pH value to 10.5 by using sodium hydroxide, soaking for 5 hours, stirring at a high speed of 20000 revolutions per minute for 10 minutes, then adding deionized water into the obtained viscous liquid to dilute, and filtering by pumping to obtain the carboxylated cellulose nanofiber aqueous dispersion liquid.
The X-ray diffraction analysis shows that the carboxylated cellulose nanofibers prepared in this example still retain the crystalline structure of cellulose i (see fig. 2 a), wherein the crystallinity CI is 74.6% as calculated by the method of Segal et al, indicating that the purity of the carboxylated cellulose nanofibers obtained is very high (the crystallinity of the purified cotton used in this example is 78.8% as measured by the same method); the transmission electron microscope test result shows that the prepared carboxylated cellulose nanofiber has a diameter of about several nanometers and a length of about thousands of nanometers, and is a nanofiber material with extremely high length-diameter ratio (see b in fig. 2); in addition, the viscosity of the carboxylated cellulose nanofiber dispersion obtained in this example was 6910 mPas (25 ℃) at a concentration of as low as 0.5wt%, and was 26760 mPas (25 ℃) at a higher concentration of 0.8 wt%.
Comparative example 1
(1) The refined cotton is further ground into cotton powder with the diameter of about 10-20um and the length of about 500-1000mm by a grinder.
(2) 130 parts of water and 20 parts of sodium hydroxide were dissolved in 100 parts of water to obtain a mixed solution.
(3) 100 parts of the cotton powder obtained in the step (1) and the mixed solution obtained in the step (2) were added to a double shaft kneader having a rotation speed of 150rpm, stirred at 35℃for 80 minutes, and mixed and alkalized cellulose was prepared.
(4) 230 parts of isopropyl alcohol (IPA) and 60 parts of sodium monochloroacetate were added to a double shaft kneader having a rotation speed of 150rpm while stirring, and after stirring was continued for 30 minutes, the temperature was raised to 70℃to carry out carboxymethylation reaction for 90 minutes. After the reaction, the mixture was neutralized to pH7 with acetic acid, washed with aqueous methanol (50% by volume), drained, dried and pulverized to obtain sodium salt of carboxymethylated cellulose.
(5) The sodium salt of the obtained carboxymethyl cellulose was dispersed in water to prepare an aqueous dispersion having a mass concentration of 1% (w/v), and the aqueous dispersion was treated 3 times with a high-pressure homogenizer of 140MPa to obtain a dispersion of nanofibers of carboxymethyl cellulose. The viscosity and crystallinity of the obtained dispersion were measured by the above-mentioned methods, and the result showed that the dispersion of the carboxymethylated cellulose nanofibers having a mass concentration of 1% prepared in this comparative example had a crystallinity of 64.5% and a viscosity of 3180 (25 ℃).
Comparative example 2
The difference from example 2 is only that the crude product is subjected to a back-flushing with aqueous methanol (50% by volume) in step (3); the rest steps and parameters are the same as in example 2. The same effect verification as in example 2 was performed, and the result shows that the crystallinity of the carboxylated cellulose nanofibers prepared in this comparative example was 68.6%; the viscosity of the carboxylated cellulose nanofiber dispersion was 255 mPas (25 ℃ C.) at a concentration of 0.5wt% and 3890 mPas (25 ℃ C.) at a concentration of 1 wt%.
As can be seen from comparison of example 2 with comparative example 1 and comparative example 2, the carboxylated cellulose nanofibers prepared by the method of example 2 have higher crystallinity and higher viscosity; the higher viscosity side reflects the higher purity of the carboxylated cellulose nanofibers prepared in example 2; the method is characterized in that in the preparation process of the carboxylated cellulose nanofiber, the generation of byproduct carboxymethyl cellulose (sodium) is often accompanied, so that the prepared carboxylated cellulose nanofiber has low purity; conventionally, aqueous methanol (volume concentration of 50%) is adopted for cleaning, and the byproduct carboxymethyl cellulose (sodium) cannot be eluted; the invention adopts deionized water to wash the prepared carboxylated cellulose crude product, and can wash off the byproduct carboxymethyl cellulose (sodium), thereby improving the purity of the carboxylated cellulose, and the viscosity of the carboxylated cellulose aqueous dispersion liquid is improved when the reaction is carried out on the viscosity.
The invention improves the carboxylation technology of refined cotton or bleached wood pulp on the basis of a Williamson etherification method, improves the etherification substitution uniformity, further adopts a unique reverse cleaning process to remove byproduct carboxymethyl cellulose (sodium), then carries out high-pressure homogenization on the acidic aqueous suspension of the carboxylation modified product to obtain carboxylated cellulose nanocrystals (the length-diameter ratio is less than 80:1), and carries out high-speed shearing on the alkaline aqueous suspension of the carboxylated modified product to obtain carboxylated cellulose nanofibers (the length-diameter ratio is more than 200:1 and even more than 400:1).
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.
Claims (10)
1. The preparation method of the carboxylated cellulose nano-fiber and the nano-crystal is characterized by comprising the following steps:
alkalizing a cellulose raw material, performing carboxylation reaction, performing suction filtration to obtain a crude product, and performing back flushing and suction filtration on the crude product by using water to obtain a carboxylated cellulose pulp filter cake;
adding the carboxylated cellulose pulp filter cake into water, and regulating the pH value to obtain carboxylated cellulose nano fibers or nano crystals;
when the pH is regulated to be acidic, carboxylated cellulose nanocrystalline is obtained; and when the pH value is regulated to be alkaline, the carboxylated cellulose nanofiber is obtained.
2. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 1, wherein the cellulosic raw material is purified cotton or dry bleached wood pulp.
3. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 1, wherein the cellulose raw material is alkalized with a mixed solution containing potassium hydroxide; the solvent of the mixed solution containing potassium hydroxide is water and an organic solvent; the organic solvent is isopropanol and/or absolute ethanol;
in the mixed solution containing potassium hydroxide, the volume of the organic solvent is 10-15 times of the volume of water, and the mass ratio of the potassium hydroxide to the water is 1:10.
4. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 3, wherein the mass ratio of the cellulose raw material to the potassium hydroxide is (1-3): 1.
5. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 1, wherein the alkalizing treatment is carried out at a temperature ranging from 30 to 35 ℃ for 40 minutes.
6. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 3, wherein the carboxylation reaction is specifically: chloroacetic acid, isopropyl chloroacetate and a catalyst were added to the reaction solution after the alkalization treatment, and the mixture was reacted at 70℃for 1 hour.
7. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 6, wherein the mass ratio of potassium hydroxide to chloroacetic acid and isopropyl chloroacetate is (3-3.5): (1.8-2.1): (2.5-3.0); the catalyst is a mixture of potassium iodide and sodium acetate in a molar ratio of 1:1; the catalyst is used in an amount of 0.5-1.5% of the total molar amount of the chloroacetic acid and the isopropyl chloroacetate.
8. The method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 1, characterized in that said pH adjustment is acidic, in particular from 3 to 5; the pH value is adjusted to be alkaline, specifically, the pH value is adjusted to be 10-11; the method further comprises the steps of soaking, stirring, homogenizing, centrifuging, washing, or soaking, stirring at a high speed and filtering after the pH is regulated.
9. Carboxylated cellulose nanofibers or nanocrystals produced by the process according to any one of claims 1 to 8.
10. A method for improving the purity of carboxylated cellulose nanofibers or nanocrystals, which is characterized in that the method for preparing carboxylated cellulose nanofibers and nanocrystals according to claim 1 is adopted.
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