CN113718543A - Method for cleanly preparing cellulose nanocrystals by combining organic acid hydrolysis with nano-micro-jet homogenization one-step method and product - Google Patents
Method for cleanly preparing cellulose nanocrystals by combining organic acid hydrolysis with nano-micro-jet homogenization one-step method and product Download PDFInfo
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/001—Modification of pulp properties
- D21C9/007—Modification of pulp properties by mechanical or physical means
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/001—Modification of pulp properties
- D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
- D21C9/005—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives organic compounds
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
- D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
- D21H11/18—Highly hydrated, swollen or fibrillatable fibres
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- Engineering & Computer Science (AREA)
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- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
The invention discloses a method for cleanly preparing cellulose nanocrystals by combining organic acid hydrolysis with a nano-micro-jet homogenization one-step method and a product; the method comprises the following steps: adding a cellulose raw material into an organic acid aqueous solution, and carrying out hydrolysis reaction to obtain a hydrolyzed fiber suspension; then filtering, and separating filtrate and filter residue; performing dialysis treatment on the filter residue by using deionized water, taking a retention solution, diluting, and homogenizing by using high-pressure microjet to obtain a nano cellulose mixed solution; and centrifuging, separating supernatant and fiber precipitate, drying the supernatant to obtain the cellulose nanocrystal, and drying the fiber precipitate to obtain the cellulose nanofibril. The method does not need to add any catalyst, the used medicament is safe and non-toxic, the reaction conditions are relatively mild, the process is easy to control, the whole operation process is green and environment-friendly, and the product has excellent performances of large length-diameter ratio, good dispersion stability, high thermal stability and the like, and has wide application prospect in nano cellulose-based reinforced materials.
Description
Technical Field
The invention belongs to the field of natural polymer material preparation, and particularly relates to a method for cleanly preparing cellulose nanocrystals by an organic acid hydrolysis combined nano-micro-jet homogenization one-step method and a product.
Background
Due to the demand of sustainable development, in order to alleviate the pressure of resources and energy sources brought by industrial development, more and more researchers turn the attention to degradable natural polymer cellulose which is widely available in higher plants, 50% of the wood content and 90% of the cotton content, and in addition, the cellulose is distributed in tunica, algae, fungi, bacteria and invertebrates, and even a smaller part of the cellulose is stored in marine animals. Annual yield of native cellulose is estimated to exceed 7.5x1010Ton, is considered the most abundant renewable resource on earth.
Nanocellulose prepared by nanocrystallization of natural cellulose comprises Cellulose Nanocrystals (CNC) and Cellulose Nanofibrils (CNF), wherein the CNC refers to rod-shaped fibrous crystals with widths and lengths of 5-70 nm and hundreds of nanometers respectively; CNF refers to entangled nanofibers with a diameter of 5-60 nm and a length of several micrometers. CNC has the advantages of high aspect ratio, large specific surface area, excellent mechanical properties, easy chemical modification of the surface, etc., and has been widely used as filler for reinforcing nanocomposite materials. Has shown huge potential in the fields of biomedical materials, packaging materials, electrode materials and the like due to the safety and effectiveness of the electrode material.
However, the industrial preparation of the nano-cellulose is not perfect, and the preparation cost is high, which becomes a significant bottleneck restricting the development of related nano-materials. The CNC prepared by the most traditional hydrolysis method of inorganic strong acid (sulfuric acid, phosphoric acid, hydrochloric acid and the like) has poor thermal stability and low crystallinity, and can cause serious environmental problems of equipment corrosion, waste liquid pollution and the like. The mild biological enzymolysis method has high cost, long time consumption and low yield, and is difficult to realize industrial production. At the present stage, enterprises with large-scale preparation of nano-cellulose are still basically using methods with serious pollution and high energy consumption, such as inorganic strong acid hydrolysis, TEMPO oxidation and the like, and development of green, environment-friendly and efficient preparation technology is the main direction of future development of nano-cellulose.
Related studies (e.g., Chen reports on Green chem.,2016,18, 3835) suggest that Green, recoverable organic acids (e.g., formic, oxalic, maleic, etc.) can be used to hydrolyze cellulosic feedstocks to make CNC. Compared with the traditional method, the organic acid hydrolysis method has the advantages of mild reaction conditions, small corrosion to equipment, high acid recovery rate, environmental friendliness and the like. Some polybasic organic acids (such as oxalic acid, citric acid and the like) contain more than two carboxylic acid functional groups, and have a plurality of ways of reacting with cellulose, and the prepared nano-cellulose has higher carboxyl content and larger functional application potential. However, since the organic acid has weak acidity, the single organic acid hydrolysis reaction has problems of long time and low yield, and the yield can be improved by adding inorganic strong acid catalysts (such as sulfuric acid and hydrochloric acid), but the catalysts are toxic and unrecoverable, which greatly limits the application of the nanocellulose to materials such as food and medicine, and thus cannot meet the requirements of green preparation and high value-added application.
The pretreatment by organic acid hydrolysis combined with scientific physical assistance is an effective means for improving the yield of the nano cellulose, and Chinese patent 201610041840.1 reports a preparation method of the nano cellulose fibrils, and only a single product CNF is obtained by the pretreatment by citric acid hydrolysis combined with other mechanical actions with high energy consumption. At present, no report is found on a method for preparing high-yield CNC by combining organic acid hydrolysis with a microfluidization homogenizing one-step method, a microfluidization homogenizer has the advantages of short time, high efficiency, convenience in operation, applicability to large-batch industrial production and the like, cellulose nanocrystals can be separated from fibers to a greater extent through microfluidization treatment, and the sizes of all fiber pulp can be uniformly reduced. The invention further improves the yield of CNC and the residual CNF, two components are obtained by one-time centrifugal treatment, and the total yield can reach more than 95%.
Disclosure of Invention
Aiming at the problem of low yield of nano-cellulose prepared by an organic acid method, the invention aims to provide a method for cleanly preparing high-yield CNC by one step through combining organic acid hydrolysis with nano-microjet homogenization. The method has simple and efficient steps, and finally obtains the upper light blue cellulose nanocrystalline suspension through centrifugation; the colloidal nanometer cellulose cellosilk turbid liquid can be obtained by collecting the lower layer fiber precipitation, and the total yield reaches 95%.
The invention aims to provide a method for preparing high-yield CNC by using organic acid hydrolysis combined with nano-micro-jet homogenization, the process is green and environment-friendly, the materials are nontoxic and harmless, the prepared nano-cellulose is easy to functionalize in the later period, and the method has the advantages of high surface electronegativity, high thermal stability and the like, and has application potential in the fields of biomedicine, tissue engineering, food health care, beauty and daily chemicals.
The purpose of the invention is realized by at least one of the following technical solutions.
The invention provides a method for cleanly preparing cellulose nanocrystals by combining organic acid hydrolysis with a nano-micro-jet homogenization one-step method, which comprises the following steps:
(1) organic acid hydrolysis reaction: adding a cellulose raw material into an organic acid aqueous solution, heating under a mechanical stirring state to perform hydrolysis reaction (acidolysis reaction) to obtain a hydrolyzed fiber suspension;
(2) filtering (preferably carrying out vacuum filtration) the hydrolyzed fiber suspension in the step (1), separating filtrate and filter residue, washing the filter residue, and recovering organic acid in the filtrate;
(3) and (3) dialysis treatment: performing dialysis treatment on the filter residue obtained in the step (2) by using deionized water (the deionized water is used for dialysis until the conductivity is the same as that of the deionized water), taking a retention solution (the retention solution is a material which is not separated out of the outside of the bag in the dialysis bag), diluting, and homogenizing by using high-pressure microjet to obtain a colloidal nano cellulose mixed solution;
(4) treating by a micro-jet nano homogenizer: and (3) centrifuging the nano-cellulose mixed solution obtained in the step (3), separating a supernatant and a fiber precipitate, wherein the supernatant is cellulose nanocrystals dispersed in water and is in a light blue transparent state, drying the supernatant to obtain the cellulose nanocrystals, and drying the fiber precipitate to obtain the cellulose nanofibrils.
Further, the cellulose raw material in the step (1) is more than one of microcrystalline cellulose, bleached bagasse pulp, bleached wood pulp, bleached straw pulp, bleached cotton pulp, bleached bamboo pulp and the like.
Further, the organic acid in the step (1) is more than one of citric acid, maleic acid, tartaric acid, oxalic acid and the like; the concentration of the organic acid aqueous solution is 50-80 wt%.
Further, the mass ratio of the cellulose raw material to the organic acid aqueous solution in the step (1) is 1: 10 to 1: 30.
preferably, the mass ratio of the cellulose raw material to the organic acid aqueous solution in the step (1) is 1: 20.
Further, the temperature of the hydrolysis reaction in the step (1) is 80-100 ℃, the time of the hydrolysis reaction is 0.5-6 hours, and the stirring speed in the stirring state is 250-500 r/min.
Preferably, the stirring speed in the stirring state in the step (1) is 300 r/min.
Further, the method for recovering the organic acid in the filtrate in the step (2) is rotary evaporation, cooling crystallization or reduced pressure distillation.
Further, the filtration in the step (2) is vacuum filtration; and the vacuum filtration is carried out by adopting a G4 sand core funnel, deionized water is continuously added for filtration and washing in the vacuum filtration process, and the mass ratio of the deionized water to the organic acid solution is 8: 1-10: 1.
Preferably, the mass ratio of the deionized water to the organic acid solution is 8: 1.
Further, in the step (3), deionized water is used for carrying out dialysis treatment on the filter residue in the step (2) until the conductivity is the same as that of the deionized water.
Further, in the step (3), the reserved solution is diluted to have a mass percent concentration of 0.1 wt% -1 wt%.
Further, the high-pressure micro-jet homogenization in the step (3) is carried out by adopting a micro-jet nano homogenizer; the pressure of the high-pressure microfluidization homogenizing is 12000-18000 psi, and the frequency of the microfluidization homogenizing is 1-7 times.
Preferably, the microfluid nano-homogenizer is a D8(200nm) high-pressure reaction chamber.
Preferably, the high pressure microjet homogenization pressure is 16000 psi.
Further, the rotation speed of the centrifugation in the step (4) is 8000-10000r/min, and the centrifugation time is 10-30 min.
Preferably, the rotation speed of the centrifugation in the step (4) is 9000r/min, and the centrifugation time is 15 min.
Preferably, the drying manner in the step (4) is freeze drying or spray drying.
The invention provides a cellulose nanocrystal prepared by the method.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the preparation method provided by the invention selects the organic acid to hydrolyze the cellulose raw material to prepare the nano-cellulose, has the characteristics of wide raw material source, low risk and cost of the preparation process, environmental protection, no pollution and the like, and meets the coexistence requirements of sustainable production and environmental protection. Compared with the traditional method for preparing the nano-cellulose by hydrolyzing the inorganic acid, the method has the advantages of less water consumption, clean and environment-friendly process and no equipment corrosion; compared with other methods for preparing the nano-cellulose by hydrolyzing organic acid, the method has the advantages that the yield is greatly improved, the assistance of a catalyst is not needed, and the introduction of harmful substances and the recovery cost of the catalyst are reduced.
(2) The nano micro-jet homogenization auxiliary means adopted by the invention has high efficiency, short time effect and simple feeding and discharging mode, and is very suitable for industrial production;
(3) the preparation method provided by the invention can separate the cellulose nanocrystals from the fibers and uniformly reduce the size of the fiber slurry through microfluidization and homogenization treatment, thereby improving the yield of the nanocellulose crystals and the residual nanocellulose fibers to a greater extent.
(4) The organic acid used in the invention can be successfully recovered and recycled, and the recovery rate is over 85 percent.
(5) The method prepares the high-yield cellulose nanocrystal by a simple one-step method, and has the advantages of high CNC (computer numerical control) length-diameter ratio, good dispersion stability and high thermal stability; the excellent performance greatly widens the application field of the composite material in the aspect of various reinforced materials.
Drawings
Fig. 1 is a photograph of a water-dispersed suspension of nanocellulose prepared by citric acid hydrolysis in combination with microfluidization homogenization according to example 3, the left is a product 1 pale blue cellulose nanocrystal, and the right is a product 2 milky cellulose nanofibril.
Fig. 2 is an atomic force microscope photograph of cellulose nanocrystals and nanofibrils prepared by citric acid hydrolysis combined with microfluidization homogenization according to example 5, with product 1 cellulose nanocrystals on the left and product 2 cellulose nanofibrils on the right.
Detailed Description
The following examples are presented to further illustrate the practice of the invention, but the practice and protection of the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.
Example 1
A method for cleanly preparing high-yield Cellulose Nanocrystalline (CNC) by combining oxalic acid hydrolysis with a nano micro-jet homogenization one-step method. The method comprises the following steps:
(1) under the conditions that the rotating speed is 400rpm and the temperature is 100 ℃, 10g of absolutely dry bleached bagasse cellulose is added into 200ml of oxalic acid aqueous solution with the concentration of 80 wt% for reaction for 2 hours, and hydrolysis suspension is obtained;
(2) and (2) after the reaction is terminated, carrying out vacuum filtration and washing on the hydrolysis suspension obtained in the step (1) through a G4 sand core funnel, continuously adding deionized water (the addition of the deionized water is 1600mL) in the vacuum filtration process, obtaining white solid fiber and filtrate through vacuum filtration, pouring the solid fiber into a dialysis bag, and dialyzing with the deionized water until the conductivity of the solid fiber is the same as that of the deionized water. Meanwhile, the oxalic acid solid is recovered by cooling and crystallizing the filtrate, and the recovery rate is over 85 percent.
(3) And (3) pouring out the retained fibers in the dialysis bag after dialysis, diluting the fibers into 0.1 wt% solution by using deionized water, and homogenizing the solution for 3 times by using a nano micro-jet homogenizer at the chamber pressure of 15000psi to obtain the mixed solution of the cellulose nanocrystals and the cellulose nanofibrils.
(4) Centrifuging the mixed solution for 20min at 10000r/min until the mixed solution is completely separated to obtain supernatant and fiber precipitate, wherein the supernatant is nano cellulose crystal dispersed in water and is light blue transparent. And drying the supernatant to obtain cellulose nanocrystals, and drying the fiber precipitates to obtain the cellulose nanofibrils.
Example 2
A method for cleanly preparing high-yield Cellulose Nanocrystalline (CNC) by combining tartaric acid hydrolysis with a nano micro-jet homogenization one-step method. The method comprises the following steps:
(1) 10g of oven-dried bleached bagasse cellulose was added to 200ml of a 50 wt% aqueous solution of tartaric acid at a rotation speed of 500rpm and a temperature of 100 ℃ for reaction for 6 hours to obtain a hydrolyzed suspension.
(2) And (3) after the reaction is terminated, carrying out vacuum filtration and washing on the hydrolysis suspension obtained in the step (1) through a G4 sand core funnel, and continuously adding deionized water (the adding amount of the deionized water is 1800mL) in the vacuum filtration process to obtain white solid fibers and filtrate through vacuum filtration. The solid fiber is poured into a dialysis bag and dialyzed by deionized water until the conductivity is the same as that of the deionized water. And (3) carrying out rotary evaporation on the filtrate at the temperature of 55-60 ℃ and at the speed of 150r/min, and recovering to obtain white tartaric acid solid, wherein the recovery rate is up to 98%.
(3) And pouring out the retained fibers in the dialysis bag after dialysis is finished, diluting the fibers into a 1 wt% solution by using deionized water, and homogenizing the solution for 3 times by using a nano micro-jet homogenizer at the chamber pressure of 18000psi to obtain a mixed solution of the carboxylated cellulose nanocrystals and the cellulose nanofibrils.
(4) Centrifuging the mixed solution for 30min at 8000r/min until the mixed solution is completely separated to obtain supernatant and fiber precipitate, wherein the supernatant is nano cellulose crystal dispersed in water and is light blue transparent. And drying the supernatant to obtain cellulose nanocrystals, and drying the fiber precipitates to obtain the cellulose nanofibrils.
Example 3
A method for cleanly preparing high-yield Cellulose Nanocrystalline (CNC) by combining citric acid hydrolysis with a nano micro-jet homogenization one-step method. The method comprises the following steps:
(1) 10g of oven-dried bleached bagasse cellulose was added to an aqueous solution of 80 wt% organic acid at a rotation speed of 350rpm and a temperature of 100 ℃ for 4 hours to obtain a hydrolyzed suspension.
(2) And (3) after the reaction is terminated, carrying out vacuum filtration and washing on the hydrolysis suspension obtained in the step (1) through a G4 sand core funnel, continuously adding deionized water (the adding amount of the deionized water is 1600mL) in the vacuum filtration process, and carrying out vacuum filtration to obtain white solid fibers and filtrate. The solid fiber is poured into a dialysis bag and dialyzed by deionized water until the conductivity is the same as that of the deionized water. And (3) carrying out rotary evaporation on the filtrate at the temperature of 55-60 ℃ and at the speed of 150r/min, and recovering to obtain a white citric acid solid, wherein the recovery rate is over 95 percent.
(3) And pouring out the retained fibers in the dialysis bag after dialysis is finished, diluting the fibers into 0.5 wt% solution by using deionized water, and homogenizing the solution for 3 times by using a nano micro-jet homogenizer at the chamber pressure of 18000psi to obtain a mixed solution of the carboxylated cellulose nanocrystals and the cellulose nanofibrils.
(4) Centrifuging the mixed solution for 15min at 9000r/min until the mixed solution is completely separated to obtain supernatant and fiber precipitate, wherein the supernatant is nano cellulose crystal dispersed in water and is light blue transparent. And drying the supernatant to obtain cellulose nanocrystals, and drying the fiber precipitates to obtain the cellulose nanofibrils.
Dissolving the prepared cellulose nanocrystals in water, as shown in the left diagram of fig. 1, to obtain light blue cellulose nanocrystals;
the cellulose nanofibrils prepared as described above were dissolved in water to obtain milky-white cellulose nanofibrils as shown in the right diagram of fig. 1.
The yield of the nano-cellulose crystal is 43.2 percent, and the length-diameter ratio is 69; the yield of the nano cellulose fibers is 51.5 percent, and the length-diameter ratio is 102; the total yield is 94.7%. Initial thermal degradation temperature range of nanocellulose crystals and nanocellulose fibrils: 300 ℃ and 310 ℃.
Example 4
A method for cleanly preparing high-yield Cellulose Nanocrystalline (CNC) by combining citric acid hydrolysis with a nano micro-jet homogenization one-step method. The method comprises the following steps:
(1) 10g of oven-dried bleached bagasse cellulose was added to an aqueous solution of 80 wt% organic acid at a rotation speed of 350rpm and a temperature of 100 ℃ for 4 hours to obtain a hydrolyzed suspension.
(2) And (3) after the reaction is terminated, carrying out vacuum filtration and washing on the hydrolysis suspension obtained in the step (1) through a G4 sand core funnel, continuously adding deionized water (the adding amount of the deionized water is 2000mL) in the vacuum filtration process, and carrying out vacuum filtration to obtain white solid fibers and filtrate. The solid fiber is poured into a dialysis bag and dialyzed by deionized water until the conductivity is the same as that of the deionized water. And (3) carrying out rotary evaporation on the filtrate at the temperature of 55-60 ℃ and at the speed of 150r/min, and recovering to obtain a white citric acid solid, wherein the recovery rate is over 95 percent.
(3) And pouring out the retained fibers in the dialysis bag after dialysis is finished, diluting the fibers into 0.5 wt% solution by using deionized water, and homogenizing for 5 times by using a nano micro-jet homogenizer at the chamber pressure of 18000psi to obtain a mixed solution of the carboxylated cellulose nanocrystals and the cellulose nanofibrils.
(4) Centrifuging the mixed solution for 20min at 9000r/min until the mixed solution is completely separated to obtain supernatant and fiber precipitate, wherein the supernatant is nano cellulose crystal dispersed in water and is light blue transparent. And drying the supernatant to obtain cellulose nanocrystals, and drying the fiber precipitates to obtain the cellulose nanofibrils.
The yield of the nano cellulose crystal is 50 percent, and the length-diameter ratio is 76; the yield of the nano cellulose fibrils is 40.1 percent, and the length-diameter ratio is 98; the total yield is 90.1%. Initial thermal degradation temperature range of nanocellulose crystals and nanocellulose fibrils: 300 ℃ and 310 ℃.
Example 5
A method for cleanly preparing high-yield Cellulose Nanocrystalline (CNC) by combining citric acid hydrolysis with a nano micro-jet homogenization one-step method. The method comprises the following steps:
(1) 10g of oven-dried bleached bagasse cellulose was added to an aqueous solution of 80 wt% organic acid at a rotation speed of 350rpm and a temperature of 100 ℃ for 2 hours to obtain a hydrolyzed suspension.
(2) And (3) after the reaction is terminated, carrying out vacuum filtration and washing on the hydrolysis suspension obtained in the step (1) through a G4 sand core funnel, continuously adding deionized water (the adding amount of the deionized water is 2000mL) in the vacuum filtration process, and carrying out vacuum filtration to obtain white solid fibers and filtrate. The solid fiber is poured into a dialysis bag and dialyzed by deionized water until the conductivity is the same as that of the deionized water. And (3) carrying out rotary evaporation on the filtrate at the temperature of 55-60 ℃ and at the speed of 150r/min, and recovering to obtain a white citric acid solid, wherein the recovery rate is over 95 percent.
(3) And pouring out the retained fibers in the dialysis bag after dialysis is finished, diluting the fibers into 0.5 wt% solution by using deionized water, and homogenizing the solution for 7 times by using a nano micro-jet homogenizer at the chamber pressure of 18000psi to obtain a mixed solution of the carboxylated cellulose nanocrystals and the cellulose nanofibrils.
(4) Centrifuging the mixed solution for 20min at 10000r/min until the mixed solution is completely separated to obtain supernatant and fiber precipitate, wherein the supernatant is nano cellulose crystal dispersed in water and is light blue transparent. And drying the supernatant to obtain cellulose nanocrystals, and drying the fiber precipitates to obtain the cellulose nanofibrils.
The atomic force microscope pictures of the prepared cellulose nanocrystals and cellulose nanofibrils are shown in the left as the product 1 cellulose nanocrystals and in the right as the product 2 cellulose nanofibrils.
The yield of the nano-cellulose crystal is 38.5 percent, and the length-diameter ratio is 98; the yield of the nano cellulose fibrils is 53.3 percent, and the length-diameter ratio is 190; the total yield is 91.8%. Initial thermal degradation temperature range of nanocellulose crystals and nanocellulose fibrils: 300 ℃ and 310 ℃.
The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.
Claims (10)
1. A method for cleanly preparing cellulose nanocrystals by combining organic acid hydrolysis with a nano-micro-jet homogenization one-step method is characterized by comprising the following steps:
(1) adding a cellulose raw material into an organic acid aqueous solution, heating under a stirring state to perform hydrolysis reaction to obtain a hydrolyzed fiber suspension;
(2) filtering the hydrolyzed fiber suspension in the step (1), separating filtrate and filter residue, and recovering organic acid in the filtrate;
(3) performing dialysis treatment on the filter residue obtained in the step (2) by using deionized water, taking a retention solution, diluting, and homogenizing by using high-pressure microjet to obtain a nano cellulose mixed solution;
(4) and (4) centrifuging the nano cellulose mixed solution obtained in the step (3), separating supernatant and fiber precipitate, drying the supernatant to obtain the cellulose nanocrystals, and drying the fiber precipitate to obtain the cellulose nanofibrils.
2. The method for cleanly preparing the cellulose nanocrystals by combining organic acid hydrolysis and nano-micro-jet homogenization one-step method according to claim 1, wherein the cellulose raw material in the step (1) is more than one of microcrystalline cellulose, bleached bagasse pulp, bleached wood pulp, bleached straw pulp, bleached cotton pulp and bleached bamboo pulp.
3. The method for cleanly preparing the cellulose nanocrystals by combining organic acid hydrolysis with a nano-micro-jet homogenization one-step method according to claim 1, wherein the organic acid in the step (1) is more than one of citric acid, maleic acid, tartaric acid and oxalic acid; the concentration of the organic acid aqueous solution is 50-80 wt%, and the mass ratio of the cellulose raw material to the organic acid aqueous solution in the step (1) is 1: 10 to 1: 30.
4. the method for cleanly preparing the cellulose nanocrystals by the one-step method of organic acid hydrolysis combined with the homogenization of the nanometer micro-jet as claimed in claim 1, wherein the temperature of the hydrolysis reaction in the step (1) is 80-100 ℃, the time of the hydrolysis reaction is 0.5-6 hours, and the stirring speed in the stirring state is 250-500 r/min.
5. The method for cleanly preparing the cellulose nanocrystals by combining organic acid hydrolysis and nano-micro-jet homogenization one-step method according to claim 1, wherein the method for recovering the organic acid in the filtrate in the step (2) is rotary evaporation, cooling crystallization or reduced pressure distillation.
6. The method for cleanly preparing the cellulose nanocrystals by combining the organic acid hydrolysis with the nano-micro-jet homogenization one-step method according to claim 1, wherein the filtration in the step (2) is vacuum filtration; and the vacuum filtration is carried out by adopting a G4 sand core funnel, deionized water is continuously added for filtration and washing in the vacuum filtration process, and the mass ratio of the deionized water to the organic acid solution is 8: 1-10: 1.
7. The method for cleanly preparing the cellulose nanocrystals by combining the organic acid hydrolysis with the nano-micro-jet homogenization one-step method according to claim 1, wherein in the step (3), the filter residue in the step (2) is dialyzed by deionized water until the conductivity of the filter residue is the same as that of the deionized water;
in the step (3), the concentration of the reserved solution is 0.1 wt% -1 wt% after dilution.
8. The method for cleanly preparing the cellulose nanocrystals by combining the organic acid hydrolysis with the nano-micro-jet homogenization one-step method according to claim 1, wherein the high-pressure micro-jet homogenization of the step (3) is carried out by using a micro-jet nano-homogenizer; the high pressure is 12000-18000 psi, and the high pressure microjet homogenizing times are 1-7.
9. The method for cleanly preparing the cellulose nanocrystals by the organic acid hydrolysis combined with the nano-micro-jet homogenization one-step method as claimed in claim 1, wherein the rotation speed of the centrifugation in the step (4) is 8000-10000r/min, and the centrifugation time is 10min-30 min; the drying mode is freeze drying or spray drying.
10. Cellulose nanocrystals prepared by the process according to any one of claims 1 to 9.
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