CN109705226B - Method for preparing carboxylated nanocellulose by utilizing citric acid hydrolysis and combining ultrasonic assistance - Google Patents
Method for preparing carboxylated nanocellulose by utilizing citric acid hydrolysis and combining ultrasonic assistance Download PDFInfo
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Abstract
The invention discloses a method for preparing carboxylated nanocellulose by utilizing citric acid hydrolysis and combining ultrasonic assistance. The method takes bleached fiber pulp board as a base material, then adds the base material into citric acid aqueous solution for acid hydrolysis, prepares cellulose nanocrystals through ultrasound and centrifugation, and prepares cellulose nanofibrils through a high-pressure homogenizer by residual solid fibers. The method is green, nontoxic, short in time consumption, low in risk in the preparation process, high in yield and easy to recycle, so that the cost of nano cellulose preparation is greatly reduced. In addition, the prepared cellulose nanocrystalline and cellulose nanofibrils have higher dispersion stability, excellent specific surface area and higher carboxyl content, and provide more chemical ways for further modifying the nanocellulose. Finally, the prepared nanocellulose has no residue of toxic and harmful substances, so that the nanocellulose has wide application prospect in the aspect of functional materials taking cellulose as a substrate, in particular in the aspect of materials related to human health.
Description
Technical Field
The invention belongs to the field of green preparation of nanocellulose, and particularly relates to a method for preparing carboxylated nanocellulose by utilizing citric acid hydrolysis and combining ultrasonic assistance.
Background
Cellulose is the most abundant renewable resource on the earth, is also the most abundant natural polymer compound in nature, widely exists in cell walls of various plants, algae, fungi and the like, has the advantages of no pollution, degradability, no toxicity, reproducibility, low cost, easy modification and the like, and is expected to replace petroleum to become a main raw material of energy and chemical industry in the future world.
Nanocellulose refers to cellulose with a diameter of 1 to 100nm, and can be divided into cellulose nanocrystals and cellulose nanofibrils according to size morphology. The cellulose nanocrystals are short in length and are rod-like cellulose with a length of about 100nm to 300nm obtained by acid or enzyme hydrolysis of the amorphous region of cellulose; the nanocellulose fibers are long, are network cellulose with different lengths of hundreds to thousands of nanometers, and are generally prepared by a mechanical method.
Nanocellulose prepared by physical or chemical methods not only retains higher reactivity, but also has outstanding physical and chemical properties, such as: the nano-sized nano-cellulose has the advantages of nano-size, excellent mechanical property, higher Young's modulus, larger specific surface area, low thermal expansion coefficient and the like, and the properties lead the nano-cellulose to have wide application prospect in the aspects of material science and engineering. At present, the main preparation method of the cellulose nanocrystalline is obtained by destroying an amorphous region of cellulose through inorganic acid hydrolysis, can obtain higher yield, and is increasingly mature. However, there are also drawbacks in many respects, for example, the mineral acid is too acidic and can excessively degrade cellulose and thus deteriorate the natural properties of nanocellulose; equipment is corroded in the preparation process, filtrate generated by hydrolysis is not recoverable and reusable, and a large amount of waste is generated, so that the environment is damaged; the price of inorganic acid is high, the preparation risk is high, and the preparation cost is high, so that the inorganic acid is not suitable for large-scale production; and the surface of the nanocellulose prepared by inorganic acid such as concentrated sulfuric acid is provided with a certain group, so that the further functional utilization of the nanocellulose is limited. In recent years, there are reports on the preparation of cellulose nanocrystals by using organic acids, however, the reported methods have the problems of low yield, relatively high price of medicines, toxicity of the organic acids and additional catalysts, and the like, so that the prepared nanocellulose is greatly limited in many applications related to human health, such as biological materials, food packaging, skin care, cosmetics, and the like, and the requirements of efficient and green preparation of nanocellulose and later high-added-value applications cannot be met.
Citric acid, an environmentally friendly weak organic acid, is present in a large amount in many fruits and vegetables, and in bones, muscles and blood of animals, and also promotes metabolism of human bodies, and thus is widely used in industries of foods, beverages, medicines, cosmetics, etc., and is relatively inexpensive and harmless to human bodies. In the invention, more than 95% of citric acid can be recovered and reused through crystallization after the nano-cellulose is prepared, so that the cost for preparing the nano-cellulose can be effectively reduced and the influence on the environment is reduced. In addition, the citric acid has three carboxylic acid groups, and has various ways of reacting with cellulose, and the prepared nano cellulose also has higher carboxyl content, and the prepared nano cellulose has larger functionalization potential by combining the original hydroxyl groups. In addition, the purpose of carboxylation is achieved while citric acid is hydrolyzed, and the additional means and consumption required by the traditional nanocellulose for carboxylation are avoided, so that the cost of nanocellulose functionalization is further greatly reduced.
At present, a method for preparing carboxylated nanocellulose in one step with high yield by combining citric acid hydrolysis with ultrasonic assistance is not reported.
Disclosure of Invention
The invention provides a method for preparing carboxylated nanocellulose by combining citric acid hydrolysis with an ultrasonic-assisted one-step method, which is environment-friendly and mainly aims at various defects existing in the process of the existing nanocellulose preparation method. The method has the characteristics of wide raw material sources, low preparation cost, relatively short time, recyclable medicine, environmental protection, no toxicity and no pollution. In addition, the nano cellulose prepared by the method has relatively high yield, large specific surface area and large carboxyl content, and the product is nontoxic, so that a foundation is laid for the cellulose-based functional material, especially for biological materials, foods, health products and other materials.
The object of the present invention is to provide a method for preparing carboxylated nanocellulose using citric acid hydrolysis in combination with ultrasound assistance, which nanocellulose is easy for further functionalization in the later stage.
The above object of the present invention is achieved by the following technical means.
A method for preparing carboxylated nanocellulose by utilizing citric acid hydrolysis and combining ultrasonic assistance uses bleached fiber pulp board as a base material, and the carboxylated nanocellulose is prepared by utilizing the citric acid hydrolysis and combining ultrasonic assistance method.
Preferably, the carboxylated nanocellulose includes cellulose nanocrystals and cellulose nanofibrils.
Preferably, the citric acid is aqueous citric acid.
Preferably, the bleached fiber pulp board is one or a mixture of a plurality of microcrystalline cellulose, bleached bagasse pulp, bleached wood pulp, bleached straw pulp, bleached cotton pulp and bleached bamboo pulp.
Preferably, the method specifically comprises the following steps:
s1, adding citric acid into water, and dissolving to form a citric acid aqueous solution;
S2, crushing the absolute bleached fiber pulp board, and adding the crushed absolute bleached fiber pulp board into a citric acid aqueous solution to fully react under the condition of stirring;
S3, separating fibers from the reacted fiber suspension by a vacuum suction filtration method, and recovering citric acid solid particles from the filtrate by a rotary evaporation crystallization method;
s4, washing the separated fiber to be neutral by a centrifugal method, separating cellulose nanocrystalline from the fiber to the maximum extent by an ultrasonic method, separating cellulose nanocrystalline dispersion by the centrifugal method, and obtaining solid cellulose nanocrystalline after freeze drying or spray drying;
S5, precipitating the residual fiber solid after cellulose nanocrystals are separated by a high-pressure nano homogenizer to prepare cellulose nanofibrils, and obtaining the solid cellulose nanofibrils after freeze drying or spray drying.
Further preferably, the temperature of the dissolution in step S1 is 100 ℃.
Further preferably, the stirring speed during the dissolution in the step S1 is 300r/min.
Further preferably, the concentration of the aqueous citric acid solution in step S1 is 60 wt% -80% wt%.
Further preferably, the stirring speed in the step S2 is 200r/min-400r/min, the reaction time is 0.5-4 hours, and the reaction temperature is 80-120 ℃.
Further preferably, the spin-steaming in step S3 is performed at 70℃and 60 r/min.
Further preferably, the G4 sand core funnel for vacuum filtration in step S3.
Further preferably, in the step S4, deionized water is repeatedly added for centrifugation at 4000r/min to neutrality; the power of the ultrasonic wave is 600W-1200W, the time is 10-30min (every 5s of ultrasonic wave has 5s interval), and the ultrasonic wave is carried out for 2 times.
Further preferably, the high-pressure nano homogenizer in the step S5 is a D8 (200 nm) high-pressure reaction chamber, and homogenizing is performed for 6-7 times.
Compared with the prior art, the invention has the following effects:
(1) The citric acid is used as a common organic weak acid with relatively low price, is widely used in the industries of foods, beverages, medicines and cosmetics, is harmless to human bodies, and the nano cellulose prepared by hydrolysis of the citric acid has the characteristics of wide raw material sources, low risk and cost in the preparation process, environmental protection, no pollution and the like, and meets the requirements of sustainable production and environment protection coexistence.
(2) The invention adopts ultrasonic method to assist, and uses short-time ultrasonic to assist, thereby beating the cellulose nanocrystalline which is just fallen off but not fallen off after acid hydrolysis, and greatly improving the yield of the cellulose nanocrystalline. Compared with the traditional method for preparing the nano cellulose by inorganic acid hydrolysis, the water consumption is low, and no waste liquid and waste residue are produced; compared with other organic acid hydrolysis to prepare nano cellulose, the method has higher yield, and does not need the assistance of a catalyst, so that the produced finished product is reduced, and the introduction of toxic substances is also reduced.
(3) The energy consumption for preparing the cellulose nanofibrils by the method is lower than that of the cellulose nanofibrils prepared by the traditional mechanical method.
(4) The citric acid used in the invention can be successfully recovered by more than 95 percent.
(5) The cellulose nanocrystals and nanofibrils prepared by the method have smaller length and width dimensions and stable dispersibility, and provide good material support for later application in material reinforcement.
(6) The nano-cellulose prepared by the invention has higher carboxyl content, reduces more extra processes and medicine consumption necessary for traditional nano-cellulose carboxylation, greatly reduces the cost, and provides more means for further functionalization and wide application of the nano-cellulose.
Drawings
Fig. 1a is an atomic force electron microscope picture of the prepared cellulose nanocrystals.
Fig. 1b is an atomic force electron microscope image of the produced nanofibrils.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
The following further illustrates the invention in connection with specific examples, which should not be construed as limiting the invention. Simple modifications and substitutions of the method, steps or conditions of the invention without departing from the spirit and nature of the invention are intended to be within the scope of the invention; the technical means used in the examples are conventional means well known to those skilled in the art unless otherwise indicated.
Unless specifically stated otherwise, the reagents, methods and apparatus employed in the present invention are those conventional in the art. The reagents and materials used in the present invention are commercially available unless otherwise specified.
Example 1: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) At 100℃5g of the oven dried bleached bagasse pulp board was crushed and added to an aqueous solution of citric acid (80 g of citric acid, 20ml of deionized water) having a concentration of 80% by weight, and reacted for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min at 4000r/min, and separating cellulose nanocrystals (atomic force microscope images of the cellulose nanocrystals are shown in figure 1 a); the remaining precipitate was diluted to 1wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine (see figure 1b for atomic force microscopy).
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 32.2%, the surface carboxyl content is 0.6mmol/g, the yield of the cellulose nanofiber is 63.44%, the surface carboxyl content is 0.3mmol/g, and no precipitation occurs after standing for 30 days.
Example 2: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) 5G of the oven dried bleached bagasse pulp board was added to an aqueous solution of citric acid (70 g of citric acid, 30ml of water) having a concentration of 70wt% at a temperature of 100℃for reaction for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 26.17%, the surface carboxyl content is 0.4mmol/g, the yield of the cellulose nanofiber is 71.84%, the surface carboxyl content is 0.2mmol/g, and no precipitation occurs after standing for 30 days.
Example 3: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) 5G of the oven dried bleached wood pulp board was crushed at 100℃and added to an aqueous solution of citric acid (80 g of citric acid, 20ml of water) having a concentration of 80% by weight to react for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 31.26%, the surface carboxyl content is 0.65mmol/g, the yield of the cellulose nanofiber is 70.67%, the surface carboxyl content is 0.3mmol/g, and no precipitation occurs after standing for 30 days.
Example 4: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) 5G of the oven dried bleached wood pulp board was crushed at 100℃and added to an aqueous solution of citric acid (70 g of citric acid, 30ml of water) having a concentration of 70% by weight to react for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 24.73%, the surface carboxyl content is 0.45mmol/g, the yield of the cellulose nanofiber is 74.5%, the surface carboxyl content is 0.25mmol/g, and no precipitation occurs after standing for 30 days.
Example 5: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) At 100℃5g of the absolute dried bleached straw pulp board was crushed and added to an aqueous solution of citric acid (80 g of citric acid, 20ml of water) having a concentration of 80% by weight and reacted for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 34.6%, the surface carboxyl content is 0.65mmol/g, the yield of the cellulose nanofiber is 64.53%, the surface carboxyl content is 0.35mmol/g, and no precipitation occurs after standing for 30 days.
Example 6: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) At 100℃5g of the absolute dried bleached straw pulp board was crushed and added to an aqueous solution of citric acid (70 g of citric acid, 30ml of water) having a concentration of 70% by weight and reacted for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 25.67%, the surface carboxyl content is 0.4mmol/g, the yield of the cellulose nanofiber is 69.63%, the surface carboxyl content is 0.25mmol/g, and no precipitation occurs after standing for 30 days.
Example 7: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) At 100℃5g of an absolute dry bleached cotton pulp board was crushed and added to an aqueous solution of citric acid (80 g of citric acid, 20ml of water) having a concentration of 80% by weight and reacted for 2 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 20.81%, the surface carboxyl content is 0.3mmol/g, the yield of the cellulose nanofiber is 77.63%, the surface carboxyl content is 0.15mmol/g, and no precipitation occurs after standing for 30 days.
Example 8: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) 5G of an absolute dry bleached cotton pulp board was crushed and added to an aqueous solution of citric acid (70 g of citric acid, 30ml of deionized water) having a concentration of 70wt% at a temperature of 100℃for reaction for 2 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 16.56%, the surface carboxyl content is 0.2mmol/g, the yield of the cellulose nanofiber is 81.63%, the surface carboxyl content is 0.1mmol/g, and no precipitation occurs after standing for 30 days.
Example 9: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) At 100℃5g of the absolute dried bleached bamboo pulp board was crushed and added to an aqueous solution of citric acid (80 g of citric acid, 20ml of deionized water) having a concentration of 80% by weight, and reacted for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 36.56%, the surface carboxyl content is 0.65mmol/g, the yield of the cellulose nanofiber is 61.44%, the surface carboxyl content is 0.35mmol/g, and no precipitation occurs after standing for 30 days.
Example 10: preparation of carboxylated nanocellulose by citric acid hydrolysis combined with ultrasonic-assisted one-step method
(1) At 100℃5g of the absolute dried bleached bamboo pulp board was crushed and added to an aqueous solution of citric acid (70 g of citric acid, 30ml of water) having a concentration of 70% by weight and reacted for 4 hours to obtain a hydrolyzed suspension.
(2) The hydrolyzed suspension was vacuum filtered through a G4 sand core funnel to yield solid fibers and filtrate. Repeatedly adding deionized water into the fiber, centrifugally washing the fiber to be neutral at 4000r/min, and performing rotary evaporation on the filtrate at 70 ℃ and 60r/min to obtain white citric acid crystalline solid.
(3) The washed fiber is ultrasonically treated for 20min under 900W (5 s interval after every 5s of ultrasonic treatment) by an ultrasonic cell breaker, and 200ml of deionized water is added after the ultrasonic treatment is finished and then the ultrasonic treatment is performed for 20min.
(4) Centrifuging the cellulose suspension after ultrasonic treatment for 10min by 4000r/min, and separating cellulose nanocrystals; the remaining precipitate was diluted to 1 wt% and the cellulose nanofibers were prepared using a high pressure nanomachining machine.
(5) The yield of the cellulose nanocrystalline prepared in the experiment is 24.36%, the surface carboxyl content is 0.45mmol/g, the yield of the cellulose nanofiber is 69.85%, the surface carboxyl content is 0.25mmol/g, and no precipitation occurs after standing for 30 days.
Claims (6)
1. The method for preparing carboxylated nanocellulose by utilizing citric acid hydrolysis and combining ultrasonic assistance is characterized in that a bleached fiber pulp board is taken as a base material, and the carboxylated nanocellulose is prepared by utilizing the citric acid hydrolysis and combining ultrasonic assistance, and the method specifically comprises the following steps:
s1, adding citric acid into water, and dissolving to form a citric acid aqueous solution;
s2, crushing the absolute bleached fiber pulp board, and adding the crushed absolute bleached fiber pulp board into a citric acid aqueous solution for full reaction;
S3, separating fibers from the reacted fiber suspension by a vacuum suction filtration method, and recovering citric acid solid particles from the filtrate by a rotary evaporation crystallization method;
S4, washing the separated fiber to be neutral by a centrifugal method, separating cellulose nanocrystalline from the fiber to the maximum extent by an ultrasonic method, separating cellulose nanocrystalline dispersion by the centrifugal method, and obtaining solid cellulose nanocrystalline after freeze drying or spray drying; the power of the ultrasonic wave is 600W-1200W, and the time is 10-30min; the ultrasound is performed at intervals of 5s after every 5s of ultrasound;
S5, precipitating the residual fiber solids after cellulose nanocrystals are separated by a high-pressure nano homogenizer to prepare cellulose nanofibrils, and obtaining the cellulose nanofibrils of the solids after freeze drying or spray drying;
the concentration of the citric acid aqueous solution in the step S1 is 60-80 wt%;
the reaction time in the step S2 is 0.5-4 hours, and the reaction temperature is 80-120 ℃.
2. The method of claim 1, wherein step S3 is performed using a G4 sand core funnel for vacuum filtration.
3. The method of claim 1, wherein the washing of step S4 is repeated with deionized water added to centrifuge to neutrality.
4. The method according to claim 1, wherein the high pressure nano-homogenizer in step S5 is a D8 high pressure reaction chamber, homogenizing 6-7 times.
5. The method of claim 1, wherein the carboxylated nanocellulose comprises cellulose nanocrystals and cellulose nanofibrils.
6. The method of claim 1, wherein the bleached fiber pulp board is one or more of microcrystalline cellulose, bleached bagasse pulp, bleached wood pulp, bleached straw pulp, bleached cotton pulp, and bleached bamboo pulp.
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| CN114716572A (en) * | 2022-03-07 | 2022-07-08 | 浙江理工大学 | One-step preparation process of multi-functionalized nano-cellulose |
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