CN108219008A - Nano cellulose crystal and method prepared by acid hydrolyzed cellulose microfibril - Google Patents
Nano cellulose crystal and method prepared by acid hydrolyzed cellulose microfibril Download PDFInfo
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- CN108219008A CN108219008A CN201810074902.8A CN201810074902A CN108219008A CN 108219008 A CN108219008 A CN 108219008A CN 201810074902 A CN201810074902 A CN 201810074902A CN 108219008 A CN108219008 A CN 108219008A
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- 229920002678 cellulose Polymers 0.000 title claims abstract description 62
- 239000001913 cellulose Substances 0.000 title claims abstract description 62
- 239000013078 crystal Substances 0.000 title claims abstract description 43
- 210000001724 microfibril Anatomy 0.000 title claims abstract description 43
- 229920001046 Nanocellulose Polymers 0.000 title claims abstract description 32
- 238000000034 method Methods 0.000 title claims abstract description 32
- 239000002253 acid Substances 0.000 title claims abstract description 10
- 239000000835 fiber Substances 0.000 claims abstract description 82
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 52
- 239000000725 suspension Substances 0.000 claims abstract description 50
- 238000006243 chemical reaction Methods 0.000 claims abstract description 37
- 238000005903 acid hydrolysis reaction Methods 0.000 claims abstract description 27
- 230000007935 neutral effect Effects 0.000 claims abstract description 27
- 230000007062 hydrolysis Effects 0.000 claims abstract description 13
- 238000006460 hydrolysis reaction Methods 0.000 claims abstract description 13
- 238000001035 drying Methods 0.000 claims abstract description 9
- 239000002002 slurry Substances 0.000 claims abstract description 8
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 55
- 239000011259 mixed solution Substances 0.000 claims description 33
- 239000000243 solution Substances 0.000 claims description 23
- 239000011122 softwood Substances 0.000 claims description 17
- JHJLBTNAGRQEKS-UHFFFAOYSA-M sodium bromide Chemical compound [Na+].[Br-] JHJLBTNAGRQEKS-UHFFFAOYSA-M 0.000 claims description 16
- 238000001704 evaporation Methods 0.000 claims description 13
- 239000005708 Sodium hypochlorite Substances 0.000 claims description 10
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 claims description 10
- 108010059892 Cellulase Proteins 0.000 claims description 9
- 229940106157 cellulase Drugs 0.000 claims description 9
- 238000004537 pulping Methods 0.000 claims description 9
- 108090000790 Enzymes Proteins 0.000 claims description 8
- 102000004190 Enzymes Human genes 0.000 claims description 8
- 229940088598 enzyme Drugs 0.000 claims description 8
- 238000001914 filtration Methods 0.000 claims description 8
- 239000007853 buffer solution Substances 0.000 claims description 7
- 238000000265 homogenisation Methods 0.000 claims description 7
- 230000010355 oscillation Effects 0.000 claims description 6
- 238000005406 washing Methods 0.000 claims description 6
- 238000000227 grinding Methods 0.000 claims description 4
- 238000006400 oxidative hydrolysis reaction Methods 0.000 claims description 4
- 239000001509 sodium citrate Substances 0.000 claims description 4
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 claims description 4
- 230000007071 enzymatic hydrolysis Effects 0.000 claims description 3
- 238000006047 enzymatic hydrolysis reaction Methods 0.000 claims description 3
- 230000000415 inactivating effect Effects 0.000 claims description 2
- 238000002156 mixing Methods 0.000 claims description 2
- GDOPTJXRTPNYNR-UHFFFAOYSA-N methyl-cyclopentane Natural products CC1CCCC1 GDOPTJXRTPNYNR-UHFFFAOYSA-N 0.000 claims 3
- 238000000502 dialysis Methods 0.000 abstract description 25
- 238000010494 dissociation reaction Methods 0.000 abstract description 4
- 230000005593 dissociations Effects 0.000 abstract description 4
- 238000004519 manufacturing process Methods 0.000 abstract description 4
- 239000000126 substance Substances 0.000 abstract description 4
- 238000005265 energy consumption Methods 0.000 abstract description 3
- 239000002351 wastewater Substances 0.000 abstract description 3
- 210000002421 cell wall Anatomy 0.000 abstract description 2
- 235000010980 cellulose Nutrition 0.000 description 36
- 238000004108 freeze drying Methods 0.000 description 23
- 238000003756 stirring Methods 0.000 description 20
- 239000012153 distilled water Substances 0.000 description 18
- 239000007787 solid Substances 0.000 description 10
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 9
- 238000005303 weighing Methods 0.000 description 7
- 108010084185 Cellulases Proteins 0.000 description 6
- 102000005575 Cellulases Human genes 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 238000002360 preparation method Methods 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 238000009835 boiling Methods 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 4
- 239000000706 filtrate Substances 0.000 description 4
- 230000002378 acidificating effect Effects 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000002779 inactivation Effects 0.000 description 3
- 150000007522 mineralic acids Chemical class 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- RKMGAJGJIURJSJ-UHFFFAOYSA-N 2,2,6,6-tetramethylpiperidine Chemical compound CC1(C)CCCC(C)(C)N1 RKMGAJGJIURJSJ-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 239000003814 drug Substances 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- KYARBIJYVGJZLB-UHFFFAOYSA-N 7-amino-4-hydroxy-2-naphthalenesulfonic acid Chemical compound OC1=CC(S(O)(=O)=O)=CC2=CC(N)=CC=C21 KYARBIJYVGJZLB-UHFFFAOYSA-N 0.000 description 1
- 235000017166 Bambusa arundinacea Nutrition 0.000 description 1
- 235000017491 Bambusa tulda Nutrition 0.000 description 1
- 244000166124 Eucalyptus globulus Species 0.000 description 1
- 229920000168 Microcrystalline cellulose Polymers 0.000 description 1
- 244000082204 Phyllostachys viridis Species 0.000 description 1
- 235000015334 Phyllostachys viridis Nutrition 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000011425 bamboo Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000012847 fine chemical Substances 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 235000019813 microcrystalline cellulose Nutrition 0.000 description 1
- 239000008108 microcrystalline cellulose Substances 0.000 description 1
- 229940016286 microcrystalline cellulose Drugs 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- 239000006228 supernatant Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
- C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
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- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Biochemistry (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
The nano cellulose crystal and method prepared the present invention relates to a kind of acid hydrolyzed cellulose microfibril first takes slurry defibrination that pretreatment, isolated fiber after hydrolysis pretreatment are hydrolyzed again；Obtained fiber is configured to fibrous suspension, carries out high-pressure homogeneous processing and drying, obtains cellulose microfibril；Cellulose microfibril is taken to be configured to the microfibril suspension that mass concentration is 1%~2% with acid solution, is reacted 5~8 hours at 30 DEG C~45 DEG C；After reaction, obtained mixed liquor is subjected to dialysis until neutral, is then evaporated to thick, be dried to obtain nano cellulose crystal.The present invention prepares nano cellulose crystal using pretreatment with reference to mechanical dissociation assist acid hydrolysis, reduces the generation of wastewater from chemical industry, reduces production cost and carrying capacity of environment；The efficiency that sour water solution destroys fiber finer cell wall is improved, increases reaction rate, improves yield, saves energy consumption.
Description
Technical Field
The invention belongs to the field of nano materials, and particularly relates to a nano cellulose crystal prepared by acid hydrolysis of cellulose microfibrils and a method.
Background
Generally, the nanocellulose crystal (NCC) refers to cellulose with at least one dimension of space size of 1-100 nm. Compared with natural cellulose and microcrystalline cellulose, the composite material has the advantages of large specific surface area, high crystallinity, high hydrophilicity, high modulus, high strength, superfine structure, high transparency and the like. Therefore, the compound has wide application prospect in the aspects of fine chemical engineering, composite materials, medicine carriers, medicine slow release and the like. The commonly used method of preparation of nanocellulose crystals is the inorganic acid hydrolysis method, the most commonly used inorganic acid being sulphuric acid. In addition, phosphoric acid and hydrochloric acid are used, and sulfuric acid and hydrochloric acid are mixed in a certain proportion for use. However, a large amount of waste acid and impurities are generated by pure strong acid treatment, the preparation process is time-consuming, multiple in steps, high in energy consumption, large in water resource consumption and high in equipment requirement. Therefore, there is a need for a method for optimizing the process of preparing nanocellulose crystals by mineral acid hydrolysis.
Disclosure of Invention
The invention aims to overcome the problems in the prior art, and provides a nano cellulose crystal prepared by acid hydrolysis of cellulose microfibril and a method, which can reduce the generation of chemical wastewater and improve the efficiency.
In order to achieve the purpose, the invention adopts the following technical scheme:
the method comprises the following steps:
(1) taking pulp, grinding the pulp into slurry, then carrying out hydrolysis pretreatment, and separating to obtain fibers after the hydrolysis pretreatment is finished;
(2) preparing the fiber obtained in the step (1) into fiber suspension, and carrying out high-pressure homogenization treatment and drying to obtain cellulose microfibrils;
(3) preparing microfibril suspension with mass concentration of 1-2% by taking cellulose microfibril and using acid solution, and reacting for 5-8 hours at 30-45 ℃;
(4) and (4) after the reaction in the step (3) is finished, dialyzing the obtained mixed solution until the mixed solution is neutral, evaporating the mixed solution to be viscous, and drying the mixed solution to obtain the nano cellulose crystal.
Further, in the step (1), the pulp is prepared by bleached softwood pulp absolute dry pulp or bleached softwood fiber absolute dry pulp and water, and the concentration of the pulp is 10-15%.
Further, in the step (1), the grinding time is 15-20 min.
Further, in the step (1), the hydrolysis pretreatment is to perform acid hydrolysis, enzyme hydrolysis or oxidative hydrolysis on the ground pulp; wherein,
the acid hydrolysis comprises the following steps: firstly, mixing the pulp after pulping with sulfuric acid to prepare a fiber suspension with the concentration of 2-4%, reacting for 20-50 min at 40-50 ℃, filtering and washing after the reaction is ended, and collecting fibers;
the enzymatic hydrolysis comprises the following steps: adding cellulase and the pulp after pulping into a sodium citrate buffer solution with the pH value of 4-5 to prepare a fiber suspension with the concentration of 2-3 percent, carrying out oscillation reaction at the temperature of 50-55 ℃ for 2-3 hours, inactivating and filtering after the reaction is finished, and collecting fibers;
the oxidative hydrolysis comprises the following steps: preparing the pulp after pulping into 1-2% fiber suspension by using water, then adding TEMPO solution, sodium bromide and sodium hypochlorite solution into the fiber suspension, reacting for 1-2 hours, filtering and washing, and collecting fibers; wherein the mass ratio of oven-dried fibers, TEMPO, sodium bromide and sodium hypochlorite in the fiber suspension is (1-2): 0.11 g: 0.32 g: 1.5 g; the concentration of the TEMPO solution was 0.11g/mL and the concentration of the sodium hypochlorite solution was 0.5 g/mL.
Further, in the step (2), the concentration of the fiber suspension is 1-1.5%.
Further, in the step (2), the number of times of homogenization treatment is 10-20 times, and the homogenization pressure is 100-150 MPa.
Furthermore, in the step (2), the drying is carried out for 12 to 24 hours at the temperature of between 10 ℃ below zero and 50 ℃ below zero.
Further, in the step (3), the acid solution is sulfuric acid with a volume fraction of 40-50%.
Further, in the step (4), the drying is carried out for 12-24 hours at-10 ℃ to-50 ℃.
A nanocellulose crystal produced by the method described above, characterized in that: the nano cellulose crystal is a rod-shaped structure or a spherical structure, and the average grain diameter is 30 nm-70 nm.
Compared with the prior art, the invention has the following beneficial technical effects:
compared with a large amount of impurities and waste acid generated in the traditional process of preparing the nano-crystalline cellulose by using the inorganic acid, the method disclosed by the invention has the advantages that the nano-crystalline cellulose is prepared by combining pretreatment with mechanical dissociation to assist acid hydrolysis, the generation of chemical wastewater is reduced, and the production cost and the environmental load are reduced;
secondly, the method prepares the nano cellulose crystal by combining pretreatment with mechanical dissociation to assist acid hydrolysis, greatly improves the efficiency of destroying fiber cell walls by acid hydrolysis, increases the reaction rate, improves the yield, and saves energy consumption, and the yield can reach 60-80%;
compared with the traditional method for preparing the nano-crystalline cellulose by sulfuric acid hydrolysis, the method has the advantages of mild conditions, low temperature and simple preparation method, and the nano-crystalline cellulose prepared by the method can meet the requirements.
Drawings
Figure 1 is an SEM image of NCC prepared by acid pretreatment of example 1.
FIG. 2 is an SEM image of enzyme pretreatment for preparing NCC in example 2.
FIG. 3 is an SEM image of NCC prepared by oxidation pretreatment of TEMPO in example 3.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention provides a method for preparing nano-crystalline cellulose by combining pretreatment with mechanical dissociation assisted chemical treatment and biological treatment, and nano-crystalline cellulose with spherical and rod-shaped structures is prepared. The preparation method comprises the following steps:
(1) pulping the pulp with the mass concentration of 10-15% for 15-20 min by using a PFI pulping machine to obtain pulp I; wherein, the fiber of the pulp adopts bleached softwood pulp absolute dry pulp or bleached softwood fiber absolute dry pulp;
(2) pretreating the slurry I with sulfuric acid, cellulase or 2,2,6, 6-tetramethylpiperidine oxynitride (TEMPO);
acid hydrolysis is carried out in a constant-temperature water bath kettle, slurry I and sulfuric acid with volume fraction of 40-50% are respectively added into a round-bottom flask to prepare fiber suspension with concentration of 2-4%, and the fiber suspension is reacted for 20-50 min at 40-50 ℃ and is continuously stirred. And (3) after the reaction is finished, stopping the reaction by using 20-30 times of distilled water, then filtering by using a Buchner funnel, repeatedly washing by distillation, and collecting fibers when the filtrate is neutral.
The cellulase is compound cellulase, exo-cellulase or endo-cellulase; wherein, the enzyme dosage of the compound cellulase and the exo-cellulase in the step (2) is 5 FPU/g-10 FPU/g oven dry fiber, and the enzyme dosage of the endo-cellulase is 20 CMCU/g-60 CMCU/g oven dry fiber. The enzymatic hydrolysis is to add the slurry I and cellulase into a sodium citrate buffer solution with the pH value of 4-5 to prepare a 2% -3% fiber suspension, react in a constant-temperature water bath oscillator at the temperature of 50-55 ℃ for 2-3 hours at the oscillation speed of 70-120 r/min, and inactivate in a boiling water bath for 10-15 min after the reaction is finished; the fibers were then filtered and collected. The cellulase can also be dissolved in a sodium citrate buffer solution with the pH value of 4-5, and then the slurry I is added.
The conditions of the TEMPO oxidation pretreatment are as follows: preparing 1-2% fiber suspension from the slurry I with water, firstly fully stirring for a period of time, adding 0.11g of TEMPO (1 ml of solution) and 0.32g of sodium bromide, stirring to fully dissolve the fiber suspension, then adding 1.5g of sodium hypochlorite (3 ml of solution) for a small number of times, stirring for reaction, ensuring that the total reaction time is 1-2 hours, finally filtering, repeatedly washing with distilled water, and collecting fibers.
(3) Preparing the fiber obtained in the step (2) into a fiber suspension with the concentration of 1-1.5%, then carrying out high-pressure homogenization treatment on the fiber suspension through a high-pressure homogenizer for 10-20 times at the homogenization pressure of 100-150 MPa, and finally carrying out freeze drying at-10-50 ℃ for 12-24 hours to obtain the cellulose microfibril; wherein, the circulation is preferably carried out for 10 times, and the pressure is preferably 100 MPa;
(4) weighing a certain amount of the cellulose microfibrils obtained in the step (3), preparing a suspension with a mass concentration of 1-2% by using 40-50% by volume of sulfuric acid, and reacting at 30-45 ℃ for 5-8 hours while stirring at a stirring speed of 30 r/min;
(5) pouring the mixed solution obtained in the step (4) into a dialysis bag for dialysis until the pH value reaches neutral;
(6) evaporating the mixed solution obtained in the step (5) to be viscous by using a rotary evaporator, and then carrying out freeze drying at-10 to-50 ℃ for 12 to 24 hours to obtain the nano cellulose crystal.
Wherein the pulp concentration is mass concentration.
Example 1
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 3g (absolutely dry) of the ground pulp (simultaneously, the pulp is additionally weighed to measure the moisture) is weighed and placed into a round-bottom flask, 50 percent sulfuric acid is added, and the pulp concentration is adjusted to be 3 percent. And (3) placing the round-bottom flask into a constant-temperature water bath kettle, setting the temperature to be 45 ℃, reacting for 30min, continuously stirring, taking out the round-bottom flask after the reaction is finished, and adding 30 times of distilled water to terminate the reaction. Then filtered with a buchner funnel, washed repeatedly with distilled water until the filtrate is not acidic, the fibers are collected and the water is equilibrated. Taking 1g (oven dried) of fiber after acid hydrolysis to prepare fiber suspension with concentration of 1%, and then processing 10 times by a high pressure homogenizer with homogenizing pressure of 100 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-40 deg.C for 12 hr to obtain cellulose microfibril. Taking 2g (absolute dry) of cellulose microfibrils, adjusting the concentration to be 1% by using 50% sulfuric acid, and reacting in a water bath kettle at the temperature of 45 ℃ for 8 hours at the stirring speed of 30 r/min. Transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and freeze-drying for 24 hours at the temperature of minus 40 ℃ to obtain the nano-cellulose crystal.
As shown in fig. 1, the obtained nanocellulose crystals: rod-like structure, average particle size of 30nm, yield of 60%.
Example 2
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 3g (absolutely dry) of the ground pulp (simultaneously weighing the pulp for measuring the moisture) is weighed into a conical flask, 5FPU/g of absolutely dry fiber compound cellulase is added, and a cellulose suspension with the concentration of 3% is prepared by using a citric acid buffer solution with the pH value of 4.8. Placing the conical flask in a constant temperature water bath oscillator at 50 ℃ for reaction for 2 hours, wherein the oscillation speed is 70r/min, and immediately placing the conical flask in a boiling water bath for inactivation for 10min after the reaction is finished. Filter with buchner funnel, wash repeatedly with distilled water, collect fiber and equilibrate moisture. Taking 1g (oven dried) of fiber after enzyme hydrolysis to prepare fiber suspension with concentration of 1%, and then processing 10 times with high pressure homogenizer with homogenizing pressure of 100 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-40 deg.C for 12h to obtain cellulose microfibril. Taking 2g (absolute dry) of cellulose microfibrils, adjusting the concentration to be 1% by using 50% sulfuric acid, and reacting in a water bath kettle at the temperature of 45 ℃ for 8 hours at the stirring speed of 30 r/min. And transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and performing freeze drying at-40 ℃ for 12 hours to obtain the nano-cellulose crystal.
As shown in fig. 2, the obtained nanocellulose crystals: spherical structure, average particle size 40nm, yield 65%.
Example 3
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 3g (absolutely dry) of ground pulp (simultaneously, the pulp is additionally weighed to measure the moisture) is weighed and put into a conical flask, and distilled water is used for preparing the pulp with the concentration of 1 percent, and the pulp is continuously stirred to be fully dispersed. 0.11g TEMPO (1 ml solution) and 0.32g sodium bromide were added thereto, and the mixture was stirred until it was sufficiently dissolved, and 1.50g sodium hypochlorite (3 ml solution) was added thereto over 30min (a small amount of the solution was added several times), and the mixture was stirred for 1 hour. Filter with buchner funnel, wash repeatedly with distilled water, collect fiber and equilibrate moisture. Taking 1g (oven-dried) of TEMPO treated fiber to prepare a fiber suspension with the concentration of 1%, and then treating for 10 times by using a high-pressure homogenizer with the homogenizing pressure of 100 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-40 deg.C for 12h to obtain cellulose microfibril. Taking 2g (absolute dry) of cellulose microfibrils, adjusting the concentration to be 1% by using 50% sulfuric acid, and reacting in a water bath kettle at the temperature of 45 ℃ for 8 hours at the stirring speed of 30 r/min. And transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and performing freeze drying at-40 ℃ for 12 hours to obtain the nano-cellulose crystal.
As shown in fig. 3, the resulting nanocellulose crystals: spherical structure, average particle size 70nm, yield 80%.
Comparative example 1 (acid-free Pre-treatment and high-pressure homogenization, other conditions were the same as in example 1)
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 3g (absolutely dry) of the ground pulp (simultaneously, the pulp is additionally weighed to measure the moisture) is weighed and placed into a round-bottom flask, 50 percent sulfuric acid is added, and the pulp concentration is adjusted to be 3 percent. Placing the round-bottom flask in a water bath kettle, setting the temperature at 45 ℃ and the rotating speed at 30r/min, after reacting for 8 hours, pouring the mixed solution into a dialysis bag for dialysis until the pH value of the mixed solution is neutral. And (3) centrifuging the neutral mixed solution at a high speed, treating the supernatant to be viscous by using a rotary evaporator, and freeze-drying for 12 hours to obtain the nano-cellulose crystal.
The obtained nanocellulose crystals: spherical structure, average particle size 210nm, yield 40%.
Comparative example 2 (without pretreatment, other conditions were the same as in example 1)
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 1g (absolutely dry) of the ground pulp is weighed (meanwhile, the pulp is weighed to measure the moisture), and the concentration of the pulp is adjusted to 1% by using distilled water. Treating with high pressure homogenizer for 10 times, homogenizing under 100MPa, centrifuging, collecting solid, and freeze drying. 2g of freeze-dried fiber (oven-dried) was taken, adjusted to a concentration of 1% with 50% sulfuric acid, and reacted in a water bath at 45 ℃ for 8 hours with a stirring speed of 30 r/min. Transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and freeze-drying for 12h to obtain the nano-cellulose crystal
The obtained nanocellulose crystals: spherical structure, average particle size 140nm, yield 50%.
As can be seen from example 1 and comparative examples 1 and 2, the present application effectively improves the yield of NCC and the average particle size of the obtained product is smaller.
Compared with other preparation methods, such as royal sea English et al, discuss that eucalyptus pulp is used as a raw material, and the optimal process for preparing NCC by adopting a sulfuric acid method is that the concentration of sulfuric acid is 55%, the temperature is 52 ℃, and the time is 4 hours. The results of Wangzhifei et al using bamboo pulp as raw material and using response surface optimization method to optimize its technological parameters show that the optimum process for preparing NCC is sulfuric acid concentration 60%, temperature 53 deg.C, hydrolysis 128min, then yield 55.28%. The method reduces the concentration and temperature of the sulfuric acid and improves the yield.
Example 4
Bleached softwood fiber pulp with a concentration of 12% was treated with a PFI refiner for 18 min. 2g (absolutely dry) of the ground pulp (simultaneously, the pulp is additionally weighed to measure the moisture) is weighed and placed into a round-bottom flask, 40 percent sulfuric acid is added, and the concentration of the pulp is adjusted to be 2 percent. And (3) placing the round-bottom flask into a constant-temperature water bath kettle, setting the temperature to be 40 ℃, reacting for 50min, continuously stirring, taking out the round-bottom flask after the reaction is finished, and adding 20 times of distilled water to terminate the reaction. Then filtered with a buchner funnel, washed repeatedly with distilled water until the filtrate is not acidic, the fibers are collected and the water is equilibrated. 1.2g (oven-dried) of the fiber after acid hydrolysis is taken to prepare a fiber suspension with the concentration of 1.2 percent, and then the fiber suspension is treated for 15 times by a high-pressure homogenizer with the homogenizing pressure of 150 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-10 deg.C for 24 hr to obtain cellulose microfibril. Cellulose microfibrils (1.5 g) (absolutely dry) were taken, adjusted to a concentration of 1.5% with 40% sulfuric acid, and reacted in a water bath at 30 ℃ for 7 hours with a stirring speed of 30 r/min. Transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and freeze-drying for 24 hours at the temperature of minus 10 ℃ to obtain the nano-cellulose crystal.
Example 5
Bleached softwood fiber pulp with a concentration of 15% was treated with a PFI refiner for 20 min. 4g (absolutely dry) of the ground pulp (simultaneously, the pulp is additionally weighed to measure the moisture) is weighed and placed into a round-bottom flask, 45 percent sulfuric acid is added, and the pulp concentration is adjusted to be 4 percent. And (3) placing the round-bottom flask into a constant-temperature water bath kettle, setting the temperature to be 50 ℃, reacting for 20min while continuously stirring, taking out the round-bottom flask after the reaction is finished, and adding 25 times of distilled water to terminate the reaction. Then filtered with a buchner funnel, washed repeatedly with distilled water until the filtrate is not acidic, the fibers are collected and the water is equilibrated. 1.5g (oven-dried) of the fiber after acid hydrolysis is taken to prepare a fiber suspension with the concentration of 1.5 percent, and then the fiber suspension is treated for 20 times by a high-pressure homogenizer with the homogenizing pressure of 120 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-50 deg.C for 14 hr to obtain cellulose microfibril. Taking 2g (absolute dry) of cellulose microfibrils, adjusting the concentration to be 2% by using 45% sulfuric acid, and reacting for 5 hours in a water bath kettle at the temperature of 40 ℃ with the stirring speed of 30 r/min. Transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and freeze-drying for 14h at-50 ℃ to obtain the nano-cellulose crystal.
Example 6
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 2g (absolutely dry) of the ground pulp (simultaneously weighing the pulp for measuring the moisture) is weighed into a conical flask, 10FPU/g of absolutely dry fiber exo-cellulase is added, and a cellulose suspension with the concentration of 2% is prepared by using a citric acid buffer solution with the pH value of 4. Placing the conical flask in a constant-temperature water bath oscillator at 52 ℃ for reaction for 3 hours, wherein the oscillation speed is 100r/min, and immediately placing the conical flask in a boiling water bath for inactivation for 12min after the reaction is finished. Filter with buchner funnel, wash repeatedly with distilled water, collect fiber and equilibrate moisture. Taking 1.1g (oven dried) of fiber after enzyme hydrolysis to prepare fiber suspension with concentration of 1.1%, and then processing with high pressure homogenizer for 12 times, wherein the homogenizing pressure is 110 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-20 deg.C for 20h to obtain cellulose microfibril. Cellulose microfibrils (1.2 g) (absolutely dry) were taken, adjusted to a concentration of 1.2% with 45% sulfuric acid, and reacted in a water bath at 35 ℃ for 6 hours with a stirring speed of 30 r/min. And transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and performing freeze drying at the temperature of minus 20 ℃ for 20 hours to obtain the nano-cellulose crystal.
Example 7
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. 2.5g (absolutely dry) of the ground pulp (simultaneously, the pulp was additionally weighed to measure moisture) was weighed into a conical flask, 40CMCU/g of absolutely dry endo-cellulase was added, and a 2.5% cellulose suspension was prepared using a citric acid buffer solution having a pH of 5. And placing the conical flask in a constant-temperature water bath oscillator at 55 ℃ for reaction for 2.5 hours, wherein the oscillation speed is 120r/min, and immediately placing the conical flask in a boiling water bath for inactivation for 15min after the reaction is finished. Filter with buchner funnel, wash repeatedly with distilled water, collect fiber and equilibrate moisture. Taking 1.4g (oven dried) of fiber after enzyme hydrolysis to prepare fiber suspension with concentration of 1.4%, and then processing with high pressure homogenizer for 14 times, wherein the homogenizing pressure is 130 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-30 deg.C for 15h to obtain cellulose microfibril. Cellulose microfibrils (1.4 g) (absolutely dry) were taken, adjusted to a concentration of 1.4% with 45% sulfuric acid, and reacted in a 38 ℃ water bath for 5.5 hours with a stirring speed of 30 r/min. And transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and performing freeze drying at-30 ℃ for 15h to obtain the nano-cellulose crystal.
Example 8
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. Weighing 1.5g (absolutely dry) of ground pulp (simultaneously weighing the pulp to measure water content), placing into a conical flask, preparing into 1.5% pulp with distilled water, and stirring to disperse the pulp sufficiently. 0.11g TEMPO (1 ml solution) and 0.32g sodium bromide were added thereto, and the mixture was stirred until it was sufficiently dissolved, and 1.50g sodium hypochlorite (3 ml solution) was added thereto over 30min (a small amount of the solution was added several times), and the mixture was stirred for 1.5 hours. Filter with buchner funnel, wash repeatedly with distilled water, collect fiber and equilibrate moisture. Taking 1.3g (oven-dried) of TEMPO treated fiber to prepare a fiber suspension with the concentration of 1.3 percent, and then treating the fiber suspension for 18 times by using a high-pressure homogenizer with the homogenizing pressure of 140 MPa. Centrifuging the suspension, collecting the solid, and freeze-drying at-35 deg.C for 13h to obtain cellulose microfibril. Cellulose microfibrils (1.6 g) (absolutely dry) were taken, adjusted to a concentration of 1.6% with 45% sulfuric acid, and reacted in a water bath at 35 ℃ for 6 hours with a stirring speed of 30 r/min. And transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and performing freeze drying at-35 ℃ for 13h to obtain the nano-cellulose crystal.
Example 9
Bleached softwood pulp with a concentration of 10% was treated with a PFI refiner for 15 min. Weighing 2g (absolutely dry) of ground pulp (meanwhile, weighing the pulp to measure moisture), putting into a conical flask, preparing into 2% pulp with distilled water, and continuously stirring to fully disperse the pulp. 0.11g TEMPO (1 ml solution) and 0.32g sodium bromide were added thereto, and the mixture was stirred until it was sufficiently dissolved, and 1.50g sodium hypochlorite (3 ml solution) was added thereto over 30min (a small amount of the solution was added several times), and the mixture was stirred for 2 hours. Filter with buchner funnel, wash repeatedly with distilled water, collect fiber and equilibrate moisture. Taking 1.5g (oven-dried) of TEMPO treated fiber, preparing fiber suspension with concentration of 1.5%, and then treating with a high-pressure homogenizer for 16 times, wherein the homogenizing pressure is 135 MPa. Centrifuging the suspension, collecting the solid matter, and freeze-drying at-45 deg.C for 12h to obtain cellulose microfibril. Cellulose microfibrils (1.8 g) (absolutely dry) were taken, adjusted to a concentration of 1.8% with 45% sulfuric acid, and reacted in a 38 ℃ water bath for 5.5 hours with a stirring speed of 30 r/min. And transferring the mixed solution after the reaction into a dialysis bag for dialysis until the pH value is neutral, evaporating the neutral mixed solution to be viscous by using a rotary evaporator, and performing freeze drying at-45 ℃ for 12 hours to obtain the nano-cellulose crystal.
Claims (10)
1. A method for preparing nano cellulose crystals by acid hydrolysis of cellulose microfibrils is characterized by comprising the following steps: the method comprises the following steps:
(1) taking pulp, grinding the pulp into slurry, then carrying out hydrolysis pretreatment, and separating to obtain fibers after the hydrolysis pretreatment is finished;
(2) preparing the fiber obtained in the step (1) into fiber suspension, and carrying out high-pressure homogenization treatment and drying to obtain cellulose microfibrils;
(3) preparing microfibril suspension with mass concentration of 1-2% by taking cellulose microfibril and using acid solution, and reacting for 5-8 hours at 30-45 ℃;
(4) and (4) after the reaction in the step (3) is finished, dialyzing the obtained mixed solution until the mixed solution is neutral, evaporating the mixed solution to be viscous, and drying the mixed solution to obtain the nano cellulose crystal.
2. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (1), the pulp is prepared by bleached softwood pulp absolute dry pulp or bleached softwood fiber absolute dry pulp and water, and the concentration of the pulp is 10-15%.
3. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (1), the grinding time is 15-20 min.
4. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (1), the hydrolysis pretreatment is to carry out acid hydrolysis, enzyme hydrolysis or oxidative hydrolysis on the pulp after pulping; wherein the acid hydrolysis comprises the following steps: firstly, mixing the pulp after pulping with sulfuric acid to prepare a fiber suspension with the concentration of 2-4%, reacting for 20-50 min at 40-50 ℃, filtering and washing after the reaction is ended, and collecting fibers;
the enzymatic hydrolysis comprises the following steps: adding cellulase and the pulp after pulping into a sodium citrate buffer solution with the pH value of 4-5 to prepare a fiber suspension with the concentration of 2-3 percent, carrying out oscillation reaction at the temperature of 50-55 ℃ for 2-3 hours, inactivating and filtering after the reaction is finished, and collecting fibers;
the oxidative hydrolysis comprises the following steps: preparing the pulp after pulping into 1-2% fiber suspension by using water, then adding TEMPO solution, sodium bromide and sodium hypochlorite solution into the fiber suspension, reacting for 1-2 hours, filtering and washing, and collecting fibers; wherein the mass ratio of oven-dried fibers, TEMPO, sodium bromide and sodium hypochlorite in the fiber suspension is (1-2): 0.11 g: 0.32 g: 1.5 g; the concentration of the TEMPO solution was 0.11g/mL and the concentration of the sodium hypochlorite solution was 0.5 g/mL.
5. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (2), the concentration of the fiber suspension is 1-1.5%.
6. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (2), the number of times of homogenizing treatment is 10-20 times, and the homogenizing pressure is 100-150 MPa.
7. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (2), the drying is carried out for 12 to 24 hours at the temperature of minus 10 to minus 50 ℃.
8. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (3), the acid solution is sulfuric acid with the volume fraction of 40-50%.
9. The method of claim 1 for preparing nanocellulose crystals by acid hydrolysis of cellulose microfibrils, wherein: in the step (4), the drying is carried out for 12-24 hours at the temperature of minus 10 ℃ to minus 50 ℃.
10. A nanocellulose crystal produced by the process of claim 1, characterized by: the nano cellulose crystal is a rod-shaped structure or a spherical structure, and the average grain diameter is 30 nm-70 nm.
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